corex gyan

104
- 1 - 1.COREX IRON MAKING Liquid hot metal, either for production of steel or pig iron for foundry, has been traditionally produced in the blast furnace using metallurgical coke, produced from coking coal ,as reductant and energy supplier. This call for a need of an alternative iron making technology also for conserving the depleting reserves of good quality coking coal, making use of non-coking coal reserves, exploiting large price differential of imported metallurgical coal and non-coking coal. In recent years, Smelting Reduction (SR) processes have been under development throughout the world. The basic principle of a SR process is to smelt the pre-reduced iron ore/sinter/pellets with non-coking coal and oxygen in a reactor called Melter-Gasifier. Compared to the conventional Blast furnace process; SR processes have many advantages with respect to raw materials, energy cost, investment cost, economy of scale and environmental pollution. COREX process, which is one of the commercially and technologically proven alternate routes of Iron making. The COREX technology is based on the physical separation of reduction and melting process, which are carried out in two reactors. In the Melter Gasifier (MG), reduction gas is generated and liquid hot metal is produced .The Reduction Shaft (RS) which is located above the Melter Gasifier, is designed for the reduction of iron oxides. Smelting reduction is an emerging technology for making hot iron using non- coking coal. Till today various smelting reduction processes like COREX, ROMELT, HISMELT, AUSMELT, DIOS etc. have been developed of which COREX is the first and so far only commercially established smelting reduction process, which is developed by Voest Alpine Industrianlagenbau (VAI), Austria. The stable and highly successful operation of four COREX plants (1 POSCO, Korea, 2 JVSL, India, 1 SALDANHA, South Africa) confirms that COREX process is a proven and viable alternative to conventional blast furnace technology. 1. INTRODUCTION: COREX is the one of the commercially and technologically proven alternate routes of Iron making. While even today’s world’s most of the hot metal or liquid iron is produced through the giant Blast Furnace route, very small fraction of iron is produced through the alternate routes. COREX process gives advantage of power generation and makes integrated steel complex totally independent of petro-based products due to availability of COREX gas as fuel.

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1.COREX IRON MAKING

Liquid hot metal, either for production of steel or pig iron for foundry, has been traditionally produced in the blast furnace using metallurgical coke, produced from coking coal ,as reductant and energy supplier. This call for a need of an alternative iron making technology also for conserving the depleting reserves of good quality coking coal, making use of non-coking coal reserves, exploiting large price differential of imported metallurgical coal and non-coking coal. In recent years, Smelting Reduction (SR) processes have been under development throughout the world. The basic principle of a SR process is to smelt the pre-reduced iron ore/sinter/pellets with non-coking coal and oxygen in a reactor called Melter-Gasifier. Compared to the conventional Blast furnace process; SR processes have many advantages with respect to raw materials, energy cost, investment cost, economy of scale and environmental pollution. COREX process, which is one of the commercially and technologically proven alternate routes of Iron making. The COREX technology is based on the physical separation of reduction and melting process, which are carried out in two reactors. In the Melter Gasifier (MG), reduction gas is generated and liquid hot metal is produced .The Reduction Shaft (RS) which is located above the Melter Gasifier, is designed for the reduction of iron oxides. Smelting reduction is an emerging technology for making hot iron using non-coking coal. Till today various smelting reduction processes like COREX, ROMELT, HISMELT, AUSMELT, DIOS etc. have been developed of which COREX is the first and so far only commercially established smelting reduction process, which is developed by Voest Alpine Industrianlagenbau (VAI), Austria. The stable and highly successful operation of four COREX plants (1 POSCO, Korea, 2 JVSL, India, 1 SALDANHA, South Africa) confirms that COREX process is a proven and viable alternative to conventional blast furnace technology.

1. INTRODUCTION: COREX is the one of the commercially and technologically proven alternate routes of Iron making. While even today’s world’s most of the hot metal or liquid iron is produced through the giant Blast Furnace route, very small fraction of iron is produced through the alternate routes. COREX process gives advantage of power generation and makes integrated steel complex totally independent of petro-based products due to availability of COREX gas as fuel.

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1.1 HISTORY :

Chronology of COREX development and establishment.

These are some of the strength of COREX technology over other Iron making process: It is a two-stage process, Reduction and Smelting. It is a clean iron making technology, which is flexible in term of operation and usage of raw materials of less stringent quality. Various fines such as iron bearing fines, limestone & dolomite fines can be directly used into the furnace. About 10-15 % of the total iron bearing material can be replaced with direct use of Iron bearing fines. The gas coming out as by-product is a clean gas having very high calorific value i.e. ~ 2000 Kcal/Nm.3 this can also be used in many areas like:

¾�Power plants.

¾�Production of DRI.

¾�Lime Calcination plant.

¾�Hot strip mill reheating furnace.

2005

2005

Essar Steel (Hazira) Limited, Hazira, C -_2000 x 2

Bao Steel, China C - 3000

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¾�Fuel gas within the Iron and Steel complex.

Advantages of Corex Process:

¾�Easy and fast correction of hot metal and slag chemistry with in 2 –3 hrs as the process is divided into two stages.

¾�Excellent quality hot metal. High hot metal temperature (1480 – 1520oC) offer great

advantage in the subsequent process of steel making.

¾�Easy stop and restart of the furnace. After restart, furnace can attain its rated capacity within a short duration i.e. 2 - 3 hrs without effecting the quality of hot metal.

¾�It is the only commercially established alternative route of iron making an efficiency

very much comparable to the conventional route.

¾�Environment friendly process as this technology does not require setting up the coke oven and sinter plant. The emissions from COREX contain only insignificant amount of NOx, SOx, dust, phenols, sulphides, ammonia etc. The million worth of saved carbon over the years can also be sold as a part of carbon trading.

1.2 COREX FACILITIES

I Melter Gasifier 1 Tuyeres 26 Water-cooled Copper body.

2 Level indicator 5pair Source and Detector, Water-cooled Copper body.

3 Dust Burner 4 Water cooled Copper body.

4 Staves 184 Cast iron boby expect row 5 and row 6, Copper

body for row number 5 and 6.It is water Cooled.

5 Drilling machine 1 Drilling is Pneumatically Operated and seweling by hydraulic.

6 Mud gun 1 Hydraulically Operated. Both swelling and ramming.

7 Dust Recycling System 4 Each DRS consists-Hot Gas Cyclone, LowerDust Bin, Disc gate, Injector, T-piece and dust burner.

8 Generator Gas Duct (GGD 4 Water-cooled four numbers of generator In-liner.

9 Coal Screw 1pair Upper coal screw and lower coal screw.

10 Coal lock hopper system 1 Consists of feeding bin, intermediate bin and

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charging bin, two set of material flaps and seal flaps, Pressurising and depressurizing system.

11 Coal Reffler 1 Located center of MG dome to take care coal distribution.

12 Coal in liner 4 Located just below the refler,on which reffler is mounted.

13 Heating Unit 1 For both coal and oxide, heated oil is circulate to the Lock hopper system for smooth charging operation.

II Reduction Shaft

1

DRI screws 6 Hydraulic driven.

2 DRI down Pipes 6 It is vertical DRIconveying line, DRI discharged from Screws is conveyed to the MG through this line.

3 Oxide Lock hopper system 1 Consists of feeding bin, intermediate bin and charging bin, two sets of material flaps and seal flaps.

III Gas System 1 Cooling Gas System 2 Baumco Scrubber (B S) 1 Number just before cooling gas packing scrubber.

It facilitates to cool the high temperature gas.

3 Cooling Gas Packing Scrubber (CGPS)

1 To cool and clean the Excess Gas produced in the System (Gas remained excess out of total gas produced and the reducing gas used for reduction in the reduction shaft).

4 Excess Gas Venturi Scrubber

(EGVS) 1 to clean excess gas, it is further cleaned and

Venturies are used for Pressure Control. It consists of mist eliminator (EGME) , water level control tank.

5 Cooling Gas Venturi Scrubber (CGVS)

1 to clean the gas going the Cooling Gas Compressor.

6 Cooling Gas Compressor 1 One working one stand-by. It is used to Boost the

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(CGC) gas Pressure by 1 bar more than the pressure to the inlet cooling gas pressure. This gas is added into four-generator gas duct through temperature control valve (TRC’s) to reduce the generator gas temperature; normally Temperature is reduced to 850 deg C from 1050 deg C. This reducing gas is then taken in to RS for Oxide reduction.

IV Top Gas System 1 Top Gas Packing Scrubber

(TGPS) 1 To cool and clean the top gas which is coming out

from Reduction Shaft. 2 Top Gas Venture Scrubber

(TGVS) 1 To further clean the top gas and control the

Pressure. It consists of one mist eliminator and one water level control tank.

V Export Gas System A Low Pressure (LP) Gas Line 1 Pressure Control Valve (PRC) 1 It controls the line pressure for Low Pressure (LP)

export gas consumer; It is located in Export gas after flare stack.

2 Solenoid Valve ( SOV) 1 It is located after PRC in LP export gas line .It is in open or close condition depends upon consumer requirement.

3 Goggle Valve (GV) 1 It is located after SOV in LP export gas line .It is can be manually / automatically operated. It is used for mechanical isolation during long shut down for perfect sealing of process gas system from export gas network.

4

Shut off Valve (SHV) 1 It is located after GV.It used for same for gas isolation during plant shut down.

B High Pressure (HP) Gas Line

1 Goggle Valve (GV) 1 It is located in HP export gas line .It is can be Manually / automatically operated. It is used for mechanical isolation during long shut down for perfect isolating of process gas network from export gas network.

2 Pressure Control Valve (PRC) 1 It controls the line pressure for high Pressure (HP) export gas consumer; It is located after HP goggle valve.

3 Solenoid Valve (SOV) 1 It is located after PRC in HP export gas line .It is in open or close condition depends on consumer requirement.

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4 Flare Stack 1

It is having four burner (flare tip), Ignition panel and fuel gas (NG/LPG) for pilot ignition.

5 Seal pots 5 It is for HP gas line ,in which Two number in Top gas system ( export gas 1) one number in Excess gas system (export gas 2) ,one in flare stack drain and one more in HP line.

6 Flare Stack 1 It is having four burner (flare tip),Ignition panel and fuel gas (NG/LPG) for pilot ignition.

7 Seal pots 5 It is for HP gas line ,in which Two number is for Top gas system ( export gas 1) one for Excess gas system (export gas 2) ,one for flare stack drain and one more for HP line.

1.3 EQUIPMENT

MAJOR REACTORS:

AUXILLAIRIES:

I. Reduction Shaft [RS] II. Melter Gasifier [MG]

i. Coal blending station [CBS] ii. Coal drying plant [CDP] iii. Raw material stock house [RMHS] iv. Gas cleaning system v. Water Cleaning system vi Cast house[C/H] vii Pig casting machine [PCM] viii Cooling gas and air compressors [CGC]

1.4 PROCESS DESCRIPTION: COREX consists of two reactors, the reduction shaft and the melter gasifier. Figure –1 shows the COREX process schematically. The reduction shaft is placed above the melter gasifier for easy descend of material by gravity. The functions of reduction shaft and the melter gasifier are explained in the following

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Figure-1: Flow sheet of COREX® process

1.5 Reduction shaft: Iron ore, pellets and additives (i.e. limestone and dolomite) are continuously charged into the reduction shaft via lock hopper system located on the top of the shaft. The burden descends through the shaft by gravity. The reduction gas is injected through the bustle located about 5 meters above the bottom of the shaft at 830oC temperature and over 3 bar gauge pressure. The gas moves in the counter current direction to the top of the shaft and after the exit from the shaft it is termed as top gas. The top gas temperature is around 300oC. Some amount of Coke is also added to the shaft to avoid clustering of the burden inside the shaft due to sticking of ore/ pellets and to maintain adequate permeability in the burden. Following are the primary reactions taking place inside the shaft. Reduction of iron oxide by CO and H2 and transforming the iron oxides to metallic iron. Fe2O3 � Fe3O4 � FeO � Fe Calcination of limestone and dolomite CaCO3 = CaO + CO2 (endothermic) CaMg (CO3) 2 = CaO. MgO + 2 CO2 (endothermic)

BU

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Carbon deposition reaction and formation of Fe3C 2 CO CO2 + C (exothermic) 3 Fe + 2CO Fe3C + CO2 (exothermic)

After a residence time of about 6 hrs. Inside the shaft, the iron bearing material gets reduced and achieves the metallization to the extent of about 80 - 90 %, and is termed as DRI. Subsequently, 6 discharge screws convey the DRI from the reduction shaft to the melter gasifier. The reduction gas is nearly fully de-sulphurized in the shaft due to the presence of the burnt lime and dolomite according to the following reactions. CaO + H2S = CaS + H2O MgO + H2S = MgS + H2O A low content of the hydrogen sulphide of the top gas is important with respect to the further usage of the COREX gas.

The metallization degree of the DRI and the calcination of the additives are strongly dependent on the following parameters.

¾�Amount and quality of the reduction gas flow. ¾�Temperature of the reduction gas. ¾�Reducibility of the iron carrier. ¾�Grain size of the solids charged. ¾�Reduction gas distribution in the shaft. ¾�Retention time in the shaft. ¾�Plant Pressure and Pressure drop in the shaft.

The specific reduction gas flow is maintained at about 1000 - 1200Nm3/ton of iron carrier charged to the shaft. 1.6 Melter gasifier: The melter gasifier can largely be divided into three reaction zones as the following.

¾�Gaseous free board zone (Upper part or dome) ¾�Char bed (Middle part above oxygen tuyeres) ¾�Hearth zone (Lower part below oxygen tuyeres)

Due to continuous gas flow through the char bed, there also exists a semi-fluidized bed in the transition area between the char bed and the free board zone.

The hot DRI at around 750-800oC along with the calcined limestone, dolomite is continuously fed inside the melter gasifier through DRI down pipes. The DRI charging pipes are uniformly distributed along the circumference near the top of the melter gasifier so as to ensure proper distribution of material over the char bed. Additionally non-coking

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coal, quartzite and required quantity of coke are continuously charged by means of lock hopper system and coal screws. Like reduction shaft the melter gasifier also operates at an elevated pressure in excess of 3-bar gauge. Oxygen plays a vital role in COREX process for generation of heat and reduction gases. It is injected through the tuyeres, which reacts with carbon present in the char will generate CO and H2 and Heat. This hot gas ascends upward through the char bed. The sensible heat of the hot gases is transferred to the char bed, which is utilized for melting iron and slag and other metallurgical reactions. The hot metal and slag are collected in the hearth. The efficiency of the furnace depends largely on the distribution of this gas in the char bed and utilization of the sensible heat of the gas. The dome temperature is maintained between 1030 and 1070oC which assures cracking of all the volatile matter released from the coal. The gas generated inside the melter gasifier contains fine dust particles, which are separated in hot gas cyclones.

The dust collected in the cyclones is recycled back to the melter gasifier through the dust burners, where the dust is burnt with additional oxygen injected through the burners. There are four such dust burners located around the circumference of the melter gasifier above the char bed. The gas generated inside the melter gasifier is cooled to the reduction gas temperature (~830oC) through the addition of cooling gas. A major part of this gas is subsequently fed to the reduction shaft. The excess gas is used to control the plant pressure. This excess gas and the reduction shaft top gas are mixed prior to the take over point. Thereafter this gas is termed as COREX export gas. Following are the reactions taking place inside the melter gasifier. ¾�Drying of coal (100oC). ¾�Devolatilisation of coal (200 to 950oC) and liberation of methane and higher hydrocarbons. ¾�Decomposition of volatile matter. Due to the higher temperature prevailing in the melter gasifier free board zone, the hydrocarbons are cracked into hydrogen and elementary carbon. CnHm = nC + (m/2) H2

It is desirable that all higher hydrocarbons are cracked in the free board zone so as to assure generation of a good quality reduction gas. Maintaining a dome temperature between 1030 and 1070oC confirms the same. Further reactions in the freeboard zone are outlined as the following.

CO2 + C = 2 CO Boudouard reaction

H2O + C = CO + H2 Water gas reaction

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CO + H2O = CO2 + H2 Shift reaction

¾�Decomposition of unburnt limestone and dolomite. ¾�Residual reduction of iron oxide. ¾�Direct reduction of FeO in the DRI takes place by carbon in the char bed. ¾�Burning of coal char by oxygen.

Burning of the coal char takes place near the tuyeres. The maximum temperature inside the melter gasifier exists in front of the tuyeres. The following carbon gasification reaction takes place in the tuyere area.

2C + O2 = 2CO 2CO + O2 = 2CO2 C + CO2 = 2CO

¾�Later, Melting and formation of hot metal and slag.

The typical analysis of COREX hot metal and other by-products is shown in Table 1.

The typical analysis of the various gases produced in COREX is shown in Table 2. In order to achieve higher degree of metallization and sufficient carbonization of the DRI, the contents of CO2 and H2O in the reduction gas should be below 5%.

Table-2 Typical analysis of COREX gases ANALYSIS TOP GAS REDUCTION GAS EXPORT GAS

CO % 43 - 46 65 - 70 45 - 47 H2 % 18 -20 20 - 25 19 - 21 CO2 % 30 – 35 3 - 8 30 – 33

CH4 % 1 - 2 1 - 2 1 - 2

ANALYSIS

(%)

C

Si

S

P

Ti

CaO

MgO

SiO2

Al2O3

FeO

Fe2O3

TiO2

HOT METAL

4.5

0.6

0.04

0.15

0.06

SLAG

0.80

0.26

34.5

13.0

31.7

17.0

0.50

SLUDGE

35.6

0.81

0.25

7.94

3.20

9.18

4.38

30.61 0.29

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The efficiency of the COREX primarily depends on the following.

¾�Size and chemical analysis of the raw materials; specially the coal. ¾�Reduction gas quality & shaft condition for good rmetallization of the DRI. ¾�Optimum distribution of oxygen between the tuyeres and dust burners. ¾�Permeability of the char bed. ¾�System pressure. ¾�Melting rate. ¾�

COREX export gas is suitable for a wide range of applications as stated above. Tapping of hot metal and slag takes place approximately 8 to 10 times per day with a tapping capacity of approximately 300 thm/tap. The tap hole is opened by a pneumatic drilling machine. For closing of the tap hole hydraulically operated clay gun is provided. After opening the tap hole, hot metal and slag discharges into the main iron trough, where slag is separated from hot metal by means of a skimmer. Hot metal flows from the main iron trough through the iron runner and a tilting runner into open ladles positioned on ladle transfer cars below the cast house platform. The slag proceeds from the main iron trough through a runner system to slag granulation plant or slag dry pits, in case the slag granulation plant is not available. To operate the tap hole opening and closing machines a central hydraulic system is installed.

1.7 PROCESS CONTROL: ¾�Raw material quality charged to the furnace is controlled at the screening station to ensure required size as a first stage of control. ¾�Sample checking for input raw materials as per quality plan. ¾�Weigh bins/feeders are connected to DCS in control room to weigh raw materials accurately charged to the furnace. The load cells of the weigh feeders are calibrated as per the frequency in the calibration plan. ¾�Coal and Oxide feed rate varied to control the process parameters and hot metal quality. ¾�Controlled oxygen flow to the tuyere and dust burner. ¾�Thermocouples for In-burden Temperature measurement inside the reduction shaft. ¾�Delta-p inside the reduction shaft to ensure proper permeability of the burden. ¾�Reduction gas temperature going into the reduction shaft ¾�Controlling of specific top gas to ensure proper metallization of the burden. ¾�Dome temperatures inside the melter gasifier to control the composition of the generated gas. Control of Char bed level to ensure proper hot metal & slag quality. ¾�Adjustment of slag quantity and basicity B2 (CaO/SiO2) to control the Slag Alumina, Viscosity and sulphur distribution. ¾�Plant pressure control. ¾�Maintaining proper tap-to-tap time for ensuring proper drainage of the hearth.

1.8 RAW MATERIALS

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Table 3: Physico-chemical properties of Iron bearing material

Parameter Analysis Chemical Analysis Fe - Total 64 -65 % SiO2 + Al2O3 d �����

Al2O3 d �����

P < 0.10 % S < 0.03 % Cold Tumbling Test Tumbler index (+6.3 mm) > 95 % Abrasion Index (-0.5 mm) < 5 % Static Reduction Test [Under load] Reducibility (dR/dt)40 > 0.4 % O2/min Metallisation Degree > 90 % Disintegration Index (-6.3 mm) Pellets < 10 %, Ore < 20 % Abrasion Index (-0.5 mm) Pellets < 3 %, Ore < 5 %

Table 4: Physico-chemical properties of COREX coal

Parameter Analysis Chemical Analysis Fixed carbon % > 58 % Volatile matter % 26-32 Ash % < 12 % Sulphur % < 0.60 Phosphorous < 0.06 Chlorine < 0.04 Calorific value Kcal/Kg > 7000 Ash analysis SiO2 < 60 Al2O3 < 30 Na2O + K2O < 1.5 Thermal Stability + 10 mm % > 80 - 2 mm % < 3 CRI % < 35 CSR % > 40 Free Swelling Index 1 -3

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Table 4: Typical analysis of Additives

ANALYSIS LIMESTONE DOLOMITE QUARTZ

CaO % 46.79 27.98 0.14 MgO % 3.83 19.84 - SiO2 % 5.20 6.81 97.88 Al2O3 % 1.16 0.53 0.90 Fe2O3 % 0.96 0.49 0.62 P2O5 % 0.04 0.01 0.01 SO3 % 0.01 0.01 0.01

1.9 BLAST FURNACE:

The blast furnace is the first step in producing iron from iron oxides. Blast furnace equipment is in continuous evolution. In Blast furnace coke is used for heat generation, production of reduction gases and to maintain adequate bed permeability. Blast furnaces will survive into the 2000 millennium because the larger, efficient furnaces can produce hot metal at costs competitive with other iron making technologies.

SIMILARITIES BETWEEN BLAST FURNACE AND COREX PROCESS: 1.Both the process is used for the production of hot metal (liquid pig iron). 2.Except fuel and oxygen, similar raw materials could be used in both the processes. 3.Overall reactions taking place in both the routes are quite similar, except those of coal devolatization and cracking etc. 4.The function of the hearth and concept of tapping of hot metal and slag, cast house design, slag & hot metal handling practices are identical in both Blast furnace and Corex. 5. Hot metal composition is same in both processes. However, Corex HM temperature is relatively higher and sulphur in the HM is lower compared to BF.

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1.9 DIFFERENCES BETWEEN BLAST FURNACE AND COREX.

SL. NOBLAST FURNACE COREX

1 Blast furnace is single tall process vessel where from top to bottom the following sequential activities take place. Elimination of both combined and un-combined water from the raw materials, calcination of fluxes, formation of sponge iron, sub sequentially melting of iron and gangue material forming liquid slag and finally accumulation of liquid slag and metal in the hearth for intermittent tapping of liquid.

Corex is two stage reacting vessel. Upper one is called as reduction shaft where solid stage metallisation takes place with the reaction of reducing gas generated in lower vessel called Melter Gasifier. Sponge iron (DRI) & coal is fed to melter gasifier from top and oxygen is blown through the tuyeres. Burning of carbon with oxygen generates the heat required for melting of the sponge iron and slag. Additionally the gas generated during combustion of carbon is utilized for reduction purposes in the reduction shaft.

2 Uses Hot blast (pre heated air) at tuyeres. Uses 99.9% pure oxygen.

3 Uses Coke as primary reductant and gas generation source with hot blast.

Non-Coking coal is used as reductant and the source of gas along with oxygen.

4 Iron bearing material is used in the form of Sinters normally, in addition of some % of lump ore. Presently some %age of pellet has also been introduced into the burden.

Pellets, Sinters, Lump ores can be used as source of iron bearing material. However, use of sinter in Corex does not provide any additional benefit.

5 Due to the need of coke oven and sinter plant this route is not environmental friendly when compared to COREX.

Highly environmental friendly due to absence of coke oven and sinter plants. The pellet used in Corex is environmental friendly process.

6 Coke is costlier and the world reserve of coking coal is depleting very fast.

Non coking coal is cheaper and reserve is plenty.

7 Process is less flexible and needs more response time for the changes.

Highly flexible and very lesser time for correcting the hot metal and slag chemistry.

8 Low calorific value off gas is generated (about 800-1000 Kcal/Nm3) which cannot be used unless enriched with higher calorific value gas.

Medium calorific value off gas is generated (about 2000 Kcal/Nm3), which can be used for power generation, fuel gas for internal purpose, DRI plant, fertilizer manufacturing process etc.

9 BF can not be operated with any fines (undersized raw material).

Significant amount of various fines can be fed to Corex, which provides a cost saving and pollution control as well.

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2.RAW MATERIALS FOR COREX

2.1 Introduction

The production for Hot metal is the basis for steel making and is traditionally performed

via the route of Coke Oven Plant and Blast Furnace. An economically operated Blast Furnace

requires typically Sinter as an Iron Carrier and a basic amount of Coke.

The COREX process provides an alternative production route for the Hot Metal with

reasonable advantages compared to the Blast Furnace. Besides the economical impact due to the

possible use of a wide variety of raw materials and the environmental benefit the process

flexibility offers an enormous advantage in operating a metallurgical process.

2.2 The basic raw material required for COREX operation are classified under the

following major heads.

a. Ferrous Material (Iron Bearing)

¾�Lump Ore

¾�Pellets

¾�Sinter

b. Carbonaceous Material

¾�Coal

¾�Coke

c. Additives

¾�Dolomite

¾�Limestone

¾�Quartz

2.3 Specifications for Raw Materials

Criteria for Ferrous Material

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Additional Criteria for Ferrous Materials

Criteria for COREX Coals

Lump Ore:

Fetot Grain Size

60 % min. 6 - 32 mm

Pellets:

Fetot Grain Size

60 % min. 6 - 20 mm

65 % min. 10 - 30 mm

65 % min. 8 - 16 mm

Tolerable: Preferred:

Criteria Guideline Value: Remark: Chemical Analysis: SiO2 + Al2O3 max. 6 % slag operation S max. 0.01 % S in hot metal Static Reduction Test: Reducibility min. 0.35 % O/min Metallisation min. 87 % end of test DI-6.3 max. 15-25 % disintegration index after drum AI-0.5 max. 5-8 % abrasion index after drum

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Additional Criteria for COREX Coals

2.4 Raw Materials used in different COREX Units

Coals for Blending

Max. 12 %

0 - 50 mm

Tolerabl

Max. 12 %max. 5 %

0 - 50 mm > 50 % + 15 mm < 10 % - 2 mm < 5 % - 1 mm

Preferred

< 8 % < 5 %

< 0.5

8 - 40 mm d50: 20 - 30 mm < 5 % - 8 mm

before dryer after dryer

Grain

Coal or Coal- Blends

Proximate Analysis [dry] Fixed Carbon Volatiles Ash Fixed Carbon/Ash

min. 50 % max. 30 % max15 % min. 2.7

min. 55 % max. 30 % max. 12 % min. 3

55 - 65 % 25 - 27 % 5 - 10 % > 5

Moisture

Sulfur [dry]

Criteria: Guideline value: Remark: Chlorine max. 0.04 % corrosion Swelling Index up to 6 Thermo-mechanical Stability + 10 mm min. 70 % after pyrolysis - 2 mm max. 5 % + 10 mm min. 25 % after NSC drum 600 rev. - 2 mm max. 22 % Reactivity of Char RI max. 50 % CO2, 1100 °C, 60 min RSI>5 min. 40 % + 5 mm after NSC drum Mechanical Strength of Coal + 10 mm min. 70 % after Micum drum 100 rev. - 2 mm max. 16 %

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Coals used in POSCO Steel

Coals used in SALDANHA Steel

South

(%)

(%)

(%)

9

65 0.5

Mount

16

53 0.4

Thorley Blackwater (PCI)

Bays

Water Coalex

14

56 0.5

Ash [dry]

C fix [dry]

S total

Volatiles [dry] (%) 26

31

30

Optimum

11

57 0.7

32

7

38 55 0.4

Ensham

8

27 65 0.4

South Africa Australia

United

12

33 55 0.4

Van Dijksdrift

(%)

(%)

(%)

14

0.6

Grootegeluk

12

63

0.8

Delmas

Ash [dry]

C [dry] fix

S total

Volatiles [dry] (%) 2525

17

57

0.9

26

61

South Africa

Optimum

12

56

0.7

32

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Coals used in Jindal Steel South Africa Australia China

Dou

glas

Opt

imum

G

root

egel

uk

Gun

neda

h

SB

W

She

ll

Ens

ham

M

etro

polit

an

Cen

tenn

ial Ill

awar

a

Dat

ong

Sha

nxi

Ash (Dry) (%) 14 12 12 11 10 12 9 11 13 10 9 9 Volatiles (Dry) (%) 28 32 27 33 26 33 29 20 27 22 31 30

C fix (Dry) (%) 58 56 61 56 64 55 62 69 60 68 60 61

S total (%) 0.9 0.7 0.7 0.7 0.4 0.5 0.4 0.3 0.4 0.4 0.6 0.9

Ores/Pellets used in POSCO

Ores/Pellets used in JINDAL

Algarrobo CVRD

Pellets

Fe

SiO2

Al2O3

CaO

MgO

K2O

P2O5

SO3

(%) 65.2 65.8

(%) 2.1 2.5

(%) 0.5 0.6

(%) 2.6 2.5

(%) 0.4 0.1

(%) < 0.02 < 0.02

(%) 0.06 0.06

(%)

Mt. Newman

Lump Ore

64.3

3.0

1.0

1.3

0.1

< 0.02

0.12

< 0.020.02 0.01

Pellets

Peru

Pellets

65.5

3.6

0.5

0.5

0.8

0.1

0.02

0.02

Sishen

Lump Ore

66.6

3.1

1.0

0.1

0.1

0.12

< 0.1

0.02

LKAB IHG

65.6

2.1

1.5

0.1

0.0

0.02

0.01

66.3

2.0

0.3

0.3

1.6

0.04

0.06

< 0.01

0.09

Lump Ore Pellets

Sweden South Africa BrazilChile Peru Australia India

GIIC

Pellets

66.0

1.9

0.6

1.5

0.6

0.02

0.07

0.01

Bahrain

- 20 -

Ores/Pellets used in SALDANHA

2.5 Overview and Operation Management of COREX Material Handling Section

Fe SiO 2 Al 2 O 3 CaO MgO K 2 O P 2 O 5 SO 3

(%) (%) (%) (%) (%) (%) (%) (%)

Ramu Minerals Lump Ore

66.2 1.5 1.1 0.2

0.1 0.00 0.07 0.01

Kariganur Lump Ore

67.4 0.8 0.6 0.1

0.0 0.01 0.17 0.01

Mandovi Pellets

64.7 3.1 1.9 1.1 0.1 0.02 0.09 0.01

Kudhremukh

65.1 4.1 0.5 1.0 0.1 0.01 0.01 0.00

Pellets GIIC

Pellets

66.0 1.9 0.6 1.5

0.6 0.02 0.07 0.01

Essar Pellets

66.1 2.6 1.4 0.8 0.1 0.02 0.07 0.01

NMDC Lump Ore

65.4 1.3 2.2

0.1 0.1 0.02 0.10 0.02

JVSL

64.7 3.2 2.0 1.5 0.2 0.02 0.07 0.01

Pellets India Bahrain

VMPL Lump Ore

66.1 1.6 1.7 0.1 0.0

0.01 0.01 0.01

CVRD DR-Grade Pellets

Fe

SiO2

Al2O3

CaO

MgO

K2O

P2O5

SO3

(%) 66.6

(%)

(%)

(%)

(%)

1.9

0.9

1.3

0.5

(%) < 0.05

(%) 0.07

(%) 0.13

Sishen Lump Ore

66.6

3.1

1.0

0.1

0.1

0.12

< 0.10

0.02

Brazil South Africa

- 21 -

Silo04 900m3

To CDP

Screened coal

Tripper Car Conv.

Silo03 900m3

Silo02 900m3

Silo01 900m3

From Jetty

Fines to

Yard Screened

coal

To stacking

Reclaimed co

Stacker Re-claimer

ESSAR

- 22 -

Wet coal bunker

Wet coal bunker

Dedusting Bag filter

Dust

silo

ID

Mixing air

Combustion air

Fuel

LPG

Pilot

Compressed

Perforated plate Dryer

Off

Pneumatic

Dosing

Divertor

From

Wet

Hot

Clean

Dry Coal Conveyor

Dry Coal Conveyor

Tanke

Dry Coal Bin

Dry Coal Bin

Weigh bin

Vibro

Weigh bin

Charging

Dry Coal

From

Batching

Skip Charging Intermediate

Feeding

Reduction

Divertor

Dry Coal

Loc Hopper

DDRRYY CCOOAALL HHAANNDDLLIINNGG

- 23 -

225 B04

250m3

225 B03 250m3

225 B02 250 m3

225 B01 250m3

265 B01

260m3

225

225

225

From RMHS

137F1

225

255 B02

150m3

235 B01

900m3

265B02 to 265B07

To Reduction Shaft

255

255 B01

150m3

235

235

From mines

Fines to bunker

To stacking

Reclaimed materials

Stacker Re-claimer

MANUAL

TO COREX STOCK HOUSE

OSP

From Jetty

ESSAR

- 24 -

Theoretical Calculation for Consumption of Raw Materials Operating condition Melting Rate (Full Capacity) 106 TPH 870048 Tons/Year Coke Rate 15 % Furnace Operating Period 342 Days RAW MATERIAL RQUIREMENT FOR MAKING OF ONE TON OF HOT METAL

Material Specification Bulk Density Quantity

(in T/M3) in Tons in M3 To Reduction Shaft Pellet + Ore 65 % Fe 2.1 1.50 0.70 Dolomite + Lime Stone 350 Kgs/THM 1.45 0.35 0.23 Coke to RS 100 Kgs/THM 0.65 0.1 0.15 Total 1.99 1.09 To Melter Gassifier Coal 0.90 0.85 1.12 Coke 0.65 0.05 0.08 Flux (Quartz) 1.5 0.025 0.01 Total 0.925 1.21

225 B03

250m3

225 B02

250m3

225 B01

250m3

255 B02

265 B07

265 B01 260m3

235 B02 800m3

235 B01 8000m3

From CDP

From RMHS

TOP VIEW

225 B04

250m3

255 B03

255 B04

255 B01

265 B06

265 B03

265 B02

265 B04

265 B05

- 25 -

3 COAL DRYING PLANT 3.1General

In Coal Drying Plant, the moisture of Coal is reduced to below 5 %. Wet coal is fed to the Vibrating dryer and the hot gas is passed through the coal bed from the bottom. The vibrating dryer is a perforated trough that vibrates with some amplitude and as a result the coal moves forward. Due to passing of hot gas through the bed the heat exchange takes place and the moisture in the coal is driven out.

3.2 Coal Drying Plant consists of the following major equipments 1. Wet Coal Bunkers.

2. Belt Weigh Feeder.

3. Coal Dryer.

4. Hot Air Generator with burner assembly.

5. Hot Gas Dedusting System.

6. Dry Coal Transport System.

7. Dedusting Dust Conveying System.

Hot Gas Generator System comprises the following ¾�Combustion Chamber

¾�Mixing Chamber

¾�Flame Detector

¾�Mixing Air Fan

¾�Combustion Air Fan

¾�Hot Gas Ducts

Hot Gas Dedusting System Comprises the following ¾� Bag House

¾� Off Gas Duct

¾� Explosion Vent

¾� Hot Gas Fan

¾� Clean Gas Stack

- 26 -

3.3 SYSTEM FLOW

Bag Filter

Dust Silo

ID Fan

Pneumatic Conveying line

Clean Air Stack

Tanker

Explosion Duct

Vent Filter

HOT GAS DEDUSTING

DP

m bar

Screw Conveyor

Rotary Air Valve

Feed Bin

Pressure Vessel

Valves

Screw Conveyor

Rotary Air Valve

IGV

Purge Valve

- 27 -

Mixing Air Fan

Combustion Air Fan

Fuel Gas

LPG Main

Pilot LPG

Perforated Plate Dryer

Hot gas

Wet Coal

Hot Gas Duct

Hot Gas Chamber

HOT AIR GENERATOR

°C

M3/h

M3/h

Off Gas °C

M3/h

- 28 -

Perforated Plate Dryer

Hot gas

Dry Coal Conveyor Mod-01

Wet Coal Bunker

Hot Gas Duct

Rod Gate

Belt Weigh Feeder

Off Gas

Swivel Conveyor

VIBRATING DRYER

Hot Gas Chamber

Bunker

°C

- 29 -

3.4 OPERATING INSTRUCTIONS

Dedusting System

¾� Check pre-condition for the Dedusting Group Start-up.

¾� Keep all the drive controls in Remote mode and set it to Auto

¾� Start the Dedusting Group in Auto Mode

After the start condition is initiated

¾�Pneumatic conveying sequence starts

¾�After a delay the Rotary Air Valves starts

¾�With some delay the Screw Conveyor Starts.

¾�The Bag Filter cleaning sequence starts.

¾�Then the Hot Gas Fan Starts

¾�After the fan is run for 10 secs the inlet damper control is set to E1 mode with control

loop of Dryer hood pressure set to 0.005 Bar.

Burner Group

¾�Check Pre-Condition for Burner Group Start-up.

¾�Keep all the drive controls in Remote mode and set it to Auto.

¾�Ensure the level of Wet Coal Bunker to be at High Limit.

¾�Start the Burner Group in Auto Mode

After the start condition is initiated

¾�The combustion air fan and the mixing air fan are started. ¾�A fuel gas is selected and other fuel gas lines are closed tightly. ¾�The purging mode is started when fuel gas is available and the air fans are running

and the burner is in a rest status. ¾�Combustion Air Flow is set to a set point of 2000m3/h and MAF Damper is opened 30%. ¾�The purging mode is ‘ON’ when both valves have almost reached the set points. ¾�The purging time is 10 minutes. ¾�When this time is elapsed the purging mode is reset and the ignition mode is started. ¾�Combustion Air Flow is then set to a set point of 1000m3/h and MAF Damper is

- 30 -

closed. ¾�When these conditions are reached, the ignition valves are opened. ¾�With opened valves the ignition transformer is energized. ¾�During the ignition supervision time (60 sec) if the pilot burner flame detector is not healthy, the ignition mode is reset and after all valves has reached their home position

the Burner Group starts again with the purging mode. ¾�When the ignition valves are open and the Flame detector is healthy for at least 10 sec

the ignition burner is confirmed to be‘ON’ and then bleed valves closes. ¾�After the valves are closed the Combustion Air Flow Controller is set to a set point of 2000m3/h and MAF Damper to an output of 30%. Also Fuel Gas (COREX Gas/CNG)

valve is set to 25% dependent if Export gas or CNG used.

DRY COAL TRANSPORT

¾�Check pre-condition for the Dry Coal Transport Group Start-up.

¾�Keep all the drive controls in Remote mode and set it to Auto

¾�Start the Dry Coal Transport Group in Auto Mode

After the start condition is initiated

¾�At first the Stock House Top conveyor 149F11 starts. ¾�Next to this, the conveyor 149F01 (and 149F02 in case module-01 group is started) starts along with fines conveyor 149F03. ¾�For the Dry Coal Bins 235B01 and 235B02 Diverter Gate position is ensured. ¾�The Dry Coal Screen starts on receiving the run feedback of 149F01. ¾�Then after a delay of few seconds the conveyor 147F01 starts.

DRYER

¾�Check Pre-Condition for Dryer Group Start-up.

¾�Before start-up of Burner Group itself, keep all the drive controls in Remote mode

and

set it to Auto

¾�Start the Dryer Group in Auto Mode

After the start condition is initiated ¾�The Swivel conveyor starts (the position of swivel conveyor to be predetermined to

set the destination of Dry Coal).

¾�After a delay, the Vibrating Dryer Starts.

¾�Soon after that the Belt Weigh Feeder starts with a set feeding rate of 10 TPH.

- 31 -

After achieving the desired parameter and stabilizing the system the feed rate to be

increased to achieve the maximum output.

4. SKIP CHARGING 4.1. General The Skip System is used to hoist the raw material up to the top of the COREX tower. The skip systems in principal consists of the skip bucket, which is running up and down along the skip bridge and the winch system with rope guidance as well as supervision system for the control of the skip system. The skip system has to control the speed at top and bottom very accurately for safety. For the purpose of it each end positions are provided with different limit switches, which enable to control the speed of skip in steps. The winch system of both skip hoists are provided with hydraulically operated disk brakes for emergency purposes. The skip motor is controlled by means of frequency converters.

4.2. Skip Diagram

DESCRIPTION OF LIMIT SWITCHES

FULL

EMPTY

FULL

EMPTY EMPTY

FULL

EMERGENCY STOP SAFETY STOP STOP

SLOW SPEED INCHING SPEED

INTERMEDIATE BIN

CHARGING BIN

FEED BIN

REDUCTION SHAFT

SKIP CHARGING BIN

SKIP CHARGING BIN

FULL

EMPTY

OXIDE LINE COAL LINE

- 32 -

The Speed Control Diagram

Technical Data

DESCIPTION OXIDE COAL

CAPACITY OF BUCKET 12 M3 12 M3

WEIGHT OF BUCKET EMPTY FULL

12.0 TONS 35.5 TONS

09.0 TONS 18.9 TONS

TRAVEL DISTANCE 110.8 Mtrs 99.3 Mtrs

BRIDGE INCLIBATION 55.0 ° 57.7 °

CYCLES 8 Cycles/Hr 12 Cycles/Hr

SPEED 1.04 Mtrs/Sec 1.52 Mtrs/Sec

SPEED AT INSPECTION 0.1 Mtrs/Sec 0.1 Mtrs/Sec

CYCLE TIME 325 Secs 250.8 Secs

ROPE DIAMETER 48 mm 35 mm

GEAR RATIO 48.75 24.98

MOTOR SPEED 0 – 750 RPM 0 – 750 RPM

DIA OF ROAD DRUM 1300 mm 1300 mm

V2

V1

V3

V1 V1

V2

V3

V1

UP DOWN

S - 580

S - 510

S - 511

S - 512

S - 513

S - 514

S - 515

S - 517

S - 581

S - 516

EMERGENCY STOP

SAFETY STOP

DUMP POSITION

FILLING POSITION

SAFETY STOP

EMERGENCY STOP

V1 : 100 rpm V2 : 200 rpm V3 : 900 rpm

- 33 -

ROPE FORCE 297.055 N 158.390 N

4.3. Skip Operation

PRECONDITIONS

¾�The Skip bucket must be parked at the bottom positioned. ¾�All safety systems must indicate healthy conditions and satisfies the interlock. ¾�Select the local switch to remote. ¾�The drive system (Frequency converter) must be operational and ready without any

fault indication. ¾�Lock Hopper feeding bin is in empty condition.

START

¾�Select skip hydraulic pump in sequence and give Start command to the group. ¾�Select electric motor in sequence. ¾�Select skip charging bin gate in Auto. ¾�Select skip group in Auto. ¾�Give Start command to the Skip Group. ¾�If the Oxide skip starts automatically, it first runs with empty bucket when the

feeding bin of lock hopper is empty. After this initial operation the skip is now in auto mode

ready for charging material accordingly.

STOP ¾�Give stop command: The command is complete when the Coal skip is at bottom parking position. ¾� If Coal Skip trips, it can only be controlled by local operation from the skip winch station.

START SKIP IN MANUAL (from LOCAL BOX) This mode can be used when the skip is tripped due to any problem or the test is needed after maintenance.

¾�Switch local switch to local from remote. ¾�Switch group switch to manual from Auto in CCR. ¾�Push “UP” or “DOWN” button switch and adjust the speed by the potentiometer at the Local Control Box. ¾�Stop the skip in any position by pushing “STOP” button. ¾�If the skip control is interrupted and the skip bucket stops at other places than at

the bottom, it is necessary to bring the skip bucket down to bottom parking position from the local control box. This ensures that the system is investigated properly for eliminating the reason of fault.

- 34 -

SLACK ROPE This is the signal to detect the loosening of wire rope.

ROPE LENGTH Signal to detect the deviation of distance between the the position of slow limit switch and the input value of the cam switch.

LOCAL - OFF - REMOTE

EMERGENCY STOP

STOP

SAFETY

SLACK ROPE

ROPE LENGTH

STOP

SAFETY STOP

EMERGENCY STOP

MOTOR AMPS SPEED MOTOR TEMP

DISTURB

UP

UP

OFF

STOP

DOWN

DOWN

EMERGENCY STOP

SPEED

DOWN

°C % %

SLOW

UP UP

FAST

FAST

SLOW

SLOW

SLOW

DOWN

DOWN

FAST

SLOW

LOCAL CONTROL PANEL

- 35 -

5 LOCK HOPPER SYSTEM 5.1 General The COREX plant is equipped with two Lock Hopper Systems to charge the Raw Material into the pressurized reactor vessels of the plant. One system is used to charge Coal by means of the Lock Hoppers and coal screws into the Melter Gasifier and the other one is used to charge Ore and Additives into the Reduction Shaft through charging distributor. In principle the Lock Hopper System comprises of the following items:

¾�Feeding Bin ¾�Upper Material Flap ¾�Upper Seal Flap ¾�Intermediate Bin ¾�Pressurizing Valves ¾�Depressurizing Valves ¾�Lower Material Flap ¾�Lower Seal Flap ¾�Coal / Oxide Charging Bin ¾�Charging Distributor (only for Oxide System).

5.2 Operation Principle:-

The system is generally operated in automatic mode. In this mode, the level monitoring instruments of each bin is initiating the charging and discharging of material in the bin and the low level in the Feeding Bin/Intermediate Bin is calling the new batch, which is supplied by the skip charging system. The other mode is on Manual basis, which means that the individual control of flaps is performed on operator’ s action from CCR. Under normal circumstances the Lock Hopper system is operating on AUTO mode and doesn’ t need any special supervision by the operator, since the program will monitor any delay in the process steps and an alarm will be generated if the sequence is interrupted. As a precondition for the system the run feedback of the Lock Hopper Hydraulic System is required. If the Lock Hopper hydraulic is not in operation, the AUTO signal will be switched to manual and an alarm is generated. In order to prevent the intrusion of Hot Gas from Melter Gasifier to the Coal Charging system, Nitrogen is injected into the system to make a gas seal. The charging distributor is meant to set the profile of the burden in the Reduction shaft to achieve uniform gas distribution for effective and maximum reduction of the oxides. Operator can activate the charging distributor only if the level of the shaft is below LOW-LOW and the movement of that will be a very slow action, either inward or outward.

- 36 -

Lock Hopper Operation

Manual-Mode

Can be selected by the operator if: x� Sequence is not running & Sequence is not in HOLD-mode Sequence changes to MANUAL-mode if: x� Sequence is in HOLD-mode & End Step has finished (120s) x� Sequence is in HOLD-mode & Operator presses the RESET-button. Auto-Mode Can be selected by the operator if: x� Sequence is not running & Sequence is not in HOLD-mode If the sequence is not running and from Manual- to Auto-Mode selected all valves will be closed. Hold-Mode Sequence changes to HOLD-mode if: x� Valve or Pressure measurement fault x� Step alarm x� Operator presses the HOLD-button

Reset of Sequence Sequence will be reset if: x� Sequence is in HOLD-mode & Operator presses the RESET-button x� Sequence is in HOLD-mode & End Step has finished (120s) x� Operator presses the STOP-button & End Step is running 5.3 START and STOP of Sequence Start of Sequence Sequence is started if: x� Sequence is in AUTO-mode & Operator presses the START-button Stop of Sequence Sequence is stopped if: x� Operator presses the STOP-button x� COREX-Process trips In case the sequence is stopped following steps are finished and/or interrupted. Then the sequence jumps to the End-Step, Stops and is Reset. x� Step 1 / Preconditions: interrupted x� Step 2 / Depressurize: finished

- 37 -

x� Step 3 / Down charge 1 and Step 4 / Close Flaps 1: finished x� Step 5 / Prepressurize: interrupted x� Step 6 / Pressurize: interrupted x� Step 7 / Addl. Depressurize: interrupted x� Step 8 / Waiting: interrupted x� Step 9 / Down charge 2 and Step 10 / Close Flaps 2: finished x� Step 11 / Close All Valves: finished x� Step 12 / End Step: finished

Effects of Sequence-Reset x� All Depressurizing valves are closed x� All Pressurizing valves are closed x� Material and sealing flaps remain in their present position. Effects of Sequence-Hold x� All Depressurizing valves remain in their present position x� All Pressurizing valves are closed x� Material and sealing flaps remain in their present position

Effects of COREX-Process Trip x� If the COREX-Process trips the sequence wil be stopped and the intermediate bin depressurized, regardless whether the valves are in Manual or Auto. x� Step 1 / Preconditions x� Step 2 / Depressurize x� Step 3 / Down charge 1 and Step 4 / Close Flaps 1 x� Step 5 / Prepressurize x� Step 6 / Pressurize x� Step 7 / Addl. Depressurize x� Step 8 / Waiting x� Step 9 / Down charge 2 and Step 10 / Close Flaps 2 x� Step 11 / Close All Valves x� Step 12 / End Step

- 38 -

6. General Conception of Process Control

6.1 COREX Operation Control The basic operation control is the control of gas flow rate and permeability for

reduction in the shaft furnace and the oxygen flow rate control and the heat energy control for melting iron in- the melter gasifier. COREX process should be controlled as following diagram of the operation management for maintaining proper reduction rate and hot metal temperature & quality.

Top Gas Temp

Reduction Gas Flow & Temp

Reduction Shaft

Quality of Lump Ore / Pellets

Melter Gasifie

Export Gas

Oxygen Flow Rate

Hot metal & Slag Quality

Quality of coal & coke

Shaft Press Drop

RS Inburden Temp

Metalisation

Melting Rate

Dome Temp

Gas Generation &

Quality

- 39 -

6.2 Melting Rate

Melting rate Oxygen rate HM Quality Metallization Coal feed rate RM Quality (coal) Shaft operation DRI feed rate Slag Chemistry Material distribution RM quality Fixed bed level Gas distribution

Total gas generation DRI metallization Descending rate Dome temperature Melting rate quality & reduction gas flow Plant pressure control

Melting rate Melting rate is rate of melting or quantity of HM produced per hour. In case of corex mainly it is controlled by tuyeres oxygen flow followed by DRI & Coal feeding. But it is affected by many parameters like metallization, RM quality, slag volume and other parameters.

COREX operation control should satisfy the basic precondition for maintaining proper hot metal temperature of molten iron & slag and making iron with good quality. Each character of operation control shows as following table.

- 40 -

Purpose Indication Influence Control method 1. Reduction control

-Hot metal temperature and quality

-Analysis of DRI

- In burden Temp

- Top gas component

-Reduction gas

Flow rate and temp

-Descending rate

-Top gas control valve

DRI screw rpm

Reduction gas temp

2. Melting rate control

-Hot metal temp

Production

-Ore batch

DRI screw speed

-Reduction rate

-Hot metal temp

-Dome temp

-Oxygen rate

-DRI screw rpm

3.Shaft permeability control

-Reduction gas rate

-Uniform gas profile

-Pressure drop in shaft

-Size distribution

-Ore decrepitating

-Shaft temp

-Reduction gas flow rate

-Descending rate

-Input Raw material

4. Fixed bed control

-Hot metal temp & quality

Level in MG -Coal quality & quantity

-HM Temp

-HM/ Slag drainage.

-Dome temp

-Coal screw rpm

-Oxygen rate

-Dome temp

-System pressure

5. Dome temp control

-Prevent tar generation

-Dome temp

-Gas component

-Coal quality & quantity

-Oxygen rate

-Gas velocity & analysis.

-Coal and DRI screw

-Dust burner oxygen

-System pressure

6.Sysrtem pressure control

-Dome temp

-HM temp

System pressure -Oxygen rate

-Coal quality

-Amount of gas generation

-Excess gas control valve

-Oxygen rate

-Coal rate

7.HM temp control

-HM quality

-Liquidity of iron & slag

-HM temp

-Race way brightness

-Oxygen rate

-Reduction rate

-Fixed bed

-Oxygen rate

-Melting rate

-Coke rate

8. HM quality control

-HM quality

-Analysis of iron and slag

-Fixed bed level

-HM temp

-Additive rate

-Fixed bed level

-HM temp

- 41 -

-Reduction rate

-RM quality

6.3 Melting rate vs. oxygen consumption. Oxygen consumption rate (sp oxygen) is normally inversely proportional to the melting rate. Generally as the latter increases the former become lower due to relatively reduced heat loss for emission in initial stage of restarting melting rate usually low.

It is not advisable to run the corex with low melting rate for the prolonged period because fuel consumption rate will increase and shaft going to be unstable due to higher retention time of burden. Then the quality of HM getting effected.

Similarly very high melting rate also lead to quality as well as the other problems like DRS jamming, gas cleaning, lower Metalisation etc,. In higher melting rate quantity and quality of the reduction gas and also retention time of burden in shaft is a big constraint leads to lower HM temperature and more coke requirement. So it is necessary to optimize the melting rate within boundary considering all process parameters, raw material and system availability.

800

700

500

O2 consumption

Nm³/hr

20 40 60 80 100 110

Melting rate (T/hr) 6.4 Dome Temperature Control Dome temperature to be maintained 1000 C to 1050 C depends on the coal volatile matter for proper devolatization and of coal CH4 % in cooling gas. Both low dome and very high dome temp not advisable. Low dome may lead to tar formation and chocking of ducts gap and bend jam etc, very high temperature also

Heat loss for emission- low Metalisation- high Heat exchange of burden- good

Heat loss for emission-high Metalization-low Heat exchange of burden-poor

- 42 -

will lead to coal decrepetation & refractory damage. In case the dome temperature is reached approximately 950 deg C, the generation of Metal and reduction gas is occurred

MR vs. Dome temperature: As the melting rate increase dome temperature & hot metal temp will go down because of non-metallized & un-calcinated material flow from shaft. So it is important to watch dome temperature before increasing the melting rate. Free energy (kcal/mol) -40 -20 0 20 40 1000 C Temperature

2. Indication factors Decision factors of dome temperature control are temperature measurements (TR0 1440-1442) and the composition of the cooling gas. If the dome temperature is too low, the percentage of CO2 and CH4 of the cooling gas are increased. On the contrary, if the dome is too high, the percentage of CO of the cooling gas is increased and the quality of cooling gas is gone badly. So it is important to maintain the normal dome temperature. 3. Affection factors The factors that affect the dome temperature are the feeding rate of DRI, the reduction rate in the reduction shaft, calcinations of additives the o2 amount of dust burner, the feeding rate of coal, the level of the fixed bed, total gas generation and the system pressure etc, the dome temperature is decreased as the following cases; the feeding rate of DRI is fast, the reduction of DRI is low, the calcinations of additives are low, and the feeding rate of coal is low. On the contrary, the dome temperature is increased as the following cases; the o2 amount dust burner is increased and the coal size is small. 4. The theory of the dome temperature control If the system pressure is increased the gas flow of melter gasifier is

CO+ 3H2-Æ CH4 + H20

2CO + 2H2 Æ CH4 + CO2

C + 2H2 Æ CH4

- 43 -

gone to the wall side, the velocity of the gas is decreased, the heat exchange is improved thee dome temperature is decreased, and the temperature of the hot metal is increased.

6.5MR vs. RS operation Shaft condition to be checked before increasing MR. Availability of reduction gas and quality of reduction gas is important. In the higher MR more gas required to maintain same metallization with decreased retention time. Also observe shaft 'P in burden temperature and gas utilization

6.6 MR vs. other parameters While starting the plant it is better to increase the tuyere O2 as quick as possible. After dome reaches 950 C start coal feeding and also DRI feeding. Along with DRI screw speed increases, increase the reduction gas to shaft and also coal input proportionately. Depends on s/d duration try to stabilize the process as quick as possible.

6.7 Plant pressure and tuyere velocity Both parameters are inter- related and important in the quality control and also total MG gas distribution profile as well as refractory life in long run. So it is important to maintain the constant plant pressure and tuyere velocity. Try to operate with 3.5 bar plant pressure and approximately 190-200 m/s of velocity by opening and closing tuyeres with MR 1. Purpose 1) Gas distribution and tuyere oxygen velocity control in the melter gasifier 2) To prevent the formation of fluidized bed 3) To improve the efficiency of heat exchange in the melter gasifier 2. Affecting Factors 1) Quality of coal 2) Amount of charged coal and DRI 3) Amount of generation gas 4) Dome temperature 5) Gas permeability within the fixed bed, etc.

3. Actual operations

1) Control the system pressure by oxygen & tuyere Velocity Maintain 190 -200m/sec during the normal operation. 2) If system pressure decreased, the dome temperature will be increased But the hot metal temperature is decreased.

3) In case of the formation of fluid bed is increased and the hot metal temperature is decreased, increase the system pressure.

4) If volatile matters of coal is increased and coal size is small, the fluctuation of system pressure is increased. 5) If the amount of coal to the melter gasifier is increased, generator gas

- 44 -

amount is increased because of the combustion of volatiles. System pressure is increased. Control of coal screw speed is needed according to the amount of oxygen within the melter gasifier

Relations to other parameters

1. Amount of O2 to the tuyere- system pressure Tuyere O2 Nm³/hr System pressure (bar)0 2. Dome temperature – system pressure

3. Hot metal temperature- system pressure

- 45 -

The control of system pressure is a main factor to control the hot metal temperature. The fluctuation of system pressure makes hot metal temperature decrease 6.8 CG analysis Especially CG CO2 content plays a major role in DRI metallization. Both high and very low CO2 content is not good. So it is better to control CO2 in the range of 5-8% Tools like iron ore fines, specific O2 to tuyeres, dust burners O2 and melting rate can be used for controlling the analysis. 6.9MR vs. DRI screw operations During normal plant start DRI screw can be started from 0.8 rpm. It is to be increased steps along with reduction gas and specific tuyere O2. Normally screw discharge is 165 lit/rev. Calculate every day screw discharge, because day-to-day lot of parameters discharge rate can vary day to day. Monitor screw pressure and down pipe temperature and shaft 'P to ensure shaft condition. 6.10 Char bed level control 1. Basic concept

Fixed bed is a burden that is mixed up with DRI, additive and char. -With going downward it is heated up by counter flow gas. If DRI heated up for enough time, quality of hot metal becomes better. So its level has, to be kept high as possible. In actual operation it is always sustained at the level that is belw1m of dust burner. But it is not advisable to, control dome temperature and other operation factor by controlling fixed bed level. 2. Fixed bed level control 1) Casting and level As cast progress fixed bed level tends to go slow down. If slag and metal is drained out successfully, usually down of fixed bed level is about 1 m. So in advance of cast DRI & coal screw rpm need to be increased to maintain fixed bed level. 2) Flow rate of oxygen through tuyere and level

Down speed of fixed bed is determined by flow rate of oxygen through tuyere. That is, if flow rate of oxygen increase fixed bed level is going fast down due to increasing consumption rate of char and melting rate of DRI simultaneously. So both coal and DRI screw speed have to be adjusted according to flow rate of Oxygen to keep fixed bed level.

3) System pressure and level Increase of system pressure contribute passing gas to delaying in burden. This serve as merit that quality of hot metal can improve. But if system pressure is very high, because

- 46 -

penetration distance of oxygen is too short to form central flow, burden becomes unstable.

4) Quality of hot metal and level Rising of fixed bed level make contact time between material and gas longer. Accordingly both hot metal temperature and [Si] content is higher.

3. Fixed bed level control in actual operation

1. Level control in normal and abnormal operation

Item Normal

Maximum level LRO 1602 -100 %

Minimum level LRO-1602 –0 %

In advance of plant stop increasing fixed bed level is to compensate level down during restarting, that coal screw cannot permit to start

2.Leveller position and volume

TAP HOLE

2. If the dome temperature is too high and the hot metal temp is not so low, increase the melting rate. But, the HM temp is low; increase the coal screw speed considering the fixed bed level.

Leveler position

Volume m³

Vertical height (m)

Dust burner- LRO 1602

109 1.2

LRO 1602- LRO 1603

105 0.95

LRO 1603- LRO 1604

50 0.6

LRO 1604- LRO 1605

100 1.3

LRO 1605- LRO 1606

105 1.8

LRO 1606- TUYERE LEVEL

113 2.56

LRO 1602- Tuyere

501 12.9

D/B LRO 1602 LRO 1604 LRO 1606 TUYERE

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3. The purpose of the O2 injection of dust burner is to control the dome temperature and to burn the dust inside the melter gasifier. In case the )2 amount of the dust burner is low, the following phenomenon will be occurred.

- The amount of dust circulating in MG is increased

- Fine particles of dust is increased

- The height of fluidized bed is increased

- The efficiency of hot cyclone is decreased

- The dust loading in reduction shaft is increased

- Some trouble in the gas cleaning line is occurred

The following table shows the affecting factors of the dome temperature.

Factor Dome temp

Factor Dome temp

Feeding rate of DRI

Increase Decrease Feeding rate of coal

Increase Decrease

Metalisation Low Decrease Coal size

Small Increase

Calcination Low Decrease System pressure

High Decrease

Dust burner O2 Decrease Decrease Fixed bed level

High Decrease

Fixed bed & Taping: I

Burden material load of melter gasifier in COREX is lighter than that of blast furnace because of the COREX furnace separated by reduction shaft and melter gasifier, and also the behavior of molten iron in the melter gasifier is different from the blast furnace. Molten iron of the blast furnace moves through the void of the coke deadman in the hearth due to high burden load, but COREX molten iron moves in the free space below the char dead man.

The shape of coke deadrnan and the existence of free space effect the corrosion of the brick in hearth and bottom. ’ According to tapping time, COREX char bed moves up and down because the char bed floats on slag and melten iron. Total burden weight of char bed can be calculated by the weight subtracted floating force by gas from char bed weight itself, and char bed can be floated with the balance of total burden weight of char bed and the buoyancy of slag & molten iron.

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(Precondition to float char bed on slag & iron) 1) Total burden weight Buoyancy: Deadman penetrated by slag and iron 2) Total burden weight = Buoyancy: Begin to float deadman on slag and iron 3) Total burden weight (Buoyancy: floating deadman on slag and iron

" Burden weight = char bed weight floating force by gas ('P) " Total burden weight = burden weight + deadman weight Slag buoyancy + molten iron buoyancy

2. Slag & iron behavior and tapping time

COREX char bed is floating on slag & molten iron, which cause to move the char bed up and down as tapping time. Behavior of Slag & molten iron is subjected to the balance of total char bed weight and the buoyancy of slag & molten iron. Fig 10-2 shows the behavior of char bed that comes down until the tap hole level after finishing cast. Iron & slag is continuously generated below the char bed before cast, and the char bed moves up because of slag buoyancy. When iron & slag start to drain, iron drains out at first as interface of slag and metal moves up to the level higher than the tap hole level. With Draining slag and metal, char bed moves down again. Usually char drains out from the taphole when char bed reached on the tap hole level, and then the tap hole should be closed. So char deadman is always penetrated by some of slag and char bed is always floating on slag and molten iron. It is very important to control slag, level because the characteristic of tapping effects the corrosion of the brick in hearth and bottom and tuyere melting as the slag level reached tuyere level.

Tuyere

Char bed Char + slag Slag Metal

Char bed Char+ slag Slag Metal

Char bed Char + slag

Slag

Metal

Char bed Char + slag

Slag

Metal

Finish cast Begin cast Separate slag Finish cast

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6.11 Reduction shaft Operation The reduction rate in the shaft mainly depends on reduction gas flow and quality. Also other things like gas distribution, pressure drop, material descending condition etc,.

Factors affecting the reduction rate. The ore reduction rate in the shaft should be more than 90%. Basically reduction rate depends on reduction gas flow rate. Reduction rate increases if reduction gas flow rate increase, and reduction rate decreases if reduction gas flow rate decrease. But gas distribution should be even for reduction because reduction rate could be influenced by shaft condition like pressure drop, gas flow and material descending condition.

x� Reduction gas flow rate x� Reduction gas temperature x� Material descending velocity x� Material traveling time x� Gas distribution x� Indication factor of reduction rate x� Analysis of DRI Sample x� Gas utilization x� Shaft wall temperature & vertical temperature

Flow rate control of reduction gas

Reduction gas flow is controlled by top gas control valve for ore reduction. In case of using pellet, reduction gas flow rate should be injected less than using lump ore because the reduction velocity of pellet is higher than that of lump ore, and reduction flow rate is different from each pellet and ore brand. Gas utilization decrease due to uneven gas distribution and high dust loading which result to reduce reduction rate of same reduction flow. Reduction gas flow should be properly maintained in the shaft considering ore and pellet characteristic because dust content per unit volume become high and void age decrease if reduction as flow become excessive. To keep more than 90% reduction rate in the shaft, top gas flow should be calculated Viand maintained for each material. Melting rate will be increased in case of high temperature of hot=metal if top gas flow is excessive compared with charging ore. But melting rate will be decreased in case of low. Temperature of hot metal or top gas flow will be increased if top gas flow is insufficient compared with charging ore. Brig 2-1 shows the weight loss of pellet is higher than that of lump ore during reduction, which means than reduction rate of pellet is better than lump ore. So using lump ore ’needs

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more much reduction gas to be injected to shaft than using pellet.

Reduction gas temperature control

Reduction gas is controlled by cooling gas injected to generator gas in liner according to bustle temperature, and the temperature keeps 790-.8500C for ore reduction. The temperature of reduction gas injecting the shaft with 800°C increase up to 880°C in the shaft because of ore reduction, and at this temperature ore reduction occur actively. If reduction gas temperature is extremely high, material temperature increase above 830°C, which makes pellets, be clustered due to growing metal fiber material. Clustered pellets cause to make material bridge above DRI screw, stop revolving the screws and deteriorate gas profile. So it is very important to keep the reduction gas temperature suitable. Especially for using pellets, it is necessary that reduction gas flow should be low and reduction gas temperature. keeps lower than ore.

Descending velocity and retention time of material in shaft

Descending velocity is proportioned, to retention time. In case of 90 ton/hr of melting rate, the traveling time of material is about 8 hours in the shaft. The longer retention time is, the better ore reduction become. Reduction rate becomes high due to high retention time, but dust content becomes increased and pressure drop goes up, which may cause to make uneven gas distribution, slip and hanging. Therefore descending velocity should keep as high as possible to shaft condition because it makes material void age increased. Descending velocity can be adjusted by DRI screw rpm and hot metal temperature.

Reduction rate and hot metal temperature

Reduction rate can be known by analysis of DRI sample, gas utilization and theoretical calculation. If reduction rate drop, hot metal temperature will be down. So reduction rate should be controlled previously to prevent hot metal temperature decreasing abruptly.

Generally, hot metal temperature drops after 3 hours when reduction rate decrease, and so oxygen rate or coke rate should be increased before the temperature drops. Prior to dropping reduction rate, shaft condition shows a phenomenon; vertical. Temperature, gas utilization and wall temperature below bustle decrease. Most abrupt: drop of hot metal temperature occurred in case of bad shaft condition. Specially using mixture of pellet and ore, reduction rate dropped abruptly because of high pressure drop, slip and hanging due to segregation of pellet and ore.

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Gas distribution It is of the’ most important thing to distribute reduction. gas uniform through burden to accomplish stable operation of shaft furnace as well as melter gasifier. From this, pellet can be reduced well to and additive be calcinated. To achieve even gas flow, minimum size, size distribution and reductive degradation properties of pellet has been controlled. can be judged how gas distribution is going by pressure drop, temperature variation, abnormal descending of burden and utilization of reduction gas .

Gas distribution control

Small particle regulation and size distribution control: Because larger particle guarantee gas to flow well through burden, input of small particle has to be regulated. The smaller particle is, the worse permeability is even if size distribution of particle is harrow and shape is regular. Generally resistance to gas flow increase greatly as particle size decrease below 13 mm.. Also permeability is effected by the range of particle sizes. By keeping the range of particle sizes to a minimurn permeability increase.

Degradation control of particle: Iron ore and pallet are inclined to degrade during heating and reducing. Specially pellet tends to swell at its maximum around 850 C to degradate early; Small particle generated from degradation is accumulated into pore and block the way of gas. If dust is accumulated in particular parts, dust stack is accelerated and gas flow is deviated. It can be caught in observing vertical or horizontal temperature deviation and pressure drop of burden in shaft furnace. To avoid this problem, select iron ore or pellet that cam endure degradation from heating and reduction. Also samples have to taken to be analyzed periodically.

Dust control of reduction gas: COREX reducing gas contains considerable dust generated from coal pyrolysis and pellet reduction. Most of them is captured and eliminated in hot cyclone but some is in flowed into shaft furnace and accumulated. In case that hot cyclone system is run in abnormal operation and input of dust into shaft furnace become to increase, condition of shaft furnace such as gas distribution, deviation of temperature and so on should be checked from time to time. If abnormal operation may prolong,, it has better be run after being resolving the problem.

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Gas distribution control in actual operation: It can be judged whether gas distribution is uniform or no uniform by total pressure drop of burden. Total pressure drop of burden become to increase steadily with the gas velocity on condition that other operation factor is fixed. The following figure show relationship between bounds of pressure drop and top gas flow rate in normal operation. Also Gas distribution has been controlled monitoring the differential pressure across the shaft. When pressure drop exceed critical value, slip and hanging appear. It happens when material is sticky and degraded, dead man grows up, bustle port is blocked and gas flow is deviated severely. 6.12 Hot metal temperature control.

The purposes of hot metal temperature control are first, to ensure proper behavior of melts (slag & hot metal) inside melter and during tapping to achieve dry operation of melter gasifier. Second, to obtain target hot metal quality which influences down-stream process. Especially, silicon content and sulfur content in hot metal are strongly influenced by hot metal temperature.

The key point of hot metal temperature control is to keep target hot

metal temperature stably using several control measures. The most influencing factor is metallization degree, which is directly related to the shaft performance. Every indicating and controlling parameter has their own response time according to the melting rate.

Main affecting factors Metallization (or reduction)/ degree of DRI:

Iron oxide is reduced by two step reduction path. The first step is indirect reduction by gas I solid reaction which is exothermic and mainly occurs in reduction shaft. The second step is direct reduction by liquid I solid reaction which is highly endothermic and occurs during / after melting of DRI. Therefore, the target of COREX Operation should be maximizing indirect reduction in the reduction shaft and minimizing direct reduction in the melter gasifier. If low metallized DRl is fed to melter gasifier, then heat level is decreased and fixed bed is deteriated (char consumption increase, fixed bed level decrease, char particle size decrease, gas & liquid permeability decrease) due to highly endothermic nature of direct reduction, in real operation, metallization degree itself is not referred by operator because analysis results can not cope with control actions. However, factors which affect Metalisation degree, for example top gas flow rate, top gas composition, cooling gas composition, in-burden temperature, horizontal gas temperature distribution, shaft temperature shaft delta pressure, are continuously evaluated to counter measure low metallization.

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.6.13 Melting rate and oxygen flow to tuyere

The only heat source to MG is combustion of oxygen at tuyeres front and dust burners. Oxygen flow to tuyere is increased but specific O2 flow is decreased, as melting rate is increased. HM temp is promptly controlled by O2 flow.

3.Response time

A) Indicating parameter

Factor Response

time

1st affecting factor

1 In burden temperature 7-8 Metalisation

2 Down pipe temperature 4-6 Melting rate

3 Slip and hanging 6-10 Penetration of gas

4 C/G CO2 CH4 4-6 Dome temperature

5 K CO of top gas 8-10 Distribution of gas

6 Basicity 2-3 Change the retention time

7 Brightness of tuyere 2-3 Change hot metal temp

8 Dome temp 3-4 CG Analysis

9 Fixed bed level 3-4 -

HM temp (comparison with last tap)

0-1 Change HM temp

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B) Controlled Parameter. Factor Response

time in hrs

Check place

1 Amount of tuyere O2

2-3 FRC8001

2 DRI feed rate 4-5 DRI screw rpm

3 Coke ratio 4-5 Weighing time

4 Feeding rate of coal 4-5 Coal screw pin

5 Amount of reduction gas

7-8 FRC 2001

6 Specification of coal 4-5 Mixing bin (sampling)

7 Specification of pellet

12-15 Raw material handling

8 Velocity of tuyere O2

2-4 Monitor

9 System pressure 2-4 PRC 2003

6.14 Quality control of hot metal HM quality means maintaining HM temperature and chemical composition (mainly C, Si, S,P etc,) as per the required standard. Carbon & Silicon have generally co-relation with HM temperature and retention time. So they can be controlled by proper HM temperature (i.e. also coke rate) ,certain height of fixed bed and melting rate Sulphur can be controlled by slag volume & basicity based on input raw material composition. Very high acidic or basic slag are not advisable. It is better to maintain Basicity (CaO/SiO2) in the range of 1.10. Si content in HM normally increase dramatically after restarting the furnace after shutdown due to longer retention time. P and Mn content of HM can be only controlled by input raw materials. 98%of the total P2O5 gas to hot metal.

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7. Process Gas Systems

Total gas generated in Melter Gasifier (MG) is having four outlets for carrying the gas which are called Generator Gas ducts (GGD). These Generator Gas ducts (GGD) are connected to a hot gas cyclone (HGC) for cleaning the dust carried along with the gas. The dust settled in the cyclone is further taken to a Dust bin which is located below the Cyclone and is injected in to the Melter Gasifier through a Dust Burner with Nitrogen as Injecting media and Burnt with Oxygen. The process of this dust separation in HGC and burning in the MG again is called Dust recycling system which makes the Corex process environment friendly. The Major composition of gas generated in MG: % CO : 65-70 CO2 : 05-08 H2 : 20-25 CH4 : 1 - 2 The generated gas from MG is coming out at around 1050 Deg C and which is controlled to a range of 850 Deg C for Reducing and Calcination of Additives. Control of this temperature is done by adding the cooling gas in to the GGD through Temperature control valves which is called cooling Gas addition.

Gas Holder

PDC 2212

H/C

Ore

Coal

Melter Gasifier

Shaft

Excess gas line

C/G Compressor

Top Gas Line

FRC2001 SOV2940

Export gas

PRC2210 Sludge

PDC-2207

PDC-2208

Sludge Sludge

Sludge

Sludge

PRC2203

- 56 -

The clean gas that is coming from the cyclone is taken through Bustle of the Reduction shaft for reducing the Iron Oxide and Calcination of the Additives that are charged in Reduction Shaft, which is called Reducing Gas. As shown in the schematic, the clean gas of from the outlet of HGC is taken in to the Reduction shaft bustle, through a Top gas flow control valve FRC2001. The amount of flow through the RS is depending upon the conditions and movement of Reduction shaft, which is generally 1050-1120 m3/hr/ ton of oxide charge. The gas that is coming out from the RS is called Top gas that is at around 280 -300 deg c and the major composition of the gas is follows Top gas composition:

% CO : 40-45 CO2 : 30-35 H2 : 15-20 CH4 : 1-1.5 The top gas is further passing through a packing scrubber for cooling and cleaning the gas. As shown, the gas which not passing through RS is taken via a packing scrubber which is called Cooling gas Packing scrubber which is having two outlets i.e. Excess Gas scrubber and Cooling Gas venturi scrubber. Excess gas scrubber is controlling Plant pressure through its two hydraulic actuators DN 400 & DN 800. Plant pressure is controlled always to maintain fixed velocity at the exit of the tuyeres. Top gas and excess gas after gas cleaning are connected to a gas network for the gas consumers. Gas network is controlled by the level in the gasholder and unused gas is flared as shown through a pressure control valve PRC 2210. The cooling gas venturi is connected to a Compressor which can boost the pressure by about 1 bar for cooling gas addition to GGD.

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HOT GAS CYCLONE

N2 INJECTOR

LOWER DUSTBIN

DISC GATE

DUST BURNER

MG

O2 TO TUYERS

RS

GENATOR GAS DUCT

COOLING GAS ADDITION

The hot generator gas, leaving the Melter gasifier is connected to a the refractory lined hot gas cyclone where in the dust particles settle down due to loss in momentum before entering the reduction furnace. The dedusting takes place in the upper part of the hot gas cyclone where the vortex tube is installed. In the lower part of the hot gas cyclone the dust is collected. To prevent the back stream of collected dust to the upper part a displacement cone (Chinese cap) is installed between upper and lower part of the hot gas cyclone. The hot dust is transferred via the refractory lined lower dustbin to the dust burner, which is installed in the Melter gasifier. Purge plugs are installed in the cones of hot gas cyclone and lower dust bins for fluidization purposes. The hot dust, collected in lower dustbins is transported by means of nitrogen to the dust burners and burnt in the Melter gasifier using oxygen. The combustion takes place in front of the dust burners. Both HGC and LDB are provided with Nucleonic level sources for measuring the level in individual vessels

7.1 DUST RECYCLING SYSTEM

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Grids are installed in the lower part of the hot gas cyclone and in the lower dustbin to safeguard the adjacent built in equipment against coarse particles. Dust shut-off valves are installed below hot gas cyclones and below the lower dustbins. During normal operation of the COREX –plant they are in open position and only used for maintenance purposes to block the dust flow. Knife Edge gate valve (KGV) is installed at the emergency discharge nozzles of the hot gas cyclones, the Lower dustbins, and below the T-piece of the dust recycling line. During normal operation of COREX- plant they are in closed position and only used to empty the dust recycling systems for maintenance purposes The dust burner is continuously cooled with water which is circulating from critical cooling water system (Closed Loop) and normal flow of circulation is 30m3/hr for each burner at 9 bar pressure. Nitrogen injection flow through the dust burner is normally in range of 250 -350m3/hr and oxygen flow through the burner can be varied from 500 -4500 m3/hr which is tool to control the Dome temperature. Dust Analysis:

C approx 60 % S approx 1 % Fe approx 20 % Gangue approx 19 %

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7.3 Gas cleaning systems:

REDUCTION SHAFT

TGPS TGVS TGME

TOP GAS DUCT

TOP GAS FLOW CONTROLLER

WATER SEAL TANK

CLARIFIER

CLARIFIER

TOP GAS SYSTEM

TOP GAS PACKING SCRUBBER

TOP GASVENTURISCRUBBER

TOP GASMIST ELIMINAOR

The gas leaving the Reduction shaft that is called Top gas dust laden gas with temperature in range of 280-300 deg C normally. So this Gas requires both cleaning and cooling for which it passes through a top gas-packing scrubber. First the incoming gas to the scrubber is quenched in pre scrubber and then further it is cleaned in top gas wooden packing scrubber consisting of Adjustable venturi scrubber, mist eliminator, water separator, water level control tank as shown in the above graphic. The differential pressure across the venturi scrubber is set and controlled through the shown Adjustable venturi scrubber. The top gas pre scrubber, packing scrubber and venturi scrubber are continuously circulated with process water as described in Process water systems

DP2

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7.3 COOLING GAS SYSTEM

CGPS

CLARIFIER

CGVS CGME

EXVS EXME

EXCESS GAS

WATER SEAL TANK

CLARIFIER

COOLING GAS

COOLING GAS COMPRESSOR

CGPS CONE

PRC2210

FLARESTACK

FRC2001

PRC2222

SOV2940

GV

SHV

Cooling Gas Addition to GGD

EXPORTGAS

BAUMCO SCRUBBER

PACKING SCRUBBER

VENTURIMIST ELIMINATOR

TOP GAS

The gas which is not taken to the RS is directed to the Cooling packing scrubber which is first quenched in Pre scrubber and enters the packing scrubber. The differential across the packing scrubber is controlled through Baumco scrubber Cooling packing scrubber has two outlets as shown i.e. excess gas and cooling gas in which the differential pressure is controlled through its respective adjustable venturi. The Cooling packing gas pre scrubber, packing scrubber, Excess & Cooling venturi scrubber are continuously circulated with process water as described in Process water systems

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Cooling gas compressor is a Lobe type positive displacement compressor which is used to control the temperature of the Gas leaving the MG to a range of 850 deg c. The inlet to the compressor is connected from cooling gas venturi and the compressor can boost the pressure by about 0.9 bars. There are two compressors provided for each module among which one is stand by and one is running. Each compressor is provided with separate lubrication system for both Gearbox and Compressor. Stand by compressor is always kept running with its slow speed drive so that there is no dust accumulation on the lobes. Pre conditions for Compressor start:

x� Both compressor and Gear box lubrication systems are running in order

PDC2213

TDC2419

Inlet Valve Discharge valve

Silencer

Compressor

HIC T2

DT=T2-T1

T1

CG addition to GGD

From CG PS

7.4 Cooling Gas compressor

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x� All the drives and position of valves are healthy x� Process cooling water system is running in order x� Machine cooling water system (non critical ) should be running in order x� Inlet pressure to the compressor should not be Low low

Control of the Compressor: During the start of the compressor to avoid the excess load on the compressor, one Control valve (HIC) is provided which bypasses the discharge back to the inlet f the compressor and it closes after opening the normal discharge valve. The discharge of the compressor is cooling the gas coming out from MG, which is temperature controlled and hence cooling gas flow to GGD is not constant. But the compressor being fixed displacement type, it is required to control the Pressure differential across the Compressor and a control valve is provided (PDC2213) which diverts the discharge back to cooling gas venturi. Temperature differential control (TDC2419): It is desired to avoid any condensate water that could hamper the compressor and hence a control valve is provided to maintain the differential temperature of the gas entering the compressor. The temperature measurement is just after cooling gas venturi and before entering the inlet silencer of the compressor. Normal temperature differential between these two points is 5 deg C. Part of the gas from the discharge of the compressor is used through TDC2419 for this control. Vibration control: Vibration of the compressor is online monitored in both axial and radial directions which should be ��-8 mm / sec. These vibrations could be because of two reasons basically. One is due to the unbalanced lobes due to accumulation of dust and second one is due to any loosened Foundation bolts etc. The vibrations due to the first reason i.e. unbalanced lobes can be controlled with the given ethanol injection on to the lobes which brings down the vibrations significantly. Normally each start and stop of the compressor is accompanied by the ethanol injection and it can be injected in between when ever the vibration goes high. Cooling gas addition to GGD: As described in introduction of the gas systems, the gas leaving the MG is at around 1050 deg C which needs to be controlled to a range of 850 deg c and this is done by adding cool gas through a temperature control valve in each generator gas line (TRC 2411- 2414). The pre conditions for the addition is running of cooling gas compressor and discharge pressure of the compressor is more than the plant pressure at least by 0.1 bar. Failure of the cooling gas addition due to any reason makes nitrogen valve to open till the gas addition resumes. The scheme of addition to GGD is shown here for one line, which is similar to the other three lines.

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MG

N2

N2

Cooling gas addition SOV TRC

Generator gas Duct

- 64 -

8. PLANT START AND STOP PROCEDURES

8.1 PLANT STRT:

1. Check the preconditions: Before start, confirm the below mentioned items

a. Check the dedusting systems including pneumatic dust transporting systems b. Check the charging systems of raw materials c. Check the coal drying facilities d. Check the conditions of all water treatment system e. Check the gas analyzer of C/G &T/G f. Check the all hydraulic pumps for lock hopper, scrubbers, skips etc,. g. Check the depressurizing and equalizing systems of lock hoppers h. Check if the tap holes and facilities of the cast house are ready for tapping i. Check the preconditions of cooling gas compressor (hydraulic pumps should be

operated in advance) j. Check the impulse lines of instrument system at the site and output signal for each

automatic valve in monitor k. Check the supply pressure of O2 and N2 (including N2 for instrument) – for

main: 11r0.5kg/cm³ l. Check if the labyrinth part of each DRI & coal screw is supplied with a certain

amount of nitrogen through each FIO line m. Do the poking works to each tuyere

2. Plant leakage test

a. Open all tower shut down hand valves labyrinth N2 for screws etc,. b. Ignite the burners for the flare stack c. Announce the start of nitrogen system to )2 plant d. Set the differential pressure valve for each gas scrubber for cleaning gas

generating from the MG e. Set the system pressure by using of PRC 2211 and close the FRC-2001 f. Open all hand valves for supplying O2 and close all branch valves of N2 tuyeres g. Set 6000 Nm³/hr for FRC-3020 to check the poked condition of tuyeres h. After checking N2 flow of each tuyere, reduce N2 flow to 3600 NM³/hr in order

to perform the leak test of plant. i. Do the leak check over each maintenance parts when the system pressure is reached

to 1 kg/cm³

3. Plant purge & Start CGC. a. Pressurize and depressurize the system repeatly until the O2 density of C/G is

decreased below 0.5%. b. Start the C/G compressor.

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4. OXYGEN START:

1. Check the interlocking for O2 start b. Select O2 / N2 group switch on CRT and set it “ ON” If the plant is started successfully. ¾�O2 flow The rate of tuyere is set to 22000 Nm3/hr ¾�System pressure is set to 1.2 kg/cm3 ¾�The controller for system pressure is changed to PRC-2202 from PRC-2211 ¾�Check the set value of FRC 3020 is 6300NM3/hr with open SOV-3920 ¾�Check that SOV-8906 is closed ¾�Check that the out put value of FRC-8001 is 20% as a preset value. ¾�Check the sequence that the SOV 8901 is opened when the N2 flow of FRC 3020 is

reached at 5000nm3/hr and 1 second later SOV8900 is opened ¾�Check the sequence that SOV3920 is closed when the FRC 8001 reached at

8000nm3/hr, and manual output of FRC3020 is forced to100%. ¾�10 seconds later, check the set point of FRC 8001 is set to 22000nm3/hr.

c. Check the combustion status of char in front of tuyere and the O2 flow rate of each tuyere on the CRT.

d. Check that the densities of CO & H2 in cooling gas is increasing and gas combustion status of the flare stack

e. Check the supplying condition of cooling gas to gas inliners and down pipes. f. Increase the O2 amount as 1000nm3/5 minute up to 26000 nm3/hr in steps. g. Start dust burner h. Start an upper coal screw and set the speed of it to 4 rpm. i. Start DRI screws after starting coal screw. j. Take the gas in the reduction shaft for reduction work k. Take the gas in the gas holder

5. adjust the system parameters and production rate

a. Adjust the speed of melting rate according to the time of shut down and plant conditions

b. Decide the amount of quartz by the material charging calculation according to melting rate

c. Adjust the set point values for controlling the bustle temperatures and down pipes. d. First tapping -Do the first tapping when the total charging amount of ore is accumulated approximately 200 ton.

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8.2 PLANT STOP PROCEDURE: 3 Hours before stop:

¾�Inform to all relative departments. (O2 plant, Power plant, Energy Center, all gas consumers, LRS, SMP & PPC etc.)

¾�Fixed Bed (LRO 1602) should be kept in full level. Increase the speed of the coal screw gradually 3 hours earlier before the stop of the plant.(depends on level).

¾�Increase coke rate & reduce ore fines depends on shutdown duration. 2 Hours before stop:

¾�Decrease the melting rate Decrease the DRI screw speed in step of 0.1 rpm/10 minutes up to 1.0 rpm and reduce the top gas flow rate according to ore changing amount. While reducing the top gas flow reduce SP to TGVS (PDC2208 also)

¾�Decrease the O2 amount in step 1000 Nm³/10 min and make O2 amount 29000 Nm³/hr for FRC 8001 1/2 hour before the stop of the plant, accordingly reduce coal screw speed also.

1 Hours before stop:

¾�Open last tapping before stop.

¾�Empty all dust recycling lines (Hot cyclone, Lower dust bin).

¾�Decrease the Bustle Temperature -Decrease the set point of TRC2411-2414 by 10°/15 min to 800 deg.

¾�Adjust melting rate and each process parameters - Decrease the DRI screw rpm by 0.1 up to 0.8 rpm - Decrease the O2 amount by 1000 Nm³/ 10 min and 15 min before the stop of the plant, let the amount of O2 be 26000 Nm³/hr for tuyere side.

¾�Reduce the speed of the coal screw in order to decrease tar formation (In this case, careful operation is needed to prevent the level loss of fixed bed)

10 minutes before stop:

¾�coal & ore feeding and intermediate bins are empty.

¾�The plant is ready for stop – The total gas flow through the reduction shaft should be reduced up to 30000Nm³/hr in steps.

¾�Adjust the amount of O2 flow for each dust burner according to the dome temperature. Reduce the speed of the coal screw up to 4.0 rpm.

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¾�Confirm quality of hot metal, HM temp & tuyere condition.

Stop the Plant Stop by Selecting the O2/N2 Group on CRT and initiate the stop signal of the plant. The stop command closes the oxygen to tuyeres & dust burners- 22000 Nm3/hr nitrogen enters in to tuyeres

¾� Also Depressurizing valves for coal and ore lock hoppers opens.

¾�System pressure: Auto SP to1.2 Bar.

¾�Coal and all DRI screws: stop.

15 minutes after the plant stop:

¾�-N2 flow rate via FRC3020 is changed to 12,000Nm³/h from 22,000Nm³/hr (in integral steps of 1000 m3/min).

30 minutes after the plant stop:

¾�Decrease the system pressure up to 0.7 kg/cm³.

¾�FRC3020: 12000Æ5, 000 Nm³/hr (in integral steps of 500 m3/min).

¾�Purge the plant with 0.4 to 0.7 Bar pressure. Adjust all venturi scrubber SP.

45 minutes after the plant stop:

¾�Decrease the system pressure up to 0.2 bar. If the sum of the inflammable gas wouldn’ t go down below 10%, repeat the pressurizing & depressurizing.

¾�Stop cooling gas compressor.

¾�Give clearance for opening alternate bolts in the system.

¾�Close all shutdown valves except +19 meter ramping nitrogen.

60 minutes after the plant stop:

¾�Close N2 all shut off valves for dust recycling systems on the CRT

¾�Keep minimum nitrogen to tuyere (~ 300 Nm3/hr)

¾�Depressurize so that the system pressure may be zero.

¾�Open the following valves fully to maintain the draft (negative press) toward the flare stack valves, Baumco, DN 800 & DN 400 line SOV’ s & cones.

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75 minutes after the plant stop:

¾�After getting small draft close ramping nitrogen slowly & close hand valve also. ¾�Close LP shut off valve in PB-3. ¾�Announce the completion of the plant purge after getting negative pressure & all shut

down valves closed. Start giving clearance to maintenance jobs as per schedule.

9. REFRACTORY FOR COREX Steel industry is the major consuming industry of refractories in any country. It is well known that 70-75% of the total refractories produced in any country are consumed by the Iron and Steel industry. It is therefore, essential that the refractory industry should respond and also meet the requirement of the changing demands of Steel industry particularly in terms of quality and then quantity. So, the development and growth of both Steel and Refractory industries are somewhat inter dependent. The quality of refractories produced in the country, the installation and maintenance techniques and operating practices of the various units of Indian Steel industry needs to be upgraded to improve the refractory practice in our country. This paper deals with the various refractory practices for different units for steel making like Corex, Blast Furnace, LD converter, Secondary Metallurgic units like LHF, Continuous Casting. COREX: Present day Steel industry’ s demand to produce steel at lower cost and through environmental friendly process. Worlds industrially Proven Smelting Reduction Process” COREX allows flexible, cost efficient and environment friendly production of Hot Metal. Corex technology is based on physical separation of Reduction and melting Process, which are carried out in two main reactors. There are: 1. Melter Gasifier 2. Reduction Shaft Beside above units, there are other areas where refractories are used like DRI Conveying System, Gas Circulation and Dust Recycling and Cast House where sufficient quantity of refractories are used. Here we will give main units description and the quality of refractories used 1. Reduction Shaft: Here in the reduction, the main activities occur are (a) Reduction of Iron Carriers (b) Calcination of Limestone or Dolomite Here mostly 45% dense Al2O3 bricks are used which are procured indigenously. In the Bustle area special shape in silicon carbide burled bricks are used. The main aspect for using these brick is its stability. Dome portion refractory is done by gunning with 55-60 Al2O3 mass. 9.1 Melter Gasifier (MG): Here the following function takes place:

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- Drying and volatisation of coal - Generation of reduction gases - Final reduction of Iron carriers - Melting of DRI (sponge Iron) and - Generation of liquid Hot Metal & slag This is the only unit where refractories are exposed to various severe thermal shocks. To take care of these conditions, the following quality of bricks is selected in different zone in the MG. 1. Hearth Bottom: This is similar to BF lining. Bottom most area is of two layer and graphite blocks. Above this, three layers of carbon blocks and above it mullte bricks are used on two Courses. Outer most side of the Hearth wall up to tuyere zone are ‘Micro Porous’ carbon blocks. The use of micro pore carbon blocks will limit the attack of alkali, Zn, CO and iron penetration. By adding metallic silicon and pure Al2O3 to the carbon mix as additives, will give reduced pore size to the bricks. A carbon ramming mass is provided between water-cooled staves and carbon blocks. To safe guard the hearth pad, ceramic cup lining is recently is introduced in furnaces like Blast Furnaces as well as corex hearths. Requirement of the Ceramic Cup brick: - High resistance to corrosion and corrosion by Iron and Slag - Dimensional stability (PLC at 10000C should be zero) - Resistance to Alkali vapors and CO corrosion - Ability to accommodate thermo-mechanical stress Hence, high quality SIALON bonded corundum bricks of special shape are used at the inner walls. Special inter locking pattern arrangement is done to take care of complete stability for lining. - Tuyere zone refractories: In this area of furnace, oxidation from leaking tuyeres and abrasion from swirling coal and coke at the edge of the raceway are the principal attack mechanism. Temperatures are highest in this part of the furnace. Hence high conductive refractories with excellent thermal shock resistance like sialon bond corundum bricks are used in the area. - Char bed Zone: This has generally proved to be the critical area of the furnace other than the hearth. It is at the top of the cohesive zone where liquids are beginning to form. Temperatures are high, reduction reactions are still occurring and slag formation is just begins here. High thermal conductivity nitride silicon carbide bricks are best suited for this zone. Silicon carbide-ramming mass is used to fill the gap between water-cooled staves and refractory. - Calming Zone: Temperature in this zone is lowest but the burden materials are abrasive. In addition carbon monoxide will tend to attack the refractories. High Alumina corundum base SIALON bonded bricks are preferred in this zone. The working layer in backed up by insulation layer.

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- Dome Area: This area is called gaseous free board zone also. Due to the continuous gas flow, the transition area between free board zone and char bed zone is fluidized. Gunning twin layers does entire lining of dome zone. The first is insulation and the working lining is done by 60% Al2O3 gunning mass. Proper metallic and ceramic anchors are welded in site to have the stability to the gunning material, which is to be done in panels of 1.5 Mt x 1 Mt. A protection lining is given all through the side wall starting from ceramic cup to calming zone to avoid initial thermal shocks to the main working lining. 9.2 Cast House: The refractories used in the cast house are primarily high Alumina or alumina-silcate based, since the basicity of slag is around the neutral region (varies from 0.95-1.1). In the cast house trough, the refractory has to offer multiple aspects of resistance. First, the refractory has to be strong to resist the weight of molten iron and slag; secondly, it has to resist the effect of continuous flow of iron and slag and above all the erosive / corrosive action of the slag and slag/iron. In cast house troughs, most wear takes place at the iron/slag interface followed by the slag area. The lining below the iron level is the least affected zone. In the sag area, the refractory is exposed to the chemical and mechanical effect of the molten slag. Since the choice of refractory is compatible with the slag chemistry, the erosion is not severe in the slag zone alone. The most refractory wear is visible in the slag/iron interface. There are multiple reasons for the refractory wear in this region. First, the slag being in contact with the molten iron is at its highest temperature. Secondly, at the interface there is a partial oxidation of the iron into FeO, which is highly corrosive. Thirdly, the refractory erodes both from chemical attack by the slag at the slag/metal interface along with the mechanical erosion from the continuous flow of slag and slag/iron along the lining; thus exposing new surface of the refractories. The refractory composition in this area has to satisfy the above criteria. The composition of refractories in the trough is based on Alumina as base material to provide resistance to high temperature, silicon carbide addition to provide the corrosive / erosion resistance and some amount of carbon (as graphite) to provide non-wetting characteristics. Since the development of low and ultra-low cement castables (LCC and ULCC), LCC and ULCC have been preferred as the cast house refractories, which replaced the earlier use of resin or pitch-bonded ramming mixes. The major advantage of ULCC is its ability to be repaired by recasting the lining at regular intervals until the lining becomes weak due to the oxidation of the carbon in the unaffected area of the lining. Since the development of sol-gel based castables in the early 90s, the use of monolithic refractories has taken a new direction. The change in the bonding system from high Alumina cement to colloidal silica provide not only a number of significant advantages, but also a newer application method, namely by pumping. There are several advantages of sol-gel-based castables / pumpables over low-cement castables which are as follows: (a) By nature the gel-bond castable has self-flow characteristics, it is easier to cast either by gravity or by a pump. (b) Due to the absence of minor ingredients in the mix (such as deffloculants and dispersants), the mixing time is shorter resulting in less time for casting

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(c) The high temperature bond from sol-gel bonding being mullite, the refractoriness of the gel-bond castables is much higher than of LCC, which forms less refractory compounds such as, anorthite/gehlenite (d) Due to the nature of the bonding, the sol-gel bonded castable has much superior thermal shock resistance resulting in less cracks in linings (e) Since the sol-gel bonding provides a coating on the carbon particles, the gel-bond castables also provide better oxidation resistance (f) The hot strength of sol-gel bonded castables are much higher (hot modulus of rupture @ 15000C) than that of LCC or ULCC (g) Due to less oxidation of the carbonaceous materials and better thermal shock resistance, the lining life of sol-gel base castables are longer than that of LCC or ULCC Tables 1 and 2 show the chemical and physical properties of LCC and sol-gel based castables used in Corex cast house troughs. It may be noted that at 14000C the LCC forms a glassy phase primarily consisting of anorthite and gehlenite. This provides a better compressive strength. Whereas in the sol-gel bonding, the high temperature phase is mullite which provides better MOR and not high CCS.

Table I: Chemical compositions of ULCC and gel-bond castables for blast furnace trough

Composition (%)

ULCC Gel-bonded

Al2O3 SiO2 TiO2 Fe2O3 SiC CaO

68 - 70 8 - 9 1.5 - 2.0 0.4 - 0.6 19 - 21 0.4 - 0.5

72 – 73 7.4 – 7.8 1.4 – 1.6 1.0 – 1.2 17.0 – 18.0 --

Table II: A physical property of blast furnace trough castable/pumpable mixes

Properties ULCC Gel-bonded Bulk density (kg.m3)/porosity (%) after heating at 1100C 8150C 14000C

2805/15.6 2740/19.7 2740/18.5

2915/14.3 2835/17.2 2805/18.4

Cold crushing strength (MPa) after heating at 1100C 8150C 14000C

8.9 11.7 48.2

21.8 53.1 43.3

Cold modulus of rupture (MPa) after heating at

2.1

4.0

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1100C 8150C 14000C

2.4 11.7

8.3 9.6

HMOR (MPa) at 14000C (in N2 atm)

2.2 3.8

10 SUPPORTING SYSTEM FOR FAILURE

10.1 POWER FAILURE THE ACTION GUIDE LINES IN POWER FAILURE: 1.Confirm the power failure of the plant. 2. Confirm the O2 cutoff and N2 injection to tuyeres (N2: 22000 Nm³/h) 3.Confirm the following valves are operated to power failure positions

- All venturies full open. - All valves in excess gas line open. - Flare valve open. - Plant pressure auto SP 1.2 Bar & ensure pressure is coming down. - All shutoff valves in gas system for coal dryers: close - All LRC valves of scrubber water system close.

- All water flow control valves for scrubbers close. - Confirm whether the HIC valves for MCW and stave cooling water system are open

fully and adjust these valves in few steps depends on levels of head tanks and the temperature of the return water.

- Confirm the emergency generator is running, if not, make it start in manual and make the loads start in regular order.

- The following emergency pumps (hard wired pumps> have to be run quickly:

1) Inlet cone pumps (2). 2) Gland water pump (1). 3) Stave pump (1). 4) MCW critical pump (1). 5) MCW non-critical pump (1). 6) Start both clarifier rakes from field. 7) Start + 0 meter & venturi Hydraulic pumps. 8) Ensure power for tilting runner.

4. If the tapping is in progress, this shall be kept under N2 pressure of plant. 5. If the level of a scrubber is coming down continuously, nevertheless LRC valve is closed; the

hand valves should be closed to prevent gas leakage.

6. Confirm FRC2001 is closed after 10 mins to prevent air suction in reduction shaft.

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7. Switch from the emergency power to regular power after recovering the power failure. 8. Announce the message that regular power will be “ on” for people to escape from danger places. 9. In process of back of regular power, the power failure will happened once more; therefore

careful action is needed against it. 10.2 O2 AND N2 FAILURE: COREX plant is quickly stopped as the supply of oxygen or nitrogen is interrupted by the trouble of this supply system. In that case certain flow of nitrogen is fed in to the melter gasifier via the tuyeres to establish raceways in it and prevent flowing backward of slag into the tuyeres within 3 seconds after plant trip. Preparing for a failure of the O2 main compressor N2 and O2 back up systems is installed. But if the N2 back up system does not work, nevertheless the O2 plant is tripped, which cause COREX plant to a big troubles. Requirement

Remarks

NORMAL MAX Emergency Pressure Kg/cm3

Rate Nm3/hr/THM

Oxygen 55000 60000 - 8.5 500-530

Nitrogen

14000 18000

32000 X 30 min

Down insteps

11 95 - 120

10.3 Operations according to O2 and N2 failure cases a). The power failure at Corex. COREX plant will be stopped, but N2 will be supplied by oxygen plant for purging the COREX plant. b). The power failure of Oxygen plant. It is possible to operate the COREX plant for 2-4 hours with t the back-up systems of oxygen plant. c). The compressor trouble of oxygen plant Possible to operate the COREX by nitrogen and oxygen supplied from L.P and H.P back-up system.

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11. REDUCTION SHAFT EMPTYING

11.1 REDUCTION SHAFT EMPTYING – STOP PROCEDURE ¾� Adjust coke rate to ensure Hot-metal temperature in the range of 1480 °C to 1520 °C. ¾� Aim for Slag Basicity around 1.05, with Al2O3 content 14% max. ¾� Operate the plant with 100 % Essar DR pellets. ¾� Operate the plant with good Coal blend. 12: 00 hrs before oxygen stop:

¾�Change ore batch to 30 % HBI/DRI & 70% - pellet.

¾�Charge the coke to RS at 20 % by volume in the oxide feed to the shaft along with HBI from 12:00 hrs before oxygen stop.

10:00 hrs before oxygen stop :

¾�Change ore batch to 70 % HBI/DRI & 30% - pellet.

¾�Charge the coke to RS at 25 % by volume in the oxide feed to the shaft along with HBI from 10:00 hrs before oxygen stop.

08: 00 hrs before oxygen stop:

¾�Start Temp charging to RS, Set top temp to 400 deg. ¾�Increase nitrogen (by opening the hand valve more in the field) to the lock hopper

and charging distributor to maintain the safe temperature (below 200 °C) for the seals.

¾�Change ore batch to 100 - % HBI/DRI. ¾�Start reducing the top gas considering top temp. ¾�Adjust the melting rate to 70 TPH. ¾�Stop gas to the reduction shaft by closing FRC 2001 before 6 hours of oxygen stop & then

stop charging to the shaft. ¾�Adjust slag basicity. ¾�Start reducing bustle gas temp set points to 780 deg in steps.

04:00 hrs before oxygen stop: ¾�Increase the coke rate to 35 % in steps. ¾�Consider discharge volume of DRI screw as 10 - 15 liters higher side before starting

emptying. If one of the DRI screws stops discharging, increase the speed of the other DRI screws to maintain the required melting rate.

¾�Gradually cut down on the addition of the iron ore fines to zero. ¾�Keep coal charging on higher side maintain high char bed level before stopping.

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2: 00 hrs before oxygen stop:

¾�Once two of the six DRI screws stop discharging HBI from shaft, Charge few (2 – 3 batches) of 10 m3 batch of HBI to break / clean the natural dead man in the shaft.

¾�Stop charging to the coal charging bin at the beginning of the last tap, to keep the coal charging bin empty.

¾�Empty dust recycling system bins by pushing the dust to the melter gasifier. ¾�Prepare the plant on time to fill up LRO 1602 to 100 % prior to the last tap. ¾�Adjust the last tap according to hot metal quantity of the pre ultimate tap and

number of charges put in to the shaft to clean the natural dead man in the shaft. ¾� Plan the last tap in a such a way that the last tap should be at least 150 tons of hot

metal. When only one the five DRI screws are discharging (during charging Period of destroying the dead man in the shaft), add few more batches if required to have a minimum of 150 tons of hot metal in the last tap before oxygen stop 1:00 hrs before Oxygen stop:

¾�Open the tap when at least 2 or 3 screws stops discharging. ¾�Dry the furnace to the maximum possible extent. Reduce plant pressure at the

end to 1.2 bar for better drainage. ¾�Approximately 15 - 20 minutes of the end of the last tap, stop upper coal screw

and maintain plant in operation in order to devolatize the coal and to avoid degassing of the coal after oxygen stop. Reduce oxygen to the dust burner if required. x� 00:00 hrs Stop oxygen and purge the plant. NOTE:

After oxygen stop, normal ramping / purging starts. After completion of the purging sequence, proceed with cooling of the plant. Open FRC 2001 to cool the shaft. Keep plant pressure at 1.2 bar and cooling gas compressor in operation for 90 minutes. Start decreasing the set point on bustle gas temperature in steps of 20 deg. C for every 10 minutes. Open slightly FRC 2001 to cool reduction shaft in such a way to maintain the temperature of the seals below 200 deg. C (TIO7491). [Ref detailed Ramping & purging procedure]. Stop cooling gas compressor and start depressurizing the plant and prepare the plant for shut down jobs. Stop nitrogen to the consumers (by closing the hand valves in the field) in steps as per the list enclosed. As per shutdown schedule take up the maintenance jobs.

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11.2 REDUCTION SHAFT EMPTYING – START PROCEDURE Before the start of oxygen, fill up the shaft up to 2 mtr below the normal level to allow proper headroom for inspection of Charging distributor feed legs as per filling recipes.

¾�Charge 20 tons of coke (size 13 – 40 mm) and limestone mix to the shaft before charging the DRI and pellet mix.

¾�Fill up coal charging bin with the coke rate that will be decided based on the actual shutdown time. However, as a guideline it will be same as during stop of the plant.

Pressure test is completed and tuyeres are poked and plant is ready for start. [To tart pressure test ref normal start procedure].

¾�Before starting pressure test start DRI screws with 0.3rpm. ¾�Start blowing of oxygen with 26 tuyeres with 22000 Ncum / hr and increase in

steps of 1000 Ncum / hr every 10 minutes. ¾�Keep tuyere velocity around 190 m / sec. ¾�Check the tuyeres.

Dome temperature > 700 deg. C

¾�Start dust burner system with 500 Ncum / hr of oxygen through each dust burner. ¾�Increase the oxygen in steps to reach dome temperature to 900 deg. C within 30 minutes. ¾�Start coal screws after discharging entire quantity of coke to MG from shaft and dome temp

is above 950 deg.

¾�Adjust bustle gas temperature around 820 deg. C. ¾�Open top gas flap FRC 2001 and adjust specific top gas flow at 800 Ncum / t –

DRI. Increase in steps top gas flow to 1200 N cum / t – DRI. 1 hr after feeding DRI to melter gasifier:

¾�Increase melting rate to 40 tons / hour and keep specific oxygen to the tuyeres at 700

Nm3/thm. ¾�Open nitrogen to inliners and to down pipes.

Approximately after 31/2 hours:

¾�Perform first tap, 3.5 hours after blowing of oxygen. ¾�Decrease coke rate and keep around 25 % considering the hot metal temperature. ¾�Start Changing DRI – Pellet as per reciepe. ¾�Achieve melting rate of 70 TPH before tap. ¾�Increase melting rate to 80 TPH in steps if the tap is good. ¾�Change the coal batch considering the tap analysis. ¾�Increase pellet mix in steps as per the annexure. (Consider the tap analysis before reducing the

DRI percentage in the oxide line) ¾�Adjust the specific top gas flow considering inburden temperatures of shaft. ¾� Increase melting rate in steps as per the annexure.

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¾�Decrease coke rate and keep around 20 % considering the hot metal temperature.

12. The Irregularities in Corex process & remedial actions The irregularities in blast furnace operation may arise either of the followings

¾�Due to faulty mechanical devices like valve, coolers. ¾�Due to faulty Mechanical operation like tapping, charging. ¾�Due to abnormal process occurring inside the furnace with respect to phsico- Chemical changes in the charge.

12.1 .Shaft Hanging. If uniform descent of the burden in the furnace is interrupted either by wedging or bridging of the stock or by scaffolding, it is known as ‘hanging’ . It is in fact caused by different alternative reasons: - Bridging of Ore / Pellets / DRI particles in the vicinity of coke particles which disturb the smooth ascend of the burden and uniform flow of gas across the reduction shaft. The material discharge from shaft to melter gasifier is not uniform, means each batch discharge will take different time. The following are the observation can be observed during shaft hanging.

¾�Each batch discharge time will not be the same. Some charge/batch will discharge faster and some will take more time. ¾�In burden temperature will not remain uniform some cross sectional area will show more and some area shown less. ¾�The differential pressure across the shaft and between the screw to bustle will

show more than the normal. ¾�The DRI screw discharge pressure will show more than the normal. ¾�The amount of gas can pushed in to the RS will come down, and top gas temperature will also varies drastically. ¾�Metalisation and calcinations percentage will drop drastically in the shaft, followed by increase in the thermal load on the melter gasifier.

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Remedies.

¾�Remove the Iron Ore [soft ore] from the oxide batch and reduce the gas flow to the shaft. ¾�Reduce the melting rate add some percentage of coke to over come the cold spell and drainage problem. ¾�Increase the coke volume in the shaft and observe for the uniform distribution of gas. ¾�Closely monitor the DRI screw pressure, Purge the screws which are taking more discharge pressure with nitrogen to keep screws in operation, otherwise there may be the possibility of stoppage of the Screws with high discharge pressure.

12.2 Slipping Slipping is defined as sudden sinking of the stock caused by collapse of the hanging, welding, scaffold, etc. In short it is the aftermath of these irregularities. In severe cases slipping causes chilling of the hearth. The best remedy is to allow the furnace to slip on its own by Adjustment of the gas flow and pressure. 12.3 Channeling Preferential flow of ascending gases through certain areas of the burden, because of their relatively much Better permeability is known as ‘channeling’ since this passages appears as channels. This basically arises because of improper distribution and wide size range of the charge in the furnace. Use of a more uniformly sized burden and proper distribution of charge can minimize this. Channeling Otherwise reduces the effective cross section of the furnace for gas-solid interaction and thereby decreases the productivity directly. 12.4 Chilled hearth This is very serious disorder since it affects the drainage of hot metal and slag adversely. The temperature of hot metal and slag will go down. It affects the poor slag drainage due to low temperature in turn it affects the production rate. It may due to the following reasons ¾�The change in the input raw material quality. ¾�Poor slag drainage in the last tap. ¾�Delay in tap opening due to some other problem. ¾�Water leakages from tuyere area. ¾�Low metallisized burden hit to the tuyere. ¾�Dislodging of the skull from its position, falling in to tuyere area. ¾�Wrong mix up in the burden charge, eg: - Ore charged in place of coke.

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Remedies. ¾�Charge more coke to keep furnace in hot condition. ¾�Reduce the melting rate by reducing the oxygen through the tuyere. ¾�Check the burden mix and change in the raw material quality. ¾�Take more raw material samples for chemical and physical analysis. ¾�Check the performance of the shaft. Improve the condition of the shaft, metallization and In burden temperature. ¾�Prepare the cast house as fast as possible, check the tuyeres brightness Continuously. ¾�Take out the fine material from coal charge, iron ore fines. ¾�Try to take all the slag in to the SGP. Keep slag dry pits empty for worst situation. 12.5. Generator Gas Duct (GGD Jamming: - The melter gasifier is having four gas outlet [ ducts] there are chances of chocking of these ducts below the cooling gas addition point. This is across the cross section of generator gas duct. This may observed in any one of the GGD’ s or more than one number at any given point of time. But most of the time GGD blockages occur at same location in the generator gas duct. This may be due to the high volatile matter in the coal or may be due to the low dome temperature operation. The jamming starts at slower rate at the neck position of the generator gas duct, but it will grow at faster rate as it gets more surface area for settling and develops in to the larger size across the cross section of the duct and finally block the gas passage. Followings are the consequences of GGD jamming. ¾�Gas load on other generator gas ducts will increase and in tern more cooling gas as to be added to the duct in other ducts. ¾�Localize temperature on each duct may increases than the normal temperature, if cooling gas addition is not sufficient / proper. ¾�Chance for gas channeling, it will drop the metallisation and affect the In-burden temperature. ¾�Differential pressure of shaft will rise. ¾�Screw discharge pressure will go high. Remedies ¾�Reduce the Melting rate [production rate] to have a better control over furnace operation. Reduce the plant pressure by 0.5 bar [3.5 bar to 3 bar]. ¾�Check the local shell temperature on the cooling gas addition duct. ¾�Check the total cooling gas addition to the each generator gas duct and load on the CGC, accordingly adjust the process parameter. ¾�Increase the nitrogen flow to the each dust burner injector to have positive dust flow towards furnace [say 200 Nm3/hr to 400 Nm3/hr]. ¾�Change the charging mix, adjust the coal blend for better operational parameter control and to improve the furnace condition. ¾�In worst condition like two GGD block, Plant has to be put down for GGD Cleaning, otherwise it will further Detroit the shaft condition.

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12.6 .Red spot on MG shell. Over the period of operation Melter Gasifier refractory will get eroded and MG shell will get exposed to the furnace gas, resulting in hot spots on the MG shell. It may be localized one or it may spread through out the circumference or some parts on the circumference of the MG shell, it depends on inside stave refractory conditions. It is observed that after 3 years of operation, in the stave row number 5 and in the row number 6 inside refractory will have more prone to get eroded, so furnace shell for the row number 5 and row number 6 are more suspect able for hot spots. By maintaining certain operation parameters it is possible to form the skull over stave walls, but it is always chance that this skull get re melted due to peripheral flow of gases due to drop in char bed permeability will once again results for hot spots.. Recommendations: Close the tuyeres, which are laying below the shell showing high temperature, and also reduce the melting rate by reducing the oxygen through the tuyeres. Maintain the maximum possible velocity through the tuyeres. Close monitoring of stave water temperature is required (delta ‘t’ ).

¾�Control of fines in the input raw material to the melter gasifier. ¾�Maintain the top char bed about 80%. ¾�Proper slag drainage to maintain dry hearth. ¾�Furnace to be run hotter for better drainage. ¾�Stable operation of furnace. ¾�Ramping up of the melting rate shall be at a slow pace.

If shell temperature reaches to red hotness temperature, it may require stopping the plant if not controlled by reducing the oxygen trough the tuyeres. Mist cooling and nitrogen cooling arrangement is required to cool the shell. 12.7 Tuyere burning.

The burning of tuyeres can occur due to following reason High fusion point viscous slag, which is formed above the tuyeres level Dislodging of the skull from its position and Falling in to the char bed will splash the slag on to the tuyeres, resulted in burning of number of tuyeres together. Change over from Oxygen to the tuyeres to Nitrogen should be smooth; otherwise furnace inside slag may enter in to the tuyeres and will damage the tuyeres. Improper hot metal and Slag drainages of the furnace.

The usual remedies are.

¾�Make fluid / less viscous slag. Adjust the basicity of slag. ¾�Improving the quality of the raw material.

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¾�Use low alkali burden and making same thin and acidic slag if the alkali content is high in the burden.

¾�Eliminating channeling or preferential flow. ¾�Ensuring smooth change over of nitrogen from oxygen. ¾�Ensure good drainage of hot metal and slag

12.8 Water level abnormalities in the scrubbers: Each scrubber is provided with three continuous level measurements that are bubbler type instruments. The average of these three is taken for the control of the scrubber level control that is controlled by a two-range split control valve. The control valve is consisting of one ball valve (DN 250) and one Butterfly valve (DN400), which operate with pneumatic actuators. The scrubbers are usually set for its control at about 50% level and any failure to maintain this level may cause the failure of water seal in the scrubbers and gas pass can pass through the water discharge lines of the scrubbers which is highly dangerous. Causes for abnormalities of scrubber level: The level abnormality can be either on higher side or lower side. The abnormalities can be due to errors in measurement or malfunctioning of the control valves Case1: possible errors in Measurements

x� Check whether all three are equal in range. If any one is abnormal, take it to maintenance mode and get it flushed / purged by instrumentation

Case 2: possible malfunctioning of the control valve

x� Check the outputs for the individual valves and their position feed back x� If there is any abnormality with the position of the valve, check the position in the field for its

air, valve positioner etc. if every thing looks normal, then the valve is assumed to be struck and in such case the control of the level can be shifted to the single valve by closing the manual valve in the line of the struck control valve. This operation requires special co ordination from field and control room to ensure that the isolation is trouble free.

Low low level in the scrubbers: This can cause the gas to rush in the clarifier and pump house, which is highly dangerous, and in this case all the people must be made alert and area should be evacuated. Only the trained people with suitable safety apparatus are allowed to co ordinate from the field and all efforts must be put to bring the level in the scrubbers to normal at the earliest.

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12.9 Jamming of Dust Recycling System: The effective recycling of dust back into the system and burning in the MG has huge impact not only on the process of Corex, but also on the surroundings, environment and people working. So it should be desired to see that the all four lines are running effectively. With any one line down we may be able to continue till an opportunity shutdown, but will have a bearing on all as specified above. Effect of down dust line on the process:

x� Increased dust load in reducing gas effecting the performance of Reduction shaft x� Increased coke and fuel rates resulting high cost of production x� Increased sludge load and sludge disposal problems

In normal operation, the dust settled in HGC is down charged in to the Lower dust Bin and then injected into the burner and burnt with oxygen. So it is important to see that the process of this dust injection is smooth and continuous without building any dead levels either in HGC or Dust bin. Normally dust can be discharged in open mode i.e. keeping the disc gate continuously open. But if any abnormality is found in the line like high temperature of the dust, high skin temperatures or any sluggishness in the dust discharge, the system can be operated in batch mode i.e. operate the Disc gate according to the level in dust bin. The indications for the flow of dust are the differential pressure across the dust burner and temperature in the dust line, T-piece and the levels in the HGC and dust bin etc. so any sluggishness in the dust line can be identified from the above indications and some basic steps may be followed to prevent the total jamming of the dust lines. Steps to avoid the Jamming of lines: Case I : Dust discharge from HGC to Dust bin is sluggish Indications:

1. Level rise in HGC 2. Drop in dust temperature 3. No differential pressure across the Horizontal portion 4. No level in Dust bins

Remedies:

x� Check the position of the hydraulic disc gates and Manual shut off valves x� Try nitrogen fluidizing

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Case 2: Dust discharge from Dust bin is sluggish Indications:

1. Level rise in Dust bin 2. Drop in dust temperature 3. No differential pressure across the Horizontal portion 4. Subsequent level rise in HGC

Remedies: x� Check the position of the shut off valve x� Try in batch mode x� Try nitrogen fluidizing

If the jamming is not because of any big or foreign particles like refractory bricks etc, the dust line may be through for its normal operation. But if the jamming is because of any physical obstructions, then it requires a shutdown to revive the dust line Case 3: Blockage in Horizontal line Indications:

1. Pressure rise in Dust bin and possible failure of Nitrogen injection due to Inter lock with Pressure in Dust bin

2. Drop in dust temperature 3. Max. differential pressure across the Horizontal portion 4. Subsequent level rise in HGC and Dust bin.

Remedies:

1. stop Oxygen to the dust burner and Nitrogen injection 2. close manual shut off valve below the Dust bin 3. Open the knife gate valve in the coarse particle discharge line at +21m. 4. Flush the horizontal potion two three times with given nitrogen valves

If the line could not be revived from its horizontal line blockage, then nitrogen injector will have to be stopped and Block valve is to be kept closed keeping the nitrogen SOV in front of the Burner open. In this case oxygen to the burner may be given at less than the normal flow and the line will have to be cleared in an opportunity shut down.

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12.10 Stoppage of DRI screw: Corex process has experienced many times the stoppage of DRI screws which will have a bearing on the performance of the Reduction shaft and as a whole on the process. The screws are run by Hydraulic motors and are variable speed to control the discharge of DRI feed to MG. Hydraulic pressure of the pumps is indication of the load on the screws. In normal operating conditions, pressure may be in range of 80 to 110 bar. Any thing above that requires a special attention and nitrogen flow through the Screw nozzles should be increased to reduce the load on the screw. Various reasons for the stoppage of DRI screws:

x� Blockage of DRI down pipe x� High dust load in Reducing gas x� High specific amount of Top gas x� High temperatures in the reduction shaft causing cluster formation x� Air penetration into the process during any shutdown causing fusion of the DRI x� Any foreign material like metal pieces, Refractory pieces etc. x� Bearing failure of the screw

The stoppage of any screw can be judged from the profile / Trend of the hydraulic pressure. If the pressure rise is gradual, it could be due to blockage of DRI down pipe in which case nitrogen purging may help to revive the screw while the plant is in operation. If the pressure rise is very sudden, it could be due to any obstructions with foreign material or clusters in between the screw paddles. Revival procedures of DRI screws while the plant in operation:

x� Purge the screw nozzles with Nitrogen x� Try to run the screw from field in both forward and reverse directions x� Observe the movement of the screw and if it is encouraging, stop further trials

If the screw could not be revived online, it may be tried during shutdown with all safety precaution in place.

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13. CAST HOUSE 13.1 General Cast house is where tapping is carried out to take out the hot metal and slag from the furnace using drilling machine, after draining out of estimated amount of hot metal and slag, Mud Gun closes tap hole. The hot metal will flow through refractory lined trough (Main iron runner and Tilting runner) in to the ladles. The slag that is lighter than hot metal will float above and get separated near main runner skimmer & taken in to slag granulation plant trough the slag runner. In case of heavy flow, SGP is not ready to take slag then slag is diverted in to Slag Dry Pits. Corex is having TWO number of Cast house, one granulation Plant and Two Slag Dry pits of 600 tons (SLAG) capacity. The runner is refractory lined; it will get eroded after certain amount of hot metal is taped. In Corex relining of main runner is usually done after 90,000 tons of hot metal produced from the runner, this depends on how best main runner is managed is depends upon the followings, Cast house operation, Hot metal and slag Quality, Quality of refractory, Drainage rate, Clay quality, Proper scheduling for minor repair of running trough along with stand by cast house. The following are the pre requisite for trouble free tapping

¾�Constant tap hole length. ¾�Controlled expansion in the tap hole with hot metal and slag. ¾�Even delivery speed of hot metal stream ¾�No turbulence in the stream at the tap hole exit. ¾�Smooth operating and closing of the tap hole.

To achieve the above results on a regular basis continuously, it is required to have a total system approach. It should start right from the day to day operation of the furnace, material design and proper application technology. The temperature and composition of the hot metal various from plant to plant. Higher temperature and specially the ‘Si’ content of the hot metal affects the performance of tap hole clay adversely The Tapping rate determined ( Amount per unit: t/min) of iron and slag is determined by ¾� Tap hole diameter. ¾� Tap hole length. ¾� The thickness of the molten iron and slag layer (level) ¾� Plant pressure. In order to obtain a longer tapping time the erosion of tap hole diameter due to abrasive action of metal and slag at high temperature, to be reduced. Material design for tap hole has undergone a radical change. Both siliceous and aluminous aggregate are used along with various additives and binders. Phenalic resins, tar, various oils are used as binders along with Carbides (SIC) and /or nitrides (SiN) as additives. Carbides and Nitrides imparts corrosion and abrasive resistance properties where as it also improves sinterability of the mix.

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Slight expansion has been recognized as desirable property. If may please be noted that SiC gets oxidized both under oxidizing both under oxidizing and reducing atmosphere. SiC+2FeO Æ SiO2 + Fe + C -----------(1) FeO+C Æ Fe + CO (g) --------------(2) SiC + CO Æ SiO+2C --------------------(3). SiO+CO Æ Si+CO2 --------------------(4) The last reactions are associated with volume expansion that may be beneficial for maintaining the tap hole diameter. Trough The performance of trough also will depends on ¾� Nature of the material and its characteristics. ¾� Design and Engineering of the trough. ¾� Operational Parameters. The type of construction of main trough plays an important role in de-ciding the trough life and minimizing cast house delays. Particularly important is the bottom slope which determines the flow rate of Iron / Slag in the trough which determines the erosion rate of refractory lining. Also related to the slope is the height of pool available at impact area of trough, which cushions impact energy of falling stream during tapping. Presence of such a pool determines the condition of refractory lining at the impact zone. Based on ‘Slope’ , three types of main troughs can be distinguished. a) Wet Runner/Pooling runner/Non-Drainable trough. This trough holds molten metal for inspection of refractory lining condition. All large capacity furnaces opt for this type of trough for faster evacuation of hot metal. b) Semi –wet Trough Such a trough has relatively high slope of 3 % and so wear prominent both on bottom and side wall Refractory linings. Also, the height of pool is low at the impact zone and so the wear at that area is also high. c) Dry/Non –pooling trough The slope is generally more than 5% and the iron stream directly hits refractory lining. The wear in such trough is much more in bottom and imp-act area. Such troughs are common with Blast furnace of low volume.

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13.2 COREX CAST HOUSE Facilities in Cast House NO OF CAST HOUSES : 02 NO OF TAPHOLES : 02 TAP HOLE ANGLE : 3 DEG. MAIN IRON RUNNER ANGLE : 5 DEG. RUNNER LINING : CASTABLE RUNNERS

¾�MAIN IRON TROUGH. ¾�HOT METAL RUNNER. ¾�TILTING RUNNER ¾�DRAINAGE RUNNER ¾�SLAG RUNNER ¾�CAST HOUSE SLAG GRANULATION ¾�CAST HOUSE DEDUSTING

Cast House Practice: HOT METAL PRODUCTION/DAY : 2600 MT *2 NO. OF TAPPINGS /DAY : 09 – 10 PER MODULE HOT METAL TEMPERATURE : 1500 r 20 C HOT METAL ANALYSIS : Si – 0.5 to 0.8 & S – 0.04 SLAG B2 : 1.10 TAPPING PRACTICES : x� SINGLE TAPHOLE OPERATION x� TWIN TAPHOLE OPERATION TAPPING DURATION TAP OPEN TO CLOSE : AROUND ONE HOUR TAP CLOSE TO OPEN : 1 Hr. TO 1 Hr. 30 Min (DEPENDS ON THE MELTING RATE) RUNNER LIFE : 90,000 – 100000 tons Through put. REFRACTORY CONSUMPTION : 0.42 - 0.45 Kg/THM

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13.3 Cast House Runner Refractory: ¾� MAIN IRON RUNNER : ACCMON 16SC GEL (ACC) & CASTON AT 390 (VIL) ¾� HOTMETAL RUNNER : ACCMON 16SC GEL (ACC) & CASTON AT 190(VIL) ¾� TILTING RUNNER : ACCMON 16SC GEL (ACC) & CASTON AT 190 (VIL) ¾� DRAINAGE RUNNER : ACCMON 16SC GEL (ACC) & CASTON AT 190 (VIL) ¾� SLAG RUNNER : ACCMON 16 SC B (ACC) .Cast House Runner Refractory: TYPES OF REPAIRS: AJOR REPAIR DURATION 72 Hrs. MINOR REPAIR DURATION 8 - 24 Hrs. SCHEDULE FOR MAJOR REPAIR COOLING & CLEANING : 04 Hrs BREAKING : 16 Hrs TEMPLATE FIXING : 04 Hrs CASTING : 04 Hrs SETTING : 06 Hrs TEMPLATE REMOVAL:01 Hrs SKIMMER FIXING :01 Hrs SLOW HEATING :12 Hrs FULL HEATING : 24 Hrs .Cast House Refractory: TAPHOLE CLAY : UNHYDRUS TAP HOLE CLAY CLAY CONSUMPTION : 1.35 Kg/THM MUD GUN HOLDING TIME : 30 MIN SUPPLIERS :VVEL, HI-TECH & UBIQUE

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MASS COMPOSITION: CHEMICAL Al2O3 :55 – 60% C :16 – 18 % SiC + Si3N4 :15 – 17 % OTHERS : REST PHYSICAL VM : 7 – 8 % BD : 2.1 – 2.25 g/cc GRAIN SIZE : 0-3.5 mm 13.4 Preparation before Tap opening. Checking of clay gun and Drilling machine 1. Clay Gun

¾�Check all signal lamps. ¾�Check if any sticker material is remained in the-nozzle. ¾�Check the oil level in the tank. ¾�Check the temperature of oil. ¾�Check the actuating status of motor.

2. Tap hole opener ( Drilling machine).

¾�Check the condition of Air Pressure. ¾�Check the status of each actuating part. ¾�Check the chain tension. ¾�Check the carriage movement. ¾�Check the chain for its smooth movement. ¾�Check all air lines for any leakage.

3. Tap hole

¾�Check for any gas leakage around the tap hole. ¾�Check for any sticked material is remained on the runner and to the tap hole mouth. ¾�Check for any water leakage is appeared around the tap hole.

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4. Each Runner

¾�Check the main iron trough condition. ¾�Check the slag runner condition. ¾�Check the for sand dressing in slag runner. ¾�Check for any crack at the joint between tap hole and main runner.

5. Tilting Runner.

¾�Check the bottom refractory condition in tilting runner. ¾�Check for any crack in the refractory lining in the tilting runner. ¾�Check for any jam remained in side the tilting runner. ¾�Check the tilting operation of tilting runner.

6. Tapping Material and consumption

¾�Mud gun clay: 0.3 tons /tap ¾�Lance pipe size: 2 pipes (8 mm)/ tap ¾�Drill rod + Bit: 1 number / tap. ¾�Mud gun nozzle: ¾�River bed sand: ¾�Long shovels: as operation requirement.

13.5 Tap Opening and Closing Procedure. 1. Decide the suitable time for tap opening. x� Tap closing to tap opening time is mainly depends on melting rate. x� Tap opening time is varied from normal time of opening of tap depends upon the followings.

¾�Previous tap drainage status. ¾�Quality of hot metal and slag, Temperature and Chemistry. ¾�Melter gasifier performance. ¾�Shut down preparation.

2. Drilling procedure

¾�Fix the Rod having drill bit in to the Check. ¾�Take the Tap hole opener to the tap hole face and mark the center for tap hole, it will set the direction for tap hole which connects the hot metal. ¾�If the center is posed correctly, Drill the tap hole up to 200 mm less than last tap hole length. ¾�By appearing spray and molten Braking from the tap hole ,take back the

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Tap hole opener to parking position. ¾�Replace ROD with iron bar and open the tap by using bar.

The measurement of Tap hole length. Tap hole length is measured from the scale, which is position on to the tap hole opener. Each division in the scale is equivalent to the one tenth of the meter. Maximum length can be read from this scale is 2.7 meters. 3. Procedure for taking Hot metal temperature.

¾�Insert tip into hot metal ("Yellow" light indicates rising temperature, "Red" light and "buzzer" indicates dip completed). ¾�Remove tip from hot metal. ¾�Observe the Temperature from cast house display board. ¾�Time is recorded from the control room.

4. Procedure for taking sample for hot metal and slag ¾� Prepare sample mould ¾� Clean waste material from mould surface (Ensure clean surface) ¾� Prepare sample spoon. ¾� Remove adhering metal or metal skull from spoon. ¾� Position spoon over metal runner (warm up the spoon to remove moisture). ¾� Collect the hot metal from runner in to the dry spoon and Pour it in to the mould. ¾� Pour excess metal from spoon into metal runner. ¾� Remove sample from the mould. Cool the sample and send to laboratory for analysis. ¾� Repeat the above for taking anther sample. 5. Plugging the tap hole. ¾�Plugging time can be estimated by considering the melting rate, tap speed, and tap-to-tap time, but normally final decision of tap hole plugging is done after

draining of the estimated amount of metal and slag from the furnace.

¾�Check the erosion of tap hole and drainage status of molten metal and slag. Especially, tap hole erosion is a critical view point to decide plugging. ¾�Check the gas coming out from tap hole. If it more it indicates that hearth is got emptied. ¾�Estimate the time, of plugging with considering the amount of slag is drained from furnace.

6. Emergency Plugging. ¾�When the molten metal starts overflow from runner. ¾�When Drain hole got break out. ¾�When the operation of tilting runner got failed.

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¾�When the continuous tapping is impossible due to the tap hole erosion And heavy metal and slag flow. ¾�When the un-controlled char rush in to the runner. Preparation for Next Tap.

¾�Cover the main runner with rice husk to reduce the heat loss from metal runner.

¾�Check for the erosion of sand in the slag runner and the jam in the slag runner, cleaning of the slag runner jam and dressed with sand.

¾�Take out the clay gun after 30 minutes back to the parking position, check the main iron trough condition.

¾�Empty out the clay gun barrel, Cooling the mud gun barrel, Check the clay gun nozzle and replace it with new one if necessary, check for the reducer jam.

¾�Cleaning the main trough and tap hole mouth, by taking out the jams and dressing of the runner with sand. ¾�Check the drilling machine by operating carriage and rotation. Insert the new drill rod and

prepare drilling machine for next tap. ¾�Fill the clay gun with clay and take the tap hole impression to make proper tap hole

center. ¾�Check for ladle placement, minimum three ladles are to be placed.

13.6 Abnormalities and remedies.

1.Tap close Failure a. Reason for failure

¾�Breakout in front of tap hole. ¾�Sticked material at tap hole mouth. ¾�Delay in pushing the mass (operating of the clay gun Ram). ¾�Clay gun failed to operate. ¾� b. Counter measures ¾�Safe guard the clay gun by taking it in to parking position. ¾�Reduce the system pressure from control room. ¾�In case of nozzle damage replace clay gun nozzle with new one. ¾�Place more ladles and carefully operate the Tilting Runner.

2. Erosion of tap hole Reason for failure: ¾�Due to bad Quality of clay. ¾�Wrong adjustment of tap hole center.

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Remedies: ¾� If tapping is not under control close the Tap immediately. ¾�Reduce system pressure for better control over the tapping. ¾�Enhance the supervising about tilting runner operation. ¾�When there is over flowing of molten material in main runner, plug the tap hole Immediately. ¾�After complete plugging, repair tap hole and remove sticking material

in main iron runner. 3.Self-Opening

Reason for failure ¾�Improper closing of tap hole. ¾�Bad quality of mass, its setting time should not be more than 30 minutes. Remedies ¾�Place one more empty ladle. ¾�Reduce the Plant pressure and check the clay gun nozzle, if required change with new one. ¾�Fill the clay gun with other clay. ¾�Close the tap, ten minutes after closing of the tap normalize the plant pressure. ¾�Other cast house should be kept ready for change over if required.

4.Explosion in tape hole: Reason: ¾�In case of in sufficient heating up of clay in the tap hole due to less setting time for clay before tap opening.(wet clay). Remedies: ¾�Before tapping, repeat movement of bar inward and backward about 3 times to vent the gas and to open the tape hole. ¾�In case of taping with oxygen, catch the pipe tightly as long as possible. Safety precautions to be taken before tap opening

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14 Water System

14.1.Gland Water System General Description:

The gland water system is necessary to provide the required water amount and pressure to supply all gland points on the different process water pumps with gland water. As the operation and the function of the gland water system is essential for the life time of the individual pumps, the gland water system is provided with a gland water pump always running and a standby, that will take over the operation as soon as the running pump trips. 14.2 Process Water System

The Operation of Process cooling water 1. General. The generator gas leaving from melter gasifier cool down to 850 deg C after mixed with cooling gas from compressor, and it is directed to Hot gas cyclone, where approximately 70 % of dust is removed from the gas. This gas constitute CO and H2, hence it is called reducing gas, nearly 85 % of total gas is passed in to reduction shaft and rest of the gas is

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passed through Cooling Gas packing Scrubber (CGPS) .It is further divided in to two parts, cooling gas for and excess gas. The gas which taken in to reduction shaft after reduction process it leaves the shaft, it called as Top gas, it is directed into Top Gas Packing Scrubber (TGPS) and then top gas adjustable scrubber. The gas is loaded with a lot of dust (Normally the inlet of Cooling Gas packing scrubber: 40g/Nm3; the inlet of the Top Gas packing Scrubber: 15 g/Nm3) passes through each scrubber; the gas is cooled and supposed to cleaned up to the 5 mg/Nm3 and 35- 40 deg C. The process water system provides the water in the required amount, pressure and quality for the gas cleaning systems of the COREX process. As the gas from the COREX process (top gas, cooling gas or excess gas) is hot and dust loaded, the water serves two purposes: ¾� Cooling and quenching of the hot gas. ¾�Take over the dust from the gas. For such purposes the process water is taken from the cold-water pond by means of process water pumps to the different supply points of the gas cleaning system. Once the water was in contact with gas, it has dissolved solid particles and is returned either to screw classifier or the scum scrapper or partly direct to the inlet channel of the 1st clarifier is guided to the hot water pond. From there the water is routed via the cooling towers to the 2nd clarifier .The Overflow from 2nd clarifier flows in to the cold water pond shall ensure that the required process water can be provided to gas cleaning area in case of emergency situations with the cooling towers. In this case it should be considered that the temperature increases to a value where the proper function of the system is influenced negatively. The level in the cold-water pond is controlled by keeping the level in the hot water pond in a certain height, while supplying make up water to the cold-water pond. Parts of the process water system are circulation pumps and pressure booster pumps at the gas cleaning systems. The circulation pumps connected to the packing scrubbers ensure that the cooling and quenching of the hot gas is performed properly, The separate booster pumps are provided at pump house to supply the water to adjustable venture scrubbers and for the inlet nozzles of the cooling gas scrubber on the other hand, which are located on a higher level. It has to be ensured that the availability of the process water system is very sensitive .To compensate different shortcomings the water circuit will be inhibited with the traces of chemicals that are essential for the operation of the system. The chemical dosing can only be controlled from the local control box. At the gas cleaning system of the COREX process, the water outlet of the scrubber is performed in such a way that no gas is exhausted to the ambient area. For this purpose the different vessels are provided with level control equipment. This level control equipment is checked and controlled by two parallel working level indicators on each vessels. With these

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controllers of the COREX plant .The gas system of the COREX plant. The gas system of the Corex system must serve operation condition conditions from the ambient pressure to the max. Allowable working pressure. Therefore the main water supply to the gas cleaning system is controlled by means of the flow control valves to compensate the working curve of the pumps with respect to change of the system pressure. This is necessary to avoid overload on the pump motors and /or cavitations in the pumps.

2. The Specification of Gas Cleaning

DUST DENSITY in GAS (g/ Nm3)

GAS (DEG C) SCRUBBER NAME

SUPPLY WATER VOLUME (m3/hr)

IN OUT IN OUT Cooling Gas

Packing Scrubber

1000 40 < 0.5 820 to 850

35 to 40

Cooling Gas Adjustable

Scrubber

70 <0.3 <0.2 45 to 50

35 to 40

Excess Gas Adjustable

Scrubber

140 <0.5 0.005 40 to 45

35 to 40

Top Gas Packing Scrubber

950 15 <0.5 280 to 300

35 to 40

The Pump Specification of Process Cooling Water System

PUMP NAME FLOW, PRESSURE USERS

Packing Scrubber Pump

1500 cum / hr, 8.7 bar Top gas &cooling gas packing, Baumco scrubber.

Inlet Cone Pump

210 cum/hr, 10.2 bar

The inlets of T/G,C/G packing Scrubber.

Booster Pump 500 cum / hr ,8 bar The inlet of each adjustable scrubber & the throat part of C/G Packing Scrubber.

Cooling Tower Pumps

2400 cum /hr, 4,2 bar Process Cooling Tower

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3. Pump operation and scrubber control The water pumped from a Inlet cone pumps is injected at the top part of packing scrubber is called inlet cone (dome). The water pumped from a Process cooling water (PCW) pumps and Booster pumps is supplied to scrubbers packing, scrubber throat, to the baumco scrubber and to all venturies. FRC 5120 and FRC 5121 control the flow to the scrubber packing for Top gas and cooling gas respectively. The LRC valves, which are located at the out, control the level inside the scrubber, let (Weir drain) of scrubber. It consists of two valves, ball valve and butterfly valve. The level is indicated by the level indicator, it is bubbler type and it give feed back to the controller (LRC) in term controller will control the water flow from scrubber out let and maintain the level in the scrubber.

1. Process Cooling Water Recirculation System. ¾� The water contains a high percentage of coarse material, it is drained from bottom parts of packing scrubbers (Cone drain) to the screw classifier trough Degasser. ¾� The water is drained trough LRC valve (Weir drain) from the side of each scrubber to the over feed box of the scrapper. ¾� The out put from scum scrapper and screw classifier contains thick slurry is collected separately and discharged to sludge treatment yard. ¾� The Heavy particle settles at the bottom of clarifier, which contains, slurry is taken out by using three numbers of sludge discharge pumps, which are located at the bottom of the clarifier. ¾� The water, which over flow from clarifier #1 is taken in to hot water pond. ¾� The water from hot water pond is pumped into Process Cooling Tower to reduce the water temperature. Nearly 25 deg can be reduced in the cooling tower. From cooling tower water flows in to clarifier #2. The over flow water from clarifier #2 is collected in cold water pond. The water is then pumped in to the system by process cooling water pumps.

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Pump House Lay Out Pumps Details with respect to Ponds at PUMP HOUSE

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14.3 MCW AND STAVE COOLING WATER SYSTEM 1. MACHINE COOLING WATER SYSTEM GENERAL The closed water circuits is divided in to machine cooling water system, both Critical system and Non-critical system and Stave cooling system. The system is provided with Overhead tank, which assures the constant pressure head all the time in the return water line. In emergency situation like power failure water will flow from emergency tank and protects the equipments. Circuit also consists of filters and heat exchangers before pump suction. It consists two pumps one working and one stand by. SYSTEM SPECIFICATIONS CRITICAL NON-

CRITICAL REMARKS

TOTAL FLOW 750 CUM /HR

500 CUM /HR

HOLDING VOLUME

50 CUM 30 CUM Volume of Over head tank.

SUPPLY TEMPERATURE

36 deg C/ 42 deg C

36 deg C/

42 deg C

SUPPLY PRESSURE

11.20 bar 11.20 bar

PUMP CAPACITY

750 CUM /HR

500 CUM /HR

Total pressure drop Critical :- 0.5 bar. Non critical:-0.5 bar.

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Start procedure. The group operation will be performed by the mode GROUP AUTO. 1. Preconditions. ¾� Emergency water pond level should not be low. ¾� Emergency water tank: level should not be low. ¾� All recirculation pump kept ready for start. ¾� HIC should be in closed condition.

Critical and Non Critical Water System Circuit is as shown above ,which is having two pumps one running one stand by, attached with emergency pumps which is operated during Power failure. Pumps will continuous to run unless there is pressure drop less than the minimum set discharge pressure with in the interval of defined time period. The stand by pump will starts when running pump trips. In case of power failure the running pump trips and water starts flow from overhead tank in to the system through by-pass line through control valve (HIC) in to the emergency pond at pump house. The level in the overhead tank starts reducing and it is controlled by the HIC valve. At the same time Diesel generator is started and emergency pump is taken in to operation will supply the water in to the system circuit and also fills the water in to the overhead emergency tank.

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14.4 Stave Cooling Water System. 1. General The melter gasifier is provided with cooling plates, which are installed inside the melter gasifier shell up to 23 mts. The purpose these stave cooling plates and the hearth bottom cooling is to take off the heat that is generated in the melter gasifier. The stave cooling plates are cooled by means of a closed water circuit, where the water is cooled in the heat exchangers. The emergency tank is provided to take care emergency situation, which is pressurized with Nitrogen.

Emergency Case. In case of power failure the running pump trips and water starts flow from overhead tank in to the system through by-pass line through control valve (HIC) in to the emergency pond at pump house. Stave Overhead tank Depressurizing valve opens.

The level in the overhead tank starts reducing and it is controlled by the HIC valve. At the same time Diesel generator is started and emergency pump is taken in to operation will supply the water in to the system circuit and also fills the water in to the overhead emergency tank.

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15 Heat Up and Start Up

15.1 Heat Up Flaps and Bottom Air Pipe Arrangements for Heat Up & Start Up 15.2 Heat up and Start up procedures: The process vessels i.e. Reduction Shaft, Melter gasifier, Hot gas cyclones, Dust bins and hot gas ducts etc. are lined with refractory bricks / castable which require to be dried and heated slowly. Purpose of Hearting up:

x� Removal of moisture from refractories and castables lined in the process vessels / ducts. x� To increase the temperature inside the Melter gasifier and fixed bed temperature above the

char combustion temperature to prevent explosions

MG

Shaft

Safety Flap Top Gas Flap

H/C

Dust bin Flaps (4 nos)

Burners for heat up (8 nos) From Bottom air station

DRS System

Top Gas Scrubber

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Preconditions for Heat up: x� Successful performance acceptance test of all sections of the plant x� Completion of plant pressure test at 5.3 bar x� Process, machine cooling and stave cooling water systems in operation x� Heating up thermo couples installed. x� Bottom air pipe with thermocouples installed and covered with Converter slag x� Heat up burners(8 nos) and Tuyeres installed x� Blowers for heat up burners checked ready x� Fuel gas system for heating up ready in all aspects x� Heat up flaps installed x� Raw material preparation as per requirement x� Temporary points for cooling gas and top gas analysis shifted put in use x� Provision of lances for temperature measurement in front of tuyeres x� Both tap holes are drilled and kept open x� Gas sampling at tuyeres is installed x� Condensate points on MG and RS are open x� Bottom air station checked up for flow etc. 15.3 Salient features of Heat up:

x� Heating up of Melter gasifier x� Heating up of Dust recycling System ( at around 200 deg c of Dome temperature) x� Heating up of Reduction shaft (at around 300 deg c of dome temperature) x� Charging of CRE to RS and heat x� Charging of CRE to MG and air blow through Bottom air pipe x� Dismantling of burners and installation of all tuyeres at 1000deg c of Dome temperature x� Filling of shaft with DRI / HBI x� Filling of MG with Given recipe (crushed electrodes / coke mix) x� Ensure tuyere temperature above 1000 deg c and all systems in operation x� Start oxygen through the tuyeres (Plant start)