furnace presure controller

FURNACE PRESSURE CONTROLLER

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Background

Project Objective

Outline to report


1.1 BACKGROUND

Today our life is more comfortable because of invention of modern technology. Without this technology our lives become miserable. At present we can’t imagine our life without electrical resources and equipments. In limited period of time, many inventions have been done regarding engineering field. In electrical field also much improvement has been shown in these days. There is a one major factor which affects all this invention is generation of electricity. Generation is the main plinth of the electrical field. This can be approved by thermal power plant.

There are mainly three types of power plants which are found it includes thermal power plant, hydro power plant and nuclear power plant. The variation in the design of thermal power station is due to different fuel sources used. The different fuel sources included may be coal, nuclear, natural gas; etc.In thermal power plant kinetic energy or mechanical energy has been converted to electrical energy.

At TPS, coal is used as primary fuel for generation of electricity. Coal is burnt in furnace to produce heat. The heat from combustion of coal boils water in boiler to produce steam .the steam is then piped to turbine where it rotates them. The used steam is then condensed and pumped back into the boiler to repeat the cycle. Rotation of the turbine rotates the generator rotor to produce electricity based on Faraday’s Principle of electromagnetic induction. When the turbine turns, electricity is generated and given as output by the generator, which is then supplied to the consumers through high-voltage power lines.

In India all the power plants are connected in the grid system. All the plants have been distributed in mainly four grids. These grids have been controlled by different LDC (load dispatch canters) which controlles the generation of energy and load requirements. Basically thermal power plant is operated on the base load with high load capacity and it has very high value of generation capacity.

We had got an opportunity to undergo training in one of the most precious industries of Gujarat without which the glory of Gujarat would not shine like a star in the map of India. This is the main body which provides electricity to the whole state. Now furnace is one of the parts, which produces heat on burning of coal with air. It isOne of the most critical parts of the plant where pressure needs to be regulated constantly at several instants. As if there is low value of pressure it may cause the furnace to shrink, where as the increase in pressure may cause the furnace to blast leading to very dangerous accidents causing hazards to both life and property.

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To control the pressure of furnace at sikka a multicard system was used each card with its own function. This has lead to more troubleshoot problems and more maintenance was required. So we decided a make a project on furnace pressure control system which could be a single control system, replacing the multicard system.

Even though there are measures taken to control the various parameters, the present system becomes a too hectic and requires human labour.thus there is a need to develop such a system which would not only control the furnace pressure effectively but also reduce the work load of the controlling officials.

1.2 PROJECT OBJECTIVE

This project as the name suggests is used to control the pressure of furnace. The requirement is to make a single pressure control system which would replace the multicard system. To demonstrate such a vast process with atmospheric pressure is not viable so this project is scaled down to specific values.

Here the pressure sensor senses the pressure inside the system which comprises of four fans .this signal value is given to the control system where the set point is already set up. Accordingly the intake of air to the system is adjusted such that the uniform pressure is maintained inside.

1.3 OUTLINE TO REPORT

The project report is divided into three main sections. First section gives the description about the methodology adopted for making of this project, and interfacing of different components used. Second section gives an idea about the hardware used to make this project and the components description. Third section describes the software part of this project.

1.3.1 Working Of The Project This section explains how different components are interface together to function. It also includes the methodology adopted for working of this project.

1.3.2 Hardware Section

This section gives a brief description about the different components used to make this project which include the pressure sensor, microcontroller, LCD,etc.

1.3.3 Software Section

This section gives a brief idea about the program developed which on feeding to the controller gives the appropriate control required to maintain the pressure inside the system.

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TPS

Introduction

Basic elements of

thermal power plant


2.1 INTRODUCTION

Here is the brief description of sikka thermal power station.

Fig.2.1 Operation Of Thermal Power Plant.

Detailed process of power generation in a thermal power plant

1) Water intake: Firstly, in the boiler the feed water is used demineralised water only. This DM plant takes water from the Sasoi dam. The water which used in the boiler must be totally demineralised. Water is scarce, then it is recycled and the same water is used over and over again.

2) Boiler heating: The boiler is heated with the help of coal. A furnace is used to heat the fuel and supply the heat produced to the boiler. The increase in temperature helps in the transformation of water into steam. The coal used is of bituminous type. This coal is imported from the nearby states.

3) Steam Turbine: The steam generated in the boiler is sent through a steam turbine. The turbine has blades that rotate when high velocity steam flows across them. This rotation of turbine blades is used to generate electricity.

4) G enerator : A generator is connected to the steam turbine. When the turbine rotates, the generator produces electricity which is then passed on to the power distribution systems.

5) Special mountings: There is some other equipment like the economizer and air pre-heater. An economizer uses the heat from the exhaust gases to heat the feed water. An air pre-heater heats the air sent into the combustion chamber to improve the efficiency of the combustion process.

6) Ash collection system: There is a separate residue and ash collection system in place to collect all the waste materials from the combustion process and to prevent them from escaping into the atmosphere.

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Apart from this, there are various other monitoring systems and instruments placed to keep track of the functioning of all the devices. To prevent any hazards from taking place in the plant

2.2 BASIC ELEMENTS OF THERMAL POWER PLANTS.

The different parts of a thermal power station and their functions are as described below:-

Fig2.2 Schematic Diagram Of TPS

2.2.1 COAL

For sikka power house coal received from MP and Bihar (secl) mines, by railway, at SIKKA railway station. 02 km railway track provided by GEB, for transporting this coal from sikka railway station to power house and by this way, the coal rack in 8 wheeler box type wagons directly reaches to power station coal yard. This loaded coal wagons on the tippler platform are unloaded with the help of two wagon tipplers. From w.t.hoppers coal then passes through apron feeders 1 & 2 & single roll crusher to crusher house in 200 mm size after removing iron pieces by magnetic separators, where this coal crush up 20 to 30 mm size. This crush coal is fed to bunkers through junction tower by conveyor belt. If coal receipt is more, then it is transferred to stack yard for socking.

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Fig 2.3 Coal Feeders

Pulverized coal is fired in furnace for generation of steam with the help of secondary air which, is coming from forced draft fan through regenerative air pre-heater. The flue gas generated due to coal firing are being handled by induced draft fan through super Heaters, economizer, regenerative air pre-heater, esp. and discharged through chimney. Steam generated in boiler with rated pressure, temperature and flow is being feed through main steam line to hip. Turbine and imp turbine through hot reheat line of the furnace are taped at the bottom to form a hopper with suitable on fuel and a conditions. Bottom designs most commonly used for coal fired units are of the open hopper type, often referred to as the dry bottom type. For gaseous and oil fuels, closed bottoms are generally utilized.

In the bottom type construction two furnace water walls, usually the front and rear walls, slope down toward the centre of the furnace of from the inclined. Ash and slag from the furnace is discharged through the bottom opening into the ash hopper directly below it. Depending on the height of the furnace, six to fourteen inches clearance between the

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furnace and ash hopper is allowed for downward expansion of the furnace walls. Leakage of the air at the point is prevented by either a water seal arrangement or a mechanical seal. The primary air from the discharge of F.D. fan passes through Air preheater and hot air for combustion from air preheater is led to common wind box located on the side of the furnace. There are two numbers of steam coal air preheaters are provided on discharged side of F.D. fans before air enters to air pre heaters. In order to ensure reliable and continuous operation soot blowing equipments are provided.

2.2.2 DRAUGHT SYSTEM

The draught system is used to provide furnace draught stability. The Draught is maintained by operation of induced draught and forced draught fans. The draught system consist of following equipments

FIG 2.4 INDUCED AND FORCED DRAFT FAN

INDUCED DRAUGHT FAN : the induced draught fan is provided for sucking of flue gases from the furnace and discharge to the chimney. The suction of the fan is taken from the outlet of the esp. and discharge to the chimney. The fan is facilitating to create a Negative pressure in suction to suck flue gases. The flow of flue gas can be controlled by guide vane controlling. Table shows further descriptions.

Table:-1 Induced Draught Fan

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FORCED DRAUGHT FAN :- The forced draught fan is facilitating to suck air from the atmosphere and to supply this air to the furnace for proper combustion and to maintain the draught inside the furnace for stability of furnace and firing. The flow of air can be controlled by guide vane controlling.

PRIMARY AIR FAN :- The p.a.fan is facilited to provide air to the coal pulveriser for drying the coal and lifting it to the furnace. The flow of air can be controlled by guide vane controlling.

Table:-2 Primary Air Fan

2.2.3 ECONOMIZER

The purpose of economizer is to preheat the boiler feed water before it is introduces in to the boiler drum, and to recover some of the heat from the flue gases leaving the boiler. Location of the economizer is in the rear gas pass below the rear horizontal sh .feed water is supplied to the economizer inlet header via feed stop & Check valves. It is upward through the intermediate eco header that is in counter flow to the flue gases & comes in out header, from that it is led to drum.

Table3:-Economizer

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2.2.4 SUPER HEATER

Super heater is composed of four basic stages: pendant spaced section, platen sectional rear horizontal section and the steam cooled wall and roof sections. The platen section is located directly above the furnace in the front of the furnace arch. It Absorbs heat mainly by radiation. The pendant section is located behind the screen tubes. The heat transfer mode is convection. The horizontal section of the super heater is located in the rear vertical gas pass above the economizer, heat transfer mode is Convective. This is the counter flow type primary superheater.The steam cooled wall section form the side, front & rear walls roof of the vertical gas pass.

Superheated steam from outlet of pendent goes to the turbine via the main steam line. After passing through the turbine steam is returned to the reheater via the cold reheat line. The reheater desuperheaters are located in the cold reheat lines.

Fig2.5.-Unit Showing Super Heater And Other Parts.

2.2.5 DESUPERHEATER

Desuperheater are provided in the super heater connecting links and the cold reheater lines to permit reduction of steam temperature when necessary and to maintain

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the temperatures at design values within The limits of the nozzle capacity two spray type desuperheaters are installed in the connecting links between the rear horizontal Outlet header and the platen inlet header.

2.2.6 REHEATER

Two spray type desuperheaters are installed in the cold reheat lines leading to the inlet headers. Reheater is composed of two stages, the front pendant vertical spaced platen section and the rear pendant vertical spaced platen section. The front is located bet rear water wall hanger tubes and the super heater platen section. The rear pendant is located Above the furnace arch bet the water-cooled screen tubes and rear water wall hanger tubes saturated dry steam from the drum follows the path is

steam cooled wall roof tubes steam cooled side wall tubes extended steam➔ ➔ ➔ cooled side wall tubes front steam cooled side wall tubes steam cooled roof and rear➔ ➔ wall tubes super heater rear horizontal assemblies super heater desuperheater platen➔ ➔ super heater pendant super heater➔

2.2.7 PRIMARY AIR

Combustion air that enters the fuel-burning zone and directly supports initial combustion. On pulverized coal-fired units, the primary air is used to transport the coal from the pulverizers to the burners.

2.2.8 SECONDARY AIRCombustion air introduced on the edge of the burning zone to supplement the

primary air for support of the combustion process.

2.2.9 AIR-PRE HEATER

The air heater absorbs waste heat from flue gas, then transfers this heat to incoming cold air by means of continuously rotating heat transfer elements of specially formed metal plates. Thousands of these high efficiency elements are spaced

Within twelve sector-shaped compartments of a radially divided cylindrical shell, called the rotor. The housing surrounding the rotor is provided with duct connection at both ends, and is adequately sealed by radial and circumferential sealing members forming an air passage through one half of the pre-heater, and a gas passage through the rotor. As the rotor slowly revolves the mass of elements alternate through the gas and air passage, heat is absorbed by the element surfaces passing through the hot gas stream; then, as these same surfaces are carried through the air stream, they release the stored up heat thus greatly increasing the temperature of the incoming combustion or process air.

2.2.10 SOOT BLOWER

The cleaning medium to be used is superheated steam. The cleaning device consists of an electric motor coupled to a gear driven crank mechanism which oscillates the swivel header carrying the nozzle pipe or pipes. The arc traversed by the nozzle and the rotation of the rotor subjects the entire area of the rotor to the action of the cleaning steam jet. Drain connections are provided in the steam piping layout for removing condensate from the piping system while the device is idle and just before it is placed in operation. It is located in the gas side.

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Steam consumption : 1200 kg / hr./ device at 17.6 kg / cm2

2.2.11 ELECTROSTATIC PRECIPITATOR

The electrostatic precipitator utilizes electrostatic force to separate dust particles from the gas to be cleaned. The gas is conducted to a chamber containing "curtains" of vertical steel plates. These curtains divide the chamber into a number of Parallel gas passages. A frame with secured wires is located within each passage. All the Frames are linked to each other to form a rigid framework. The entire framework is held in a place by four support insulators, which insulate it electrically from all parts which are grounded.

In unit no.1, bhel make, type 2 x faa – 7 x 32 – 13290 – 2 single pass 2Nos. Esp, 7 fields, i/l dust concent – 30.8 gms/nm3, flue gas flow 140.4 m3/s, collectingEff – 99.36 % have been installed.

In unit no.2, bhel make, type 2 x faa – 6 x 45 – 102135 – 2, single pass -2Nos. Esp, 6 fields, i/l dust concent – 45.7 gms/nm3, flue gas flow 219.4 m3/s, isCollecting effi. 99.67 %.

The function of esp is to collect the dry ash on collecting electrode by corona Effect and as is being rapped at regular interval by rapping mechanism and thus dry ash Is being collected in esp hoppers. From esp hoppers dry ash is being disposed through Wet system in ash dyke as well as being collected in silo. The dry ash collected in silo is Sold to cement / bricks manufacturer.

A high-voltage direct current is connected between the framework and theGround, thereby creating a strong electrical field between the wires in the framework and The steel curtain. The electrical field becomes strongest near the surface of the wires, sl Strong that an electrical discharge " the corona discharge " develops along the wires.

The Gas is ionized due to the corona discharge and large quantities of positive and negativeIons are formed. The positive ions are immediately attracted towards the negative wires By strength of the field. The negative ions, however have to traverse the entire space Between the electrode to reach the positive curtains.Enroute towards the steel curtains, the ions collide with and adhere to the dust Particles in the gas. The particles thereby become electrically charged and also begin to Migrate in the same direction as the ions towards the steel curtains and stick on to them.These curtains are rapped periodically to dislodge the deposited dust, which is collectedIn the hoppers.

The various parts of the precipitation are divided into two groups. :

mechanical system : it comprise of casing, hoppers, gas distribution system,Collecting and emitting system, rapping mechanism, stairways and galleries.

electrical system : it comprise of transformer-rectifier units, electronic controllers,Auxiliary control penal, safety interlocks and field equipments / devices.

2.2.12 ASH HANDLING PLANT

Ash handling plant at sikka thermal power plant comprises of specially Designed bottom ash systems. A detailed description of the system is given in the following Paragraphs:-

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The water impounded bottom ash hopper receives the bottom ash from the Boiler furnace, where it is stored and periodically discharged to the clinker grinder and Hydro ejector to convey the bottom ash slurry through the transport line to the ash slurry Sump

Fig 2.6.Ash Handling System

A maximum of eighty-three (83) tonnes of bottom ash is collected in every eight(8) hours working shift. The bottom ash system is capable of disposing the ash collected,Within one hour.

Dry, free flowing ash is collected in a total of thirty-seven (37) fly ash hoppers Consisting of twenty four (24) electrostatic precipitators, two (2) duct hoppers, six (6) air Pre-heater hoppers, four (4) economiser hoppers and one (1) stack hopper.Fly ash is evacuated pneumatically in a dry state and is conveyed to theVacuum producing hydrovactor (two nos.) Where it is mixed with water, forming ash slurry And collected in air separator tank from which the fly ash slurry flows to ash slutty sumpBy gravity. Crossover valves are provided to allow the fly ash to any of the vacuum Producing hydrovactors. A maximum of three hundred and seventy six (376) tones Approximately of fly ash is collected in every shift and the system is capable of handling

The fly ash collected within four hours.Bottom ash and fly ash collected in a slurry form is conveyed to the ash Disposal area through two (2) sets of ash disposal pumps. Each set consists of one (1)Pump in series. Interconnecting line isolation valves in disposal lines are provided to allow Usage of either pump through any of disposal lines. The ash handling system operation Starts with disposal of fly ash followed by bottom ash.

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BOTTOM ASH SYSTEM :- the water filled ash hopper, receives furnace ash from the Boiler. Chilling it as it enters the water impounded hopper to minimize clinkering andStoring it for periodic removal.The mixture of ash and water is discharged through feed gate to clinker Grinder, which sizes the clinkers. Crushed clinkers and ash water mixture fall to ejectorFeed sump and is fed to hydro-ejector. The hydro-ejector (jet pump) which provides the Jetting or pumping action by means of high pressure water, convey the mixture of bottom Ash spray through bottom ash discharge pipe line to ash slurry sump. Two flushing Header assemblies with nozzles are provided in the bottom ash hopper to agitate and Remove sedimented ash from the ash hopper.

The clinker grinder is equipped with an automatic reversing control, to takeCare of mechanical overload. If any mechanical overload occur in the grinder. The grinderStops automatically and runs in the reverse direction for approximately 10 second andagain reruns in the forward direction after 20 seconds. The same sequence is repeated For three consecutive overload and after the third cycles if over load is not cleared, thenClinker grinder will trip. It can be started again in forward direction only after re-running And mechanical over load manually and resetting the overload relay.

A pressure switch located in the bottom ash slurry transport line will sense a High dischar4ge pressure, indicating blockage or obstruction of material in the dischargePipe line. Should such a condition occur, clinker grinder stops operating depositingMaterial on grinder rolls. When the pressure drops to the present level the grinder willAgain commence operating. This pressure switch thus prevents the possibility ofAdditional ash being the discharge line enroute to ash slurry sump.If desired water pressure is to available at hydro ejector water inlet or forGrinder stops. When the water pressure at hydro ejector inlet or for grinder sealingBecome normal, the operation of clinker grinder and feed gate starts.

FLY ASH SYSTEM :- below each fly ash hopper one 8"x6" type "e" air electric Operated, self feeding. Non -overloading type material handling valve is mounted. It isEquipped with two adjustable spring loaded air intake valves. Each material handlingValve has a stainless steel slide gate to segregate the hopper from the transport line. The Slide gate is pneumatic operated and its operation is controlled by instrument at by a 4-Way solenoid valve. Pneumatic operated segregating valves are provided for branch Header isolation. The segregating valve remains open till all the material handling valves Connector to the branch header have been operated in succession and closes with last flu Ash valve in the line.

The water powered 6"x8" hydrovactor (vacuum producer) located above the air Separator tank (mounted on the tower structure) exhausts air from the 8 inch sizeTransport line running to the material handling valves. The resultant rise in vacuumOperates high vacuum switch which energies the fly ash circuit to the automatic Sequential control. This in turn energies t5he solenoid valve of material handling valve. The floe of air from the air intake valves conveys the fly ash from the fly ash hopperThrough the transport line and hydrovactor. The fly ash is mixed with water (which forms aSlurry) in the hydravactor and is discharge in to the air separator tank. This tank Separates and vents the conveying air in to the atm, and discharges the slurry by gravity In to the ash slurry sump through the pipe lines.

As long as fly ash is available at the mount of he fly ash hopper, it prevents Excessive entry of air in the fly ash system resulting in maintaining high operating

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Vacuum. On evacuation of ash. The free air from the fly ash hopper rushes into the Transport line and the system vacuum drops. This operates the low vacuum switch which Energies another circuit in the automatic sequential control where in after a preset timeDelay. The solenoid valve controlling this material handling valve gets de-energized, thusClosing the valve. This again results in raising the system vacuum and operating high Vacuum switch to energies solenoid valve of the next material handling valve in Preprogrammed sequence. The above procedure is repeated for each material handling Valve in turn. After the last valve closes, the fly ash automatic control gets de-energized The motor operated valve located in the inlet water line of the hydrovactor remind open For a further preset time to purge the discharge line of the air separator tank.

An pneumatic operated vacuum breaker provided in each transport line vents The system to atmosphere in the event the water pressure to respective hydrovactor falls Below the preset value set on the pressure switch (mounted in the inlet wate4r lines to Respective hydrovactors).Manual operation of individual material handling valve is also possible by Means of fly ash master switch mounted on the control panel. Individual bypass switched Also mounted on the control paned to allow bypassing of any fly ash hopper material Handling valve from which the fly ash removal is not desired.

ASH DISPOSAL SYSTEM:- the ash slurry, mixture of water and bottom ash/fly ash, Collected in slurry sump is pumped to disposal area by hydro seal pumps, through 10/12Inch disposal pipe line. Two (2) such sets of ash slurry pumps have been provided.The ash slurry sump is a rcc tank, which sloped bottom ash lined with Replaceable wear plater under all discharge points. Two sets of agitator nozzles provided In the slurry sump keep the solids in floating state. Ash flow valve provided in suction and Discharge of disposal pump allow isolation of each pump. Operational flexibility is Available by crossover ash flow valves which permit the use of both the discharge lines With individual pump Ash flow valves in suction line from ash slurry sump to each ash slurry pump Help pump isolation during maintenance. The pumps are ;belt driven and a special varies Pitch sheave on the pump motor allow variation of speed of pump to account for normal Wear and tear of pump and ash disposal line.

Disposal piping gas special "ezy" coupling Joints to ensure case in periodic rotation of the pipes for uniform wear.Water make-up requirements of ash slurry sump is automatically regulated by Means of diaphragm operated butterfly valve controlled by a pneumatic indicatingcontroller. The controller senses the slurry level by a ;rubber tube arrangement andsignals the valve positioner to operate the valve. Ash slurry sump high and low levels have been annunciated on the main fly ash and pumps control paned situated in the ash handling mcc room. Besides this interlock for tripping of the ash slurry pumps in the event of low level in the slurry sump ha also been provided.

2.2.13 BOILER

Steam generator of unit no.1 Natural circulation type with water cooled furnace,tangentially fired, balance draught radiant reheat type, dry bottom with direct firedtangentially fired, pulverized coal through 6 nos. bowl mills, steam flow 383 T/hr. @ 135cm2 SH pressure and 540 degree temp. Boiler rating 8863 sq. meter. Total heat input to Boiler 305.8 M. Kcal/hr.

Steam generator of unit no.2 is natural circulation type with water cooled furnace,tangentially fired, balanced draught radiant reheat type, dry bottom with direct fired pulverized coal through 4 nos. tube mills, steam flow 391 t/hr. @ 134.5 kg/cm2 SH

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pressure and 540 degree temp. Boiler rating 12665 Sq. mtr. Total heat input to Boiler 265.8 M Kcal/hr. In Boiler unit no.2, 1 and 2 mills are bowl mill with model No. XRP-603 and Tube mill having model no. BBD-3448 respectively. The function of mill is to Pulverize the coal to 200 mesh size and to feed the same in Boiler through pulverized fuel pipe with the help of primary hot air.

Pulverized coal is fired in furnace for generation of steam with the help of secondary air which, is coming from forced draft fan through regenerative air pre-heater. The flue gas generated due to coal firing are being handled by induced draft fan through superheaters, Economizer, regenerative air pre-heater, ESP and discharged through chimney.Steam generated in Boiler with rated pressure, temperature and flow is being feedthrough Main Steam line to H.P. Turbine and IP Turbine through hot reheat line

2.2.14 COOLING TOWERS

Fig 2.7Different Types Of Cooling Mechanics

The symbol for a cooling tower is designed to resemble the actual devicein the process unit. Cooled product flows out of the bottom of the tower andto the processing units. Hot water returns to a point located above the fill.The symbol will not show all of the various components of the cooling towersystem, but it will provide a technician with a good foundation in cooling tower operation and enough information to clearly see the process2.2.15 WATER WALLSThe waterwalls are tubes that are welded to spacers between the tubes toform a gas-tight wall. The water flows up through the walls as it turns to steam.

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Fig2.8 Water Wallls

2.2.16 STEAM TURBINE

The turbine is horizontal tandem compounded, reheat, impulsive type three cylinder machine, with continuous maximum economical rating of 120MW at the generator terminal at a speed of 3000 rpm. The design inlet conditions are 127.6 kg/cm2 and 538c for main steam and 2602 kg/cm2 and 538c for reheat steam.

The high pressure steam chests are located one on either side of the high pressure cylinder. Live steam from the boiler is admitted into the high pressure steam chest which

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contains two combined isolating and emergency stop valves and one governer valve. This steam chest is interconnected with the governor valve by means of a cross under pipe. Stem from these chests is supplied to the high pressure cylinder by means of 4 nos. of high pressure loop pipes. Steam after expanding through the high cylinder is passed through the reheater section of the boiler. Reheat steam is supplied to two interceptor emergency stop valves and two interceptor governor valves. From the interceptor steam chests steam is welded to the bottom half of the in let end of intermediate pressure cylinder. Steam after expanding through the intermediate pressure cylinder passes through the cross over pipes to a double flow low pressure cylinder. Finally steam from low pressure cylinder is exhausted to the condenser.

The flow of steam in the high pressure cylinder and intermediate pressure cylinder is of a double flow design. This arrangement ensures minimum axial thrust, Each flow to the low pressure cylinder is provided with a multi exhaust. The high pressure cylinder is of twin shell construction. The intermediate pressure cylinder diaphragms are of welded type. In the first eight diaphragms the rims, centres and blades are of molybdenum vanadium steel, the remaining five diaphragms have mild steel rims and centres with stainless blades.

2.2.17 CONDENSER

When steam exhaust from the turbine it exhaust in the condenser. Which is exhausted with high temperature and low pressure. Condenser is made up of copper tubes which are in large sizes. Generally two types of condenser are used one way and two way types of condensers. In sikka thermal power station two type circulating tubes are used. When water passes through the tubes and steam exhaust at the condenser it contacted with the outer surface of the tube. Cooling water passes through the tubes. When this steam contected with the water it becomes cooled.

In sikka thermal power plant cooling water is taken from the sea. Which passed through the copper tubes. Which cooled the steam hence steam cooled and become water which collected in the storage tank and further taken by the boiler feed pump. Due to the condenser water is circulating in cyclic process. So the efficiency of the plant become quite high. In sikka thermal power plant sea water is used as cooling water so no need of cooling tower for colling the condensate cooling water. This technique is quite cheap in the processing.

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The whole plant has many PLCs which controls different processes. Different PLCs have a different control principle to control different parts. These various mechanisms for control and measurement in a thermal power plant are enlisted below.

3.1 MEASUREMENT

Furnace pressure control is typically implemented in balanced draft operations. Most often the furnace pressure is maintained just slightly below atmospheric pressure to prevent flue gas leakage to the surroundings. However, too low a pressure must also be avoided to minimize air leakage into the furnace reducing efficiency and, in the extreme case, to prevent furnace implosion. Normal ranges are compound with spans on the order of 1 inH2O or less. This creates a challenge for most analog transmitters as such narrow spans generally amplify process noise created by pulsations from the varying rate of combustion as well as the ID and FD fans.A smart draft transmitter is appropriate for this application. The selected instrument should have at least a span of 0.2 inH2O and adjustable damping. This will allow use on a wide variety of furnaces.Process measurement requirements are as follows.

3.1.1 Instrument Installation For Combustion Control

Process sensing devices should be installed as close as practical to the source of the measurement with consideration being given to excessive vibration, temperature, and access for periodic maintenance. Dedicated isolation valves and impulse lines should be run to each pressure-sensing device used for control in accordance with Measurement and conditioning Filtering techniques used to condition process measurements shall not adversely affect stability or reduce control system response.

3.1.2 Mass Airflow Measurement

The mass airflow measurement shall be a repeatable signal that is representative of the air entering the furnace.

When volumetric airflow-rate measurement techniques are employed and the air temperature at the flow-measuring element varies 50°F (28°C) or more, the measured (indicated) flow shall be compensated for flowing air density to determine the true mass airflow rate.

3.1.3 Furnace Pressure Measurement

Furnace pressure shall be measured with three furnace pressure transmitters, each on a separate pressure-sensing tap.

3.1.4. Fuel measurement

The fuel-flow measurement shall be a representative measure of the total fuel energy entering the furnace.

3.1.5 Gas Analysis Measurement

a) A representative flue-gas oxygen measurement shall be provided.

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b) A representative flue-gas measurement of equivalent combustibles should be provided for monitoring under low-excess, air-firing conditions

3.2 CONTROL

Furnace (draft) pressure control is used to maintain a constant furnace pressure. This can be accomplished by a single-element feedback control loop. In this application, the air flow is controlled by the forced draft fan, while the furnace pressure is regulated by the induced draft fan. Controlling the air flow via the forced draft reduces the interaction between the air flow and the furnace pressure control loops When used, furnace pressure control is typically implemented in a feedforward fashion. As shown in Figure 2, the FD fan damper is generally manipulated by the air flow controller, and the ID fan damper is manipulated by the furnace pressure controller. When the air flow controller manipulates the flow, the furnace’s internal pressure will be disturbed unless there is a corresponding change to the flow out of the furnace. An impulse feedforward connection couples the two dampers to minimize the furnace pressure disturbance on a change in air flow. As the impulse decays, external reset feedback to the furnace pressure controller drives the integral component to maintain the new steady state ID damper position. The furnace pressure controller trims the feedforward compensation as required to control the pressure at setpoint.Control problems can result from the inherent noise of the combustion process and the relatively sluggish response of fans, dampers, or couplings in removing the large volume of hot gases. A positive pressure excursions may discharge flue gas and ash into the boiler house. The typical solution to this problem is to control at greater negative pressures to prevent upward excursions from reaching the positive pressure region. In some very large boilers, extreme negative excursions may implode furnace walls.

In order to compensate for the dynamic problems encountered in furnace pressure control, advanced control strategies such as input filtering, damping, feed forward, lead, lag, and/or adaptive gain are often required. Typical analog control systems can require several panel or rack-mounted devices to implement these strategies. The versatile combustion management solution from Moore has the required functions built-inform a complete furnace pressure control system.

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The furnace internal pressure control loop is shown schematically in the diagram above.Internal pressure control affects the loss of combustion gases through the furnace openings, as well as the entrance of cool air (called tramp air) through these openings. It is easy to understand that, with a higher internal pressure than that of the environment, furnace gas losses may be so high as to make it necessary to increase the capacity of the burners to compensate for them. On the other hand, with a lower pressure, the external cool air infiltrations cause a decrease in internal temperature with a consequent increase in fuel consumption.

The ideal pressure in a given furnace is a trade off solution in which the sum of hot gas losses and the cool air infiltration is minimized. The optimum pressure for most of the furnaces is about + 0,10 to 0,50 mm H2O measured at hearth level. This value must be determined through smoke testing in the furnace discharge door. The final value depends on the position of the probe or pressure tap.

Balanced draft furnaces are used to regulate draft pressure. Draft pressure is affected by both the Forced draft (FD) and Induced draft fans (ID). They move combustion air and flue gases through the furnace.The FD fan is used to regulate the combustion airflow and the ID fan is used to regulate furnace pressure.Air is delivered in two parts: primary air and secondary air. Primary air flow is the full-load coal flow on a mass basis. Secondary air flow is much higher (approximately 8 times more). The total air supplied is regulated to maintain the target oxygen content in the flue gas.

The Control and logic requirements are as follows.

3.2.1 AUTOMATIC TRACKING

Automatic tracking shall be provided for bumpless control-mode transfer.

3.2.2 COMBUSTION CONTROL

The combustion control, which responds to the boiler energy demand, shall be accomplished with the following:

a) Furnace pressure (balanced draft systems) control

b) Air demand and air control

c) Fuel demand and fuel control

d) Excess air

3.2.3 Furnace pressure (draft) control

The furnace pressure control shall regulate flue gas flow to maintain furnace pressure at the desired set point in compliance with the requirements .The furnace pressure control shall utilize a feed forward signal representative of the boiler airflow demand.

3.2.4 Air demand and air control

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Airflow demand shall be developed from the boiler energy demand and used to control airflow to the furnace.

There shall be a minimum airflow demand limit to prevent air from being reduced below the unit purge rate when the air control is in automatic. Suitable provisions shall be included to prevent controller windup under minimum air limit conditions.

The minimum airflow limit shall be in compliance with the requirements of NFPA 85.

The following are prerequisites for the airflow control in automatic:

a) Furnace pressure control in automatic (balanced draft systems)

b) One or more forced draft fans (or other air source) in service and the associated regulating device(s) in automatic control

Provision shall be made to ensure that the automatic regulation of air shall result in a fuel-to-air ratio that provides safe boiler operation. This shall include limiting of fuel flow or airflow to ensure that fuel flow never exceeds the safe combustion limit that the airflow will support.

3.2.5 Fuel demand and fuel control

Fuel demand shall be developed from the boiler energy demand and used to control fuel flow to the furnace.

Total fuel input shall be determined from one or a combination of calculated values, fuel measurements, or characterized fuel demand outputs.

The fuel demand/fuel input relationship shall be used to control energy balance on a Btu (kJ) basis. When the fuel control is in automatic, there shall be a minimum fuel demand limit to prevent fuel from being reduced below the level required to support stable flame conditions in the furnace. Suitable provisions shall be included to prevent controller windup under minimum fuel limit conditions.

The following are prerequisites for fuel controller in automatic:

a) Air control in automatic

b) One fuel source in service and the associated regulating device(s) in automatic control

Provision shall be made to ensure that the automatic regulation of fuel shall result in a fuel-to-air ratio that provides safe boiler operation. This shall include limiting of fuel flow or airflow under all conditions to ensure that fuel flow never exceeds the safe combustion limit that the airflow will support.

3.2.6 Excess air

Excess air shall be maintained at all loads to assure proper combustion of the fuel entering the furnace and should not allow the furnace to operate at an oxygen level in the flue gas below the boiler or burner manufacturer's requirements. Suitable provisions shall be included to prevent excess air controller windup under airflow limit conditions.

3.2.7 Final control device requirements

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All final control elements shall be designed to fail safe on loss of demand signal or motive power, i.e., open, closed, or lock in place. The fail-safe position shall be determined by the user and be based upon the specific application to meet all boiler purge and interlock requirements .

Various combustion control strategies that are based on requirements for safe, efficient, and responsive control of boilers have evolved. More sophisticated controls were developed as instrumentation became more reliable and accurate. The control strategies can be divided into two major categories: positioning systems and metering systems.

In positioning systems the fuel and air control devices are simultaneously positioned, based on energy demand. Each position of the fuel control device assumes a corresponding position for the airflow control device. A control station is normally available for the operator to trim the fuel/air ratio.The positioning system is simple and fast responding, but it cannot compensate for varying fuel characteristics, atmospheric conditions, dynamic characteristics of the fuel delivery equipment, or the imbalance of the fuel-to-air ratio during rapid load changes.

Metering systems measure the actual fuel and air delivered to the boiler. The measured flows are used in feedback control schemes to precisely regulate the fuel demand and to establish a cross-limited minimum airflow demand. The fuel flow in a gas or oil boiler can also be readily measured. Fuel flow in a coal-fired boiler cannot be directly measured, and various schemes have been developed to infer the fuel delivery rate based on other variables. In addition, the heavy equipment necessary to transport the coal and prepare it for burning presents dynamic operational and control problems.

Airflows can be measured without too much difficulty. Airflow is used in a feedback-control scheme to precisely regulate the air demand and to establish a cross-limited maximum fuel-flow demand. The airflow must be characterized to the corresponding fuel demand in the airflow demand development or in the feedback signal, but not both. The fuel-to-air ratio is adjusted by an excess air-feedback loop. The excess air loop can adjust the airflow demand or airflow feedback signal, but not both.

Furnace pressure (draft) control is required on balanced draft boilers. While either the forced draft fan(s) or the induced draft fan(s) could be used to control the furnace pressure, industry typically uses the induced draft fan to control furnace pressure. A typical furnace pressure control functional diagram is shown in Figure B.2. The control strategy uses a feed forward signal characterized to represent the position of the airflow control device(s). A median-selected furnace pressure is compared to an operator furnace pressure setpoint. Any error is used to modulate a trim controller. In a properly designed and calibrated system, the output of the furnace pressure controller will remain near its midrange for all airflows.

A manual/auto station is provided to allow the operator manual control of the furnace pressure control devices. As required, the furnace pressure demand is interlock per the requirements of the burner management system. The interlock can be for boiler purge, boiler natural draft (e.g., 100%), or fan start-up (e.g., 0%). Any interlock commands will force the manual/auto station to track the downstream demand.

Downstream of the auto/manual station, overrides, and directional blocking are provided to minimize furnace pressure excursion in either auto or manual mode. A fan override demand is provided to minimize negative furnace pressure excursions for the prevention

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of a furnace implosion. A main fuel trip (MFT) override is provided to minimize negative furnace pressure excursion as a result of a flame collapse on loss of flame. Directional blocking is provided to prevent the final control device from moving in the wrong direction and creating a larger furnace pressure error

3.3 CARD CONTROL SYSTEM AT SIKKA.

The Furnace pressure, should be maintained slightly negative relative to atmospheric (room) air pressure to prevent combustion by-products from escaping into the surrounding area through furnace openings (e.g. inspection ports, doors, feeders) and also this pressure needs to be as possible to atmospheric pressure to minimize the intake of excess air through furnace openings, referred to as tramp air. Tramp air cools the combustion gases and reduces boiler efficiency. As air is compressible, any change in the draft due to the FD fan is not seen across the furnace instantaneously. And these lead to pressure imbalance. Too low a pressure would cause air leakage into the furnace reducing efficiency and, in the extreme case; it will lead to furnace implosion.

Firing rate fluctuates so a feed forward control is used in pressure control system. Feed forward control permits the control loop to respond to changes in airflow before sensing a change in draft pressure.

The PI portion of the control loop makes fine adjustments to the ID fan in order to maintain set point. Px is the pressure transmitter which shows the pressure inside the furnace. The output is fed to an LD card and the pi controller .Ld card is used to set the high and low limits for the pressure in the furnace. PI is the controller, where the pressure value is compared with the set point And accordingly controls the induced draft fan. The various cards used in system are as shown in the figure. It consists of a master card and many other slave card are aisoused .the slave card logic controls the induced draft fan positioned at two points .

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Px

PI6-02

Ma6-03

SM6-18

LD6-16

RCM6-13

MA6-05

ID fanA-vanePOSIO

NA6-04

ID fanB- vane

POSI

NA6-06

MA6-07


FURNACE PRESSURE: ±50mmwc PX 51203-1 TAYLOR MAKE

Tb-10

61,62 TB-10

55,5342-41

Add/subAir flow

TB-10

22 Tx fail,ps fail 10nt1

Drive to maximum tb-10 tb-10

Block rate, lower 15,16

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RCM:

This has the main function of dividing the inputs. This card has a total of 4 outputs and 1 input.the input is in the form of voltge and output contains one current and three voltage forms.

MA:

This is used for changing the operation from automatic to manual mode and vice versa.to show this there is an arrangement of LED system which shows the current active mode.

LD:

This generally deals with the alarms. At sikka there are high and low alarms. Alarms aare designed to provide relay deactivations as output when the input ,a current or voltage signal depending upon input type reaches a preset trip point .the double alarm has two trip channels operating from a common input signal.a high alarm operates on increasing input signal at atrip point whereas a low alarm operate on decreasing input signals at trip point.

Adder/Subtractor:

This sub assembly has been assembled from components which have passed all previously prescribed tests.this in general adds the signals.

Thus all these hardware based cards have their own function to control the pressure inside furnace.

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4.

Imp

lem

enta

tion

meth

od

s

Methodology

adopted

Determining rules

Hardware section

Software section

Working principle


4.1 METHODOLOGY ADAPTED

Here is an approach to furnace pressure control pressure system. The requirement is to make a single control system with the help of microcontroller. Furnace pressure is converted in the form of voltage by pressure sensor. This voltage converted into digital form with the help of ADC converter and stores in the microcontroller. The set point is initially set in microcontroller, operator does that. Microcontroller compares the date received which is stored in the memory of microcontroller. Microcontroller generates the controlled output and give to the DAC converter.DAC converts the digital date into analog data for controlling the conduction of triac through opt isolator. The main unit of the controller includes the microprocessor 89C51.The program is stored in the memory of the microcontroller. The memory of microcontroller is used for running the program and storing temporarily data during the control operation. The circuit is designed with all the necessary components for the correct operation of the microcontroller. The logic routines is software implemented in the controller. It consists of a C language programmed system that includes, basically, routines for the adjustment of the rule , the membership functions and the control operation.

Pressure controllers can be manual or automatic. An equipment operator typically uses a dial on a control panel to set the pressure in a manual system. An automatic system has a feedback loop and continuously monitors and regulates the pressure through an electronic control system

ADC 0848 CHIP

ATMEL89C51 DAC0808 CHIP

Figure4 1. Basic hardware components of the controller.

4.2 DETERMINING THE RULES :

We would require to go in a logical manner to control the pressure of the furnace. This may include the following steps:

Obtain the pressure level of the furnace.

Compare the obtained value with the set point. This gives the value of the error signal. Ideally it should be zero but practically it is never so. For the proper working of furnace the error signal should be as low as possible.

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Depending upon the value of the error signal, the corresponding alarm system is activated. If the value is positive then high alarm system is activated. Also the magnitude decides whether it is a high alarm or a very high alarm.this will in turn reduce the intakes i.e the air flow is contolled by the valves and also the coal intake is reduce simultaneously.

Conversely if the value is negative then low alarm sytem is activated.here also the magnitude determines whether it belongs to the low alarm or very low alarm system.it will in turn increase the fuel intakes to increase the pressure to the set value.

Now obtain the value of the pressure of the furnace

Now compare the it with again with the set point .

Repeat the above steps until it the pressure is under our control.

4.3 HARDWARE SECTION.

In this Hardware the following components are used;

1. Pressure sensor.

2. Amplifier

3. ADC0848 Chip

4. Microcontroller ATMEL89C51

5. DAC0808

6. Timer IC555

7. Optocoupler IC (MOC3011)

8. Triac IC (BT139)

4.3.1 MICROCONTROLLER ATMEL89C51 :

The Atmel AT89 series is an Intel-8051-compatible family of 8 bit microcontrollers (µCs) manufactured by the Atmel Corporation. Based on the Intel 8051 core, the AT89 series remains very popular as general purpose microcontrollers, due to their industry standard instruction set, and low unit cost. This allows a great amount of legacy code to be reused without modification in new applications.

While considerably less powerful than the newer AT90 series of AVR RISC microcontrollers, new product development has continued with the AT89 series for the aforementioned advantages.

DESCRIPTION

The AT89C51 is a low-power, high-performance CMOS 8-bit microcomputer with 4Kbytes Flash programmable and erasable read only memory (PEROM).

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The device is manufactured using Atmel’s high-density nonvolatile memory technology and is compatible with the industry-standard MCS-51 instruction set and pin out. The on-chip Flash allows the program memory to be reprogrammed in-system or by a conventional nonvolatile memory programmer. By combining a versatile 8-bit CPU with Flash on a monolithic chip, the Atmel AT89C51 is a powerful microcomputer which provides a highly-flexible and cost-effective applications solution to many embedded control

89C51

All four ports in the AT 89C51 are bidirectional.Each consists of a latch (Special

Function Registers P0 through P3), an output driver, and an input buffer.The output

drivers of Ports 0 and 2, and the input buffers of Port 0, are used in accesses to external

memory.

In this application, Port 0 outputs the low byte of the external memory address,

time-multiplexed with the byte being written or read. Port 2 outputs the high byte of the

external memory address when the address is 16 bits wide.Otherwise the Port 2 pins

continue to emit the P2 SFR content. All the Port 3 pins, and two Port 1 pins (in the

AT89C52)are multifunctional.The alternate functions can only be activated if the

corresponding bit latch in the port SFR contains a 1. Otherwise the port pin is stuck at 0.

FEATURES

• Compatible with MCS-51™ Products

• 4K Bytes of In-System Reprogrammable Flash Memory Endurance: 1,000 Write/Erase

Cycles

• Fully Static Operation: 0 Hz to 24 MHz

• Three-level Program Memory Lock

• 128 x 8-bit Internal RAM

• 32 Programmable I/O Lines

• Two 16-bit Timer/Counters

• Six Interrupt Sources

• Programmable Serial Channel

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• Low-power Idle and Power-down Modes

Fig 4.2 pin diagram

PORT DESCRIPTION

There are totally four ports in micro controller as

• PORT 0

• PORT 1

• PORT 2

• PORT3

PORT 0

• Port 0 is an 8-bit open-drain bi-directional I/O port.

• As an output port, each pin can sink eight TTL inputs.

• When 1sare written to port 0 pins, the pins can be used as high impedance inputs.

Port 0 may also be configured to be the multiplexed low order address/ bus during

accesses to external program and data memory.

• In this mode P0 has internal pullups.

• Port 0 also receives the code bytes during Flash programming,

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and outputs the code bytes during program verification.

• External pull ups are required during program verification.

PORT 1

• Port 1 is an 8-bit bi-directional I/O port with internal pullups. The Port 1 output buffers

can sink/source four TTL inputs.

• When 1s are written to Port 1 pins they are pulled high bythe internal pullups and can be

used as inputs.

• As inputs,Port 1 pins that are externally being pulled low will sourcecurrent (IIL)

because of the internal pullups.

• Port 1 also receives the low-order address bytes during Flash programming and

verification.

PORT 2

• Port 2 is an 8-bit bi-directional I/O port with internal pullups.

• The Port 2 output buffers can sink/source four TTL inputs.

• When 1s are written to Port 2 pins they are pulled high by

the internal pull ups and can be used as inputs.

• As inputs, Port 2 pins that are externally being pulled low will source current (IIL)

because of the internal pullups.

• Port 2 emits the high-order address byte during fetches

From external program memory and during accesses toexternal data memory that use 16-

bit addresses (MOVX @DPTR).

• In this application, it uses strong internal pullups

when emitting 1s.

• During accesses to external data memory

that use 8-bit addresses (MOVX @ RI), Port 2 emits the

contents of the P2 Special Function Register.

• Port 2 also receives the high-order address bits and some

control signals during Flash programming and verification.

PORT 3

• Port 3 is an 8-bit bi-directional I/O port with internal pullups.

• The Port 3 output buffers can sink/source four TTL inputs.

• When 1s are written to Port 3 pins they are pulled high by

the internal pullups and can be used as inputs.

• As inputs,Port 3 pins that are externally being pulled low will sourcecurrent (IIL)

because of the pullups.

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Port 3 also serves the functions of various special features

of the AT89C51 as listed below:

Port Pin Alternate Functions

P3.0 RXD serial input port

P3.1 TXD serial output port

P3.2 INT0 external interrupt 0

P3.3 INT1 external interrupt 1

P3.4 T0 timer 0 external input

P3.5 T1 timer 1 external input

P3.6 WR external data memory write strobe

P3.7 RD external data memory read strobe

4.3.2.ANALOG TO DIGITAL CONVERTER ADC0804. ADC0801 can also be used here, Easy Interface to all Operates ratio metrically or with 5 Vdc or analog span adjusted voltage reference No zero or full scale adjust required 8-channel multiplexer with address logic 0V to 5V input range with single 5V power supply Outputs meet TTL voltage level specifications ADC0808 equivalent to MM74C949

Fig 4.3 Pin Diagram Of ADC

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Pin Number Description

1 IN3 - Analog Input 3





6 START - Start Conversion

7 EOC - End Of Conversion

8 2(-5) - Tri-State Output Bit 5

9 OUT EN - Output Enable

10 CLK – Clock

11 Vcc - Positive Supply

12 Vref+ - Positive Voltage Reference Input

13 GND – Ground



16 Vref- - Voltage Reference Negative Input






22 ALE - Address Latch Enable

23 ADD C - Address Input C

24 ADD B - Address Input B

25 ADD A - Address Input A




4.3.3DIGITAL TO ANALOG CONVERTER

The D/A output should range from 0 to 5 volts. The lower 8 bits from the AT89s51 should go into the 8 bits from the DAC0808. Note: I expect you to try to get the device to work by reading the datasheet and trying to understand it, if you have trouble you should come

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see me, but I expect you to have fairly specific questions that indicate you have put some thought into the problem.

Figure 4.4. Pin Configuration DAC0808

The pins are labeled A1 through A8, but note that A1 is the Most Significant Bit, and A8 is the Least Significant Bit (the opposite of the normal convention). Ground the two least significant bits.

The DAC0808 is an 8-bit monolithic digital-to-analog converter (DAC) featuring a full scale output current settling time of 150 ns while dissipating only 33 mW with ±5V supplies. No reference current (IREF) trimming is required for most applications since the full scale output current is typically ±1 LSB of 255 IREF/256. Relative accuracies of better than ±0.19% assure 8-bit monotonicity and linearity while zero level output current of less than 4 µA provides 8-bit zero accuracy for IREF>=2 mA. The power supply currents of the DAC0808 is independent of bit codes, and exhibits essentially constant device characteristics over the entire supply voltage range.

The DAC0808 will interface directly with popular TTL, DTL or CMOS logic levels, and is a direct replacement for the MC1508/MC1408.

4.3.4.ANALOG PRESSURE SENSOR

The MPX4115 series is designed to sense absolute air pressure in an altimeter or barometer (BAP) applications. The small form factor and high reliability of on chip i n t e gration makes the Motorola BAP sensor a logical and economical choice for application designers. Features · 1.5% Maximum Error over 0° to 85°C ·it is Ideally suited for Microprocessor or Microcontroller Based Systems .it is Available in Absolute, Differential and Gauge Configurations. It is Easy to Use Chip Carrier Option. operating overview integrated pressure sensor 15 to 115kpa (2.18 to 16.7 psi) 0.2 to 4.8 volts output. .

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4.3.5.OPERATIONAL AMPLIFIER LM324.

LM258 or LM358 or OP07 or LM158 can be used with necessary changes in the hardware, OP07 will required dual power supply to operate, whereas the lm358 can operate on single power supply and give good results. The OP-AMP is a basic component in the circuits of data acquisition and control. All 8051 based data acquisition board must have used the opAmps in any form, the purpose of use of OPAMPs in data acquisition system is to interface the sensors and the ADC, the ADC then give digital data to microcontrollers. Thus OPamp are used in the analog section of the data acquisition board. Like in this project a furnace is of main concern whose temperature is read, if the temp is low then set point then heater is switched ON and heater is switched off when required set point is achieved. Thus we can say that is one of the data acquisition and control project related to temperature monitoring and control projects based on microcontrollers or microprocessors.

An operational amplifier IC is a solid-state integrated circuit that uses external feedback to control its functions. It is one of the most versatile devices in all of electronics. The term 'op-amp' was originally used to describe a chain of high performance dc amplifiers that was used as a basis for the analog type computers of long ago. The very high gain op-amp IC's our days uses external feedback networks to control responses. The op-amp without any external devices is called 'open-loop' mode, referring actually to the so-called 'ideal' operational amplifier with infinite open-loop gain, input resistance, bandwidth and a zero output resistance. However, in practice no op-amp can meet these ideal characteristics.

The operational amplifier is used in the applications in filter, in wave generation, mathematical operations, and analog to digital and digital to analog conversions Offset voltage at the input of an operational amplifier is comprised of two components; these components are identified in specifying the amplifier as input offset voltage and input bias current. The input offset voltage is fixed for a particular amplifier, however the contribution due to input bias current is dependent on the circuit configuration used. For minimum offset voltage at the amplifier input without circuit adjustment the source resistance for both inputs should be equal.

4.3.6.ZERO CROSSING OPTOCOUPLER MOC3041.

It is a 6-PIN Dip Zero-Crossig Opto coupler Triac Driver output.The MOC3041, MOC3042 and MOC3043 devices consist of gallium arsenide infrared emitting diodes optically coupled to a monolithic silicon detector performing the function of a Zero VoltageCrossingbilateraltriacdriver. The MOC3041, MOC3042 and MOC3043 devices consist of gallium arsenide infrared emitting diodes optically coupled to a monolithic silicon detector performing the function of a Zero Voltage Crossing bilateral triac driver.

They are designed for use with a triac in the interface of logic systems to equipment powered from 115 Vac lines, such as solid–state relays, industrial controls, motors, solenoids and consumer appliances, etc.

Simplifies Logic Control of 115 Vac Power.

Zero Voltage Crossing Recommended for 115/240 Vac(rms) Applications Like:

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Solenoid Valve Controls Temperature Controls Lighting Controls E.M. Contactors Static Power Switches AC Motor Starters AC Motor Drives Solid State Relays

They are designed for use with a triac in the interface of logic systems to equipment powered from 115 Vac lines, such as solid–state relays, industrial controls, motors, solenoids and consumer appliances, etc.it is best to use MOC3041 which have built in zero crossing circuit.

4.3.7TRIAC BT138

Gate Turn-On Voltage (Vgt): 1.5V Peak Off-State Voltage(Vdrm): 500V On-State Current (It): 16.0A Gate Current (Igt): 25mA

Typical Voltage Change over Time (dV/dT): 250V/µs

4.3.8LCD DISPLAY

Features• Clear Easy to Read Digits• Low Power Consumption• Works with ICL7106 or equivalent• PCB Mounting

4.4 SOFTWARE SECTION.

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The software section includes Microcontroller 8051 code, written in C language using Kiel C51 compiler.

C51 code for Microcontroller 8051.

The program is written in C language and compile with C51 Kiel. It has following sub-routines to perform different functions time to time and these routines are called in main program on demand.

1. Initialization of Microcontroller :-

In this sub-routine, the microcontroller is initialized, its different special function register are given some specific values, like serial control register, Interrupt register, Timer and external interrupts of 8051. It is called at the start of program.

2. Analog to Digital conversion :-

In this sub-routine, the ADC0804 is controlled and configure through control lines interfaced with microcontroller 8051. The function like start conversion, wait for conversion complete , pick the new data, are performed in this.

3. Voltage to pressure conversion :-

As ADC0804 measure analog voltages in the range of 0v to 5v. In this is to be converted into pressure in suitable unit by applying prior developed formula.

4. Average :-

To make good results and to get stable values of pressure, 10 successive values are averaged out.

5. PWM output Generator :-

The phase angle is controlled using PWM technique software based. The firing angle of triac is controlled in this sub-routine.

6. Power control :-

By comparing the set value and running value the power is controlled by using above mention PWM technique.

4.5 WORKING PRINCIPLE

Figure 4 shows the hardware implementation of intelligent control system. Pressure is sense by pressure sensor, which gives the voltage proportional to pressure. Since the voltage receives in terms of millivolt so its need to be amplified. For amplification two stage of operational amplifier is used .

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Voltage controlled oscillator

Current to voltage converter

Digitalto analog converter

Micro controller

Switching transistor

Opto isolator

Triac

Analog to digital converter

Set voltage proportional to pressure

Pressure sensor

Furnace pressure process


Fig 4.6 Functional Block Diagram Of Intelligent Pressure Control System

Now the set pressure x volt is applied at inverting input of operational –amplifier and at non-inverting input the actual voltage from the sensor after two stage amplification is applied. In this hardware op-amp is used as comparator also. Now the error from the comparator element is sense in the ADC.ADC converts this analog error signal into digital form .Microcontroller sense this error signal and produce the controlled output in the form of digital data by processing the algorithm in EPROM proportional to error voltage, which generates the digital output. This signal is sent to the DAC .DAC produce this controlled data in the form of analog current which is converted to proportional voltage in a current to voltage amplifier. This manipulated voltage variable goes to the voltage controlled oscillator built around Timer IC 555.Voltage controlled oscillator which generates the oscillation controlled by DAC voltage generated from the microcontroller chip and controlles the oscillation.

The output of VCO goes to the base of transistor for switching action. The collector voltage of this transistor activates the optocoupler .In this hardware optocoupler is provided for isolation. If there is reverse voltage from source flows to circuit, it damages the fuzzy chip component. Optocoupler generates the current proportional to the applied

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voltage and through suitable resistance it goes to the terminal 2 of the triac .Now the other pin4 of optocoupler goes to the terminal 3 gate of the triac. Gate voltage fires of triac proportional to the phase angle of supply voltage to the furnace. The power supply to the furnace is proportional to the error voltage sense by the fuzzy controller. So in this design the controller works like a proportional controller.

.

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CONCLUSION

On completion of this project a much more reliable furnace pressure control system can be obtained, maintaining slightly negative furnace pressure can have many benefits, including:

A constant furnace condition can be to ensure safe, reliable operation of a boiler. Energy savings: Negative pressure eliminates cold air infiltration, which reduces

fuel consumption. Improved product quality: Process heating equipment with regulated pressure

control will help maintain a more uniform temperature in the furnaces and avoid cold and hot spots, which can improve product quality. For heat treating applications, furnace pressure can reduce oxidation, and for processes like carburizing, create a more stable atmosphere for the diffusion process.

Maintenance savings: Pressure control prevents excessive fluing through cracks and doors in process heating equipment, which can minimize corrosion and crack enlargement.

Emissions Reductions: Improved combustion control can reduce emissions. Thus Prevents leakage of hot combustion gases by ensuring that the furnace operates with negative pressure.

Further during the period of next session the implementation of this project in both hardware and software will be taken care of.

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APPENDIX1

GENERATOR

Type Hydrogen cooled turbogenerator

Rating Continuous

Hydrogen pressure 3 kg/cm2

Apparent output 150 MVA

Active output 120 MW

Power factor 0.8 lag

Rated voltage 13.8 kv

Rated current 6275 A

Rated speed 3000 rpm

Frequency 50Hz

Generator terminals 3 phase side + 3 neutral side

Short circuit ratio 0.6

Stator phase connections star

GENERATOR TRANSFORMER

Make Crompton Greaves

Type of cooli OFAF

MVA rating 150

No load voltage ratio 138/13.8 kv

Phase 3

Frequecy 50 Hz

Vector group Yndll

Temperature rise of oil 50c

Temperature rise of winding 55c

KIT(EC)


Type of tap changer off load

UNIT AUXILIARY TRANSFORMER

Make EMCO

KVA rating 1500kVA

Phase 3

Frequency 50 Hz

Vector symbol DY 1

Type and range of tap changer ON load

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APPENDIX 2

PRESSURE UNITS

Pascal(Pa)

Bar(bar)

Technical atmosphere

(at)Atmosphere

(atm)Torr

(Torr)

Pound-force per

square inch(psi)

1 Pa ≡ 1 N/m2 10−5 1.0197×10−5 9.8692×10−6 7.5006×10−3 145.04×10−6

1 bar 100,000 ≡ 106 dyn/cm2 1.0197 0.98692 750.06 14.50377441 at 98,066.5 0.980665 ≡ 1 kgf/cm2 0.96784 735.56 14.223

1 atm 101,325 1.01325 1.0332 ≡ 1 atm 760 14.696

1 torr 133.322 1.3332×10−3 1.3595×10−3 1.3158×10−3 ≡ 1 Torr; ≈ 1 mmHg

19.337×10−3

1 psi 6.895×103 68.948×10−3 70.307×10−3 68.046×10−3 51.715 ≡ 1 lbf/in2

REFERENCES

KIT(EC)


1. “WOODWARD” by ALAN METZER,1992, www.woodward.com2. “SIEMEN ENERGY AND AUTOMATION”, from www.sea.siemens.com/ia.3. “VERTICAL TUBE ,VARIABLE PRESSURE FURNACE FOR

SUPERCRITICAL STEAM BOILERS” BY D.K MCDONALD,THE BABOK WILCOX COMPANY,BARBERTON,OHIO,USA

4. “COAL FIRED DESIGN” by BOB BROWN,P.E. BY BIBS AND ASSOCIATES,INC.

5. “LESSONS IN ELECTRIC CIRCUITS” vol-4,2010 by KUPHALDT TONY R.6. www.oit.doe.gov/bestpractices/library.shtml

KIT(EC)

http://www.oit.doe.gov/bestpractices/library.shtml

http://www.sea.siemens.com/ia

http://www.woodward.com/

furnace presure controller

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