DESIGN BASIS REPORT MEHANICAL

Proj: Sea Water FGD System

Client: Reliance Energy Limited

DESIGN BASIS REPORT MEHANICAL.

Proj: Sea Water FGD System Client: Reliance Energy Limited

DESIGN BASIS REPORT MEHANICAL.

1. Introduction:

DUCON TECHNOLOGIES INC. USA has been awarded the contract of sea water flue gas desulphurization system (sea water FGD) for 2x 250 MW coal fired thermal power station at Dahanu, Maharastra, owned & operated by Reliance Energy limited.

The sea water FGD consists of two identical streams for each power house of 250 MW capacity with inlet gas flow of 10, 00,000 NM3/hr with sulphur dioxide (SO2) content of 1.7 mt/hr to the scrubber. Each scrubber is designed to remove 90% of SO2 using natural alkalinity in the sea water. Sea water scrubbers are generally used where the power plants are located near the sea & sea water is used for condenser cooling & also in pollution control systems like FGDs.

The Ducon patented sea water FGD system offered to this project typically consists of the following main sections-

1. GGH-gas to gas heater where the scrubbed clean gas is re heated in a rotary type regenerative heat exchanger by utilizing the sensible heat from the inlet flue gas.

2. The FGD scrubber- Ducon designed packed tower scrubber with mist eliminator to remove 90% of inlet SO2. The scrubber is designed to maintain the removal efficiency of 90% even when the inlet load is varied from 60% to 100%.Varying concentration of SO2 (1.7 TPH SO2 in 7,00,000 Nm3/hr to 10,00,000NM3/hr of flue gas ) will not affect FGD scrubber performance.1. 3. Sea water pumping station- Located at the condenser pre cooling channel area, there are total 04 nos sea water pumps, 2 each for one stream of scrubber. The sea waster is drawn from pump sump located at pre cooling channel area.

4. 4.1 Scrubber outlet water treatment section- Consisting of a mixing basin located adjacent to sea water pump sump. The scrubber water from both scrubbers flow to the mixing basin by gravity & are mixed with unused seawater from pre-cooling channel to adjust the pH & temperature of the outlet water. The mixing is accomplished by natural gravity flow & temperature gradients of the scrubber water & fresh water from precooling channel.

4.2 Oxidation chamber- The over flow from the mixing basin duly adjusted for pH & temperature is oxidized to reduce the oxygen demand due to presence of sulfites on the sea water from scrubber. Typically, SO2 absorbed in sea water is converted in to SO3 & needs to be saturated before final discharge. Hence the mixed water is oxidized using four nos of oxidation air blowers, 2 each for one scrubber. Oxidation basin is located at the down stream of mixing basin. The treated water over flows back to the precooling channel as final disposal.

A separation wall is provided over the entire length of the SWTP in order to divide the SWTP into two sections, one for each FGD.

5. Booster fan- one booster fan for each stream is located in C position, meaning between the scrubber outlet & GGH inlet in scrubber outlet gas path. With the booster fan in this location, inherent leakage in the GGH (high pressure to low pressure) is clean gas to dirty gas and therefore does not penalize scrubber performance. The booster fan is sized to take care of the additional pressure head due to GGH, scrubber, mist eliminator, & static duct pressure drop.

6. MCC room & FGD control room- There will be common FGD control room for both units. MCC room will also be common for both units in scrubber area. A separate MCC room is engineered at pre-cooling area for sea water pumps, oxidation air blowers & other related electrical power requirement in that area.

7. Control & logics will be through PLC based control system with operating desks, monitors & printers in FGD control room.

The basic design basis statements are elaborated in the following pages.

2.0 GAS TO GAS HEATER-GGH.

2.1 The dry hot dust free flue gas at passing through ESP is induced drafted by the ID fan of the power plant. The discharge of the ID fan of the power plant is directed to the GGH & where its sensible heat to transferred to the scrubbed clean gas from the FGD scrubber. This serves to reheat the exit gas to minimize the opacity in the stack, & increase the gas rise up the stack into the atmosphere.

2.1. GGH is typically used in large volumetric gas flow rates & heat recoveries are envisaged with lower temperature differences. Heat transfer fundamentals show that the heat transfer coefficients are low in gas to has heat exchange & need large heat transfer area when heat sources are at lower temperatures. Conventional heat exchangers like shell & tube type, double pipe type, or plate heat exchangers become extremely expensive in such cases from the material & maintenance point of view.

2.3 Design parameters-

Hot gas Inlet volume- 10,00,000Nm3/hr. .1. Hot gas inlet temperature- 135-145 deg C.

Hot gas outlet temperature- 92-102 deg C.

Cold gas Inlet volume- 9,99,403 Nm3/hr. .1. Cold gas inlet temperature- 44-54 deg C.

Cold gas outlet temperature- 86-96 deg C

Pressure drop across GGH- 5.5 to 8 WC.( to be confirmed by the vendor).

Drive motor capacity : 7.5 KW-tentative. Vendor specific data.1.

2.4 The GGH will be rotary regenerative type with modular heat transfer sections. This bisector modular GGH enables easy maintenance & also replacement.

GGH will be rotary type. Typical speed will be of the order of 3-4 rpm.However, it will be finalized based on the vendor recommendation to minimize the leakage of dirty gas to clean gas side.1. It will be central shaft driven with geared arrangement. Inlet gas entry will be from the top & bottom exit where as cold gas entry can be from bottom & exit at top. The approximate foot print area of the GGH is 11m x 11 m. The material of construction of the internals of the GGH will be selected to meet the corrosion & temperature resistant properties required during operation & shut down conditions. The heater elements will be suitably quoted with corrosion and temperature resistance material.

2.5 Accessories- The GGH will be equipped with air operated motor. This will be required during power failure & rotating during maintenance. However, this aspect will be finalized during the finalization of the equipment. In case of air operated motor requirement, plant air will be provided with stand alone air receiver tank, volume of which shall be equivalent to 10 minutes of operation of GGH. 1. The motor drive ON-OFF indication and speed indication will be taken to control room as well. 1.High pressure water & air cleaning soot blowers will be provided to clean the GGH on line & off line.

Inspection doors, man holes, drain points will be provided as per detailed engg requirement.

2.6. Instrumentation: There will be temperature sensors at each point at inlet & outlet connections on cold & hot gas streams. Similarly, differential pressure drop indicators with facility for local & remote indication will be provided. Similarly, motor drive indication at remote will also be provided. Soot blower ON/OFF indication, forward; retract position by means of limit switches/proximity switches will also be indicated is necessary as per detailed engg.

2.7. The possibility of eliminating the compressed air requirement for cleaning & replacing with low pressure steam & service water 1 will be looked in to, to reduce the compressed air load. It is assumed to provide LP steam at @3.0kg/cmg (saturated) at intervals for cleaning. This data is vendor specific and will be furnished during detailed engineering. 1. 2.8 Other necessary auxiliary system like fire fighting arrangement near the equipment, maintenance & operating platforms, will be provided at suitable location.

3.0 BOOSTER FAN:

3.1 Booster fan is required to take the additional load of pressure drop across the system due to FGD, GGH & ducting losses.

3.2 location of the booster fan: There are mainly two positions- A position where booster fan is located at the inlet of the GGH & C location where booster fan is located at the outlet of the scrubber. When the booster fan is in A location, the temperature of the gas to the booster fan will be same as outlet of I/D fan. The material of construction can be in carbon steel similar to I/D fan. In C position the flue gas temperature will be of the order of 44-45 deg C which is below the acid due point, & hence, the material of construction will be more expensive.

3.3. Centrifugal vs. Axial: The booster fan selected is axial type. Centrifugal fans of this size type need very large area for inlet & outlet duct connections. Also, control of gas volumes can not be as smooth as axial fans. Hence axial type fan is selected. The booster fan characteristic curves and operating point shall be in line with the characteristic curve of the existing I/D fan to offset the pressure imbalance in the system during normal operation, Trip, or shut down conditions. .1. 3.4 preliminary design data-

Inlet volumetric flow- 1,14,5870 AM3/hr.

Inlet temperature : 44 -54 deg C. (depending on flue gas inlet temp of 135-145 degC).

Static pressure head- : 292 mm WC. (To be confirmed after pressure loss calculations)

Impeller material- Titanium gr.2 /Carbon steel with FRP lining.

Casing- : carbon steel with FRP/Butyl rubber lining.

Shaft- : EN 8 with hastelloy sleeve.

Drive- direct shaft driven.

Support- simply supported, with pedestal/journal bearings.

The above parameters are subject to change during detailed engg.

3.5. Control- The fan volumetric control system will be through variable fan blade pitch. The pitch control will be based on pre set point of hot gas inlet duct pressure. The aperture opening will be controlled by means fine tuned linkage mechanism connected to the fan blade. The other options like VFD & Hydraulic coupling with scoop control will also be studied. This will be finalized based on the vendor recommendation after studying the merits of other type of controls. Also, fan vibration monitors on drive shaft will be provided. This will be interlocked with plant start permissive. The relative cost of type of control will be discussed during detailed engineering with potential vendors and final selection will be based on the techno-commercial merit.1. 3.6 Other accessories: Inspection doors, access doors will be provided. In addition, fan impeller wash spray nozzles will be provided to clean the impeller on line. Flexible bellows at suction & discharge side will have to be provided.

4.0 Scrubber: The FGD scrubber is the main equipment of FGD system. The DUCON scrubber is specially designed sea water scrubber based on the experience & expertise gained over no of years working knowledge. The scrubber is packed tower scrubber with mist eliminator. The packing are high efficiency, non clogging type with large ratio of c/s area to volume (m2/m3 ratio). Two stage chevron type mist eliminators provided. These types of mist eliminators are capable to remove 90% and more of 10 and above mist sizes. The removal of mists reduces the water carry over & also the opacity in the stack. This also reduces possible erosion problem the down stream booster fan. No of high efficiency water spray nozzles will be provided in mist eliminator section for on line periodic water spray to remove any sedimentation & deposition within the mist eliminator. This measure will ensure minimum pressure drop across the mist eliminator.

The scrubber hot gas inlet section will be provided with quench spray nozzles to cool down the gas before actual scrubbing takes place.

The sub cooled gas flow from bottom to top & the scrubber water flows from bottom to top, thus a counter current scrubber is provided. The sea water will be used for quenching & scrubbing. The alkalinity in the sea water will be utilized to absorb the SO2 in the flue gas to convert to sulphite.The clean gas will pass through the mist eliminator before entering the booster fan suction.

4.1Basic design data:

Scrubber inlet gas volume- 10, 00,000Nm3/hr.

Inlet gas temperature- 90-92 deg C

Inlet SO2 load : 1.7 T/hr @ 100% BMCR

SO2 removal efficiency : 90%.

Scrubber load variation : capable to maintain 90% removal efficiency between 60%

To 100 % BMCR.

Inlet gas pressure :( -) 102 MMWC.1. Sea water flow to scrubber- 11,000 M3/hr (of which 500 m3/hr will be for quench).

Gas outlet temperature : 44-45 deg C normal.

Pressure drop across the scrubber (tentative) - 3-4 (including mist eliminator P).

Mist eliminator : high efficiency chevron type.

Mist eliminator wash water : 80M3/hr (intermittent flow).

Type of packing : DUCON Q packs.

Approx. packing volume : 560 M3.

Basic dimensions of the scrubber: 12m x 12 m x 25 m ht.

M.O.C. : RCC wall with 6 mm FRP lining from inside.

Scrubber design conditions : Atm pressure & 95 deg C.

Packing support : FRP gratings with 72% opening.

Emergency quench tank : provided on top of the scrubber

Emergency spray nozzles : separate, provided at quench section.

Other accessories : differential pressure indicators for packing section & mist

Eliminator section, man holes & inspection doors, Level

Transmitter for emergency tank platforms & ladders.

4.2 The scrubber water will be once through flow. The bottom of the scrubber tank will be provided with downward slope for gravity flow of scrubber out let water through 1.5 m dia single pipe. Similarly, the scrubber inlet water pipe will be single 1.4 m dia RCC/FRP or equivalent1 pipe from which branches will be taken to quench section.

4.3. The sea water will be uniformly distributed across the packing area by packing tower spray nozzles connected to spray headers. Similar arrangement will be done for mist eliminator also. Part of sea water (at rate of about 88 M3/hr) will be used as mist eliminator wash water at fixed intervals for about a minute to remove any deposition.

4.4. The scrubber will be stand alone structure made of RCC structure. The scrubber foundation area will be lined with acid proof lining since the scrubber outlet water will be acidic in nature. The outlet water line will be made of FRP.The resin to be used will be decided during detailed engineering.1. However, vinyl ester lined concrete pipe will also be considered from economic point of view. The scrubber inlet water line will be made of cement with sea water corrosion resistant coating or resistant cement mixing. Due care will be taken for surface finishing during scrubber construction for smoothness & bonding of FRP lining.

4.5 One no emergency water tank will be provided on top of scrubber. Emergency water flow will be equivalent of 150M3/hr flow for five minutes. The tank will be sized accordingly (tentative size is 15.0M3).1. It will be part of scrubber with RCC structure. However, inside will be with sea water corrosion resistant coating/cement to avoid any contamination.1. The emergency water flow to the quench section will be gravity flow. Level transmitter will be provided for remote level indication & control.

5.0 Sea water pumps:

Sea water pumps are located at pump house in pre cooling channel area. There are total of 04 pumps for the entire FGD system of which 02 each will be utilized for each scrubber system. All the pumps will be working when both systems are in operation. There are no standby pumps. The discharge of two pumps will be connected to common header for each scrubber section & one single discharge line will be running up to the respective scrubber.

5.1 Sea water pumps will be vertical wet pit type pumps. Each will have separate pump sump at suction. Casing will be considered in concrete convolute similar to the existing condenser cooling pumps. This arrangement would reduce the cost of pumps. The impellers are envisaged to be semi open type

.

5.2 The sea water pumps will be direct driven, flange mounted type. Vibration monitors for the pump & motors are considered.

5.3 preliminary basic design data for each pump:

Pump volumetric Flow rate : 5,500 M3/hr.

Pump dynamic head : 30 MLC.

Qty per scrubber system : two.

Total flow per scrubber : 11,000 M3/hr.1.Fluid to be pumped : sea water at 37 deg C.

Fluid density to be pumped : 1080 Kg. /M3.

Impeller- : duplex alloy/alloy 20/eq

Casing : Ni resistant CI. .1. Type : vertical wet pit type.

The above data are basic design data based on which the detailed data sheets will be generated. The detailed data sheet will be prepared considering the margins in flow head, actual head loss calculation up to the scrubber & required flow vs. head curves of the pumps. This will be discussed with the potential suppliers.

5.4 Controls: Sea water flow will be constant flow to the scrubber without any control since DTPS is a Base Load Station and continuously operates on full load. The discharge line is approx. 1.4 mts dia. Concrete with 2mm bituminous lined pipe. .1. The scrubber water flow control will economize the power drawn by the pump in case of throttling power stations which is generally not the case at present. However, pump discharge line will be installed with a flow indicator (local only or with remote indication as necessitated during detailed engineering), to know the pump performance.1. Bearing temperature, vibration monitors will be mounted & the remote indication of the same will be made available as start permissive.

The pumps will be generally operated from FGD control room where as feeders will be at pump house MCC.

5.5 Auxiliaries:

5.5.1All the sea water pumps will have bearing lubrication system. Self lubricating pumps are checked for availability. In the event of water lubrication requirement for bearings, fresh service1 water lubrication system will be used. In such case, separate fresh service water tank & service water supply pumps will be installed. The lubricating pump (fresh service water pump) 1& main sea water pump start will be so designed to activate in parallel. The bearing cooling water outlet cooling will be either through locally mounted cooling tower with fresh service water make up water connection or through spray pond. This will be finalized during detailed engineering.1. . Flow indicator switch on lubricating water line will be interlocked with start permissive to safe guard the pumps. Similarly vibration monitors are also considered for the pumps.

5.5.2 Pumps bearing temperature sensors will also be considered for monitoring & recording. Interlocks will be provided design set high temperature recording. Proper eye bolts/lifting arrangement will be called for during maintenance.

6.0 OXIDATION AIR BLOWERS:

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6.1 There are total of 04 no oxidation air blowers- two each for one FGD system. There are no stands by blowers. Oxidation air is required to oxidize the scrubber water outlet sulfites to sulfates in order to reduce the COD content in the final discharge water to pre cooling channel. It is estimated that each FGD scrubber outlet water containing 90% of SO2 in the form of sulfite at 100% load (0.9 x 1.7 t/hr), will need about 60,000 to63,750 AM3/hr per FGD of oxidation air.1 This estimate is based on the O2 required for sulfite to sulfate, and the secondary reactions that would take place viz- metal impurities, COD & BOD in pre-cooling channel water mix, basin dilution & mixing & mechanical inefficiencies. The oxidation reaction of sulfite to sulfate takes place at rapid rate at about 30 deg C & at pH of 6.0 and can be completed in about 7 minutes. In all probabilities, this reaction will be controlling the time demand.

6.2 The oxidation blowers are located in sea water pump house at pre cooling channel area. These are high pressure fans with water spray arrangement at the discharge line for cooling the discharge air before entering the oxidation chamber. This enhances the oxidation rate & efficiency. Oxidation air will be equally distributed within the oxidation chamber through main headers, sub headers, & specially sized orifices. Oxidation air will flow from bottom to top in the chamber, taking advantage of oxidation chamber water depth. Oxidation reaction will be diffusion aeration type in the basin for best results.

6.3. The oxidation air blowers will be multistage centrifugal blowers. The head requirement is of the order of 4000-4500 MM WC

6.4 Preliminary design data: for each blower.

Oxidation air blower capacity : 31,875 M3/hr

Inlet air temperature- : 30 deg C. (ambient temp)

Outlet air temperature : 92 deg C (preliminary assumption).

Static head required : 4300-4500 MM WC.

Type of blower : multi stage centrifugal

Material of construction :Cast Iron casing, hot rolled csteel shaft,

Cast aluminum impeller, steel base and

pedestal

Drive : Direct (vendor recommendation)

Quantity : 04 nos. (two each for one FGD)

6.5 Control: Oxidation Air Blower operation will be constant.

6.6 Safety requirement: Each blower will be provided with safety relief valve at the discharge side. Discharge side pressure switches, and pressure transmitters for local & remote indication will be provided.

Vibration switches for each blower will be provided.

6.7 Accessories;

Inlet Filter and Silencer will be provided. A saturating water spray with open/close valve will be provided in the discharge piping in order to insure that the oxidation air is saturated. Flexible joints (expansion joints) will be provided in the discharge piping as required to accommodate thermal expansion as well as to minimize vibration.

7.0 ISOLATION DAMPERS:

7.1 Each FGD will have total of three isolation dampers. One will be main bypass damper & the other two will act as FGD isolation dampers. The bypass damper shall be fail to open, normally closed while the FGD isolation dampers shall be fail to close, normally open.1. Dampers will be provided with Electric Actuators (preferably Beck make) or pneumatic/hydraulic actuators which will be finalized during detailed engineering.1. Open cycle as well as Close cycle will be maximum 8 seconds each in order to insure quick response to emergency requirements.

The dampers are double louver type with provision for seal air when damper is closed. This insures zero process gas leakage.

7.2 Seal Air System Two (2) seal air fans, one (1) operating and one (1) spare are provided. The seal air fan system is common for both FGDs. The final seal air fan volume rate will be recommended by the louver damper suppliers. At the moment, the seal air fans are each rated for 10,000 M3/hr @ 2.5 Pa.

7.3. A steam heating coil is provided to preheat the seal air to 90 deg C.It is general practice to preheat the seal air for dampers to avoid condensation and corrosion of dampers and also to minimize the leakage. In the absence of heated seal air, injection of cold seal air will further assist in condensation & severing the corrosion chances. A thermostatic steam trap will be provided to run the spent steam to the condensate drain. We assume that client will be able to provide the steam requirement. Stem @3.0kg/cm2g (saturated) will be sufficient for the purpose. The required quantity and pressure can be taken from the main plant header with necessary pressure reducing valve, safety valve and piping. The quantity of stem requirement is based on the damper manufacturers recommendation which will be furnished during detailed engineering. .1. 8.0 INLET/ OUTLET DUCTING.

8.1The Inlet ducts to the FGD are supposed to be tapped from the common duct of pair of I/D fans of each power plant system. At present the discharge of each I/D fan (axial discharge) is connected to common duct which is connected to stack. The C/L of stack inlet duct is at an elevation of 14.5 M from the ground. The same is replicated at opposite side for the second system. The inlet duct to stack is 7.4 m x 3.7 M, rectangular duct with 7.4 m side as vertical depth & 3.7 m as width of the duct. The stack inlet duct free length is required to install the bypass damper & also the FGD outlet duct before entry to the stack. Our observation during the site visits show that that the available duct length is sufficient for the installation of bypass damper & FGD outlet duct on both sides. However, we propose to install the FGD isolation dampers on the ground floor, to economize on the space & maintenance of the dampers. The final FGD outlet duct size will also be approximately of the same size (7.4 m x 3.7 m). The present duct is made of 7.0 mm carbon steel plates.

8.2. The duct from the inlet tapping to the GGH inlet will be of matching size made of 7.0 mm thk carbon steel. This duct piece will be duly insulated for personnel protection. The inlet to GGH will be from the top of GGH. The outlet of this duct line will also be of same thick ness, made of carbon steel up to the FGD scrubber. Typically, the size of this duct will be 5.0m x 4.1 m., duly insulated.-, to match the scrubber inlet nozzle.

8.3 The scrubber outlet duct will be of FRP duct. Tentative thickness of the duct will be about 6-8 mm (which will be finalized during detailed engg considering the pressure loss, mechanical strength requirement). The outlet FRP duct will be brought down to the inlet nozzle of booster fan ( in axial position ) & the booster fan discharge duct of FRP will be taken up to GGH cold gas inlet nozzle. It is our intention to maintain same nozzle size on the GGH to avoid requirement of transition pieces. It is preferred to connect this duct at the bottom of GGH. The final decision will be made on the recommendation & configuration of GGH supplier. The outlet duct from the GGH 9cold gas side) will be taken up to the FGD inlet opening on the stack inlet nozzle duct piece after the by pass damper. This duct will also be of FRP. Suitable expansion bellows will be provided at suction 7 discharge side of the booster fan. Expansion bellows will also be provided on other ducts as required based on detailed engg calculations.

8.4. The common duct at the inlet to the stack needs careful evaluation. It has to be suitable for gas conditions during FGD operation as well as bypass condition. Temperature & corrosion considerations will have to be considered during selection & execution. We propose acid proof brick lined duct piece or carbon steel PTFE lined piece in this portion.

8.5 Drain points will be provided at suitable locations on duct line between scrubber out let & GGH cold gas inlet nozzle. Local pressure gauges will be connected at GGH inlet out let nozzles on both gas streams.

8.6. The ducts will be properly supported as needed by detailed engg requirement. Bends will be of long radius type to reduce the pressure drop.( depends on the space constraint as well). It is preferred to provide spool pieces at GGH nozzle, booster fan inlet/outlet nozzles to avoid duct fouling during equipment maintenance.

8.7 For all practical design calculations, 14- 16 m/s gas velocities will be considered in the duct lines.

8.8. Requirements of any purging, inert gas atmosphere, gas blanketing is not envisaged in the duct system. It is advised to run the ducts with minimum no of flanged joints to avoid leakages. The FRP duct outside surface may be protected from UV radiation by using UV retardant pigments during manufacture.

8.8 The seal air ducts for dampers will be made of carbon steel with insulation if heated seal air is required. These ducts will be distributed to all the dampers of both FGD systems.

9.0 SEA WATER INLET PIPING:

9.1 Sea water main inlet piping to the FGD scrubber will be of RCC with 2mmbituminuous lined pipe. One each main supply pipe of 1.4 m dia will be running from pre cooling channel area to scrubber area. Each pipe will be designed for maximum of 12,000 M3/hr flow and 5.0kg/cm2g pressure. The discharge of two sea water pumps meant for each scrubber system in metal construction will be connected to this common RCC pipe through Y piece or manifold whichever takes less space. This transition piece will also be in RCC with bituminous lining.. One metallic collar to match the pump discharge nozzle flange & bolt hole PCD will be embedded in the concrete pipe for connection. Same arrangement will be done at FGD the scrubber inlet nozzle side.

9.2. The sea water inlet RCC pipe at the scrubber inlet has to be branched out to packing section, quench section & mist eliminator wash spray. This can be done in two ways-

Run the main RCC pipe along the scrubber outer wall as integral part of scrubber surface which is also concrete wall up to packing section. A branch will be taken from a suitable location for quench & mist eliminator with nozzle arrangement. The branch will be metallic pipe of approx 350 mm dia for quench & 150 MM for mist eliminator.. The inside of this branch pipe will be corracoated to resist sea water corrosion.

Alternatively, the main header will be run up to the scrubber (RCC pipe.).Branches for packing section quench & mist eliminator will be taken from this main header. The branches will be of carbon steel with corracoating from inside or FRP pipes. In such case, the packing section dia will be about 1200 mm, and other branches will be as above.

The final selection will be based on detailed engg calculations & space availability & hydraulic calculations.

9.3 The inlet piping will be run through underground trenches from the pump discharge as much length as available, considering the site constraints. Drain points near the scrubber inlet section will be provided. Due care should be taken during hydraulic studies to check for hydraulic thrust on the pump body & impeller during the condition when the sea water pumps are stopped & the supply line water returns back to pump sump.condideration regarding thermal expansion, hydraulic loading, sudden stop/jerk loads will be taken care during detailed engineering stage.

9.4. Due care should be taken to avoid algae formation & sea rocks during normal operation. One/two trappings will be provided with isolation valve near the pump discharge for chlorination. Continuous chlorination of this inlet sea water is not preferred since the alkalinity of the sea water may be depleted at the scrubber since chlorine is acidic in nature. In any case, chlorination should not be more than 2-3 ppm for a short period.

9.5. Underground RCC pipes will be rested on the ground in the trench. Top of the trench will be covered with natural soil . Suitable arrangement will have to be made wherever road crossing /vehicle movement is encountered. It may be advisable to provide intermediate inspection chamber with proper marking & location identity for checking any silt deposition.

9.6. The design of the pipe will be based on fluid velocity of 1.8 to 2.0 m/sec. Proper supports will be provided as per detailed engg requirement.

10. SEA WATER OUTLET PIPING:

10.1 There will be one outlet pipe from each scrubber. This will be 1.5 m dia FRP duct line. Each pipe is designed for 12,000 M3/hr flow rate. The sea water will be acidic in nature & at about 40-42 deg C at the outlet temperature. The SO2 absorption reaction will be taking place within the duct line as well during water travel. Hence FRP duct is used. The flange connection at the outlet of the scrubber & pipe joint nozzle should match the required PCD & flange width. One temperature indicator, one pH indicator & one flow indicator will be provided on each scrubber outlet line. FRP ducting will be with vinyl ester with fiber glass reinforcement. The pipe will have sufficient grade for gravity flow to the mixing chamber at pre cooling channel.

10.2 Sea water return line will be connected at the bottom of the mixing tank. This is to avoid the vacuum break & proper mixing of fresh water with scrubber water.

10.3 The running pipe will be taken inside the trench of sea water outlet pipes. Inspection covers with blind flanges will have to be provided for observation of silt deposition.

10.4 adequate thicknesses will be provided to withstand the hydraulic load, thrust load wherever applicable. There are chances of duct lifting whenever pipe runs empty (FGD stopped). Bolted clamps/dead weight hanger supports are to be considered during detailed engg stage.

10.5 Looking in to the site lay out, distance pieces, flanged connections will be provided for maintence, inspection.

10.6 The exposed surfaces will be treated for UV radiation using suitable pigment.

11. AIR COMPRESSORS:

11.1 Air compressors are required to supply compressed air for actuation of final control elements like control valves, solenoid operated valves, actuators. In addition, compressed air is also required for GGH cleaning during running as well as shut down.

11.2 Initially it was envisaged to install 2 compressors (1W+1S) for each FGD system. It is decided to install common compressors unit for both FGDs with same concept (1W+1S). Also compressor capacity would be kept minimum with possibilities of alternate cleaning medium for GGHs.

11.3 Instrument air- Part of the compressed air will be conditioned to use air instrument air by removing moisture, dust & oil drop separation using standard equipments like heat less drying system or refrigerant cooling system whichever is cheaper.FRLs will be used for dust & oil droplet removal. It is decided to use motorized control valves wherever possible to avoid large instrument air consumption. This will also reduce tubing & sub headers for instrument air. It is preferred to use GI pipes for instrument air with final tubing of SS or PVC sheathed copper tubes.

11.4 Plant air is required for GGH cleaning & services. Plant air is also required for air operated motor meant for GGH.Since there is no spare capacity available from the existing plant at site, air compressors are required to be installed.

11.5 Low pressure/MP steam will also be considered for GGH cleaning. In the event of the agreement of GGH supplier, the same will be considered. This will reduce the compressor capacity.

11.6 compressors will be having its own air receiver tank with drain point & pressure gauges. Air compressors will have automatic operation controls like pressure switches, safety valves, etc. Compressors will be checked for screw type, piston type, for efficiency & cost effectiveness.

11.7 Capacity of the compressors as at present is estimated at 1500-2000Nm3/hr x 8 kg/cm2g. However, if the GGH cleaning can be done with steam (as approved by the supplier), the quantity can be reduced. The same will be checked during detailed engg stage.

11.8 The discharge headers will be properly routed to GGH area, instrument points & spare service points in the plant.

12.0 HP/LP PUMPS:12.1 HP pumps are used for emergency tank storage tank fill up & GGH washing. Fresh service water is used for the purpose. A common HP/LP pumping system is considered to serve both FGDs.It is now decided to use only one working HP/LP pump(100% capacity) to meet the total requirement. Fresh service water will be connected for make up as well as emergency service since it is available at 8-10 kg/cm2g pressure in the header. Suitable pressure reduction station will be provided in LP water service line in case of direct usage from the header.

12.2. HP pumps will be horizontal centrifugal pumps. One working pump is used for both FGDs.

12.3. Preliminary design data-

HP pumps capacity- 8.0 M3/hr.

Pump TDH : 75-80 MLC.

Service : fresh water pumping.

MOC : C.I casing, carbon steel impeller with EN8 shaft.

Drive motor : 5.6 KW

Drive : direct drive.

Pump will be complete with base plate, coupling, and coupling guard.

12.4. HP pump operation will be as required basis. It is used for filling up emergency tank of both FGDs & for GGH washing. Hence it can be used for tank filling & then for GGH washing. GGH washing of FGDs can be taken in sequence in normal condition. However, more frequent usage will be for GGH washing. Hence it can supply about 80 % of normal GGH wash water requirement. GGH needs about 5.7 M3/hr of wash water.

12.5 HP water will be drawn from separate fresh water service tank. The service water tank is common for HP & LP water service.

12.6. HP water is required for GGH to remove any sedimentation & soluble salt deposition. It is advised to use clean fresh water. Also, service water spray in line with compressed air to GGH covers the maximum area with minimum water consumption.

12.7. Expected deviations: The DTPS plant has suggested to the use of fire water in place of HP water by eliminating HP pumps. Fire water service is available at 8-9 kg/cm2g. This pipe is always charged & no emergencies are envisaged in supply of this water for use. Hence it was advised to check whether HP pumps can be eliminated. This aspect is being studied from process & plant utilization point & will be decided whether HP pumps can be completely eliminated.

12.8 In the event it is decided to use fire water service for the purpose, HP pumps, service tank, other civil works will be eliminated. However, one no. control valve or on/off valve with bypass arrangement, pipe lines from existing fire water service line up to two no GGHs, & emergency tank inlet will have to be incorporated.

12.9 Once it is decided to use fire water, one more control valve/on-off valve is required to fill up quench water tank which will be actuated based on quench water tank level controller.

12.10. LP pumps: The general requirements of LP pumps are similar to HP pumps. As discussed, there will be only one LP pump for both FGDs.LP will also draw fresh water from service tank which is common to HP & LP pumps.

12.11. Preliminary design data for LP pumps:

Pump capacity : 40.0 M3/hr.

Pump TDH : 25-30 MLC.

Service : fresh water to GGH cleaning.

MOC : as per pt . no. 12.3.

Drive motor- : 7.5 KW, direct driven.

12.12. LP water is required for cleaning GGH basically for wetting & final cleaning after washing with HP water & compressed air.Occassionally is used in line with compressed air for fogging & wetting GGH for cleaning.

12.13. Expected deviations: It is advised to check the possibility of using fire water for LP water service similar to HP water (pt. no. 12.7). In the event of fire water service usage as LP water, it is required to install a pressure reducing valve from main fire water header branch, with isolation & bypass valves. Further, control valve is also required downstream of PRV, for water supply to GGH. In all probability, only one control valve would suffice for both GGHs, since the general cleaning can be taken in sequence during normal operation.

12.14. The decision of using fresh service water & eliminating LP/HP pumps, service water tank etc will be decided upon comments & confirmation from the GGH supplier.

12.15. We expect only one control valve for both emergency tank filling as well as GGH cleaning as explained since the operation can be made in sequence.

13.0 Quench water pumps: quench water pumps ware allocated for filling up the emergency tanks of both FGDs. It was agreed to take tapping from HP pumps for this purpose. Since the service water line is being discussed now, only required sizes of pipes are to be taken up to quench water tanks now. Hence there are no separate quench water pumps. Even if the fresh water service tank is decided, the quench water tank will be filled from HP pumps.

14.0 PIPES & VALVES:

14.1 The sea water inlet & outlet piping are described in pt. no 9 & 10. Sea water pipes will be generally RCC and or lined with FRP/rubber lining. Fresh water pipes will be carbon steel confirming to IS-1239 or equivalent. Same pipes will be used for compressed air. Instrument air lines will be of GI for the main & sub headers. All valve on these lines will be carbon steel.

14.2. The GGH wash water outlet lines will be of FRP or equivalent since the wash water may be corrosive in nature. Similarly, booster fan drain valve, sea water outlet pipe drains etc will be generally PP/PVC valves. Alternate material will be selected during detailed engg stage in the event of metallic valve requirement. This will be checked from cost point & connectivity as well.

14.3. Wherever applicable, valves will be of rising spindle type, outside screw & yoke type. Larger size valves (that need operating force more than 35 kg f) will be provided with gear mechanism. Butterfly valves will conform to ANSI/AWWA C504-80/ BS 5155 or equivalent. Valves of 100 mm and above will be butterfly valves. The butterfly valves will be internally lined with FRP/rubber lined/equivalent elastomer to withstand the corrosion wherever applicable. However, valves of fresh water service line will be carbon steel. Valves of sizes below 100 mm will be ball/gate/globe as necessary. In the event of steam service, suitable type & size valves will be selected. Wherever, necessary, IBR approved valves will be installed. However, IBR approval for the piping system drawing will be forwarded by REL as end user. Necessary drawings & documents will be provided by DUCON.

14.4. All sampling & root valves will be of integral body bonnet type. All non return valves will have cast arrow for marking flow direction. Cushioned check valves/swing check valves will be selected as per the service requirement.

14.5 The minimum size of drain valve on equipments will be 25 mm. Drains on lines, branch tapings of pipes will be 15 mm or as per process requirement.

14.6 Insulation on steam line valves will be of chamber type in case of larger sizes for ease of maintenance & replacement.

14.7 FRP pipes will be designed for thickness based on pressure calculations. Pipes will be generally as per ASTM D-2996 standards. Hand lay up/RTM/VRTM procedures will be adopted for manufacture of pipes. Vinyl ester, epoxy/equivalent resin will be used for corrosion resistance along with glass fibre.Necessary bends/run over/crossing pipes will be provided with flange ends for maintenance & repair.

14.8 Insulation will be provided as per requirement to maintain surface temperature wherever necessary. Insulation will be generally carried with mineral wool/glass wool of adequate density. Aluminum sheets will be wrapped over the insulation with bitumen strips at the edges to protect from water/moisture.

14.9 oxidation air blower discharge pipes will be carbon steel up to the oxidation pond inlet. All the pipes within the oxidation pond will be FRP to with stand corrosion from both sides of the pipe.

14.10. Utmost care will be taken during pipe laying. Since the soil & service conditions are saline, pipes will be routed above ground unless other wise absolutely necessary. Bitumen coating on the outer surface will be considered during detailed engg stage.

14.11. Expansion loops, spool pieces, flange joints are to be considered during detailed engg stage based on the pressure & temperature ratings. HPV (high point vent) & LPD (low point drain) will be provided for hydro test purpose depending on the detailed engg requirement.

14.12. Isolation & bypass valves for control valves will be gate/globe/butterfly valve as per the application. Ball valves will be of full bore type.

15.0 BEARING LUBRICATION/SEAL WATER REQUIREMENT:

15.1. Bearing lubrication/seal water requirement is envisaged for sea water pumps. Fresh water/fire water will be used for this purpose to withstand corrosion & erosion. The seal water will be generally once through & as recommended by the pump supplier. Oxidation air blower & booster fan bearings will also need lubrication. In the event of water cooled bearings are selected/recommended by the supplier, the same will be added.

15.2 separate fire water storage tank will be provided for the purpose. Two nos (1W+1S) bearing lubrication water pumps of adequate capacity will be provided. The pumps start/stop will be interlocked with main pump running with timer operated solenoid valve at the discharge line. Automatic changer over facility will have to be incorporated for these pumps. These pumps will be generally horizontal centrifugal pumps with check valves & isolation valves.

15.3 It was also discussed that lubrication water can be recirculating type to conserve the water consumption. In such case a separate cooling tower will be installed near sea water pump house with make up water line.FRP cooling tower will be used. If the heat load is less, sprinkler pond will be considered instead of cooling tower.

16.0 PIPE SUPPORTS & PIPE RACKS:

16.1 Pipes need proper support to prevent external stress, movement & vibrations. Saddle supports, roller supports, shoe supports, hanger supports, are generally considered. Pipes will be provided with cathodic protection as necessary.

16.2 Sea water inlet /outlet pipes, in the trench will be with concrete saddles. FRP pipes will be supported with MS channel coated with FRP at intermediate lengths. Dead weight hanger supports/clamp to avoid lifting of the pipes will also be considered. Saddle supports will be bitumen coated from outside to meet the saline weather conditions.

16.3. Pipes supports within the scrubber area, booster fan foundation area will be coated/lined with acid proof lining to withstand acid corrosion.

16.4 Hanger supports, shoe supports will be provided wherever movement/expansion are taking place. Roller supports will be provided for ducts if necessary.

16.5 pipe racks will be above ground. Looking in to the level/obstruction available, pipe dia, & no. of pipes running, height will be decided. Clearance for vehicle movement below & aesthetic consideration will be considered as per architectural drawing.

16.6 Pipe rack support columns will be of structural steel fabricated with corrosion coating. Lighting supports, extended cantilever sub supports will be allowed to take from these main pipe rack supports wherever necessary.

16.7. Wherever, road crossings are envisaged, clear distance between columns will be 5.5 m . In other cases, column to column distance will be 3.5 mts. The clear gap between two pipes will be 100 mm (surface to surface) on the pipe rack wherever thermal expansion is taking place, and pipes are insulated.

16.7. Proper color coding as per REL/site standards will be used for identification of the pipes. Pipe line numbers/ flow directions will be marked in black paint once the commissioning is over.

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