PROJECT REPORT ON PRAGATI POWER CO. LTD. (SUMMER TRAINNING REPORT)
SUMBITTED BY:(MECHANICAL STUDENTS)
RISHABH SETHI CHANDRAKANT PANT ANKUSH SAXENA SIMRAT SINGH ARUN SHARMA OF
ARAVALI COLLEGE OF ENGG. & MGMT. FARIDABAD.
PRAGATI POWER CORPORATION LTD.
Introduction to P.P.C.L.
Pragati Power Corporation Ltd. is a 330 MW combined cycle gas power plant. It is a Delhi Govt. owned plant. The plant is situated heart of the city Delhi near gate no. 1 of Pragati Maidan. The power plant is a master piece of engineering by PPCL, BHEL and L& engineers who put their joint effort and erect such a huge power plant in just 17 acres of land. The plant has been installed at a total of Rs 1100 crores, out of which 70% has been financed by Power Finance Corporation Ltd. The first gas turbine of the plant was commissioned in May 2002 and second GT in December 2002. The combined plant is operational since July 2003. The gas for the project is provided through GAIL pipeline.
Salient features of Pragati Power Station
Gas Turbine: two GE Frame 9E based DLN gas turbine with MARK 5 control system. Two turbines of 104 MW, each run on natural gas. Supplied by BHEL Hyderabad.
Steam Turbine: Siemens based 122 MW steam turbines KWU based governing system. Working pressure of 80 Kg/cm2, 520 degree centigrade (HP), and 5 Kg/cm2, 202 degree centigrade (LP). Supplied by BHEL Haridwar.
HRSG: two HRSGs of individual gas turbines have been engineered, manufactured, erected and commissioned by BHEL Tiruchi.
Auxiliary plants and equipments including plant air compresser, air washers, ECW, ACW, heat exchangers, cooling towers, RODM, Fire fighting system have been engineered, erected and commissioned by L&T.
Technical Particulars DESCRIPTION
PARTICULARS
Plant Configuration Plant Capacity GT Output ST Output Fuel Main Supplement
2GTG+2HRSG+1GTG 330 MW 2*104 MW 122 MW Natural Gas Naphtha & HSD
CONFIGURATION OF PRAGATI POWER STATION: 2x104 (GT) + 122(STG) = 330 MW
Due to paucity of water this plant was designed to operate on treated sewage water which is being supplied from Sen Nursing Home & Delhi Gate STPs. Emission of oxides of nitrogen (Nox) has been limited to 35 PPM, lowest in the country, for which special technology is used by installing Dry Low Nox Combustors. With the commissioning of Pragati Power Station, total capacity of IPGCL & PPCL is 994.5MW and all our efforts are made to maximize the generation . A contract was signed with M/s BHEL for installation of 330MW gas based power plant in the vicinity of 220V, I.P. Extension, Switchyard on 05.05.2003. The station is comprised of 2x104MW gas turbines of GT Frame-9E and 1x122MW steam turbine. The Waste Heat emanating from gas turbines is being utilized to generate 122MW power through steam turbine. The hot gases of 560 o centigrade with a mass flow of approx. 14000 metric ton per hour is passed through 02 Nos. waste heat recovery boilers of generate steam. The environmental friendly quality power generation through this station is pumped to 220kV Sub Station of Delhi Transco Limited and the entire power is being utilized by citizen of Delhi.
The primary fuel for gas turbine is natural gas being supplied by M/s GAIL through HBJ pipe line. The gas is received at GAIL Terminal installed in the vicinity of the power station. M/s GAIL is committed to supply 1.75 MCMD of gas on daily basis. The caloric value of natural gas being received for power generation is in the band of 8200-8500 kilocalories. The secondary fuel for gas turbine id HSD/Naptha, which is to be used only in case no gas supply is available. Demineralized water is injected to control Nox. While machine is operated on Liquid fuel i.e. HSD/Naptha. RAW WATER Raw water requirement is met through Sewage treated water being drawn from Sen Nursing Home and Delhi Gate Sewage Treatment plant. The demineralised water requirement for steam generation is met up through sewage treated water by treating this through RODM (reverse osmosis de-mineralized) process. The production of cooling water requirement for condenser and other equipment is also met through STW after processing through Lime softening system. The plant effluent is discharged to river Yamuna after naturalizing and thus the effluent discharge is better than sewage water. Infact cleaner water is being discharged to Yamuna River, making the project more eco-friendly. EMISSION CONTROL In order to control on flue gas emission specifically Nox & CO2 a special emphasis being given. To control Nox. & CO2, State of art, Dry Low Nox.(DLN) Burners have been installed on gas turbine while on natural gas. While the machine is to run on HSD/Naphtha water injection arrangement has been provided to control the Nox. & CO2 at present the value of Nox. & CO2 is in order on 17-18 PPM and 4.22% respectively on base load while O2 is 15%. The allowable limit of Nox Approved by DPCC (Delhi Pollution Control Committee) is 35 PPM. This is the first plant in India with a facility to control Nox. Emission and is an eco-friendly power station. Also a thick belt of plantation has been grown on periphery of the power plant and small slim BS inside the power plant to make it environment friendly. Special features of pragati Power Station
1. 2. 3. 4. 5. 6. 7.
It has been built upon abandoned ash disposal area of I.P station power plant. The land condition has been improved by using sand-pile technology. GT uses most advanced Dry Low NOx Burners restricting NOx emission level to 25 ppm. Mark 5 control system of the GT makes it most reliable for fault free operation. No fresh water is being used; the treated sewage water from the two plants of D.J.B is being used. Excess drainage water shall be treated in effluent treatment plant, which will go as waste in natural drain. Solid waste will be converted into cake form and will be used for filling low line area. Water treatment plant is divided into three parts:-
a) RODM: This technology has been used for first time in north India. b) LIME SOFTNING SYSTEM: It is used for cooling water. c) EFFLUENT TREATMENT PLANT: to maintain zero water pollution, only treated effluent 8. 9.
water will be discharged into natural drainage. The plant has been planned and been executed in small area of 17 acres on two sides of existing IP extension 220 KV grid station. The project has in built power evacuation facilities at site through existing 220 KV grid station.
10. As regards pollution norms
of Water and Air Pollution, this plant is operating well within the prescribed norms and it is going to sell its carbon credit in the global market to make additional money from eco-friendly operation. 11. The plant will be operated on gas as fuel for which agreement has been signed with GAIL. 12. Duel fuel Naphtha, to be operated on gas turbine when the same is available. 0.375 Million metric Tones per annum Naphtha has been allocated to the project .
GAS TURBINE
PPCL GT CHAMBER (OUTSIDE VIEW) Introduction Gas turbines are steady flow power machines in which a gas (usually air) is compressed, heated, and expanded for the purpose of generating power. The term turbine is the component which delivers power from the gas as it expands; it is also called an expander. The term gas turbine refers to a complete power machine. The term gas turbine is often shortened to simply turbine, which can lead to confusion with the term for an expander. Gas turbines may deliver their power in the form of torque or one of several manifestations of pneumatic power, such as the thrust produced by the high-velocity jet of an aircraft propulsion gas turbine engine. Gas turbine machines vary in size from large, 250,000-hp utility machines, to small automobile, truck, and motorcycle turbochargers producing as little as 5 hp.
Gas turbines are used in electric power generation, propulsion, and compressor and pump drives. The most efficient power generation systems in commercial service are gas turbine combined cycle plants with power-to-fuel energy efficiencies of more than 50% (higher heating value basis) or 55% (lower heating value basis). Systems Eve points higher in efficiency are now under development and are being offered commercially and systems of even higher efficiency are considered feasible.
PPCL GT CHAMBER Constructional features: Compressor Stages Turbine Stages Number of Combustors Pressure Ratio Firing Temperature (°C) GT Speed (rpm)
17 3 14 12.6 1124 3000
9E Design features: 1. 17 Stage axial Compressor 2. Turbine &Accessory bases are skid mounted 3. Accessory base contains starting system, Lube oil console, shaft driven accessory gear box driving Lube, Fuel, hydraulic oil and atomizing air compressor
4. 5. 6. 7. 8.
Honey comb seals for 2nd &3rd stages 1st & 2nd stage buckets & Nozzles are air cooled Motor/ SFC starting facility Hot end drive Completely packaged and factory assembled, tested.
Gas
Turbine
System
MAJOR COMPONENTS OF GAS TURBINE 1.INLET SYSTEM 2.COMPRESSOR 3.TURBINE 4.COMBUSTION SYSTEM 5.BEARINGS 6.EXHAUST
Inlet & Exhaust Dust The GT engine, by its very nature, requires a considerable mass flow of air per KW delivered than other conventional engines. Thus, the duct sizes will be larger, if conventional power plant criteria for ducts, gas velocities are used. Of course smaller duct sizes require higher velocities & resulting greater pressure loss. Design consideration or pressure loss. Design considerations or pressure loss influences depends on Fluid dynamic and geometric consideration. Normally, when a GT unit is supplied on a turnkey basis, GT manufacture optimizes the pressure loss in the inlet & exhaust system to maximize output & heat rate of the engine. However, in case GT inlet & exhaust system are ordered are ordered separately, the GT manufacturer specifies corresponding maximum losses in inlet & exhaust system respectively, at which output & heat rate of
the machine are guaranteed. Accordingly allowable pressure drop in the dusting system is decided, taking into account pressure losses in other system components. AIR FILTRATION SYSTEM
CONCEPT We need Filtration of inlet air to prevent ingestion of contaminants to avoid Erosion, Fouling, Corrosion, Hot gas path corrosion etc. Filtration can remove some, but not all substances like oil vapour, smoke which cause fouling of compressor blades. These are needed to be removed by online or offline cleaning washing of compressor using ash free detergents. Air Air consumed by 1 GT (Frame 9 E) from atmosphere is 435 Kg/s approx. Airborne dust contains sodium & Potassium twice as in soil, arises from fine particles of soil, leads to hot corrosion. Also contains hydrocarbon from vehicular pollution and nearby power plants. Contains other solid, liquid and gaseous contaminations Dust Collection Collection efficiency varies with particle size - Lower with lower particles size. As Dust accumulates Pressure Difference rises. GE recommended DP is 2.5 inch for Panel & 4.0 inch for self cleaning type Filters Moisture tends to increase Pressure Difference in filters as more particles adhere on surface. Contaminated Air may Cause:
Erosion Fouling Corrosion Hot Gas Path Corrosion Cooling Passage Plugging
Inlet air filters – The air supplied to the gas turbine must be cleaned and conditioned thoroughly and no impurities, dust and corrosive chemicals should be present in it. For this purpose the atmospheric air is passed through air filter house that contains a number of small cylindrical filters.
Air filters
Air filter house After this the air is passed through fin fan air coolers and air washer system for controlling the temperature and than to the turbine.
Air Filtration at PPCL 1160 filter are fitted in filter house. For changing of Filter Set, a skid with four platforms was fabricated and fixed with existing tiers for quick changing of filters which saved downtime of GT from 24 hrs to 6hrs. Initially 100% synthetic, washable type filters were used, had only internal cage and did not have pleat locking. New filters of 20% synthetic media with internal and external cage along with pleat lock and dimple.
COMPRESSOR SECTION Description The axial-flow compressor section consists of the compressor rotor and the casing. Included within the compressor casing are inlet guide vanes, the 17 stages of rotor and stator blading , and the exit guide vanes. In the compressor, air is confined to the space between the rotor and stator blading where it is compressed in stages by a series of alternate rotating (rotor) and stationary (stator) airfoil-shaped blades. The rotor blades supply the force needed to compress the air in each stage and the stator blades guide the air so that it enters in the following rotor stage at the proper angle. The compressed air exits through the compressor-discharge casing to the combustion chambers. Air is extracted from the compressor for turbine bearing cooling sealing, and for pulsation control during start-up (to avoid surging). Since minimum clearance between rotor and stator provides best performance in a compressor, parts have to be assembled very accurately. Compressor Rotor Assembly Compressor wheels Forward stub shaft Each wheel and the wheel portion of the stub shaft has broached slots around its periphery. Rotor blades are inserted into these slots and held in axial position by spacer pieces. The forward stub shaft is machined to provide the thrust collar which carries the forward and aft thrust loads
Compressor Air Extraction During operation of the gas turbine, air is extracted from various stages of the axial flow compressor to: 1. Cool the turbine parts subject to high operating temperature. 2. Seal the turbine bearings. 3. Provide an operating air supply for air operated valves. 4. Air bleeds off to avoid pulsation. 5. For pulse Jet-cleaning system. 6. Fuel nozzle atomising air. 5th stage air Air is extracted from the compressor 5th stage and is externally piped from connections in the upper and lower half of the casing for cooling and sealing of all rotor bearings. 11th stage Air
Air from the compressor 11th stage is bled only during unit start-up and shut down for pulsation control. The compressor bleed valves are closed during unit operation. 17th stage Air Air extracted from the compressor 17th stage flows radially inward between the stage 16 and 17 wheels, to the rotor bore, and then aft to the turbine where it is used for cooling the turbine 1st and 2nd stage buckets and rotor wheel spaces. Compressor discharge air Air extracted from compressor discharge is used for liquid fuel atomising air, stage 1 nozzle vane and retaining ring cooling, stage 2 nozzle cooling, pulse & for Pulse Jet cleaning system. Air flow control Variable inlet guide vanes Variable inlet guide vanes are located at the aft end of the inlet casing. The position of these vanes has an effect on the quantity of compressor airflow. Movement of these guide vans is accomplished by the inlet guide vane control ring that turns individual pinion gears attached to the end of each vane. The control ring is positioned by a hydraulic actuator and linkage arm assembly.
Inlet Guide Vane Variable compressor inlet guide vanes are installed on the turbine to provide compressor pulsation protection during start-up and shut- down and also to be used during operation under partial load conditions. The variable inlet guide vane actuator is a hydraulically actuated assembly having a closed feedback loop to control the guide vanes angle. The vanes are automatically positioned within their operating range in response either to the control system exhaust temperature limits for normal loaded operation, or to the control system protection limit during the start-up and shutdown sequences. Inlet guide vanes are modulated in order to maintain various stresses, pressure and flows within required limits.
COMBUSTION SECTION This is the place where chemical energy of fuel changes into the thermal energy& flue gases comes as resultant. Description The combustion system is of the reverse flow type with 14 combustion chambers arranged around the periphery of the compressor discharge casing. This system also includes fuel nozzles, spark plug ignition system, flame detectors, and crossfire tubes. Hot gases, generated from burning in combustion chambers, are used to drive the turbine. High-pressure air from the compressor discharge is directed around the transition pieces and into the combustion chambers inlets. This air enters the combustion zone through metering holes for proper fuel combustion and through slots to cool the combustion liner. Fuel is supplied to each combustion chamber through a nozzle designed to disperse and mix the fuel with the proper amount of combustion air. The combustion system consists of: 14 combustion chambers. Fuel nozzles. Cross fired tubes. Transition pieces. Combustion liners. Spark plugs and flame detectors. Combustion Wrapper Combustion wrapper forms a plenum in which the compressor discharge air flow is directed to the combustion chambers. Its secondary purpose is to act as a support for the combustion chamber assemblies. In turn, wrappers are supported by the compressor discharge casing and the turbine shell. Combustion chambers: Discharge air from the axial flow compressor flows into each combustion flow sleeve from the combustion wrapper. The air flows up-stream along the outside of the combustion liner reaction zone through the nozzle swirl tip, through metering holes in both the cap and liner and through combustion holes in the forward half on the liner. The hot combustion gases from the reaction zone pass through a thermal soaking zone and then into dilution zone where additional air is mixed with the combustion gases. Metering holes in the dilution zone allow the correct amount of air to enter and cool the gases to the desired temperature. Along the length of the combustion liner and in the liner cap, there are openings whose function is to provide a film of air for cooling the wall of the liner and the cap. Transition pieces direct the hot gases from the liners to the turbine nozzles. All fourteen combustion liners, flow sleeves and transition pieces are identical.
Figure 2
Combustion Liner Combustion liner has following features −Improved cooling hole pattern around crossfire cube collar to minimize cracking −Added Thermal Barrier Coating (TBC) to increase part life −Improved collar material (HS-188) to increase wear resistance −Improved liner material (Hastelloy -X) to increase part life
Figure Transition piece The Function of transition pieces is to guide the exhaust gases from combustion chamber to turbine inlet. Transition pieces has following features 1. Floating seal design to reduce wear and crack resistance. 2. Cylinder mount-to-body design to increase torsional stability. 3. Extension of inspection intervals to 24,000 hours Crossfire tubes: All fourteen combustion chambers are interconnected by means of crossfire tubes. These tubes enable flame from the fired chambers to propagate to the unfired chambers. Crossfire tubes has following features: −Newly designed swirl-action cooling holes −Improved part life
Spark plug: Combustion is initiated by means of the discharge from two high-voltage, retractable-electrode spark plugs installed in adjacent combustion chambers (No.12 and 13) These spring-injected and pressure retractable plugs receive their energy from ignition transformers. At the time of firing, spark at one or both plugs ignites the gases in a chamber. The remaining chambers are ignited by crossfire through the tubes that interconnect the
reaction zones of the remaining chambers. As rotor speed increases, chamber pressure causes the spark plugs to retract and the electrodes are removed from the combustion zone. Fuel Nozzle There are two type of fuel injector nozzle1. Primary nozzle 2. Secondary nozzle There are six primaries and one secondary nozzle.
Fuel nozzle Flame Detectors: During the start up sequence, it is quite essential that an indication of flame or no-flame to be transmitted to the control system. For this reason, a flame monitoring system is used consisting of four sensors which are installed on four combustion chambers No.4, 5 and 10, 11 and an electronic amplifier which is mounted in the turbine control panel. The ultraviolet flame sensor consists of a flame sensor containing a gas filled detector. The gas within this flame sensor detector is sensitive to the presence of ultraviolet radiation, which is emitted by a hydrocarbon flame. D. C. voltage, supplied by the amplifier, is impressed across the detector terminals. If flame is present, the ionisation of the gas in the detector allows conduction in the circuit, which activates the electronics to give an output voltage defining flame. Conversely, the absence of flame will not generate any voltage defining .no flame... After the establishment of flame, if voltage is re-established to the sensors defining the loss (or lack) of flame a signal is sent to a relay panel in the turbine electronic control circuitry where auxiliary relays in the turbine firing trip circuit which shutdown the turbine. The FAILURE TO FIRE or LOSS OF FLAME is also indicated on the annunciator . If the loss of flame is sensed by only one flame detector sensor, the control circuitry will cause an annunciation only of this condition. If more than two sensors are not showing flame then only turbine trips.
TURBINE SECTION
The three-stage turbine section is the area in which the energy in the hot pressurized gas produced by compressor and combustion sections is converted into mechanical energy.
TURBINE ROTOR
Turbine Rotor Structure The turbine rotor assembly consists of a forward wheel shaft, the first, second and third stage turbine wheels and buckets, two turbine wheel spacers, and the aft turbine wheel shaft. Concentricity control is achieved with mating rabbets on the turbine wheels, spacers and wheel shafts. The turbine rotor is held together by twelve (12) bolts. Selective positioning of rotor members is performed during assembly to minimize balance corrections during dynamic balance of the assembled rotor. The forward wheel shaft extends from the first stage turbine wheel to the aft flange of the compressor rotor assembly. The journal for the No.2 bearing is a part of this wheel shaft. The aft wheel shaft connects the third stage turbine wheel to the load coupling. The wheel shaft includes the No.3 bearing journal. Spacers between the first and second stage turbine wheels and between the second and third stage turbine wheels provide axial separation of the individual wheels. The spacer faces include radial slots for cooling air passages. Labyrinth packings are provided in second and third stage diaphragms with mat with the corresponding sealing lands of the spacers. Buckets The turbine bucket length increases from the first to the third stage. The first and second stage buckets are cooled by internal airflow. Air is introduced in to each bucket through a plenum at the base of the bucket dovetail. The air flows outward through a series of radial cooling holes and exits in to the gas path at the bucket tips. The holes are spaced and sized to obtain cooling of the airfoil, with minimum compressor extraction air.
The third stage buckets are not air-cooled. The second and third stage buckets have tip shrouds with interlock buckets to provide vibration damping, and are mounted with seal teeth that reduce the tip leakage flow. The three stages of turbine buckets are attached to their wheels by straight, axial entry, multiple tangs dovetail that fit into machined cut outs in the rims of the turbine wheels. The bucket vanes are connected to their dovetails by means of shanks. These shanks locate the bucket-to-wheel attachment at a significant distance from the hot gases, which reduces the temperature at the dovetail. The turbine rotor assembly is arranged so that the buckets can be replaced without unstacking the wheels, spacers, and wheel shaft assemblies. Buckets are selectively positioned such that they can be replaced without having to rebalance the wheel assembley
BASIC SYSTEMS OF GAS TURBINE
STARTING SYSTEM Before the gas turbine can be fired and started, it must be rotated or cranked by the accessory equipment. This is done by an induction motor, operating through torque converter to provide cranking torque and speed required by the turbine for start-up. Functions of starting system 1. Crank the gas turbine before firing •breakaway from standstill •accelerate to firing speed •further accelerate to self-sustaining Speed 2.
Speed rotate gas turbine for cooling purpose after shutdown.
Start-up Functional description
In the normal starting sequence, fluid is admitted into the torque converter hydraulic circuit from the lubrication system by the integral valve. The torque convertor angle is kept at 66° to provide maximum torque during the start up from zero speed. After few seconds the starting motor is energized. Breakaway is achieved and the turbine starts to rotate & turbine speed increases to 10 % speed when the speed relay picks up. At this point when the torque convertor angle is reduced to 50% and 1 minute purging cycle starts. After completion of 1 minute purging timer, the solenoid is de-energised & oil supply to torque convertor is stopped, which results into decrease of shaft speed to firing speed (12 %). During this, the torque convertor angle comes down to its firing angle (15°). When shaft reaches the firing speed, the stop valves open and allows the start up fuel to flow into the combustion chamber for firing. If within one minute, any 2/4 flame scanner senses the flame, then warm up timer (1 minute) starts. Otherwise turbine coasts down. During this 1 minute warm up cycle, constant fuel is maintained to minimise the thermal shock during start up. When turbine reaches the firing speed, solenoid is energised. After 5 second of flame sensing, the torque converter angle is increased to maximum to cater for the acceleration cycle which i9s started immediately after completion of 1 minute warm up timer. Readjustment of the converter geometry (torque adjustment) at the end of warm-up allows the torque converter to assist in accelerating the unit up to self-sustaining speed. This speed, (about 60% of normal speed), the torque converter hydraulic circuit is drained, by de-energizing solenoid valve 20 TU-1. At the same time cranking motor 88 CR is de-energized, which effects disconnection. A crank and restart can be initiated at any time below 14 HM speed. Shut-down The shutdown order is given and the turbine speed slows down at about 3.3% speed, when 14 HP drops & the turning motor 88 TG starts. Solenoid valve is energized and the torque is adjusted to 34% allowing turning the turbine at a speed 100 rpm for cool down purpose after shut down. This cool down sequence lasts at least 14 hours. It must be manually stopped to bring turbine to standstill position. Turning The turbine is at standstill & all circuits are ready for turning. The operator turns the operation selector switch 43 of the turbine control panel to position TURNING then gives a START order. When the speed reaches about 4%, motor 88CR is stopped. The speed decreases a little and at about 3.3% speed, turning motor 88 TG starts. Re-adjustment of the converter geometry (torque adjustment) will allow a turning speed of about 100 rpm. Turning will last at least 14 hours. It must be manually stopped. 88 TM-1 is the motor that operates the vanes in torque adjustor device. Starting Motor 4 pole, 6.6kv AC, 1750 hp, 50 Hz. Motor operates at a single speed to produce the necessary horsepower for starting the gas turbine. Turning Gear System Provides the torque necessary to breakaway and rotate the turbine shaft prior to the start of the turbine. It consists of: 1. AC motor 2. DC motor 3. Worm gear assembly
DC motor rotates system upto 0.25rpm. AC motor rotates system upto 6rpm. DC motor is fitted with a ½” square drive for manual turning It Speed rotate gas turbine for cooling purpose after shutdown
1. The parts of a gas turbine... 2.
3. 4. 5. Gas turbine engines are, theoretically, extremely simple. Gas turbine have 3 parts: A compressor to compress the incoming air to high pressure. A combustion area to burn the fuel and produce high pressure, high velocity gas. A turbine to extract the energy from the high pressure, high velocity gas flowing from the combustion chamber. 6. Additionally the gas turbine will have these parts: An accessory drive gear box, to drive various pumps for fuel, water and oil. A reduction gear box, to reduce the high revolutions of the turbine to a more efficient speed for the propeller.
7. Power to the shaft... One of the gas turbine’s advantage is that power developed is usually what is wanted; a rotation force to turn a propeller or generator. It’s competitor, the internal combustion engine, operating on the batch process (intake, compression, etc) and it’s inherent mechanical losses from the acceleration and decelerations of the pistons cannot compete with the fluid process of the gas turbine. Unfortunately, the high rotational speed of the turbine is not the best speed for a propeller; which is most efficient at around 100 rpm. The remedy for this, is the coupling of a gear box to the gas turbine’s output. This allows the gas turbine to operate at it’s most comfortable torque characteristic - high speed. The reduction gear box adds to the complexity of the set up, but allows the turbine, especially the single shaft gas turbine, which have poor torque characteristic at lower rpm, to operate at their ideal speed. The speed of the turbine is less critical in a series turbine which has excellent torque characteristic at most speeds. LUBRICATION SYSTEM General The lubricating requirements for the gas turbine power plant are furnished by a common forced-feed lubrication system. This lubrication system, complete with tank pumps, coolers, filters, valves and various control and protection devices, furnishes normal lubrication and absorption of heat load of the bearing of gas turbine. Lubricating fluid is circulated to the three main turbine bearing, generator bearings, and to the turbine accessory gears and fuel pumps. Also lubricating fluid is supplied to the starting means torque converter for use as hydraulic fluid as well as for lubrication. Additionally, a portion of the pressurized fluid is diverted and filtered again for use by hydraulic control device as control fluid.
Major system components include:
Lube reservoir in the accessory base; Main lube oil pump (shaft driven from the accessory gear) Auxiliary lube oil pump and emergency lube oil pump Pressure relief valve VR-1 in the main discharge Lube oil heat exchangers Lube oil filters STEAM TURBINE
A turbine, being a form of engine, requires, in order to function, a suitable working fluid, a source of high grade energy and a sink for low-grade energy. A steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and converts it into useful mechanical work. It has almost completely replaced the reciprocating piston steam engine primarily because of its greater thermal efficiency and higher power-to-weight ratio. Also, because the turbine generates rotary motion, rather than requiring a linkage mechanism to convert reciprocating to rotary motion, it is particularly suited for use driving an electrical generator — about 86% of all electric generation in the world is by use of steam turbines. The steam turbine is a form of heat engine that derives much of its improvement in thermodynamic efficiency from the use of multiple stages in the expansion of the steam, as opposed to the one stage in the Watt engine, which results in a closer approach to the ideal reversible process. It converts the energy stored in steam into rotational mechanical energy.
Operating Principles A steam turbine's two main parts are the cylinder and the rotor. The cylinder (stator) is a steel or cast iron housing usually divided at the horizontal centre line. Its halves are bolted together for easy access. The cylinder contains fixed blades, vanes, and nozzles that direct steam into the moving blades carried by the rotor. Each fixed blade set is mounted in diaphragms located in front of each disc on the rotor, or directly in the casing. A disc and diaphragm pair a turbine stage. Steam turbines can have many stages. The rotor is a rotating shaft that carries the moving blades on the outer edges of either discs or drums. The blades rotate as the rotor revolves. The rotor of a large steam turbine consists of high, intermediate, and low-pressure sections. In a multiple-stage turbine, steam at a high pressure and high temperature enters the first row of fixed blades or nozzles through an inlet valve or valves. As the steam passes through the fixed blades or nozzles it expands and its velocity increases. The high-velocity jet of steam strikes the first set of moving blades. The kinetic energy of the steam changes into mechanical energy, causing the shaft to rotate. The steam then enters the next set of fixed blades and strikes the next row of moving blades. As the steam flows through the turbine, its pressure and temperature decreases, while its volume increases. The decrease in pressure and temperature occurs as the steam transmits energy to the shaft and performs work. After passing through the last turbine stage, the steam exhausts into the condenser or process steam system. The kinetic energy of the steam changes into mechanical energy through the impact (impulse) or reaction of the steam against the blades. An impulse turbine uses the impact force of the steam jet on the blades to turn the shaft, a simple impulse stage. Steam expands as it passes through the nozzles, where its pressure drops and its velocity increases. As the steam flows through the moving blades, its pressure remains the same, but its velocity decreases. The steam does not expand as it flows through the moving blades. A simple impulse turbine is not very efficient because it does not fully use the velocity of the steam. Many impulse turbines are velocity-compounded, which means they have two or more sets of moving blades in each stage. The extra sets of moving blades make use of the high velocity steam leaving the first set of moving blades. A row of fixed blades between the moving blades direct the steam into the next set of blades. Another type of impulse turbine is a pressure-compounded turbine. It consists of two or more simple impulse stages contained in one casing. The casing contains diaphragms that connect to nozzles. The nozzles
make efficient use of the steam pressure that remains after the steam flows through the previous stage. The pressure drops in each stage as steam expands through the nozzles. A reaction turbine uses the "kickback" force of the steam as it leaves the moving blades and .fixed blades have the same shape and act like nozzles. Thus, steam expands, loses pressure and increases in velocity as it passes through both sets of blades. All reaction turbines are pressure-compounded turbines. Many large turbines use both impulse and reaction blading . These combination turbines usually have impulse blading at the high-pressure end, and reaction blading at the low-pressure end. The blade length and size increases throughout the turbine to use the expanding steam efficiently. Blade rows require seals to prevent steam leakage where the pressure drops. Seals for impulse blading are located between the rotor the diaphragm to stop leakage past the nozzle. Seals for reaction blading are located at the tips of both the fixed and moving blades.
Steam turbine Technical specification: H.P turbine
: Single flow with 28 reaction stages.
L.P turbine
: Double flow with 8 reaction stages.
Main stop and control valves
:2
L.P stop and control valves
:2
Speed:Rated Speed
: 50.0/s
Max. Speed no time limitation
: 51.5/s
Min speed no time limitation
: 47.5/s
Critical Speed
: 1292/2492 r.p.m
HP steam flow
: 390 T/hr
LP Steam flow
: 80 T/hr
STEAM TURBINE COMPONENTS The main turbine The turbine is predominantly of condensing-tandem-compound, two cylinder,- horizontal, disc and diaphragm, reheat type with nozzle governing and regenerative system of feed water heating and is coupled directly with A. C. Generator. The HP section is a stage flow turbine whereas the LP section is a double flow. Rigid couplings connect the individual rotors and generator rotor. The hp turbine has been constructed for throttle control governing. The initial steam is admitted before the blading by two combined main steam stop and control valves. The steam from HP turbine exhaust is led to the LP turbine through cross-around pipes. Additional steam from LP stage of waste heat recovery steam generator is passed to the LP turbine via two combined LP stops and control valves.
HP TURBINE
Casing The casing of HP turbine is split horizontally and is of double shell construction. A single flow inner casing is supported by outer casing. The initial steam enters the inner casing from above and below through two admission branches.
The provision of an inner casing confines the inner temperature and high pressure steam inlet condition to the admission section of this casing while our casing is subjected to lower pressure and temp effective at the exhaust from th inner casing. This means that the joint flange outer casing can be kept small and material concentration in the area of flange reduced to minimum thus avoiding difficulties arising from deformation of a casing with flange joint due to non uniform temp rises e.g. on start up or shut down. The joints of inner casing are relieved by the pressure in the outer casing so that these joints only have to be sealed against the resulting differential pressure. Blading Blades fitted in the stationary part are called guide blades or nozzles and those fitted in the rotor are called moving or working blades. The following are three main types of blades: Cylindrical (or constant profile) blade. Tapered cylindrical (tapered but similar profile). Twisted and varying profile blades. Blades have three main parts: (a) Aerofoil: It is working part of blade and is one of the types described above, (b) Root: It is portion of the blade which is held with the disc, drum or casing and (c) Shrouds. Three types of root arrangements are commonly used. They are (1) T-roots: for small blades; (2) Fir Tree or serrated roots - for longer blades; (3) Fork and Pin root: for longer blades shrunk on disc type rotors. Shrouds can be either riveted by tannon to main blade or it can be integrally machined with the blade. Now-a-days trend is towards integral shroud for shorter) lades and shrunk fitting for larger blades. Some times lacing wires are also used u dampen the vibration and to match frequencies in the longer blades. Since in the reaction type machine the pressure drop also occurs across the moving blades it is necessary to provide effective sealing at the blade tips. This must be done to prevent leakage steam past the shrouding of the wheel and consequent loss efficiency particularly at the high-pressure end of the machine. The HP turbine blading consist of 28 drum stages. All stages are reaction stages with 50% reaction. The stationary and rotating blades of all stages are provided with inverted T roots and integral shrouds. The moving and stationary blades are inserted into corresponding grooves in the shaft and inner casing and are caulked at bottom with caulking material. The insertion slot in the shaft is closed by the locking blade which is fixed by taper pins or grub screws. Gap sealing Sealing strips are caulked into the inner casing and shaft to reduce the leakage losses at the blade tips. Cylindrically machined surfaces on the blade shrouds are opposite the sealing strips. the surfaces have stepped diameters in order to increase the turbulence of steam and thus sealing effect. Should an operational disturbance cause the sealing strips to come into contact with opposite surfaces they are rubbed away without any considerable amount of heat being generated. They can then be replaced at a later date to provide the specified clearance. Shaft seals (sealing glands) The function of shaft seals is to seal the interior of the turbine casing against the atmosphere at the front and rear ends of HP turbine. The pressure differences upstream and downstream of raised sections of the shaft seals serve to counterbalance the axial thrust resulting from steam forces. Seal rings: the seal rings, no of which depends on pressure gradient to be sealed, are divided into several segments and are mounted in grooves in the sealing housing and inner casing such that they are free to move radially. Each segment s held in position against a shoulder by helical springs. In case of rubbing the affected seal segments can retreat against springs.
LP TURBINE Casing The LP turbine casing consists of a double flow unit ad has a triple shell welded casing. Outer casing: The outer casing consists of the front and rear walls, the two lateral longitudinal support beams and the upper part. The front and rear walls, as well as the connection areas of the upper part are reinforced by means of circular box beams. The outer casing is supported by the ends of the longitudinal beams on the base plate of the foundation. Inner casing: the double flow inner casing which is of double shell construction consists of the outer shell and the inner shell. The inner shell is attached in the outer shell with provision for free thermal movement. Stationary blading is carried by inner shell. Stationary blade row segment of the LP stage are bolted to the outer shell of the inner casing.
Fig The complete inner casing is supported by the longitudinal support members of the outer casing lower half, in a manner permitting free radial expansion concentric with the shaft, and axially from a fix point. Atmospheric relief diaphragm Atmospheric relief diaphragm is provided in the upper half of each LP exhaust end section to protect the turbine against excessive pressure. In the event of failure of the low vacuum trips the pressure in the LP turbine exhaust rises to an excessively high level until the force acting on the rupturing disc ruptures the breakable diaphragm thus providing a discharge path for the steam. The diaphragm consists of a thin rolled lead blade. To insure that the remnants of the diaphragm and rupturing disc and not carried along by the blow off steam, a cage with brackets is provided. As long as there is vacuum in the condenser the atmospheric pressure forces the breakable diaphragm and the rupturing disc against the supporting flange.
Blading The drum blading stages of the double flow LP turbine are reaction stages with 50% reaction. They are located in the inlet region and thus form the front part of the blading. All stationary and moving blades are provided with integral shrouds which after installation form a continuous shrouding. All stationary and moving blades have T roots which also determine the distance between the blades. They are inserted in mating rooms in shaft and inner casing and are caulked in place with caulking material. The insertion slot in the shaft is sealed by means of a locking blade which is held in position by grub screw. The stationary blades are held in position in the groves of grub screw that are screwed into the inner casing material and the blades lock from the joined surface. Gap sealing: in order to reduce blade tip losses, seal strips are caulked into the inner casing and the turbine Shaft. The seal strips are locate opposite integrally machined seal points on the blade shroud. This design gives favourable radial clearance, in the event of rubbing due to fault, the seal strips are worn away without generating much heat. They can then be easily replaced to restore the required clearance. LP Stages The last three stages of the LP turbine are designed as reaction stages. Each stage is made up of stationary and moving blades. The stationary blade rings are made by welding inner ring blades and outer rings together into the segments and bolting them to inner casing. The two final stages have blade which are made of sheet steel and are hollow. Drainage slots are provided in the blade of these rows .through these slots any water impacting on these blades is drawn away to the condenser. When the stationary blades rings are installed in place, inner rings attached to these form a continuous ring of shrouding. The moving blades have T roots which are inserted into corresponding grooves in the turbine shaft and caulked with caulking material. The moving blades inserted in the axial grooves in the turbine shaft have curved fit tree roots. These are attached with filler pieces and secured against axial movements of the blades by retaining strips, the end segment of which are welded together at the joint. The difference in circumferential speed at the root and tip of the moving blades is taken into consideration by the twisted design of the blades Shaft seals The function of the axial shaft seal situated between the bearing casing and the LP exhaust casing is to seal the inner space of LP exhaust casing against the atmospheric pressure at the passes through the shaft.
HEAT RECOVERY STEAM GENERATOR (HRSG)
The heat that is discharged by GTs without recovering the available energy may be economically converted in to useful purposes. HRSG is a system of heat exchangers which converts this heat in to a more usable form of energy. The utilization of the wastes heat recovery system in combine cycle power plants with gas turbines is a relatively recent development brought by the development in the field of gas turbines resulting in gas turbines becoming larger in size and output, the large volume of heat available form gas turbine exhaust and rising fuel costs. One of the main features of the gas turbine is the high mass flow of air used over the stoichiometric quantity of air. Typically volume of [excess air factor] for gas turbine combustion lies between 3 and 4. This means there is more than sufficient oxygen to support secondary combustion, if required. This high mass flow in turn makes the gas turbine exhaust an ideal candidate for heat recovery steam generation. The heat recovery steam generators at PPCL are of a double pressure (HP &LP), unfired, vertical gas flow type with a self supporting stack of 70 m height. It is designed to generate steam quantities as furnished in Operating Parameters at Main Steam Stop Valve, under specified modes of operation. Feed water temperature is 151 7° C for HP and 150 ° C for LP at the design point.
Water is first heated sensibly in the economiser in the liquid phase at certain pressure till it become saturated liquid. now in the evaporator or the boiler proper, there is phase change or boiling by absorbing the latent heat of vaporization at that pressure. Now the saturated vapour is further heated at constant pressure in the superheater in the vapour or gaseous phase. It must be noted that as the pressure increases, the latent heat decreases and so the heat absorb in the evaporator decreases and the fraction of total heat absorb in the superheater increases. In hp boilers, more than 40% of total heat is absorbed in the superheaters. For steam generators operating above the critical pressure there is no evaporator or boiling section. However there is a transition zone where all the liquid on being heated suddenly flashes into vapour. Each HRSG has two different boiler drum; namely High-Pressure Boiler Drum which supplies highpressure steam to HP steam turbine and Low-Pressure Boiler Drum which supplies low-pressure steam to LP steam turbine. This arrangement ensures efficient heat transfer between the flue gases from GT exhaust and the steam turbine fluid(water). The boiler is divided into eight zones. In order of higher temperature, they are as follows: 1. HP Superheater I 2. HP Superheater II 3. HP Evaporator 4. HP Economiser II 5. LP Superheater 6. LP Evaporator 7. HP Economiser I 8. Condensate Preheater HP drum is located ahead of LP drum because low pressure steam absorbs more heat at low temperature.
Evaporator The WHRB evaporator consists of a steam drum, interconnecting unheated down comer tubes, interconnecting heated riser tubes, enclosures casing and accessories. The evaporator receives the incoming heated feed water from the economizer and generates saturated steam which is taken form the top of the steam drum, the evaporator will operator at constant saturation temperature corresponding to the drum operating pressure. The steam drum is locked at the top of the evaporator to enable natural circulation to take place water steam level will be maintained in the steam drum during operation.
Economizer The Economizer is a feed water heater operating at the steam drum pressure utilizing the heat left in the exhaust gas after the gas leaves the evaporator. The economizer will heat the incoming feed water to the evaporator. The HP economizer is constructed of modules, consisting of spiral finned tubes welded to the top and bottom headers, two rows (max.) per module, The HP economizer is designed for single pass flow on the gas side and multi-pass flow on the tube side. HP economizer modules are equipped with high point I" vents and low point I" drains for a "fully drainable" design.
Superheater Super heaters are basically steam heater receiving saturated steam from the steam drum and producing superheated steam. Super heater are located ahead of the evaporator in the WHRB exhaust gas flow stream in order to develop required superheated steam temperatures.
Condensate Pre heater Low pressure feed water heaters also called condensate Pre heater sometimes used on combined cycle units to heat the desecrator feed water thus the cycle required less desecration steam making it more efficient. The purpose of condensate pre-heater is to increase the temperature of demineralised water so that it requires lesser energy to be converted into steam which is pumped into it by Condensate Extraction Pump after passing through the condenser. Now from CPH it is pumped into de-aerator. The cycle for both LP and HP steam formation is same. CPH is constructed of modules, consisting of spiral finned tubes welded to the top and bottom headers, two rows (max.) per module. CPFI is designed for single pass flow on the gas side and multi-pass flow on the tube side.
De-Superheater Spray attemperator (de-superheater) is utilized to control the HP Steam temperature to 520 deg C. It works by sprinkling water on the steam as the steam passes through it. This lowers down the temperature but also wets the steam. The steam is dried in the next superheater and hence the temperature of the steam is controlled. That is why this De-Superheater is placed in between the two HP-superheaters. The amount of water sprinkled is also controll so that the temperature of steam doesn’t get too low that the second superheater cannot increase its temperature to the required value. By-pass Stack and Diverter Dampers DDs are provided to isolate the WHRB form its heated source. If furnished this isolation will permit running the gas turbine at times when steam is not required or when WHRB is not available. Normally the by pass dampers will have a straight open/close function though some designs can also provide degree of modulation. A by pass stack complete with silencer is required and provided when by-pass dampers are used. Expansion joint One expansion joint at HRSG inlet and one more expansion joint at Chimney inlet are provided as shown in Company‘s GA Drawing to allow for the thermal expansions.
1.1
Condensing Plant Introduction The condensing plant forms the main heat sink of the power plant unit. Need for condensing plant: Maintains a very low back pressure on the exhaust side of the turbine. Consequently the steam expands to a greater extent which results in an increase in the available heat energy for converting into mechanical work. The condensed steam is recycled and fed back to the boiler thus reducing water treatment requirement. The following systems are involved: 1. Circulating water system 2. Condenser 3. Condensate system 4. Evacuation system 5. Shaft seal steam system 1.1.1
Circulating water system
The circulating water system, whose essential components are the water pumps and piping, has the function of supplying the condenser with circulating water for removing the heat of vaporisation of the condensed steam. The circulating water must meat certain requirements i.e. it must be free of solid contaminants, which can be deposited in or in front of the condenser tubes. The strainer system and dosing equipments add in maintaining circulating water requirement and form part of the circulating water system. Components: CW PUMPS COOLING TOWER CW PUMPS Pumping is the process of addition of kinetic and potential energy to a liquid for the purpose of moving it from one point to another. CW Pumps at P.P.C.L. This pump is vertical, mixed flow type having semi open type impeller, designed for wet-pit and dry pit applications; suitable for water drawn through an open gravity intake channel terminating in twin-closed ducts running parallel to the main building. The essential components of the pump are the fluid through the suction bowl/eye provided with streamlined guide vanes, whose function is to prevent pre-whirl and impart hydraulically correct flow to the liquid. The propeller, in turn, imparts motion to the fluid. The purpose of the discharge bowl, provided with streamlined diffuser vanes, is to direct the flow of water into the discharge column. Cooling Tower at PPCL The ID cooling tower at PPCL consists of 8 cell arranged in a row and separated by block partition walls from the basin sill to the fan deck.
Components:
1. Frame and Casing: support the exterior enclosures, motors, fans, and other components with small design. It is made of reinforced concrete.
2. Fills: made of plastic or wood. These facilitate heat tansfer by maximizing water and air contact.
3. Cold water basin: located at bottom of the tower, receives the cooled water that flows down 4. 5. 6.
7.
through the tower and fills. Drift eliminator: captures water droplets entrapped in air stream that otherwise would be lost to atmosphere. It has hexagonal cells which provide change in the direction of flow of air there by arresting the drift. Louvers: to equalize air flow into the fill and to retain the water into the tower. Situated at air inlet opening in cross flow towers. Nozzle Fans: 9144 mm diameter, 8 bladed, axial flow fan sucks the ambient air through the air inlet opening of he cooling tower.
Cooling tower fan blades at PPCL
Condenser
The steam expanded to condenser pressure in the steam turbine and by pass valves condenses in the condenser by removing the heat of evaporation.
Condenser at PPCL There are two condensers entered to the two exhausters of the L.P. turbine. These are surface type condensers with two pass arrangement. Cooling water pumped into each condenser by a vertical C.W. pump thru' the inlet pipe. Water enters the inlet chamber of the front water box, passes horizontally thru'the brass tubes to the water box at the other end, takes a turn, passes thru' the upper cluster of tubes and reaches the outlet chamber in the front water box. From these, cooling water leaves the condenser thru' the outlet pipe and discharge into the discharge duct. Steam exhausted from the L.P. turbine washing the outside of the condenser tubes losses its latent heat to the cooling water and is connected with water in the steam side of the condenser. This condensate collects in the hot well, welded to the bottom of the condensers. Protective coating used against corrosion---- Epoxy paint. Four no of steam throw devices have been provided n condenser, two no. each for HP By-pass system for pumping steam during start-up and sudden load throw off.
Condenser design memorandum Design CW temp
33C
CW Temp Rise
9.C
Condenser back pressure
.101 atm.
CW Qty. flow
22400 m3/hr
No. of tubes
15330
No. of passes
2
Length of tubes
11.7 m
HOT WELL (BELOW CONDENSER – CONDENSER LEVEL UNIT PPCL) Condensate system The condensate accumulating in the condenser is fed back into the water-steam circuit by the condensate system pumps. The level controller has the function of holding the level in the condenser constant. Te control valve of level controller forms the part of the condensate system. Condensate system also provides1. Injection water for by-pass steam. 2. Injection water for the flash tank of the condenser. 3. Seal water for gland of valves in the vacuum pressure range. 4. Cooling water for the seal steam condenser. Condensate Pumps The function of these pumps is to pumps out the condensate to the de-aerator thru' ejectors, gland steam cooler, and L.P. heaters. These pumps have four stages and since the suction is at a negative pressure, special arrangements have been made for providing sealing. This pump is rated generally for 160 cu.m hr. at a pressure 13.2 Kg/sq.cm.
DE-AERATOR The presence of certain gases, principally oxygen, carbon-di-oxide and ammonia, dissolved in water is generally considered harmful because of their corrosive attack on metals, particularly at elevated temperatures. One of the most important factors in the prevention of internal corrosion in modern boilers and associated plant therefore, is that the boiler feed water should be free as far as possible from all dissolved gases especially oxygen. This is achieved by embodying into the boiler feed system a de-aerating unit, whose function is to remove dissolved gases from the feed water by mechanical means. Particularly the unit must reduce the oxygen content of the feed water to as low a valve as is possible or desirable, depending upon the individual circumstances, residual oxygen content in condensate at the outlet of de-aerating plant usually specified is 0.005/litre or less. Principle of Deaeration: The principle of Deaeration is based on following two laws. Henrys law: The mass of gas with definite mass of liquid will dissolve at a given temperature and is directly proportional to the partial pressure of the gas in contact with the liquid. This holds within close limits for any gas, which does not unite chemically with the solvent.
Solubility Law: Solubility of gases decreases with increase in solution temperature and/or decrease in pressure. Henry's law merely/defines equilibrium conditions. The actual mechanism involved in gases going into or out of solution is a result of the continuous movement of the molecules of the gas and solvent. This movement results in molecules migrating across the liquid surface and when the migration to and from the liquid is equal, equilibrium is reached. Reaching equilibrium may be hastened by deaerating the size of water particles thereby reducing the distance to be travelled by gas molecules and increasing the surface of mass ratio and by agitation, which brings internal sections of the liquid to the surface. Obviously, this is a minetic process with time an essential factor in reaching equilibrium.
Figure A constant pressure Deaerator, pegged at 7 Kg/sq.cm. abs is envisaged in turbine regenerative cycle to provide properly deaerate feed water for boiler, limiting gases (mainly oxygen) to 0.005 CC/liter. It is a direct contact type heater combined with feed storage tank of adequate capacity. The heating steam is normally supplied from turbine extractions but during starting and low load operation the steam is supplied from auxiliary source. The de-aerator comprises of two chambers: De-aerating column. Feed storage tank. De-aerating column is a spray cum tray type cylindrical vessel of horizontal construction with dished ends welded to it the tray stack is designed to ensure maximum contact time as well as optimum scrubbing of condensate to achieve efficient de-aeration. The de-aeration column is mounted on the feed storage tank which in turn is supported on rollers at the two ends and a fixed support at the centre. The feed
storage tank is fabricated from boiler quality steel plates Manholes are provided on deaerating column as well as on feed storage tank for inspection and maintenance. The condensate is admitted at the top of the de-aerating column flows downwards through the spray valves and trays. The trays are designed to expose to the maximum water surfaces for efficient scrubbing to affect the liberation of the associated gases-steam enters from the underneath of the trays and flows in counter direction of condensate. While flowing upwards through the trays, scrubbing and heating is done. Thus the liberated gases move upwards along with the steam. Steam gets condensed above the trays and in turn heats the condensate. Liberated gases escapes to atmosphere from the orifice opening meant for it. This opening is provided with a number of deflectors to minimise the loss of steam. Deaerator is provided with the following fittings. Tubular type gauge glass. High level alarm switch. Low level alarm switch. Pressure gauge. Straight thermometers with pockets. Safety valve Isolating valves for steam pipes.
. 1.2
DLN-1 Combustor The GE DLN-1 combustor is a two-stage premixed combustor designed for use with natural gas fuel and capable of operation on liquid fuel. As shown, the combustion system includes four major components: fuel injection system, liner, venturi and cap/centre body assembly.
Figure
The GE DLN-1 combustion system operates in four distinct modes, during premixed natural gas or oil fuel operation: These components form two stages in the combustor. In the premixed mode, the first stage thoroughly mixes the fuel and air and delivers a uniform, lean, unburned fuel-air mixture to the second stage.
1.3
Mode/Operating Range
Primary – Fuel to the primary nozzles only. Flame is in the primary stage only. This mode of operation is used to ignite, accelerate and operate the machine over low- to mid-loads, up to a pre-selected combustion reference temperature. Lean-Lean – Fuel to both the primary and secondary nozzles. Flame is in both the primary and secondary stages. This mode of operation is used for intermediate loads between two pre-selected combustion reference temperatures.
Figure
Secondary – Fuel to the secondary nozzle only. Flame is in the secondary zone only. This mode is a transition state between lean-lean and premix modes. This mode is necessary to extinguish the flame in the primary zone, before fuel is reintroduced into what becomes the primary premixing zone. Premix – Fuel to both primary and secondary nozzles. Flame is in the secondary stage only. This mode of operation is achieved at and near the combustion reference temperature design point. Optimum emissions are generated in premix mode.
The load range associated with these modes varies with the degree of inlet guide vane modulation and, to a smaller extent, with the ambient temperature. At ISO ambient, the premix operating range is 50% to 100% load with IGV modulation down to 42°, and 75% to 100% load with IGV modulation down to 57°. The 42° IGV minimum requires an inlet bleed heat system. If required, both the primary and secondary fuel nozzles can be dual-fuel nozzles, thus allowing automatic transfer from gas to oil throughout the load range. When burning, either natural gas or distillate oil, the system can operate to full load in the lean-lean mode. This allows wet abatement of NO x on oil fuel and power augmentation with water on gas. The spark plug and flame detector arrangements in a DLN-1 combustor are different from those used in a conventional combustor. Since the first stage must be re-ignited at high load in order to transfer from the premixed mode back to lean-lean operation, the spark plugs do not retract. One plug is mounted near a primary zone cup in each of two combustors. The system uses flame detectors to view the primary stage of selected chambers (similar to conventional systems), and secondary flame detectors that look through the center body and into the second stage. The primary fuel injection system is used during ignition and part load operation. The system also injects most of the fuel during premixed operation and must be capable of stabilizing the flame. For this reason, the DLN-1 primary fuel nozzle is similar to GE’s MS7001EA multi-nozzle combustor with multiple swirl-stabilized fuel injectors. The GE DLN-1 system uses five primary fuel nozzles for the MS6001B and smaller machines and six primary fuel nozzles for the larger machines. This design is capable of providing a well-stabilized diffusion flame that burns efficiently at ignition and during part load operation. In addition, the multi-nozzle fuel injection system provides a satisfactory spatial distribution of fuel flow entering the first-stage mixer. The primary fuel-air mixing section is bound by the combustor first-stage wall, the cap/center body and the forward cone of the venturi. This volume serves as a combustion zone when the combustor operates in the primary and lean-lean modes. Since ignition occurs in this stage, crossfire tubes are installed to propagate flame and to balance pressures between adjacent chambers. Film slots on the liner walls provide cooling, as they do in a standard combustor. In order to achieve good emissions performance in premixed operation, the fuel-air equivalence ratio of the mixture exiting the first-stage mixer must be very lean. Efficient and stable burning in the second stage is achieved by providing continuous ignition sources at both the inner and outer surfaces of this flow. The three elements of this stage comprise a piloting flame, an associated aerodynamic device to force interaction between the pilot flame and the inner surface of the main stage flow, and an aerodynamic device to create a stable flame zone on the outer surface of the main stage flow exiting the first stage. The piloting flame is generated by the secondary fuel nozzle, which premixes a portion of the natural gas fuel and air (nominally, 17% at full load operation) and injects the mixture through a swirler into a cup where it is burned. Burning an even smaller amount of fuel (less than 2% of the total fuel flow) stabilizes this flame as a diffusion flame in the cup. The secondary nozzle, which is mounted in the cap center body, is simple and highly effective for creating a stable flame. A swirler mounted on the downstream end of the cap/centerbody surrounds the secondary nozzle. This creates a swirling flow that stirs the interface region between the piloting flame and the main-stage flow and ensures that the flame is continuously propagated from the pilot to the inner surface of the fuel-air mixture exiting the first stage. Operation on oil fuel is similar except that all of the secondary oil is burned in a diffusion flame in the current dry oil design. The sudden expansion at the throat of the venture creates a toroidal re-circulation zone over the downstream conical surface of the venturi. This zone, which entrains a portion of the venture cooling air, is a stable burning zone that acts as an ignition source for the main stage fuel-air mixture. The cone angle and axial location of the venturi cooling air dump have significant effects on the efficacy of this ignition source. Finally, the dilution zone (the region of the combustor immediately downstream from the flame zone in the secondary) provides a region for CO burnout and for shaping the gas temperature profile exiting the combustion system.
WATER TREATMENT PLANT Boiler makeup water to the extent of 1.5-2% of the total flow is required to replenish the loss of water through leakage from fittings and bearings, boiler blow-down escape with non condensable gases in the Deaerator, turbine glands, and other causes. This makeup water needs to be treated prior to feeding it to the boiler for –
Prevention of hard scale formation on the heating surfaces, Elimination of corrosion, Control of carry-over to eliminate the deposition on super heater tubes, Prevention of silica deposition and corrosion damage to turbine blades.
The cooling water makeup also demands significant amount of water at a prescribed parameters of PH turbidity, conductivity etc. Also, water is needed for various other plant activities at various levels of cleanliness such as fire fighting, service water etc. This entire water requirement is met by the water treatment plant of the power plant. Thus, the water treatment plant treats the water according to the requirements to which it needs to be put at various sections in the power plant. This whole process largely comes under water treatment, which starts at the point, raw water enters the plant boundaries and continues till the water id dispatched after treatment to its desired destination. Water treatment process Water treatment process which is generally made up of two sections: 1. Pretreatment section 2. De-mineralization section Raw, water is received from two sewage treatment plants namely, Delhi Gate Sewage Treatment Plant and Sell Nursing Home Sewage Treatment Plant. This water is not suitable for use in the power plant and has to be treated. Raw water contains a variety of impurities such as –
suspended solids and turbidity, Organics, Hardness(salts of calcium and magnesium), alkalinity(bicarbonates, carbonates, hydrates), Silica, and Dissolved gases(O2 and CO2)
Lime Softening Plant Firstly, the water is stored in the raw water reservoir. From there it is, pumped to the Lime Softening Plant (LSP) where the turbidity and the hardness of water are reduced. Here, lime, chlorine, poly electrolyte and ferric alum are dosed in the stilling chamber. Ferric alum reduces the turbidity of the water and poly electrolyte enhances sludge formation. Lime is added to the raw water to remove the hardness while chlorine neutralizes the biological matter The main purpose of lime softening is to reduce the calcium and magnesium hardness associated with carbonate and bicarbonate alkalinity. In addition, lime softening removes any carbon-dioxide dissolved in
the raw water. These reductions can lower the total dissolved solids and the alkalinity of the treated water. The chemical reactions involved are as follows:CO2 + Ca(OH)2 → CaCO3 + H2O Ca(HCO3)2 + Ca(OH)2 → 2CaCO3 + 2H2O Mg(HCO3)2 + Ca(OH)2 → 2CaCO3 MgCO3 + 2H2O MgCO3 + Ca(OH)2 → 2CaCO3 + Mg(OH)3
CLARIFICATION When water is allowed to stand for sometime in a big tank or reservoir, most of the suspended material settles down. The decanted water is quiet clear and is taken out from outlet located at convenient points. This process of clarification can be accelerated by adding coagulants such as ALUM (alluminium sulphate) or ferrous sulphate or sodium aluminate. These result in the formation of a FLOC or precipitate of aluminium hydroxide which tends to amalgamate colloidal, organic and suspended impurities that settle down. The tank in which the whole process takes place is called clarification tank. Prior to it, there is a stilling chamber where the dosing of lime, chlorine and alum is done. This dosed water is allowed to stand in the clarifier. The suspended impurities settle down in a specified period of time called settling time. The tank has a scraper which scraps the bottom surface of the tank for suspension and guides it out of the tank through sludge outlets. The clarified water flows out of the tank from suitable outlet points provided at the top. If the impurity is not binding to form FLOC, polyelectrolyte (PE) is dosed to speed up the sludge formation. FILTERATION Water filtration is the process of separating suspended and colloidal impurities from the water by passing it through a porous medium. A bed of granular filter material or media is used in most power plant applications. A filter may be defined simply as a device consisting of a tank, a means of supporting a working filter bed within the tank, suitable filter media, and necessary piping, valving and controls. These can be of two types:* GRAVITY FLOW FILTERS: In which the natural head of water above the filter bed and low point of discharge at the filter bottom providing the pressure differential needed to move the water through the filter bed. * PRESSURE FILTERS: As their name implies, they operate on line under service pressure, filtering the water as it flows through the tank on its way to service or storage. A granular medium like sand is commonly used for filtration. The pressure difference across the filtering medium is an indication of solid accumulation. When it reaches a given point, the solid have to be removed by backwashing of the filtering bed. CHLORINATION The main target for chlorination of water is to oxidize impurities like algae mass, bacteria etc. Chlorination is found very effective for treatment of water for industrial use and for drinking purpose. The condenser cooling water and raw water for demineralization need to be chlorinated to destroy organic in order to prohibit bio-fouling of equipments.
REVERSE OSMOSIS DEMINERALIZATION It is a type of Membrane Desalination for desalination of brackish water to produce de-mineralized water fit for steam turbine cycle and auxiliary equipments cooling. Reverse Osmosis As related to water solution, osmosis occurs when two solutions of different concentrations are separated by a semi-permeable membrane. The membrane allows only water molecules to cross the membrane barrier. Water will flow from the lower concentration side to the higher concentration side until equilibrium is achieved. The resulting difference is the height of the liquid column represents the OSMOTIC PRESSURE. Reverse osmosis occurs when sufficient pressure is applied to the higher concentration side to reverse the water flow. The osmotic pressure required to the reverse direction of water flow increases as the concentration of the brine increases. During the reverse osmosis process, water flows to the area of lower concentration and the higher concentration solution become more concentrated. To overcome the increased concentration, additional pressure is required to continue the reverse osmosis process. For example, normal osmotic pressure of sea water is about 2654 kPa, but to achieve reasonable product flow rate about 5274 kPa is required to achieve a 50% conversion. Additional pressure beyond this pressure value will further increase the process flux (the amount of product discharged per unit of membrane area). In reverse osmosis process the dissolved ions concentrate on the high-pressure side of the membrane, and purified water passes through the membrane to create a product stream on the low-pressure side. The semi permeable membranes are very sensitive to contaminants and impurities, and proper pretreatment of reverse osmosis feed water is essential to prevent membrane fouling. A reverse osmosis system, therefore, usually consists of two parts: pre-treatment equipments to filter and chemically condition the water and a group of reverse osmosis modules to reduce the concentration of dissolved solids. The two basic types of reverse osmosis membrane materials are ASYMMETRIC and THIN FILM COMPOSIT. Asymmetric membranes consist of a very thin, dense surface layer with a micro porous substructure. The substructure is designed to provide support for the surface skin, without impeding permeates flow. CELLULOSE, ACETATE and AROMATIC POLLYMIDES are the most common asymmetric material. Cellulose acetate membranes are susceptible to annealing and a reduction in flux if operated at higher temperatures. The membranes are also prone to HYDROLYSIS at extreme PH but are relatively insensitive to chlorine. Aromatic polyamides membranes are most resistant to hydrolysis but are more sensitive to chlorine then cellulose acetate membrane. Both are subject to compaction. Like asymmetric membranes, thin film composite membranes consist of a very thin, dense surface layer with a micro porous substructure. In the asymmetric membranes, these layers are created simultaneously out of the same polymer. In a composite membrane, the layers are produced separately, which increases both the flexibility and complexity of the membrane design and construction. The best reverse osmosis membrane would offer high flux, high rejection rate, high chlorine resistance, high fouling resistance, and a strong, durable composition, as well as allow for a wide range of variation in operating temperature, pressure, and pH. Membrane advances continue to broaden the acceptable operating limits, prolong membrane life, lower installation and operating cost and improves the recovery and rejection rates for reverse osmosis system. Proper pre-treatment of reverse osmosis feed water is essential in the prevention of membrane fouling. Membrane cleaning frequency serves a general guide for evaluating the effectiveness of the pretreatment system. A cleaning frequency of more than once a month indicates inadequate pre-treatment. Types of fouling that can be prevented or reduced by pre-treatment include the following:
Membrane scaling, Metal oxide fouling, Plugging, Colloidal fouling, and Biological fouling
Once fouling occurs, the membranes must be cleaned. Thorough cleaning will remove most foulants; however, membranes must be cleaned irreversible fouling occurs. The four types of reverse osmosis ELEMENT CONFIGURATION ARE PLATE AND FRAME, TUBULAR, HOLLOW FIBER, and SPIRAL WOUND. A plate and frame module is one of the oldest reverse osmosis devices. Although it is conceptually simple, the high capital costs involve in construction contribute to making the plate and frame configuration most suitable for the process application characterized by low rates and high value products. The hollow fibre configuration consists of a bundle of hollow porous fibres. The external wall of each fibre is lined with a semi-permeable membrane, with the fibre providing the necessary support for the membrane. This configuration is also similar to a shell and a tube design. Feed water flows through the shell side and the SYSTEM PRESSURE drives water molecules through the membrane and into the fibre. The product system is retrieved from the tube side, and the reject stream continues out the shell side. Hollow fibre devices offer the highest membrane remove all suspended and colloidal solids in the feed stream because the devices are particularly susceptible to fouling and once foul, are difficult to clean. The spiral wound configuration consists of sheets of brine transport material, product transport material, and membrane material, sealed on three or four sides and rolled into a perforated tube. As the brine flows longitudinally down the element, the system pressure causes the water to pass through the membrane into the product transport layer and flow spirally towards the centre of the element. As the product reaches the centre, it flows out the unsealed side and through the tube perforations, allowing the product flow to exit the element out either end of the tube. The brine continues to flow longitudinally down the element through spacers that form the brine transportation. A unique advantage of spiral wound system is the ability to place several elements together in a single pressure vessel. Spiral wound elements are more resistant to fouling and are easier to clean than hollow fiber element. Somewhat more space is required for spiral wound system than for corresponding hollow fiber application. Reverse osmosis has been used on its own or in combination with other treatment systems in many applications for effective, economical water treatment. RO/DM plant is used to reduce the salt content of the water. The water is treated in the following order:
Figure
1. Twin Bed Gravity Filter Water from the LSP goes to the Twin Bed Gravity Filter (TBGF) where the solid particles are further reduced. Here, ferric chloride, poly electrolyte and Chlorine is dozed. Ferric chloride and poly electrolyte reduce the turbidity while chlorine neutralizes the biological matter. At the end of the process in TBGF, the turbidity of the water is around 1-2 NTU. 2. Activated Carbon Filter The filtered water from the TBGF is pumped to the activated carbon filter (ACF). Here, the turbidity of the water is further reduced and color as well as chlorine is removed. After ACF, as a precaution Sodium Meta-Bi- Sulphate (SMBS) is added to the water to remove the residual chlorine as chlorine can damage the reverse osmosis membrane. SMBS is added through cartridge filters. Also, an anti-sealant, BC-1190, is added to avoid scaling of RO membranes.
3. Cartridge Filter In these filters again impurities of order 5 micron are removed. There are three CFs. At a time only one of them is in service. After this stage most of the parameters are met such as PH is around 7.0 and turbidity is 0.11 NTU, but the conductivity is 1508 .7 S/cm. 4. Reverse Osmosis Stage After the water is made fit for the Reverse Osmosis (RO) membranes, the water is pumped to the first stage of the RO plant. The first stage consists 1 of' 16 identical vessels wherein each vessel consists of 6 membranes of length 1 m. Here, water loses 98%, of its conductivity. From here water is pumped to the permeate break tank. 5. Permeate Break Tank Permeate break tank has only one purpose, to provide a head for the pumps Inur1ping water to the RO stage II. 6. Reverse Osmosis Stage II RO stage II consists of 8 identical vessels same as that of the RO stage I. Here, the water loses 90% of the remaining conductivity. 7. Degasser Flower The water's dissolved carbon dioxide is removed here. 8. Permeate Storage Tank Water is then pumped to the permeate storage tanks for storage. There are two permeate storage tanks each of capacity 1200 m3.
ION EXCHANGER This filter water is now used for demineralising purpose and is fed to cation exchanger bed, but enroute being first de-chlorinated, which is either done by passing through activated carbon filter or injecting along the flow of water, an equivalent amount of sodium sulphite through some stroke pumps. The residual chlorine which is maintained in clarification plant to remove organic matter from raw water is now detrimental to cation resin and must be eliminated before its entry to this bed. Normally, the typical scheme of demineralization up to the mark against average surface water is a three bed system with a provision of removing gaseous carbon dioxide from water before feeding to Anion Exchange. Resins Resins, which are built on synthetic matrix of a styrene divinely benzene copolymer, are manufactured in such a way that these have the ability to exchange one ion for another, hold it temporarily in chemical combination and give it to a strong electrolytic solution. Suitable treatment is a so given to them in such a way that a particular resin absorbs only a particular group of ions. Cation & Anion exchanger resin Resins, when absorbing and releasing cationic portion of dissolved salts, are called cation exchanger resin and when removing anionic portion is called anion exchanger resin. The present trend is of employing strongly acidic cation exchanger resin and strongly basic anion exchanger resin in a DM Plant. The chemically active group in a cationic resin is SOx-H (normally represented by RH) and in an anionic resin the active group is either tertiary amine or quaternary ammonium group (normally the resin is represented by ROH). The reaction of exchange may be further represented as below: Cation Resin RH + Na ——>R Na +H2 SO, KKHC1 CaCaHNO3 Mg.Mg. In the form of (Resin in H 2CO3 -Removed by chloride sulp-exhaustedaeration in hate, nitrate or form) degassing tower or bicarbonate) Anion Reain ROH +H 2 SO4 ————> RSO4 + H2O HC1C1 HNO3 NO3 (Mineral acids obtained from cation exchangers) Regeneration of resins Recharging the exhausted form of resin i.e. regeneration employing 5% of acid/ alkali as below: Cation Resin Na RK+HCP ———— > RH +NaC 1 CaKC1 2 MgCaC12 MgC12 Exhausted (fresh (removed by resinresing)rising) Anion Resin: R SO4 +NaOH--------> R OH +Na2 (fresh(removed by resin) resin) rinsing)
SO4 ClNaCl NO3NaNO3 (exhausted
As seen above the water from the ex-cation contains carbonic acid also sufficiently, which is very weak acid difficult to be removed by strongly basic anion resin and causing hindrance to remove silicate ions from the bed. It is therefore a usual practice to remove carbonic acid before it is led to anion exchanger bed. The ex-cation water is trickled in fine streams from top of a tall tower packed with rasching rings, and compressed air is passed from the bottom. Carbonic acid break into CO^ and water mechanically (Henry's Law) with the carbon dioxide escaping into the atmosphere. The water is accumulated in suitable storage tank below the tower, called degassed water dump, from where the same is led to anion exchanger bed, using acid resistant pump. The ex-anion water is fed to the mixed bed exchanger containing both cationic resin and anionic resin. This bed not only takes care of sodium slip from cation but also silica slip from anion exchanger
very effectively. The final output from the mixed bed is extra-ordinarily pure water having less than 0.2/Mho conductivity, H 7.0 and silica content less than 0.02 ppm. Any deviation from the above quality means that the resins in mixed bed are exhausted and need regeneration, regeneration of the mixed bed first calls for suitable back washing and settling, so that the two types of resins are separated from each other. Lighter anion resin rises to the top and the heavier cation resin settles to the bottom. Both the resins are then regenerated separately with alkali and acid, rinsed to the desired value and air mixed, to mix the resin again thoroughly. It is then put to final rinsing till the desired quality is obtained. It may be mentioned here that there are two types of strongly basic anion exchanger. Type II resins are slightly less basic than type I, but have higher regeneration efficiency than type I. Again as type II resins are unable to remove silica effectively, type I resins also have to be used for the purpose. As such, the general condition so far prevailing in India is to employ type II resin in anion exchangers’ bed and type I resin in mixed bed (for the anionic portion). It is also a general convention to regenerate the above two resins under through fare system i.e. the caustic soda entering into mixed bed for regeneration, of type I anion resin, is utilized to regenerate type II resin in anion exchanger bed. The concept of utilizing the above resin and mode of regeneration is now a day being switched over from the economy to a higher cost so as to have more stringent quality control of the final D.M. Water.
Mixed Bed Water from the permeate storage tank is pumped to the mixed bed. Mixed bed is basically an IonExchanger. There are three mixed beds but only one of them is operational at a time. The conductivity of water at the inlet of the mixed bed is 0.1% while that required in the I IRSG for steam generation is less than 0.1 %. DM Storage Tank The water from the mixed bed is pumped to the DM storage tank. This is the end-product of the process. This water, de mineralized water, is used for the generation of steam. There are two tanks each of capacity 1200 m3. Even though there is approx. 96'%recovery from the boiler, water is still required in such quantity to steam only a limited number of times before the steam it produces is of poor quality. FILTERED WATER PUMP The soft water so obtained is stored in this chamber and is distributed through lour channels to Reverse Osmosis Dematerializing plant (RODM), Cooling towers (CT), Heat Recovery Steam Generator (HRSG) and Heating Ventilation and Air Conditioning (HVAC). If pre-treatment of the water is not done efficiently then consequences are as follows: SiOg may escape with water which will increase the anion loading. Organic matter may escape which may cause organic fouling in the anion exchanger beds. In the pre-treatment plant chlorine addition provision is normally made to combat organic contamination. Cation loading may unnecessary increase due to addition of Ca(OH)g in excess of calculated amount for raising the pH of the water for maximum floe formation and also AKOrDg may precipitate out. If less than calculated amount of Ca(OH), is added, proper pH flocculation will not be obtained and silica escape to demineralization section will occur, thereby increasing load on anion bed.
FIRE PROTECTION SYSTEM The combined cycle power station represents a large capital investment in high technology plant and equipment, the loss of which would entail disruption to the power system and a larger reduction revenue. It is necessary to protect this investment against fire damage and to this effect an elaborate fire detection and protection system is being provided throughout the power plant. The areas to be protected by fire detection and protection system in a combined cycle gas project are : 1. Power house building consisting of gas turbine generator and its auxiliaries, steam turbine and its auxiliaries and waste heat recovery boiler equipment and its auxiliaries. 2. Gas regulating station 3. Liquid fuel storage and unloading area 4. Cable galleries/spreader room 5. Transformer switchyard and other transformers located in the plant area 6. Various control rooms 7. Administrative office and other auxiliary equipment buildings 8. Covered and uncovered stores The various fire detection and protection system are: High Pressure Water Spray System The high pressure water spray system applies water in the form of a conical spray consisting of droplets of water travelling at high velocity. The automatic operation of flow control/ can be through wet detection or dry detection-Initiation System Separate 2x100% capacity pumps and header is provided for H.V.W. spray system. This system is provided to protect transformer and gas reducing station (for indoor installations) and lube oil storage tanks. Medium velocity Water spray system The medium velocity water system applies water in finely divided droplets travelling at medium velocity to control the fire and the same time renders adjacent areas safe by cooling action. This system is operated manually and protects tanks containing flammable/combustible liquid such as Naphtha. The discharge density shall not be less than 10.2 litres per minutes per sq. metre. Sprinkler System The sprinkler system consists of a pipe work array filled with water having sprinkler needs at laid down intervals which operates at a predetermined temperature. Conventional cable galleries are not provided in the combined cycle power plant, however the spreader rooms where power cable are is protected by sprinkler system.
Detection of fire in cable spreader room is through combination of smoke detector i.e. ionisation type & optical type detector fully cross zoned. Beside this, linear thermal sensors are also used. The discharge density for this system shall not be less than 12.2.Ipm/sq.M Foam Injection System To extinguish the fire inside tanks containing flammable/combustive liquids, foam is produced by mixing foam concentrate with water in the required proportion and aerating the resultant solution. Low expansion floroprotein in foam concentrate is used as foam concentrate. Foam injection is carried out manually only. Foam extinguishing system is provided for floating roof tanks storing Naphtha, tank car unloading manifold and the dyke area surrounding the tanks.
CO2 Extinguishing System After deflected of halon extinguishing system modular CO2 extinguishing system is envisaged in control panels, fuel gas control block of Gas turbine (under sound proof enclosure), GT sound proof enclosure, bearing housing within exhaust diffuser and the cable space below electronic equipment room. These systems are designed to achieve 34% concentration by volume in the areas to be protected and are equipped with optical type and ionisation type smoke detectors. Temperatures detectors are installed in the bearing housing within exhaust diffuser. Fire Alarm System An automatic fire detection system is provided for an early warning throughout the power plant area. This system detects the outbreak of fire at the inception stage and facilities to take remedial action at the initial stage to prevent/reduce damage of costly equipments. Since Combined cycle plant operation is simpler as compared to thermal power plant and the manpower required is less, the computerized early warning system is preferred than the conventional fire alarm system. Computerized addressable type early warring systems which have following advantages: 1. The system has provision for automatic sensitivity compensation 2. Each detector is individually addressed 3. The system has facility for complete data logging. 4. The system is on modular basis and can be expanded at a later date. 5. The interface units are provided for connecting open type alarm initiating devices such as pressure switches, potentials free contracts etc. 6. Exact location of fire can be known from the fire alarm control panel.
Potable Extinguishers Portable pressurised water type and CO 2 type extinguishers are provided at strategic locations inside the entire power station area. For 600 MW combines cycle power plant, approx. 75 nos. water type and 100nos. of CO2 type portable extinguishers are provided.
Air Conditioning Plant Air conditioning is the process to control the air parameters according to the requirement as per the conditions. The parameters that involved in the air condition are: Temperature Humidity Purity For the purpose of the human comfort, the pure air for breathing must involve Temperature: 25 ± 2°C Humidity: 50-60% RH At PPCL there are two main air conditioning plants installed for air conditioning in: Facility building Control room Plant for facility building: Installed by: Temp. Maintained: Relative humidity: Plant for control room: Installed by: Temp. maintained: Relative Humidity:
voltas 25±2°C 50-60%
Blue Star 22±2°C <50%
Voltas Air conditioning Plant Capacity No of units Refrigeration cycle Refrigerant Compressor Type Expansion Design
120 Tons 2 Vapour Compression R22(CHClF2) Reciprocating Capillary tubes
Specifications GT Stages – 3 Ignition speed – 600 Self sustained speed – 1500 Critical speed – 1292/2492 Exhaust temp- 543 ◦C Compressor Stages – 17 Flow – axial o/p – 403 kg/sec pr. Ratio – 12.78 bleeding – 4 points CPHRCP X 3 Stages – 2 Make – Mather Platt Flow- 455 m3/hr Rpm-1482 Power-310 kW Name installed Stages Make Flow(m3/sec) Rpm Power(kW)
CPHRCP 3 2 Mather platt 455 1482 310
CW - STG 3
ACW 3
ECW 3
CW –GT 2x2
12200 490 1075
Mather platt 710 1485 75
Mather platt 710 1485 150
710 1485 150
A COLLAGE OF PPCL SUMMER TRAINNING
