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Combined Cycle Power Plant Combined Cycle Power Plant The Combined Cycle Power Plant consists of two gas turbine - generator units Siemens V 94.2, two heat recovery steam generators, a steam turbine - generator complete with a condenser and condensate / feedwater system and all required auxiliaries. A gas turbine that drives its own generator, exhaust into a special boiler called a Heat Recovery Steam Generator (HRSG) that generates steam for use in Steam Turbine. One of the principal reasons for the popularity of the combined cycle power plants is their high thermal efficiency. Combined cycle plants with thermal efficiencies as high as 52% have been built. Combined cycle plants can achieve these high efficiencies because much of the heat exhaust from the gas turbine(s) is captured and used in the Rankine cycle portion of the plant. Refer figure. The heat from the exhaust gases would normally be lost to the atmosphere in an open cycle gas turbine. Another reason for the popularity of combined cycle plant is that it requires less time for their construction as compared to a conventional steam power plant of the same output. Although it takes longer time to build a combined cycle plant than a simple gas turbine plant. Natural gas Block-3: Combined Cycle Gas Turbine, Compressor, HRSG & Steam Turbine Condensat e Steam Condenser Cooling Gland Steam H P S t o p V a l v e H P S t e a m C o n t r o l Steam Turbine Cycle Rankine Cycle Steam from auxiliary Gas Turbine Cycle Brayton Cycle
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Page 1: Combined Cycle Principles

Combined Cycle Power PlantCombined Cycle Power PlantThe Combined Cycle Power Plant consists of two gas turbine - generator units Siemens V 94.2, two heat recovery steam generators, a steam turbine - generator complete with a condenser and condensate / feedwater system and all required auxiliaries.

A gas turbine that drives its own generator, exhaust into a special boiler called a Heat Recovery Steam Generator (HRSG) that generates steam for use in Steam Turbine. One of the principal reasons for the popularity of the combined cycle power plants is their high thermal efficiency. Combined cycle plants with thermal efficiencies as high as 52% have been built. Combined cycle plants can achieve these high efficiencies because much of the heat exhaust from the gas turbine(s) is captured and used in the Rankine cycle portion of the plant. Refer figure. The heat from the exhaust gases would normally be lost to the atmosphere in an open cycle gas turbine.

Another reason for the popularity of combined cycle plant is that it requires less time for their construction as compared to a conventional steam power plant of the same output. Although it takes longer time to build a combined cycle plant than a simple gas turbine plant. Natural gas is the most common fuel used by combined cycle gas turbine power plants. At KAPCO three fuels are used i.e. Gas, HSD and Furnace Oil.

The main components of a Combined Cycle include the following:

Gas Turbine Diverter Damper

HRSG

Steam Turbine Feedwater Pumps

Condenser and Condensate Pumps

Cooling Tower

Block-3: Combined Cycle Gas Turbine, Compressor, HRSG & Steam Turbine

Condensate Extraction

Pumps

Steam Condenser

Cooling Tower

Gland Steam Condenser

HP S

top Valve R

ight

HP S

team C

ontrol Valve

Steam Turbine CycleRankine Cycle

Steam from auxiliary steam boiler

Left

RightGas Turbine CycleBrayton Cycle

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etc

Introduction to GT V94.2 and STIntroduction to GT V94.2 and ST

1.0MECHANICAL PLANT

The two gas turbines are provided to fire natural gas, high speed diesel oil and furnace oil (heavy fuel oil).

The Siemens V94.2 gas turbines are driving the air cooled generators, which have max. output power of 170 MVA (144 MW at pf = 0.85). The gas turbines flue gasses are directly conveyed to the adjacent heat recovery boilers the energy of which is transferred to the feedwater loop.

The HP-system of the boiler is producing the HP steam. For this purpose it has to be supplied with the right amount of feedwater at any time during its operation: e.g. during start up, load variations etc. Additional it has to produce steam of a specific quality, which means of correct pressure and temperature which varies again with the different operation modes and load conditions. The HP-system generates steam at 60 bar / 530 °C from the thermal energy contained in the GT exhaust gas.

The LP-system of the boiler is producing the LP-steam. For this purpose it has to be supplied with the right amount of feedwater at any time during its operation: e.g. during start up, load variations etc. The LP-steam in the range of 3-10 bar is used for condensate heating and for the feedwater deaeration in the deaerator.

The main steam flows to the steam turbine which drives the air cooled generator of max. 175 MVA (150 MW at pf = 0.85). The steam turbine is designed as a single - shaft machine with separate HP and LP sections. The HP section is a single flow cylinder and the LP section is a double flow cylinder. Turbine bypass system is to dump the extra steam in the condenser during startup and steam unloading conditions. Both the exhaust steam and the bypass steam are condensed by means of a water cooled box type condenser.

Condensate pumps take suction from the condenser hot well and discharge through the gland steam condenser and the LP-preheater to the feedwater storage tank. One condensate storage tank for controlling the water level is provided. The condensate is further deaerated in the feedwater tank to the specified oxygen content. LP-feedwater pumps feed the water from the storage tank to the drums of the preheating system in the HRSG's in order to preheat the feedwater in the feedwater storage tank. An auxiliary steam system supplies steam for the turbine gland sealing and for the feedwater tank heating during start up.

Prepared by: Fazal-ur-Rehman Babar Siemens Gas Turbines V 94.2Cell: 92 322 6729767

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HP-feedwater pumps deliver the feedwater into boiler drums of the steam generators at the design pressure under all operating conditions. The function of the circulating water system is to provide a heat sink for the condenser and remove the heat to the environment via the cooling tower. Further the system is connected with the closed cooling water system via the service cooling water system.

The task of the service cooling water system is to remove the heat absorbed by the closed cooling water system in cooling components of the gas turbine generator, the steam-, condensate- and feedwater cycle via the closed cooling water heat exchanger and to transfer this heat to the circulating water system.

A water treatment plant consists of a make-up water demineralization plant, regeneration station with chemical storage tanks and regeneration wastes neutralization is installed with all necessary equipment for satisfactory operation of the CCPP.

Furthermore a chlorination plant for the main circulating water system and for the fresh water (Muzafargarh Canal) system is installed.

2.0ELECTRICAL SYSTEM

The figure 1.1 shows the electrical systems configuration of the CCPP in a simplified manner. Each gas turbine generator unit and the steam turbine generator unit are interconnected via its own main transformers to the 220 kV switchyard.

The gas turbine generator is capable of being fully automatically started by electrical energy fed from the main grid via 220/11 kV main unit transformer and the unit auxiliary transformer. The steam turbine generator unit can be started via the 11 kV switchgears either from unit 13 or from unit 14 which are connected by means of bus-coupler to the 11 kV switchgear of the steam turbine generator.

The auxiliary power system is designed to meet all plant auxiliaries and related buildings service requirements. Power for the auxiliary power systems is fed from the unit auxiliary transformer via the 11 kV switchgear. Low voltage auxiliary transformers supply the 380 V unit switchgear as a 100% back-up. The second supply is interlocked from the first, so that an operation without interruption shall be possible.

The emergency diesel set has sufficient capacity for emergency supply of the units, turning gears and emergency light. The capacity covered the gas turbine units as well as the steam turbine unit.

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The DC system consists of a 220V DC and 24V DC system. The 220V DC system feed all power, control and protection equipment as required. The 24V DC system feed the I & C equipment and the protection equipment as required. The capacity of each battery charger is 100% of the power requirements of the whole plant extension. Each battery is designed to allow for normal operation as well as for safe shut-down of the plant in case of a total black-out.

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3.0CONTROL SYSTEMThe CCPP plant features a high level of automation with plant start up, operation and shut down being carried out by the TELEPERM ME control and data acquisition system. For the control system the total plant is divided into following five functional areas:

1. Gas Turbines2. Heat Recovery Boilers3. Water/Steam Cycles4. Steam Turbine5. Auxiliary Plant

The I & C equipment associated with these functional areas is distributed throughout the plant and transmit the measured values and plant status information to local processing units contained within Power Control Centers. These PCC's are prefabricated units and enclosed in containers where also the plant related switchgear is arranged.

The Central Control is located in the Control Room Building 15 UCA (CCR-3). Information transfer between the control room and the local plant is achieved via a duplicated data highway. Central redundant data acquisition and control processors are located in the control room building for alarm monitoring, logging and plant status display. The interface between plant and operator is located in the both central and local control rooms. From here, all plant control functions can be carried out during both normal and emergency situations.

At Block-3, for the process automation of the CCPP, the TELEPERM ME process I & C system is used. Its functions are: acquisition and processing of process data, open and closed-loop control, calculation and optimizing as well as supervision, signaling, operation and monitoring of the process in interactive mode on the screen and using miniaturized control room equipment.

4.0Start-up from Unit Coordination ProgramThe plant can be operated in a simple-cycle and a combined-cycle operation.

Simple-Cycle OperationThe procedure for startup of the gas turbine in simple-cycle operation is as follows:

- Diverter damper upstream of the steam generator closed, bypass path open

- Starting of gas turbine, purging of the turbine through bypass stack during runup to ignition speed

- Ignition of the gas turbine burners- Runup to rated speed and loading of the gas turbine

Combined-Cycle Operation

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Page 7: Combined Cycle Principles

Two procedures are possible for startup of the heat recovery steam generator (HRSG):

- Startup of the gas turbine as a function of output load control- Startup of the gas turbine as a function of exhaust temperature

control

The gas turbine is started up as described in the simple-cycle operation, however, the gas turbine exhaust gas temperature is kept below < 350 °C. After the purging process (for 1 min), gas turbine output is increased to rated power. The rated temperature is achieved at about 60% gas turbine output. Startup of the HRSG is performed by opening the diverter damper upstream of the steam generator and thus simultaneously closing the bypass path.

In the case of gas turbine startup under temperature control, the bypass path remains closed after the steam generator has been purged. The gas turbine load is controlled at the permissible temperature transients for the thick-walled components of the steam generator, piping and steam turbine.

For gas turbine startup under load control, the diverter damper is set at an intermediate position after the steam generator has been purged such that the cross-section of the line to the steam generator is opened by about 20%. After expulsion of the water and when the level in the drums stabilizes and the steam temperature is almost equal to the gas turbine exhaust gas temperature, the diverter is opened in stages. Whenever a temperature change in the HRSG permits, a defined time pulse is released to open the diverter damper a stage further.

The main steam line is warmed up, in accordance with a specified mean warmup transient, for the leading item (strainer casing). Controlled warmup of the LP-steam line to the feedwater tank is not necessary owing to the reduced wall thickness.

The steam turbine is started up under speed control. As soon as the generator is synchronized with the grid system, the valve lift, which is limited by the Turbine Stress Evaluator (TSE), is increased by the startup control until the turbine assumes the full steam mass flow, the turbine bypass station closes and the initial pressure controller is activated.

The pressure in the LP-evaporator system is governed by the LP-startup station. If sufficient hot steam is extracted to the feedwater tank, the LP-startup station closes and lowers the response setpoint.

5.0Plant Design According to Weather Conditions The HRSG / Steam Turbine plant are capable of utilizing the exhaust gas from the gas turbines when operating over full range of operating conditions up to base load according to Kot Addu site ambient temperatures from 1 °C to 50 °C (design temperature) and at relative humidity of up to 80 % (design ambient relative humidity for electrical and I & C equipment).

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Page 8: Combined Cycle Principles

The machines are designed according to the following performance data:

Ambient Temperature = 30°C,Relative Humidity = 60 %Atmospheric Pressure = 0.996 bar.

The electric output of Block-3 (GT-13, 14 & ST-15) is 406 MW (Net Power Output = 397 MW), 129 MW from each gas turbine and 148 MW from the steam turbine. The heat input amounts to 818 MJ/sec so that the overall net efficiency is 48.5 %.

Combined Cycle ComponentsCombined Cycle ComponentsSome of the components are described here;

1.0 The Gas TurbineThe first major component of the combined cycle power plant is the gas turbine. Gas Turbine is a machine which runs with the action of flue gases on its turbine blades. Flue gases are produced by burning the fuel. When gas turbine exhausts directly to the atmosphere, it is said to be operating in "open cycle" mode. When a gas turbine exhausts into a heat recovery steam generator (HRSG) the resultant steam is used to operate a steam turbine, this operation is called “combined cycle”.

A model of gas turbine 13, 14 is shown. Unit 13, 14 gas turbines consist of a single body including 16 stage Compressor, 2 Combustion Chambers and 4 stage Turbine. The turbine rotor has two bearings one at the air inlet of compressor side and second in the turbine exhaust. The body is divided in various planes to facilitate inspection. Mechanical power generated in the turbine is used to drive both the compressor and the generator. The electric power is available at the generator terminals in 11KV.

The gas turbine uses air as working fluid which is drawn in through filters and sound absorbers, it is compressed in the compressor up to 10 bar. Compressed air is directed into the combustion chambers. Fuel is added and burnt in the combustion chamber, and the resultant flue gas is heated up to approx. 1050 °C for the turbine inlet. The hot gases are expanded to atmospheric pressure in the turbine and transfer their energy to the turbine blades, where its energy is used to drive the shaft. The compressor and turbine blades are arranged on a common shaft and connected to the generator via the intermediate shaft. The exhaust gases leave the turbine through the

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Page 9: Combined Cycle Principles

exhaust diffuser for being discharged into the bypass stack or to the HRSG for combined cycle operation.

1.11.1 Main Components of a Gas TurbineMain Components of a Gas Turbine1.1.1Intake Air Filters

These provide clean, filtered and dust free air to the compressor inlet.

1.1.2Compressor

Air is drawn in and compressed when passing through rows of rotating blades and stationary vanes. At the end of the compressor, before reaching the combustion chamber, the air is compressed to about 10 bar and has been heated to about 300°C by compression.1.1.3Combustor / Combustion Chamber

The combustor or combustion chamber is the heart of the engine; here the combustible mixture of compressed air and fuel is burnt. The hot gas output temperature becomes 1000°C to 1300°C; its volume becomes more than doubled by the temperature rise where as pressure remains constant.

1.1.4Turbine

The turbine section converts the thermal and kinetic energy of the combustion gases into rotational mechanical energy. Gas turbines like steam turbines have three or four stages of rotating and stationary blades. However; because gas turbines work with lower initial inlet pressures, they have fewer stages and less change in blade height from inlet to exhaust. Turbines normally consist of combination of impulse and reaction types. The gas turbine also differs from the steam turbine in;

(1) the type of blading material used(2) the lower ratio of blade length to wheel diameter(3) less number of turbine stages

Flue gases flow to the turbine with a very high velocity v of about 80 m/s (288 km/hr). It means it has high kinetic energy ½mv2. The kinetic energy of flue gases is converted to mechanical energy when flue gas is expanded in the stages of turbine transferring its energy to the turbine rotor. The volume of flue gases is increased by expansion and thus temperature is decreased and at the exhaust it is about 500 °C.

The turbine parts which are mechanically stressed are at the same time subject to very high temperature, so that these parts are designed with special material and cooling paths are provided for cooling air to flow.

1.1.5Exhaust diffuser

It diverts the de-energized (but still hot) flue gases into the ambience to complete the cycle. It is fitted with filter and silencer.

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2.0 Heat Recovery Steam Generator (HRSG)The HRSG is basically a heat exchanger composed of a series of economizer, evaporator and superheater sections. These sections are positioned from gas inlet to gas outlet to maximize heat recovery from the gas turbine exhaust gases. The heat recovered in the HRSG is used to supply steam to the steam turbine at the proper temperature and pressure. The exhaust gases temperature leaving turbines are in the range as given bellow:

Unit No. Exhaust temperature Steam flow rate1 & 2 500 °C to 550 °C 205 Tons/hour on Gas

220 Tons/hour on FO3 & 4 550 °C to 610 °C 210 Tons/hour5 – 8 480 °C to 530 °C 150 Tons/hour on Gas

160 Tons/hour on FO13 & 14 530 °C to 550 °C 203 Tons/hour on Gas

200 Tons/hour on FO

High temperature gas represents a source of heat energy, some of which can be recovered thus the output and the efficiency of a combined cycle power plant is increased.

The function of a heat recovery steam generator (HRSG) is to recover the waste heat available in these exhaust gases and transfer that waste heat to water and steam. The heat is used to generate steam at high pressure and high temperature. The steam is then used to generate additional power in a steam turbine driven generator. The HRSG provides a link between the gas turbine and the steam turbine in a combined cycle plant. Therefore, the HRSG is a key component in combined cycle efficiency.

2.12.1 Main Components of an HRSGMain Components of an HRSG2.1.1Diverter Damper

At outlet of the gas turbine, upstream the boiler, a diverter is provided which makes it possible to send the exhaust gas directly to the atmosphere, by means of a bypass stack or to heat the boiler by opening the path towards the HRSG. The diverter is provided with hydraulic actuators. The actuators have been sized to permit intermittent operation of the damper to a predetermined position, but not regulated control. The ‘close position’ is with the blade closed to HRSG and the open to bypass stack. The ‘open position’ is with the blade open to HRSG and the close to bypass stack.

The diverter damper is actuated through the various modes of operation by an electrically controlled hydraulic system. This hydraulic system comprises an independent, self contained power unit connected electrically and hydraulically to the diverter blade.

The power unit consists of a weather proof enclosure containing a system of two motor pump units, one control valve assembly, a hand pump system and 3 hydraulic accumulators.

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Page 11: Combined Cycle Principles

2.1.2Water & Steam Heaters

The water and steam are heated at different steps according to the flue gas temperature. These include HP Economizer, HP Evaporator, LP Evaporator and Superheater.

2.1.3Drums

HP drum and LP Drum or LP separator tank are installed to separate steam from water.

2.1.4Pumps

These pumps are installed for the circulation of water and they include HP Feedwater pumps or HP Evaporator recirculation pumps, LP Feedwater pumps or LP Evaporator recirculation pumps, HP Economizer recirculation pumps etc.

2.1.5Soot Blowers

They clean soot deposits from the tubes on flue gas side of the Boiler.

3.0 Steam TurbineThe Steam Turbine is a power unit which produces power from a continuous action of steam on its turbine blades, the steam being delivered to the turbine at a high pressure and exhausted to the condenser at a low pressure.

Steam turbine converts the heat energy of superheated high-pressure steam, coming from the boiler or HRSG, into rotational mechanical energy. The conversion of energy in the turbine occurs in two steps.

First, the heat energy in the steam is converted into kinetic energy of a steam jet by nozzles (stationary blades).

Second, the steam jets blow on buckets or moving blades mounted on a rotor to produce a mechanical force and torque.

The mechanical energy of the steam turbine is then used to drive a generator to produce electrical energy. The steam turbine generator is, by itself, a very simple machine with few moving parts. It is not unusual for a steam turbine-generator to operate continuously for more than a year without shutdown.

3.13.1 Main Components of a Steam TurbineMain Components of a Steam Turbine3.1.1Turbine

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Page 12: Combined Cycle Principles

The turbine converts the thermal and kinetic energy of the steam into rotational mechanical energy. ST-15 has 26 stages of HP and 8+8 stages of LP turbine and their sealing steam system. There are two types of turbine blades, Impulse and Reaction types. Normally, turbine consists of combination of impulse and reaction types.

Turbine PrincipleSteam enters the rotating channels with absolute velocity ‘c’ with reference to the fixed parts. When magnitude and direction of both velocities are known we get the relative velocity ‘w’ with reference to the rotating blades. Circumferential velocity ‘u’ at rotating blade tip can be calculated by the difference of ‘c’ and ‘w’.

Impulse Type Turbine

The basic idea of an impulse turbine is that a jet of steam from a fixed nozzle pushes against the rotor blades and impels them forward. The velocity of the steam is about twice as fast as the velocity of the blades. Only turbines utilizing fixed nozzles are classified as impulse turbines.

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Velocities in Steam Turbine Stages

Rotating wheel

Guide wheel

Stage 1 Stage 2

Guide wheel

c absolute velocity

w velocity in rotating channel

= relative velocity

u circumferential velocity

Indices

1 Inlet rotating wheel2 Outlet rotating wheel

U1 = C1 – W1

U2 = C2 – W2

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Reaction Type TurbineA reaction turbine utilizes a jet of steam that flows from a nozzle on the rotor. Actually, the steam is directed into the moving blades by fixed blades designed to expand the steam. The result is a small increase in velocity over that of the moving blades. These blades form a wall of moving nozzles that further expand the steam. The steam flow is partially reversed by the moving blades, producing reaction on the blades. Since the pressure drop is small across each row of nozzles (blades), the speed is comparatively low. So more rows of moving blades are needed in a reaction turbine than in an impulse turbine.

3.1.2Condenser and Vacuum Pumps

It condenses steam when it finishes its work and exit from the turbine. Vacuum pump regularly runs to evacuate any air accumulation in the condenser.

3.1.3Cooling Tower

This is provided to cool the close circulating water from the condenser. It removes the latent heat of steam and converts it into condensate.

3.1.4Lube Oil system

It supplies lubrication and cooling for all bearings like compressor, turbine, generator and supplies oil to the hydraulic oil system, torque convertor and turning gear.

3.1.5Generator

The generator is connected to the gas turbine. Generator converts the mechanical output power of the gas turbine into electricity. When rotor rotates in the stator, there is a relative motion between conductor and rotor’s magnetic field. Voltage is induced by this relative motion into the three coils of stator winding. When north and south poles of rotor magnetic field pass before a stator winding then alternating currents of sinusoidal (~) wave shape are produced. In this way three phase currents are produced by the three phases of stator winding as shown in figure.

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132 KV

Page 14: Combined Cycle Principles

The generator is air cooled in closed circuit. Generator output is at 11KV; it is stepped up by main transformer to 132 KV or 220 KV and sent to WAPDA via transmission lines.

2.0Thermodynamic Cycles2.12.1 Gas Turbine (Joule-Brayton) CycleGas Turbine (Joule-Brayton) CycleThe thermodynamic cycle of a gas turbine is referred to as the Joule-Brayton Cycle (or simply Brayton Cycle). The four processes of the Brayton Cycle are represented on a temperature-entropy (T-s) diagram shown in figure. Entropy is a property of substances that describes the availability of energy to do work. The T-s diagram is useful in analyzing thermodynamic cycles because it reveals the amount of heat required to make a process occur in a cycle. If a process can be represented as a curve on the T-s diagram, the area under the curve is the amount of heat required to make that process occur.

Each process in the Brayton Cycle can be drawn on the T-s diagram. The first process is the compression of air in the compressor represented by the line A-B. As the air is compressed, its temperature and pressure increases and there is a corresponding increase in enthalpy. As work is done on the air, the air stores this energy in the form of temperature and pressure. The power (energy) to perform this work originates from the turbine, which is directly coupled to the gas turbine compressor through a common shaft.

The second process is the addition of heat to the cycle at a constant pressure by burning of fuel represented by the line B-C. The temperature of the gas that results from the combustion increases considerably from the temperature of the air at the compressor outlet. Normally air temperature at the compressor outlet is 300°C and the flue gas temperature is increased up to 1000°C or 1300°C.

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Compression

CombustionHEAT ADDED

HEAT REJECTED

Expansion (Turbine)

Brayton CycleT-S Diagram

Tem

pera

ture

Heat

Four Processes of Gas Turbine

Compression A-BCombustion B-CExpansion C-DHeat Rejection D-A

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The third process is the expansion and cooling of the gas as it passes through the turbine, is represented by the line C-D. Here, the energy of the hot pressurised gas is used to perform work.

The final process in the Brayton cycle is the cooling of the hot gas that exhausts to the atmosphere represented by line D-A. The exhausted gas mixes with ambient air, thus decreasing in temperature.

Amount of heat that is required to make Brayton cycle work is represented by the area under lines B-C. The area under the line D-A represents the fraction of heat that is rejected. The area between these two lines represents the heat that is converted to useful mechanical energy. The heat converted to useful mechanical energy is 20% to 25% of the total heat required to make the process work.

2.1.1Thermodynamics of Gas Turbine

The energy at the input is available as fuel (furnace oil or gas) and it represents chemical energy. At the output we have energy in the most valuable form as electrical energy. Electricity is easily transported, easily controlled and easily applied at all instances when energy is used. There are several steps when energy is converted from its chemical form to electrical form:

Step 1: Chemical energy is converted to thermal energy (heat) in the form of a flow of hot "flue gases".

Step 2: Heat energy is transformed to kinetic energy by increasing speed of flue gases in nozzles.

Step 3: Flue gases act on rotor blades and rotate, in this way kinetic energy is converted to mechanical energy.

Step 4: The mechanical energy is used to drive the generator rotor, and it is converted to electrical energy.

Energy Conversion Processes :Chemical Energy Heat or Thermal Energy Kinetic Energy Mechanical Energy Electrical Energy

Now we look at first two steps more closely.

2.1.2Cyclic Process

These first two steps are only possible as parts of a thermodynamic cyclic process because nature does not grant any gifts without being paid; i.e. we must come back to the initial conditions where we started.

Such a cyclic process describes how the fluid changes its state during its flow through a given machine. State of the fluid can be

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STEP 4

Generator loss(0.8 %)

ExhaustHeat Energy(61 %)

Air

Turbinemechanical loss(0.5 %)

Combustion Chamberradiation loss (2 %)

CompressorMechanical loss(0.5 %)

FUEL

STEP 1

STEP 2& 3

Page 16: Combined Cycle Principles

described by a couple of parameters which are inter-dependent. These parameters are:

- Pressure P- Temperature T- Entropy S

We use these parameters to draw "T-S diagrams" which apply to the actual fluid. For our present considerations we can use the T-S diagram for air which is applicable for flue gas, too. In the range of cyclic processes we commonly use the laws for ideal gases which are valid here. By means of T–S diagrams

- cyclic processes can be made apparent- cyclic processes can be evaluated how efficient they are- we learn how the machine has to be designed in which a given cyclic process takes place.

In the following we apply these three uses to our gas turbine process:

2.1.3Gas Turbine Cycle of GT 1,2 & 13,14

The ideal gas turbine process normally applied named "Joule-Brayton - Cycle" is defined by two isentropic and two isobaric changes of state.

It begins at ambient conditions and an isentropic compression of the fluid (air). It means that the change of state of the fluid is made at constant entropy, i.e. free of any friction and free of any heat transfer across the boundaries of the machine. At the end of this ideal compression, both pressure and temperature are increased but entropy remained the same. Now heat is added to the fluid by burning the fuel in the compressed fluid. Thus, entropy and temperature are increased but pressure remained the same. Hereafter the flue gas is expanded during an isentropic change of pressure and temperature. The flue gas is now at ambient pressure again but at elevated entropy and elevated temperature.

In order to complete the cyclic process the flue gases are blown into the atmosphere and the energy content is dissipated, i.e. wasted. This is the price we must pay for having converted the energy from a lower to a higher value.

2.1.4Evaluate

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7

°C

kJkg °K

8

Ideal Joule – Brayton Cycle

Tem

pera

ture

Expansion(Turbine)

Exhaust

Ambient Conditions

Specific Power available at Coupling Flange

Entropy

Heat Input(Combustion)

Evaluation of Energy1 square is equivalent to 20 MW

-100

0

100

200

600

400

800

1000

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The T-S diagram is handy for representing energy and heat per fluid mass unit. These values appear as areas; e.g. 1 square shown on the T-S diagram is equivalent to 20 MW.

It means, that if we know the mass-flow we can easily calculate

- the power available at the coupling flange- the heat to be put in

Flue gas mass flow:

Unit 1, 2 Unit 13, 14 Unit 3, 4 Unit 5-8426 Kg/sec 471 Kg/sec 322 Kg/sec 406 Kg/sec

2.22.2 The SteamThe Steam--Water (Rankine) CycleWater (Rankine) Cycle

The Rankine Cycle used in conventional steam power plants can be represented on a T-h diagram. As with the Brayton Cycle, each line segment corresponds to a process in the cycle. A simple Rankine Cycle consists of only four components; the boiler (often called a steam generator), a turbine, a condenser and a boiler feed pump. Boiler is shown with a superheater, thus the steam entering the turbine is above saturation temperature.

The first process in Rankine Cycle (Line 1-2) is the increase in pressure of condensate from condenser by the boiler feed pump. Increase in pressure occurs with a slight increase in enthalpy (h).

The second Rankine Cycle process (Line 2-3) is the addition of heat to water entering the boiler. Within the boiler, the water is transformed from a liquid to steam (a gas). The generation of steam is assumed to occur at a constant pressure. Additional energy is added to steam as it passes through the superheater (Line 3-4). Steam is then expanded and cooled as it passes through the turbine as represented by Line 4-5. Here, the energy of steam is used to perform work.

The last process in the Rankine Cycle is the condensation of steam that exhausts from the turbine, represented by line 5-1. During

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Figure: Rankine Cycle T-h diagram

Boiler

Boiler Feed Pump

h

T

HEAT ADDED

HEAT REJECTED

Steam Turbine

Super heater

Condenser

Boiler Feed Pump

Condenser

Steam Turbin

e

Super heater

Boiler

1

2

3 4

5

Page 18: Combined Cycle Principles

condensation, considerable heat, called the latent heat of vaporization, is lost.

The heat required to make the Rankine Cycle work is determined by the area under the lines between points 2 to 4; and the heat lost from the cycle is under the line between points 5 and 1. The area between the lines represents the heat that is converted to useful mechanical energy. The useful mechanical energy is only about ⅓rd of the heat required to make the cycle work.

The efficiency of conventional steam power plants is about 30% to 35%. Actual steam power plants are considerably more complex than the simple cycle shown in Figure, because components such as Condensate pump, Feedwater tank, Economizer, LP & HP Feedwater heaters and Air preheater are added to improve efficiency. Typically only 85% to 90% of the heat energy input is absorbed in Boilers. This means that the boiler is only 85% to 90% efficient. Additional auxiliary equipment, such as fans and soot blowers, use part of the power produced usually around 5%.

2.2.1Actual Steam - Water Cycle / T-s diagram

The T-s diagram (Fig 4.3) illustrates the thermodynamic conditions and parameters in the actual water- steam cycle.

Clausius established entropy in mathematic formulas in order to determine transformability of heat energy. Later on Belpair found that principle of entropy can be presented by areas of transferable amounts of heat in the T-s diagram.

If one follows the various stages of the water-steam cycle, they can be presented in the T-s diagram. The area below the curve depicts the supply or release of heat energy in order to reach a new condition. The temperature axis must then however be extended to the absolute "0 °K" point. In calculations temperatures are stated in Kelvin, which means the origin in the diagram is 0 °K (- 273.15 °C).

The region of wet steam can be easily recognized in the T-s diagram. The hill, the left margin of which equals x = 0, that is pure water, is remarkable. The right curve represents saturated steam (x = 1). All points in between these margins depict wet steam with a certain share of water.

One must be careful, because the diagram shows the specific entropy ‘s’ in units of kJ/kg/°K. So you should keep in your mind, that the shown values of entropy are good for 1 kg of the media at the given point.

This T-s diagram shows the turbine cycle all over the Plant i.e. Steam Turbine and HRSG. It starts with the condenser outlet to the feedwater tank. The area underneath this line is the amount of heat brought to the cycle from the LP evaporator into the feedwater tank by the LP steam.

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Outlet Superheater

HP-Turbine Outlet

Condenser Inlet

h [kJ/kg]v [m3/kg]p [bar]

Values at Triple Point:p = 0.006112 barT = 0.01 °Cs = 0.00 kJ/kg/°K (arbitrary)

Values at Critical Point:p = 221.2 bar (3206.2 psia)T = 374.15 °C (705.4 °F)

v = 0.00317 m3/kgh = 2107.4 kJ/kgs = 4.4429 kJ/kg/°K

(0.00 °C = 273.15 °K)

HP-Drum Inlet

100

200

300

400

500

600

T [°C]

01 2 3 4 5 6 7 8 9s [kJ/kg/°K]

s = Specific Entropy

T =

Tem

pera

ture

HP-Drum Outlet

Feedwater Tank

Condenser Outlet

1 2 3 4 5 6 7 8 9

100

200

300

400

Page 20: Combined Cycle Principles

The area underneath the line feedwater tank to HP drum inlet shows (theoretically) the amount of heat drawn from the exhaust gases by the economizer. The HP evaporator draws the heat underneath of the horizontal line in between HP drum inlet and HP drum outlet. The superheating is done nearly at the same pressure, but up to higher temperature. The steam condition becomes far away from the saturated condition, so the end of the turbine gets better conditions concerning the arising of water. Due to the heat transfer for superheating the enthalpy will rise too, gives the turbine a higher "capacity of work".

The arising heat underneath of the line "outlet superheater" to "condenser inlet" is the heat, Clausius was thinking of Conversion of heat energy into mechanical energy causes a rising of the entropy, which is sometimes explained as an arising of losses. These losses in that connection are losses due to "intermolecular friction", not losses to the environment.

The amount of heat shown underneath the line "condenser inlet" to "condenser outlet" has to be given to the environment to condensate the steam of the turbine and to close the circuit. To calculate the real amount of heat, one has to multiply this value with the actual mass flow.

2.32.3 The Combined CycleThe Combined CycleCombined cycle is a power plant in which consists of a gas turbine, Boiler and a Steam Turbine. In this cycle a gas turbine is connected to a steam turbine via a boiler. The steam turbine cycle makes use of much of the heat in the gas turbine exhaust gases. Thermodynamically, the combined cycle can be represented by joining the high temperature Brayton cycle with the moderate pressure and temperature Rankine cycle. An example of a combined cycle showing the Brayton cycle (gas turbine) and the Rankine cycle (steam turbine) on a T-h diagram is shown in Figure.

The area enclosed by the Rankine cycle is within the area that represents the heat rejected from the Brayton cycle. Thus, the Rankine cycle area represents the heat energy that is converted to useful mechanical energy that would other-wise be rejected to the atmosphere. A large portion of the heat lost from the Brayton cycle is used in the Rankine cycle. A much greater fraction of the heat added to the cycle is actually converted to useful mechanical energy in the combined cycle than either the Brayton cycle or the Rankine cycle alone. The Rankine cycle parameters (pressure and temperature) are selected to match the temperature of the available gas turbine exhaust gases. Usually, the pressure and temperature used in the Rankine cycle portion of the combined cycle plant are much lower

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Gas Turbine Cycle

Heat Rejected

Combined Cycle T-h Diagram

Steam Turbin ce Cycle

Page 21: Combined Cycle Principles

than those used in conventional Rankine cycle plants. The lower pressure and temperature are necessary because the gas turbine exhaust gas, while very hot, is not nearly as hot as the flue gas entering the convection pass of a conventional fuel fired boiler.

The challenge in joining the Brayton and Rankine cycles in a combined cycle plant is the degree of integration needed to maximize efficiency at an economic cost. The simple combined cycle can consist of a single gas turbine, HRSG, steam turbine, condenser and auxiliary systems. In addition, if the environmental regulations require, an emissions reduction system can be directly integrated within the HRSG.

Advantages of a Gas Turbine

1. Its operation is simple, can be started quickly and can be put on load in very short time. For these reasons, gas turbine power plants are able to meet peak - load demand, such as at evening peak.

2. They require lower capital investment and occupy less space. The starting cost of the plant is lower than equivalent steam power plant.

3. The time required for their construction is short. The plant does not require heavy foundation and a large building.

4. The maintenance of the plant is easier and maintenance cost is lower.

5. The lubrication of the plant is easy. In this plant lubrication is needed mainly in compressor bearing, turbine bearing and bearing of auxiliary equipment.

6. The gas turbine power plant requires less water as compared to condensing steam power plant.

7. Gas Turbine auxiliary consumption is very less and there are very little standby losses in the gas turbines as compared to a Steam Turbine.

8. There is a great simplification of the gas turbine power plant over the steam turbine power plant due to less auxiliaries and absence of boilers with their feed water evaporator and condensing system.

Disadvantages of a Gas Turbine

1. Major part of the work developed in the turbine, about 60%, is used to drive the compressor. The remainder of the turbine work is available to produce power by driving a generator. Therefore network out put of the plant is lower.

2. For it starting purpose starting motor is required.

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3. Since the temperature of the parts in the combustion becomes too high, so services conditions become complicated even at moderates pressures. Similarly, the first stage turbine blades face high temperature flue gases, therefore these are made with special material and these are coated with high temperature material.

4. On open cycle its thermal efficiency is low and it is about 34%. However in combined cycle mode the overall thermal efficiency is can be even higher than 45%.

General Definitionsa. Newton

The force required to give a mass of 1 Kg an acceleration of 1 m/sec2.

b. JouleWork done is 1 joule when a force of 1 Newton moves a body by 1 meter.(1 joule = 1 Newton-meter).

c. WattPower is the rate of doing work. One watt is the power or rate of doing work when 1 joule of work is done in 1 second. (1 watt = 1 joule/sec).

d. CalorieThe calorie is the quantity of heat required to raise the temperature of one gram of water one degree centigrade (more accurately, from 15.5 to 16.5 °C).The multiple is the kilocalorie, quantity of heat required to raise the temperature of 1000 grams of water one degree centigrade.The "thermie" equal to 1000 kilocalories, is the quantity of heat required to raise the temperature of 1000 kilograms of water one degree centigrade

e. BTU (British Thermal Unit)BTU is the quantity of heat required to raise the temperature of 1 pound (1lb) of water by one degree Fahrenheit (1°F) (more accurately, from 63.5 to 64.5° F).

1 BTU = 252 calories = 0.252 kilocalorief. Calorific Value

It is the heat evolved by burning a unit mass of fuel. For example 40,200 kJ of energy is released when one kg of Furnace Oil is burnt and 32,400 kJ of energy is released when 1 M 3

of Gas is burnt.

g. Fuel Equivalent210 Ton Fuel Oil = 9.9 MMCF of Gas = 1 GWh

h. Specific Heat

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The specific heat of a substance is the heat in calories required to raise the temperature of one gram of the substance one degree centigrade.In effect there are two sorts of specific heat:

i. Cv - specific heat at constant volume,Quantity of heat required to raise the temperature of the mass unit of the gas, one degree centigrade, at constant volume.

j. Cp - specific heat at constant pressure,Quantity of heat required to raise the temperature of the mass unit of the gas, one degree centigrade, at constant pressure.Note: the ratio Cp/Cv generally is labeled .Besides, it is important to note that in the processes that constitute the thermodynamic cycle of a gas turbine, Cp can be considered as constant.

k. Latent HeatIt is the heat used to change the state of a substance e.g. change of state from water to steam at the same temperature in HP evaporator. Similarly it is the heat rejected (to cooling tower) in condenser when turbine exhaust steam at 40 °C is converted to water (condensate) at the same temperature.

l. Entropy (S)It is the heat quantity evolved in a process when the temperature considered uniform during the process. S is expressed in calories per degree centigrade.

m. Enthalpy (h)It is the heat supplied to the fluid at constant pressure. It is measured in kJ/kg. The fall of enthalpy is equivalent to mechanical work output.

n. Net Power and Work Output (P, W)are those available at generator terminals.

o. Power and Work at Turbine Flanges (P f , Wf)are those directly available from the sole engine, before reduction gear, auxiliaries, etc.

p. Specific Power (Ps )is the power output for each mass flow unit running the cycle.

q. Specific Work (Ws )It is the work obtained from the mass unit running a cycle.

r. Mechanical Efficiency (m )is the ratio between the work output at turbine flange and the internal work of the gas on the blades.

s. Combustor Efficiency (b )

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Page 24: Combined Cycle Principles

is the ratio between the heat actually supplied to the gas in the engine combustion system and the heat that a fully burned fuel should have released.

t. Overall Efficiency (g )is the ratio between the net power output and the product of fuel flow multiplied by its lower heating value.

u. Heat Rate (HR)is the inverse of the Overall Efficiency. It is the heat in BTU or kJ required to generate 1 kW of energy.

v. Thermal Efficiency (t )

This equation shows that thermal efficiency depends upon pressure ratio only which relates to the compressor.

w. Exhaust Temp Calculation

This equation shows that thermal efficiency depends upon pressure ratio only which relates to the compressor.

x. Pressure RatioIt is the ratio of compressor discharge pressure to the inlet pressure;

y. Work RatioIt is the ratio of Net work and Gross work;

Electrical definitionsa. Coulomb (C)

It is the quantity of charge of 6.02 1023 electrons or protons.

b. Ampere (A) It is the unit of current and it is equal to 1 coulomb charge flowing in 1 second.

1 Ampere = 1 Coulomb/sec.

c. Volt (V)

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Pressure ratio rp =

P2

P1

t = 1 – 1

rp(1– 1/)

where:rp = pressure ratio = 1.4 (a constant for flue gas)

Work ratio =

Net workGross work

work of expansion – work of compression

work of expansion

=

Tf = Tx × CPDPatm

k

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The potential difference is 1 Volt if 1 Joule of work is done for moving 1 Coulomb of charge between two points. (1 V = 1 J/C).

d. Ohm (Ω) It is the resistance in which a dc current of 1 Ampere generates heat at the rate of 1 joule/second (1 watt).

e. Watt (W) It is the unit of power (P). Between two points if the potential difference is 1 volt and current is flowing 1 Ampere then the electrical power is 1 watt. (P = V I). 1 kW = 1000 watt. Domestic electric energy meters measure electricity in kWh (1 Unit = 1 kWh), it means 1 Unit of electricity is consumed if an electric iron of 1000 watt work for 1 hour or if a bulb of 100 watt light for 10 hours.

Gas Turbine Terminology

TurbineIt is a mechanical component in which the thermal energy of the working medium is converted to mechanical energy by kinetic action on a rotary element.

Single shaft turbineSuch turbine in which turbine and compressor are on one shaft is called single shaft turbine.

Turbine stageIt consists of a set of stationary nozzles and one row of moving blades which are mounted on one disc.The flue gas expands through the stationary nozzles to a lower pressure, thus releasing kinetic energy which is absorbed by the moving blades.

Turbine rotor blades or Bucket (GT 5-8) Aerofoil sections mounted on a rotor disc and proportioned to transfer energy from the flue gas volume to the turbine rotor.

Turbine stationary blades or Nozzles (GT 5-8) or Diaphragm (GT 3,4)A stationary element of the turbine blades used to expand the flue gas and increase its velocity by reducing pressure and direct it against the rotating blades.

Axial compressorThe mechanical component through which the air pressure is increased.

Compressor bladesAerofoil sections mounted on a disc and proportioned to press the air through each successive row of compressor stationary blades or diaphragms.

Compressor stationary blades or diaphragmsA stationary element containing a set of stator blades used to compress the air and direct it towards the rotating blades.

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Page 26: Combined Cycle Principles

Combustor basketThe mechanical component of the combustion system in which the fuel is burnt to increase the temperature of the flue gas.

Transition pieceMechanical component which directs the hot gases from combustor basket to the segmental opening leading to the turbine inlet.

Fuel nozzleThe component of the combustion system which meters the fuel to the combustor basket with the proper dispersion pattern.

IgniterThe component of the combustion system which at a pre-determined point is energized to provide the spark for igniting the fuel in the combustor basket.

Cross flame tubeA mechanical interconnection between combustor baskets for the purpose of carrying the flame from a fired to an unfired combustor basket.

Temperature control systemUnder any normal conditions of operation, it limits input fuel as necessary to prevent the temperatures in the turbine from exceeding allowable limits.

Turbine temperature detectorThat component of the control system which senses the temperature of the flue gases and provides the signal to limit the fuel input to the combustor baskets when maximum pre-determined temperature is reached.

Ignition speedThe speed of the compressor shaft at which ignition and fuel are applied.

Self-sustaining speedThe minimum speed of the compressor shaft at which the turbine will continue to operate at no-load without cranking power.

Idling speed:The specified operating speed of the compressor shaft for no-load operation.

Rated speedThe speed of a designated shaft at which it runs on load.

Trip speedThe speed at which the overspeed protective device operates.

Cranking speedThe speed at which the turbine is rotated for washing.

Starting powerThe external power which is required to accelerate the compressor, its turbine, and any connected load to self - sustaining speed in a specified time.

Journal-bearing

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Page 27: Combined Cycle Principles

This bearing is used to support the rotating elements (shaft) and it maintains the radial position of the rotor with respect to the stator.

Thrust bearingThis bearing supports the axial thrust of the rotor to the bearing housing and it maintains the axial position of the rotor with respect to the stator.

Bearing housingAn enclosure used to contain and support the shaft bearings and may be of the bracket or pedestal type.

Interstage sealsMechanical device used to restrict the leakage of the air or flue gas between stages.

Compressor bleed valveAn open-close line used to blow off a portion of the air from a stage of compressor during a start-up or a shut down period.

Rotor assemblyThis is the rotating element of the gas turbine which includes all parts attached on the shaft and has provision for coupling.

Discs or WheelsThey constitute the gas turbine shaft. On these discs the rotating blades are assembled.

Wheel space or Disc CavityIt is the space between rotor wheel and diaphragm of the stator blade. Here thermocouples are placed to measure the temperature.

Shroud or SealA shaped metallic strip next or connected to the blades in order to limit the leakages.

Governing system ; which includes but it is not limited to: Speed governor on the load shaft with load setting device for

manual operation at the machine and/or control panel Check of turbine maximum over-temperature Emergency over-speed governor on the load shaft.

Speed governing systemA system of control elements and devices for the control of the speed or power output of a gas turbine and includes a speed governor, speed changer, fuel control mechanism, and other devices and control elements required to actuate the fuel control valve.

Speed governorThe primary speed-sensitive element which is directly responsive to speed and which positions or influences the action of other control elements.

Fuel control mechanismThis mechanism controls the flow of fuel to the gas turbine.

Speed changer

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Used to change the setting of the speed governing system for the purpose of adjusting the speed and/or load of the gas turbine during operation.

Control panelA component on which are mounted the devices used to regulate and monitor the necessary functions for safe operation of the gas turbine.

Controlling deviceOne which automatically initiates action of a system which controls conditions during the normal operation of the gas turbine.

External control deviceAn element which is responsive to signals that are external to the gas turbine. It may be pneumatically, hydraulically or electrically actuated from the signal source and acts to control the energy input to the gas turbine.

Protective deviceOne which, alone or as part of a system, controls or signals in some predetermined manner, abnormal conditions which may occur during the operation of the unit or system to which it is connected.

Warning device

One which by visible or audible means, or both, indicates that an abnormal operating condition exists.

Baseplate (bedplate)

A structural metal frame for supporting the gas turbine and its auxiliaries as a unit.

Inlet silencer

The elements system which decreases the sound power level transmitted by the air at the inlet of the compressor.

Exhaust silencer

The elements system which decreases the sound power level transmitted by the flue gases leaving the gas turbine.

Auxiliary gear or Accessory drive

Converts the gas turbine speed to the speed required by the auxiliary equipment.

Accessories

Apparatus deemed necessary for the proper functioning and safety of operation of the gas turbine.

Starting equipment

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The starting equipment shall be capable of bringing the gas turbine up through the normal starting cycle to self-sustaining speed.

Turning gear

The turning gear rotates the gas turbine rotor at low speed prior to starting and immediately after shut-down to assure uniform temperature distribution in the rotor.

Heat Recovery Steam Generator or Exhaust heat boiler

Used to recover and transfer heat from the flue gases leaving the gas turbine to generate steam or hot water.

Lubricating system ;

Closed forced-feed system including the following:

Oil tank of sufficient capacity and oil piping Tank oil level indicator Main oil pump-sized to supply oil requirements for the complete

gas turbine unit during normal operation Auxiliary and Emergency lube oil pumps with means for testing their

operation System for automatically activating emergency and auxiliary lube

oil pump Temperature measuring device in the oil feeding manifold Lube oil coolers Pressure gauge on oil feeding manifold Relief valves

Supervisory instrumentation ;

Electro-pneumatic system for checking and monitoring of unit performances. It include

Master control switch for semi-automatic start and for stopping the gas turbine

Speed changer checking system Relay to provide the necessary functions of control and

protective operations of the gas turbine Starting and sequence indicating lights Temperature indicator for the turbine exhaust temperature Speed indicator for output shaft Loss of flame indication Annunciator with audible alarm and individual malfunction

indicators for overspeed, flameout, low lube pressure, high bearing oil temperature and high turbine cooling water temperature

Pressure gauges for measuring lube oil manifold pressure, fuel pressure, overspeed oil pressure and control air pressure.

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GAS TURBINES DESIGN DATA:

Description Unit 1, 2 Unit 13, 14 Unit 3, 4 Unit 5-8Gas TurbineModel V-94.2 V-94.2 TG-50 MS 9001 EManufacturer Siemens (Germany) Siemens (Germany) FIAT

M/s GIE (Italy)M/S ALSTOM France

Control ISKAMATIC TELEPERMEA/EHF

Conventional relay type; Fiat Hi Tech

Mark IV Speedtronic control

Design Load 114.75 MW 97.1 MWBase Load rating according to IDC test in 1996

94 on GAS91 on HSD91 on FO

110 / 107 on Gas105 / 103 on HSD105 / 103 on FO

84 / 83 on GAS83 / 84 on HSD

80/79/80/80 on Gas76/76/77/76 HSD76/76/77/76 on FO

Base Load rating according to ADC test

94 on GAS91 on HSD91 on FO

110 / 107 on Gas105 / 103 on HSD105 / 103 on FO

84 / 83 on GAS83 / 84 on HSD

80/79/80/80 on Gas76/76/77/76 HSD76/76/77/76 on FO

Starting time upto 3000 RPM

4 Minutes 4 Minutes 25 Minutes 10 Minutes

Spining Reserve 20 MW 20 MW 2 MW, after 90 Sec 4 MWAuto Loading gradient

11 MW/minute upto base load

11 MW/minute upto base load

6 MW/minute 8 MW/minute

App. net thermal efficiency

26 %(open cycle)

29 %(open cycle)

25 %(open cycle)

27 %(open cycle)

Critical speed 1500 – 1850 rpmTurbineTurbine Stages 4 4 4 3Max. Turbine Inlet Temperature

1050 °C 1050 °C 1050 °C 1050 °C

Turbine exhaust temp. at full load

500 to 530 °C 500 to 550 °C 550 to 610 °C 480 to 550 °C

Heat rate (kJ/kWh) 11,200 on Gas11,300 on HSD11,600 on BFO

Flue gas mass flow 426 Kg/sec 471 Kg/sec 322 Kg/sec 406 Kg/secFuel flow (kg/s) 8.73 on Gas

9.28 on HSD8.55 on BFO

Description Unit 1, 2 Unit 13, 14 Unit 3, 4 Unit 5-8CompressorCompressor Stages 16 16 20 17Discharge pressure varies acc to speed

1-9 bar 1-9 bar 1-9 bar 1-9 bar

Compression Ratio 9.11 9.11 12 9.11Inlet guide vanes Fixed Variable,modulated Variable,modulated Variable,modulated

at 34°, 57°, 84°Bleed valves № 1.1 is electric

operated,№ 1.2 is air

№ 1.1 and № 1.2 are air operated,and both are at

3,№ 1, stage 6 close above 2800 rpm.

4, close with comp discharge air & open with spring.

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operated and both are at stage 5, these close above 2950rp.№ 2 is air operated, at stage 10, close above 2300 rpm

stage 5, these close above 2940 rpm.№ 2 is air operated, at stage 10, close above 2280 rpm

№ 2, stage 12 close above 2700 rpm.№ 3, stage 15 close above 1900 rpm

All close at 95% speed

Starting SystemStarting Device S.F.C

Max. startup rating 2900 kW

S.F.CMax. startup rating 2900 kW

11KV – 1915 KW 6.6KV – 1000 KW

Declutching Speed 2100 to 2300 RPM 2100 to 2300 RPM 1910 to 1980 RPM 1800 RPMCombustion and Fuel SystemNo of Combustors 2 2 18 Nozzles 14 reverse flowFuel Nozzles/ Burners

8 per combustion chamber

8 per combustion chamber

1 per combustor 1 per combustor

Spark Plugs 1 for each nozzle 1 for each nozzle 2, located at burners 12 & 13.

2, electrode type, spring-injected, self-retracting, located at burners 12 & 13.

Flame detectors 2, one at each left and right chambers

2, one at each left and right chambers

4, ultra-violet type, FD1,2 at nozzle 1,FD3,4 at nozzle 18.

4, ultra-violet type, located at burners 3, 4, 5 & 11.

Fuel pump 1, Electric motor driven. Fixed displacement, screw type pump

2, Electric motor driven. Fixed displacement, screw type pump

1, Electric motor driven. Fixed displacement, screw type pump

1, Accessory gear-driven, Fixed displacement, screw type pump

Flow divider - - Ram type Circular, free wheeling, 14 elements

Fuel oil emergency stop valve (ESV)

Open by hydraulic control oil, close by spring force

Open by hydraulic control oil, close by spring force

Air operated Open by electro- hydraulic servo control oil, close by spring force

Description Unit 1, 2 Unit 13, 14 Unit 3, 4 Unit 5-8Combustion and Fuel SystemFuel oil control valve

At return line, hydraulic control

At return line, hydraulic control

Air operated VC 3 Fuel bypass valve and flow divider control the fuel oil flow

Fuel oil pressure low

6-7 bar 6-7 bar 5-6 bar

Fuel oil pressure high

65 bar 65 bar 65-70 bar 65-70 bar

Dosing pumps 2 pumps with low and high range

2 pumps with low and high range

2 pumps with low and high range

2 pumps with low and high range

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Page 32: Combined Cycle Principles

Lubrication SystemLube Oil Grade TRESSO-46 TRESSO-46 TRESSO-32 DTE-724Total Oil Capacity 11.4 m3 13.5 m3 10.5 m3 3,300 gallons or

12,540 litresMax. Oil Level 320 mm from top 320 mm from top

12.13 m3

Min. Oil Level 440 mm (from top of oil tank)

440 mm from top10.54 m3

Main lube oil pump One AC motor driven Press = 5 bar

No. 1, AC motor driven

2, AC motor driven Pressure = 4-5 bar

1, accessory gear driven, Pressure

Auxiliary lube oil pump

1, AC motor driven No. 2, AC motor driven

Any one can be selected as main and other standby

1,AC motor driven, vertical,submerged, centrifugal type

Emergency lube oil pump

1, DC motor drivenPressure = 1.2 bar

1, DC motor driven Pressure = 1.2 bar

1, DC motor driven Pressure = 1.2 bar

DC motor driven, vertical,submerged, centrifugal type

Jacking oil pump 1, AC motor drivenPressure = 140 bar

1, AC motor drivenPressure = 140 bar

Nil Nil

Bearings at Compressor, Turbine and Generator RotorQuantities 2 + 2 2 + 2 2 + 2 3 + 2Lubrication Pressure lubricated Pressure lubricated Pressure lubricated Pressure lubricated№ 1 bearing MBD11, Journal

Located at Turbine Exhaust

MBD11, JournalLocated at Turbine Exhaust

Located in inlet casing assembly, Active and inactive thrust

Journal EllipticalActive thrust Tilting pad,

self-equalizingInactive thrust Tilting pad,

non-equalizing№ 2 bearing MBD12, Journal +

Thrust, Located at Compressor air Intake

MBD12, Journal + Thrust, Located at Compressor air Intake

Located in compressor discharge casing, Elliptical journal

Description Unit 1, 2 Unit 13, 14 Unit 3, 4 Unit 5-8№ 3 bearing MKD11, Located at

Generator on Compressor side

MKD11, Located at Generator on Compressor side

Located in exhaust frame, Journal, tilting pad

№ 4 bearing MKD12, Located at Generator on slip-ring side

MKD12, Located at Generator on slip-ring side

Hydraulic supply systemMain hydraulic supply pump

- - Accessory gear driven, variable positive displacement, axial piston

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Page 33: Combined Cycle Principles

Auxiliary hydraulic supply pump

- - AC motor driven88HQ

Control oil systemBooster oil pump 1, AC motor driven

Press = 8-9 bar1, AC motor driven 2, AC motor driven -

Atomizing air systemMain compressor no air atomizing

fuel burn, pressure atomization

no air atomizingfuel burn, pressure atomization

Accessory gear driven 51,000 rpm, centrifugal type

Starting (booster) compressor

- - - Axial flow, positive displacement, belt driven by ACmotor

Air pre-cooler - - - Water-to-Air heat exchanger

Data from Performance SectionFuel Calorific Values Sui Gas : 32,400 kJ/m3,

HSD : 36,300 kJ/LtrFO : 40,200 kJ/kg

Net Complex Output (MW) in IDC 1996 1345 MWNet Complex Output (MW) in ADC 2004 1360 MWMaximum Generation in a Month (April 2004) 789,665 MWhMaximum Generation in one day 35,667 MWhMaximum Plant Load 1541 MW

Conversion1 mm of Water Column 2.81 mbar; 2.107 mm of Mercury1 bar (= 1 M water column) 14.7 PSI = 100,000 Pascal3412 BTU = 3600 kJ 1 kWh

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Page 34: Combined Cycle Principles

STEAM TURBINES DESIGN DATA:

Description Unit 9, 10 Unit 11, 12 Unit 15Steam TurbinesMake ABB, Germany RATEAU, France SIEMENS, GermanyType DK 2056 VEGA 209 110 B 030-16, N30-2X5-B-9Rated Power 112.2 MW 103.4 MW 148.6 MWNo. of Cylinders 2 1 2First CylinderStages 16 Reaction 12 HP, 5 LP 26 ReactionSecond CylinderStages 7+7 reaction double flow - 8+8 reaction double flowHP steam inlet pressure

47.9 bar 40 bar 57 bar

Temperature 495 °C 510.8 °C 528 °CLP steam inlet pres 3.99 bar - 5.78 barTemperature 190.6 °C - 221 °CVacuum 0.091 bar (a) 0.091 bar (a) 0.091 bar (a)

Turning GearsMake ABB, Germany FLENSER, France KWU, GermanyDrive AC motor driven

reduction gearAC motor driven reduction gear

57 bar

Turning Speed 43 rpm 50 rpm 58 rpm

CondensersMake ABB, Germany DELAS KWUType Spring mounted surface

condenserRigid mounted surface condenser

Rigid mounted surface condenser

Water passes 2 2 2Cooling Area 8204 m2 8651 m2 9982 m2

Circulating water flow

5.690 m3/sec or20,484 Ton/hr

Vacuum 0.091 bar (a) 0.091 bar (a) 0.091 bar (a)Total steam flow 110.551 Kg/sec 97.64 Kg/sec 128.04 Kg/secCW flow 4681.6 Kg/sec 4626 Kg/sec 5650.1 Kg/secCW vel in tubes 1.91 m/sec 1.95 m/sec 1.9 m/secCW inlet temp 29 °C 30 °C 28.5 °CCond pres loss 0.38 bar 0.46 bar 0.41 barNo. of tubes 13000 12532 16032 + 1236Tube outer dia 24 mm 24 mm 23 mmTube thickness 1 mm 1 mm 1 mm & 0.7 mmTube Material CuZn28Sn

X 2CrNiMoAdmiralty BrassStainless Steel

CuZn28Sn1F32X 2CrNiMo N17135

Corrosion prot forWater Box

Rubber Lined Epoxy Paint Epoxy Paint

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Page 35: Combined Cycle Principles

Description Unit 9, 10 Unit 11, 12 Unit 15Circulating Water PumpsMake TORISHIMA KSB TORISHIMAType 1200-SPB PHZ 900-990 SPV 1200Flow 9630 Ton/hr 8360 Ton/hr 11320 Ton/hrTDH 23.2 m 17.2 m 22.3 mNPSH 5 m 3.5 m 12.3 mSpeed 325 rpm 590 rpm 295 rpmPower 920 KW 462 KW 1000 KWMaterialCasing JIS FC25 Cast Iron JIS FC 250Shaft JIS S45C Carbon Steel JIS S45CImpeller SCS1 Bronze GCu SN10 SCS1

Condensate PumpsType WKTA-200/2 FEX.36-3 12QLQC 21/60/3Flow (t/h) 403.1 422 465TDH (m) 75.6 96 195NPSH (m) 3.3 33.4 2.5Speed (rpm) 1480 1480 1480Power (kw) 130 KW 150 316MaterialCasing JIS SCPM 2 A420CM ASTMA 48 CL.35Shaft JIS SUS42OL2 Z15CN16-02 ASTMA 276-410Impeller JIS SC51 Z4CND13-412 ASTMA 743CA6NM

LP Feedwater PumpsMake TORISHIMA INGERSOL DRESSER WORTHINGTONType RPK50-400 ERP100-200 HEDFlow (t/h) 30 175 39.24Head (m) 190 6.7 20NPSH (m) 1.9 7.8 0.884Speed (rpm) 2945 2950 2980Power (kw) 55 30.1 65MaterialCasing JIS SCS1 A216GrWCB A216 GR WCBShaft JIS SUS420J2 A193GrB7 A276 – 410Impeller JIS SCS1 A473CA6NM A487 GR – CA6NM

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Page 36: Combined Cycle Principles

Description Unit 9, 10 Unit 11, 12 Unit 15

HP Feedwater PumpsMake TORISHIMA BYRON JACKSON WORTHINGTONType HGC 4/8Flow (t/h) 206.9 183.5 337Head (m) 831.2 675 933NPSH (m) 6 6.51 10.50Speed (rpm) 2970 2980 2980Power (kw) 671 1200

MaterialCasing SFVE2 A743-CA-6MM A 487 GR CABNMShaft 13CR A276-TP410 A 276 TY 410Impeller SCS1T2 A743-CA-6MM A 487 GR CABNM

Vacuum PumpsMake SIEMEN HIBON SIEMENType 2BW4303-0=OML49 SHR215006H00.950 2BE 1303-OZY4ZHOGGING OPERATIONSuction Pressure 0.3 bar 0.39 bar 300 mm barDesign Flow 5200 m3/h 25.5 kg/h 30 Kg/hrsRated Power 65 kw 42 kwHOLDING OPERATIONSuction Pressure 0.0326 bar 0.083 bar 0.1 barSuction Temp. °C 40 44 100Design vapor mixture flow 37.3 Kg/h 108 Kg/h 67.5 Kg/h

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G E N E R A T O R S Description Unit 1,2 Unit 3,4 Unit 5-8 Unit 9,10 Unit 11,12 Unit 13,14 Unit 15Type TLRI

108/41SGTIC 243704

T 229-320 WX 21L-064LL

T-229-320 TLRI 108/36

TLRI 108/41

Make KWU ERCOLE MARELLI

ALSTHOM ABB ALSTHOM KWU KWU

Rated Out Put (MVA)

135 87 125.95 132 121.647 170 175

Power Factor 0.85 0.85 0.85 0.85 0.85 0.85 0.85Rated Voltage (KV):

10.5 11.0 11.5 11.0 11.5 11.0 11.0

Rated Current (A) 7423 4567 6223 6928 6107 8923 9185Frequency (HZ) 50 50 50 50 50 50 50Speed (RPM) 3000 3000 3000 3000 3000 3000 3000Over Speed Limit (RPM)

3600 3600 3600 3600 3600 3600 3600

Field Voltage (V) 333 142 151 236 146 432 432Field Current (A) 641 810 2110 1495 2011 946 865Short Circuit Ratio 0.5 0.6 0.51 0.5 0.58 0.502 0.534Direct-Axis sub-transient Reactance (Xd) per unit

0.148 0.114 0.195 0.17 0.175 0.183 0.176

Direct-Axis Transient Reactance (Xd) per unit

0.242 0.145 0.275 0.26 0.252 0.304 0.286

Direct-Axis Transient Open circuit time constant T’d (Sec)

13.3 11.6 6.56 7.4 7.2 11.34 10.8

Direct-Axis Transient short circuit time constant Td (Sec)

0.27 0.04 0.40 0.04 0.25 1.56 1.62

Rotor Resistance (ohm)

0.3638 (at 20 C)

0.175 (at 75 C)

0.0508 (at 20 C)

0.1165 (at 20 C)

0.226 (at 20 C)

0.3242 (at 20 C)

0.3671 (at 20 C)

Stator Resistance (ohm)

0.00061(at 20 C)

0.0011(at75 C)

0.00107(at 20 C)

0.00079(at 20 C)

0.001 (at 75 C)

0.00058(at 20 C)

0.00053(at 20 C)

Insulation Class F F F F F F FExcitation system SEMIPOL

(Static)STATIC ROTA

DUCT (Rotary) Brushless

STATIC ROTA DUCT (Rotary) Brushless

SEMIPOL (Static)

SEMIPOL (Static)

Cold Air Temp C 55 50 50 33.3 36 40 40

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Page 38: Combined Cycle Principles

SWITCH GEARS

Description Unit 9, 10 Unit 11, 12 Unit 15

220 KV CIRCUIT BREAKERSMake Nova Magrin Galiloo Italy GEC ALSTHOM SIEMENSType SF6 / Air operated SF6 / Hydraulic oil

operatedSF6 / Hydraulic oil operated

Rated Voltage 145 KV 145 KV 145 KVRated current 2000 Amp 2000 Amp 2000 AmpRated breaking capacity

40 (KA) 40 (KA) 40 (KA)

BIL 1050 KV 1050 KV 1050 KVNo. of circuit breaker

6 18 9

132 KV CIRCUIT BREAKERSMake Nova Magrin Galiloo Italy Nova Magrin Galiloo ItalyType SF6/Air operated SF6/Air operatedRated Voltage 145 KV 145 KVRated current 1600 Amp 3000 AmpRated breaking capacity

40 (KA) 40 (KA)

BIL 650 KV 650 KVNo. of circuit breaker

17 1

11 KV CIRCUIT BREAKERSDescription Unit 1,2 Unit 3,4 Unit 5-8 Unit 9,10 Unit 11,12 Unit 13,14Make SIEMENS

GermanyNova Magrin Galiloo Italy

Marlin Gerin

AEG Marlin Gerin

SIEMENS ABB

Type Vacuum Air Magnetic

SF6 Vacuum SF6 Vacuum

Rated Voltage 12 KV 12 KV 12 KV 12 KV 12 KV 12 KVRated current 1250 Amp 1250 Amp 1250 Amp 630 Amp 800 AmpRated breaking capacity

25 (KA) 25 (KA) 25 (KA) 25 (KA) 25 (KA) 20 (KA)

No. of circuit breaker

26 24 42 40 36 48

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Page 39: Combined Cycle Principles

UNIT POWER TRANSFORMERS

Description Unit 1,2 Unit 3,4 Unit 5-8 Unit 9,10 Unit 11,12 Unit 13,14 Unit 15Make TRAFO

UNIONANSALDO ALSTHOM TOSHIBA ALSTHOM TRAFO

UNIONTRAFO UNION

Rated Power MVA 117.6/147 77/95.5 125 90/135 112/125 168 190Rated Voltage KV (LV/HV)

10.5/139 11.139 11.5/240 11/139 11.5 / 240.18

11 / 258 11 / 258

Rated Frequency 50 Hz 50 Hz 50 Hz 50 Hz 50 Hz 50 Hz 50 HzNo of Phases 3 3 3 3 3 3 3Rated Current (A) (LV/HV) 8083/611 5012/396 6276/300 7090/561 6276/300 8819/422

8083/661

Connection Symbol

YNd11 YNd11 YNd11 YNd11 YNd11 YNd11 Ynd11

Type of Cooling ONAN/ONAF

ONAN/ONAF

ONAN/ONAF

ONAN/ONAF

ONAN/ONAF

ONAN/ONAF

ONAN/ONAF

Temp. Rise °C Winding/Oil

55/50 55/50 55/50 55/50 55/50 55/50 55/50

Type of Tap Changer

On Load On Load Off Load On Load Off Load Off Load Off Load

Total No. of Taps 17 15 09 17 09 11 11Impedance % 9.2/11.5 10.9 14.5 12.63 14 14 15.5Connection (HV/LV)

Star/Delta Star/Delta Star/Delta Star/Delta Star/Delta Star/Delta Star/Delta

UNIT AUXILIARY TRANSFORMERSDescription Unit 1,2 Unit 3,4 Unit 5-8 Unit 9,10 Unit 11,12 Unit 13,14 Unit 15Make SIEMENS O.T.E ALSTHOM PEL ALSTHOM TRAFO

UNIONSIEMENS

Type of cooling ONAN ONAN ONAN ONAN ONAN ONAN ONANRated power (KVA)

1000 2500 1250 630 630 800KVA 1250

Frequency (Hz) 50 50 50 50 50 50 50Impedance % 5.47 8.38 5.5 4.09 4.21 % 5.8 % 5.98Rated voltage KV (HV/LV)

11/0.4 11/0.415 11.5/0.4 11/0.4 11/400 11/400 11/0.4

Rated current (AMP)

52.5/1443.4

131.2/3478

6.56/1804 33.1/909.3

33.1/909.3 42/1155 65.6/1804.2

Vector group DYN11 DYN11 DYN11 DYN11 DYN11 DYN1 DYN11Total no. of taps 5 5 5 5 5 5 5Type of tap changer

Off Load Off Load Off Load Off Load Off Load Off Load Off Load

Temp. rise oil/winding

50/55 55

Connection (HV/LV)

Delta/StarΔ / Ү

Delta/StarΔ / Ү

Delta/StarΔ / Ү

Delta/StarΔ / Ү

Delta/StarΔ / Ү

Delta/StarΔ / Ү

Delta/StarΔ / Ү

Weight of oil KG 1035 1200 5100 600 385 1257

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GENERATOR EXCITATION TRANSFORMER

Description Unit 1,2 Unit 3,4 Unit 9,10 Unit 13,14 Unit 15Make SIEMENS STEM-

TRENTOMAY &CHRISTE

TRAFO UNION

TRAFO UNION

Type of cooling ON ONAN AN AN ANNo. of phases 3 3 3 3 3Operation Continuous Continuous Continuous Continuous ContinuousRated power(KVA) 630 450 800 1660 1025Frequency 50 50 50 50 50Rated current HV/LV(A)

33.06/673.6

23.6/927 42/1499.6 87.1/1229 53.5/845

Rated voltage HV/LV(B)

11000/940 11000/280 11000/380 11000/780 11000/700

Type of tap changer

Off Load Off Load Off Load Off Load Off Load

No. of taps 5 5 5 3 3Vector group YD-5 YD-11 YD-5 YD5 YD-5Temp. Rise at 50 C Winding/oil 50/45 50/45 50/45 50 CImpedance % 5.55 7.0 6.05 5.9 5.8

EXCITATION SYSTEMDescription Unit 1,2 Unit 3,4 Unit 5-8 Unit 9,10 Unit 11,12 Unit 13,14 Unit 15Type STATIC

with Carbon Brushes.

STATIC with Carbon Brushes

Rotating Diodes

STATIC Rotating Diodes

STATIC STATIC

Make AEG Telefuncon

Ercole Marelli

Alsthom MAY & Christe

Alsthom AEG Telefuncon

AEG Telefuncon

Rated power (kw) 215 115 319 353 293.6 408 366Rated voltage (V) 342 142 151 236 146 423 423Rated Current (A) 658 810 2110 1495 2011 946 865Converters / Blade 6 3 18 3 18 6 6Duty Continuous Continuous Continuous Continuous Continuous Continuous Continuous

Class of Insulation F F F F F F FSupply source Auxiliary Auxiliary Auxiliary Auxiliary Auxiliary Auxiliary Auxiliary

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HEAT RECOVERY STEAM GENERATORSDescription Unit 1,2 Unit 3,4 Unit 11,12 Unit 15Boiler output (T/H) 208 180.8 96.25 234Design Gauge Pressure (bar) 62 62 51 60.7Superheater outlet Pressure (bar) 47.1 48 42 60.7Superheater Steam Temp. (°C) 505 500 512 530Heating Surface AreaLP Evaporator (m2) 4345 10200 7439 9914HP Economizer (m2) 18200 17950 13139 33909HP Evaporator (m2) 28220 22820 26014 34578HP Superheater (m2) 5415 3212 9794 5693Total heating Surface (m2) 56180 54182 56386 84094

REQUIREMENTS OF WATER AT HRSGs

FEED WATER AND WATER FOR SPRAY ATTEMPERATOR

Description UnitGeneral requirements - Clear and ColorlessConductivity at 25 °C µS/cm 0.2PH-Value at 25 °C - 9Oxygen O2 mg/kg 0.02Total Iron Fe mg/kg 0.02Total Copper Cu mg/kg 0.003Silica SiO2 mg/kg 0.02Carbon dioxide CO2 mg/kg Not detectableHardness mval/kg Not detectableKMnO4 Consumption mg/kg 5Oil mg/kg 0.3

BOILER WATER

Description UnitConductivity at 25 °C µS/cm 150PH-Value at 25 °C - 9.5 – 10.5Silica SiO2 mg/kg 5Phosphate PO4 mg/kg 61

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Symbols in System DiagramsSymbols used in System Diagrams are stipulated in DIN 2481. This standard provides the full scope of symbols which are used in power plant engineering. An excerpt of this standard containing most frequently used symbols in the system diagrams is filed here.

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DIN Standard Valve Symbols

Gate valve orMain slide valve

Shut off valve general

Hand Operated

Solenoid Operated

Fluid Operated

Piston Operated

Diaphragm Operated

Non-return valvewithout spring

Non-return valvewith spring

Controllednon-return valve

Coupling general

Separator general

Safety relief valveSafety shut off valve

Air Filter

Liquid Filter

Throttle valveadjustable

Non-returnvalve general

Motor Operated

Strainer

Angle valve or ball valve

Check valve

Pressure reducing valve

Butterfly valve

Control valve

Three way valve

Four way valve

Ball/cock valve

3-way cock valve

Cooling Tower general

Fitting with constantsetting action

Shut off through valve

Fitting with safety function

Non-returnthrough-valve

Throttle valve withconstant restriction

Page 43: Combined Cycle Principles

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Fitting with constantsetting action

Non-returnthrough-valve

Orifice

Mixing section

Surface heat exchanger

Flow meter

Special Accessories

Generator

Tank

Ignition gas cylinder

Combustion chamber

Pump general

Centrifugal pump

Reciprocating pump

Rotary pump

Screw pump

Gear pump

Compressors

Root Compressor

Diaphragm Compressor

Reciprocating

Turbo Compressor

Liquid ring Compressor

Screw Compressor

Compressor general

Inspection glass

Gas Turbine

Steam Turbine

Burner

Rotary vane

DIN Standards Pumps