GAS TURBINE GENERATOR (GTG)

The GTG is divided into five compartments. They are:

1. Diesel engine
2. Combustion chamber
3. Gas Turbine
4. Gear box
5. Alternator & Exciter

The Diesel engine compartment has a Diesel engine, which runs at 2400 rpm, whose shaft is coupled to the common shaft. In case, if the GTG is tripped, the Diesel engine is started with DC supply and the engine rotates the shaft and when engine attains 2400 rpm the diesel engine automatically disengages from the shaft and the turbine runs, from that power is produced.

After the diesel engine shaft, there are four motors. They are:

1. Main oil pump
2. Hydraulic pump
3. Atomized oil pump
4. Main compressor motor

When the shaft rotates, the four motor rotates and lubricates the bearings and internally removes the heat from the alternator, turbine, etc..,

The main compressor compresses the filtered air to high pressure. Nearly 80% of the air is used for cooling. The high-pressure gas and air enters the combustion chamber and mixes in the ratio of 1:20. The gas to the combustion chamber is maintained at 9.6 kg/cm². There are ten combustion chambers arranged in a cylindrical manner. Two electrodes produce the firing inside each chamber. Then the charge is burnt inside the chamber.

The burnt hot gas enters the gas turbine. The gas turbine has fixed blades and moving blades. The hot gas moves between the fixed and moving blades in a zigzag manner and rotates the moving blades. Hence the shaft rotates. The turbine rotates at 5100 rpm. The waste exhaust gas is send to STG through diverter damper ducts.

Then there is reducing gearbox, which reduces the speed through gear arrangements. The speed of the turbine is reduced to 3000 rpm. In this speed the Gas Turbine Generator rotates.

The shaft is coupled to alternator. The alternator rotates and the exciter develops the necessary flux required to produce power. The alternator produces a power of 22.9MW. The output of the alternator is given to control room and Motor Control Center (MCC).

HEAT RECOVERY STEAM GENERATOR (HRSG) & STEAM TURBINE GENERATOR (STG)

The exhaust gas from the GTG is send to Heat Recovery Steam Generator (HRSG) through ducts. The HRSG uses the exhaust gas as its fuel. The HRSG consists of:

1. Economizer
2. Evaporator
3. Super heater- 1
4. Super heater-2

The water going to the boiler should be Ultra pure. So we are using DM water. The makeup DM water is pumped to the boiler through Boiler FEED pump (BFP). The boiler is horizontal type water tube boiler. The water level in the boiler is maintained constant by 3 element device. According to the amount of evaporation the water is feed into the boiler. In the HRSG area several number of Resistance Temperature Detectors (RTD) are placed at different positions to measure the temperature. The boiler and Super heater has two spring loaded Safety valves.

The hot gas from the duct first heats the super heater-2 and then heats super heater-1. It then heats the evaporator and enters the drum of the boiler, where the water is converted into steam, which finally reaches the economizer.

The steam from the boiler passes through evaporator, where the water is evaporated and then goes to super heater-1, where the steam becomes super heated steam. In the super heated stage pure steam is obtained, there will not be any water particles. For further purification the super heated steam is steam to super heater-2 where it is further heated to remove the wet steam particles.

The super heated steam is send to Steam Turbine (ST). The ST has a generator that regulates the steam flow. The steam having a pressure of 48 kg/cm² at a temperature of 390^° C is passed into the turbine. The ST runs at 7500 rpm and it is reduced to 1500 rpm using gear controls. The turbine rotates in a similar way as that of GTG and produces power. The STG produces a power of 9.6MW.

The exhaust from the STG is passed to condenser. The water in the condenser condenses and drops into the hot well. From the hot well the water is pumped to deaerator, which removes the oxygen present in the water. Then the water is cooled and collected in a sump. The water is feed again into the boiler by BFP and the cycle continues.