Gas Turbine Power Plant

Gas Turbine Power Plant

The gas turbine power plant converts the energy of natural gas or other liquid fuels to mechanical energy. And mechanical energy is used to rotate a gas turbine. The gas turbine is connected with the same shaft of the alternator that converts mechanical energy into electrical energy.

Hence, the gas turbine converts the energy of natural gas to electrical energy. This type of plant is used to generate a small amount of electrical power to utilize for a home or business application.

Schematic Diagram of Gas Turbine Power Plant

The below figure shows the basic schematic diagram.

Gas cycle power plant
Gas cycle power plant

Components

The components used for the gas turbine power plant is explained as the below.

Compressor

The main function of the compressor is to provide high-pressure air. Generally, the rotatory type of compressor is used in the plant. Air at atmospheric pressure is drawn by the compressor via the filter which removes the dust from the air.

The blade of the compressor pushes the air between stationary blades to raise its pressure. Thus, air at high pressure is available at the output of the compressor. The flow of a large amount of air into the compressor creates high noise levels.

Regenerator

The exhaust system of the gas turbine power plant discharges the hot gases the exhaust gas that leaves the turbine is around 550 deg. C. Regenerator recovers heat from the exhaust gases of the turbine.

The exhaust is passed through the regenerator before discharging to the atmosphere. A regenerator consists of a nest of tubes contained in shell. The compressed air from the compressor passes through the tubes on the way to the combustion chamber. In this way, the compressor is heated by the hot exhaust gases.

Combustion chamber

It mainly facilitates raising the temperature of the gases. The air at high presser from the compressor is passing to the combustion chamber via regenerator. In the combustion chamber, heat is added to the air by burning oil or gas. It attains a very high temperature of about 3000F.

Gas Turbine

The products of combustion which consist of a mixture of gases at high temperature and pressure are passes to the gas turbine. This gas in passing over the turbine blades expands and thus produces mechanical output. Some gas turbines are Microturbine, Armature gas turbine, Radial gas turbine, etc.

Alternator

The mechanical output is given to the alternator. The alternator converts the mechanical energy of the turbine into electrical energy. The output of the alternator is given to the bus-bar through transformers where the voltage level is increased to the transmission purpose.

Starting Motor

Before starting the turbine, compressor has to be started for this purpose electrical motor has to be mounted on same shaft as that of turbine.

The motor is energized by the batteries. Once the unit is started, a part of the mechanical power of the turbine drives the compressor and there is no need for the motor.

Advantages of Gas Turbine Power Plant

The advantages of power plant is listed as below.

  • Simple in Design

As compare to a thermal power plant, gas turbine power plants are much simple in design since no boiler and their auxiliaries are required.

  • Smaller in size

Since a gas turbine power plant does not require a boiler, feedwater arrangements, etc. hence much smaller in size as compared to a steam power station of the same capacity.

  • There are no standby losses

However, in the steam station, these losses occur because the boiler is kept in operation even when the steam turbine is supplying no load.

  • Lower operating cost

The initial and operating costs are much lower than those of equivalent steam power station.

  • It has less water requirement compared to the steam power station as no condenser is used.
  • The maintenance charges are quite small.
  • The starting time is less as compared to the steam power station (6 to 7 Hrs.) from the cold conditions.

Disadvantage of Gas Turbine Power Plant

The disadvantages of power plant is listed as below.

  • An external device is required for starting the plant

Before starting the turbine, the compressor has to be operated for which power is required from some external source. However, once the unit is started the external power is not required as the turbine itself supplied necessary power to the compressor.

  • Output is low

Since the grate part of the power developed by the turbine is used in driving the compressor, the net output is low.

  • Low overall efficiency

The overall efficiency of such a plant is low (about 20%) because of the exhaust gases from the turbine contain sufficient heat.

  • Lower life

The temperature of the combustion chamber is too high (3000 deg. F) thus resulting in lower life.

Combined Cycle Power Plant

The amount of air needed for combustion drawn through the large air inlet section where it cleaned, cooled, and controlled, to reduce noise. The air then enters the gas turbine where it is compressed, mixed with natural gas, and ignited, which caused it to expand.

The pressure created from the expansion rotates the turbine blades, which attached to a shaft and a generator, creating electrical energy.

combined-cycle power plants
combined-cycle power plants

The hot gas exits the turbine at about 1100 deg.  Fahrenheit and then passes through the Heat Recovery Steam Generator. In the Heat Recovery, Steam Generator consists of layers of foot tall tube bundles which are filled with high purity water.

The hot exhaust gas coming from turbine passes through these tube bundles, which act as a radiator, boiling the water inside the tubes, and turning that water into steam. The gas then exits power plant through exhaust stack at a much cooler 180 degrees, after having given up most of its heat to the steam process.

The steam turbine is located on top of the condenser, across from the cooling tower. Steam enters the turbine with high temperature and pressure. The pressure of the steam used to rotate the turbine blades that attached to a rotor and a generator. Producing additional electricity.

After the steam spent in the turbine process, the residual steam leaves the turbine at low pressure and low heat. This exhaust stream passes into a condenser to be turned back into the water.

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