The basic principle of all most all power generating stations except solar power generating stations is producing electricity by rotating the shaft of alternators by means of the prime mover. Major efforts are applied to arrange the motion of the prime mover in these power plants. In all cases any kind of turbine action is required to move the prime mover, in other words, we can say, the turbine is the prime mover. There is a special type of power generating station where gas turbine is used as the prime mover. This power generating plant is called a gas turbine power plant. Here the air is first compressed at desired pressure then it is brought to a combustion chamber where the compressed air is heated up by means of fuel combustion.
Then this highly compressed hot air is released from the combustion chamber through the nozzle to a turbine, called gas turbine. During expansion of pressurized and hot air, mechanical work is done to rotate the turbine. As the turbine rotates, the alternator also rotates since a common shaft is shared by both turbine and alternator in the gas turbine power plant. It is needed to be mentioned here that not only the turbine and alternator, the air compressor is also fitted on the same shaft.
This is because the mechanical power developed by the gas turbine can be shared by the air compressor for its operation along with the alternator. The mechanical energy required to compress the air must be more than the mechanical energy developed by the compressed air. But here the mechanical energy developed in the gas turbine by compressed air contributes both for compressing the air and producing the electricity. How can it be possible? The answer to this question is that the required energy developed in the system comes from the heat energy produced by combustion of fuel. Here, in the gas turbine power plant, compressed air only acts as a fluid. This type of power plant is not used for producing electrical power in commercial scale but normally used as a standby plants in a hydroelectric station for supplying auxiliary electricity during starting of the main power plant.
Advantages of Gas Turbine Power Plant
- There is no need of boiler as in the case of a steam power generating plant. As the boiler is not used the auxiliaries associated with the boiler are also absent in the gas turbine power plant hence the design is much simpler than the steam power plant.
- For the same reasons as mentioned above, the size of the gas turbine power plant is much smaller than that of a same capacity steam power plant.
- The manufacturing, engineering, installation and commissioning costs are much lower. The running cost is also less than that of same rated steam power plant.
- As the design and construction are simpler than a same capacity steam power plant, the maintenance cost also smaller in the gas turbine power plant.
- Gas turbine itself is much simpler in design and construction than a steam turbine.
- This power plant can be started much quickly even in cold condition.
- In steam power plant the boiler is kept operative even at off-load condition because restarting a boiler is much expensive and time-consuming process. But in the case of a gas turbine power plant entire plant can be kept inoperative at offload condition. Hence, this system is free from standby losses.
Disadvantages of Gas Turbine Power Plant
- For running the gas turbine system, compressed air is required. When the plant runs, the compressor runs and supplies the required compressed air. But when the plant just starts its operation, there is no compressed air previously available but this required compressed air cannot be produced before the compressor is run. The drawback of the system can be overcome by running the compressor by some external means before actual starting the plant.
- In this system, a major part of the mechanical power developed by the gas turbine is utilized to run the compressor which causes the low output of the system.
- A major portion of the heat energy of fuel combustion is lost to exhaust air. The exhaust heat cannot be reutilized efficiently like as in the case of a steam power plant.
- The internal temperature of the combustion chamber is very high. This highly tempted part of the system reduces the overall life span of a gas turbine power plant compared to other forms of a power plant.
1.Bunty B. Bommera
2.Dakshata U. Kamble