The gas turbine has experienced phenomenal progress and growth since its first successful development in the 1930s. The early gas turbines built in the 1940s and even 1950s had simple-cycle efficiencies of about 17 per cent. The reason was the low compressor and turbine efficiencies and low turbine inlet temperatures due to metallurgical limitations of those times. Therefore, gas turbines found only limited use despite their versatility and their ability to burn a variety of fuels. The efforts to improve the cycle efficiency concentrated in three areas:
1. Increasing the turbine inlet (or firing) temperatures.
2. Increasing the efficiencies of turbo-machinery components.
3. Add modifications to the basic cycle.
Gas Turbines work on the Brayton cycle. Incorporation of inter-cooling, regeneration (or recuperation), and reheating doubles the efficiency of early gas turbines. The back work ratio of a gas turbine cycle improves as a result of inter-cooling and reheating. However, this does not mean that the thermal efficiency will also improve. Intercooling and reheating will always decrease the thermal efficiency unless they are accompanied by regeneration. There are two reasons for it. One is because inter-cooling decreases the average temperature at which heat is added. The other is reheating increases the average temperature at which heat is rejected. Hence, Inter-cooling and reheating are always work in conjunction with regeneration in gas-turbine power plants. The improvements come at the expense of increased initial and operating costs. They cannot be justified unless the decrease in fuel costs offsets the increase in other costs.
Relatively low fuel prices, the general desire in the industry to minimize installation costs, and the tremendous increase in the simple-cycle efficiency due to the first increased efficiency options to approximately 40 per cent left little desire for incorporating these modifications. With the continued expected rise in demand and cost of producing electricity, these options will play an important role in the future of gas- turbine power plants.
Gas turbines installed until the mid-1970s suffered from low efficiency and poor reliability. In the past, large coal and nuclear power plants dominated the base-load electric power generation. Baseload units are online at full capacity or near full capacity almost all of the time. For varying large amounts of the
Now electric utilities are using gas turbines for base-load power production as well as for peaking, making capacity at maximum load periods. Gas Turbines can go off or on quickly. The construction costs for gas-turbine power plants are roughly half that of comparable conventional fossil fuel steam power plants. The conventional fossil fuel power plants
A recent gas turbine manufactured by General Electric uses a turbine inlet temperature of 1425°C (2600°F) and produces up to 282 MW while achieving a thermal 4 efficiency of 39.5 per cent in the simple-cycle mode. Over half of all power plants to be installed in the foreseeable future are forecast to be