Gas-Turbine Electric Power Plant

Gas-Turbine Electric Power Plant


a thermal power plant in which a gas turbine is used to drive the electric generator.

Gas-turbine electric power plants were created to take advantage of underground coal gasification processes. The first such power plant in the USSR, the Shatki Brown Coal Underground-Gas Electric Power Plant (Tula Oblast), was built in an area where there are deposits of high-ash and moist brown coal. Electric power plants working on coal were not widely developed mainly because it was found that particles in the gases quickly wear down the vanes of the gas turbines.

During the 1950’s and 1960’s gas-turbine electric power plants were built throughout the world. Their overall capacity exceeded 2,000 megawatts by 1970. In the USA and Great Britain thermal units with a capacity of more than 500 megawatts are as a rule supplied with gas-turbine plants (25-35 megawatt capacity) to handle peak-hour loads. Automatic gas-turbine electric power plants employing aviation turbines in combinations of two to four turbine gas-units (each with a capacity of 10-20 megawatts) are also widely used. Gas-turbine electric power plants may be mounted on semitrailer vans or railroad flatcars and used at new extraction sites, especially in oil fields (where the gas-turbine plants can work on the accompanying natural gas) or at construction sites (as temporary power plants). Gas-turbine electric power plants may be used as reserve sources of power, switched on in case of an emergency in the energy system. Gas-turbine electric power plants that are designed to meet peak-hour loads have a simplified thermal layout without provision for regeneration; they have an efficiency rate of about 20-25 percent. The cost of a standard kilowatt at such electric plants is about 50 percent of the cost of a standard kilowatt at a modern steam electric station. Gas-turbine electric power plants are highly automated as a rule and are equipped with remote control apparatus. The station starts to operate and generate power automatically; its auxiliary equipment, such as the apparatus that refills the tanks with oil and fuel, is under similar control. Mobile gas-turbine power plants are rarely used, because their efficiency is relatively low and equipment costs high, compared for example to diesel-operated power stations. Atomic gas-turbine power plants are being planned (USA); in these plants, high-temperature graphite-gas reactors will heat the operating gas (helium) to 800°-1000° C.

Combined steam- and gas-turbine electric power plants have a bright future. In these plants fuel and air are supplied to a combustion chamber under pressure; the products of combustion and heated air are sent to a gas turbine. After passing through the first stages of the turbine, the products of combustion are led off into an intermediate combustion chamber, where a portion of the fuel is burnt with the excess oxygen present in the gases. The combustion products leave the intermediate combustion chamber and enter the further stages of the turbine, where their continued expansion and cooling take place. The exhaust gases may be used to heat water or to manufacture low-pressure steam in a steam generator. Air is supplied to the combustion chamber by a compressor situated on the same shaft as the turbine. The technical design of gas-turbine plants is noted for simplicity; the need for auxiliary equipment and pipelines is minimal. The combined steam- and gas-turbine plant normally works on the cycle of a steam-turbine plant, but to meet peak-hour loads it is switched over to the cycle of a steam and gas plant. In this way high initial temperatures of the operating body are attained, whereas little heat is lost in the exhaust. Thus efficiency is high, and capital expenditures are somewhat reduced.

The first steam- and gas-turbine unit in the USSR was put into operation in 1964 at Leningrad’s State Electric Power Plant No. 1 and had a capacity of 16 megawatts. It was mounted onto the existing 30 megawatt steam turbine. Later a combined unit with a capacity of 200 megawatts was planned. The following components are found in a steam and gas unit: a 35-40 megawatt gas turbine designed for gas at 700°-770° C entering the turbine; a standard steam turbine (160 megawatts) designed for a pressure of 13 meganewtons per sq m and 565/565° C; and a high-pressure steam generator with an output of 450 tons per hour and designed for 14 meganewtons per sq m and 570/570° C.