THE SIMPLE, OPEN, GAS-TURBINE POWER CYCLE

The power plant consists of three elements: the compressor, the combustion chamber, and the gas turbine.

In the actual gas-turbine power plant, 65 to 80 per cent of the turbine output is required to drive the compressor. In the steam-turbine power plant, the working fluid is condensed with a very large reduction in volume so that less than 1 per cent of the turbine output is required to operate the boiler feed pump which corresponds to the air compressor of the gas-turbine power plant. Consequently, for the same net plant output, the gas turbine must produce three to four times as much power as a steam turbine. Such heat-transfer equipment as boilers, economizers, superheaters, condensers, feed-water heaters, forced- and induced-draft fans, and extensive piping system, all of which are necessary in an efficient steam power plant, are eliminated in the simple gas-turbine power plant. However, if maximum efficiency is desired in the gas-turbine power plant, large heat exchangers, water-circulating pumps and piping are necessary, and the gas-turbine plant loses much of its simplicity.

The efficiency of a simple gas-turbine power plant depends upon the temperature of gas supplied to the turbine and upon the pressure ratio, р2/p1

For a given turbine-inlet temperature, there is a particular pressure ratio which gives maximum efficiency, and. this optimum pressure ratio increases with inlet temperature. The marked increase in efficiency with increase in inlet temperature should be noted. As the high-temperature characteristics of metals are improved and inlet temperatures higher than 1,500° F become practical, the use of the gas turbine as an economical prime mover will expand rapidly.