An analysis of the effects of heat exchange and heat refluxing in the generation of electricity with a gas turbine

Six incremental but accumulative thermal schemes to improve the operation of a natural-gas-fired turbine in conjunction with a single steam turbine were analyzed in detail. Each of these was found to improve the efficiency and increase the electrical output, and to be justified economically on the basis of fixed and operating costs. The best overall scheme from a combined economic and thermodynamic point of view consisted of steam inputs to the turbine at three different pressure levels and the use of 13 separate heat exchanger sections (fours preheaters, three evaporators, and six superheaters). The overall efficiency based on the lower heating value of the natural gas was increased from 37.9% to 57.4% and the electrical output from 220 to 340 MW as compared to the bare gas turbine exhausting to the atmosphere. Further incremental improvements were found to be possible technically but not advisable economically because of the diminishing return per unit of expenditure.