The improvement of energy efficiency of cogeneration system by replacing desuperheater with steam–air preheater

Abstract

Industrial processes require thermal energy in form of saturated steam. Cogeneration system in a process industry uses an industrial boiler to produce superheated steam, which is subsequently expanded in a condensing-extraction steam turbine. The extracted steam is sent to the process, and the remaining steam is condensed in a condenser. Since the extracted steam is superheated, it must be mixed with cooling water in a direct-contact heat exchanger before the resulting saturated steam is sent to the evaporation process. A more energy efficient method of desuperheating, which requires the replacement of the direct-contact heat exchanger with a non-contact heat exchanger, is investigated in this paper. Extracted superheated steam is desuperheated, and air temperature is increased in this heat exchanger. The performances of the conventional cogeneration system that uses direct-contact heat exchanger for desuperheating and the modified cogeneration system that uses non-contact heat exchanger for desuperheating are compared. Simulation results indicate that the modified cogeneration system is more energy efficient than the conventional cogeneration system because the power output of the modified cogeneration system is larger than that of the conventional cogeneration system under the same operating conditions.