To increase the efficiency of a combined cycle power plant, it was suggested in a double-pressure heat recovery steam generator to carry out a reheat of water steam that had been spent in a high pressure cylinder of a steam turbine. The researchers introduce a mathematical algorithm and calculation methodology of the waste-heat boiler. It is proved that after re-superheat of water vapour in a double-circuit waste-heat boiler after the high-pressure superheater (with vapour already used in the high-pressure cylinder of a condensing steam turbine), a CHP-plant efficiency and reliability increase. Calculations for the combined cycle gas turbine unit PGU-450 were performed. It is shown that when the reheater is installed in the recovery steam generator, its efficiency increases by 2.15%. At the same time the efficiency of CCGT for power generation is increased by 3.36%, the degree of dry water steam used in the turbine is increased by 0.082. Consequently, the specific consumption of conventional fuel for electric power generation is reduced by 6.1%. Re-superheating of the total flow of water vapour allows to increase CGP-450 steam-gas unit efficiency by increasing the parameters of the steam entering the low-pressure cylinder of the steam turbine.

No abstract

To increase the efficiency of a three-circuit combined-cycle plant, it is proposed to perform double resuperheating of water vapor in the high pressure loop (intermediate superheater ISH-1) and in the cooler part of the heat recovery boiler (intermediate superheater ISH-2). It was found by calculation that the implementation of the double reheated steam at high pressure and the tail of the WHRB increases the electrical efficiency of PGU-420 by 0.92 % compared to the option of a single resuperheat (from 60.45 to 61.37 %). The capacity of PGU-420 increases by 3.7 % (from 422.94 to 438.61 MWt). The specific reference fuel consumption is reduced by 1.5 % (from 203.47 to 200.42 g/(kWfh)). The steam dryness factor increases by 6.03 % (from 93.2 to 99.23 %). The steam turbine efficiency increases by 1.15 % (from 36.26 to 37.41 %), and steam turbine power increases by 11.61 % (from 134.94 to 150.61 MWt). The economic effect of the implementation of the second water vapor resuperheating in monetary terms is 48.0 million rubles per year when the cost of fuel equivalent is 3700 rubles/t. f e. and at the operating time of 7500 h/year.