On the issue of modernization of steam-gas power units

Combined cycle power plants are an efficient solution for combined heat and power generation; however, during the summer period, their electrical output decreases due to the high ambient air temperature at the gas turbine compressor inlet. This study examines an alternative approach – increasing the thermal output of a combined cycle plant by installing a block-type supplementary firing unit in the heat recovery steam generator. Using a 450 MW combined cycle power unit as an example, it is shown that the application of the supplementary firing unit allows increasing the thermal output from 237 to 320 Gcal/h (a 35% increase), the electrical output by 6% in district heating mode and by up to 11% in condensing mode, with a slight increase (3%) in the specific equivalent fuel consumption for electricity generation. Firing additional fuel between the high-pressure superheater and the evaporator ensures stabilization of steam parameters and eliminates the need to activate additional district heating equipment (steam turbines or hot water boilers) during the transitional months (April, October). An analysis of climatic conditions is performed, confirming the feasibility of using the supplementary firing unit to cover heat loads in the ambient temperature range from –5 to +10 °C. The proposed retrofit improves the flexibility and economic efficiency of the combined heat and power plant, eliminating the need to purchase new generating equipment.