The Upgrading of the Combined-Cycle Cogeneration Plant with Heat-Recovery Steam Generators for Large Cities of the Russian Federation

In most large cities of Russia, the annual heat consumption exceeds the annual electricity consumption more than twice as a rule. On the contrary, the electric power of the combined-cycle cogeneration heat-power plant (CCCHPP) with heat-recovery steam generators (HRSG) is much higher than the thermal power of the cogeneration extraction of its steam turbine plant. This necessitates equipping combined-cycle gas turbine–combined heat and power plants (CCGT–CHPP) with additional heat sources to cover the heat loads of the heating season, which exceed the heat capacity of the cogeneration extractions of the combined-cycle gas turbines. The article shows that the use of water-heating boilers in this capacity has a number of serious disadvantages. These disadvantages can be eliminated by equipping HRSGs with afterburner units (ABUs), which burn the gas fuel in the residual oxygen of the exhaust gases of the gas turbine engine (GTE) directly in the HRSG. The range of thermal loads can be expanded, and the efficiency of the ABU application can be significantly increased by mounting the ABUs in the HRSG downstream from the high-pressure steam superheater upstream from the high-pressure evaporator. Furthermore, it is necessary to integrate a number of new components into the HRSG configuration, such as a water low-pressure steam superheater (WLPSSH) used instead of the gas LPSSH, a reduction device, and a peak network heater included in the heating plant of the steam turbine unit as the third stage of the network water heater at high (peak) thermal loads. By the example of the PGU-450T CCCHPP, the fundamental possibility of implementing the proposed modernization of its complete HRSG without making any changes to the design of the steam turbine is shown. Since the low-pressure drum of this HRSG is additionally equipped with a deaeration unit, the upgraded HRSG of the PGU-450T plant had also to be equipped with a water condensate heater upstream from the deaerator and additional shut-off and control valves that maintain the pressure in the deaerator and assure the subcooling of the water condensate at the deaerator inlet within the permissible range of all operating modes as well as under changing thermal loads all the year round.