Эффективность замкнутых газотурбинных установок при различных способах и программах регулирования

Abstract

Closed-cycle gas turbine units can be used as power plants for advanced nuclear power stations, spacecraft, ground, surface and underwater vehicles. The purpose and power capacity of closed gas turbine units (CGTU) determine their specific design schemes, taking into account efficient operation of the units both in the nominal (design) mode and in partial power modes. Control methods of both closed and open gas turbine units depend on the scheme and design of the installation but the former differ from the latter mainly in their ability to change gas pressure at the entrance to the low-pressure compressor. This pressure can be changed by controlling the mass circulating in the CGTU circuit, adding or releasing part of the working fluid from the closed system as well as by internal bypassing of the working fluid. At a constant circulating mass in the single-shaft CGTU, the temperature of the gas before the turbines and the shaft speed can be adjusted depending on the type of load. The rotational speed of the turbine shaft, blocked with the compressor, can be adjusted in specific ways, such as changing the cross sections of the flow of the impellers. At a constant mass of the working fluid, the pressure at the entrance to the low-pressure compressor varies depending on the control program. The efficiency of the CGTU in partial power modes depends on the installation scheme, control method and program. The most economical control method is changing the pressure in the circuit. Extraction of the working fluid into special receivers while maintaining the same temperature in all sections of the unit leads to a proportional decrease in the density of the working fluid in all sections and the preservation of gas-dynamic similarity in the nodes (compressors, turbines and pipelines). Specific heat flux rates, and therefore, temperatures change slightly in heat exchangers. As the density decreases, heat fluxes change, as the heat transfer coefficient decreases more slowly than the density of the working fluid. With a decrease in power, this leads to a slight increase in the degree of regeneration and cooling in the heat exchangers. The underestimation of these phenomena in the calculations can be compensated by the underestimation of the growth of losses in partial power modes.