Известия Томского политехнического университета: Инжиниринг георесурсов (May 2019)
Influence of gas turbine unit working medium properties on combined cycle thermodynamic effectiveness
Abstract
The use of different fuels in the gas-turbine unit alters the combustion products composition, in particular the ratio between the amounts of diatomic and triatomic gases. In turn this fact leads to a change in heat capacity, adiabatic index and specific costs of working medium compression and expansion and the recovery boiler thermal capacity. The article analyzes the impact of working medium properties changes with different fuels - methane, carbon monoxide and hydrogen, which leads to different triatomic gases content in the combustion products. We also consider the costs and the working fluid properties changes, with additional cyclic air heating before the combustion chamber of gas turbine unit. The purpose of this paper is a comparative analysis of the gas turbines cycle thermodynamic efficiency with different contents of triatomic gases in the combustion products, the amount of which depends on the used fuel properties, as well as on additional cyclic air heating before the combustion chamber. The studies were performed by the calculation method with the model, which takes into account the dependence of the specific heats and the performance adiabatic compression of air and fuel in the compressor and the expansion of the combustion products in the turbine on temperature. Besides there is an additional air heating in the air heater, but the air flow after the compressor for the first turbine stage cooling is not included. Found that the air pre-heating in the air heater decreases the thermal efficiency of the combined cycle power plant, regardless of the usage pattern of the air heater flue gas. Moreover, the exhaust gases use for heating the combustion air of air heater increases cost and capacity of the air compressor and the turbine, but not as much impact on efficiency CCP reducing as flue gas heat input to the working fluid of steam turbine cycle.
