Thermodynamic and Economic Analysis of a Gas-Turbine Combined Heat and Power Plant Considering Operational Flexibility

Abstract

The operational flexibility is improved to decouple the thermoelectric limitation of the combined heat and power (CHP) system and meet the dynamic changes of heat and electrical loads in an affordable economic and thermodynamic cost. A gas-turbine CHP system combined with thermal energy storage of molten salt is proposed in this paper. The thermodynamic models of components are constructed and simulated in Ebsilon, and the indicators are defined to evaluate thermodynamic and economic performances and operational flexibility of the coupled CHP system. The thermodynamic analysis indicates that under the design conditions, when CHP operates without thermal energy storage, gas turbine has the largest energy and exergy losses due to the combustion irreversibility, accounting for 51.28 and 55.76% of total energy and exergy losses, respectively. In addition, the effects of thermal energy storage capacity on system performances are analyzed and discussed. The results indicate that when the capacity of the thermal energy storage increases from 0 to 2000 kWh, the primary energy ratio is decreased by 4.56%, the exergy efficiency only declines by 0.74%, and the economic revenue of the system is also reduced by 15.70%. But the adjustable ability of the heat and electricity is increased by 44.84%. The optimal thermal energy storage size of the CHP plant is comprehensively determined according to the integrated benefits of energy, economic, and operation flexibility.