Thermodynamic and economic analysis of a gas turbine set coupled with a turboexpander in a hierarchical gas-gas system

Abstract

Investment per specific electric capacity of power plants and combined heat and power plants operating exclusively according to the Joule cycle (Simple Cycle Power Plants) is more than two times lower compared to combined gas-steam systems. This paper discusses a system comprising a turboexpander with a compressor and an air heater installed instead of a steam turbine. The results of thermodynamic calculations carried out for many alternatives gas turbine designs, including ones with and without heat regeneration and for hierarchical gas-gas system are analyzed. Using energy balances, the energy efficiency of various configurations of systems was calculated. In the presented economic calculations, aspects related to the ratio of the annual electricity production to the annual heat production play the role of important factors, as technology applied in combined heat and electricity generation, system energy efficiency, specific investment and sales price of the generated electricity determine the results. From the calculations we can see that the gas-gas system is more economically feasible than the gas-steam system in terms of heat production. With regard to electricity production, the gas-steam system is slightly more profitable than the gas-gas system. This advantage decreases along with the decrease in the gas price.