Thermodynamic Analysis of Injected Water Recovery Systems for the Humid Air Turbine (HAT) Cycle

Abstract

Abstract The Humid Air Turbine (HAT) cycle is an inter-cooled gas turbine cycle, having an air-water mixing evaporator before the combustion chamber, and a heat recovering system for the exhaust gases. The considerable amount of water consumed in the mixing evaporator (about 1200–2400 m3 daily for a 100 MW unit), represents a significant drawback to the use of the HAT cycle as well as of other steam injected gas turbines. In fact, this means high operational costs for water treatment, and eventual legislative restrictions limiting the use of water, not to mention the environmental impact of the depletion of water resources. The aim of this paper is to evaluate the changes in the performance of the HAT cycle when a water recovery system is added in the exhaust gases, and to determine the heat exchangers conditions for maximum water and heat recovery. Finally, the size of a surface condenser for water recovery is determined for a given HAT cycle power output. The results show the possibility to recover up to 85% of the consumed water and up to 30% of input heat from the condensation of the water contained in the exhaust gas. The paper also examines all the thermodynamic processes in each cycle component from the viewpoint of recovering water from the exhaust gas. Since part of the water contained in the exhaust gas is due to the inlet air humidity and the combustion process, the relative amounts of water and their contributions to the overall heat recovery are also calculated.