Performance of a Novel Combined Cooling and Power Gas Turbine With Water Harvesting

Abstract

A thermodynamic design-point performance analysis is performed on a novel cooling and power cycle that combines a semiclosed cycle gas turbine called the high-pressure regenerative turbine engine (HPRTE) with a vapor absorption refrigeration system (VARS). Waste heat from the recirculated combustion gas of the HPRTE is used to power the VARS. Water produced as a product of combustion is intentionally condensed and harvested. A part of the VARS cooling is used to chill the gas entering the high-pressure compressor, allowing water condensation and extraction as well as large efficiency gains. The remaining cooling capacity is provided to an external refrigeration load. The cycle is modeled using zero-dimensional steady-state thermodynamics, considering conservative values of polytropic efficiencies, a conservative model for turbine blade cooling, conservative values of pressure drops for the turbomachinery, including heat exchangers, and accurate correlations for the properties of the LiBr–H2O mixture and the combustion products. The cycle is shown to operate with a thermal efficiency greater than 40% for parameters appropriate to medium sized engines, while producing about 1.5kg of water per kilogram of fuel (propane) consumed. This thermal efficiency is in addition to the large cooling effect generated in the evaporator of VARS, equivalent to 3–4% increased efficiency. The efficiency would be greater than 51% without turbine cooling bleed. The refrigeration ratio, defined as the ratio of external refrigeration load to the net work output, is found to be 0.38 for the base case. The water extracted is found to be a strong function of the recirculation ratio and low pressure compressor ratio PRc1. Based on these and prior results, which showed that the HPRTE is very compact and has inherently low emissions, it appears that this cycle would be well suited for distributed power and some vehicle applications, especially ones with associated air conditioning loads.