Performance of a Novel Semi-Closed Gas Turbine Refrigeration Combined Cycle

Abstract

A thermodynamic performance analysis was performed on a novel cooling and power cycle that combines a semi-closed gas turbine called the High Pressure Regenerative Turbine Engine (HPRTE) with an absorption refrigeration unit. Waste heat from the recirculated combustion gas of the HPRTE is used to power the absorption refrigeration cycle, which cools the high-pressure compressor inlet of the HPRTE to below ambient conditions and also produces excess refrigeration depending on ambient conditions. Two cases were considered: a small engine with a nominal power output of 100kW, and a large engine with a nominal power output of 40 MW. The cycle was modeled using traditional one-dimensional steady-state thermodynamics, with state-of-the-art polytropic efficiencies and pressure drops for the turbo-machinery and heat exchangers, and curve-fits for properties of the LiBr-water mixture and the combustion products. The small engine was shown to operate with a thermal efficiency approaching 43% while producing 50% as much 5°C refrigeration as its nominal power output (roughly 50 tons) at 30 °C ambient conditions. The large engine was shown to operate with a thermal efficiency approaching 62% while producing 25% as much 5°C refrigeration as its nominal power output (roughly 20,000 tons) at 30 °C ambient conditions. Thermal efficiency stayed relatively constant with respect to ambient temperature for both the large and small engine. It decreased by only 3–4% as the ambient temperature was increased from 10 to 35 °C in each case. The amount of external refrigeration produced by the engine decreased sharply in both engines at around 35 °C, eventually reaching zero at roughly 45°C in each case for 5°C refrigeration. However, the evaporator temperature could be raised to 10°C (or higher) to produce external refrigeration in ambient temperatures as high as 50°C.