Closed-Cycle Micro Gas-Turbine System with Overexpansion Turbines and Heat Regeneration for Underwater Application

Underwater machinery has an important role to play in the development of the Arctic offshore fields; such machinery must feature substantial energy capacity and be capable of long-term stand-alone operation while isolated from the base infrastructure. Of the various types of power plants, the most promising technology is the closed-cycle gas-turbine units (CGTU), which feature large power density. This paper analyzes the cycles of the CGTU of various designs; for the baseline, the research uses a heat-regenerating CGTU, as it is more cost-effective compared to simple-cycle CGTUs; besides, this design is preferable for micro gas-turbine units capable of using single-loop cycle with air-oxidized organic fuels. The fluid is nitrogen as the main component, mixed with fuel combustion products. Excess fluid (nitrogen and carbon dioxide) is removed from the cycle and goes overboard. It is proposed to further enhance the simple-cycle cost-effectiveness by the deep recovery of the exhaust-gas heat in the turbo-compressor utilizer (TCU), which consists of an overexpansion turbine that drives the exhaust compressor, and recuperator, with a gas cooler being placed in-between. It has been found out that the cost-effectiveness of a CGTU with a TCU is 15...25% more cost-effective than the baseline CGTU; the power density is 1.5 times larger on average while sustaining optimal engine compressor pressure boosting.