Hybrid Gas Turbine and Hydraulic Air Compressor System

Abstract

Using a hydraulic air compressor (HAC) instead of a mechanical driven compressor in a gas turbine based system can provide significant performance benefits. In particular very high thermal efficiencies can be achieved at modest firing temperatures. Although the HAC based hybrid system has many applications this paper reports on a study and analysis of such a hybrid as it might be integrated into a coal to electricity power plant. In this specific case the HAC is used to provide both compressed oxygen depleted air to a recuperated, fired turbo-expander and low-pressure oxygen enriched air to a coal gasifier. The oxygen enriched air improves the lower heating value of the derived coal gases obtained allowing them to be compressed economically and injected into the combustion system. Run-of-stream applications of the HAC can provide thermal efficiencies on the order of 70% or higher, whilst pumped approaches can achieve efficiencies around 50%. The pumped water HAC combined with a recuperated gas turbine is effectively an intercooled, and recuperated (ICR) cycle. In the non-pumped HAC systems the very high thermal efficiencies can provide coal to electricity conversion efficiencies on the order of 60%. The actual efficiency depends strongly on the type of gasifier employed and on whether or not the gasifier employs waste heat recovery. The overall cost of electricity so generated is very competitive despite the high capital costs associated with coal handling and gasification.