Development of a Partial Oxidation Gas Turbine (POGT) for Innovative Gas Turbine Systems

Abstract

Gas Technology Institute (GTI) has been advancing the POGT concept since 1995. The progress to date of a GTI-led team on the development and testing of a POGT prototype, and POGT-based systems are presented. There are two main features that distinguish a POGT from a conventional gas turbine: the design arrangement and the thermodynamic processes used in operation. One unique feature is utilization of a non-catalytic partial oxidation reactor (POR) in place of a typical combustor. An important secondary distinction is that a much smaller compressor is required, one that typically supplies less than half of the air flow required in a conventional gas turbine. From a thermodynamic point of view, the working fluid provided by the POR (a secondary fuel gas) has much higher specific heat than complete combustion products. This allows higher energy per unit mass of fluid to be extracted by the POGT expander than is the conventional case. A POR operates at fuel rich conditions, typically at equivalence ratios on the order of 2.5, and virtually any hydrocarbon fuel can be combusted. Because of these fuel rich conditions, incomplete combustion products are used as the hot section working fluid. A POGT thus produces two products: power and a secondary fuel that usually is a H2 rich gas. This characteristic can lead to high efficiencies and ultra-low emissions (single digit NOx and CO levels) when the secondary fuel is burned cleanly in a bottoming cycle. When compared to the equivalent standard gas turbine bottoming cycle combination, the POGT provides an increase of about 10 percentage points in overall system efficiency. Two areas of recent development are addressed in the paper: POGT development and experimental evaluation of a 7 MWth pressurized non-catalytic POR installed at GTI; and examples of POGT-based systems for combined generation of power, heat, syngas, hydrogen, etc. The POGT design approach to convert an existing engine into a POGT by replacing its combustor with a POR together with concomitant modifications of other engine components is discussed. Experimental results of the POR operation include descriptions of major operating conditions: start up, light off conditions, lean combustion mode, lean-to-rich transition, and operation in rich partial oxidation mode at different loads and air to fuel ratios. The overall efficiency of a POGT two-stage power system is typically high and can approach 70% depending on the POGT operating conditions and the chosen bottoming cycle. The bottoming-cycle can be either a low pressure (or vacuum) combustion turbine, or an internal combustion engine, or a solid oxide fuel cell, or any combination of them. In addition, the POGT can be used as the driver for cogeneration systems. In such cogeneration systems the bottoming cycle can be a fuel-fired boiler, an absorption chiller, or an industrial furnace. The POGT is ideally suited for the co-production of power and either hydrogen, or synthesis gas (syngas), or chemicals. Some of these important applications are discussed.