Using synthesis gas heat to produce work via an externally fired gas power cycle

Abstract

Synthesis gas production requires significant amounts of energy. Efficiency improvements and introduction of renewable or non-carbon energy sources are needed to reduce carbon dioxide emissions. Downgrading of high level heat in synthesis gas cooling trains contributes significantly to exergy losses. Recently, turbine expansion of synthesis gas was investigated by various authors, as one method to reduce exergy losses. However, using synthesis gas as a working fluid poses risks to rotating machinery. Thus an externally fired gas power cycle is proposed, which also allows flexibility to incorporate various types of renewable energy sources. In this study helium is the working fluid and nuclear energy the heat source. A helium-steam combined cycle arrangement is simulated and analysed using energy, exergy and cost analysis. Hot synthesis gas is used to provide additional heat to the helium-steam combined cycle via indirect heat exchange, thereby allowing a close match between the temperatures. Further cooling of the synthesis gas via steam generation is also employed. The work output of the integrated system versus a standalone case was increased by at least 19%. The specific exergy destruction in kW/MW work output was reduced by 38% and the specific equipment cost in $/MW work output increased by 22%.