Heat recovery aspects of importance for the product mix and GHG emission reductions in a bio-SNG system

Journal article, 2014

This paper presents the impact of adjusted operating parameters (superheating temperature and backpressure or condensing mode) for the heat recovery steam cycle (HRSC) by external conditions on the product mix (SNG; power and heat) in a commercial scale gasification-based bio-SNG (biomass derived synthetic natural gas) production system. The GHG reduction potentials for a case with a condensing HRSC and for a case with the HRSC in backpressure mode producing heat for CO2 separation of the flue gases are evaluated. Pinch technology was used to identify the potential for heat recovery and process integration. Small changes in the operational parameters of the HRSC can result in significant changes of the conversion efficiencies of heat and power. With an HRSC in back-pressure mode, reducing the power production by 4 MW compared to the condensing case, it is possible to produce ~60 MW of heat for district heating. This study shows that approximately one third of the carbon input to the gasifier ends up in the SNG, whereas one third is separated prior to methanation and one third is emitted as CO2 in the flue gases from the combustor of the indirect gasifier. If infrastructure for CO2 storage is available, and CO2 separated from the process and from the flue gases is stored, the GHG emission reductions from the bio-SNG system can be doubled compared to a case without CO2 storage possibility..