Integration aspects for synthetic natural gas production from biomass based on a novel indirect gasification concept

Other conference contribution, 2008

An innovative indirectly heated biomass gasification unit has been recently built at Chalmers University of Technology as an integrated extension of a standard circulating fluidised bed (CFB) boiler for heat and power production. The gasification medium can be varied between steam, oxygen, combustion flue gases or recirculated syngas. In this paper a process for production of synthetic natural gas (SNG) based on this biomass gasification technique is proposed and investigated with emphasis on evaluation of possible heat integration options. Special attention is given to possible options for cogeneration of heat and power. The increase in electricity production from the power cycle is achieved by two means: combusting the non-reacted char from gasification in the boiler and extracting high temperature excess heat from the syngas to SNG conversion steps. It is shown that the amine-based CO2 separation stage is a large heat sink. The reduction of the steam demand for the CO2 absorbent regeneration stripper is of crucial importance to have a maximum of high temperature excess heat available from the gasification process to be used in the steam power cycle. The cold gas efficiency for SNG production comparing biomass input to SNG output is about 60 % for the proposed process. This performance indicator however does not consider the electricity production increase. The balance between SNG yield and increased electricity production is mainly dependant on the gasification efficiency since the amount of char from gasification that is used in the boiler directly influences the yield of synthetic natural gas.