Production of synthetic natural gas (SNG) from coal and dry biomass - A technology review from 1950 to 2009

SNG production from coal or biomass is considered again due to rising prices for natural gas, the wish for less dependency from natural gas imports and the opportunity of reducing green house gases by CO₂ capture and sequestration. Coal and solid dry biomass (e.g., wood and straw) have to be converted to SNG by thermo-chemical processes (gasification followed by gas cleaning, conditioning, methanation of the producer gas and subsequent gas upgrading). During the 1970s, a number of methanation processes have been developed comprising both fixed bed and fluidised bed methanation. Meanwhile several new processes are under development, especially with a focus on the conversion of biomass. While coal based systems usually involve high pressure cold gas cleaning steps, biomass based systems require, due to the smaller unit size, different gas cleaning strategies. Moreover, the ethylene content of a few percent, typical for methane-rich producer gas from biomass gasifiers, is a challenge for the long-term catalyst stability in adiabatic fixed bed methanation due to the inherent high temperatures.This paper reviews the processes developed for the production of SNG from coal during the sixties and seventies and the recent developments for SNG production from coal and from dry biomass.