Cleaning and Conditioning of Biomass Gasification Gas to Produce Biomethane

Abstract

Nowadays, it is urgent to develop new energy production and utilisation routes to achieve sustainable development with low environmental impact. Gasification of biomass wastes followed by biomethane production may contribute to achieve these goals. The objective of this paper is to study hot cleaning and upgrading processes of gasification gas to allow it to be suitable for biomethane production. Gas produced by gasification of eucalyptus wastes at 750 ºC and 850 ºC was used to study the hot gas conditioning process. For this, two sequential fixed bed steps with different catalysts or sorbents and at different temperatures were tested. In Pathway A, a low cost natural mineral, limestone, was used in both steps at temperatures from 500 º to 700 ºC. In Pathway B, limestone was used in the first step and in the second one, a nickel-based catalyst was tested. The effect of temperature was also studied by using temperatures between 500 ºC and 700 ºC. Pathway B showed to be the best option, especially at the highest temperature tested, producing a syngas richer in H2 and CO2, with very low contents of tar and heavier gaseous hydrocarbons. Pathway B was also effective for great NH3 and H2S reductions, around 90 %, leading to final NH3 and H2S concentrations of around 158 and 21 mg/m3, respectively. Further reductions will be studied by testing new multi-functional and more specific catalysts in the next studies, accordingly with new biomethanation catalysts requirements.