Sorption-enhanced gasification (SEG) of agroforestry residues: Influence of feedstock and main operating variables on product gas quality

Abstract

Sorption-enhanced gasification (SEG) is a promising route for the conversion of biomass into synthetic fuels. There are important aspects regarding syngas quality (e.g. tar composition and/or gaseous contaminants such as H2S) that may influence the scaling-up of the process and should be assessed. Experiments were performed in a 30 kWth bubbling fluidised gasifier to evaluate the effect of the feedstock used, temperature, sorbent-to-biomass (S/B) ratio and/or steam excess on such quality aspects. Larger amounts of tars were found for straw, which corresponded to highly stable tars (benzene, toluene, naphthalene and phenanthrene). Temperature, S/B ratio and steam excess favoured tar decomposition, causing the contribution of PAHs to total tar to increase. PAHs and phenol contents were found to be related to and dependant on the temperature and S/B ratio. Elutriated CaO particles reacted with the H2S formed until equilibrium conditions were reached, leading to syngas H2S contents of between 15 and 85 ppm. Sulphur in the syngas represented no more than 15% of the total sulphur introduced into the reactor, whereas 65–85% ended up as CaS with the partially converted sorbent particles leaving the reactor.