Preparation of biochars for co-gasification from sweet sorghum bagasse

Abstract

Biochar is a solid product obtained through torrefaction, liquefaction or pyrolysis of organic material. It can be used for soil amendment, activated carbon for sequestration, or as bio-coal for gasification or co-gasification. A recent patent on GreenCoal showed the potential of biochar to lower sulphur emissions and increase coal reactivity during co-gasification with low grade discard coal. Co-gasification of biochar and coal with increased reactivity, translated to increased syngas production using existing synthetic fuel plants without the need for modifications to accommodate biomass in the feed. In this study biochar for co-gasification purposes was produced from sweet sorghum bagasse using hydrothermal liquefaction at low heating rates (2.5 K.min-1) in large (1 L) reactors. The effect of reaction temperature and biomass loading on biochar yield and characteristics were investigated with and without the addition of a calcite (CaCO3) catalyst. Prepared biochars were characterised using SEM, ultimate analysis, proximate analysis, BET, XRD/XRF and FTIR. High biochar yields (558.7 g.kg-1 bagasse) were obtained with very little oil and gas products forming. Biochar yields decreased with an increase in temperature and increased with an increase in biomass loading. Elemental analysis showed an increased higher heating value (HHV) for all the prepared chars compared to the original bagasse. Characterisation of the chars showed that the additional of a calcite catalyst increased the biochar yields and significantly changed the structure of the chars. The study showed that lignocellulose materials such as sweet sorghum bagasse can be used to prepare biochars with characteristics similar to young lignite coal, without the minerals and sulphur present it coal