Hydrogen-rich gas production from sorption-enhanced sludge gasification using CaO-based biochar derived from crab shell as a CO2 sorbent

A CaO-based biochar (CSC) prepared from waste crab shell was used as a low-cost CO2 sorbent to enhance sludge steam gasification for H2-rich gas production. The effects of gasification temperature and CSC addition on sludge gasification performance were investigated. Results showed that the sludge steam gasification can be evidently enhanced with CSC addition and produced H2-rich gas with CO2 removal. The appropriate gasification temperature for CSC sorption-enhanced gasification should be below 800 ℃. With CSC addition at 700 ℃, H2 content increased to 63.2% (36.4% of pure sludge case) while CO2 content reduced to 3.5% (34.5% of pure sludge case). Meanwhile, the H2-rich syngas with high H2/CO ratio (up to 10.2) was achieved. At higher gasification temperature of 800 ℃ and 900 ℃, the CO2 absorbed in the CSC will be released via the decomposition reaction of CaCO3 and adding CSC showed slight effect on sludge gasification. Although the Ca content in CSC was less than 36%, CSC showed almost the same positive effects on H2 production and CO2 reduction compared to pure CaO in sludge gasification process. These findings indicated that CSC has the potential to replace CaO for sorption-enhanced gasification for sewage sludge disposal.