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.