Hydrogen-rich gas formation characteristics during microwave-induced high temperature pyrolysis of sewage sludge

Pyrolysis of sewage sludge was conducted in a single-mode microwave reactor and an electric-heated tube furnace, respectively. The effects of particle size, moisture content, pyrolysis temperature, and structure of microwave receptor on the yield and composition of hydrogen-rich gas were studied. The results indicate that the sludge particle size within 0~5.00 mm has no obvious effect on the mass distribution of pyrolysis products. However, H₂ and CO concentrations increase with decreasing of particle size. When the size decreases from 2.50~5.00 mm to <0.45 mm, the H₂ concentration increases from 31% to 34%, and that of CO increases from 17% to 22%. Both the sludge moisture content and the pyrolysis temperature have great influences on distribution of the pyrolysis products. Higher moisture content or pyrolysis temperature will lead to markedly higher concentrations of H₂ and CO. When the sludge moisture content increases from 0 to 83%, H₂ concentration increases from 32% to 42%, and CO concentration increases from 20% to 31%. Microwave absorber in powder phase can transform more volatile compounds into incondensable gas than that in fixed phase, and the concentrations of H₂ and CO also increase slightly.