Urban Sewage Sludge Pyrolysis And Steam Gasification Of Residue

Sewage sludge is the by-product of the urban sewage treatment plants. With the progress of social civilization and environmental standards, sewage disposal ability and treatment capacity is increasing year by year in China, resulting in a growing amount of sludge.And sludge treatment and disposal has become a worldwide issue. At present domestic sludge treatment and disposal rate is very low, mainly landfill and farm application, also part of incineration, and these treatments will lead to different levels of secondary pollution. Sludge pyrolysis technology has recycling energy and useful material, technology is not complicated, gas energy products don't need storage, to different material composition it can flexible operation etc.This paper used fixed-bed reactor to obtain fuel gas, and did pyrolysis of sludge recycling research from urban sewage treatment plant. The main findings of this study are summarized as follows:The pyrolysis experiments were conducted using sludge as raw materials, and investigated effects of different reaction conditions on the pyrolysis effect. Obtained that in the operating conditions of this experiment, the best reaction conditions for producing hydrogen-rich gas were: Temperature for 900℃, solid-phase residence time 12min, the use of nickel-based catalyst. At this point, the gas yield was 31.51%, the content of H₂ in the obtained gas was 18.82%, the gas yield was calculated 0.34m3/kg, H₂ production rate reached 2.83mol/kg, gas heat value 8039.77kJ/m3. The composition of the tar which were generated at 500℃was analysed,and found that the content of N and O was high, if used for combustion may produce more secondary pollutants.Dry and wet sludge mixed with biomass respectively, for conducting pyrolysis experiments. The results showed that, when dry sludge and biomass ratio was 67% vs 33%, gas yield and H₂, CH₄ and CO of gas were significantly lower than the results of sludge and biomass pyrolysis alone. This shows that mixing of dry sludge and biomass pyrolysis may be inhibited. Pyrolysis experiments were conducted using the mixture of wet sludge and biomass, with the proportion of biomass increasing, the temperature increased, the gas production rate increased.Steam gasification of sludge pyrolysis residue for hydrogen-rich gas was studied. The influence factors on gasification performance, including gasification temperature, residence time, steam flow and catalyst, were investigated. The optimum conditions for obtaining hydrogen-rich gas from residue were: Temperature for 850℃, solid-phase residence time 15min, the use of dolomite catalyst. In this case, the gas yield was 0.51m3/kg, H₂ yield reached 13.07mol/kg, gas heat value was 7278.5kJ/m3. The content of H₂ in the obtained gas was 56.90%.