Analysis Of Biogas Releasing Influence Factors In Microwave-induced Catalytic Pyrolysis Of Sewage Sludge

Microwave-induced pyrolysis of sewage sludge can achieve the goals ofrecycle and reduction treatment of sewage sludge. Biogas which is rich in H₂andCO is product of pyrolysis, biogas can be used as fuel owing to its advantages suchas large output, high calorific value. This thesis firstly discussed some influencefactors such as the final pyrolysis temperature, moisture content and addingdolomite and nickel-based catalyst in pyrolysis. Then the releasing rule of biogaswas studied. On this basis, with the purpose of optimizing pyrolysis conditions andpromoting the release of biogas, SEM-EDS, TG-DTG and GC-MS were used toanalyze the mechanism of the catalysts. The solid, liquid and gas phase product ofmicrowave-induced pyrolysis of sewage sludge were emphatically analyzed. Thestudy has much important significance for realizing the optimization andengineering application of the process of microwave-induced pyrolysis of sewagesludge producing biogas.The results of influencing factors of sewage sludge pyrolysis experimentshowed that the biogas productivity and the content of H₂and CO increase with thehigher pyrolysis temperature,800℃for the best. Dolomite and nickel-basedcatalysts can significantly promote the generation of biogas during sludge pyrolysis.With the moisture content of sewage sludge increasing, biogas productivityincreases quickly（80%for the best）.The influence of catalysts on microwave-induced pyrolysis sewage sludgeexperiment showed that nickel-based catalyst and dolomite have promoted thereleasing of biogas. Under the conditions of800℃and5%percent （nickel-basedcatalyst/sludge）, the productivity of biogas reached the maximum, increasing from976.7mL/g to1203.3mL/g. At the same time, the productions of hydrogen andcarbon monoxide reached the maximum values, increasing from29g/kg to35.8g/kg（increased by23.4%） and from302.7g/kg to383.3g/kg （increased by26.6%）,respectively. The sum of H₂and CO reaches the60percentage of total biogas.Catalysts can improve the efficiency of microwave energy utilization, and reducethe pyrolysis temperature required. These two catalysts can improve the quality ofbiogas by catalyzing a series of complicated gas reforming reaction. Nickel-basedcatalyst can promote biogas reforming reaction to get more H₂and CO, less C_xH_y.Dolomite can promote biogas reforming reaction to get more C_xH_y. Overall,nickel-based catalyst has better catalytic effect for biogas releasing.By analyzing the mechanism of microwave-induced pyrolysis sewage sludge, itwas found that nickel-based catalyst mainly work at500⁶00℃,converting C_xH_ytoH₂and CO by catalyzing gas reforming reaction. Dolomite mainly work at 500⁸00℃,promoting the releasing of C_xH_y. Nickel-based catalyst mainly catalyzecyclopentane, pentanol, cyclohexane,dibutyl phthalatein bio-oil cracking. Dolomitemainly catalyze pentane, amyl alcohol, dibutyl phthalate, pyrrole in bio-oil cracking.Thus the quality and productivity of biogas are improved.TG experiments showed that these two catalysts could both promote the weightlosing process of sludge and reduced the reaction activation energy of sludgepyrolysis. The activation energy of sludge pyrolysis with nickel-based catalyst islower. Using first order reaction kinetics equation to calculate the kineticparameters, reaction activation energy E=1.17KJ/mol, frequency factor A=19.73min^-1.