| High-temperature Microwave-induced pyrolysis technology for sludge has the advantage in obvious sludge reduction, effective fixation of heavy metals, kill of pathogenic microorganisms, to achieve nontoxic, besides biogas rich in H2 and CO is produced during the process of pyrolysis, which can be used as fuel. It a good prospect of engineering applications. In this study, the high-temperature pyrolysis experiment is operated on a pilot-scale microwave equipment to obtain high-quality biogas. using the intermittent experiment method to investigate the pyrolysis final temperature, heating rate, residence time, activated carbon ratio in pyrolysis gas composition and content, determine the optimum condition. With the above parameters for continuous microwave hightemperature pyrolysis experiment, to obtain the biogas rich in H2 and CO. Hydrogen sulfide releases during the process of pyrolysis of sewage sludge, which pollutes the air. Using XPS, GC-MS and GC analysis methods to detect the yields of sulfur compounds in the solid residue, bio-oil and biogas, respectively. Sewage is mixed with lime for the microwave-induced pyrolysis to achieve H2 S fixation, then using chemical absorption method to remove the remaining H2 S in the gas, to get clean biogas.The single factor experiment was used to investigate the factors which influence the micro-induced pyrolysis of sludge.(1) with the final temperature getting higher, the yield of the biogas increased, and the distribution of H2 and CO in the biogas increased, too. The optimum of the final temperature is 900℃.(2) The increase of the heating rate had the promotion effect on the gas production, and the H2 and CO components also increased.(3) In a certain range, the increase of residence time can produce more biogas, and the content of H2 and CO was higher, too. The optimal residence time is 50 min.(4) Activated carbon is microwave absorbing substance, adding activated carbon can increase the heat transfer efficiency of pyrolysis, and increased both gas production and H2 &CO component content, the best activated carbon ratio is 30%. The optimum condition is determined: final temperature of 900℃, residence time of 50 min, active carbon ratio of 30% and MW power of 1600 W, a 6-hour experiment of continuous microwave-induced pyrolysis of sewage sludge was operated under the optimum conditions. As a result, 16.13 kg of biogas, 5.49 kg of liquid oil, 6.33 kg of solid residue was produced after consumption of 28 kg of sewage sludge. The conversion rate of gas products was as high as 57.8% in which the content of H2 and CO reached 67 %, to achieve the expected results.The concentration of H2 S in the biogas produce by microwave-induced pyrolysis of sludge is detected by GC, which is 0.375 mg/m3, far more than the value of flue gas emission standards. Batch experiments were operated to investigate the H2 S release mechanism, the three phases products of pyrolysis were measured separately. XPS was used to analyze the solid residue, mercaptan, inorganic sulfide, thiophene, sulfoxideand sulfone and sulfate were resisted in the solid residue. With the temperature increase, mercaptan contents declined sharply, and inorganic sulfide and thiophene were produced in a large amount. The bio-oil-S was detected by GC-MS method, which was mainly consist of the aliphatic-S compounds, aromatic-S compounds and theophany-S compounds. When the temperature went higher, the content of aliphatic-S compounds and aromatic-S compounds decreased, and the content of theophany-S compounds increased. The GC was conducted for the analysis of the biogas, H2 S increased obviously at temperatures from 100 to 500℃ and then increased slowly from 500 to 800℃ until reaching the maximum values. By analysis, inorganic sulfide, aliphatic-S compounds and aromatic-S compounds decomposed to release H2 S in the different stages of the pyrolysis. H2 S can be fixed by Ca O to form Ca S to achieve the H2 S removal. In the experiment, 5%(wt.%) lime was added to the sewage sludge to procedure the microwave-induced pyrolysis. The higher the lime added, the higher the removal rate was. When 15%(wt.%) lime was added, the concentration of H2 S is 0.091 mg/m3 by GC, with a significant removal. then using the three methods to achieve further residual H2 S removal. Compared the effect of H2 S removal, the method of Cu-Fe absorption was choosen as the method of desulfurization, which the removal rate of H2 S reached over 98%, The biogas can be directly used. |
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