| It has been greatly concerned about the treatment of sewage sludge. Thermalutilization is considered as one of the important technologies. Thermal drying of sewagesludge is an necessary intermediate process during all thermal processing which isclassified into several categories, i.e. incineration, pyrolysis, gasification and so on.Thermal processing of sewage sludge is a combined course between evaporation ofwater and devolatilization. The odorous compounds among volatiles during thermal dryingprocess have a critical healthy risk on human body. Few researches focused on the emissioncharacteristics of volatiles during the integrated thermal drying process, but in fact dryingconditions have remarkable effects on whether devolatilization starts after completion ofevaporation or the two processes overlap, and the reactions between volatiles and H2Oshould not be ignored. Emission characteristics of volatiles during low-moderatetemperature devolatilization of sewage sludge was investigated.Conclusions:It was shown that the concentration of NH3and NO2are much higher than those ofNO and HCN in these4nitrogen-containing gases. It was proposed that NH3were formedfrom desorption, decomposition of ammonium salts and amino. There were other routes forNH3to release. The emission of NO, NO2and HCN was improved by O2through thereaction among nitrogen-containing gases.The emission of6sulfur-containing gases（H2S, SO2, CH3SH, CS2, C2H6S2&COS）were investigated during low-moderate temperature devolatilization. It was shown that theconcentrations of H2S, SO2and CH3SH are much higher than those of CS2, C2H6S2andCOS in these6sulfur-containing gases. It was proposed that H2S, SO2and CH3SH weremainly formed from transformation of organic sulfur in sewage sludge. The reactionbetween FeS2and CH4was concluded the main cause of CS2formation, CH3SH wasbelieved as a precursor of C2H6S2. The transformation from organic sulfur in sewage sludgeto sulfur-containing gases was improved by CO2. O2also played a dominant role duringdecomposition process of CH3SH. The weight loss of the solid at150℃under three atmospheres was due to evaporationof water, and adsorptions led to the little release of gases. The char yield under air was lessthan those under N2and CO2. Sulfur concentration of char under air was less than thoseunder N2and CO2as well. A chart was presented to describe the sulfur distribution andtransformation which included the distribution of sulfur in sewage sludge, organic sulfur insewage sludge transformed to sulfur-containing gases and tar, decomposition of sulfate,pyrite transformed to sulfur-containing gases, reactions among sulfur-containing gases andother possible reactions. |
