| Sewage sludge is the byproducts of municipal wastewater treatmentplants.Recovery energy and useful materials from sludge have become a challengeof environmental technology. Microwave pyrolysis is a technology which attracts lotsattentions for its effective reduction of sludge, high added value of byproducts, stablity ofheavy metals and controlled pollution smoke. This paper discussed the influences ofprocessing conditions on microwave pyrolysis and analyzed the characteristics,components and emission rules of the gases and oils. The feasibility and safty of theglass-ceramics production from solid residue were investigated in the paper. Toevaluate potential of the microwave pyrolysis technology, the energy conversionefficiency and economic benefit were also analyzed in this paper.The influences of dehydration and digestion on microwave pyrolysis of sludgewere stuied. The results showed that the sludge with80%water content which couldreach800℃in3minswas proper for microwave pyrolysis. It was found that highsolid yield was achieved after digestion treatment which was not proper forpyrolysis. SiC, active carbon and solid residue could be used as microwave receptorto help sludge reached high temperature and the best additive ratio was solid residue:sludge=3:50. Oil yield reached the highest value under400~600W input powerwhile gases obtained the highest yield under1000~1200W.TG/DTG analysis was used to determine the charicteristics of sludge in themicrowave field. The evalution rules and mechanisms of gas products frommicrowave pyrolysis was investigation by FTIR and GC. The main components ofgases were H2, CO and CH4, which accounts for59.61vol%of gases. The highestconcentration of H2was41.5%which was reached at500℃. CO was mainly formedat400and600℃, at which carboxyl, aether and half-char were decomposed andhydroaromatic cycle was dehydrogened. CH4was mainly formed in the regions of350~500℃and700~810℃. It was related with the decomposition of-OCH3,toluene, aliphatic chain with oxygen-containing functional groups. The cyclizationof carbon chain long-chain aliphatics were also the main origin of CH4. The hazardcomponents of gases were HCN、NH3and H2S. HCN、NH3were generated bydecomposition of ammonium, protein and heterocyclic nitrogen. H2S was mainlyfrom the aliphatic sulfide and sulfate.The results of GC-MS showed that oils mainly were comprised by alkanes,alkenes, monocyclic aromatic hydrocarbons (MAHs), phenol and little polycyclicaromatic hydrocarbons (PAHs). Alkanes mainly contained pentadecanes andhexadecanes, which were the results of first cracking of fat, protein and amylase.The formation of alkenes was attributed to the removal of proton from alkanes. Thehighest yield of alkenes was found at800℃.The highest content of MAHs was30%and it was reached at600℃.1000~1200℃was the generation region of PAHswhich mainly originated from the condensation of alkenes and MAHs. Net recovered energy was found in the both of gases and oils production. Oilsproduction by microwave heating had higher yield rate of energy.The heaing regime, crystalline phases, microstructures, physical chemicalproperties and heavy metals stability of glass-ceramics prepared from solid residuewere studied. The results showed that the nucleation and crystallization of themicrowave-prepared glass-cramics were759.8and969.5℃which reduced thetemperatures of electric furnace by79.9and15.6℃, respectively.The correspondingmajor phases of900,950and1000℃crystallization temperature were thewollastonite, the mixture of wollastonite and anorthite and the anorthite. Thehighest bending strength was110.2MPa, which was15.2and25.2MPa higher thantraditional-prepared and natural marble. The lowest thermal expansion coefficientwas4.1×10-6/℃which was2.7and3.9×10-6/℃lower than later two. TCLP resultsshowed that leaching concentration of heavy metals were much lower than limitconcentration in national identification standard of hazard waste. |
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