Thermodynamic Analysis And Experimental Study Of Copper Slag Temperature Catalytic Gasification Of Municipal Solid Waste

Based on the perspective of environmental protection and energy resource optimal utilization,more and more scholars at home and abroad pay close attention on municipal solid waste gasification technology to find an approach of higher energy conversion of MSW. Given the complex components of Municipal Solid Waste(MSW)and the gasification technical problems such as low gasification efficiency, low heating value of gas and higher tar content, the combustible biomass (sawdust,confetti) and high polymer(plastic, rubber) were regarded as gasification feedstock and steam was regarded as the gasification medium in this study. At present, the tar is the main factor which restricts the development of the gasification technology. Catalytic pyrolysis of tar is the most effective conversion method,then it is necessary to find a cheap and efficient catalyst for tar cracking. Olivine used for MSW gasification is the cheaper and resistance catalyst and the catalytic components mainly are Fe or Fe oxides. The composition of copper slag which is generated by the copper smelting process is similar to olivine’s and its main mineral phases are2FeO·SiO2and Fe3O4. In addition, higher heat should be provided for the endothermic reactions of MSW steam gasification.In view of that, it was studied that MSW steam gasification using high-temperature copper slag as catalyst and using high temperature copper slag waste heat as the heat source in this paper.Firstly, the thermodynamic model of MSW steam gasification was established based on the method of minimum gibbs free energy through thermodynamic calculation of MSW steam gasification system.The influence of gasification temperature and S/M (steam quality/materials quality) on MSW steam gasification features was predicted by model. The correctness of the model was verified by comparing model predicted results with the experimental results from literature. Model predicted results indicate that the influence of gasification temperature and S/M on gasification efficiency and fixed carbon conversion rate is different response surface and the regression equation can be expressed as following: the gasification efficiency of sawdust, confetti, plastic and rubber is η=c+aT+b(S/M)+dT(S/M) and fixed carbon gasification conversion rate of sawdust, plastic and rubber is Xc=c+aT+b(S/M)+dT(S/M) and fixed carbon gasification conversion rate of confetti is Xc=c+aT+b(S/M)+dT(S/M)+eT2+f(S/M)2.The RMS errors of between model predicted results and experimental results in literatures are less than10%which is within the scope of the engineering permissible error and the model can simulate MSW steam gasification accurately.Secondly, The various components of MSW steam gasification experiment was studied by gasification experimental bench and various components of producted gas were detected offline by Gas Chromatography(GC),then the applicability of the model was verified by comparing model predicted results with the experimental results. Experimental results show that the influence of gasification temperature and S/M on gasification efficiency and fixed carbon conversion rate of MSW components gasification is different response surface and the regression equations are consistent with the model predicted results. The optimal condition of MSW gasification is following:sawdust gasification:T=950℃, S/M=2.0, gasification efficiency is84.79%, fixed carbon conversion rate is86.64%,Confetti gasification:T=950℃, S/M=1.74, the gasification efficiency is86.74%, fixed carbon conversion rate is79.57%; Plastic gasification:T=950℃, S/M=2, the gasification efficiency is28.18%, fixed carbon conversion rate is50.33%; Rubber gasification:T=700℃, S/M=2, the gasification efficiency is50.11%, and fixed carbon conversion rate is28.78%and the RMS errors of between model predicted results and experimental results are less than10%which is within the scope of the engineering permissible error and the model is suitable for simulating MSW steam gasification.Thirdly, techniques such as XRD、SEM、BET、H2-TPR、TG、FT-IR, GC-MS analysis were used to characterize catalytic activity of copper salg and catalytic gasification experiment using copper slag catalyst was studied by in the two-stage fixed bed catalytic gasification test bench. XRD characteristic results show that the characteristic peaks of fayalite(Fe2SiO4) weaken gradually to disappear and the characteristic peaks of SiO2appear and the characteristic peaks of magnetite (Fe3O4) enhance then weaken and the peak of hematite (Fe2O3) gradually strengthened with calcination temperature increasing. SEM and BET characteristic results show that specific surface area of pre-calcined copper slag larger than untreated copper slag. H2-TPR characteristic results show that high calcination temperature is benefit for the formation of magnetite and hematite. Catalytic experimental results show that H2percentage increases significantly and the yield of gas grows by8%～18%and gasification efficiency and fixed carbon conversion rate increases by8%approximately under the catalysis of copper slag. The calcined copper slag for1000℃-4h shows the highest catalytic activity. The catalytic mechanism of copper slag showed that the catalytic activity compositions of copper slag are Fe3O4and Fe2O3which promote reaction of generating CO and H2such as CH4-H2O(CO2),C-H2O(CO2),C2-H2O(CO2),CnHm-H2O(CO2) and CaHbO(tar)-H2Oand its catalytic activity depends on the percentage content of Fe3O4and Fe2O3and the catalytic activity increases as the percentage content increasing.Finally, the temperatures of copper slag were measured before and after catalytic gasification and the waste heat of different temperature of copper slag and the waste heat recovery utilization rate were calculated based on the average specific heat method. Results show that the waste heat of copper slag increases as temperature increasing and the waste heat of copper slag is1155.34KJ/kg with950℃and1507.82KJ/kg with1250℃. Temperature changement of copper slag increases before and after catalytic reaction and waste heat recovery utilization rate increases from16.96%to21.81%as atalytic gasification temperature increasing from700℃to950℃.