Study On The Reaction Characteristics And Kinetics Of Co-Pyrolysis And Co-Gasification Of Paper Sludge And Bituminous Coal

Co-pyrolysis and co-gasification of paper sludge and bituminous coal can not only effectively avoid the problems of low utilization efficiency and serious environmental pollution when paper sludge and bituminous coal are pyrolyzed and gasified separately,but also can give full play to the pyrolysis or gasification of paper sludge and bituminous coal.It is of great significance to the efficient and clean utilization of paper sludge and bituminous coal.During the co-pyrolysis and co-gasification of the paper sludge and bituminous coal,the pyrolysis and gasification characteristics,mineral composition and coke structure will undergo important changes.This paper analyzed the co-pyrolysis and co-gasification characteristics and kinetics of paper sludge and bituminous coal under different blending ratios by thermogravimetric analysis,and explored whether there was a synergistic effect in the co-pyrolysis and cogasification process of them.By analyzing the Fourier Transform Infrared Spectroscopy(FTIR),In-situ DRIFTS,X-ray Diffraction(XRD)Raman spectroscopy(Raman)spectroscopy of paper sludge and bituminous coal co-pyrolysis and co-gasification of char under different blending ratios,to study the evolution of the carbon structure and minerals of them in the co-pyrolysis and co-gasification process.Paper sludge was pyrolyzed before bituminous coal and the pyrolysis temperature range overlapped,so co-pyrolysis was prone to interaction.The pyrolysis of the two was divided into three stages:the first stage was the devolatilization of the paper sludge;The second stage was the devolatilization of the bituminous coal,accompanied by the carbonization of the paper sludge.The third stage was the mineral pyrolysis of paper sludge.As the blending ratio of paper sludge increased,the total weight loss rate was higher and the maximum weight loss rate increased.The blending of paper sludge with bituminous coal reduced the pyrolysis start temperature and termination temperature,and improved the pyrolysis reaction characteristics of bituminous coal.The activation energy required for the co-pyrolysis of paper sludge and bituminous coal was significantly lower than the activation energy required for the separate pyrolysis,indicating that there was a synergistic effect in the co-pyrolysis process.Pyrolysis char of bituminous coal contains quartz,periclase,hematite and calcium sulfite.Calcium sulfide was formed by the reaction of CaO and H2S produced by the decomposition of organic matter in coal.The minerals in the pyrolysis char of paper sludge A include calcite,calcite,calcite and quartz,and the pyrolysis char of paper sludge B contains mullite,talc and periclase.The weakening of the diffraction peaks of calcite and the appearance of calcite and calcite indicated that calcite decomposed.CaO reacted with aluminosilicate to form gehlenite at high temperature,which reduced the catalysis of calcium-containing substances in mixed pyrolysis char.The appearance of mullite was due to the thermal transformation of kaolinite,and the appearance of periclase was due to the decomposition of dolomite.With the increase of the blending ratio of paper sludge,the diffraction peaks of calcite,mullite and gehlenite strengthened,and the diffraction peaks of portlandite first strengthened and then weakened,indicating that the co-pyrolysis of papermaking sludge and bituminous coal promoted the decomposition of calcite,the thermal transformation of kaolinite,and the formation of portlandite and gehlenite,indicated that the co-pyrolysis of the two had a synergistic effect.The FTIR analysis conclusion was basically consistent with the XRD conclusion.In-situ infrared analysis shows that the aliphatic structure of paper sludge was richer than that of bituminous coal,and the aromatic carbon skeleton was less than that of bituminous coal.The activity of the fat structure is higher than that of the aromatic structure,so the pyrolysis reaction activity of paper sludge is higher than that of bituminous coal.There were two obvious carbon peaks in the Raman spectra of paper sludge and bituminous coal.With the increase of the blending ratio of paper sludge,the positions of the G and D peaks remain basically unchanged,but the intensity gradually decreased.This is due to the higher content of aromatic hydrocarbons in bituminous coal while the higher content of aliphatic and oxygen-containing functional groups in paper sludge.With the increase of the blending ratio of paper sludge,the intensity of the two characteristic peaks of the paper sludge and bituminous coal co-pyrolysis first decreased and then increased,because the pyrolysis of the paper sludge preceded the bituminous coal to form a graphite-like structure,the bituminous coal devolatilization was affected,and the content of alkaline earth metals in the mixture increased,which has a positive effect on the intensity of the Raman spectrum.The complex change trend of carbon structure parameters show that the interaction of paper sludge and bituminous coal is not single in the co-pyrolysis process,and the interaction of different sludge samples,blending ratios and pyrolysis stage is quite different.The co-gasification of paper sludge and bituminous coal was divided to three stages.The first stage(200-500?)was the devolatilization of paper sludge and bituminous coal;the second stage(800-900?)and third stage(900-1100?)were paper sludge and bituminous coal semi-coke gasification stage,respectively.The decrease of co-gasification start temperature,end temperature and the temperature Tmax correspond to the maximum weight loss rate of semi-coke gasification stage,indicating that the blending of paper sludge improved the gasification of coal char.The activation energy of the first and third stages of co-gasification of paper sludge and bituminous coal decreased and increased with the increase of the mixing ratio of paper sludge,respectively.Because the active molecules were gradually consumed and the catalytic substances were deactivated in the gasification process,and the higher ash content in the paper sludge was likely to cause blockage of the active sites.The kinetics has a high degree of fit,and the correlation coefficients R2 are all greater than 0.96.The bituminous coal gasification residual char contains quartz,gehlenite,magnetite and calcite.Paper sludge A gasification char contains calcite,gehlenite,lime and quartz.Paper sludge B gasification residual char contains lime,quartz,mullite,magnesite,talc,calcite and anorthite.Anorthite was formed by the reaction of lime produced by the decomposition of calcite and metakaolinite produced by thermal conversion of kaolinite.With the increase of the mixing ratio of paper sludge,the intensity of the 002 crystal plane peak gradually decreased,and the diffraction peak gradually becomes narrow and sharp,indicating that the content of ordered microcrystalline structure increased.The diffraction peaks of calcite and lime gradually also increased.In the gasification process,the gasification agent carbon dioxide has the effect of inhibiting the decomposition of calcite.However,the diffraction peaks of the gehlenite,gradually weakened or even disappeared,indicating that the co-gasification of paper sludge and bituminous coal inhibited the formation of gehlenite from calcium-containing substances reacted with clay minerals containing Al and Si.