| The great demands of energy have caused huge depletion of coal and simultaneously led to severe resource and environmental problems,which forces us to seek a clean and renewable resource to partially replace coal resources.Abundant biomass energy resources,low impact on the environment,renewable,great development potential,but it is difficult to be used on a large scale due to its inherent shortcomings.Pyrolysis pretreatment of biomass can significantly improve its performance.The co-gasification of biomass and coal can give full play to the advantages of high coal energy density and high biomass reactivity,and make up for the deficiency of separate gasification of biomass energy,which is of great significance for the largescale industrial utilization of biomass energy and the optimization of China’s energy structure.In this paper,corn stalk,rice stalk,wheat stalk and bituminous coal were used as experimental materials.Biochars were prepared at 200-600℃,its structure and chemical properties were investigated.The CO2 reaction characteristics of biochar and biochar/coal were studied by thermal analysis technology.Finally,the kinetic model suitable for co-gasification reaction was established by data fitting to analyze the co-gasification behavior.With the increase of biochar preparation temperature,the fixed carbon and volatile content of biochar increase,the volatile content decreases,the atomic ratio of O/C and H/C decreases,and the energy quality of biochar improved continuously.Scanning electron microscopy(SEM),specific surface area and porosity analyzer(BET),Fourier infrared absorption spectroscopy(FTIR)and X-ray diffraction(XRD)were used to analyse the structure and chemical characteristics of biochar.The results show that the pore structure and specific surface area of biochars increase significantly,while the pore volume increases first and then decreases.The polar functional groups in biochar are decreasing,the aroma degree is increasing,the carbon structure is more stable,and the heat resistance is enhanced.Higher fixed carbon content and more stable carbon structure increase the starting temperature,ending temperature and maximum weight loss rate of biochar non-isothermal gasification process.Isothermal gasification experiments show that the gasification performance of biochar samples prepared at low temperature(200-300℃)is slightly higher than that of the original sample,while the gasification performance of biochar samples prepared at medium and high temperature(400-600℃)is lower than that of the original sample.The difference in gasification performance is the result of the joint action of carbon structure stability,alkali metal content and specific surface area in biochar.The co-gasification rate of biochar and coal is directly proportional to the addition of biochar.The synergy in the co-gasification process mainly occurs in the later stage of the reaction,and the higher the proportion of biochar,the stronger the synergy.By studying the promoting effect of biomass ash on coal gasification process,X-ray diffraction(XRD),scanning electron microscope and energy spectrum analysis(SEM-EDX)were used to analyze the physicochemical structure of biochar/coal co-pyrolysis coke and gasification residue,and determined that the promoting effect of alkali metals in biochar on gasification process is the key factor leading to synergistic effect In the process of co-gasification,the aromaticity of co-pyrolysis coke decreases,the stacking height of aromatic layer decreases,and the alkali metals in semi coke hinder the ordering process of copyrolysis coke and inhibit the.At the same time,alkali metals are enriched on the surface of coal char and react with carbon matrix in the gasification process to become the active center of gasification reaction and promote the co-gasification reaction.The kinetic calculation shows that the random pore model has a better fitting effect on the gasification process than the shrinking core model and homogeneous model.With the increase of the proportion of biochar,the lower the activation energy of the sample co-gasification reaction,the stronger the gasification reaction activity.Figure[32]Table[10]Reference[116]... |
