Effect Of Mechanical Thermal Expression Dehydration On Spontaneous Combustion Tendency And Moisture Re-absorption For Lignite

China's lignite resources are abundant and its thermal efficiency is low when it is directly burned.Lignite has rich oxygen-containing functional groups.The inherent porous porosity structure aggravates the occurrence of low-temperature oxidation spontaneous combustion and moisture re-adsorption,which brings huge safety hazards and is not conducive to storage and transportation.Its efficient upgrading and clean utilization have important energy strategic significance.In this paper,Zhaotong lignite was selected as the research object and the mechanical thermal expression process was proposed.The well-formed samples were obtained while removing moisture.The upgraded samples with different conditions were obtained by changing the time and temperature.With FTIR,SEM,MIP,XRF,TG-DSC and other characterization methods were used to analyze the physicochemical properties of raw coal and upgraded samples.The experimental test equipment was built independently and the spontaneous combustion tendency of coal was determined by cross-point temperature?CPT?,adiabatic heating rate(R₇₀),oxidative combustion characteristic temperature point and other indicators.The moisture re-adsorption rules of each upgraded sample under different temperature and humidity conditions were studied,and the isothermal adsorption and adsorption kinetic models were established to explain the process and difference of relapse.The water content of Zhaotong lignite is as high as 56.12%.It has low metamorphism,loose overall structure,rich oxygen-containing functional groups on the surface and abundant pore structure.The macropores of about 100?m are mostly,and the porosity is as high as 43.41%.This provides sufficient conditions for coal re-adsorption and low temperature oxidation.Different structural sites reflect different reactivity during combustion.The water content,pore structure change,ash and mineral content,particle size and the number of oxygen-containing functional groups of the upgraded coal are the main factors affecting the spontaneous combustion of lignite.With the decrease of water content,the tendency of spontaneous combustion increases gradually;The pore volume decreases,and the transformation of large pores into smaller pores and mesopores can inhibit the spontaneous combustion of lignite;The reduction of ash and mineral content leads to the tendency of spontaneous combustion to be higher than the same moisture dried with nitrogen;Above the critical diameter?1-2mm?,the spontaneous combustion tendency increases with the increase of particle size.The advantage of the MTE process for suppressing lignite spontaneous combustion lies in the size of the molded product;Destruction of some oxygen-containing functional groups can inhibit the occurrence of relapse and low-temperature oxidation reactions.The moisture re-adsorption rate of the sample decreases with the increase of the mechanical thermal expression temperature.The difference of the mechanical thermal expression time is small.Increasing the particle size can suppress the amount of moisture re-adsorption and prolong the time to reach the relapse equilibrium.Changing the ambient temperature and humidity,the sample absorbs the most at30°C and the moisture re-adsorption amount increases with the increase of humidity.The adsorption isotherm type of the upgraded coal belongs to the type II isotherm adsorption,which is suitable for the Dent model.The adsorption amount of the first layer is affected by the oxygen-containing functional groups such as hydroxyl group and carboxyl group,and the change of the first layer decreases with the increase of the mechanical thermal expression temperature.The difference in mechanical thermal expression time was not significant.The second layer adsorption did not change significantly.The quasi-secondary kinetic model has a great fitting effect on the moisture re-adsorption law of the sample.The adsorption rate constant is positively correlated with the temperature,but gradually decreases with the increase of the environmental humidity.The increase of the mechanical thermal expression temperature can suppress the adsorption rate constant of upgraded sample,while the effect of mechanical thermal expression time is not clear.The paper has 47 pictures,11 tables,and 89 references.