Study On The Co-pyrolysis Characteristics And Synergistic Effects Of Small Particle Size Low-rank Coal And Biomass

China's low rank coal is rich.Low rank coal pyrolysis is an easy-to-use way to utilize coal at a high value,but the conversion rate of pure low rank coal pyrolysis is not high.The pyrolysis process of biomass and low rank coal is similar.The low rank coal has a lower H/C while the biomass has a higher H/C.Using the difference in physical and chemical properties of the two substances,the small particle size low rank coal and biomass are fully mixed for co-pyrolysis to study their co-pyrolysis characteristics,and the two resources are used to complement each other in material structure and properties to achieve the efficient and clean utilization of low rank coal and biomass.This paper takes Sub-bituminous coal and corn straw as the research objects,understands the basic material characteristics of the research objects through industrial analysis,elemental analysis and calorific value test,etc.On this basis,the pyrolysis characteristics of Sub-bituminous coal and corn straw are studied through a synchronous thermal analyzer.It is found that due to the difference in the material structure and chemical characteristics of biomass and low rank coal,the pyrolysis temperature range of the volatiles of the two is different.The thermal decomposition of Sub-bituminous coal mainly occurs around 220?-715?,and the maximum weight loss rate reaches 1.79%/min at 445?.The thermal decomposition of corn straw mainly occurs around 160?-525?,and the maximum weight loss rate is 6.38%/min at 335?.As the heating rate increases from 10?/min to 40?/min,the devolatilization index D of Sub-bituminous coal increases from 2.102×10^-7 to 7.355×10^-7,the devolatilization index D of corn straw increases from 1.470×10^-6 to 6.438×10^-6,increasing the heating rate can improve the release of the volatiles of Sub-bituminous coal and corn straw.Using the deviation?W between the experimental value and theoretical calculation value of the TG curve of Sub-bituminous coal and corn straw to evaluate the synergistic effect,it can be fond that when the heating rate increases from 30?/min to 40?/min,?W increases from 3.115%to 8.035%.At a high heating rate,a synergistic effect occurs in the co-pyrolysis process of Sub-bituminous coal and corn straw,which promotes the release of volatiles during the co-pyrolysis process.As the heating rate increases,the synergistic effect of the co-pyrolysis process of Sub-bituminous coal and corn straw increases.The kinetic model of the pyrolysis process is established and the pyrolysis reaction mechanism is derived using the Malek method.It is found that the most probable mechanism function for the pyrolysis of Sub-bituminous coal is the reaction order n=2,and the corresponding reaction mechanism function is1)1)??=?1-?²,??=?1-?^-1-1,the most probable mechanism function for the pyrolysis of corn straw is the shrinking cylinder,and the corresponding reaction mechanism function is1)1)??=2?1-?₂¹,??=1-?1-?₂¹.Through the pyrolysis test of Sub-bituminous coal,corn straw and their mixture in a fixed-bed pyrolysis device,the influence of the addition of corn straw on the distribution and performance of pyrolysis products of Sub-bituminous coal is studied.It is found that the pyrolysis carbon yield is the highest among the pyrolysis products of Sub-bituminous coal,corn straw and their mixture.The pyrolysis volatiles yield of corn straw is significantly higher than that of Sub-bituminous coal.The addition of corn straw makes the pyrolysis carbon yield decrease by 0.17%,the pyrolysis oil yield decrease by 1.93%,the pyrolysis water yield increase by 0.78%,and the pyrolysis gas yield increase by 1.32%.The gas composition is detected by gas chromatograph and it is showed that the yield of CH₄ is the highest in the hydrocarbon gas products of the pyrolysis of Sub-bituminous coal,corn straw and their mixture,and the yield of CO₂ is the highest in the inorganic gas products of the pyrolysis of Sub-bituminous coal,corn straw and their mixture.The addition of corn straw reduces the yield of H-containing gas products,and increases the yield of CO and CO₂,and reduces the calorific value of pyrolysis gas.Observing the apparent morphology and structure of Sub-bituminous coal and its pyrolytic carbon,corn straw and its pyrolytic carbon through JSM-IT200 scanning electron microscope,it is found that the surface of Sub-bituminous coal particles is rough,and many dense pores are formed on the surface of the pyrolytic carbon after pyrolysis,which results in an increase in the porosity of the pyrolytic carbon.The surface of the corn straw particles is smooth,and after pyrolysis,a rich macropore structure is formed on the surface of the pyrolytic carbon.Some macropores collapse under the action of thermal stress and surface tension to connect some pores together to form pore channels.This study provides theoretical support for the synergy in the co-pyrolysis process of Sub-bituminous coal and corn straw,and provides a reference for the large-scale engineering application of the co-pyrolysis technology of Sub-bituminous coal and corn straw.