Process Mechanism And Product Characteristics Of Low Rank Coal Pyrolysis Using Inner-rotatory Moving Bed Reactor

The pyrolysis technology of low rank coal is one of the key technologies in the coal staged conversion path,which faces problems such as dust entrainment,dust removel and product control.The inner-rotatory moving bed(IRMB)pyrolysis technology that integrates the advantages of low dust entrainment and high heat transfer rate is a high-efficiency conversion technology for the low rank coal with small particle size.Therefore,the technology has a good application prospects and its basic theories need a detailed study.In this thesis,the axial and radial movements and mixing process of particles in the IRMB reactor were firstly analyzed by means of cold test and numerical simulation.Then,a particle group pyrolysis model for IRMB process was established based on the mechanism analysis of heat transfer and reaction,which was subsequently verified by pyrolysis test.Finally,the characteristics of semicoke and coal tar were studied to obtain the control technical method.The particles'movement test and simulation results showed that the particles in the IRMB reactor presented an irregular spiral movement pattern.The mean residence time of particles displayed a linear relationship with the length of rotating shaft and a power function with the rotation speed,but no significant relationship with the particle size(1-6 mm).The total average velocity of particles in the IRMB reactor was related to the rotating shaft speed,and the relationship was a power function under the speeds?10 r/min while a linear function under the speeds>10r/min.Under the rotating shaft speed of 5 r/min,the instantaneous average velocity of particles was concentrated in the range of 0.015-0.030 m/s,and the particle radial diffusion coefficient,D_r,was mainly distributed in the range of 0-2 mm²/s with a highest value of 16 mm²/s and an average value of 1.72 mm²/s.The Lacey-mixing index reached about 0.8 when the rotating shaft rotated for a round.Based on thermogravimetric test,the average activation energy E₀,pre-exponential factor k₀ and standard deviation of activation energy in the distributed activation energy model for pyrolysis were calculated to be 246.35k J/mol,3.08×10¹⁵s^-1 and 35.9 k J/mol respectively by means of equal conversion method and Pattern Search method.The unit particle group was treated as"virtual particle",and a mathematical model for the pyrolysis process of low rank coal in IRMB reactor was established.Experimental verification showed that the maximum error between predicted value of semicoke yield and pyrolysis test value was 4.93%.The maximum heating rate of the particle group was 0.33-0.69?/s when the reactor wall temperature was set as 550-750?.When the reactor wall temperature increased from 550?to 750?.The maximum instantaneous release rate of volatile matter increased from 0.64×10^-4/s to 1.79×10^-4/s.The minimum pyrolysis time of particles should be kept above 90 min to reach the thermal equilibrium stage in the reactor.The ignition point and explosiveness of semicokes could be adjusted by the coordination of pyrolysis temperature and time in the IRMB reactor.The gasification reactivity index R of semicoke kept decreasing with the temperature increased at the same pyrolysis time.The change of R value was in connection with the disappearance of various types of methyl carbons in the macromolecular structure of semicokes.Under the pyrolysis time of 90 min and 150 min,the burning-out characteristic index C_b,combustion stability index R_w,comprehensive combustion characteristic index S_N of semicokes showed an uniform attenuation with the increase of pyrolysis temperature.Under the conditions of pyrolysis temperature of 550-750? and pyrolysis time of 90-150 min,the distance between microcrystalline lamella d₀₀₂ reduced,the mean height of lamella L_c and the dimension of lamella L_a raised generally with the increase of temperature and time.Through the coupling design of reactor structure and combustion process,including heating flue isolation of coal pyrolysis zone and dust settling zone,exhaust gas distribution and high-temperature air combustion,the differential distribution of temperature field in the reactor was realized.It could increase coal tar yield and the content of light fraction as much as possible when the coal pyrolysis zone at the bottom of the reactor was controlled at a relatively high temperature(650-700?)and the dust settling zone upper in the reactor was controlled below 500?.The highest content of light fraction(boiling point<360?)in the tar obtained under the optimal pyrolysis conditions was 72.2%.The contents of quinoline insolubles in the tar obtained from the pyrolysis pilot test were less than 1%by the process of multi-stage dust removal that was included in the IRMB technology.