| Micro spout bed(MSB)has attracted more and more attention because of its wide application range,high heat and mass transfer efficiency,small gas back-mixing and other characteristics.In this dissertation,aiming at the gas back-mixing characteristics in the micro spouted bed reactor(MSBR)and the influence of the degree of back-mixing on the activation energy(E),the effect of the different operating conditions on gas back-mixing in the micro fluidized bed reactor(MFBR)was firstly studied,The activated coke combustion is taken as a model reaction to obtain the effect of the degree of gas back-mixing in the MFBR on the reaction kinetics,the difference of gas back-mixing between MSBR and MFBR was systematically studied,the operating conditions of gas flow approaching the plug flow in the MSBR were optimized,and the rice husk pyrolysis is finally taken as a rapid reaction model to study the different in the E calculated between MSBR and MFBR under the same operating conditions.It revealed the fact that the E becomes larger with decreasing the degree of gas back-mixing in the reactor,clarified that the gas back-mixing between MSBR and MFBR is different,that is,the degree of gas back-mixing in the MSBR is lower than that in the MFBR under the same bed diameter and gas flow conditions,revealed that the height of E(t)peak E(t)h and variance?t2 of the gas residence time distribution function in the MSBR satisfy the normalization correlation and the relative residence time difference between ideal plug flow and real gas flow is 10%,E(t)h is larger than 2.0,?t2 is below 0.15,and verified that the gas flow in the MSBR is more accessible to the plug flow characteristics than the MFBR.(1)The effect of gas back-mixing on kinetics of gas-solid reaction in MFBR.The influence of the operating conditions,such as inner diameter(D)of the reactor,fluid velocity(Ug)and the particle size(dp)of bed material(quartz sand),on the gas back-mixing in MFBR and was investigated.How the gas back-mixing affects the kinetics was also studied.The results show that the gas back-mixing in MFBR becomes less serious as D and dp decrease and Ug increases.This causes the gas flow to approach the plug flow.The activated coke combustion reaction is taken as a model reaction.We found that the concentration of the gas product CO2 measured per unit time gradually increases as the degree of gas back-mixing in the reactor decreases,bringing about the increase of E.This indicate that it is necessary to minimize the gas back-mixing in the reactor.(2)Comparative study of gas back-mixing in the MSBR and MFBR.The axial diffusion model(ADM)was applied to describe the gas residence time distribution(RTD)and the applicability of the ADM in the MSBR and MFBR was verified.The gas RTD was obtained by the mathematical method of deconvolution.The difference in the gas back-mixing between the MSBR and MFBR was investigated with the same bed diameter,operating gas volume and the mass of bed material.The results show that the degree of the gas back-mixing decreases with the decrease of D and dp and the increase of Ug,which is the same as the results measured by MFBR.However,under the same operating conditions,the gas RTD curves measured in the MSBR show smaller variance?t2,bigger height of E(t)peak E(t)h and smaller relative residence time difference between ideal plug flow and real gas flow?tr,indicating that the degree of the gas back-mixing in MSBR is smaller than that in MFBR.(3)Study on the gas flow approaching the plug flow in MSBA.The influence of the gas RTD in MSBR under different operating conditions and structural parameters was systematically investigated by the method of pulse tracing.The characteristics of the gas back-mixing in MSBR were also studied,and the structure of the reactor was optimized.Combined the changes in the pressure drop with the particle system investigated in this dissertation,it revealed that E(t)h and?t2 of the gas residence time distribution function in the MSBR satisfy the normalization correlation,and the relative residence time difference between ideal plug flow and real gas flow is 10%,E(t)h is larger than 2.0,?t2 is below 0.15.When the inner diameter of the reactor is 10 mm,the inverted cone angle is 60°,and the nozzle diameter is 1.5 mm,the degree of gas back-mixing in the MSBR is smallest,and the gas flow can be regarded as plug flow.The gas generated in the reactor discharge orderly to ensure that the concentration of the gas product can be accurately tested online,and that more realistic reaction information can be obtained for calculating reaction kinetics.It provides a basis for further experimental applications and accurate measurement of reaction information.(4)The difference in the kinetics of rapid reaction between MSRB and MFBR.The rice husk pyrolysis in MSBR was taken as an example to study the formation characteristic of different gas products and the behavior of pyrolysis based on its measured time-series variation of relative content of major product gases online measured by Process Mass spectrometry.The different in the E of the rice husk pyrolysis reaction between MSBR and MFBR was studied under the same operating conditions.The results show that the E obtained by MSBR is higher than that measured by MFBR,verifying that the gas flow in the MSBR is easier to approach the plug flow.In this dissertation,by exploring the influence of gas back-mixing in the reactor on the calculation of kinetic parameters,the necessity of gas back-mixing optimization was obtained.Furthermore,the structural parameters and operating conditions of the newly developed micro-spouted bed reactor were optimized to obtain the operating conditions of plug flow in the reactor,and the reactor was applied to the rapid reaction analysis.The development of the instrument will expand the application range of the original micro-fluidized bed reactor,and realize the fine mixing and heat and mass transfer of particles on the basis of near plug flow,thus providing a new test method for the real kinetic analysis of rapid reaction. |
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