Numerical Simulation Of Pyrolysis Process Of Metal Chlorides

Because of its quantum,interface,small-scale and macroscopic quantum tunneling effect,ultrafine metal oxide has been widely used in various fields of people's daily life.The traditional preparation method may cause many problems such as long process,low efficiency and serious environmental pollution.Aimed at these problems,the preparation of ultrafine magnesia and ceria through jet pyrolysis reactor is developed independently by this research group.This technique has the advantages of high innovation,low cost,energy conservation and environmental protection,which has important theoretical significance and practical application value.Numerical simulation is adopted to research gas-gas and gas-solid pyrolysis reaction process in the independently developed jet pyrolysis reactor in this paper and the dynamics model of gas-gas and gas-solid pyrolysis reaction is corrected.The flow characteristics of phases in process of jet pyrolysis and components distribution of reactant and resultant in the reactor are described by using Fluent software combined with user-defined function(UDF).The main contents and results are shown as following:Firstly,the pyrolysis process of magnesium chloride in jet reactor is simulated.The distributions of pressure,velocity,temperature and material component in the reactor are investigated under changing conditions of four groups of reaction temperature,five groups of gas phase inlet velocity,five groups of MgC12 flow rate of materials inlet,and twenty-seven groups of the particle shape parameters(extension factor a,fullness index k and diameter ratio?).Mixing uniformity and concentration variation in the reactor are analyzed in varying conditions of three groups of diameter ratio between straight pipe and throat n,three groups of drainage-tube angle(?),three groups of drainage-tube diameter d and three groups of end straight pipe length L4.(1)The overall distribution of the reactants in the reactor is consistent at different reaction temperatures.With the increase of reaction temperature,the reaction rate becomes higher,and the concentration of the reactants becomes higher,the optimal reaction temperature is 1473K.The O2 flow rate at the inlet of gas phase is selected as 120L/h,which can ensure high reaction efficiency and reduce accumulation of reactants in the reactor.The higher the MgCl2 flow rate of material inlet is,the higher the reactor temperature and the higher the MgO concentration becomes.The bigger the diameter ratio ? is,the rougher the MgO particles becomes,which more easily deposit in the reactor;When extension factor ?(?)0,the particle extends and contracts,which influences yield of MgO.The degree of influence is related to the extension factor a,fullness index k and diameter ratio ?.When a=-0.25,k=1 ?=1,the yield of MgO is higher,which is 96.88%,when a=0.25,k=2,?=1.59 the yield of MgO is lower,which is 80.39%.(2)In order to ensure uniform mixing of two phase fluid and full reaction in the pyrolysis reactor,the ideal parameters of the reactor are as follows:n=5/2,0=90°,d=0.025m,L4=0.01m.According to the relationship between the amount of material and parameters,dimensional analysis is adopted,the empirical formula is as following:Q = 0.497p-0.15d0.149V0.851?0.15n-0.0285Then,aimed at pyrolysis process of CeC13 in the jet pyrolysis reactor coupling of the combustion reaction,the phase change process and the gas-solid heterogeneous chemical reaction,the combustion effects of three different fuels are investigated.The fluid flow and component distribution of the reactor are studied in varying condition of five groups of gas phase inlet velocity,five groups of CeC13 concentration at material inlet,twenty-seven groups of the particle shape parameters(extension factor a,fullness index k and diameter ratio?),three groups of diameter ratio of straight pipe to throat n,three groups of drainage-tube angle 0,three groups of drainage-tube diameter d and three groups of end straight pipe length L4.The results show as follows:(1)Choosing CH4 as fuel,the heat produced by combustion can meet the requirement of evaporation phase change and CeC13 pyrolysis reaction.The concentration distribution of resultant indicates:The initial concentration of CeO2 is 0,CeO2 is produced with pyrolysis reaction,which is mainly deposited in the middle and lower part of throat and expansion pipe with the influence of gravity.The concentration changes into lamellar distribution.Conditions permitting,the quality of Ce02 products can be raised by lowering fuel inlet velocity or increasing the concentration of CeC13.When ?(?)0,that is,flex of particles happens,which can influence the rate of recovery of CeO2.Fullness index and diameter ratio affect the rate of recovery of CeO2.When a=-0.25,k=1,?=1,the rate of recovery of resultant CeO2 is higher,which is 98.73%,when a=0.25,k=1,?=1.5,the rate is lower,which is 92.05%.(2)In order to ensure uniform mixing of two phase fluid and full reaction in the pyrolysis reactor,the ideal parameters of the reactor are as follows:n=10/5,0=90°,d=0.01m,L4=0.1m.According to the relationship between the amount of material and parameters,dimensional analysis is adopted,the empirical formula is as following:Q = 2.29 ×10-4 p0.262d-0.248v1.257?-0.266n0.0765Finally,according to the similarity theory and amplification criterion,the amplification simulation of metal chloride pyrolysis reactor is studied.The results show:Geometric proportional amplification can be adopted for amplification,the corresponding relation between the gas phase inlet velocity V of pyrolysis of magnesium chloride and the drainage tube diameter d of the reactor is V = 0.0221d-0.175,and the corresponding relation between the different gas phase inlet velocity V of pyrolysis of cerium chloride and the drainage tube diameter d of the reactor is:V = 0.0209 d0.96.Through numerical simulation and reactor amplification by using the operational and structural parameters derived by the relation,The error between the theoretical calculation value of material and the numerical simulation value is less than 10%,and the error between the theoretical calculation value of yield of metal oxideand the numerical simulation value is less than 10%.In conclusion,in this paper,through modification of the pyrolysis reaction dynamics equation,simulation of gas-gas pyrolysis in jet reactor and coupling of combustion,phase changing and gas-solid pyrolysis,the multiphase flow behavior in the new kind of reactor is described precisely and the accurate prediction of quality of products is realized,which lays atheoretical foundation for the industrial promotion of the two self-developed equipment and technologies.