| The flow characteristics of gas-solid two phase flow in the MTO reactor is very complex,and it is difficult to obtain the two phase separation process and the operation conditions of cyclone inlet.Hence with the reactor and two-stage cyclone separator as the research object,based on CPFD numerical simulation methods,sedimentation and centrifugation process of particles in the reactor with cyclone are calculated,and particle concentration and particle diameter of cyclone inlet are obtained.It is necessary to provide a reference to design high efficiency,low energy consumption and optimal matching two-stage cyclone separator.According to the particle concentration changes along the axial direction in the reactor,the reactor is divided from into dense-phase acceleration region,dense-phase transport region,reducer transport region,settlement transition region and settlement transport region.The results show particle deposition on the wall of reducer transport region.There are mainly120μm~200μm particles in the dense-phase acceleration region and dense-phase transport region,60μm~120μm particles in the reducer transport region,0~60μm particles in the settlement transition region and settlement transport region.When operating gas velocity fluctuates at 0.30m/s~0.42m/s,median particle diameter of settlement transport region is stable in the range of 30μm~38μm,and current settlement height ensures that reactor has a greater operation flexibility.Through settling and separating of particles in the reactor,particle concentration of cyclone separator inlet is 1.217kg/m~3,which is only 0.3%of the reactor bottom.Median particle diameter of cyclone inlet is about 28μm,which is only 17.3%of the reactor bottom.A large number of particles are separated by sedimentation in the reactor,and only part of particles which are smaller than 58μm enter the cyclone separator.The results show that separation efficiency of two-stage cyclone separators is 70.35%for 1μm particles,and more than 99%for 3μm particles.Under different working conditions,with the increase of particle concentration in the cyclone separator inlet,separation efficiency of the first-stage cyclone separator decreases obviously,but separation efficiency of the second-stage cyclone is almost unchanged.The two-stage cyclone separator can not only improve the separation performance and,but also ensure that the cyclone system also has a greater operational flexibility.Pressure of the second-stage separator is about 2 times of the first-stage separator,separation efficiency for 1μm particles of the second-stage separator is about 2.5 times of the first-stage separator.It is necessary to improve the separation performance of the first-stage separator,ensuring the separation ratio of the first and second stage separator equilibrium.The study shows that some problems exist in the structure of the first stage separator.Firstly,in particle escape case,more than 80%particles escapes from the exhaust pipe with short circuit flow.Secondly,energy consumption in cone swirl zone is large,accounting for more than40%of the total energy consumption.Thirdly,column zone is main separation space in seperator,however,its tangential velocity peak value in the first-stage is only 54%of second grade separator.Therefore,the surface response method is used to optimize the structure of exhaust pipe,cone zone and column zone of the first-stage separator,and get the structural parameters of the separator when the separation performance is optimal.After the optimization of the structure,compared with initial model,the separation efficiency for 3μm particles of the first and second stage cyclone separators are respectively increased 31.99%and 6.44%.The total efficiency and the total pressure drop are respectively increased 3.53%and 1.49%.The pressure drop ratio of the first and second stage cyclone separator is reduced from 2 to 1.29.The new two-stage cyclone has the advantages of high efficiency,low power consumption and uniform separation performance. |
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