Research On The Hydrodynamics Of Moving-bed Reactor For Methanol To Propene

Moving-bed reactor for methanol to propene production is a promising technology to replace petroleum technology to produce alkene. Because the flow pattern of catalysts is close to plug flow, catalysts could maintain best activity if the discharging rate is settled according to catalysts life, and the products quality could be guaranteed. However, because of the special structure and complicated hydrodynamics of moving-bed reactor, especially the radial moving-bed reactor, systematic research on particle flow pattern, gas and solid flow distribution, and flowing problems in the reactor has rarely been involved in. These areas affect the equipment a lot, including production safety, stability, continuity, high quatity and quality. Therefore, it is imperative to conduct researches on these areas of radial moving-bed reactor to deeply understand the multiphase flow property of the reactor, so as to optimize its operating efficiency and increase production economy. At the meanwhile, it is also of profound theoretical and practical significance to develop the holistic technology and reactor for moving-bed methanol to propene production with self-intellectual property rights.Based on the existing methanol to propene technology, particle flow pattern, gas and solid flow distribution, and flowing problems in the reactor have been investigated separately and the particle residence time distribution model, the cavity and pinning model have also been established through theoretical analysis and cold mold expetiments. In addition, the gas distribution with the radial and axial direction in the reactor and the influencing factors of pressure drop were investigated, and the acoustic-emission model to predict particle moving speed and discharging rate have been established separately. The results of these researches have significant importance on reactor design and developing, technology optimization and catalyst modification. The main results of this thesis can be summarized as followed:(1) Based on systematic investigation of the influencing factors for particle residence time distribution, the changing trend of particle flow pattern with the factors was obtained and the predicting model was also established. Besides, two different types of optimized catalyst discharging pipe were designed, which decreased flowing dead zone in the reactor and improved particle flow pattern.The influence factors on particle residence time distribution including oprerating gas velocity, particle discharging rate, particle discharging pattern, and gas flow pattern were investigated through systematic experiments. The results showed that the peak width of the residence time distribution decreased and the peak became more symmetrical as the increasing gas velocity. Particle flow pattern was closer to plug flow with central discharging pipe. The predicting model for residence time distribution was established by simplified zone model, and the validity of the model was verified through the experiment data from two-dimensional and three dimensional cold mold reactors. In addition, two optimized catalyst discharging pipes were proposed, which decreased flowing dead zone and made particle flow patern closer to plug flow.(2) The characteristics of gas and solid phase distribution were studied and the influencing factors of pressure drop in the bed were investigated. Moreover, the acoustic-emission model to predict particle moving speed and discharging rate was established.At specific operating conditions, pressure distribution in radial and axial direction and the influence of factors on pressure drop was studied through systematic experiments. It is found that, pressure drop increased with reactor depth, and the pressure difference between two horizontal catalyst layers decreased along gas flowing direction. Besides, pressure drop increased with the increase of operating gas velocity, and decrease of particle discharging rate and the average particle size. The pressure drop of Π type flowing pattern was larger than that of Z type flowing pattern. Based on acoustic emission detecting technology and power spectroscopy analysis, the models to predict particle moving speed and discharging rate in moving-bed reactor were established, and the accuracy of the models and their validity for on-line detection of particle velocity in moving-bed reactor was verified by experiment data.(3) Two types of particle flowing problems in radial moving-bed reactor——cavity and pinning phenomenon have been investigated, and the predicting models for cavity and pinning size were established separately based on pressure drop analysis, force analysis, and dimensionless numbers analysis. Moreover, the measures to eliminate or decrease cavity and pinning size were proposed according to experiment results.The influence of four factors on cavity and pinning size was studied, including operating gas velocity, particle discharging rate, gas flow pattern, and catalyst characteristics. The results showed that cavity area and pinning width both increased with the increase of gas velocity and average particle size. While particle discharging rate increased, cavity area increased but pinning width decreased. Besides, cavity area and pinning width in Π type flow pattern were both larger than that in Z type flow pattern. According to pressure drop, dimensionless numbers and force analysis, two model to predict cavity area and pinning width were established separately, and the measures to eliminate or decrease cavity and pinning were also proposed based on the changing trend of cavity and pinning with different factors.(4) Based on the experiment results of particle flow pattern, gas and solid flow distribution, and flowing problems in moving-bed reactor, the conceptual design of industrial moving-bed methanol to propene reactor was presented and feasible designs were chosed according to calculation results.Concerning the successful application of radial moving-bed reactor on industrial continuous catalytic reforming production, and the restrictive conditions obtained from cold mold experiments for technology operating conditions and reactor design, the design principles were put forward, which aimed at the determination of three key size variables, the reactor inner diameter D, the central pipe out diameter d, and the height of packed catalyst bed h. Based on Aspen simulation to obtain feeding flux and physical parameters, and also using the size of industrial reactor as reference, the radial moving-bed reactor size for producing10000tons of propene per year and500000tons of propene per year was calculated and verified separately. Moreover, the optimal designs at different conditions were chosen based on cold mole experiments.