Modeling Of Turbulent Fluidized-Bed Reactor For Acrylonitrile Production From Propene-Ammonia-Air

Acrylonitrile (AN) is an important kind of organic compound, which is widely used in the production of artificial fibre, resin, rubber and other organic compounds. The current trend of acrylonitrile production is to enlarge productive-equipment-scale, but the industrial equipments in our country were small or middle scale, which made our country lie in the adverse situation for the higher raw material and energy consumption. In such a situation, we engage in solving the chemical engineering problems appearing in the reconstruction of AN-equipments and developing the model for industrial turbulent fluidized-bed reactor, which has not only academic value, but special practical significance as well. The AN-reactor we dealt with was one kind of turbulent fluidized-bed reactor with inner vertical heat exchangers and other inner structures, and the catalyst used was MB-98. Based on widely consulting the relative literatures, we learned that there were no reports on the modeling of turbulent fluidized bed with inner vertical structures and the kinetics of propene ammoxidation on MB-98, so the research work we were confronted with would be innovative, but more challengeable.For the reaction kinetics, we used the former reaction network and relative kinetic equations of propene ammoxidation on Mo-Bi/(-Al2O3, and applied chemical process optimization method to identify the relative kinetic parameters with commercial data, and finally developed new kinetic model.For the reactor model, based on QIN Jiguang`s model, we divided the bed into two sections, i.e. the dense-phase section and the dilute-phase section. After taking the influences of the inner heat exchangers and the legs of cyclone separators on flow and reaction into account, we farther divided the dense-phase section into two parts, including the section above the heat exchanger and the section under the heat exchanger. For the first section under the heat exchanger, we proposed the equivalent column idea to simulate the influence of inner structures on the performance of the reactor, and obtained the model finally: in the dense section, lug flow for cloud phase and tanks-in-series model for emulsion phase; in the dilute section, pseudo-homogeneous one-dimension plug flow model was used.For the hydrodynamic parameters (the key parameter is the bubble size), taking the influence of inner vertical heat exchanger on flow into account, from the bubble-growth theory, we used optimization idea to identify the parameters in flow-model with 50 group of commercial data, and got a new formula applied to the calculation of bubble size for industrial turbulent fluidized bed, and calculated the average bubble diameter and the bed-height exactly.In the last part of this paper, we examined the degree of accuracy of the reactor model developed with commercial data not used during the development of the models, and the results showed that the model could describe the performance of the industrial reactor exactly. With the help of this mathematical model, we simulated and discussed the influence of operation conditions on the yield and selectivity of AN, such as temperature, pressure, concentration, etc. and put forward some advices for improving the AN-yield in the industry.