(59u) Gas Hydrodynamics of a Novel High-Speed MTO Loop Reactor: The Bypassing and Backmixing Along with Residence Time Distribution

Methanol to olefins (MTO) was an attractive technique to solve such problems as limited oil resource and increasing olefins demands. Many institutions and companies have developed different MTO reactors for industry application. Most of them chose turbulent fluidized bed as the reactors. However there exists a large extent of gas backmixing and long residence time in such reactors, which is detrimental to the MTO reaction. A novel MTO airlift loop reactor with high speed operation condition was developed, with turbulent or fast fluidized bed upward flow in the draft tube in parallel with bubbling or turbulent bed downward flow in the annulus. It aims at improving the flow characteristics of gas-solid phase and optimizing the olefins yield and selectivity. The conversion is a function of the gas hydrodynamics, which is vital for the present research. The novel high-speed MTO loop reactor comprises a fluidized bed and a draft tube for internal circulation of solids, forming separate aeration of the annulus and providing more flexible operation. The gas bypassing between the draft tube region and the annulus region was investigated, aiming at understanding the gas distribution law and qualifying the gas flowrate within the two regions. The gas backmixing in the draft tube region of loop reactor and the average gas residence time in the whole loop reactor were measured by gas-tracing method. The gas backmixing and the average gas residence time in the free fluidized bed were also investigated with the same method to provide a comparison with the novel high-speed MTO loop reactor. The entrained gas from the separation region to the annulus region was analyzed to explain the results of the average gas residence time varying with different operation conditions. Experiment results show that the high-speed MTO loop reactor exhibits little gas backmixing in the draft tube region and shorter average gas residence time compared to that in the free fluidized bed, implying a better conversion and selectivity. Based on the results of those gas hydrodynamics data, the optimal operation conditions can be chosen for the novel MTO reactor.