Study On Particle Flow Characteristics In A Novel MTO Reactor

The scholars applying loop reactors to gas-solid systems have already developed gas-solid loop reactors with varied structures and put the advantages of the circulating bed into the gas-solid reaction system successfully in China.Lots of catalyst particles were taken to the freeboard within the bottom dense phase zone of traditional MTO reactors is a turbulent bed when the superficial gas velocity exceeds 1.0 m/s.The purpose of accurately controlling reaction products could be achieved by adding a vertical transport pipe on the upside of the freeboard for quickly removing and transporting the reaction products into gas-solid mixer to restrain side reaction happening,as well as reducing the products standing time.The paper have investigated the characteristics of particle flowing within the two bed of reactor mentioned above by experimentally researching in a set of MTO coupled reactor cold state experimental devices with a circulating bed and a free bed at the bottom.The results of the experiments will provide the basis for industrial design and amplification of the MTO coupled reactor as well as determination of the proper reaction in MTO.The main research results are mentioned as follows:(1)The correlation formula in the paper for counting the riser circulation amount calculated through the riser gas velocity and the pressure drop of the fully developed zone was proposed and verified under experiments in the two devices.The obtained maximum average relative error between the calculated value and the measured one is approximately 12.51%,which proves that the results of correlation have high accuracy.(2)The circulation bed is an important place for mass and heat transfer because the uniform distribution of the particle density in it is wider leading to be more favorable for the full contact and mixing between particles and gas than that in the free bed.Under the same working conditions,the circulation of both the free-and circulating-bed risers increased as the height of the static bed rises,while the circulation of the free bed was larger than that of the circulating one.(3)The overall back-mixing ratio of the free-and circulating-beds particles tended to increase first and then decrease along the axial direction.The partial back-mixing ratio of the particles in the dilute phase separation zone of the circulating bed was distributed as parabola distribution along the radial direction with a higher value closed to side wall region and a lower one in central region.As for the free bed,the local back-mixing ratio in the dilute phase separation zone of the free bed was parabolically distributed along the radial direction when the superficial gas velocity was as high enough.Instead,when the apparent gas velocity and the axial position were relatively low and high respectively,the local backmixing ratio was approximately distributed as a‘W'shape along the radial direction which had a higher value in the center area and lower one closed to the boundary wall.(4)The turbulent area in the circulating bed was significantly larger than that of the free one before the the particles flow completely reaching to the turbulent condition,due to a faster pace approaching turbulent fluidization the circulating bed had than the free bed under the same condition of fluidized air volume.(5)The velocity of particle circulation in the annulus region increased as the increase of the axial height.When the annulus gas velocity was standing constant,the particle circulation velocity in the annulus region grew with the rise of gas velocity in the draft tube.The upward particles circulation velocity of the draft tube increased first and then declined along the axial direction.The particle circulation fluxs increased first and then dropped with the increase of the annulus gas velocity.