Research On Reaction Behaviour With Gradient Field In Quick-Contact Cyclone Reactor

As oil becoming heavier and poorer in quality, the quality and selectivity of product is deteriorative because of core-annular flow, bad mass and heat transfer effect, backmixing of catalysts in risers. On account of the shortages of risers, the development of new technology and equipment is very necessary and of great significance. The quick-contact catalytic cracking cyclone technology was put forward based on quick-contact catalytic cracking technology and hydrocyclone technology. The research was mainly focused on the gradient characteristics of gas-solid two-phase, transport characteristics, the reaction depth in the quick-contact cyclone reactor. The work provided theoretical basis for the research and development of this new technology.Firstly, the gradient model of gas-solid flow was established on account of the gradiant distribution characteristics in the cyclone reactor by using kinetic theory of granular flow. The 3d gradiant flow field and second vortex flow characteristics were analyzed. Then the effects of velocity and solid holdup distribution with different model parameters were studied by the comparison between calculation results and experimental data. The results show that the distribution of gas-solid in the mixing chamber is uniform, the uneven distribution of velocity, concentration and pressure in the separation chamber is obvious, the gradient field is advantageous to the separation of the two phases.Secondly, the effects of different inlet structures were investigated by the mixing process. The results show that the reactor with tangential inlet pipes at the top of the mixing chamber has the best mixing effect. The contact time of oil gas and catalysts is about 0.25 s in the mixing chamber. The influences of particle sizes, entrance locations and gas-solid phase velocities on the separating efficiency were investigated. The results show that there exists short circuit flow in the reactor when the particle size is smaller than 3 μm, the influence of gas velocity is greater than solid velocity on the particle trajectory and separating efficiency. The influence of gas-solid slip characteristics with different parameters(gas capacity, catalysts to oil ratio, particle size and density) was further studied, then the slip velocity model was established.Then the transport characteristics and residence time distribution in the cracking reaction process were studied, the residence time distribution model was established. The results show that the RTD curve is unimodal distribution, the backmixing degree of the gas phase is greater than that of catalysts. The contact time of oil and catalysts is longer than other gas compositions, and the separation of catalysts and products is thorough.Finally, the product rate and selectivity in the quick-contact cyclone reactor was researched by using lumping kinetic model of catalytic cracking. The conversion model was established. The gradient reaction characteristics were studied and the cracking yield was compared with the riser reactor. The simulated results show that the gradient distribution of products due to density difference under the action of centrifugal force is helpful to increase the contact time between oil and catalysts, and also beneficial to quick separation between products and catalysts. Compared with the riser reactor, the quick-contact cyclone reactor has an advantage in terms of gasoline selectivity.