INVESTIGATION OF THE INTERFACIAL HEAT TRANSFER EFFECTS ON PRODUCT YIELDS OF A COMMERCIAL SCALE FCC RISER REACTOR

摘要

Fluidized catalytic cracking (FCC) riser reactors are widely used by the refining industry to convert heavy oil to gasoline and other lighter products. The conversion process involves three phases: liquid oil droplets, catalyst particles, and oil vapor. The interfacial heat transfer among the phases is responsible for the droplet vaporization and the subsequent cracking reactions. It has great impacts on the riser performance, i.e., oil conversion rate and product yields. Computational fluid dynamic (CFD) computer codes were used by a few investigators to study the effects of various operating and design conditions on riser performance. CFD code generally includes a convective heat transfer model for the interfacial heat transfer between gas/droplet and gas/particle. In fact, an FCC riser flow that carries dense catalyst particles can have frequent collisions between droplet/particle and particle/particle. The conventional treatment may not be adequate for the study of the performance of an FCC riser reactor. In this research, additional droplet/particle and particle/particle heat transfer models were developed and incorporated into a three-phase reacting flow CFD code. The particle/droplet heat transfer model assumes that catalyst particles would collide with oil droplets in the riser flow and the heat carried by the particles is transferred to the droplets by conduction on each collision. The particle/droplet collision frequency is calculated from the particle and droplet number densities. The particle/particle heat transfer model also assumes that heat is transferred by particle collisions. The CFD code was used to investigate the effects of interfacial heat transfer on the performance of a commercial scale FCC riser reactor. The computational results show that the particle/droplet heat transfer is extremely important when oil droplets are large and particle/particle heat transfer has a strong impact on the temperature uniformity. The full paper will present the new interfacial heat models and the computational results of this investigation. The results will show the effects of interfacial heat transfer parameters on the yields of various petroleum products (gasoline, diesel, olefins, and dry gases) through the mixing, vaporization, and reaction processes in the reactor.