Numerical Simulation Of The Gas-solid Two-phase Flow In TMP Diameter-changing Reactors

Fluidized bed technology was widely encountered in petro-chemical, energy and metallurgy industry. Riser reactor has become one of the most ordinary used equipment in solid catalytic process because of the great success of Fluid Catalytic Cracking process. Enhanced propylene production through catalytic pyrolysis of heavy oil has become a promising technology to promote economic performance of enterprise. While, innovations should be introduced to archive high catalyst-oil ratio and appropriate residence time simultaneously, riser reactor with changing-diameter could be a probable solution. Ideal riser reactor for thus purpose should be made up of several sections with different diameter. Numerical simulations based on computational fluid-dynamic (CFD) technique have been performed to investigate the hydrodynamics of gas-solid two phase flow in a bench scale experiment. Commercial code FLUENT was used in the research and a suitable model was developed .Flow pattern of the gas-solid two phase flow in an industry scale reactor also has been simulated. Effect of different nozzle configuration and its influence on catalyst distribution in reactor were investigated and discussed.Experimental measurement on bench scale equipment indicates that the volume fraction of the catalyst in the larger diameter section of the riser was much higher comparing with the traditional riser, so the catalyst aggregating should have more evidence to influence whole flow pattern. Improved drag model based on EMMS (Energy-Minimization Multi-scale) model should have better ability to predict the dense solid flow behavior in the riser. Constant solid reserve was keep by setting solid inlet velocity according to the solid outlet flux. Kinetic Theory for Granular Flow (KTGF) model was used for solid phase. A value of 0.85 was used for particle restitution coefficient in the simulation. It was noticed that, CFD simulations results basically agree well with the measured experimental measurements. 3D CFD simulation gave better precision than 2D cases due to the more accurate description of real equipment in 3D simulation.Different configurations of nozzles and reactor structure on an industry scale reactor have been investigated by CFD simulation also. According to the numerical simulation, extra notice should be paid to the large-diameter zones, where the main reactions zone. By suitable retrofit, the axial distribution of catalyst particles could be improved significantly, in nozzle zones the solid volume fraction was higher and the catalyst radial distribution was well-proportioned. Ordinary core-annual structure was very weak and the collision between high velocity catalysts was avoided, so the attrition of the catalyst could be eliminated. High gas velocity could be gained in following small diameter riser section, so the undesired by-pass products could be controlled reasonably.