Riser reactors utilize co-current flow of gas and catalyst particles in the "fast-fluidization" mode. The intense mixing of the gaseous reactant with the catalyst promotes heat and mass transfer, enabling high reaction capacities per unit volume of the reactor. A major application of this technology is fluid catalytic cracking of fuel oil to produce gasoline. In this application, the oil feed is injected as a liquid spray which needs to be vaporized before the vapor-phase cracking reaction can occur. Slow or poor vaporization of the liquid can dramatically reduce the reactor yield and product quality. In spite of its importance, the phenomenon of liquid evaporation in fast-fluidized beds has not been investigated.;The experimental part of this study is the first-known attempt to measure the rate of liquid spray evaporation in the riser of a circulating fludized bed. To simulate the hydrodynamic and superheated characteristics of riser reactors, sand particles of 125 micron diameter were fluidized by air, and a spray of liquid nitrogen was injected at the bottom of the riser. Several traversing pitot tubes at different elevations were used to obtain the cross-sectionally averaged gas volume fluxes. A mass balance then permitted calculation of the volumetric evaporation rate (kilogram evaporated per unit time per unit reactor volume) as a function of elevation in the riser The results of 15 test cases show that the actual evaporation process is substantially slower than predicted by a simple model based on co-current flow of isolated solid particles and liquid drops.;The theoretical part of this study is the rigorous derivation of a three-dimensional, three-phase gas/liquid/solid cluster model using ensemble averaging techniques. Because the cluster is treated as a mixture phase of solid particles and gas flow, there are two sets of conservation laws to describe the behavior of particles in both the cluster ensemble scale and three-phase ensemble scale. The closure conditions utilized in the model include the form of cluster, liquid contact area fraction, effect of transpiration, effect of atomization and coalescence of droplets. Numerical solutions for the 15 text cases in the CFB have been accomplished using a ;This three-phase model can be used to predict the evaporation process in CFBs for a variety of hydrodynamic conditions to account for the liquid and particle thermal properties, as well as scaling effects.
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