Yaghoub Behjat - Department of Chemical Engineering, Iran University of Science and Technology, Tehran, Iran
Shahrokh Shahhosseini - Department of Chemical Engineering, Iran University of Science and Technology, Tehran, Iran
Mahdi Ahmadi Marvast - Engineering and Process Development Division, Research Institute of Petroleum Industry, Tehran, Iran

This study was conducted aiming at the better understanding of phase interactions and microstructure of the evaporating droplets in a gas solid fluidized bed (FCC riser) using CFD techniques. An Eulerian model was used for both gas and catalyst particles. The flow field and injected evaporating liquid droplets were modeled using Lagrangian approach. A new drag model was applied, which accounts circulation of flow inside a droplet to investigate the droplet hydrodynamics. In addition, a new heat transfer model for vaporization of feed droplets has been applied. The new heat transfer model considers the vapor leaving the droplet during vaporization tends to move the hot surrounding gases away. FCC riser hydrodynamic model predictions were validated by comparing them with corresponding experimental data, reported in the literature. The distributions of volume fraction of each phase, gas and catalyst velocity, gas and particle temperature in the riser were computed. In addition, temperature, evaporation rate and diameter changes of the droplet in the riser reactor were calculated. The simulation results indicated that the droplet lifetime could be divided into two overlapping phases. The time needed to heat up the droplets was very short thus this step was not a controlling step of riser operation. In the other phase, temperature tended to rise more slowly once the rate of evaporation became substantial. The results also showed that the total mass of a droplet evaporated in a fraction of the riser reactor.

CFD modeling, FCC riser, gas-liquid-solid flow, droplet evaporation