(156c) A New Generic Modeling Approach for Gas-Solids Riser Reactor

For the purpose of optimum design and efficient operation of gas-solid riser reactor, it is essential to develop a simple and reliable method to estimate solids local concentration and solids residence time in a gas-solid riser flow. Although industries adopted traditional approach can provide some flow information such as local solids concentration based upon directly converting pressure drop, the effects of solids acceleration and energy dissipation are always overlooked which is believed to be significant especially in the acceleration and dense phase transport regions. The energy dissipation in these regions is mainly due to the interfacial friction between interstitial gas and suspended solids, inter-solids collisions, as well as solids-wall fraction. Through a comprehensive review of the modeling approaches in the riser reactor, it is revealed that most momentum-based models fail to account for the energy dissipation of inter-solids collisions. This paper presents a new generic modeling approach based on mechanistic energy balance to analyze the different partitions of the axial gradient of pressure by solids acceleration, collision-induced energy dissipation and solids holdup in gas-solid riser flows. Based on this new modeling approach, more reasonable estimation of axial distributions of solid holdup and resulted solid velocity can be quickly obtained. The model predictions were validated by many available experimental data and good agreements have been achieved.