Parametric analysis of internal gas separation within an ebullated bed reactor

Ebullated bed reactors are commonly found within resid hydroprocessors used to thermally crack and catalytically hydrogenate atmosphere and vacuum tower residue in heavy oil upgrading. These units have historically experienced very high solids-free gas holdups above 30%, displacing heavy feed and limiting product throughput, with significant focus placed on the effects of the internal recycle geometry on column performance. A fully functional 3D CFD framework for simulating the gas separation region is presented here, capable of capturing tangential and rotational fluid motion and transient gas separation dynamics. The model is applied to a first-generation recycle cup separator design and is used to explore operational parameters (fluid velocity, bubble size/holdup, recycle rate, and foam generation) and the choice of momentum coupling strategy on gas entrainment and separation efficiency. The results provide a framework for comparison and evaluation of future designs as well as fundamental insight in the separation dynamics in the freeboard region of this reactor, with efforts ongoing to compare and contrast fundamental operating modes of multiple separator designs.