Ebullated Bed Reactors (EBRs) are multiphase reactors in which solid catalyst particles are fluidized with gas and liquid to create a uniform flow distribution. EBRs have a recirculating liquid phase, which causes rigorous mixing in the reactor. The liquid phase is recycled in the reactor through a centrifugal pump. If the pump is housed inside(outside) the reactor, it is called internal(external) recycling EBR. Current work is focused on the internal recycling EBR. The performance of these reactors is governed by fluid hydrodynamics and operating parameters. The main objective of this work is to simulate internal recycling fluid flow in the EBR. Computational fluid dynamics (CFD) has been used to simulate this reactor system. A 2D axisymmetric geometry is considered for cold flow simulations in the present CFD model to understand the behaviour of this system. We develop a methodology to model a system without including the details of the pump. The pump effect is mimicked in the boundary conditions of the computational domain. The effect of the suction pressure on the recycle ratio is studied. The flow patterns of the system are studied for the annular and recycle regions of the reactor for industrially relevant recycle ratios of 2, 4 and 6. Time taken to attain steady state varies with the axial positions within the reactor. The effect of the recycle ratio on the transients of the reactor system is analyzed.
Keywords: Ebullated Bed Reactors, Hydrodynamics, Internal Recycling, Cold-flow simulations, Computational Fluid Dynamics