(319c) CFD Simulation of CO2 Regeneration of Carbonated MgO Based Solid Sorbent in a Carbon Capture Process

There is an ever-increasing global pressure to reduce the emissions of CO₂, by capturing carbon from large stationary sources such as fossil fuel power plants. Currently, commercially available carbon capture technologies requires a relatively large volume of low-pressure steam from the power plant’s steam cycle for regeneration that decreases the net power produced by the plant. Novel solid sorbents are believed to be an energy efficient solution to the problem.  Thus in this work a novel regenerative process for high temperature CO₂ removal from Syngas using a MgO-based sorbent has been proposed. One of the major advantages of this high temperature sorbent is the elimination Syngas cooling/reheating that is necessary for current CO₂ separation systems. We have also shown that the circulating fluidized bed (CFB) concept ensures continuous CO₂ removal processes based on the dry sorbent concepts. However, one of the challenges in the way of deployment of this promising technology, among other novel technologies, is the fact that the majority of them are still in the lab or bench scales and, to be successfully scaled-up, a powerful tool such as Computational fluid dynamics (CFD), is needed to bridge the gap between lab/bench scale and large scales needed for demonstration. On the other hand, despite of the long history of CFB operations, complete understanding of the origin and nature of the inherently complex flow patterns observed in these devices is still lacking and beside experimental studies, advanced and rigorous numerical modeling is essential to shed light on the complex behavior and flow structure in these systems.

In this study first a high capacity, highly reactive MgO - based regenerative sorbent was developed for the purpose of CO2 capture. Then a series of sorption and regeneration experimental runs were performed and a second order shrinking core reaction model for regeneration was developed based on our experimental data and was incorporated in our CFD simulation of CO₂ regeneration process. Our and literature experimental data on fresh, carbonated, and regenerated sorbent particles have shown that the sorbent particle size distribution and density do not change significantly during the carbonation and regeneration processes. Therefore constant particle size and density were assumed for all of our CFD simulations. In addition simulation of the hydrodynamics of the entire circulating fluidized bed system loop were performed to obtain realistic values for the solid phase circulation rate to be used in simulation of the regeneration process. Then  two dimensional both batch continuous  and three dimensional continuous CO₂ regeneration process operating at the bubbling flow regime along with second order shrinking core reaction model was simulated using our CFD model.  Our calculated CO₂ regeneration and conversion are in line with expected experimental expectation.