(350d) CFD-PBE Simulation of Carbon Capture Process Using Regenerable Solid Sorbent

There is an ever-increasing global pressure to reduce the emissions of green house gases, particularly CO₂, by capturing carbon from large point 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 produced power by the plant. Novel solid sorbents are believed to be an energy efficient solution to the problem [1].

In this work a novel regenerative Sorption Enhanced Water Gas Shift (SEWGS) process for high temperature CO₂ removal from Syngas using a MgO-based sorbent has been proposed. The sorbent augments or replaces the CO conversion catalysts currently used in WGS reactors and improve overall WGS thermal efficiency. The major advantages of this high temperature sorbent include reducing the amount of WGS catalyst required to fully shift the Syngas to CO₂ and H₂ and eliminating 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 [2, 3]. 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, i.e. 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 structures 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. Existing mono-disperse continuum models i.e. Eulerian-Granular models describe multiphase systems (e.g. fluidized beds) using an average size and/or density for the dispersed phase or ad-hoc modifications of mono-disperse theory to include effects of polydispersity on interphase exchange properties such as drag. If the dispersed phase property distribution is wide or changing due to the particulate processes or heterogeneous chemical reactions, then the results of such models are no longer accurate. The first goal of this study was to improve these models by considering the effect of polydispersity through a novel mathematical approach. As a result, a two-way coupled Computational Fluid Dynamics-Population Balance Model (CFD-PBM) along with an efficient numerical solution for the population balance equation has been proposed [4]. The coupled CFD-PBE model along with the two-zone variable diffusivity shrinking core reaction model [5] was utilized in baseline design of a bench scale high temperature, high pressure regenerative carbon capture process in a circulation fluidized bed (CFB).

References

[1]        Abbasi, E. (2013). Computational Fluid Dynamics and Population Balance Model for Simulation of Dry Sorbent Based CO₂ Capture Process (Doctoral Dissertation).

[2]        Abbasi, E., & Arastoopour, H. (2011). CFD Simulation of CO₂ Sorption in a Circulating Fluidized Bed Using Deactivation Kinetic Model. In Proceeding of the Tenth International Conference on Circulating Fluidized Beds and Fluidization Technology, CFB-10, edited by TM Knowlton, ECI, New York (pp. 736-743).

[3]        Abbasi, E., Abbasian, J., Arastoopour, H. (2013). Numerical Modeling of Sorption-Enhanced Water-Gas-Shift Reaction in a Circulating Fluidized Bed Reactor, 2013AIChE Annual Meeting.

[4]        Abbasi, E., Arastoopour, H. (2013). Numerical analysis and implementation of finite domain complete trial functions method of moments (FCMOM) in CFD codes. Chemical Engineering Science, 102, 432-441.

[5]        Abbasi, E., Hassanzadeh, A., Abbasian, J. (2013). Regenerable MgO-based sorbent for high temperature CO₂ removal from syngas: 2. Two-zone variable diffusivity shrinking core model with expanding product layer. Fuel, 105, 128-134.