(53b) Numerical Modeling of Sorption-Enhanced Water-Gas-Shift Reaction in a Circulating Fluidized Bed Reactor

One of the promising pre-combustion technologies for carbon capture in power plants is the Sorption-Enhanced Water-Gas-Shift (SEWGS). SEWGS is a high-pressure and high-temperature regenerative dry sorbent process that combines CO₂ capture with the WGS reaction. WGS is an equilibrium controlled reaction in which carbon monoxide reacts with water vapor to form carbon dioxide and hydrogen. When the amount of CO₂ production is high, as it is the case in power plant applications, multiple reactors operating at progressively lower temperatures are required to reach a high level of CO₂ removal. However, if one of the syngas products, either H₂ or CO₂, can be continuously removed from the reactor, i.e. by CO₂ capture, equilibrium will be shifted and the conversion of CO to CO₂ can be accomplished in a single reactor. Therefore, a SEWGS process for continuous separation of CO₂ or H₂ would be desirable. This 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 eliminating or 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 developed a highly durable Potassium-promoted MgO-based sorbent for SEWGS^1,2 which has been tested successfully in packed and dispersed bed reactors at lab scales. Furthermore, to describe the behavior of the sorbent at various operating conditions an explicit reaction model suitable for CFD calculations called two-zone variable diffusivity shrinking core model with expanding product layer has been developed³. However, in order to utilize this sorbent continuously at large scale processes a circulating fluidized beds (CFB) is needed which ensures continuous CO₂ removal processes based on the dry sorbent concepts^4,5. To design a CFB system and afterward to bridge the gap between lab/bench scale and large scales needed for demonstration a powerful tool, i.e. Computational fluid dynamics (CFD), is needed.

In this work, we used an Eulerian-Granular model in combination with our reaction model, to evaluate the performance of the proposed SEWGS process in a bench scale circulation fluidized bed based on the design of NETL C2U experiment⁶. The model is an extension of our previously published 2D model^5,7 which was employed in the simulation of riser part of a CFB. We have extended the model to a full-loop 3D model of CFB including riser, cyclone, down-comer, regenerator, and seal pots. A major limitation of riser section simulations is that the solid inventory of the riser or the solid circulation rate should be known a priori, which was eliminated by considering the whole system. Initially, NETL C2U experimental data on the reactor’s hydrodynamics were used to validate the numerical model. Next, the numerical model will be used to evaluate the sorbent performance in the CFB reactor. This work facilitates implementation of new technologies for CO₂ capture in fossil fuel power plants and eventually paves the path toward production of H₂ as a clean fuel for electricity generation.

References

[1]  Hassanzadeh, A., “A regenerative process for carbon dioxide removal and hydrogen production in IGCC”, Thesis (Ph.D.), Illinois Institute of Technology, 2007.

[2]  Hassanzadeh, A., & Abbasian, J. (2010). Regenerable MgO-based sorbents for high-temperature CO₂ removal from syngas: 1. Sorbent development, evaluation, and reaction modeling. Fuel, 89(6), 1287-1297.

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

[4]  Yi, C., K., Jo, S., J., Seo, Y., Lee, J., B., Ryu, C. K., “Continuous operation of the potassium-based dry sorbent CO₂ capture process with two fluidized-bed reactors”, International journal of greenhouse gas control, 1(2007): 31-36.

[5]  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).

[6]  Clark, S., Snider, D. M., & Spenik, J. (2013). CO₂ Adsorption loop experiment with Eulerian–Lagrangian simulation. Powder Technology.

[7]  Abbasi, E., & Arastoopour, H. (2011). Numerical Simulation of CO2 Removal Process Using Solid Sorbent In a Fluidized Bed: A CFD-PBE Model. In 2011 AIChE Annual Meeting.