(356c) Challenges in CFD Simulation of the Entire Circulating Fluidized Bed (CFB) Loop for Carbon Capture Process

Near-term applications of CO₂ capture from pre-combustion systems will likely involve physical or chemical absorption processes. However, these commercially available processes (e.g. SELEXOL) operate at low temperatures, imparting a severe energy penalty on the system and, consequently, their use could significantly increase the costs of electricity production. Therefore, development of high-temperature regenerative processes based on solid sorbents offers an attractive alternative option for carbon capture, at competitive costs. We have developed a regenerative high-temperature CO₂ capture process that is capable of removing more than 98% of CO₂ from a simulated water-gas-shift (WGS) mixture at IGCC conditions using highly reactive and mechanically strong MgO-based sorbents and a circulating fluidized bed (CFB) loop.

CFB loop-based reactors have the potential to be among the most important devices in the chemical and energy industries. CFB reactor ensures a continuous carbon dioxide removal process in a relatively compact unit using solid particles that makes it an excellent candidate for chemical looping of MgO-based sorbents for CO₂ capture and regeneration. Furthermore, computational fluid dynamics (CFD) provides an excellent approach to the reactors and entire CFB loop design in a systematic and economically feasible way. To use CFD to perform simulations of the CO₂ capture regenerative process, a model based on the multiphase flow dynamics governing equations taking into account the sorption/regeneration and the WGS kinetics is needed. Therefore in this work a CFD approach was used to describe CO₂ sorption and regeneration in the circulating fluidized bed loop reactor similar to the NETL carbon capture unit (C2U) experimental setup using an MgO-based sorbent. In this presentation we will discuss challenges involved in conducting numerical simulation (CFD) of the entire CFB loop. These challenges include developing fluid –particle drag force and Particle phase pressure and viscosity expressions which are applicable to entire range of solid concentration regimes from very dilute to packed moving bed, and significant computational time requirement to simulate three dimensional case of reacting system in such a complex geometry.

In addition, the key experimentally verified parameters needed for the CFD modeling of the sorption/regeneration and the WGS reaction rates and their dependence on the operating conditions (i.e., temperature, pressure, gas composition, catalyst/sorbent ratio, etc.) were also developed.