Particle flow, agglomeration, mixing, physical and chemical adsorption in circulating fluidized bed adsorbers

Circulating Fluidized Bed Adsorbers (CFBAs) are regarded as a potentially effective technology to capture some of the above pollutants.; In order to analyze CFBA systems in detail, a new approach has been developed for solving the Navier-Stokes equations for a gas-mixture/solids-mixture system. Sub-models are also developed to be combined with the gas/solids hydrodynamics model to simulate capture of multiple pollutants. Specific tasks accomplished include the following. (1) A model for fine particle agglomeration in CFBAs has been developed. It can model the influence of different factors on agglomeration, such as the geometry of a CFBAs, the superficial gas velocity, initial particle size distribution (PSD), and type of agglomeration mechanism. It is found that the Brownian agglomeration mechanism can be neglected compared to agglomeration by mean shear and turbulence. Sorbent particles are shown to capture fine particles effectively for certain conditions. A simplified version of this model has been developed for coupling with the hydrodynamics model. (2) A mixing model based on a core-annulus model of a CFBA has been developed to simulate the particle residence time distribution (RTD). Thus, macrochemical reaction can be simulated by combining microchemical reaction dynamics with the particle RTD. This has been applied to simulate SO₂ removal by chemical adsorption onto dry lime. (3) A “gas mixture” and “solids mixture” model has been developed to simulate fine particle agglomeration onto sorbent particles, sulfur dioxide removal through chemical adsorption with lime, and mercury vapor removal through physical adsorption with activated carbon. The “gas mixture” is composed of fine PM, sulfur dioxide, mercury vapor, oxygen and inert gas; while “solids mixture” is composed of solids-1 and solids-2. Solids-1 is composed of lime (CaO) and CaSO₄, and solids-2 is activated carbon. (4) A new approach for solving the Navier-Stokes equations governing gas/solids two-phase flow with chemical reaction has been developed. The approach combines a time-derivative preconditioning strategy for a gas/solids two-phase flow model with extensions of low-diffusion flux-splitting upwinding techniques. The combined framework is used to simulate jet-induced bubble formation within a minimally fluidized bed, flow within a circulating fluidized bed without chemical reaction, a downward fluidized bed, and gas mixture/solids mixture flow within a prototype CFBA device. (Abstract shortened by UMI.)...