Numerical Investigation of Solid-Fueled Chemical Looping Combustion Process Utilizing Char for Carbon Capture

Abstract

The in-depth understanding of the gas–solid flow and reaction behaviors, and their coupling characteristics during the chemical looping combustion (CLC) process has the guiding significance for the operation and optimization of a chemical looping combustor. A three-dimensional numerical model is applied to investigate the char-fueled CLC characteristics in a fuel reactor for efficient CO2 separation and capture. Simulations are carried out in a bubbling fluidized bed fuel reactor with a height of 2.0 m and a diameter of 0.22 m. The initial bed height is 1.1 m, and hence the height–diameter ratio of the slumped bed is five. The oxygen carrier is prepared with 14 wt% of CuO on 86 wt% of inert Al2O3. In the process of mathematical modeling, a Eulerian-Eulerian two-fluid model is adopted for both of the gas and solid phases. Gas turbulence is modeled on the basis of a k–ε turbulent model. The reaction kinetics parameters are addressed based upon previous experimental investigations from literature. During the simulation, the gas–solid flow patterns, composition distributions, and reaction characteristics are obtained. Moreover, the effects of solids inventory and fluidizing number on the reaction performance are elucidated in-depth. The results have shown that the reaction rates have close relationship with the flow patterns and the distributions of gas concentrations. Compared to the steam-char gasification over sand, the application of char-fueled CLC can effectively promote the conversion of gasification products. In addition, higher CO2 concentration at the outlet can be achieved by increasing the initial solids inventory or decreasing the fluidizing number. Some calculated values are verified by the previous data, indicating that the current three-dimensional models are reasonable to study the process mechanism of char-fueled CLC.