Process and Reactor Level Simulations of Calcium Looping Combustion

Calcium looping (CaL) is a recent technology for carbon capture from coal fired power plants which consumes less energy than other approaches such as oxy-fuel. In this paper, first a system level model is developed in ASPEN PLUS to calculate the energy penalty of introducing Calcium looping in a coal fired power plant. Several simplifications and assumptions are made to model the Calcium looping process. The relationship between the energy penalty due to CaL and carbon capture efficiency is used to validate the process model for both pre-combustion CaL and post-combustion CaL; it agrees well with the experimental data and simulation results available in the literature. The simulation shows an increasing marginal energy penalty associated with an increase in the carbon capture efficiency, which limits the maximum carbon capture efficiency to around 95-98% before the energy penalty becomes too large. In the second part of the paper, a reactor level model is built using ANSYS FLUENT to perform a CFD simulation of a fluidized bed where the carbonation reaction (one of the two major reactions in CaL) takes place. Both planar and axi-symmetry models of the reactor are considered and the carbon capture efficiency is evaluated for various combinations of the velocity and CO₂ mole fraction at inlet of the reactor. It is found that reducing the inlet velocity has a significant impact on the carbon capture efficiency by increasing the residual time of the gases inside the reactor. Based on these results, the relative merit of Calcium looping versus Chemical Looping Combustion is examined.