Analytical evaluation of CaO-CO₂ loop for CO₂ removal

Post-combustion CO₂ removal from flue gas at power plant via a two-bed CaO-CO₂ loop (CaL) with heat provided by in-situ oxy-fuel combustion has been investigated. Based on the principle of chemical reaction engineering, a simple analytical model with one variable N only (solids circulation ratio) has been built and used for analysis of the CaL process systematically, which includes effects from sorbent reactivity, fuel impurity and the utilization of fuel heat to looping. From the model, the minimum heat duty and the looping penalty are obtained. Both of them are impacted by fuel sulfur and ash significantly. The result also indicates that the optimum solids circulation ratio N will be located between the two minimum points. The furnace factor is important, because it can eventually reduce the fuel firing rate, fuel ash and sulfur effect, oxygen requirement and related auxiliary power, and increase steam cycle efficiency. As found, the heat duty approaches to infinite at a critical solids circulation ratio N_C, which is a constraint to the operable N and the fuel burned. All of the effects are interconnected by the model.