Novel Lime Calcination System for CO₂ Capture and Its Thermal-Mass Balance Analysis

In conventional lime calcination processes, because of fuel combustion in the kiln, the carbon dioxide (CO₂) from limestone decomposition is mixed with the flue gas, which results in energy requirement for gas separation in the carbon capture process. Here, a novel lime calcination system with carrier gas (CO₂) heating and air cooling is proposed to avoid the mixing problem of the CO₂ and the flue gas. This system consists of a new shaft kiln with four processing zones and a furnace system, where fuel combustion, limestone reaction, and lime cooling are carried out separately. Therefore, while obtaining qualified lime products, the CO₂ from limestone decomposition can be captured without a gas separation process, which accounts for 70% of the total carbon emission in lime production. Furthermore, a thermal-mass balance model was developed for the new system. Based on the model calculation, the energy consumption level of the new system was clarified via a case study. Moreover, parametric analyses were performed to examine the influence of the coefficient of excess air, the coefficient of lost carrier gas, and the calorific value of coal gas on the system performance such as the energy consumption and the CO₂ captured.