Conceptual design of a packed bed for the removal of SO2 in Oxy-fuel combustion prior to compression

Flue gas cooler (FGC) is commonly used in Oxy-fuel projects for cooling the flue gas as well as removing most of its moisture and SO2. Due to enriched CO2 concentration in the flue gas, sodium tends to be wasted as NaHCO3, and the design of the column needs to consider both the effective use of sodium solutions and SO2 absorption rate. Conceptual design on a packed bed was carried out to determine the column diameter, column height, L/G ratio and initial solution pH. Kinetic modelling was used for the design of packed bed. Results indicate that SO2 absorption into NaHCO3 is accompanied by significant formation of HSO3- and minor formation of SO32-; CO2 absorption is accompanied by the initial accumulation of dissolved CO2 until saturation and desorption of CO2 afterwards. In the CO2 desorption region, the desorption rate of CO2 is close to the absorption rate of SO2. A higher initial pH results in higher discharged pH and HCO3- in liquid while a lower pH leads to a significant increase in the column height. The optimum initial pH can be determined by the best uniformity of pH along the column. This results in a discharged pH ranging from 5.13 to 5.91 and agrees with the operational pH range of 5-6 from our previous steady state experiments. The influence of L/G ratio is primarily on the liquid phase mass transfer coefficient and secondarily on the interfacial wetted area. A higher L/G ratio results in a shorter column height but a higher HCO3- concentration. Therefore, the L/G ratio should be optimized based on both reasonable column height and HCO3- concentration. Overall, this paper sheds light on the design of the scrubber for the treatment of SO2 from Oxy-fuel combustion. (C) 2016 Elsevier Ltd. All rights reserved.