Experimental and modelling study on co-absorption of SO2 and CO2 during desulfurization process by flue gas cooler for oxy-fuel combustion flue gas

This paper aims to set up the theoretical model for co-absorption of SO2 and CO2 into sodium based solutions. Instantaneous reaction for SO2 hydrolysis is assumed. For the hydrolysis of CO2, there are two assumptions: finite kinetics and instantaneous reaction. Based on these two assumptions, the absorption rates of SO2 were separately calculated and compared with dynamic experiments in the well stirred reactor. The trend for the absorption rate of SO2 was well predicted by the instantaneous reaction for CO2. The relative error for the absolute rates of SO2 is high. The prediction based on the finite kinetics for CO2 hydrolysis at pH>3 agrees well with experiments. The influences of CO2 on the SO2 absorption rate is primarily through gas phase mass transfer coefficient and total sulphur concentration at the same pH. Depending on the existence of CO2 on SO2 absorption rate, five pH regimes for interaction were observed. At pH>11.42, the absorption rate of SO2/N2 is higher than that of SO2/CO2 due to the influence of gas phase mass transfer coefficient. At 7.8<pH<11.42, the absorption rate of SO2/N2 is similar with that of SO2/CO2 due to the counteraction of gas phase mass transfer coefficient and total sulphur in liquid. At 5.41<pH<7.8, the absorption rate of SO2/CO2 is higher due to the influence of total sulphur in liquid. At 2.8<pH<5.41, the absorption rate of SO2/CO2 is relative lower primarily due to the influence of gas phase mass transfer coefficient. At pH<2.8, the absorption rate of SO2/N2 is similar with that of SO2/CO2 due to liquid phase controlled region. Conversion of carbon and sulphur based ions at different pH and controlling regions for SO2 absorption rate were obtained. The work provides guidance for the design and operation of flue gas cooler for oxy-fuel combustion flue gas. © All Right Reserved.