Novel technology for synergistic SO2 reduction during the carbonation process via a CaO-Char mixed system

A novel method to effectively achieve synergistic SO2 reduction during the carbonation process by the as-designed CaO-biochar system is developed. Coconut shells and calcined-limestone were used as biochar and calcium sources (denoted as CSC and LS), respectively. The introduced reductant creates the reduction condition making the Ca-based sulfation suppressed and the desulfurization prefers to undertake the reduction pathway during the simultaneous CO2/SO2 removal process. The competition of SO2 and CO2 for the calcium active sites is weakened, effectively alleviating the negative effect of SO2 presence on CO2 carbonation and generating valuable sulfur-product. With the mass ratio of LS and CSC is 3, the carbonation conversion of the LS-CSC(1:3) is 34% higher than that of the LS and the reduced-sulfur ratio of the system reaches about 85% indicating an effective CO2 capture synergistic SO2 reduction. The CO produced via the Boudouard reaction between CO2 and char is sufficient to play an important role in SO2 reduction, which effectively promotes the decarboxylation process in the reduction of SO2. It also facilitates the sulfur transfer from the reduced intermediate on the solid phase to the gas phase as a form of COS, promoting the reduction of SO2 through the Claus reaction.