Study on the formation of PCDD/Fs in PVC chemical looping combustion

Abstract

CaSO4 oxygen carriers with silica sol were prepared and their reaction performances with CH4, CO and H2 were experimentally investigated. The formation characteristics of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in PVC combustion by means of chemical looping combustion (CLC) based on CaSO4 oxygen carrier and air were studied in a tube furnace system. The results show that CaSO4 oxygen carriers with silica sol can be completely reduced by CH4, CO and H2. The reaction time of CH4 and H2 is much shorter than CO. The chemical looping combustion of PVC can effectively inhibit the formation of PCDD/Fs. The yield and International Toxicity Equivalent Quantity (I-TEQ) of PCDD/Fs produced in CLC are 2270.9 pg/g and 290.2 pg(I-TEQ)/g, much lower than those in air combustion which are 34172.5 pg/g and 732.8 pg(I-TEQ)/g. It is mainly because fuel doesn't directly contact with O2 in CLC, the oxidative cleavage of large carbon molecule and the conversion from HCl to Cl2 are significantly reduced which will inhibit the low temperature de novo synthesis and precursors reaction of PCDD/Fs.