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

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 2 270.9 pg/g and 290.2 pg(I-TEQ)/g, much lower than those in air combustion which are 34 172.5 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.