Oxygen effects on the evolution of hydrogen chloride and chlorine gas during combustion of PVC-CaCO3 based cable

Abstract

This paper investigates the migration and evolution of chlorinated (Cl-) chemicals during the combustion of polyvinyl chloride-calcium carbonate (PVC-CaCO3) composite cable outer sheath under different oxygen (O2) concentrations. Previous studies have mainly focused on the combustion of cables and subsequent generation of gaseous products under ambient air, and there is limited knowledge on the combustion behavior when the O2 concentration of the combustion air varies, especially at elevated, above ambient level. In this paper, the variations of Cl-contents in the remaining solid residues and Cl-gaseous products were studied under different O2 concentrations and external heat fluxes. The results show that when the O2 concentration increases from 12 to 18 %, the increased surface temperature enhances the pyrolysis rate and the hydrogen chloride (HCl) yield which increases from ∼0.15–0.18 g/g. Over 18–24 % O2 concentration, the HCl yield diminishes sharply and continuously, from ∼0.18–0.13 g/g with increasing O2 concentration. By 30 % O2 concentration, HCl yield has reduced by more than 40 %. Under O2-rich combustion, a large amount of chlorine gas (Cl2) is presence in the combustion products following the reduction in HCl yield, where over 75 % converted HCl was oxidized to form Cl2. HCl competes for O2 which is also required for carbon monoxide (CO) oxidation, and the O2 consumed for HCl oxidation is approximately 3 times that of CO oxidation. Under 12–18 % O2 concentration, the presence of high HCl yield inhibits CO oxidation, resulting in an increase in CO yield with intensified pyrolysis.