Presence of Chlorine Radicals and Formation of Molecular Chlorine in the Post-Flame Region of Chlorocarbon Combustion

Abstract

This study is concerned with the formation and persistence of atomic and molecular chlorine in the late stages of chlorocarbon combustion under fuel-lean conditions as well as in postcombustion cooling stages, since chlorinecontaining hazardous organic pollutants including dioxin precursors can be formed through reactions involving these active forms of chlorine. In bench-scale experiments with a chlorine-containing fuel mixture (C 2 H 4 /CH 3 Cl or CH 4 / CH 3 Cl, with Cl/C in the range of 0 to 2.2%) the fuel is oxidized in a relatively short time (10-20 ms). The major chlorine-containing product is HCl; however, the cooled combustion gases contain significant concentrations of Cl 2 (up to 18% of the total chlorine load), with the exact amount depending on the fuel equivalence ratio, the residence time in the combustor, the H/C ratio of the fuel, and the rate of cooling of the gas products. Calculations indicate that the Cl 2 measured in the cold exhaust gas is formed by recombination during the quenching of Cl radicals present at high temperature. The model predicts that, under conditions found in practice, Cl radicals can likewise be present in significant concentrations (1 to 5% of the total chlorine) in combustion products at the exhaust. Due to kinetic constraints, Cl radicals can then persist at surprisingly low temperatures (down to ca. 500 K) before recombining to form Cl 2 .

Mechanisms for formation, chlorination, dechlorination and destruction of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs)

“…Chemical kinetic simulations [134][135][136] have been conducted to investigate the availability and the transformation of three gaseous species of chlorine. These simulations were performed to simulate ''realistic'' conditions of de novo formation of PCDD/Fs and PCDD/F chlorination in the gas phase in terms of temperature (oxidative conditions in the temperature range between 200 and 400 C) and the various forms of chlorine (Cl , HCl and ClO).…”

Toxic Substances From Coal Combustion-a Comprehensive Assessment

“…We attempted a second method for chlorine speciation, which used a potassium iodide solution to collect the chlorine gas [67]. This system was set up similar to EPA method 26A, but the collection train was split into two parallel sections.…”

Kinetics of the reactions of C2H5, n‐C3H7, and n‐C4H9 radicals with Cl2 at the temperature range 190–360 K

“…This is particularly true for the reactions that have been subjected to direct studies 2. Reactions (B) can also be important in the combustion and incineration processes of chlorinated hydrocarbons, especially under the conditions of incomplete combustion and when the ratio of hydrogen to chlorine is low 3,4.…”