An experimental and modeling study of the inhibition of benzene combustion by HCl, in a fluidized bed

Fluidized beds often burn fuels containing aromatic hydrocarbons and chlorine. This work uses a bench-scale fluidized bed and some detailed calculations to investigate the inhibition of benzene oxidation by hydrogen chloride. Carbon monoxide and carbon dioxide were measured in the freeboard of the fluidized bed reactor over a range of HCl and oxygen concentrations and bed temperatures. For fuel-lean conditions, the presence of HCl causes the CO emissions to increase significantly. HCl addition also increases the unburned hydrocarbon levels. For fuel-rich conditions, the inhibitory effect of HCl is reduced. The experimental measurements indicate, in spite of the large surface areas available to quench radicals, most of the oxidation occurs within the fluidized bed and not in the free board. Model predictions agree qualitatively with experimental measurements made in the bench-scale fluidized bed; the trends with HCl concentration, equivalence ratio and temperature are correct. However, the model tends to under-predict the HCl inhibition of hydrocarbon and carbon monoxide oxidation. The model suggests that the inhibition of CO oxidation by HCl is the result of reduced radical levels due to reduced chain branching. The model shows less HCl inhibition of hydrocarbon oxidation because of Cl radical reactions with benzene and intermediate hydrocarbons.