Thermodynamic analysis and kinetic modelling of dioxin formation and emissions from power boilers firing salt-laden hog fuel.
Both organic chlorine (e.g. PVC) and inorganic chlorides (e.g. NaCl) can be significant chlorine sources for dioxin and furan (PCDD/F) formation in combustion processes. This paper presents a thermodynamic analysis of high temperature salt chemistry. Its influence on PCDD/F formation in power boilers burning salt-laden wood waste is examined through the relationships between Cl2, HCl, NaCl(g) and NaCl(c). These analyses show that while HCl is a product of combustion of PVC-laden municipal solid waste, NaCl can be converted to HCl in hog fuel boilers by reactions with SO2 or alumino-silicate materials. Cl2 is a strong chlorinating agent for PCDD/F formation. HCl can be oxidized to Cl2 by O2, and Cl2 can be reduced back to HCl by SO2. The presence of sulphur at low concentrations thus enhances PCDD/F formation by increasing HCl concentrations. At high concentrations, sulphur inhibits de novo formation of PCDD/Fs through Cl2 reduction by excess SO2. The effect of NH3, CO and NOx on PCDD/F formation is also discussed. A semi-empirical kinetic model is proposed. This model considers both precursor and de novo formation mechanisms. A simplified version is used as a stack emission model. The kinetic model indicates that stack dioxin emissions will increase linearly with decreasing electrostatic precipitator (ESP) efficiency and exponentially with increasing ESP temperature.
Duo
Wenli
W
Pulp and Paper Research Institute of Canada, 3800 Wesbrook Mall, Vancouver BC, Canada V6S 2L9. wduo@paprican.ca
Leclerc
Denys
D
D000393:Air Pollutants / Q000032:analysis* / Q000737:chemistry; D001572:Benzofurans / Q000032:analysis / Q000737:chemistry; D002713:Chlorine / Q000737:chemistry; D002947:Cities; D000072338:Dibenzofurans, Polychlorinated; D004147:Dioxins / Q000032:analysis* / Q000737:chemistry; D005740:Gases / Q000032:analysis* / Q000737:chemistry; D006851:Hydrochloric Acid / Q000737:chemistry; D017745:Incineration; D007220:Industrial Waste; D007700:Kinetics; D008956:Models, Chemical; D010100:Oxygen / Q000737:chemistry; D000072317:Polychlorinated Dibenzodioxins / Q000031:analogs & derivatives / Q000032:analysis / Q000737:chemistry; D018570:Risk Assessment; D017640:Silicates / Q000737:chemistry; D012965:Sodium Chloride / Q000737:chemistry; D013455:Sulfur / Q000737:chemistry; D013458:Sulfur Dioxide / Q000737:chemistry; D013816:Thermodynamics; D014934:Wood
D000393:Air Pollutants; D001572:Benzofurans; D000072338:Dibenzofurans, Polychlorinated; D004147:Dioxins; D005740:Gases; D007220:Industrial Waste; D000072317:Polychlorinated Dibenzodioxins; D017640:Silicates; D013458:Sulfur Dioxide; D012965:Sodium Chloride; D002713:Chlorine; D013455:Sulfur; D006851:Hydrochloric Acid; D010100:Oxygen