Characteristics of PCDD/F distributions in vapor and solid phases and emissions from the Waelz process.
The Waelz process is a classic method used for recovering zinc from electric arc furnace (EAF) dusts containing relatively high concentrations of PCDD/Fs (polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans) as well as volatile metals, such as Zn, Pb, and Cu, and chlorine. As a result of the operating temperature in the cooling process and high carbon and chlorine contents, significant PCDD/Fs are formed in the typical Waelz process, causing public concerns regarding PCDD/F emissions. In this study, flue gas and ash samplings are simultaneously conducted at different sampling points to evaluate the removal efficiency and the partitioning of PCDD/Fs between the vapor and solid phases in the Waelz plant investigated. With the environment (temperature window, sufficient retention time, chlorine, and catalysts available) conducive to PCDD/F formation in the dust settling chamber (DSC), a significantly high PCDD/F concentration (1223 ng TEQ/Nm3) is measured in flue gas downstream from the DSC of the Waelz plant investigated. In addition, the cyclone and bag filter adopted in this facility can only remove 51.3% and 69.4%, respectively, of the PCDD/Fs in the flue gas, resulting in a high PCDD/F concentration (145 ng TEQ/Nm3) measured in the stack gas of the Waelz plant investigated. On the basis of treating 1 ton of EAF dust, the total PCDD/F discharge (stack gas emission + ash discharge) is 840 ng TEQ/kg EAF dust of the Waelz plant investigated. Because of the lack of effective air pollutant control devices for PCDD/Fs, about 560 ng TEQ/kg EAF dust are discharged via stack gas in this facility.
Chi
Kai Hsien
KH
Graduate Institute of Environmental Engineering, National Central University, Chungli 320, Taiwan.
Chang
Shu Hao
SH
Chang
Moo Been
MB
D000393:Air Pollutants / Q000032:analysis*; D001572:Benzofurans / Q000032:analysis*; D002244:Carbon / Q000032:analysis; D002713:Chlorine / Q000032:analysis; D003300:Copper / Q000032:analysis; D000072338:Dibenzofurans, Polychlorinated; D004784:Environmental Monitoring; D017745:Incineration; D007221:Industry; D007854:Lead / Q000032:analysis; D000072317:Polychlorinated Dibenzodioxins / Q000031:analogs & derivatives* / Q000032:analysis; D015032:Zinc / Q000032:analysis
D000393:Air Pollutants; D001572:Benzofurans; D000072338:Dibenzofurans, Polychlorinated; D000072317:Polychlorinated Dibenzodioxins; D007854:Lead; D002713:Chlorine; D002244:Carbon; D003300:Copper; D015032:Zinc