Chi Kai Hsien, Chang Shu Hao, Chang Moo Been
Graduate Institute of Environmental Engineering, National Central University, Chungli 320, Taiwan.
Environ Sci Technol. 2006 Mar 15;40(6):1770-5. doi: 10.1021/es052030d.
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.
韦尔兹法是一种经典方法，用于从电弧炉（EAF）粉尘中回收锌，这些粉尘含有相对高浓度的多氯二苯并对二恶英和多氯二苯并呋喃（PCDD/Fs）以及挥发性金属，如锌、铅和铜，还有氯。由于冷却过程中的操作温度以及高碳和氯含量，在典型的韦尔兹法中会形成大量的PCDD/Fs，这引发了公众对PCDD/F排放的担忧。在本研究中，在不同采样点同时进行烟气和灰样采样，以评估所研究的韦尔兹工厂中PCDD/Fs的去除效率以及气固相之间的分配情况。在所研究的韦尔兹工厂的粉尘沉降室（DSC）中，由于环境（温度窗口、足够的停留时间、氯和可用催化剂）有利于PCDD/F的形成，在DSC下游的烟气中测得PCDD/F浓度显著较高（1223 ng TEQ/Nm³）。此外，该设施中采用的旋风除尘器和袋式过滤器分别只能去除烟气中51.3%和69.4%的PCDD/Fs，导致在所研究的韦尔兹工厂的烟囱气体中测得的PCDD/F浓度较高（145 ng TEQ/Nm³）。以处理1吨电弧炉粉尘为基础，所研究的韦尔兹工厂的PCDD/F总排放量（烟囱气体排放 + 灰渣排放）为840 ng TEQ/kg电弧炉粉尘。由于缺乏针对PCDD/Fs的有效空气污染物控制装置，该设施中约560 ng TEQ/kg电弧炉粉尘通过烟囱气体排放。
