Conversion of HBr to Br2 in the flue gas from the combustion of waste printed circuit boards in post-combustion area. (10th September 2017)

• Record Type: Journal Article
• Authors: Xiao, Hanxi; Zhou, Zhihua; Zhou, Hu; Liu, Qingquan; Ren, Wenxia; Lin, Huiling; Zhu, Hepeng; He, Chao; Tian, Kun
• Is Part Of: Journal of cleaner production. Volume 161(2017)
• Page Start: 239
• Page End: 244
• Publication Date: 2017-09-10
• Subjects: Inorganic bromine -- Conversion -- Post-combustion area -- Waste printed circuit boards -- Flue gas; Factory and trade waste -- Management -- Periodicals; Manufactures -- Environmental aspects -- Periodicals; Déchets industriels -- Gestion -- Périodiques; Usines -- Aspect de l'environnement -- Périodiques; 628.5
• DOI: 10.1016/j.jclepro.2017.05.117
• Languages: English
• ISSNs: 0959-6526

Abstract

Abstract: It is crucial to prevent the secondary pollution when recycling wastes. During the recycling of waste printed circuit boards by the pyrometallurgical process, bromine in the raw materials is normally released in the form of HBr/Br2 into the flue gas. In the present work, for the first time the conversion of HBr to Br2 during the cooling of flue gas in the post combustion area (PCA) was studied to provide evidences for the control of PBDD/Fs and the recycling of Br. The 1200 °C flue gas was cooled down at various cooling rates in a lab-scale system. The influence of PCA operating conditions, i.e., cooling temperature (Tc), residence time in the cooling zone (RTcz) and Oxygen partial pressure (PO2 ), on the conversion ratio was studied systematically. And the study was based on the newly developed method to determine HBr and Br2 contents in the flue gas at various temperatures. For each RTcz, i.e., 0.3, 0.5 and 0.7s, the ratio first increases with decreasing Tc to a maximum value at Tcmax and then decreases as Tc further drops. Tcmax depends on RTcz. For Tc = 200 °C and RTcz = 0.3s, approximately 31.1% HBr is converted to Br2 . This is 51% lower than the highest. Moreover, at lower Tc and longer RTcz, the ratio can be less than that at higher Tc and shorter RTcz, vice versa. Accordingly, when cooling the system to a certain temperature, the shorter the RTcz is, the lower the conversion ratio will be. PO2 slightly influences the ratio. These are vital to the determination of Br sources for PBDD/Fs formation in PCA, which is valuable for the future pollution control. Besides, extension of the cooling time in the lower temperature range (from 200 °C at RTcz = 0.3s to 50 °C) within 300s greatly improves the ratio up to 91%. This provides the basis for the Br recovery rather than removal by chemical agents. Graphical abstract: Highlights: The real-time concentrations of Br2 and HBr in the flue gas at various temperatures were obtained. When cooling the system to a certain temperature, the shorter the time is, the lower the conversion ratio of HBr will be. PO2 slightly influences the conversion ratio. Rapid cooling to lower temperatures significantly decreases Br2 in flue gas of the specific temperature range. Proper extension of cooling time in the lower temperature range promotes the generation of the Br2 obviously.