Combustion Characteristics And Bromine Conversion Characteristics Of Waste Printed Circuit Boards In High Temperature

The significance of research on waste treatment lies in the recycle of resource. Among the present processing methods of waste printed circuit boards (PCBs), pyrometallurgical processing featuring high temperature combustion is most promising due to its high recycling ratio of resources contained in waste PCBs. High temperature combustion is a key during this PCBs recycling. Research on the two crucial technical challenge in the high temperature combustion of PCBs, the characteristics of high temperature combustion and the conversion of bromine during the whole combustion process, were conducted in present work.The pyrolysis and combustion characteristics of waste PCBs in various stage during thermal treatment were investigated by using a thermogravimetric analyzer (TGA). For the first time, the study discovers that during same temperature range of volatiles evolution stage, compared with that under pyrolysis condition, the evolution of volatiles decreases by24.4%under combustion condition. This is quiet different with that of common fuel. The result shows that in the combustion organization practice of waste PCBs, reducing the oxygen supply during the early stage of combustion will promote the volatiles emission and thereby promote ignition and stable combustion.The effect of operating condition on combustion completion of waste PCBs was investigated by using the continuous feeding drop tube furnace. The results show that combustion efficiency depends on temperature, excess air factor (EAF) and the mean residence time in high temperature zone. For the first time, the research discovers that temperature has the most significant effect on CO conversion. In the case of lower temperature combustion, the conversion of CO to CO2is inhibited due to the conversion of HBr to Br2, while at1200℃or higher the concentration of CO in flue gas decreases dramatically. High temperature is required to improve the combustion performance. These results were verified by further proven experiments conducted in the self-designing pilot. The research provides theoretical basis for the combustion organization practice of waste PCBsDuring the combustion of PCBs. organic bromine converts to HBr firstly and transfer into flue gas, in the presence of oxygen, most of the HBr converts to Br2. With the temperature increasing, the conversion of organic bromine to inorganic bromine increases. At1200℃or higher, an EAF of1.6or more, organobrominated compounds are successfully decomposed (more than99.9%). Thereby, with increasing combustion temperature, the formation of brominated dioxin by high temperature homogenous reaction is decreased greatly and the precursor for bominated dioxin formed by the low temperature heterogeneous catalytic synthesis is reduced. Research on the conversion of inorganic bromine in flue gas during cooling was conducted using the pilot, and for the first time, it was discovered that much HBr in flue gas convert to Br2during flue gas cooling. This is very important for the practice process selection of inorganic bromine removal and the further study of bominated dioxin formation characteristics:the process should be more suitable for separation of Br2from flue gas rather than HBr; during the flue gas cooling, Br2, the more active bromine source in gas phase for brominated dioxin formation by fly ash catalyzed de novo synthesis, increases continuously with the decrease of temperature.