Numerical study on the role of microwave–metal discharge in microwave pyrolysis of WPCBs

摘要

Abstract As a promising green technology, microwave heating is highlighted by its high efficiency and low consumption, especially in the fast pyrolysis treatment for e-waste recycling. Electric discharge induced by microwave–metal interaction plays a significant role in the process, and its contribution to heat generation is, however, always hard to define qualitatively through direct experiments. In this simulation, a microwave heating model featuring the pulsed microwave–metal (MW-m) discharge was designed in multi-dimensions, using COMSOL Multiphysics software, to emphatically probe the depth and extent of the hot-spot effect as well as its auxo-action on the pyrolysis process of waste printed circuit boards (WPCBs). The energy loss generated by MW-m discharge was added into the models in the form of a built-in fluctuating heat source, and it is found that at a relatively low microwave energy-to-heat conversion rate (31.5%, 220.5?W), due to the unique thermal effect of microwave–metal discharge, it can achieve an ideal pyrolysis effect. Based on the results, the instantaneous heat by discharge is generated in the similar trend of radiation pulses, and the local temperature of discharge spots can reach more than 2000?K the instant the discharge occurs, shortening the overall pyrolysis from dozens of minutes to around 200?s.