Numerical Simulation And Experimental Study On Heat Transfer Characteristics Of Waste Printed Circuit Boards Pyrolysis

With the advent of electric age,as the important component of electronic devices,the number of printed circuit boards(PCBs)scrapped was growing.It has been caused widespread concern that the waste PCBs' harmless,resource and batch dispose process.As a method to dispose the waste PCBs,pyrolysis technology is becoming more and more mature.However,the key point to dispose the waste PCBs in a large batch is enhancing the efficiency of heat and mass transfer of pyrolysis furnace.It has meaningful academic value and practical significance that study on the heat transfer process inside the particle of PCB through theoretical and experimental analyzed to optimized design the pyrolysis furnace for enhancing effective thermal utilization and pyrolysis rate.In this paper,the internal heat transfer mathematical models are established in pyrolysis processes for single particle of PCB in the fixed bed,and the effect of anisotropy of thermal conductivity,thermal properties changing with temperature and the reaction heat are considered.The inner thermal distribution of the particle board is simulated through finite element method,and the effects of parameters variation are discussed.TGA curve of single particle board during simulation pyrolysis process which is obtained based on the temperature variation results of nodes is compared with the experimental results of thermal gravimetric analysis to verify the rationality of single-particle heat transfer model.Experimental study of enhancing heat transfer is carried out on the basis of model analysis and the influence on the temperature distribution within material layer,weight loss and weight loss rate of PCBs is analyzed with the changing of agitation speed,furthermore the optimal operation condition under the current experimental conditions is obtained through the energy consumption analysis.The results are as follows: the main heat transfer mode between the PCBs particle and environment within pyrolysis furnace is heat convection,and the inverse function relationship between the convective heat transfer coefficient and particle size is obtained.The anisotropy of thermal conductivity,the change of thermal property parameters with temperature and the effect of reaction heat generated during pyrolysis can not be neglected in the established of the single particle heat transfer model.The main way of heat transfer in PCB material layer is turned to the heat convection between particles and pyrolysis gas from pure contact thermal conductivity among particles through the agitation in fixed bed pyrolysis furnace.The agitation improve thermal weight loss of material,and the thermal weight loss rate increase with agitation speed,however the weight loss will have little increment when agitation speed over 18r/min.Three peaks in heat weight loss rate curve changing with time represent the most intense reaction time for three sections,respectively.The overall weight loss rate increase with the agitation speed increment and it is mainly reflected by that of upper material.Material are divided into three zones including unpyrolyzed area,and part of the pyrolyzed zone and complete pyrolyzed zone from top to bottom in the fixed bed pyrolysis furnace,which is consistent with previous findings of scholars.There is almost no unpyrolyzed zone with agitation,and all materials are partially or completely involved in the pyrolysis reaction.Under the condition of the agitator speed of 18r/min,the thermal utilization of material is the highest,and the maximum value is 30.52%.