Experimental And Numerical Simulation Study Of Enhanced Heat Transfer By Cracking Of Plastics

With the continuous development of the plastics industry,a large number of waste plastics are discarded causing white pollution,which has become a worldwide environmental management problem.Cracking,which does not cause pollution to the environment and has high economic value,is the best way to deal with waste plastics because of the recycling of resources.However,there are still many difficulties in the field of plastic cracking,such as poor thermal conductivity of plastics,uneven heating of cracking heating process,easy coking,and reduced heat transfer efficiency of cracking reaction process.In response to the above problems,this study optimizes the existing cracking equipment by adding a certain amount of heat-conducting medium to the cracking process to make the temperature of waste plastics rise quickly and evenly,which not only improves the cracking efficiency and the quality of cracking products,but also improves the coking condition on the wall of rotary kiln,providing a new technical method for the efficient cracking of waste plastics.The details of the study are as follows:1.The green electromagnetic coil heating method is used to optimize the existing waste plastic cracking equipment,so that the cracking rotary kiln heats up quickly and evenly,and the kiln temperature is precisely controllable,and it is found that the addition of waste FCC catalyst can improve the cracking efficiency,and the highest recovery rate of cracking oil is obtained when the waste FCC catalyst is 10% of the plastic mass,and the best cracking effect.2.Experimental research shows that adding different particle sizes and different filling rates of heat-conducting media will promote the cracking reaction of waste plastics to different degrees.When the particle size of heat-conducting media is 15 mm and the filling rate is 20% of the volume of waste plastics,the heat transfer effect is the best and the cracking reaction is the most complete,which not only shortens the cracking time,but also improves the cracking efficiency.3.The heat transfer model of heat transfer medium and plastic pellets in the cracking process was constructed by EDEM,and the average temperature rise curve of plastic pellets and T*RMS values of each plastic pellet were analyzed in the EDEM post-processing.The average temperature of the particles in the rotary kiln is higher and the temperature uniformity of the plastic particles is good.The simulation results are basically consistent with the experimental results,which verifies the reliability of the heat transfer process of plastic pellets simulated by EDEM.4.The results of the cracked oil by GC/MS showed that there was little difference in the composition of the cracked oil between the two methods with and without the addition of thermal conductive medium,but the percentage content of low molecular chains(<C10)in the former cracked oil increased significantly,which proved that the addition of thermal conductive medium made the breakage of polymer carbon chains more complete and adequate,the obtained cracked carbon black is in the form of fine powder.In summary,the addition of specific types and specifications of heat-conducting media in the cracking process of waste plastics can effectively improve the problems of uneven heating,low energy utilization and easy coking in the cracking process of plastics,and provide a new and feasible method for the cracking of waste plastics.