Hongting Ma

Experimental study on the heat transfer characteristics of waste printed circuit boards pyrolysis

In order to study the appropriate and advanced technology for recycling waste printed circuit boards (PCBs), a fixed bed pyrolysis device with stirring function has been designed and developed. The effect of rotating speed on the temperature distribution and mass change in the pyrolysis process of FR-4 PCB has been analyzed. The heat transfer and pyrolysis characteristics of different granular layers with and without stirring have been investigated. The results indicate that the stirring can change the main way of heat transfer from conduction to convection in the PCB layers. As the increase of rotating speed, the temperature rising rate of material at the bottom of the pyrolysis furnace gradually decreases, while the heating rate is increasing at the upper layer, and the temperature difference between the upper and bottom layers is gradually reduced. When the rotating speed varies from 0r/min to 18r/min, the weight loss of the material increases from 3.97% to 6.76%, and the overall pyrolysis degree is improved. During the pyrolysis process, the material layer can be divided into three zones along the vertical direction, namely complete pyrolysis zone, partial pyrolysis zone and non-pyrolysis zone. As the rotating speed is 0r/min, the thickness of each zones is 6cm, 6cm and 3cm, respectively. However, when the rotating speed is increased to 18r/min, the non-pyrolysis zone disappears, and the thickness of complete pyrolysis zone and partial pyrolysis zone increase to 9cm and 6cm, respectively.

Experimental investigation on the heat transfer characteristics in process of printed circuit boards pyrolysis under nitrogen flow

Pyrolysis process has many advantages, if integrated in the process of precious metals recovery from scrap printed circuit boards (PCBs). The heat transfer characteristics of PCB during pyrolysis have a significant influence on the pyrolysis efficiency and energy consumption. In order to improve the heat transfer performance and efficiency of energy utilization and reduce the energy costs, a fixed bed pyrolysis experiment device was established and investigated experimentally under high temperature nitrogen flow. The temperature distribution of waste PCB particles layer was measured, and the heat transfer characteristics was investigated. The experimental results indicate that the size of the PCB particle has an obvious effect on the pyrolysis reaction time and the migration rate of pyrolysis. The larger the particle size is, the shorter the pyrolysis reaction time is and the faster the migration rate is. When the square particle sizes are 1.5 cm, 2.5 cm and 3.5 cm wide, the average migration rates of pyrolysis reaction zone along the vertical direction are 0.47 m/h, 0.50 m/h and 0.63 m/h, respectively. Pyrolysis region and pyrolysis state have obvious effects on the temperature rising rate and temperature gradient along vertical direction.