Experimental Investigation On Resource Technology Of Scrap Printed Circuit Boards Particles Using Fluidized Bed

With the development of information technologies, the amount of waste electrical and electronic equipments (WEEE) continues to increase rapidly due to limited service life. Printed circuit board (PCB) is an important part of electrical and electronic equipments. It includes plastic, refractory oxides and metals, which is characterized by an abundance of quantity, hazard effect to human health and high commercial value. Accordingly, the recovery of PCB is an important research project in the fields of chemical engineering and environmental engineering.The experiments were carried out in a fluidized bed of 56 mm in diameter and 1600 mm in height to determine the fluidization characteristics of different diameter scrap printed circuit board particles. Experimental findings showed that the fluidization characteristics of scrap printed circuit board particles depended on the average sizes and type of particles. The scrap printed circuit boards particles, belonging to Geldart A group with strong viscous force, whose fluidization features were similar to those of Geldart C, was difficult to fluidize. The scrap printed circuit board particles belonged to Geldart B and the minimum fluidization velocity increased as the average size increased. It has been found that the minimum fluidization velocities calculated by Ergun equation approached 94.5%, 114% and 91.8% of experimental minimum fluidization velocities for the particles of Geldart B group. For scrap printed circuit board particles, belonging to Geldart A group, the minimum fluidization velocities calculated by equations were smaller than experimental minimum fluidization velocities, and a model of force balance about cohesive particles was developed to evaluate fluidized characteristics. For scrap PCB particles belonging to Geldart B group, the mixture degree decreased when the mixture composition of scrap PCB particles and sands increased under the same superficial velocity. The mixture degree increased when the velocity increased under the same mixture composition of scrap PCB particles and sands. Thermal kinetic behaviors of scrap printed circuit boards were investigated using integral method. Pyrolysis process was divided into two stages characterized by DTG curve. The activation energy of the first stage was greater than it of the second stage. Because bisphnol A and epichlorohydrin contained aromatic compounds, aromatic hydrocarbon was the main composition at 316.1℃and 349℃in TG-FTIR, and the volatile compound contained C-O and C-Cl function under different temperatures from infrared spectra.The fluidized bed reactor was used to pyrolyze scrap printed circuit boards particles in inert gas conditions, and the high boiling liquid and solid products were analyzed using elemental analyzer and FTIR. The liquid content increased with increase in temperature or gas velocity. The main composition of liquid products was aromatics compounds which contained O-H, C=C, S=O and substituted functional group of benzene. The solid products contained carbon and fiberglas.Pressure fluctuation range and variance of PCB particles from top bed were larger than those from down bed. When the gas velocity increased, pressure fluctuation range and variance of PCB particles and SiO2 particles decreased. CaCO3 particles with strong viscous force was difficult to fluidize, whose variance fluctuation was large. When the gas velocity increased, the channeling stabilized and the variance decreased. Pressure fluctuation range increased owing to the ascending and coalescence of bubbles and the major frequency of pressure fluctuation signals was small in the fluidized state. Pressure fluctuation range decreased and the major frequency of pressure fluctuation signals was high in the channeling.