Research On Waste Crystalline Silicon Solar Panels Resource Recovery Technology

As a kind of clean and renewable energy, solar energy has attracted worldwide attention. In recent years, solar cell production of our country has increased rapidly and domestic installed capacity has grown steadily. The life cycle of solar cell is about25years. After that, the conversion efficiency of the battery will drop sharply. As a new type of Waste Electrical and Electronic Equipment(WEEE). solar cell panel contains an abundant of secondary resources, such as high white tempered glass, copper, aluminum, silver and high-purity polycrystalline silicon, which have high recycling values. The more installed capacity of the solar cell panel, the more potential waste in the future. The disposal and recycling of scrapped cell panels have got worldwide attention. Based on collection, analysis and comparison of the domestic and foreign crystalline silicon solar panels treatment resources data, this paper put forward the roadmap of the recycling of crystalline silicon solar panel, which was meaningful for its harmless handling and pollution control.On the basis of comparison and analysis of the structure and the physical and chemical properties of the material of solar panels, the dismantling methods of solar panels was studied. Artificial disassemble method was simple and direct. It could separate the aluminum frame, but only in a physical way. which made it unable to separate the important value in the cell panels. Organic solvent could dissolve the EVA to separate glass and cells, but there were problems such as glass broken, long time solvent dissolution and organic liquid waste disposal. Heat treatment method couled effectively deal with EVA in the panels and maintain full glass. It was a high-energy consumption method and need to deal with the waste gas and liquid products. Comparing the advantages and disadvantages of these three methods, we finally choose heat treatment to dispose solar panels.Through the research of the thermo-gravimetric(TGA) of EVA, PET and PVF, which were three kinds of typical plastics of the panel, we’ve learned that in the atmosphere of N2and O2, the weightlessness rate of EVA was over99%and the weightlessness end temperature was about500℃and540℃respectively. PET had a weightlessness rate of about85%and an end temperature of about550℃in N2atmosphere. The data in O2atmosphere was more than99%and about535℃respectively. The weightlessness rate of PVF was about73%in the atmosphere of N2and O2and the weightlessness end temperature was about850℃and560℃respectively. Making use of the TGA experiments of these three kinds of plastics, we’ve laid a theoretical foundation for the argument of tube furnace experiments.Under N2and air atmosphere respectively, we used the tubular furnace experiment system to treat the cell panels without TPT. Then we analyzed the gaseous products and liquid products of the heat treatment by using GC-MS. The result showed that when heat treatment was done to the cell panels only remaining EVA, under two kinds of atmosphere, the gaseous products contained propane, methane, carbon dioxide, Ethylene, ethane and propylene. In N2atmosphere, the generation is2.45mg/g、5.62mg/g、3.35mg/g、10.84mg/g、4.29mg/g and6.24mg/g respectively. In air atmosphere, the generation was2.30mg/g、8.02mg/g、123.22mg/g、12.04mg/g、3.32mg/g and6.81mg/g respectively. In these two kinds of atmosphere, the types of liquid products of heat treatment was not that different. The main products were long straight alkanes and olefins. And there was a little of cycloalkanes, alcohols and aromatic compounds such as toluene, phenanthrene, anthracene etc.The recycling of crystalline silicon cells took three steps. First of all, use NaOH solution to recvcle the aluminum electrodes in the back of the cell. Then use HNO3solution to recycle the batteries positive silver electrode grid line. In the end. HF solution could be used to remove the anti-reflector on the surface so that pure poly-silicon can be recvcled.Considering the experimental results and other factors, three reaction steps could be taken at room temperature. The highest concentration of NaOH solution was30%. and charging should be taken into consideration when the concentration was less than10%. HNO3could choose the highest concentration of5mol/L, and should be no less than3mol/L. The concentration of HF kept moderate, at about20%. Through the above three steps, the silicon wafers purity could get above99.9%.