Sorting, Size Reduction, Washing, And Blending Of Waste Plastic
Sorting is the process in which mixed plastic waste is sorted according to the specific type of plastic. This is done by using mechanical means and/or manually. Mechanical sorting is able to identify all types of plastics (e.g. PVC, PET, PP, PE, ABS, PC, POM, PMMA) and its colors. However, mechanical means will not be 100% accurate. Manual supervision and sorting is in place to ensure proper segregation.
The plastic wastes come in different shapes and sizes. We will use machines such as Shredder and Crusher to reduce the materials to a size of suitable for our end use. If it is of high grade quality plastic, the size is kept as 25mm x 25mm x 25 mm and for medium grade plastic it is about 10mm for lower grade plastic the shredding/crushing is done to make very fine pieces of plastic. The purpose is to ensure a smooth and constant flow of the plastic wastes into the system like pyrolysis plant or to plastic extruder machines.
Washing Waste Plastic
Once the waste plastic has been identified and separated into 3 different categories, the cleaning process can begin in separate batches, this usually starts with washing to remove paper labels, adhesives and other impurities, all the labels on your plastic containers, bottles and even your wheelie bin need to be completely removed as these will lower the quality of the finished recycled plastic.
The crushed plastic materials could be of different quality and grade. In order to achieve a homogenous batch of recycled materials with the same quality, we need to blend the crushed materials so that the materials are evenly distributed. This is done through blending and tumbling machines.
Treatment Process Pyrolysis
Pyrolysis is a chemical reaction which involves breakdown of larger molecules into smaller molecules in presence of heat. After blending, high grade shredded plastic waste is loaded to pyrolysis plant. Oil, hydrocarbon gas and carbon black are generated from this process and hydrocarbon can be used for heating reactors in plant and carbon black as raw material for industries for various uses like manufacturing charcoal, solid fuel etc.At the end of the process, pyrolysis oil is routed to underground storage, hydrocarbon gas is routed to gas storage facility and carbon black is removed through solid separation process and collected and stored.
After blending, the materials are now ready for extrusion. Extrusion is a melting process where the materials are fed into a hopper and melted in the heated barrel with rotating screws. During the melting process, additives (e.g. antioxidant, impact modifier, lubricant, calcium carbonate, talc) are sometimes added to aid the extrusion process or modify the plastic properties. The rotating screws will mix and push the melted materials out of the die opening in strands. These strands travel through a water tank to cool and solidify. At the end of the water tank, the strands are cut into pellets by a pelletiser. Non-uniform (either undersized or oversized) pellets are sieved out by the shifter. The remaining pellets are conveyed into storage tanks and then packed into 25kg.
Low grade plastics identified and separated during segregation process are fine shredded by adjusting the shredder blades. Finely shredded/crushed materials washed and dried and then stored. Research and past experience at different places of world already established use of these materials in Road construction and for preparing long lasting eco friendly railroad support/tie.