PROCESS Sorting Washing decontamination Process.
The waste material is processed through a Mars recycling plant. Firstly the waste material is sort in state of art Plastics Bottle Sorting Plant. The input-bottles to feed the plant, comes from urban and industrial collection sites and are pre-sorted. At the first step of the system the packing ropes of the bottles bales are removed and they are then conveyed into a Sorting Plant. Mixed Plastics Sorting Plant Description; Mixed Plastics means what it is a Post Consumer Plastics waste usually contains a very high proportion of recyclable materials such as Poly Ethylene LDPE or HDPE, Polypropylene PP, Polyethylene terephthalate PET, Polystyrene PS, Poly Vinyl Chloride PVC, Cardboard, Plastics films, Non Ferrous and Ferrous, which are separated by mechanical sorting. Polymers, paper or films are subsequently inspected at manual sorting stations for quality optimisation.
The bottles are transported through a metals separator and then, to a belt conveyor for the visual control. From this point the bottles are conveyed into a screened cylinder where they are subjected to a water washing shower. the bottles are well separated from each other and the small parts are removed. At this step there is also the separation and elimination of the most part of the labels that are collected – with other impurities – and automatically conveyed to the containers for the dump. At the pre-washing outlet bottles fall onto a ballistic sieve which make them drip and separate from any possible labels.
The bottle stream is then stored in a “Constant Feeder» that ensures a continuous feeding to the following stages and allows short interruptions of the pre-installed machines. The “constant feeder” extraction belt is equipped with electronic loading cells and has the function to dose the bottles stream through a weighing system by adjusting the feeding capacity to the detection section. From the constant feeder the bottles are continuously dosed to two NIR electronic control stations in series to sort out other contaminant polymers. A belt is foreseen for an eventually future installation of a colour detector. The detected and rejected bottles are collected on a belt and conveyed to the secondary NIR. The detected and sorted bottles are then manually controlled on a selection belt and conveyed to the wet grinders to be reduced into flakes. The flakes are conveyed to the pre-floatation step to separate and to remove the most part of Polyolefin’s, the paper labels still present and the floating pollutants, before reaching the washing step.
Through the pre-flotation it is partially avoided to dissolve in the water some substances such as inks etc., with the aim to keep the water cleaner in the next steps. The perfect cleaning of the flakes from the residual pollutants is therefore essentially concentrated on the removal of various impurities still stuck to the flakes.
The system remove therefore the remaining labels, various impurities that are still stuck to the flakes and first of all detach and remove the glue and prevent its redistribution of flakes. All these important functions are perfectly performed by a machine, the FRICTION WASHER.
In the Friction Washer the heating is indirectly by steam, and the flakes are subjected, at very high temperatures, to a strong but non-destructive friction action, which causes the reduction to pulp of the labels and the hot removal of the glue. A next flotation tank removes any impurity lighter than water, coming from the Friction Washer, such as the PE caps and labels. The flakes are then conveyed to the centrifuge with fresh water rinsing system, which removes also the soda.
A final hot air drier removes the humidity. A sever selects the material at the required size. The oversize flakes are ground by a dry grinder. The flakes are then stored in two homogenising silos, A de-duster removes the fine particles, that are stored in the self cleaning filter, before the optical sorter. The whole plant is put in operation and controlled from the control room by means of a computerised system interfaced with the PLC of the plant power cabinet.