PHOTO: Hume Machinery’s ‘FS’ series wash plants function as elements of integrated systems and several criteria need to be attended to in order to achieve optimum performance. In both cases, the material arrives from either a granulator or shredder, via conveyor or agitator and, following the wash stage, departs to a squeezer/drying system and thence into a hopper for re-extrusion
HUME Machinery of Wynberg, Johannesburg, is one of South Africa’s top suppliers of recycling systems and in particular wash plants.
This is an area which has until now received little attention. The main reason for the new interest is the increased demand for recycled materials: up till quite recently the bulk of recycled material was sourced from either factory scrap or ‘closed-loop’ cycles, where relatively clean scrap was purchased by recyclers.
But the level of demand has been such that collection of post-consumer material, particularly from landfill sites, has become feasible. The problem, however, is that this material tends to be dirtied by various contaminants, such as sand, to varying degrees.
Hume specialises in the provision of wash plants and the integrated system components which can handle such material.
The process starts with the granulating or shredding of the material, with the next step being the wash plant. Different types of plants are available for the different plastics: Hume’s ‘FS’ series plants are able to process all different types of plastic with slight variations to facilitate the different requirements. Different granulator screens and blade configurations are also needed in the granulator stage to prepare the material effectively.
Different types of components are used in washing/drying systems, such as hot washers, friction washers, dewaterisers or squeezers. Chemical washing, using caustic soda, is also possible. The soda is corrosive, however, other problems can arise if the bath is not designed and built with the correct steel. The chemical can also prove costly.
The most common wash plants are for polyethylene and polypropylene, as the wash process is not as intense as it is for PET. These plastics are called floaters and react the same way when it comes in contact with water, thus allowing the plant to be more productive as a larger variety of material eg. HD, LD and PP can be washed as they all float.
The process is not as simple for other materials, such as PET and PVC, where the contaminants tend to be kept in suspension.
It is also important to note that the drying of rigid materials is easier than for film and flexible materials. With the latter, drying is more intense as these materials are more difficult to dry.
Hume Machinery also supplies a range of sizes, with plants that can wash up to ton of material an hour being available. If you’re not currently involved in the recycling sector, be advised: this is a large quantity to process an hour!
There is the possibility that the quality of material received by recyclers will improve, due to the implementation of ‘sorting at source’ systems by some municipalities and the greater role being played by industry bodies such as POLYCO, PETCO, SAVA and the PSPC, which are helping to coordinate the buyback centres for the collection of polyolefins, PET, PVC and polystyrene respectively.
A critical aspect of the process is water supply and water treatment, which unless controlled can lead to excessive costs, and this is to be covered at a SAPRO meeting in the near future.
Hume machinery has supplied Implats as well as Enviroserv with wash plants.
www.humemachinery.com