Nature of recovery closed loop open loop and energy recovery

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Closed loop recycling refers to the situation where the recycled item is re-made, e.g. using PET bottles to make new PET bottles. This reduces the amount of raw material going into this product. Open Loop recycling refers to the case where different items are made, e.g. using PET from collected bottles to make synthetic fibre or plastic lumber. In this case, the amount of raw material going into PET bottle production is not reduced, and the savings arising here from the recycling of PET are at the expense of a renewable raw material - timber or natural fibres. Most current recycling is of the open loop form. Curlee (1986) identified three separate classes of recycling activity for plastic.

Primary. This corresponds to closed loop recycling. It is where waste is processed into a material with characteristics similar to the original product. For most materials with long established and successful recycling markets - e.g. gold or aluminium - this is what happens. For post-industrial plastic scrap primary recycling is the main activity. For post-

consumer plastics this has proved to be difficult because of contamination, and the difficulties of separation, associated with the complex and mixed nature of the waste.

  1. This includes reprocessing waste into materials that have characteristics less demanding than the original material. An example would be the recycling of plastic waste into plastic lumber used as fence posts. Performance may still be important though, and the uncertain characteristics may limit applications. An example of this is the use of plastic lumber in marine applications where its resistance to rot might make it an attractive material. However, laboratory studies have shown that its engineering properties are inferior to those of wood, it is prone to damage from UV radiation, and suffers from deformation under load. Plastic lumber has variable elasticity and this has been judged to limit its areas of application. (Breslin et al, 1998).
  2. Tertiary recycling produces basic chemicals and fuels by taking the plastics back to the basic monomers and polymers. Pyrolysis and hydrolysis are examples of this. This has been an area of much research. It has proved to be feasible although expensive. Although it is the area where the petrochemical companies would have comparative advantage, economic considerations lead them to continue to rely on oil as a basic input, rather than recycled plastics.

If material recycling cannot be undertaken efficiently, waste plastic can be used as a fuel. It has a high calorific content, and where MSW is incinerated, fuel such as oil might need to be added if plastic content were not present. Where it is burnt by itself it has an average calorific content of 12 000 BTU per lb, which is similar to that of anthracite.

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