30/06/2011

Module C – processing the light fraction (fibres)

Module C – processing the light fraction (fibres)

Over the past few weeks, a number of modules for the plant were explained in the newsletter. This time we will be discussing the first expansion of module C, a component installed just before the spectacular opening on 28 April last.


Module C processes the fibre fraction discharged by module A. This fibre fraction consists of a whole variety of fibres, both man-made and natural, for example seat coverings, coconut mats, foam (seat filling), plastic film, etc. In module C, the fibres are agglomerated, a process whereby a more compact fibre is formed through the addition of heat. The fibres in fact slightly curl up.

Process

Given the nature of the material, it will contain a degree of contamination in the form of metal particles, copper wires adhering to the fibre, plastic, as well as small stones and pieces of glass trapped between the fibres and in this way carried along with the fraction. To be able to successfully agglomerate this material, it must undergo initial pre- processing.

  • The first pre-processing stage takes place in an impact mill supplied via a dosing bunker. In this device, the small copper wires are thrown around in such a way that they break free from the fibre material, and are turned into wads of wire. The wads, together with all other small material particles, are separated for further processing, in a sieve.
  • The sieved-out material is passed over a separating table; the light fraction is returned to the fibre flow while the heavy fraction is passed on to a magnet that separates out the steel. Subsequently, via another separating table, the copper is removed and the aluminium separated out via an eddy current. What remains, mainly plastics, is transported to module B.
  • The material that is not sieved out and the light fraction that is returned from the separating table are passed through a spinner. In this device, the dust is removed from the material under considerable force. At the same time, any heavy metals contained in the dust are removed. The light fraction is then clean enough to be agglomerated.
  • The agglomerators are supplied from a second dosing bunker, that receives its material from the spinners. In the agglomerators, the material is spun in batches, whereby the temperature rises due to the friction between the individual material parts and the wall of the spinner. As a result, the shape of the material changes. It shrinks, sticks together, curls up, is torn free again, etc. The final condition is determined by the process time and the temperature. The process time can be adjusted, while the temperature is influenced by atomising water onto the material during the agglomeration process.

Processing a batch takes approximately six minutes. The cooling water evaporates and passes out of the agglomerator in the form of steam via a vapour outlet, to be condensed back into water, in a condenser.


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