AN IMMENSE, WIDELY DISPERSED, HETEROGENEOUS ARRAY

Wooden poles are an essential component of overhead cable systems. Several million of them are in service today in every country (in France, there are approximately 25,000,000). The actual number of poles and their density can vary widely, depending on the region.

In the course of normal maintenance and servicing operations carried out on these systems, some hundreds of thousands of poles are withdrawn every year. The average useful life of these wooden poles is approximately 35 years. However, their life cycle is affected by two very important factors : there are today wooden poles still in existence in the field which are very much older, because they are part of tertiary networks or special connections. The other factor is connected with accidental dammage caused by agricultural machinery, traffic accidents, forest fires, thunder storms, changes to the layout, lines being placed underground etc.

These wooden poles are non-homogeneous not only in terms of their distribution, their age and their state of repair but also in terms of the different types of industrial treatment they have undergone. Some have been treated by immersion, others have been impregnated by the BOUCHERIE process, others still autoclaved according to the Rüping, Estrade or Bethell method. The type of preservative used has also undergone continual changes : pentachlorophenol, creosote, metal salts, copper sulphate up to the mid 70’s; CFK (copper, chromium, fluorine), CCB (copper, chromium, boron) and above all CCA (copper, chromium, arsenic) since then.

The question of recycling is therefore becoming pressing as a result of the changes in the regulations which are forcing those operating the systems to find ways of dealing with these products with the aim of recycling them.

    THE NEW OBLIGATIONS IMPOSED BY THE REGULATIONS


According to the new regulations on waste, all waste products consisting of wood which has been impregnated or coated with substances containing heavy metals, PCP, lindane, or creosote, in particular, have been classified as "dangerous waste" (EEC terminology) or DIS (French terminology). Such types of wood waste and, speaking in general terms, all those which have characteristics preventing them from being included under the "biomass" category, must be separated from other types of waste and subjected to special treatment or treated at landfills of class I.

  LANDFILL SITES OF CLASS I

Since the present regulations are aimed at reserving landfills of class I exclusively to "ultimate waste" and wooden waste products cannot be classified as belonging to this category, we need to look for other solutions.

  RECYCLING BY INCENERATION

Numerous studies and experiments have been carried out on burning contaminated wood by various organisations and university research institutions, in particular in the USA and Canada, but also in Europe, in Germany, Holland, Denmark, Switzerland and the UK. Their conclusions contain three common points :

1. Burning of wood that has been impregnated or coated with a wash of oils or chemical products such as release agents, paints, varnishes, glues or preservatives, requires special precautions because of the toxicity of the fumes which are released during such combustion processes. This toxicity is due to the fact that the heat releases the chemical products and liberates most of their components in the gaseous form. The phenomenon is even more evident in the case of the heavy metals contained in varnishes, paints and preservatives.
   
   
2. The household waste incinerators, and most of the incinerators used for industrial waste, are not equipped to retain this type of toxic element specially at the concentrations involved..
   
   
3. The tests carried out to reduce the level of concentration of these toxic elements in the smoke by dilution, by mixing different percentages of polluted wood with household waste, have failed. At each attempt, these mixtures have caused the destabilisation of the combustion conditions in the incinerators resulting in the appearance of highly dangerous and uncontrollable chemical compounds.

Even more critical is the fact that the experiments carried out on wood treated with CCA have shown that it can be incinerated only on its own and only in a specially designed incinerator.

     SOME THOUGHTS ON THE EFFECTIVENESS OF
   RECYCLING AND WAYS OF ORGANISING IT

In order to be considered effective, a recycling system must be capable of dealing with all the problems without any drawbacks or negative consequences for the environment.

Designing a recycling system capable of effectively dealing with each of the difficulties immediately raises several questions : how to organise the collection, how many treatment plants are required, where should they be set up, what capacity should they have?

Although it is essential for the technical solution adopted to be capable of solving the problem as a whole, the "principle of proximity" should be taken into account as well as the necessity not to add additional costs to old wood, which is valueless in any case.


To take the French example into consideration, half a million poles are being withdrawn every year; this is equivalent to 7,500 full articulated lorry loads. How to organise the turn-around and loading of these vehicles with any real chance of success, with the product being of varying size and quality, randomly scattered over France in irregular quantities? This seems all the more problematic as allowance must be made for seasonal variations, difficulties of access, the control of the means of transport and their co-ordination. Operating at regional level would appear to be the only realistic scale of operation.


Assuming that the use of poles in France is suddenly stopped. With one recycling plant operating at a rate of 500 000 pieces per year, 50 years would be required to treat all the posts/poles that are at present in place.

  THE TERMS OF ANY SOLUTION WOULD THEREFORE
   BE AS FOLLOWS:

To be effective, a recycling station for old wooden poles will need to have a reduced radius of collection and dimensions suitable for the activity concerned. In addition, the system or the process selected will need to make it possible to treat all wooden poles/posts irrespective of their quality, their age, the type of wood, their method of treatment or level of pollution.

It is such a solution which Thermya SA intends to make available to the owners of systems in the form of the ‘CHARTHERM’ process.

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