Release of Metals during the Pyrolysis of Preservative Impregnated Wood

Abstract

This paper describes an experimental facility for the pyrolysis of non-treated and CCA-treated wood particles. In a typical experiment, 10 grams of wood are loaded into the reactor. This reactor is a stainless steel circular tube with a diameter of 5 cm and a length of 20 cm. A flow of heated nitrogen is forced through the reactor. The reactor tube is thermally guarded with a heating tape with a controlled heating power such that the reactor outlet temperature equals the inlet temperature. At the outlet of the reactor, the nitrogen flow contains non-condensible pyrolysis gases as well as microscopic tar droplets. The gas flow is cooled in a highly compact coiled water cooled heat exchanger before passing through a filter.

The experimental results show that the loss of arsenic from the wood relative to the overall loss of mass is dependent upon the reactor temperature and the duration of the pyrolysis process, increasing with increasing temperature or duration of the heating period. It is shown that there exists an optimal combination of temperature and duration which yields a minimum loss of arsenic. At these conditions, the release of copper and chromium is negligible.

A qualitative study of the gaseous and liquid products, resulting from the pyrolysis process at these optimal conditions, is carried out by forcing the pyrolysis gas through a water scrubber and a glass fibre filter.