Abstract: Thermal plasma pyrolysis of waste tyres for recovering energy was performed in a nitrogen plasma reactor. The main gaseous products were identified by chromatography as H2, CO, CH4, C2H2 and so on. From a series of experiments, the effects of the process parameters of thermal plasma pyrolysis were investigated. Under our experimental conditions with steam injection, the total contents of H2 and CO reached up to 38.3% in the gas product, C2H2 up to 4%, and the maximum calorific value of the pyrolysis gas was 8.96 MJ/m3. The results indicate that plasma -assisted thermal decomposition of waste tyre particles may be a useful way for recovering energy and useful chemicals.
Key words: thermal plasma; pyrolysis; waste tyres; waste recycling

1 INTRODUCTION
      Motor vehicle tyres are nondurable goods, neither fusible nor soluble under normal conditions and cannot be remoulded into other shapes without serious degradation. Common treatments such as land filling or direct incineration (without recovery of value) not only waste the resources but also increase the area of land with pollution. The increasing production of tyres has caused considerable disposal problem. To explore the real potential of waste tyres for possible material and energy recovery, an efficient strategy should be found.

      Thermal treatment and resource recovery seem to be among the most advanced and significant disposal methods. Pyrolysis has the potential of transforming solid wastes into useful recyclable products, but conventionally leads to a wide spectrum of pyrolysis products which are difficult to be separated and utilized. Recently, attention has been paid to plasma-assisted pyrolysis. The pyrolysis gas, having an appreciable calorific value, can be used for combustion; similar viewpoint has been reported by other authors; Chang et al.[1] used old tyres as the raw material for production of syngas by thermal plasma pyrolysis, and the combustible heat value of the produced gas was 4～7MJ/m3. Compared with the conventional pyrolysis, plasma pyrolysis has a number of unique advantages. For example, it provides a circumstance of high temperature and high energy for reaction, the reaction sample is heated up to a high temperature rapidly, and some reactions will take place which would not appear in conventional pyrolysis. It is an appropriate method for polymer pyrolysis. The main objective of the research work reported in this paper is to study the conversion and to characterize the gaseous product in N2 plasma jet of waste tyres.

2 EXPERIMENTAL
     The center of the experimental setup is the plasma reactor with a maximum electric power input of 55 kV?A. A schematic of the reactor is shown in Fig.1. It consists of two main parts: the arc-discharge plasma generator (typical operating conditions are listed in Table 1) and the reaction chamber (1000 mm in height and 50 mm in inner diameter), in addition to some accessories. The core temperature of the plasma torch at the entrance of the reaction cavity was calculated from enthalpy of the working gas (nitrogen) to be in the range of 2500～3500 K. Running water was used to cool the system. The waste tyre sample was provided by Guangzhou Resource Recycling Company, the particle size of the sample used in this study was 50～80 mesh. The proximate, ultimate analyses and calorific value are listed in Table 2. Gas product samples were withdrawn through the sampling line, collected by rubber bags and analyzed in a GC-20B-1 gas chromatography system (Shimadzu,Japan). Solid residues were saved in the ash tank. Gaseous product yield was determined in each experiment by measuring the volume and calculating the weight of gas products. The solid residue yield and the fly ash yield were determined by mass balance.

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