Waste tyre

Use peaked in the 1950s and has fallen steadily since then. Recent environmental pressures have raised the profile of recycling and reclaiming and there is now much research in this field with a view to finding effective disposal methods for waste tyres. See Refining. 

Environmental impact of energy recovery from waste tyres... 

In the past, landfills have been the preferred method of waste tyre disposal because burial eliminates the fire hazard associated with above-ground storage, as well as the unsightliness of tyre piles. However, problems with this method have become increasingly apparent. Because of their composition, tyres are neither decomposable, nor can they easily be compacted (Blumenthal 1993). Therefore, tyres occupy large volumes of landfills, contributing to the already prevalent problem of landfill crowding. 

Several approaches have been made to reduce the number of landfilled, stockpiled, or illegally dumped tyres. Markets now exist for about 78% of all waste tyres (Fig. 3a), up from 34.5% in 1990 (Blumenthal 1993). These markets continue to grow due to innovative approaches, which include improvements in design and material to increase the lifetime of a tyre, as well as various alternatives to tyre disposal (Table 2). 

Whole waste tyres can be utilized for many practical purposes including crash barriers for both... 

A larger-scale tyre combustion experiment was performed by Lemieux Ryan (1993) in order to collect emission data from a simulated open waste tyre fire. In addition to identifying a large number of organic compounds, including... 

The relatively large heating value of tyres makes the use of TDF or whole tyres for combustion in utilities, industry, and manufacturing the most promising method for waste tyre management. 

Atal, A. Levendis, Y. A. 1995. Comparison of the combustion behaviour of pulverized waste tyres and coal. Fuel, 74, 1570-1581... 

Z3A [Zero environmental damage, 3rd Alternative] A process for pyrolysing waste tyres using microwave energy. Developed and piloted in the 1990s by Amat, Crewe, UK. Not yet commercialized. 

Pyrolysing waste tyres in TG, three weight loss stages are reported [34] 200-330°C, 330-400°C and 400-500°C. The first step corresponds to the thermal decomposition of the mixture of oils, moisture, plasticizers and other additives, the second one to that of NR and the third one to the decomposition of BR and SBR content of the tyre. The pyrolysis conditions influence strongly the resulting oil [35]. 

Li et al. [16] also stndied the influence of pyrolysis temperature on the pyrolysis products derived from solid waste in a rotary kiln reactor. They used an externally heated laboratory-scale rotary kiln pyrolyser (Figure 19.8). The length of the rotary kiln was 0.45 m with an internal diameter of 0.205 m. Kiln rotation speed can be adjusted from 0.5 to 10 rpm. The raw materials used in this study were polyethylene (PE), wood and waste tyres. The results obtained by Li et al. [16] reiterated that as the reaction temperature profile changes so does the product yield (Figure 19.9). 

There are a few companies that advertise on the Internet proprietary processes for micro-wave pyrolysis of wastes. Not surprisingly, considering what was presented in the previous section, most of these refer specifically or specially to the pyrolysis of waste tyres. 

The gas fluidized-bed reactor is the most efficient approach to pyrolysis. In this reactor the waste plastic is suspended around the heating medium and snbjected to pyrolysis by means of immersed heating tubes and gas-solid convective heat transfer. At present the only difficulty with this reactor is the problem of its structure. Fluidized-bed pyrolyzers have been designed for pyrolysis of waste tyre mbber in Taiwan and in Hangzon. A schematic apparatus of a fluidized-bed pyrolyzer is shown in Fignre 27.2. 

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