Tyre Recycling

Tyres are a disposal problem as they consume considerable airspace relative to their weight and cannot be compacted.

South Africa has an extremely well-developed re-treating industry due to sanctions, and re-treating tyres is still one of the best ways to obtain maximum use from them while temporarily reducing their contribution to the waste stream. Ultimately, however, tyres still need to be disposed of.

It is worth noting they have a calorific value well above that of coal, and therefore lend themselves to uses as a fuel in cement kilns and ordinary furnaces for the production of electricity.

Tyres in landfill sites create problems as :

• They are not compactable and when trampled, they spring back again.
• They add to the fire hazard in landfills because they burn easily.
• In a fire, only about a third of a tyre's oil is consumed. The rest seeps into the ground or, not finding it's way into an aquifer or water supply source, mingles with the rotting garbage and in turn, can cause further landfill fires.
• They encourage breeding of mosquitoes and tropical diseases e.g. Malaria, Yellow Fever.
• They collect gas which makes them rise to the surface causing aesthetic problems, damage to final cover/capping.

Increased awareness of environmental issues is making the disposal of waste tyres in landfill sites unacceptable in environmentally conscious countries.

Re-using of old tyres

World-wide there are several ways of reusing tyres:

• Shredded rubber can be mixed with asphalt for road surfacing and making children's playgrounds.
• Tyres can be recycled into rubber based products such as heavy duty rubber mats, shoe soles, mats for cars, hinges for gates, rubber cords for tethering animals, bags and seating.
• Tyres can be burnt for energy recovery, as well as crumbed and mixed with soil to aid drainage in parks and as sea defences to reduce coastal erosion.

Benefits of using tyres with asphalt

During 1992 more than 4000 tons of rubber crumb were used internationally for bitumen binding modification in road surfaces. The benefits of using rubber crumb are:

• Low temperature flexibility is improved and high temperature softening point is increased.
• Cracking of the road surface is significantly reduced.
• Skid resistance is improved as well as dispersal is improved.
• Noise levels are reduced.
• The chief drawback is the high initial cost of the product and increased processing costs.

Cement Kilns

The alternative that has been cited as providing an environmentally sound solution is the cement kiln. Cement kilns can dispose of tyres in a clean operation, while at the same time utilising the energy released.

Advantages of disposing scrap tyres in cement kilns

• Researchers claim that in disposing of tyres in cement kilns, there is:
• Complete combustion at high temperatures;
• No black smoke;
• Combustion gases scrubbed by lime in the kiln;
• 100% utilisation of available energy;
• Little residue (other than ash);
• Partial replacement of coal saves fossil fuel;
• No health hazard.

The process

• Tyres can be burnt either whole or reduced in size by shredding. When installing a whole tyre feed system, the installation cost is high but the operating and maintenance costs can be low. Although the shredded tyre feed system has an initial lower installation cost, higher operating costs and higher maintenance are involved.
• Burning process control measures.
• Tyres are weighed to control the feed rate to the kiln;
• Carbon monoxide and oxygen levels in the exhaust gas are continuously analysed;
• The primary fuel (coal) is automatically increased in the event of tyre feed failure;
• Maximum 20-25% replacement of coal with tyres.

To successfully destroy tyres, it's important that:

• The temperature is sufficiently high to ensure complete burning.
• The energy produced by burning tyres is absorbed by the process materials in the kiln system;
• The tyres stay in the kiln long enough to ensure complete burnout before the kiln burning zone is reached.

Drawbacks

• Initial conversion costs of the kilns are high, and at present only about 25 percent of coal can be replaced with tyres.
• In South Africa a number of cement plants are evaluating switching to burning tyres. However, coal is relatively cheap in South Africa and while tyres are a major problem, with the exception of the Gauteng area, there are not enough scrap tyres to make conversion worthwhile.

Cut waste by:

• Buying long-life tyres.
• Extending their wear through regular maintenance and checking tyre pressure frequently.
• Consider buying retreads if available.
• Giving old tyres to playgrounds, suspended on metal chains or ropes they make excellent swings.
• Tyres filled with soil make ideal plant holders.