If tyres burn, why don’t we set them alight and save the planet?
Riots in the streets are nearly always accompanied by stacks of burning tyres defining the no-go zone. They burn very well, although smokily. Once started, they’re almost impossible to put out.
So why aren’t they used more widely as fuel if they burn so well. After all, there is a millions of tyres discarded worldwide every year. They are no good for landfill, because they don’t decompose, and are hard to keep below the surface. In fact, I know of a pile of over 200 million tyres outside L.A. waiting for someone to devise a use for them.
Furnaces to burn them have been developed, and the resulting heat used to raise steam, or for central heating. These take either whole tyres, or shredded tyres, use a conveyor feed system to load the furnace, but somehow haven’t been widely adopted. Someone has to load the conveyor, too!
The reason for non-adoption is possibly “acid rain”. When rubber is vulcanised, it is combined with sulphur. This process cross links the rubber molecules, and converts the rubber material into a stable, three dimensional lattice, which is elastic. The level of sulphur is generally 1 to 2 percent. This level of sulphur is around the same as for high sulphur coal. When burnt, (oxidisation) it becomes sulphur dioxide, and other oxides such as sulphur tri-oxide, dependent on the air/fuel mix. Burn coal, you get carbon dioxide, burn tyres you get sulphur dioxide. High sulphur coals are very much out of favour.
In the atmosphere, these oxides of sulphur combine with water to form sulphuric and sulphurous acid, which pollutes the air, kills vegetation and our forests which are the lungs of the world.
So a great deal of research into the design of the furnace to minimise these effects and scrub the exhaust gases clean of smoke and pollutants is required, which makes the furnace more expensive.
Then there’s the costs of collecting the old tyres, sorting , classifying, shredding, and the costs of disposal of the ash that results from the burning, though the steel content can be recovered as slag from the furnace grate. However, there awaits big rewards for the designer of a furnace that will be easily portable, has a captive market for its product (heat), and a ready supply of worn out tyres available at preferably no cost.