A Safe Use For Used Treads

Niagara Catholic High School, Niagara Falls, NY





At last count, there were approximately three billion trashed tires strewn about the country. Each year the United States adds 250 million tires. California, alone, discards 20 million tires a year. Along with this, Americans wear 50 million pounds of rubber off their tires every two weeks.

Of the 250 million tires trashed each year, only 43 million are recycled. The recovery rate is only about 18%, and tires now make up one percent of all municipal solid waste. While the problem of overflowing tire-landfills seems to have more of an impact on densely populated areas like California where there are more cars used for transportation, this is a problem that affects everyone.

Retreading is a good way to extend the life expectancy of tires and keep them out of landfills. Usually a tire is replaced simply because the tread is gone. A good tire can be retread several times. Air Force One lands on retreads, the Blue Angels' jets land on retreads and almost all commercial airliners roll on retreads. Most buses and taxis use them too. Even Frito-Lay and UPS (United Parcel Service) trucks drive on retreads.

At one point, 30 percent of all passenger tires were retreaded. That was down to six percent in 1991, believed to be due to poor retreading. The public seems to associate retreads with the amount of rubber tire casings on the highways, and chose not to buy them.

While there are many possible solutions to the overwhelming amount of tires trashed each year, most of them lead to an excessive amount of pollution, unacceptable rises in cost, and/or destruction of the terrain.

Some solutions involve using the tires as a type of building material. Others involve using tire "crumbs" to add to asphalt for paving roads, runways, playgrounds and running tracks. Pavement that contains rubber crumbs lasts longer, is more flexible and is more resistant to the weathering elements. Tires can also be used to stabilize the shoulders of highways and the slopes of drainage canals. Dirt racetracks seeded with crumbed tires are easier on horses. They can be used to make hockey pucks, mud flaps, carpet padding, and office floor anti-fatigue mats. Used tires are used to fashion silent stairs.

Tire crumbs can also be used on the floors of playgrounds because they are softer than gravel. They can be set up as playground tunnels, swings, fences, crash barriers and dock bumpers. In some places tires are used in oceans as artificial reefs to attract fish. They are also used as porous breakwaters and to weigh down ocean dragnets.

Tires can even be used in farming. Crumbed tires added to soil will increase porosity and allow more oxygen to grass roots. Some aerial crop dusters use burning tires as wind socks.

Still, while these are all wonderful ways to make use of the tires, there is no way these uses will ever come near to even slowing the rate tires are piling up .

Besides the destruction of the terrain, there are also health problems involved in the improper storage of trashed tires. When tires are simply left in large piles, they become health hazards. Whole tires left in landfills are ideal breeding grounds for disease-carrying rodents.

Another health risk resulting from the improper storage of tires is the mass breeding of mosquitoes. While they are in general considered a minor annoyance, mosquitoes can be a real health hazard.

Large piles of tires stacked on top of each other can also trap enough oxygen to start a fire. When tires burn they send off billows of black acidulous smoke full of hydrocarbons, benzene, and other toxic pollutants. In Platteville, Colorado, in 1987, a pile burned for four days.

In Winchester, Virginia, a fire involving seven million tires, burned from 1983 until 1984, lasting nine months. This fire cost the federal government nearly $1.2 million to extinguish. These are only two of the sometimes devastating fires that have resulted from the improper care of billions of tires.

Fluid bed boilers could become one of the best ways to properly dispose of the tires without causing environmental damage. A fluid bed boiler is currently being used by a cogeneration company in Niagara Falls, New York.

The fluid bed boiler consists of two main structures, the combustion chamber and the cyclone. Inside the combustion chamber, a bed material consisting of limestone is mixed with the fuel and is "fluidized" with air which transports the solids up the full height of the chamber. Combustion occurs as the fuel ascends the chamber. Heat is removed by a series of tubes containing water that line the walls of the chamber. This water can be removed to run turbines and produce electric power. The hot gases and burned solids exit at the top of the combustion chamber and enter the cyclone.

In the cyclone, the solids are separated from the hot gases and any unburned solids are returned to the combustion chamber for reburning with fresh fuel. Fly ash is formed inside the cyclone from small solid particles of burned and unburned matter. This fly ash and the hot gases flow to the separators, where the hot gases are cleared of any dust and released into the atmosphere.

The technology for using the tires exists in the fluid bed boiler. We suggest using tires that have been shredded for fuel in these boilers. Since the boilers produce electricity, the machines to fragment the tires could be powered by the boilers. Then the shredded rubber could be fed into the boilers as the sole fuel or mixed with coal to augment this fuel.

The major problem involved in burning tires is the production of sulfur dioxide, which causes air pollution. A fluid bed boiler could be the perfect solution to this problem. The calcinated limestone produces gypsum. Gypsum is used to make "dry-wall," a material used in construction work.

Another major problem with the burning of tires has developed recently with the production of steel-belted tires. Because of the low temperature of the boiler, the steel is not melted. We propose a method to reclaim this steel. Using a series of belts and magnets, this steel could be removed and recycled. The fly ash and the steel fibers are the solid wastes produced by this process. A series of moving belts could remove the ash with the steel wire from the boilers. The belts carrying the ash and the wires move until they reach a set of belts above them containing electromagnets. These electromagnets would attract the steel wires and draw them out of the fly ash.

The steel wire recovered from the tires could be recycled in steel plants. The wires could even be put back into new tires. By recycling the steel wires, the electricity used to produce the steel would be saved as well as conserving the iron ore from which it is made.

This procedure could be very economical. Not only would it eliminate the problem of the excess tires now in landfills, but it would also lessen our dependence on foreign sources of hydrocarbons. Since the United States is depleting its fossil fuel reserves, this would benefit our country's industries now and in the future. The tires will always be readily available since people continue to drive cars. Because the sulfur dioxide would no longer be a problem, it would be considered a "clean fuel."

The time needed to implement this procedure is relatively short. For industries currently using fluid bed boilers, the time required to convert from using coal to using tires as fuel would be even less. The energy produced by this process could be used in industries or for private home use. The electricity could be sold to local electric companies or could replace them altogether. The steam produced could be used in local industries or used to run turbines.

Our project uses existing technology to solve the problem of "tire-pollution" as well as conserving this nation's natural resources, while creating a new energy source.