Many people don't know about them. According to experts, over 2 billion of them are scattered about the continental United States, some illegally. Perhaps 225 million more pile up each year. There is no place for them. Nobody wants them around. Collectively, they constitute a problem that won't go away.
The problem is used tires.
Today, after years of research and development, a few entrepreneurs and companies claim they can solve it and make a profit while they are at it. All that's needed, they claim, is cash and time.
Abroad, some companies in Britain, Japan and West Germany have been turning tires into fuel, or plan to.
At the moment in the US, however, retreaders recycle only a small percentage of them. Most of the rest are dumped on the surface. They are barely biodegradable, and most landfills won't accept them. Abandoned, they provide a breeding place for mosquitoes.
Yet a used tire contains as much energy, pound for pound, as coal. Since 1968 man Pxy le have tried various ways to solve the problem. Now some new ventures are trying once again to make money from used tires:
* Duane Plank, a recycling entrepreneur in Washington State, who has been working on a technique for converting used tires to fuel oil for the past 11 years, built two working small-scale plants from scratch and plans to build larger when he gets a financial backer.
* Wolfgang Kutrieb, president of the Wisconsin-based Kutrieb Corporation, says that after a three-year R&D project his company is ready to manufacture a small system that can take used tires and turn the byproducts into steam or electricity.
* David Robison, executive vice-president of Gulf Resources Inc., says that his company has a process and the financial backing to start up tire recycling plants.
But rubber recycling experts are skeptical.
''I've been in this business for 15 years,'' says Jerry Sharf, secretary-treasurer of the Rubber Recycling Division of the National Association of Recycling Industries (NARI), ''and no one has turned garbage into gold yet.''
The basis for all these projects is pyrolysis, a process that is used to drag oil out of oil shale by heating the shale in an oxygen-free environment until it breaks down into its basic components. When this process is turned on used tires , it decomposes them into fuel oil, gas, steel, carbonacious char (a fuel that is equivalent to coal), and carbon black. The process can be modified to favor the recovery of any one product. Pyrolyzers say they can convert tires into marketable products, thereby getting rid of the used tire waste.
Richard Wilde, project manager of the Department of Energy's Idaho Energy Conservation branch, points out that while the process may be physically possible, it may not be economically feasible.
''It's very confusing,'' Mr. Wilde says. ''Many people are making claims that they have solved all of the problems (in the process). We don't find any of these processes to be marketable.''
According to industry experts, the problems that face would-be pyrolyzers are considerable. Besides just managing to get a guaranteed supply of old tires, pyrolyzers must develop a market to sell their goods in and get recession-weary investors to help back their projects.
Attracting outside capital seems to be the worst problem. Like Mr. Plank, who says he can recover half the weight of a tire in usable fuel oil, you may have a market, and a tire supply, but you need capital to build your plant.
Plank, a self-educated pyrolyzer, is in the recycling-waste disposal business. He has built two very small pyrolyzer plants out of scrap, and is hoping to build one that will handle 25 tons daily. This would give him the output needed to take up the offer from a refinery that wanted to buy his products. But his business, while small, is diversified, and this keeps him busy.
While project capital may be a problem to some, to Mr. Kutribe, at the Kutribe Corporation, it is better to build the equipment and sell it to others than to get in the business yourself. His company's process, claimed to be nonpolluting, handles only 500 pounds of used tires an hour. Mr. Kutribe is quick to explain that his product is meant to solve the tire problem for the customer who has a problem with disposal, and not to provide fuel oil.
The Kutribe process can be modified to produce heat and electricity from the gas and oil extracted from the tires. Business is picking up, according to Kutribe.
Gulf Resources Inc. is one of the few companies that is trying to go nationwide with pyrolyzing plants. It has come a long way. It's been selling plants to investors, retaining a management contract that will give Gulf Resources 25 percent of any profits. While most pyrolysis processes recycle some of the energy they produce, the Gulf Resources process operates on outside energy. The company maintains that the process is economically feasible.
Contracts for 4,000- to 6,000-tire-a-day plants have been closed in Maine, Texas, Oklahoma, and Colorado. Contracts for a 25-year supply of old tires in each area have also been drawn up.
While these three individuals and companies are used here as examples of trends in the pyrolysis arena, a great deal of skepticism remains. The pyrolysis process has been around for years. Many investors have tried to come up with some pyrolysis process that will turn the heaps of burned rubber into profits.
But few of the operators have progressed past the pilot plant stage. ''We have heard claims that people have systems that are economically practical,'' says Jerry Sharf of NARI. ''Show me one that makes money.''