September/October 1992
Scrap tires are being recovered in many different ways. Will these options solve the stockpile problem and can scrap recyclers be part of the solution?
BY KENT KISER
Kent Kiser is associate editor of Scrap Processing and Recycling.
The question of what to do with scrap tires was born in the 1890s—albeit on a minuscule scale—when B.F. Goodrich Co. introduced pneumatic rubber tires for automobiles. Today, a century later, that question has become a challenge of gargantuan proportions. In the United States , more than 2 billion scrap tires awaiting some recovery or disposal solution are overflowing in legal and illegal stockpiles, where they can be fire hazards, breeding grounds for disease-carrying mosquitoes, and environmental eyesores. On top of that, another 242 million or so tires are discarded every year.
The good news is that scrap tires are eminently recoverable. In fact, approximately 27 percent of the old tires discarded in the United States last year were recycled or recovered for energy. The bad news is that the remaining 73 percent—or 176 million tires—were landfilled or stockpiled, and efforts to find recycling solutions to meet this monumental supply have faced market, political, and/or technical obstacles. Still, many believe these hurdles can be overcome, providing new answers to the question of what to do with scrap tires.
The First Steps
Common sense says that the first step toward mitigating the scrap tire problem is to not add to it. In fact, the Environmental Protection Agency (EPA) ranks source reduction as the first option in its waste management hierarchy. For scrap tires, source reduction means reducing the number of tires discarded each year, either by extending tire life through proper maintenance or reusing tires.
Reuse includes on-the-car as well as off-the-car applications, with the latter primarily in civil engineering uses such as artificial reefs or breakwaters, highway crash barriers, erosion control, planters, berms, and playground equipment. "While these uses certainly are environmentally sound applications for scrap tires, they're limited to niche situations and make only a minor contribution to the overall solution," says Michael H. Blumenthal, executive director of the Scrap Tire Management Council (Washington, D.C.).
Recycling is the next-best management practice in the EPA's hierarchy. And the most sensible and economical recycling option, says the American Retreaders' Association (ARA ) (Louisville, Ky.), is retreading—a process that gave new life to about 31 million tires last year. Of these, approximately 8 million were passenger car tires, 8 million were light-truck tires, and 15 million were truck tires, whose high replacement cost makes retreading cost-effective.
Those numbers could be much higher, according to the EPA, which claims that twice as many passenger-car and light-truck tires could be retreaded every year. Bob Majewski, ARA 's technical director, points out, however, that while more light truck tires are indeed being retreaded, the market for retreaded passenger-car tires has been declining for years due to the availability of inexpensive new tires and dwindling capacity to retread passenger tires.
Even if the EPA's assertions are correct and retreading increases in the United States , markets for ground scrap tire rubber are unlikely see much growth since very little postconsumer ground rubber is consumed in the process. Tread rubber manufacturers currently can use only 3 to 7 percent ground scrap rubber in retreaded tires, mainly from in-house overflow, or "flash," scrap, says Majewski, with lesser amounts from buffings of scrap tire treads.
Various technical concerns will likely prevent this percentage from increasing. "There's a point where you start losing traction and wear," he notes. "The rubber has to link together, and some of the ground scrap rubber might not link." Mixing different types of rubbers—synthetic with natural, for example—or rubbers with different hardnesses can potentially create hard spots, porous areas, and other problems that could reduce tire performance.
Recycling Pros and Cons
Of course, retreading isn't the only tire recycling option. Tires can be split or punched to make floor mats, shoe soles, washers, dock bumpers, muffler hangers, and other products. Tires can be chipped and used as a landfill base or cover, a bulking agent in sewage sludge composting, or a base or sub-base material in road construction.
Finely ground, or crumb, rubber can be molded into traffic cone bases, bumper pads, truck mud flaps, stable mats, commercial/industrial flooring, surfacing for gyms and athletic tracks, carpet underpads, friction brake materials, truck bed liners, even hockey pucks, or it can be melted and used as a spray sealant on roofs. One scrap tire processing firm, Continental Turf Systems Inc. (Continental, Ohio), grinds scrap tires into pieces the size of pencil erasers and sells the product—called Tire Turf—as a substitute for gravel or wood chips in playgrounds, jogging trails, riding arenas, and other applications. The firm charges 3 cents a pound to accept scrap tires and sells its product for 9 to 10 cents a pound.
While these new-product recycling uses consume about 2 million scrap tires a year and may seem limited only to the manufacturer's imagination, they face stiff price and performance competition from other materials, are hampered by limited markets, and—in some cases—run aground on environmental/leachate concerns.
So what about the seemingly most obvious recycling use of all—new tires? One problem with such direct recycling of tires is that vulcanization—the process that makes tires durable by forming a bond between the rubber's carbon and sulfur molecules—makes it virtually impossible to return rubber to its virgin state. Even pyrolysis, which distills rubber to oil, carbon black, and steel, can only break up the chains of carbon-sulfur molecules, not the bond itself.
In addition, Blumenthal notes, "Not all tires are the same. They're highly engineered products made of many different kinds of carbon black, rubber, and oil." There are also performance concerns when mixing virgin and scrap rubber. "For every 1 percent of recycled rubber you put into the tread portion of a new tire," Blumenthal says, "there's an equal 1 percent reduction in the durability of that portion." For these reasons, the use of reclaimed rubber in new tires is never likely to exceed 2 percent.
Similar difficulties exist when trying to bond thermally set tire rubber with thermal plastics to create such products as recycling bins, leaving this market equally limited.
On the Road Again
Perhaps the most promising large-scale recycling market for ground rubber lies in rubber-modified asphalt, which currently consumes an estimated 5 million scrap tires a year.
According to the Scrap Tire Management Council, consumption could grow to 34 million tires by 1995 and to 68 million tires by 1997 thanks to the passage of the Intermodal Surface Transportation Efficiency Act—the highway bill—in December 1991. The act requires that states lay a minimum percentage of rubber-modified asphalt in the roads they resurface using federal funds, beginning at 5 percent in 1994 and rising to 20 percent in 1997.
The market for rubber-modified asphalt—and, thus, ground rubber—also seems promising because the material reportedly offers several advantages over traditional asphalt: Manufacturers claim—and some tests show—that it can be applied at half the thickness, lasts twice as long, and offers increased flexibility, more skid resistance, reduced cracking, improved noise reduction, and better de-icing qualities.
Despite these purported advantages, rubber-modified asphalt can cost 20 to 100 percent more than conventional asphalt, partly due to the costs of tire processing as well as the existence of patents on some rubber-modified asphalt processes. And although these additional costs may be offset by a longer asphalt life, Markets for Scrap Tires, an EPA report, notes that governments often make economic decisions on paving based on "road miles paved per year, rather than life-cycle cost of the pavement."
Rubber-modified asphalt also faces noneconomic obstacles, such as concerns about emissions when ground rubber is added to hot-mix asphalt and about the recyclability of asphalt rubber roads. Moreover, there's a dearth of long-term test results on rubber-modified asphalt, conflicting test results from the states that have used the material, a lack of national specifications for rubber-modified asphalt, a lack of information exchange between states, and limited expertise in applying such pavement. "You can't pave every road with this material," Blumenthal observes, "and not every type of rubber-modified asphalt can be used in all situations."
Still, the use of ground scrap tire rubber in asphalt and other applications appears to be a promising growth market, though the opportunities for scrap tire processors vary greatly. While there is 50- to 100-percent overcapacity in ground-rubber production in certain regions, some parts of the country have no capacity, Blumenthal notes. "It comes down to an individual company basis," he says. "Even if somebody is chomping at the bit to get into the scrap tire business, certain fundamental issues must be addressed, such as proximity to tire supplies and access to consumers."
Officials with Continental Turf Systems, which produces ground scrap-tire rubber for rubber-modified asphalt, say they had to struggle to find asphalt companies that had the necessary equipment and expertise to lay rubber-modified asphalt. Even then, the firm had to prove that it could produce the proper grade of ground rubber, and it had to build up an inventory of the rubber to prove it could meet the consumer's supply demands, says Scott Lane, Continental's president.
Harnessing Energy
The magnitude of the scrap tire problem has forced tire manufacturers and governments to figure out how to recover the most scrap tires in the shortest amount of time, using environmentally and economically sound processes. While most people consider source reduction and recycling preferable, combustion of tires for energy represents the current largest use for scrap tires. In fact, U.S. cement kilns, pulp and paper mills, electric power-generating utilities, and dedicated tire-to-energy plants consume 47 million tires a year—about a third of all tires discarded.
These consumers have found advantages to using scrap tires. Tires have a higher energy value than coal and, in cement kilns, a tire's steel belts and beads can replace the iron ore needed to make cement, thus reducing the manufacturer's raw material costs. Furthermore, tires reportedly have no adverse effects on a plant's air emissions, and can even improve emissions in some instances.
In addition, many combustion facilities can now recover energy from whole tires, further reducing their feedstock costs. While this clearly diminishes market opportunities for scrap tire processors, the trend toward use of whole tires could save recyclers money if they have been paying to discard tires from auto hulks, equipment repairs, and so on.
Among the most prominent consumers of whole tires is Oxford Energy Co. (Dearborn, Mich.), which operates a tires-to-energy plant in Modesto , Calif. Built adjacent to a tire stockpile estimated to contain more than 35 million tires, the plant consumes about 5 million whole tires a year, generating 14 megawatts of power, which is sold to Pacific Gas & Electric. Oxford operates a similar plant in Sterling, Conn., that consumes about 9 million tires a year, and plans to build other tire-to-energy plants in Michigan andNevada .
A handful of cement makers also burn whole tires for fuel in their kilns, but Bridgestone/Firestone Inc. (Nashville, Tenn.) is hoping to increase their numbers by offering the free use of its patent for introducing scrap tires mid-kiln in the calcining zone. Modern kilns with preheaters or precalciners can easily accommodate whole tires, but the 200 or so "conventional" kilns in the United States have heretofore had to use shredded tires—also known as tire-derived fuel (TDF)—due to technical constraints. By using the Bridgestone/Firestone patent, the tire manufacturer reports, conventional kilns—which can each consume 500,000 to 2 million scrap tires a year—can begin using whole tires.
The drawback is that kiln modifications necessary to employ the patent technology could cost $100,000 to $500,000 per kiln. Nevertheless, the savings in coal and iron ore costs would offset this expenditure in about a year, says Blumenthal, who is coordinating licensing of the patent through the Scrap Tire Management Council.
The TDF Potential
Despite the expanding use of whole scrap tires as a fuel source, markets for TDF at electric-power utilities, some cement kilns, and pulp and paper mills seem likely to grow as well. Pulp and paper mills, for instance, which now consume approximately 12 million scrap tires a year, can use up to 15 percent TDF with their traditional fuel—wood chips—with only minor equipment modifications.
The key issue for TDF viability is the price of competing fuel, such as wood chips, petroleum coke, and coal. But the equation also must include the costs and aggravations inherent in obtaining new or revised permits, which may eliminate the projected cost savings of changing fuels. Other constraints stem from the public's misperceptions about and resistance to any type of tire burning, as well as the lack of national TDF specifications.
As a processing market, scrap recyclers could find TDF worth pursuing, but many TDF users are bypassing the recycler by installing their own processing equipment on-site. Wisconsin Power & Light Co. (Madison, Wis.), for instance, has installed a $1.5-million scrap tire processing system in its Rock River generating plant in Beloit, Wis., to test the use of TDF in the operation's boilers. The plant, which expects to consume up to 1.2 million scrap tires a year, deals directly with its suppliers, including new tire dealers, municipalities, and tire collectors/haulers in Wisconsin.
From Here to Profitability
In the end, can the combined effects of reuse, recycling, and combustion solve the scrap tire problem? Blumenthal thinks so. By 1997, "we should really be making inroads into the tire stockpiles," he predicts. Some success stories already exist in states such as Minnesota and Oregon, he notes, which have virtually eliminated their tire stockpiles, and other states are following their lead. Nearly every state has passed laws or regulations governing scrap tires, and many states are offering grants, loans, and rebates to entrepreneurs to recycle or recover scrap tires.
While scrap recyclers have had little economic reason to handle scrap tires, these government programs could help create market niches for them. "If scrap recyclers are in a state that offers some sort of financial or fee support, handling scrap tires may make sense," Blumenthal says. "It's a case-by-case, state-by-state basis." For scrap companies that don't see much growth in traditional scrap markets, scrap tires could represent a new opportunity. "Many recyclers are receiving tires along with their current scrap flow," Blumenthal says, "and they already have the processing and marketing infrastructure set up." As markets are created or expanded, scrap recyclers must decide whether to join the fray or risk being shut out. "The markets are developing, and new markets are coming up all the time," Blumenthal remarks.
In the long run, perhaps the day will come when every scrap tire—stockpiled or newly generated—is recovered in some way, when scrap tires are transformed from no- or low-return items to profitable scrap materials.
Anything's possible. •
Scrap tires are being recovered in many different ways. Will these options solve the stockpile problem and can scrap recyclers be part of the solution?