WASHINGTON-Cement makers are the largest users of tire-derived fuel and their demand is growing, according to the Scrap Tire Management Council. More than half of the 253 million scrap tires generated in the U.S. last year were processed into a usable fuel source. TDF is an excellent supplement to coal and other fossil fuels in cement kilns, which number about 150 in the U.S., said STMC Executive Director Michael H. Blumenthal.
``Not all of them will use tires as a supplemental fuel,'' Mr. Blumenthal said. But the goal is to get at least half of them using TDF, he said.
The use of tires as fuel in cement kilns goes back to 1973 in Europe. The fuel appeared in kilns in the U.S. in the mid-1980s.
Currently, close to 40 U.S. cement kilns use TDF. Mr. Blumenthal said increasing that number to 75 could result in a demand of between 150 million and 180 million tires by the cement industry-higher than the 130 million used overall as TDF by cement makers, paper and pulp mills and power plants in 1995.
TDF is a ``critical market to the success of a comprehensive scrap tire program,'' Mr. Blumenthal said.
``TDF is really making a dent in the piles,'' said Bill Barbin, director of compound technology projects at Goodyear.
``We need to focus on TDF, because the number of units we're utilizing says this is the best alternative use for scrap tires,'' Mr. Barbin said.
Recycling needs to be an economically viable process, and the most economically viable way to use tires is to burn them, he said. Economic viability is a big issue, especially with an estimated 800 million scrap tires in stockpiles in the U.S., he added.
Once you throw a tire into a stockpile, you limit it to two uses-TDF and civil engineering applications, Mr. Blumenthal said.
On average, cement kilns that use TDF replace about 18 percent of their fuel with tires, Mr. Blumenthal said. Since tires generate about 14,000 to 15,000 British thermal units per pound-compared with coal's 11,000 Btu per pound-``it's a tremendous cost savings to a company,'' he said.
Cement makers usually get a tip fee for using whole tires, ranging from 15 to 25 cents per tire. About 60 percent of the kilns burning TDF use whole tires, according to the STMC leader.
There is no technical downside to using tires, according to TDF advocates.
A tire contains about 2.5 pounds of steel, which replaces the iron that is put into cement.
Tires also are low in moisture, containing less than 1 percent. Moisture in the cement-making process forces firms to use more energy, Mr. Blumenthal said.
Emissions are not a problem, he added. At worst, there is no difference between TDF and coal. At best, the use of tires results in a net reduction of emissions, he said.
Plus, any ash or residue from the tires becomes part of the cement mix, leaving no waste.
Despite their advantages, it's unlikely tires ever will supplant coal in cement kilns. Mr. Blumenthal cited several reasons for that.
``Zinc more than anything else is the limiting factor,'' he said.
A cement company usually can't use more than 25 percent TDF because of its zinc content. The higher the zinc content, the longer it takes for cement to set. ``That is not what they need. They can't accept that,'' he said.
Also, if a cement company wanted to go exclusively to TDF, it couldn't get enough tires, Mr. Blumenthal said.
Finding TDF producers already is a big problem for many cement kilns, because there's about a 150-mile transporting limit, according to Goodyear's Mr. Barbin. Transporting TDF beyond 150 miles makes it economically unfeasible to use, he said.
Mr. Blumenthal added that some kilns are being paid much more to burn hazardous wastes-such as solvents, thinners and household chemicals-as a supplemental fuel. ``There's no need for them to change,'' he said.
Other cement companies shy away from TDF because they don't want to deal with it, or they haven't prioritized setting up the right technology.
There had been a lull in interest for a year or two because cement firms were running at more than 100-percent capacity and couldn't afford to shut down. ``That is over now, and we're seeing a lot more companies come on line with tires,'' Mr. Blumenthal said.
The STMC executive believes close to 50 kilns will be burning TDF by the end of 1997.