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Terry Gray 

Call with Industrial Economics 

August 24, 2009 

Terry Gray’s Comments on IEc/EPA Draft Materials Characterization Paper on 

Scrap Tires 

• In terms of the sectors that generate scrap tires, we appear not to cover scrapped 

vehicles. Recommends that we check the RMA report for info on tire yards or scrap 

yards. This isn’t a key generating sector though, so it’s not a huge omission. 

• He liked how we standardized the 2005 and 2007 data from the RMA reports to 

compare the 2005 and 2007 data. 

• Where we state that the heat content of whole tires is 14,000 Btu/lb and that the 

corresponding value for TDF is up to 15,500 Btu/lb, it would be useful to mention 

that the difference is due to the removal of wire. 

• On page 4, where we state that the metal in tires provides a benefit to cement kilns, 

we should clarify that it’s the reinforcing steel in the tires. 

• On page 4, we state that the use of whole tires in units other than cement kilns is 

limited because whole tires do not fit in many other units. It would be more correct to 

say that the use of whole tires is limited by whether they are compatible with the 

combustion and handling characteristics of individual combustion units. 

• On page 5 we state that the use of TDF in combustion units is typically limited to 

blends of 10 to 30 percent of total energy input due to the high rates of heat release 

and the low moisture content of TDF. It would be more appropriate to say less than 

30 percent. 

• The total of the numbers in Exhibit 5 doesn’t match the main text. 

• Are 100 percent of truck tires diverted to ground rubber as we state in our paper. 

Terry thinks it would be more appropriate to say that a higher percentage is diverted 

to ground rubber, where processors are available. 

• On page 6, we state that the reluctance of State transportation agencies has hindered 

the development of Rubber Modified Asphalt markets. This reluctance reflects 

concerns about cost and performance. 

• Economics drives the landfilling and monofilling of scrap tires, as these are often the 

least costly management options. 

• Some, not most, tire processors send TDF to end users indirectly through brokers. 

• Regarding footnote 1 in Exhibit 8, he doesn’t agree that whole tires have better 

combustion characteristics than chipped tires, but he agrees that there are energy 

savings from avoided shredding. 

• Regarding the processing discussion on pages 8 and 9, Terry recommends that we 

clarify that as you go to smaller particle sizes, you can more easily remove the wire 

from the tire. Also, metal removal per se doesn’t increase processing costs. It’s 

making the smaller particle size requires to remove metal that increases processing 

costs. The price of TDF increases with smaller particle size with metal removal. 

• He recommends that we remove the brief discussion of cryogenics from the paper 

because it’s currently not feasible for commercial applications. 
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• Regarding pyrolysis, he recommends adding that the solid char product is among the 

low value outputs that we allude to. 

• With respect to the processing of tires from stockpiles, when tires from large 

stockpiles are processed, it’s usually onsite at the stockpile itself. Stockpile tires can 

also be used for some civil engineering applications. 

• Be sure to indicate that TDF has been approved for use in facilities in 34 states, per 

RMA’s report. 

• Only a few states pay kilns to accept tires. Kilns are paid up to $0.25 per tire. 

• Regarding NOx emissions, he thinks that the available data are inconclusive. He 

believes that using tires leads to a reduction in NOx emissions in most, but not all 

cases.