Waste Tires Scrab Manufacturer Mail

Air pollution control agency personnel have an increasing need for technical information describing the air pollution implications of several methods of waste or scrap tire disposal. Environmental concern for tire disposal has historically focused on the solid and hazardous waste issues involved. Further, much information has already been written describing the comparative merits of disposal alternatives such as recycling, pyrolysis, and burning for fuel, in minimizing scrap tires and maximizing recycle markets. Air quality issues resulting from waste tire disposal issues, however, have not been as well documented.

The U.S. Environmental Protection Agency's Control Technology Center recognizes the need for data describing the air quality impacts of two of these disposal options — the controlled burning of tires to recover its fuel value and pyrolysis for fuel and carbon black. The purpose of this report is to summarize available air emissions and control data and information on tire pyrolysis and burning tires for fuel.

This report describes air pollution issues by source category. Chapter 2 contains an overview describing the types of process units primarily burning tires. Chapter 3 describes dedicated tire-to-energy facilities. Portland Cement plants with experience burning tires are covered in Chapter 4. Chapter 5 summarizes the experience of pulp and paper plants in burning chipped tires as a supplemental fuel. Electric utilities burning tires as a supplemental fuel are described in Chapter 6. Chapter 7 includes any other industrial facilities with experience burning rubber. Last, Chapter 8 contains information on tire pyrolysis.

1.1 WASTE TIRE GENERATION AND DISPOSAL

Waste tires are generated in the United States at an estimated rate of approximately 240 million tires (approximately 2.4 million tons) per year.1,2 These estimates do not include tires that are retreaded or reused second-hand; retreading and reuse are considered to extend the life of a tire before it is scrapped.

Of the 240 million, between 170 and 204 million waste tires generated annually are estimated to be landfilled or stockpiled.1,2 Tires pose a unique landfill problem, not only because of their large numbers, but also because the materials used to ensure their durability and safety also make their disposal difficult. For example, whole tires do not compact well, and actually "rise" through a landfill mass to the surface as the dirt surrounding them compacts.1 Further, when stored in the open (either in a landfill or in a tire stockpile), tire piles provide breeding grounds for insects such as mosquitoes and rodents. One mosquito, the Asian Tiger Mosquito, is slowly migrating across the country, and is of particular concern, because it can carry dangerous diseases such as encephalitis. Tires retain heat and provide many pockets of still, shallow water that are ideal for mosquito breeding. Open tire piles also can ignite easily, creating toxic smoke and fumes, and are difficult to extinguish. The resulting sludge creates a serious ground water pollution problem.

Approximately 8 to 11 percent of the scrap tires generated annually (approximately 192,000 to 264,000 tons/year) are estimated to be burned for fuel.1,2 Section 1.2 below discusses the advantage and disadvantages of tires as fuel.

Disposal options other than landfilling, stockpiling, or burning account for approximately 5 to 16 percent of the tires generated.1,2 These options include manufacture of fabricated products such as car moldings; reclaiming of the rubber; manufacture of asphalt rubber for road binding material, sealcoat, or asphalt paving aggregate; formation of underwater reefs or highway barriers; and tire export.1,2 Table 1-1 provides additional detail on the estimated number of tires for various recycle and energy recovery options. Altogether, the existing stockpile inventory on a national scale is estimated to be approximately 2 billion tires (20 million tons).1'2

1.2 WASTE TIRES AS FUEL

Tires can be burned whole, or can be shredded or chipped before burning. Tires that are shredded into pieces are called Tire-Derived-Fuel, or TDF. TDF that is very small (i.e., less than 1/4" diameter) is sometimes called crumb rubber. Crumb rubber can be burned or can be fabricated into other rubber products. TDF that results from tire recapping operations is called rubber buffings, and is made up of small one-half inch slivers. Material handling capabilities of facilities burning whole tires must be able to accommodate a fuel that is large, heat intensive, and contains a significant amount of metal. Burning TDF also requires material handling creativity, but TDF is more readily adaptable to the material handling and combustion capabilities of many fuel-burning sources. TDF can be shredded to sizes as small as 1-inch square.

Radial wire is the mat of steel placed under the tread to enhance tread strength and durability. Bead wire consists of many strands of high tensile strength steel that provide strength and reinforcement to the tire side walls. Radial and bead wires can account for as much as 10 percent of the total weight of a tire.3 The remainder of the weight of the tire is about 60 percent rubber, and 30 percent fiber.

Table 1-1. Scrap Tire Generation (millions of tires per year)

Markets for Scrap Tire Study1

Scrap Tire Management Council, 19902

Total Scrap Tires

Generated

242

240

Landfill/

Stockpile

187.8

170.4 - 204.0

Energy Recovery

25.9

19.2 - 26.4

Fabricated

Products

11.1

2.4 - 12.0

Reclaim Rubber

2.9

4.8 - 12.0

Asphalt Rubber

2.0

1.2

Reefs/Barriers

0.3«

0.2 - 4.8

Tire Exports

12

4.8 - 9.6

Retreadb

33.5

12

Reuseb

10

0

* Includes use for playground equipment and erosion control.

b Retreaded tires and reused tires are not considered "scrap" tires. Thus, although the number of tires retreaded or reused are reported here for completeness, they are not included in the estimates of total scrap tires generated.

1.2.1 Waste Tire Characteristics and Composition

Tires are a good fuel for several reasons. Tires contain about 15,000 Btu's per pound (about 300,000 Btu's per tire). Coal heating values range from 6,000 to 13,500 Btu's per pound. Further, they are compact, have a consistent composition, and contain a low moisture content. Also, many components of tires, such as sulfur and nitrogen, compare favorably to coal in percent makeup. Table 1-2 compares composition of tires to that of midwest coal.4 Table 1-3 compares composition of various types of tires.5 Most trace metal levels in tires are equivalent to the levels in coal; zinc and cobalt are higher in tires.6 Figure 1-1 shows trace metal level of whole tires compared to bituminous coal.6

On the other hand, the size of whole tires requires the ability to feed large fuel to a burner, and their strength makes them difficult to cut into more manageably sized pieces of fuel. Also, chlorine, ash, and volatiles are present in higher quantities in tires and TDF than in most coals. Further, the metal contained in tires, in the form of the radial wire and bead, wire can be a problem in many fuel applications. For example, loose or molten wire can clog ash exit or grate combustion openings in boilers.

1.2.2 Waste Tire and TDF Cost Considerations

Sources desiring to bum tires may obtain them in several ways. Whole tires can be obtained from two basic sources. First, tires can come from the "flow"; that is, from retail businesses collecting old tires on a daily basis. This includes tire manufacturers, tire retail stores, and tire collectors, sometimes called tire jockeys. Tire jockeys cull the tires they collect for those that can be reused or retreaded, and then sell the remainder. Second, tires can

Table 1-2. Comparative Fuel Analysis, by Weight4

Fuel

Coaponent

Heating

Valu*

Table 1-2. Comparative Fuel Analysis, by Weight4

Fuel

Coaponent

Heating

Valu*

Carbon

Hydrogan

Oxygen

Nitrogen

Sulfur

Ash

Heistur«

Btu/lb

TDF

83.87

7.09

2.17

0.24

1.23

4.78

0.62

15,500

Clarifier Sludge

4.86

0.49

2.17

0.47

0.26

3.16

88.69

924

Coal

73.92

4.85

6.41

1.76

1.59

6.23

5.24

13,346

Uood Uaata

TMt 1

30.98

3.16

23.33

0.13

0.04

1.31

41.05

5,225

Teat 2

28.29

2.37

20.95

0.13

0.03

1.49

46.73

4,676

Teat 3

25.67

2.54

19.17

0.12

0.03

1.11

51.36

4,031

Test 4

24.71

2.44

18.46

0.12

0.02

1.13

53.12

4,233

Table 1-3. Comparative Composition and Fuel Value of Various Tire Types5

Coaponanta, UtX

Table 1-3. Comparative Composition and Fuel Value of Various Tire Types5

Coaponanta, UtX

Value (Btu/lb)

C

h

<h

«î

S

Ash

Fl

Fl berg l aas bait

13,974

75.8

6.62

4.39

0.2

1.29

11.7

<0.02

Steal belted

11,478

64.2

5.00

4.40

0.1

0.91

25.2

<0.02

Nylon

14,908

78.9

6.97

5.42

<0.1

1.51

7.2

<0.02

Polyester

14,752

83.5

7.08

1.72

<0.1

1.20

6.5

<0.02

Kevlar Baited

16,870

86.5

7.35

2.11

<0.1

1.49

2.5

<0.02

B

10000

a

1000

3

!

100

Im

a

t!

10

&

s

1

« mm

S s

ni

0 B O

0.01

O

0.001-

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