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Background | Cement Industry | Pulp and Paper Industry | Electric Utilities | Industrial/Institutional Boilers | Dedicated Tire-To-Energy Facilities
Scrap tires are used as fuel because of their high heating value. Using scrap tires is not recycling, but is considered a beneficial use — it is better to recover the energy from a tire rather than landfill it. In , 130 million scrap tires were used as fuel (about 45% of all generated) — up from 25.9 million (10.7% of all generated) in .
Tires can be used as fuel either in shredded form - known as tire-derived fuel (TDF) — or whole, depending on the type of combustion device. Scrap tires are typically used as a supplement to traditional fuels such as coal or wood. Generally, tires need to be reduced in size to fit in most combustion units. Besides size reduction, use of TDF may require additional physical processing, such as de-wiring.
There are several advantages to using tires as fuel:
EPA supports the highest and best practical use of scrap tires in accordance with the waste management hierarchy, in order of preference: reduce, reuse, recycle, waste-to-energy, and disposal in an appropriate facility. Disposal of scrap tires in tire piles is not an acceptable management practice because of the risks posed by tire fires, and because tire piles can provide habitats for disease vectors, such as mosquitoes.
In , more than 290 million scrap tires were generated in the US. Nearly 100 million of these tires were recycled into new products and 130 million were reused as tire-derived fuel (TDF) in various industrial facilities. TDF is one of several viable alternatives to prevent newly generated scrap tires from inappropriate disposal in tire piles, and for reducing or eliminating existing tire stockpiles.
Based on over 15 years of experience with more than 80 individual facilities, EPA recognizes that the use of tire-derived fuels is a viable alternative to the use of fossil fuels. EPA testing shows that TDF has a higher BTU value than coal. The Agency supports the responsible use of tires in portland cement kilns and other industrial facilities, so long as the candidate facilities: (1) have a tire storage and handling plan; (2) have secured a permit for all applicable state and federal environmental programs; and (3) are in compliance with all the requirements of that permit.
This information is also contained in a printable fact sheet on TDF (PDF) (1 pg, 12K, about PDF)
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Of the 130 million scrap tires used as fuel per year:
–Rubber Manufacturers Association,
About 53 million tires per year are consumed as fuel in US cement kilns. The cement industry burns scrap tires as fuel in kilns used to make clinker—a primary component of portland cement. A cement kiln is basically a large furnace in which limestone, clay, and shale are heated at extreme temperatures and a chemical reaction transforms them into clinker. Clinker is ground together with gypsum to form Portland cement.
The use of whole tires as kiln fuel is possible for some type of cement kilns. For these cement kilns, truck loads of whole tires, usually in enclosed vans, are delivered to the end of a conveyor. Tires are manually unloaded from the truck onto the conveyor. The conveyor feeds the tires to a mechanism that inserts one tire at a time into the kiln at specified time intervals. The advantage of utilizing whole tires is that there are no costs to create tire chips. The removal of the steel is unnecessary since cement kilns have a need for iron in their processes. Tire chips may also be utilized because there is very little manual labor involved in handling chips versus whole tires, however, producing chips from whole tires increase costs.
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About 26 million tires per year are consumed as fuel in boilers at US pulp and paper mills. Pulp and paper mills have large boilers which are used to supply energy for making paper. This energy is normally supplied by wood waste, however, wood varies substantially in heat values and moisture content, so the mills often supplement the wood fuel with other fuels,such as coal or oil, to make the operation more stable. TDF is also used in many plants as a supplement to the wood because of its high heat value and low moisture content.
The main problem in using TDF in the paper industry is the need to use de-wired tires. The wires often clog the feed systems. Also, the mills sometimes sell the resulting ash to farmers who require the ash to be free of iron. De-wired TDF can cost up to 50% more than regular TDF.
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About 24 million tires per year are consumed as fuel in boilers at electric utilities. In the electric utility industry, boilers typically burn coal to generate electricity. TDF is often used as a supplement fuel in electric utility boilers because of its higher heating value, lower NOx emissions, and competitive cost as compared to coal. However, only certain types of boilers are conducive to burning TDF.
Cyclone boilers are the most used of all the utility boilers for burning TDF. They are good because they require no changes to be made to the boiler itself which reduces the capital investment. Therefore, the only additional equipment needed is a conveyer to transport the tire pieces into the boiler. Cyclone boilers cannot accept whole tires which increases the cost of obtaining the fuel (the optimum size of the tire pieces is 1 inch x 1 inch and it must be de-wired). Stoker fired units are also economical. In the stoker boilers, the residence time of the fuel is longer so larger tire pieces can be used. The optimum size of these pieces is 2 inches square. This reduces the cost of obtaining the fuel for Cyclone boilers and makes it more economical.
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Approximately 17 million tires per year are consumed in industrial boilers.
According to a Rubber Manufacturers Association survey in , 19 industrial facilities were using TDF in their boilers to supplement their fuel usage. Industrial boilers are smaller than utility boilers and typically use a variety of fuels. When utilizing TDF, tires are typically shredded. Not all boilers are compatible with TDF. Clumping and clogging are common and preclude the use of TDF in many facilities.
Another impediment is the metal in the tires — if not removed before combustion, it ends up in the ash and can create disposal problems. Each facility must evaluate the impact of TDF on their air emissions and ash disposal. Industrial facilities must apply for the appropriate permits from their state and/or local regulatory authorities before commencing operation.
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Approximately 10 million tires per year are consumed as fuel at dedicated tire-to-energy facilities. A dedicated tire-to-energy facility is specifically designed to burn TDF as its only fuel to create energy.
According to a Rubber Manufacturers Association survey at the end of , there was only one dedicated tire-to-energy facility operating in the US. The dedicated tire-to-energy facility, Exeter Energy Limited in Sterling, Connecticut burns mainly whole tires and consumes 10 million tires per year. This facility serves as a major scrap tire market for scrap tires in New York and northern New Jersey. The second dedicated tire-to-energy facility in the US is located in Ford Heights, Illinois and was not in operation at the end of .
Even though dedicated tire-to-energy facilities have been demonstrated to achieve emission rates much lower than most solid fuel combustors, there are no known facilities under construction or consideration. The length of time and cost of construction, as well as the deregulation of the utility industry hinders further expansion of this industry.
For more information, please visit tyre recycling machinery.
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A major use for scrap tires is fuel. Tire-derived-fuel (tdf) is a fuel derived from scrap tires of all kinds. This may include whole tire or tires processed into uniform, flowable pieces that satisfy the specifications of the end-user. Scrap tires are used as fuel either shredded or whole depending on the type of combustion unit.
TDF is the oldest and most developed market for scrap tires in the U.S. Industrial facilities across the country, including cement kilns, pulp and paper mills and electric utilities use tdf as a supplemental fuel to increase boiler efficiency, decrease air emissions and lower costs. More than 52 percent of the 300 million scrap tires generated annually are consumed as tdf in these facilities providing a cleaner and more economical alternative to traditional fuels.
The U.S. Environmental Protection Agency (EPA) described TDF as a high Btu-value fuel with lower emissions, including lower greenhouse gas emissions, than comparable traditional fuels, in a Advanced Notice of Proposed Rulemaking. In earlier studies, EPA concluded, &#;With proper emission controls, burning tires for their fuel energy can be an environmentally sound method of disposing a difficult waste.&#;
Scrap tires make an excellent fuel because of their high heat value. Each tire has energy potential. The heating value of an average size passenger tire is between 13,000 and 15,000 Btu/lb., which compares with about 10,000 to 12,000Btu/lb. for coal. The primary reason for using tire fuels is to save fuel costs. Further, they are compact, have a consistent composition and low moisture content-all benefits to the fuel user. Another major reason for combusting tires as fuel is to decrease the number of scrap tires disposed in landfills or stockpiles.
Nationally scrap tires represent a potential energy source of 1.01 quadrillion Btu per year based on a discard rate of 300 million tires per year each weighing an average 22.5 lbs with 15,000 Btu per pound. This is equivalent to 17 million barrels of crude oil and represents about 0.24 percent of the U.S. energy needs. Given this energy value, it is clear that scrap tires compete with comparable traditional fuels including coal, petroleum coke and wood wastes.
While some combustion systems, typically cement kilns, can accept tires whole, most combustion systems require the tires to be processed to certain sizes and purity to ensure the material consistently meets the needs of the particular fuel user. Shredding scrap tires to produce tdf uses standard material processing technology which includes shredding and removing dirt or other contaminants.
Processing tires into tdf involves two physical processing steps: chipping/shredding and metal removal. In the first step, tires are either fed into the shredder whole or have the beads removed prior to shredding. The processing equipment is typically high-shear, low-torque shredders. Scrap passenger and truck tires up to 48 inches in outside diameter can be initially reduced in these rotary shear shredders to pieces ranging in size from 1&#; to 4&#;, depending on the end-use.
To produce tdf-size shreds and chips, whole tires are reduced to nominal 2 inch pieces using one shredder or a series of shredders, screening equipment and magnetic separation equipment. Magnetic separators are required to remove the steel. A screen in the discharge of the shredder controls the shred/chip size where the two-inch sized material falls through the screen openings while the oversized material is re-circulated back to the shredder. Because a significant amount of rubber is entrained and lost in the wire removal stream, downstream shredding and wire removal can be employed to recover additional rubber, make a cleaner steel product for sale as scrap and to avoid landfilling this wire/rubber material. If smaller-sized tdf (1-inch or crumb rubber) is specified, then more size reduction, metal and fiber separation, classifying, screening and cleaning equipment may be required.
TDF has the flexibility to be used in variety of industries. These include:
Cement manufacturing companies use whole tires and tdf to supplement their primary fuel for firing cement kilns. Several characteristics make scrap tires-either whole or shredded&#; an excellent fuel for the cement kiln. The very high temperatures and long fuel residence time in the kiln allow complete combustion of the tires. There is no smoke, odor or visible emissions from the tires. .Because the ash is incorporated into the final product, there is no waste. The metal wire contained in the tdf is captured as a raw material or ingredient in the cement making process. Each passenger car tire contains about 2.5 pounds of high-grade steel. The steel portion of the tire becomes a component of the cement product, replacing some or all of the iron required by the cement manufacturing process.
The Portland Cement Association (PCA) reports that studies have shown that the use of tires as fuel can reduce certain emissions. According to a PCA study of emission tests from 31 cement plants firing tdf, there were no statistically significant differences in the emission data sets for sulfur dioxide, nitrogen oxides, total hydrocarbons, carbon monoxide, and metals between kilns combusting tdf and non-tdf firing kilns.
Separate studies conducted by governmental agencies and engineering consulting firms have also indicated that tdf combustion either reduces or does not significantly affect emissions of various contaminants from cement kilns. In a study, the United States Department of Energy estimated that the combustion of tdf produces less carbon dioxide (CO2) per unit of energy than coal. This means that when tdf replaces coal in a Portland cement kiln, less CO2 will be produced.
Long term experience shows that tires are being used successfully in cement kilns and good quality cement products are being made while using scrap tire fuels. Higher production rates, lower fuel costs and improved environmental quality achieved when tire fuels are combusted in cement kilns continue to define scrap tires as a viable fuel choice for cement kilns.
Pulp and paper companies use tire-derived-fuel as a supplement to wood waste-the primary fuel used in pulp mill boilers. The technology is proven and has been in continuous use in the U.S. since the early s. The heating value of the wood waste fuel ranges from about 7,900 to 9,000 Btu/lb. on a dry basis. Tdf&#;s higher heat value of 15,000 Btu/lb. facilitates uniform boiler combustion, and helps overcome some of the operating problems caused by fuels with low heat content, variable heat content and high moisture content. The consistent Btu value and low moisture content of tdf and its low cost in comparison to other supplemental fuels make tdf an especially attractive fuel in the pulp and paper industry. In addition, pulp and paper mills have the ability to burn tdf without major equipment modifications offering yet another advantage to the use of tdf.
Pulp and paper mills continue to increase their use of tdf to help decrease fuel costs and improve both emissions and combustion efficiency. In addition, the use of tdf in pulp and paper mill boilers helps the mills improve their public image in their local regions by demonstrating environmental responsibility. High energy costs, improved reliability in the tdf processing industry and the consistent product quality of tdf are primary reasons for ongoing growth in both the number of mills consuming tdf and in the amount of tdf consumed per mill.
Electric power utilities use tire-derived-fuel as a supplemental fuel to produce power in boiler operations. Boilers at electric power plants use fuel to generate power for municipalities and industries .In the electric power industry, tdf is used mainly as an additive to other fuels, primarily coal. For electric power utilities, tdf must be correctly sized to fit in fuel conveyors and must be well mixed to ensure proper combustion. Typically, the tdf must be sized at 1 inch x 1 inch and be almost completely dewired for use in the cyclone boilers commonly used in electric power plants. Some electric utilities use stoker-fired units which, because of the longer residence time, can accommodate 2 inch x 2-inch tdf. Smaller, wire-free tdf -50 mesh to 200 mesh can be used in electric power plants that burn pulverized coal.
In electric power utility applications tdf provides an economic fuel with constant Btu content and low moisture. Electric utilities also found that the quality of emissions actually improves with the increased use of tdf as a supplemental fuel. Because of its higher heating value, lower emissions, competitive cost, and ability to create stable operating conditions in the boiler, tdf remains an attractive fuel for the electric power generating industry.
For most industrial and institutional boiler systems, tdf sized 2 inch x 2 inch or less and 95 percent wire-free is an accepted fuel. In industrial boiler applications, combustion of tire derived fuel generates energy in the form of steam and/or electricity, displacing the need to generate energy from other power generating facilities and from other fuels, usually coal. This displacement not only offsets the use of certain fuels, it also offsets the pollution emitted from other fuels. Tdf combustion in industrial boilers can emit less sulfur dioxide and nitrogen oxide than most types of coal on a net energy output basis. Tdf use in industrial boilers remains steady but faces challenges for increased use due to plant closings and depressed markets and overall economic conditions.
One facility specifically designed to burn whole tires or tire-derived-fuel as its only fuel is fully operational in the U.S. This tires-to-energy plant, a 25-megawatt electric-generating facility, has combusted tires to produce electricity for nearly twenty years and currently consumes nearly 10 million tires annually. Historically, the tires-to-energy plant has achieved emission rates below those at electric generating plants with solid fuel combustors powered by traditional fuels.
The U.S. EPA created a Fact Sheet on tdf through the collaborative efforts of EPA&#;s Resource Conservation Challenge subcommittee on TDF. In , the agency posted the TDF statement on the EPA website. The EPA statement is as follows:
EPA supports the highest and best practical use of scrap tires in accordance with the waste management hierarchy; in order of preference: reduce, reuse, recycle, waste-to-energy, and disposal in an appropriate facility. Disposal of scrap tires in tire piles is not an acceptable management practice because of the risks posed by tire fires, and because of the use of tire piles as a habitat by disease vectors such as mosquitoes. The use of scrap tires as tire derived fuel (TDF) is one of several viable alternatives to prevent newly generated scrap tires from inappropriate disposal in tire piles, and for reducing or eliminating existing tire stockpiles.
EPA testing has shown that TDF has a higher BTU value than coal. Based on over 15 years of experience with more than 80 individual facilities, EPA recognizes that the use of tire derived fuels is a viable alternative to the use of fossil fuels, and supports the responsible use of TDF in Portland cement kilns and other industrial facilities provided the candidate facilities have developed a TDF storage and handling plan, and have secured a permit for all applicable State and Federal environmental programs and are in compliance with all requirements of this permit.
The American Society for Testing and Materials (ASTM) approved ASTM -01, an International Standard for TDF, in . ASTM Standard D--01 &#;Standard Practice for Use of Scrap Tire-Derived Fuel&#; offers end-users and potential end-users an industry-accepted standard against which they can compare all tire chips.
The standard:
The American Society for Testing and Materials (ASTM) is a not-for-profit organization that provides a forum for the development and publication of voluntary consensus standards for materials, products, systems and services. The ASTM process is open to producers, users and consumers.
According to ASTM, a standard is a document that has been developed and established within the consensus of the Society and meets approval requirements of ASTM procedures and regulations. Generally, standards are incorporated into specs or plans.
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