Tires and TDF as Supplemental Fuel in Electric Utility Boilers

This section discusses electric utility plants that use whole tires or TDF supplementally to produce power in boilers. Facilities that combust 100 percent tires to produce power were discussed in Chapter 3, Dedicated Tires-to-Energy Facilities.


As described in Chapter 2, many boiler configurations have been tested and commercially operated burning whole tires or TDF on a supplemental basis. In the utility industry, coal-firing boilers are primarily of the pulverized coal conf iguration.

As of the Summer of 1991, at least nine boilers at seven plants were burning, or planning to burn, whole tires or TDF on either a test or commercial basis. Currently, one pulverized coal boiler at a utility plant is testing use of whole tires. Three cyclone-fired boilers at utilities are currently testing TDF use. One utility currently operates two underfed stoker boilers that use TDF on a commercial basis. One utility tested TDF unsuccessfully in a fluidized bed combustion (FBC) boiler that was a retrofitted spreader stoker design, and two utilities are currently constructing new FBC boilers to accommodate TDF use. Table 6-1 lists these plants and summarizes information about their TDF experience, boiler configuration, and air emissions testing.


Boilers at electric power plants use fuel to generate power for municipalities and industry. The heat generated by the

Table 6-1. Electric Utilities with TDF Experience as a Supplemental Fuel






Illinois Power •stduln Generating Station •aldwln, IL

Manitowoc Pil>llc Utility Manitowoc. Ul

Northern States Power French Island, Ul

Ohio Edison Company Toronto, OH

Test basis; 3/91 most recent test. 1"x1"; 2X during test burn; 100 tpd TDF; add TDF at coal reclaim prior to hanraer ■ills; also eventually want to teat adding TDF after banner ail I and adding various slits TDF.

Current use; <10X; 2"x2" wire-free; alx with coal using • proportioning belt feeder; can't use in cold weather because tire pile freezes

Test in 1982; Unsuccessful; electrified filter bed for PM Inadequate because swtal in tirea shorted out device; also heat level In boiler too high.

2 tests 1990; Whole tires ip to 20X Itu content; tires burned down to residual netal within 18-foot drop to boiler bed

Yes; 3/91 test burn on Unit No. 1; tested PM, S02, beryl 11 us, cadiiui, lead, total chromium, and zinc; 2X TDF during test.

Test In May 1990; tires dropped In at S different rates equating to 0, 5, 10, IS, and 20 percent tires as fuel. All particulate and SO] Halts were net.

2 twin cyclone fired boilers, universal pressure, balanced draft, turbine rated S60 MU; output capacity of 4,199,000 Ib/hr steaa at 2620 pslg and 100S*F; burns Illinois coal; controlled by Ueatern Precipitation ESP, design gas voltne of 1,730,000 ft /aIn with 99X efficiency; 600 ft stack.

Rebuilding two 90,000 Ib/hr utderfed stoker/spreader boilers for TDF when tire pile thaws; have 80,000 Ib/hr coal-fired stoker/spreader, and 1 coal-fired ISO.OOO boiler; coat Is <1X sulfur. Also hsve 1 new 200,000 Ib/hr circulating fluldlzed bed, plan to burn some TDF here too. PBC has llnestone sorbent for SO] reduction.

ISO.OOO Ib/hr steam capacity bufabtii« fluldlzed bed; retrofitted from spreader/stoker design; priaary fuel is wood watte.

Pulverized coal-fed, front-fired, wet bottom, noncontinuous tap. Tires dropped into boiler.

Nave temporary test burn penal t; References 1-5

References 6 and 7

References 8 and 9

Ohio EPA and USEPA have approved permits allowing tire Input 141 to ■ 20X itu level. References 2, 10, 11, 12. and 13

to o






s3 O

Otter Tell Power Co. Big Stone City, SO

Testing since 10/89; current use is 2"x2" Mire free at 10X; no Metering system, TDF is dunped Into the coal handling system as it is received; one supply problem is wet TDF chips freeze to rsil cars and are difficult to

440 MU, 3,250,000 Ib/yr cyclone-fired boiler; 3000*F; lignite Is primary fuel;

Uould burn higher percentage, but •re limited fay TDF supply.

References 2 and 14

Traverse City Light t Power

Traverse City, Ml

•United Developo«nt CroLf) Southern Electric Intl. Niagara Falls, NY

United Pouer Association Elk River, MN

Wisconsin Power ft Light Rock River Gen. Station Belolt, Ul

Under construction; designed for i<p to <20X TDF, wire-free. Ccamer-clal operation will begin on coal only. Test TDF after stable on coal

2 1979 tests: 1 test at OX, SX, and 10X TDF, wirefree, 2", polyester type tires, emissions testing done; 1 test with 2*-6"TDF, wire-in, rstes from 5X to 65X, no air testing done.

Test program since 8/89; heve tested crunb at 10X with no problems; 1"x1" TDF tested Mp to 7X level wire-In


Yes; first test only; tested for PM, SO], NO,, CI, and H2S04.

Yes; 7X TDF; measured PM, SO,, SO,, CO, organice, HCl, HF, trace metals, dioxln, and furan, PCB's, and POHs

468,000 Ib/hr, 52 MU, circulating fluldlzed bed. Bed augmented by limestone for SOj control. Pulse-Jet FF planned, air-to-cloth ratio of 3.88.

3 boilers; TDF tested In 2 stoker-fired with traveling grate, 135,000 Ib/hr, 12 HU; Also have 1 pulverized coal, 235,000 Ib/hr, 25 HU, no TDF testing; all designed for coal, 2 also natural gas.

2 boilers; both cyclone-fired 75 HU, 525,000 Ib/hr; esch has ESP.

Reference 15

Reference 16

All 3 boilers vent to one FF. Plant waiting for economical and adequate supply of TDF before Initiating ccsiaerclal operation. Reference 17

Note 1: Test data are available for NY State Ges and Electric, Beinbrldge Plant, Biwhamton, NY, end for Northern Indiana Power, South Bend, Reference 13.

Note 2: Illinois hss modified their reguletlons so that no permit atodlficatlon la needed for permit holdera wanting to burn tires or TDF >4> to the 20X level. The Stste mat be notified of the fuel change, however. Reference 13.

burning of the tires rises into the radiation chamber. In this chamber, the heat causes water contained in pipes in the refractory brick wall to turn to steam. The high-pressures steam is forced through a turbine, causing it to spin. The turbine is linked to a generator that generates power. After passing through the turbine, the steam is condensed to water in a cooling system, and returned to the boiler to be reheated.

This section summarizes the experience of electric utility facilities that have tested TDF or tires, or that are using them in commercial operation. This section will describe the technical operation and modifications needed to accommodate TDF or tire use. The air emissions data and other environmental information will be described in sections 6.3 and 6.4 of this chapter respectively.

6.2.1 Materials Handling

Materials handling provides the first challenge to burning TDF in a utility boiler. TDF must be correctly sized so as to "fit" in fuel conveyors, and must be well-mixed, to ensure proper combustion.

Two plants have tried conveying TDF to the boiler through coal crushing equipment. At Illinois Power and Light, mixing of the coal and the TDF has to occur at the front of the conveying system, because the remainder of the system is closed.5 Thus, TDF must be able to go through the hammer mills at this time.5 In the future, the company would like to test having the TDF bypass the mill, because although the TDF caused no operational mill problems, the TDF size did not decrease appreciably.1

Wisconsin Power and Light (WP&L) experienced several problems conveying the TDF through the existing coal blending facility.18 First, the crushers did not significantly reduce the size of the TDF. Second, the crusher has magnetic separators to remove large ferrous metal pieces that can damage the coal crushers. These magnets pulled the small crumb rubber from the conveyor. Therefore, to use TDF the magnet had to be turned off, which was unsafe and could cause damage to the crusher. Subsequently, Wisconsin Power and Light added an additional coal yard conveyor to safely blend TDF with coal downstream from the coal crushing equipment.18

Other companies have tried various methods of mixing fuel and TDF either on conveyors, or in storage. Otter Tail Power did not modify its existing lignite handling, feeding and burning equipment to burn TDF. Initially, TDF was fed into an auxiliary conveyor and mixed with lignite after the crusher house. The mixture then entered the boiler building on a single conveyor. In more recent tests, however, the TDF was pushed into a rotary car dumper and conveyed to live storage, where natural mixing with the lignite occurs.21

United Power used a coal/TDF blending system in which TDF was blended with coal at the reclaim hoppers. A variable speed conveyor belt was used to control the mixture during fuel reclaim.17 This system worked well for the low (up to 10 percent) TDF fuel blends, but problems were experienced in the tests using up to 65 percent TDF. Specifically, the material plugged up the fuel conveying system at the reclaim hoppers and at the coal scales.17 Further, the larger pieces of TDF segregated to the outside areas of the fuel storage bunkers, resulting in a non-uniform fuel blend that plugged the inlet to the stokers, and resulted in uneven fuel distribution on the furnace grates.

Wisconsin Power and Light has also experienced the problem of plugging of the coal feeders by oversized TDF; a plugged feeder must be manually dismantled and unplugged, causing several hours of unit derating. The company is working with suppliers to achieve more consistent and accurate TDF feed size.1®

Two of the utility boilers reported here used 1-inch TDF, one at the 2 percent level and one at the 7 percent level. Three have used 2-inch TDF up to the 10 percent level. One has burned whole tires up to 20 percent of their Btu requirement.

Flyash and slag handling systems also require consideration, and sometimes modification. At Wisconsin Power and Light, the slag is sold to a buyer that can not tolerate wire content. Therefore, a magnetic separator is required to remove small pieces of steel wire that become incorporated into the slag during combustion.18

At United Power Association, ash was unaffected by TDF use at the 10 percent level.17 However, when TDF provided as much as 65 percent, by weight, of the fuel mix, a dust control problem with the ash resulted as it was conveyed from the ash storage silo to the ash storage pit. The ash appeared to be significantly finer and more resistant to wetting, and use of wetting agents had to be increased.

6.2.2 Combustion

Generally, TDF contribution to combustion is a positive one. TDF provides an economic fuel with a constant Btu content and low moisture.

One boiler utilizing TDF on a continual test basis, Otter Tail Power, burns lignite as a primary fuel.21 Because lignite has a relatively low Btu content (6200 Btu/lb), TDF offers improved flame stability to their operation.12

However, in initial tests burning 1-inch TDF at the 25 percent level, at Otter Tail, a significant amount of the rubber carried beyond the radiant section of the boiler.21 The facility now does not exceed 10 percent levels of TDF input.

Wisconsin Power and Light also found that if larger TDF were burned, the oversize pieces were swept out the bottom of the boiler with the slag. Some carry over is acceptable, because some combustion does occur in the furnace behind the cyclone. Even if partially burned TDF does exit the boiler, WP&L personnel state that it is quickly extinguished in the slag tank and removed by screening. Nevertheless, WP&L limits TDF size to 1-inch, wire-in. No operational or equipment changes to the boiler were necessary for WP&L to utilize TDF as a supplemental fuel.18

Ohio Edison made modifications to its boiler so that whole tires could be added to the boiler at varying feed rates. The rate of addition of whole tires was chosen to result in TDF percentage in the fuel corresponding to baseline (0 percent),5, 10, 15, and 20 percent.12

United Power Association reported very even boiler operation including longer, hotter flames during their initial tests of up to 10 percent TDF. A higher smoke generation rate was reported when burning TDF, but the fabric filter operated successfully (although more frequent cleaning was required due to increased pressure drop over the system). United Power conducted another test, burning up to 65 percent TDF, by weight, although no emissions tests were run. The boiler had no operational problems combusting the TDF up to 50 percent TDF. In fact, this high TDF fuel blend showed a significant combustion advantage in starting up the boilers, because the rubber ignited at a lower temperature than the subbituminous coal. However, at TDF levels from 50 to 65

percent, the grates did not always maintain an adequate layer of ash to prevent overheating damage, and the fuel tended to seal the grate combustion holes, causing incomplete combustion.17


Air emissions testing data from five facilities were evaluated for this report. The results are summarized here, by pollutant. The most extensive testing was performed by WP&L, who tested criteria pollutants, heavy metals, dioxins and furans, and other organic compounds. Table 6-2 summarizes test data for all criteria pollutants at WP&L.18 Ohio Edison tested particulate, S02, NOx , and lead; emissions results from this whole tire test are provided in Table 6-3.12 Illinois Power tested PM, metals, and S02; their emissions data are summarized in Table 6-4.4 In 1979, United Power Association performed two TDF tests at their Minnesota facility, and conducted air emissions tests during the first test burn for particulate, NOx, S02, sulfuric acid, and chloride.17 These emission results are summarized in Table 6-5.17 Northern States Power tested TDF in their wood-fired utility boiler in 1982, without much success.9 Their emissions data are summarized in Table 6-6.9 Comparisons of the data from these plants are provided in the pollutant specific discussions that follow; the Northern States Power data are not included with graphical summaries of the other four facilities, because its boiler is wood fired, while the other four co-fire the TDF with coal.

6.3.1 Particulate Emissions

Three of the five data sets show that particulate emissions decreased overall with increased TDF loading. A fourth company, Illinois Power, did not provide baseline data by which to compare emissions. Figure 6-1 compares the

Table 6-2. Air Emission Test Data for Wisconsin Power And Light18


100% Coal

7% TDF

Change (%)

Particulate Matter, lb/MBTU




Sulfur Dioxide, lb/MBtu




Nitrogen Oxides,lb/MBtu




Carbon Monoxide, lb/hr




Hydrocarbons (as CH4) , lb/hr




HCl, lb/hr




HF, lb/hr




Table 6-3. Emission Results at Ohio Edison12


Table 6-3. Emission Results at Ohio Edison12


Tira Feed Rata





Run 2 Run 3


0.0764 0.0370 0.0760

4.71 5.15 6.03

0.761 0.598 0.445

0.0000938 0.0000931 0.000102






Day 2 5X Tires

Rw 1 Run 2 Rw 3

1 tire par 34 seconds

0.0472 0.0959 0.0719

5.44 5.83 5.93

0.391 0.547 0.593

0.0000973 0.0000997 0.000101






Day 3 10X Tires

tin 1 Run 2 Run 3

1 tire per 17 seconds

0.0414 0.0892 0.0385

5.62 5.76 5.74

0.324 0.478 0.504

0.0000977 0.0000966 0.0000947






Day 4 1SX Tires

Rui 1 It in 2 Rui 3

1 tire per 11.3 seconds

0.0781 0.0776 0.0889

4.85 5.80 5.75

0.342 0.455 0.531

0.0000931 0.0000986 0.0000982






Run 2 Run 3

1 tire per 8.5 seconds

0.0377 0.0380 0.0603

5.03 5.38 5.60

0.313 0.407 0.440

0.0000881 0.0000934 0.0000921






* On day 4 (1SX TDF), tira feed supply probleas resulted in several interruptions of tire simply to the boiler.

* On day 4 (1SX TDF), tira feed supply probleas resulted in several interruptions of tire simply to the boiler.

Table 6-4. Summary of Emission Rates Burning 2% TDF at Illinois Power, Baldwin Generation Station4 March 21, 1991

Pollutant lb/hr


PM (ESP inlet) PM (ESP outlet) S02

Beryllium Cadmium

Total Chromium Lead

Zinc (filter catch only) _

17,926.93 922.7

0.00966 0.02387 0.56249 0.08095






Table 6-5. Summary of Emission Rates from Testing at United Power Association, Elk River, MN17

May, 1979

Pollutant lb/ lb/ lb/ _lb/hr_W«tu_lb/hr_>»>8tu_lb/hr_HHBtu

Particulate 5.49 0.021 3.55 0.015 2.61 0.009


(as CIO inlet to fabric filter 8.1 0.029 7.2 0.029 7.7 0.027

Table 6-6. Summary of Emissions from a Wood-fired Utility Boiler Cofiring TDF Northern States Power Co.9 French Island, WI

November, 1982

100% Uood-Uaata_7% Hubbar Buffing»_71 TDF_


_ppa (dry) Ib/HMBtu ppa (dry) tb/WH8tu ppa (dry) tb/HHBtu


_ppa (dry) Ib/HMBtu ppa (dry) tb/WH8tu ppa (dry) tb/HHBtu



































Polyaroaatic hydrocarbon«



* Excaada Uiaconaln liait of 0.15 lb/M«tu

* Excaada Uiaconaln liait of 0.15 lb/M«tu

tfl C

fi 3

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