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Use of Tire Derived Fuel

In 1996, power boiler #4 was converted to a bubbling fluidized bed configuration for more efficient burning of hog, wood waste, and sludge from the effluent treatment plant. Three months later, the supply of good quality hog fuel from the sawmill disappeared due to the sudden collapse of the Japanese lumber market. Instead, the main supply became the lower grade hog produced from dryland log sort debris. The addition of rubber tires to the fuel mix became the answer to the poor hog fuel burning rate. TDF increased boiler bed temperatures by about 55 degrees C, resulting in better combustion efficiencies with some emission decreases, including for dioxin.

After the 1998-1999 TDF burning trials, Catalyst was given a permit to burn TDF at a "rate not to exceed 5% by weight of the wood waste feed, to a maximum of 40 tonnes of TDF per day": The current usage is around 3000 tonnes per year.

Tire Derived Fuel, (TDF), is made by removing the heavy bead or rim from car and truck tires and shredding them to produce chips that are about 2 inches or smaller. Some of the metal alloy radial wire is removed magnetically but tonnes still remain, posing pollution and disposal concerns.

The controversy around TDF stems from the possibility of toxic emissions to air, water, and land. The root of the problem can be found in the hazardous constituents of the tires themselves. They are manufactured from petrochemical feed stocks, such as styrene and butadiene, which are both classified as human carcinogens. When burned, SBR rubber (a styrene-butadiene polymer) releases styrene, several benzene compounds, and butadiene.

Due to the cost of real and synthetic rubber, about twenty-five percent of most tires today are made of aromatic extender oils that are also carcinogenic. Dienes, turpenes, carbon black, Kevlar, rayon are just a few other tire components that are toxic and/or toxic when burned.

Destruction of toxics inherent in TDF requires high combustion temperatures, high residence times, and high oxygen. Even during TDF burn trials, when extra care and precautions are employed, these conditions are not always achieved. Periods of poor combustion and combustion upsets are not uncommon in cement kilns and pulp and paper boilers. The question is, how often do these events occur? Without better monitoring equipment the answer will remain elusive.

TDF was first used in cement kilns that fire around 1500 degrees C producing silicate residues that are typically insoluble. Power boiler #4, in Port Alberni, operates at much lower temperatures averaging about 400degrees C, with a maximum limit of 870 degrees C. Toxic chemicals are much less likely to be destroyed in this lower temperature environment. Due to the boiler heat limitation, hog moisture content must be kept around 55-60 percent to prevent overheating.

Tires also contain around 20 different metals including aluminum, antimony, arsenic, barium, beryllium, cadmium, chromium, cobalt, copper, iron, lead, magnesium, manganese, mercury, nickel, selenium, silicon, tin, titanium and zinc. None of these are destroyed by burning. A number of them are toxic in extremely tiny concentrations. For example, cadmium is toxic in parts per trillion.

TDF generates large zinc and manganese emissions. Zinc oxide is used in the vulcanization process of tire manufacture. The 2010 NPRI figure for zinc, (which, as with all figures, is a two year rolling average) was .91 T release to water and 30 T disposed of in the Catalyst landfill.

Zinc contamination of air and water can lead to many health problems such as stomach cramps, skin irritations, vomiting, nausea and anemia. Very high levels can damage the pancreas, disturb protein metabolism, and cause arteriosclerosis. Exposures to zinc chloride can cause respiratory disorders. Zinc bio-accumulates in fish found in waterways contaminated by zinc leachate or effluent.

Manganese is also used in tire manufacturing to help rubber polymerize. Catalyst Port Alberni NPRI 2010 figures for manganese are 14T release to water and 42 T disposed to the Catalyst landfill.

Although manganese inhalation can lead to respiratory disorders, the primary effect of chronic manganese exposures is on the nervous system. Occupational exposures have led to irreversible damage to the area of the brain controlling balance and fine motor coordination resulting in Parkinson's-like symptoms.

Tires are 1.6% sulphur. Burning them creates suphur dioxide (SO2). The 2010 NPRI figure for SO2 was 192 T release to the air.

Very small quantities of metals like arsenic, lead, mercury and chromium are toxic to humans and can damage aquatic systems and wildlife. For example, in 2002, a Colorado cement kiln using TDF had a 5 pound increase in annual mercury emissions. This is enough to contaminate 2000 twenty-acre lakes to the point where the fish cannot be eaten due to methyl mercury bioaccumulation.