Burning of Tire-Derived Fuel
Tire-derived fuel (TDF) is produced by chipping rubber tires and removing large metal strips with a magnet. These rubber chips contain many small metal wires. Pacifica Papers wants to burn 40 tonnes a day of these rubber chips along with 800,000 tonnes of hog fuel in their power boiler (5% TDF by volume).
Pacifica Paper's power boiler uses a modern fluidized sand bed combustion process with an electrostatic precipitator to remove particles. The BC Ministry of Environment considers this boiler "state of the art" with suitable pollution control devices that will safely burn TDF. Ministry officials speak of the practical benefits of burning TDF: "Tires provide a steady constant fuel source that keeps the sand bed hotter and requires less natural gas thus keeping costs down and making the mill more profitable." They say that tire are made essentially of solidified natural gas but that is not the full story. Tires contain substances that are not in natural gas such as styrene, 1,3-Butadiene, aromatic extender oils and carbon black.
Dr. Neil Carman, Ph.D. in Chemistry, is a Texas Air Control Board Investigator of toxic air emissions from synthetic rubber plants. He writes: "Tires are manufactured from petrochemical feedstocks such as styrene and butadiene which are both being classified as human carcinogens. Styrene is a benzene derivative and burning tires releases styrene and several benzene compounds. Butadiene is a highly carcinogenic four-carbon compound that may also be released from the styrene-butadiene Polymer formed during combustion."
"Aromatic extender oils," writes Dr. Carman, "comprise about 25% of most tires today and are known to cause cancer in lab animals as well as being suspected human carcinogens. These are highly aromatic---multiple benzene-containing chemicals---petroleum waste materials with complex ring structures that are even more difficult to burn than benzene." (Benzene has a highly stable ring structure that makes good combustion far more difficult than burning natural gas or straight chain carbon compounds.) He continues: "Anything with benzene will require higher combustion temperatures, higher residence times and higher oxygen to break apart the six-carbon ring with electron clouds above and below that protect the ring from easy chemical breakdown. The thick black oil and black smoke that one sees when tires are burning outdoors is due solely to the aromatic extender oils; they too require higher combustion temperatures, higher residence times and higher oxygen to break down fully to CO2 and water." It may be that Pacifica's power boiler has the constituents necessary to break down these benzenes when it is operating at full capacity but what happens to the efficiency during inevitable upsets of good combustion conditions?
It is well-known that burning tires produces dioxins. Environment Ministry officials say the high temperatures in the boilers will destroy, not produce dioxins. But as the air stream leaves the boilers and goes up the stack, lower temperatures could cause dioxins to re-form. We need reassurance from Ministry experts that this will not happen.
Another major constituent of tires (2% by weight) is zinc oxide, which is used to cure rubber. In high dosages, zinc is an immune system suppressant. Ministry officials say that during earlier test burns, 100% of the zinc was collected by the precipitator and ended up in the fly ash. Zinc isn't all that ends up in the fly ash or bottom ash. Other toxic byproducts from tire burning can include cadmium, mercury, lead, nickel, beryllium xylene, toluene, phenol, mono-chlorobenzene, naphthalene, formaldehyde and acetaldehyde. Workers have to collect and handle both fly ash and bottom ash, which is transported to the industrial landfill, deposited there and hopefully covered immediately to prevent wind-blown distribution.
Another concern is the possible production of air-borne particulates smaller than pm10 which are drawn deep into the lungs by breathing and can enter the bloodstream through the capillaries.
It is important to remember that chemicals do not vanish, they are merely transferred from one medium to another. And to realize that combustion upsets due to mechanical breakdown and human error will result in periodic high emission levels. We look forward to Ministry of Environment officials holding a public meeting to discuss community concerns with the burning of Tire Derived Fuel.
