Auto Fluff – What to do with the remaining 25 percent?
The recycling of scrap metals from automobiles is a little known success story. While community and municipal blue box campaigns tout a 25 percent success rate, a 75 percent recycling rate for automobiles is often overlooked. However, the 25 percent that remains, called auto fluff, is a recycling dilemma that demands attention and solutions. Why?
Estimates indicate that 700 000 automobiles are disposed of in Canada annually, generating approximately 700 000 tonnes of ferrous scrap materials and 200 000 tonnes of auto fluff. Auto fluff is a complex mixture of non-ferrous materials including plastics, foam, textiles, rubber and glass. Because this fluff is complex and is contaminated with rust, dirt and a variety of fluids, its recyclability poses a challenge to Canadian shredding operators.
As well as the difficulties inherent in recycling auto fluff materials, Canada’s recycling industry must also deal with recent auto manufacturing trends. In an effort to achieve better fuel economy and reduce emissions, automobile manufacturers are using lighter weight, non-metallic materials. Newer automobiles are manufactured using less metal, while the use of plastics and other non-ferrous components is increasing. The net effect leaves shredders with lower volumes of recyclable metal and greater volumes of auto fluff for disposal or recycling.
Consequently, the need to explore new and innovative ways to recycle auto fluff, or to recover valuable resource material from this waste, is an urgent environmental and economic issue. The National Research Council’s Institute for Environmental Research and Technology works with Canada’s plastics industry, auto manufacturers and shredding operators to identify opportunities to recover potentially valuable resources from this waste stream. Some options being investigated are the use of the material as an alternative landfill day cover, the combination of auto fluff materials with other recycled plastics to produce composite materials, and using shredded material as a pyrolytic feedstock to recover chemicals and fuels.
Recycling Automotive Glass
Currently, about 75 percent of junked vehicles are shredded to recover iron and steel. After the ferrous material is magnetically separated, the remainder (225-250 kg/car) contains 16 percent of glass originating from windshields, side windows and sunroofs, most of which is not normally recovered and ends up in landfill.
Experienced car dismantlers report that up to 30 percent of windshields are broken, because of current methods of sealing and trimming. Unless car makers change design practices, this breakage rate is unlikely to decline. Current practices in glass recovery include removal for reuse, cryogenic “crumbing” of glass windshields and heat-assisted separation of sandwiched glass. A Japanese company, Asahi Glass Co. Ltd., has patented a method where the laminate is softened, allowing for the recovery of glass without contamination by plastics.
New developments in auto glass such as “heads-up display,” quick defrost windshields, new tinting techniques, metallic crystal alignment films and implosion proofing by a new inner polymer laminate will further complicate the recovery or reuse of these glasses.
Recycled glass is put to various uses. If uncontaminated by plastic, it can be melted and spun into fibreglass or moulded into other products. Other uses include glass beads and reflective additives. Impure glass can also be considered for incorporation into architectural aggregate, or ground for abrasives.
Used Oil Recycling
Of the approximately 1 billion litres of lubricating oil sold in Canada each year, only 250 million litres are currently recovered. The process of returning used oil back to its original useful state is called “re-refining.” Used oil can be re-refined into lubricating oil many times with only minor losses and the process takes only one-third the energy of refining crude oil into lubricating oil.
Lubricating oil consists of hydrocarbons (long chains of carbon atoms). Most lubricating oil molecules will generally have between twenty-five and forty carbon atoms in these hydrocarbon chains. Collected used oil is usually a mixture of different types of lubricating oils, which has been contaminated or chemically changed. Dirt, metal particles, fuels, oxidized oil and water are the most common contaminants. Chemical changes are also possible where one or more of the hydrogen atoms in the hydrocarbon chain is replaced by oxygen, sulphur, or other elements or molecules.
One commercial process for recycling used oil is known as the vacuum distillation/hydrotreating process. It involves two basic steps: a distillation step to remove trapped waste water and fuel, and a hydrotreating step to remove other impurities such as sulphur, nitrogen and chlorinated compounds.
Distillation of used oil occurs in four stages. The first stage removes water, most of the solvents and any light fuels (e.g., gasoline). The separated water is treated in the wastewater treatment system and released back into the environment, while the light organics are used as fuel at the site. The dewatered oil goes through a second distillation step where the remaining fuel oils are removed in a vacuum fuel stripper. In this process, the oil is heated under vacuum at lower temperatures, thus avoiding the high temperatures that would cause the hydrocarbon chains to break into small fragments or coke up (form a solid material similar to coal). The removed product, a material similar to home heating fuel, is used as fuel at the re-refinery.
The third and fourth distillation steps are identical and are performed in machines called thin film evaporators. These evaporators operate at lower vacuum and higher temperatures than the vacuum fuel stripper. The objective is to vaporize the lubricating oil as gas, leaving the dirt and other physical impurities behind. In the thin film evaporators, the oil flows down a double-pipe heat exchanger where a set of wiper blades spreads it against the wall of the central pipe. This aids the evaporation process. The lubricating oil gases are collected and condensed into liquid oil. Any material that does not evaporate in the third and fourth stage evaporator can be used as an asphalt extender in roofing and asphalt paving.
After distillation, the liquid oil is chemically treated using hydrogen gas at high temperature and high pressure. These conditions result in replacing any missing hydrogen atoms in the hydrocarbon chains and effectively removing sulphur, chlorine, oxygen and other impurities.
The final oil product is a base-oil stock of a quality similar to the virgin lubricating oil. The recycled oil is blended with different additives to produce motor oils, hydraulic oils or other specialty oils.
Information provided by: Frank Wagner at 1-800-265-2792 ext. 325, Safety-Kleen, Breslau, Environmental Health and Safety Department.
Scrap Tire Recycling
At present, approximately 40% of the scrap tires produced annually in Canada and the United States are reused, recycled or recovered. Since 1990, when 14 million tires caught fire in Hagersville, Ontario, provincial regulations have limited the number of tires that can be buried in landfills or stored above ground. While landfill use is declining, the recycling of tires is growing. However, demanding product specifications for safe, durable tires make them more difficult and expensive to break down. Some experts say that reclaiming original components from scrap tires is like trying to recycle a cake back into its original ingredients.
Tires, which are generally composed of approximately 65% rubber, 10% fibre and 25% steel by weight, can be recycled in two forms: processed and whole. Whole tire recycling involves using the old tire, as is, for other purposes (e.g., landscape borders, playground structures, dock bumpers and highway crash barriers). The recycling of processed tires, on the other hand, requires first reducing the tire to smaller pieces. This can be accomplished by chopping, shredding, or grinding at ambient or cryogenic temperature. Cryogenic processing involves cooling scrap tire rubber with liquid nitrogen. Rubber, steel, and fibre are then separated out using magnets, screens and density techniques. The main difference between ambient and cryogenic methods is that they produce products of different size and have readily apparent cost differences. Cryogenic processing achieves smaller rubber particles than ambient processing, but is more costly. Crumb rubber (from either process) can be used as a substitute for virgin rubber in a variety of products such as bonding tape, irrigation pipes, carpet underlay, footwear, recreational surfaces, waterproofing compounds for roofs and walls, joint and crack sealants, and as an additive in asphalt cement for paving roads. Finely processed, cryogenic ground rubber can be combined with polymers to produce materials used in applications traditionally reserved for plastics.
Approximately 60% of scrap tires are currently used as fuel. Whole or shredded tires are burned (scrap tires have about 10% more heat value by weight than coal). Fifteen percent of processed scrap tires are recycled into rubber products and twenty five percent are used as gravel substitutes in landfill liners and experimental road beds.
Automotive Battery Recycling
There are approximately 20 million vehicles in service on Canadian roads, with each car or truck having a lead-acid battery containing 8-12 kg of lead. Lead-acid batteries are classified as secondary (rechargeable) wet cell batteries. These batteries are composed of a plastic casing containing several cells connected in series to give a total battery potential of about 12 V. The anode consists of a lead grid filled with spongy lead, and the cathode is a lead grid filled with lead dioxide. Both electrodes are immersed in a solution of 38% (by weight) sulphuric acid. When the battery discharges, solid lead sulphate formed in the cell reaction adheres to the grid surfaces of the electrodes and the sulphuric acid is consumed. Charging the battery, by passing a direct current through it, reverses the chemical changes and regenerates the acid.
The demand for lead-acid batteries shows steady growth, and is likely to continue to grow in the foreseeable future because of both the growth in conventional vehicles and the emerging popularity of the electric car. While a number of battery technologies are under development, it is generally believed that none yet offers comparable economies to the lead-acid battery. At present, approximately 90% of used lead-acid batteries are being recycled. The lead-acid battery recycling industry must address a number of environmental issues regarding air, water, and solid waste management practices that have an impact on the collection, transportation, and recycling of spent batteries.
The commercial process used to recycle lead-acid batteries is designed to recover:
The lead sulphate/lead oxide battery paste (after desulphurization), which is later treated in a smelting furnace to recover lead.
Lead grids and poles, which can be treated in a smelting furnace with a metal yield of 90%.
Polypropylene, which can be sold directly or upgraded to produce high-quality pellets.
Anhydrous sodium sulphate, as a detergent-grade product for resale to detergent manufacturers and glass works.
The main features of the recycling process include:
Pre-crushing of batteries to remove the sulphuric acid solution.
Initial separation of iron material by a magnetic separator.
Wet-screening to separate the battery paste (a mixture of lead sulphate and lead oxide).
Separation of the metallic lead and plastic components in a hydrodynamic separator, isolating the various components due to their density differences. In water, polypropylene floats, lead sinks and separator material and ebonite overflow to a vibrating screen. The water used in the hydrodynamic separator is collected in settling tanks for reuse.
The recovered battery paste is treated with a sodium carbonate solution in a desulphurization process to convert the lead sulphate to lead carbonate and sodium sulphate. The former is treated for lead production. Because the lead sulphate has been converted to carbonate form, the smelting process operates at lower temperature with no sulphur oxide emissions. The sodium sulphate solution is crystallized and dried to produce a detergent-grade sodium sulphate powdered product.
http://www.nrcan.gc.ca/mms/canmet-mtb/mmsl-lmsm/rnet/autoarte.htm May 1996