Propellants in spray cans are highly flammable and the pressure filling means the cans represent a problem during waste incineration. This is why few firms specialising in this flow of waste have established themselves in the market.
Aerosol cans are made either from tin or aluminium. Inside, alongside the filled propellant gases and the cosmetics, paints or lacquers, there are also small amounts of plastics, primarily fitted in the valve devices. In Germany, the manufacture of aerosol cans using ozone-damaging propellant CFCs ceased in the 1990s. Nowadays, the industry uses other mixtures in hair sprays, deodorants, paint sprays and other atomisers, usually consisting of propane, butane or dimethyl ether. But even using these newer substances, the disposal is anything but free of problems.
The propellants are highly flammable, and the pressure filling means that the cans form a highly explosive mixture during shredding. For this reason, spray cans that are still filled represent a considerable danger in waste incineration systems. This means that only a small number of disposal companies have specialised in these specific waste fractions in Germany.
But one that has undertaken this work is Seiba Entsorgungstechnik, based in Neunkirchen, Saarland. It has fundamentally modernised its spray can processing by installing the QZ 1200 Querstrom-zerspaner from German plant engineering and construction firm MeWa Recycling Maschinen und Anlagenbau.
“Instead of cutting, the QZ separates the cans into individual component parts using a chain principle”
In principle this is the same QZ system as used in waste electronic and electrical equipment (WEEE)recyclers such as SWEEEP and Wincanton in the UK. The main task, to disintegrate the input (aerosol cans, WEEE, refrigerators) into their component parts, is done by the QZ at all of these plants. But because MeWa delivers turnkey plants, the process is different in each one. The QZ for aerosol recycling in Neunkirchen is smaller in size, so takes a smaller throughput, for example, and the separation technology after the QZ is different for the different applications.
Where rotor shears were previously used to shred the aerosol cans, the MeWa QZ 1200 operates a completely new concept. At the same time as Seiba replaced its shredding unit, the entire waste gas plant was upgraded. Seiba obtains some of its material from disposal companies around Germany, as well as from France and the Benelux states. The remaining quantities are partially filled cans from the manufacturing industry.
After 20 years of operation, Seiba decided to replace its obsolete rotor shears with the QZ from MeWa, along with new explosion and gas protection facilities, to achieve lower wear and higher throughput. The QZ is versatile in being able to separate the different metal-plastic composites that make up this waste stream. Instead of cutting, the QZ separates the cans into individual component parts in seconds using its chain principle.
Residual liquids are extracted from the machine and drained off, while the hollow metal bodies are separated from the plastic components. The exposed metals and plastics are cleaned in a water bath and separated into three fractions, aluminium, ferrous metals and plastic, using a magnet and an NE cutter. The extracted materials are passed on by the plant to recycling firms in the region.
The benefits of using the Querstromzerspaner in this process compared with rotor shears are the low wear to its chain, the generally low maintenance overheads and significantly higher throughput. A number of safety levels ensure a disposal process in the plant that is environmentally compatible, and to ensure the customer has the highest possible recycling safety, Seiba has installed video surveillance.
First of all, the pressurised aerosols are picked up by scanners at the initial check. An employee then picks out extraneous materials, the material flow is metered via vibrating channels and integrated scales and sent across a conveyor belt to the QZ. A sluice system ensures that no gases can escape from the Querstromzerspaner into the hall. To prevent gas explosions, the oxygen concentration in the barrel is monitored electronically and nitrogen is sprayed in at regular intervals.
The propellant gases that are released are separated, together with the inert gas, via condensation and used thermally. The process and hall air is routed via a waste gas cleaning stage with downstream filter. It goes without saying that the plant is approved in line with federal emission protection laws, and has been inspected/approved with respect to safety by TÜV Süd, the German technical inspection association.
Used in this special application, the MeWa QZ shows once again how versatile it is when deployed for the separation of composite materials.
Harald Pandl is marketing manager at MeWa Recycling Maschinen und Anlagenbau
- The QZ will feature at the RWM exhibition in Birmingham from 14-16 September in Hall 17,Booth 422
AEROSOL RECYCLING IN THE UK
Aerosols account for 4% of the metals packaging stream in the UK, according to the British Aerosols Manufacturers’ Association (BAMA). It estimates that there are about 25,000 tonnes of tin-plated steel and 4,500 tonnes of high-grade aluminium available to be recycled from aerosols.
Last year BAMA, along with other industry partners, was involved in an initiative to increase the amount of aerosols and foil collected for recycling by local authorities. BAMA reports that 76% of local authorities are now participating, a huge improvement on the 7% doing this about eight years ago. There are no tonnage figures available because aerosols are collected along with the other metal packaging in the waste stream.
In the UK, aerosols from commercial and industrial sources are classified as hazardous waste, and BAMA says it supplies its members with detailed guidance on how to empty industrial aerosols safely. The guidance, Recycling Empty Aerosols from Industrial, Commercial and Institutional Premises, says that if aerosols are punctured and the contents removed, the metal and plastic components can then be recovered and recycled, with any product residue removed and disposed of as hazardous waste.
Empty aerosols will typically have 3% by weight of their initial contents left, and about half of this will be propellant gas that will disperse as soon as the aerosol is punctured.
The BAMA guidance recommends puncturing aerosols as soon as possible in a designated area that is assessed under the requirements of the Dangerous Substances and Explosives Atmospheres Regulations 2002, and that a competent person needs to conduct a Control of Substances Hazardous to Health assessment of the contents, with operatives fully trained and wearing appropriate personal protective equipment. The punctured containers can then be recycled along with other recyclable metal items.