If you asked most people to look at a waste facility, they would probably dismiss it as an enormous pile of trash. But there’s actually a fortune in untapped energy waiting to be reclaimed in that trash. One of the more promising developments in recent years is the transformation of landfill waste into fuel.
RDF (Refuse-Derived Fuel) consists largely of waste plastics and biomass, reduced to the appropriate size and cleared of non-combustibles and hazardous materials. It can be sold in its semi-processed form as finely shredded material, or compressed further into pellets, bricks, or logs. RDF is used alongside traditional sources of fuel such as coal in power plants. It’s also used as a fuel in the cement industry.
Komptech, a company that specializes in waste treatment machinery, offers a complete system for refuse-derived fuel, consisting of the “Terminator XF” waste pre-shredder, “Brini” separator, and “Rasor” post-shredder. All machines are designed to use minimal energy themselves, for the highest possible net energy output of the RDF.
The main requirement in turning garbage into fuel is to sort the combustibles from the rest of the waste. That starts with shredding, to reduce the material to a uniform particle size. One of the challenges presented by municipal waste is the high content of synthetic materials, such as carpets, mattresses, tapes and other fabrics, that are very resistant to shredding. Komptech has solved this problem with a new cutting geometry on their Terminator XF, by reducing the gap between the teeth on the drum and the comb. In addition, raised rings between the teeth keep material up where it can be reliably shredded against the comb. The teeth are specially contoured to aid penetration of the material and provide better feed. The tooth holder itself is seated inside the drum, and can be changed with simple hand tools.
The next step in reclaiming RDF is to remove non-combustibles. The Brini, a specialized mechanical separator, divides materials into 3 so-called “fractions”: a 2D fraction of plastic, paper, and packaging materials suitable for RDF, a fine fraction of dirt and other material unsuitable for fuel, and a 3D fraction of non-combustiibles such as glass, stones and metals. Since the Brini uses very little power, operating costs are low. Its solid steel construction minimizes wear and tear, and access panels to all components make maintenance easy.
The 2D material separated out by the Brini is then fed into a slow-running post-shredder called the Rasor, which further shreds it into consistent, finer sized particles. Instead of operating intermittently, power varies based on the material feed, for maximum efficiency. The Rasor’s cutting gap self-adjusts for optimal cutting with minimal space between the blades, resulting in less power needed to cut the material. The cutters are hydraulically clamped and can be changed without shutting the system down, saving time and money. The Rasor can shred material down to 1.25 inches or less.
The final result is a fuel which is suitable for power plants like the Elk River Station in Minnesota, which runs completely on RDF and reduces waste by 300,000 tons per year. RDF can also be used to fuel the rotary furnaces used in the cement industry.
Refuse-derived fuels not only reduce the amount of trash in our landfills, they are also a great way to make use of a resource that formerly was literally wasted. RDF can even help reduce the amount of sulfur and nitrous oxide released by coal power plants. Power consumption is greatest in densely-populated areas, which also produce the greatest amount of waste, so the supply is usually close to where it’s needed.
Refuse-derived fuels are becoming an important energy alternative. There is a never-ending supply, and RDF requires no drilling, mining, or long-distance transportation. Processing wastes into RDF also creates a source of income for municipal waste operations. It’s a win-win proposition for everyone.
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