Material recovery facilities (MRFs) typically sort commodities such as paper and cardboard, plastic, metal and glass from commingled recyclables collected from residents and commercial customers. While equipment that includes screens, optical sorters, magnets and eddy current separators can achieve a high level of separation, not all incoming materials are recoverable. This fraction, albeit a small percentage, can add up, especially at facilities that are processing high volumes. These residuals often have to be shipped to other facilities for further process, but it comes at a cost.
In South Kirkby, United Kingdom, Shanks Waste Management, headquartered in the U.K., has found a way to create value from MRF residuals and from mixed municipal solid waste (MSW) to achieve nearly zero waste going to landfill and an estimated 95% recyclables recovery rate—all in one place. The approach involves two separate processing systems. Developed by Plessisville, Canada-based recycling system manufacturer Machinex, the first system sorts traditional recyclables, and the second system creates a refuse-derived fuel (RDF) from mixed waste.
The combined systems are designed to process 230,000 tonnes of recyclables and waste from homes and businesses in the Wakefield District of West Yorkshire County, England.
Shanks opened the waste treatment facility in January 2016.
Jonathan Menard, Machinex executive vice president of sales and strategic positioning, reported in February 2016, “All acceptance tests have been passed, and the two systems were commissioned on time.”
Shanks selected Machinex in 2013 to design, manufacture and install two fully independent sorting and recovery systems in separate buildings on the South Kirkby site. The project required a close working relationship among Machinex, Shanks and several contractors.
Machinex describes the first of the two systems as a mixed dry recyclables (MDR) sorting plant, which processes 36,000 tonnes of plastic, glass, metal, paper and cardboard annually at a capacity of 19 tonnes per hour.
A purity rate of 95% is the goal, using Machinex screens, optical sorters, a glass clean-up system, an air capture system for plastic film, ferrous magnets and a eddy current system for nonferrous metals, according to the supplier.
Machinex describes the technology used to recover newsprint as a combination of news disc screens installed on top of each other, as well as a new optical unit. The optical unit is designed to eject contaminants, including cardboard, card stock of various colours and rigid and film plastics. The technology used to recover mixed paper includes a 3D finishing screen combined with a mixed paper optical sorter. This optical unit ejects mixed paper contaminants, including rigid and film plastics and metals.
“To increase the fibre recovery, there is also the possibility to manually reroute all fibre types, such as magazines, directories or any missed paper, on the container and residue lines,” Menard describes.
He says while the facility is able to reach a news purity rate of 95% to 96%, the current U.K. market prices for news and mixed paper grades have precluded Shanks from producing bales of news with such a high purity rate.
“It currently makes more economical sense to process a bit more tonnage in the plant and generate one sole mixed paper grade with a purity of 97% to 98% with all generated fibre,” Menard says.
“If the market changes, Shanks will be able to go back to the original scheme, which was to separate the news from the mixed paper,” he adds.
The second system segregates a variety of materials from MRF residuals and from MSW—material that previously would have been sent to landfill—at 30 tonnes per hour, Menard says. “The MSW facility takes in pure household waste, which contains a wide range of recyclable, nonrecyclable, organic and inert material,” he says.
The main goal of the MSW system is to obtain a final fraction that meets the standards to produce refuse-derived fuel (RDF). “The priority is to remove RDF contaminants by maximising organics recovery and ferrous and nonferrous metals recovery,” the company says.
The RDF produced by Shanks is designed for use by Ferrybridge Multifuel 1 (FM1), West Yorkshire, U.K., which uses various waste-derived fuels for its 70-megawatt (MW) power station.
A vibratory screen segregates the organic fraction from other waste. It is then treated using an autoclave before being sent to an anaerobic digestion (AD) plant. Ferrous and nonferrous metals, plastic film, paper and rigid plastics can be sorted using a combination of air treatment systems, ballistic separators, optical sorters, magnets and eddy current separators.
An important aspect of the second system is flexibility; the plant operator can select the most appropriate recyclables to be recovered according to market values and the desired calorific value of the RDF produced, Menard explains.
The remaining organic fraction is treated using an autoclave. The autoclave sterilizes the material before it is fed into an anaerobic digester, which Shanks is still commissioning.
“The MSW facility has been designed to maximise the removal of organics at a very early stage within the process,” Menard describes. This material first has the metal removed and is then conveyed directly into the feed system for the autoclave process. “This process will sterilise the remaining material before it is fed into an anaerobic digestion plant, where it will be converted to biogas for renewable energy generation,” he says.
The 65,000-tonnes-per-year digester will power the plant and export energy back to the grid—enough to power 3,000 homes.
The residue from the digester will be used as a nutrient-rich soil conditioner, Menard says.
WORKING IN TANDEM
The MDR and MSW systems work in parallel, he says. They are not interconnected aside from the exchange of material; residue from the MDR system becomes infeed for the MSW system.
The MSW sorting technology generates a super light fraction comprised of either mixed paper or plastic film that is separated with the help of an optical unit. This material goes through a quality control station before being baled using a Machinex two-ram baler.
“If the market changes, Shanks will be able to go back to the original scheme, which was to separate the news from the mixed paper.” – Jonathan Menard, Machinex
“It is the operator’s choice to eject either the mixed paper, the plastic film or nothing, so that the super-light stream becomes RDF,” Menard says.
The final RDF product is specified according to the calorific value required and the client’s needs.
He adds that the project of building two systems at one facility is unique and “represents a real showcase as it includes two significant facilities installed in front of each other.
“The overall facility has the capability to process a wide range of materials delivered to the site,” he continues.
Nigel Catling, Shanks capital infrastructure director, says, “Machinex worked closely with the Shanks team and Wakefield Council to deliver two efficient facilities in South Kirkby. Both of these facilities were swiftly brought into use, delivering good throughputs and quality materials.”
Catling says Shanks is working to optimise both systems to fulfil their potential.