Realizing waste’s full potential

Material recovery facilities (MRFs) typically sort out commodities from single-stream recyclables such as paper and cardboard, plastic, metal containers and glass from single-stream materials collected from residents and commercial customers. While equipment from screens, optical sorters, magnets and eddy current separators and others can achieve a high level of separation, not all materials that are fed through the system are able to be included in the final product. This fraction of material, albeit a small percentage, can add up, especially at facilities that are processing at high volumes. These residuals often end up going to landfills at a cost to the recycler.

In South Kirkby, U.K., Shanks Waste Management has found a way to create value from MRF residuals as well as mixed municipal solid waste (MSW) to achieve nearly zero waste going to landfill, an estimated 95 percent recovery rate. The unique approach involves two separate processing systems.

The two systems, developed by Plessisville, Quebec-based recycling system manufacturer Machinex, separates traditional recyclables in the first system and creates a refuse-derived fuel (RDF) with the second system. Shanks opened the waste treatment facility in January. The combined systems are designed to process 230,000 metric tons of residual waste and recycling from homes and businesses in the Wakefield District of West Yorkshire County, England.

Jonathan Menard, Machinex project director reported in February 2016, “All acceptance tests have been passed and the two systems were commissioned on time.”

Machinex was selected in 2013 by Shanks to design, manufacture and install the two fully independent sorting and recovery systems in separate buildings on the site.

TWO-SYSTEM APPROACH

Machinex describes the first of the two systems as a mixed dry recyclables (MDR) sorting plant, which annually processes 36,000 metric tons of plastic, glass, metal containers, paper and cardboard at a capacity of around 20 metric tons per hour. “A purity rate of 95 percent will be achieved by Machinex screens, optical sorting and a glass clean-up system, an air capture system for plastic film, ferrous magnets and an on ferrous eddy current system,” according to the company.

The second system segregates a variety of materials from MRF residual waste and MSW—material that which previously would have been sent to landfill—at 30 tons per hour, according to Menard. “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 RDF. “The priority is to remove RDF contaminants by maximizing 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), a powerstation based in West Yorkshire, U.K., which uses various waste-derived fuels for its 70-megawatt (MW) power station. (See sidebar “From Fuel to Power.”)

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 plastics can be sorted by a combination of air treatment systems, ballistic separators, optical sorters, magnets and eddy current separators.

FUEL FLEXIBILITY

An important aspect of the second system is flexibility, since 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, explains Machinex.

Menard says the main flexibility with the MSW system is centered around the ability of the system to produce an RDF output material to meet customer specifications.

“The installed equipment has the ability to control the calorific value of the fuel, dependent on client specification and/or requirement,” he says.

The remaining organic fraction is treated using an autoclave. The autoclave gets the organics ready for the digester. “This process will sterilize the remaining material before it is fed into an anaerobic digestion plant, where it will be converted to biogas for renewable energy generation,” Menard explains.

“The MSW facility has been designed to maximize 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.”

The energy produced from the 65,000 metric-ton-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, according to Menard. Shanks is still commissioning the anaerobic digestion portion of the plant.

SET APART

Menard says building two systems at one facility “represents a real showcase as it includes two significant facilities installed in front of each other.”

He adds, “The overall facility has the capability to process a wide range of materials delivered to the site. Allowing householders to deliver direct to the sites household waste recycling center (HWRC). Any of these materials delivered can typically be processed by one of the installed processes, within the individual process buildings.”

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 optimize both systems to fulfill their full potential.

The author is editor of Renewable Energy from Waste and can be reached at ksmith@gie.net.