Density and uniformity are the qualities sought by those in the fuel pellet and briquette markets.
How to best prepare fuel products made from discarded materials can vary greatly, with two of the biggest variables being the residual material being used and the method of consumption.
In almost all cases, however, producers of refuse-derived fuel (RDF), specified recovered fuel (SRF), fuel cubes and other engineered fuels made from residuals seek to create a product that is uniform and dense.
The uniformity is tied into product quality issues, while the density (which likewise can be a sign of quality in most fuel consumption applications) also can make a product shippable over longer distances.
Pinning for Pellets
Cube and briquette production is a common fuel preparation method in some sectors, but many other processes work best when pellet mills are the production machinery of choice.
Vecoplan LLC, High Point, N.C., refers to pellet mills as “the heart of every system” in the biomass production processes it installs and notes on its website that its own pellet mills feature “belt-driven dual drives for increased performance and lower maintenance costs.”
The company says it offers “complete pellet production systems, from processing the raw material to bagging the finished pellets. Equipment in a typical line includes size reduction, conveyance, metering, pelletizing, cooling, screening, packaging and customized system controls.”
Another pellet machinery producer, Germany’s Amandus Kahl, with roots tracing back to 1876, says the energy crisis of the 1970s “induced Kahl to deal with the issue of pelletizing renewable raw materials.”
The company subsequently produces pelletizers that are designed to densify a wide range of materials, including scrap wood, sawdust, plastic, paper and mixed residuals or waste.
As described by the www.pellet mills.net website, a typical pellet mill consists of several components and contains several stages of production.
A feeder first accepts material as it enters the pellet mill and carries it to “one or more conditioning chambers.” Such chambers may involve exposing the inbound material to steam or to a bonding agent.
From there, the feed material enters the equipment’s pelleting chamber, where the material “is compressed by roller shells and is forced through the holes of the pellet die,” according to www.pelletmills.net.
The website refers to the pellet die as “the most important part” of the mill. The pellet die can either be a ring die or a flat die.
In the pelleting or compression chamber that houses the die, “Pellet rolls press or roll the raw material through the small holes of the pellet die,” the website states.
Emerging from the pellet dies are long strands of pellets, which are then cut by a mechanized knife to give the finished pellets their distinctive shape before they exit via the output chute.
In some processes, a cooler device is deployed because the pellets are hot after the pelleting process is completed. “Pellets are then sifted, and finished pellets are output from the plant, ready for bagging or use,” according to www.pelletmills.net.
Greenwood Energy, a New York-based company with a residual materials fuel pellet production facility in Green Bay, Wis., accepts a variety of inbound materials to create a fuel pellet that it says can compete with or supplement coal as a boiler feedstock. (See “A Working Model” in the Spring 2012 issue of Renewable Energy from Waste.)
“Our high-quality fuel pellets, produced from nonrecyclable, industrial paper and plastic [materials], are a direct substitute for coal but with a lower carbon and overall emissions footprint,” the company states on its website, www.gwenergy.com.
Greenwood Energy says it tests its pellets to ensure its system is creating a dense, uniform, high-Btu (British thermal units) product. “Our pellets are regularly tested during production for consistency in composition, environmental quality and energy content,” the company website states.
Before the feed material Greenwood Energy accepts makes it into a pellet mill, it goes through several treatment steps involving shredding, purification and particle uniformity. Vecoplan LLC was a key equipment supplier in outfitting the Green Bay facility. (See the article “Flexible Solutions” at www.REWmag.com/flexible-solutions-vecoplan- greenwood-energy.aspx.)
In addition to meeting internal quality standards, companies also can seek to meet a wider standard and can examine testing and measurement of SRF and RDF fuels summarized in reports by the European Committee for Standardization (CEN, www.cen.eu), based in Brussels.
The agency’s report EN 15400:2011, “Solid recovered fuels – Determination of calorific value,” specifies a method for the “determination of gross calorific value of solid recovered fuels at constant volume and at the reference temperature 25 degrees Celsius.”
In the United States, the report can be purchased through the American National Standards Institute (ANSI) website at www.webstore.ansi.org.
Cubist Stylings
Pablo Picasso may be most closely associated with “cubism” in the art world, but the cube shape also has had loyal adherents in the recycling and waste processing industries. Companies including RUF GmbH & Co. of Germany; Warren & Baerg of Dinuba, Calif.; and Lundell Enterprises Inc. of Cherokee, Iowa, offer equipment that can turn a wide variety of materials into cubes or briquettes for shipment and consumption.
In the Winter 2012 issue of Renewable Energy from Waste, a feature story on Balcones Fuel Technology (BFT), Little Rock, Ark., describes in part how that company produces its fuel cubes.
The company’s General Manager Jay Saxton told Renewable Energy from Waste that BFT seeks “nonrecyclable, postindustrial, nonchlorinated coproducts” as feedstock, in particular looking for discarded materials fitting the profile of “dry, high Btu material with little ash (noncombustibles) and low sulfur content.”
The end result, says Saxton: “Our fuel cubes are typically a mixture of plastic, mainly polyethylene, and cellulosic fiber.”
Turning loose materials into cubes is a production step with a long history, especially if one traces the method back to making bales of hay in the agricultural sector.
The production of smaller briquettes has long been common in the compression of certain scrap metals (such as turnings and other smaller pieces), and the methods deployed in that sector have spread into related sectors.
California’s Warren & Baerg, founded in 1966, says its machinery designed for industrial markets “can process materials such as paper, newsprint, cardboard, wood waste, municipal solid waste and sludge wastes at rates of four to seven metric tons per hour per [cubing machine].”
Consumption as a fuel product is the intended result. “The fuel cubes produced have characteristics similar to coal or wood fuel and can be used in most industrial boilers,” the company states on its website, www.warrenbaerg.com.
The plastics-to-fuel stream has been one niche into which the company has placed its cube machinery. Warren & Baerg machinery has been part of the BFT process in Little Rock.
The company also has placed cubing systems into the biomass, agricultural residues and MSW (municipal solid waste) sectors. “The range of cubing systems we manufacture can convert many loose, low-density materials into a dense, alternative fuel that is economical to transport and efficient to burn,” Warren & Baerg states on its website.
“Nonrecyclable (low market value) papers, newsprint, polycoated or waxed cardboard, preconsumer industrial fiber wastes, wood processing and manufacturing wastes and postconsumer combustible fiber wastes can all be processed through our Model 250 or 250W cuber at rates of one to eight tons per hour,” says the company. “Secondary additives such as paper mill short fibers (sludge), coal fines and pet coke (petroleum coke, an oil-refining byproduct) can be added to form a blended fuel.”
Germany’s RUF has a subsidiary in North Olmsted, Ohio, (near Cleveland) to reach the American market with what it calls its line of “sophisticated industrial briquetting systems.”
RUF describes its mold press briquetting method as a four-step process:
- Material used to make briquettes is transported into the precharging chamber by a conveying screw.
- The precharger presses the material to a controlled density (to ensure consistent briquette size).
- The main pressing ram transfers the material into the mold and forms the briquette into its final shape and density.
- The reciprocating mold moves sideways, and the briquette is ejected by parallel ejectors as a second briquette is formed.
On www.ruf-briquetter.com, RUF lists more than 20 materials that its equipment can convert to cubes, including wood dust, wood chips, tire wire and polystyrene.
Long-time New England recycling and waste hauling company New Bedford Waste Services LLC (NBWS), New Bedford, Mass., is one of the most recent companies to announce an endeavor in the fuel cube market.
NBWS, along with sister company ABC Disposal Service Inc. and WERC-2 Inc. of Pocasset, Mass., announced plans in May 2013 to build and operate a facility in Rochester, Mass., to be known as Zero Waste Solutions LLC (ZWS) and which is scheduled to open by the summer of 2014.
The 90,000-square-foot solar-powered facility will accept municipal solid waste, construction and demolition debris, single-stream recyclables, commingled recyclables and source-separated recyclables.
Downstream of its recycling processes, the ZWS facility will employ WERC-2’s technology to produce Eco-Tac fuel briquettes, a solid fuel product that burns, handles and stores like high-Btu coal, according to the company. Eco-Tac will be marketed to biomass and coal-fired plants in states where the product is cleared for use.
On its website, www.werc-2.com, the company refers to its Eco-Tac fuel briquettes as “a manufactured alternative fuel” that can serve as a substitute for or be cofired along with coal or woody biomass.
“Eco-Tac is composed of common elements of postrecycled refuse,” states the company, which also “guarantees over 11,000 Btu per pound with limited moisture content and predictable outputs.”
WERC-2 says the compact, cubed shape of Eco-Tac “permits truck, rail or ship transport without problems of odor, leakage or rodent attraction.”
Other advantages of the cubes, according to WERC-2, include that the recycled binding ensures fuel consistency and stability and the extended shelf life allows for better inventory management.
“By combining the capabilities of our transfer stations and hauling operations with WERC-2’s innovative technologies, we will be able to develop an extremely efficient facility,” says Michael Camara, president of NBWS. “The technologies allow us to process a larger percentage of materials, which can then be recycled and reused. We will be able to recycle as much as 95 percent of the materials accepted at ZWS.”
The author is editor of Renewable Energy from Waste and can be contacted at [email protected].