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DMS Environmental has been producing engineered fuel for the past five years, but it wasn’t until three years ago that the recycling and alternative waste services company was able to really increase its productivity. The Terre Haute, Ind.-based company installed a multiple-stage shredding system that, according to Owner Mark Taylor, allowed it to run more efficiently.

DMS procures material that would otherwise be destined for landfills or incineration to make an engineered fuel product that replaces coal in cement kilns. Manufacturing the fuel has created a win-win scenario for the company. The feedstock is obtained from commercial & industrial (C&I) customers who are interested in recycling as much as possible. “We give them alternatives for what is remaining to help them try to minimize their landfill footprint,” says Taylor. “I see a lot of interest from industries because they are all looking for ways to be landfill free.”

At the same time, interest from cement companies in using coal alternatives is increasing. “The cement companies are all very interested in working hard to try to figure out the best way to run [a coal alternative] and get it permitted. I am seeing more and more cement kilns working toward that and I see more coming on in the future,” Taylor adds.

The discarded materials used in DMS’ fuel range from various rigid and film plastics to rubber along with other materials. It arrives at the facility in loose form from roll-off containers or in bales and Gaylord boxes.

The company blends high-density materials with low-density materials and those that have a high Btu (British thermal unit) value with those that have lower Btu values. Combined, these materials create what Taylor calls “a common blend.”

When material arrives at the facility in its various forms, it is first blended in a pit. It is then loaded into the first of a series of shredders. Once the material passes through the first shredder, it is conveyed to the next shredder and then to the next shredder. Each shredding stage continues to reduce the size of the material.

The final product ranges from 0.5 inch to 2 inches and remains in its loose form. It is not pelletized. The fuel is currently delivered to four different cement plants in the Midwest and used as a coal substitute in their kilns.

Process Improvements
When entering a new area of business, there is always some trial and error. When DMS first began producing engineered fuel, it was using what Taylor describes as a “single-rotor, high-rpm rotary grind system.”

That type of shredder was not ideal for DMS’ operation. Taylor says the combination of high-Btu value and friction from the high-speed system would create issues such as melting. “Some rotary grinders would be good for certain materials,” admits Taylor, “but for what we were doing, we needed a robust system that could handle a lot of various materials.”

DMS switched to a lower-rpm, high-torque shredding system from SSI Shredding Inc., Wilsonville, Ore. Taylor says the transition has allowed the company to increase its production. Rather than using one shredder to size material all the way down to spec, the series of shredders DMS now uses work together. “We will shred it to a certain large size and then it will be conveyed into another shredder that will minimize it even more rather than try to do a single pass down to the proper sizing, which is a lot slower if you are trying to get down to small sizing,” Taylor says. “This allows us to run a lot faster and more efficiently, and the shredders help each other out.”

While the engineered fuel is mostly consistent, the series of shredders also allows DMS to adjust its process based on the customers’ needs. All batches of fuel are checked for quality and reshredded if necessary.

DMS follows recommended guidelines for shredder maintenance, including checking the feed systems, inspecting teeth for excessive wear and changing the oil. DMS says it does its best to ensure only wanted material enters the shredders, but on occasion a piece of metal or other contaminant enters the system. When that happened on the old system, the metal would damage the machinery. Taylor says if it happens on the shredders he has now, “It just catches onto the teeth and stops the machine. We can take that piece of metal out and start back up.”

DMS can processing 36,000 tons of material per year. Taylor emphasizes that the primary reasons for changing its shredding system to the SSI multiple-stage shredding equipment was to stop melting from occurring and to process a variety of material. “It has allowed us to be more versatile in what we are running and how we are running it.”

The author is managing editor of Renewable Energy from Waste and can be contacted at [email protected].