Energy Tablets

Researchers in Missouri have developed a biomass compactor they say can produce tablets with higher material density, and therefore higher energy density, than other unified biomass products on the market.
By Lisa Gibson | October 26, 2010

Jesse VanEngelenhoven and his colleagues had two goals in mind when they began designing their biomass compressor. They wanted to develop a system that yielded a product sized somewhere between bales and pellets, and perhaps more important, they were determined to make the system less energy intensive than the pelletizing process.

Three years later, VanEngelenhoven, research director of Columbia, Mo.-based Ecologic Tech, has real physical evidence that the idea holds water, or in this case biomass. With the help of the University of Missouri’s Bradford Research and Extension Center, VanEngelenhoven and fellow researchers constructed the tabletizer, a machine that compacts biomass so tightly it can squeeze four times as much material into a tablet as a hay baler can wrap into a bale.

“Conventional methods of unitizing biomass are either balers or pelletizers,” VanEnglenhoven says. “What we wanted to do is try to fill that gap and be more efficient than the pelletizers.” Work on the system began in 2007 and took off in 2009 with receipt of a U.S. DOE grant to build.

Perfect Partners

The partnership between Ecologic Tech and the Bradford Research and Extension Center was a no-brainer, as the two have complementary research opportunities and an existing relationship through the University of Missouri. Ecologic Tech was founded in 2000 by a retired MU civil engineering professor who had been with the school for 30 years. “We have a close relationship,”

VanEngelenhoven says of his company and the university. “Bradford Research farm had the biomass and the facilities to build the machine and to provide biomass. With the relationship we already had with the university, it worked out really well.” Bradford owns 600 acres of land planted with switchgrass, wheat, miscanthus and corn, and leases another 280 acres planted with the same crops, according to Tim Reinbott, farm superintendent. Harvests from Bradford’s fields are traditionally used for other testing such as in research projects for graduate students and faculty at the university, he adds.

But biomass isn’t the only thing the Bradford center contributed to the project. The tabletizer was built in Bradford’s lab and represents the first piece of biomass equipment to take up space there, Reinbott says, adding that his team’s research focuses mostly on in-field evaluation and testing dealing with harvesting, crop rotation and economics. “[Ecologic Tech] did the design and we just provided the area for them to do it,” he says.

Testing on the equipment was also done in the lab and, besides Bradford’s crops and residues, also featured sawdust, wood chips, pine cones and waste paper. “The only thing that didn’t really behave itself without a little bit of effort was the switchgrass,” VanEngelenhoven says. “Everything compacted really well.” Reinbott echoed that conclusion, saying corn stover seemed to yield the best tablet product.

The Tabletizing Process

The tabletizer works like this: a hopper with a hydraulic motor turns the auger and feeds the 4- to 6-inch diameter cylindrical mold with biomass. Then a ram pounds the biomass tightly into the mold, shrinking the material from about 10 inches to 2, which is smaller than most biomass briquettes.

“Basically, it squeezes the snot out of it,” VanEngelenhoven laughs. The mold then turns and ejects the compacted tablet. The pressure exerted on the biomass in the mold is about 20,000 pounds per square inch, enough to force the material to adhere together without additional binders. “We don’t put anything extra in it,” VanEngelenhoven says. Long, coarse-cut feedstocks are favorable in the process, as they stick together more easily, he adds.

The resulting tablets have an average density of 55 pounds per cubic foot, compared with average bale density of 15 pounds per cubic foot and pellet density of about 45 pounds per cubic foot, VanEngelenhoven boasts. “So it’s significantly better than a baler, but it uses more energy as well,” he says. “So in that realm, you have to try to compare how much energy this machine is using versus another machine and is there one that’s inherently better? And the answer is, it depends on what you want it to do.” If the densified material is being used at a power plant or to burn for heat in a home, a bale doesn’t fit the bill because it’s too big, VanEngelenhoven says. “So if you want something smaller, you can go with pellets, or now you have this option.”

Each tablet weighs about 1.2 pounds and the time it takes to produce them depends on how much material is being compacted and how fluffy it is, VanEngelenhoven says. He considers corn stover, corn stalks and switchgrass to be fluffy. “The density is really low and you have to get a lot of volume to get to 1.2 pounds.”

The tablets have not been tested extensively for energy density, but VanEngelenhoven says the higher material density will bring along with it higher energy density. The experiments have been geared toward use of the tablets in power plants, but VanEngelenhoven says he has not evaluated whether the material would make good feedstock for gasification processes.

Testing thus far has centered on the speed of tablet production and energy use. By comparison, VanEngelenhoven says pelletizers on average produce between 20 and 30 pounds of biomass per horsepower of energy per hour. “We were trying to beat that number and, given the measurements we took and the speed that the machine operates at, we were able to basically double that number,” he says. 

Scaling Up

The tabletizer has only been constructed on a lab scale, but a commercial system wouldn’t be much bigger in size. “This will produce the size of tablets that we want, but the difference between this and a commercial-scale machine would be that a commercial machine would need a bigger hydraulics system,” VanEngelenhoven says. A commercial system would also need a larger motor than the lab-scale’s 20 horsepower engine in order to operate heavier hydraulics and make the machine economically feasible.

Ecologic Tech has applied for more DOE funding to help with the build out, but does not yet know if it will receive the money. Scaling up, unfortunately, is dependent on outside funding and if that grant doesn’t come through, the company will look to commercial partners to push forward. “The timeline is really funding dependent,” VanEngelenhoven says. “Right now we’re kind of in a place where we want to further develop the machine, but the cost associated with building the next prototype makes it prohibitive for us. Since we’ve got other technologies in our stable that appear to be more profitable, that’s where we’re devoting our resources at this time.”

Reinbott hopes to spark interest in some of the students doing projects at the extension center in further developing the system and helping with the scale up. Many have expressed a desire to pursue the project and Reinbott says they realize the importance of such a process. “We’d like to see it fully developed,” he says. “I think there’s more to do and further testing.”

Costs for the commercialized system will be $100,000 to $200,000 but most likely will not be for single-user applications. “Most people won’t be able to use the entire capacity of the machine by themselves,” VanEngelenhoven says. “We are talking 17,000 tons per year and that’s a lot of biomass.”

As international export trends develop for wood pellets, one can’t help but wonder if the tablets could enter and enhance those markets. VanEngelenhoven responds with an enthusiastic yes. “Absolutely,” he says. “Simply because we can produce a product that has a significantly higher density than pellets and so because of that fact, our shipping costs will be lower and our energy density will be higher.”

Author: Lisa Gibson
Associate Editor, Biomass Power & Thermal
(701) 738-4952