Densifying Biomass: Biomass Tablets at 20,000 PSI

MU's Bradford Research and Extension Center farm and a local business have built a machine that can compact corncobs, switchgrass and other biomass so four times as much material can fit in the same amount of space.

Instead of needing an 18-wheeler truck to move biomass to burn as fuel for electricity and ethanol, the same amount could be transported in a dump truck. _Missourian

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Biomass is an inherently bulky and clumsy material for transport. Finding ways to compress and/or densify biomass very close to the source is crucial toward building a thriving biomass economy. Otherwise, a significant amount of energy will be wasted simply transporting the biomass to pre-processing, processing, and refining facilities.

Current methods of densifying biomass include compression into pellets and briquettes, and fast pyrolysis conversion to bio-crude. But those processes involve complex multi-process machines which are difficult to transport. University of Missouri ag researchers along with collaborators have developed a special hydraulic press at 20,000 psi (as opposed to 3,000 psi typical for briquette presses) which achieves an almost 20% improvement in mass compression over briquettes and pellets, and almost 4 X better mass compression than commercial balers.

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.” _BiomassMag

As commercial versions of these presses become available, private startups will move from farm to farm -- or from farm region to farm region -- to compress biomass for more convenient and economical hauling to either point of use, or further processing into fuels or materials.

The tablets could provide fuel for co-firing with coal in stocker and fluidized-bed boilers for power generation, fuel for heating buildings and feedstock for producing charcoal. Primary markets would be power plants and ethanol plants. _MUNews

As economies of scale bring the costs of production down, individuals and communities may elect to install their own boilers to provide combined heat and power using compressed biomass.

One ton of compressed biomass is roughly equivalent to 3 barrels of heating oil in energy content. The biomass press described above can use a wide range of raw biomass without having to grind or heat the feedstock before compression into tablets.