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Char-crossed fuel

The challenge with biochar is holding it all together.

The fine, black soot-like material is a byproduct of biomass gasification. Biochar could be used as a coal substitute if it could be compacted into granules or pellets for easy handling. AURI is working with the Chippewa Valley Ethanol Company (CVEC) in Benson to solve this problem.

CVEC, a 48-million-gallon corn dry mill, operates Minnesota’s only commercial biomass gasifier. The flexible-fuel reactor is powered by wood, corn cobs and glycerin and will eventually supply most of the plant’s energy.

Biochar is produced when organic materials are heated with limited oxygen, a thermochemical reaction called pyrolysis. The process yields renewable biogas — a natural gas substitute, which CVEC uses to run the ethanol plant — and biomass charcoal or “biochar.” When CVEC’s gasifier is operating at full capacity, it will generate about 5,000 tons a year of biochar.

Half carbon, biochar has the consistency of talcum powder. “It’s hard to handle,” says AURI scientist Al Doering. Compacting the material into solid granules or pellets would greatly improve handling ease and safety, he says. Granulated biochar could be blended with other products, moved with standard equipment, and shipped more economically.

But as it turns out, compacting biochar is not easy. Unlike combustion ashes, biochar isn’t the least bit adhesive.

Previous efforts to “densify” the material have failed, Doering says. Yet cost-effective biochar handling is essential for advancing Minnesota’s gasification industry. “We’re going to see a lot more of this material coming onto the market as gasification develops in the state.”

One idea AURI is working on is blending biochar with low-value agricultural fibers, which readily form durable pellets. Fiber candidates include sugar beet processing waste, wood and ground corn stover or other crop residues. Doering is leading processing trials at AURI’s coproducts lab in Waseca.

Meanwhile, Bepex International, a Minneapolis food and materials handling company, is looking at compacting biochar into larger briquettes. “We’ll see what is least costly and most effective,” Doering says.

Green fuel from black char

Solving the handling problem would open up several new uses for biochar: as a soil amendment for weathered, low-organic-matter soils; as a tool to lock carbon in the soil, reducing greenhouse gases; as a renewable fuel.

Using biochar as a renewable fuel is the most promising opportunity at the moment, Doering says, although that could change if Congress funds carbon credits, which would pay for practices that sequester carbon.

CVEC biochar has an energy value of about 7,000 BTUs per pound, says Vincent Copa, the plant’s process engineer. That’s just a little less than wood or sub-bituminous coal. And it does not have impurities, such as sulfur and mercury, that produce harmful emissions, Copa says.

If biochar can be economically pelleted, it could be co-fired with coal, Copa says. CVEC is exploring this possibility with the nearby 17-megawatt Willmar municipal power plant. “Biochar could replace some coal and could also improve emissions,” he says. Willmar Municipal Utilities has already put up two wind turbines and is pursuing other forms of renewable power, such as co-firing corn cobs.

CVEC now pays about $75 per ton to dispose of its biochar in a landfill. Successful densification could save disposal costs and keep a useful product from being wasted, Copa says. “This is important to Minnesota as we develop sustainable green-power systems.”