Intensity in density

AURI evaluates cubing, pelleting and other densification methods that make biomass easier to transport

By Dan Lemke

Waseca, Minn. — Being called “dense” is not a compliment — unless you’re biomass.

Interest in biomass energy is growing nationwide. Power plants are evaluating corn stover, native grasses, straw and other crop residues to be burned for energy. The U.S. Department of Energy has provided more than $200 million to help build six cellulosic ethanol plants around the country.
 

That’s because agricultural biomass contains significant energy. An AURI analysis shows that corn stover contains more than 7,700 Btu per pound, wheat straw generates more than 7,300 and miscanthus, a tall, dense grass, contains more than 7,800 Btu per pound. In comparison, shelled corn contains about 8,100 Btu per pound.
 

But biomass also presents more challenges than most other fuel sources

“In most cases biomass is bulky, light and has some handling, storage and transportation considerations,” says Al Doering, associate scientist at AURI’s coproducts lab in Waseca.
 

“There is usually a small harvest window for biomass, plus the moisture content can vary greatly.”
A large straw bale, for example, “will start to deteriorate if it’s exposed to the elements for very long.”
 

Processing the biomass into smaller, more concentrated forms such as pellets, cubes or blocks could significantly impact biomass fuel use.
 

“Densification is potentially the big breakthrough for biomass,” says Bill Lee, general manager of the Chippewa Valley Ethanol Cooperative in Benson. CVEC is installing a gasification system that Lee expects will be operating by the end of the year. “A lot of effort has been focused on the technology for converting biomass, but not nearly enough on how to move it from the field to the facility. Until we do, it’s difficult to see how we are going to have wide-scale use.”

So AURI is partnering with university researchers, commodity groups and industry to identify the best processes and technologies for densifying biomass.
 

“There are a lot of reasons to look at densification options,” Doering adds. “It can reduce cost and improve storage, it makes it more economical to transport, reduces losses from deterioration from the elements, makes handling easier and more easily standardized and increases combustion efficiency.”
 

The AURI initiative will be conducted in two phases. First, various densification technologies will be evaluated such as pelleting, cubing and making briquettes.

Phase two will include scale testing and validating the most promising technologies.

Given the interest in biomass, densification information will likely have widespread use. Doering says the potential to use agriculturally-based biomass for cellulosic ethanol, gasification, co-firing with other fuels or for pellet-fuel production, depends on the ability to collect, transport and store the feedstock economically.

Lee says identifying breakthrough technologies is vital to developing multiple markets with fuel providers and end users, as well as addressing fuel-efficiency, transportation, storage and retention
concerns.
 

Densifying raw commodities will add cost to the process, Doering says, but “you’ll likely make up for those costs through increased efficiency, reduced transportation costs and end up with a product that is more easily stored and handled than bulk biomass.”

Doering expects to complete the first phase of the initiative later this fall.