Coal, Renewables

Compactor turns yard waste into coal substitute


COLUMBIA, Mo., Oct. 4, 2000 (St. Louis Post-Dispatch)—While developing a method for sending coal through a pipeline, pipeline researchers at the University of Missouri also discovered how to make logs of just about anything.

They found that if the compacting machine at the Capsule Pipeline Research Center in Columbia is loaded with yard waste or other biomass instead of coal, the result is a very compact biomass log that can be used in an ordinary coal-fired power plant to supplement its fuel.

“Fallen leaves, grass, yard waste — these things are very loose. You can’t just haul it to the power plant and put it in the boilers to burn,” said Henry Liu, director of the Pipeline Center.

To be usable in existing coal-burning plants, the biomass has to be as dense as coal and as easily transported. That’s where the Pipeline Center’s compactor comes in.

Once crushed and ground into burnable powder, the yard-waste logs also burn about as well as coal — with “roughly the same heating value as Wyoming coal,” Liu says.

Several samples of these biomass logs sit in a conference room near Liu’s office in Columbia. Plain office paper has been compacted into a rock-solid slab six inches in diameter and two inches in length. A log made from sawdust has the consistency and texture of sandstone. And in a telling indication of the great force of the compacting machine, an ordinary 2-by-4 piece of lumber has been reshaped into a perfectly rounded cylinder of dark brown wood.

Burning biomass instead of digging coal out of the ground is much better for the environment, because biomass contains far less sulfur and other pollutants than coal, and because the carbon dioxide emitted by burning is readily reabsorbed into living plant life and soil, says Carl Maronde, project manager at the Department of Energy’s National Energy Technology Laboratory in Pittsburgh.

Maronde and the Department of Energy have expressed some interest in Liu’s log compactor because of its relatively low cost compared with other methods of compacting biomass, and because his logs are easy to transport.

“We have a direct interest in looking at the use of biomass for cofiring with coal,” Maronde said. “One of the advantages of the compacting technology by Dr. Liu is that you can save on transportation costs.

“People have used pelletization techniques, but that’s quite expensive. What attracted us to bio-logs is that you make a fairly large piece of biomass. There’s some major economy of scale in not having a lot of little pellets.”

Maronde also notes that, because Liu’s technology effectively turns garbage into fuel, it might prove to be a cheaper alternative to coal in some cases — a strong economic driver for more environmentally friendly power plants.

The primary weakness of Liu’s logs is that they are not resistant to water. Unlike coal, yard waste tends to absorb water quite well and can disintegrate in rain or other inclement weather.

Still, the Department of Energy remains somewhat optimistic, and is considering Liu’s log-compacting technology for an extended trial out of the lab.

If selected for such trials, Liu’s experiments should be completed within three years. Some other projects being considered by the Department of Energy for extended testing in this program are a technology that magnetically separates toxic mercury from coal; a method for recycling the unburned carbon in fly ash; and a composite fuel made from coal and sewage sludge.

For all this, Liu remains eager to point out that the biomass compactor is the very same machine he uses to compress coal for shipping by pipeline.

That’s the great thing about technology, he laughs: “You develop one thing and then it turns out that you can use it for many things you didn’t initially expect.”

© 2000 St. Louis Post-Dispatch via Bell&Howell Information and Learning Company; All Rights Reserved.