Turning Slash into Cash

A portable plant might make it economical to transform huge amounts of logging "waste" into energy -- right in the forest.

A small company in Ottawa, Canada, says it has developed an economical way of turning North America's vast supply of forest waste, called "slash," into a carbon-neutral liquid for power generation and chemical production.

Advanced Biorefinery’s modular pyrolysis system is designed for use in the forest. The complete system also includes a reactor and a condenser, not shown here. (Credit: Adam Valenta)

Its approach is built around a modular, quick-to-assemble pyrolysis plant that can follow logging companies into the bush and directly convert their leftover trimmings into a clean-burning renewable fuel.

The trimmings, also known as forest slash, are the unwanted branches, tops, stumps, and leaves that are removed during logging and typically burned in piles at the sides of roads.

It's a tremendous amount of wasted energy. In the United States alone, 16 percent of wood resulting from logging activities is slash, or 49 million tons in 2004, according to the U.S. Department of Energy.

The problem has been that forest slash is bulky, low-density material usually located in remote logging areas, says Peter Fransham, president of Advanced Biorefinery. This abundant, essentially free feedstock is too expensive to collect and transport, he says, particularly if the nearest refinery is more than 60 miles away.

"It doesn't take long before the cost of trucking exceeds the value of the biomass," says Fransham, who's also an engineer and research scientist. So Advanced Biorefinery flipped the problem on its head. "We take the machine to the biomass as opposed to the biomass to the machine," he says.

That machine is a transportable "dry distillation" plant capable of processing 55 dry tons of forest slash per day into a mixture that includes 60 percent bio oil and 40 percent charcoal, ash, and synthetic gas.

The green bio oil -- which contains no sulphur dioxide and half the nitrogen oxide of conventional oil -- can be burned in boilers, turbines, and diesel generators to produce heat and power. It also contains acetic acid, acetol, glyoxal, and formic acid, which can be used in a number of chemical markets, from foods to fertilizer.

And of course the transportation costs are dramatically lowered by processing the biomass on-site and converting it into high-density liquid, which packs a lot of energy in a fraction of the volume, says Fransham, who has been working on his system for 18 years.

"If you look at the value going down the highway, [the contents of] a wood-chip truck has a value of $1,000, whereas a tanker load of bio oil has a value of around $8,000."

A key innovation behind Advanced Biorefinery's plant is its modular and self-sufficient design. The system is composed of six modules, each roughly eight feet high, eight feet wide, and 20 feet long. They're easily transported by container truck and can be bolted together and operational within a week of arriving at a site.

"What they've got at the core works very elegantly," says Rick Whittaker, vice president of investments at Sustainable Development Technology Canada (SDTC), a not-for-profit foundation that provides early-stage funding for clean-technology companies.

SDTC announced in July that it would contribute financing toward a pilot project involving Advanced Biorefinery and a major forest operator in northern Ontario. "Now they've got to prove it works to the customer. They're ready to take it to a larger scale," says Whittaker.

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The fast-pyrolysis process they use is familiar. The plant rapidly heats the biomass to 1,000 degrees F in an oxygen-starved environment, shattering its molecular structure and producing the oil, along with charcoal and gas.

Fransham says many pyrolysis plants, including those based on popular but complex fluid-bed designs, were difficult to scale up without sacrificing modularity. He decided to design a more flexible and simple system in which the biomass is almost instantly vaporized by hot steel shot, which transfers heat more efficiently than other approaches.