A University of Washington (UW) team has made new headway on a solution to remove beetle-killed trees from the forest and use them to make renewable transportation fuels or high-value chemicals.
By introducing a fungus that prevents critical nutrients and water from traveling within a tree, the mountain pine beetle has destroyed more than 40 million acres, or about 16 million hectares, of forest in the western United States, amounting to an area the size of Washington state in the U.S. Pacific Northwest.
These trees, which are standing dead sometimes within several weeks of the initial attack, can fall at any moment or add fuel to a wildfire, and scientists and land managers are left scrambling to deal with millions of the precarious dead giants. Harvesting the wood for lumber is out of the question, because the infestation stains the wood and causes the tree to crack on the inside.
"We came up with a different way of converting wood into oil -- that's really the main accomplishment of this project," said Fernando Resende, a UW assistant professor of bioresource science and engineering in the School of Environmental and Forest Sciences and senior author of study published in the journal Fuel.
"Not only do we want to reduce the costs, but we are hoping to increase the value of what we produce so we have a better chance of making it commercial."
Known as "fast pyrolysis," the process of heating wood and other natural materials at extreme temperatures to create oil is being widely explored in research labs across the United States. Each system varies, but the general process involves heating small pieces of organic material in an oxygen-free chamber at about 500 degrees Celsius, until the solid material becomes a vapor. As the vapor rises and moves into other chambers, it cools and becomes a dark brown liquid fuel.
The resulting product, called "bio oil" by scientists, is already used in some European countries.
The beetle-killed trees are a good fit for making bio oil, Resende said, in part because the entirety of a tree becomes extremely dry when it is killed by an infestation. That makes for a simpler fast-pyrolysis process, because it isn't necessary to first dry the wood before heating it to extreme temperatures.
In the UW method, woodchips are placed on a rotating surface and a hot stainless steel plate moves down from above, crushing the wood. The woodchips become hot from direct contact with the metallic surface, and the chemical transformation from solid to vapor begins. The system can break down woodchip-sized pieces, though the UW team has turned an entire log into bio oil.
The researchers said the method could be used in mobile pyrolysis units so dead trees can be processed on site, saving on transportation costs associated with moving large pieces of wood out of the forest. The mobile units -- cylinder-shaped reactors that sit on a small flatbed truck -- are already being used for standard wood-to-oil processing, and the UW team said their improvements could make the process more efficient and cost effective.
"If you can extract the wood and process it using fast pyrolysis, not only will you free up space and safety hazards in the forest, but you also have the organic liquid that could potentially be used for products," Resende was quoted as saying in a news release.