Swathes of forest stand dead, useless and dangerous they are victims of the mountain pine beetle epidemic. But where some see disaster, others see opportunity. Researchers at the University of Washington (UW) have developed a practical solution to recycle the dead giants.
Publishing their research in the Journal of Fuel in April, the UW researchers from the School of Environmental and Forest Science outline a new fast pyrolysis method that they believe will enable wide-spread utilization of the beetle-riddled trees as an energy resource.
The outbreak of mountain pine beetles in western North America has destroyed areas of forest the size of Washington State. Cracked and stained, the pine slopes are no good for mainstream lumber and pose a land management problem for the forestry services as the dead trees provide perfect kindling for forest fires and are liable to fall, endangering the public.
“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,” explained Fernando Resende, senior author and UW Assistant Professor of Bioresource Science and Engineering, in a UW press release.
Fast pyrolysis is the quick heating of bio-matter to produce a vapor that is condensed into bio-oil, a liquid fuel. The advantage to the new fast pyrolysis reactor invented by the UW researchers is its capability of processing larger chunks of wood, which could defray wood grinding and lumber transportation costs that have previously acted as a barrier to use of the technique.
“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,” said Resende.
Bio-oil produced by fast pyrolysis is already being used to fuel some European hospitals, and teams of researchers across the globe are experimenting with the technique to produce other forms of fuel, such as gasoline and diesel.
Fast pyrolysis techniques have been in development for 30 years, using different reactor methods to heat bio-matter up to 400-600°C, at 500°C/s, while in the absence of oxygen. The UW researchers were able to decompose larger chunks of wood into bio-oil at equal conversion efficiency to other methods, by using an ablative reactor that rotates the bio-matter while crushing with a heated metal surface.
These new reactors can be converted into mobile units for transportation to sites of forest harvesting and subsequent on-site manufacture of bio-oil. As a mobile unit, the ablative reactor eliminates not only the wood grinding steps that account for 7-9% of current cost but also the lumber transportation step, further increasing the cost efficiency.
The 42 million acres of dead beetle-riddled trees are perfect fodder for fast pyrolysis, already dried out by the feeding of beetle larvae and fungus that the beetles carry. And although the necessity for surface area exposure limits the scalability of the ablative reactor, this is not a concern for the necessarily smaller mobile units to fit onto the back of flatbed trucks.
This article was written by Louisa Cockbill, a writer for dusk magazine. To learn more about mountain pine beetles and how the forestry services are responding to the epidemic see the supporting post on Louisa’s blog: Science FYI.