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Finding Redemption in Beetle-Killed Pine Forests

By Todd Murray

Who would have thought that loggers would drive into forests, grind dead trees, and squeeze out jet fuel?

Dr. Fernando Resende and Guanqun Luo, a PhD candidate at the University of Washington School of Environmental and Forest Sciences, are researching “fast pyrolysis” as a way to convert beetle-killed trees into bio-oil.

Renewed interest in bio-oil from wood biomass has arisen for a multitude of reasons. While the idea is not new, there have been major advances in technology, market incentives, and social changes that compel exploration of alternative fuels.

Forests Filled with Dead Trees

Given the perfect conditions, bark beetle outbreaks can leave wide swaths of forestland full of dead trees. Since 1997, bark beetles have affected more than 42 million acres of forestland in the Western United States. About 45 million acres in British Columbia Canada have been affected by Mountain Pine Beetle. Adjacent provinces are also experiencing beetle outbreaks due to forest health and climatic factors.

With the peak outbreaks of the Mountain Pine Beetle beginning to subside, millions of acres of dead pines still stand. Wood quality for the lumber industry is compromised. Wood is stained blue by an infesting fungus that hitches a ride on the bark beetles. Wood moisture is low and can cause cracking, or checking, in milled products. The commercial value of the trees continues to plummet as time goes on. In addition, risk of fire increases as trees begin to fall. In fact, fire risk elevates significantly after 10 years following a beetle outbreak.

Quick Cooking

Fast pyrolysis describes the quick ‘cooking’ of organic matter at high heat in the absence of oxygen to create bio-oil, a free-flowing liquid. Alternatively, slow pyrolysis produces predominantly bio-char, a charcoal solid. There are many ways to create bio-oil using fast pyrolysis. The use of “ablative fast pyrolysis” involves rubbing wood chips against a hot plate, which melts the wood into vapor that is rapidly cooled into the liquid form of bio-oil.

Dr. Resende sees positive attributes found in beetle-killed trees. Up to 90 percent of the wood’s moisture can leave in the first 15 years of beetle-kill. The low moisture content makes beetle-killed trees an excellent feedstock for fast pyrolysis, because wood with high moisture content needs to be dried prior to pyrolysis.

Matching Technology to Feedstock

Through a two-year grant proposal, Dr. Resende set out to test the four different decay stages of beetle-killed lodgepole pine ranging from green trees to trees four years postmortem. A chemical compound profile analysis revealed that even four years after death, the quality of the pyrolysis product made from the trees is not compromised.

Making economic sense to convert forest biomass to fuel has been difficult. Transportation costs from logging sites to conversion facilities quickly lose any attractiveness as distance grows from the forest. Hauling low value woodchips alone doesn’t make economic sense. Woodchips further need to be processed and ground into finer particle sizes. Wood chips require further drying before being processed into bio-oil. Bio-oil then requires upgrading to be used as a transportation fuel. Each handling step of getting usable fuel from the forest costs significant money.

Matching up mobile fast pyrolysis technology to good biomass feedstock helps balance the books on bio-oil. Mobile units that can process the dried beetle-killed trees into a high-value bio-oil product achieve the required economic targets. Using ablative pyrolysis also reduces the cost of grinding wood chips into small particle sizes (particles do not need to be small). Transporting a product like bio-oil with a much higher energy density (more energy per weight) greatly reduces the costs of transportation. Targeting a minimum of seventy-three percent of dry weight into bio-oil offsets the costs of production.

Bench-top Units

Dr. Resende’s lab is in the process of constructing bench-top ablative pyrolysis demonstration units to achieve economically feasible bio-oil yields. Other mobile pyrolysis units have been developed but Resende’s design maximizes the utilization of beetle-killed trees.

As alternative fuels are explored, it is clear that there is no single replacement for fossil fuels. The best route is to match appropriate conversion technology with the appropriate biomass feedstocks. In this case, all the clichés of making lemons into lemonade and finding silver linings apply to the beetle-killed forests of North America.

Todd Murray is the Extension Educator and Director at WSU Skamania & Klickitat County Extension. www.wsu.edu