Co-firing as Part of the Solution to Dead Biomass in the West

In the midst of severe droughts and diseases affecting large expanses of California, Nevada, and Colorado, some scientists have started to envision a way to address several problems at the same time: using the dead trees to fuel coal plants.

The idea of using biomass to help fuel coal plants is not new: biomass can replace up to 20 percent of the coal used in many burners before extensive retrofits are required. The practice of burning two different types of materials simultaneously, called co-firing, emits less carbon and fewer other pollutants as well. It also makes it possible to use resources that would otherwise go to waste without having to build a new, dedicated biomass power plant. And, it reduces emissions from coal plants still operating.

But the idea of using drought-killed trees in coal power plants has had a mixed reception from environmentalists, industrialists, and researchers alike. Many members of the environmental community have been reluctant to condone any burning of waste biomass in the fear that it is a slippery slope to growing trees strictly for biomass burning.

Burning biomass to generate electricity should be carbon neutral: as they grow, plants absorb carbon from the atmosphere, which is then released again during their combustion. But things can become complicated in practice, and the argument surrounding the carbon neutrality of biomass energy generation is contentious. Trees reach their peak carbon absorption capacity after about 10-15 years of growth. Cutting down large numbers of mature trees can therefore become a significant issue, since young, newly-planted trees lack the carbon absorption capacity necessary to offset the emissions from burning their more mature predecessors. Conversely, proponents of co-firing harvested trees say that with selective logging, the loss in carbon absorption becomes nominal in relation to the carbon savings from co-firing coal and biomass. But what if the trees are already dead? The emission of carbon from the naturally decomposing trees is inevitable, and the potential of these trees to fuel wildfires adds an extra element of concern.

Forest management experts have been struggling with dead tree disposal for years. Dead trees in otherwise healthy forests do not present a problem, but a swathe of dead trees in a drought- or disease-stricken forest represent a major threat. One solution, open pile burning, involves cutting down the dead trees, collecting them, and burning them in a bonfire-like fashion. While this method does mitigate the risk of wildfires, it also emits criteria air pollutants (particulate matter, carbon monoxide, volatile organic compounds and nitrogen oxides), greenhouse gases, and air toxins in an uncontrolled environment. Another practice is prescribed (or controlled) burning, which shares many of the drawbacks of open pile burning. Prescribed burning is a strategy commonly employed by fire companies to create fire breaks, which effectively stops a wildfire from sweeping across a large area that may include vulnerable residential neighborhoods. Prescribed burns also improve wildlife habitat and forage production and facilitate the natural succession of plant communities. There are considerable benefits to burning on-site (e.g., the restoration of nutrients to soil), but there are other alternatives that do not involve burning at all, such as chipping. Chipping takes dead trees, puts them through a woodchipper, then redistributes the fragments onto the forest floor. The wood chips are also conducive to water retention and erosion prevention. However, the wood chips do act as kindling for wildfires, which by some estimates contribute to approximately 30 percent of carbon emissions annually.

These strategies have not come close to attenuating the crisis that the Western United States faces. In California alone, there are 66 million dead trees still standing, and in Wyoming and Colorado, approximately 100,000 trees die every day from the pine beetle, an insect infestation that affects about eight percent of Colorado’s 22 million acres of forest. Additionally, the U.S. Department of Energy estimates that lumber remnants from the logging industry are in excess of 100 tons -- all contributing fuel to wildfires. Western forest regions are also substantial carbon sinks, and risk emitting an appreciable amount of carbon into the atmosphere during the decomposition of dead trees. Forest management services are struggling to address the sheer quantity of dead biomass.

To alleviate the looming threat of unbridled wildfires, organizations have begun to reach out to coal-fired power plants to remove dead trees from high-risk areas and burn them as fuel. Supporters of this solution argue that while biomass energy production does emit carbon, the trees will emit that carbon by decomposing anyway, so we may as well take advantage of the biomass and use it to reduce the amount of fossil fuel burned. Phil Duffy, president of the Woods Hole Research Center and a critic of biomass energy, conceded that “because beetle-kill wood will decompose anyway, […] this case comes closer to being carbon neutral than others.” In fact, there is hope that this large scale retrieval of dead wood will stymie the spread of pine beetles.

Co-firing in coal plants is not the only option to turn dead trees into energy. Colorado’s White River National Forest Service, part of the U.S. Forest Service, has a standing contract with Western Range Resources, which cuts down the area’s dying and rotting trees to transport them to the new biomass plant in Gypsum, only a 30-minute drive away. The company can convert cumbersome logs into wood chips at the chop site, providing an easier and more space-efficient means of transport. Nevertheless, some experts remain wary of using dead trees in power plants because the transport costs seem to outweigh their value as a fuel: “While woody biomass wastes represent a significant renewable energy resource, the cost to process and transport the material for use as fuel to produce electricity often well-exceeds the combined value at the biomass electricity generation plant” (California Agriculture).

While the idea of co-firing rotting trees is still in its relative infancy, many are jumping on the bandwagon as a quick fix to the persistent problem of drought and pine beetles. Though not a silver bullet, it would seem co-firing does indeed have a role to play as we seek to dispose of large quantities of dangerous, dead wood. With climate change catalyzing and intensifying droughts across the planet, forest management in the American West may prove to be a testing ground for the world.

 

Author: Sasha Galbreath