Biomass for the Masses

Darren McAvoy is an Extension Assistant Professor of Forestry at Utah State University and a Fellow of the Society of American Foresters. He directs the Utah Forest Landowner Education Program and chairs the Utah Biomass Resources Group. He was formerly a Consulting Forester and prescribed fire specialist at Inland Forest Management in Sandpoint, Idaho. He was a sawyer on the Montana based Flathead Hotshot Crew and is a veteran of the 1988 Yellowstone Fires. He holds a M.S. in Communications from Utah State University and a B.S. in Forestry from Colorado State University.

Utah Biomass Resources Group

USU Forestry

Science Moab: What is biomass, in a nutshell?

McAvoy: The sun shines and creates these beautiful forests and landscapes through the process of photosynthesis. Something is eventually going to happen with that material, it’s either going to burn or rot, it’s going to be collected, or perhaps some of it’s going to be eaten by animals and humans. Our effort is to collect the unused portion of it, and to try to make a product out of it. And biomass is anything that has ever grown, from animals to plants, and everything in between.

Science Moab: What does your biomass resources group do?

McAvoy: What our main goal turns out to be is reducing hazardous fuels. That’s a forestry term for excess woody debris that exists in the woods. In Utah, it often can be in the form of juniper that has expanded over the last 100 years, which can include upland conifer debris or the leftovers from logging. For harvested timber, only about a third of the lot makes it to the sawmill. If it’s conifer, when it is logged or harvested, they call it whole tree harvesting. They cut down the tree and they drag the whole tree to a central processing facility, and that’s where all this excess material tends to stack up, so it’s already collected in that process. With juniper, that material is very hard to collect and bring to a central point. Most often, juniper has just chipped up and then spread out in the woods. And then we do a lot of work with invasive species, in particular tamarisk and Russian olive. They tend to grow along the river bottoms in Utah and have significant impact on the ecology of those river bottoms. And there’s many efforts going on around the state by the federal and state governments to remove that invasive material.

Science Moab: Can you explain the process of producing biochar?

McAvoy: The biomass group started off in 2009 with a gasifier, a device that we put wood into. We cook the wood at super high temperatures, like 800 degrees Celsius, in the absence of oxygen, and that turns all of that material into a gas. We run that gas through a generator, and we make enough power for about two homes. But, a farmer couldn’t just put a barrel of wood on it and walk away for eight hours and let the woodchips do their work. So that made it highly impractical. My evolution towards burning things in boxes led me from that gasifier to a very sophisticated pyrolysis machine that cooks the wood at slightly lower temperatures and turns it into different products. About a quarter of the material turns into a biochar. Biochar is essentially charcoal intended as a soil amendment. Since that machine was so expensive to operate, we chipped all the material before we put it into any of these higher tech machines. I went to a biochar conference in Oregon and I got exposed to these Oregon kilns, small metal boxes about five foot by five foot. And we take raw logs, not chipped material, so we don’t have a lot of cost and energy into processing it. And so we have a process of burning the wood in those kilns, creating a form of pyrolysis. We call them flame cap kilns, because we load them up with logs up to 10 inch diameter in a crisscross pattern that creates enough oxygen in there to get the fire going. And there’s no openings in the bottom of the kiln, it’s sealed, just the top is open, so we top-light it, which is a critical part of the process. As it burns down, it forms this cap of flames that consumes most of the combustibles as they rise up through the column, resulting in a cleaner and safer burn than open pile burning, which is the standard business practice in forestry when we have excess. All that material is going up in carbon dioxide and other greenhouse gasses when you do that. When we make biochar, we preserve about a third of the carbon in that material. Over the course of the morning, you keep adding as the fire allows, and maybe by lunchtime, you’ll have a kiln full of coals, and that is in fact biochar.

Science Moab: What challenges are you dealing with currently?

McAvoy: Some of the more challenging parts of it right now are the transportation of the kiln. The big box kilns are 2000 pounds, so even though you can drag it up on a trailer and haul it with a typical pickup, that’s still a lot. Tires would melt during the process, so we can’t just put wheels on it. Recently, I saw a portable sauna that is being advertised for rent. It’s got these wheels that raise up and down when they’re not needed. I’m hoping to learn more about that technology, and maybe import it here to see if we can make our kilns more transportable. Another route of investigation I’d like to go down is measuring the air quality impacts from these kilns and do a direct comparison to open pile burning. I’d like to convince state organizations who oversee smoke management to allow us more leeway when we’re using the kilns then with open pile burning, because they are so much cleaner, but I need a fair bit of money to develop that data to do that research.