New research finds likely cause, solution for pellet-derived CO

Clarkson University researchers believe they have figured out the cause of wood pellet-derived carbon monoxide, and a potential solution.

The issue has been debated and closely studied after several reported deaths in Europe resulted from exposure to high levels of CO believed to have been generated in certain wood pellet storage scenarios. Multiple studies performed over the last couple of years have presented varying results and conclusions, but Philip Hopke, director of the Center for Air Resources Engineering and Science at Clarkson University, is confident the issue is close to being resolved.

In the latest research performed by Hopke and coauthor Mohammad Arifur Rahman, it was found that as a byproduct of the autoxidation of unsaturated compounds in the wood pellet’s fiber—fatty acids and terpenes (organic compounds produced by plants)—hydroxyl radicals are formed, neutral forms of the hydroxide ion that are highly reactive. When these radicals react with hemicellulose, the research found, it results in CO generation at potentially dangerous levels when pellets are stored in confined spaces.

To understand the mechanistic pathway of CO offgassing, Hopke and Rahman conducted several experiments during which CO was measured and evolving organic compounds were analyzed using gas chromatography-mass spectrometry. The ultimate conclusion of the work was that if autoxidation initiation can be eliminated, CO offgassing from pellets would be substantially reduced. The resulting research paper states, “Destruction of the reactive compounds with ozone led to a suppression of CO formation, suggesting an approach to process the wood fiber that would result in low or no CO emission wood pellets.”

On treating wood fiber with ozone as a means of CO-generation prevention, Hopke said he is fairly confident in what the researchers believe is a workable solution, and that further research has been granted additional support by NYSERDA, funds that will be used to purchase an auger and perform lab studies. “Once we know what time and concentration of product is needed to passivate the fiber—previously we saturated the fiber—we will try pressing pellets,” he said. “We believe we can pump ozone into the auger in the pellet mill that brings the fiber to press, so it is already small, dry particles.”

The researchers hope to do a full-scale trial later in the year, once the lab studies are complete.   

On potential challenges, Hopke said whether the ozone and other oxidants might reduce the amount of lignins and interfere with the binding of the pellets is an issue to be tested during the lab studies, but he is doubtful it will be an issue. “That would be a big problem,” he said. “We don’t think that will happen, but we want to be sure before moving forward to the full-scale trials.”