DSS144: Biomass Fibre Pile Management with Dr. Shahab Sokhansanj

In today’s episode of the Dust Safety Science podcast, Dr. Shahab Sokhansanj, who is an agricultural engineer and adjunct professor at the University of British Columbia, goes over best practices for biomass fibre pile management.

Dr. Sokhansanj received his first degree, in power and machinery and agriculture, from the University of Tehran. He then went to Michigan State University, finished his Ph.D. in grain drying, and joined the University of Saskatchewan after a couple of years of postdoctoral work at the University of Minnesota. He worked with issues related to grain storage, grain drying, and later on, the handling of forage material like alfalfa and grasses.

After becoming an adjunct professor at the University of British Columbia in the Chemical and Biological Engineering Department,, Dr. Sokhansanj became involved with the safety aspects of handling wood pellets. He was recently interviewed about safe biomass fire pile management for Canadian Biomass magazine.

Dust Control During Wood Pellet Handling Has Become More Critical Thanks to Recent Sawmill Dust Explosions.

“Of course, dust became one of the major concerns regarding the handling of the material. This became more critical after there were some fatalities from dust explosions in sawmills in Northern British Columbia,” he says. “The Wood Pellet Association became quite concerned about the dangers of dust. So at the University of British Columbia, we have a group for research – Biomass and Bioenergy Research Group. One of the areas that we’re concerned about is material handling and pellet durability, making sure that pellets are durable so they don’t break up into dust particles.”

The Biomass and Bioenergy Research Group (BBRG) is working on preparing biomass feedstock for downstream processing. This material is bulky, usually has a high moisture content, and tends to be contaminated with dirt, soil, stones, and other materials. The BBRG fractionates this material into the right particle size, dries it, and turns it into pellets.

There are challenges associated with long-term storage of these materials on the farm as well as in the forest:

Moisture: Even sawdust will have a high moisture content if it comes from material found on the forest floor. The number one issue that leads to material degradation is moisture. Deterioration means that it self-heats. During that process, the heat will propagate through the pile and may eventually cause combustion.
Contamination: Depending on where it was acquired, some material is contaminated by dirt. Dirty material can cause the pile to be spoiled.
Preservation: Material needs to be preserved from the elements. If it will be stored for a long time, it has to be covered.
Variety of material: Unlike sawdust, material taken from a forest floor is not uniform. It can contain hardwood leaves, softwood needles, and other matter. Each material has its own chemical composition and reacts to the environment differently.

How Can Companies Avoid Smouldering in Their Storage Piles?

Dr. Sokhansanj recommended that companies form small piles instead of large ones, so they can be broken apart and cooled down more easily if self-heating occurs. The temperature and moisture should be carefully monitored to ensure that overly moist conditions do not occur.

“We don’t put pellets or tubes or other forms of biomass in shipping containers,” Dr. Sokhansanj says. “First, you cannot usually fill them up. Usually, you fill them up about half and they shift during the transportation. Containers also go through cyclic heating and cooling. We handle them in a ship’s hold, which is much safer.”

Equally important is equilibrium moisture, which is the moisture content of the material given the relative humidity of the air. It determines how long material can stay in a given state. A pile created in Prince George, BC, will exhibit different behaviour than a pile in a hot place like Alabama or Florida. Air conditions therefore have an effect on a pile’s moisture levels and how long it can be stored.

How Does Smouldering Occur?

When piles heat up, two things happen. One is that the material gives off heat when it absorbs moisture. The other one is oxidation. Air causes the material to oxidize, but the process is much slower than moisture absorption.

“We still don’t understand fully how the material heats up to the point of combustion,” says Dr. Sokhansanj. “We understand how microbial activity is the start of self-heating. Then moisture absorption-desorption might be another, and then oxidation. But how it evolves into pyrolysis, we really do not have a clear pathway yet, and that’s an area where we would really like to continue our research.”

Conclusion

Dr. Sokhansanj encouraged academics to share their knowledge with those in the biomass industry. Methods include publishing articles, participating in events, and working on projects that are as relevant to industry members as possible.

“Keep at it, keep working with them, and make it relevant,” he says. “Show them that you know how they can sustain their industry in a competitive world.”

If you would like to discuss further, leave your thoughts in the comments section below. You can also reach Dr. Shahab Sokhansanj directly:

Email: [email protected]
Website: [email protected]

If you have questions about the contents of this or any other podcast episode, you can go to our ‘Questions from the Community’ page and submit a text message or video recording. We will then bring someone on to answer these questions in a future episode.