Wood pellets are used both in the home and for industrial applications. The UK is the world leader in wood pellet imports, bringing in over nine million tonnes in 2020.
As the world looks for more sustainable sources of energy to replace fossil fuels, global production of wood pellets has increased dramatically, from around 1.7 million tonnes in 2000 to almost 58 million tonnes in 2021. Wood you believe it? Anyway, here’s the answer to the question ‘how do they produce wood pellets?’
A Short History of Wood Pellets
During the 1970s, a global shortage of oil drove the world to look for a long-term substitute for fossil fuels. Due to their desire to become energy independent – not being at the behest of the world’s major oil and gas suppliers – and having a thriving timber industry, Sweden was the first country to pioneer the development of wood pellets.
They opened manufacturing plants in the early 1980s but as the price of oil recovered, using wood pellets was only of interest to a tiny percentage of people who chose to live ‘off grid’ and was not a viable industry.
However as the 1990s rolled around, a clearer understanding of the need to protect our environment coupled with a stark warning about the legacy of burning fossil fuels revived the world’s interest in wood pellets as an affordable, renewable and sustainable fuel source.
Today, the wood pellet industry is worth billions of pounds and is set to grow substantially over the next few decades. Here’s how wood pellets are made.
How Wood Pellets are Manufactured
Wood pellets are made from all sorts of by-products – sawdust, wood chips and small pieces of leftover wood – from wood manufacturing including timber and furniture makers.
The first step in answering the question ‘how are wood pellets made’ is to reduce the wood to roughly the same size and consistency. The raw materials are loaded into a huge grinding machine where they’re pulverised by heavy steel hammers into uniform pieces.
The small pieces of wood contain around 45 percent moisture so they need to be dried. From the grinder they’re sent to a rotating dryer – not dissimilar to your tumble dryer at home but on a massive scale – where the moisture level is reduced to around 11–12 percent.
The wood is small, but it’s still not small enough, so the next stage is the milling. To get it small enough to be made into pellets, it’s milled into roughly the size of rice grains.
The journey of how wood pellets are produced, from fibrous furniture fragments to fuel, is fascinating, but there are still a few stages to go. From the milling machine, the wood is transferred to a row of presses that make the pellets themselves.
Each press displays a digital readout of the moisture level of the wood to ensure it’s correct. Too wet and the pellets will break up, too dry and they can burn too quickly. As an additional failsafe, random samples are sent to the on-site lab to be tested.
The pellet press is a huge drum with perforated rollers. As the drum spins round, the rollers apply pressure which compresses the fibres by 400 percent. It sends the compressed wood out through the holes and a blade slices it to lengths of around half a centimetre.
The compression generates heat which in turn draws out any tree sap which is still contained inside the wood. The sap – known as lignin – acts as a type of natural glue and it seals the shape of the pellet so they don’t fall apart.
The Finishing Touches
The process of how wood pellets are produced is now complete, but they’re still a bit warm and have a tendency to clump together. A quick fifteen-minute stint in the cooler with air blowing through them dries the lignin, and the pellets separate from each other.
Once the pellets are dry, they’re packed on an automated production line into bags ranging from 5kg up to 1,000kg. Once sealed, they can be shipped out all over the world. This is the final step in the process of how wood pellets are made.