Before we look at how torrefied wood pellets are made, we need to discuss what they actually are. The best way to think about torrefied wood pellets is as the next evolution of pellet fuel. They are superior in every aspect to standard wood pellets and address some of the current issues with pellet fuels. With torrefied wood pellets the same general process of how to make wood pellets applies. However, there are some important differences which I’ll discuss below.
Torrefied biomass is known by several other names such as ‘man-made coal’ and ‘bio-coal’. That’s because that’s basically what torrefied wood pellets are, man-made coal. Now the difference between bio-coal and fossil fuel based coal is the age of the carbon.
When we burn fossil fuel based coal we are releasing carbon that has been out of the carbon cycle for millions of years. Therefore increasing the carbon dioxide within our atmosphere. However torrefied wood was part of the current carbon cycle, therefore burning this material only returns the same carbon to the existing cycle. The new biomass grown as its replacement will absorb those carbon emissions and the cycle begins again. This is why the process is referred to as been carbon neutral.
How Torrefied Wood Pellets are Made
The video below from Blackwood Technology gives a good overview of their torrefied wood pellet process. The wood pellet making process starts off very similar to the standard process. Virgin wood is first chipped, then processed through a hammer mill. The wood is then dried down from 50% moisture to below 15% with a standard biomass dryer. For normal wood pellet production once below 15% moisture, the material is ready for the pellet mill. However, this is where the process differs from a normal wood pellet plant.
To produce torrefied wood pellets the biomass is then heated to around 300 degrees Celsius in a zero oxygen environment so combustion does not take place. After around 30 minutes this produces a much purer form of carbon fuel, with very low moisture content. The torrefied wood is then processed via a series of ring die pellet mills to produce the torrefied wood pellets.
What are the Benefits of Torrefied Wood Pellet?
Standard wood pellets absorb moisture very easily, hence why they are such a good product for horse bedding. Torrefied wood pellets repel moisture, therefore addressing one of the key issues with current wood pellet fuel. Torrefied wood pellets also produce no smell, no visible smoke and contain a much higher energy content than current pellet fuels. 1kg of torrefied wood pellets contains the same amount of energy as 2kgs of standard premium grade wood pellets.
With a much higher energy density, it means pellet fuel customers would require less pellet fuel deliveries. It also means you only need a pellet store of half the size of that you would require for standard wood pellets. Another benefit is the reduced transportation with torrefied wood pellets. As customers require less fuel to meet their heating requirements, the same pellet tanker can serve double the number of customers.
Is it only Wood which can be Torrefied?
No, you can produce torrefied pellets from any biomass including Switchgrass, Miscanthus, Straw and Hemp. Therefore torrefied fuel technologies have a big role to play in making pellet fuel a more viable option for consumers.