How do you make wood pellets?

Wood pellets, a product that until relatively recently was cheap, readily available and environmentally friendly. As prices have spiralled out of control, more people have started to wonder if they can make their own wood pellets. And the answer is yes - you can. And with relatively little effort.

Producing wood pellets requires certain equipment. The most important is of course the pellet press. It processes the raw material into the finished pellets. Whether you also need a mill depends a little on the type of raw material you have. For a homeowner who wants to process downed twigs and branches into pellets, a so-called hammer mill may be needed, which chops the garden brush into a fine sawdust that can then be pelletised in the pellet press. If you are close to a carpenter's workshop, for example, you can at best get sawdust for free, sometimes for a small symbolic sum of money. In this case, no further processing is required, and the sawdust or shavings can be pelletised directly.

The pellet press needs to be a wood pellet press. Not all pellet presses work to produce wood pellets, and most of the machines on the market are actually so-called feed presses. They look very similar on the outside, but differ on the inside. These so-called feed presses are, as the name suggests, designed to press grain and corn. Not wood pellets. Buying the wrong machine can be a costly and tedious affair. It is therefore very important that you make sure that the machine you are considering buying is compatible for wood pellet pressing, even if it is a few thousand dollars more expensive. At Skånekraft, we stock several pellet machines that are designed for efficient and continuous production of wood pellets.

Here are some of our machines designed for wood pellet production

The raw material is at least as important as the pellet press. For pelleting to be an economic solution, including machine purchases, electricity prices and labour time, the supply of raw material needs to be good. And preferably free of charge, or at least very cheap. The operating costs are in most cases quite modest, even with high electricity prices. Even with high electricity prices, a wood pellet press with a 7.5 kW motor consumes less than 7.5 kW in normal operation. So if we assume a crazy electricity price of 10 SEK/kWh, the cost per kilo of pellets will be around 30 öre, excluding labour and raw material costs. The calculation is based on the sky-high electricity price of 10 SEK/kWh, effective consumption of around 5 kWh, and around 160 kilos of finished pellets per hour. Which is roughly in the middle of the capacity of 120-200 kg, for the machine in question.

The best species for pelleting are spruce, pine and oak. Other species are of course also good, but the best results are achieved when pelletising softwoods. Birch, beech and larch should be mixed with other, more easily pelletised species to achieve good results. In the case of birch, this is primarily because the species does not contain the amount of lignin required to effectively bind the sawdust into pellets. Beech and larch are rich in resin, which can cause blockages in the pellet press. However, such a blockage is easy to fix. The die is removed and the pellets are tapped out with a mandrel.

Over the years, a more common material for pelleting has become so-called GROT, or garden rice in common Swedish. Here, a small amount of bark is added to the pellets, which can turn the finished pellets brownish. This pellet can also ash more than regular wood pellets, but this is marginal. And no pellet equipment we have tested to burn such pellets has had any problems handling the amount of ash. The tests have been done in several boilers and smaller pellet stoves. The only noticeable difference is in the ash box. It needs to be emptied a little more often than usual.

The moisture content of the raw material is important. In the large pellet factories around the world, very sophisticated drying systems are used that can dry the raw material with very high precision, sometimes to within a tenth of a per cent. We don't have such systems when we press our own pellets. So for us, moisture meters and natural drying are the way to go. It takes longer to dry manually, and requires a bit of carving to get a feel for what works, but once you have learnt to feel the sawdust with your hand, the moisture meter is hardly needed anymore. Normally, softwoods bind to very fine pellets of around 10-16%. Hardwoods, slightly lower.

When the pellets are successfully pressed, they will be very hot, often steaming, much like a hot cup of coffee. By the time the pellets reach room temperature, they have dried noticeably, and in nine cases out of ten are ready to be burned immediately. During the cooling stage, the pellets also harden, making them more shelf stable. Monitor the cooling process and avoid storage vessels that are too deep, as the moisture that evaporates needs to be able to flow freely without being absorbed by other pellets. Spreading the pellets out for a few tens of minutes on a flat, cool surface, such as a press on a concrete floor, is sufficient. After this time, the pellets can be stored airtight without risk of condensation.

Below is a brief introduction to our wood pellet presses for home use (in Swedish)