How to make pellets from autumn leaves?

One product that has become more interesting to many people recently is leaf pellets. A product that was unthinkable just a few years ago when pellets were a product you bought - not produced on your own. As pellet presses have become more common in garages, sheds and barns, interest in alternative materials has also grown. Leaf pellets are among these.

Leaf pellets are exactly what they sound like: firewood pellets made from autumn leaves. Most people who press leaf pellets do not distinguish between the leaves, but rake and mix freshly. It would certainly be possible to produce pure maple leaf pellets, for example, but there is no evidence that a pure product would be superior to a mixed product.

When we at Skånekraft sent leaf pellets to Eurofins' fuel lab in Lidköping, the results were surprising, surprisingly good in fact. Although the results were not without problems, there were many interesting aspects of leaves as a raw material for pellet production. The report spoke for itself. The energy value of the pellets was a whopping 4.98 kW per kilogram. Almost one kilowatt more than conventional wood pellets. At the same time, sulphur emissions were only a quarter of the average for purchased wood pellets. A modest 0.089 %. The problems started when analysing the ash production. It was high. The different samples showed levels around 1.4 - 9 %. In many cases, too much ash production to be efficiently ash removed from small pellet stoves. However, several pellet stoves have such sophisticated ash removal systems that leaf pellets can be burned efficiently without affecting operation. There will only be more ash to empty.

So the results were a bit mixed. A cheap product to produce, with friendly and environmentally friendly flue gases and high energy content, but with high ash production. In other words, not a pellet for everyone.

Another problem is the amount of leaves produced in a typical garden. Large amounts of leaves on the lawn may look like a lot to the eye, but by the time the leaves are pelletised they have been compacted and take up much less space than the untreated autumn leaves. The weight is always 1:1 though. One kilo of raw material always becomes one kilo of pellets.

A pellet press, and in some cases also a hammer mill, is needed to produce leaf pellets. Whether or not a hammer mill is needed depends on whether or not a wood pellet press is used. In practice, all of our machines can be used for efficient leaf pellet production. However, the wood pellet presses have a sophisticated grinding function which allows the leaves to be fed into the machine in their untreated state. If instead a so-called feed press the leaves need to be chopped with a hammer mill before being poured into the pellet press. Thus, it is often cheaper to buy a small 4 kW wood pellet press than to buy an equivalent feed press and a hammer mill.

However, if you do not have a pellet boiler or pellet stove, many ash-rich pellet types, including leaf pellets, can be burned in a pellet basket. In such an application, the pellet basket replaces wood and can be a cheap, space-efficient and economical alternative to wood burning. Pellets in a pellet basket burn for a very long time, and a kilogram of pellets can burn for over an hour, with good heat as a result.

Here is an introduction to leaf pellet production in our 7.5 kW wood pellet press