Biomass fuel

Combustible biomasseBiomass fuel wood-energy chipsA quality biomass fuel is made from woodchips and has to meet several quality specifications:
– A particle size fitted for the type of biomass boiler in which the fuel will be used.
– A humidity fitted for the type of biomass boiler.
– Few or no big chunks nor fine particules (sawdust).
– Chips that are not stick-like (sticks have a natural tendancy to stick together, meaning that they tend to stay in the biomass silo instead of being moved by the auger).

In all cases, it is important to check the compatibility between the biomass fuel and the boiler or furnace you want to use. Some biomass boilers will need a high quality biomass fuel with precisely dimensioned particles and no more than 20% humidity, some other boilers will be able to process fuels with some bigger chunks and humidity up to 35% (for example Säätötuli biomass boilers).

Harvesting leftovers used for biomass fuelBiomass fuel is mostly made with branches, treetops, non commercial trees, hog, sawmill leftovers, etc. It is made from residuals and also called wood-energy chips. Wood-energy chips are far from the quality and cost of the woodchips commonly used in the pulp and paper industry.

Accumulating biomass harvester headForestry trailer and crane

The biomass fuel can be harvested on a cost-effective manner with tools connected to a forestry tractor. The accumulating harvester head is a good way to harvest small trees as it does not need to put down a harvested tree, but is able to harvest a bunch before putting the whole lot on the ground. A forestry trailer is then used to get the future biomass fuel out of the woods.

Economical woodchip dryer

Freshly cut wood will usually have a moisture content around 50-55%, which is far too high for a quality biomass fuel (except in huge industrial boilers). It is of utmost importance to lower the humidity.

If fresh wood is chipped, the woodchips will begin to heat up due to a fermentation process. This has to be avoided at any cost as the fermentation will destroy part of the energy content, but also presents two major issues:
– woodchip piles that have been fermenting can catch fire spontaneously.
– the bacteria and yeasts that are fermenting will create spores that will go in the lungs when the woodchip is loaded in a truck or a silo.

Two economical methods to lower the humidity are seasoning and the economical drying solution on the picture above.

If the wood is cut, the branches and trunks can be simply piled in a manner that air can circulate through. If it is left to season as such for about a year, it will naturally drop down the humidity around 35% (ideal to be used in a Säätötuli boiler, but a little high for some other brands).

The economical dryer of the picture above is a low-cost way to dry woodchips during the summer season. It is simply a warehouse (or even a tent) with a floor that can distribute an airflow that is pushed by a fan through the woodchips. This system will not work on freezed wood, but is a good solution on summertime. The air can be heated, but the system will also work with ambiant air. The fan will push the air through the woodchips. The airflow will dissipate humidity, but also help to prevent the fermenting process by feeding oxygen to the microbial livestock in the woodchips. For an optimal drying, it is wise to connect the fan to a hygrometer that will stop the fan when it is raining.

Biomass chipper with feeding conveyorOne of the main steps to produce biomass fuel is of course the chipping of the wood. The quality of your chipper will play a major role on the quality of the woodchips you will produce.

Seasoned wood can be chipped and stored directly after the chipping operation. It is not recommended to chip directly inside the silo of the biomass plant. Direct chipping to the silo may result in compacted woodchips that will jam the system that transfers the woodchips from the silo to the burner. If you wish to chip directly into a biomass silo, it is highly recommended that you direct the output chute of your chipper to a wall. If the woodchips hit the wall and then drop by gravity, the risk of compacting the chips is highly reduced.

If you are using the economical woodchip dryer, it is recommended to make it a multi-step operation: first chip about 1 meter (3-4 feet) of chips on the floor, then let it dry (2-3 weeks on summertime), and repeat the operation by chipping a new layer on top of the dry one.

On this website, we present chippers that have been selected for their ability to produce quality biomass fuel.

You can see the whole process of small-scale biomass fuel production in Finland on the video below.

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