Posts Forestry

An uncomplicated artificial dryer has been developed for drying forest chips.

Finland should increase the use of bioenergy and wood-based fuels, such as forest chips, in particular.

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The wood chip dryer constructed in a shipping container was test last autumn in Raahe. (Photo: Jaakko Repola / Luke)

“Forest chips consist of wood harvested from the forest for use in energy generation.The raw material for forest chips is stored either in stockpiles at roadside landings to await chipping or the wood is transported after storage to terminals or to the end use facility for chipping,” says Juha Laitila, Principal Research Scientist at the Natural Resources Institute Finland (Luke).

End use facilities and terminals have their own wood chippers or crushers, which handle the chipping process.

The most common method is to chip the wood at roadside landings and transport the forest chips to a power plant by wood chip truck.

Forest chips are accumulated especially in the management of young forests, from logging residues in regeneration fellings and from stumps and rot damaged trunks.

New innovations, for example, in forest chip drying, are required in order to utilise this leftover material, improve quality and avoid dry matter losses arising from storage.

Forest chips are used in heating buildings, in small-scale district heating plants and in heating and power plants for towns and industry.

The quality of fuel chips varies, as drying of the raw material is dependent on the weather.

There may be interruptions in the operation of heating plants making it necessary to use other energy sources, such as oil.

Moisture in fuel chips is detrimental, as it affects heating value and the amount of energy obtained from the chips.

“The higher the moisture content of fuel chips, the less energy they provide,” Laitila summarises.

Moisture in fuel chips is detrimental, as it affects heating value and the amount of energy obtained from the chips.

Damp forest chips burn imperfectly, which means that emissions increase.

Weight limits for road haulage have changed and transportation of freshly felled wood has become more cost efficient.

There is new demand for drying technology relating to heat production.

Metsähaketta tehdään esimerkiksi harvennusmetsien energiapuusta. (Kuva: Juha Laitila / Luke)
Forest chips are accumulated especially in the management of young forests, from logging residues in regeneration fellings and from stumps and rot damaged trunks. (Photo: Juha Laitila / Luke)

Luke is involved in a project to develop an artificial dryer for drying forest chips.

Its operating prerequisites and cost benefits will also be evaluated.

Last year, SFTec Oy, a company located in Oulu, constructed a dryer based on its own technology in a shipping container.

“There are a wide range of artificial dryers on the market. The advantage of our dryer lies in that relative to its size the equipment is efficient, easily moveable and it is suitable for various materials, including wood chips,” says Managing Director Jani Isokääntä.

The first drying test has been carried out using stem wood chips.

Laitila and his colleagues are currently calculating supply chain costs based on artificial drying and comparing them with the traditional approach.

He is not going to speculate yet on whether artificial drying is economically sensible.

“The decisive issue is the operating cost and whether the benefits achieved through drying cover the costs it incurs.”

Kosteus on tärkeimpiä hakkeen laatuun ja lämpöarvoon vaikuttavia tekijöitä. (Kuva: Juha Laitila / Luke)
Moisture in fuel chips is detrimental, as it affects heating value and the amount of energy obtained from the chips. (Photo: Juha Laitila / Luke)

Next spring, wood chip drying will be started in Rovaniemi at the heating company of Mikkone Oy, which is both a producer and an end user of wood chips.

“It would be great if we could promise customers wood chips that are always equally dry,” says Managing Director Mikko Sirviö.

He regards the dryer´s energy consumption as the biggest challenge.

He hopes that, for example, waste heat from hydroelectric power plants and closed landfill sites could be utilised in drying wood chips.

According to Isokääntä, the waste heat from heating plants could also be used to run the dryer.

In that case, the forest chips would heat same heating plant whose surplus heat has been used to dry the forest chips.

The artificial dryer has multiple benefits.

“The drying time for forest chips can decrease from months to hours or even minutes. At the same time, quality will improve, as rot no longer has time to affect the wood.”

Money tied up in stocks is saved when the wood is rapidly deployed and more energy is obtained from the dry fuel chips.

During conditions of severe frost, especially, the artificial dryer enables more energy to be obtained from fuelchips.

The forest chips can be dried during milder periods and stored.

The forest chip dryer interests, for example, small heating companies and heating plants on the municipal scale.

“The artificial dryer can also be used by current and future biorefineries and power plants whose operation is based on wood gasification.

Drying is of paramount importance for the proper functioning of the process,” Laitila points out.

Likewise, large farms and greenhouses may be future users of the wood chip dryer.

 

Text: Riitta Salo-Kauppinen, Luke

Photo on top of the page: Jaakko Repola, Luke.

Published in Finnish in Maaseudun Tulevaisuus 23 of January 2017.

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