BioHub Model » Design and operation » Processing

Processing

A terminal might not only be a place where the biomass is stored and reloaded. The biomass can be processed in different ways, making the terminal to be a kind of industry as well. Drying of the biomass is a process that is wanted for energy assortments, but should be avoided for assortments like pulpwood and sawlogs. Comminution and screening are common examples on processes at a terminal, but also debarking might be done. Those processes have been studied in Biohub. Examples on future possible upgrading processes of the material at a terminal are pelletizing and torrefaction.

Comminution

Comminution is a process when the forest biomass is divided in small pieces. This is done on energy assortments before combustion, but also on debarked pulpwood. There are mainly two principles of comminution techniques; chipping and crushing. Chipping is done with sharp tools and crushing with blunt tools. Chipping requires less energy, but the material must be clean from soil and other impurities. Crushing is a less sensible technique and can be done of assortments like stumps with a high content of soil in the material.

Debarking

Debarking is the process when a log is divided in stemwood and bark. Debarking can for example be done of individual sawlogs with a technique for this, or on a continuous flow of pulpwood logs in a debarking drum. Bark is today used for energy production but might in the future be used in other industrial processes as well. More information on bark can be found on the section raw material quality.

Screening

Screening is a process when the smallest fractions and impurities like soil particles are sorted out from a batch of comminuted material. This is done to increase the quality of the material since small fractions like needles for example increase the ash content of a fuel. On the other hand, needles have a high content of certain chemicals that might be of interest for other processes.

Read more about:

Machinery and equipment

Read more about loaders here.
To utilize a tree in pulp manufacturing, biorefining or in energy production, the particle size has to be reduced, i.e. roundwood and other tree-based assortments have to be comminuted. Disc chippers are used in pulp manufacturing to reduce particle size in Nordic countries but them are prone to damage caused by contaminants and have less use as mobile versions. Instead, mobile versions of drum chippers are used in the comminution of the roundwood and forest residues at terminals. Mobile crushers are more tolerant for impurities and can be used when materials containing sand and stones, stumps for example, are comminuted. Here you can read more about comminution of spruce.
Debarking denotes the removal of bark surrounding the stem of a tree. In pulp manufacturing, bark is a component that causes problems during processing and reduces pulp quality and thus bark has to be removed carefully.

Bark is also removed at sawmills and veneer mills. In addition, debarked firewood billets are also sold because debarked firewood produces smaller amount of emissions, especially at the moment when the fire is ignited. Drum debarkers, rotary debarkers and rotor debarkers are used in Nordic countries nowadays but other technologies such as flail chain debarkers, for example, are available too. All of them are available as mobile versions to be used at terminals.
Mobile diesel powered terminal machines are usually used on all small terminals. On large terminals it can sometimes be an alternative with stationary solutions for some of the machines.

Stationary machines have the advantage that they can be electrically powered, but this also put some requirements on the electrical grid. In general, the fixed costs are higher with electrically powered machines, but the running costs and the environmental burden is lower.
Screens can be used to sort particles according to particle size or shape. Controlling chip size, especially chip thickness, is very important in kraft pulp manufacturing for optimal process yield and pulp quality. Screens can be used in energy production to optimize fuelwood quality too. Disc and star screens, bar screens, gyratory screens and roll screens are used at pulp mills to produce optimal chip size distribution and wave screens for removing fines from pin chips. Trommel screens can be used in separating a fines fraction from chips. Both particle density and particle size have effect on separation in density separators. Wind sifters (wind screens) and air density separators are used in pulp manufacturing to sort tree-based components. These can be used to separate particles according to their size or density, separate knots from regular wood chips, for example, but also to separate high-density impurities such as stones. Optical sorters in which separation is based on a particle color are also available. Here you can find more information about screening and sieving of bark, crushed spruce stumps and biomass.