Pellets

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Processing of Wood Scrap into High-quality Pellets
Pelletising of Wood Scrap

• The technology of pelletising has got its roots within industry of animal feed. About 50 years ago this kind of compaction had been industrially used for the first time.
  
• The advantage of pelletising is mainly to be seen in the minimization of volume.
  
• Pelletising of wood scrap has become accepted only in the last years.
  
• Wood pellets are produced out of natural, dry strand and sawing scrap, which are by-products of the wood-working industry.
  

Production Cost

The production costs have to be calculated according to the individual structural condition. When pelletising wet raw material in-house, waste heat from block heat and power plants can be used.

Investment in machinery
Investment in infrastructure
Price for the raw product
Capacity of the plant
Energy consumption and energy costs

Foreign energy input with regard to production of pellets, referring
to the heating value:
Pelletising without drying
Approx. 1,3 - 2,7 %

Pelletising with drying
approx. 8,5 - 16,2 %

Mechanical Stability of Pellets

According to a standardised measurement procedure the corrosion behaviour of the pellets serves as a gauge for mechanical stability. The corrosion stability of the pellets is influenced by different factors: raw material (consistence, distribution of grit size and portion of bark), preparation (drying/conditioning), humidity, technology of pelletising, concept of plant, transport of pellets, intermediate and final storage (moisture absorption).

Erection of a Pelletising Plant
 
In order to fulfil the valid norms of pelletising a plant has to be built as follows:

Drying of strand and sawing scrap, if the moisture exceeds 15 % H2O. Before the milling, the conditioning (preparation) of the ground products, the palletising, the cooling, the storage and the filling a preliminary, efficient selection of metals and non-metals is imperative.

Milling
   

• If the raw products dispose of a very different size they have to be crushed by means of a hammer mill or they have to be screened on a sieve which assures a constant structure. This is a pre-condition for a good pellet quality. Choosing the proper bats and boring of the sieves we receive a product with as few fine parts as possible.
  
  
• Construction of the Hammer Mill

Welded construction of steel jacket
Front doors
Basic frame of solid steel construction for mill and motor
Installed and wear-resistant disc rotor with electrode wheel bearing assembly
Hardened bats adopted to the product
Easy change of the sieve
Rotary current squirrel-cage motor, protection class IP 55, isolation class F
Temperature control of the milling area
Hammer mill, capacity 7,5 – 45 kW
Hammer mill, capacity 55 – 200 kW

Conditioning
 
Experience has shown that an optimum conditioning is absolutely necessary. The sawing scrap is intermediately stored in a container in front of the processing plant. By means of a dosing screw the product is now evenly lead into the processing plant. Based on the measured moisture values, water or steam are added. The shavings are intermediately stored in a maturation container for about 15 – 20 minutes, so that the added moisture is able to penetrate evenly. With this residence time we achieve an even product humidity and thus support the pelletising process decisively.

In order to obtain an optimum conditioning of the pressed goods, the paddles of the processing plant can be regulated with regard to their incline so that the stipulated residence time in
the processing plant can be determined exactly.

Pelletising — Advantages of our Wood Pelletising Press
 
Compact and modular construction
Especially developed presses for the production of high-quality pellets
Easy exchange of the cavity and the roll
Cost-efficient plant from series production
Automatic lubrication
Efficiency of pellet press: 800 – 3000 kg pellets/h (different models)


Important Preconditions for a Trouble-free Pelletising:

Composition of the raw product
Even structure of the product to be pelletised
Sufficiently long conditioning (15 – 20 minutes)
Content of moisture before pelletising: 10 –14 %

A dosing screw with a variable rotation speed carries the product out of the “maturing silo” into the press room where the actual pelletising takes place. Special reels press the material through the borings of a rotating and vertically placed ring cavity. The diameter of the borings and the length of the channel can be adapted to the raw product as well as to the final product. At the exit of the cavity the pellets are cut to the length required.

Cooling

After the pressing the hot pellets are cooled down in a cooler in a way (about 50°C above ambient air temperature) that they can be filled into silos or bags.

The pellets heated up to approximately 90°C are cooled down by means of ambient air in a shaft or band cooler.

A counter flow sucks the air through the pellets. The air withdraws the existing heat.

The air extracted during the cooling-down as well as the fine parts are separated in a cyclone and lead back into the production cycle. After the cooling the pellets are stable and well transportable, and they are carried by means of a mechanical or pneumatic transport into the consignment and bagging silos.