Production technology
Standard pellet production plant scheme:
- Raw material storage
- Separator
- Hammer mill
- Pneumatic transport
- Storage hopper of pellet-press
- Pellet-press
- Conveyer
- Cooler
- Vibrosieve
- Packing line
- Big bags
Manufacturing process consists of four stages:
Spliting up
Raw material preparation – uneven byproduct fractions, including lump wastes, laths, slab are split up into sawdust.
The whole process is aimed at reducing the size of raw material fractions in order to facilitate the work of the pellet-press.
First large sized wood wastes are split up into chips in chippers or rollers. The chips go into hammer mill where they acquire final size depending on the sieve hole diameter.
The technological process of the plant allows producing pellets from roundwood, with possibility to use other kinds of raw material – slab, damp lump wastes, damp chips, sawdust, shavings, dry stock
Drying
Split up wood chips go to drum dryer. Extra moisture is bled by hot air produced by heat generator. The temperature of drying agent coming into the drum dryer is about 400⁰C, of the outgoing - 100⁰C. The drying stage is aimed at reducing the natural humidity of wood stock of 40-60% to the level required for pelleting (8 – 14%). Pellet-presses are equipped with moistening systems, which allow overdrying the stock (humidity less than 10%) and bringing it up to required humidity directly before pelleting.
Pelleting
At pelleting stage the dried chips are made into pellets with 6 – 8 mm diameter in special pellet-presses. The process of pellet forming takes place after the raw material gets between rotating die and rollers.
As a result of friction against the walls of the working channel of the die during the process of wood stock pelleting the temperature goes up to 110⁰C and more. At such temperature lignin that is present in wood stock melts and acts as “glue”, which keeps the pellets from fractionizing.
Cooling
Pressed pellets acquire necessary firmness just in the process of cooling.
Packing
Pellets are packed into big bags of 620 – 1000 kg, small bags of 15 – 25 kg and in bulk to various containers (10-20 tons). While packing into big bags a regulated gate is used at the hopper exit point. While packing into small bags s semiautomatic packing line is used.
