The production of fuel pellets from straw can be subdivided into the following technological areas:
I. The raw material storage area:
The moisture content of the raw material should not exceed 10-12% for the subsequent pelletization process to be successful; therefore the collected straw should be stored in bales in a humid-free environment.
II. The grinding area:
In this area the grinding of straw takes place; the processing is done in two stages:
– the coarse grinding stage – during this stage the straw is sent in bales from the storage area to a straw-cutting machine where it is being ground into pieces of chaff 20-80 mm long.
– the fine grinding stage – during this stage the chaff is being fed from the straw-cutting machine into a hammer mill where it is being further ground until the size of particles is fine enough for them to be pelletized. From the hammer mill the ground raw material is being fed into a blending hopper.
III. The pelleting area:
The ground raw material is being fed from the blending hopper into a dispenser, from where it comes in pre-determined doses into a mixer where it is being treated with vapor and, if required, with water; that makes it more conformable to pressing. After that the moistened raw material is being fed into a pelletization chamber, where the pelletization process proper takes place. After being treated by the pellet mill the pellets contain excessive moisture; their temperature is about 80°С; they are also excessively fragile; due to all these factors they are being sent to the next processing stage, which is cooling. During the process of cooling the temperature of pellets drops to the environmental level, the excessive moisture is withdrawn and the pellets acquire the necessary degree of firmness. Certain spilled particles are present in the bulk of the product processed in this way. These particles are being filtered out with the help of a sifting vibrator and sent back for the re-processing.
IV. The packaging area:
The ready-made pellets, depending on the type of an enterprise’s transportation infrastructure and the consumer demands, can be packed into soft "big bag" containers of 500-1000 kg each or be dispatched in bulk.