Technological process of production of pellets from wood chips

Wood chips of natural humidity enter the warehouses - «moving floors for wet chips» (pos.1). When its volume is enough, then it is unloaded to the «vibrating conveyor with screen zone» (pos.2), which excludes big pieces from entering the production line.

After sifting, the material is lifted to the required height using a «double chain conveyor» (pos.3) and discharged into a «buffer tank with a multiple dosing screw conveyor» (Pos.4), which provides loading of wet wood chips into a «hammer mill»(pos.5), which grinds the material to a fraction suitable for feeding to the dryer. The crushed material is discharging by «double chain conveyor» (pos.6).

Then it is feeding into the «buffer tank of the dryer» (pos. 7), which dosing material into the «belt-type drying unit» (pos. 9) by the «dosing screw conveyor» (pos. 8). Belt dryer removes excess moisture from the material due to its interaction with high-temperature air. The dried material is unloaded into a «double chain conveyor» (pos. 10), which transports the material to the «moving floor for dry material» (pos. 12). In case the humidity sensors will determine the material moisture level after the dryer is too high (drying technology violation, for example), the automation system will provide release of defective raw materials using «double chain conveyor dumping of sub-standard material» (pos. 11). Thereby, it will exclude the possibility of defective materials getting on the line.

«Double chain conveyor» (pos. 13) unloads the material from «moving floor for dry material» (pos. 12), raises it to the required height and moves to «buffer tank with a multiple dosing screw conveyor» (pos. 14) providing the loading into the «hammer mill for dry material» (pos. 16), which regrinds the dried material to a fraction suitable for pelleting. Meanwhile, «pneumatic separator with built-in magnet» (pos. 15), that is installed in front of the hammer mill, excludes the ingress of foreign inclusions (large fraction, stones, metal particles, etc.). Unloading of crushed material from the hammer mill is carried out by «discharge pneumatic transport unit with a distribution screw conveyor» (pos. 17).

Dry regrinded material is unloaded from the pneumatic unit to the «moving floor for dry material» (pos. 18), and then using «double chain conveyor» (pos. 19) is served in «automatic humidity stabilization system» (pos. 20) which maintains the moisture of raw material at the required level (10-12 %). After the moisture stabilization system, the prepared material is transported to the «batch-mixer» (pos. 22) by a «double chain conveyor» (pos. 21). The design of the batch-mixer provides the maximum degree of material homogenization before feeding to the pellet mill and allows to increase the technological process efficiency and significantly reduce the load on the executive press elements. From the batch-mixer, the material is loaded into the «Promill pellet mill» (pos.23) in which fuel pellets are being formed.

During the pelletizing process, a large amount of steam is produced. Besides, just after the pellet mill, pellets have a high temperature. In order to reduce this temperature «counter-flow cooler» (pos. 25) is applied in which the product is cooling with cold air stream, and special transport systems are used for moving of hot pellets from the pellet mill to the counter-flow cooler – in this case this function fulfills a «chain conveyor belt made of stainless steel» (pos. 24).

To remove the dust during transportation to packaging area a «pellet’s vibration screen» is used (pos. 26). Then, the finished product is moved in «silo for pellets» (pos. 1-30) by «chain conveyors» (pos. 27, pos. 29) and bucket elevator (pos. 28). Packaging of pellets in transport containers occurs in the «semi-automatic system for loading pellets into big bags» (pos. 32), where they are fed from the silo using a «chain conveyor» (pos. 31).

Dust generated at different stages of the pellet production is removed by an aspiration system with a «distribution screw conveyor» (pos. 33). If dry sawdust is available, it is fed into the pelletizing line using the «dry material supply system from the customer's production line» (pos. 34).