Screw Type Extrusion Pellet Mill

Screw type extrusion pellet mill adopts the screw rod to extrude the biomass material, heating from the outside to maintain the temperature for pelletizing. Among the gaps between the screw rod and the formation sleeve, the lignin content and fiber content in the biomass material is softened without any addictive or adhesives to form the feedstock through extruding.

1.Classification of screw type extrusion pellet mill
According to the amount of rod, it can be classified into single rod screw pellet mill, double rod screw pellet mill and multi rod screw pellet mill. The single rod screw pellet mill is widely used; the double rod screw pellet mill adopts two mutual clenching shifting screw rods. The later two types are not widely used due to their complicated structure, it mainly used for the formation of other feedstock.

According to the shape of cross section, it can be classified into round shape with hollow heart or polygon with hollow heart (square, five positions and hexagon etc.) of pellet mill. Setting a section of round shape of cross section at the bottom of screw rod, the finished product of pellet fuel has a hollow center. Through changing the shape of the cross section of the formation sleeve, the shape of the formation pellet fuel is like square, five positions and hexagon etc.

2. Construction of screw type extrusion pellet mill and the working process
The screw type extrusion pellet mill mainly contains motor, driving part, feeding device, screw rod, formation sleeve and electricity heating controlling etc, the screw rod and formation sleeve is the most important spare parts.

During operation, the collective material which has been cutting or crushed is feed into the feeding hopper of pellet mill through the feeding machine and belt conveyor or by labor evenly, through the pre-compression and moving along the direction of the diameter of screw rod, they enter into the rotary groove at the top of the rod. Under the continuous rotation of extrusion and the high temperature, the biomass material are compressed into the pellet fuel from the formation sleeve and conformal cylinder with a certain density and shape.

3. Features of screw extrusion pellet mill
The main advantages of screw extrusion pellet mill are: simple structure, easy operation, small volume and less occupation. The price of the product is low and it has good result for compression of biomass material like sawdust. The finished product of pellet fuel with hollow center in round shape or other shape are fit for making carbonized fuel. The disadvantages are fast wearing speed of screw rod and formation cylinder. The service life is short and the energy consumption is high per unit, which is about 125Kw•h/t. It has bad performance to the biomass material like crop straw with lower economic efficiency; the matched equipment has bad performance with low automatic degree which is difficult to form scale production, it can not be used for large industrialized applying. Therefore, screw type extrusion pellet mill are mainly used to make machine made charcoal with rodlike shape pellet fuel, to meet the demand of agriculture, animal husbandry, metallurgy, factory, experiment, hotel, civilian barbecue.

4.The screw type extrusion pellet mill with big diameter rod
Due to the big size of rod of the diameter of the screw type extrusion pellet mill, the feeding amount and pushing speed is much faster under a certain rotating speed which generate bigger resistance force. The wearing of screw rod is much faster for the normal formation of biomass material. So, the power consumption of screw type extrusion pellet mill with big diameter rod is big and the service life of the main spare parts is low with low adaptability to the raw material. But the production efficiency is high which can realize discharging with many holes, simple structure and low cost for equipment.

In order to improve the adaptability of rotary type pellet mill with big size of diameter of screw rod, the service life of main spare parts are lengthened to reduce the energy consumption. At present, the pellet mill with big diameter of screw rod is mainly used to process biomass material which is mostly curing material. After treatment of spaying addictive, fermentation, digest and extracting of biomass material, the lignin content and fiber content in the biomass material has been softened with smooth surface, this is called curing material. This kind of extruding biomass material can basically make up the primary disadvantages of the varied formation pellet mill. Adopting the pellet mill with big size of diameter can take good advantages of its won features to effectively reduce the resistance and energy consumption of formation process, to lengthen the service life of screw rod and formation cylinder.

The extrusion pellet mill with big diameter of screw rod has good formation performance to curing material like the cow dung, furfural residue, the residue of vinegar, wine lees and mushroom substrate. It can compress the cow dung as briquette fuel to solve the pollution problem. Except for formation to the above material, it can be used for making briquette, pellet or stick from coal powder and slush.

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Small Pellet Mill
Biomass small pellet mill is a kind of special equipment which takes sawdust, palm, peanut shell and other crops as raw materials and compressed them into pellets. The pellets produced by this kind of equipment have big density, high heat value, combustion resistance. Due to its small volume, simple operation, it can be used for making pellets at home.

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