Wood Pellet Machine Converts Biomass Into Fuel Pellets

Date: 08/12/2020 08:30:45 From: wood-pellet-plant.com Clicks:

Recently, he received a consultation from a Canadian customer. He said that he needed to buy a wood pellet machine to convert biomass into fuel pellets. He says:"I am very interested in purchasing a wood pellet machine to convert hemp biomass into energy pellets to operate a boiler on my farm. Thank you for your time and have a great day. Cheers Frank."

Biomass pellets are generally a superior fuel when compared to their raw feedstock. Not only are the pellets more energy dense, they are also easier to handle and use in automated feed systems. These advantages, when combined with the sustainable and ecologically sound properties of the fuel, make it very attractive for use. The standard shape of a fuel pellet is cylindrical, with a diameter of 6 to 8 millimeters and a length of no more than 38 millimeters. Larger pellets are also occasionally manufactured; if they are more than 25 millimeters in diameter, they are usually referred to as "briquettes."

Wood Pellet Machine Converts Biomass Into Fuel Pellets

Description of the Pelleting Process

The process of manufacturing fuel pellets involves placing ground biomass under high pressure and forcing it through a round opening called a "die." When exposed to the appropriate conditions, the biomass "fuses" together, forming a solid mass. This process is known as "extrusion." Some biomass (primarily wood) naturally forms high-quality fuel pellets, while other types of biomass may need additives to serve as a "binder" that holds the pellet together.

However, the creation of the pellets is only a small step in the overall process of manufacturing fuel pellets. These steps involve feedstock grinding, moisture control, extrusion, cooling, and packaging. Each step must be carried out with care if the final product is to be of acceptable quality.

Feedstock Grinding

Standard-sized pellet mills generally require biomass that is ground to particles that are no more than 3 millimeters in size. Several types of equipment are available to carry out this task. If the biomass is quite large and dense (e.g., wood), the material is first run through a "chipper," and then run through a hammer mill or similar device to reduce the particles to the required size. Smaller and softer biomass (e.g., straw) can be fed directly into the hammer mill without first being chipped.

Moisture Control

Maintaining an appropriate moisture level in your feedstock is vital for overall quality of the final pellets. For wood, the required moisture level of the feedstock is at or near 15 percent. Other types of biomass have other requirements--you may need to experiment a bit. Moisture can be removed from the feedstock by oven-drying or by blowing hot air over or through the particles. If the feedstock is too dry, moisture can be added by injecting steam or water into the feedstock.

Extrusion

The pellet is actually created in this step. A roller is used to compress the biomass against a heated metal plate called a "die." The die includes several small holes drilled through it, which allow the biomass to be squeezed through under high temperature and pressure conditions. If the conditions are right, the biomass particles will fuse into a solid mass, thus turning into a pellet. A blade is typically used to slice the pellet to a predefined length as it exits the die. Some biomass tends to fuse together better than other biomass. Sawdust is an especially suitable feedstock for pelleting because the lignin that is naturally present in the wood acts as a glue to hold the pellet together. Grasses tend to not fuse nearly as well, and the resulting pellets are less dense and more easily broken. The proper combination of input material properties and pelleting equipment operation may minimize or eliminate this problem. It is also possible to add a "binder" material to the biomass to help it stick together, or to mix a fraction of sawdust, with similar results. Distillers Dry Grains (a product of the corn ethanol industry) are reported to improve the binding properties of some biomass.

Wood Pellet Machine Converts Biomass Into Fuel Pellets

Cooling

Pellets, as they leave the die, are quite hot (~150°C) and fairly soft. Therefore, they must be cooled and dried before they are ready for use. This is usually achieved by blowing air through the pellets as they sit in a metal bin. The final moisture con- tent of the pellets should be no higher than 8 percent.

Packaging

Pellets are typically sold in 18-kilogram bags, which can be easily filled using an overhead hopper and conveyor belt arrangement. The bags should be clearly labeled with the type of pellet, their grade (i.e., premium or standard), and their heat content.

Economic Considerations

The cost of setting up a pellet plant is not cheap; as a rule of thumb, expect to pay $70,000 to $250,000 per ton-per-hour capacity. The wide variation in costs is a function of the size, quality, and availability of the equipment. Larger capacity equipment is often more expensive on a per-ton basis because of the greater durability of the equipment and (usually) higher quality of the resulting pellets. Be cautious about selecting the cheapest available equipment--you may regret it later if the equipment ends up being of poor quality. Another important factor to consider when selecting equipment is the availability of spare parts and repair professionals. In general, about half of the purchase cost of equipment will be for the pellet machine, and half for the other devices.

Operating costs will include the cost of feedstock, energy, labor, and maintenance of the equipment. Typically, pellet dies will need to be replaced after every 1,000 to 1,500 hours of operation.

Energy Requirements for Pellet Manufacture

Pellet manufacture requires quite a bit of energy, both for drying damp feedstock and for running the various pieces of machinery. Large plants typically burn a portion of their feedstock to provide heat for drying, whereas smaller facilities often use other means. As a rule of thumb, a pelletizer requires between 50 and 100 kilowatts of electrical demand for every ton per hour of production capacity. In addition, electricity is usually needed to operate any chopping, grinding, drying, cooling, and bagging equipment that is in use. If a reliable source of electricity is not available, gasoline or diesel-based equipment is available.

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