How to build a pellet plant?

Developing biomass pellet fuel has good ecological benefits and social benefits from the long run. The Chinese government believes that developing the biomass pellet fuel not only protect the environment and mitigate climate change but also promote the development of agriculture continuously. The government has regulated the related policy and taxed to promote the development of the pellet energy industry. Wood pellets have increased tremendously in popularity as a heating fuel during recent year, with many homeowners and commercial facilities choosing pellet stove or boiler over traditional wood-fired equipment due to their relative ease of use. As a result, the demand for fuel pellets has also grown quickly. However, wood is not the only suitable feedstock for manufacturing pellet fuel. A wide array of biomass materials can be used to manufacture pellets.

Under this condition, let’s understand more about the pellet fuel and how to build a pellet plant.

The features of the pellet fuel 
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. 

Raw materials for biomass material includes wood blocks, wood sawdust or saw shavings, bark, tree branches and twigs as well as rice husk, wheat straw, cotton stalks, maize stalks, corn cobs, bagasse, palm EFB, bamboo. As long as the material you have belongs to biomass substance, you are able to turn it into pellet fuel actually.



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. Large pellets are also occasionally manufactured; if they are more than 25 millimeters in diameter, they are usually referred to as” briquettes”.

A high-quality pellet is dry, hard and durable, with low amounts of ash remaining after combustion. According to the pellet fuels institute, premium pellets must have an ash content of less than 1 percent, whereas standard pellets may have as much as 2 percent ash.

A 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.

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, the materials is first run through a chipper, and then run through a hammer mill to reduce the particles to the required size. Smaller and softer biomass 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 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 hit 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 though 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 tend to fuel together better than other biomass. Sawdust is an especially suitable feedstock for pelleting because the lignin that is naturally present in the wood act as glue to hold the pellet together. Grass tends 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.

Cooling:
Pellets, as they leave the die, are quite hot (150C) 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 content of the pellets should be no higher than 8 percent. 

Pellet cooling is a dynamic process that involves simultaneous heat and mass transfer between the pellets and the cooling air. Pellet cooling occurs as a result of both evaporative cooling and convective cooling. Evaporative cooling is the transfer of water from the pellets to the air which results in both moisture reduction and cooling in the pellets. Convective cooling also occurs and depends on the temperature difference between the pellets and the air, the amount of pellet surface area, and the heat transfer coefficient.

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 and heat content.



Select the address of the pellet plant 
In recent years, more and more enterprise enter into the biomass pellet plant along with the development of our country sawdust combustion industry,  what should be noticed during the selection of in address for pellet plant?
1.the sawdust pellet plant (wood pellet plant) should be chosen at the place where there are abundant raw materials for pellet plant with convenient transportation.The field should be close to the traffic arteries. This is not only advantageous to the production and transportation, but also lowered the cost and easy to the selling of the products.
2.The location should be flat in terrain, the earth should be strong and tough and underground water table should be lower with well ventilated, it should avert from the region that may be flooded by water or in the danger of slip or landslide.
3.The surrounding environment of the field should be avert from plant which discharge flammable, combustible and poisonous gas or harmful dust and the residential area; the area around the filed should has spacious temporary places, for the purpose of storage and drying of the sawdust materials.
4.The spot should be suited one's measures to local conditions and economical use of land, which can make full use of the wasteland or idly field.
If it is possible, the original idle place and factory warehouse could be used possible to reduce the investment.
5.The place should be considered the fire prevention problem fully, the neighborhood should have water resources either to meet the demand for production, life and fire control.
6.The area of the biomass pellet plant should be up the standard of the transportation demand and hygiene request during the production processing, and it should be kept the space for development.
7.The palace should be selected nearby the village to solute the labor force problem.

 

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. A pellet mill requires between 50-100 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.

Economic considerations 
The cost of setting up a pellet plant is not cheap; the wide variation is cost is a function of the size, quality and availability of the equipment. Large capacity equipment is often more expensive on a per-ton basis because of the greater durability of the equipment and higher quality of the resulting pellets. Another important factors to consider when selecting equipment is the availability of spare pats 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, pellets dies will need to be replace after every 1000 to 1500 hours of operation.

Technology issues about pelletizing 
There are factors affected the pellet quality during pelletizing process. They are moisture content, compression rate of the die and particles sizes.

Moisture content of Material
This factor will exert a deciding impact upon whether a drying system is needed for a pellet plant. According to statistics and experience of us, moisture content of 13%-15% is commonly suitable for a variety of raw material species. However, fresh wood or agro waste is supposed to be dried prior to pellet mill. Some clients of us even use 50% or 70%, because sometimes raw material is exposed just in the open air. Especially they are dampened by rainfall or socked in rain water or snow water, which demands the moisture content should be lowered. Excessive moisture content of raw material cannot be pelletized and material will stuck together like paste. Not only will efficiency of pellet mill will be affected, but also your budget for pellet plant will be adjusted as well.

Size of raw materials 
Size of material is another pivotal factor influencing pelletizing and your investment in pellet plant. Different sizes of materials will need different technological processes for a pellet plant design. For example, if you put rice husk into use, there will be no need for you to use hammer mill or another kind of crusher to dwindle size of material into required one. Generally, the size of material for pelletization remains about 4mm or 5mm. Oversized material cannot pass through pellet mill ring die pores smoothly. Usually pellet diameter is either 6mm or 8mm as per pellet market demands, therefore, oversized material cannot be squeezed via ring die pores. On the other hand, pellet mill performance will stay unstable with electricity current fluctuating, which is harmful to pellet mill per se and the quality of pellets will also be affected adversely, perhaps too much mealy material yet lower formed pellet yield. Hence, material should be reduced in size with either wood debarker, wood chipper, wood crusher or hammer mill. But it depends upon what size of material you will use. Some clients have more wood blocks or wood logs, or tree branches and twigs. In this regard, the abovementioned machines should be put into use before material is poured into pellet mill. Also your budget and investment in the pellet plant should cover those pretreating equipment.

Compression ratio
For example, hardwood demands a lower compression ratio while softwood with a higher one. We once exported pellet plant to Bulgaria where clients used beech as raw material and the compression ratio of ring die remaining 7.5:1. And clients in Indonesia using bangkirai,cruing and meranti batu which will be processed with the compression ratio reaching 5:1and Australian clients have ring die with the value reaching 4.5:1 due to the use of hardwood eucalyptus which happens to be a commonly abundant wood material across Australia. From time to time, hard-to-pelletize raw material should be mixed with binding agent vegetable oil, clay, starch, oil, or wax and besides, raw material under pelletization also goes through steam, a small amount of which is generated under the high temp and high pressure conditions. The scorching vapor is also a catalyst to keep material cured and softened to strengthen its cohesiveness. In summary, material species issue is quite important to be known by pellet plant manufacturer and supplier.

In a nutshell, to construct a pellet plant means detailed negotiations and consistent conversations. Each responsible supplier of equipment should understand the point. Kingman as the professional pellet plant manufacturer and supplier will constantly offer the best solutions for you. We will win more clients with our reliable work and equipment.

---------------------------------------------------------------------------------------------------------------------------------------------------