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How To Make Your Own Wood Pellets – Small Pellet Mill And Pellet Plant

By Jack Huang    May 19, 2015
Make your own wood pellets by small and industrial pellet mill


Wood pellets review

Over the last decade, there has been a major factor that has a great effect in the pellet fuel market. That is wood pellets, which are the most common type of pellet fuel and are generally made from the waste materials such as dried sawdust, wood shaving, industrial wastes and so on. In general, as a new type of fuel, pellets are widely used in many countries and our daily life because of its characteristic advantages:

Various raw material

In the past, the logs are always regarded as the traditional fuel material. Compared with the logs, wood pellets can be made from any biomass materials such as straws, sawdust, grasses, energy crops, crop straw etc.

Environment-friendly

After the production processing, the pellets contain less water and are denser than logs. It ensures that during the burning, wood pellets release less carbon dioxide to the atmosphere than just burning logs. That is to say, pellets produce less ash and less smoke.

Low-cost

After comparing with many fuel options, wood pellets are a little expensive than wood, sawdust etc. But as for other fuel options such as oil, natural gas or electricity, it is much cheaper. 

Table 1. Comparison of typical fuel options
1 ton of pellets is equal to
120 gallons of heating oil 16,000 ft³ of natural gas
170 gallons of propane 4,775 kilowatt hours of electricity

How to make your own wood pellets with small pellet mill and large pellet mill

Typical production processes in a small pellet mill

Small pellet mill is typically seen in the biomass densification industry. On the market, it is actually equals to the flat die pellet mill. It is mostly for home-use: for heating or animals’ feed and make our life convenient. For example, as for in-housing heating system, you can build your own style by yourself and pellet your own wood pellets. Besides, in order to make different feed pellets to different animals, various aperture or mold can be chosen according to their own requirements.
Production processes includes 3 steps:

First step: Raw material receiving and resizing
Raw materials are various such as wood waste (sawdust, wood shaving etc.), farm waste (straw from plants, corn stalks and corn cobs etc.), yard debris (grass, leaves, tree sticks etc.) and other biomass materials.

The raw materials before and after resized
The size of the raw materials before feeding into the pellet mill shouldn’t be larger than 1 inch (2.5cm), so you should use a hammer mill to reduce the size and make it as small as possible. The hammer mill can run at a high speed ranging from 3000RPM to over 8000RPM. Through the size of holes in the screen, which can range from as little as 1mm up to 10mm or more, the particle size is dictated. Because of a large range of screens to produce various particle sizes, the hammer mills become the most popular choice in pellet production plants.

Second step: Pelletizing

Electric-motor-small-pellet-mill
The dried materials will be forced through the die hole of a small pellet mill with great pressure produced by a roller. Generally, the common types are D type (rotating die type) and R type(rotating roller type). And in order to make the best pellets, different types of engines are available, for example, electric engine, diesel engine, gasoline engine and PTO are all optional. 

The common types: D type and R type 
The common types: D type (die driven type) and R type (roller driven type)

Pelletizing:

The raw materials are forced into pellets with great pressure.

Typical engines of small pellet mills:
Typical engines of small pellet mills: electric engine, diesel engine, gasoline engine and PTO

Third step: Bagging 
After the process, wood pellets will be packaged into bags for better protection and  transportation.

Packaging the wood pellets for better protection and transportation.

Typical production processes in a wood pellet plant

Pellet plant is another important type of pellet mills. And it is mainly consisted of wood chipper, hammer mill, dryer, pellet machine(usually use the ring die pellet machine), cooler and other auxiliary facilities(such as conveyor, packing machine and so on).
Production processes includes 8 steps:

First step: Initial size reduce
A wood chipper should be used to make the raw materials into small pieces.
The raw materials should be pre-processed before the production process. Size reduction is an important consideration in pelletization because it can be the limiting factor in production as well as one of the most costly steps in the entire process. A wood chipper is always used to pre-process the raw materials such as hardwood and so on. After chipping, the chipped woods should be reduced into the proper size, less than 6mm.

Second step: Drying
The air flow dryer is usually used to handle the materials with a high moisture.
The raw materials need to be dried before it turns into pellet mills. As for standard wood pellet plant, the best choice is always the drum dryer, also called flash dryer that works with high temperatures. Totally, drum dryers have relatively low cost and simple operation procedures. They have a tumbler which continually exposes the green material to hot air. The other choice is a flatbed dryer, which works at a relatively low temperature. After drying, the desired moisture content can be achieved.

Third step: Initial sieving
In order to ensure the quality of pellets, impurities must be screened out of the raw materials such as metals, stones or others. Before the raw materials turned into pellets, it should be screened for stones, plastic and other pieces of metal etc. The bigger stones and other materials are separated manually or installing a stone trap to separate the raw materials from the foreign objects. Others such as ferrous metals are picked away with a magnet from the conveying belt.

Fourth step: Grinding
The hammer mill reduce the size of the raw materials.
The grinding is a process accomplished by the hammer mill to reduce the size through the force of blunt hammers to 4-8 centimeters. In this step, the raw materials must be dry. And the size of grind are always controlled by screens.

Fifth step: Pelletizing
In this step, it usually forms the raw materials into pellets. Through the die hole of pellet mills with great pressure, the wood pellets will be extruded by the machines and become hot and soft, which must be sized properly to the operator’s requirements.

Sixth step: Cooling
Air cooling turns hotly extruded pellets into harden and strengthened.
In order to make the best wood pellets, air cooling is the necessary process to turn hotly extruded pellets into harden and strengthened. Once the pellets leave the press, they are very hot and plastic, easily deformable product at this time. Every effort must be made to handle this product as gently as possible until it is cooled, dried and hardened. After cooling, the final moisture content will be as low as 6% and the pellets will be transported through the conveyor belt to the storage shed.

Seventh step: Final sieving
In this step, the formed and cooled pellets are usually screened to remove oversized particles and fines prior to shipment to the customers. The degree depends on local market conditions and individual specifications.

Eighth step: Storage and Packaging
After the production process, in order to ensure a convenient use and better appearance, pellets are packaged into small bags since the pellets are less subject to abrasion during delivery. As for the storage of wood pellets, especially in summer. During the summer, there is a little requirement in the market, so the wood pellets will be stored for a long time. It should be kept in a dry condition, so it is very important that the building is water-tight and the wall can withstand the pressure of the pellets, to prevent rain or condensation. In general, pellets are distributed through truck or other vehicles. 

The production process of a wood pellet plant
The production process of a wood pellet plant: chipping, screening, drying, pelletizing, cooling, packaging, storage and distribution.

Global demand of wood pellets

Wood pellet global consumption prediction

global wood pellet demand prediction
Source: Hawkins Wright, Wood Pellet Association of Canada.
Through the relevant researches in recent years, it is obvious that the wood pellets market has a good future and there is still a big demand of wood pellets over the world.
On the other hand, compared with traditional fuel options, wood pellets are more friendly to the environment. It will be an important part of the development of environment protection. Besides, as a new fuel option, wood pellets can turn the raw materials into fully burning. That is to say, a little wood , a lot heating. So no matter for home-use or for trade, wood pellets still has a good future.