Biomass Fuel Densification Processing Methods and Equipment

As a new source of energy, biomass is known for its renewable, inexhaustible, cleanliness and convenience. However, raw biomass has many drawbacks such as irregular shape, small buck density, low heat value, etc. The ideal way of utilizing biomass energy is densifying biomass materials into solid fuel such as pellets and briquettes. After densifying, all these above drawbacks can be overcome. In this article, we are going to talk about the densification processing methods of biomass fuel, including the working principles and main components of the equipment for densified bio-fuel. We will also analyze the performances comparison between different types of biomass densifying machinery. As a pellet mill manufacturer, ABC Machinery is doing the best in developing equipment of densified biomass fuel.

pellets briquettesBiomass energy featured of clean, renewable and inexhaustible is in the third place of the world’s energy list. 14 % energy consumption of the world is supplied by biomass energy. Among various biomass materials, agricultural straw is one of the most common one. China for example, a famous agricultural country, has abundant resource of agricultural straw with wide distribution and different variety. In the past years, large amount of biomass is used in countryside of China. But its irregular physical form, low volume density and low heat value make the use of biomass inefficient and difficult to popularize. Plenty of biomass is discarded or burned directly in the field and this way not only produces great pollution to the environment but also waste the biomass resources. The ideal method to make use of biomass is making them into pellets or briquettes by use of densifying equipment such as pellet mill and briquette machine. In the densification process, under mechanical force bulk biomass can be extruded or compressed into solid fuel which is featured of uniform shape and size, high heat value and the volume density can reach up to 600kg/m3. Densified biomass fuel is more convenient and cost less to store, transport and use. It is the excellent alternative for traditional fuel such as raw wood and coal.

Pellets vs. Briquettes

In the international market, pellet fuel and briquette fuel are the two main kind of densified biomass fuel at present. Pelletizing and briquetting share the same raw materials and processing principles. But pellets and briquettes have different size and needs different processing equipment. Referring to size, pellets are generally 6-12mm in diameter (the length is 4-5 times of the diameter). While the diameter of briquettes is larger than 25mm and the length is 50mm or more. Then, from the view of processing equipment, pellets are made by use of pellet mill (pellet press), while briquettes are extruded by briquette press. Besides, briquetting process has lower requirement on the feedstock. Biomass with larger particle size and higher humidity can be made in to high quality briquettes, but unacceptable for pellet mills.

  1. Pellet mills can be divided into flat die mill and ring die mill.
  2. Briquette Press can be divided into piston type press, screw type press and roller type press.

Pelletizing / Briquetting Methods and Equipment

Next, we will show you the working principles and main working parts of pellet machine and briquette machine. The purpose is to offer a reference for the development of pelletizing and briquetting equipment.

Flat Die Pellet Mill

flat die mill

Structure Diagram of Flat Die Pellet Mill

1. Electric Motor
2.Transmission Box
3. Main Shaft
4. Flat Die
5. Pressing Rollers
6. Feeding Hopper

Pellet mill is the key equipment for pellet compression. Flat die mill and ring die mill are the two common types of pellet making machines in the international market. Flat die mills come first. The core part of flat die pellet mill is a horizontal flat die, and a set of roller. Flat die pellet mills can further be divided into die-turning type (rotating die with a set of static rollers) and roller-turning type (static die with a set of rotating rollers). Roller-turning type flat die mill is more popular. Flat die mill has cheaper price, lighter weight and simpler structure when compared with ring die mill.

straw pellet mill
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Working principles of Flat Die Pellet Mill

Start the machine and then feed the raw materials into the mill from the feeding hopper. Under the action of gravity, the raw materials will fall on the top of the flat die. While the roller is rotating on the flat die, the material powder will be extruded through the holes in the die to form pellets and then be discharged from the bottom of the die and fell out of the pellet mill. Flat die type pellet making machine is normally used in small scale pellet production such as home use.

Ring Die Pellet Mill

Working Process of Ring Die
1.Ring Die 2.Pressing Roller 3.Cut-off Knife

Working Process of Ring Die

Structure Diagram of Ring Die Pellet Mill

1.Feeding hopper  2.Conditioner  3.Pellet pressing chamber
4.Gear box   5.Discharge openíng  6.Electric motor

Structure Diagram of Ring Die Pellet Mill

The structure of ring die pellet mill is more complicate and sophisticate, generally composed of feeding hopper, conditioner, pelletizing chamber, electric motor and gear box. The key working part is a vertically mounted large ring die.

ring die pellet presses
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Working Principle of Ring Die Mill

The raw materials are fed in from the feeding hopper and then a screw feeder will send them into the conditioner for the controlled addition of steam. Out of the conditioner, the raw materials will have proper moisture content and ready for pelletizing. In the pellet pressing chamber of the machine, the raw materials will be compressed by rotating rollers and extruded through the holes of the ring die.
Flat die mill and ring die mill are the two main types of pellets. One the other side of the die, formed pellets are cut into uniform length by cut-off knives. Finally, high quality biomass pellets will fall down and be discharged out of the machine. Ring die pellet mill has longer working life, higher efficiency and lower power consumption than flat die mill. The price is relatively higher. Ring die pellet machine is essential for large scale pellet plants.

Briquette Press

Screw Briquette Press Structure
1. Feeding Hopper   2. Heating Element   3. Screw Conveyor   4. Barrel   5. Cut-off Knife
Structure Diagram of Screw-type Briquette Press
Structure Diagram of Piston-type Briquette Press
1. Piston    2.Die   3. Screw Conveyor   4. Feeding Hopper
Structure Diagram of Piston-type Briquette Press
Structure Diagram of Roller-type Briquette Press
1. Feeding Hopper   2. Screw Conveyor   3. Roller
Structure Diagram of Roller-type Briquette Press
 
  • Screw Type Briquette Press: The main working parts are feeding hopper, screw conveyor, heating element, die, barrel and cut-off knife. During the briquetting process, the feedstock is fed from the feeding hopper and then be conveyed through the barrel. The barrel is coated with heating element. When briquetting, the raw materials are pressed to the die, the temperature in the barrel can be increased to 200 ˚C. Under high temperature and pressure, the raw materials will be forced through the holes in the die and be made into briquettes. Because of the high temperature during the briquetting process, the surface of final briquettes are partially carbonized. It is also why biomass briquettes are easier to be ignited and burnt.
  • Piston Type Briquette Press generally includes a piston, screw conveyor, die and feeding hopper. The piston is generally energized by a mechanical flywheel or hydraulic system. The piston reciprocates and extrudes the raw material through the die where raw materials are pressed into a briquette. Compared with other types of briquette presses, piston type press is featured of lower energy consumption and less wear of working parts.
  • Roller Type Briquette Press: A roller press consists of a feeding hopper, a screw propeller and two cylindrical rollers. The two rollers are parallel and rotate on horizontal axes in opposite directions. While the rollers rotating, the raw material are drawn and fill the pockets of the two rollers. In the pockets, the raw materials are compressed and made into briquettes. The production of roller press is also continuous and its capacity is higher than other types of press. However, the durability and density of finished briquettes are lower
briquette presses
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Performances Comparison between Different Types of Densifying Equipment

Types of equipment Ring die mill Screw-type press Piston-type press Roller-type press
Moisture content of raw material 10-15% 8-9% 10-15% 10-15%
Particle size of raw material Smaller Smaller Larger Larger
Wearing of working parts Worse Worse Less Less
Output continuity Continuous Continuous Intermittent Continuous
Energy consumption (kWh/ton) 16.4-74.5 36.8-150 37.4-77 29.91-83.1
Output ( ton/hr ) 5 0.5 2.5 5-10
Density ( kg/m 3 ) 800-1000 1000-1400 1000-1200 600-700
Maintenance requirements Lower Lower Higher Lower
The combustion performance Good Best Average Average
Fuel carbonization  No Yes No No
Gasification adaptability Good Good Good Good
Co-firing adaptability Good Good Good Good
Biochemical transformation adaptability Good Bad Good Good
Products consistency Good Good Bad Bad
 
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