Briquettes versus pellets
The process of pelletizing
Pelletizing is the process of compressing or molding a material into the shape of a pellet. A wide range of different materials are pelletized including chemicals, iron ore, animal compound feed, and more, however, here only mentioned in relation to biomass. Wood pellets are normally used for fuel and pellets from agricultural biomass for animal feed.
The most common pellet mills are ring die mills. In the ring die there are radial slot throughout the die. Powder is fed into the inside of the die and spreaders evenly distribute the powder. Two rollers then compress the powder through the die holes. Two cutters are used to cut the pellets free from the outside of the die. The most normal diameter for pellets is 6 mm, sometimes 8 mm or larger. The high pressure of the press causes the temperature of the wood to increase greatly, and the lignin plasticizes slightly, forming a natural “glue” that holds the pellet together as it cools. Pellet mills are made with capacities from 2-300 kg/h, but the most effective pellet mills range form 2.000 kg up to 5.000 kg/h.
The process of briquetting
A mechanical briquetting press is built like an eccentric press. A constantly rotating eccentric connected to a press piston presses the raw material through a tapered die where the briquette is formed. The tapered die is connected to an extension die that keep the shape of the briquette. Large flywheels secure a very quiet and balanced operation. On a mechanical press the required counter pressure will only be adjusted by mounting a die with a different tapering angel and the length and type of the extension die. C.F. Nielsen has developed a large variety of dies for various types of wood and other biomass in order to cope with customer requirements to the quality and shape of the briquettes.
The most normal diameters for briquettes are 75 mm and 90 mm diameter. A briquetting press generates considerably higher pressure than a pellet mill and a higher temperature is generated by the 270 strokes of the piston combined with the friction through the tapered die. The process forms a natural glue and most often no additives are needed. Mechanical briquetting presses are made from capacities of 150 kg/h and upwards to 3.000 kg/h.
Briquette processing is more efficient than pelleting because the biomass does not necessarily have to be preprocessed or uniformly ground up through a hammer mill, which results in less preparation. Another advantage of briquetting is that production can be decentralized. Briquetting waste byproducts and reusing them onsite for energy rather than transporting them to another location or to a landfill can save logistical and disposal costs. Briquetting generally use less kwH per ton produced. From an investment point of view, the capex and opex costs are less for briquettes than for pellets. With respect to logistical costs pellets are more advantageous when shipping on a vessel as the bulk density is higher than briquettes, however, when shipping on a truck briquettes have the same advantage as the bulk density is sufficient to reach the maximum tonnage on a truckload.
The advantages of biomass briquetting are not limited to being used in modern industrial plants or solid fuel boilers. In developing countries, the use of briquettes is increasing to replace firewood and charcoal and by using many field or process residues deforestation and CO2 is reduced.
Advantages to briquetting versus pelletizing
C.F. Nielsen is recognized as the world leading manufacturer of mechanical briquetting presses and the company continues to develop solutions to make a briquetting press the best alternative for densification of biomass. In the following we have summarized the most important advantages comparing briquettes with pellets:
- Investments costs – are less for a briquetting plant, not only the press itself, but also all other installations such as electrical installation, cooling, size of buildings etc.
- Operational costs – power consumption is less, especially as the raw material does not need to be downsized to the same extend. Spare part costs are lower and operations more simple
- Simple technology – a briquetting press can be operated by skilled laborers and does not need much education
- Moisture content – a briquetting press can handle a higher range of moisture in raw material – from 6-18%
- Decentralized production – briquettes can be made on site where the raw material is, thus saving considerably logistical costs
- Logistical costs – briquettes have a high bulk density, but are in comparison with pellets, best for shipping on a truck as the bulk density is sufficient to reach the maximum tonnage on a truckload
- Developing countries – briquettes produced on a mechanical press can be made from many types of wastes including agricultural wastes and replace firewood and charcoal
|Preparation of raw material*||Briquettes||Pellets|
|Requirement for max particle size||20x5x3mm||2x2x2mm|
|Requirement for moisture content||6-16%||10% +/-0,5%|
* Industrial briquettes and pellets
|Power consumption||35kW per ton||90kW per ton|
|Wear - spare and service parts - clean wood||2 Euro per ton||5 Euro per ton|
|Wear - spare and service parts - abrasive materials||5 Euro per ton||10-15 Euro per ton|
|Man power||1 hour per 24 hour operation||24 hours per 24 hour operation|
* Data based on briquetting press with approx 1500kg per hour
** Data based on general information. Specific data should be obtained from the pellet press manufacturer
|Data of briquettes and pellets||Briquettes||Pellets|
|Max. obtainable density||1,2||1,2|
|Max. obtainable bulk weight per m3||650kg||700kg|