The Art and Advantages of Briquetting
Biomass is recognized as an efficient and an environmentally friendly alternative to fossil fuels. Densification of biomass is an important element in trading and handling biomass, as densified fuel offers logistical advantages, and becomes a commodity ensuring high energy content and homogenous quality. Within densification, pellets are best known, but briquetting offers many alternative advantages.
Traditionally, briquetting technology was established for developing countries to produce briquettes of local residues, for use in household cooking stoves and restaurants. Later, as the capacities of the machines increased, briquettes were used in industrial boilers to create heat, steam and power for industry and power plants. Within the past 20 years, briquetting has also found its way to households in industrialized countries as consumer logs for wood-burning stoves and fireplaces.
In recent years, as the focus on renewable energy has grown, the applications for briquettes have grown concurrently, as have different technologies and new applications.
Briquetting technologies include mechanical briquetting presses, hydraulic briquetting presses and screw presses; it is important that customers select the best technology for their applications.
The mechanical briquetting press is built like an eccentric press, and has a very simple design. A constantly rotating eccentric, connected to a piston, presses the raw material through a conical die system, where the briquettes are being formed. Large flywheels secure a very quiet and balanced operation. The press operates with 270 strokes per minute. The briquettes are cooled and hardened in a cooling line, which also serves as transportation of the briquettes. The presses work fully automatic, resulting in a smooth operation with very little maintenance and service. The robust design ensures a long life span and the presses can operate up to 7,000 to 8,000 hours per year.
C.F. Nielsen has more than 70 years’ experience with briquetting machines and, over the years, has developed new equipment and increased capacities, so that the range is now from 200 kilograms per hour (kg/h) up to 5.000 kg/h per machine. The briquettes can be produced in sizes from a diameter of 50 millimeters (mm) to 120 mm, and in square form from 55 mm by 55 mm to 100 mm by 100 mm. Other shapes can also be produced.
The main advantage of a mechanical briquetting press is that the press can be used both for consumer logs and industrial briquettes for boilers. Industrial briquettes can either be made as short pucks, at random lengths or cut to a defined length. Further advantages are high capacity, low production costs, and multiple densities.
In a hydraulic press, the raw material is pressed into a precompression chamber by a dosing screw. In the chamber, the exact amount of material is precompressed. The main piston transfers the raw material into the die that forms the briquette into its final state and required density.
The compression process of a hydraulic press is relatively slow. The compression cycle can be between six and 25 cycles per minute, depending on the amount loaded or the density of the briquettes. Hydraulic briquetting presses were traditionally small, with capacities from 50 kg/h up to 200 kg/h. Briquettes were round, with a diameter of 50 mm to 75 mm. However, today, hydraulic briquettes can be made in primarily rectangular forms with a capacity up to 1.5 tons per hour. The traditional size is 150 by 60 mm, but bigger briquettes can be made.
C.F. Nielsen’s BPH-Quattro briquetting press, a hydraulic press has a capacity of up to 600 kg/h. The briquetting press is a self-contained unit, with a small dosing bin, PLC control panel and the briquetting press. The press can produce briquettes with a high density due to a large main motor and cylinder.
The rectangular briquette is a uniform-sized briquette that is easy to store. The briquettes have a lower density slightly below 1, which gives a shorter burn. The press can produce good briquettes from mixed materials of larger particles, and is very compact. The briquettes are typically used as consumer briquettes for fireplaces and wood-burning stoves.
In an extruder briquetting press, the raw material is fed into a chamber by a feeding screw. The raw material is compressed by a compression screw into the conical die and extension die. The compression screws are conical in shape. The screw operates with approximately 800 revolutions per minute, and during the process high heat—up to 300 degrees Celsius—is being generated in a combination of friction and heating of the die system.
The BP Shimada Screw Press has capacities up to 500 kg/h. The press is a self-contained unit with a small bin, PLC control panel, smoke hood and saw. The screw press is a machine for high-quality briquettes with a very high density. The machine is a more delicate press, requiring very homogenous raw material with very fine particles (between 2 and 6 mm) and the moisture content between 6 and 8 percent. If these requirements are met, the machine will produce state-of-the-art briquettes that will burn longer than all other alternatives. The briquettes are typically used as consumer briquettes or logs for fireplaces and wood-burning stoves.
Recent Trends, Projects
Today, briquetting is obtaining renewed attention. A briquetting machine is more simple and easier to operate, which opens new possibilities in new markets such as Africa, Asia and Latin America.
Furthermore, briquetting presses can handle a larger range of raw material such larger particles, waste with higher ash content and special raw materials. Some examples of these applications include the following.
• The world’s largest plant for consumer logs. One of the largest producers of pallets wanted to produce more than 100,000 tons of briquettes per year, with exact weight of each package at 10 kg. A line of 12 BP6500 briquetting presses, automatic saws with check weighing systems was delivered.
• Reducing deforestation. In Kenya, 65 percent of energy comes from wood from forests causing deforestation. At the same time, agricultural residues are burned in the field. Waste from pineapple fields are now being briquetted on four BP6510 briquetting presses with a total capacity of 6 tons per hour, improving sustainability.
• Creating value from waste. In New Zealand, a company was looking to find a solution for the dust byproducts from their MDF production. The dust produced during the manufacturing process needed careful and costly disposal. The dust was converted to briquettes and sold to a greenhouse, turning the waste into a considerable profit maker.
• Getting the best of demolition wood. A German company had a trucking business collecting different types of waste. The best raw material, including old pallets, is now being used for consumer logs. The company has three BP65100 briquetting presses with a total capacity of 3.5 to 4 tons per hour.
• Low cost for production of torrefied wood. Torrefied wood is a difficult raw material with high friction and very little binding in the raw material. Briquetting has a considerable lower power consumption and a general lower consumption. Several presses have been sold for laboratory testing and production lines.
• Increasing gas production in anerobic digesters. Normally, wheat straw cannot be utilized in biogas plants, as straw cannot absorb water. When straw is being briquetted, the process creates small steam explosions, which together with high heat and mechanical treatment, changes the structure of the straw. Adding 10 percent briquettes to animal slurry can increase biogas production by 150 percent.
• Turning refuse-derived fuel (RDF) and solid recovered fuel (SRF) into a profit maker. In many countries, RDF/SRF is a waste that costs high tipping fees to dispose of. When the raw material is converted into briquettes, it becomes a fuel that can be sold for energy.
• Briquettes for cooking stoves. In Africa, charcoal is being used for cooking stoves. A “village concept” has been created, enabling small villages to convert agricultural waste and other types of waste to small briquettes for cooking.
Contact: Esben Mikkel Vestergaard
Area Sales Manager, C.F. Nielsen