Briquetting
The briquetting is a process of press agglomeration of materials. This agglomeration of the particles under increased pressure allows dust or chips to be compacted into cylindrical or octagonal briquettes . Initially developed for dusty fine coal, the process is now used for numerous materials. For example, wood dust and chips are compressed into wood briquettes , and grinding and milling waste ( metals , foam polystyrene , chips and other plastics), furnace dust, peat , waste paper , fine fractions from natural fiber processing and even sewage sludge are compressed in this way.
Functionality and properties
In press agglomeration, heaped up particles are compressed by the action of external pressure forces . The number of contact areas between the particles increases; The rearrangement of the particles reduces the porosity and the plastic deformation in the contact area greatly increases the adhesion . As a result of the high frictional forces that occur , local sintering processes can occur. With briquetting, on the one hand the volume of the particles to be briquetted is considerably reduced (for wood briquettes by a factor of about 1: 6 - 1: 8, for expanded polystyrene even by a factor of 1: 200). On the other hand, as a result of the agglomeration, the material acquires properties that are similar or equal to those of comparable solid material (e.g. coal, solid wood, etc.).
Advantages of briquetting compared to the original material are primarily the high density and, in the case of briquetted fuels , the high energy density and the associated fuel homogeneity, as well as the improved metering options. The agglomeration also has logistical advantages (better handling, low dust generation during handling processes) and, due to the low water content, especially with wood briquettes, improved storage stability. By aggregates the chemical and technical characteristics such as the fuel properties at briquetted coal and wood can also be changed. The main disadvantage is the high cost of briquetting (and pelleting), which is offset by the high demand and high oil and gas prices, especially for fuels.
The higher the dust content in the fraction to be briquetted, the more likely the briquettes will crumble. They may disintegrate if stored for a long time. In the case of hard coal briquettes, binding agents such as tar are therefore added during briquetting.
Procedures
There are essentially three methods used for briquetting. In addition to the extrusion presses that are mainly used, roller presses and a press chamber process can also be used. In all three processes, the particles are compressed using external pressure. Today only hydraulic briquetting systems are used almost exclusively for briquetting. To reduce friction and thus sintering, lubricants (such as glycerine , graphite , paraffins ) are often added.
The typical performance range of small hydraulic briquette presses is between 50 and 100 kg / h. In the case of presses for briquetting wood or plastics, special care is required so that no metal parts get into the press and thus damage collets or other tool parts. Due to the considerable hydraulic forces, malfunctions can occur more frequently.
During the war and post-war times, when coal was scarce and expensive, besides the industrial steam, ram or hydraulic briquette press, briquetting by hand or with the simplest self-made constructions was widespread. Above all, paper or sawdust was moistened, pressed together with string or two boards tied together and dried. These homemade briquettes were burned instead of coal.
Briquetting of waste materials
The press agglomeration of metallic and non-metallic raw materials makes an important contribution to the recycling industry. Industrial waste material (chips, dust, sludge, etc.) is compressed in a briquetting press under a high compression pressure and processed into briquettes. The finished briquettes represent a valuable secondary raw material. In contrast to loose metal chips, briquettes can be melted down again without any problems. When briquetting grinding sludge, coolants and lubricants are pressed out, which can also be returned to the cycle. From an economic point of view, the briquetting of waste materials represents a considerable increase in the value of the starting material. In addition, there are advantages through the volume reduction for storage and transport of the material, as well as a reduced attack surface for oxidation processes.
literature
- Karl Schwister : Pocket book of process engineering. 3. Edition. Fachbuchverlag Leipzig / Hanser, Munich 2007, ISBN 978-3-446-41058-9 .
- Hans Hartmann, Janet Witt: Briquetting. In: Martin Kaltschmitt, Hans Hartmann, Hermann Hofbauer (Hrsg.): Energy from biomass. Basics, techniques and procedures. Springer Verlag, Berlin / Heidelberg 2009, ISBN 978-3-540-85094-6 , pp. 265-267.
- P. Pucher, S. Konetschnik: Agglomeration of Fe- and Cu-containing residues. Montanuniversität Leoben, Department of Non-Ferrous Metallurgy, Leoben, Austria 2008.
Web links
- J. Tomas: Agglomeration. (pdf; 2.20 MB)
- www.briquettingsystems.com (English)
- Grinding sludge briquetting