Pelletizing

A pellet (english pellet, balls ', ' beads ' from Old French pelote, games Ball ' and Latin pila, play ball ',' ball ',' pile ' - hence linguistic relationship with the pill and the peloton ) is a small body of compacted material in spherical or cylindrical shape. Most often the term is used in the plural, because pellets do not individually but are used as bulk.

The process for the production of pellets, assigned in process engineering of agglomeration is referred to as pelleting. Pelleting is used in many different areas, such as the processing of fuels (eg wood pellets), the conditioning of raw materials and waste and other things. The purpose is to improve the handling of the pelletized material, for example by increasing the density, avoidance of dust and / or improve feed.

Is the pressed material is relatively large ( about 4 cm in diameter ) or in a square shape, it is called briquette. As an intermediate stage today also called Maxi pellets are 16 - 20 mm cross-section produced. This production technology has been developed mainly for pressing wet biomass, but also waste of wood, with the advantage of less energy consumption.

Purpose

Pelleting of a material can offer several advantages:

• Increase in the bulk density: by pressing the pellets, the bulk density with respect to the starting material can be significantly increased. Wood pellets have approximately 650 kg / m³ for example, a multiple higher bulk density than sawdust with about 200 kg / m³. Storage and transport costs are much lighter, and the transport- is increased.
• Improve the handling of the material: By converting the small-scale material ( eg dust / powder, sawdust) into pellets to avoid dust during storage, transport or use. When toxic material such contamination is avoided and combustible materials to prevent dust explosions.
• Standardization of material size: Due to the conversion of starting material into pellets of a certain size an equalization of the size-related properties is achieved. Thus, for example, conveyor systems ( screw conveyors, etc. ) as they come in, inter alia, wood pellet heating systems used to operate reliably. The controllability can be improved.
• Mobility: material must be transported in large quantities, such as firewood and feed can be carried in pellet form by blowing a stream of air quickly and efficiently, for example by a truck in a storage silo.
• Avoiding separation: If the starting material is a heterogeneous mixture of different substances (eg animal feed), the pellet can prevent segregation.

Species

Pelleting is applied in many areas:

• In biogenic fuels: Wood pellets from sawdust, other waste of wood, but also from forest wood are becoming increasingly important. They are usually in pellet fuel. In Germany and Austria wood pellets for pellet boiler according to DIN 51731 or ÖNORM 7135 are standardized. Wood pellets of inferior quality are used as industrial pellets as Beifeuerung in power plants. Are less common
• Peat pellets,
• Straw pellets or
• Residual pellets, for example from waste grain mills

• Sugar beet pulp pellets; in sugar production from sugar beet squeezed the residues are processed into pellets and the animals ( cows ) as feed.

• Intermediate in the pharmaceutical industry for pressing into tablets or capsules for filling in
• Precursors of the iron production are iron ore pellets.
• With pellets of uranium dioxide fuel rods for nuclear reactors in a fuel element factory filled (assembly ) are.
• Catalyst pellets are used in heterogeneous catalysis reactions as the carrier for the actual catalyst

Manufacturing process

A raw material is comminuted and pressed through a die, such as a flat die. This causes the material is compressed evenly and strong. Pellets are always dry. Binder may be used for a better consistency. Wherever the material to be compacted to a sticky, adhesive substance, can be achieved to a granulate with a pelletizing plate, an inclined rotating disk or drum agglomeration. In this way, for example, expanded clay, cat litter is formed, and the like.

Concentrated feed

Feed pellets are made to reduce dusting of the feed and to improve drying.

Wood pellets

The production of wood pellets can be divided into several steps:

• Provision of raw materials: Certain properties must be satisfied by the raw materials, so that on the one hand the production of pellets is technically possible. On the other hand they also affect the quality of the final product. If, for example, not debarked wood used, the ash content over, according to various standards for certain quality classes permissible values ​​may increase.
• Raw material preparation: If roundwood used as may be necessary to debarking. By comminution, e.g. with a hammer mill, chips are generated. The smaller the chip, the better pelletization is possible. By adjusting a water content of 10 to 15%, the bonding properties can be optimized.
• Resource addition: In addition to the naturally present in the wood lignin may be necessary to further binder, such as starch or molasses. Additional tools may be added, optimize, for example, the ash softening.
• Pelleting ( pressing): With a pug mill press, the starting material is forced through a flat or annular die ( flat or annular die ) with the holes according to the desired pellet diameter. The heat generated during compression heat (up to 130 ° C), the binder is activated and provides for a connection of the individual chips. A knife cuts the pellet strings after emerging from the die to the desired length.
• Delivery: The pellets are delivered in bulk in silo vehicles with bubbler or packaged in bags or big bags.

Through various pellet Standards is a classification into different quality classes.

Ore pellets

Ore pellets typically have a diameter of 10 to 15 mm and, in addition to the iron ore and aggregates, so that they can be used without further processing as Möller for the production of pig iron. For pelleting the ore powder is mixed on rotating plates or in rotary tubular drums with water. The thereby forming damp Erzkügelchen are called green pellets. They are then dried and fired 1000-1200 ° C, before the actual ore reduction follows.