english русский česky

solidifikace,homogenizace,solidifikační linka,peletizace,peletizační linka

Pelletizing of dust particles

Pelletizing is a method of making lumps of dust or sludge material, based on moistening of fine-grained raw material in a rotary equipment. Rotary movement causes that individual particles of the raw material aggregates a creates so-called nucleus that is bundled up with other material and this process creates spherical particals, pellets, of the desired size.

Properties of the produced pellets depend on chemical and physical properties of the bundled up material. Granulometric composition of the primary raw material has the biggest influence on strength and resistance of the pellets. Ussually as smaller grains of the material bundle up, as higher strength of the pellets. Possibility of pelletizing of input material is always necessary verify by half-operating exam and specify suitable additives.

Size of pellets: 4 - 30 mm (can be up to 50 mm)

Input material:

fly ash of power and heating plants,
coal dust and sludge,
foundry dust,
glass batches.

ecological dumping, recycling (reuse), production of artificial aggregate, dusting powder and filling, taking off weight of soil, drainage.

elimination of dustiness, reduction of bulk density of the granulated material, reduction of leaching, the granules keep their shapes, are not dissolved and are rigid and bearable.

Description of technology and scheme of pelletizing line

List of machines and equipment

  1. Pelletizing pans
  2. Double-sprindle mixing conveyor
  3. Dosing conveyor - wastes
  4. Dosing conveyor - additives
  5. Pipeline with fittings and control system dosing of mixing water
  6. Power mains control panel, circuit breakers, frequency convertes, wiring
Description of pelletizing line
Basic technological scheme of line for flue ash treatment is shown here. Flue ash is fed from the tank /1/ by a spindle /3/ in the twin mixer /4/, in which an admixture is fed in case of need. Raw material is premoistened in the mixer in order to reduce dustiness. Prepared mixture is fed in the pelletizing pan or drum /5/. Produced green pellets are fed by the conveyor /6/ to the shipping tank.

Pelletizing of phytomass and waste paper

Pellets producing by pelletizing of phytomass and waste materials, e.g. paper are utilizable like alternative fuel for combustion.

Wood mass (fast-growing woods too), mass of plants (energy plants), waste biomass from plant production and from woodworking, waste material, e.g. paper are utilizable for pellets producing.

Best known are wood pellets, bark pellets, alternative pellets, peat pellets a mixed pellets, producer by mixing e.g. with dust from classical fossil fuel.

Size of pellets 6 - 8 mm - diameter, can be larger too, as for demands of customer

Input material:
  • crushed wood mass, sawdust, shavings
  • milled bark
  • straw, grain (corn) dust, tails, ends from grains cleaning
  • energy plants
  • peat
  • waste paper

Fabrication of artificial aggregate

Production process of ultra-lightweight, resp. artificial aggregate from flue ashes arises from experience with treatment of lumpiness of fine-grained concentrates, especially from sintering (agglomeration) and ore pelletizing. As a matter of this experience it is possible to apply for the fabrication of artificial aggregate from flue ashes the solidification methods for formed batch (e.g. pelletizing) through burning-in at high temperatures or through cold solidification by means of added binding agents. The possibility of use of flue ashes for the fabrication of artificial aggregate is determined by its chemical composition and in particular the content of residual unburned carbon whereas the ash-free dry mass has to be by the Czech standard CSN 722068 up to 6% and the sulfur content up to the maximum of 2%.

Artificial aggregate can be made by two methods:
  1. by sintering at high temperature
  2. by lump making of flue ash and curing of lump made product at normal temperature
Fabrication of artificial aggregate at high temperature
In case of hot solidification, the desired product strength will be obtained by carry-over of the slag component of raw material in the melting and its solidification. That's why the chemical composition of flue ash has a considerable effect whereas the content of SiO2 min. 50%, of Al2O3 20% is recommended, and for fusing point depression CaO or MgO is being added. Optimum fuel quantity is 5 - 10%, and for firing also the residue of undeburnt fuel from primary coal can be utilised. The disadvantage of the heat treatment of flue ash so as to obtain artificial aggregate is a high investment, thermal and thereby also operation exigence of the process.

Fabrication of artificial aggregate at low temperature
These methods are based on addition of binding agents allowing to obtain the strength through physico-chemical changes of these materials. As binding agents lime, cement, water glass can be used, eventually in mixture with other active ingredients. Some flue ashes, especially from fluidized bed boilers show, though hydraulic properties so that the addition of a binding agent so as to obtain sufficient strength is not necessary. This method is compared to hot solidification less capital-intensive and less expensive as for operation. The disadvantage is that the mechanical properties of aggregate are mostly lower than by thermal processes. The production process convenient for the treatment of flue ash lumpiness so as to obtain a suitable size like aggregate is pelletizing.

Use of artificial aggregate
Granulate produced through pelletizing of flue ashes from power stations can be used in building industry, agriculture or for improvement of dumping conditions. The bulk density of such artificial aggregate is lower than that one of natural aggregate. After deposition into ground the granules do not dissolve and keep their spherical shape.

Use in building industry
Artificial aggregate made of flue ashes can be used on construction sites for fillings of excavations or as a partial substitution for natural aggregate in production of concrete and walling components - there was also made a successful try to produce blocks for dry-walling.

Use in agriculture
In case of observance of environmental conditions, the artificial aggregate can be used for improvement of soil.

Use for waste disposal
By making artificial aggregate from flue ashes the conditions for their disposal are improved. If the filling contains min. 50% of pelleted flue ash, the bulk density of filling material will increase of about 15%, i.e. increase in dump capacity. Flue ash in pellets is solidified, i.e. the dump stability is increased and dustiness reduced upon subsequent drying of filling. The conditions for transport of filling material to the dump will be improved - the bigger is the fraction of pelleted flue ash, the more are reduced dustinenss and sticking of material on conveyor belts, resp. transport means.