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Lignite Upgrading

AUTHOR: Gordon R. Couch
DATE: May 1990

This report covers the main processes for beneficiation, including drying and mineral matter removal, and of thermal upgrading.

Possible products include:

  • a cleaner fuel from which ash has been removed;
  • a fuel with a higher specific energy or calorific value because of removal of water and/or ash;
  • high-grade briquettes;
  • dried powder;
  • lignite-water slurries;
  • syngas;
  • substitute natural gas (SNG);
  • liquid fuels and/or chemicals.

Lignite is used mainly for minemouth power generation. It is generally regarded as uneconomic to transport over long distances because of the high moisture content and hence low specific energy content. Precautions must be taken to prevent spontaneous combustion. One of the key questions is whether lignite can be upgraded into a form of energy which is economically transportable other than by power line. This could either be a more energy-dense solid fuel for a remote power station or it could involve the use of the energy in another form. Various possibilities are being actively investigated.

There is a group of processes involving the removal of inerts, mineral matter and water, but which leave the carbonaceous material unchanged. There are also processes which involve thermal upgrading where there may be evolution of oxygenated compounds and of some volatiles, resulting in an increased dmmf heating value of the coal.