Types of Coal Upgrading Technologies

Coal and Related Carbon Resources / Lignite, Graphite, Graphene, & Carbon Uses

Date posted: 09/14/16

The U.S. has recently ratified its climate agreement to lower carbon emissions regulations, and other countries around the world are doing the same. With that in mind a number of companies have been focusing on improving the value of low-rank brown coal or lignite coal. These companies take varying approaches, but in general, the main goal is to remove moisture and pollutants, raising the coal calorific value to be more in line with that of high-grade coal. That potential change in calorific value is in itself a strong incentive to upgrade coal, but there are environmental considerations as well. Burning brown coal typically releases high levels of carbon and other pollutants, but upgrading coal reduces these pollutants and lowers carbon emissions. Indeed, brown coal can be even more clean-burning than black or high-grade coal in some cases. Furthermore, an upgrade can also help with transportation issues for coal. Lignite is difficult to move over long distances, but upgraded low rank coal is easier to transport. Coal upgrading technologies have existed for over a century, as the first coal upgrading process was put into operation over 100 years ago in 1855. That method took the form of drying and pressing brown coal at the von der Heydt mine in Ammendorf, Germany, with a patent for a pipe dryer to dry brown coal first being registered in 1884. Four traditional examples of technologies used to dry or upgrade coal include hot gas drying, steam drying, hydrothermal dewatering and mechanical thermal expression. Hot gas drying involves flushing coal with hot flue gas. More specifically, the permitted method of this method is called flash mill pre-drying. That process involves milling and drying raw coal at once in a mill that is aerated by hot flue gas from the upper levels of a furnace changer. Although it is listed as a major coal upgrading technology, hot gas drying is not an efficient method for upgrading coal.