Home News X-ray transmission technology ramps up efficiencies in dry coal beneficiation

X-ray transmission technology ramps up efficiencies in dry coal beneficiation

Dry Coal Destoning

Published: 11/11/2010
Category: Products

In the latest advance in the dry coal beneficiation of coal, world leader in ore sorting systems CommodasUltrasort has introduced cutting edge X-ray transmission (XRT) technology capable of delivering separation efficiencies equal to conventional wet processing methods while reducing operational costs and enhancing downstream processing.

Most coal beneficiation plants use water intensive separation processes such as dense medium separation (DMS) or jigging plants. In recent years, interest in dry coal separation technologies has gained momentum because water is becoming scarce resource in many coal producing regions, also resulting in increased costs; dry coal has a higher heating value than wet coal; transportation of wet coal is more expensive and because of the costs involved in the environmental rehabilitation of coal slimes.

"With XRT technology, no slurry is produced, resulting in reduced groundwater pollution due to acid drainage and salt accumulation in water circuits," says General Manager Southern Africa CommodasUltrasort, Lütke von Ketelhodt. "XRT technology is also less capital intensive because it does not require the extensive infrastructure and water handling requirements associated with dense medium separation.
"Another advantage is that de-shaled dry coal will burn more effectively than wet coal, improves efficiencies when generating electricity in thermal power stations. XRT sorting also enables pyrite removal, thereby reducing the sulphur content of the coal."

XRT technology is particularly suitable for the dry beneficiation of coarse coal in the size range -120+50mm at 150t/h and -50+12mm at 80 tons per hour. Moisture content does not affect separation efficiency.
In South Africa, two contracts have been awarded to fully explore the benefits of this technology following successes achieved during a full production pilot operation at Arnot in Mpumalanga.
The CommodasUltrasort PRO Secondary XRT sorter installed at Arnot handles 150-200tph of run of mine coal for dry de-stoning and de-shaling. An up-scaling to 500tph or even more can easily be done by combining four of these units. As the installation requires electrical power only and little infrastructure, it can also be provided as a semi-mobile solution.

Sorting by numbers

XRT imaging conducts particle-by-particle sorting, using a dual energy X-ray line-scan sensor, which generates images of the transmitted x-rays. The dual energy X-ray system allows for a rapid approximation of the atomic number range, which is used in combination with the high resolution image to evaluate mineral content and properties. Since XRT does not involve surface layer detection, the technique is insensitive to surface coatings and dust.
Because shale and stone have a higher atomic density than coal, a density can be selected to determine if a particle should be regarded as coal or discard. In effect, this is organic versus inorganic separation, with coal being the organic component. Sulphur, in the form of iron pyrites, is also detected and discarded, thus reducing the sulphur content of the coal.

Test work has shown that the XRT sensor system can also distinguish between and separate different grades of coal at varying ash content criteria.
XRT has proven effective not only for the de-shaling of coal and removing pyritic sulphur but also for separating coal and torbanite, which causes contamination at some of South Africa’s coal mines, adds von Ketelhodt.
“A mix of coal and torbanite isn’t suitable for firing power stations or for export coal. However, this type of oil shale contains valuable smokeless fuel which can be pyrolized and converted into liquid fuel.

“Since coal and torbanite have similar overall rock densities, separation technologies such as DMS or jigging do not work. Sorting on average atomic density, XRT has proven able to separate clean coal from a shale/torbanite mix during the first pass, with torbanite and shale separated during the second pass.”
Tests on a 500 kg lignite sample collected from collieries in Texas also showed the effectiveness of XRT in the removal of pyritic sulphides to produce clean power station lignite. With the separation of pyritic sulphides locked up in lignite, mercury levels have also dropped significantly.
“With sensor based sorting technology gaining more and more significance in the mining and mineral process industry and the proven efficiencies of XRT technology in producing clean coal for further use, we believe this sorting technology has the potential to become an integral component of future dry coal cleaning plants, says von Ketelhodt.