Effective desliming of fine coal between 40 and 100 microns has been something the industry has struggled to achieve. The industry standard is to use classification cyclones for this duty. However, the nature of cyclone classification means that it is not as effective in a coal application as in the separation of other minerals. The density difference between mineral content and coal is such that significant quantities of high-quality oversize miss-reports to the cyclone overflow. This can be proven by simply taking a 40-micron hand sieve and screening the overflow of a deslime cyclone in any CPP.
In addition, the -40-micron material tends to flow with the water split, which is typically 30% to the underflow. Due to the density difference, this misplacement is biased towards particles with high mineral content (ash). With recent advances in spiral technology, that is seeing spirals effective in separating particles down to 40 microns, fine desliming will have to receive more focus.
Vietti Slurrytec is developing a desliming technology consisting of an up-current classifier, combined with a chemical modifier targeting ultrafine clay particles. By dispersing these particles (which would otherwise clump together), they can report to overflow.
The technology has been tested on fine coal in a controlled environment using a bench-scale unit (Exxaro, 2017). The results from the bench-scale testing have shown far more efficient separation at 40 microns than that achievable with cyclones. Vanadium has been selected as Vietti Slurrytec’s local partner in the development of the KraVi in Australia.