Influence of hydrocyclone underflow jet diameter on washing efficiency of steam coal from the Cige¾ Colliery

Abstract

The contribution describes results of steam coal washing in water-only (WO) cyclone at various diameter of underflow jets. The overflow jet with the diameter of 68 mm was used. In the case of underflow the following jet were applied: 18 mm, 15.6 mm and 14.5 mm.Washing products were subjected to chemical, grain size and float-sink analyses. Mass yields of these products were also determined to compute the material balance of coal components. Conclusively, the partition curves have been constructed and cut points as well as errors probable and imperfections were determined. The Grumbrecht´s efficiency of preparation was also computed.Ash and total sulphur in dry matter were observed in washing products. The overflow product with the lowest content of ash i.e. 11.62 % was won at the underflow jet diameter of 18 mm, but also at the lowest yield and combustible matter recovery. The highest recovery of combustible matter was achieved at the diameter of 15.6 mm, however at the highest ash content..The grain size analysis resided in the sieving of overflow and underflow products into following classes: –0.5 mm, 0.5–1 mm, 1–2 mm, 2–3 mm and +3 mm. On the basis of mass yields the partition curves were constructed with the aim to determine a classifying effect. Only in the case of jet ratio 68/18 it was possible to determine basic characteristics: d50 = 2.2 mm, Ep = 1.74. It has to be mentioned that the coarser grain went to overflow and finer concentrated in underflow in all three cases. Hence, it is reverse situation as at a classical classifying hydrocyclone.The float-sink analyses were conducted at the following densities: 1.3, 1.4, 1.5, 1.7 and 1.8 gcm-3. According to obtained results, i.e. mass yields into density classes, the comparison of separation efficiency with regard to the grain size as well as to the ratio of overflow and underflow jets diameters has been also carried out.The best sharpness of separation was achieved at the underflow jet diameter of 18 mm. Summary parameters are as follows: Ep = 0.255 and W = 68.58 %. The both values are almost twice higher as in the case of other jet diameters. Also in this case the errors probable for all grain sizes are the lowest and the Grumbrecht´s efficiencies attain the highest values. As to grain size the best results were obtained for the class of 1-2 mm and 2-3 mm, respectively, at all tested diameters of underflow jet.The reduction of underflow jet diameter results in a low enhancement of mass yield into overflow as well as in the increasing of ash content and combustible matter recovery in this product. The separation sharpness at smaller jets diameter was worse and the increasing of slurries creation at the mass yield of 40 % with the ash content over 70% can be observed.

Keywords

• WO-cyclone
• steam coal
• washing
• partition curves