A comparative classification efficiency of hydro cyclone and high frequency screen – an experimental study

In coal preparation plants, classifying cyclones are commonly used to generate the pre-classified feed to the Reflux Classifier (RC) from coal fines. However, the efficiency of classification cyclones is low and generates a high amount of fines in the RC feed resulting in poor product quality. To address this issue, high frequency (HF) screen was explored as an alternative to classifying cyclone to generate desired RC feed. In the HF wet screening experimentation, the effect of four critical operational parameters such as feed rate, feed density, spray water and aperture size on the classification efficiency was investigated comprehensively. The overall screening efficiency of HF screen is in the range of 89-98%. HF wet screen generates lesser average percentage of fines (<250μm) at approximately 10% compared to 30% for the classifying cyclone. The classifying cyclone performance curve was modelled using modified Plitt's equation and imperfection in the range of 0.3 - 0.5. The corrected cut size (d_50c) of the classifying cyclone was in the range of 130 -180 μm in comparison to ~250 μm for HF wet screen. The best operating conditions observed were at the aperture size of 230 μm, feed rate of 236 TPH, feed solids concentration of 12.1% with the spray water of 45 m3/hr.