Abstract

Abstract This study investigates the influence of different operating parameters on the performance of the two density separators to determine their applications and limitations within the fines cleaning circuit. Two types of spirals are tested and results of different operating conditions are compared with those of the water-only cyclone. The following operating parameters are examined: cutpoint control and limitation in relation to size, particle size in relation to sharpness of separation and influence of clay slimes on the performance. The spiral's cutpoints show limited change with decrease in particle size and are mainly influenced by change in feed rate. Generally the spirals cutpoints are lower for the finer particles and higher for coarser particles ( + 0.3 mm) than those of the cyclones. However, the cutpoint control is easier to achieve in the cyclone, particularly for coarser particles. A single spiral is capable of achieving an equal or better separation efficiency (E p and error area) than a two stage water-only cyclone but at higher cutpoint for the 0.6–0.15 mm fraction. The sharpness of separation in the spiral deteriorates slower with decrease in particle size than that of the cyclone. Furthermore, the increase in clay amounts in the feed has no influence on the spiral separation and performance while deteriorating rapidly for the cyclone, particularly with clay contents over 30%. Several advantages of using the spiral are indicated, however, the study also shows that for certain coals using cyclones or combination of cyclones and spirals can help achieve the optimum recovery depending on the washability of fine particles.