Coal Preparation » Fine Coal
A 480mm-diameter novel classifying cyclone, known as the JKCC, was tested at Dartbrook Coal Handling and Preparation Plant (CHPP) to assess its performance in an industrial environment. The JKCC was installed in a primary CC bank and operated together with other 480mm commercial CCs. The two types of CCs were identical in nominal diameter, diameters of inlet, overflow and underflow and body length.
The JKCC was initially lined with hand-patterned ceramic, whose quality was very poor, while the commercial CC has a smooth polyurethane liner. It was found from a series of tests that an unusually large amount of water (~14%) reported into the JKCC U/F due to flow turbulence inside the cyclone. The JKCC was pulled out for modification - several flanges of the JKCC were re-machined and the liner was changed to polyurethane.
A second series of tests was conducted on the JKCC and a nearby commercial CC in the cyclone bank. The parameters varied in the test work included the position of both the CCs, and vortex finder and spigot for the JKCC, each at 2 levels. The feed pressure was very stable at 151 kPa over all the tests. Cyclone performance was assessed by efficiency curve, the parameter a representing the shape of the efficiency curve and the water recovery to the U/F. The JKCC performance was now similar to the commercial CC in terms of the a value (around 2.10) despite the poor manufacturing quality of the JKCC. The average water recovery in all the tests was lower in the JKCC (4.4%) than that in the commercial CC (5.5%), and the separation size was higher. However, the JKCC performance was not as beneficial as expected from previous pilot JKCC studies.
It was therefore removed from the bank and transported to the JKMRC pilot plant for investigation and further test work. The test work was carried out in a dense medium cyclone tower, and many variables (feed pressure, inlet design, nozzle dimension and vortex finder) were studied. Since the overflow pipe was very long in the test rig, a breather pipe was installed on top of the overflow pipe to prevent siphon effects on cyclone performance.
The tests in the pilot plant indicated that when the inlet area was decreased by 50% or the feed rate decreased by one third, particle separation in the JKCC was significantly improved, and the a value was 3.04 and 2.69 respectively in two tests, which are all higher than that of the commercial CC to be compared at Dartbrook. The study also found that the feed pressure, inlet design and the inlet nozzle shape to be tested had no obvious effects on the cyclone performance according to the a value (2.0 or nearby), which was similar to the test results at Dartbrook. It should be noted that the JKMRC has designed and tested a 600mm JKCC in a mineral processing plant in South Africa, which demonstrated that the cyclone design and scale-up procedure are unlikely to be the issues affecting the 480mm JKCC performance, and that the industry-sized JKCC is compatible with large feed rates.
The big difference between the two JKCCs was the fabrication quality, in particular the alignment. An alignment measurement for the 480mm JKCC showed that the average distance between the centre line to side wall of the spigot is substantially different, and the offset is about 18.5mm, while the offset for the 600mm JKCC is only 4mm. It is most likely that the marked misalignment in the 480mm JKCC is the major reason for its unexpected performance. When the feed rate is small, the influence of the offset on particle separation is relatively small; thereby the separation efficiency is high. However, when the feed rate becomes large, the offset inevitably worsens the particle discharge and causes misplacement in the cyclone O/F and U/F.