The CMI centrifuge is a positive discharge scroll type centrifuge employing a profile wire screen mounted within a basket which is fastened to an outside rotating frame and an inside solid cone equipped with spiral flights. The belt driven gears produce a differential speed in the two (2) rotating elements. Both elements rotate in the same direction, however, the screen element rotates at approximately 1.52 greater RPM peripheral speed than does the inner cone section.
The mechanics of the dewatering action is relatively simple, whereby, the feed impacts the apex of the truncated cone which distributes the slurry to the inner screen surface. Upon reaching the screen, the coal is forced downward due to centrifugal force and its own mass while the wire screen allows the free water to pass to the effluent trough. The flights on the inner cone sufficiently retard the downward movement of the material so as to produce the desired surface moisture reduction.
Numerous performance tests have shown the recovery to range from a low of 81% to a high of 93% with the average being roughly 84%. Total moisture based on some 200 plus tests average 23.8% having a dry ash content of 14.9%.
These machines have proven to be extremely dependable and exhibit exceptional availability. In five (5) years of service we have experienced one major rebuild which was caused by a leaking seal and broken oil line, resulting in loss of lubricating oil and spalling in the main bearings. The most frequent operational problem centers on a buildup in the discharge zone which requires a shut down with subsequent cleaning.