Cyclones are a dust collection device that separates particulate from the air by centrifugal force. The cyclone works by forcing the incoming air stream to spin in a vortex. As the air stream is forced to change direction, the inertia of the particulates causes them to continue in the original direction and to be separated from the air stream.
Although the cyclone is simple in appearance and operation, the interactions inside a cyclone are complex. A simple way to explain the action taking place inside a cyclone is that there are two vortices that are created during operation. The main vortex spirals downward and carries the coarser particles. An inner vortex, created near the bottom of the cyclone, spirals upward and carries finer dust particles.
Cyclones are cost-effective and low-maintenance devices, and they can handle high temperatures. They also reduce loading on the primary collector and allow for the dry recovery of product. However, it is difficult to predict the performance of cyclones, and they pose particular design challenges. Accurate inlet data are necessary, and they require significant plant space.
Cyclones have low efficiencies in removing fine particulate. They are typically used as a precleaner to remove coarser particles that could otherwise damage the bags in fabric collectors or plug wet scrubbers. It should be noted that adding a cyclone to a ventilation system may not reduce overall system resistance because the drop in resistance at the baghouse (due to lower dust loading) may be more than offset by the pressure drop of the inertial cyclone collector. Pressure drops range from 3 inches wg for low-efficiency inertial cyclone collectors and up to 8 inches wg for higher-efficiency models.
Reference
NIOSH Mining Program Report of Investigations, «Dust Control Handbook for Industrial Minerals Mining and Processing», second edition.
