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When properly designed, the simplest cyclone may be the most efficient
Cyclones are among the simplest and most easily fabricated pieces of processing equipment. They are used extensively in the chemical process industries (CPI) for gas-solids separation. In petroleum refineries, for example, cyclones are used in the reactors and regenerators of fluid catalytic cracking (FCC) units, in fluid coking units, and following fluidized-bed incinerators that handle refinery-waste streams and sludges. In the food, pharmaceutical, chemical and metallurgical industries, cyclones are used to recover powder products and dusts from smelters and dryers. This article focuses on some of the design precautions, essentials and peripherals necessary to achieve a desired cyclone performance.
Considering the enormous amount and variety of materials recovered via cyclones in the CPI, any advances in the technology would be eagerly sought and adopted. Yet the most highly efficient cyclones still represent the simplest configurations. Sophisticated innovations, such as multiple ports, auxiliary aeration, vortex stabilizers, and rotating internals, are not necessarily superior to simple, properly proportioned cylinders with tangential inlets. Proper cyclone design requires the optimization of these proportions to maximize the recovery of entering particles, and predict the recovery as a function of velocity, solids loading, pressure drop and other operating parameters.
Details on the basic dimensioning procedure for designing a cyclone, together with worked examples, are readily available in the literature [1].
Definitions
A conventional cyclone (Figure 1) consists of a cylinder with a tangential opening through which a dust-bearing gas stream enters at high velocity. Under such conditions, a centrifugal force is imparted to the particles, usually on the order of several hundred g's, driving them to the cylinder wall. The particles slide down the wall to an exit port, while the spiraling gas stream exits from the opposite end. Thus, a cyclone operates as a fluid-driven centrifuge.
The early design approach [2], reflected in the guidelines presented in this article, continues to be the only complete and logical basis for a dimensioning procedure that yields consistent verifiable results. But this only happens when strict attention is paid to inlet and outlet peripherals.
Cyclone dimensions
In general, the final cyclone design is a compromise between collection efficiency and equipment complexity, with due consideration of space limitations and costs. Some key...