Foam-Breaking Cyclones

Various types of equipment and techniques have been employed to suppress foam formation in biological and process equipment. These include both chemical and mechanical methods. Chemical methods include various defoaming chemicals (silicone oils, non-ionic surfactants, etc.) Mechanical methods employ sprays, wire mesh elements, heat, live steam injection, air or steam-operated ejectors, sonic horns, vacuums, centrifuges, and the use of large re- 

Relatively little fundamental information on the design and performance of foam-breaking cyclones appears in the literature. What little is known about them, at least from the user s point of view, is more descriptive than quantitative. This chapter reflects the state of affairs. Even so, it is the writers hope that the information contained herein will provide the reader who is unfamiliar with these, most interesting separators, with a basic understanding of the art and practice underlying their application and performance. 

Since the design of defoaming cyclones is based largely on tests and experience, it is difficult to provide any firm design guidelines herein. However, 

Mohan and Shoham (2002) report that their cylindrical-bodied three-phase gas/water/oil cyclone separator (CLCC separator, see Fig. 14.1.2) was able to break foams at gas entrance velocities in excess of 40 ft/s (12 m/s). Foam breaking was not effective at low gas velocities, i.e., 10 ft/s. 

As mentioned earlier, foam-breaking or defoaming type of cyclone separators have enjoyed considerable commercial success in recent years, especially in refinery and drilling/wellhead installations handling dirty and/or heavy crudes. This is largely due to  

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FIGURE 7.12 Simplified schematic diagram of cyclone foam breaker. (With kind permission from Springer Science+Business Media Gas Cyclones and Swirl Tubes Principles, Design and Operation, Foam-breaking cyclones, 2008, p 327, Hoffmann, A.C., Stein, L.E., Chapter 14.)... 

One of the problems in applying foam-breaking cyclones is that it is difficult to quantitatively predict, a priori, just how well they will perform in practice. 

The designer has the task of sizing a foam-breaking cyclone system so that it can physically handle the combined vapor and liquid volumetric throughput without excessive liquid carryover and excessive gas carryunder . For example, the gas-phase vortex (shown in Fig. 14.1.1 above) must not be allowed to dip below the bottom opening of the cyclone—a condition known as gas blow out . Gas blow out is most likely to occur at maximum gas rates and low liquid rates. 

Foam-breaking cyclones can be installed in either vertical or horizontal vessels. In some offshore drilling operations, certain vapor-liquid separation vessels are routinely retrofitted with defoaming separators if there is a known or suspected foaming problem. This is usually possible since the individual tubes can pass through existing manways and be assembled inside the main separator vessel. If necessary, the separator assembly can be supported off the inside walls of the main vessel, as well as the vessel s inlet, thereby avoiding hotwork . 

In tall, vertical vessels, the distance from the vessel inlet to the liquid level may far exceed the height required by the foam-breaking cyclones. This is especially true at low liquid levels within the main separator vessel. Under these conditions the cyclone body tubes may need to be extended so that their bottom openings are always submerged and sealed. 

Fig. 14.3.6. A twin-tube G-Sep CGI foam-breaking cyclone cluster. Courtesy Kvaemer Process Systems...

Swirling flow, or vortex flow, occurs in different types of equipment, such as cyclones, hydrocyclones, spray dryers and vortex burners. Swirling flow also plays a central role in the developing fields of fluidics and process intensification. It is also the basis for the operation of foam-breaking or defoaming separators that have received significant industrial attention in recent years. 

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