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Debottlenecking Vertical Vapor-Liquid Separators
ChE in Action: Koch-Otto York
Vessels used for the separation of liquid and vapor can be found in many processes in the chemical industry. From evaporation systems to petroleum refineries, these relatively simple vessels can successfully remove nearly all entrained liquid from a two-phase process stream. The importance of the vapor velocity in such a vessel is obvious to anyone who has ever designed one (the vapor velocity is the key design parameter in determining the geometry of the vessel). So what happens when your existing vessels must now handle additional capacity?
Figure 1 shows a very basic vertical vapor-liquid separation vessel. The vessel includes minimal features such as a standard wire mesh pad and a vortex breaker. While adding up to 20% capacity to this vessel may be only a matter of changing the mist eliminator, significant scale up or changes in the vessel duty may require even more changes. If exisiting vessels can be utilized, significant capital cost can be saved.
Figure 2 shows that be adding a pipe extension to the vessel wall opposite the entrance, with the opening on the bottom half of the pipe, additional disengagement can be realized upon the mere entrance of the vessel. Changing from a horizontal to a vertical mist eliminator with direct liquid return to the bottom of the vessel also offers a significant increase in separation capacity. In fact, some have reported a capacity increase of up to 300% with the noted modifications. The exit nozzle may or may not have to be relocated. The nozzle may not present any problems if it's located at the top of the vessel with the modified construction. One process variable to be watched closely when considering such a revamp is the available pressure drop through the vessel.
If you need assistance in debottlenecking your vapor-liquid separators, contact Koch-Otto York at one of their office.
Mist Elimination Brochure from Koch-Otto York, Bulletin ME5601-3, Copyright 2001, Koch-Glitsch, Inc.