Figure 5b VTC device
Courtesy of EGS Systems, Inc.
Figure 5a VTC Systems principle of operation Courtesy of EGS Systems Inc.
This is where the preflash tower is at a major advantage. Should a foamover occur, it only affects its overhead prod - uct and does not contaminate the atmospheric tower or its pumparounds and hydrotreaters. In addition, with a pre - flash tower, operators get ample warning of a foamover. A foamover floods the preflash tower trays, which can easily be observed by a differential pressure rise (a reliable dif - ferential pressure transmitter must be provided!). Once the operators see a differential pressure rise, they have enough time to divert the naphtha product out of the product tank into a slop tank, preventing any contamination. A thorough discussion of foam-related issues and their control when using crude unit preflash drums is presented by Barletta, Hartman, and Leake.1 This article discusses in detail how the entrained foam impacts product yields and qualities. It also discusses the use of vortex tube clusters (VTC) systems in crude unit preflash drums. When it comes to vortex or cyclone foam separators, there are two popular technologies. One is the VTC systems from
Figure 6a GIRZ cyclonic gas inlet device Courtesy of Sulzer Chemtech
the top, and the liquid drains from the bottom. Figure 6b demonstrates the effectiveness of the GIRZ cyclonic gas inlet device in preventing foamovers. However, even though this technology helps reduce the chances of foaming, it was recommended⁶ that the preflash drum should be sized large enough to prevent foaming. Even though vortex foam sep - arators are highly reliable, infrequent failures have occurred, mainly due to mechanical issues involving supports, and it takes only one good foamover to contaminate the products from an atmospheric tower badly. Although these separators may be costly, they are effec - tive in eliminating foamovers and protecting product quality. Fluor has good experience with both technologies, and has pioneered the use of VTCs together with MPC.1⁰
EGS Systems, described above1 , 11 and shown in Figures 5a and 5b . The other is Sulzer’s proprietary GIRZ cyclonic inlet device, shown in Figures 6a and 6b . Figure 5a illustrates the principle of vortex foam separators operation. The foam is separated by the cen - trifugal forces that send the liquid to the walls, forming a continuous liq - uid phase, while the vapour forms a continuous phase that concentrates in the centre. The vapour exits from
Figure 6b Action with and without GIRZ cyclonic gas inlet device in a demonstration flash drum with foam
Courtesy of Sulzer Chemtech
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PTQ Q1 2024
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