Elimination of AGO side stripping could allow repur- posing of the AGO side strip- per and two kerosene side strippers in parallel. This dual kerosene side stripper oper- ation could embrace higher stripping stream rates for the target kerosene yield and enhanced kerosene flash point. Repurposed kerosene side stripper (from the AGO side stripper) internals were converted into trays. Progressively varied tray spacing values were applied to optimise the number of side stripping trays and tray capac- ity at a given side stripper elevation. Fouling-resistant fixed-valve trays with pro - gressively varied open areas were selected. New trays were also designed with special supporting devices to avoid hot work to the column shell. Stripped vapour from the repurposed kerosene stripper is returned through the exist - ing heavy naphtha stripper vapour line. These modifica - tion ideas minimised external piping work and avoided col- umn shell modifications. The modified CDU is shown in Figure 8 , with modifications highlighted in red. Table 3 summarises the per- formance changes. Kerosene yield and flash point improve -
O gas
Cold re ux
Sour water
Top pumparound
Unstabilised light naphtha
Heavy naphtha
Stripping steam
Kerosene
Diesel pumparound
Stripping steam
Diesel
Desalted crude
Stripping steam
Crude heater
AGO
Stripping steam
ATB
Figure 8 Case study 2 modified crude distillation unit configuration
ments require higher overhead condenser and top pump- around duties from the CDU. Existing condenser and top pumparound circuit capacities are confirmed to handle the required duties. Reduced crude atmospheric column over- head temperature is also verified not to cause any salting at the crude distillation column top and overhead circuit. Conclusions Side strippers should not be overlooked in CDU operations. A proper understanding of the unique nature of side strip- per processes and the development of pertinent optimisa- tion strategies can enhance CDU performance. Acknowledgements This article is an updated version of a presentation given at AIChE Spring Meeting ‘Kister Distillation Symposium’, 7-10 April, 2025, in Dallas TX. The author would like to thank Isaac Brown for his help in field troubleshooting and process evaluations to develop the solutions. Many of his contributions are among the pages of this article.
References 1 McCabe, W., et al , Unit Operations of Chemical Engineerin g, McGraw-Hill Company, 5th Edition. 2 Lieberman, N., Process Design for Reliable Operations , 2nd Edition, Gulf Processing Company. 3 Kister, H., Distillation Design , McGraw-Hill Company. 4 Lee, S. H., et al , High-performance trays alone do not guarantee per- formance improvements, PTQ Q2 , 2012. 5 Watkins, R., Petroleum Refinery Distillation , 2nd Edition, Gulf Processing Company. 6 Hanson, D., et al, Low-capital crude unit revamp increases product yield, Oil & Gas Journal, May 24, 2003. Soun Ho Lee is the Director of Technology with Valero Energy Corporation in San Antonio, Texas. He is in the Strategic Technology and Development group, where he oversees large projects and advanced optimisation and troubleshooting in the areas of fractiona- tion and separation. Email: SounHo.Lee@valero.com
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PTQ Q3 2025
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