DIB performance comparison
Operating parameter
Pre-optimisation
Post-optimisation
Feed point
#21 tray
#9 tray + ∆ 15%
Feed rate, b/d
Base Base Base Base
Feed temperature, ºF Reflux temperature, ºF Reflux ratio, volume basis
Base
- ∆ 1.3ºF - ∆ 5%
All from one Source!
Side reboiler unit steam consumption, lb steam/bbl feed Bottom reboiler unit steam consumption, lb steam/bbl feed RVP of the bottom product, psia
Base
+ ∆ 9%
Base Base
- ∆ 7%
- ∆ 1.2 psi
Table 2
column traffic would be fulfilled to achieve the target DIB feed rate and RVP value. Case study 2: Post-optimisation performance According to evaluation results, the DIB feed point was relocated from tray #21 to tray #9. The number of stripping trays was increased by 11. Bottom reboiler duty was maintained at the maximum duty available, and the side reboiler duty was increased to meet the required total reboiler duty and tar - get DIB bottom temperature. A major benefit of the optimisation is that these changes were simply accomplished while the unit remained in service. Another test run after the optimisa - tion was arranged to verify the per - formance enhancement. The pre- and post-optimisation test run data are summarised and compared in Table 2 . The target DIB feed rate and RVP of the bottom product were met. Column fractionation was even enhanced despite a lower reflux ratio. These performance enhancements were acquired without unit outages. As the optimisation moves were implemented with fouled column con - ditions, further fouling could erode these performance enhancements. To ensure performance improvements on a long-term basis, post-optimisation performances have been monitored for more than two years. Operating trends show an enhanced DIB feed rate and the RVP of the bottom prod - uct are well maintained. There has been no sign of downgraded per - formance for more than two years of operation. Rebalanced reboiler
duties are also stabilised at the target performances. Summary Fouling impacts distillation unit per - formance/run length adversely. It is extremely difficult to resolve the foul - ing problem without unit outages. However, identifying non-optimum parameters and building pertinent optimisation strategies can enhance distillation unit performances and avoid unit outages. Acknowledgements The article is an updated version of a pres - entation given at AIChE Spring Meeting, Kister Distillation Symposium, March 13-16, 2023, in Houston TX. References 1 Kister H, Hanson D, Morrison T, California Refiner Identify Crude Tower Instability Using Root Cause Analysis , AIChE Spring Meeting, April 22-26, 2001. 2 Kister H, Distillation Design , McGraw-Hill Company, 1992. 3 Lee S H, Balanced distillation equipment design, PTQ, Q1 2017. 4 Hanson D, Lee S H, Reducing FCC main fractionator operating risks, PTQ , Q1 2021. 5 Hanson D, Piping Circuits Result in Distillation Column Underperformance , Fractionation Research Institute Annual Meeting Experts Panel, May 4, 2022. Soun Ho Lee i s the Subject Matter Expert for fractionation and separation with Valero Energy Corporation in San Antonio, Texas. He is in the Strategic Technology and Development group, overseeing large pro - jects and advanced optimisation and trouble - shooting in fractionation. Email: SounHo.Lee@valero.com
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