When there is suspected fouling in a wash bed or evidence of a little wash oil in the tower bottoms, there is a ten- dency for refiners to increase the flow rate to the wash bed spray header to try and avoid dry-out of packing. This practice can create an undesirable condition of very elevated entrainment since traditional spray nozzles atomise more effectively with higher differen- tial pressure. Theoretical entrainment values based on empirical data show a very clear difference in behaviour between the maximum free pas- sage-style nozzles and SMDmax at various differential pressures, as illus- trated in Figure 7 . Even at relatively high differential pressures, the SMDmax spray nozzle tends to minimise over-atomisation, which is a very favourable performance characteristic of a spray nozzle in this service. Independent third-party test- ing also shows that this trend holds true up to a differential pressure of 25 psi, suggesting that these new spray nozzles not only create a favourable droplet spectrum, but do so for a larger range of flows. It is also important to note that the free passage of the nozzles depicted in Figure 7 is vastly different. The SMDmax spray nozzle has a 38% larger free passage by size, which equates to nearly a 90% larger free cross-sectional area. Conclusion Extensive droplet testing shows that a new nozzle technology can greatly reduce entrainment from vacuum dis- tillation wash bed sprays. Reducing entrainment through the proper implementation and operation of the SMDmax spray nozzle technology has significant operational implications for the downstream community. At certain operating points, theoretical Stokes’ Law-based entrainment cal- culations for a counter current spray application of the SMDmax in a tower of ~0.4°C factor result in a reduction of entrainment of 300% in comparison to traditional spray nozzles commonly used in this service. This decrease in entrainment allows for greater operational flexibility of the wash bed spray distributor. Since more gasoil will make it to the wash bed packing, the refiner can choose
to optimise yields by reducing wash rates or operate more conservatively, knowing that a greater volume of gasoil is making it through the pack- ing and into vacuum tower bottoms. In addition, the refiner can leverage the new spray nozzle’s favourable droplet spectrum across a large range or flow rates to avoid being entrain - ment limited at higher differential pressures. This next-generation spray nozzle not only features a larger free passage than maximum free pas- sage-style nozzles but will ultimately help refiners address challenges with distillation efficiency and reduce the chances for unplanned shutdowns and maintenance.
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SMDmax is a mark of Lechler Inc.
References 1 Hanson D W, Lieberman N P, Lieberman E T, De-entrainment and washing of flash-zone vapors in heavy oil fraction - ators , https://static1.squarespace.com/ static/5c92ba8e01232c369bea6695/t/5d9f- 77b53c54f020a71d5647/1570731958072/ deentrainment+and+washing+of+- flash+zone+vapors.pdf 2 Pilling M, Roza M, Vacuum Tower Wash Section Design: Myth and Reality, https://folk.ntnu.no/skoge/prost/pro- ceedings/distillation10/DA2010%20 Conference%20Proceedings/8.%20 Process%20Troubleshooting/OR52%20 Roza%20Vacuum%20Tower%20Wash%20 Section%20Design.pdf 3 Trompiz C J, Fair J R, Entrainment from Spray Distributors for Packed Columns , Masters Thesis, (Publication not in the pub- lic domain – University of Texas at Austin Chemical Engineering Masters). 4 Bete Original BETE MaxiPass ® MP – Maximum Free Passage Product https://bete.com/wp-content/ uploads/2022/01/BETE_MaxiPass.pdf Alejandro Lago is Regional Sales Manager and a Mechanical Engineer from University of Texas-Austin at Lechler USA. Email: alejandrolago@lechlerusa.com Ashwin Patni is Director of Process Technology at Lechler USA. He holds a grad- uate degree in chemical engineering from Missouri University of Science and Technology and an MBA from Northwestern University. Email: ashwinpatni@lechlerusa.com
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