PTQ Q1 2024 Issue

diets. These may include adjust- ments to skimming rates, conveyor speeds, solids loading rates, and gas- to-solids ratios. With higher loads that may include more emulsion, and more smaller solids (more net surface area and more net negative charge), chemical treatment programmes may require adjustment. Not only the dosage but also the choice of coagulants and flocculants may require changes, so the chem- ical injection systems and controls should allow for easy adjustments and replacement. In some cases, online monitoring of parameters such as turbidity, TSS, or total organic car- bon (TOC) has the clear advantage of allowing for real-time automation of the chemical programme at the pri- mary treatment. This can significantly reduce the variability of this stage’s effluent and help stabilise secondary treatment operation. As opportunity crudes’ challenging nature often leads to more fine par - ticles and higher levels of emulsions in the process wastewater streams, source control and source treatment of these various streams can facil- itate overall wastewater operation and prevent more general upsets. For example, desalter brine streams may be treated separately when they are affected by contaminants associated with heavy crudes, and further treat- ment of specific components of the brine stream may make sense in some circumstances. To improve effluent treatment quality, ensure all assets are properly cleaned and maintained, as more solids means more chance of settling and fouling, resulting in reduced volumes and reduced efficiency. By reducing avail - able tank volume, solids accumulation reduces equalisation capacity, and reaction time for the treatment chem- istry, so a regular cleaning programme can present a significant benefit. Secondary treatment systems do not suffer as much from the presence of contaminants as the speed at which these new and adverse conditions pres- ent themselves. The biological waste- water system is amazingly resilient if shocks are avoided and the microbes have adequate time to acclimate. Source control, adequate equalisation, 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 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. Operating parameter Feed point Feed rate, b/d Feed temperature, ºF Reflux temperature, ºF Reflux ratio, volume basis Side reboiler unit steam consumption, lb steam/bbl feed Bottom reboiler unit steam consumption, lb steam/bbl feed RVP of the bottom product, psia Table 2

and primary treatment optimisation are key to reducing shock loads. When controlling the secondary system, choose a method, such as con- stant sludge age, constant MLSS, or constant F:M and stick with it. However, new conditions may warrant a new approach. For example, if a 25-day sludge historically provided optimum results, new crude slates and associ- ated contaminant loading may warrant a 30-day sludge age. Some even notice a ‘seasonal’ sludge age approach is needed based on ‘crude seasons’. The goal of secondary treatment is to remove all contaminants via bac- teria that metabolise them, form floc and then settle out in clarifiers or are removed through filtration methods. This should leave clear, contami- nant-free water discharged in the overflow. Increased organic loading associated with opportunity crudes could push clarifier solids loading out - side of their operating limits. If clarifiers become a pinch point, the chemical programme should be optimised to encourage faster set- tling. Routine bioaugmentation, which consists of the addition of specialty bacteria populations to the secondary treatment’s biomass, can help improve organics removal and optimise solids settling characteristics. Coagulants and flocculants may also be required, even if not necessary when operating on a more traditional and stable crude diet, to consistently meet the desired effluent quality. In case of upset, listen to the data Even while keeping critical waste- water assets in top condition, com- municating frequently with process units, monitoring from head to tail, and adjusting operating strategies to the ‘new normal’, wastewater upsets do still happen due to extreme cir- cumstances. Even the best-run plants have experienced upsets due to unex- pected crude incompatibility, extreme weather, power outages, or other uncontrollable circumstances. The stress of upset conditions can lead to emotional decision-making by operation, and the loudest voice in the room often gets the most attention; be sure the loudest voice is your monitor- ing data. 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. 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. 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 Post-optimisation #9 tray + ∆ 15% Base - ∆ 1.3ºF - ∆ 5% + ∆ 9% - ∆ 7% - ∆ 1.2 psi

DIB performance comparison

Pre-optimisation

#21 tray

Base Base Base Base

All from one Source!

Base

Base Base

Duranit ® Catalyst Support Material

Support Plates/ Grids

Droplet Separators / Demisters

Feed Devices: Gas / Liquids

Liquid distributors / Collectors

Random Packings - Ceramic

-Metall - Plastic

Software and Consulting

Get in touch: info@vff.com

Check out: Image Movie VFF

Vereinigte Füllkörper-Farbriken GmbH & Co.KG P. O. Box 552, 56225 Ransbach-Baumbach, Germany, +49 26 23 / 895 - 0, info@vff.com

95 27

PTQ Q4 2023 PTQ Q1 2024