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Can you discuss your experience with using CFD for hydroprocessing reactor troubleshooting?

Mar-2025

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Louise Jivan Shah, Topsoe, ljsh@topsoe.com

Topsoe recognises the importance of CFD in the design, development, and troubleshooting of our reactors, and we have successfully integrated it into our workflows from an early stage.

Despite the challenges associated with multiphase models in CFD, these limitations have been addressed by validating our CFD models for critical assumptions using in-house measurements and literature information. This validation process ensures that our simulations closely represent the real-world behaviour of our reactors, giving us confidence in the results. Thanks to our in-house 2,000+ central processing unit (CPU) cores high-performance computing cluster for running these computationally demanding CFD simulations.

One of the major benefits we have experienced is the ability of CFD to provide meaningful insights and information that are difficult to obtain through plant-scale measurements. Troubleshooting in hydroprocessing reactors often involves identifying the root cause of observed deviations, such as temperature radials in the reactor beds. With CFD, we have been able to strengthen our hypotheses by analysing the impact of different design and process deviations on the observed deviations.

For instance, when we observed a temperature radial in our reactor, we utilised CFD to understand how various factors contributed to the observed deviations. These included design deviations (for example, as-intended vs as-built) and process deviations (for example, actual operating vs design-basis conditions). By simulating different scenarios and analysing the results, we gained a better understanding of the underlying causes and were able to develop targeted solutions.

Overall, the implementation of CFD for hydroprocessing reactor troubleshooting has been highly beneficial for Topsoe. It has allowed us to address issues more effectively, improve reactor performance, and optimise our processes. The insights and information generated through CFD have proven invaluable in enhancing our understanding and decision-making capabilities.

Mar-2025
Rainer Rakoczy, Clariant, rainer.rakoczy@clariant.com

The role of numerical methods for the simulation of fluid flows has become key for understanding and optimisation in uncountable areas in technology and engineering. Fixed catalyst bed hydrogenation calls beside an appropriate catalyst solution for the optimum dispersion of the desired feed and the applied hydrogen. The design of reactor dimensions, grading, and internals such as flow distributors or quench lines needs immense support from CFD, especially on the process engineering side.

As a catalyst vendor, the shape of the applied materials can be key. Therefore, Clariant started to look into optimising shapes as well. Some decades ago, for some hydroprocessing applications, a unique computer design shape (CDS) was developed and commercialised in several product series as CDS material, and the advantages, especially from the macroscopic surface area, are very much enjoyed by the applicants.

Mar-2025
Zumao Chen, Becht, zchen@becht.com

The application of computational fluid dynamics (CFD) for troubleshooting hydroprocessing reactors has proven invaluable in diagnosing complex operational challenges, optimising designs, and enhancing reactor performance. CFD, often coupled with kinetic modelling, is particularly effective in addressing flow maldistribution in hydrotreating and hydrocracking reactors. For example, modelling the inlet distributor through the catalyst beds of a downflow reactor allows for improved distribution and mixing in both radial and vertical directions (see Figure 1).

CFD analysis also enables the modelling of complex reactor configurations, such as ebullated bed reactors, where the catalyst bed is fluidised by the upward flow of liquid feed, gas, and recycle liquid. By analysing catalyst, oil, and gas residence times and mixing, CFD provides critical data for evaluating and quantifying the effectiveness of various design configurations. This facilitates targeted design modifications to resolve maldistribution and improve overall reactor performance.

In troubleshooting scenarios, such as operational upsets or dynamic process changes, CFD offers a powerful tool for analysing time-dependent behaviours. Breaking the timeline into discrete periods and simulating each phase provides insights into the causes of process disruptions and supports the development of effective solutions.

CFD’s utility extends beyond reactors to associated systems. For example, it has been used to address flow distribution issues in complex geometries like elbows and tees in coke drum dual inlet piping systems, where design adjustments, such as adding wedges, successfully balance vapour and liquid flow rates to reduce thermal and mechanical stresses. Similarly, CFD has been applied to optimise steam distribution in hydrocarbon outlet headers of proprietary Catofin reactors, minimising coke formation and damage to liners. Additionally, in high-velocity environments like waste heat boilers, CFD accurately predicts erosion rates and identifies critical failure zones, enabling targeted design enhancements and improved inspection protocols.

CFD has also addressed thermal management challenges, such as optimising heat transfer in storage tanks. Simulations can lead to adjustments like closer steam coil spacing in molten sulphur tanks, which maintain wall temperatures above the acid dew point, preventing corrosion and improving system reliability.

Overall, CFD has consistently demonstrated its predictive power by validating design changes, reducing downtime, and ensuring long-term equipment integrity. Its role in troubleshooting and optimisation underscores its importance in enhancing process safety and performance in hydroprocessing reactors and their associated systems.

Mar-2025