Building up a Catalyst Database in VMGSim
More detailed use of specific catalyst selection has been increasing in VMGSim due to the rigorous molecular structure environment solutions our refinery reaction package provides. Companies are now looking to take bench scale or pilot plant scale performance data from catalyst runs and apply them to full scale simulation models. Two of the most common units for application of this technique have been in the Hydrotreaters and Hydrocrackers. With a database generated containing multiple guard and main catalysts it becomes possible to then study and optimize a multi-bed unit based on desired product, hydrogen consumption, and service time run specifications within VMGSim.
There are some common steps that need to be taken to generate and use a catalyst database in VMGSim:
1. Match PIONA kinetic tuning for a catalyst type
The experimental data needs to be collected and kinetic tuning regression completed in order to create a specific catalyst in VMGSim’s refinery reactors. This can be accomplished by recreating the experimental apparatus in a flowsheet and then a regression of the involved kinetic pathways using VMGSim’s built-in regression tool.
Heat loss in the reactors can be used to mimic conditions for situations where the experimental vessels are isothermal. Only in these situations the “Ambient Temperature” in the Summary tab’s ambient data should be set to the isothermal value desired (e.g. 300 C). To increase the heat transfer flux to the reactor to maintain this temperature (balancing any heat of reaction effects) the “Conv HTC Amb” and “Conv HTC Cat” multiplier variables for heat loss in the Yield/Settings tab should be increased to values well above 1.0.
2. Collecting the finalized catalyst kinetic tuning data
The kinetic rate information is ready to be stored once the performance data of the catalyst has been regressed and matched to known trends. Care should be taken in scale up of situations with small scale data due to mechanisms such as even flow distributions in the catalyst beds not being scalable and a potential source of full scale simulation error.
In order to store the catalyst kinetics the same can be copied into an Excel spreadsheet for transfer into another VMGSim reactor unit. Alternatively, a command line script can be stored within a “.tst” file to be recalled into any separate case.
3. Apply catalyst kinetic tuning per stage bed in VMGSim
Changing the catalyst function type of a reactor bed is too simple to capture the detail of a specific catalyst tuned to detailed data. Instead any stage beds should be broken up into separate reactor unit operations within the VMGSim flowsheet and connected back to front (with any hydrogen quench being added between units). At this point a catalyst database of tuned values from either an Excel spreadsheet or “.tst” file (updating the unit operation name in the “.tst” as needed) can be applied to any single or multiple beds within the simulation.
With the use of VMGSim’s built-in optimization tool the stage bed catalyst weight can be combined with catalyst costs and service time deactivation effects to find the best combination of catalyst beds to achieve required overall unit performance.
Please contact your local VMG office for more information.
Glen Hay, M.Sc., P.Eng., VMG Calgary