Multitubular Reactor Assessment with MTSolve Analysis Tool

Matros Technologies, Inc. (St. Louis, MO) offers new service for quick and accurate evaluation and analysis of performance of catalytic multitubular reactors. The service can be applied for partial oxidation processes such as: ethylene into ethylene oxide, butane or benzene into maleic anhydride, methanol into formaldehyde on iron molybdene catalyst, propene into acrolein, propene into acrolein and aclylic acid, ortho-xylene or naphalene into phthalic anhydride, anthracene into antraquinone, etc. Besides, this service can be applied for acetoxylation of ethylene and acetic acid into vinyl acetate, ammoxidation of propylene into acrylonitrile, oxychlorination of ethylene into 1,2-dichloroethane and vinyl chloride, and others.

Using the data from individual pressure drop measurements in the reactor tubes and advanced MTSolve analysis tool, it is now possible to predict essential process parameters and precisely answer these questions:

    • will the required performance be reached with actual, non-uniform catalyst loading reflected by the tube-by-tube pressure drop measurements?
    • what tubes should be left as they are, repacked or plugged?
    • what is the impact of plugging vs. repacking of the tubes that are farthest from the median pressure drop?

In addition, our analysis tool will give the plant personnel knowledge both about yield, conversion and hot spot temperature expected in individual tubes and about yield, conversion and pressure drop for the entire reactor. If necessary the information can be presented in terms of consumption of raw material per unit of product, amount of desirable and side products or other parameters. The tubes for repacking will be selected based on the comparison between the repack costs and reactor productivity losses expected if the tubes left unchanged.

Modern catalytic multitubular reactors for have tens of thousand tubes catalyst filled, externally cooled or heated tubes. The product yield depends on catalyst activity and selectivity, heat and mass transfer between the catalyst and gas within each tube, and heat removal from tube walls. Many years of academic research and commercial applications by our team members lead to understanding that uniformity of performance of different tubes has foremost impact on the entire reactor operation, including process safety, control, catalyst lifetime, and production capacity.

Ideally, all tubes must work uniformly. In real life, there always are small deviations in packing density, catalyst amount or cooling, between tubes. Furthermore, all tubes operate at the same pressure drop. Differences in packing density and/or catalyst amount result in different flow rates through tubes. Tubes with less catalyst or looser packing take higher amount of gas, while those with more catalyst loading or denser packing reduce it. The flow rate deviations amplify the deviations caused by different catalyst amounts or packing density.

As a result, sub-optimal catalyst loading in just a few tubes results in notable losses of product yield for the entire plant. Higher then optimal loading leads to tube overheating and catalyst destruction due to thermal stress. Leak of non-reacted gas through or high outlet temperature after tubes with sub-optimal amount of catalyst create fire / explosion hazards downstream the reactor. Initial deviations in tube performance often increase with time. Even small initial deviations can cause big problems in operating reactors.

We have long been studying the just described positive feed back mechanism. To better understand and develop methods to control this phenomenon, we formulated a mathematical model and conducted extensive simulation studies. The result is our MTSolver software and new service offered to chemical plants.

Typically, plants employ specialized companies for replacement of the catalyst that has served its due. The new catalyst loading should be equilibrated throughout the tube array. Another company is hired to measure pressure drop in tubes filled with the new catalyst and blown by a certain amount of atmospheric air. The measurements provide information for catalyst loading quality control. Pressure drop in each tube is compared with the average value obtained for all tubes altogether. Plant personnel evaluates the deviations and chooses tubes for repacking that have pressure drop substantially lower or higher then average.

However, the pressure drop data cannot be directly used for evaluating the reactor operating parameters. Criteria for selecting tubes that should be repacked solely depends on plant engineer' intuition and experience. As a results, the selection is not necessarily optimal. Some tubes, which were left as they are, can work poorly to cause losses in the process yield. On another side, tubes that actually would affect the performance only slightly could be repacked thus extending reactor downturn and causing production losses.

Matros Technologies offers a unique service for quick and precise evaluation of the reactor operating parameters from tube pressure drop data using MTSolve, a robust and efficient software developed based on our fundamental knowledge of tubular reactors operation.

The software first uses pressure drop data to evaluate packed bed permeability in each tube. The permeability is an effective parameter characterizing packed bed density and amount of catalyst altogether. Then, it organizes the tubes in groups depending on permeability, and simulates the real catalytic process for each group. The process model used for simulation incorporates equations for mass and energy conservation in each tube group, as well as the equations for pressure drop and flow rate in the entire reactor.

There are two levels of modeling accuracy. The first level model includes reaction kinetics data derived from the broad spectrum of academic and applied researches. Its predictions are qualitatively correct and may serve as a good approximation to the expected performance. Much more precise estimates can be obtained using information about actual catalyst pellet and tube sizes, previous operation data, and information about expected catalyst performance (preferably, reaction kinetics data). Matros Technologies realizes confidential nature of this information and is committed to ensuring protection of all customer data. No information about catalyst composition and/or method of preparation is needed.

For MTSolve analysis to be effective, pressure drop through each and every tube must be known and taken into account. Until recently, obtaining this huge amount of data for short time and with high precision has been all but unrealistic. Fortunately, TubeMaster Inc. (Louisville, KY) recently developed unique method and tools for quick and precise pressure drop measurement that takes a few hours to test all the tubes in the reactor. Matros Technologies joined forces with TubeMaster to provide chemical plants with unparalleled insight into reactor performance and the most precise recommendations on optimal tube repack selection. As a result, all measurement and data processing can be done on site, in direct interaction with plant engineers.

With its speed, simplicity and accuracy, combination of TubeMaster measurement system and MTSolve process analysis software can be applied not only for catalyst loading quality control, but also for the analysis of past operation of tubes filled with aged catalyst. Coupled with these measurements, our process analysis tool will give valuable information for improving process performance.

 

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