Transformation computation problem
Thread Content
Question: The R-K method is used to calculate the axial distribution of bed temperature in adiabatic reactors, showing a trend from low to high, whereas in actual production the highest temperature occurs in the upper part of the catalyst bed. As the catalyst is used for a longer period of time, this hot spot gradually moves downward. What is the reason for this difference? Question: Should macroscopic kinetic equations or eigenkinetic equations be used in the calculations? There are several types of sulfur-resistant shift reaction catalysts available nowadays; what are the differences between them?
There are three types of sulfur-resistant shift catalysts, I think. Specifically, it comes down to the different pressures used: at pressures of 0.8–2.0 MPa, spherical sulfur-resistant shift catalysts are generally used, with r-alumina as the carrier ； At pressures of 2.0–4.0 MPa, a wide-temperature sulfur-tolerant shift catalyst is used; it has a strip shape with a magnesium-aluminum spinel structure ； For pressures above 4.0 MPa, wide-temperature sulfur-resistant shift catalysts are used, which are also strip-shaped and have a titanium-based support. There are these three types of catalysts, and the specific choice depends on the conditions provided by the manufacturer; even for the same type of catalyst, its formulation can be adjusted according to the manufacturer’s requirements. The main factor guiding this decision is the catalyst’s kinetic equation. We specialize in sulfur-resistant shift catalysts; we have all types available, and our technology as well as our performance are excellent. If you are interested, please contact us by email so that we can provide you with some professional materials and information.
In the calculations for adiabatic fixed-bed reactors, macroscopic kinetic equations are sufficient. If the reactor model established is a **first-order model, it is usually a set of differential equations that include mass balance and heat balance (differentials with respect to the catalyst bed height) ； If the reactor model established is a one-dimensional transient model, then the time variable must also be taken into account, typically through a system of partial differential equations that includes mass balance and heat balance ； The key is that the kinetics must be reliable, and at the same time you must take into account the issue of reaction heat!
I haven’t seen the second type you mentioned. Are there any papers or materials on it?
If you want to consider the variation of the bed temperature distribution over time, then you must take into account my second reactor model! There is also a lot of relevant literature, and it’s included in textbooks too! You may refer to the book \"Modeling and Mathematical Analysis Methods for Chemical Engineering Problems\", edited by Li Xi, published by Chemical Engineering Press! They should be available in all major bookstores across the country! !
Since the catalyst loading in the shift converter is always greater than the amount of catalyst required for the shift reaction, the shift reaction initially takes place mainly in the upper part of the shift converter. As the catalyst is used for an extended period, the upper part of the catalyst ages, so the reaction shifts downward, and the hot spots also move downward!