Gas pressure calculation of reactive species in a fixed bed reactor

[Hologram0110]

Hi everyone,
I'm a university student doing some RA work which involves modelling the gas pressure in a tubular fixed bed plug reactor with an exothermic gas-solid reaction. I know the pressure will be influenced by three things: viscous drag, gas reacting with the solid and temperature increasing.

I'm not a chemical engineer, so I'm not really familiar with these types of calculations. I've done my best to Google, but I can only seem to find models for non-reacting species and no temperature change. I've found two main models: Darcy's Law (low Reynolds number, incompressible fluids) and Ergun equation.

My rough calculations put the Reynolds number approximately 1~2. Does anyone know where I can find a model which includes production/removal of gas as well as temperature changes?

 

[uby]

There are many more variables here than you may realize. The reaction rate can be very complex, the rate of heat transfer would need to be estimated, the local porosity in the bed would need to be modeled to assess the local gas conditions, etc.

This sounds like it's better suited for simulations than analytical modeling.

But, I've found that Poirier and Geiger's Transport Phenomena in Materials Processing is a very accessible introduction to these kinds of problems.

 

[Hologram0110]

Sorry if I didn't make it clear, I'm doing finite-element modeling using COMSOL multiphysics. So I'm not really looking for an analytical solution so much as a set of algebraic and differential equations to solve numerically.

I've already got a reaction rate model which is a function of temperature, steam partial pressure, particle size and reactant depletion. I've also already got a basic transient heat-transfer model which includes conduction and convection assuming the gas and solids are in thermal equilibrium.

I've also already implemented the Ergun model for pressure drop through a packed bed. However it doesn't consider the effects of removing gas from the flow and increasing the temperature which is why I'm looking for a better model. I have a physics background and this just seems like something that should have a standard modeling approach but I haven't found it yet.

 

[Chestermiller]

Hi everyone,
I'm a university student doing some RA work which involves modelling the gas pressure in a tubular fixed bed plug reactor with an exothermic gas-solid reaction. I know the pressure will be influenced by three things: viscous drag, gas reacting with the solid and temperature increasing.

I'm not a chemical engineer, so I'm not really familiar with these types of calculations. I've done my best to Google, but I can only seem to find models for non-reacting species and no temperature change. I've found two main models: Darcy's Law (low Reynolds number, incompressible fluids) and Ergun equation.

My rough calculations put the Reynolds number approximately 1~2. Does anyone know where I can find a model which includes production/removal of gas as well as temperature changes?

See a text on reaction engineering such as Levenspiel or Scott Fogler's book.

 

[alphy]

I understand your struggle in finding a suitable model for your specific situation. The calculation of gas pressure in a fixed bed reactor with a reactive species is a complex task, as it involves multiple factors such as viscous drag, gas-solid reactions, and temperature changes.

One possible approach is to use a combination of Darcy's Law and the Ergun equation, as you have mentioned. However, these models may not fully account for the production/removal of gas and temperature changes.

To address these limitations, you may need to consider a more advanced model that takes into account the reaction kinetics, heat transfer, and mass transfer within the reactor. This could involve solving a system of differential equations, which can be challenging but will provide a more accurate representation of the gas pressure in your reactor.

I suggest consulting with a chemical engineer or a research group that specializes in reactor design and modeling. They may be able to provide you with a more comprehensive model or guide you in developing one that suits your specific needs. Additionally, there are also software programs available that can assist with such calculations.

Overall, it is important to carefully consider all the factors that may influence gas pressure in your reactor and use an appropriate model that takes these factors into account. Good luck with your research!