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 modelled 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

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