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[donthurtme]

I am trying to model a low pressure adiabatic methanol synthesis unit using synthesis gas as the feed. I have used Polymath to set up the balance and rate equations and have solved the reaction for a once through plug flow reactor. I have found that I need to add more reactors in series so that I may cool the mixture in between reactors to optimize conversion, and I will also add a major recycle stream from the last reactor to the first. Polymath doesn't allow for these modifications and so I would like to simulate the process in ASPEN if possible.

The synthesis reaction uses an Arrhenius rate constant but is also an equilibrium reaction with a complex rate law (ie simple power law models don't apply). The reaction data I have found in literature defines the rates of formation of the products in terms of partial fugacities, which I have simplified to mean simply partial pressure (a fair assumption I believe). One rate law, for example, looks like

r' = k1* [K1 * (p1*p2^3/2 - p3/(K2*p2^1/2))] / [(1+K1*p1+K4*p4)*(p2^1/2+K3*p3)]

where
k = arrhenius rate constant
K = arrhenius equilibrium constant
p = component partial pressure (bar)
r' = overall rate of formation (mol/s/kg catalyst)

How may I model one of these reactors in ASPEN?

This has been a frustrating problem for me so I thank you for your input.