3 replies to this topic

[phoenix]

HI,
I am designing a CSTR. It has two feed streams entering into it one is a gas which is sparged from bottom and the other is a liquid feed. A stirrer is present inside the reactor, which is concave blade stirrer.
Can i use the performance equation of a mixed flow reactor?. I am confused because in the derivation of MFR performance equation only liquid phases are considered.
Also I need some good refrence, from where I can design this reactor.

[Doggert]

The reactor design is going to be based on the concentrations of your reactants, not on the form. Unless you have a reactant in large excess, you can probably assume that your rate equation is second order:

r = kCaCb (very, very, general)

Thus, the rate is based on the concentration and temperature (for the k value) - NOT what form. The trick in design is getting from the phase you are in (gas) to the proper concentration.

The primary focus of discussion of gas-phase reactions in undergraduate work is to show how to get to the concentration data from either a gas or liquid phase input.

If this is an undergraduate class, you should already know how to get to the concentrations you need in order to solve this problem. You need to choose a limiting reactant, and then proceed with the design as normal from there.

If this is a graduate class, then you would also probably be dealing with a residence time distribution for the gas bubbles in the reactor. Your derivations of the proper equations would come from the theory involved in this - which your professor should have gone over extensively.

Remember - in your derivations the aspect of liquid or gas phase only comes into play as far as you being able to determine flow concentrations as well as inhibiting your ability to assume that your volumetric flowrate at the beginning is the same as that of the end.

You need to supply much more information for any further help, I would think.

[Doggert]

Phoenix,

For a more detailed look at this, please look at this book:

"Chemical Reactor Analysis and Design" by Froment and Bischoff, 1990 Edition

Chapter 14, "Multiphase Flow Reactors", handles what you are asking about - specifically, section 14.3.7 - "Stirred Vessel Reactors".

Good luck.

[phoenix]

Thanks alot. I am going to look into this book.