2 replies to this topic

[Art Montemayor]

Christine:

I'm going to address this issue mainly because I have a daughter named Christine also. I'm going to proceed as if I were talking to her. Even though she is far and above my IQ superior (she's an Ob-Gyn surgeon), she sometimes denotes a lack of common sense when it comes to practical matters.

First, and foremost, as Chemical Engineers you and I must come to an agreement: There is no such thing as an "average size" for a reactor. Every reactor has a specific set of basic data and specifications attached to its service and it must comply to those requirements. Rarely, if ever, will you find a pair of reactors that are exactly alike or of "average" size. As an engineer you must practice the required methodology of being specific and accurate in what you describe. It's one thing to discuss reactor design with a lay person or a "junk scientist" at a cocktail party, but when I talk about reactor design with another ChE, I have to be demanding on specifics and accuracy.

You and I both know that if you don't know the amount of raw material being fed to a reactor, it is virtually impossible to determine or calculate anything involving this unit process - especially the size! Consequently, there is no help that can be obtained involving the design of your project reactor without identifying all the required basic design data. The only thing I could discuss about it at this stage is the color it should be painted - I would paint it Maroon, because that is my university's school color.

Please go back, obtain and organize all the basic data that is required to design this unit operation. If you have been assigned this project it must be because you have already studied and have been lectured on reactor design methods. Once you have all the basic requirements, then you can sit down and study the method of attacking the problem. Right now, your problem is not the reactor, it's the lack of basic data.

Good Luck.

Art Montemayor
Spring, TX

[David Southall]

To add a little to what Art is saying, you aren't going to get very far unless you at least know flowrates, temperatures, pressures, compositions, conversion required, and either rate constants with order of reaction or some sort of experimental data.

When I did my project at uni, I did a reactor. I knew at least what went in terms of flowrate and composition from my mass balance. Then you need to specify a suitable conversion and temperature/pressure to operate at. I sat down and worked out the reaction from stoichiometry and some experimental data I found.

As it happened, my reaction was a catalytic reaction, so I did a patent search for catalysts used for that process, which gave enough basic data to carry-out a preliminary design. I didn't have rate constants, but you can get round that by evaluating design equations for the experimental set-up and your proposed set-up, then divide one by the other to eliminate the rate constant.

I would also set up a spreadsheet for my calculations if I were in your position; 'good' equipment design is often an iterative process. Decide what factors you will optimise by, then keep iterating the design until you are satisfied with the solution (i.e. you've met as many of your constraints as possible).

Unfortunately, reactor design doesn't necessarily stop with evaluating the volume or catalyst surface required. Cost and mechanical design issues are also important. As to when to stop optimising, that can be a bit of an art in itself.