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Hi,

I've completed my 2nd year in ChE and I have been assigned a project in my summer internship in a plant, that asks to increase the capacity of a Rerun distillation column which is being flooded in the top section.

My question is basically, what different ways are there to reduce flooding in a column and thus increase the capacity of the column? My mentor gave me some hints about altering the pressure so as to get a vacuum operation going, or preheat the feed before it enters the column.

I am in the process of setting up the Aspen flow diagram with all the equipment, so I was wondering if anyone could give me some hints/tips on what to alter when running the aspen simulation to reduce this unwanted flooding.

Thank you

[Art Montemayor]

The first and best tip I can offer is to go back and study the basis and the basics of what you are being asked to resolve:

• What type of “flooding” are you referring to? Be specific, because you will spend the rest of your college career looking to solve the basic problem. You must be specific about what type and where in your column you are experiencing the alleged flooding.
• Are you looking to reduce or to eliminate the existing flooding? It makes a big difference on what your scope is in order to form a game plan for the solution. Also, be specific as to the capacity conditions the column is flooding under. Is the column at design capacity conditions? Are you looking for more capacity than the original design capacity? You say you want to “increase the capacity of the column”. Do you mean that you want to produce above the design figure, or do you mean that the existing production is below design and you want to achieve or get closer to design capacity?
• The hints your mentor gave you are not avenues to resolving the problem – unless you consider changing the internals (or the externals) of the column. Is changing the internals of the column an option? Changing the pressure may involve modifying the mechanical design of the vessel itself. Preheating the feed may mean you force more vapor into the rectification (top) section and may require more reflux – possibly aggravating the flooding there.
• What type of internals do you have? Is a change-out an option? If so, a simulation program will not give you any help here. You will have to resort to manufacturer’s software or consultation on the capabilities of their structured packing, they sieve trays, or to their valve trays. It all depends on the other factors I mention above.

As I said, you have to concentrate on basics, and you have to have a good handle and understanding of what your scope of work is and what your basic data amounts to. You must make an accurate and detailed inventory of all your major equipment involved, tabulating their capacities, mechanical ratings, and limitations. Here, I refer to the column proper, its internals, its reboiler, and its overhead condenser.