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[rohantheneo]

Hi,
I want some help regarding my internship where I have to design a CS2 recovery system. The feed will be CS2 250 ppm, H2S 200 ppm and rest is steam (all gases at 85 C). The object is to decrease pollution by CS2 and have recovery of greater than 25%. I want to ask that as I will be performing some operation on pilot scale, I need a small distilation column just to see whether that method is suitable for this recovery or not and I will have to use adsorption or something else.

Can anybody please help me in designing a distillation column. I have to decide on Height, Diameter, Tray spacing, Tray material. What are the equations and/or heuristics to decide these specifications? Any help is appreciated!

[Art Montemayor]

As a young intern, out in industry (probably for the first time), you need to put away your academic cap and start thinking on a practical, common sense basis. That is the first and most important help I can offer you. The rest of the help will fall into place naturally and quickly – if you heed some of the advice being given. The steps you need to take to resolve this problem are, in my opinion, the following:

• Sit down and write down your scope of work. Also, write down all your basic data. This is best done in an Excel workbook.
• Conceptually sketch out what you propose to do, trying to separate the components you desire using the various Unit Operations you know or are aware of.
• Draw a proposed flow diagram and generate a mass and heat balance that describes the major streams.
• Do not waste your time on such specific details as height, diameter, tray spacings, equations, etc. yet. First establish the necessary Unit Operations that will comply with the fore mentioned scope of work.

Your PFD must make engineering sense. If you are starting with a vapor mixture, the majority of which is steam, you must quickly decide if it makes sense to deal with a Unit Operation based on separating out the components while maintaining the steam as a vapor. I don’t believe that is practical; but it is your decision. If you are proposing a distillation operation, then you must have also come to that conclusion and have decided to first condense the vapor stream.

While condensing the vapor stream, you will find that the carbon disulfide and hydrogen sulfide will be essentially inerts and will have to be vented from the condenser. But they will also be in equilibrium with the steam condensate product – and may even go into solution with the condensate. What does your scope say about this?

Your common sense should tell you that you can’t “distill” a liquid with dissolved gases. You have to STRIP it and for that you use a stripper – not a distillation column. Up to this point you have generated two obnoxious streams where you have to extract the CS₂ and H₂S – but again, what does your scope have to say? Are you also required to separate the two bad compounds from each other?

I hope that by now you realize that you have failed to furnish the Forum with sufficient information to even attempt to help you. It is time for you to make an effort in this project and generate the basic work product I describe above and submit it for discussion. We can certainly help you --- but you also have to do some work and help us help you. Otherwise, this thread will merely grow with continuing questions, guesses, estimates, and more questions, but no resolution. Please furnish the Forum with an Excel workbook that contains the stuff described above and which can serve as a foundation for the eventual solution – which will probably involve several Unit Operations.