3 replies to this topic

[justpop]

Hi everyone! I'm currently designing a distillation column and I'm still a student. I just want to ask, how do I know the operating temperature and pressure? Is this based on the feed? My system is Methanol-Water. We were taught how to calculate the Design Temperature and Pressure but I'm not sure how to get the operating ones. Am I the one to give these or necessary calculations in finding it should be done? Please help me! Thank you very much!

[Art Montemayor]

Justpop:

 

If you were taught how to calculate the design temperature and pressure of a distillation tower, then you must have employed the operating temperature and pressure.  You can’t arrive at one without the other.  Therefore, I don’t understand your dilemma or query.

 

Use your common sense: how can you arrive at a design condition if you don’t know what you are going to operate at?

 

 

Please explain HOW you were taught and WHAT you were taught.  Perhaps that may help us to find out what you are really confronting.

[Pingue2008]

Justpop,

 

The information that you are asking should be given to you by your professor. if you knew the  feed pressure, I could have suggested to calculate the  saturated temperature at that pressure.

 

Thank you,

[Pilesar]

The designer of the process determines the operating conditions of a distillaiton tower. The operating conditions you select have consequences. Will you have a heat source to boil the bottoms? Will you have a cooling utility to condense the overheads? How is the difficulty in separation affected by pressure? How are the column diameter and wall thickness affected by pressure? What feed pressure is available? What product pressures are needed? If you have a feasible separation, you should consider capital costs and operating costs. It helps to find how other designers have set operating conditions, but that is not foolproof. Try not to operate in the vacuum region because air leakage can cause explosive conditions. High pressure requires thicker walls but often a smaller diameter column. If you do not have anything else to go by, choose a pressure slightly above atmospheric and calculate the column size and temperature profile. If this requires refrigeration to condense, increase the pressure until you can use cheaper cooling water. Are the overheads easy to condense but the bottoms are too hot? Then reduce the pressure until you get a nice balance. You should be able to find one or more reasons to justify your final operating pressure selection.