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Deethanizer Column


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#1 khayala963003

khayala963003

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Posted 11 January 2018 - 09:53 AM

Hi
I am doing short cut distillation column design for deethanizer. Process is methanol to olefins. Feed is C2H6, C2H4, C3H6, C3H8, CH4, H2, C4 and C5. Feed temperature and pressure are 10°C and 29 bar. I am trying to find condenser and reboiler pressure. Is there any source I can use for an assumption?

#2 Pilesar

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Posted 11 January 2018 - 12:48 PM

At the top of the column you will have the C2 and lighter components. At the bottom will be the C3 and heavier. How will you get reflux for the column? Answer: You will have to condense at least the C2 portion of the overhead stream. To do that, you will have to use a utility colder than the condensing temperature. The condensing temperature is function of pressure. This pressure must be lower than the available feed pressure. What utility do you have available? The bottom of the column will probably be about 10 psi higher than the condensing pressure. You also have to boil the bottom of the column. What will be the boiling temperature at that pressure? Do you have a utility that can reboil the column at that pressure? There will be some trial and error involved to find a good optimal pressure that satisfies the competing criteria. Your choices have a cost so this is really an economic optimization problem. Lower pressures require larger equipment volumes. Higher pressures may require thicker equipment walls. Lower pressure can often improve the ease of separation by distillation. In general, you may want to keep your pressure reasonably high in order to feed downstream units. As the designer, you have options. Evaluate several options and choose what fits the best.






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