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Batch Distillation Question - Reasoning?

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#1 Na3BrO


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Posted 23 March 2019 - 05:08 PM

In studying for the PE exam, I came across a problem that I do not understand. There is an exam question on a practice PE exam that goes something like this:


A liquid mixture of A and B is to be processed in a batch distillation column. The still is at 90 psig, and at the boiling points of A and B are 131 and 158, respectively. At 30 psig, the minimum-boiling azeotrope forms at 126.


The unit is equipped with a 50 ft2 condenser, U=155 BTU/hr-ft2-F. Cooling water is available at a design temperature of P with a maximum discharge temperature of 124. The condenser duty is 282,500 BTU/hr. The outlet water temperature is most nearly:


I can set up the equation just fine to solve for the needed Tcout (Q=UATlm). However, there is no indication to me about which Thot I should use. The solutions selected the 126 azeotropic temperature, but with no reason given.


What am I missing that would indicate the condenser is operating at 30 psig such that the inlet vapor is an azeotrope at 126? The problem even stated that the still was operating at 90 psig.

#2 clarenceyue


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Posted 08 April 2019 - 08:24 PM

I don't think we can help you if you do not give us the full context of the question, I believe there is more to this question then what you have given us. Please provide us with more information if you want us to give you some hints. 


I await your reply.

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