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Process Engineering Flash Tank Chart


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#1 trevortnt

trevortnt

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Posted 01 September 2009 - 06:10 PM

Hi the flash tank diagrams completely baffle me and I only have a few hours left until my process engineering exam.

The question:
A liquid mixture of n-butane and n-heptane (4:6 molal ratio) at 140F is to be separated in flash tank at 100 psia. The enthalpy concentration chart H-X is attached and should be used to answer the questions:
a) What are the temperature T1 at whch mixture starts to boil and minimum temperature at which complete evaporation is a achieved.
B) What are the ranges of the mole fraction of C4 in the vapor and liquid phases respectively in the temp ranges from T1 and T2?

could anyone please help explain to me the diagram and also how where I would start to obtain the answers?

thanks
chris

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#2 abhi_agrawa

abhi_agrawa

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Posted 01 September 2009 - 08:19 PM

Christo,

In the attached H-x chart, there are 3 different regions:

1) Sub-cooled liquid - below the curve which starts at H = 19000 and x = 0 and H = 4000 and x = 1.
2) Superheated vapor - above the curve which starts at H = 29000 and x = 0 and H = 11000 and x = 1.
3) Two-Phase - between these curves.

At the curve 1) the mixture is saturated liquid, and at 2) it is saturated vapor.

Also shown in the curve are the isotherms ie. constant temperature lines.

So, for the composition of your interest, read the temperature from these isotherms at the curve 1) or 2).

You can do several other types of calculations from this curve also eg. you have a 2-phase mixture and you flash it, then what will be the vapor and liquid composition?

Hope this helps,
Abhishek

#3 breizh

breizh

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Posted 02 September 2009 - 07:10 AM

Christo ,
You got already plenty of information from Abhishek , now let us know your answers .
Don't forget we are not here to do your homework . :)
Regards
Breizh




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