Cannot separate vapor liquid mixture using separator

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Cannot separate vapor liquid mixture using separator

Postby arvind.prasad » 17 November 2017, 07:14

The attached flowsheet is for separation of methanol two phase stream. Stream 15 is a two phase mixture. It has vapor in equilibrium with liquid. It enters a Flash Separator Sep. The intention to put in a flash is to separate vapor from liquid. The will obviously require no heat. Therefore the simulation parameter are zero pressure drop and the outlet temperate same as the inlet temperature.
On simulating this flowsheet, in pvf mode i get warning, "message: TEA warning: PVF inside-out flash failed: Trivial solution for equilibrium calculation
message: WARNING: Flash Sep: temperature post-check failed for liquid product (temperature deviation too high). Using TP flash."
On using TP flash option. the vapor has liquid and the liquid has vapor, but there are no warnings. Any suggestions to deal with the warning??
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Flash Problem Jasper.fsd
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Re: Cannot separate vapor liquid mixture using separator

Postby jasper » 17 November 2017, 10:18

On the liquid side, the P-VF flash gives an answer at a temperature that is not the right one. This can happen, because the answers to P-VF flashes are not unique. The flash that is performed, is a backup, it is a TP flash at the right T. But this does not place the stream exactly at the phase bounary - there is a tad bit of vapor in this case.

That is what the warning means. If the result is ok to you you can ignore or accept it.
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Re: Cannot separate vapor liquid mixture using separator

Postby arvind.prasad » 17 November 2017, 11:50

Thanks for the clarification.
jasper wrote:On the liquid side, the P-VF flash gives an answer at a temperature that is not the right one. This can happen, because the answers to P-VF flashes are not unique. The flash that is performed, is a backup, it is a TP flash at the right T. But this does not place the stream exactly at the phase bounary - there is a tad bit of vapor in this case.

That is what the warning means. If the result is ok to you you can ignore or accept it.
arvind.prasad
 
Posts: 54
Joined: 02 December 2012, 14:39


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