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3

# Prv Fire Case Load Calculation For Mixture.

5 replies to this topic
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### #1 Halflight

Halflight

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Posted 24 June 2024 - 11:55 AM

Dear Members,

I usually calculate a liquid-filled fire case for the mixture as 5 mol % vaporizing @ relieving pressure.
I think it's good engineering practice because of the following two reasons.

1. Avoids excessive impact of minor amounts of light ends which may flash off at the initial boiling point.
2. Generally, for the same heat input, relief of the lighter components results in the largest calculated relief device.

Therefore, 5 mol % vapor fraction will lead it to reasonable conservative design, besides I think 5 mol % vapor fraction will be reached in few minutes.
But I'm considering TEG/water mixture right now and in this case it doesn't make sense with that logic.
TEG has much higher boiling point than water and much lower latent heat than water.
So, 5 mol % vapor fraction didn't provide conservative design and the most conservative design would be make relieving conditions to final boiling point of TEG/water mixture.
But assuming it to final boiling point is not reasonable so, I wonder which percent of mole fraction is both conservative and reasonable design.

Thank you.

### #2 PaoloPemi

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Posted 25 June 2024 - 12:40 AM

you can adopt some "conservative" estimate (see API etc.) or try to solve phase equilibria + heat balance, several tools available, see for example this previous thread :

https://www.cheresou...ure-using-hysys

### #3 Pilesar

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Posted 25 June 2024 - 12:20 PM

You may find useful discussion from several years ago:  https://www.cheresou...f-vaporization/

### #4 shvet1

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Posted 29 June 2024 - 01:48 AM

For such cases we use equilibrium vapor composition at relieving pressure

### #5 latexman

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Posted 29 June 2024 - 05:41 AM   Best Answer

We use the component with the lowest heat of vaporization.  It is simple and conservative.

### #6 Halflight

Halflight

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Posted 08 July 2024 - 12:36 PM

Dear All,

Sorry for the late response and thanks for every comments.

I solved this problem with using the component with the lowest heat of vaporization.

Even assuming relieving component as TEG, it didn't cause any major concerns.