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# Tank Vapor Composition

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### #1 vinay

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Posted 08 September 2009 - 05:35 AM

I need to figure out the vapor composition ( fraction of HC & air) in an atmospheric open vented tank containing condensate (density-765 Kg/m3), Can anyone please help me out with a step by step procedure for doing this analysis. The RVP of condensate is 85 Kpa.

Regards,

### #2 demank

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Posted 08 September 2009 - 09:58 PM

I need to figure out the vapor composition ( fraction of HC & air) in an atmospheric open vented tank containing condensate (density-765 Kg/m3), Can anyone please help me out with a step by step procedure for doing this analysis. The RVP of condensate is 85 Kpa.

Regards,

As long as in atmospheric condition (101.325 kPa), I think there is no HC vapor.

### #3 MrShorty

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Posted 09 September 2009 - 09:40 AM

It certainly isn't right to say that there is no HC in the vapor, especially if the RVP is 85 kPa.

If this were a pure compound with a vapor pressure of 85 kPa (something like isopentane at around room temperature), then I'd keep the vapor pressure of the HC the same (85 kPa), use Dalton's law to figure the remaining pressure as N2 (or whatever the blanketing gas is), so we'd get ~26 kPa. Then go back to Dalton's law to get the mole fractions. Characterizing the liquid with a reid vapor pressure suggests that you have a mixture or distillation cut that consists of many different components. In the absence of all the information necessary to do a full fledged flash calculation, I'd probably use the above approach as a reasonable 1st estimate.

### #4 herrani

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Posted 10 September 2009 - 03:01 AM

It certainly isn't right to say that there is no HC in the vapor, especially if the RVP is 85 kPa.

If this were a pure compound with a vapor pressure of 85 kPa (something like isopentane at around room temperature), then I'd keep the vapor pressure of the HC the same (85 kPa), use Dalton's law to figure the remaining pressure as N2 (or whatever the blanketing gas is), so we'd get ~26 kPa. Then go back to Dalton's law to get the mole fractions. Characterizing the liquid with a reid vapor pressure suggests that you have a mixture or distillation cut that consists of many different components. In the absence of all the information necessary to do a full fledged flash calculation, I'd probably use the above approach as a reasonable 1st estimate.

I think it would be really helpful if you could get hold of the distillation curves (ASTM D-86 for example) for your distillate, with special emphasis on the light ends. The shape of the curve could give you an indication of which hydrocarbon fraction will be mostly evaporating at your storage temperature.