Bubble Point, RVP & TVP of Hydrocarbon Condensate

[MIANCH]

Hi All,
I noted in my simulation, Bubble point, RVP and TVP are very much different from each other, especially RVP and TVP, can someone explain this difference as both measured at 100F and pressure 450 psig.
Thanks

 

[georgeverghese]

Bubble point temp is the initial boiling point of a multicomponent mix at a given pressure - not to be confused with the term IBP when used to characterise petroleum fractions. So the bubble point temp will be much lower than the IBP obtained from a ASTM D86 test for example.
Similarly, the bubble point pressure is the initial boiling pressure of a mix at a given operating temp

RVP is (as far as I know) the vapor pressure of a petroleum fluid at 100degF and 1atm abs

TVP is the actual vapor pressure of a hydrocarbon mix at a given P and T

So the value reported as RVP for this high pressure fluid in your simulation is referencing 1 atm abs. This can be confusing, since the composition of the fluid at 1atm will be different from that at 450psig / 100degF. I would not put much faith in this value of RVP as it is not clear what composition it is referencing.

 

[MIANCH]

Hi George,
Hysys measure RVP and TVP at 100 F, even pressure and temperature conditions are different. further, TVP calculation includes water and nitrogen while my stream has only hydrocarbons. I'm confused on TVP, why Hysys considered water plus nitrogen and oxygen as well.

 

[georgeverghese]

RVP and TVP should only be for the hydrocarbon phases of the stream. When in doubt, I would do a phase L-L split and then get the TVP of the hydrocarbon product stream.

 

[PaoloPemi]

according API TDB the Reid vapor pressure (Rvp) is the absolute pressure exerted by a mixture (in psi) determided at 100 F and at a feed vapor to liquid volume ratio of 4 (see ASTM D 323 for details about apparatus and procedures, that is important to understand what Rvp means...),
a software can estimate Rvp by following many steps including addition of 20% vol. air ... results are close to experimentally determined Rvp.
I do not know the details of the procedure in Aspen, the software which I utilize (Prode Properties) includes a method to calculate Rvp which does not require to include water and you can define a stream composed by hydrocarbons only

Differently from Rvp, the True Vapour Pressure (Tvp) or Bubble Point (Bp) vapour pressure, determined at at operating temperature, is the equilibrium vapour pressure of a mixture when the vapor /liquid ratio is about zero...
again, a software can estimate Tvp / Bp with accurate models as modern EOSs, the results are very accurate...

 

[MIANCH]

RVP Properties
The RVP properties can be calculated using the following correlations:

Reid VP at 37.8 C
True VP at 37.8 C
API 5B1.1
API 5B1.2
ASTM D323-73/79
ASTM D323-82
ASTM D4953-91
ASTM D5191-91
ASTM D6377-16
Aspen API
Modified ASTM
Note: Since ASTM D6378-10 is very similar to ASTM D6377-16 from a calculation perspective, ASTM D6377-16 can be used for both of them.
The Reid VP at 37.8 C and True VP at 37.8 C correlations are grouped under the Standard correlation type on the Correlation Manager. The remaining correlations are grouped under the RVP correlation type.

In order to apply some of the RVP correlations to your stream, the components in the stream must comply with the requirements of the correlation.

[highlight #FCE94F]If you want to use the following RVP correlations, nitrogen, oxygen, and water must be present in the stream:[/highlight][highlight #FCE94F][/highlight]

ASTM D323-82
ASTM D4953-91
ASTM D5191-91
ASTM D6377-16
If all three components are not present within your stream, a warning message will appear in the trace window.

Note: Electrolytes cannot be used with any of the RVP correlations. If an electrolyte component is present in the stream and you try to add a RVP correlation, HYSYS will not allow you to use it. If the RVP correlation is already applied to a stream and you later add an electrolyte component, HYSYS will automatically remove the electrolyte component from the given stream.
API 5B1.1 (Naphtha)

This property correlation is useful for gasoline and finished petroleum products, but not crude or oxygenated blends. The TVP is correlated against the RVP, temperature, and slope of the ASTM D86 distillation curve at the 10% point. This property solves the corrected version of the API databook equation of the correlation for the RVP. A recognized limitation of the API Naphtha correlation is that the D86 10% point can have a similar gradient for vastly different streams.

API 5B1.2 (Crude)

This property correlation is generally used for condensate and crude oil systems (typically wide boiling preprocessed hydrocarbons). TVP is correlated against RVP and the temperature. This property solves the API databook equation of the correlation for RVP.

 

[PaoloPemi]

MIANCH,
is that a copy and paste from Aspen documentation ?
Yes, you can estimate Rvp with many different EOS models (at least that is possible with Prode Properties, I would presume with Aspen, too).
Yes, you can correlate ASTM D6377 with ASTM D323 etc. , there are graphs and correlations for that (see API / ASTM documents).
Since I suppose your question is specific to your sofware operating and results and not about API / ASTM methods probably you should contact Aspen for specific assistance...

 

[MIANCH]

Paolopemi, noted, surely will ask Aspen. Further I will check API/ ASTM methods also.
Thanks

 

[georgeverghese]

"TVP calculation includes water and nitrogen while my stream has only hydrocarbons. I'm confused on TVP, why Hysys considered water plus nitrogen and oxygen as well."

There is nothing wrong I see with a TVP output from Hysys when water, oxygenates are present in the stream - it is merely the total vapor pressure at that P/T for a stream of any composition.