17 replies to this topic

[Ghasem.Bashiri]

Dear friends

Do you know procedure of Aspen HYSYS for calculate water dew point?
When I set water mole fraction in a given stream HYSYS predict -214°C as water dew point temperature in 10 Bara. What is the accuray of HYSYS for his calculation?

Is "Dew" have meaning in such low temperature?

Regards
A.Bashiri
Ghasem.Bashiri@gmail.com

[marthin_was]

the topic you are talking about for pure water or water contained in gas stream?

since for pure water, the dew/buble point (since its 1 component) at 10 bara is 180 deg C, for your reference at 1 bara dew/buble point of water is 100 deg C

I got those number by put vapor fraction on water stream = 0.9999



marthin

Dear friends

Do you know procedure of Aspen HYSYS for calculate water dew point?
When I set water mole fraction in a given stream HYSYS predict -214°C as water dew point temperature in 10 Bara. What is the accuray of HYSYS for his calculation?

Is "Dew" have meaning in such low temperature?

Regards
A.Bashiri
Ghasem.Bashiri@gmail.com

[Ghasem.Bashiri]

For Gas Mixture: C1-C6 with water

[Padmakar Katre]

Dear,
The stream flash calculation can be used to determine the boiling point and dew point of
mixtures with and without inerts present by applying the following.

The bubble point of a liquid at the given pressure is determined by a flash calculation at a
vapour fraction of 0.

The dew point of a vapour at the given pressure is determined by a flash calculation at a
vapour fraction of 1.

For a pure component the bubble point and the dew point are identical so a flash calculation
at a vapour fraction of 0 or 1 will yield the same result

[Ghasem.Bashiri]

Dear My friend
I know method for dew point in HYSYS (vapor fraction =1 or 0).
But what about water dew point in -110°C in a Natural gas mixture?
Are HYSYS prediction accurate?
"Dew" or "Ice" point of water.
Do we have "water dew" in such temperature?
Regards

[Padmakar Katre]

Dear,
I am so sorry if I would have hurt you by posting a general reply to your query.We can have dew point of water but what result you got is something doubtful.I don't think the water dew point tempearture at 10 bara pressure would be so low.I don't have the oil and gas experience only what I can say about your query is this mixture will have a dew point range in which water as it is high boiler in the mixture will condense first but tempearture you got which is in minus I have doubt.I have a paper which may help you in understanding the problem.I am not able to upload here.if you share you mail id I will send a copy of it.
Else you can download a trial version of the software available from the link below

http://www.gpenginee...dtmixprops.html
And try your luck.

You may read this also - ISO 18453:2004
Natural gas - Correlation between water content and water dew point
ISO 18453:2004 specifies a method to provide users with a reliable mathematical relationship between water content and water dew point in natural gas when one of the two is known. The calculation method, developed by GERG; is applicable to both the calculation of the water content and the water dew point.ISO 18453:2004 gives the uncertainty for the correlation but makes no attempt to quantify the measurement uncertainties.
Please ignore this if it is not relevant.

[Ghasem.Bashiri]

Dear My friend
My problem is that I dont know reliability of HYSYS for this prediction.
And Other problems that I mentioned.
My email: Ghasem.Bashiri@gmail.com

[smalawi]

hi,

how reliable is hysys, mmmmmmmmm... many plants were designed by hysys some worked and some did not, at the end of the day hysys is just a tool, equations to approximate what should be and its the engineer who makes the decisions.

experiance on the other hand is quite useful, try to find similar applcation with well established practices and proven trac record. the gas engineers handbook and gpsa handbook may have some clues about what you need, i prestonally perfer to relay on valaidated data even if its old and conservative.

to find out if an aqeous phase will from with hysys just go to utilits, property table. fix the pressure and vary the temperature. add aqeous phase fraction on vol/wt or mol, generate the table and narwo the temperature range to bracket the first drop.

remember that the phase envelp is in 3d and meta stable regons or deveations might be nearby, use this method with care

hope this helped

cheers,

smalawi

[Padmakar Katre]

Dear Ghasem.Bashiri,
I sent you the document.One thing to tell you aske your seniors how they used to determine the Dew point temperature when this HYSYS like simulation softwares were not available get some ideas do hands on calculations based on the data and then Analyse the Hysys results are these ok or something absurd?Hope you will get the answer.

[MrShorty]

I'm a little uncertain as to how you are using the term "Dew Point." There generally two uses:

1) Dew point is defined as the point at which liquid (or solid) is first formed. If you have a gas mixture at 10 bara and cool it isobarically (keeping the pressure constant), you will reach a temperature at which the first liquid (or solid) condenses out of the vapor. This is the dew point, and the things we usually want to know are what the temperature is at which this occurs and what is the nature of the liquid (or solid) that is formed.

Using this definition of dew point and hypothesizing a gas mixture that is pure methane, I calculate a dew point of -124 C using the vapor pressure curve reported by DIPPR. This should be a minimum dew point temperature, because your other components have higher boiling points. This dew point is also much higher than the "water dew point" reported to you by HYSIS. I don't believe that the -214 reported by Hysis has much to do with the temperature at which liquid will form.

2) The second use of the term dew point (or water dew point) is simply as a measure of water content. I'm not certain of the specifics (it's not a unit of measure I use), but I expect it is based simply on the partial pressure of water and the vapor pressure curve of water (solid or liquid depending on whether the partial pressure is below or above the triple point pressure of water). I expect that this is the -214 C that Hysis is reporting to you. This value doesn't necessarily tell us anything about the actual dew point (as defined above) of the mixture, because it doesn't take into account the nature of the gas mixture. It simply allows someone to know how much water the gas stream contains. It would appear that your water concentrations are so low that the actual dew point is going to be more a function of how much C2-C6 you have in the gas stream rather than the water content.


I hope that makes sense. At this point, I would ask you to specify which "dew point" you are actually after.

[Aimenisa]

hai,

Anyone here have the Gas properties extension for hysys? If yes, could you email it to my email imaimen@gmail.com

Thank you in advance for the help

Cheers

[PaoloPemi]

when doing VLE calc's the result depends mainly from the thermodynamic model which you selected, water is a polar fluid which in many cases forms a separate phase, you should select a proper model and options, I have access to a different tool (see http://www.prode.com...ydrocarbons.htm ) but I expect that your simulator does about the same :

use tha tables in GPSA manual to get a estimate

when you have water in natural gas the most accurate option is a EOS with complex mixing rules (Huron Vidal or Wong Sandler) and multiphase

other options could be available in your software which I don't know.

[hshethna]

There is a property called Water Dew Point in HYSYS. If you go to stream Properties page and click the "+" sign and select Gas Properties from the tree view, under Gas Properties there is a water dew point property.

[Ali-Jabbaran]

Hi dear Bashiri
I think your stream has 0% water content
you can change this value to a very low number such0.000001
hysys will answer a reasonable value

[marchem]

I agree with the suggestion to adopt the ISO 18453, despite the (relatively) limited range of application it provides quite reliable results, it has been included in several sofware products, see GasCalc (Ruhrgas), Prode Properties (Prode), GERG etc.

[lugoman]

HYSYS will also give a false water depoint temperature if glycol is present in the stream. I run into this constantly when simulating natural gas dehydration units. If this is the case for you, one can use a component splitter to sequester the glycol in the bottom stream while forcing the natural gas components into the overhead stream. Then, the gas properties utility will provide you with a better estimate of the water dewpoint of the overhead stream.

[frpe]

a different approach is to consider water phase as immiscible (with hydrocarbon's condensate) and estimate fugacity with vapor pressure correlation, in several cases this may give reasonably results.
If I remeber correctly ISO 18453 is based on a modification of Peng Robinson Equation of State, I have read the spec's, errors 2-4 C

[Dmitry]

HYSYS will also give a false water depoint temperature if glycol is present in the stream. I run into this constantly when simulating natural gas dehydration units. If this is the case for you, one can use a component splitter to sequester the glycol in the bottom stream while forcing the natural gas components into the overhead stream. Then, the gas properties utility will provide you with a better estimate of the water dewpoint of the overhead stream.

I used your method, after dehydratuin at 3.92 MPa I got:
Water Dewpoint temperauture minus 8 C,
Hydrate formation minus 12 C

Than I used splitter to remove glycol from gas and I've got next:

Water Dewpoint temperauture minus 15 C,
Hydrate formation minus 10,6 C

The Hydrate formation temperature increased is correct, but why Water Dewpoint temperauture reduced, I thought it should be more than minus 8C (minus 7,6,5 ....). Colud you tell me what is wrong?