12 replies to this topic

[Sid8lye]

Dear All, 

Today had a discussion on saturating a gas stream with water. Two methods came upfront. 

1. Simulate dry GAS stream and a water stream. Mix them in a mixer separate them in a separator and add water till the liquid stream of the separator shows slight amount of water.

 

2. Do the same simulation but keep on adding water till the gas stream molar fraction of water shall be constant (i.e) the gas cannot carry any more water irrespective of how much is the water dropout quantity.

 

1st method I have learned and practicing since 3.5 years when I was working in "On-shore" engg consultancy

2nd method was discussed and is being followed In my current organisation an Offshore consultancy 

 

Kindly Advice

[Bobby Strain]

They seem to be the same. But if you want to process the saturated gas, the separator is probably the best implementation.

 

Bobby

[PaoloPemi]

I agree with Bobby,

however I would suggest to evaluate carefully the EOS to use for phase equilibria calc's,

according some tests on Extended Peng Robinson included in your simulator results as predicted amount of water and dew point in natural gas mixtures can be wrong.

Edited by PaoloPemi, 26 February 2014 - 05:20 PM.

[ColinR33]

If you go to the Aspen support website they have a "Saturate" extension that you can download and install.  This will become a unit operation thta you can call up and install into your simulation.

 

Cheers,

Colin

[RockDock]

I would use the saturate extension, as Colin suggests, but any of the three methods should work well.

[IUR]

All three suggested methods are correct in my opinion .

[newaiam]

pls I'm trying to create a hypothetical component of oil (triglyceride of palmitic oleic and linoleic acid) in hysis but I need to build d unifac structure
my difficulty is how to specify a branched chain in my structure box
pls can anyone help me out?

[PaoloPemi]

newaiam, it is not clear if you wish to add UNIFAC structure to an existing component or create a new one, in that case you may simply use a different model.

 

for natural gas-water equilibria,

as said in my previous post I believe that errors in EOSs

available in many simulators, such as Peng Robinson & VDW mixing rules

do not allow accurate estimates,

you may consider GERG models (when available) or a EOS with temperature

dependent Kij or a EOS with complex mixing rules,

to give you an idea of the errors, I compared

calculated dew points with experimental data for

std. and extended Peng Robinson plus the

Extended Peng Robinson with Temperature Dependent BIPs

available in Prode Properties,

for a stream with 98% C1 .. C6 and H2O in the range 1-80 Bar

 

errors of 2-5 K (or more) for extended Peng Robinson 

errors of 1-2 K for Extended Peng Robinson with Temperature Dependent BIPs

 

these errors have a much larger impact than the limited errors

in fugacity which you may expect from saturating gas with water in excess.

Edited by PaoloPemi, 13 May 2014 - 07:21 AM.

[dungnt]

Plz someone show me how  to gas stream molar fraction of water's a constant in hysys !

[marchem]

a constant amount of water in vapor phase can depend from several reasons,

you may be, for example, above water dew point,

as suggested by Paolo in post #8 make sure to have selected a suitable model

since differently you may get unreliable results.

[chem expert]

Gas flow is 30MMSCFD, gas composition on dry basis is provided  with WGR 20bbl/MMSCFD.

Considering this water as FREE WATER .i have done simulation by  first saturating the gas with water saturator extension(HYSYS) and then adding this 600bbl/day water stream separately.As per my understanding the water added by water saturator is associated water as composition is on dry basis and 600bbl/day water added as separate stream is free water which can be separated by separator.This is making a total flow of 34 MMSCFD.

gas flow of 30 MMSCFD is summed up by adding  dry gas+saturated water i.e 23mmscfd and remaining is associated water.

 

KINDLY CORRECT ME IF I AM WRONG AND LET ME KNOW HOW TO PROCEED FOR CURRENT SCENARIO??

[PaoloPemi]

in most cases WGR or water/gas ratio is  defined as the ratio of the volume of water

to the volume of gas at *standard conditions*,

if that is your case use the values calculated with that definition to define compositions,

once you have composition simply solve a multiphase equilibria at *operating conditions*

to calculate compositions of vapor and liquid phases...

in general, for these calc's, you do not need saturate etc. extensions

but a good and reliable thermo model :-)

see also my post #8 for phase equilibria for HC + water

[AlbertHahn]

Dear All, 

Today had a discussion on saturating a gas stream with water. Two methods came upfront. 

1. Simulate dry GAS stream and a water stream. Mix them in a mixer separate them in a separator and add water till the liquid stream of the separator shows slight amount of water.

 

2. Do the same simulation but keep on adding water till the gas stream molar fraction of water shall be constant (i.e) the gas cannot carry any more water irrespective of how much is the water dropout quantity.

 

1st method I have learned and practicing since 3.5 years when I was working in "On-shore" engg consultancy

2nd method was discussed and is being followed In my current organisation an Offshore consultancy 

 

Kindly Advice

The results should be the same either way. something must be wrong if they are not.  The most important thing is the thermodynamics model. some models may give you wrong result.