hydrate formation sofware 2

[mpetier]

can you experts suggest some Excel application for calculating hydrate formation temperature conditions (with inhibitors as methanol) with 1 - 2 degrees accuracy ?
It's for natural gas, pressure range 1 - 50 Atm
thanks,
Maurice

 

[apetri]

I do not think there are simple procedures which give accurate results, mainly because (according my experience) hydrate equilibria conditions are not easy to predict :-((

consider as example the natural gas mixture

Methane 0.8746
Ethane 0.0425
Propane 0.019
n-Pentane 0.0003
Nitrogen 0.043
Carbon Dioxide 0.02
Water 0.0006

as first step you may wish to estimate the hydrate formation pressure at some minimum temperature for example 0 degrees (273.15 K) to see if inhibitor is required

the problem is that there is not free water (all water in vapor phase) and simple procedures can produce wrong results,

anyway, if you adopt some rigorous procedure you'll get for the formation pressure a value about 11-12 Bar (hydrate structure II),
Prode Properties (CPA-PR model) calculates 12 Bar, another application (School of Mines) 11.5 Bar , values are close but you need to run a complex code (ok, Prode works with Excel but it is not Excel code...).

Supposing now you wish to estimate the amount of methanol required to increase the hydrate formation pressure above 20 Bar (assuming it is the max operating pressure in your plant)
again, Prode Properties (CPA-PR model) calculates about 22 Bar (as formation pressure at 0 C) for ths composition

Methane 0.87438
Ethane 0.0425
Propane 0.019
n-Pentane 0.0003
Nitrogen 0.043
Carbon Dioxide 0.02
Water 0.0006
Methanol 0.00022

another software (School of Mines) calculates about 20 Bar (as formation pressure at 0 C) for the composition

Methane 0.8743
Ethane 0.0425
Propane 0.019
n-Pentane 0.0003
Nitrogen 0.043
Carbon Dioxide 0.02
Water 0.0006
Methanol 0.0003

as you see in the case of Prode Properties the required amount of mathanol is about 33 % of water amount
while in the other case is 50 % of water amount...
if you run a large plant this is not a little difference...
Also if you select different thermo models (for example PR-NRTL(WS) instead of CPA-PR) in Prode you may get a little different results,

for these (and other) reasons it is better to use rigorous models but (unfortunately) these are not simple.

 

[EmmanuelTop]

Free software for Hydrate calculations is available at:

http://hydrates.mines.edu/CHR/Software.html

An article which provides information/comparison of accuracy of CSMHyd and other software:

https://xa.yimg.com/kq/groups/3004572/1807151059/name/fpe04b.pdf

GPSA Databook is another resource providing Hydrate calculation methods, including inhibitor (MeOH) injection requirements. I have seen many engineering companies using the equations presented therein.

Some other useful papers:

http://www.bre.com/portals/0/technicalarticles/GPA04.HYDRATE INHIBITION WITH METHANOL.pdf

http://www.gasliquids.com/papers/gpa_dublin_2004.pdf

Dejan IVANOVIC
Senior Process Engineer

 

[mpetier]

apetri,
great answer, thank you,
actually for hydrate we utilize Katz's equilibrium constants or Baillie and Wichert's chart, while, for inhibitors, Hammerschmidt's equation and similar methods (altough I know there are several limits).
You say that Prode works with Excel, is it a Windows product ?

EmmanuelTop,
thanks for the links, CSMHyd is good but it's a DOS software with many limits,

Maurice

 

[apetri]

mpetier,
perhaps you may try to code your methods in Excel but do not expect the same accuracy of rigorous methods,
there is a commercial product (look for Hydrate Plus) which should adopt a similar methodology.

There are not many products which solve multiphase equilibria with hydrates,
I confirm that CSMHyd is good but it assumes the presence of free water and in the above example gives uncorrect results,

I have the windows version of Prode Properties which works with Excel, see

http://www.prode.com/en/phaseenvelope.htm

the distribution file includes an Excel page to print hydrate formation pressures and temperatures.

 

[rense]

Maurice,
for 1-2 degrees accuracy you must go with rigorous methods,
at least that is my experience...

 

[rotw]

apetri

you say
I confirm that CSMHyd is good but it assumes the presence of free water and in the above example gives uncorrect results,

I thought hydrate will form only in presence of free water or am I wrong ?

Thanks

"If you want to acquire a knowledge or skill, read a book and practice the skill".

 

[apetri]

no, you may have a vapor-solid equilibria, meaning there is not a liquid phase,
consider as example this mixture at 273.15 K (0 degrees C)

Methane 0.8747
Ethane 0.0425
Propane 0.019
n-Pentane 0.0003
Nitrogen 0.043
Carbon Dioxide 0.02
Water 0.0005

Prode Properties predicts hydrate formation (vapor-solid equilibria) at 13.9 bar,
another software (with a equivalent procedure based on multiphase equilibria), predicts 13.2 Bar

CSMHyd assumes presence of free water and predicts about 10 Bar

if you reduce the amount of water differences will be greater