Methane Hydrates 1

[Kam999]

Does anybody have any informatin about the problems that gas hydrates can cause in natural gas pipelines and under what circumstances these hydrates are formed.
What precautionary control measures have to be implemented to off set their effects. We are using natrual gas as a commodity ( it is not related to natural gas exploration).

Thanks,
Muhammad Ehtisham
ehtisham3@yahoo.com

 

[TD2K]

This is one link:

http://www.du.edu/~jcalvert/econ/hydrates.htm

The GPSA Engineering databooks also has information on hydrates and predicting under what conditions they will form. Essentially, you need free water and your hydrocarbon gas within the necessary pressure and temperature (the pressure and temperature are affected by the gas composition). Gases other than hydrocarbons will also form hydrates, see the above link. For hydrocarbons, the largest molecule that will form a hydrate is butane if I remember correctly. I've also seen arguments that hydrates will form with water vapor only and not require free water to be present. However, reducing the water content of pipeline gas is an effective way of preventing hydrates so I'm not so sure about not needing liquid water.

Treatment is usually to dehydrate the gas either by solid dessicant or to contact of the gas with glycol or methanol (methanol is often used to 'melt' the hydrates if they occur). Again, the GPSA data books have more informaton on this.

Both Pro II and Hysys will predict the temperatures and pressures hydrates will form at in a given stream.

 

[Kam999]

Thank you very much. I really found very helpful material on this web site and moreover GPSA link is also helping me out in understanding Hydrates formation.
Could you please specify more about ProII & Hysys? If I am not wrong these are simulation software , how they help in predicting hydrates formation?
I will appreciate.

Thanks once again.

Muhammad Ehtisham

 

[TD2K]

Pro II and Hysys are simulation software as you suspected. Correlations have been developed to predict the temperature, for a given pressure and composition, that hydrates will begin to form and those have been built into the programs. I believe, when I last talked to SimSci and Hysim that they felt these temperature predictions were within a degree of two (F) of the actual experimentally determined temperature. We used to use a margin of about 10F above the predicted hydrate temperature to allow for equation inaccuracies, data innacuracies and normal process variations in temperature/pressure/composition. I frankly don't remember if I ever ran both simulators on the same stream to see what the comparison in results were.

Both Pro II and Hysys (actually, I'm more familar with the older Hysim program) would develop a hydrate formation curve for any stream you wanted showing for each pressure, what the associated formation temperature was (Hysim was much easier IMO, the current version of Pro II supports getting a hydrate curve but in a completely bastardized method). Anyway, as long as you stayed above that temperature, hydrates wouldn't be a problem (knock wood). I know for Hysim (not sure about Hysys, the later version) that you could inject either glycol or methanol with a stream and it would predict the effect they would have on the hydrate formation temperature. Alternatively, you could use the GPSA method (Hammerschmidt).

 

[Kam999]

Wonderful thank you very much.
It really helped me in clearing up my confusion. Just out of criusoity , I am asking is there any special course, one has to take to learn these softwares or any chemical engg. with books can learn this on his own. I am working as Co-op student in a refinery and in near future going to start my Master in Chemical Engg and I have plans to take some Process Control & Process Simulation courses , would you mind telling me what kind of back ground is required to study these courses, I am assuming strong base of differentiation, integration, matirces & algebaric equations is required, am I right?

Thanks,

Muhmmad Ehtisham

 

[dcasto]

WinSim

http://www.winsim.com

is another commercially available program. There is even a stripped down version if you are not doing complex refining similations.

 

[Kam999]

Thanks dcasto. This is really very helpful site.