6 replies to this topic

[EAGLE80]

Hi,

I need forum expert guide related to Methanol as Hydrate Inhibitor. Sour gas coming from plant inlet separator has very small amount of saturated water (0.02 mole% in 350MMSCFD gas) but due to low temperature and high pressure, system is in hydrate formation region. This gas is being transported to another plant via 35km long pipeline and during winter, small amount of water drop out is observed along the pipeline. Pipe size is 24" and water at pipeline outlet is around 2bbl/d while along the pipeline it is 3bbl constant (resulted extracted from Olga).

As system is in hydrate region, it is proposed to inject Methanol as there is no MEG recovery and circulation system available. But from PVTSim I observed that up to certain amount of Methanol, the hydrate formation curve is not shifted to left but after certain amount the curve is drastically shifted to right and even not covering full operating window. This is some surprising to me. Is this due to reason that water is too low to dissolve methanol and maximum Methanol is vaporized? Please shed your experienced light on this. How this system can be justified with methanol injection or some other mitigation has to considered.

Attached is the snap shots with different  Methanol injections rates. 

Thanks in advance.

 

   

Attached Files

•  Hydrate Curve.docx   33.74KB   26 downloads

[PaoloPemi]

for hydrate formation conditions different thermo models have been proposed,
for detailed information you may read for example Clathrate Hydrates of Natural Gases by Sloan which includes also CSMGem software,
I have also Prode Properties which has three different models for hydrates,
comparing CSMGem vs. Prode I get some different values,
I expect the same comparing  CSMGem vs. PVTSIM vs. Prode vs. HYSYS vs. Promax etc. etc.
what I would say is that you should take calculated values with some care,
possibly, you have to interpret calculated values keeping in account the limits of the model (for example is the model based on free water ? how does the model keep in account inhibitors ? ) etc. etc.
For critical cases you may compare against experimental data (if available) or require assistance from developer  or
compare different models.

[ankur2061]

MTQ80,

 

Read the article on hydrate inhibitor injection calculations at:

 

http://www.cheresour...n-calculations/

 

Regards,

Ankur.

[EAGLE80]

Thanks for the inputs. As I mentioned that gas has very small quantity of water  (0.02 mole% in 350MMSCFD gas) and it is noted that water hold up is very very small (.001%) and most of water is being swept with gas. However gas conditions are already in hydrate formation zone, what is possibility in reality that hydrate will form due to presence of very small amount of water. Although conditions predict hydrate formation but free water is not available in reasonable quantity and Methanol inhibition shall be considered or not? As a alternate can more frequent pigging is mitigation to prevent any hydrate formation.

Question is Methanol shall be injected or not under these conditions. Thanks.

[twell]

under proper conditions you may expect the formation of hydrates proportional to water amount in your stream,

in your case 0.02 % of 350 MMSCFD  ...

according my experience with different software tools you may find 20-40% (weight) differences in calculating amount of inhibitors such as methanol or glycol,

here you may find some numerical examples 

 

http://www.eng-tips.....cfm?qid=379197

 

I would expect that comparing PVTSIM , PRODE, PROMAX  or other software tools errors should be in that range,

if you'll notice larger differences you may contact the developers. 

[RockDock]

I don't expect the hydrate curve to shift to the right with any amount of methanol. I don't know why you see that.

 

I've never heard of PVTsim or Prode, but the industry standard software used to design this process is ProMax. Just contact Bryan Research to do a model for you. I'm sure they would love the opportunity to show you a comparison of ProMax to PVTsim. I'd be curious to see the comparison, too.

[marchem]

This is an old post and probably EAGLE80 is not reading the replies.

 

Anyway, I have utilized both PVTSIM and PRODE PROPERTIES for hydrate calc's and I have never found  an example of methanol reducing the hydrate formation pressure.

 

Maybe you have some wrong settings...