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Methanol Injection For Hydrate Prevention


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#1 mido

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Posted 19 February 2019 - 01:09 PM

We operate a 8 in gas pipeline 32 km long the flow rate about 30 mmscfd, last days we observed a hydrate in a 3 in valve at inlet of
2 indirect heater located at the end of the gas pipeline. I know that 3 in inlet of indirect heater is unsuitable but for temporary solution we decide to inject methanol, (which better inject methanol at inlet of pipeline or at end of pipeline just before the restriction?).and how can i calculate meoh quantity required to prevent hydrate?
Knowing that the gas is not dehydrated and the pressure at pipeline inlet is 750 psi temperature about 140 f while at the outlet 470 psi and temperature 50 f.some condensate formed at outlet about 200 bpd.

#2 Pilesar

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Posted 19 February 2019 - 01:58 PM

The hydrate may form well upstream of the restriction and only snagged at the valve. So inject the methanol before the hydrate forms. It is much better to keep hydrates from forming than to try to remove them. Review the GPSA Engineering Data Book Chapter 20 for help in calculating minimum methanol injection rate.



#3 mido

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Posted 20 February 2019 - 02:36 AM

I simulate it in hysys and found that hydrate begin forming at 2 km from the end of pipeline. Unfortunately i have only 2 injection point one st pipeline inlet and one before plugging valves just 30 meters ,so which is better for injection?

#4 PaoloPemi

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Posted 20 February 2019 - 08:46 AM

the best option (as suggested) would be to inject the inhibitor just before the zone of possible hydrate formation,

there could be several problems injecting at the beginning of a long pipeline,

a simulation can help but make sure that resultls are accurate

with natural gas , water and methanol I have found that CPA EOS with Huron Vidal or equivalent mixing rules can predict accurate values for  pressures / temperatures for hydrate formation (up to 50% methanol / water content fractions),

I have a different software ( Prode Properties ) and I am not sure you have access to the same models,

anyway several books as Clathrate Hydrates of Natural Gases  etc.include discussion and data useful to test the models...



#5 mido

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Posted 20 February 2019 - 03:40 PM

I used hysys for simulation and peng Robinson as a fluid package ....i only have access to hysys ....is there any other fluid package better than peng Robinson?

#6 PaoloPemi

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Posted 21 February 2019 - 01:48 AM

Peng Robinson (with vDW mixing rules) is good for vapor / liquid fugacities of natural gas mixtures,
for hydrate phase and / or non-ideal mixtures such as water-methanol etc. there are more elaborate models (see my previous post),
to answer your question, with inhibitors (methanol etc.) I solve a multiphase equilibria, for an example see

https://www.prode.com/en/hydrate.htm

simulators (as Aspen Hysys)  include specific models for hydrate phase, for a description see textbooks as the mentioned  Clathrate Hydrates of Natural Gases (Sloan) or Natural Gas Hydrates: A Guide for Engineers (Carrol) etc.

 

you can calculate / estimate  hydrate formation curve without inhibitor and then include corrections or solve  a multiphase equilibria (see above),

by the way, there are many threads at cheresources.com discussing this topic...






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