Methyl Alcohol used as a method of removing water from pipe?

[GasDistEng]

Hi-

For years I have always known that Methyl Alcohol has been used as a method of removing water from natural gas piping. For example - a pressurized natural gas pipe has a small amount of water trapped in it. Some in the liquid phase, some in the vapor phase. The water, under certain flow, and temperature conditions will vaporize and cause problems at meters, regulators, burner tips etc - especially in cold weather. Methyl Alcohol or Methyenol (please forgive the spelling on that) is injected (in liquid form) to help remove the water - or so I've always been told. Occasionally Isopropyl is used too. Does anyone know the explanation to as why this helps remove the water? Perhaps it just mixes with the water and prevents freezing?

For the most part - the Methyenol is injected into the pipe so as the flow will carry it. In most cases the Methyenol is dumped into the pipe just before it comes out of the ground (in the vertical pipe rise).

Thanks

 

[btrueblood]

Yes, methanol (or ethanol, or isopropyl alcohol) are all anti-freeze compounds when mixed with water. Also, in liquids (e.g. gasoline) methanol can be added to absorb water and permit it to become mixed up to a few percent of water. This is the function of fuel drying additives for vehicles. Not sure if the latter effect works in a NG pipeline (not sure if methanol will "mix" with highly compressed nat. gas). I'm pretty sure the methanol does not mix into the gas stream, since some wells/fields use recycling equipment to scavenge returning methanol out of the line, re-distill (to remove water) and re-inject it.

 

[aspearin1]

Methanol, Ethanol, IPA, and pretty much all alcohols interact with water via hydrogen bonding. This hydrogen bonding is what makes these smaller alcohols miscible with water. It is also what makes water removal from alcohol (a.k.a. distillation) difficult at lower water concentrations. If you use a high purity alcohol (dry alcohol) it will hydrogen bond with a residual amount of water, until it reaches a saturation point, effectively dehydrating your system. Think of it similar to dry air. Dry air can evaporate water until it reaches a saturation point, at which point the water remains condensde.

ChemE, M.E. EIT
"The only constant in life is change." -Bruce Lee

 

[MortenA]

GasDistEng:

Are you thining of the situation where a pig is run through the pipeline with a "plug" og eg MeOh or any of the other alcohols that you have mentioned?

This will very effectivly "catch" any water (since these componds mix well with water). Leftover alcohol will evaporate when the pipeline is in operation

Best regards

Morten

 

[danthemeterman]

We use Methanol on a regular basis in the Propane world. I suggest to my customers that if they have a specific transport tank casing them problems to inject the tanh with approx. 1/2 gal. to app. 3000 gals. and let stand for a nonspecific peroid of time(Again depends on ambient or stream temp) to allow the methanol to do its job while the liquid is in the static phase. I hope this helps.