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Permalink Reply by Mac Davis on August 23, 2009 at 13:33

OK, how? Are large LNG transport trucks pressurized? Is the LNG cooled far enough below the boiling point at the point of origin that it stays liquid long enough to get to the destination without boiling?

If you have an LNG fueling station, and for some reason, you don't dispense the fuel fast enough, how do you keep the methane liquid? If you have an LNG transport truck and you can't make it to a place to unload, what keeps the methane liquid?

If a LNG powered fleet truck breaks down and gets stranded somewhere, what happens if you can't rescue or repair it before the pressure in the tank exceeds the safe level?

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Permalink Reply by Les Bamburg on August 23, 2009 at 14:53

Mac, LNG is essentially always at its boiling point. When stored in a pressurized container, the boiling point temperature simply increases with increasing pressure. So a liquid with a boiling point of -260F at 15 psi increases to -195F at 147 psi.

The pressurized storage containers are designed to provide sufficient "shelf life" for the liquid with plenty of safety margin. This is no different than liquid nitrogen, liquid hydrogen or liquid oxygen storage systems.

Yes, the transport trucks that currently haul LNG are pressurized. California has some of its LNG supply transported for over 600 miles.

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Permalink Reply by RR on August 23, 2009 at 16:03

Les B, you have impressed this old retired school teacher in the above and previous discussions. Care to share your background and education? You are definitely a source of knowledge for this forum. Thanks, RR.

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Permalink Reply by Mac Davis on August 24, 2009 at 7:45

Yes, the transport trucks that currently haul LNG are pressurized.

Thanks, that's the critical piece of info in the physics puzzle.

Do you have any rough idea of the time frame before such a tank needs to vent or otherwise do something with the gas? Hours, days, months? They do have some sort of emergency venting or other overpressure system, don't they?

I understand that you're saying that normal operations don't require any refrigeration or consumption for refrigeration.

Thanks again.

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Permalink Reply by Les Bamburg on August 24, 2009 at 9:19

Mac, generally LNG can be stored in transport trucks for 3-4 days without requiring any venting of boil-off gas.

Permalink Reply by Mac Davis on September 6, 2009 at 10:35

What happens if an LNG tanker gets stranded somewhere? Closed roads, stuck in the mud, can't unload at the end of its journey, etc.? Truck stolen and the tank gets abandoned somewhere?

Does the tanker automatically vent at a certain pressure with no operator intervention? Does it vent slowly enough that the escaping gas doesn't pose an explosion hazard? Are there procedures to flare the gas, use it somehow, offload it to other tankers, etc.? Is this an emergency situation, or does the equipment handle it safely with no human intervention? Do you need to evacuate the area around the tanker?

It seems you could design a tanker truck system to vent the gas slowly and still keep the LNG liquid without being a big hazard unless some idiot parks it indoors and lets it vent.

Same question for an LNG refueling station. For some reason, the LNG isn't getting used. Closed roads, power outage, etc.

I see that LNG isn't odorized, so escaping methane is more "silent but deadly" than commercial natural gas.

Permalink Reply by Larry Bailey on August 24, 2009 at 11:11

Back in 1994 a Texas company, EcoGas, signed a contract with the state of Louisiana to convert ALL of the state's gasoline-driven vehicles to LNG. In return for this "favor," EcoGas would be given exclusive rights to refuel those vehicles. A number of vehicles were converted to LNG with EXCELLENT results before the effort failed. There were several trials in Texas of Wal-Mart trucks being fueled with LNG, and the drivers much preferred that fuel over diesel. The concept was sound; the timing was wrong. Maybe the timing is right now...

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Permalink Reply by Keith Mauck (Site Publisher) on September 8, 2009 at 8:48

As smart as he is - he's not in the trucking biz, I'll run this one by my dad...

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