Liquid Natural Gas Vapor Pressure

Technically its in a super critical fluid/gas state so it can be what ever pressure you want it to be. Basically if you double the pressure you have double the mass of NG in the same volume.

The real practical upper limit pressure will be either how much your tank can withstand and/or how high of pressure your compressor system can pump which is going to be relative to their cost and design.

1,000,000psi! What sort of material is this container made from - Unobtainium?

[Deleted.]

Why only in August?

I only do question based on July days, sorry Merry Xmas anyways

GA for the only to the point answer to OP.

Thanks so much for your information. What reference did you use?

15000psi internal pressure for a vessel is feasible. Storing LNG in a nonvented tank would be safer and more efficient (no lost of fuel). A 12" Dia. tank 4' long could hold about 24 gal. The range for for LNG is over twice the range of CNG for the same volume of storage. With the high strength steels and carbon strands available today, it can be done.

Oh, if the comment "Questions should have some relevance to practicality" was applied to the questions asked on CR4, there would be on CR4.

Have some fun today,

PAPADOC

RMFR

HAVE A PROSPEROUS 2013

AND COME UP WITH SOME PRACTICAL IDEAS--HA HA

If you google "critical point of methane" you'll find any number of hits, but Air Liquide has a nice graph of vapor pressure vs. temperature here.

To be clear on one point: at temperatures above its critical temperature, it's impossible for a substance to exist as a liquid; it can only exist as a gas -- albeit one that is compressible to liquid-like densities. So technically, one can't properly speak of a "vapor pressure" of LNG at ambient temperature. However it's perfectly reasonable to ask what the pressure would be if a sealed container of LNG were allowed to warm to ambient.

As to what you were actually getting at, yes, it's possible to store methane at ambient temperature and pressures high enough that its density is comparable to that of LNG. But the kind of tanks that could do so would definitely not be cheap or light.

For comparison, the compressed hydrogen tanks that the DOE's hydrogen vehicle program aimed for were multi-layer carbon filament-wound tanks, rated for hydrogen at 10,000 psi. A few have been produced and tested. I believe the production cost, for the limited number made, was on the order of a few hundred thousand $ per tank. As I recall, the manufacturer (Quantum Technologies?) projected that in limited mass production, the cost could be reduced to a few tens of thousands per tank. The goal for large scale mass production was to get it below $10,000 per tank. They were sized to deliver 300 miles of driving range for a mid-sized sedan. (Those numbers are all from the top of my increasingly unreliable head, so don't take them as gospel. They're just what I think I recall from following the program over the years.)

Hope that bit of cold water doesn't dampen you Christmas cheer. Season's greetings to all. It's time for me to call my brother in Colorado, and see how the skiing looks.

Thanks, that helps a lot. Although the gas won't be liquid at ambient temperature, if the pressure is maintained, the amount will be the same. That is, the mass of the gas will be the same as when it was cooled and in the liquid stage. That's going to be one hellava thick gas. So, if we had a tank that could safely withstand the 15000 psi internal pressure, we could fill it with LNG, let it go to ambient temperature, use it to power your car and get a decent range for your car.

So, the compressed natural gas will probably be improved by using stronger compressors and stronger tanks. However, the stronger compressors will get costlier and costlier.

They are already doing it.

• Liquefied Natural Gas (LNG) as a Transportation Fuel

Oh, yes, LNG has been used for quite a while in heavy duty vehicles. And, the tanks are allowed to vent. LNG isn't being used in passenger cars. At least, I haven't found any reference to them.

• All Roads Lead to Natural Gas-Fueled Cars and Trucks - Forbes
• Liquefied Natural Gas in trucks and cars | ClimateTechWiki Please have a look at these links also.

Thanks, these links were very informative. Conversion to natural gas for passenger cars and pick-ups is further along than I thought.

One of my pet peeves / sources of frustration is the "chicken and egg" problem that so often prevents good ideas and sound practices from being implemented.

It's a stupid waste to just vent the boil-off from an LNG tank. (Not to mention the fact that, in terms of greenhouse effect, venting methane to the atmosphere is 20x more harmful than releasing a corresponding volume of CO2). The sensible thing to do is to use a fraction of the boil-off stream to power a cryogenic refrigerator that can re-liquefy the remainder of the stream. The rate of loss is cut dramatically, and what ends up in the atmosphere is a small amount of CO2 in place of a much larger amount of CH4.

Some (most?) LNG tanker ships do re-liquefy boil-off, if the boil-off exceeds what's needed to run the ship. The volumes and the savings are easily large enough to justify the cost of the equipment. The same could be done for trucks and even for autos, but it would take high-volume mass production to get the cost of the units low enough to make economic sense. The familiar chicken-and-egg problem: you need a large market in order to achieve costs that will enable a large market.

IMHO, questions should not be based on flights of fancy, with ifs & buts. Questions should have some relevance to practicality.

It's just that, at ambient temperature, the material isn't LNG, as has been explained in this forum before. The conditions make it a gas at all pressures. Therefore, there is no concept of 90% capacity, as the structural materials of the container, and therefore their ultimate tensile strength, are unknown.

you're banging your head against the wall

You're right. Only one person has answered my question. I guess I could put some LNG in a hydraulic cylinder that's good for 20000psi internal pressure, drill and tap and put in a pressure gage, throw it out in the sun and see what the internal pressure gets up to.

It seems to be too difficult for most to calculate.

RMFR

PAPADOC

Two things come to mind: What material has 1,000,000 PSI? LPG tanks are filled to only 80% of capacity because of expansion. So even if the pressure was enough to keep the liquid natural gas, the expansion of the liquid would split the tank anyway. LNG tanks must have a vent so the pressure does not does not exceed the pressure of the tank.

So there is no material that has 1-million psi, the expansion of LNG can not be prevented by pressure alone, it must be vented to prevent over pressure. And this must be a hypothetical question that is a homework assignment.

Since LNG is mainly composed of Methane, CH4 gas, you could use the pressure -Enthalpy Chart for CH4 as a reference to have an idea of the Vapour pressure problem of LNG. this link gives such a chart:

http://www.nt.ntnu.no/users/haugwarb/Phase_diagrams_and_thermodynamic_tables/PhaseDiagrams/Methane.PDF

As can be seen, you need to cool the gas container to less than -90°C to have a reasonably attained pressure that will liquefy the gas.(for LNG, it will be different and depends on the composition of the mixture of gases, which depends on the source of the LNG).

If the temperature is near the ambient, the liquid LNG will become a gas and the pressure will increase tremendously ( difficult to say how much...). The vessel might fail from the weakest part first(??).

You need to have a double vessel with a vacuum space and insulation to keep the temperature down so that the gas stays in liquid form inside the tank.

calculations are not easily made due to the different compositions . Rely on the figures that will be supplied by the suppliers etc.

Whatever it was (LNG) when filling the container, it won't be once it reaches 110 F. That will be above the critical point.

And then what happens? (the original question)

Obviously, when any cryogenic liquid reaches the critical point, it can no longer be characterized as having liquid properties, and does not particularly behave with linear compressibility (as would an ideal gas). The phase diagram (actually state diagrams) that plot pressure and volume, or other state variables such as density and temperature, are well known, and you were provided with links to these.

The pressure will be intense at 40 C. With all the present progress in CNG applications, why take the risks of even higher pressures with even heavier cylinders?

My next question: So you have this LNG vehicle parked in your garage? What happens when the vapor vents away (suppose you have vapor re-condensation system that failed) into the garage, and the water heater pilot flame gets ahold of this? I don't even want a CNG vehicle parked in my garage in the event of a leak, nor do I want to have a place to plug in a compressor to re-charge the CNG tank in my garage. Outdoors, maybe so.

You are such a pessimist. Cant' you take some risk in the interest of progress and understanding of the general progress??!??

please don't quote me on this I need to ask a friend of mine tomorrow. but I remember an exploration show when I was a kid showing a piece of crystallised natural gas. I remember hearing about it forming in the pipelines. My friend is a field operator for a large producer. And here's my to bits about compressing NG to that high of pressure or letting it warm to pressure. 15,000 psi is easy and done regularly with liquids but with NG?..I would like to watch.........from a distance of course. I have seen NG vented at 31 mpa.(about 4,400psi) from a 1 inch valve, in my guesstimation it could roll a car off the end of the catwalk 40 or so ft. away. scared the crap outa me, it took over 20 ft. before the jet of NG expanded to more than a hand span.

Ps. I don't think the hyd. cylinder is strong enough, typical hyd. systems run 2,000 to 2,500 psi with surge pressures ranging up to maybe 7,500 psi my best guess would put a typical heavy equipment grade cylinder between 12,000 and 15,000psi burst pressure depending on the size,age and application it came from.

We use 3inch pup joints for surge bottles on our cement pumps they are rated for 72 mpa.( 10,500psi) they weigh about 120 lbs. It takes an impressive amount of power to move the cement at pressure and volume of a cube per. min. we have two 450 hp. deck engines cranked up to do it. I say this to give a visual on how much energy is being stored in the confined gas. If it were to rupture the vessel ,,,,well like I said, neat to see ,,,,from a distance.lol

You are talking about methane ice. It takes 1 molecule methane + 5 molecule water. 50 atmospheric pressure and near freezing temperatures will get it. Unless the liquid / gas is free of water, it will clog up pipes. It is forming naturally in seabeds, if conditions are right.

Actually, if kept cold, "blue ice" will hang around more or less stably, even in a laboratory, and I have done so with a sample brought in from a high pressure gas line.

The sample was "fizzing" methane a bit, so I got rid of it quickly. I would not call 35 C anywhere near freezing temperature. Apparently, the methane changes the ice bonding just enough to stabilize to higher than the normal freezing point of water by a lot, but exceed the upper temperature limit and it essentially explodes.

Methane hydrates in the oceans of the world are mostly offshore. They are estimated to contain ten times all forms of land based methane. Several nations are trying to figure out how to tap them. http://en.wikipedia.org/wiki/Methane_clathrate

and http://www.naturalgasasia.com/japan-begins-methane-hyderate-test-drilling-4590

and http://eatingjellyfish.com/?tag=methane-hydrates