Long Term Storage LH2

John · Senior Member

Long Term Storage LH2

GoogleNaut · Guru

That is essentially how a reliquification system works to remove heat from the tank. Although it uses a compressor which takes hydrogen vapor from the tank, compresses it, and then chills the compressed hydrogen with liquid helium--this causes it to condense. The hydrogen condensate is then returned to the tank; helium vapor is sent to its own compression, cooling loop and condened. Helium condensate is returned to its own tank...

The very act of extracting vapor from the tank will cool it--because it uses the available heat energy to cause vaporization.

Helium liquification will probably also need a liquid nitrogen intermediate cooling loop--and a liquid nitrogen loop can be used to chill a liquid oxygen tank. I'm not sure what you'd use for the next refrigereant step--liquid ammonia maybe, but I'm not sure.

It is however very energy intensive: for each watt of heat removed at the helium end may require 100 to 1000 watts of power in the form of electricity to power all the refrigeration. Expect to expend 50-100 Kilowatts just for this...

It gets more efficient and easier the larger the system is: bigger tanks have higher thermal mass, are easier to insulate, and the refrigeration system will be more efficient for the given capacity...

Cryogenic refrigeration systems are also pretty heavy--I know work is underway to miniaturize them for the expected CEV/Mars vehicle, but that's a long ways off.

-- Edited by GoogleNaut at 13:24, 2008-07-26

john fraz · Veteran Member

Boiloff is always an issue, but form sources I've seen it's kept down to about 1% per month.

Another option is to account for the loss and use some form of ISRU to refuel where-ever you go. Practically endless opportunities: Mars/ moons, NEAs, or Mars itself, if you're going down to explore.
It also makes sense to settle for lesser performance and use a simpler propellant -simpler to find/refine, and simpler to store: water.

GoogleNaut · Guru

One idea I am exploring which is not new or original is mining comet nuclei for volatiles--and bringing back those volatiles to a 'central' storage facility or shipping 'hub.' Water, as it turns out, is a denser source of hydrogen than even liquid hydrogen itself. So if you can take the weight penalty of shipping oxygen, then shipping water is volumetrically more efficient than hydrogen. At the depot, you can purify and then electrolyze the water to recover both hydrogen and oxygen and compress and liquefy both, which is 'perfect' for rocket propellants.

NUKE ROCKY44 · Senior Member

Some ideas are: Solid State Systems: Metal Hydrides and Chemical Hydrides.

Solid State Systems:

Metal Hydrides and Chemical Hydrides metal hydrides will absorb hydrogen under every high presssure, and in the process of absorbing hydrogen, lots of heat is released. If you want to get hydrogen back, then you have to supply heat and the hydrogen will be released for you to use. So you would have some type of metal chunks in segmented tanks in supplying hydrogen when its needed.

These still need R &D work but this is the future of extreme long term storage without the extra energy of storage.

GoogleNaut · Guru

The trouble with metalic hydrides is that they are heavy for the amount the amount of hydrogen they store...they are also temperature sensitive...in that they have to be warmed up to release the hydrogen...and the rate of hydrogen release is not nearly fast enough to support use in a reaction engine...

For long term storage of hydrogen, your best bet is to store it as water...water contains a higher density of hydrogen than even liquid hydrogen. This is ideal for a non-cryogenic long term depot storage...

For longterm cryogenic storage--a large spherical cryostat (tank) with a good, multilayer (about 5 layers) sunshade will provide almost ideal passive cooling..active cooling loads could be pretty small. Such a sunshade design should be very similar in most respects to the sunshade design for the future James Webb Space Telescope--this is a passively cooled, near infrared telescope with a 8 meter aperture (I think.) It uses a five layer sunshade to reduce the temperature of the telescope to a just a few degrees above absolute zero.

NUKE ROCKY44 · Senior Member

Isn't water/ice just as heavy to store??

You can tailor release/usage of H2 in metal/chem Hydrides.
Don't you saturate H20 with too much H2 when added?

The other option is storage of metastable H2, wonder what problems other than typical dangers and complex production senarios presented??

I think you still have to apply active stir/cryo-condition H2 even under sun shade.

-- Edited by NUKE ROCKY44 at 23:37, 2008-10-13

GoogleNaut · Guru

The density of hydrogen in water--in the form of H2O--is higher than cryogenic liquid hydrogen. So if you needed to transport both hydrogen and oxygen--you could transport it as water instead...

Cryostirring is needed to keep parts of the tank not it direct contact with cryogenic fluids from becoming warmer--and causing a vapor 'flash' if fluid does come into contact with the tank. But I think that by proper design of a large sunshade, and reducing or eliminating radiative heat coupling from nearby spacecraft structures (as well as direct thermal conduction through the structures) passive cooling will keep the tank very cold. A low pressure pump with a centrifugal vapor separator located inside the tank should provide adequte stirring, as well as a sink for boiloff vapor: the extracted vapor is then compressed, reliquified and reinjected into the tank...

Metastable H2 is really difficult and maybe impossible...the risk of catastrophic energy release is substantial. A tank detonation with a full load 220,000 kg+ of metastable hydrogen would be tremendous--like a small nuke going off!

Metallic hydrogen--also a very interesting substance--cannot be manufactured without application (and maintaining) hundreds of Mega Pascals of pressure...actually a few GigaPascals are needed I think...Think in terms of the pressure that exists deep in Jupiter's atmosphere--where does the mettalic hydrogen mantel begin?

NUKE ROCKY44 · Senior Member

Yea, agree metallic H2 is a bit futuristic I think that would involve manufacturing (gravity without mass/bulk) force in physics we don't fully understand just yet. If you could it would solve the quantity and long term storage of H2 issue.

H20 is ideal for both H2+O2 but the weight of water is massive in space for the quantities we discuss.

It would be interesting to compare and rate the different techniques for both hydrogen and oxygen storage since these are undoubtedly high value fuels in space maybe other than propane (accent fuel use). I think propane is a choice fuel because it can easily be manufactured on Mars among other perchloate solid fuel manufacture on Mars.

Do you know of a space fuels source chart around the web??

GoogleNaut · Guru

As a matter of fact, I do know of one. Robert A. Braeunig has and maintains an excellent website brim full of wonderful spaceflight information, from basic theory of rockets, to pretty advanced orbital mechanics information...

His website is at:
http://www.braeunig.us/space/index.htm

Specific information of many propellant combinations can be found at:

http://www.braeunig.us/space/index.htm

Propane is not listed, unfortunately, but its many properties can be obtained doing a search in wikipedia, or referencing a CRC Handbook of Chemistry and Physics.

Propane can be synthesized using Fischer-Tropsch synthesis, and could be made on Mars, certainly. However, it is susceptable to freezing. At the very cold temperatures that could be expected during a Martian winter night, a pressurized cylinder with liquid propane will freeze...adding insulation and heaters will be necessary, as propane like water expands when it freezes: a ruptured cylinder is a possibility. Liquid methane, slightly easier to make than propane, has a low enough melt point that freezing cannot happen at the temperatures that exist on Mars.

Long term storage of liquid hydrogen on Mars shouldn't be that big of a problem though: a large spherical double wall (vacuum jacketed) tank, heavily insulated, should do just fine on Mars. If most of the refrigeration is done during Martian nightime, then the cooling efficiency is greatly increased. Freezing some of the hydrogen could allow phase change cooling during the day.

G R L Cowan · Veteran Member

GoogleNaut wrote:

... Propane can be synthesized using Fischer-Tropsch synthesis, and could be made on Mars, certainly. However, it is susceptable to freezing. At the very cold temperatures that could be expected during a Martian winter night, a pressurized cylinder with liquid propane will freeze...adding insulation and heaters will be necessary, as propane like water expands when it freezes: a ruptured cylinder is a possibility.

I think you are thinking of some other substance, not propane.

It freezes below 86 K, so it definitely won't freeze anywhere on Mars. Maybe the solid is less dense, I have no information on that. If so, it might be a problem at Pluto.

--- G.R.L. Cowan, author of How fire can be tamed

GoogleNaut · Guru

At standard pressure (1 atm) propane freezes at 86 K. But I think it can freeze at higher temperatures with higher pressure (like the 5-7 atmospheres of pressure in a typical propane bottle)...I've heard stories of it freezing in cylinders, bursting them, and then spilling liquid propane on the ground in Siberia...I can't seem to locate any of those anechdotal stories, so I am forced to think that might be an 'urban myth.'

Of course, simply not over filling the cylinders alleviates the problem (the liquid propane can expand and contract with some volume.) Propane can make a good rocket fuel--many of its combustion properties in air are very similar (almost identical) to ethyl alcohol vapor. It can even be used as a direct replacement for R-12 refrigerant (I didn't know that until I did Wikipedia search...I learn something new everyday!)

Methane and propane can be synthesized with Fischer-Tropsch synthesis (as can all of the hydrocarbons) by 'tuning' the catalysts and conditions of formation (pressure, temperature, and adjusting partial pressures of reactants)--followed by cooling, filtration, compression (and cooling again) and then fractional condensation. Returning other hydrocarbon species for reprocessing (partial or complete break down, followed by a resynthesis step) assures almost 100% material efficiency.

G R L Cowan · Veteran Member

GoogleNaut wrote:

At standard pressure (1 atm) propane freezes at 86 K. But I think it can freeze at higher temperatures with higher pressure (like the 5-7 atmospheres of pressure in a typical propane bottle)...

Maybe there is a freezing point curve on the web somewhere. But if freezing point rises with pressure, it always happens that the solid is less voluminous than the liquid. Only if freezing point diminishes with increasing pressure can it be true that expansion occurs on freezing.

--- G.R.L. Cowan, author of How fire can be tamed

john fraz · Veteran Member

NUKE ROCKY44 wrote:
Isn't water/ice just as heavy to store??

Yes, and unless you're using it in a steam rocket, it's not readily usable, and if you're burning in in a chemical rocket (or putting it through a bi or tri-modal NTR, it's not complete. In a chemical rocket, you need about 6-7 times the mass of O2 as H2

OTOH, water is easy to carry around, and the suggestion of Zuppero and others is that the extra simplicity might be worthwhile, compared to the extra efficiency and necessary complexity of breaking water up.

P.E.R.M.A.N.E.N.T. - - 3.5 Storability of Propellants
http://permanent.com/t-mikesc.htm

GoogleNaut · Guru

I've been studying many different methods of transporting and storing cryogens: I currently don't know the best way to do it--or if there is a single "best
way."

If you can afford the weight penalty of carrying around the oxygen, then density becomes the predominant factor: and transporting water as a hydrogen carrier makes more sense. I've emailed Dr. Franklin Ramon Chang-Diaz about the possibility of running a VASIMR on oxygen alone as propellant, but this is a very non-trivial task as ionized oxygen is just about the most reactive chemical species in the universe: erosion of internal engine surfaces will likely be a serious problem. If it weren't, then liquid oxygen alone could be used as reaction mass for the VASIMR engine. However, I haven't entirely given up on that idea: there may be ways to protect the RF helicon antennas by encasing them in RF-transparent fused silica glass: this may help reduce or eliminate erosion of the RF surfaces all together. Of course, more work will have to be done...

However, as a general rule, if you store cryogens in bulk, you want to use a large spherical tank: the surface area to volume ratio makes heat leakage into the vessel the least. Erecting sunshades and designing for passive cooling will probably be necessary--but very low (almost neglieable) boiloff rates could be created by such an arrangement. Boiloff may be even lbecome low enough that a single, modest liquid helium cryosystem may be used to provide all necssary cooling to an orbital "tank farm."

Of course if your depot was also producing propellants (presumably by electrolysis of water) then you're still going to need that heavy, complex, high powered compressor/cryoliquifier setup to overcome latent heat of condensation.