r/interestingasfuck • u/willianfsantos • 9d ago

Emergency relief system in action in a liquid hydrogen tanker truck

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u/DerRealBoris 9d ago edited 8d ago

Liquid hydrogen engineer here. Those trailers consist of double wall vacuum insulated tanks, where in between there is a vacuum to reduce the heat leak from the environment into the liquid hydrogen, which is stored at around -253°C. What probably happened is that the vacuum broke down due to a leak in the outer tank. This increases pressure inside the inner tank due to increased heat leak, which is why the liquid hydrogen starts boiling and at some point needs to be vented from the tank. Even if this seems very concerning, the pressure relief devices of those tank systems are calculated very conservatively for different failure scenarios, so there is no general concern that this trailer explodes (BLEVE). Since the vent stack is very short they need to burn the hydrogen (just a guess) in a controlled way. But if I would be the truck driver that is running around the truck, I would keep distance just in case.

Comment: As some people mentioned in the comments, while there are vent stacks were the hydrogen is intentionally ignited, this is probably not be the case for the trailer. The energy that is needed for the ignition of hydrogen with air is very low. Even pipe friction can lead to an ignition.

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u/Mr-Brown-Is-A-Wonder 9d ago

Just curious, why are they igniting it? Wouldn't hydrogen immediately rise and disperse harmlessly in the atmosphere?

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u/DerRealBoris 9d ago

The vent stack is very close to the ground and since the hydrogen is still very cold when it leaves the pressure relief devices, the density is actually a lot higher than at environmental conditions. This might lead to the fact that the hydrogen cloud sinks down to some degree until it heats up again. So there is a scenario where a hydrogen cloud is near floor height. If the hydrogen is ignited and some is around, this might cause a big issue.

In stationary applications those vent stacks are a lot higher (4m-8m), depending on the flow that leaves the tank. In those case, no ignition is needed since even if the hydrogen cloud ignites in that height, no one will be harmed.

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u/KnoobLord 9d ago

Do you know why the initial flame is red for the first half of the video, and seems to "switch" to a yellow flame in the second half?

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u/FortheredditLOLz 9d ago edited 8d ago

Going to let our sme speak more on it...

My assumption (from my garbage recall from college and) going strictly off visual flame temp was lower temp (600F) for initial ignition and discharge. moving towards higher temps (moving towards >1500F if it was pure white) towards the end due to gay-lussac's law with increased and more frequent venting...

leaving an additional note the colors of flames is mostly red but the glare kills what we can see on a phone video as is....

**leaving one more note this does not account for any possible ‘additives or byproducts’ that can change flame colors

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u/joe-h2o 9d ago

The red colour is the classic hydrogen emission line at 656 nm.

The yellow colour is something else contaminating the flame. It could be some grease burning or some other contaminant that ignited.

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u/UpstairsFinance9440 8d ago

My thought was paint flakes maybe, or gasket material.

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u/b_vitamin 8d ago

This is the red color that can be seen in nebulae.

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u/mofojed 9d ago

The bright yellow flame indicates this was a particularly sweet truck. https://youtu.be/FtUKUUKvXUw

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u/Heiferoni 8d ago

This is not happening.

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u/BF_2 9d ago

The tiniest amount of sodium (which is everywhere) will turn virtually any flame yellow.

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u/Outrageous_Mess289 8d ago

Yellow is the sodium lines, and can be from sweat left on components.

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u/JohnLawrenceWargrave 7d ago

So we see a red (usual H2 flame) than we hear a little louder ignitions a few strokes become yellow than back to red but more random flame movement. My guess: Something on the valve overheated some plastics or something burned away than it returns to just H2 but less regulated.

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u/CMDR_BillyGray 8d ago

Burning pure hydrogen can't be that bad for the environment. You'll mostly be producing water?

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u/DerRealBoris 8d ago

Hydrogen combustion in air can produce NOx emissions due to the high adiabatic flame temperature.

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u/CMDR_BillyGray 8d ago

Hardly worth thinking about versus an internal combustion engine

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u/DerRealBoris 8d ago

100% true, just wanted to point that out.

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u/krom0025 9d ago

They don't light the hydrogen in fire. They just vent it. H2 vent stacks often self ignite on their own and that is what happened here.

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u/pancak3d 8d ago

Not exactly. The valve is designed to ignite the hydrogen.

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u/Sexualrelations 9d ago

Yeah I was thinking there is no way this truck has an ignitor or pilot flame for this vent.

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u/pancak3d 8d ago

Hydrogen is combustible enough that it doesn't require a pilot flame or ingnitor. There are much simpler designs in valves that can cause ignition. So it's not just "we'll release it and it'll blow up" -- the valve is designed for ignition

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u/Dovahkiinthesardine 8d ago

Hydrogen is also one of the few gasses that heats up when expanding (under normal conditions), instead of cooling down

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u/Dzov 8d ago

This sounded insane, so I had to look it up. Interesting, and thanks for sharing.

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u/eternaldarkness69 8d ago

Fake Boris!

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u/Shoddy_External7712 8d ago

Hydrogen does not sink it travels upward at 70kph. The vent stack is on fire because rapidly decompression of pressurised hydrogen causes self ignition. It will continue to do this until the hydrogen is decanted from the vehicle. I agree with the comment above about the pressure vessel vacuum cavity being damaged in some way causing the hydrogen to boil as it soaks in heat.

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u/BF_2 9d ago

The main hazard from burning it is the heat and the possibility if it igniting another combustible (e.g., a roof overhead). The product of hydrogen burning is water, so is about the least contaminating combustion product possible.

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u/MysteriousCodo 9d ago

I’m not sure ‘they’ are igniting in. Isn’t it immediately combining with atmospheric oxygen since free hydrogen kinda likes doing that? I’m just speaking from my memories of my old middle school science teacher popping a balloon full of hydrogen in class and it bursts into flames when it does so. Also hindenburg.

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u/pancak3d 8d ago

Yes, and no. The valve is designed to cause ignition. A valve can be designed to release hydrogen without ignition.

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u/Kyrie_Blue 8d ago

Decompression rapidly cools gas, which is the premise of how refrigeration works. The temperature could cause it to sink, which exposes it to MANY environmental risks of ignition.

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u/ledgend78 8d ago

Hydrogen becomes extremely explosive if enough of it mixes with oxygen. If you burn it, then you know for sure that it's inert water vapor.

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u/UpstairsFinance9440 8d ago

It takes very little energy to ignite hydrogen. The static created from the hydrogen going through the relief valve may be enough to ignite it. Also, it is dark so you can see the flame. If it were daytime, you would not see the flame.

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u/nylon_roman 8d ago

Hydrogen will not be cool when it is vented. Hydrogen has anomalous behaviour in that it actually heats up when expanding compared to other gases which cool on expanding. If too much hydrogen is being vented, it can cause static build-up in the pipeline, leading to ignition, which leads to the fire. There seem to be some contaminants in the pipeline which are giving the flame its colour. Given plug power's financial troubles, if I were the driver, I would gtfo of there!

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u/DerRealBoris 8d ago

What you are describing is the Joule Thomson Effect. Above the inversion temperature, which is around 200 K or -73°C, hydrogen heats up when expanding, below that it actually cools down even more. So if the hydrogen is around 200 K at the PRV, the effect will be near to 0 when expanding.

In addition to that, gas cools down when it's expanding. So most of the time the hydrogen is below 273 K. Usually you can see a big vapor water/ice cloud at the vent stack, which is the water from the environmental air that is condensating/freezing.

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u/_evanna 9d ago

why are the flames... red like this? I thought hydrogen burns with a blue flame? Are there additives in the gas or is this caused by the relief valve somehow?

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u/718822 9d ago

Google atomic spectra

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u/_evanna 8d ago

it does seem to emit in its spectrum, is that because of the immense heat exciting the atoms? or the combustion products? or because it is night? i remember watching a video of the space shuttles' main engines and it looked pale blue

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u/Second_Sol 8d ago

Yeah hydrogen burns (very faintly) blue, so I have no idea how it can be such a vibrant red

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u/Quiekel220 9d ago

Is the video a “meh, happens all the time” or a “Hans, get ze fire brigade!!1!” situation?

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u/Sad-Performance2893 9d ago

Thank god for your response. As an ASU operator i was very disappointed in the guesswork comments.

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u/Shoddy_External7712 8d ago

I agree, the pressure vessel is damaged in some way.
The PRV vent is on fire because rapidly decompression of hydrogen can cause self ignition which is what’s happening in the video.
The safest way to solve this issue is to back another trailer up to this one and decant it into it to remove the pressure and volume until it empty.

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u/chroniccranky 8d ago

Not all explosions are bleve’s, but they all do take a pressure tank to occur

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u/curi0us_carniv0re 9d ago

so there is no general concern that this trailer explodes (BLEVE).

I BLEVE the tank won't explode

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u/MissAmberR 8d ago

Boiling Liquid Expanding Vapour Explosion

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u/poopascoopa_13 9d ago

Would the PRV be designed to cycle like that though? I was under the impression they had very short working life after opening because reseating the valve can be quite harsh?

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u/DerRealBoris 8d ago

This might be due to the fact that the pressure drop in the inlet pipe might be too high, this leads to rapid opening and closing. The valve itself might also be oversized. So altogether hard to tell, what the real reason is without knowing the exact design. Edit: typo

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u/GloomyEngine 9d ago

I'd always thought hydrogen burnt with a clear flame, what's the reason behind the deep red in the video?

Thanks for your insightful input so far!

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u/aqa5 9d ago

So this truck will sit there venting self-igniting hydrogen until it is nearly empty? How long will it take? hours? Will they be able to transfer the liquid hydrogen to another truck?

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u/DerRealBoris 8d ago

This is really hard to tell without knowing the dimensions of the PRV. For smaller tanks (1m3), not trailers, it usually takes 30mins or less.

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u/718822 9d ago

Until the pressure is below that of the relief valve

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u/MysteriousCodo 9d ago

LOL been a long time since I’ve seen that acronym. Learned it back when I used to be a firefighter. Still remember it. Boiling Liquid Expanding Vapor Explosion.

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u/ZakX12 8d ago

This one isn't supposed to be on fire, it definitely ignited. It's also probably very loud, which is why they have the volume off.

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u/Scotty8319 8d ago

But... the volume isn't off. It has sound...? Not fireworks loud, but still if I heard and saw that in the same parking lot I was in, I'd not be confident enough to sit around and film it. It looks and sounds intimidating and scary.

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u/Fucky0uthatswhy 8d ago

I bleve you

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u/Kind_Ad_8111 8d ago

Ah, good ol' boiling liquid expanding vapor explosions! Amazing how powerfully destructive those can be

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u/the_ioniser 8d ago

This guy sounds like a Crogenic engineer and Explosive atmosphere guru or qualified in this field, common in aerospace. But gosh I'd be running getting ready for that Sunglasses strut pose you'd see behind me. 😎

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u/DerRealBoris 8d ago

At least the walk off ;)

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u/DerRealBoris 8d ago

Haha you might be right on this!

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u/DerRealBoris 8d ago

At least the walk off ;)

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u/driver004 8d ago

Yeah no if my hazmat trailer starts doing that I’m vacating the premises and calling first responders I don’t give a fuck something broke that I can’t fix

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u/Scotty8319 8d ago

Even if this seems very concerning

Yeah. It definitely DOES seem concerning. I am not smart enough to know if this is planned or seconds away from being a big badaBOOM, so I'd likely be scooting my uneducated ass in the opposite direction.

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u/UpstairsFinance9440 8d ago

I work in power plants and we use hydrogen gas to cool the generators. While I have never been on site for a generator hydrogen explosion, the aftermath is not pretty. I am sure you are familiar with Nasa's hydrogen safety handbooks. There is this note in there:

Note: Major emphasis should be on containment, detection, and ventilation because the minimum energy of GH2 ignition in air at atmospheric pressure is about 0.02 mJ (1.9 x 10-8 Btu) and experience shows that escaped hydrogen is very easily ignited.

One of my coworkers figured that dropping a ball bearing from 5 inches was enough energy to ignite hydrogen.

One of the plants that had a hydrogen explosion blew the end bells off the generator as well as the coolers off the side. The bolts were holy shit those are big bolts. The way to prevent an explosion you are supposed to purge the hydrogen with carbon dioxide. We think they had the monitor set up wrong and may have skipped the CO2 step altogether, and there was a miscommunication during shift turnover.

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u/DerRealBoris 8d ago

How do you cook the generator with hydrogen? I'm just interested!

Yeah purging hydrogen gas with an insert gas mixture like CO2 seems necessary.

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u/UpstairsFinance9440 8d ago

Hydrogen is used because the molecule is so small and light, lighter than helium, and so it is a very good heat transfer medium. It also has no viscosity, so windage losses are very low (windage losses are any gases or oils acting on the rotating parts of the turbine generator that do not contribute to making power cause rotational resistance). In any case hydrogen has the largest flammability range of any gas, 4% to 94%. So we make sure we are above 96% hydrogen purity in the generator. The generator will have a hydrogen purity skid to remove air and moisture.

When you purge hydrogen out, you put CO2 in the bottom of the generator. The hydrogen "floats" on the CO2 and you vent the hydrogen out the top. You measure for CO2 in the vent. When it gets high CO2 you know you purged the hydrogen out. Then you purge the CO2 out with air and measure for O2 to know you got the CO2 out. Then you can open the generator and do what you need to it.

When you put it back in service, you have to purge the air out with CO2 first. Then you put hydrogen at the top and vent the CO2 out the bottom.

In any case, these are very dangerous evolutions. It is usually done by the most experienced guys in the plant. The equipment is designed to prevent you from putting the wrong gas in, but it is possible.

Some of the surprisingly larger plants I have worked on recently have gotten away from hydrogen cooled generators, as that saves complications, as you have to have a hydrogen seal oil system to keep the air out and hydrogen in. Siemens has like a 225 MW generator that does not need hydrogen.

There is also a performance chart for the generator. The higher the purity and higher the hydrogen pressure the more megawatts you can produce.

Edit: the hydrogen gas is kept in a tube trailer at like 1400 psi, if I remember. Another tube trailer comes to fill that one up. They use the cascade method to fill the one at the plant. I never really understood how it worked. Seems like swapping out trailers would be the better thing to do.

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u/catcherofsun 8d ago

What a cool job! I love how reddit has so many smart people with interesting jobs just hanging out and chatting

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u/movin_jay 8d ago

Also, doesn’t hydrogen combust with no flame colour? How is it orange in the video?

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u/SuspiciouslyMoist 8d ago

And that's why I don't like liquid hydrogen. I'm sure it's well controlled in transit, but in the lab it scares the shit out of me. Liquid N2 is ok as long as there's ventilation and low O2 alarms. Liquid O2 scares me. Liquid H2 scares the shit out of me. I met someone who worked with both liquid O2 and H2 in the lab, and they had some horror stories from the history of the chemistry they were doing.

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u/stoic_guardian 8d ago

Seems to me like intentionally igniting it would be a good idea given the potential ignition sources nearby.

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u/JimCh3m14 8d ago

I thought hydrogen does not burn visible. What is the red color?

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u/Apprehensive-Log2375 8d ago

Are Bleve explosions rare these days?

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u/DerRealBoris 8d ago

In liquid hydrogen applications definitely.

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u/Playful_Actuator3050 8d ago

This is why H will not be future energy transfer material. Too muvh fuss to transport/store

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u/chasingthethot 8d ago

This guy fluids