Compressing Hydrogen

[iain/hsm]

We could dedicate these breathing hydrogen posts in the compressor section to all the mice rats rabbits dogs squirrel monkeys and Papio Baboons that all did it first without a single slightest sign of acute or chronic intoxication or problem. Thanks to the choice of hydrogen used the compression process and capability to produce and compress.

Hydrogen is manufactured from either a catalytic process or an electrolytic process with the electrolytic process being the most common Further using water may appear to most to be the purest cleanest process than cracking hydrocabonic molecules but its the micro trace elements that are the concern for breathers of said gas.
These three (3) in particular you wont find in the breathing air or gas purity charts but need to be aware if considering hydrogen as a breathing gas:

Hydrogen cyanide suggested max 0.4 ppm
Phosphuretted Hydrogen suggested max 0.012 ppm
Arseniuretted Hydrogen suggested max 0.002 ppm

 

[Storker]

Hydrogen is manufactured from either a catalytic process or an electrolitic process with the electrolitic process being the most common

This is wrong.

Nearly 50% of the world's hydrogen production is by steam reforming of natural gas. About as much is produced from petroleum or coal via synthesis gas (a mixture of H2 and CO) followed by the water gas shift reaction. Electrolysis of water only makes up some 4% of the world's hydrogen production. Cite: Hydrogen production - Wikipedia since I can't be bothered to dig up a proper reference.

 

[iain/hsm]

This is wrong.

Not if you want to breathe the stuff at depth it's not. LOL

 

[iain/hsm]

comment wasn't directed at someone like you who is an engineer that designs compressors.
To your second point, I wouldn't have the balls to use it in an oiled compressor, so it would be Rix or if already using pressurized hydrogen, the Haskel wouldn't really bother me.

It will bother you if and when we get onto gas compression and if we keep referring to Wikipedia in the post for reference. But this being specific to breathing hydrogen now is as good a time as any to introduce another aspect of breathing gas production and compression in deep diving gas applications. The Olfactory threshold of small molecular weight compounds at depth.

By example the Rix SA series of compressors the SA stands for Sweet Air because it neither adds or subtracts from the inlet gas purity and neither deforms the clean air definition that if made by others requires additional filtration.

Now as the odourless to odorous response depends on both the gas, the partial pressure PP of the impurities within the gas but also to the pressure (depth)

For example Krypton is a good reference gas believed by most to be odourless because that's what is stated in Wikipedia. However from a divers perspective at 2 bar ATA it begins to take on a chloroform like odour and at 6 to 12 bar ATA a definite odour is perceived. Surprisingly Methane with consideration to offshore diving bells Methane gives off the same chloroform like odour but at the deeper range.
Although odour of a gas is due to a higher concentration of the substance on the receptor cells in the pure gas the PP depth environment is another additional factor to consider hence its method of production and its oil free compression.

 

[broncobowsher]

They steam production I learned about when 15 years ago the world was going to shift auto fuel to clean Hydrogen. But where does the Hydrogen come from? Grade school education says you just put a little electricity into some water and you have it. Little more research found that the bulk of the commercially available Hydrogen is from steam reforming of natural gas. Now your clean Hydrogen car is just another hydrocarbon burner but the carbon is hidden away.

Here is another fun one with playing with Hydrogen. Hydrogen Embrittlement. Remember Showbiz Pizza (now Chucky Cheeze)? Related to that as well. And a little lesson on what a K-cylinder can do to a building (and the hydrogen didn't ignite, just a cylinder rupture).
Experimental Gases, Danger, And The Rock-afire Explosion
And he was doing it through a scuba compressor (which itself didn't blow up)

 

[iain/hsm]

For the first part, to make breathing Hydrogen

H2 + 1/2 O2 .......> H20 + 137 Kcal

The combustion comes from the highly exothermic reaction, hence the "Let there be Light" component for big bang enthusiasts. The explosion happens only when the proportions become stoichiometric. It is also the loadest bang you will ever hear in your life and filling a number of plastic bin liners with hydrogen with a small ignition squib timer is a great way to enjoy breaking the sound barrier at a gentle wind speed and doing good by making a gentle rain on a tender herb at the same time.

Hydrogen Embrittlement is another interesting aspect more for the diving cylinder and defined filling procedures. We could explore that filling aspect more if you like.

But again be aware not all is in wikipedia, Although hydrogen embrittlement is well known.
From our divers persective crack growth can only occur in a pure hydrogen atmoshere as soon as you replace the pure hydrogen with a hydrogen helium oxygen trimix the cracking process quickly stops and stabilizes.

The oxygen has a stablizing effect by making a oxide layer deposit on the cylinder wall combined traces of water vapour and oxygen also have a greater inhibiting effect than water vapour or oxygen alone

 

[iain/hsm]

Another interesting consideration with making a hydrogen helium oxygen tri mix is that the flamabillity risk does not decrease with an increase in the helium concentration. And this needs to be understood and brings us back to the stoichiometric ratio between the hydrogen and helium in the required mix

 

[broncobowsher]

Hydrogen does not require a stoic ratio in order to combust. It has the widest range of flammability there is. Super lean to super rich. When burned in an Otto cycle engine the mixture is generally extremely lean. Reduces power to the point that a larger displacement engine is usually needed. The lean mixture is needed for durability of the valves. I suspect the lean mix is simply trying to get an EGR effect and use the mass of the extra air as a thermal buffer. The flame is also capable of propagating through fine cracks. Valves that don't seal correctly will let the combustion flame light off the charge in the intake. Also crankcase explosions (from blowby) are an issue that need addressing.

Partial pressure blending would scare the crap out of me. Many years ago I made a very crude gas grill (bored, made with junk from work, young, curious). Got a 5-gallon (20 liter-ish) metal drum that was used for canola oil. I had access to a natural gas line. I used a screwdriver and a hammer to beat a series of "V" shaped slots in the sides near the bottom. Stuck the raw natural gas line in, tossed in a match and opened the valve. It was rather interesting to watch. The gas line filled the drum with natural gas. The air vents allowed air into the drum of natural gas. If you took a moment and realize you were watching the inverse of regular combustion. The air was burning in a natural gas environment. Now translate that into pumping pure oxygen into a hydrogen environment. Once the gasses are mixed, you are outside the flammability window, but getting there isn't the same. Going the other way isn't much better, starting with oxygen and adding hydrogen you have most of the filling cycle where you have a combustible mixture inside the tank for a lot of the filling cycle. You just about need to do it as a continuous blending.

 

[The Ruttmeister]

Here is another fun one with playing with Hydrogen. Hydrogen Embrittlement. Remember Showbiz Pizza (now Chucky Cheeze)? Related to that as well. And a little lesson on what a K-cylinder can do to a building (and the hydrogen didn't ignite, just a cylinder rupture).
Experimental Gases, Danger, And The Rock-afire Explosion
And he was doing it through a scuba compressor (which itself didn't blow up)

That's actually a fascinating link, as it sounds like the hydrogen was only a contributing factor, with carbon monoxide causing significant cracking when stored in steel at pressure. But it also is interesting that even though the cylinder contained a high ratio of hydrogen and violently ruptured, the hydrogen escaped the building (through the hole in the wall!) fast enough that there was no combustion.
I have seen people wiser than me point out that hydrogen is less hazardous than is commonly perceived, as it dissipates very very quickly when allowed to. This seems a data point that supports that!

The embrittlement issue can be addressed by using CF tanks. And we already have people routinely using 100% O2 which is basically a flamethrower in a bottle if you do something dumb (like connect a reg with flammable lubricants in it). I don't see why its impossible to figure out safe use of Hydrogen in SCUBA.

Given that the cost of Helium is already pushing people to use rebreathers, how expensive does it have to get for the questions of how to safely handle Hydrogen as an alternative become worth answering?

 

[Storker]

Not if you want to breathe the stuff at depth it's not. LOL

Nice move, coming up with the qualifier afterwards. Kinda changes the meaning of what you originally wrote.