Question CNG HP Storage cylinders as cascade option.

[iain/hsm]

In American you lot have to add Metcaptan at a detectable limit of 1/5th of its lower explosive limit or 5% of natural gas in air with a normal persons detectable sense of smell at concentrations of 1% of gas in atmospheric air.

By contrast us lot don't add smell to high pressure gas pipelines but only when the pressure is reduced to the domestic towns ring main but the chemical compound we use has a detectable threshold to humans at around 0.1 ppb (parts per billion)

You could argue that because HP CNG isn't chemically treated then these cylinders would be OK (in the UK) but in practice a high pressure compressor for CNG requires low pressure at the inlet therefore treated gas is commonly used. By contrast booster pumps are used in the high pressure pipelines.

But the odour molecules dissolve into the cylinder internal shell both in the compressor and the storage cylinders by a process known as adsorption and as is common with poorly designed Italian scuba compressors so is desorption and is also quite apparent.

The amount of chemical odour lost from the gas and then adsorbed into the wall of the cylinder is dependant on pressure which in our case is detrimental at high pressure and as the odourant creates a film on the surface of the cylinder this binds into the metal by a process known as covalent bonding.

Your back to that smelly dog and the tinned dog food your feeding it with smelling badly and worse still for a very long time. Hence why it's not recommended to feed your dog tinned dog food I guess or use re purposed CNG cylinders for breathing purposes. Iain

 

[iain/hsm]

Damn, I was too late. Iain beat me to it.

You snooze you loose. LOL

 

[Tracy]

In American you lot have to add Metcaptan at a detectable limit of 1/5th of its lower explosive limit or 5% of natural gas in air with a normal persons detectable sense of smell at concentrations of 1% of gas in atmospheric air.

By contrast us lot don't add smell to high pressure gas pipelines but only when the pressure is reduced to the domestic towns ring main but the chemical compound we use has a detectable threshold to humans at around 0.1 ppb (parts per billion)

You could argue that because HP CNG isn't chemically treated then these cylinders would be OK (in the UK) but in practice a high pressure compressor for CNG requires low pressure at the inlet therefore treated gas is commonly used. By contrast booster pumps are used in the high pressure pipelines.

But the odour molecules dissolve into the cylinder internal shell both in the compressor and the storage cylinders by a process known as adsorption and as is common with poorly designed Italian scuba compressors so is desorption and is also quite apparent.

The amount of chemical odour lost from the gas and then adsorbed into the wall of the cylinder is dependant on pressure which in our case is detrimental at high pressure and as the odourant creates a film on the surface of the cylinder this binds into the metal by a process known as covalent bonding.

Your back to that smelly dog and the tinned dog food your feeding it with smelling badly and worse still for a very long time. Hence why it's not recommended to feed your dog tinned dog food I guess or use re purposed CNG cylinders for breathing purposes. Iain

It definitely ruins the compressors for breathing air as well. I have an ancient 3200psi K14-85 that I use to pump CNG. It is tapped right off my home's meter. Every time I change the oil in that thing it nearly takes your breath away. The Mercaptan has completely ruined that pump for anything else. Luckily it is perfect for that application. Slow speed, cool running, relatively low pressure. It just sits there and pumps for however long it needs to run with zero complaints.

 

[Ty Hamby]

In American you lot have to add Metcaptan at a detectable limit of 1/5th of its lower explosive limit or 5% of natural gas in air with a normal persons detectable sense of smell at concentrations of 1% of gas in atmospheric air.

Well, I have learned more about smelly dogs than I thought this thread would bring. That said..... what if the vessel never saw any CNG. What if someone was to visit a website where government agencies discard their fraud, waist, and abuse of taxpayers monies. Lets hypothesize about a potential bad purchase some bureaucratic imbecile made. Would this provide an opportunity for a metcaptan free nonpregnant cylinder, that could then be used to store breathing air? Is methane used in testing during manufacturing. Is this something someone knows? I may just plop down $25 quid and do some puffs of my own. For science, of course.

 

[Tracy]

Well, I have learned more about smelly dogs than I thought this thread would bring. That said..... what if the vessel never saw any CNG. What if someone was to visit a website where government agencies discard their fraud, waist, and abuse of taxpayers monies. Lets hypothesize about a potential bad purchase some bureaucratic imbecile made. Would this provide an opportunity for a metcaptan free nonpregnant cylinder, that could then be used to store breathing air? Is methane used in testing during manufacturing. Is this something someone knows? I may just plop down $25 quid and do some puffs of my own. For science, of course.

If they never saw use, then yes they could be suitable. But the only way to find out would be to purchase it and see if they stink. Depending on purchase price, might be worth the gamble. I purchased some unused CNG ASME spheres many years ago and they were just that, clean and unused.
I also purchased some CNG ASME horizontal bottles that could never be cleaned enough to kill that smell.

 

[broncobowsher]

I recall another story about mercaptan, but with Propane. The short of it, old farm house on Propane. Not occupied in many years. People bought it and were moving back in. Still had a propane tank that still had product in it. Turned it on. House blew up. They didn't smell anything. There was research done and it was found that the mercaptan was added to the propane. But over time it impregnated the cylinder walls and the smell in the propane was lost. Thus the couple that were in the house didn't smell the Propane leak when the gas was turned back on. More important, the mercaptan was embedded in the walls of the Propane tank. That is a lot lower pressure than natural gas.

 

[Ty Hamby]

If they never saw use, then yes they could be suitable. But the only way to find out would be to purchase it and see if they stink. Depending on purchase price, might be worth the gamble. I purchased some unused CNG ASME spheres many years ago and they were just that, clean and unused.
I also purchased some CNG ASME horizontal bottles that could never be cleaned enough to kill that smell.

Thank you. In the end i passed on 4) 60"x16" 3600psi CNG type3 cylinders. They were new and never used. I figured, i have enough projects going on in my life right now. They sold for less than $100 out the door.