If by “rapidly” and “quickly” you mean “in a lot less than an hour” then OK.
Liquid propane can flow out of a tank for a remarkably long time, depending on the temperature, aperture size and tank construction, and as @Bonivus_elderheart noted, in the video it looks like that’s what’s happening at the point when the tank is kicked. Note the flareup as the liquid is sloshed out of the hole!
Before it can expand into a gas, the liquid propane has to take up heat (PV=nrT) and this is not at all instantaneous. If you release the valve on a large tank, you will see ice forming on the steel as all the heat is forcibly sucked out. As that steel gets colder and colder there is less available heat and the process of liquid/gas state conversion slows down, and the pressure drops at the outlet. Eventually the outlet can even ice shut once there isn’t enough internal gas pressure to blow off the ice. If you are burning the released gas very nearby, this of course provides more heat and prevents icing up, but it takes measurable time for the heat of the burning gasses to be transferred to the liquid remaining, so if there’s a large volume of liquid it could take ten minutes or more to convert it to gas.
There’s a table of vaporisation rates based on temperature and wetted thermal transfer area here.
You are right, but at first propane doesn’t have to draw heat from the outside, as long as liquid’s temperature is well above boiling point. It’s very similar to superheated water:
Of course for such violent effect the depressurization must be very rapid, more like tearing gas cylinder apart than opening the valve. When depressurized at room temperature, the propane is already superheated by about 60 degrees C.
Once the temperature drops, the boiling and evaporation slows down due to required heat transfer, exactly as you said. At this point most of the propane is still in liquid state due to large amounts of heat needed for phase change.
I own hand held 110kW propane torch, and it manages to cool down 9kg gas cylinder in about 2 minutes to the point of limiting it’s output.
My friend Pedro the Cruel and I wanted to build a combination camp shower and keg chiller using this effect - the idea being that we’d heat water with propane and suck the heat out of the beer at the same time. Unfortunately we never got it to work, and the math guys (I am not a math guy!) did some analysis and said it would not be possible unless we ran the shower for impractical amounts of time at dangerous temperatures.
Or worse, the valve gets cold enough that it freezes open, which is a super scary scenario if you are trying to contain a leak.
Propane is one of those fuels that both demand respect and punish poor treatment. It’s not as merciless as, say, acetylene (It’s more stable for starters), but there’s a reason most firefighters call the standard 20 pound tank of propane a barbeque bomb. (I’ve been calling the smaller 1 pound cylinders grenades, but that’s just my sick sense of humor.)
Remember propane is also heavier than air, so a leak inside will pool near the floor until it finds an ignition source. I carry four tanks of acetylene, but they are stored upright, and you are there when using them. When not in use the valves are shut. Acetylene is also almost exclusively used by trained professionals, so it is in fact safer.
Rules of thumb for portable bottles: keep acetylene upright only. Other than that, if it’s sold by volume, then it’s a gas, so lay the bottle any way you want, it’ll come out gaseous. If it’s sold by weight, it’s liquid, if you want gas stand it upright with the valve at the highest point, if you want the liquid phase turn it upside down with the valve at the lowest point.
Yeah, I hate propane heat (which I have) for exactly this reason. Proper methane (natural gas) is delivered at way lower pressure and does not pool, so it’s a bit safer.
This is why you are supposed to fill them with water and dish soap and allow it to sit for some time prior to draining it and then cutting. The water obviously pushes out any remnant flammable gas that may be inside.
Pipes and tanks that have had HVAC propane in them for many years will stink an incredibly long time, I can tell you that from experience! I would expect a good detergent would break it down, but I just threw the damn things outside once I figured out what was going on.
Possibly? I know that soapy water is used for leak detection on all forms of pressure vessels- tanks and tires at least. It’s probably less helpful on politicians because the lies come off too easily.
One of the small pleasures of my scientist days was that my route to the lab each morning took me past the big nitrogen tanks right at the time when they were refilled.
Huge condensation clouds; it was like walking through a Dr Who set.
