May 7, 2020 at 3:21 pm #3645658
Before I devote some serious cabbage to the project I’m looking for input on the concept of a UL propane stove with a 300 BAR (4,351 PSI) refillable 0.6L composite fuel bottle like shown on the lower right here:
Using something like a re-jetted Fire Maple Split/Blade remote canister stove:
I wouldn’t fill the fuel bottle to a higher pressure than standard propane cylinders like Coleman (I think that’s about 200 PSI).May 7, 2020 at 4:15 pm #3645663
IsoPro has almost as much BTU/LB as propane. With that stove, you can invert an IsoPro canister for liquid feed. I would imagine a propane bottle would be pretty heavy in comparison. Propane cost would be much cheaper if you refilled from bulk . . . but can you refill and how many times before the valve might fail?
Caffin would know more than me.May 7, 2020 at 4:40 pm #3645669
Better in cold weather, better power-to-weight ratio, lower cost by refilling from bulk, less waste.
I have an inquiry in to the company that makes the 0.6L composite fuel bottles to see how they compare to an empty steel “8 oz” isobutane canister. Given the relative strength differences a composite bottle rated for the same pressure as standard propane bottles should be lighter.May 7, 2020 at 5:07 pm #3645670
Yes, lower cost and especially less waste are points to consider.
However, I don’t think there is much difference in performance when IsoPro is inverted. Boiling points for IsoPro are usually stated for upright canisters.
Of course I’ll defer to Caffin or David Thomas.May 7, 2020 at 5:41 pm #3645676
Yes, I’m hoping our resident stove innovator and science whiz will contribute their thoughts.
From some research on the internet:
Propane has a boiling temperature of -43.6°F vs. butane at 28.4°F.
Butane can reach maximum temperatures of around 2,400 degrees Fahrenheit. The maximum temperature of propane is around 3,600 degrees Fahrenheit.
Total heating value after oxidation of propane is 19768 BTU/lb. and butane is 19494 BTU/lb. So energy per gram is almost the same. But it’s not just the BTU output that’s important, it’s the transfer rate. It involves BTU generation in the flame, as well as flame velocity.
Propane has a higher burning velocity. That means that even if the energy stored in a given volume of butane were slightly higher (it’s not), you’d get the energy out of the propane faster. Even more significant is the combustion ratio. Propane takes less volume of oxygen or air (mostly oxygen plus nitrogen) to burn. What that means is that for the energy in a given volume of butane, more oxygen is required to get it out. Those other gases, nitrogen and oxygen, are also at room temperatue when mixed with the fuel, and share in the energy release by the fuel to heat it to flame temp. That results in the stated amount of BTUs being released by that volume of fuel gas, but it’s diluted through a much larger total volume of flame gas, thus giving a lower flame temperature, especially when burned in air (remember all that excess nitrogen)
It’s the combination of higher flame temperature, and higher flame velocity, that allows propane to perform betterMay 7, 2020 at 7:07 pm #3645690
I’d be very interested in a few of those. That’s a really high pressure rating – compatible with CNG (although that’s many $1,000s for the compressor station).
1) cheap refilling to the point of being essentially free,
2) no-fuss operation down past stupid-cold temps,
3) ease of refilling (no concerns about blends of butane/propane, and
4) extremely widespread fuel availability if you bring your refilling valve along (any BBQ grill, any RV, any hardware store selling 1-pound Coleman propane cylinders). Not a trip to REI but stopping any friend’s or friendly person’s house lets you refill.May 7, 2020 at 7:28 pm #3645696
I know, crazy high pressure capability! I’m hoping to find either a carbon fiber or titanium bottle with the same pressure rating as regular steel propane bottles/tanks. Not easy to find, but it would be great to be able to use cheap and refillable propane.May 7, 2020 at 11:25 pm #3645724”V” (CzechClown)BPL Member
David G. – Do the bottles you speak of have a Lindel value on top, to which you could attach a stove ?May 8, 2020 at 12:54 am #3645729
Not sure. Haven’t heard back from the company yet but my guess, based on the huge differences in pressures (4300 vs. 200), is no. Not sure they come with a valve at all, as opposed to a threaded opening to accept different kinds of valves or fixtures. I kind of assumed I would have to make some kind of adapter.May 8, 2020 at 1:27 am #3645730”V” (CzechClown)BPL Member
David – I sent you a private messageMay 8, 2020 at 2:15 am #3645732
The idea of putting 300 BAR in a screw-thread canister is ‘exciting’. That is more than 30x the rated strength. Really ‘fun’ stuff. Just about good enough for metallic hydrogen. More likely though is scuba gear and other oxygen supplies (fire, mountaineering, etc).
I wonder about the size of the bank loan needed for those bottles though. Probably many hundreds of dollars each. Bet they are heavy too: the original application would not have been worried about that.
At one stage Sievert in ?Sweden? sold fly-spray style canisters of straight propane. They would not export them to Australia: too warm.
In the end, I lost interest as a remote inverted canister stove with any of the ‘normal’ canisters solves all the problems anyhow.
CheersMay 8, 2020 at 10:29 am #3645772
“Normal” butane set ups do not solve the problems of availability, long-term fuel cost and waste. And propane offers the possibility of faster boil times with fewer grams of fuel at much lower temperatures.
The barrier to using propane for backpacking seems to be the higher vapor pressure of propane and corresponding weight of disposable steel pressure vessels. If that issue can be solved it opens up many possibilities.
What threads are you talking about? 30X more than rated strength? Did you miss where I said I would not fill the bottle to more than the normal 200 PSI for propane canisters?
I don’t know how heavy the bottles in the picture are. They are intended for medical purposes, hence the high pressure ratings. As I mentioned, I have written to the manufacturer asking about weight and cost. Whatever bottles rated to 300 BAR weigh, bottles rated to 14 BAR (200 PSI) can obviously be made to weigh far less. And the cost of the bottles is related to the scale on which they are manufactured. If manufacturing is scaled up the cost per unit goes down.
I am also trying to find suitable titanium bottles. If I can’t source them I may try making my own. It’s an intriguing possibility, because titanium bottles could be made the same size and shape as butane canisters for compatibility with existing stove designs.
The idea is to see if I can make a proof of concept prototype that meets criteria of safety and weight. If that can be achieved, then tackle the issue of cost. I may end up with a “one off” but it will “fun.”May 8, 2020 at 11:47 am #3645788
Found a source of spherical titanium pressure bottles in India in diameters 100mm – 600mm. Have written about weight and cost to that manufacturer too.May 8, 2020 at 11:49 am #3645792
While it’d be great if those are UL and so strong, I don’t see how it’s possible. To hold in 10 times the pressure, the walls need to be 10 times as thick. Higher strength-to-weight materials and a more efficient shape (like those hemispherical bottoms) can help a few fold, but not and order of magnitude better than steel.
I’ll often fondle and caress some of the hair spray and sun-screen spray cans in the store, especially in sample sizes. They’re aluminum cylinders, with strong, inverted bottoms and seem like they’d handle a lot of pressure not because they were designed to a high burst strength, but because of their small diameter and the minimum wall-thickness to avoid dents and flexing in an upper-end product. Alas, they’re not lindal valves but something akin to spray paint cans or butane for lighter refills.May 8, 2020 at 12:01 pm #3645798
Here are some data points for “5-gallon” (really about 4.4 gallons), 20-pound propane-capacity cylinders in pounds of tank per pound of propane and cost:
Steel: 0.90 pounds steel/pound propane, $49
Aluminum: 0.72 lbs Al / propane, $260
Composite: 0.61 lbs composite / propane, $151 (actually 17-pound capacity which is why I used lb/lb.)
These are all mass-produced and available globally, although only the steel version is mass marketed at Home Depot, from Blue Rhino at the supermarket, etc. So I expect the weights are pretty well optimized (without getting into crazy-strong fibers and resins).
There aren’t a lot of people who’ll pay for the weight savings – a plumber who hauls their tank around with them all day, forklifts (I’ve had to schlep an empty across a big warehouse and bring a full one back to the out-of-fuel forklift and 5 pounds lighter is 5 pounds lighter), and I see aluminum ones being flown in small planes to remote locations. Mostly I’ve seen composite and aluminum ones used for corrosion resistance in coastal and marine settings.
Those prices perhaps show why our fuel comes in steel containers.May 8, 2020 at 1:30 pm #3645814
Since I have a TIG welder and DIY argon purge box I may try my hand at fabricating a small titanium spherical bottle myself. Also may try welding some kind of adapter into one of those high end aluminum hair spray or sunscreen bottles.
Back when I was 17 (if you’re into archeology) I was a mechanical engineering pressure vessel designer for Fluor Corporation. I remember that the forces on the walls of the vessel went up by a square of the radius, so smaller diameter makes a BIG difference.
Per UG-27 of ASME Section VIII, Division 1 the formulas for calculating wall thickness:
Cylindrical shell: thickness = PR/SE – .6P
Hemispherical head or spherical shell: thickness = PR/2SE – .2P
P = Design pressure (PSI) = 200
R = Inside radius (in.)
S = Allowable stress (psi)
E = Weld joint efficiency factor (25% for a safety factor of 4)
Using these formulas for steel I get a wall thickness of 0.03″ for a 4.25″ diameter cylinder (like a large butane canister), 0.01″ for a 4″ diameter sphere, and 0.01″ for a 2″ diameter cylinder.
As for weight, based on the fact that titanium is about 60% the weight of steel and that both large and small steel butane camp stove canisters weigh approximately 4 oz, I would estimate that a titanium canister of the same shape would weigh 2.4 oz and a spherical bottle of the same volume would be even lighter, in the neighborhood of only about an ounce.
No doubt I’ve messed up these calculations. It’s about 45 years since the last time I did them.May 8, 2020 at 4:03 pm #3645860
>> I would not fill the bottle to more than the normal 200 PSI for propane canisters?
DoT regulations require testing at 50 C, and the vapour pressure of propane at 50 C is about 22 bar or 320 psi. And the regs have a hard requirement that they permit zero failures during testing.
While this may not be relevant for private construction, it is worth noting all the same for personal safety.
I do not know whether propane can cause hydrogen embrittlement (it has plenty of dangling hydrogens after all), but that is something to take into consideration as well. A bottle rated for oxygen may not be rated the same for propane.
CheersMay 8, 2020 at 4:05 pm #3645863
>> I’ll often fondle and caress some of the hair spray and sun-screen spray cans in the store, especially in sample sizes.
We are not supposed to mention that!May 8, 2020 at 7:17 pm #3645891Chris FormyDuvalBPL Member
Bernzomatic did briefly sale propane in small cans. I never got around to buying any before they disappeared from the local hardware store. Hikin’ Jim did a write up several years ago. I assume either something bad happened or somebody realized something bad could happen combined with low sales. I remember them being more expensive than 8oz stove canisters not to mention much more than the heavy 16oz cans otherwise I would have gotten them, you know, just in case I ever had a need.May 8, 2020 at 9:50 pm #3645908
Just don’t dunk it in LO2…May 8, 2020 at 10:16 pm #3645909
On a serious note, I think this is a great idea. Propane is clearly superior to butane and even iso-mixes. Butane only gets used in backpacking because the canisters are lighter. People spend a lot of bucks to drop weight off of there backs around here. I would guess if you can get a reusable canister for under $100 that weighs less than an isobutane canister for the same volume, you would have a market. For under $100, you would probably need to find an overseas manufacturer.May 8, 2020 at 10:30 pm #3645913
Sent some to Roger for testing but they didn’t survive transit:May 8, 2020 at 10:34 pm #3645914
There aren’t a lot of people who’ll pay for the weight savings
Some composite 20lb propane tanks are translucent — you can see how much propane is in the tank.May 8, 2020 at 11:12 pm #3645915
>> Some composite 20lb propane tanks are translucent — you can see how much propane is in the tank.
Really? I would love to see a pic. URL?
CheersMay 9, 2020 at 2:04 am #3645923
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