Propane Vaporization Help
Propane Vaporization Help
(OP)
I will have a propane burner that burns vapor at a max rate of 140 MMBtu/hr. The Application is a large grain dryer which only operates in summer in the south when lowest ambient temp is around 70F at night and much higher during the day (90-100F). I'm looking at two options: the first is going with a 30,000 gallon tank and a vaporizer, and the second option is getting multiple 30,000 gallon tanks and relying on ambient air to do the vaporization. To figure the cost difference in the two options, I need figure out how many 30,000 gallon tanks I would need to do the required vaporization. I found a spreadsheet online that helped me calculate the tank vaporization using ambient temp, tank dimensions, and percent fill. The sheet only went up to 20F for ambient, but I interpolated up to 70F since it looks like a linear relation. For a 30,000 gal tank with a length of 792" and diameter of 108", at a 60% fill, at 70F ambient, I find that the tank can vaporize approximately 42.8 MMBtu/hr. Assuming I keep my tanks topped off at least 60% full, I could get by with (4) 30,000 tanks.
Option 1:
30,000 tank cost = $45,000
Water bath vaporizer cost = $100,000
total = $145,000
Option 2:
(4) 30,000 tanks = $180,000
So, in option 2, for $35,000 I could do the same vaporization with no moving parts, maintenance issues, or additional energy input plus gain 90,000 gallons of additional storage. I'm thinking about going with option 2. Can anyone punch some holes in this logic for me? Also, I know code say we can't paint our tanks black, but it would seem like that would help vaporization and could decrease tank count. Perhaps paint it black and have a shade that is in place when we aren't pulling from it. I've also thought of other creative methods to decrease tank count, such as bathing the tanks with water from a nearby pond that gets as hot as bathwater in August, or solar water heaters. It has to work on cloudy days and at night though! Any other ideas?
John
Option 1:
30,000 tank cost = $45,000
Water bath vaporizer cost = $100,000
total = $145,000
Option 2:
(4) 30,000 tanks = $180,000
So, in option 2, for $35,000 I could do the same vaporization with no moving parts, maintenance issues, or additional energy input plus gain 90,000 gallons of additional storage. I'm thinking about going with option 2. Can anyone punch some holes in this logic for me? Also, I know code say we can't paint our tanks black, but it would seem like that would help vaporization and could decrease tank count. Perhaps paint it black and have a shade that is in place when we aren't pulling from it. I've also thought of other creative methods to decrease tank count, such as bathing the tanks with water from a nearby pond that gets as hot as bathwater in August, or solar water heaters. It has to work on cloudy days and at night though! Any other ideas?
John





RE: Propane Vaporization Help
What is the pressure relief set at the tank for? That would be the main driver whether you want to try coloring the tank black for example and someone doesn't move it into shade for example. Also, are you renting these tanks or buying them?
The pond is an interesting idea, are the ponds large enough to provide the heat you'll need to vaporize this much propane? Can you just back the tanks into the pond so they are partially submerged (you need to be able to get them out later of course)? You'll get a lot better heat transfer water to tank than air to tank. However, a rental pump with a distributor header to distribute water over the top of the tank wouldn't be that difficult to fabricate either and give you much the same effect.
What sort of propane pressure do you need for the burner? I'm thinking 10 to 25 psig would be ample and that corresponds to a pretty low temperature in the tank or are you constrained to a higher minimum pressure because of a minimum design temperature. I'd be interested in seeing what the basis behind the spreadsheet calculations are.
Water vaporization systems I've seen have been pretty low maintenance, I'm not sure I'd be all that worried about it.
Final thought. Can you get a single tank and burner and do a field check to see what a tank would supply? You could then try the water spray idea and see how it works?
RE: Propane Vaporization Help
I guess the whole idea is: why spend a whole of lot of money on vaporizers if I can do the same thing with more tanks at about the same price and gain a whole lot of storage capacity - of course this only works since I'm running during the summer. Wouldn't work if we had to run during the winter, which is ok though.
John
RE: Propane Vaporization Help
If your vaporizer costs $100,000 you are using the wrong equipment or vendor. Hot air balloons have vaporizers that are simply a coil of tubing around the burner flame. I would expect this to be pretty standard equipment for large burners.
RE: Propane Vaporization Help
Trust me, large vaporizers are pricey. They are a few brands that can handle the truckloads/day volumes I'm talking about - algas, alternate energy, etc. if you experience in other brands that are less expensive please feel to mention them - ill take a look.
RE: Propane Vaporization Help
RE: Propane Vaporization Help
RE: Propane Vaporization Help
The main question is: can I substitute either more tanks or ambient summer heat in lieu of off-the-shelf vaporizers.
Related questions:
Is my calculation of how much a 30,000 tank will vaporize at 70F ambient correct?
Are there creative ways (off the shelf or not) to warm the tank so that it vaporizes more than at just 70F ambient, which will decrease my tank count?
RE: Propane Vaporization Help
RE: Propane Vaporization Help
RE: Propane Vaporization Help
Good luck,
Latexman
RE: Propane Vaporization Help
RE: Propane Vaporization Help
I've done some more research on this subject and now the central question seems to be what's the vaporization capacity of a 30,000 gal tank @ 70F and 60% filled. Most rule-of-thumb charts I've seen online are from the ASME and only go up to 20F. I interpolated and came up with 42.7MBtu for 70F which is where I'm basing on how many tanks I would need to obtain the amount of vaporization. I'm now questioning my logic, because I had a local propane guy say that the charts only go to 20F, because you hit a wall on how much the tank can vaporize, and that I must buy vaporizers with my burner capacity. My answer to him was that the charts only go up that far because most people in North America use their propane tanks all year long and 20F is a good place to stop the charts. So can anyone shed some light on this? How do we take the charts out to 70F or higher temps? I've attached an example chart so you can see what I'm talking about.
RE: Propane Vaporization Help