1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Pressure Canner BTU's Needed to Reach 20 PSIG?

  1. Mar 30, 2015 #1

    I've built a pressure canner that I'm using as a process reactor. I have had it pressure tested to 20 psig and have a pressure relief valve set at 30 psig. I need help in figuring out the following questions:

    How do I figure out the btu's required to bring the thermal mass of the steel canner at 60 F up to 300 F?
    ~ Elevation is 300' above sea level.
    ~ Propane is fuel source.
    ~ The canner is broken into three steel pieces, but welded together:
    1. Bottom plate is 36" in diameter and 1/2" thick.
    2. Vertical pipe (wall) is 3/8" thick and has a outside diameter of 36" and is 36" tall.
    3. Top plate is 40" in diameter and is 3/4" thick.

    How do I figure out the btu's required to fill the canner with steam at 20 psig?
    How much water is needed?
    ~The internal volume is 36643.536 cubic inches

    The answers will help determine how much propane I will need to use. I do understand that once the first process has been done, the steel will hold onto 200+ degrees F of heat and the second process will take less fuel to heat to 20 psig. But if I assume the 60 F to 300 F was each process, I can assume a tank will last me so long (when actually it will last longer).
  2. jcsd
  3. Apr 1, 2015 #2


    User Avatar
    Gold Member

    Hi Duncan!

    I worked on your problem for a bit yesterday, but nearing the end, I think I suffered a minor stroke.
    No worries, I'm much better now.

    Anyways, what I decided was, that although your problem is "textbook solvable", the real world answer will be nowhere near that.
    There are just too many variables.

    About the only things I was able to determine, was that your vessel has a mass of 386 kg, the change of temperature was 133 degrees Kelvin, and 180,000 joules are required to change your vessel per degree Kelvin.

    Constants I used:
    specific heat capacity of steel: 0.466 J gm-1 K-1
    density of steel: 7900 kg/m3

    C = CP * m
    Q = C ΔT

    ps. Do you know a guy named Dave Orange?
  4. Apr 1, 2015 #3
    Thanks for the help, sorry about the minor stroke...I had one just now trying to figure out what that triangle was in the equation...

    Which Dave Orange? The Klingon actor from Start Trek or the 25 other Dave Oranges on Linked-In?

    I may just have to do trial and error with a 200k btu burner and see how many reactions I can get from the tank of propane...
  5. Apr 1, 2015 #4
    Dave Orange.jpg
    Is this the Dave Orange your talking about?
  6. Apr 1, 2015 #5


    User Avatar
    Gold Member

    Just ask next time.
    I don't remember the historical reason for why the triangle means "a change of", but I know what it means.

    The one who lives in Rainier Oregon.

    That was my next suggestion.

    Just remember to collect all the data:
    ambient air temp
    wind speed
    weight of propane used
    distance of burner from bottom of boiler
    diameter of burner
    number of holes in the burner
    temperatures of various parts of the boiler whilst warming it up

    I could add more variables, but I don't think Greg could afford the bandwidth.

    You might know him as "Handsome Dave".
    Sorry that I don't have a picture of him. I'll ask around.
    Last edited: Apr 1, 2015
  7. Apr 1, 2015 #6
    Dave Orange from Rainier, OR... That's ironic... I grew up in Rainier, OR. How are you associated with him? My family lived there from the early 80's to late 90's, my father worked at the nuclear power plant - Trojan - owned by Portland General Electric.
  8. Apr 1, 2015 #7


    User Avatar
    Gold Member

    I met his future wife, back around the mid 1980's.
    Ha! Irony, upon irony. One of the first applications I submitted for work, after I exited the Navy back in 1983, was sent to PGE, to work at Trojan.

    Small world.

    ps. I last visited Fairbanks when I was about 7. We lived in Anchorage. Dreadfully rickety bridge we had to cross on the way their. It looked to be about 3 miles down to the bottom of the canyon. Odd to think that Alaska and I are the same age.
    Last edited: Apr 1, 2015
  9. Apr 2, 2015 #8
    Hello Duncan,

    Here's my best try at it. Ok, first lets figure out the volume which is 3.14 x (18x18) x 36" = 36,625 cubic inches rounded off. 1 gallon of water is 231 cubic inches. 36,625 cubic inches divided by 231 cubic inches per gallon = 158.55 gallons. 1pound of water = 8.345 pounds. 8.345 x 158.55 gallons = 1,323.1 pounds of water. 1 BTU is the amount of energy required to raise the temperature of 1 pound of water by 1 degree F. From the steam tables I came up with 259 degrees F at 20 psi so I'll call it 260. 260-60 ambient = 200 degrees we want to raise it so 1,323.1 pounds of water times 200 = 264,620 BTU. Propane has 92,500 BTU/gallon so 264,620 divided by 92,500 = 2.86 gallons of propane. I know atmospheric type steam boilers are only about 70-75% efficient so I'd take that 2.86 x a 1.3 = 3.72 gallons of propane. This is not taking into account steel thickness. 300 feet elevation will only change your BTU slightly so this should be fairly close. I would welcome others thoughts on it but this is my story and I'm sticking to it. My wife is now going to have me committed after explaining to her what I was working on! Lol. Anyways hope this helps.

  10. Apr 19, 2015 #9
    Thank you Nascarnut,

    That is very helpful! I still have yet to actually fire the canner up...But Amerigas is delivering the 120 gallon tank this week. So it looks like I should be able to get close to 30 uses out of a tank.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Pressure Canner BTU's Needed to Reach 20 PSIG?