So I've got these three propane tanks...

Discussion in 'Reverse Flow' started by jcbigler, Jun 2, 2015.

  1. jcbigler

    jcbigler Smoking Fanatic SMF Premier Member

    So I have these three old, unused propane tanks on the property.

    They belong to my in-laws, but I have been given permission to cut one of them up and build a smoker out of it. 

    (Disclaimer: yes I will contact a professional propane tank technician to evaluate, drain and render safe for cutting before I do anything)

    The first one is probably in the best shape, and will likely be used again. 200-250 gallons I think, it's about 8 feet long and maybe 3 feet wide? Apologies for the lighting and shadows. There also seems to be an ant colony living in the valves under the orange cap.  I think this one would be the ideal size, but it is in the best shape and will probably be used again for propane. 


    The second one is smaller, a litter shorter and narrower, maybe 6 feet long and 2 to 2 1/2 feet wide, but the hardest to get to. Judging from the size compared to the first one, I think maybe it's in the 150 to 175 gallon capacity?


    The third one is the biggest. It's maybe 6 or 7 feet long, but a good 3 1/2 or 4 feet wide. Looks like it could be close to 300 gallons. It will also be the easiest to get to and remove as it is not covered in brush and vines. 


    My goal is to build a large smoker that I can use for larger events, like weddings and social functions, maybe some competitions. In fact my brother has asked me to smoke a bunch of pulled pork and ribs for his wedding in June of 2016. So I figure: instead of wasting a bunch of money renting a smoker, why not just waste a bunch of money and build one and then have it to keep? 

    So, I want to build a reverse flow smoker with two levels of slide out shelves in the main cooking chamber and a vertical warming/cooking chamber over the firebox. I would like to be able to smoke up to 8 briskets easily and a dozen racks of ribs, all at the same time. And it will be trailer mounted, probably with a smaller grill for cooking a small number of hamburgers and hot dogs to keep me and my crew alive while I am smoking the real food. 

    Hopefully when my father-in-law gets in in a coupe of weeks we can tackle these propane tanks and get them into a position for better pictures and a thorough evaluation and measurements. I think the 3rd tank may be too deep to really use effectively. So the smaller one may be the one I end up using assuming it is big enough to do what I want with. 

    I would appreciate any insight into which tank to chose and why. 
     
    Last edited: Jun 2, 2015
  2. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

  3. smokejumper

    smokejumper Smoking Fanatic

    Short and fat is where it's at. Tank #3 would be my choice hands down.

    You get the most rack space for the tank volume, and it will fit on a smaller trailer.
     
  4. lendecatural

    lendecatural Smoking Fanatic

    Yup, go with the fat girl this time for sure...
     
  5. jcbigler

    jcbigler Smoking Fanatic SMF Premier Member

    By the looks of it, I could probably go three high on the shelves with the big one. Two wide, by three high, is a tonne of meat! Might not have to even bother with the vertical cooker and warmer if the dimensions are that big. I just think the ergonomics of having shelves that are almost 4 feet deep would be less than ideal.
     
  6. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Have doors on each side of the smoker... check out boykjo's new smoker he just built...... doors are smaller and lighter..... easier to open.. no deep reaching.....
     
    Last edited: Jun 3, 2015
  7. smokejumper

    smokejumper Smoking Fanatic

    I would have two racks side by side at each level, each half the width of the door opening. When pulled out, you can access the stuff in the back from the side of the rack. The door would only be 5' to 6' wide, so the racks would be 2 1/2' to 3' wide which is manageable. You could even go 3 across for even narrower racks.
     
    Last edited: Jun 3, 2015
  8. What Propane Tanks ???   I just see smoker waiting to be built

    Gary
     
  9. jcbigler

    jcbigler Smoking Fanatic SMF Premier Member

    Ha hah...you and me both! 

    Been talking to my in-laws. Surprisingly they are both in favor of me cutting up one of them. I think we will keep the middle sized one for use in the future. The other two are fair game. But until I can pull them out of the brush and get them back to our barn to measure and evaluate I won't be able to make a final decision on which to use and what the design should be. 

    What's the standard welder set up to use for tanks like these? I've been looking at small mig welders. I know that we have an old arc welder in the back of the barn. My dad said he can teach me either method in a weekend. 
     
  10. smokejumper

    smokejumper Smoking Fanatic

    There is no "standard welder setup".

    There are at least a half a dozen welding methods that work well. For smokers or any other stuff you want to weld

    Stick welding with an "old arc welder" is one of the best if you learn how to do it.

    Take your dad up on the offer and learn to stick weld. What you learn there will apply to other methods as well, but you can do everything you need to with the arc welder.
     
  11. jcbigler

    jcbigler Smoking Fanatic SMF Premier Member

    So I took my father in law with me to go check out the various tanks that we have and get some more accurate measurements.

    Turns out that the one that I thought was the middle sized one is actually the biggest one. It's 500 gallons, 119" long by 37" wide. I don't know what the thickness of the metal is, I'll assume that it is 3/8" thick? 

    Here are some better pictures of it. We're going to disconnect it and drag it out into a better working area on Wednesday probably. 



    The smallest of the two tanks is about 8' long by 30" wide, which I think is actually 7' 10", which would make it a 250 gallon tank by the standard sizes that I have found online. 

    The other one that I thought was the largest, seems to be an odd size. It is about 8' 6" long and about 36" wide (maybe 37"?). So it's about a foot and a half shorter than the 500 gallon, but close to if not the same width. Maybe it's in the 400 gallon range?

    I also found this very small compressor/propane tank, which I might build into a micro smoker. The tank itself looks to be about 26" long and 14" wide. 


    Now that I know the actual size of the large tank, I'm going to start running the numbers through the build calculator and then sketch up a design or two.
     
    Last edited: Jul 5, 2015
  12. Here is one I just finished building out of a 24"x10' propane tank. It ended up having a 30" firebox and a 66" smoke pit. The top rack slides out. If you go bigger in diameter all I would say to do is build all your racks to slide out and you will be fine.


    And get some long grilling tools.
     
    Last edited: Jul 8, 2015
  13. One other thing. Every propane tank I've ever tried to cut a door out of with all kinds of different tools has sprung on me. I weld a brace inside my door now before I finish cutting it out.
     
  14. inkjunkie

    inkjunkie Master of the Pit

    I prefer Mig welding. Not much of a learning curve. When done correctly damn near 0 splatter. You will need an angle grinder with both cutting and grinding wheels. If you will be cutting plates a plasma cutter sure does help.

    All that being said I was following a thread on another site. Fellow welded for a living. He used an Arc machine and an oxy-acetylene torch for cutting. He did all the cuts free hand, no guides were used.
     
  15. [​IMG]
     
  16. jcbigler

    jcbigler Smoking Fanatic SMF Premier Member

    I've been working on the design specs for these smokers. 

    Currently looking at the large 500 gallon and/or the small 250 gallon tanks. 

    Here's what I have come up with for the two tanks:

    500 gallon tank

    External

    Length, 119"

    Width, 37" 

    Thickness (assuming) .25"

    Internal

    Length 118.5"

    Width 26.5" 

    Cook Chamber internal volume = 123,992.4 cubic inches, 536.76 gallons

    Firebox Internal Dimensions:

    Length 34"

    Width 26.68"

    Height 35" 

    Firebox internal volume = 43,653.4 cubic inches, which is 106% of the recommended volume

    Smoke Stack Dimensions

    Length 34"

    Width 9" 

    Smoke Stack Internal volume = 2163 cubic inches

    Firebox to Cook Chamber Opening (this is where I'm still not sure that I have the right number):

    Partial round, Height 18", width 35.59" = 452.4 square inches. The Calculator calls for 496 square inches. Does this seem right? The height of the RF CC-FB opening would need to be more than the internal radius of the cook chamber, or wider than the diameter of the cook chamber. ???

    Firebox Vent Openings:

    I have 6 openings, 3 on each side of the FB each measuring 5" wide and 7" high for a total of 210 square inches

    And 2 openings on the upper side of the firebox in line with the CC-FB opening, 5" wide and 5" high, 50 square inches

    Firebox Vent openings total = 260 square inches, 174.7% larger than needed. 

    Attached is a Sketchup model of the 500 gallon smoker (the guy is about 5' 6" for scale):

     
  17. jcbigler

    jcbigler Smoking Fanatic SMF Premier Member

    The 250 Gallon Tank :

    External

    Length, 94"

    Width, 30"

    Thickness (assuming) .25"

    Internal 

    Length,  93.5"

    Width, 29.5"

    Cook Chamber Internal Volume = 63,906.7 cubic inches, 276.67 gallons

    Firebox Internal Dimensions:

    Length 28"

    Width 29"

    Height 28"

    Firebox internal volume = 22,736 cubic inches, which is 107% of the recommended volume

    Smoke Stack Dimensions:

    Width 6"

    Height 34" 

    Smoke Stack internal volume  = 1128.2 cubic inches

    Firebox to Cook Chamber opening

    Partial round, Height 13", width 29" = 260.1 square inches. The Calculator calls for 255.6 square inches, so it's 101.7% of the recommended opening size.  

    Firebox Vent Openings:

    I have 6 opening, 3 on each side of the firebox, each one is 4" wide and 4" high, for 96 square inches total

    and 2 upper vent openings inline with the CC-FB opening, which are also 4" high by 4" wide, for 32 square inches total. 

    Firebox Vent Openings total = 128 square inches, which is 166.9% of the recommended openings. 

    Attached is a Sketchup of the 250 gallon smoker. The guys is about 5'6" for scale. 

     
  18. jcbigler

    jcbigler Smoking Fanatic SMF Premier Member

    Some other random thoughts here.

    The 500 gallon tank is really big. But it doesn't seems like it can cook twice as much meat.

    I'm not running a barbecue business (yet). But I think that the 250 will cook enough for me to cook for 150-200 people for weddings and private parties etc...

    The rails for the cooking grates have the following specs:

    500 Gallon Smoker

    Lower rails: 36.75" wide, by 35.98" deep (2 each)

    Upper rails: 36.75" wide, by 28.5" deep (2 each)

    Upper grates located approximately 9" above the lower grates

    Total area for cooking grates = 4,733.4 square inches

    250 Gallon Smoker

    Lower rails: 34,25" wide, by 29" deep (2 each)

    upper rails: 34.25" wide, by 25" deep (2 each)

    upper grates located approximately 6.5" above the lower grates

    Total area for cooking grates = 3,699 square inches

    The 250 gallon smoker has 78% of the total square inches for cooking grates as the 500 gallon smoker. The cooking grates are 2.5" closer together from top to bottom on the 250. Is 6.5" inches enough room to get a single layer of briskets or pork butts on the bottom rack without touching the upper rack? 

    Probably going to build insulated fireboxes to help retain heat and make them more fuel efficient. 

    Either way, these will be mounted to a trailer, and I need to be able to tow the whole package with my Tacoma (tow package, max 6,500lb tow capacity). I don't think that will be a problem with either one. But I will build some utility boxes and wood boxes also on them.

    The ergonomics also seem better with the 250 as it can sit up a little higher and still be able to reach the upper cooking racks and not have to reach quite as far to get to the back of the racks either. 

    Also considering building a vertical warming chamber/cook chamber above the firebox to increase capacity/warm holding. 
     
    Last edited: Jul 20, 2015
  19. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member


    Firebox to Cook Chamber Opening (this is where I'm still not sure that I have the right number):

    Partial round, Height 18", width 35.59" = 452.4 square inches. The Calculator calls for 496 square inches. Does this seem right? The height of the RF CC-FB opening would need to be more than the internal radius of the cook chamber, or wider than the diameter of the cook chamber. ???



    That happens on long/skinny tanks.... To reduce friction loss from flow under the length of the RF plate, you can install the FB farther into the CC.... as far as you want.... AND it's OK to lower the RF plate to something comfortable.... I would still leave the gap at the non FB end to spec. or larger.. The 180 deg. change in direction, is a good source for loss of air flow...
     
  20. jcbigler

    jcbigler Smoking Fanatic SMF Premier Member

    What is the spec for the air gap at the opposite end of the cook chamber? I haven't seen anything specific. I was just going to leave the whole dome of the tank open and only take the RF plate to the end of the cylindrical part of the tank, which would be about 81" from the end of the FB/CC opening. 
     
    Last edited: Jul 20, 2015

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