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Steam Requirements / Boiler Sizing

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  • Steam Requirements / Boiler Sizing

    I'm in the process of sizing my steam boiler for a 15 BBL 3-vessel brewhouse with a steam-jacketed mash tun and HLT. The total steam requirements (#/hr) are:

    Mash Tun 420
    Brew Kettle 380
    HLT/Combitank 440

    However, I'd really like to only get a 399kbtu boiler for environmental, space and cost reasons. We won't be doing back to back brews on the same day for many years, and the 399 kbtu boiler will heat up the HLT from 60 to 212 in 90 minutes or so, which wouldn't really put much of a dent in our brew day timing.

    Is there a situation where I'd want to be able to provide full steam to two components (or three) simultaneously?

    I would expect the sequence of events to go like this (for a decocted lager)

    1. Heat up HLT to strike temperature (HLT only)
    2. Dough in. (nothing)
    3. At some point during the mash, decoct some mash. (Mash Tun or Combi only)
    4. Mash-Out (Mash Tun only)
    5. Lauter (probably brew kettle only)
    6. Heat the wort to a boil and boil. (Brew kettle only)

    What are your thoughts? Additionally, if a vessel has a steam requirement of say, 440 #/hr steam, and I provide 400... do I just get 10% less heat transfer rate?

    I'm a licensed Mechanical PE, but I've never worked with low pressure steam-jacketed vessels before.

    Cheers,

    baybrewer

  • #2
    I am by no means a steam expert but I can share with you the things I have learned with the two different systems I have had set up in our breweries. The first and smaller of our two systems is a 5bbl and is fired with a low pressure (~195K BTU) boiler and our 20bbl is fired with a high pressure 25hp (~825K BTU) with a pressure reducing valve. We run the low pressure at 14psi and the high pressure boiler at 80psi with the PRV reducing to 15psi just before the drops. The performance of your system is highly dependent on the design of the total system not just the boiler rating, especially important with the low pressure boilers is correctly sizing the header so that your boiler will have a large enough reserve of steam, think of it as storing heat for when your appliance calls for it. In low pressure (and high pressure systems) it is possible to have such a high call rate that you can collapse the steam column in the supply header and have your boiler totally lose steam if the boiler is undersized or the header doesn't have enough reserve steam, it will take a very long time to get back up to pressure. Additionally pay attention to the traps on the return side and how much pressure differential it takes to open them as well as the plumbing for the condensate return. If you are planning on running the return condensate via steam pressure to the return tank remember that for every inch you have to push the condensate column up you will loose efficiency as you are using some of the steam energy to move the condensate. All of these factors in addition to length of run from the boiler, using the correct steam solenoids on the supply side (another pressure differential dependent item), proper insulation of the header and drops, will seriously affect your system performance. I would highly recommend that you hire an engineer that really knows steam to design your system it will pay off in dollars and performance in the long run. My two cents. If you would like to discuss further please feel free to email or PM me and maybe we could talk on the phone or email if you like.

    Prost.
    Luch Scremin
    Engine 15 Brewing Co.
    luch at engine15 dot com

    Comment


    • #3
      I could help you with sizing, but I would need to know more about the vessels and the pressure/temp requirements.

      Remember that even with the small saturated steam boilers, you have to plan for some blowdown. Usually 3.5% that goes straight to the drain.

      You mentioned a thermal limit to the boiler. Is this based on the net heat input or the steam output? That greatly affects selection as well.

      I assume you are firing natural gas. At this point you are looking at a mass/enthalply balance and then working up the losses and inefficiencies of the system. I would have some time next week to play around with a few options, shoot me a PM and see what we can come up with. No matter what, you will have to hire an engineer that can probably seal drawings for your new boiler and gas piping so that it meets ASME and NFPA codes.
      Homebrewer/Future part-time brewer
      but I do have 1 professional brew under my belt and on the books, and its still on the menu at that particular bar even though its not being served right now.

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