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Wood Gasification Boiler Basics

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by jebatty, Feb 14, 2013.

  1. jebatty

    jebatty Minister of Fire

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    I prepared material for a conference yesterday. Here is a piece of that material that may be helpful to better understand some basics.

    Basics of installation for a wood gasification boiler.
    1. All plumbing after the boiler to the heating system/emitters is essentially the same as with any other type of hot water boiler, whether wood, electric, propane, natural gas.
    2. Unique aspects of the installation.
    a. Boiler return water protection: usually required – thermostatic valve, mechanical or motor driven, or loading unit – mixes boiler output with return water from the system to return water to the boiler at a temperature generally above 140F. This is important to prevent condensation of water vapor in the boiler and corrosion.
    b. Flue: generally Class A chimney (high temperature, stainless steel, double wall, insulated, rated at 2100F).
    c. Hot water storage, optional to required: allows for increased efficiency in operation and longer times between boiler firing.
    3. Important considerations.
    a. For proper boiler sizing and heating system design: calculation of heat loss for all heated structures.
    b. For heating system design: determination of required hot water flow rates, selection of proper pipe sizes to carry the water flow, determination of flow resistance in piping and heat emitters (pump head) at required flow rate(s), selection of circulating pump(s) to meet performance requirements.
    c. For greater flexibility in use and operation: low temperature heat emitters which provide needed heat at water temperatures of 140F or less, such as radiant in floor, radiant panels, high performance baseboards, etc.
    d. For greater efficiency and reduction in cost: locating the boiler (and storage, if any) in a space that otherwise would be heated: captures boiler operation heat loss for usable heating.
    4. Wood supply.
    a. Must be “well seasoned,” that is, dried to a moisture content usually in the 15-20% range, although some boiler manufacturers permit higher moisture content. Must not be “green” wood. Wood cut, split and stacked in the open air, with good air circulation, will take about one to three full summers to dry to a moisture content of 15-20%, depending on the wood species.
    b. Generally should be cut to lengths between 18 inches and 2 feet, depending on the boiler, for ease of handling and loading. Should be split to diameters recommended by the manufacturer, generally 3 to 6 inch diameters.
    c. Should plan to have sufficient well seasoned wood on hand at the beginning of the heating season to meet expected need for wood fuel.
    d. Wood suppliers providing “seasoned” wood usually supply wood not dried sufficiently for satisfactory burning.

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  2. Burning Alaska

    Burning Alaska New Member

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    Thank you very much. Succinct and helpful overview. I stumbled across it while searching for storage basics. Can you point me to a good thread with a nice overview of storage that is along the same lines as your post above? I’m looking for a couple things in particular: weighing the merits of pressurized vs. unpressurized storage, and a good overview of construction of a storage system (I’m leaning toward the “re-purposed propane tank” setup, but could be persuaded in a different direction if someone presented a cogent argument).

    Thanks again

    David
  3. Fred61

    Fred61 Minister of Fire

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    Why do folks indicate wood drying time measurment in "summers"? Is it a belief that wood doesn't dry in the winter or is it just one of the new metaphors for a unit of measure for people in need of a perspective, like measuring length in "football fields" and volume in "olympic swimming pools"? Both of which drive me insane when I hear them.
  4. ewdudley

    ewdudley Minister of Fire

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    I know what you mean, seems like you can't go the lifetime of a housefly without hearing one.
  5. DaveBP

    DaveBP Minister of Fire

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    I haven't heard any of those in a coon's age.
  6. Fred61

    Fred61 Minister of Fire

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    Turn on the TV and watch the nightly news.
  7. ewdudley

    ewdudley Minister of Fire

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    It's been a month of Sundays since I've seen the nightly news, more like once in a blue moon.
  8. Fred61

    Fred61 Minister of Fire

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    It took me a minute or two to get it. DUH!!! They're all over the place. I'm getting overrun.
  9. It's because
    You're slower than a herd of turtles stampeding through peanut butter.


    j/k
  10. Fred61

    Fred61 Minister of Fire

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    Maybe the brain is the first to go!
  11. Tennman

    Tennman Minister of Fire

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    Great job Jim. Seems appropriate for these points to added to that catch all Sticky. From my time hanging around here, now for over 5 years, heat loss calcs, wood quality, storage benefits, boiler selection are discussed frequently. But your item 3b, tends to be the most ignored of your list. The advice from my "Professional Expert" and "it worked for me" advice resulted in compromises in my system. Back in the day.... ~5 years ago... I was assured 1 1/4" dia pex is all I need and a Taco 0007 or 0010 is plenty. Well, I bought a bunch of 1 1/4" pex THEN did the flow calcs from the Taco TD10 datasheet. Bottom line, because of my distance (~340' round trip), fitting count, and the fact I had already purchased 1 1/4" pex - my flow velocity was ~20% higher than preferred and the only pump that had the horsepower for the job was the biggest Taco, the 0013. Had I ignored the "advice" and done the datasheet first, 1 1/2" pex would have saved me a lot of electricity expense (smaller pump) over the life of my system. Smaller pump, way lower flow velocity resulting in less "drag" or head loss, etc, etc. For those of us that have long runs, your item 3b is a big deal. 'Course most of ya'll's runs are far shorter than mine, but it's wise to double check advice of some "Professionals" and... put the boiler as close to the demand as possible. Cheers
    Burning Alaska likes this.
  12. BadgerBoilerMN

    BadgerBoilerMN New Member

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    There is more to pipe size than flow. If you store water you don't have to worry about low return temperatures.
  13. heaterman

    heaterman Minister of Fire

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    Nice summary Jim.

    Only thing I would add would be in item 2b and that would be a simple pump aquastat as an option to keep boiler temps elevated.

    That and I would probably CAPS LOCK, bold face, italicize and underline the part about seasoned wood. :)
  14. jebatty

    jebatty Minister of Fire

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    This might be true in your method of operation, but not in mine, and as a matter of basics and principle, I think it would be a mistake to not have a design plan which insures boiler return water of 140F or above, that is, boiler return water protection. I run my storage regularly down to 100F, as that is the input temp to my radiant floor. So water temp much less than 140F is the normal return to my boiler. Boiler return water protection is essential.

    Heaterman's comments are right on.
  15. Tennman

    Tennman Minister of Fire

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    After re-reading my post above I need to clarify. I was referring to a distibutor of boiler systems and components that gave me bum advice on some equipment very early on in my system build. It was all the guys here that kept me out of the weeds. Sorry, didn't want my comments misconstrued to think I was implying advice from the guys here to whom I'm very grateful. My point was be careful with advice from some distributors.
  16. +1
  17. henfruit

    henfruit Minister of Fire

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    We must always do the math first.Then purchase. Cut the board twice still to short.
  18. 711mhw

    711mhw Feeling the Heat

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    Nice "report" Jim
    My sys. was a "new const" situation and luck'ly (I am cheap) I did pay a radiant design company for a sys. design, everything worked perfect from the start.
  19. heaterman

    heaterman Minister of Fire

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    If you don't mind my asking and you don't mind sharing that info, what was the cost of having the radiant company do your design?

    Reason I ask is that I think it would be helpful for people to know. After seeing many many folks dive in and "just do it", and then having a system that works poorly or maybe not at all, a few hundred spent for the design part of the process.
    Floydian likes this.
  20. 711mhw

    711mhw Feeling the Heat

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    That's a hard one to nail down. I used http://nrtradiant.com/ one of the guy's there is pretty active on a forum that I was reading trying to educate myself that covers a bunch of energy saving building practices, including radiant heating, I was impressed with him (Rob) and they were also in my state. Anyway they deducted all design fees from material purcahses, and yes I did check them against some of the internet sellers just to keep them honest. This was not necessary! They provided me with thorough, detailed drawings that allowed me, not a plumber or boilerman, to install my complete sys. myself, saving the hired plumber's cost and an added plus is, I fully understand my system because I built it. I've had no "do-overs" with sizing pumps etc. and they knew that I was using the WG from the start and even spoke with them. Sorry to not (really) answer you, but it was pretty much (at minimum) free the way I see it.
    Floydian likes this.
  21. Floydian

    Floydian Feeling the Heat

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    Me too! I spent lots of time on the phone and emailing with Rob and he didn't charge me for any of his time. I was very happy spending my money with them, knowing I had a pro on my side, even though I could have saved a couple hundred bucks buying online. Well worth the consultation I received!

    Noah
  22. 711mhw

    711mhw Feeling the Heat

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    Rob's a good dude. He knows his stuff, and he turned me on to this forum.

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