In loving memory of Kenis D. Keathley 6/4/81 - 3/27/22 Loving father, husband, brother, friend and firewood hoarder Rest in peace, Dexterday

making my own owb in the future had an idea and want some input

Discussion in 'OWB's and Gasification Boilers' started by shaggy wood dump hoarder, Jan 14, 2015.

  1. nsmaple

    nsmaple

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    Getting the smoke & nasties to burn in a boiler is not straightforward with the effect of the liquid cooling. Think of it more like the water is cooling the fire, rather than the fire is heating the water.

    You need 3 basic sections/areas, between where the wood goes in, & what remains after it burns hits the chimney - a firebox where the wood goes & burns initially (water jacketed), a secondary burn chamber that is insulated by refractory that the smoke travels to next and gets mixed with some fresh air (that's the serious burn), then it goes through tubes in the water jacket that extracts the heat from the serious burn before the burned gases hit the chimney. If you don't have the secondary chamber insulated from the water, the temps won't build high enough for the smoke to burn. And if there is not enough air (oxygen) there too, the smoke won't burn.

    It's not straighforward compared to a typical boiler design, but once you see one in person & operation - it's a pretty simple arrangement. The trick is getting all those areas coordinated with each other, and the right balance of air going where it's needed, when it's needed. My gassifier couldn't be much simpler and is even more simple than my old smoker - the only control on it at all is an aquastat that starts the boiler pump when it gets hot. It doesn't have any fans or associated fan controls - and like coal reapers (same brand), doesn't even have any door gaskets becuase the draft is induced rather than forced. It just burns wide open until the fuel is all gone - no dampering of the fire. Really easy to clean, I could even do it while it's burning if I really wanted to. Very simple, but the engineering to get it there was likely pretty substantial. And likely involved some trial & error.

    I think the best advice I can think to give is, go see a real secondary burner in action before investing anything in a build. Then make a decision.
     
    campinspecter and coal reaper like this.
  2. shaggy wood dump hoarder

    shaggy wood dump hoarder

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    Thanks nsmaple, looking at it that way makes a bit more sense, sounds like lots and lots of tinkering before even being full time operational (building myself that is) but luckily I've plenty of time to research before I even start to draw up some serious plans. This is something I will do in the future once I get caught up with life, (having just bought a house that needs lots of work last year trying to fund a wedding getting firewood and on and on) it all takes a lot of time:hair:! But it's nice to have good input from people, so that once I start this I will have much less guess work and a lot better idea of what I need to do, I do like the negative airflow idea and I now understand better the gassifier operation. I've seen them in the manufacture process when I looked at a little shop getting parts for my buddies boiler and all the tubes now make sense.
    Do you know how precise this air to exhaust ratio must be? Or the size of the secondary burn box?or any other details on the secondary?

    I very much appreciate the input! From everybody!
    Just trying to do a better part in not smoking out the whole country side :thumbs:
     
  3. shaggy wood dump hoarder

    shaggy wood dump hoarder

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    Also your saying you add wood and it all burns completely up in one burn? You must have a ton of thermal storage? If my boiler burned a whole load in a single burn my 200gallons would all be boiling over! Also that's another thing I would like to do hopefully before next heating season is get a thermal storage tank in my basement so I can do longer hotter burns, it smokes less and less the longer it burns
     
  4. nsmaple

    nsmaple

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    I have 660 gallons.

    I measured my firebox at about 3 cu.ft. useable, even though it specs I think 4.5. Likely a lot smaller than yours. Most I have burned this winter in a day is 2 loads, over 8 hours. Usually 1.5 loads over 6 hours. 20 year old 2700 sq.ft. two storey on exposed hilltop.

    (Secondary/gassification chamber is about 1/4 the size of the firebox)
     
  5. shaggy wood dump hoarder

    shaggy wood dump hoarder

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    Very helpful! It'll be a decent base. I may even just modify the stove I have in some point in time but that's quite a bit of work as well.
    The 660gallons,is that something you added to it to have that much or is that was original?
     
  6. nsmaple

    nsmaple

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    The boiler itself holds very little - around 30 gallons. Makes for a quick startup. The 660 gallons is piped to it - two 330 gallon LP tanks stacked one on top of the other. Some gasifiers can operate conventionally - and damper the fire or control a fan. But they work much better & cleaner if they can burn wide open, and some actually require storage be attached. Mine is one of those since there is no control on the air intake and has a small volume. Wide open until the wood is gone - batch burning.

    The 'downside' to that is, I have to make a new fire every day. But I wouldn't go back to the old one & ways for anything - even with making a new fire every day, I have way less maintenance overall. Dealing with creosote & cleaning my chimney has become a distant bad memory.
     
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  7. jackel440

    jackel440

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    I designed and built my downdraft Gasification and they are great machines when maintained and operated correctly.
    There are different ideas and designs out there and all of which work.You need to do lots of research and go inspect the different stoves to get an idea of operation and principle.I like the design of the Portage&Maine brand stoves.The large Garn stoves are a possible future build I would like to do in the future.My gasification I built incorporates design points I liked and took from P&M, Nature's Comfort GT500 and a few others.
    I also agree that running a stove full throttle will produce the most efficient clean burn.I plan to have 2k gallons of storage water in the future and then only burn my stove a few times a week.
    I feel that your design you drew has too many shortfalls.By pulling exhaust gas and just reintroducing it to the fire box will not cause ignition of the gases.Your pipe will eventually pack with ash and creasote and will no longer function.
    you need a concentrated "nozzle"to force the exhaust gas through and then introduce fresh combustion air to it to reignite the gas.By using a downdraft design through the coal bed the gases pass the cherry red coals.Then combustion air is introduced and the "wood gases"will ignite.You need refractory to hold the heat and to take the high heat of the secondary burn.
    I have seen upto 1700° burns in my secondary chamber on my type K thermocouple.That was with real dry wood.
    You will need to have some sort of refractory to help cause the secondary burn.
    you will want to run "Dry seasoned" wood for proper operation.This is the most important part.I have fought not having dry enough wood which is my fault.
    My stove currently holds 440 gallons of water.4' deep firebox which is an octagonal shape.The reason is heat transfers from a flatter surface than a round shape.My refractory lined tunnels have no issue staying hot our cooling down too much by being surrounded in water.Why wouldn't you want to take the btu's absorbed by the brick and transfer that to the water anyways?That's the whole point is to heat water as efficient as possible.I have my stove set at 185° with a 10° differential.I have found if I run it any hotter I can get boiling in the water tank.
    I use a 500cfm blower which forces air in two different directions.First to the main fire box to burn the wood and then the second is to the refractory chamber to introduce combustion air to the four nozzles in the floor of the burn chamber.
    You can check out some videos of my boiler build on YouTube just search for me "jackel440"
    Good luck with your build
     
  8. shaggy wood dump hoarder

    shaggy wood dump hoarder

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    Thank you jackell that's a lot of information I've decided after a little bit of reading on here I'm probably not going to pull the exhaust gases like in the picture, i was just out looking at it burn a minute ago, inn the back of the stove there's a wall that hangs down with a6 or 8inch gap on the bottom and two 4inch holes in the top that fire just whirls through. When i open the door even with the fan on, in the right circumstances i can watch the gases start lighting up with the New oxygen in the system, its actually super cool to watch when i have coals completely covering the blower holes this happens in a calm matter actually no singed facial hair from the giant flame that rolls out!
    Thank you jackell! This is super super helpful! I just wish i was closer to doing my build so i could have this all fresh in my mind. I might have to find a notebook write this all down and lock it up tight!