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OWB to gasifier retrofit

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by DSheckells, Jan 8, 2008.

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  1. DSheckells

    DSheckells New Member

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    Hello, my name is Deon and I have been lurking out here for several weeks reading. I have already converted my stove to a downdraft configuration with steel. I am trying to convert my Taylor T1000 OWB to a gasifier and need some information about gasifier construction to allow me to do this. Which means I am ready to make refractory pieces to replace the steel retrofit pieces in my firebox

    My stove is a 250,000 btu/hr . I am curious about fan cfm vs nozzle size ( I think that is correct ) vs cross section dimension of heat exchanger/stack.

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  2. Nofossil

    Nofossil Moderator Emeritus

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    Good luck. I think that the rule of thumb is something like six pounds of air per pound of wood, and something between 15 and 20 million BTU per cord of wood. From that you could begin to calculate it if you had fan curves, but you're going to have to do a lot of experimenting in any case. Gasifiers are simple, but the design is not.

    My brother built one from scratch, but he copied the critical dimensions from a 'known good' design.
  3. Eric Johnson

    Eric Johnson Mod Emeritus

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    I tend to agree with nofossil. If it was easy to make a Taylor into a gasifier, they would sell them that way, because it would consume half as much wood and give them a tremendous marketing advantage. There's not much to a gasifier when you look one over, but as nofossil so ably points out, everything is pretty highly engineered from the ground up. I think you might hit a few brick walls in the way the Taylor is built that would make it difficult or impossible to convert.

    We're not trying to discourage you from a noble cause, just trying to provide a reality check.

    We have a member here, Garnification, who built a Garn-style gasifier from scratch. I'd be curious to read his reaction to what you're proposing.

    In any event, good luck, Deon, and keep us posted.
  4. DSheckells

    DSheckells New Member

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    NoFossil, my woodburner has a firebox that is 28 H X 32 W X 48 D with eight 3.5" dia. tubes in the firebox to exhaust flue gasses pushed by a 265 cfm fan mounted in the door. The stove came with a piece of sheet metal that you block off the air inlet to control stove combustion. Stove also has about 750 gal of water storage. I said all of that to say "no science came installed in this OWB" (opinion, don't be offended anyone!)

    I have used the stove for almost 15 years in the middle of the city, the way I have always reduced smoke is by running the stove at a reduced rate by blocking off the fan inlet.

    On your gasifier how many cfm is the fan capable of moving? What is the size of the opening at the bottom of the firebox? Is the woodbox surrounded by water or refractory? I am just planning on making an educated guess based on dimensions from proven designs. No complex controllers just higher combustion temps through the use of refractory and or brick. The current modifications have worked miracles, stove can for the first time pass opacity requirements if need be. I am working on a band-aid not a cure. If and when my owb shoots craps I will probably buy a gasifier to replace my current stove. I will have to build a boiler room since OWB installations have been outlawed in our city. Your calculations are out of my league. . .but appreciated.
  5. Eric Johnson

    Eric Johnson Mod Emeritus

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    My EKO 60, at 205 Kbtu is closer to your output than nofossil's, which is 80 K. But we have the same boiler, basically.

    Mine has two draft induction fans. I don't know their output offhand, but I'll try to find out. The gasifier consists of a conventional firebox on top, with a heavy bypass damper at the back. The base of the firebox is a refractory mass with two ceramic nozzles in the center. The nozzles are fed superheated air through channels in the sides, supplied by two secondary air tubes made of steel pipe with holes drilled in the sides. They slide into the refractory mass on either side of the nozzles. Attached is are a couple of pics of the blowers, and the secondary air tubes with the blowers removed.

    When you want to initiate gasification, you close the bypass damper, forcing the flow of wood gas, or smoke, down through the nozzles, where it is mixed with the superheated air and ignited. The resulting flame jets blow down into the secondary combustion (gasification) chamber, where they are deflected back up at the refractory mass to keep it red hot. You need red hot refractory and superheated air for gasification to occur. The hot gas exhausts out the back of the gasification chamber and up through 10 heat exchanger tubes which contain turbulators. Gas that was 2,000 degrees in the gasification chamber exits into the chimney at about 300 degrees. Water surrounds the entire boiler on the top, sides and back, with poured refractory cement comprising the bottom of the gasification chamber and the door. Ashes are cleaned out through that door.

    The first two pics are self-explanatory (literally). The third one is the view through the chimney outlet of the bypass damper and the turbulators coming out the top of the hx tubes. On more recent versions of the EKO, you keep the hx tubes clean by rocking the turbulator assembly up and down. The fourth pic is a flash shot of gasification in progress. The refractory brick is shaped to deflect the heat back up into the refractory mass, as explained earlier.

    If you want to see a cutaway drawing of the boiler, you can visit the Cozy Heat website (banner above) and click on the EKO link. Most of the specs are there, as well as a video of the gasification flame. Ditto for the Econoburn gasifier (lower banner), which is a similar design.

    Attached Files:

  6. DSheckells

    DSheckells New Member

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    Eric, I completely understand and agree. I will not post my true opinion of my OWB. But I have made a multi-pass heat exchanger utilizing the eight tubes in the stove but my combustion is still incomplete so I am trying to get a nice hot-spot before flue gasses reach the heat exchanger. So cfm vs exhaust nozzle dimensions are important to try and maintain stove capacity. I also have a 1000 gal water tank that I am planning on adding to this system. So I can have as long a burn time as possible.

    I heat 2 old houses for a total of approximately 6000 sq. ft. and burn a cord of wood about every two weeks. . .

    I have looked at many of the projects on the site, I am impressed with the craftsmanship and designs. I am not in that league.
  7. Eric Johnson

    Eric Johnson Mod Emeritus

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    Sounds like you came to the right place. Did I mention that gasifiers produce no smoke under normal operating conditions?

    There's guy on my way to work with a Taylor. I know they've been around for a long time--one of the first OWBs, if not the original. He usually dosen't produce too much smoke. I pass by woodstoves on the same trip that produce a lot more. But being right out where everyone can see it, his Taylor probably gets blamed for all the smoke in the neighborhood.

    Another guy just up the road is heating a fab plant and series of retail outlets with 3 or 4 Johnson OWBs. When the wind blows a certain way, it smokes out the convenience store/gas station across the highway. He should get a decent wood-fired industrial boiler, but that would require permits and probably a licensed operator.
  8. Nofossil

    Nofossil Moderator Emeritus

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    I suspect that these are some of the critical operating parameters in a gasifier:

    - The ratio of primary to secondary air
    - The degree of combustion in the primary chamber (percentage of flammable gases in primary outlet)
    - The nozzle velocity
    - Secondary combustion environment - dwell time and surface temps

    Our boilers have a water jacket surrounding the primary chamber. Keeping the secondary combustion away from the water jacket helps secondary combustion. You want about 50% more oxygen than the secondary combustion would theoretically need, but experimentation is probably the only way to dial it in.

    To use an automotive analogy, the blower(s) essentially are the throttle, and the secondary air inlet controls are the air/fuel ratio.
  9. Eric Johnson

    Eric Johnson Mod Emeritus

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    The cutaway diagram of the EKO appears to show the water jacket extending down below the bottom of the refractory, and around the gasification chamber. What you say makes sense and since you've actually built one, I guess I defer to your experience, but you would think there would be water at least around the tubes at the rear of the gasification chamber.
  10. Nofossil

    Nofossil Moderator Emeritus

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    Yes, the water jacket extends all the way to the bottom - all thre sides of the secondary chamber as well. Keeping the secondary combustion from being quenched by that cold steel is part of the reason for the 'trough' that EKO provides as well as the impetus for my expensive gravel project.
  11. Eric Johnson

    Eric Johnson Mod Emeritus

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    I wondered about that the other day, nofossil, when contemplating the shape of that trough. As I understand it, part of its purpose is to deflect heat back up towards the nozzle. Is your labyrinth designed to do that, as well as extract more heat?

    I notice in the pics of the older EKOs that the "trough" was actually a piece of curved ceramic mounted on a steel stand. Presumably the steel didn't hold up under the intense temps over time. If you look at alternative designs like the BioMax and the Atmos, they have relatively small, curved refractory secondary combustion chambers that I suspect would be more work to keep clean than the EKO design. But they don't have the steel water jacket quenching the gasification, either.

    Attached Files:

  12. Nofossil

    Nofossil Moderator Emeritus

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    Yes - the primary purpose of my labyrinth is to provide more time for secondary combustion before the gases encounter cold steel. I also try to ensure that they then travel the full length of the side walls.

    Now that I have thermocouples, I can do more precise studies.
  13. Eric Johnson

    Eric Johnson Mod Emeritus

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    I understand what you're trying to accomplish. My question was whether it deflects the heat back up into the nozzle and refractory mass, as the two designs pictured above obviously go to some lengths to try to achieve?
  14. Nofossil

    Nofossil Moderator Emeritus

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    It certainly has that effect, though I wasn't aiming for that specifically. The nozzle empties into a trough that's 4.5" square and about 18" long. The flame completely fills the trough and shoots out little jets through any gaps between the walls and the bottom of the refractory.

    I'm not convinced that reflecting heat back up is as important as just ensuring that there's plenty of time and turbulence for the combustion process to complete before the gases are cooled down.
  15. Eric Johnson

    Eric Johnson Mod Emeritus

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    I suppose you're in a position to find out now, with your thermocouple monitoring, but everyone seems to go to great lengths to get that curved shape right up against the nozzle openings, so I suspect it has some value beyond the obvious aesthetics.
  16. Eric Johnson

    Eric Johnson Mod Emeritus

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    Here's what it says on the blowers, Deon, as well as a cutaway view of the boiler. Sorry, I don't provide translation services. Maybe you or someone else knows what some of these numbers mean relative to your questions.

    Attached Files:

  17. guy01

    guy01 Member

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  18. guy01

    guy01 Member

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    common you guys this is a worthy goal help the guy out
    there is a bunch of smart people here I'd help but I don't know too much
    would there be a way to rig a secondary air tube or tubes to add air in the chamber from the link i had?
  19. Eric Johnson

    Eric Johnson Mod Emeritus

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    I think nofossil and I have provided as much information as we can come up with, Guy. And so have you.

    He's probably working on the mod in your link right now. Pretty impressive. Nofossil has some experience with alumina board.

    Other than that, he's in rather uncharted waters, and I doubt there's much more information to be conveyed. Most of us don't have a lot of experience with OWBs, though I think we'd certainly all like to see them become cleaner-burning and more efficient.
  20. guy01

    guy01 Member

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    sorry ( kinda) my dad has an old taylor he quit using but if we can make it efficient I'll fix it up and heat them guys back up
    My motives are always suspect
    Guy
  21. kuribo

    kuribo Feeling the Heat

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    If you look into the gasification process and study the different designs on the market, I think you will find that what is necessary for gasification is a primary combustion chamber supplied with primary air within which the fuel is heated to release the volatile gases, and a secondary combustion chamber where high temperatures and secondary air burn the volatile gases. These gases are then led through a heat exchanger/labyrinth to transfer the heat to a fluid.

    If you can partition the inside of your present OWB combustion chamber using cast refractory pieces into two chambers (there are both updraft and downdraft designs), one larger (primary) and one smaller (secondary), provide each with an air supply which you can adjust, and provide for a nozzle between the chambers which you can replace with different size openings to allow for some experimentation, I think with some trial and error you will be able to improve greatly on your present OWB. You will also need to construct the partition so as to route the combustion gases out in a way that allows them to transfer their heat to the water jacket.

    Study existing designs, as well as masonry heaters, which use gasification with a natural draft, to give you the basics of how these work. Then play with the airflows and nozzle size. I plan on doing this myself and based on my research, I think it is entirely feasible.

    I can think of many reasons why the manufacturers of OWBs haven't converted their standard product other than it isn't possible or easy. I have talked to several that are planning to introduce gasifiers in the near future and from what I have been told they won't be radically different that their current product. You might look at the one that just hit the market made in Mauston, WI. Check out the fire box and nozzle and how it leads the combustion gases through a firebrick lined maze.
  22. DSheckells

    DSheckells New Member

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    Thanks for the help and interest everyone, had to work late tonight. Actually Nozzle dimension is probably the first thing I might need more info about. Eric thanks for the photos and info, since your stove is close in BTU size. I only have about 6 inches of room to spare in the bottom of the stove so secondary combustion chamber will have to be designed in that space. So approximate size of the opening/nozzle ( length and width and how thick the refractory is ) in your burner will be where I start my design.
  23. Eric Johnson

    Eric Johnson Mod Emeritus

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    I'll be happy to measure the nozzles for you Deon, next chance I get. I could have done it earlier today when I cleaned it out, but it's red hot now. You can download the EKO manual from the www.newhorizoncorp.com website, and the spec sheet and brochure on the Cozy Heat website above, for openers. That will give you the dimensions of the secondary combustion chamber, which I suspect is pretty important. It has a poured refractory cement "floor."

    Is the Greenfire the one from Mauston, kuribo? Have you seen one work? What, in your view, would be some other reasons for OWB mfgrs. not making gassifiers instead of standard OWBs? I know Central Boiler has tried for years to produce a low/no smoke model in their lineup, without any success until just recently, reportedly.

    There's a Wood Doctor dealer near me. Last time I went by, they had a big, dark green (or maybe it was brown--I'm color blind) OWB sitting out there with the stock WDs. I'm guessing it's either a pellet burner, or their new gasifier that I've heard rumors about. I'll have to check it out.
  24. DSheckells

    DSheckells New Member

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  25. brad068

    brad068 Feeling the Heat

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    The Mauston built boiler is E3400. I have seen this boiler in person, operating and it does perform well. The reason owb manufacturers don't build them is that they don't understand them. I had one gentlemen tell me why do you burn your fire so hot, your just wasting the wood! I think this is the mentality of the owb manufacturers/ dumpster fabricators/ hair care and tire centers :lol: .
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