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Question 4 those that have run both OWB and gassifier hydronic

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by ISeeDeadBTUs, Jan 16, 2008.

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  1. ISeeDeadBTUs

    ISeeDeadBTUs Guest

    I see hundreds of OWB while driving around during any given week. And in MOST cases, I am quite underwhelmed by the smoke. Though I might not want to live less than 100' from one, I don't SEE that much of a big deal.

    But since I never owned/operated a OWB (only wood stoves in my youth before the GreenWood) I am hoping some of you can clarify . . .

    Assuming the same wood is used, shouldn't an OWB and a gassifier produce about the same 'smoke' DURING IDLE? It seems to me that if either one is loaded and up to temp so that no air is being introduced, both units - no matter how effective the heat extraction design - should emit the same particulates. Obviously, if the OWB is not running hot - as I suspect happens too often - then the OWB is not idling, just burning inefficiently, then 'smoke' is going to be a big issue.

    Just wondering from those of you that have run both.

    Jimbo

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  2. wdc1160

    wdc1160 New Member

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    One key consideration is that the average OWB can have output at 350K -- rarely do individuals own 350K gassers. So I guess unless you compare similar outputs it may not be apples to apples.

    Also the fact that the average OWB is oversized is another reason we hear horor stores about plumes of smoke.
  3. ISeeDeadBTUs

    ISeeDeadBTUs Guest

    Well, the Central Boiler salesman tried to upsize me when I was considering their unit. But I still wonder how oversizing leads to that much more 'smoke'. If it's oversized (and for that matter, the CB has almost 500 gal of water so the storage should help somewhat) then it should IDLE more, and I can't see why an oxygen starved load of dry (the wood should be dry after an hour or so even if it wasn't when it was loaded) wood should 'smoke' any more in an inefficeint design than in an efficient gassifier. Unless of course the load is not really oxygen-starved . . .
  4. Eric Johnson

    Eric Johnson Mod Emeritus

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    In my limited experience with the gasifier, the hot refractory and downdraft smoke path through it, burn off a lot of the smoke that goes up the stacks with a conventional OWB design. So I think even in an apples-to-apples comparison (and yes, most OWBs are way oversized compared to most gasifiers), you're going to get more smoke out of an OWB.

    But like you, Jimbo, I think OWBs get a bad rap. IME, they smoke about as much as a pre EPA woodstove most of the time. Their biggest problem is that they're sitting out in the yard attracting attention and scorn. Drive around the countryside and do an objective comparison of smoke coming out of chimneys and the smoke being produced by OWBs, and I think you'll come to the same conclusion.
  5. ISeeDeadBTUs

    ISeeDeadBTUs Guest

    Lol Eric, one day you'll actually come to work and I'll buy yer lunch if you'll buy me a drink, or two ;-)

    But back to the analysis . . . I buy your explanation of smoke path but it still seems to me that on idle, the smoke path wouldn't cut down on particulates. But that's why I asked people that have burned both.

    And I agree 100% on the visible smoke seen. Some days my drive is 2.5 hours one way, through the Mohawk Valley and ADK's, and in my non-scientific observation, most OWB produce less smoke than most stoves/fireplaces. And I bet many of us in this room load our units in such a way that we don't get the smoke that a careless OWB loader might.

    I wonder if anyone has ever done a study to see what sort of radius is effective in diminishing particulate matter.
  6. Eric Johnson

    Eric Johnson Mod Emeritus

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    Well, stop in. I'm usually there M-W-F. The Five Corners Cafe beats Slickers all to bits, although I don't think they serve booze, so I guess that's out.

    When my boiler goes into idle mode, there are still flames coming out of the nozzles. So some of the particulates are being burned.
  7. dumbodog00

    dumbodog00 New Member

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    I have an OWB that I have been burning mostly slab wood in this year. The wood has been drying since May. I use 2 or less wheelbarrows of wood a day. It smokes the first couple of firings after I load it, but after that, you can't even tell it is burning. If I put a shovel of coal in it (which the burner is rated for), it smokes a little longer until the coal gets hotter. Most of the day anyone driving down the road cannot tell if it is burning or not.
  8. wdc1160

    wdc1160 New Member

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    assuming same demand and same output potential.

    1. A OWB uses two methods to dampen output (that I have seen)
    rapid cooling of waterjacket with water to help stop oxidation
    Stave for air with damper.

    Gasser only uses air damper (that I have seen)

    2. Normal wood fire have output that is shaped like a bell. Almost everyone with a wood appliance knows at the top of the bell heat supply can overcome demand (normally).
    We try to flatten the bell. I thought that it might be possible that gassification boilers might be able to flatten the bell
    Slowing down gasification may not create waste(or very much) if the temps still remain at 1500F

    3 With a full load wood in a gasifier during the start up you shouldn't put out more than 200lbs of water.

    With a full load in a OWB you may burn off 1000lbs(likely more) in a boiler with comparable output.
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