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Gasifier pulsating and puffing

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by Nofossil, Nov 11, 2007.

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  1. Nofossil

    Nofossil Moderator Emeritus

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    Every once in a while, my EKO 25 will get into this mode on startup where it does a low frequency pulsation - vibrates the boiler and the chimney. Can feel it through the house. I think it correlates with too much small wood that's too dry, but I'm not sure.

    Often when it does this, it will also have mini-explosions in the upper chamber that blow smoke backwards through the fan and slam the metal one-way fan damper shut. Eventually it will settle down and operate correctly, but it's annoying and hard to stop. Observation of the gasification chamber leads me to say that secondary combustion is not complete when this is happening. Flue temperatures also run higher - 300 - 325 vs 250 normally.

    Anyone else seen this or have any insight on the dynamics of what's actually happening inside?

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  2. joeski206

    joeski206 New Member

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    I am interested to see responses. My greenwood on rare occasion does the same thing. I will have coals left, add wood for the night and as it begins to burn it will start this 1 per second PUFF__PUFF_PUFF_PUFF like a freight train, smokes like a groan then eventually settles down, stops smoking and comes back up to temp, i stopped this by not letting the coals get to low or the temp to low, hard to do if you away for a long time, but if you can dont let it go to long or the temp get to low before a refill.... also use bigger logs, stay away from scraps and twigs...this seems to have helped me as well.
  3. Eric Johnson

    Eric Johnson Mod Emeritus

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    Any puffing I've experienced happens when I'm messing around with the air controls.

    You might check your gaskets, nofossil. In my experience with conventional boilers, air leaks can cause ignition of the wood gas created when the boiler goes into idle mode. Not sure how that relates to gasifiers, which are supposed to burn the gas before it goes up the stack, but I'm guessing that if it's a relatively recent development, it probably has something to do with the wear parts--the gaskets being one of the few on that boiler. Excessively dry wood and insuffient air supply in cooler weather have also been mentioned to me as causes for puffing.
  4. Hbbyloggr

    Hbbyloggr New Member

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    When small diameter wood ( presenting a large surface area) is heated ,excess volatile hydro-carbon gas( methane) is at the point of ignition , only limited by the lack of O2. When the o2 is leaked into the chamber it reaches the flash over point, then the limited O2 is used up...but that created more heat to drive out the hydrocarbon gas from the wood...again without sufficient O2. The system cycles itself until a balance is met or the temps are high enough in the gasifier section to handle the methane overload.
    Same thing happens when you throw 2-3 gal of drain oil into your old shop wood stove and close off the damper.
    I learned my lesson with that fine maneuver years ago. Now we have a dedicated waste oil heated. Much safer, indeed.
    Hbbyloggr
  5. TCaldwell

    TCaldwell Minister of Fire

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    i have experienced the same puffing with the garn, the manual states as you guys deducted too much sqft. of surface area of wood burning for the volume of air provided. garn's reccomendations are push the wood closer to the rear of the primary chamber, towards the secondary chamber, load less wood , stand a firebrick between the supply air and the fire. the first two work well, the brick sometimes does not. What i have found to work is capping the top of the load with wood that is slower to ignite,ie oak plank or higher moisture content wood. I am speaking from two horizontal burn chambers in line, not a downdraft gasifier,good luck
  6. hkobus

    hkobus Member

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    Very intresting. I have been working on this very thing. I agree with the flash over scenario. I only see this when I fired the boiler from "cold" and there is too few embers over the nozzle. The charcoal startup trick has worked well to reduce this, but the key I believe, is to start the fire with a lot of small wood and get it very hot to ceate the ember layer. With a thin layer the secondary air from the nozzle can go up when an irregular burn creates a vacuum and blow back "down" after the flashover. The flame is now separated from the nozzle and the gas and air mix in the "trough" and burn uncontrolled in the lower chamber, cousing the "rumble".
    I spend 2 hours "tuning" the air flow yesterday, blocking part of my nozzle may be part of the issue. Untill I find time and funds for the storage tank, it will have to work. I am running about 24/7 at -4 to 6 C outside temps and let the unit cycle at 67C. As long as the unit is hot and there are lots of embers in the nozzle area, I seem to get away with just about anything.

    Henk.
  7. Nofossil

    Nofossil Moderator Emeritus

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    Thanks for the comments and suggestions. I'm going with the theory of too much really dry small wood. More experiments soon - I'm on an every-other-day cycle right now, so next fire should be tomorrow night.
  8. antknee2

    antknee2 New Member

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    I stumbled on a way to quickly stop pulsating on my Seton w-130 by turning on the inline draft inducer fan for about a minute and open the outside door .
  9. slowzuki

    slowzuki Feeling the Heat

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    Its interesting the Jetstream manual I have addresses this problem for them too. It doesn't happen as often because the thing usually runs at 200% excess air. It was built before the days of electronic speed controls. But it you load lots of small diameter wood the mini-explosions will rattle the smoke box. Opening the loading door to shut off the forced draft while the induced draft continues tends to stop it.
  10. Eric Johnson

    Eric Johnson Mod Emeritus

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    Interesting, Henk. I've been running on one nozzle for a couple of weeks and it works just great. It's a really good strategy for running a gasifier hard in warmer weather when you don't have hot water storage. With half the capacity it takes longer to get up to temp, but that's just a matter of planning ahead. Once it hits its stride, it just rolls right along.

    I'm wondering about how best to tune the air controls. Do you think it's best to do it when the boiler is hot, or when it's cold? I could think of good reasons for either approach.

    Like any boiler or stove, you learn how to operate it to your needs over time. But like you, I've found it to be a really forgiving unit--easy to operate and once you get it gasifying, it tends to stay in the groove.

    And I should add that it ranks high on nofossil's "wife approval factor" (WAF) scale. Yesterday she said to me, "You know that $7,000 you spent on that boiler? If it keeps me this warm all winter, then it paid for itself." Let's see, it's 30 degrees outside, the boiler is only running on one nozzle and the house is 80 degrees. I think keeping the house warm all winter is not going to be an issue with this boiler.
  11. TCaldwell

    TCaldwell Minister of Fire

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    I might be off base but it seems maybe a variable speed draft inducer controlled by a oxygen sensor and thermocouple located in the flue pipe just beyond the appliance could regulate the volume of combustion air as needed. I bet nofossil could do this in his sleep.
  12. Nofossil

    Nofossil Moderator Emeritus

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    If I ever got any sleep....

    I just lit a new fire using mostly larger wood. Took much longer to get to gasification, but no puffing. Seems like there's a fine line - I've gotten gasification in as little as six minutes after ignition by using small stuff, but too far in that direction seems to lead to the dreaded puffing phenomenon.

    I've been working on getting my combustion temperature probe back online. It's reporting 3300F at the moment, which is a flat-out lie - it has a max sensing temp of about 2500. If you want a real-time snapshot of my system temperatures and I/O, you can view my controller's own web page - I think it's cool, anyway. The combustion temperature is divided by 10 to make it fit better with the other temps.
  13. Tony H

    Tony H New Member

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    After reading about the puffing issue and the idea that O2 leakage could be an cause, I was looking thru the install manual for the EKO ( considering purchase) there was a section about the rope seals and how to adjust the doors as the seals wear. Just thought it might be worth a look to see if that could help.
  14. Nofossil

    Nofossil Moderator Emeritus

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    Leaking seals can be a real problem, but fortunately one that I've had very little problems with. When I got my EKO, there was a tiny divot in the metal flange that the upper door gasket seals against. That resulted in very noticeable and noxious fumes. A dot of high-temp silicone and a piece of saran wrap cured it, and I've been good ever since.

    The puffing problem seems to correlate with too much small dry wood. I'm going to be very systematic about paying attention to what I start fires with to verify, but that seems to be the pattern.
  15. ISeeDeadBTUs

    ISeeDeadBTUs Guest

    I'd concur I guess, but not as technically as the scientists among us.

    Spring and fall here in NY, I can keep my house warm enough just by getting my inside boiler and DHW tank up to max temps when the sun goes dow, then let my outdoor GreenWood go out. This is best and cheapest accomplished with dimensional lumber. Over fueling (or is it air-starving) the fire will make the GW sound like a locomotive. Usually clears up on its own in 5 or less minutes. And my neighbors are all far enough away so they can't see the smoke ;-)

    Jimbo
  16. Eric Johnson

    Eric Johnson Mod Emeritus

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    I had kind of a weird experience last night. It was one of those foggy, damp, cool evenings. I fired up the EKO with a few pieces of wood on the coals, got gasification going good, and stepped outside to check on the chimney. I had a big plume of what looked like white smoke coming out the stack. At first I thought it was steam because of its color, but it seemed to linger longer than you'd think steam would. And I'm burning very dry wood. I followed the plume around trying to get a whiff when it came close to the ground, but smelled nothing. It cleared off after about a half hour, and that was that.

    I don't think it was smoke because gasification was going strong and when I looked in the combustion chamber, it was all orange and yellow flame--no smoke to be seen.

    On my way to work this morning I passed through some foggy weather and noticed that everyone's woodstoves were producing what looked like excessive amounts of smoke. More than usual, at any rate. So I suspect something atmospheric is going on here, but I'm not sure exactly what.
  17. Nofossil

    Nofossil Moderator Emeritus

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    I'm not a meteorologist, but that doesn't stop me from acting like one.

    I think you're seeing water vapor. If the air is cool and dry, the water vapor on your flue gas condenses as it hits the cooler outside air, producing what most people call 'steam'. Real steam is actually colorless and perfectly transparent. This condensed water vapor is made up of really tiny droplets which quickly evaporate as long as the air is dry. If the air is really moist, it will take far longer for the droplets to evaporate.
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