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Gasifier Secondary Air Control Operation

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by Jim Post, Dec 19, 2007.

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  1. Jim Post

    Jim Post Member

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    I have been paying closer attention to the secondary air control on my tarm boiler this year. According to the manual the drier the wood, the more secondary air you need to achieve optimal burn. I have found that increasing the secondary air to achieve an optimal burn also reduced the amount of ash that is produced. As the burn progresses to the coaling stage, more ash is produced if the secondary air is reduced. The manual says adjust secondary air until the flames are just breaking over the front edge of the combustion tunnel. Anybody else adjust the secondary air control as the burn progesses or do you just set it and forget it? Have you noticed any difference in ash production based on secondary air control?

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  2. Eric Johnson

    Eric Johnson Mod Emeritus

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    That's interesting. I didn't know that about the dry wood or the ashes. I've played around with mine a little, mainly trying to get my stack temps down and get a cleaner burn on startup, but nothing systematic to where I can report any results. Sounds like the Tarm has a viewing glass or some other way of seeing the results of your adjustment. On the EKO, you can open the gasification door and see the flame, and I assume that you could fine tune it from that if you knew what to look for. At the moment, I really don't. I'm also not sure whether it's best to play with the secondary air adjustment when the boiler is up to temp or cold, but I assume it's the former.

    I started a thread showing how you adjust the primary and secondary air in an EKO in which I asked some of these questions, but nobody seems to know much more about it than me. Or if they do, they're not saying. I think nofossil had some interesting observations, as usual. Most of the rest of us are on our first season with our boilers.

    So I'll be keeping an eye on this thread, olpotosi. Thanks.
  3. Nofossil

    Nofossil Moderator Emeritus

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    Ashes is an interesting variable that I hadn't considered.

    Based on what I'm learning, you should adjust primary air to lower stack temp - think of it as your throttle.

    For any given primary air setting, you then want to adjust secondary air to maximize your combustion temperature, which presumably increases your stack temperature as well. Max temperature means max efficiency.
  4. Tarmsolo60

    Tarmsolo60 Feeling the Heat

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    After playing around with the secondary air adjustment on my tarm I saw little difference in the flame appearance other than the velocity of it. My stack temps were high so I decided to adjust the primary air adjustment to see if that gave better secondary air control. I adjusted the primary air as far down as I could and that made a big difference on my flame appearance and also lowered my stack temp at least 200 degrees. the boiler now seems to be burning better and gasifying quicker, makes sense, i'm now not blowing as much heat up the chimney. I can't really say I noticed any ash difference other than maybe now the aren't being blown to the back of the boiler now. One thing I thought of that might affect your air adjustments is I run my boiler without the sheetmetal top on it because it is in my shop and makes cleaning easier, I didn't know if having the top off would make more air available because it doesn't have to draw all air through the small vents openings stamped in the sides, thus requiring dampening down primary air. Also, my boiler is in a space that is about 35-40 degrees and I didn't know if there being more oxygen in cold air would make enough of a difference to require air adjustment. Right now I have the primary air ajusted way down and my secondary air is all the way to the right looking at the boiler. I haven't moved it since and it seems to be running well with a lower stack temp.
  5. Eric Johnson

    Eric Johnson Mod Emeritus

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    How would you adjust the primary air on an EKO, nofossil? Those two sliders under the blower plate, or would the slider on the blower itself be sufficient?
  6. Jim Post

    Jim Post Member

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    The tarm has a viewing port in the lower door that you can spend a lot of time trying to keep clean. I usually just open the lower door to check secondary combustion flame conditions when the draft fan is on. This year I have been burning mostly well seasoned oak and I've been keeping the secondary air 3/4 to full open. My ash production has been greatly reduced from previous years. Now I am getting into some wood that isn't quite as dry and I have been adjusting secondary air down to less than 1/2 open for the majority of the burn. If I find a lot of coals in the combustion tunnel I rake them out onto the floor of the boiler and increase the secondary air. These coals will burn down to ash quickly with the increased secondary air flow.

    In years past, I had noticed that increasing secondary air once you are in gasification will decrease smoke at the top of the chimney. I think this just reflected getting to the optimal burn phase and more complete combustion.

    It's getting close to time for my midwinters chimney inspection and cleaning I will be interested to see If I notice any difference in the amount of build up on the chimney.

    Stay warm!
  7. Nofossil

    Nofossil Moderator Emeritus

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    Mine has a slider on the blower itself. I would expect that within limits, that would alter the total amount of air without significantly changing the ratio of primary to secondary.
  8. Eric Johnson

    Eric Johnson Mod Emeritus

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    I've been burning very dry wood, and last night I opened the secondary air ports up to 6 turns, from the 3.5 recommended. Now I get a lot faster startup and a cleaner burn early on. So thanks for pointing that out.
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