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EKO Observation: Consequences of Idling a Gasifier

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by Eric Johnson, Nov 18, 2007.

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  1. Eric Johnson

    Eric Johnson Mod Emeritus

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    Or whatever you want to call them.

    I was at a loss to explain the smoke I was getting out of my EKO 60, especially first thing in the morning when firing it up. After everything gets going good (i.e., nothing but flames in the gasification chamber and temps climbing) I was still getting a fair amount of smoke out the stack. Given the absense of smoke in the gasification, chamber, I really couldn't figure out what was going on. It would smoke for about an hour, and then burn clean for the rest of the day, no matter what I threw at it.

    So that was a big mystery. I tried fooling around with the air controls. Managed to get the flame to burn even hotter, but still getting smoke. These things are supposed to burn clean; I've seen mine do it many times. I thought maybe the bypass damper was slightly open, allowing smoke to bypass the nozzles. Turned out not to be the case.

    I believe what is happening is that at night when I've filled the firebox up and gone to bed, the boiler satisfies the heat demand at times and goes into extended idle periods. When this happens the blowers shut off, but the exhaust still exits through the heat exchanger tubes. In the process, it deposits creosote in the tubes. The next time you fire it up good--usually the next morning--fire shoots into the tubes and burns off the creosote. Since there's no nozzle to burn off the smoke, it exits the old fashioned way, out the stack.

    This problem can be avoided with hot water storage, I believe, since with an adequate buffer, you can fire the boiler hard and get the heat you want out of it without ever letting it idle. It takes a little practice, but I think it will be relatively easy to time and allocate wood loading to maintain tank temp while keeping the boiler working most efficiently. This is particuarly true with a big boiler like I have, since it's harder to balance output to demand when you don't have storage, especially in relatively mild weather. I've also tried throttling it back by blocking off one of the two nozzles with a firebrick, and that works also works pretty well.

    So while it's true that you can idle a gasifier, you do see greater emissions (both during idle and later, as noted) and consequently lower efficiency. What's the solution? Stop fooling around on the computer, Eric, and get the damn tank and hx finished!

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  2. Nofossil

    Nofossil Moderator Emeritus

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    In every endeavor, there's a point in time to stop thinking and act. We tend to miss that point in one direction or the other all too often....

    During this season, I'm able to fire the boiler once every 2-3 days. The heat storage tank is wonderful for that. You won't regret having it on-line.
  3. Eric Johnson

    Eric Johnson Mod Emeritus

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    Does the theory make sense, nofo?

    It's burning clean as a whistle, now. Took about an hour to burn off the gunk, if that's in fact what's happening.

    Actually, I'd be working on the hx today, but it's too nice to be down in the basement with a torch. So I'm splitting up the rest of my wood instead.
  4. Nofossil

    Nofossil Moderator Emeritus

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    Doesn't feel quite right to me. First, it would take a lot of creosote. I never saw that much. Second, the metal surfaces in mine have water on the other side - I doubt that they ever get hot enough to burn off anything. If you scrape the side walls of the lower chamber after it's been idling a while, what do you get? I get very light brown ash - not flammable.

    All 43 cords? You da man!
  5. Eric Johnson

    Eric Johnson Mod Emeritus

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    You have a much smaller boiler, nofo, so I bet you didn't see much idling even before you had a tank. I think there's flame shooting up through those heat exchanger tubes when it's going full bore. And when flame hits creosote, IME, it burns.

    Having said that, I did inspect the chimney the other day and it has a layer of fine, brown soot. Nothing resembling creosote. You'd think there would be some there if what I'm guessing is correct. I'm pretty sure it wouldn't burn off, as the chimney temps are way too low for that.

    Actually, just cord #43. I'm right up against the clothesline. No more room for wood. And yes, frozen wood splits A LOT EASIER than thawed wood. The connections between the fibers shatter instead of tearing. Good thing, too. There's some big, gnarly yellow birch in this pile.
  6. Nofossil

    Nofossil Moderator Emeritus

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    My brother-in-law is coming up from Massachusetts for Thanksgiving - maybe I should bring him over to help split it. He's something of an expert at splitting yellow birch ;-)
  7. TCaldwell

    TCaldwell Minister of Fire

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    eric, after having a harmon boiler in my basement for 7 years, 13 cord per year down the bilco stairs, cleaning boiler and flue once a month not withstanding efficiency probably below 50%, and still hearing the oil boiler kick on more often than not, it was a tough learning curve. When i installed the garn i placed a tekmar temp sensor on the aquastat well, now i can read the boiler temp from the kitchen wall and know when it is time to fire,aside from being lazy , i will second the burn and store for being easier to control.
  8. hkobus

    hkobus Member

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    Erik,

    What temps do you run the boiler water at? Since it has been mild here I have ran it at 65*C with my nozzle restriction in. It would take a while to heat up and and probably too cool. I was getting a lot of creosote in the upper chamber, but I cleaned the tubes this week-end, and found nothing. The only thing in the top of the HX was ash dust.
    Then I went to clean the by-pass, and found massive creosote deposit on the inside and below the baffle. I have had issues opening it at times and wonder if some creosote get's on the HX this way. And it may not close well after and have some leakage.
    I also noticed that in the early stage the flame is maily orange, this may be incomplete combustion, but no visible smoke until in the stack? Since I removed the restictors and increased the set temp to 71*C, result: cleaner upper chamber and no sticky bypass and no smoke after reload. ( even after running empty, boiler temp still 60*C, blue flame right away)
    Henk.
  9. Eric Johnson

    Eric Johnson Mod Emeritus

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    I always run it at 80. I'll probably try to get that 5 or 10 degrees hotter one of these days.

    I have the same problem with the bypass damper sticking occasionally. The first time I took off the chimney connector and opened it from behind. That was a pain in the ass. After that I tried whacking on the lever with a hammer, but it's shaped in such a way that you really can't get a good smack. Finally, not wanting to damage anything, I turned the loading door handle around so that you can open the loading door while the damper is closed. It's only a issue on reload, usually after the thing has been idling and a little creosote has glued the damper shut. Now I just open the door and poke the damper open from the inside with a stick. Problem solved.

    I've wondered about the flame color, too. When running hardest with new wood, I get yellow and orange flame. Later in the cycle, there's more blue. I'm running both nozzles now, but had good luck with just one.

    This morning I had a few coals left in the firebox. I tossed three pieces of branchwood in, and went back into the house and had a cup of coffee. When I went back out, about 10 minutes later, there was a small, clean-burning fire roaring. I put in about 4 or 5 bigger pieces and initiated gasification. No smoke. Took a shower and got ready to leave for work and tossed a few more big chunks into the firebox. Still no smoke. When I get home tonight at around 6:00, the house will be around 73 degrees and there will be a few coals in the boiler. Repeat process, substituting beer for coffee. That's with weather in the 20s and 30s. Plenty of room for more wood in the firebox when it gets colder.

    Do you have the mechanical hx cleaner on your 40, hog?
  10. slowzuki

    slowzuki Feeling the Heat

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    Eric I was wondering if the smoke isn't from the hx tubes but rather the stuff stuck to the bypass damper? Our wood supply got soaked a couple of weeks ago and we have been getting creosote like crazy. This morning a small little fire of my wife's in the stove (not boiler) lit the chimney up! She was a little excited at the new stove black paint burning in all at once.
  11. Eric Johnson

    Eric Johnson Mod Emeritus

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    The firebox has a nice coating of creosote growing on it, and that includes the inside surface of the bypass damper. And that's as it should be. However, there's none that I can see anywhere else in the boiler, and that includes the back of the damper, which seems to fit tight. If it didn't I'd probably get smoke all the time and creosote deposits around it. This is not a big deal. Even when I do get smoke it's minimal, white and not very noxious. And it usually goes away pretty quick.

    But I'd still like to know where it's coming from.

    I don't know why everyone seems to discount the creosote-in-the-hx-tubes theory. I get a little whiff of smoke sometimes during idle (though not always). Seems to me this smoke had to draft down through the nozzle unburned, up through the hx tubes, and out the chimney. That's probably 25 feet of travel, roughly five feet of it through hx tubes cooled by the surrounding water to something like 175 degrees. Why wouldn't creosote accumulate there under these conditions? And as soon as you fire the thing back up, you've got flames shooting into the tubes, which would, one would think, tend to burn off any creosote that did manage to grow on the hx surface.

    One question is as follows: If I load the boiler up before going to bed and it cranks away until 2:00 a.m. when the house zones are satisfied and then goes into idle, why doesn't the creosote burn off at 5:00 a.m. when the house starts to cool off and the boiler comes out of hibernation and fires until the rest of the wood is gone? I think that's because late in the cycle, you're not getting flame anymore. Instead, you're getting hot gas at that point in the wood's combustion cycle. So it doesn't burn off. However, when I stoke it up with a fresh load of wood at 7:00 a.m., plenty of flames shoot into the tubes.

    The other mystery would is why there is no creosote accumulation in the chimney, despite the fact that it sees some smoke and rarely sees temps over 300 or 350.

    Inquiring minds want to know.
  12. tboom

    tboom New Member

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    I have heard alot about the EKO boiler but havent heard much about the burn time or wood consumption looking at eko 60 can any one help
  13. Eric Johnson

    Eric Johnson Mod Emeritus

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    Sorry, I forgot to mention burntime in my email response to you.

    The EKOs have huge fireboxes, low wood usage and consequently long burn times. Under most conditions, I think you could load it to the gills once a day and if you have a hot water storage tank, probably once every two or three days in milder weather. I like to play with mine, so I'm fooling around with it all the time (I'm talking about the boiler, here).

    To get to your question about wood usage, nofossil has about 3,000 square feet of living space and a 900-gallon storage tank connected to an EKO 25 and I think he says he can fire it every other day in weather like we've been having here in the Northeast, which is probably in the 20-40 range. I think he said he burns about 5 cords a season.

    Wood consumption is not a big issue with me since I have an unlimited supply of dry wood and I really like cutting it. My two biggest priorities are having a nice, warm house 24/7, an unlimited supply of hot water at the tap and a clean burn. I also don't like getting up at 4:00 a.m. when it's below zero to tend the boiler.

    The EKO 60 gets straight As on all of the above, with plenty of capacity to spare.
  14. slowzuki

    slowzuki Feeling the Heat

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    Eric I don't discount the hx theory but there should be creosote in the top part of the tubes too that doesn't burn off. The jetstream sends all of its smoke out the tubes always with no bypass damper so creosote does accumulate at the start of a burn. Only the first foot or less gets cleaned off from the fire so you have to cleaned the tubes every few weeks. The turbulators do burn off and stay clean much more so than the tubes since they can get as hot as the gas stream.

    Ken
  15. Nofossil

    Nofossil Moderator Emeritus

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    Is it possible that you get smoke if one nozzle ignites and the other doesn't? I don't suppose there's any reason that they would have to both be ready to gasify at the same time.

    It's curious that I've never seen this, even during the season when I didn't have a storage tank.
  16. Eric Johnson

    Eric Johnson Mod Emeritus

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    I ran it for a couple of weeks with just one nozzle blocked off and was pretty much the same deal. Earlier, when running two nozzles before I got the air adjusted, one nozzle would light off before the other one, and the result was smoke. However, you could see it in the gasification chamber, whereas I swear there's no smoke in the refractory chamber when this is happening.

    I doubt that your boiler idled much even without storage, nofo. A 60 kw boiler can get ahead of itself a lot faster than a 25, I would think.
  17. tboom

    tboom New Member

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    I am trying to find out what is the best boiler for the money. I think I have narrowed it down to either a Tarm or EKO does anyone have any suggestions
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