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Wood Gun - char buildup in heat exchanger

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by mcgilvra, Mar 1, 2010.

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  1. mcgilvra

    mcgilvra New Member

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    We have a Wood Gun E140 SS Model. It's a great unit so far but gets a black scale buildup in the heat exchanger (swirl chamber). It reduces efficiency a lot and must be cleaned about once a month. It's a major undertaking with a rotary wire cup and two 12" drill extensions, and it requires removing the blower motor. Anybody have a tip on prevention or easier cleaning? Thanks.

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  2. Gooserider

    Gooserider Mod Emeritus

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    Are you burning with storage? How much time are you spending idling? What are your return water temps? Could be wrong, but I'd be willing to bet that increasing the temperatures in the HX and / or cutting back on idle would help reduce the scale. Other possibility is if your wood isn't as dry as it should be - what is the moisture content of the INSIDE of your splits?

    Gooserider
  3. Fred61

    Fred61 Minister of Fire

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    I would check to see that the air intake damper is sealing completely. The swirl chamber is the last area to see the burned gasses and should be perfectly clean at that point. Gooserider is also correct in suspecting wet wood. I ran my 140 for ten years and that area never had a build-up. It was always white. Idling should not make a difference since the Wood Gun completely shuts down on idle. The only way smoldering would occur would be if you had a leak in the damper or doors. Although return water temps are important for reasons we all know, I don't see where they would affect that area and cause build-up of scale. If you are getting scale at that point because of wet wood the build-up that is reducing heat transfer is not the only thing that is reducing your efficiency. You must also be getting a lousy incomplete burn and sending tons of unburned gasses up the chimney.
  4. Gooserider

    Gooserider Mod Emeritus

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    You have much more "hands on" with a WG than I do Fred, but my thought on the first batch of questions was that maybe the OP wasn't burning hot enough to get the HX up to the temp needed to burn the crud off - and the stuff I was asking about were the reasons that I could think of for the HX not getting hot... Good thought on the air intake door, as that would cause a smolder and make some creosote heavy smoke to build up.

    Gooserider
  5. Perfect Heat

    Perfect Heat Member

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    Fred,
    What is considered a normal amount of creosote build up in the fire box area of a WG 140? I have been burning my WG for approx 2 weeks (using wood with a MC of 22 to 25%) The inside of the fire box has a thin layer of shiny black on it. Sometimes it flakes off but the back of the fire box does not. I have checked the seals on the doors and cleaned with a wet rag. No significant amount of creosote on any.

    Just wondering if this is normal.

    Terry
  6. Fred61

    Fred61 Minister of Fire

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    I'd say you're doing quite well, especially if you are getting flaking. That means you are burning pretty hot with a minimum of idling. The flaking means you are drying it out. Don't be surprised if you see more build-up on the water jacketed surfaces as the weather warms and more idling occurs. All down draft gassifiers are going to have a build-up of goop in the upper chamber because your actual fire is down in the tubes and you are basically just baking the wood in the upper chamber. If or when you shut down for the summer you should try to remove some of the build-up and put some sort of rust preventer on the surfaces in preparation for the humidity.
  7. Fred61

    Fred61 Minister of Fire

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    Goose
    I wanted to get back to you earlier but my computer got infected and I had to take it to the Geek, so I was without it for a while.
    I wasn't questioning your thoughts, just adding my 2 cents. You have a unique and admirable ability to troubleshoot this stuff.
    I just wanted to add that the burned or burning gasses have gone the length of the boiler through ceramic tubes and then go back through two water jacketed fire tubes before entering the swirl chamber. By the time the gasses enter the jacketed firetubes they should have been completely burned and should leave no crud. The swirl chamber is also surrounded by water so you and I know it would be difficult or impossible to burn off the crud at that point. It should be fly ash at that by the time it gets to the swirl chamber. I believe that the turbulence within the swirl chamber produces an abrasive blasting action that keeps the walls clean and able to transfer heat by keeping the layer of fly ash thin, but it's not going to abrade tar.
  8. muncybob

    muncybob Minister of Fire

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    Yep, just as Fred says...you are doing fine. My ceramics are clean but the rest of the fire box is black. Just keep the seals clean(they usually are for me) and be sure you have no air leaks and all should be fine.
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