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Bridging load in EKO..

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by hkobus, Jan 24, 2008.

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  1. hkobus

    hkobus Member

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    Any of you Orlan/Eko users ever running in to, what I call the wood "bridging" in the firebox. :mad: I happens every once in a while, that the glowing embers over the nozzle burn away and leave an opening between the nozzle and the wood load. This results in more smoke from the stack than I like, because the secondary burn stops. When I stir the load a bit so it comes down, it goes right back to full gasifying instantly.
    Has anyone run into this and maybe come up with a solution for it. I do not have the time to baby sit the unit, so looking for some ideas.

    Thanks,

    Henk.

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  2. Nofossil

    Nofossil Moderator Emeritus

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    A guy with a Tarm just started a thread on what sounds like the same issue. I've never had the problem, though I think I've come close when I use a lot of bigger pieces and no small ones. A mix of sizes seems to be best for these. In my old non-gasifier, I'd use bigger chunks to get it to burn longer. I don't think that's the right approach with these.
  3. hkobus

    hkobus Member

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    I did read that thread, what I see is the exact opposite. The wood burns away from the nozzle and leaves it wide open. I have tried mixed sizes, with mixed results.
    Does anyone remove the ashes from the nozzle area? This may allow the wood to drop closer to the nozzle, but is not standard procedure, as far as I was told this has to go through the nozzle on it's own.
  4. Eric Johnson

    Eric Johnson Mod Emeritus

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    Some people apparently need to scoop the ashes out of their fireboxes, Henk, but I just rake mine down through the nozzles and into the ash pit.

    I know what you're talking about with the bridging, but it's never been a problem for me. I rarely fill the firebox up all the way. Generally, I try to pile the wood in a pyramid shape over the nozzles so that the largest amount of wood is directly over the nozzles. Maybe that has something to do with it.

    Typically, I load the thing before going to work in the morning and then my wife will go out around 2:00 in the afternoon and throw a few chunks in. Then I load it back up at night when I get home. There's usually a good bed of coals to work with.

    Don't know if that helps.
  5. eekster

    eekster New Member

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    I had this happen a couple of times also, the wood wedged against the sides and burned out the whole lower layer of wood. When I load, I over lap the split wood and then add a couple of 4"-6" logs on top, gives it more weight and by the time the split burns down, the logs are red hot and give the final long burn to make it through the night. Hope this help it works for me. Keith
  6. barnartist

    barnartist Minister of Fire

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    your not alone, I too have it happen. Seems to happen more with wedge split pieces, so if you have some smaller unsplit pieces, put those in the mix. Biggest ones on top help them to fall too. I usually have to stuff wood in there like a puzzle to get as much in there as possible, so it happens and loss of gas does to. And water temp.
    Stinks when your not around too.
  7. jebatty

    jebatty Minister of Fire

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    Query for those who can provide some objective measurement of performance: what effect, if any, does bridging have on the total heat output over the course of a full burn?

    Both EKO and Tarm users have mentioned “bridging” and a number of ways to reduce bridging have been suggested. I experience this also (Tarm Solo Plus 40), and when I notice it it, I too mess the load up a bit to collapse the bridge. Yet, I know I could not have noticed this every time, and in fact, I have burned full loads without ever checking the progress. So I suspect bridging has occurred and collapsed on its own without intervention. No matter what during the burn, the end result is a bed of fine ash.

    It is clear that during a burn, flue temp drops during the bridge, and rises when the bridge is collapsed. But does bridging really reduce overall efficiency or heat output of the full burn? Does bridging really merit any serous attention?

    Actual data would be appreciated. Thanks.

    (a copy of this post is being place in both the EKO and Tarm bridging threads)
  8. jebatty

    jebatty Minister of Fire

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    A little follow-up to a no bridging burn. I had a pile of dry 4" pieces leftover as I was cutting the 24" logs for the old OWB down to 20" for the Tarm. I ran through 2 loads in my burn today using the 4" material, no bridging at all. Don't rush to re-cut all your wood to 4"!!!
  9. Eric Johnson

    Eric Johnson Mod Emeritus

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    Bridging is something I've never had a problem with. I tend to make smaller fires, and stack the wood in a pyramid pattern over the nozzles whenever possible. Maybe that has something to do with it.
  10. sled_mack

    sled_mack New Member

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    The first year I had a lot of bridging problems. Wet wood seems to make it a lot worse, as do big pieces. I try to put small pieces in the middle, and the big pieces on the side so that they fall down on the middle and push the bridge down.

    I don't have any hard data on what happens when it bridges, but I do know that I lose all secondary burn and it smokes terribly when it bridges. That's always my first indication that there is a problem. Usually, if it's been bridging for a while, the outlet water temp is almost the same as the inlet. To me, this means I'm wasting wood and not getting any heat.
  11. hkobus

    hkobus Member

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    I second your post Sled_mack, I also believe wet wood is part of the challenge. I don't have much of an option for this season anymore, but will have more dry wood next year. The size of the splits is an issue to. I see it at times that when you fill the whole boiler, some pieces jamb in tight when two are side by side. More pieces in the width of the chamber may work better.
    Like Erik, I tried making smaller fires when I am close to home, this works as well but not always possible.
    Trying to cut smaller chunks may lose some of the loading capacity and need faster reload. I have at times added some pelleted feed (spilled at the bins when delivered)to the load and it extends the burn time. We could do the same with cob corn etc. A local farm is pelleting oat hull and wheat shorts for pellet boilers and commercial fluid bed boilers, I am going to ask him if he could press briquettes from this to supplement my loads. This may than help prevent the bridging when mixed in at loading.
    I have tried this with short pieces cut from trusses, it keeps the load loose and burns or chars faster than hard wood, it then makes space to let the rest fall down.

    Henk.
  12. barnartist

    barnartist Minister of Fire

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    Hog, you must really have trouble. I do as well but not all the time. If you have any round unsplit pieces put them in the middle of each layer of wood. Maybe since I idle allot my wood falls on its own, but I know it does smoke and I cant get any heat when it happens. Are you leaving any ash at the sides of the upper chamber? I rarely clean or rake ashes up there, and maybe this packed ash serves as a funnel effect for the new wood load.
  13. jebatty

    jebatty Minister of Fire

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    A few post higher up in this thread I mentioned that some real data would be helpful. Some of you have mentioned that you get smoke when bridging occurs. I do not get smoke.

    I see flue temp drop about 50-100 degrees during the bridge, then if I do nothing, after a period of time the bridge collapses and everything continues as normal, but no smoke during this period. My normal operating flue temp is 400-600, with the low temp only occurring as the load has burned down to coals. So the flue temp drop during a bridge still is around 500, and gasification or near complete combustion still continues.
  14. sled_mack

    sled_mack New Member

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    Jim,

    What kind of real data are you looking for? I'm not sure I have the instrumentation to provide much more than observation - lots of smoke and no heat. But if there is something specific you are looking for, I'll see if I can capture it next time it happens.
  15. jebatty

    jebatty Minister of Fire

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    About 8 posts above this one is where I brought up the data questions. I guess if there is some way to measure total btu output when bridging is ignored, but observing to see if bridging occurred, as opposed to total btu output when load is monitored and bridges are manually collapsed as soon as noticed, that might be helpful to see how material, if any, heat loss is when bridging occurs. Make any sense? Thanks.
  16. barnartist

    barnartist Minister of Fire

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    Jim,
    why do you burn so hot? Your letting alot of btu's go up the stack.
  17. jebatty

    jebatty Minister of Fire

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    I realize I'm on the hot side, and that efficiency may be down about 5% (600 vs 400). Some say 300 is OK, but it seems to me anything less than that is skirting on the edge.

    My 22' chimney (6" stainless) produces a very high draft. I have chosen not to damper the chimney because I don't favor any chimney obstructions.

    I burn very dry pine almost exclusively. Moisture content is 10-15%. The bark and sap are high in volatiles and burn intensely. Before the adjustments highlighted below, I was getting flue temps maxing out at 900.

    I have greatly restricted the forced draft on the Tarm way below full open. With this adjustment temps dropped to max of 650-750. I added chain turbulators, which dropped the max to 600, and usually around 525-550. As the burn progresses, it holds at 400-450. I also added a draft fan speed control, and I can cut the draft further by slowing down the fan, but I have opted for a "light it and forget" burn pattern. I don't want to adjust the fan based on temp or type/moisture content of wood. The ideal would be a fan that slows down or speeds up based on flue temp. That's something I would consider, but as of yet I have not seen that as available. The Tarm allows for adjusting primary and secondary air, which will change the flue temp, but again I have opted for a middle setting on the "light it and forget" burn pattern.

    My plate hx (5 x 12 x 30 plate) with Taco 007 pushes lots of water, and at the 450-500 range I am stripping all the heat to storage the boiler produces, with virtually no idling. That would also hold true at lower temps, but I'm choosing a small reduction in efficiency for more btu's, and still without idling.

    I do have some wood other than pine, and I really don't want to readjust the draft when I switch to other wood.

    Please comment or provide additional ideas. Thanks.
  18. barnartist

    barnartist Minister of Fire

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    I must have been jinxed because I bridged badly this morning, been fighting it all day. My fault I think, I put a long skinny piece I was too lazy to cut in the boiler diagonally.
    I would love to see a fan speed control that adjusts to stack temp.
    For me, I dislike seeing flue temps above 350. Just feels wasteful. But I don't burn much pine. Do you smoke much from pine? I think if I used it I wouldn't get very far from a burn with it.
    Just think if you could somehow filter the leftover heat that goes up the chimney, your house would be like Jamaca in a few minutes.
  19. sled_mack

    sled_mack New Member

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    Jim,

    I agree about measuring BTUs with/without bridging. Unfortunately, I'm not set up to do that. I'm using from my tank at the same time I'm charging it. If I knew I could force a bridge (kind of like taking your car to a mechanic - it always sounds fine at that time), I could isolate my tank and check before/after temps of the tank.

    Does your Tarm have a separate fan for primary and secondary air? My EKO has two fans, but each supplies one side of the boiler's primary and secondary air. I'm not sure that changing overall fan speed based on stack temp alone would be enough. But I'm not sure what other variables would be needed to adjust both the overall air flow and the primary/secondary ratio to get the best results?

    I'd like to change the fan config on my EKO so that one fan is primary and the other secondary. That would make controlling each much easier, and allow a lot more experimentation on what works best.
  20. jebatty

    jebatty Minister of Fire

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    Virtually no smoke, except on initial start-up with a cold boiler, but that usually disappears within about 10-15 minutes. By that time secondary burn/gasification is in full swing. I get the wispy steam if its quite cold out, but in the 20's and above don't even see that.

    The Tarm has one forced draft fan, air enters from the top of the firebox. There is a diversion lever which splits the air between primary and secondary. As one increases, the other decreases, and vice versa. There is an adjustment damper on the draft fan to provide fixed amount of total forced draft.

    I recall from another post a mention of a digital stepper actuator on the fan draft control, rather than speed control. That might work better than controlling motor speed.

    The Tarm's control panel obviously is set up for more than is covered by the manual. There are lots of connections possible, along with a unused switch for a circulator. Might hunt down the manual used in Europe to find out the full capability of the controller.
  21. ebbci05

    ebbci05 New Member

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    I have an EBW-100 boiler that is one month old. I have had this bridging problem quite a bit. When it happens it burns the bottom out and all the coals. My water temperature will drop from 170-120. Once I knock it down it takes a long time to get gasifying. Usually it happens at night when I fill it quite full. I also have only been getting about 3-4 hours out of a full load, and this is getting quite annoying. I too can't be home all the time to keep checking it. My wife does go check it but can't take the time to mess with it either. I think that if I don't fill it full, I would be out there every 2 hours :mad: Anyway, I know that when my wood bridges, the water cools off very fast and it takes a long time to regain the heat that I lost. I don't have smoke when this happens so I don't have anyway to tell except to check it every so often.
    Eric
  22. barnartist

    barnartist Minister of Fire

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    Eric, you described it perfectly. There is definately heat and wood losses.
    I am home during the winter and can mess with it, but hate making all the trips outside.
    I bought a wireless spa type sensor I use to monitor my water temp. I think radio shack sells it. The transmitter has a long probe that I simply slide between my main house loop pipe and some insulation.
    The temp is off by about20 degrees, (160 = 180 ) and will only go up that high, but this device alone has really helped me know what things are doing. I even have it set to a low temp alarm.

    I know your away, so im not sure if this helps, but it might help your wife some.
  23. sled_mack

    sled_mack New Member

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    I hope you don't get too discouraged too quickly. I think most of us went through some (at times a lot) learning pains.

    I don't know anything about your boiler specifically. But, at first I was having the same type of problem where the coals would burn out with wood still sitting in the firebox. Eventually, I figured out that I was putting too much air into the boiler. In an effort to get the fire hot, I was essentially blowing it out. After many phone calls to where I bought it, he convinced me to get a fire going and turn the air down to the minimum that would sustain secondary gassification. Then I made my adjustments from there, only adding a little more air. My experience is that too little air will cause the secondary gassification to go out after an hour or so.

    I suggest starting a new post describing your entire system - plumbing, connection to existing heating system, storage, heat load, etc. People can give much better advice with more information.

    That being said, you and barnartist are having very similar issues. I'm curious to know how similar your setups are? There is a description of my setup in a post call New guy - Long Post. I'm very happy with how my EKO is working. A few more changes now and over the summer, and I think I'll be even more happy with it. Don't give up yet!
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