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Burning scrap 2x4s - How to control puffing

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by hartkem, Jan 15, 2013.

  1. hartkem

    hartkem Member

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    I was able to get a 16' trailer load of 2x4 scraps today for free. I want to burn this at about a 50-60% ratio to cord wood. I know if I just throw it in the way my eko 40 is set now it will puff. Do I need more or less primary / secondary air to control this? I have the newer controller on my EKO and usually run it at 60% with wide open fan shutter.

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  2. maple1

    maple1 Minister of Fire

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    Have you tried any yet? Just thinking if you pack it tight together as possible it should help? (Less surface area).
  3. Fred61

    Fred61 Minister of Fire

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    I would close the fan opening to 50% for starters and you may want to close it up even more if puffing. I burn small, extremely dry splits in my 25 and I'm running my fan at 40% with only about 30% opening on the fan and still get some puffing periodically.
  4. hartkem

    hartkem Member

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    I haven't tried burning any yet. I wanted to know what settings I needed to adjust so I could dial it in. I will see how packing tight works with my current settings
  5. maple1

    maple1 Minister of Fire

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    I thought puffing was from too much wood gassing for the air (oxygen) available to ignite it properly? So wouldn't you introduce more air? I haven't experienced it, yet, that I know of anyway.
  6. huffdawg

    huffdawg Minister of Fire

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    I would try burning some first without making adjustments.. See what happens . Then play with fan speed and shutter opening.
    When my eko 40 starts puffing I turn the fan speed up and it goes away
  7. avc8130

    avc8130 Minister of Fire

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    Puffing? on an EKO? With all of your former WG experience you should be a pro at this.

    I think maple1 is on to the cause, but I think the universal solution around here is to damper down. There seem to be 2 ways to actually deal with it:
    1. Allow MORE air to sustain the desired high rate of gassification/burn the fire has.
    2. Damper DOWN to reduce the overall size/intensity of the fire.

    I think either will work if you can far enough to either side to control it.

    Surface area seems to have a large impact. Reducing the surface area would reduce puffing as less area of wood will be exposed to oxygen to fire. Scrap 2x4s are going to be tough.

    ac
  8. Fred61

    Fred61 Minister of Fire

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    Wood Gun ------ Eko,Two totally different animals. I have experience with both.
  9. goosegunner

    goosegunner Minister of Fire

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    Do you have storage?

    Do you need to load more than once to charge storage?

    I have very little if ever puffing problem if my Econoburn is hot and has a good coal bed. Cold starts with small dry wood is when it happens. I think it is a combination of too much fuel / lack of o2 / poor ignition source.

    I would try using the stuff only when the boiler is up to temp and going strong.

    gg
  10. Nofossil

    Nofossil Moderator Emeritus

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    My experience suggests that more primary air is the answer to puffing. With really dry wood and lots of surface area, you may get more heat than you want. When primary combustion is really active and I want to reduce fan speed to limit combustion temp, I find that I have to do periodic 'purge' cycles at full fan speed to prevent puffing.
  11. mr.fixit

    mr.fixit Member

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    You could cover a small portion of the nozzle with a piece of fire brick to throttle back the output.
    Probably would take some experimenting with the size of opening and the air settings.
    Seems like it would be easy to overfire with alot of small pieces that are very dry.

    Hardest part may be handling the scraps,hard to pick up with a shovel and hard to pick up by hand to load.

    Maybe a conveyer belt to drop them right into the boiler!
  12. TCaldwell

    TCaldwell Minister of Fire

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    This is not always as it seems, under normal full burn conditions, with the correct ammt of total combustion air divided to primary and secondary ducting, you will get a o2 increase with more secondary air, and or decreasing primary air. Usally the o2 feedback to a controller with a optimised algorithim will determine the correct p/s settings. Problems can occur when p/s air settings are not proportioned correctly, this results from mismatched tuning constants and non linearized dampers. Linearized dampers will correctly move to the controller output, not to percent of damper travel, when you controller asks for a 30% output it wants 30% air volume, not necessarily 30% damper travel. Now project this to 2 dampers simultaneously it really compromises the controller to determine the correct output to the dampers and get the wanted control. Sorry, a little off topic for hartkems situation, another puffing scenario comes when the fixed damper settings are giving too much secondary air. The fire will start normally, flue or secondary burn temp will start to rise, then the temps and o2 will both start to drop about 5-10 minutes into burn. What is happening is that the secondary air volume is too great, extinguishing the fire, cooling the gasses below secondary burn temp, resulting in alot of unburned flue gas, smoke out the flue. This is a extreeme, normal puffing will start before this happens. If you want to burn alot of this wood, you will have to change your p/s air settings. I would start by stacking wood tightly together and monitor flue temps, you want a moderately increasing temp slope from start this means the fire is controlled, too fast is out of control, usally a controlled start of burn will lead to a good rest of burn. Try either decreasing primary and or increasing secondary to do this, slowly, with larger or wetter wood you would go the other way.
  13. ewdudley

    ewdudley Minister of Fire

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    Just got done with some hemlock slab-wood that would tend to take off, extinguish gasification with smoke, and then woof. I agree with the advice to pack tightly and restrict primary air.

    Another trick I've seen mentioned here from time to time is to get some charcoal started and then cover the whole nozzle with a long flat piece of wood. This seems to help the fire to grow more slowly and steadily with high velocity streams of gas traveling towards the nozzle under the base split.
  14. Duetech

    Duetech Minister of Fire

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    I think Huffdawg is pretty much on key with try it first and adjust as needed. Giving more speed in his scenario will give a constant and stabilized pressure increase in the primary (because the smaller primary opening). Too low of a pressure air in the primary allows pre-gasification ignition of the gasses in the primary by allowing the gasses to rise upward and meet with the incoming oxygen. Poof.
  15. hartkem

    hartkem Member

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    Update:

    I have been burning mostly scrap 2xs for the last 5 days or so. I usually throw in 2 small splits and then load the boiler full with scrap. I have my fan turned down to 50% and the fan opening about 30% open. I checked the boiler today about 2 hours into the burn and there was very slight puffing but not much. The flame is dark orange so I think im running a little rich. I have noticed that the ash is darker now than it was when I was burning splits. I am getting about 8-9 hrs between firings. I was able to go 12 hrs with splits but since this wood is so easy to get its worth the extra effort. I think I will try closing the primary a little to see if I can get a blue flame. I think the scrap Im burning is wetter than I thought. It doesn't feel as dry as the split cord wood. Also my bypass damper is starting to stick again which hasn't happened since I was burning pine.
  16. Downeast Farmer

    Downeast Farmer New Member

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    So, Fred61, since you've had experience with both, would you mind comparing them? I'm wondering why you switched from Wood Gun to Eko, being in the market for a boiler....
  17. Fred61

    Fred61 Minister of Fire

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    I had the Wood Gun installed in my former residence. I hesitate to go over, once again, my experiences with the Wood Gun because most of them were bad. Over time, I have posted my adventures with the unit and have been accused of bashing. I was trying to help those who now have Wood Guns and possibly warn those who are contemplating a purchase.

    I can't or won't list all the trials and tribulations I encountered here but I'll give you a sample. Starting with inadequate cabinet insulation and the fact that the design uses the doors as targets for the combustion causing wear of the door refractory and gaskets. Primitive controls and excessive wear of the refractory from the high volume of air that flows through the unit. Most users on this site have experienced a few of the small problems I encountered such as explosions but they haven't had them long enough to experience the serious problems I encountered. I didn't know it at the time, but recent thoughts are indicating to me that they are not as efficient because the high volume of air is fooling the stack temperature test. I could easily be wrong on this thought but it did occur tome after operating the EKO.

    Comparing the EKO to the Wood Gun: They both get the job done but the Gun uses brute force like a bull dozer and the EKO does the job with a little more finesse like a ballerina. I installed my Gun in 1980 and sent it to the salvage yard in 1988 and went back to oil and a Vermont Castings stove for support. Even with all the problems that plagued me, I was still convinced that, if you were going to burn wood, gassification was the way to go if only the boiler would not eat itself up.

    After moving to my small retirement home in 2000, I started looking for a way to replace oil as there seemed to be no price ceiling. Thats when I discovered the Euoropean boilers. When I saw that Wood Gun was still peddling boilers, I naturally assumed they had made progress on design. After researching, I found that basically few improvements have been made over the one I purchased. I think technology has passed them by. It happens alot. I worked for a company that was a pioneer in rotating magnetic memory devices in 1960. Start-ups passed them by in a matter of 10 years and they hung on by their fingernails for another 10 years, Gone now!
    So there you have a fraction of the reasons that turned me away from Wood Gun. There are boilers emerging that improvements in controls but you must evaluate them to see if they are right for your application. If I were in the market for a boiler right now I would buy the unit I have in my basement but I don't recommend it to everybody because they may have different needs such as lamda control.
    I will say that your boiler is only as good as your dealer that sold it to you. I bought my boiler from Mark at Ahona and would highly recommend him as a supplier.
  18. Downeast Farmer

    Downeast Farmer New Member

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    Thanks for all that, Fred61; it doesn't sound like bashing to me--learning from the experience of others is my main motivation for following these threads.
  19. James Reimer

    James Reimer New Member

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    As mentioned in an earlier response, could you arrange them in a way that they would be tightly packed together to mimic a larger log? I don't know if you could get enough air into there to satisfy the gassing otherwise.
  20. hartkem

    hartkem Member

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    I have been trying the best I can but I light the fire with small scraps first then throw in a few splits and then pack the 2x4s in. Its hard since there is a lot of smoke. I tried putting all the wood in first before lighting the fire but it seems to take longer to get good gasification. Im going to trying reducing my primary inlet opening and see what happens. It is burning decent with only minimal puffing but Im getting much more smoke than with cord wood. I think some of the smoke is due to the 2x4s aren't as dry as they should be.

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