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Econoburn combustion test

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by heaterman, Jan 13, 2008.

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  1. heaterman

    heaterman Minister of Fire

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    FYI, I played with an Econoburn 100 for about 3 hours this afternoon to see what kind of numbers I could get on the combustion analyzer. I was very pleasantly surprised.

    First off, a wood burner is a different beast because the fuel supply is always changing. You can set the air shutter for best performance and 15 minutes later the combustion numbers are all out of whack as your fuel changes state. So you pick an average setting and run with it. I wound up with a tad more air than the factory setting.

    That being said, I'm pretty impressed with what I observed in the roughly 3 hours that I played with this boiler. I asked the owner if he would give me a ring when he had a fire in it that was about 2 hours into a burn so I had an average starting point. When I got there the boiler had a good bed of coals underneath 3 chunks of logs that were fully carbonized. I stirred the fuel a bit to settle the chunks and stuck the Testo in the flue to see what was going on. The burner was in full gasification mode with nearly the entire lower chamber filled with bluish yellow flame.

    These are the numbers:

    Flue gas temp 368*

    CO 2630 PPM

    CO2 11.2%

    O2 5.1%

    Efficiency 87.6%

    Flue draft -0.04 wc"

    Sounds like a good running oil burner except for the CO.

    The next step was to load it with wood and see what happened to the numbers leaving the air gate setting as it was. I added approximately 25-30 pounds of wood and opened the flue gate to let the new wood get going. During this stage the excess air went way up and correspondingly the CO2 fell into the 5% range. I figured this was normal as the combustion air was blowing pretty much straight through the firebox. At this point the numbers looked like this.

    CO 1618 PPM

    CO2 5.4%

    O2 11.5%

    Efficiency 76.4% (that was as low as I saw it through the whole cycle)

    After about 15 minutes I closed the flue gate to put it in gasification mode and monitored the analyzer. The unit started gasifying but the excess air remained high, like over 90%. It took me a minute to tumble to what was going on. The unit was in gasification mode, the wood seemed to be fully involved flame wise so why was the excess air so high? Although the unit was gasifying, the wood had not reached the temperature where it is carbonized. As this began to happen the excess air dropped, the CO2 went back up and the efficiency climbed back over 80%. After another 45-50 minutes the numbers reached nearly the same point as the initial test. After another 15 minutes or so the unit reached what I would guess to be peak burn as flue gas was reaching 450*. The gasification chamber was filled with flame and the flue gas numbers actually looked as though it could use more air as the CO2 was over 13%. CO went ballistic, reading 4500PPM before I pulled the analyzer. I'd guess that during this brief period of 10-15 minute the efficiency was crowding 90%. Very soon after that the fire passed its peak and the numbers began to look more normal..... as if 80% from a wood burner is normal.

    Conclusions:

    You have to give a gasifying wood burner plenty of air in order to ensure that you can sustain gasification all the way through the burn cycle. If you set it to low you can lose a lot during the peak burn time period.

    Econoburn has done their homework on boiler design. The boiler cranks out efficiency and burns clean. Although the wood being used by this homeowner is not quite what it should be (24-35% moisture on the logs I tested) the boiler handles it well with little sign of creosote buildup in the heat exchanger area. There is a pretty good coating inside the fire box. I'm sure it would be less with the moisture content recommended by Econoburn (<25%)

    In this day of $3.00 fuel oil, soon to be crowding $4 unless I miss my guess, we in the heating profession are going to be seeing a lot more alternative type systems going in. It's our responsibility to acquaint ourselves with what's good and what's not. The Econoburn boiler is a good place to start. It's a pressurized sealed unit so it eliminates a lot of the inherent problems of open systems. As I understand it, they have the folks from ASME in the factory as of right now reviewing their manufacturing processes and will soon have the {H} rating making it acceptable for installation everywhere. They also have the same unit available soon in an outdoor model.

    Home owners considering burning wood will do themselves a favor by using a unit like this as opposed to a typical outdoor wood burner with their sub 40% efficiency and horrible particulate emissions.

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  2. Eric Johnson

    Eric Johnson Mod Emeritus

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    Thanks for the Econoburn report, heaterman. I like the look of that boiler a lot and though I've never seen one up close, it looks like a real winner. I know Dunkirk is a respected name in conventional boiler mfg. and design (I live right outside of Utica, NY), so I'm fairly confident they know what they're doing. I'm anxiously awaiting the unveiling of the outdoor version. Lots of current OWB owners are going to be upgrading to outdoor gasifiers like the Econoburn, BioMax, Blue Forge, etc. in the next couple of years, I think.
  3. Bartman

    Bartman Member

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    Heaterman,
    Nice report on the Econoburn. That being said, can one safely assume that while using this boiler optimum flue temps should be in he 400 degree range for good all around gasification? If so, couldn't controls be in place to monitor flue temps and throttle the air by the use of flue temp controllers and electric air dampers with feedback capability?
  4. heaterman

    heaterman Minister of Fire

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    Thanks........my better half stares blankly and her eyes start getting that glazed look when I start talking about boilers...........but I love what I do.

    I appreciate where you're coming from but what you're talking about can only be achieved when you have a constant fuel source. As your wood burned down the blower would increase speed to try and keep the flue gas target temp met albeit with no fuel supply. If you could ensure a constant fuel supply you could indeed set up the blower to maintain gasification. The issue then would become what controls the water temperature. The control would have to consider the water temp first, then try to maintain gasification within that parameter.

    In some European made (Viessmann) pellet boilers (constantly available fuel source) the manufacturer has included this feature along with water temp targets that move automatically based on outdoor air temperature. WAAAAYYY cool!!

    AFA ideal flue gas temp, I'd say that peak efficiency was around 330-350* while the unit was in gasification mode.
  5. Bartman

    Bartman Member

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    My buddy's got family overseas, I wonder how much of a hassle it would be to import one here.
  6. Nofossil

    Nofossil Moderator Emeritus

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    Great data! Love to see how other brands / designs compare.
  7. jebatty

    jebatty Minister of Fire

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    Really neat to see this. Anyone have any idea what the added cost would be to provide a boiler with a control system that would monitor outside air, draft, temp, CO, CO2, O2, and have the ability to control these to achieve very high efficiency through most of the burn? And then translate to extra btu's recovered?
  8. Bob Rohr

    Bob Rohr Minister of Fire

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    Jim

    I installed a biomass boiler a few years back that had a probe in the flue passage. I believe it is a lambra (sp) sensor like the automotive industry uses for vehicle emission sensing. It was supposely watching the emissions in the flue and adjusting air flow via the variable speed blower.

    hr
  9. TCaldwell

    TCaldwell Minister of Fire

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    Jebatty, last week i talked to a company, i will get you the name when i can find it again, they distribute and install fixed mount flue gas analyzers that monitor and modulate fan speed to your perameters, all for industry {deep pockets} he very easily understood what I was drooling for but starting at 4k plus your variable speed motor sort of took the starch out of my...
  10. Eric Johnson

    Eric Johnson Mod Emeritus

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    Welcome to the Boiler Room, master of sparks. I appreciate your contribution.
  11. Bartman

    Bartman Member

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    Monitoring flue gases with an O2 sensor and related controls can be costly and difficult to engineer, but if it can be done by just monitoring flue temps, that is possible for little money. Two days ago I just won 6 Red Lion temp controllers on eBay for less than $60, with a rod type thermocouple in the flue, and possibly one closer to the fire, temp settings could be dialed in and fan airflow could be "stepped" in stages, or varied if using PID type controllers.
  12. barnartist

    barnartist Minister of Fire

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    Im really likeing this thread heaterman. I am wondering though how telling the fan speed to slow down when stack temp gets to high will effect it when out of wood?
    If it was trying to rais the fan speed it would be different. Am I just off the wall?
    When measuring flue, where should it be monitored to get a fair measurement-in the stack itself, or right outside of the exchanger? Your right, seems like a stack above
    400 is losing too much on the exchange.
  13. Bartman

    Bartman Member

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    You don't have to control fan speed, I'm about to experiment with an actuator to open and close a shutter on my fan's intake.
  14. Nofossil

    Nofossil Moderator Emeritus

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    Can I beg you to start a new thread with pictures, part numbers, and description? I'm looking to do that if I can't come up with a simple circuit to vary fan speed under the control of my computer.
  15. jebatty

    jebatty Minister of Fire

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    The shutter (or damper) on the fan is what the Tarm has. Fan blows constant, just open or close the shutter/damper to control air input. So, a control to adjust this over the burn based on flue temp makes some sense. Let us all know!
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