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Optimum Gasifier Operation

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by Eric Johnson, Feb 9, 2008.

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  1. Eric Johnson

    Eric Johnson Mod Emeritus

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    The mantra with modern downdraft gasifiers like the EKO, Tarm, Econoburn, etc. is that they are best operated full-out, both for the sake of efficiency and longevity.

    That raises the question in my mind about whether the absolute optimum way to run one of these boilers would be full-out, 24/7 for (let's say) the life of the boiler. Would a boiler run this way outlast one operated in a more typical, heat-and-cool pattern over time? If I can get 20 years out of an EKO under normal use, in other words, would my neighbor, running his full-blast all the time expect his to last as long? Or longer?

    Or, would the boiler that is run more aggresively simply produce more btus over its (shorter) lifetime?

    Presumably, it would be possible to design a system with a high enough heat load and enough storage to run a boiler run in this fashion.

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  2. barnartist

    barnartist Minister of Fire

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    Im not sure you'll get much except opinions on this one. Maybe the steel wouldn't expand and contract as much with constant temps. Im thinking we'll have refactory and nozzle problems that will be the boiler demise.
    Im still wondering this, if im running my boiler that idles 50% of the time, and other than more smoke and ash, if this really hurts the boiler. I have steady water temps, so is the only damage to the stack?
    Nice question though.
  3. jebatty

    jebatty Minister of Fire

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    I think opinions is right. The mfr might chime in here. To me it seems it depends on the design and engineering of the boiler and its various components. Not an especially good analogy, but compare a pro or commercial grade chainsaw and its residential alternative. The pro/commercial in most instances will run far longer, under more extreme conditions, and heavy use compared to the residential. Besides, for the home user, running flat out continuously would take an ocean for storage.
  4. Eric Johnson

    Eric Johnson Mod Emeritus

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    It's all theoretical, of course (he said, trying to sound informed and competent), but it's one of those things that bugs me when I think about it.

    You wouldn't really need an ocean of storage if the gasifier was just one component of a much larger system (that included, say, oil or gas boilers). The wood gasification boiler would run full-out all the time, with the fossil fuel backups kicking on during periods of heavy demand. Say, a 200K btu gasifier as part of a 1 MM btu/hr design. Even during periods of relatively low demand, the wood boiler would go full blast.

    And of course, routine maintenance would include replacing the nozzles and refractory as needed.
  5. wdc1160

    wdc1160 New Member

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    I would vote that you could squeeze out more btu’s during a 24/7 burning life. But the life would be a shorter calendar life. Maybe not if you had a really short summer. Like above the 50th parallel maybe. Yah, that’s the correct answer.
  6. Eric Johnson

    Eric Johnson Mod Emeritus

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    Let's assume no summer or other downtime, other than routine maintenance.

    When manufacturers of logging equipment want to torture test their new models, they send prototypes down to Brazil to work 24/7 on those big eucalyptus plantations that span thousands of square miles. They put something like 20,000 hours on a machine in a couple of years, doing the routine maintenance, just to see how they perform and for how long.
  7. wdc1160

    wdc1160 New Member

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    I vote 24/7 then. Over a boiler operating say 8 hrs a day, then cooling the rest of the time.
  8. sled_mack

    sled_mack New Member

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    Does it matter? None of us can really acheive that anyway.

    That being said, I think you would need to know what the cause of the failure is at the 20 year mark. If it's corrosion on the water side of the jacket, then water treatment would be more important than constant burning. If it's cracks in the steel, then constant burning would be a big help.

    Another option to consider is slow startups. But, that is hard to acheive with a gassifier. At least for me, it's either on or off. It's not quite like a modulating gas burner.

    I think there are other factors as well. Like water flow through the boiler. Keeping a high enough water flow should reduce the stress on the boiler steel by reducing hot spots in the boiler.

    The only place I see this info being useful is when sizing a system. There may be some merit to a really huge (10,000 gal water) storage tank if it means a smaller boiler can be run full out most of the time. As long as the burn cycles were long enough to allow the user to fill it before it goes out, it would see long periods of maintaining a high temp. If the tank does get saturated with heat, the boiler could be shut down for many days, thus greatly reducing the number of hot/cold cycles.
  9. hkobus

    hkobus Member

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    Than also assuming we have all the time in the world to keep the load optimal( and money for the units :) ) and no cycles, by reloading before getting to the end of the load or bridging, why not have more than one gasifier in the system. When the load reduces let one or more shut down and cycle through the units in the system. I have heard of this done for green houses, not practical or affordable for me!

    But back to topic, it this any different from any engine, going from start to full load and back to shutdown. Or keeping them idling for extended periods of time for convenience and losing efficiency?
    I would like to get my system to the point where I can fire it with reasonable time between loads and having backup storage to add to the convenience and efficiency.

    Henk.
  10. Nofossil

    Nofossil Moderator Emeritus

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    I see a pattern in these threads...

    With enough modulation range, you could perhaps keep the boiler 'in the zone' 24/7. At present, I'm skeptical that you can modulate that much. More experiments to be done.
  11. solarguy

    solarguy New Member

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    For the most part any wood boiler is going to be a steel shell with the firebox surrounded by a water jacket. If you can get 20 years out of a wood boiler you've done real well. If we look at the steel oil boilers, they stay hot year round & rarely will you get 20 years out of one of them.

    I think the most important thing to do w/ a wood burner is disconnect the flue & cap it off in the down season. This prevents the boiler from pulling a draft which in turn creates condensation.
    Water treatment is also important, it's good to check the ph of your heating system every year.
    Spraying the firebox w/ WD40 a couple of times during the down season doesn't hurt.
  12. Eric Johnson

    Eric Johnson Mod Emeritus

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    Webmaster Craig suggests hanging an incandescent lightbulb in the firebox during the down season.

    I had an old Royall 6150 that dated from the late '70s and was still going strong at the end of last season before I sold it to another guy, so I guess it depends. Tarm claims to have a 20-year warranty, which I assume covers the pressure vessel, if nothing else, though obviously they have to be satisfied that the right return water protection was installed.

    I understand that as boilers become more efficient, one of the trade-offs is longevity, but I don't see how the Royall is that much different than a modern gasifier like a Tarm or an EKO in construction. Something to do with the gasification, maybe?
  13. solarguy

    solarguy New Member

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    >Webmaster Craig suggests hanging an incandescent lightbulb in the firebox during the down >season.

    I know a couple of folks that do that but I hate burning electricty:)
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