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Gasifier performance using cold intake air.

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by Seyiwmz, Dec 20, 2007.

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  1. Seyiwmz

    Seyiwmz Member

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    I've read in other posts the mention of using cold intake air for their gasifier. If I understand correctly, the colder the air, the more oxygen it contains. This would seem to be of benefit, but does the colder intake air affect the gasification process in other ways. I'd be willing to put in an extra duct from the outside to deliver the oxygen rich air if I'm not creating other problems. Currently, I intake the air from the garage I keep the boiler, and the temp usually hovers around 60. The garage temp would presumably increase if I intaked from the outside. I was wondering if anybody has experience in these techniques and found favorable results. I run an EKO 40. Thanks

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  2. Eric Johnson

    Eric Johnson Mod Emeritus

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    I'm pulling air directly from the outside, through a vent in the sidewall of my boiler room. My boiler behaves differently as the outside ambient temp changes, so that might have something to do with it. But I'd say it performs pretty well under any conditions, just differently. Ideally, I think combustion air should be as warm as possible for optimum efficiency, but I have no idea how the gasification process is affected by secondary air temps. I hope somebody around here does.
  3. slowzuki

    slowzuki Feeling the Heat

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    Gasifiers already operate at excess air. Using cold air should prolong the startup period and perhaps lower boiler efficiency a touch. I doubt you would see more than a degree or two difference in your garage. Most are so leaky from doors etc that combustion appliances causing negative pressure are a minor heat loss.
  4. Nofossil

    Nofossil Moderator Emeritus

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    I believe that you want the hottest air you can get, especially at startup. The reason for a cold air inlet is so that the boiler doesn't create a vacuum in your house and draw cold air in through every little crack and crevice.

    I'm adding a cold air inlet, and my plan is to heat it as much as possible - probably by passing it along the stovepipe en route to the boiler. Haven't worked out the details yet.
  5. Eric Johnson

    Eric Johnson Mod Emeritus

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    I thought about that, too. The area around the stovepipe would be the best place to pre-heat combustion air, I would think.

    Do you think an inline fan would be a good way to draw it forward to the blower?
  6. Nofossil

    Nofossil Moderator Emeritus

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    Until I get a good baseline, I don't want to mess with it. Adding another fan or adding too much flow resistance would have the effect of changing the airflow. Rather than add another fan, I'd rather open up the EKO's blower inlet adjustment a bit. I especially wouldn't want to be forcing air through the EKO's fan when the controller wants it to be off.
  7. Eric Johnson

    Eric Johnson Mod Emeritus

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    I was kidding around in another thread about installing one of those old "heat saver" in-chimney hot air heat exchangers, but that might be a pretty good hx for preheating combustion air. With no creosote, it wouldn't present the safety hazard that they do in a more traditional application. Whether or not that would kill the draft is another issue for consideration.

    You could also probably fabricate a shell-type hx for your stovepipe out of a tee or a couple of tees that are a couple inches larger in diameter than the pipe, but then you'd have to calculate how big it would have to be and figure out how to seal it off and attach it. I don't know if I have enough clearance for all that extra hardware.

    BTW, you're absolutely right about using the boiler's existing blowers to suck air, instead of trying to blow it with an inline fan. Early morning brain lock is about my only excuse for tossing that idea out.
  8. brad068

    brad068 Feeling the Heat

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    Hey Eric,
    Thats what I thought of trying on my boiler. I was planning on installing one of those in the exhaust stream and then fabricating a box and piping to suck air through the hx tubes of one of them. I believe that the combustion air needs to be preheated alittle more on my unit. I read some where that optimal air temp is @120*. I think its worth a shot.

    P.S.
    I bought some thermometers at wal-mart the other day. The Wal-mart #006019710551 (item# T704-5514) $4.74 each in the grill section. The are 12" long and have a range from 50* to 550*. Excellent for some experimentation.
  9. Eric Johnson

    Eric Johnson Mod Emeritus

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    It probably won't work on a crude, cold war downdraft gasifier.

    I've been thinking about this and while my first thought was that you'd have to pipe the air all the way to the intake on the boiler, I guess all you'd really need to do would be pull the air in from the outside and through the hx and then into the boiler room. At least in my case, since my enclosure is only about 3x7x5. I see the heatsaver they have on Ebay comes with a blower. I'm not sure how hard it would be to hook up the intake pipe, but probably not too bad. I'd like to find one for a lot less than $200, which about what that one nets out at. There's gotta be a million of those old things kicking around somewhere. Maybe not so fancy, but who cares?

    I generally try to stay clear of WalMart, but $5 instack thermometers in the right range is too tempting to pass up. My Condor is calibrated up over 2,000 degs, so it really is a relatively crude tool for the job. And it cost me $25+
  10. brad068

    brad068 Feeling the Heat

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    I thought you might get a kick out of that!! I heard that the EKO is built in the same factory as the Belarus tractors. Just kiddin'. At least they are a high efficiency boiler. I would like to get a probe into my secondary chamber but the placement is arkward, thats why I monitor at my first inspection plate, the fan housing and the boiler exhaust exit. I suspect that my secondary chamber is in excess of 2000* when the ceramic tube which is 2' long and 8" I.D/10" O.D. glows bright orange. My first temp gauge is 15' from the secondary chamber and that usually stays @1000*. My boiler can hold a 3' by 3' piece of heavy cardboard sucked against the firebox door opening when the draft inducer is running. That alot of air movement and thats why they need long flue paths.
  11. barnartist

    barnartist Minister of Fire

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    Glad I started reading this thread.
    So, my boiler (Eko) sits outside, in a lean-to of my garage. Iv'e also wondered this. Should I then duct my fan intake FROM my warmer garage to the fans. Better yet, I currently have installed a majic heat unit in my stack. Im pretty sure Eric, you thought it be best to get it out of there. But I could run a duct from that thing to the fans. How to make that look decent I don't know. But I am always adjusting those fan openings, so would need a way to get to that yet. For those of you who have yet toinsulate the belly of your boiler, you could rig a duct from that area up to the fans.
    By the way, im even more convinced now that I want a way to slow my fans to a crawl when the boiler approaches top temp. NoFo, if you can make a poor mans variable speed pump, make a barnartist version of a variable speed fan :)
    Heck, at some points throught the winter im pulling in 0 degree air through the fans. Add to that the cold temperature of the wood I just threw in. (thanks leaddog). No wonder it takes so long for the sucker to restart.
    Those meat gauges work well and are very acurate. Great for reading storage tank temps.
    I love this forum. I must sleep now.
  12. jebatty

    jebatty Minister of Fire

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    Using the stack to preheat combustion air should provide some preheat, but it also will affect the draft by cooling the exhaust stream, and for those pushing stack temp to the minimum, this could introduce a condensation/creosote issue.

    What about using a small gravity hot water loop? Take a SlanrFin-type baseboard unit, pull some fins off, cut it to lengths to cover the cold air inlet, solder on some elbows to connect the lengths. Now all intake air is warmed by the small hw register. BTW, the fins push right back on if you take off too many.
  13. steam man

    steam man Minister of Fire

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    30 years of operating industrial boilers and I haven't seen one yet that likes cold air. They smoke more overall with cold air. Mainly you see this at startup. You just end up heating the air to combust anyway. The denser air is a moot point since your not really compressing anything. (I did have a friend design a turbocharged boiler with a pressurized casing that was used by the Navy decades ago-interesting animal). The boilers I currently operate have a rotary air heater to reclaim stack heat loss. However they use a bypass damper at low loads/startup to keep stack temps up. My home boiler uses a Field Controls power vent with an outside air combustion air-tee similiar to what was described above. Now if someone were to make a combustion air tee with a bypass damper/stack temperature control...................maybe a bimetal operated air damper...................I can hear the wheels turning now.
  14. mikeyny

    mikeyny Feeling the Heat

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    My boiler is in the detached garage. I built a shell around the chimney, insulated it and ran 4 inch pipe to the intake damper on the bottom of my tarm. I use a small fan to push the cold air through. I am not sure how much difference it makes but it makes me feel better by re-claiming some more heat that would have gone up the chimney. It has been three yrs now, I only use it when it real cold outside. It drops the stack temp by about 150 to 200 degrees. Although it may be doing something bad somewhere I have not seen it yet. I dont see any condensation or draft problems. I never have creosote in my chimney because I run flat out all of the time and this old tarm does gasify to some degree.
    Mike
  15. steam man

    steam man Minister of Fire

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    My boiler is in the detached garage. I built a shell around the chimney, insulated it and ran 4 inch pipe to the intake damper on the bottom of my tarm. I use a small fan to push the cold air through. I am not sure how much difference it makes but it makes me feel better by re-claiming some more heat that would have gone up the chimney. It has been three yrs now, I only use it when it real cold outside. It drops the stack temp by about 150 to 200 degrees. Although it may be doing something bad somewhere I have not seen it yet. I dont see any condensation or draft problems. I never have creosote in my chimney because I run flat out all of the time and this old tarm does gasify to some degree.
    Mike

    As long as your stack never hits condensing temp you should be OK. I am not sure my oil boiler's outside air intake warms the air that much. I have noticed some metal gone on the outside of the power vent an wondered if the stack has been cooled too much. The tee has been on about three years but the power vent has been there about 18. Not too bad.
  16. Eric Johnson

    Eric Johnson Mod Emeritus

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    My understanding is that some OWBs take that into account and draw their primary (only) combustion air from the top of the unit so that they're putting warm air into the boiler. I'm no engineer (by a long shot), but I have heard that it makes a big difference in efficiency.
  17. steam man

    steam man Minister of Fire

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    One other thought-does anyone here ever circulate hot water from their home boiler to the wood boiler to preheat it before lite off? Anyone seen an improvement in lite off, especially smoking??
  18. Eric Johnson

    Eric Johnson Mod Emeritus

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    That's an interesting idea. I decommission my gas boiler at the beginning of the heating season, so I couldn't do that, but I can see circulating warm water from the tank through the EKO before a cold startup, especially if I try to run it in the summer on a once-weekly basis for DHW. That would be easy to do, and would probably work pretty well. I have fooled around with charcoal and different kindlings trying to get a jump on the gasification, but it sure would help to have 150-degree water in the pressure vessel.

    You're bucking for the "Good Idea of the Week" award, steam man.
  19. jebatty

    jebatty Minister of Fire

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    With storage on my Tarm, if I start the pumps the storage hw circulates through the hx and heats the boiler water.

    Everyone has their fire-up start technique. What works best for me is X crossed kindling wood, rather loose so draft air can move through the kindling, about 3 deep, top down start. This gets going quickly. Then add some smaller dry splits to get a pretty good blaze going. All of this takes about 5 mintues. Shut the bypass damper, flames start shooting through the nozzle almost right away, and in another 2-5 minutes the nozzle is blasting flame into the tunnel. Then add about 1/3 load of wood, wait another 5 minutes or so, then fill the firebox. Walk away until burned down to low coals, either re-load or let it burn out.
  20. Eric Johnson

    Eric Johnson Mod Emeritus

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    I like dried pine cones.
  21. steam man

    steam man Minister of Fire

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    You’re bucking for the “Good Idea of the Week” award, steam man.

    That's kind of funny-a couple of weeks ago I got a nomination for "Best Practices" award by coming up with a cheap solution to an expensive problem. It was so simple it was almost embarassing. Actually, on the industrial side, some kind of warm up is typical in my field through air preheaters or warm water. Steam water tube boilerscan be stressed easily and require slow warm up. But I suppose any small boiler would fair better through a slow warm up.

    Got to get the dog to the vet..........
  22. barnartist

    barnartist Minister of Fire

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    so it sounds agreeable to many that warm intake air is a nice benifit to the sytem
  23. ISeeDeadBTUs

    ISeeDeadBTUs Guest

    The GW runs the smoke stream arounf the air inlet tubes before it exits the stack. I have no idea if it's effective because I have nothing to compare it to. But my GW is outside, so it probably is taking in colder than ideal air. Who knows . . .
  24. Eric Johnson

    Eric Johnson Mod Emeritus

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    I think that's a fact. Getting there might be more trouble than it's worth in some cases, however.
  25. leaddog

    leaddog Minister of Fire

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    The eko warms the air as it blasts the air into a chamber before it goes into the primary and secondary. I would be careful of pushing to hot of air into the fans as They might over heat. The fan motors are cooled by the air as it passes though. It is then heated before going into the chambers. I would also be sure you don't cool your stack with those heat savers. I run alot of times stack temps 225f later in the burn.
    leaddog
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