Question on gasifier secondary air flow

warno Posted By warno, Sep 10, 2017 at 5:07 PM

  1. warno

    warno
    Minister of Fire 2.
    NULL
    

    Jan 3, 2015
    876
    239
    Loc:
    illinois
    How much air flow is actually supposed to flow to the nozzle area of a gasifier boiler? What is the rough percentage of flow to both primary and secondary air outlets?

    I'm in the process of converting my boiler to try to achieve gasification and I'm not sure how much flow i need into my secondary passage.

    Any help would be great thank you
     
  2. TCaldwell

    TCaldwell
    Minister of Fire 2.
    NULL
    

    Oct 26, 2007
    858
    80
    Loc:
    860-868-9014 h 203 948 0864 c nw corner ct.
    I suspect the total airflow is based upon the boilers firing rate, I'm sure with some digging you can come up with a equation. If I recall you had ballparked your firing rate, if you can match that to a established gasified on the market with its airflow as a starting point. The other option is a small say 1/2 hp 3ph motor with vfd so you can find the sweet spot. Automation direct has matching vfd/motor combinations that have 120vac input, for reasonable money. With respect to primary /secondary air, the split size and moisture content and internal air ducting will dictate the optimum static positions. Feel free to call me, I have some spare parts that might help you.
     
  3. maple1

    maple1
    Minister of Fire 2.
    NULL
    

    Sep 15, 2011
    7,714
    1,349
    Loc:
    Nova Scotia
    Which I'd say, all means - make all air flows totally adjustable. Even just variations through the burn cycle, or for varying draft conditions on different days, or a different mix of wood in a load, can lead to you wanting to make some tweaks. Which gets into the beauty of a lambda system - but that would be another level...
     
  4. cumminstinkerer

    cumminstinkerer
    New Member 2.
    NULL
    

    Feb 2, 2016
    42
    5
    Loc:
    central iowa
    Warren,
    If you get the air flow figured out let me know lol, I still cant get mine right all the time. fire me a text when you have a chance, I can give a refresher of what I have right now and what I am thinking after playing some yesterday. I am running for DHW on the weekends, just trying to conserve propane, and give me a chance to experiment when its not a must to have the thing running, I can let it go out and make changes this time of year.
     
  5. jebatty

    jebatty
    Minister of Fire 2.
    NULL
    

    Jan 1, 2008
    5,485
    764
    Loc:
    Northern MN
    A question of optimum in an ever changing burn scenario or "good enough" based on a relatively constant split size, species, typical wood load, and moisture content. And then how, where and how much air to feed both the primary and secondary burn chambers. I recall form the manual for my Tarm, now entering its 11th heating season, that uses a simple lever to adjust a constant total air flow between the primary and secondary, that the most practical answer for a simple system is "set it and forget it," which I have done. I rarely adjust the air flow from a setting which seems to be "good enough."
     
    warno likes this.
  6. warno

    warno
    Minister of Fire 2.
    NULL
    

    Jan 3, 2015
    876
    239
    Loc:
    illinois
    A good enough setting would be great. I can always try to tune it in for better. I mean adding my storage last year helped a ton since I could batch burn, but it still smoked abit until everything got rolling good.
     
  7. SuperSpy

    SuperSpy
    New Member 2.
    NULL
    

    Oct 12, 2017
    27
    7
    Loc:
    Michigan
    From my experience, (I was researching building a gasification boiler before buying one) it doesn't take much air to achieve the secondary burn. My 155 gallon boiler just uses a ~4" squirrel cage blower and a ~2.5" tube with what's basically a plug attached via chain to a stepper motor to control the air. Even in it's high burn mode where the secondary is getting the most air that gate is only open 1/2-3/4 of an inch.

    My advice is to start very small and work your way up instead of the other way around. It doesn't take much air to get the process started. My boiler when really hot will sometimes do it intermittently without even the secondary system running, just from the little bit of draft as the primary blows across the coals.
     
  8. TCaldwell

    TCaldwell
    Minister of Fire 2.
    NULL
    

    Oct 26, 2007
    858
    80
    Loc:
    860-868-9014 h 203 948 0864 c nw corner ct.
    Any updates on the modifications?
     
  9. warno

    warno
    Minister of Fire 2.
    NULL
    

    Jan 3, 2015
    876
    239
    Loc:
    illinois
    Sorry i haven't followed up in awhile, been finishing up soccer and other things for the year.

    I have got the refractory wall in and the primary and secondary air tubes plumbed. I'm hoping for a fire this weekend since apparently it got cold all the sudden. 70s last week 40s this week. :eek: I'll be back with the results of the burn this weekend. Fingers crossed.
     
  10. warno

    warno
    Minister of Fire 2.
    NULL
    

    Jan 3, 2015
    876
    239
    Loc:
    illinois
    So i guess i didn't change anything much at all. I don't know if things just aren't hot enough or not enough secondary air or what. Turns out the relocation of the primary air was bad because it blows a huge flame right at my loading door and it got hot enough to crack my welds holding in my insulation sand/brick. Also pushed enough heat forward and down to burn the handle off my latch of my ash door. So I'll be tearing everything out to put my primary air back down under the fire where it was.

    Heres some pictures of what I've got going on.

    Heres my primary air and the secondary is the 1" pipe that goes out the bottom.

    20170909_174105.jpg

    Secondary air inlet. It goes right into my fire grate that is made of pipe.

    20170909_174111.jpg

    Heres my primary (2") and secondary outlets. The secondary is the 1" pipes welded into a square and stuck into the fire grate. There's 15) 3/8" holes drilled in the 1" pipes. 5 in each side of the nozzle opening and 5 on top.

    20170910_135626.jpg

    And here's my refractory brick installed around the nozzle area

    20171028_133514.jpg


    Also what causes the fan to make this chugging sound?

     
  11. TCaldwell

    TCaldwell
    Minister of Fire 2.
    NULL
    

    Oct 26, 2007
    858
    80
    Loc:
    860-868-9014 h 203 948 0864 c nw corner ct.
    Before you tear it down my inclination would be to balance the airflows, the chattering is from too much primary air in relation to secondary air. Try restricting the primary air, maybe a adjustable baffle or damper that is outside the firebox so you can adjust on the fly.
    What is the square inch relationship of your primary and secondary air inlets, looks like maybe the primary is 2-1/2 inch, do the secondary holes add up to this?, a starting point would be to have equal flow capabilities.
    Don’t give up, I think we should be able to get a burn out of this with minor mods!
    I’m home today feel free to call me on either phone in my avatar.
     
  12. TCaldwell

    TCaldwell
    Minister of Fire 2.
    NULL
    

    Oct 26, 2007
    858
    80
    Loc:
    860-868-9014 h 203 948 0864 c nw corner ct.
    Sorry, I was asking questions about numbers that you posted, to compare area of flows currently, primary, 2 inch=3.14, 15 3/8 holes=1.65, it appears you have approx twice the primary area of airflow as secondary requiring approx 1/2 inch holes, please check my math on that or others chime in before you think about drilling.
     
  13. warno

    warno
    Minister of Fire 2.
    NULL
    

    Jan 3, 2015
    876
    239
    Loc:
    illinois
    Your math looks good to me. But either way I'll have to take everything out of the box to put my primary air back the way it was when I built it. With the air blowing into the coal bed now, instead of under it like before, it bows a torch like flame at the feed for and front refractory and gets everything on the front of the boiler to hot.

    This is my handle on my ash pan door. This door/area of the boiler has never been hot enough i couldn't touch it. Let alone melt the rubber from my latch handle.

    20171028_163926.jpg


    Once i get the primary air redirected in under the coal bed again I'll rebuild the refractory wall and put more air into my secondary tube via a second fan. Then I'll try it again.

    On a side note i do think it was trying to go because at one point once things started getting really hot, water up around 130°F and climbing, it started making a sound like an old tractor trying to start. It would kind of chug, no smoke, chug, no smoke. I stood there and watched it do this for a good 5 minutes or so just hoping it would take off.
     
  14. warno

    warno
    Minister of Fire 2.
    NULL
    

    Jan 3, 2015
    876
    239
    Loc:
    illinois
    I went and opened my ash pan door tonight to check out how my aluminum ash scoop favored. It took some damage. The mid-point handle on my scoop is just under where my primary air blows just above my fire grate. It takes alittle over 1200 degrees to melt aluminum and heres what we have...

    20171029_183329.jpg
     
  15. SuperSpy

    SuperSpy
    New Member 2.
    NULL
    

    Oct 12, 2017
    27
    7
    Loc:
    Michigan
    That is a _lot_ of secondary air space.

    My 170k BTU unit only has a 2-2.5 inch hole as then entire secondary chamber, and the burn port itself is all refractory not steel.

    The aluminum pan will never survive and should be steel as well. Mine will easily get over 1400F in it's secondary chamber and that's not even measured at the flame nozzle.

    If I were you, as a test, I would put some scrap steel down over the secondary tubes and leave only one the center opening in the grate open to airflow.

    EDIT: The chugging sound is probably the gasses lighting off in the secondary, then blowing out as they are overwhelmed with incoming air. My unit does this to some extent when the fire is very hot and I have the door open when I'm loading it.
     
  16. warno

    warno
    Minister of Fire 2.
    NULL
    

    Jan 3, 2015
    876
    239
    Loc:
    illinois
    Mine as modified right now is a horizontal. All the flue gases are pushed out the back of the fire box. The reason my aluminum pan, which had survived 2 years prior, melted was because i changed my primary air ducting. It was blowing right in the coal bed making things way hotter then even before. I completely understand in a down draft situation no aluminum would survive ever.

    I'm in the process of ducting my primary air to the front now to blow the fire towards the back at my refractory wall.
     

Share This Page