[Stoves] Too much turbulence can be bad??? Re: Airflow For Biomass Fired Appliances- Natural Draft Stoves

Sun Apr 21 10:30:37 CDT 2013

Stovers,

This message was held in the Moderator's box, so I will resend it now.

Paul S. Anderson, PhD  aka "Dr TLUD"
Email:  psanders at ilstu.edu   Skype: paultlud  Phone: +1-309-452-7072
Website:  www.drtlud.com

On 4/14/2013 9:49 PM, Paul Anderson wrote:
> Dear Alex, Lanny, Dean and all,
>
> We are learning things about short flames and flame color that should 
> have been learn years ago!!!   Thank you both (and others) for getting 
> this information to us.
>
> And Crispin has been telling us all along (and showing up with his 
> device at ETHOS etc) that a combustion analyzer is useful. We (the 
> generic we) need to get more serious.
>
> And Dean wrote:
>>
>> >The very hot yellow/white flames easily make black carbon.
>> >The less hot deeper yellow/red flames make less/no black carbon.
>>
> Notes:
> 1.  Why isn't a combustion analyzer (as used for furnace work) part of 
> the standard equipment for stove testing, either for formal protocol 
> testing or for more simple testing at our workshops and factories?
>
> 2.  Is this "turbulance" and "forced air" (flame height and color) 
> information telling us something about the "fan-jet" or "vortex" 
> stoves like Philips-FA and the Biolite and the RTI FA stove tested in 
> Kenya and others with STRONG forced air.   The Kenya study (presented 
> by Mike Sage at GACC Forum) found that the emissions were not as low 
> as were hope for stoves with fans.   Is it possible that the extra 
> turbulence of those stoves is actually working against their lowering 
> of emissions?
>
> To me, this is BIG and I hope that CSU and Tami and Aprovecho and 
> testing centers can check on this with modeling and testing.    (or is 
> this basic knowledge in some specialist fields?  )
>
> Be sure to read Alex's message below if you have not already done so.
>
> Paul
> Paul S. Anderson, PhD  aka "Dr TLUD"
> Email:psanders at ilstu.edu    Skype: paultlud  Phone: +1-309-452-7072
> Website:www.drtlud.com
> On 4/14/2013 8:59 PM, Alex English wrote:
>> Yes, in the stoves world TLUDs with fans are comparatively clean 
>> burning. I'm just saying it doesn't necessarily follow that they are 
>> at their best when their flame is shortest.
>>
>> Any burner will have a range of emissions including a sweet spot 
>> where it performs best. There are lots of variables to consider. Some 
>> require better instrumentation.
>> For a TLUD with a fan, or a boiler with a fan, you can shorten the 
>> flame with extra secondary air. As you know, if it isn't needed for 
>> combustion then is robs heat, that may be needed for optimum 
>> combustion. Yes long/tall flames can have sooty tips. So there are 
>> potential trade offs. When I can see the flame and my combustion 
>> analyser at the same time I have often seen that a long flame has 
>> lower CO/CO2, less excess air and higher heat transfer efficiency.  
>> Not enough air and it will be even longer with poorer emissions. 
>> Flame colour is a clue, its the numbers that inform. Better mixing 
>> from higher pressure blowers/fans can shift the range of flame 
>> lengths shorter. Stated another way, the optimum flame length is 
>> unlikely the shortest.
>>
>> I'm being warmed by my ND pellet stove right now. After the secondary 
>> air ports the flame travels horizontally through a 2.5 inch tube, 12" 
>> long. For this firing rate the sweet spot is when the  flame fingers 
>> are shooting out six inches past the tube end. More secondary air 
>> shortens it back inside the tube. Less secondary lengthens it and 
>> turns it more orange and larger. CO/CO2 increases in both cases. 
>> There will be no visual emissions from the chimney for any of these 
>> scenarios. Real time PM and NOx numbers might enlighten this tale some.
>>
>>  I've seen a large chip boiler cut its CO in half improve 4% points 
>> of thermal efficiency just by closing some secondary air ports. The 
>> flame lengthened by roughly 25%.
>>
>> Years ago when I was testing my Reed style fan TLUD on low power. It 
>> had the smallest of flames but the flame didn't fill the chamber 
>> cross section of the chamber below the pot. Some of the pyrolysis 
>> products were sneeken past the flame and condensing brown (not soot) 
>> on the pot. Less secondary air, a larger flame, and perhaps a 
>> different geometry could have helped. The problem went away at higher 
>> firing rates with a bigger and somewhat taller flame.....
>> ....but I burnt the food and went hungry:(
>>
>> Alex
>>
>>
>>
>>
>> On 14/04/2013 5:18 PM, Lanny Henson wrote:
>>> A response from Alex English! made my day.
>>> Fan powered TLUDS have a nice short flame height, are they not clean 
>>> burning?
>>> Lanny
>>>
>>>     ----- Original Message -----
>>>     *From:* Alex English <mailto:english at kingston.net>
>>>     *To:* Discussion of biomass cooking stoves
>>>     <mailto:stoves at lists.bioenergylists.org>
>>>     *Sent:* Sunday, April 14, 2013 2:25 PM
>>>     *Subject:* Re: [Stoves] Airflow For Biomass Fired Appliances-
>>>     Natural Draft Stoves
>>>
>>>     Lanny,
>>>     I understand the comment below but I think flame height can be
>>>     shortened with excessive excess air. The lowest emissions CO/CO2
>>>     and highest temperatures, at some power levels, in appliances
>>>     that I have tested has often been when there is a significantly
>>>     taller tail of flame.
>>>
>>>     However, don't believe  all tall tails :)
>>>     Alex
>>>
>>
>>
>>
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>>
>

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