[Stoves] Combusting woodgas: was Re: basics: Need different flame-speeds different mixture-procedures?

[frank]

Dear Paul and others,

I was reading about producing 17.7 watts with an efficiency of > 70 % 
using a process called microbial fuel cells (MFC) generating hydrogen. 
Is 17.7 watts enough  to run the fan you need?

Also: if alcohol is mixed into water that is used to mist into the stove 
at a rate equal to produce the added heat needed to create steam -would 
that work?

Hope your travels are successful!
Frank

Paul S. Anderson wrote:

>Dear Martin, Crispin, Jeff and all,
>
>Thank you for your very productive comments.
>
>Jeff wrote:  Forced secondary air is noisy.
>Perhaps in some cases because of size of the units and types of 
>combustors, but
>not in the TLUD units by Reed and by Anderson.
>
>Crispin, what is "The FSP stove..."  P is for Propane?
>
>Quoting "Boll, Martin Dr." <boll.bn at t-online.de>:   (much snipped)
>  
>
>>- For wood-gas:
>>
>>There is a good chance that the flame blows out itself, because the speed of
>>the outstreaming woodgas is too high.(Higher than 40cm per second?)
>>
>>For woodgas the gas-jet _must be_ slow for not blowing out. Therefore the
>>turbulence is _far less_.
>>    
>>
>
>My observations come from TLUD gasifiers, especially the natural draft version
>called the Champion Stove.
>
>A key piece of the stove is the "concentrator disk" that is above the 
>container
>with the pyrolizing fuel and below the "internal chimney" that give 
>draft up to
>the level of the pot (so that an external chimney after the pot is not
>necessary).
>
>Important to note that the secondary air enters BELOW the concentrator disk,
>coming in radially from all sides, and then upward through the (generally) 3
>inch (7.5 cm) hole.  Therefore, the secondary air and the combustible 
>gases are
>mixing even before reaching the hole.
>
>In this case, when operating at the higher heat setting (because of 
>more primary
>air being allowed to enter at the bottom) it is common to have the base of the
>flame a cm or two above the disk.  Good turbulence/mixing/swirling.  It is
>possible to put a bluff body into the pathway of the flaming gases, helping to
>maintain the flame.
>
>When operating at low heat settings, it is common for the base of the 
>secondary
>combustion to actually be below the the hole in the disk.  This is not a
>problem at all.  The objective of combusting very nearly all of the gases is
>accomplished.
>
>If the hole in the disk is too small, the rising pyrolysis gases cannot 
>fit fast
>enough through the 3 inch hole.  Instead, some escape laterally throught the
>small (3 mm or 1/8th inch) gap between the disk and the upper edge of the fuel
>container.  That is a poor result.  Hole sizes of 2 inches and smaller were
>found to be too small, and of 4 inches diameter or larger to be too big.
>
>Therefore, to answer your question:
>  
>
>>Is this small turbulence big enough to make a comparable good mixture for
>>clean burn??
>>    
>>
>
>The turbulance is sufficient.  I do not know if it is "small" or not.
>
>  
>
>>-Even by a normal kitchen gas-burner there is a gas-air premixture. Is this
>>premixture not more necessary by a slower jet-speed coming out of the
>>nozzle?
>>    
>>
>
>I have explained at least one way to accomplish this pre-mixing, and that the
>results are excellent.
>
>  
>
>>I guess:
>>There must be at least a jet-blow against a baffle to get a stable flame.
>>    
>>
>
>Not required.
>
>You ask several excellent questions for which I do not have answers, but the
>questions deserve quality research (such as by graduate students with equiped
>laboratories and knowledgeable engineering-type professors).
>
>  
>
>>-What is the good range of speed for that? -What are good 
>>combinations for pressure difference  and diameter of the
>>nozzle, for a given gas/woodgas?
>>
>>-What is the good premixing ratio of woodgas and air? And has the premixing
>>air to be preheated? (For: quicker reaction time; and/or no precipitation
>>out of the woodgas?)
>>
>>- Would a static-mixer be helpful te reach a good gas/air mixture with low
>>speed instead of a high-speed-jet?
>>    
>>
>
>Plea:  I hope that some person or institution will undertake these and other
>research questions about woodgas combustion devices for the cookstove 
>sizes!!! I will gladly assist with whatever I can contribute. (There is 
>no holding back
>on information about TLUD experiences.)  But such efforts are far beyond my
>resources, time, and interests.  My efforts are to make TLUD technology
>functional and acceptable to people who can benefit from these 
>cookstoves. Others are needed for the engineering work.  I hope that 
>"Engineers Without
>Borders" and other qualified persons or entities will discover the academic
>(and social) richness that awaits the initial researchers who examine what the
>prototype developers have accomplished.  (My current progress in India will be
>released at or before ETHOS 2008 in January.)
>
>My bias shows when I say:  Within a short time woodgas technology at the scale
>for household usage should be evident as a major and practical advance for
>residential cookstoves and diverse biomass fuels.
>
>Paul
>  
>

-- 
Frank Shields
Soil Control Lab
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