[Gasification] Gasification Digest, Vol 9, Issue 7

[Brennan R Henderson]

John

I had a similar question to yours that I posted in November 2006.

http://listserv.repp.org/pipermail/gasification_listserv.repp.org/ 
2006-November/005839.html

I was unable to get the answer that I wanted, so I just put some wood  
and air
into my gasifier and tried it out, although I still don't know what  
the ratio is
supposed to be.

Brennan Henderson


On 5-Mar-07, at 1:21 PM, John Bertl wrote:

> I need help in understand a fact of gasification given by Mr. T. B.  
> Reed.
> I calculate a significantly different number than the one he provides.
> I understand that Mr. Reed is a moderator of this list.  Maybe he can
> elucidate.
>
> In the 1988 publication “Handbook of Biomass Downdraft Gasifier  
> Engine Systems” on page 24
> Table 4-2 “Typical Properties of Producer Gas from Biomass” Mr.  
> Reed states
>
> Air Ratio Required for Gasification: 2.38 kg wood/kg air   (lb/lb)
>
> Air Ratio Required for Gas Combustion:   1.15 kg wood/kg air (lb/lb)
>
>
> When I use the formula given as the overall global reaction of  
> biomass combustion
>
> CH(1.4)O(0.6) + (1.05)O2 + (3.95)N2 = CO2 + (0.7)H2O + (3.95)N2
> wood              +    oxygen + nitrogen
>
> Wood
> C = 1    x 12  = 12
> H = 1.4  x  1  = 1.4
> O = 0.6  x 16 = 9.6
>
> Total =      23 atomic weight
>
> Air
>
> O = 1.05 x 16 x 2 = 33.6
> N = 3.95 x 14 x 2 = 110.6
>
> Total =       144.2 atomic weight
>
> 144.2  /  23  = 6.27
>
> Therefore, 1 kg wood needs 6.27 kg atmospheric air for combustion  
> not 1.15 kg
>
> Why do we have a different ratio???
>
> Using the formula for gasification where 0.4 O2 is needed instead  
> of 1.05 O2, I get
>
> 54.9  /  23  = 2.39
>
> This is almost the exact same number but in reverse ratio!!
>
> Table 4-2 says it was modified from data done by Reed in 1981 but I  
> have not been able to get a
> copy of that reference (which is true of almost all references  
> given in literature on gasification.)
>
> Elsewhere in the handbook it says “Complete oxidation of biomass  
> with oxygen requires an air
> ratio of 6.36.  This number is closer to my 6.27 but again I can’t  
> see how we could differ so
> significantly with the numbers given in the handbook accurate to  
> three places.  What ratio is Mr. Reed talking about when he says  
> 2.38 and 1.15???
>
> Anyone??????  I must be having a geriatric moment as I cannot come  
> up with any explanation.
>
> By the way - this page can be viewed at
> http://tpub.com/content/altfuels01/0276/02760032.htm
>
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