[Gasification] Gasification Digest, Vol 9, Issue 7

[John Bertl]

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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