Hi Ralph:

Stoichiometric air to fuel ratio for biomass fuel:  

Stoichiometric Reaction for the combustion of the biomass fuel with oxygen:

C H0.81 O0.1496 N0.047 + 1.1277 O2 ---->  CO2 + 0.405 H2O + 0.0235 N2

1 Mole of Biomass Fuel = 1*12 +0.81*1 +0.1496*16 + 0.047*14 = 15.8616 Kg

1 mole of O2 = 32 kg

Oxy/Fuel)Sto = 1.1277 * 32 / 15.8615 = 2.259 kg of oxygen/kg of fuel

Since 21 mass-percent in air is oxygen

Air/Fuel)Sto = 2.259 * 100/21 = 10.76 kg of air/kg of fuel

10.76 Kg of air per kg of this Biomass Fuel

Chaouki Ghenai 

Hi, Ralph:

Just to be precise, I should add that in fact the mass of 1 mole of the biomass fuel is 15.8616 grams (not "kg"), as well as the mass of 1 mole of O2 is 32 g. But in the end of the day - and the most important bit of Chaouki's answer - the air/fuel ratio still remains as 10.76 kg of air per kg of biomassa fuel (or g/g, if you prefer). Sorry for the correction.

Regards,

Jose

My impression is that only the C and H components should be taken into account when calculating the oxygen consumption. The nitrogen component porducec probably molecular nitrogen and the oxygen component molecular oxygen. Is not that so?

Is my calculation correct for emperical formula of said biomass?.. i just calculated it from its ultimate analysis and also if i had a 3kg of biomass?? would the stoichiometric ratio still affect?

C-75.61%

H-5.16 %

O-15.08 %

N-4.15 %

Could you give me also a reference for calculating elemental composition of biomass?.. thanks ahead!

Dear Ralph, The elemental compsotion is determined by the elemental analyzer, it is OK The molar contents are also OK. In 100 g of the biomass you will have 75,61/12 = 6,3 mol, hydrogen: 5,16/1 = 5,16 mol hydrogen. 1 mol carbon consumes 32 g (1 mol) O2, i.e. 6,3 mol consumes 201,67 g. 1 mol hydrogen (atom) which is equivalent to 1/2 mol hydrogen molecule (H2) consumes half mol (16 g oxygen) thus 5,16 mol hydrogen atom 41,28 g oxygen. In my opinion the nitrogen content need not be tane into account, as it will form N2 gas (unless under very extreme conditions) and the oxygen content will also not consume oxygen, it will form O2 or used during oxidation. These latter are, of course, assumptions, therefore 100 g biomass will APPOXIMMATELY consume 242,9 g oxygen. This is true if the oxidation is complete, e.g. no partially oxidized products are formed.

I feel that the question has been precisely answered by Dr. Chaouki Ghenai.

for exact calculation i support the information provided by Gyorgy Banhegyi, We should not put N and O in our Stoichiometric calculations which are not taking part during combustion reaction unless it forms O2 and in depth some side reaction may also occur but could be negligible in this case. So overall calculation should be made on the basis of gram of biomass.

Can someone help me to find stoichiometric fuel/air ratio if i have a biogas of 80% CH4 and 20 % CO2?

Please, any body can provide combustion equation and air-fuel ratio calculation for complete combustion of bio-syngas with CO=20%, H2 = 15%, CH4=5% by volume.