Biomas combustion air/fuel ratio

[dianad]

Hi,

In my calculations, and assuming that i have biomass with humidity of 40%, i've calculated the air/fuel ratio = 0,7 kgair/kgfuel.

Can anyone confirm this value as correct or approximate?
Thanks

 

[IRstuff]

seems low:

http://en.wikipedia.org/wiki/Butanol_fuel#Air-fuel_ratio

TTFN

FAQ731-376

 

[Feric]

Hi there:

Here is a free MS Excel spreadsheet that might be useful in carrying out combustion calculations with coal/oil type fuel compositions:

http://engware.i-dentity.com/eng-tips/combustion.xls

Thanks,

Gordan

G. Feric, PE

http://engware.i-dentity.com

 

[dianad]

Hi,

Thanks fo rthe replies!
Sorry, but i'm searching for this value for boilers that burn biomass in wood chips version and not converted in butanol to burn in internal combustion engines.

Thanks

 

[Feric]

dianad:

Just find the fuel composition on weight basis, know the stoichiometry and oxidant composition and as a result flame temperature, oxidant to fuel ratio and combustion products breakdown on weight and mole basis will be provided by the spreadsheet for you.

Thanks,

Gordan

http://engware.i-dentity.com

 

[25362]

It is common to assume an amount of 0.7 lb air per 1000 Btu released. If the calorific value is 5000 Btu/lb, the air needed would be 3.5 lb/lb of fuel.

 

[IRstuff]

The fact that it's wood chips just makes the ratio worse

TTFN

FAQ731-376

 

[dianad]

Thank you all!

25362,

So, what do you think i may use, your 3,5 lb/lb fuel or my 0,7 kg/kg fuel?

thanks

 

[25362]

To dianad,

You asked for a rough figure. I don't know how you estimated the quantity of air needed. Follow Feric's advice. It seems your figure of 0.7 kg/kg fuel refers to oxygen, which converted to air becomes ~3.0 kg/kg fuel.

See, please, the air requirements for a fuel oil with a P_i=10,000 kcal/kg, one needs about 11 normal m³/kg, which is about 13.5 kg air/kg fuel, which would correspond to about 0.72 lb/1000 Btu.
Of course, fuel oil practically doesn't contain oxygen in its chemical composition.

You need to add excess air for a perfect combustion which in the case of refuse may be quite a %.

Here is a short table showing the amount of air in lb/1000 Btu liberated as needed for complete combustion:

methane 0.73
methyl alcohol 0.67
propane 0.73
benzene 0.74
glucose 0.69
cellulose 0.68

I hope this message is of help.