[nottigal]

hope someone can help me with this question, i can't figure out how to solve it.
here'sthe question;

Calculation on a biomass fuel-fired boiler

A biomass is used as a fuel for a central heating boiler. It is necessary to heat 650 litres/h of water returning to the boiler at 24c back up to 80c
The known data of the biomass is shown in Table 1. They are dried to a moisture content of  ¼ of the initial (as received ) value before used. 
Assume that with 20% of excess air is used, complete combustion takes place. Efficiency of the heat transfer from the flue gas to the water is 60%. All sulphur and nitrogen in the biomass reacts to SO2 and NO2. No ash is carried out with the flue gas.

Table 1:
Moisture content %wt (fresh biomass): 53
Net CV as received. MJ/kg: 10.6
Ash %wt db :0.9
H %wt db: 5.6
S %wt db :0.03
N %wt db :0.6
Bulk density kg/m3 :850

a)    What is the composition of the biomass, including moisture after drying?
 My answer:
moisture content , 21.99%
Ash: 1.49%
C: 66.17%
H: 9.29%
S: 0.05%
N: 1%

b)   What is net CV after drying?
107.8MJ/kg * not sure if it’s correct  ..i used the formula GCV=NCV + (no of moles of hydrogen produced* latent heat of vaporization of water at 25c)

c)   What is the flue gas composition (by weight)?
* I tried to balance the chemical equation but can’t, is the S and N inside the hydrocarbon? Or it’s in gaseous state? The questions says the S and N all reacts to SO2 and NO2..does it react with the excess oxygen? Should I use mass balance to find the flue composition?

[eugenedakin]

Hi nottigal,

For question #2, I would assume that the S and N are part of the biomass.  The DNA and proteins in biomass contain sulphur and nitrogen which are typically part of a carbon chain in some way shape or form.

When you worked out the answer for question a), you have completed half of the answer for c.  You can assume that there will be SO2, CO2, NO2 and H2O in your flue. 

Your just about there. Well done!

Eugene

[nottigal]

thanks. so i should find the empirical formula of the carbon chain first right? or is there another method?

[eugenedakin]

Hello nottigal,

Yes, first start with the empirical formula.  I think that you have figured it out

I wish you the best.

Eugene