Question

A coal with the following composition was burnt in a power plant with 25.0% excess air. Waht is the percent CO2 shown by Orsat analysis? The air drawn into the furnace at that location has 0.021 moles of water vapor per mole of dry air.

Coal analysis:

Carbon 64.0%; Hydrogen 4.3%; Nitrogen 1.1%; Sulfur 1.6%. The lab also reported that the coal contained 5.0% moisture and 13.7% ash.

Answer 1

BasisL 100 gms of coal. It contains 64 gm coal. 4.3 gm Nitrogen, 1.1 and sulfur= 1.5.

Moisture= 5 gm

Moles = mass/atomic weight , atomic weights : C= 64, H= 4.3, N=1.1 and S= 32, O= 16

Moles: C= 64/12= 5.33, H2= 4.3/2=2.15, N2= 1.1/28=0.0393, S= 1.5/32=0.047

Oxygen is required for coal, hydrogen and Sulfur as per the following

C+O2--->CO2 moles of Oxygen = 5.33 moles, H2+0.5O2--->H2O moles of O2= 2.15/2= 1.075

S+O2--->SO2, mole of oxygen required= 0.047

total oxygen required= 5.33+1.075+0.047=6.452 moles

dry air contains 21% O2 and 79% N2, moles of air required= 6.452/0.21=30.72

Moles of air suppled = 25% excess, moles of air suppled actually =1.25*30.72=38.4 moles

moles of water in dry air = 0.021*38.4 =0.8064

Products : CO2= 5.33, SO2=0.043 ( same as mole of C and moles of S respectively)

N2= 38.4*0.79 =, 30.34 O2 unreacted= 38.4*0.21( supplied)- 6,452 ( utilized)=1.612 moles

total moles on dry basis = 30.34(N2)+1.612(O2)+0.043(SO2)+5.33 (CO2)=37.325 moles

Mole % of CO2 = 100*5.33/37.325=14.28% (since orsat gives dry analysis, water is not accounted for)