C 70%; H 18.5%; O 3%; N 4%; S 1.5%;
ash 3%
A fossil fuel with the following composition by mass:
C 70%; H 18.5%; O 3%; N 4%; S 1.5%;
ash 3%
has been burned in a boiler, when 100% excess air is supplied. Combustion efficiency is 0.75 Calculate:
Air is supplied at atmospheric pressure and 18 C with 0.008 specific humidity. The fuel has an average temperature of 35 C when enters the boiler. Use Dulong formula to estimate the net calorific value of the fuel. The specific heat capacity of fuel is 3.2 kJ/kg,K.
Combustion equation for coal:
C + O2 => CO2 (12 kg C)+(32 kg O) => (34 kg CO2)
Combustion equation for hydrogen:
2 H2 + O2 => 2 H2O (4 kg H)+(32 kg O) => (36 kg H2O)
Combustion equation for sulphur:
S + O2 => SO2 (32 kg S) + (32 kg O) => (64 kg SO2)
| Fuel Analysis |
. |
. |
. |
|
Constituent |
Mass fraction |
Required oxygen |
Product mass |
|
. |
. |
kg/kg fuel |
kg/kg fuel |
|
Carbon |
0,700 |
1,867 |
2,567 |
|
Hydrogen |
0,185 |
1,480 |
1,665 |
|
Oxygen |
0,030 |
-0,020 |
0,010 |
|
Nitrogen |
0,040 |
0,000 |
0,040 |
|
Sulphur |
0,015 |
0,015 |
0,030 |
|
Ash |
0,030 |
0,000 |
0,030 |
|
. |
1,000 |
3,342 |
4,342 |
|
Analysis of Supplied Air |
. |
. |
. |
|
Specific Humidity |
0,008 |
. |
. |
|
Composition by mass |
. |
. |
. |
|
Constituent |
Dry Air |
Humid Air |
. |
|
N2 |
0,76280 |
0,75670 |
. |
|
O2 |
0,23290 |
0,23104 |
. |
|
CO2 |
0,00300 |
0,00298 |
. |
|
Ar |
0,00130 |
0,00129 |
. |
|
H2O |
0,00000 |
0,00800 |
. |
|
SO2 |
0,00000 |
0,00000 |
. |
|
. |
1,00000 |
1,00000 |
. |
|
Air required per kg of fuel |
14,46 |
Stoichiometric A/F ratio |
kg/kg |
|
Excess Air |
1 |
. |
. |
|
Actual A/F ratio kg/kg |
28,92757 |
. |
. |
|
Exhaust Gases |
. |
Wet Mass |
Dry Mass |
|
Constituent |
Mass |
Composition |
Composition |
|
N2 |
21,92942 |
0,73373 |
0,78344 |
|
O2 |
3,34167 |
0,11181 |
0,11938 |
|
CO2 |
2,65276 |
0,08876 |
0,09477 |
|
Ar |
0,03730 |
0,00125 |
0,00133 |
|
H2O |
1,89642 |
0,06345 |
0,00000 |
|
SO2 |
0,03000 |
0,00100 |
0,00107 |
|
. |
29,88757 |
1,00000 |
1,00000 |
|
Exhaust Gases |
. |
. |
Volume |
|
Constituent |
Kg/kmol |
Mole Fraction |
Composition |
|
N2 |
28 |
0,02620 |
0,74260 |
|
O2 |
32 |
0,00349 |
0,09901 |
|
CO2 |
44 |
0,00202 |
0,05716 |
|
Ar |
40 |
0,00003 |
0,00088 |
|
H2O |
18 |
0,00353 |
0,09990 |
|
SO2 |
64 |
0,00002 |
0,00044 |
|
. |
. |
0,03529 |
1,00000 |
|
Mass balance |
. |
. |
. |
|
Fuel |
1,00000 |
. |
. |
|
Supplied Air |
28,92757 |
. |
. |
|
. |
29,92757 |
. |
. |
|
. |
. |
. |
. |
|
Exhaust Gases |
29,88757 |
. |
. |
|
Ash |
0,03000 |
. |
. |
|
. |
29,91757 |
. |
. |
Dulong suggests the following formula for gross calorific value (GCV) of fossil fuels when oxygen content is less than 10%
GCV = 337 C +1442 (H - O/8) + 93 S
GCV is in (kJ/kg). C, H, O, S are percentages on weight basis for carbon, hydrogen, oxygen and sulphur. The net calorific value for a constant pressure combustion is:
NCV = GCV - mc * hfg
mc is the mass of condensate per unit quantity of fuel and hfg is the latent heat of steam at 25 degree Celsius which is 2442 kJ/kg.
| Supplied Air Temp. |
18 |
. |
. |
|
Fuel Cp |
3,2 |
kJ/(kg.K) |
. |
|
Gross Calorific Value, GCV |
49866 |
kJ/kg |
. |
|
Net Calorific Value, NCV |
49711 |
kJ/kg |
. |
|
Combustion efficiency |
0,75 |
. |
. |
|
. |
. |
. |
. |
|
. |
Enthalpy |
Mass Flow |
m*h |
|
. |
kJ/kg |
kg/s |
kJ/s |
|
Supplied Air |
38,31 |
28,93 |
1108,10 |
|
Fuel |
64,00 |
1,00 |
64,00 |
|
Fuel Energy Supplied |
49710,80 |
1,00 |
37283,10 |
|
. |
. |
. |
38455,21 |
|
Exhaust Gases |
1284,94 |
29,93 |
38455,21 |
|
Exhaust Gases Temp |
964, |
C |
. |