Combustion of Coal, Using Thermo Utilities, MS Excel Add-ins

Dry anthracite with the following composition by mass:

C 90%; H 3%; O 2%; N 1%; S 1%; ash 3%

has been burned in a boiler, when 150% excess air is supplied. Combustion efficiency is 0.75 Calculate:

1. the stoichiometric air-to-fuel (A/F) ratio
2. the A/F ratio
3. analysis of combustion products (dry and wet)
4. temperature of exhaust gases

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. The net calorific value of the fuel at 15 C is 33 500 kJ/kg. The specific heat capacity of fuel is 3.2 kJ/kg,K.

Combustion Equations

Combustion equation for coal:

C + O2 => CO2 (12 kg C)+(32 kg O) => (44 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	0,900	2,400	3,300
Hydrogen	0,030	0,240	0,270
Oxygen	0,020	-0,020	0,000
Nitrogen	0,010	0,000	0,010
Sulphur	0,010	0,010	0,020
Ash	0,030	0,000	0,030
.	1,000	2,630	3,630
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	11,38	Stoichiometric A/F ratio	kg/kg
Excess Air	1,5	.	.
Actual A/F ratio kg/kg	28,45867	.	.
Exhaust Gases	.	Wet Mass	Dry Mass
Constituent	Mass	Composition	Composition
N2	21,54461	0,73210	0,74469
O2	3,94500	0,13405	0,13636
CO2	3,38469	0,11501	0,11699
Ar	0,03670	0,00125	0,00127
H2O	0,49767	0,01691	0,00000
SO2	0,02000	0,00068	0,00069
.	29,42867	1,00000	1,00000
Exhaust Gases	.	.	Volume
Constituent	Kg/kmol	Mole Fraction	Composition
N2	28	0,02615	0,77058
O2	32	0,00419	0,12346
CO2	44	0,00261	0,07704
Ar	40	0,00003	0,00092
H2O	18	0,00094	0,02769
SO2	64	0,00001	0,00031
.	.	0,03393	1,00000
Mass balance	.	.	.
Fuel	1,00000	.	.
Supplied Air	28,45867	.	.
.	29,45867	.	.
.	.	.	.
Exhaust Gases	29,42867	.	.
Ash	0,03000	.	.
.	29,45867	.	.
Supplied Air Temp.	18	C	.
Fuel Cp	3,2	kJ/(kg.K)	.
Net Calorific Value	33500	kJ/kg	.
Combustion efficiency	0,75	.	.
.	.	.	.
.	Enthalpy	Mass Flow	m*h
.	kJ/kg	kg/s	kJ/s
Supplied Air	38,31	28,46	1090,14
Fuel	64,00	1,00	64,00
Fuel Energy Supplied	33500,00	1,00	25125,00
.	.	.	26279,14
Exhaust Gases	892,07	.	.
Exhaust Gases Temp	774,	C	.