Solid Fuels W:o

1. A furnace is fired with Sub-bituminous (SubB) coal containing 10.3% moisture, 34% VCM and 7.7% ash.
It is
also known to contain 1.2% N and 1.57% S. Its calorific value is 22 MJ/kg. Calculate its:
a) proximate analysis
b) modified analysis
c) ultimate analysis
d) analysis of VCM
e) calorific value of VCM
2. A coal-fired boiler uses a high volatile A bituminous coal with an ultimate analysis of 75.2% C, 5.19% H,
8.72% O, 1.5% N, and 1.6% S. 60% excess air is supplied. Assume CO to CO 2 ratio of 0.175. The flue gas leaves
at 300oC, 740 torrs. Calculate:
a) complete analysis of the flue gas if air is supplied supplied at 28 oC, 100 kPa and essentially dry
b) m3 air supplied/100 kg coal
c) calorific value of coal
d) AFR
e) % of the calorific value lost due to:
i. unburnt combustible
ii. uncondensed water
iii. sensible heat of stack gas
3. An industrial plant uses a high grade semi-anthracite coal analyzing 90.04% C, 0.79% S and 1.2% N on ash
and moisture free basis. If this coal were burned in excess air saturated with water at 30 oC and 105 kPa, a flue
gas with the following orsat analysis results: 10.83% CO 2, 0.22% H2, 8.17% O2 and the remainder N2 and SO2.
Calculate:
a) ultimate analysis of coal (ash/moisture free)
b) % excess air
c) AFR
4. Athracite, the highest rank coal is hard, glossy, black coal used primarily for residential and commercial
space heating. In combustion operation, the anthracite used showed 92.8% and 1.3% ash. If this coal is burned
in dry air at 28oC, 1 atm, a combustion gas with the following orsat analysis results: 14.15% CO 2, 5.77% O2,
79.9% N2, 0.03% SO2 and 0.08% NO. The combustion gases leave at 600oC and 800 mmHg. Calculate:
a) ultimate analysis of the anthracite coal
b) calorific value of the anthracite coal (MJ/kg)
c) % excess air
d) AFR
e) complete analysis of combustion gases
f) mg/NCM of SO2 and NO2
g) thermal efficiency of combustion
5. A medium volatile bituminous coam (mvb) has an “as received” analysis of 27.13% VCM, 62.52% FC, 7.11%
ash, 0.95% S and 1.28% N. Its calorific value is 32.3 MJ/kg. This coal is burned in excess air supplied at 30 oC,
756 torrs with 80% RH. Partial orsat analysis of the stack gas shows 9.78% CO 2 and 2.45% CO. Calculate:
a) % excess O2
b) complete orsat analysis of the stack gas
c) m3 stack gas (270oC, 768 mmHg)/kg coal
6. Sugarcane bagasse analyzing 44.8% C, 5.35% H, 37.55% O, 11.91% ash, 0.38% N and 0.01% S was used as
fuel in a local burner. Orsat analysis of the stack gas shows 10.87% CO2 with no unburned Hydrogen and
Carbon. All S burns to SO2 and N is converted to N2. Dry air is 30oC, 100 kPa. Stack gas leaves at 300oC and 750
mmHg. Find:
a) GCV of the sugarcane bagasse using:
b) % excess air
c) complete orsat analysis of the burner gas
d) thermal efficiency
PROBLEMS
1. A sample of lignite was found to contain 34.55% moisture, 22.91% FC, 7.2% ash, 1.1% S and 0.57% N with a
calorific value of 16.45 MJ/kg. Calculate:
a) proximate analysis
b) modified analysis
c) ultimate analysis
d) analysis of VCM
e) calorific value of VCM
2. A burner uses Pittsburgh coal analyzing 14.1% ash, 2.1% N and 4.3% S. Excess air is supplied dry at 22 oC and
1 atm. The stack gases at 285oC, 765 mmHg analyzes 9.65% CO2, 1.16% CO, 0.24% SO2, 0.58% H2 and 9.16% O2.
Calculate:
a) equivalent ratio
b) complete ultimate analysis
c) m3 air/kg coal
d) m3 SG/ kg coal
3. On an “as received basis” basis, the proximate analysis of a representative coal from the Semirara Plant is
32% VCM, 35% FC, 10% ash, 1.2% N and 6.2% S. Its calorific value is 23.78 MJ/kg. On the assumption that this
coal is burnt with 150% excess air so that the molal ratio of CO 2 to CO is 5:1. Calculate:
a) m3 dry air (at 25oC, 750 mmHg)/kg coal
b) complete analysis of the flue gas
c) m3 flue gas (at 240oC, 770 mmHg)/kg coal
d) %CV lost due to
i. unburnt combustibles
ii. uncondensed water
iii. sensible heat
4. A boiler is fired with coal containing 72.63% C, 14% ash, 1.6% N and 1.2% S burnt under conditions that the
elimination of combustibles from the residue is complete. The air enters the furnace at 25 oC, 760 mmHg wuth
80% RH. The flue gas goes to the stack at 280oC and 110 kPa. The average flue gas orsat analysis is 8.41% CO2,
2.52% CO, 0.76% H2 and 9.86% O2. Assume that all sulfur and nitrogen in the coal burns to SO2 and N2
respectively. Calculate the following:
a) % excess air
b) ultimate analysis of coal
c) m3 flue gas/kg coal
d) m3 air/kg coal
5. A certain coal is pulverized and burnt in a burner. Analysis of coal showed 70% C, 10.7% ash and 1.2% N. The
residue is substantially free of combustible. A sample of the flue gas collected and analyzed in an orsat
apparatus over mercury contains 8.3% CO2, 3.32% CO, 0.32% SO2, 3.32% H2 and 9.53% O2. Air supplied is at
30oC, 1 atm and saturated with water. Calculate:
a) % excess O2
b) complete analysis of coal
c) m3 flue gas (at 250oC, 1 atm)/kg coal
d) mg SO2 per normal cubic meter
6. A high volatile B bituminous coal analyzing 22% VCM, 64% FC, 4% M, 1.4% N and 1.6% S has a calorific value
of 32.5 MJ/kg. It is burned in excess air supplied essentially dry at 28 oC and 1 atm. The stack gases leave at
250oC, 740 mmHg and contain 8.37% CO2, 4.19% CO and 2.51% H2. Calculate:
a) % excess O2
b) complete orsat analysis of the stack gas
c) m3 stack gas/m3 air

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1. A furnace is fired with Sub-bituminous (SubB) coal containing 10.3% moisture, 34% VCM and 7.7% ash.

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