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Handouts
LINK: Combustion Engineering
Topics:
Amagat's Law of Additive Volumes
Dalton's Law of Partial Pressures
Stoichiometric Combustion
Chimney (or Stack)
Exercises
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1. A fuel is represented as C5H8 is burned with 35% excess air. If the mass of fuel is 0.20 kg, find the mass of air required. a. 4.8 b. 3.8 c. 5.8 d. 6.8 2. The analysis of products of combustion on dry basis, when C6H18 is burned with atmospheric air, is given as follows: CO2 = 15%, CO = 2%, O2 = 3%, N2 = 80%. Compute the actual air-fuel ratio. a. 10.5 b. 11.5 c. 12.5 d. 13.5 3. A boiler burns fuel oil with 20% excess air. The fuel is represented as C15H30.Calculate the molal air fuel ratio. a. 70.6 b. 75.6 c. 85.6 d. 65.6 4. Given the following ultimate analysis: C = 68.5%, N2 = 3%, H2 = 3%, O2 = 4%, S2 = 8%, Ash = 5.5%, Moisture = 8%. Using 30% excess air, determine the actual air-fuel ratio. a. 8.8 b. 9.8 c. 10.8 d. 11.8 5. A certain coal has the following ultimate analysis C = 72%, N2 = 4%, H2 = 3%, O2 = 3.5%, S2 = 6.5%, Ash = 5%, Moisture = ?. Determine the heating value in Btu/lb. a. 12364 b. 12345 c. 12354 d. 12344 6. A flue gas has the following volumetric analysis: CH4 = 70%, C2H6 = 30%. Assume combustion with 20% excess air at 1 bar, 23oC wet bulb and 30oC dry bulb, what is the partial pressure of water vapor in kPa? a. 15.19 b. 16.10 c. 17.20 d. 14.32 7. There are 25 kg of flue gases formed per kg of fuel oil burned in the combustion of C12H26. Determine the percent excess air. a. 26.18 b. 27.18 c. 32.18 d. 24.18 8. A boiler uses 2500 kg of coal per hour and air required for combustion is 18 kg per kg coal. If ash loss is 12%, determine the mass of gas entering the chimney. a. 48000 b. 47532 c. 47200 d. 47100 9. The gas density of chimney is 0.80 kg/m3 and air density is 1.18 kg/m3. If the driving pressure is 0.32 kPa, determine the height of the chimney. a. 65 b. 45 c. 75 d. 86 10. The actual velocity of gas entering in a chimney is 6 m/s. The gas temperature is 28oC and a pressure of 98 kPa with a gas constant of 0.288 kJ/kg-K. Determine the chimney diameter if the mass of gas is 54,000 kg/hr. a. 2.6 b. 3.6 c. 1.6 d. 2.2 11. A coal fired steam boiler uses 3200 kg of coal per hour. Air required for combustion is 16.2 kg/kg coal at barometric pressure of 98 kPa. The flue gas has temperature of 290oC and an average molecular weight of 31. Assuming an ash loss of 10% and allowable gas velocity of 8.8 m/s, determine the chimney diameter. a. 2.3 b. 1.2 c. 1.8 d. 1.5 12. A steam generator with economizer and air heater has an overall draft loss of 23.2 cm of water. If the stack gases are 188oC and if the atmospheric pressure is 100 kPa and 28oC, what theoretical height of stack in meters is needed when no draft fan is used? Assume that the gas constant for flue gases is 0.280 kJ/kg-K. a. 605.9 b. 705.9 c. 614.9 d. 619.9 13. A power plant in an altitude having an ambient condition of 95 kPa and 23oC. A flue gas at a rate of 5.5 kg/sec enters the stack at 198oC and leaves at 162oC. The flue gas gravimetric analyses are 20% CO2, 8% O2 and 72% N2. Calculate the height of stack required for a driving pressure of 0.18 kPa. a. 63.9 b. 53.9 c. 58.3 d. 69.9 |
Liquid Fuels
For the combustion of Octane with 10% excess air, find (a) the actual air-fuel ratio, (b) the theoretical air fuel ratio and (c) show the balanced molal equation.
SOLUTION:
Gaseous Fuels
Volumetric analysis of natural gas burned with 10% excess air: CO2 = 2.4%, N2 = 1.8%, CH4 = 64.1% and C2H6 = 31.7%. Find (a) the actual molal air fuel-ratio and (b) show the balanced molal equation.
SOLUTION:
Solid Fuels
For the gravimetric or ultimate analysis of coal with 10% excess air: Carbon (C) = 45%, Hydrogen (H2) = 20%, Oxygen (O2) = 10%, Nitrogen (N2) = 15%, Sulfur (S) =5%, Ash = 3% and Moisture content = 2%. Find (a) The theoretical air-fuel ratio, (b) the actual air-fuel ratio and (c) heating value of the coal, in kJ/kg.
SOLUTION:
