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FUELS AND COMBUSTION A bituminous coal has the following composition:C = 71% H = 5% O = 7% N = 1.S = 3% Ash = 8% W = 3%Calculate the higher heating value of coaland for complete combustion find the theoretical weight of air required in kgair/kg coal? The following ultimate analysis of typical fuel o...

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FUELS AND COMBUSTION 1.

A bituminous coal has the following composition:

C = 71.5% H = 5.0% O = 7.0% N = 1.3 S = 3.6% Ash = 8.2% W = 3.4% Calculate the higher heating value of coal and for complete combustion find the theoretical weight of air required in kg air/kg coal? 2.

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The following ultimate analysis of typical fuel oil, ash and moisture free: C=0.8663 lb H=0.1127 lb O=0.0019 lb N=0.0028 lb S=0.0163 lb Calculate the following for “complete” or theoretical combustion with air, in pound of fuel: A. Oxygen required from air B. Nitrogen required from air C. Air required D. Water formed from combustion E. Carbon Dioxide formed F. Total mass of flue gas It is required to find the theoretical volume of air at 20oC and 100 kPa absolute pressure to burn one kilogram of coal. The ultimate analysis of coal-as-fired is as follows: C=65.65% H=5.87% O=18.61% S=1.51% Ash=5.36% W=3% Calculate the higher heating value of liquid Dodecane fuel. The chemical formula of Dodecane is C12H26. Liquid Octane (C8H18) fuel is burned with ideal proportion of air. Calculate the ideal air-fuel ratio by weight. Fuel oil in a day tank for use of an industrial boiler is tested with hydrometer. The hydrometer reading indicates a S.G.=0.924 when the temperature of the oil in the tank is 35oC. Calculate the higher heating value of the fuel.

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A diesel electric plant supplies energy for Meralco. During a 24 hour period, the plant consumed 200 gallons of fuel at 28°C and produced 3930 KWhr. Industrial fuel used is 28°API and was purchased at P5.50 per liter at 15.6°C. What is the cost of fuel be to produce one KW-hr? 8. Methane is burned completely with 25% excess air. Compute the number of moles of nitrogen in the products of combustion per mole of the fuel. 9. A typical industrial fuel oil, C16H32 with 20% excess air by weight. Assuming complete oxidation of the fuel, calculate the actual air fuel ratio by weight. 10. Ethane is burnt with just twice the stoichiometric amount of air. How much kilogram air is used to oxidize 6 kg of fuel? 11. A furnace burns natural gas with a volumetric analysis as follows: Methane=85%, Ethane=12%, Propane=3%. The gas flow rate is 3 0.50 m /s and 25% excess air is required for complete combustion. Combustion air is supplied to the furnace at 25oC and 1 atm pressure. Find the molal air-fuel ratio and the volume flow rate of the flue gas in m3/s. 12. A gaseous mixture of methane (CH4), ethane (C2H6), and propane (C3H8) has partial pressures respectively of 95 kPa, 105 kPa, and 50 kPa. What is the mass percentage of methane in the mixture? CHIMNEY 1.

If the actual draft required for a furnace is 6.239 cm of water and the frictional losses in the stack are 15% of the theoretical draft, calculate the required stack height in meters. Assume that the flue gas have an average temperature of 149°C and molecular weight of 30. Assume air temperature of 21°C.

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A 15 kg/s gas enters a chimney at 10 m/s. if the temperature and pressure of a gas are 26oC and 100 kPa respectively, what is the diameter of the chimney. Use R=0.287 kJ/kgK. 2.52 kg of coal per second are consumed by a steam boiler plant and produced 18.54 kg of dry flue gs per kg of coal fired. The air temperature outside is 32oC, the average temperature of the flue gases entering the chimney is 343oC and the average temperature of the flue gases in the chimney is 260oC. The gage fluid specific volume is 1.005x10-3 m3/kg and a theoretical draft of 2.286 cm of water at the chimney base is needed when the barometric pressure is 101.3 kPa. Find the diameter of the chimney in meters. A steam generator with economizer and air heater has an overall draft loss of 21.78 cm of water. If the stack gases are at 177°C and if the atmosphere is at 101.3 Kpa and 26°C, what theoretical height of stack in meters is needed when no draft fan are used? Assume that the gas constant for the flue gases is the same as that for air. A power plant situated at an altitude having an ambient air of 96.53 Kpa and 23.88°C. Flue gases at a rate of 5.0 kg/sec enter the stack at 200°C and leaves at 160°C. The flue gases gravimetric analyses are 18% Co2, 7% O2 and 75% N2. Calculate the height of stack necessary for a driving pressure of 0.20 Kpa.

SUPPLEMENTARY PROBLEMS FUELS & COMBUSTION 1. A diesel power plant consumes 650 liters of fuel at 26oC in 24 hours with 28oAPI. Find the fuel rate in kg/hr. Answer: A A. 23.83 B. 24.85 C. 22.85 D. 26.85

2. A boiler burns fuel oil with 15% excess air. The fuel oil may be represented by C14H34. Calculate the molal air fuel ratio. Answer: B A. 14 B. 117.69 C. 102.34 D. 17.14 3. A diesel power plant uses fuel that has a density of 892.74 kg/m3 at 15.67oC. Find the heating value of fuel. Answer: A A. 44,900 KJ/kg B. 19,301 Btu/lb C. 43,000 KJ/kg D. 4356.2 KJ/kg 4. A certain coal has the following ultimate analysis: C = 69% N2 = 5% H2 = 2.5% S = 7% Moisture = 8% O2 = 3.5% Ash = 5% Determine the heating value of fuel used.Answer: A A. 26,961.45 KJ/kg B. 45,256 KJ/kg C. 25,002.4 KJ/kg D. 26,000 KJ/kg 5. A diesel power plant uses fuel with heating value of 45,038.8 KJ/kg. What is the density of fuel used at 30°C?Answer: D A. 0.900 kg/li B. 0.887 kg/li C. 0.850 kg/li D. 0.878 kg/li 6. A diesel engine consumed 945 liter of fuel per day at 30°C. If the fuel was purchased at 15.5°C and 30° API at P5.00/li, determined the cost of fuel to operate the engine per day. Answer: B A. P5677.50 B. P4677.50 C. P4888.90 D. P5000.00 7. A cylindrical tank 3 m long and 2 m diameter is used for oil storage. How many days can the tank supply the engine having 27° API with fuel consumption of 60 kg/hr. Answer: B A. 4.84 B. 5.84 C. 7.84 D. 8.84 8. Determine the minimum volume of day tank in m3 of 28° API fuel having a fuel consumption of 200 kg/hr. Answer: B A. 10.43 m3 B. 5.41 m3 C. 6.87 m3

D. 7.56 m3 9. Given the following ultimate analysis: C = 70% O2 = 4% N2 = 5% S2 = 6% Moisture = 8% H2 = 3% Ash = 5% Using 25% excess air, determine the actual air fuel ratio. Answer: A A. 11.46 B. 24.85 C. 23.85 D. 26.85 10. A 650 Bhp diesel engine uses fuel oil of 28° API gravity, fuel consumption is 0.65 lb/Bhp-hr. Cost of fuel is P7.95 per liter. For continuous operation, determine the minimum volume of cubical day tank in cm3, ambient temperature is 45°C. Answer: A A. 5,291,880 cm3 B. 5,391,880 cm3 C. 5,491,880 cm3 D. 5,591,880 cm3 11. A 650 Bhp diesel engine uses fuel oil of 28° API gravity, fuel consumption is 0.65lb/Bhp-hr. Cost of fuel is P7.95 per liter. For continuous operation, determine the cost of fuel per day at 45°C. Answer: B A. P42,870.45 B. P42,070.45 C. P42,570.45 D. P42,170.45 12. A logging firm in Isabela operates a Diesel Electric Plant to supply its electric energy requirements. During a 24 hour period, the plant consumed 250 gallons of fuel at 80°F and produced 2700 KW-Hrs. Industrial fuel used is 30° API and was purchased at P3.00li/at 60°F. Determine cost of fuel to produce one Kwh. Answer: C A. P3,043/KW-h B. P4,043/KW-h C. P1,043/KW-h D. P2,043/KW-h 13. A logging firm in Isabela operates a Diesel Electric Plant to supply its electric energy requirements. During a 24 hour period, the plant consumed 250 gallons of fuel at 80°F and produced 2700 KW-hrs. Industrial fuel used is 30° API and was purchased at P3.00/li at 60°F. Determine the overall thermal efficiency of the plant. Answer: A A. 26.08% B. 43.23% C. 43.12% D. 18.46%

14. A diesel electric plant in one of the remote provinces in the south utilized diesel fuel with an °API of 28 at 15.6°C. The plant consumes 680 liters of diesel fuel at 26.6°C in 24 hrs, while the power generated for the same period amounts to 1,980KW-hrs. Determine overall thermal efficiency of the plant. Answer: A A. 26.47% B. 12.34% C. 23.45% D. 34.34% 15. A circular fuel tank 45 feet long and 5.5 feet diameter is used for oil storage. Calculate the number of days the supply tank can hold for continuous operation the following conditions: Steam flow = 2000 lbs/hr Steam dry and saturated at 200 psia Feedwater temperature = 230°F Boiler Efficiency = 75% Fuel oil = 34° API Answer: B A. 12.34 B. 17.58 C. 13.45 D. 23.44 16. A steam generator burns fuel oil with 20% excess air. The fuel oil may be represented by C14 H30. The fuel gas leaves the preheater at 0.31 Mpa. Determine the actual air-fuel ratio in kg air per kg fuel. Answer: A A. 17.89 B. 15.67 C. 12.34 D. 19.45 17. A steam generation burns fuel oil with 20% excess air. The fuel oil may be represented by C14H30. The fuel gases leave the preheater at 0.31 Mpa. Determine partial pressure of H2O. Answer: C A. 23.34 kpa B. 29.34 kpa C. 35.7 kpa D. 32.34 kpa 18. In the boiler design, it is desired to have the flue gas exit temperature above the dew point. Estimate the dew point temperature of the flue gas produced by combustion having the gravimetric analysis of: Answer: D N2 = 71.84% CO2 = 20.35% O2 = 3.61% H2O = 4.20% A. 32°C B. 23°C C. 45°C D. 39°C

19. A flue gas has following volumetric analysis: CH4 = 68% C2H6 = 32% Assume a complete combustion with 15% excess air at 101.325 Kpa, what is the partial pressure of water vapor in Kpa. Answer: A A. 15.95 B. 23.12 C. 12.45 D. 27.34 20. The dry exhaust gas from oil engine has the following gravimetric analysis: CO2 = 21.6% O2 = 4.2% N2 = 74.2% Specific heat at constant pressure for each components of the exhaust gas in Kcal/kg °C are: CO2 = 0.203 O2 = 0.219 N2 = 0.248 Calculate the gas constant in J/kg°K.Answer: A A. 272 C. 274 B. 276 D. 278 21. The dry exhaust gas from oil engine has the following gravimetric analysis: CO2 = 21.6% O2 = 4.2% N2 = 74.2% Specific heat at constant pressure for each component of the exhaust gas in Kcal/kg °C are: CO2 = 0.203 O2 = 0.219 N2 = 0.248 Calculate the specific gravity if the molecular weight of air is 28.97 kg/kg-mol. Answer: C A. 0.981 B. 1.244 C. 1.055 D. 0.542 22. The dry gas from oil engine has the following gravimetric analysis: CO2 = 21.6% O2 = 4.2% N2 = 74.2% Specific heat at constant pressure for each component of the exhaust gas in Kcal/kg °C are: CO2 = 0.203 O2 = 0.219 N2 = 0.248 Calculate the specific heat for the gas in KJ/kg - °K. Answer: B A. 0.872 B. 0.992 C. 0.452 D. 0.673 23. A bituminous coal has the following composition: C = 71.5% H = 5.0% O = 7.0% N = 1.3 S = 3.6% Ash = 8.2% W = 3.4% Determine the theoretical weight of Oxygen in lb/lb of coal. Answer: C A. 2.870 B. 3.120 C. 2.274 D. 6.233

24. There are 20 kg of flue gases formed per kg of fuel oil burned in the combustion of a fuel oil C12H26. What is the excess air in percent?Answer: A A. 26.67% B. 18.34% C. 12.34% D. 20.45% 25. A gaseous fuel mixture has a molal analysis: H2 = 14% CH4 = 3% CO = 27% O2 = 0.6% CO2 = 4.5% N2 = 50.9% Determine the air-fuel ratio for complete combustion on molal basis.Answer: C A. 2.130 B. 3.230 C. 1.233 D. 1.130 26. A steam generation burns fuel oil that has the following chemical analysis by mass in percent: Answer: C C = 85.3 H2 = 14.1 S = 0.5 N2 = 0.1 A. 19.85 C. 17.93 B. 11.14 D. 14.20 27. Calculate the theoretical air needed for the complete combustion of ethane C2H6 for 20 kg fuel. Answer: D A. 432.23 kg B. 287.45 kg C. 234.45 kg D. 320.32 kg 28. A fuel oil burned with 50 percent excess air, and the combustion characteristics of the fuel oil are similar to C12H26. Determine the volumetric (molal) analysis of CO2 in the production of combustion. Answer: B A. 9.34% B. 8.66% C. 6.34% D. 7.45% 29. Fuel oil, C12H26 is burned in air at atmospheric pressure. The Orsat analysis of the products of combustion yields. CO2 : 12.8% O2 : 3.5% CO : 0.2% N2 : 83.5% Determine the percent excess air. Answer: C A. 12.34% B. 8.34% C. 10.52% D. 18.45%

30. An unknown fuel has the following Orsat analysis: CO2 : 12.5 CO : 0.3% O2 : 3.1% N2 : 84.1% Determine the actual air – fuel in kg air per kg fuel. Answer: A A. 17.13 B. 12.34 C. 19.23 D. 23.23 31. What mass of liquid oxygen is required to completely burned 1000kg of liquid butane, C4H10 on a rocket ship? Answer: C A. 4568 B. 2746 C. 3586 D. 6345 32. A volumetric analysis of a gas mixture is as follows: CO2 : 12.5% O2 : 4% N2 : 82% CO : 2% What is the percentage of CO on a mass basis? Answer: D A. 1.0% B. 1.5% C. 1.2% D. 1.9% 33. What is the percent theoretical air for a combustion process to which the fuel and combustion gas analysis are known as follows:Answer: A Fuel: % by volume CO2 : 12.4% CO : 27% H2 : 2.2% N2 : 58.4% Combustion gas: % by volume CO2 : 24.6% O2 : 1.0% H2 : 74.4% A. 111 B. C.116 C. 121 D. D.126 CHIMNEY 1. A boiler uses 2500 kg of coal per hour and air required for the combustion in 16 kg per kg coal. If ash loss is 10%, determine the mass of the gas entering the chimney. Answer: A A. 42,250 kg/hr B. 78,300 kg/hr

C. 85,452kg/hr D. 33,800 kg/hr 2. The gas density of chimney is 0.75 kg/m3 and air density of 1.15 kg/m3. If the driving pressure is 0.25 Kpa, determine the height of chimney. Answer: B A. 54.6 m B. 63.7 m C. 74.6 m D. 68.5 m 3. The actual velocity of gas entering in a chimney is 8m/sec. The gas temperature is 25°C and pressure of 98 Kpa with a gas constant of 0.287 KJ/kg-°K. Determine the chimney diameter if mass of gas is 50,000 kg/hr. Answer: D A. 1.57 m B. 1.81 m C. 3.56 m D. 1.39 m 4. A coal fired steam boiler uses 3000 kg of coal per hour. Air required for combustion is 15.5 kg per kg of coal at barometric pressure of 98.2 Kpa. The flue has temperature of 285°C and an average molecular weight of 30. Assuming an ash loss of 11% and allowable gas velocity of 7.5 m/sec, find the diameter of chimney. Answer: C A. 2.0 m B. 1.53 m C. 1.91 m D. 2.5 m 5. A power plant situated at an altitude having an ambient air of 96.53 Kpa and 23.88°C. Flue gases at a rate of 5.0 kg/sec enter the stack at 200°C and leaves at 160°C. The flue gases gravimetric analyses are 18% Co2, 7% O2 and 75% N2. Calculate the height of stack necessary for a driving pressure of 0.20 Kpa. Answer: D A. 59.56 m B. 60. 15 m C. 55. 83 m D. 56.95 m 6. A power plant situated at an altitude having air of 96.53 Kpa and 23.88°C. Flue gases at a rate of 5.0 kg/sec enter the stack at 200°C and leaves at 160°C. The flue gases gravimetric analysis 18% CO2, 7% O2 and 75% N2. Calculate the diameter of stack in meters for a driving pressure of 0.20 Kpa.Answer: B A. 0.50 m B. 0.95 m C. O.60 m D. 1.15 m

7. A steam generator with economizer and air heater has an overall draft loss of 21.78 cm of water. If the stack gases are at 177°C and if the atmosphere is at 101.3 Kpa and 26°C, what theoretical height of stack in meters is needed when no draft fan are used? Assume that the gas constant for the flue gases is the same as that for air. Answer: D A. 565 B. 535 C. 545 D. 550 8. If the actual draft required for a furnace is 6.239 cm of water and the frictional losses in the stack are 15% of the theoretical draft, calculate the required stack height in meters. Assume that the flue gas have an average temperature of 149°C and molecular weight of 30. Assume air temperature of 21°C.Answer: C A. 215 B. 230 C. 220 D. 210 9. A steam boiler plant consumes 9,000 kg of coal per hour and produces 20 kg of dry flue gases per kg of coal fired. Outside air temperature is 32°C, average temperature of the flue gas entering the chimney is 343°C and average temperature of dry flue gas in the chimney is 260°C. The gage fluid density of 994.78 per m3 and the theoretical draft of 2.286 cm of H2O at the chimney base is needed when the barometric pressure is 760 mm Hg. Determine the height of the chimney.Answer: A A. 46 B. 50 C. 40 D. 56...