Chapter 3 Steam

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(1)CHAPTER III: FUELS AND COMBUSTION.

(2) 1. A bituminous coal has the following compositions: C= 71.5%. O=7.0 %. S=3.6 %. H=5.0%. N=1.3%. Ash=8.2%. W=3.4%. Calculate for complete combustion of the theoretical weight of air required in kgair/kgcoal.. a. 9.80 b. 8.80. c. 7.80 d. 6.80. Solution:

(3) :. 0 11.5 34.5 4.3! 8. 7.0% 11.5"71.5%% 34.5 5.0% 4.33"3.6%% 8 ' -./01 *. +, ( ) -.23/4. 2. Calculate the higher heating value of liquid dodecane fuel. The chemical formula of Dodecane is C12H26.. a. 48, 255 kJ/kg b. 55,641 kJ/kg. c. 60,221kJ/kg d. 35,245 kJ/kg. Solution: 56 13,500 60890 9::

(4) : % % % % :;. ;< =. > =: ∗ 100 > <. 12"12% ∗ 100 84.71% 12"12% 1"26% > AB : ∗ 100 > <. 1"26% ∗ 100 15.29% 12"12% 1"26%. 56 13,500 "0.8471% 60890 ".1529% 56 20,745.93. ;< D+, EFF. ,D -G/-. =. 3. Calculate the minimum volume of day tank of 28°API fuel having a fuel consumption of 1kg/s..

(5) a. 94.71 m3 b. 97.41 m3. c. 91.74 m3 d. 79.41 m3. Solution: I. J K. ! L: B:MA K: !NOP.QR . 141.5 141.5 °TU 131.5 28 131.5. !NOP.QR 0.887. K 0.887"1000%. K 887 :;. V JW. V M 3600M 24 I V 1 B A 887 W J 1. X *Y. DZ[\. 4. It is required to find the theoretical volume of air at 20°C and 100 kPa absolute pressure to burn one kilogram of Franklin County coal. The ultimate analysis of coal-as-fired is as follows: C= 65.65%. O=18.61. Mois.= 3%. H= 5.87%. S=1.51%. Ash= 5.36%. a. 9.43 m3air/kgcoal b. 7.43 m3air/kgcoal. c. 8.43 m3air/kgcoal d. 6.43 m3air/kgcoal. Solution: L <J ]<B: I. J^ T. ! L: J:. 0 J 11.5 34.5 4.3! 8. 0.1861 J 11.5"0.6565% 34.5 0.0587 4.3"0.0151% 8 J 8.84 :;. V _à V bc_d.

(6) I. 8.84. <M; X Y. D\. Ve V _à 0.287 "20 273 f% V bc_d V _à f Vg 100 h J. [\/01 -.23/4. 5. A 650 BHP diesel engine uses fuel oil of 28° API gravity, fuel consumption is 0.65 lb/BHP-hr. Cost of fuel is P 7.95 per liter. For continuous operation, determine the minimum volume of cubical day tank in cm3, ambient temperature is 45°C.. c. 5,291,880 cm3 d. 7,352,789 cm3. a. 4,372,890 cm3 b. 5,987,909 cm3 Solution: I. J K. ! L: J: J "0.65%"650% 422.50 ! L: K: !NOP.QR . = . 141.5 141.5 °TU 131.5 28 131.5. !NOP.QR 0.887. !NiPR !NOP.QR j1 0.0007" 15.6%k !NiPR 0.887j1 0.0007"45 15.6%k !NiPR 0.869. K 0.869 1000 :; I. V V 869 W JW J. 191.61 JW 0.220495 ∗ "24 869 . I 5,291,880 <M;. blm n_o. X34. 3p q/r )/s- F, E*Z, ++, 2[\ .

(7) 6. 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 per liter at 60°F. Determine the over-all efficiency of the plant.. a. 26.08% b. 25.06%. c. 29.07% d. 30.01%. Solution: t<u< U:u<. 2700 V> 24 J 56. ! L: 56 :. 56 41,130 139.6 "°TU% 56 41,130 139.6 "30%. 56 45,318. Ve V. ! L: J:. !NQvw !NOP.QR . 141.5 °TU 131.5. !NQvw !NOP.QR 0.876. !Nxvw !NhQ.QR 0.876j1 0.0007"26.6 15.6%k !Nxvw !NhQ.QR 0.00952 J KI J y0.869 . 1000V 250 0.003785JW z { | }~ 1. JW 24. J 0.00952 :;. V M. V M. 2700 24V> 0.00952"43.318%V> ,. E,+ 31 E. ,+%. 7. A circular fuel tank 45 ft long and 5.5 ft diameter is used for oil storage. Calculate the number of days the supply tank can hold for continuous operation at the following conditions. Steam flow= 2000lb/hr Steam dry and saturated at 200 psia Feedwater temperature= 230°F Boiler efficiency=75% Fuel Oil=34°API hg at 200 psia =2786.6 hf at 2300F=461.3.

(8) 200 uM "1.38 T %: 2786.6 230w "110R%: 461.3. Ve V. Ve V. c. 17.57 days d. 19.26 days. a. 15.21 days b. 16.23 days Solution: g. AM :. > J.

(9) < J MM

(10) <. ! L: J:. 56 41,130 139.6 "34% 56 45,876.4 Ve/V. J M J = :. 200 uM "1.38 T %: 2786.6 230w "110R%: 461.3 J 2000 . = V 907.03 . Ve V. Ve V. J J 56. 0.75 . "907.03%"2789.6 461.3% J "45,876.4%. J 61.38. V . ! L: > : !NOP.QR . 141.5 141.5 °TU 131.5 34 131.5. !NOP.QR 0.855. Kd 0.855 1000 Id . V V 855 W W J J. "5.5%h "45% 1069.12 W 4.

(11) >d 30.27 JW 855. V JW. >d 25,880.57 V .. <M; :. 25,880.5 V 421.645 M. V 61.38 . s ZY. FY q/r. 8. Liquid Octane (C8H18) fuel is burned with ideal proportion of air. Calculate the ideal air-fuel ration by weight.. a. 13.72 kg air/ kg fuel b. 14.56 kg air/ kg fuel. c. 15.05 kg air/ kg fuel d. 10.69 kg air/ kg fuel. Solution: : =

(12) : < :B :. jx Ox kd j0h 3.76 gh kà → j=th h 0 3.76gh kacnb ;. : :. : 1"8% = = 8 V J. : 1"18% 2"% 9V J. t: 2 2= 12.5 V J g: 3.76 47 V J. x Ox 12.5 th 47 gh → 8th 9h 0 47gh <M;. 12.5"32% 47"28% -./01 ZF. ,F -.p4 1"96% 1"18% 9. A typical industrial fuel oil, C6H32 with 20% excess air by weight. Assuming complete oxidation of the fuel, calculate the actual air-fuel ratio by weight.. a. 17.56 kg air/ kg fuel b. 15.76 kg air/ kg fuel. c. 16.75 kg air/ kg fuel d. 17.65 kg air/ kg fuel. Solution: : =

(13) : < :B :. jOQ Wh kd j0h 3.76 gh kà → j=th h 0 3.76gh kacnb ;. : :. : 16 ="1% = 16 V J : 32 2"% 16V J.

(14) t: 2 2= 24 V J g: 3.76 90.24 V J. x Ox 24 th 90.24 gh → 16th 16h 0 90.24gh. < : ]< :

(15) 20% MM :. x Ox Z. E"24 th 90.24 gh % → 16th 16h 0 Z. E"90.24gh %. ;. : tA ::. t: 1.2"24%"1% 16"2% 16 2B. B 4.8 V J. < : ]< ::. jx Ox kd j28.08 th 108.28 gh k_à → j16th 16h 0 4.8th 108.28gh k_c acnb < < :. 28.8"32% 108.28"28% 12"16% 1"32% _. -./01 ' ZY. F ( / -.p4. 10. The ultimate analysis of coal is given below: C= 68.5%. S= 1.5%. H= 2.5%. O=3.5%. Ash= 12.0%. Calculate the higher heating value of coal.. a. 25,300 kJ/kg b. 28,300 kJ/kg. c. 27,300 kJ/kg d. 26,300 kJ/kg. Solution: t 56 33,820 144,212 9,304! 8 56 33,820"0.685% 144,212 0.025 E, E+,. \. -G. -.. 0.035 9,304"0.015% 8. 11. 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 35°C. Calculate the higher heating value of the fuel.. a. 43,852.13 kJ/kg b. 53, 852.13 kJ/kg Solution:. c. 58,352.13 kJ/kg d. 48, 352.13 kJ/kg.

(16) 56 41,130 139.6 "°TU%. 0.924 !NOP.QR j1 0.0007"35 15.6%k. !NOP.QR 0.937. °TU °TU . 141.5. !N15.6R. 141.5 0.937. 131.5. 131.5. °TU 19.50 <M;. 56 41,130 139.6 "19.50% D\, +FE. Z\. -G -.. 12. A steam generator burns fuel oil with 20% excess air. The fuel oil may be represented by C14H30. The flue gas leaves the preheater at 0.31 Mpa. Find the minimum stack temperature to avoid condensation.. a. 73°C b. 63°C. c. 83°C d. 53°C. Solution: : ]< :. jx Ox kd j0h 3.76 gh kà → j=th h 0 3.76gh kacnb ;. : :. : 14 = = 14 V J. : 30 2"% 15V J. t: 2 2= 21.5 V J g: 3.76 80.84 V J. Oi Wv 21.5 th 80.84 gh → 14th 15h 0 80.84gh < : ]< ::. Oi Wv Z. E"21.5 th 80.84 gh % → 14th 15h 0 Z. E"80.84gh %. ;. : tA ::. 1.2"21.5%"2% 14"2% 15 2B B 4.3 V J. Oi Wv 25.8 th 97 gh → 14th 15h 0 4.3th 97gh. ;A : N== M

(17) , u uMM<

(18) L u:.

(19) T 0.31 . 15 0.03569 u. 14 15 4.3 97.

(20) u: Ju < _ @0.03569 u 73R. [0s0[[ )/2- )[1/)1 0 Y\°. 13. 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.. c. 1.233 d. 1.130. a. 2.130 b. 3.230 Solution: J ^ :

(21) tA :: 0.14h 0.070th → 0.14h t. 0.03i 0.060th → 0.03th 0.06h t. 0.27t 0.135th → 0.27th. J M tA : "0.070 0.060 0.135%th. < tA : : uB< 0.265 th 0.0060th 0.259 th 0.259 0.259"3.76% [34/01 Z. E\\ [34p4 1. 14. In a boiler design, it is desirable to have the flue gas exit temperature above the dewpoint. Estimate the dew point temperature of the flue gas produced by combustion having the gravimetric analysis of: N2= 71.84%. O2=3.61%. CO2= 20.35%. H2O= 4.20%. Assume that air infiltration and leakage are negligible.. a. 39°C b. 41°C. c. 42°C d. 43°C. Solution: :L LJ : AMM : L <J : AMM L 100 V < : gh . 71.84V 2.565 V J 28V V J. th th . 20.35V 0.4625 V J 44V V J. 3.61V 0.1128 V J 32V V J.

(22) h t . 4.2V 0.2333 V J 18V V J. J M 2.565 0.4625 0.1128 0.2333 3.3736 V J M T uMM<

(23) L u : < M T_a_ca . T J_a _ca 0.2333 101.3 Jc_d 3.3736. T_a_ca 7 fu 0.007 u. <M;.

(24) u: Ju < _ @0.007 u \*R 15. If the theoretical air-fuel ratio is 15, what is the approximate higher heating value in kJ/kgfuel?. a. 46755 kJ/kg b. 56755 kJ/kg. c. 45765 kJ/kg d. 55765 kJ/kg. Solution: Ve 56 V 3117. 15 . 56 3117. DYFF. -G -.. 16. There are 20kg 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?. a. 20.17 b. 16.56. b. 26.67 d. 8.21. Solution: J=<M: ]< : Oh hQ :. Oh hQ 18.5 th 18.5"3.76% gh → 12th 13h 0 18.5"3.76%gh. 18.5"32% 18.5"3.76%"28% V _à 14.94 2"12% 26"1% V d. 20 V M 1V < _. V _à 19 _ V d :;.

(25) ¡¡ ¢ ¡ ¢ ¢ _ % MM ¡ ¢ % MM . 19 14.94 14.94. % £¤2 '01 ,. EYZYF 31 EY. ZYF% 17. A diesel electric plant supplies energy for Meralco. During a 24 hr period, the plant consumed 200 gallons of fuel at 28°C and produced 3930 kW-hr. Industrial fuel used is 28°API and was purchased at P 5.50 per liter at 15.6°C. What should the cost of fuel be produce one kw-hr?. a. P 1.05 b. 1.10. c. P 1.069 d. P1.00. Solution: ! L: B:MA 15.6R:. !NOP.QR . 141.5 141.5 °TU 131.5 28 131.5. !NOP.QR 0.887. 1V V 0.887 KOP.QR 0.887 ! L: B:MA 28°:. !NhxR !NOP.QR j1 0.0007" 15.6%k. !NhxR 0.887j1 0.0007"28 15.6%k !NhxR 0.879. V . 1V V KhxR 0.879 0.879 T u V . 5.50 T 6.20 u V 0.887. M u V> : . 200. V T 6.20 3.785 0.879 3930V> . V. ¥ Z. ,F 1 -¦ 1. 18. A fuel oil is burned with 50% excess air. What is the volume rate flow in m3/min of the wet products at a pressure of 102 kPa and a temperature of 350°C when the fuel is burned at the rate of 45kg/min? Assume that the combustion requirements of the fuel oil are similar to those of C12H26.. a. 1865 b. 3526 Solution:. c. 2462 d. 4563.

(26) < :

(27) 50% MM :. Oh hQ Z. F"18.5 th 18.5"3.76% gh % → 12th 13h 0 18.5"3.76%gh Oh hQ 27.75 th 104.34 gh → 12th 13h 0 9.25 th 104.34gh. 27.75"32% 104.34"28% V _à 22.41 12"12% 26"1% V d. 45V < J<:

(28) uB< M 22.41 1 23.41 V _à /V d " % min J<:

(29) uB< M 1053.45. V J:. ! L: M :M :

(30) uB< M: Components CO2 H 2O O2 N2. No. of mols 12 13 9.25 104.34 138.59 3,979.52 V 28.71 138.59 V J ^. Ve 8.314 0.2896 28.71 V f. ! L: L <J

(31)

(32) uB< M: TI J^. 102I 1053.45"0.2896%"350 273% <M;. X Z+\. \YF. [\ [0s. 19. A fuel gas has the following volumetric analysis: CH4=68%. C2H6=32%. Assume complete combustion with 15% excess air at 101.325 kPa, 21°C wet bulb and 27°C dry bulb. What is the partial pressure of the water vapour in kPa?. a. 9.62 b. 12.81. c. 17.28 d. 15.94. Solution: J=<M: :

(33) :. 0.68i 0.32h Q 2.48th 2.48"3.76%gh → 1.32th 2.32h t 2.48"3.76%gh J=<M: :

(34) 15% MM :. 0.68i 0.32h Q Z. ZFj2.48th 2.48"3.76%gh k → 1.32th 2.32h t 2.48"3.76%gh.

(35) 0.68i 0.32h Q 2.852th 10.72gh → 1.32th 2.32h t 0.37th 10.72gh J M : uB< M 1.32 2.32 0.37 10.72 17.73 T uMM<

(36) L u ¥ª/)1 «/31 ZF. F*F -¥/. 101.325"2.32% 14.73. 20. The following is an analysis of coal in percent: C=74. O2=8. S=1. H2=6. N2=1.6. Ash=9.4. If burned in a boiler, the coal produces the following Orsat analysis in percent: CO2= 12. O2=6.5. CO= 0.1. The refuse contains 0.0008 kg of carbon per kg of coal burned. Determine the percentage of excess air used.. a. 45.6% b. 46.5%. c. 54.6% d. 56.4%. Solution: ¡¡ ¢ ¡ ¢ ¢ _ % MM ¡ ¢ . ! L: & : _. 0 0.08 11.5 34.5 4.3! 11.5"0.74% 34.5 0.06 4.3"0.01% 8 8. V _à 10.278 V bc_d. gh : uB< M 100 "12 0.1 6.5% 81.4%"=A L <J%. V : uB< M 0.12"144% 0.001"28% 0.065"32% 0.814"28%. V : uB< M 5.28 0.028 2.08 22.792 30.18 V acnb V gh 22.792 0.7552 V uB< M 30.18 an 0.74 0.008 0.732 V bc_d. : uB< M . 5.28 0.028 0.0481 V 30.18"3.67% 30.18"2.33%. g: 1V 2.67 V th 3.76 V th . 1V 1.33 V th 2.37 V th .

(37) V ®_ 1 0.732 15.218 V bc_d 0.0481. gh d`n V bc_d. . 11.493 14.965 0.768. g: gh M 76.8 "77%%% =A

(38) : :. <M;. % MM . 14.965 10.278 ,. DF, 31 DF. ,% 10.278. 21. A gaseous mixture has a dew point temperature of 15°C. The total pressure is 143. 27 kPa. Determine the amount of water vapour present in 100 moles of the mixture. Note: Saturation pressure at 15°C is 1.7051 kPa. c. 1.19 d. 2.0. a. 1.10 b. 2.19 Solution: T T . I¯ I. I¯ 1.7051 143.27 100 <M;. X« Z. Z* [34 22. A coal fired utility boiler has the following characteristics: Coal Feed Rate=6,940 kg/hr Electric Power Rating= 50<W Refuse Removal Rate= 410 kg/hr Carbon in Refuse= 30% Ultimate Analysis in percent: C= 76.56. O2= 7.70. S= 2.44. H2= 5.50. N2= 1.70. Si=6.10. Heating value of coal is 32,773 kJ/kg If stack gas particle collectors are required to meet the limit of 0.043kg particulates per million kg of fuel set by Environmental Management Bureau under the jurisdiction of the DENR, what efficiency must the collection system have? Molecular weight of Si=28.09.. a. 99.999953% b. 89.999953% Solution:. c. 79.999953% d. 69.999953%.

(39) J<: <:=<:B ": <M% "0.30%"410% 123 J<: <:=<:B ": <M% V !` th "28.09 32% 2.139 V !` 28.09. V . 123 V 160.66 0.7656 . g: M M u: u A !` th :. J<: !` : < =<:B 0.061"6779.3% . 413.54V . J<: !` th ": <M% 410 160.66 249.34. V . J<: A M "u < % B =A < M 884.56 249.34 635.22 JB J<: u < : < M 0.043 : : A, **. ****F\%. 63522 0.00029842 635.52. V 6940 1,000,000 . V . 23. The dry exhaust gas from oil engine has the following gravimetric analysis: CO2= 21.6%. N2= 74.2%. O2=4.2%. Specific heats at constant pressure for each component of the exhaust gas in kCal/kg°C are: CO2= 0.203. N2= 0.248. O2=0.219. Calculate the specific gravity if the molecular weight of air is 28.97kg/kgmol.. a. 1.055 b. 1.155. c. 1.255 d. 0.958. Solution: :L L: LJ : AMM L <J : AMM: Ju:: t2 t2 g2. N LJ 0.216 0.042 0.742. :; J <

(40) , : . 1 V 30.56 0.032721 V J. <M; !N . 30.56 Z. ,FF 28.97. I <J 0.216/44 0.004909 0.042/32 0.01312 0.742/28 0.026500 V J 0.032721. V.

(41) 24. A coal fired steam boiler uses 3000kg of coal per hour. Air required for combustion is 15.5 kg per coal at a barometric pressure of 98.2 kPaa. The flue gas has a temperature of 285°C and an average molecular weight of 30. Assuming a ash loss of 11% and an allowable gas velocity of 7.5m/s, find the diameter of the chimney.. a. 1.88m b. 1.64m. c. 2.88m d. 2.64m. Solution: I <J

(42) L A MM M : I® |. h } "I . % 4. ! L: I® :. > MM uB< M u V < MM<J: 11% M MM:. >n® 1 M MM _. >n® 15 1 0.11 15.89. V ®_ V bc_d. MM

(43) M u MM: J:A: J® 15.89"3000% 47,670. V . N M :M : < M: ^. Ve 8.314 8.314 0.277 30 V f . I <J

(44) M: I® . J® ^® ® "47.670%"0.277%"285 273% JW 75032.19 T® 98.2 . I® 20.84 <M; 20.84 |. JW M. h } "7.5% 4. ° Z. ++ [. 25. A certain coal has the following ultimate analysis: C= 70.5%. H=4.5%. O2=6%. S= 3.0%. Ash= 11%. Moisture= 4%. N2=1.0%. A stoker fired boiler of 175,000 kg/hr steaming capacity uses this coal as fuel. Calculate the volume of air in m3/hr with the air at 60°F (15.6°F) and 14.7 psia (101.325 kPa) the coal is burned with 30% excess air. Boiler efficiency of 70% and factor of evaporation of 1.10..

(45) a. 212,861.04 m3/hr b. 221,861.04 m3/hr. c. 218,261.04 m3/kg d. 281,261.04 m3/kg. Solution: I. J^ J"0.287%"15.6 273% T 101.325. ! L: J M M :. 0 11.5 34.5 4.3! 8 . 0.06 11.5"0.705% 34.5 0.045 4.3"0.03% 8 V _à 9.53 V bc_d . t 56 33,820 144,212 9,304! 8 56 33,820 0.705 144,212 0.045 56 29,503.17 . Ve. V. 0.06 9,304"0.03% 8. J J 56. 0.70 . 175,000"2482.7% J "29,530.17%. J 21,018.335 J_ 21,018.335 J_ 260,396.15 <M; I_à . V bc_d . V bc_d V _à 12.39 V bc_d V _à . "260,396.15%"0.287%"15.6 273% 101.325. X/01 EZE, +Z. ,D. [\ 1. 26. Methane gas burn completely when supplied with 30 percent excess dry air. The gaseous products are cooled at 32°C and 1 atm pressure. Determine the mass of moisture condensed per kg fuel.. a. 1.302 b. 1.924. c. 1.816 d. 1.614.

(46) Solution: J=<M: ]< :

(47) : i 2 th 7.52 gh → th 2h 0 7.52gh. J=<M: ]< :

(48) 30% MM :. i Z. \"2 th 7.52 gh % → th 2h 0 Z. \"7.52gh % i 2.6 th 9.776 gh → th 0.60h 0 9.776gh. J M J = :. T_ca 4.8 VT. 32R. ;A : M

(49) :. T J T 1 J 0.60 9.776 4.8 J 101.3 J 11.36. J 0.565 V J L u. J M JM< :B:MB 2 0.565 1.435 V J <M;. V lcà bcnn "1.435%"18% Z. ZD V d 12 1"4% 27. A diesel power plant consumed 1m3 of fuel with 30°API at 27°C in 24 hrs. Calculate the fuel rate in kg/hr.. a. 36.21 b. 26.25. c. 29.34 d.39.42. Solution: J KI. ! L: B:MA K: J KI. ! L: B:MA K: !NOP.QR . 141.5 141.5 0.876 °TU 131.5 30 131.5. !Nh±R 0.876j1 0.0007"27 15.6%k !Nh±R 0.869. Kd 0.869 1000. V V 0.869 W W J J.

(50) <M; J 869. V 1JW | } JW 24M. [ \. EZ. -. 1. 28. A coal has the following ultimate analysis: C= 60. H2= 6%. Ash= 5%. N2= 5%. O2= 9%. Moisture=8%. S2= 7%. Determine the actual air-fuel ratio using 20% excess air.. a. 10.66 kg air/ kg coal b. 11.66 kg air/ kg coal. c. 12.66 kg air/ kg coal d. 9.66 kg air/ kg coal. Solution: 0 11.5 34.5 4.3! 8. 0.09 11.5"0.6% 34.5 0.06 4.3"0.07% 8 V _à 8.88 V bc_d. "1 % "8.88%"1.20% _ <M;. ' -./01 Z,. ( / -.23/4 29. The ultimate analysis of a petroleum fuel is 87.1% carbon and 12.9% hydrogen. A certain test of dry products of combustion gives the following analysis by volume: 12% CO2; 0.30% CO; 4.6% O2; 83.1% N2. Calculate the number of atoms of carbon and hydrogen of the hydrocarbon fuel.. a. n=7.26, m=12.90 b. n=8.36, m=7.26. c. n=8.26, m=13.9 d. n=13.90, m=8.26. Solution: To obtain the no. of atoms of carbon and hydrogen in one mole of the Hydrocarbon fuel (Cn Hm) divide the individual mass of carbon and hydrogen by their corresponding molecular weight: : J. 87.1 Y. E /)3[ 3p 2/1²3s 12. 12.9 ZE. *, /)3[ 3p rq13.s 1.

(51) 30. The analysis of natural gas fuel used in a gas turbine power plant has the following percentages by volume: CH4= 80%. C2H4=5%. H2=10%. CO=2%. and the remaining non-combustible gases. Find the volume of air supplied per hour if the gas consumption is 20,000 m3/hr assuming 40% excess air.. a. 285,500 m3/hr b. 348,500 m3/hr. c. 260,000 m3/hr d. 360,000 m3/hr. Solution: J=<M: ]< :

(52) :. 0.80i 0.10 h 0.05h i 0.02 t th 3.76 gh → =th h 0 3.76gh ;. : :. C: 0.80(1)+0.05(2)+0.020=b H: 0.80(4)+0.10(2)+0.05(4)=2c O: 0.02c+2a=2b+c N: 3.76 (a). b=0.92 c=1.80 A=1.81 6.8 kgmol. 0.80i 0.10 h 0.05h i 0.02 t 1.81th 6.8gh → 0.92th 1.8h 0 6.8gh. W 1.81 6.80 8.61 J M J_à 8.88 W 0.80 0.10 0.05 .02 0.97 J M Jd. I <J M<uu B u < =<: 20,000 I_à 8.88 <M;. JW. :B 40% MM . W W J_à JW J_à "1.40% |20,000 } 248,536.08 | } W Jd. X/01 ED+, F\. ,+. [\/01 1. 31. A diesel power plant uses fuel with heating value of 43,000 kJ/kg. What is the density of the fuel at 25°C.?. a. 840 kg/m3 b. 873 kg/m3 Solution: Kd !Nd K. ! L: !Nd @30R:. !NOP.QR J:. 141.5 °TU 131.5. 56 41,130 139.6 "°TU%. c. 970 kg/m3 d. 940 kg/m3.

(53) 43000 41,130 139.6 "°TU% °TU 13.395 !NOP.QR . 141.5 0.98 13.395 131.5. !NhPR 0.98j1 0.0007"25 15.6%k 0.97 <M;. Kd 0.97 1000 ³p4 *Y,. -. [\. V JW. 32. Calculate the calorific value of coal which has the following analysis: Carbon 81%, Hydrogen 5%, Oxygen 5.6%, Sulfur 1% and the remainder is ash content.. a. 33,688.35 kJ/kg b. 32,135.45 kJ/kg. c. 12,456.34 kJ/kg d. 32,457.45 kJ/kg. Solution: t 56 33,820 144,212 9,304! 8 56 33,820 "0.81% 144,212 0.05 \\, ++. \F. -G -.. 0.056 9,304"0.01% 8. 33. What is the calorific value and the minimum mass of air required per kilogram of fuel oil which is composed of 85.2% carbon, 12% hydrogen, 1.6% oxygen, 1.2%impurities.. a. 13.87 kg air/kg fuel b. 14.55 kg air/kg fuel. c. 12.57 kg air/kg fuel d. 15.75 kg air/kg fuel. Solution: t 56 33,820 144,212 9,304! 8 56 33,820 "0.852% 144,212 0.12 56 45,831.66. Ve V. 0.016 9,304"0% 8. < :. 0 11.5 34.5 4.3! 8. 0.016 11.5"0.852% 34.5 0.12 4.3"0% 8.

(54) ' -./01 Z\. +Y ( ) -.p4 34. A petrol has the following analysis: 85.5% carbon, 14.4% hydrogen, and 0.10% sulphur. Calculate the volume of air at 1.0 bar and 15°C required for perfect combustion of 1kg of the fuel. Note Rair=0.287 kJ/kg-K.. a. 12.24 m3 air/ kg fuel b. 13.45 m3 air/ kg fuel. c. 15.54 m3 air/ kg fuel d. 14.57 m3 air/ kg fuel. Solution: ! L: : _. 0 11.5 34.5 4.3! 8. 11.5"0.855% 34.5"0.144 0% 4.3"0.001% V _à 14.80 V d . :; I. "14.80%"0.287%"15 273% [\/01 ZE. ED -.p4 100. 35. A fuel used in a boiler contains 86.1% carbon, 12.5% hydrogen, and 0.4 oxygen and 1% sulphur. There are 40% excess air supplied to the furnace and the fuel rate is 400 kg/hr. Calculate the mass of air and the heat energy transferred to the air per hour if it enters the air heater at 18°C and leaves at 130°C. Note Cp=1.00 kJ/kg.K. a. 7,794.26 kJ/kg, 890,093.12 kJ/kg b. 8678.45 kJ/kg, 980,045.32 kJ/kg Solution: ´400 V d µ. . M<uu A u < . _ . ! L: : _. 0.004 11.5".861% 34.5 0.125 4.3"0.01% 8 V _à 14.24 V d. V _à "14.24%"1.40% 19.94 _ V d J "19.94%"400% Y, *YD. E. -. 1. =. : A LB =A :. c. 7,345.35 kJ/kg, 670,035.45 kJ/kg d. 8,987.76 kJ/kg, 567,098.57 kJ/kg.

(55) 5 J ∆. 5 7,974.26"1%"130 18% +*,, ,*\. ZE. -G 1. 36. A fuel has the following constituents: Carbon 85%, hydrogen 13%, Oxygen 2%, When burning this fuel in a boiler furnace the air supply is 50% in excess of the theoretical minimum required for complete combustion, the inlet temperature of the air being 31°C and funnel temperature is 280°C. Compute its calorific value, air-fuel ratio and percentage of heat energy supplied:. a. 47,134.03 kJ/kg, 21.26 kg air/kg fuel b. 35,897.54 kJ/kg, 12.21 kg air/kg fuel. c. 14,576.24 kJ/kg, 17.27 kg air/kg fuel d. 45,457.13 kJ/kg, 12.54 kg air/kg fuel. Solution:. . L < < :. t 56 33,820 144,212 9,304! 8 56 33,820 "0.85% 144,212 0.13 DY, Z\D. ,\. -G -.. 0.02 9,304"0% 8. =. < :. 0 11.5 34.5 4.3! 8. 0.02 4.3"0% 11.5"0.85% 34.5 0.13 8. V _à 14.7 V d. < < V < :. "1 % "14.17%"1.50% _ ' -./01 EZ. E ( / -.p4. . T : : A M<uu B: % . 5 56.

(56) ; B

(57) A, 5: 5 J ∆ "21.256 1%"1.005%"280 31% FFY,. Z <M;. -G -.p4.

(58) DY, Z\D. ,\. -G ' -./01 -G ; EZ. E ; FFY,. Z -. ( / -.p4 -.p4. 37. Experiment revealed that the calorific value of an oil fuel by means of a bomb calorimeter, the mass of a sample fuel was 0.75 gram, the mass of water surrounding the bomb was 1.8kg with some water in the fitting 0.47 kg, and the temperature rises by 3.3°C. Considering that the specific heat of water is 4.2 kJ/kg-K, compute the calorific value of this oil in Mj/kg. a. 41, 949.6 kJ/kg b. 35,345.2 kJ/kg. c. 47,457.23 kJ/kg d. 31,687.45 kJ/kg. Solution: : A ^ MB =A < : A :MB

(59) :B : Jc`d 5c`d J_a ·¸¹º» ∆_a . 0.75 5 "1.8 0.47%"4.2%"3.3% 1000 c`d. 304 DZ, *D*. . -G -.. 38. A fuel consists of 84% carbon, 13% hydrogen, 2% oxygen, and the remainder incombustible solid matter. Calculate the calorific value of the theoretical mass air required per kg of fuel and the mass analysis of the flue gas if 22kg of air are supplied per kg of fuel burned.. a. 46,795.83 kJ/kg, 14.06 kg air/ kg fuel b. 45,787.87 kJ/kg, 15.06 kg air/ kg fuel Solution:. . I < < :. t 56 33,820 144,212 9,304! 8 56 33,820 ".84% 144,212 . 13 D, Y*F. +\. -G -.. . 02 9,304"0% 8. =. J MM :. 0 11.5 34.5 4.3! 8. 0.02 11.5"0.84% 34.5 0.13 4.3! 8. ' -./01 ZD. , ( ) -.p4. c. 34,576.78 kJ/kg, 14. 75 kg air/ kg fuel d. 45,567.78 kJ/kg, 15.67 kg air/ kg fuel.

(60) 39. A fuel oil has the following contents: 85.5% carbon, 11.9% hydrogen, 1.6% oxygen, and 1% impurities. Calculate the percentage CO2 in the flue gas for complete combustion. a. 20.94 % b. 30.94% Solution: 0 11.5 34.5 4.3! 8. 0.016 11.5"0.855 34.5 0.119 4.3"0% 8. V _à 13.77 V d. MM uB< J=<M::. J 13.98 V _à 1V d 0.01 V Ju<M J 14.97. V _à V d. 2 th JB 3 ∗ 0.855 3 <M;. % th . 3.125 ∗ 100 14.97. %,E E,. *D %. c. 35.5% d. 17.56%.

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