Question

1.f) Methane gas (CH4) enters a combustion chamber at a rate of 3 kg/sec at a temperature of 25 °C. A 200% theoretical air is supplied at a temperature of 400K. At the middle of methane combustion process (i.e., after 50% of methane gas is burnt), liquid propane (C3H8) at 25°C is injected at a rate that produces neither CO nor O2 in the flue gases. Assume steady state and adiabatic process at 1 atm, calculate the following i. The mass flowrate of air ii. The mass flowrate of propane iii. Partial pressure of water vapor in the product iv. The temperature in the combustion chamber just before propane injection v. The flue gas temperature Species CH4 (g) C3H8 (1) H2O(g) CO2(g) N2 (g) O2(g) Heat of Specific heat kJ/Kmol.K formation KJ/Kmol.1 CP -74873 55.84 -131817 99 -241826 47.574 -393522 37.037 0.0 30.574 0.0 38.321

Answer 1

Som Chy 3kg/ see CHy + 20₂ → xo₂ + 2H₂O 187.5 mol e Dho sec mok of Chly 2000 mul mw 16 Anos] Required A2 → 2X1875 = 375 mol 200% theoritical Air supplied, Ring Supplied 750 mo) (1) Mass flow of Air Assumption - 21%. Oz? 794 N2 J 750₂ Air 750 = 3571.42 mol Molar .21 M.W=29 of Air mass flow Air flow = 3571.42 x 29 g Mas flow rate of Air = 107.57 kg/see (1) Cz Mg + 50 - 300, +4₂0 75 375 O₂ left after Chy combustion - So 375 moll mole of Propane for complete combustion 2 375 - 75 mol man flow of propune = 75x44 g LMW=44 log Gi = 3.3 Kgle

- Partial pressun of 10 vapor To teal mols of flue gas by Chy I by Gho | Total CO2 y 187.5 225 412.5 H₂O → 375 300 1675 N₂ → 1410.71 141071 282142. 1 Total 3908.92 mol fraction of ho is 675 .0.1726 3908.92 Partial Pr= mol Jrx Total prosure = 0:1726* 1 011726 atm Total prunun = 1 atm (given) ♡ Temp Just before or propane injection 50% methane combustion Chy Air look 25°C 298 K the of Chy C+ 2H2 - Cry ③ =-74873 - H₂ + 4 O₂ → H₂O Dha= -241826 ® - cta CO₂ Dhos = -393522 CHy + 2O₂ CO₂ + 2H₂O Reverse egn and multiply 2 by 2 andodd allegn sh = 74873 - 2X241826-393522. of Chu comon = - 802301 KI/krout oxn

CHY H₂O CO2 CP (Kokman) 53.84 47.574 27.037 30.574 38.321 Oz 501 comon of any Composition of components at time of CHy → 93.75 562.5 N 2821:42 co → 93.75 Ho - 187.5 o energy in by Cry by Air L by xxn - energy out by jlugas 298 (nep dT + nedt thun gas 1 93.75X230 93.75X-802301 + 298 400 00 m 0 N2 293 298 -75215718.75 +/750x38 321 dT +(282142 x 30.574 dT + / 93.75 x 58.89 dT (562.5 x 33.221dt +6282,42X20574d1 +92.75 X 3103+7+ 1825xwswar Los @ 28 DE 298 Co) 2 -0

Shadt - atte. I -86946008.95 + (T-298) 125445.0013 0 T-298 = 6931 (Pear ita) T= 991.1k