A gaseous fuel containing methane and ethane is burned with excess air. The fuel

Question

A gaseous fuel containing methane and ethane is burned with excess air. The fuel enter the furnace at 25 degree C and 1 atm, and the air enter at 200 degree C and 1 atm. The stack gas leaves the furnace at 1000 degree C and 1 atm and contains 5.32 mole % CO_2, 1.60% 7.32% O_2, 12.24% H_2O, and the balance N_2. (a) Calculate the molar percentages of methane and ethane in the fuel gas and the percentage excess air fed to the reactor. (b) Calculate the heat (KW) transferred from the reactor per 10 m^3/s of fuel gas (c) If 90% of the heat generated from (b) above is used to produce a 20 bar steam 400 degree C from its liquid at 20 degree C, determine the volumetric flow rate of the product steam.

Explanation / Answer

for combustion of methane the equation is:

CH4+2(O2+3.76N2)--------> CO2+2H2O+7.52 N2

HERE, % of excess air is not mentioned in the problem, so by considering that methane burned at 25% excess air,

CH4+1.25*2(O2+3.76 N2)---------> CO2+2H2O+0.5 O2+9.4 N2

HERE,

NCH4 = 1; Ntotal = 2+0.5+9.4= 11.9

the formula for percentage is:

VCH4/Vtotal= NCH4/Ntotal= 1/11.9= 84%

same for C2H6

2C2H6+7O2-------------> 4CO2+6H2O

NC2H6=2; NTOTAL= 4+6=10; therefore percentage of ethane is 200%

for % excess air:

CH4+Z(O2+3.76 N2)----------> CO2+2(H2O)+7.52(N2)

Z= 1+2/2=2.5

% THEORETICAL AIR= AF/AFtheo = 110%

% excess air= 10%

for (b) anD (c) more information needed as time for liquid flow or cross sectional area of fluid and width of that portion of fluid

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