Chemical Engineering Question 100 mol/minute of propane gas is burned completely

Question

Chemical Engineering Question

100 mol/minute of propane gas is burned completely in a continuous reactor with air to form carbon dioxide and water. Develop an Excel spreadsheet to calculate the adiabatic flame temperature if the gasses are fed at 30oC, 1atm for the following cases:

% Excess Air = 0%, +10%, +25%, +50%, +75%, +100%, +150%, +200%

Use heat capacity data from Table B.2 for all components in the combustion reaction.Turn in a hard copy of the Excel spreadsheet as well as a plot of adiabatic flame temperature vs.% excess air.

Explanation / Answer

propane (C3H8) combustion can be represened as

C3H8+ 5O2-----> 3CO2+ 4H2O

the probelm can be divided into two parts. one mass balance and the second energy balance

mass balance

1 mole of C3H8 requires 5 moles of oxygen and gives 3 moles of CO2 and 4 moles of H2O. moles of air = 1/0.21 ( since air contains 21% O2 and 79% N2) = 4.76 moles. ( this data can be used for calculation of air flow rate requireemnt for any moles of feed)

excess air to be supplied = 4.76*(1+x/100), where x = % excess air

N2= 4.76*(1+x/100)*0.79

O2 = 4.76*(1+x/100)*0.21

the products of combustion contains 3 moles of CO2, 4 moles of H2O, 4.76*(1+x/100)*0.79 and oxygen= 4.76*(1+x/100)*0.21- 5.   The mass balance on spread shee it shown below.

Energy balance

heat trasnferred= enthalpy of products + heat of reaction - enthalpy of reactants

since reactants are at 25 deg.c and 1 atm, enthalpy of products =0

for adiabatic operation , heat transferred = 0

enthalpy of prodcucts =- heat of reaction

heat of reaction = -2220.1Kj/mol

So heat of reaction for 100 mol/min = -2220.1*100 Kj/min=2220100 Kj/min=2220100/60 Kj/sec= 37002 Kj/sec= 37002 KW

CP/R data : CO2 : 5.457+1.045*10-3 T, O2= 3.639+0.506*10-3*T, N2= 3.280+0.593*10-3 T , H2O= 3.470+1.450*10-3 T

enthalpy change= number of moles* integral of CpdT ( between T and 298)=37002 KW

Products of combustion Moles of propane ( moles/min) oxygen Air   required ( mol/min) % excess air air to be upplied N2( Mole/min) O2 (in air supplied) CO2 H2O N2 O2 100 500 2380.952381 0 2380.952381 1880.952381 500 300 400 1880.952 0 100 500 2380.952381 10 2619.047619 2069.047619 550 300 400 2069.048 50 100 500 2380.952381 25 2976.190476 2351.190476 625 300 400 2351.19 125 100 500 2380.952381 50 3571.428571 2821.428571 750 300 400 2821.429 250 100 500 2380.952381 75 4166.666667 3291.666667 875 300 400 3291.667 375 100 500 2380.952381 100 4761.904762 3761.904762 1000 300 400 3761.905 500 100 500 2380.952381 150 5952.380952 4702.380952 1250 300 400 4702.381 750 100 500 2380.952381 200 7142.857143 5642.857143 1500 300 400 5642.857 1000

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