700 kmol/h of oxygen (02) is fed into a reactor. The combustion of methane (CH4)

ID: 707505 • Letter: 7

Question

700 kmol/h of oxygen (02) is fed into a reactor. The combustion of methane (CH4) and O2 produces three compounds, namely carbon monoxide (CO), carbon dioxide (CO2) and water (H2O). The reaction can be represented by the equation as shown below 4CHs+702 2CO 2CO2 8H20 Use the following molecular weights: C- 12 kg/kmol, H-1 kg/kmol, O-16 kg/kmol, N- 14 kg/kmol Consider two possible combustion scenarios below 2.1) (4 marks) The combustion involves 10% excess of CH4 (excess based on stoichiometry) and all the O2 is used up during the reaction. No CO, CO2 and H2O are found in the input stream. Determine the mass fraction of CO and CO2 in the output stream. Provide all your answers to three decimal points co Co2

Explanation / Answer

700 kmol/h O2

The reaction is: 4CH4 + 7O2 --> 2CO + 2CO2 8H2O

Thus, toichiometric requirement of CH4 = 700/7 x 4 = 400 kmol/h CH4

2.1) We use 10% excess i.e. 440 kmol/h CH4

O2 is the limiting reagent, hence the the products from the reaction are formed accordingly.

Product:

CH4: 40 kmol/h = 40 x 16 = 320 kg/h

CO: 200 kmol/h = 200 x 28 = 5600 kg/h

CO2: 200 kmol/h = 200 x 44 = 8800 kg/h

H2O: 800 kmol/h = 800 x 18 = 14400 kg/h

Total mass flow rate = 29120 kg/h

Mass fraction of CO XCO = 5600/29120 = 0.19231

Mass fraction of CO2 XCO2 = 8800/29120 = 0.3022

2.2) O2 is consumed at 700 kmol/h and CH4 is stoichiometrically supplied. Additionally, inlet streams have

79/21 x 700 mol/hr N2 = 2633.33 kmol/h = 2633.33 x 28 = 73733.33 kg/h N2

CO: 5 kmol/h

CO2: 10 kmol/h

H2O: 15 kmol/h

Thus, at the outlet, stoichiometric amounts of products will be formed, with no CH4 or O2, and in addition there will be compounds as present in the inlet stream.

CO: 200 kmol/h + 5 kmol/h = 205 x 28 = 5740 kg/h

CO2: 200 kmol/h + 10 kmol/h = 210 x 44 = 9240 kg/h

H2O: 800 kmol/h + 15 kmol/h = 815 x 18 = 14670 kg/h

Along with N2: 73733.33 kg/h

Total mass flow rate: 103383.33 kg/h

Mass fraction of CO2: XCO2 = 9240/103383.33 = 0.08938

Mass fraction of N2 : XN2 = 73733.33/103383.33 = 0.7132

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700 kmol/h of oxygen (02) is fed into a reactor. The combustion of methane (CH4)

700 kmol/h of oxygen (O2) is fed into a reactor. The combustion of methane (CH4)

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700 kmol/h of oxygen (02) is fed into a reactor. The combustion of methane (CH4)

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