Question

A fuel containing 40 mol% CH4 and 60 mol% C2H6 enters a furnace at a rate of 100 mol/s, at 300C and Pabs=5 atm. Incomplete combustion occurs in the furnace. Air is fed to the furnace at 20% excess. (a)What is the partial pressure of CH4 ?__________ (b)What is the volumetric flow rate of the fuel ?__________ c) Calculate the feed rate of oxygen, in mol/s___________________ d) Calculate the feed rate of air, in mol/s___________________

Answer 1

1) the partial pressure of CH4 = pressure of mixtureX mole fraction of CH4 = 5 atm X 0.4 = 2 atm

2) volume flow rate = moles rate X Gas constant X temperature / Pressure

Volume flow rate = 100 X 0.0821 X 573 / 5 = 940.86 L /s

3) The combustion equations will be:

CH4 + 2O2 --> CO2 + 2H2O

So for each moles of CH4 we need 2 moles of O2 which means that

For 40 moles /s we will need 80moles / second flow rate of oxygen

C2H6 + 7/2O2 --> 2CO2 + 3H2O

For 1 mole of ethane we need 3.5 moles of O2

so for 60moles / s we will need 210 moles of O2 /s

Total mole /s of oxygen required = 290 moles / second

Provided 20% excess air is used

So The feed rate of oxygen = 290 + 0.2 X 290 = 348 moles /second

d) We know that % of oxygen in air is : 21% by volume

so for 21 moles of oxygen we will need 100moles of air

So for 1 mole = 100/21 moles of air

so for 348 moles / s = 1657.14 moles / s of air