An exhaust air stream contains 4000 ppm methane, 1000 ppm ethane, and 5% oxygen from a landfill.

Question

a. How many moles of oxygen are required for combustion?
b. Does additional air need to be added to the exhaust gas to reach the required amount of oxygen?
c. If so, what percentage of make-up air must be added?

What will be an ideal response?

Answer 1

????????????????????????? ? ????????4



????????4 +3????2 ? ????????2 +2????2????



Since n (mols) ? ? (volume) in the gas phase, then:





The total O2 required = 12,000 ????????????? + 35,000 ????????????? = 155,000 ????????????? of O2 = 15,5% O2 > 5% in the landfill gas



Therefore extra “make-up” air is required.



Substituting yields:



Therefore the mixture can contain a maximum of 34% landfill gas to have enough O2 in the air. Solve iteratively to find the effects on dilution of the fuel. If landfill gas is diluted to 34%, then;

Methane concentration = 40,000(0.34) = 13,760 ppm

Ethane concentration = 10,000(0.34) = 3,437 ppm

Total oxygen required to burn both gases becomes 53, 381 ppm = 5.3%



Under this assumption 3% make-up air is needed with 97% of the landfill gas to completely oxidize the landfill gas.