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Natural gas containing 85 mole % methane (CH4),3 mole\% ethane (C2H6),3 mole\% benzene (C6H6), 5 mole\% hydrogen (H2), and the rest water vapour (H2O) is burnt with 20% excess air. The air contains 1.5 mole\% water. Calculate (a) the ratio of moles of air required per mole natural gas fed. (10 marks) (b) the composition of the flue gas in mole\% assuming that the combustion is complete with all C going to CO2 and all H going to H2O. (15 marks) Assume that dry air is 21 mole\% oxygen and 79 mole\% nitrogen. May 2015