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Flammability of a hydrocarbon gas mixture in air is very much dependent of its composition. In a refinery, two stream of waste gases, stream 1 (30 vol% carbon monoxide, hydrogen 30 vol% and 40 vol% carbon dioxide) flowing at a rate of 100 kmol/h and stream 2 (40 vol% methane, 30 vol % carbon monoxide and 30 vol% hydrogen) flowing at a rate of 100 kmol/h are premixed with air prior to burning in an atmospheric crude oil preheater. a. Estimate the lower and upper flammability limits of the combined waste gas mixture. b. To ensure better combustion stability, the combined waste gas mixture will be premixed again with a supplementary fuel such as ethane prior to feeding to the heater. By doing so, the lower flammability limit of the waste gases / cthane fuel mixture will be further lowered to below than 5 mol%. An engineer suggests that the combined waste gases/ ethane mixture should contain approximately 20 vol % ethane. Is his suggestion justified? Support your answer with appropriate calculation c. Propose an alternative approach to improve combustion stability and efficiency if addition of supplementary fuel is not possible. Compound Flammability limit in air (% vol fuel in fuel-air mixture) Lower limit Upper limit (LFL) (UFL) 15 CH, CH. CH Co H2 5.3 3 2 12.5 4 12.5 9.5 74 75 Flammability limit of hydrocarbon fuels at 25C and 1 atm