Natural gas (CH4) is burned in a furnace using 15% excess air based on the complete combustion of CH4. One of the concerns is that the exit concentration of NO (from the combustion of N2) is about 415 ppm. To lower the NO concentration in the stack gas to 50 ppm it is suggested that the system be redesigned to recycle a portion of the stack gas back through the furnace. You are asked to calculate the amount of recycle required. Will the scheme work? Ignore the effect of temperature on the conversion of N2 to NO; that is, assume the conversion factor is constant.