A thermal process (in this example a large rotating dryer) operating at 1500 degrees F is said to have air emissions of 5 lbs/hr formaldehyde (from the presence of formic acid) and 2 lbs/hr acetaldehyde (from the presence of acetic acid). The air stream from the thermal process is quantified as 75,000 cu. ft. per minute.
The problem asks us to use kinetics and the Arrhenius equation to predict the level of formaldehyde and acetaldehyde air emissions if the the thermal process temperature was reduced to 750 degrees F (and assuming all else equal).
The basic idea is that you have a reactor (rotating dryer). The problem doesn't state the type of reactor, but I would assume it to be a CSTR (continuously stirred reactor). You are given the initial temperature (1500 F) and the initial flow-rates of the exiting emissions. You can determine the concentration of these emissions by using the total flow rate (v = 75,000 ft^3/min)
Concentration = (emission flow-rate) / (total flow-rate) = moles / ...
The level of formaldehyde and acetaldehyde at half of an orignal temperature are calculated.