In {TAIL ~ an alternative embodiment}, {HEAD ~ the average gas superficial velocity} is maintained above a minimum level 
In
In { TAIL ~ an alternative embodiment } , { HEAD ~ the average gas superficial velocity } is maintained above a minimum level
REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH