30,000 lb/hr of combination whose average properties correspond to hexane is vaporized from 40,000 lb/hr of feed at its bubble point at 105 psig. The boiling range is from 300 to 350 oF, and heat supplied by steam at 398 oF. Obtainable for the service is a 19¼ in. ID, 1-2 exchanger having 132 1 in. OD, 14 BWG, 16'00" long tube arranged for tube passes on 1 ¼ in. square pitch. Shell baffles are spaced 12 in. a part. What is the dirt issue and the pressure drops.