ANS:B - 30

Tray spacing in a distillation column used in a petroleum refinery typically ranges from 30 to 60 inches. The tray spacing in a distillation column is determined based on various factors such as the diameter of the column, the properties of the feedstock, the desired separation efficiency, and the specific design requirements of the distillation process. In the case of larger diameter columns commonly found in petroleum refineries (10-12 ft. in diameter), the tray spacing is typically on the higher end of the range, between 30 to 60 inches. This spacing allows for sufficient contact time between the vapor and liquid phases on each tray while accommodating the larger diameter of the column. It also facilitates adequate residence time for separation and ensures efficient mass transfer between the phases.