Prevent preflash drum foaming

Understanding the various process implications of preflash drums and troubleshooting operating problems is important. Preflash drums are used on many refinery crude units. Preflash drum foaming causes significant unit operating problems, but is often not recognized. If a preflash drum is undersized and entrains flashed crude to the atmospheric column, these problems can occur depending on the preflash drum vapor feed location to the atmospheric column: black distillate products (high distillate product contaminants); decreased atmospheric gas oil (AGO) and increased atmospheric tower bottoms (ATB) yields; and increased light material in the vacuum column feed--decreased vacuum gas oil (VGO) yields due to higher operating pressures. In several refinery unit revamps over the last 10 years, significant atmospheric column distillate yield losses resulted when preflash drums were installed or preflash drum operating temperatures were increased. In one location, the preflash drum was referred to as the quench drum because the atmospheric column distillate yield losses were high when the preflash drum was installed. The paper discusses preflash drum theory, effect of preflash drum operating temperatures, atmospheric column flash zone temperature, atmospheric column preflash drum vapor field location, trouble-shooting and identifying entrainment, revamps crude unit design, troubleshooting high ATB production, and final recommendations.