Considerations for crude unit preflash drums and preflash towers
A guide to debottlenecking, revamping, designing, and operating crude unit preflash facilities based on literature and the authors’ experience
Henry Z Kister and Walter J Stupin (dec.) Fluor Maureen Price Maureen Price Consulting LLC
P reflash drums or towers are extensively used in crude feed trains between the desalter and the atmospheric tower heater. Preflash drums or towers have been discussed by many literature references, each focusing on one or a few important aspects and provid - ing valuable guidelines. None of these attempted to bring together all these lessons in a manner that can guide engi - neers involved in the debottleneck, revamp, design, and operation of crude units. Purpose and location in the crude train In crude oil refining, a preflash drum or tower is a vessel that flashes a portion of the light components of the crude
as well as some water upstream of the atmospheric tower charge furnace. The use of preflash drums or preflash towers between the desalter and the crude atmospheric tower is typically done to manage crude hydraulics, as part of grassroots unit design, to increase crude capacity, or to allow processing of lighter crudes as part of a revamp. As the preflashing term suggests, the primary function of these devices is to flash the lighter (volatile) portion of the crude oil before it enters the furnace inlet control valves. These control valves distribute the feed to the various heater passes. Flashing upstream of these valves makes it impossible to distribute the feed to the heater passes ade - quately. Pass flow imbalances cause heater bottlenecks,
Top-PA
Naphtha
Water
Mid-PA
Steam
Kerosene
Bottom-PA
Steam
Diesel
Desalter
Crude atmospheric column
Preflash drum
Steam
Gasoil
Water
Crude preheat
Crude oil
Steam
Atmospheric residue
Crude heater
Figure 1 Preflash drum scheme with the drum overhead routed to the flash zone of the atmospheric tower
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PTQ Q1 2024
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