Crude Unit Preflash Drums and Columns
SUMMARY
Preflash drums and preflash columns have significant effect on crude charge hydraulics. The reason for using preflash equipment are discussed, including general design considerations and problems that are created if they are designed incorrectly.
TEXT
Some crude units have preflash drums or preflash columns (preflash drums/columns) between the desalters and atmospheric column, while others do not. Preflash drums and columns are inherently large diameter and tall (or long). They are also high capital cost and should only be used where necessary.
Preflash drums or columns are used to manage crude hydraulics during grass roots crude unit designs and to increase crude capacity when revamping. The installed cost difference between the drum and column alone is relatively small. However, adding the cost of the columns' peripheral equipment including the condensing system overhead drum and pumps raises investment cost considerably. However, when existing atmospheric column condensers, drums and overhead pumps are major limits to raising throughput or prevent the processing of lighter crude oils, installing a column and condensing system can be more cost-effective than modifying an existing atmopsheric column overhead system. This work can be completed before the turnaround to reduce downtime.
Drums or columns flash a portion of the crude and water between the desalter and crude charge heater. The amount of hydrocarbon vapourised depends on the temperature and pressure in the drum or column. Two-phase feed is created when the operating pressure is reduced upstream of the drum or column. A drum is a single-stage flash...