AM-91-45 REVAMPING VACUUM UNITS FOR HVGO QUALITY AND CUTPOINT

Description:

The recent trends of HVGO cutpoints above 1050 F and the concommitant increases in Conradson Carbon Residue (CCR). nickel, and vanadium in the heavier crudes make vacuum unit optimization important. Various design parameters affect HVGO quality and should be considered in any vacuum column revamp design, since optimization can significantly improve HVGO quality at high cutpoints. This paper analyzes four factors affecting HVGO quality: (I ) the distribution of contaminants in the crude oil; (2) mode of column operation; (3) overflash rates; and (4) wash zone efficiency. In the analysis, a common Middle East crude was chosen and four modes of column operation were studied; dry, wet, damp without stripping. and damp with stripping. The analysis shows that a well designed stripping section utilizing the maximum quantity of stripping steam (while minimizing coil steam consistent with minimizing cracking) and minimum flash zone oil partial pressure will yield the highest quality HVGO at any given cutpoint.