(155d) Vacuum Distillation - System Type

Crude oil refining uses three major types of systems for vacuum crude distillation:

• Dry:           no steam
• Damp:
  • Velocity steam in heater only
  • Velocity steam in heater and stripping steam
• Wet:           velocity steam in heater, stripping steam, and the vacuum system has a precondenser

Each of these systems has benefits, costs, and limitations. The paper:

• Compares performance of the systems.
• Identifies the requirements each system has for reliable operation.
• Shows the applicable ranges where each system is favored.
• Lists revamp strategies for different processing objectives.

Additionally, performance versus partial pressure is investigated. The wet system has been reported in having superior quality products for the same yield. The question addressed is what causes the superior product quality? Is it an inherent factor in the system or is it strictly related to differences in relative volatility with partial pressure changes?