In refinery vacuum distillation, column pressure is kept very low to avoid cracking and enable vaporization of high-boiling components. Choose the typical absolute pressure range maintained in a vacuum crude distillation column (in mm Hg abs).

Introduction / Context:
Vacuum distillation allows separation of heavy crude fractions at temperatures low enough to limit thermal degradation. Achieving this requires reducing the column absolute pressure to a narrow low range with steam ejectors or vacuum pumps.

Given Data / Assumptions:

• Unit: vacuum crude distillation column (VDU).
• Pressure units: mm Hg absolute.
• Target: avoid thermal cracking while ensuring adequate vaporization.

Concept / Approach:
Lowering absolute pressure reduces component boiling temperatures (per vapor–liquid equilibrium), enabling separation at less severe thermal conditions. Typical refinery operation targets tens of mm Hg absolute near the flash zone and rectifying sections, balancing separation efficiency with equipment and ejector capacity limits.

Step-by-Step Solution:

Verification / Alternative check:
Design texts and operating guidelines commonly cite 20–80 mm Hg abs ranges in flash zones, depending on crude and target cut points.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing absolute with gauge pressure; the specification is in absolute mm Hg.

Final Answer:
30 to 80