Petroleum refining — electrical dehydrators for crude oil In refinery desalting/dehydration units that use an electrostatic field to coalesce and remove dispersed water and salts from crude, what are the typical combined operating conditions (pressure and temperature) maintained inside the electrical dehydrator?

Introduction / Context:
Crude oil entering a refinery carries emulsified brine and fine solids. Electrical dehydrators (electrostatic desalters) use a high-voltage field to coalesce brine droplets so they settle and can be drained. Correct pressure–temperature conditions are critical to prevent vapor formation, lower viscosity, and maximize droplet coalescence.

Given Data / Assumptions:

• Device: electrostatic crude dehydrator/desalter.
• Objective: remove water and dissolved salts before atmospheric distillation.
• Operating window: moderate pressure to suppress flashing; moderately elevated temperature to reduce viscosity and interfacial tension.

Concept / Approach:
Raising temperature decreases crude viscosity and improves water droplet mobility, enhancing coalescence. Sufficient pressure keeps the crude subcooled, preventing vapor bubbles that disrupt the electric field and dispersion band stability. Typical practice is roughly 90–130°C and a few kilograms per square centimeter gauge pressure.

Step-by-Step Solution:
Identify normal temperature range for desalting: about 90–110°C (often 95–110°C depending on crude).Identify normal pressure range: a few kgf/cm2 to keep the system liquid-full and avoid flashing (around 4–8 kgf/cm2 common).Among the choices, 6.5 kgf/cm2 & 95°C matches standard industry practice for many crudes.

Verification / Alternative check:
Operating manuals and refinery guidelines show electrostatic desalters commonly at roughly 90–120°C and 3–10 kgf/cm2. This keeps salt-in-crude low while limiting energy use and equipment stress.

Why Other Options Are Wrong:

• 1 atm & 110°C: risk of flashing for light crudes at near-atmospheric pressure.
• 20 kgf/cm2 & 110°C: unnecessarily high pressure; no added benefit in coalescence.
• 50 atm & 150°C: far above normal; would increase cost and safety concerns without process gain.

Common Pitfalls:

• Running too cool (poor coalescence) or too hot (emulsion instability, energy waste).
• Insufficient pressure causing vapor formation and loss of electric field effectiveness.

Final Answer:
6.5 kgf/cm2 & 95°C