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Mercury Removal Unit (MRU) Design

GPSA Section 21 · Campbell Gas Conditioning · LNG Feedstock Protection

Mercury Removal Unit Design Calculator
Sizes MRU vessels using material balance, contact time requirements, and superficial velocity limits. Calculates adsorbent mass, bed dimensions, and pressure drop for sulfur-impregnated carbon, metal sulfide, or silver-impregnated media. Results include design assessment per GPSA guidelines.

Feed Gas Conditions

MMSCFD
psia
°F
Sulfur-impregnated carbon: max 120°F for full capacity

Mercury Content

µg/Nm³
µg/Nm³
LNG Specs: Typically <10 ng/Nm³ (0.01 µg/Nm³); some projects require <1 ng/Nm³

Adsorbent Selection

months
Sulfur-Impregnated Carbon: Industry standard for natural gas. 10-20 wt% Hg capacity, non-regenerable, operates at ambient to 120°F. Forms stable HgS.

Why Mercury Removal is Critical

Mercury causes catastrophic liquid metal embrittlement (LME) of aluminum brazed heat exchangers in LNG plants. Even trace amounts (ppb levels) lead to:

  • Aluminum amalgamation: Hg penetrates grain boundaries
  • Stress corrosion cracking: Failures under normal loads
  • Equipment damage: $50-100M+ replacement costs
  • Production loss: Extended shutdowns for repairs

Typical Mercury Levels

Region µg/Nm³
N. America (onshore) 0.01-0.5
North Sea 0.1-10
Indonesia/Malaysia 50-500
Middle East 1-50
Australia NW Shelf 0.5-20

Design Considerations

  • Lead-lag config: 2+ vessels for continuous operation
  • Contact time: Min 2-5 seconds for equilibrium
  • Velocity: 0.5-1.0 ft/s to prevent fluidization
  • L/D ratio: 1.5:1 to 3:1 for good distribution
  • Inlet conditioning: Remove liquids, filter solids
  • Monitoring: Online Hg analyzer recommended