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Mercury Removal Unit (MRU) Design Calculator

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

Frequently Asked Questions

Why is mercury removal required for LNG and gas processing plants?

Mercury causes aluminum amalgamation and stress corrosion cracking in cryogenic heat exchangers, potentially resulting in catastrophic equipment failures costing $50-100M+ in replacement and extended production losses. LNG specifications typically require less than 10 ng/Nm³ mercury.

What adsorbent is used for mercury removal from natural gas?

Sulfur-impregnated activated carbon is the industry standard for natural gas mercury removal. It has 10-20 wt% mercury capacity, is non-regenerable, and operates at ambient to 120°F. Mercury reacts with sulfur to form stable HgS.

What are the key MRU design parameters?

Key design parameters include minimum contact time of 2-5 seconds for equilibrium, superficial velocity of 0.5-1.0 ft/s to prevent bed fluidization, L/D ratio of 1.5:1 to 3:1 for good flow distribution, and lead-lag vessel configuration for continuous operation.

What are typical mercury levels in natural gas by region?

Mercury levels vary significantly by region and reservoir. The calculator accounts for regional variations and designs the bed size to achieve the required outlet specification, typically less than 10 ng/Nm³ for LNG feed protection.

What does the mercury removal unit calculator design?

It designs mercury removal units for LNG and gas processing, calculating bed sizing, adsorbent mass, contact time, and pressure drop per GPSA and industry standards.

Why is mercury removal important in gas processing?

Mercury must be removed to prevent corrosion of aluminum heat exchangers in LNG plants and to meet environmental and product specifications.

What parameters does this MRU calculator compute?

It calculates adsorbent requirements, vessel dimensions, contact time, and pressure drop for mercury removal bed design.