Dehydration & Demercurization Skid
CNOOC Wushi Oilfield Group -- Onshore Terminal Processing System
The Wushi Oilfield Processing Challenge
The Wushi Oilfield produces crude oil and associated natural gas from offshore wells in China's Bohai region. Production is transported to an onshore terminal in Shandong Province via submarine pipeline for processing before product separation, export, and distribution.
Offshore crude oil and gas arriving at the onshore terminal presents a combination of processing challenges that do not occur in purely onshore or purely offshore production:
Why This Was a First-of-Its-Kind Design
The simultaneous requirement for deep gas dehydration (to below 1 ppmv water content for LNG liquefaction) and mercury removal -- integrated into a single skid package as part of a larger offshore crude oil terminal processing system -- had not previously been implemented in this combined form in Shandong Province. The design required process engineering that coordinated the placement and duty of the dehydration and mercury removal stages, ensuring that neither function compromised the performance of the other and that the combined system met the LNG feed gas specification requirements.
The Integrated Dehydration and Demercurization Skid
LINSON OIL designed and fabricated the integrated dehydration and demercurization skid as a key processing component of the Wushi onshore terminal system. The skid integrates molecular sieve gas dehydration with mercury removal in a single factory-assembled and tested package.
Molecular Sieve Dehydration
The dehydration section uses a twin-tower molecular sieve adsorption-regeneration cycle to reduce the gas water content to below 1 ppmv -- the specification required for safe LNG liquefaction. The molecular sieve type (4A, appropriate for natural gas dehydration) was selected for the Wushi gas composition and inlet conditions.
The twin-tower design allows continuous operation. The PLC-controlled automatic switching system cycles the towers on a timed basis, with the online dew point analyser providing continuous verification of the dehydrated gas specification at the outlet.
Mercury Removal Guard Bed
Downstream of the molecular sieve dehydration section, a mercury adsorbent guard bed provides the mercury removal stage. The guard bed contains a mercury-specific adsorbent -- sized for the mercury concentration in the Wushi inlet gas and the required outlet specification to protect the downstream cold box. The guard bed is positioned after the dehydration stage because dry gas conditions maximise mercury adsorbent performance and extend adsorbent service life.
Process Integration
The integration of dehydration and mercury removal into a single skid required careful process sequencing: the dehydration stage must be completed before mercury removal, as the mercury adsorbent performs poorly in the presence of free moisture; the regeneration gas for the molecular sieve beds must not be routed through the mercury adsorbent bed; and the combined system must maintain the pressure, temperature, and flow conditions specified for the LNG liquefaction inlet across the full operating range of the offshore field production.
Control System
The integrated PLC control system manages the complete dehydration and mercury removal process: molecular sieve tower switching sequence, regeneration gas heater operation, online dew point monitoring, mercury breakthrough monitoring (where mercury analyser is included in scope), alarm management, and SCADA data transmission to the terminal control room.
Technical Scope Summary
What Was Delivered
| Component | Description |
|---|---|
| Molecular sieve adsorber vessels (×2) | Twin-tower design; pressure vessels per GB 150; sized for Wushi inlet gas flow rate and water loading |
| Molecular sieve adsorbent | 4A type; loaded and quality-verified before commissioning |
| Mercury adsorbent guard bed vessel | Sized for Wushi inlet mercury concentration and outlet specification |
| Mercury adsorbent | Sulphur-impregnated or specialty adsorbent per mercury removal design |
| Regeneration gas heater | Electric type; sized for sieve bed regeneration duty |
| Regeneration gas cooler | Cools regeneration gas after heating stage before condensate knockout |
| Regeneration gas knockout drum | Removes water knocked out during regeneration gas cooling |
| Switching valve manifold | Pneumatically actuated high-cycle ball valves; automatic sequencing |
| Online dew point analyser | Continuous outlet dew point measurement; integrated with PLC switchover logic |
| PLC control panel with HMI | Automatic cycle control; alarm management; SCADA integration |
| Structural skid frame | All equipment, piping, and instrumentation on common structural skid |
| Inter-stage piping | GC2-licensed; ASME B31.3 compliant; factory-installed and tested |
| FAT | Full system cycle simulation; all safety and shutdown functions tested |
Certification Relevance
This project required LINSON OIL to hold:
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Special Equipment Manufacturing License (A2) Adsorber and guard bed vessels
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Radiation Safety Permit Applicable to projects involving mercury monitoring or radiation-source level instrumentation
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CNAS Accredited Laboratory Vessel weld NDT; hydrostatic testing
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ISO 9001:2015 Quality management system covering the full project scope
2025 Shandong Province First-of-its-Kind Equipment
The Dehydration and Demercurization Skid delivered for the CNOOC Wushi Onshore Terminal was designated a 2025 Shandong Province First-of-its-Kind Equipment by the provincial industrial authority.
This designation is awarded to equipment that represents a genuine technical first for the province -- not a performance award or a marketing certification. The evaluation criteria include: whether the equipment configuration has been implemented in this form before in the province, whether it addresses a specific technical challenge with a novel engineering solution, and whether the design has been independently verified as technically sound.
The 2025 designation confirms that the combined dehydration and mercury removal integrated skid -- as applied to an offshore crude oil terminal processing system of this type -- was, at the time of delivery, the first of its kind in Shandong Province.
What This Means for Buyers
For oil and gas operators evaluating LINSON OIL as a potential equipment supplier, this designation provides independent, government-issued confirmation of two things:
- 1. LINSON OIL's engineering team can develop solutions for process requirements that have no existing standard reference design.
- 2. The solution developed was validated as technically credible by an external review process -- not just by LINSON OIL's own engineering team.
Working on a Dehydration, Mercury Removal, or Integrated Terminal Processing Project?
If your project involves deep gas dehydration, mercury removal, or integrated offshore-to-onshore terminal processing -- in China or internationally -- LINSON OIL's process engineering team can review your requirements and identify whether our delivered experience on the Wushi project is directly applicable to your application.
Send us a project brief and we will respond within 1-2 business days.