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Mercury Removal Unit (MRU)
Reliable mercury removal to protect downstream equipment and support consistent gas processing
Mercury is present in most natural gas fields at concentrations ranging from less than 10 parts per billion to greater than 1 part per million in elemental, organic, and inorganic forms. Because mercury is toxic and highly reactive, it must be removed to protect downstream processes. If left untreated, mercury can poison catalysts and attack aluminum equipment through liquid metal embrittlement, leading to cracking, equipment failure, unscheduled shutdowns, and in some cases fires. Mercury removal units use adsorption processes to reduce mercury concentration prior to further processing or sale.
Why is mercury removal important for natural gas processing?
Even trace amounts of mercury can have severe operational consequences. Mercury can poison catalysts used in downstream units and cause liquid metal embrittlement in aluminum equipment, particularly cryogenic heat exchangers. This corrosion mechanism leads to crack initiation and propagation, contributing to equipment damage and unplanned outages.
How is mercury removed from natural gas?
Mercury removal from natural gas is typically achieved using adsorption technology, either with non regenerative or regenerative adsorbents.
In both approaches, mercury laden gas enters the top of an adsorption tower and flows downward through the adsorbent bed, where mercury is captured. Treated gas exits the bottom of the vessel for further processing or sale.
Regenerative systems may use two or more adsorption towers, allowing one bed to be regenerated while the others remain online. Regeneration is performed by flowing heated gas upward through the bed so contaminants captured near the inlet can be removed without flushing the entire bed.
Mercury removal process flow showing upstream liquid gas coalescing, adsorption for mercury removal, optional regeneration, and downstream gas particle filtration prior to sales or further processing.
What does a gas plant require from a mercury removal unit?
A mercury removal unit must support consistent operation while protecting sensitive downstream processes. Typical requirements include:
- Reliable treatment of raw gas to support natural gas or LNG production quotas
- Consistent control of mercury content, typically below 10 ng/Nm3
- Protection of downstream aluminum equipment against liquid metal embrittlement
- Minimisation of adsorption bed degradation or capacity loss that could lead to premature replacement
What challenges can impact mercury removal performance?
Mercury removal system performance can be affected by upstream contamination, liquid ingress, and solids carryover that reduce adsorption efficiency and damage downstream equipment.
What challenges can impact mercury removal performance?
Adsorption efficiency can decline when foreign materials such as glycol, amines, lubricating oils, corrosion inhibitors, or solids coat the adsorbent pores. This reduces mercury removal performance and increases the risk of downstream liquid metal embrittlement, as well as premature bed replacement.
How this is addressed
Mercury removal efficiency and adsorption bed life can be supported through effective liquid and solid removal upstream of the adsorbent beds. High efficiency liquid gas coalescers such as SepraSol™ Plus liquid/gas coalescers and Medallion™ HP liquid/gas coalescers are used for this upstream protection.
How can liquid water damage adsorption beds?
Continuous low level ingress or slug flow of liquid water into adsorption beds can cause thermal shock. This can damage the bed structure and reduce overall system reliability.
How this is addressed
Protecting adsorbent beds from traces or slugs of liquid upstream of desiccant beds supports stable operation. Coalescer assemblies with dual sump provisions can accept most liquid slugs without bypass or loss of removal efficiency. Oleophobically treated coalescers support continuous liquid removal and rapid recovery from short term overloads, helping reduce pressure drop and the risk of carryover.
Video showing Pall liquid/gas coalescers used for upstream filtration in gas processing applications – move from the sidebar to here.
Why are desiccant fines a concern downstream of mercury removal?
Desiccant fines entrained in mercury free gas can damage downstream equipment including cryogenic heat exchangers, compressors, pipelines, and catalyst beds.
How this is addressed
Dry gas particulate filtration downstream of adsorption beds helps remove desiccant fines and other contaminants before gas enters sensitive equipment. Pall solutions include DGF dry gas particulate filters such as Profile® Coreless dry gas filters.
How does the mercury removal process flow work?
In a typical process, mercury laden gas first passes through a liquid gas coalescer to remove free liquids. The gas then enters the adsorption vessel where mercury is removed. Treated gas may pass through a gas particle filter before being routed to sales or further processing.
Both non regenerative and regenerative adsorption systems follow this general flow, with regenerative systems incorporating additional vessels to allow adsorption and regeneration to occur independently.
Key application and filtration considerations
| Application | Pall products | Description |
|---|---|---|
| Contactor inlet coalescer | Liquid gas coalescers are used at the contactor inlet to protect adsorption beds from liquid and solid contamination. By maintaining adsorber efficiency and capacity, upstream coalescing supports productivity, process and equipment reliability, and the ability to maintain on spec mercury content. | |
| Downstream protection | Dry gas filtration downstream of mercury removal beds is used to eliminate adsorbent dust and fines from mercury free gas streams. This supports downstream process reliability by protecting cryogenic equipment, compressors, pipelines, and catalyst beds. |
Frequently Asked Questions
What forms of mercury are found in natural gas?
Mercury may be present in elemental, organic, and inorganic forms.
Why must mercury be removed before LNG processing?
Mercury removal protects aluminum heat exchangers and cryogenic equipment from liquid metal embrittlement.
Are all mercury removal units regenerative?
No. Mercury removal units may be designed as either non regenerative or regenerative adsorption systems.
Why is upstream liquid removal important?
Liquids can foul adsorption media, reducing mercury removal efficiency and shortening bed life.
How are desiccant fines managed after mercury removal?
Dry gas particulate filtration removes desiccant fines before gas enters downstream equipment.
