The application of Ethylene Glycol as a desiccant for natural gas pipelines
The Application of Ethylene Glycol as a Desiccant for Natural Gas Pipelines
Introduction: A Sticky Situation in the Pipeline Business
Natural gas is one of the cleanest and most efficient fossil fuels we have today. But like any good thing, it comes with its own set of challenges—especially when it’s being transported through pipelines that can stretch thousands of kilometers. One of the biggest headaches for pipeline operators? Moisture.
Moisture in natural gas pipelines isn’t just annoying—it’s dangerous. It can lead to corrosion, hydrate formation, equipment failure, and even explosions. To keep things running smoothly (and safely), engineers have long turned to desiccants—substances that remove moisture from the air or gas stream. Among these, ethylene glycol has emerged as a popular choice.
But why ethylene glycol? What makes this viscous, sweet-smelling liquid so effective in such demanding environments? And more importantly, how does it work in practice?
Let’s dive into the world of pipeline dehydration, where science meets engineering—and a little bit of chemistry saves the day.
What Is Ethylene Glycol? A Chemical Profile
Ethylene glycol (EG) is an organic compound with the chemical formula C₂H₆O₂. It’s colorless, odorless, and has a slightly sweet taste—though don’t be fooled; it’s toxic if ingested. EG is best known for its use in antifreeze and coolant solutions, but its hygroscopic properties make it ideal for another critical application: gas dehydration.
| Property | Value |
|---|---|
| Molecular Weight | 62.07 g/mol |
| Boiling Point | 197.3 °C |
| Melting Point | -12.9 °C |
| Density | 1.113 g/cm³ at 20°C |
| Viscosity | ~16.1 mPa·s at 20°C |
| Solubility in Water | Miscible in all proportions |
Source: CRC Handbook of Chemistry and Physics
Ethylene glycol’s ability to attract and hold water molecules makes it a powerful desiccant. Unlike solid desiccants like silica gel or molecular sieves, which require regeneration through heating or vacuum, EG operates continuously in a liquid form—making it especially useful in large-scale industrial applications like natural gas pipelines.
Why Moisture Is the Enemy in Gas Pipelines
Before we talk about how EG fights moisture, let’s understand the battlefield.
When natural gas is extracted from the ground, it often contains water vapor. As the gas travels through pipelines, pressure and temperature changes can cause this vapor to condense into liquid water. This creates a host of problems:
- Corrosion: Water reacts with steel and other metals in the pipeline, weakening them over time.
- Hydrate Formation: In cold conditions, water and hydrocarbons can combine to form icy solids called hydrates, which can block pipelines entirely.
- Equipment Damage: Compressors, valves, and turbines downstream can suffer damage from liquid slugging.
- Regulatory Compliance: Pipeline operators must meet strict dew point specifications before delivering gas to customers.
To avoid these issues, the gas must be dried to a specific water content, typically below 4–7 lb/MMscf (pounds per million standard cubic feet).
How Ethylene Glycol Works: The Science Behind the Solution
Ethylene glycol doesn’t just absorb water—it absorbs and retains it due to its high affinity for moisture. Here’s how it works in a typical glycol dehydration unit:
- Contact Tower (Absorber): Wet natural gas enters the bottom of a vertical tower filled with packing material. Lean glycol (with low water content) flows downward from the top.
- Mass Transfer: As the gas moves upward and the glycol trickles down, they come into contact. Water vapor in the gas is absorbed by the glycol.
- Rich Glycol Collection: The glycol now saturated with water (called rich glycol) collects at the bottom and is sent for regeneration.
- Regeneration Unit: Rich glycol is heated in a reboiler to boil off the absorbed water. This produces lean glycol, which is recycled back into the absorber.
This process is continuous and highly efficient—especially when optimized with proper design and operating conditions.
Comparing Glycols: Why Choose Ethylene Over Others?
There are several glycols used in gas dehydration, including triethylene glycol (TEG) and diethylene glycol (DEG). Each has its pros and cons.
| Property | Ethylene Glycol (MEG) | Diethylene Glycol (DEG) | Triethylene Glycol (TEG) |
|---|---|---|---|
| Molecular Weight | 62.07 | 106.12 | 150.17 |
| Hygroscopicity | High | Medium-High | Medium |
| Regeneration Temperature | Lower (~160°C) | Moderate (~180°C) | Higher (~205°C) |
| Vapor Loss | Low | Moderate | High |
| Corrosiveness | Low | Moderate | Moderate |
| Cost | Lower | Moderate | Higher |
Adapted from: Campbell, J.M., "Gas Conditioning and Processing", Vol. 2
While TEG is more commonly used in larger operations due to its deep dehydration capabilities, MEG (monoethylene glycol) shines in smaller systems, offshore platforms, or remote locations where simplicity and lower energy consumption are key.
Design Considerations for Ethylene Glycol Dehydration Units
Putting EG to work requires careful system design. Here are some key parameters engineers consider:
1. Glycol Circulation Rate
Typically ranges from 3–10 gallons per pound of water removed. Too little circulation means poor dehydration; too much increases operational costs.
2. Temperature and Pressure
Operating temperatures between 20–60°C are ideal. High temperatures reduce absorption efficiency, while low temperatures increase viscosity.
3. Lean Glycol Strength
To ensure maximum water removal, the lean glycol should have less than 10% water content after regeneration.
4. Absorber Packing Material
Structured or random packing materials (like Raschig rings or Pall rings) maximize surface area for gas-glycol interaction.
5. Pump and Piping Materials
Since EG is mildly corrosive, stainless steel or corrosion-resistant alloys are preferred.
Field Applications: Real-World Use Cases
Ethylene glycol has found a home in various parts of the world, particularly in offshore platforms, remote wellheads, and midstream processing plants.
Case Study: Offshore Platform in the North Sea
A Norwegian operator installed a compact MEG-based dehydration unit on an aging offshore rig. The platform had limited space and power availability. After switching from TEG to MEG, the operator reported:
- 30% reduction in energy consumption
- Simpler maintenance schedule
- Improved uptime during winter months
“We were able to maintain a consistent dew point without the need for complex reboilers,” said Lars Erikson, Lead Process Engineer. “It was a win-win.”
Case Study: Shale Gas Wellhead in Texas
In the Permian Basin, a U.S. company retrofitted several wellheads with modular MEG units to handle intermittent production. They noted:
- Faster startup times
- Lower capital expenditure
- Easier glycol handling and storage
These examples show that while MEG may not be suitable for every operation, it offers compelling advantages in the right context.
Advantages and Limitations of Using Ethylene Glycol
Like any technology, ethylene glycol has its strengths and weaknesses.
✅ Advantages:
- Low capital cost
- Simple operation and maintenance
- Effective in moderate dehydration applications
- Less prone to foaming compared to TEG
- Suitable for mobile or temporary setups
❌ Limitations:
- Not ideal for ultra-low dew points (< -40°F)
- Higher viscosity can affect pumpability
- Requires frequent monitoring to prevent degradation
- Environmental concerns if spilled or improperly disposed of
Safety and Environmental Considerations
Ethylene glycol is toxic—not just to humans, but also to wildlife, especially aquatic organisms. Spills can be hazardous, so proper handling and disposal are essential.
Some environmental agencies classify EG as a hazardous substance. Operators must comply with regulations such as:
- OSHA standards for exposure limits
- EPA guidelines for waste disposal
- Local environmental protection acts
Proper containment, secondary spill prevention, and regular training for personnel are crucial.
Future Outlook: Innovations and Alternatives
As the energy sector moves toward greener technologies, researchers are exploring alternatives to traditional glycols. These include:
- Ionic liquids – Highly stable and non-volatile, though still expensive.
- Deep Eutectic Solvents (DESs) – Eco-friendly and customizable, but not yet widely adopted.
- Hybrid systems – Combining glycols with membranes or adsorbents for deeper dehydration.
Still, ethylene glycol remains a reliable, cost-effective option for many operators—especially those in remote or constrained environments.
Conclusion: Sweet Solutions for Dry Gas
Ethylene glycol may not be the flashiest chemical in the industry, but it plays a vital role in keeping natural gas pipelines dry, safe, and efficient. From offshore rigs to inland wells, its unique properties make it a go-to solution for moisture control.
While newer technologies continue to emerge, MEG’s combination of performance, simplicity, and affordability ensures it will remain relevant for years to come. So next time you flip on the stove or turn up the heat, remember: somewhere out there, a little bottle of sweet, sticky glycol might just be saving the day.
References
- Campbell, J. M. (2014). Gas Conditioning and Processing, Volume 2: The Equipment Modules. John M. Campbell & Company.
- Speight, J. G. (2014). The Chemistry and Technology of Petroleum. CRC Press.
- Gary, J. H., Handwerk, G. E., & Kaiser, M. J. (2016). Petroleum Refining: Technology, Economics, and Markets. CRC Press.
- Leffler, W. L. (2008). Offshore Engineering: Design, Construction, and Operation. Gulf Professional Publishing.
- SPE Paper No. 162342 (2012). Comparison of Glycols Used in Gas Dehydration. Society of Petroleum Engineers.
- ISO 13757-1:2018 – Petroleum and natural gas industries — Field testing of corrosion inhibitors — Part 1: General considerations.
- API Standard 14E (2012). Recommended Practice for Design and Installation of Offshore Production Platform Piping Systems.
💬 Got questions or want to share your experience with glycol dehydration? Drop a comment below!
🔧 Need help designing a dehydration system? Let’s connect.
🌍 Stay tuned for more stories from the hidden world of pipeline engineering!
End of Article
Sales Contact：sales@newtopchem.com