How to Size a Natural Gas Dehydration Unit for Your Processing Plant

When designing or upgrading a gas processing facility, selecting the right natural gas dehydration unit isn’t just a matter of checking flow rates and moving on. The wrong choice can result in unnecessary downtime, off-spec gas, or wasted operational costs. For seasoned engineers and operators, proper sizing comes down to one key goal: consistently meeting moisture specifications under real-world plant conditions.

Here’s a breakdown of what really matters when choosing the right natural gas dehydration unit for your plant.

1. Define Your Flow Capacity and Dew Point Target

Your starting point should always be how much gas needs to be processed, and how dry it needs to be.

Typical dehydration units must remove water to achieve outlet gas dew points of 7 lbs of water/MMSCF for pipeline specs or fuel gas applications. For cryogenic or LNG-related processes, this could go as lower °, requiring a more specialized setup

Sizing tip:

Reference the gas stream’s inlet water content, which depends on pressure and temperature. Use resources like the GPSA Engineering Data Book to determine how many pounds of water need to be removed per MMSCFD.

For example, at 1000 psig and 80°F, untreated gas can contain 70–100 lbs of water per MMSCFD. A dehydration unit must be sized to consistently remove that, even during peak load or humid conditions.

2. Don’t Just Match Average Load—Plan for Variability

Overdesigning a unit can be wasteful, but under-sizing is far worse. It leads to desiccant exhaustion, poor regeneration cycles, or glycol slippage (in TEG systems).

Facilities with seasonal demand swings or variable upstream flow should size for maximum expected flow rate, not just daily average. This ensures water content specs are met even when throughput spikes.

For regenerative desiccant systems, make sure bed volume supports the moisture load with a reasonable regeneration frequency. For TEG systems, size your glycol circulation rate to match expected water removal—roughly 3–4 gallons of TEG per pound of water is a common industry benchmark.

3. Consider Inlet Pressure, Pressure Drop, and System Losses

Pressure matters. At higher inlet pressures, natural gas holds less water vapor, which often improves dehydrator efficiency. But pressure drop across the unit must be minimized—especially in low-pressure gathering systems or fuel gas skids.

Desiccant/Regenerative dryers using pressure swing adsorption (like twin-tower systems) will also require purge gas during regeneration—typically 10–15% of flow. That’s not insignificant, so be sure to factor purge loss into total gas availability when specifying unit capacity.

For example:

If your plant runs at 500 SCFM and the dryer has a 15% purge rate, your effective output is ~425 SCFM. Sizing your unit without accounting for this would lead to chronic underperformance.

4. Match the Unit to Your Environment and Maintenance Preferences

In classified hazardous areas, such as Class 1 Division 1 zones, explosion-proof dehydrators like the HLSXG are the go-to when low water content/dewpoints are required. They eliminate ignition risks, require no reboilers, and route purge vapors safely to a flare or recovery system.

Plants in remote areas often prefer regenerative desiccant systems with automatic cycling and low voltage control options, allowing for unattended operation.

Compare that to TEG units, which involve pumps, reboilers, and potential VOC emissions—viable, but more maintenance-heavy. In either case, always check ASME ratings, instrumentation compatibility, and service accessibility.

Get the Size Right

A well-sized natural gas dehydration unit does more than just dry gas—it prevents hydrate blockages, protects downstream equipment, and keeps your product on-spec day after day. Getting the size wrong can result in higher energy use, missed moisture targets, or costly interruptions.

Whether you’re working with fuel gas lines, pipeline injection systems, or conditioning gas for NGL recovery, thoughtful sizing backed by real field data makes all the difference.

To explore dehydration solutions that align with your plant’s pressure, flow, and performance goals, visit Air Vacuum & Process, Inc. and see how their systems can fit into your gas processing operation.

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