Gas dryers (Nafion)
Selective drying for highly accurate gas measurements
Nafion® dryers are the industry standard for selectively removing water vapour from gas streams without affecting other gas components. They are used worldwide in emission measurements, laboratories, medical systems and OEM applications where a stable moisture balance is crucial.
How does a Nafion® dryer work?
The core of a Nafion® dryer is a special ionic polymer (Nafion®) with unique selective permeation properties. The drying principle works as follows:
- The humid gas flows through a tube or membrane of Nafion®.
- Nafion® only lets water molecules through, because water is attracted and absorbed by the sulphonic acid polymer.
- The water diffuses through the membrane wall and is removed on the outside by a purge gas stream or dry environment.
- The other gas components (such as NOx, SO₂, CO₂, NH₃, VOCs) are fully retained.
First-order kinetic reaction: extremely fast drying response
Nafion® removes water according to a first-order kinetic reaction. This means:
- The rate of water transport depends directly on the difference in water activity (moisture concentration) between the inside and outside of the membranes.
- As a result, equilibrium is reached very quickly, usually within milliseconds.
- The drying process adapts immediately to changing moisture loads, without the delay or inertia of coolers or absorbers.
Practical advantage:
Even rapidly fluctuating moisture levels are neutralised immediately, providing crucial stability for gas analysers.
Main advantages of Nafion® drying
- Selective removal of water vapour without affecting other gas components
- Equilibration in milliseconds thanks to first-order kinetics
- No condensation in analyser lines
- High chemical resistance to acids, bases and corrosive gases
- Fast response time and very stable measurements
- Low maintenance and long service life
Difference between BE, MD and PD drying systems
Although all models use the Nafion® membrane principle for water removal, they differ in construction, operation and field of application.
Key specifications
| Series | Description | Key specifications |
|---|---|---|
| BE (Braided Exchanger) Series | Compact dryer for standard gas streams. Robust and low-maintenance design. | Flow up to 4 l/min · 80 °C · 80 psig |
| MD (Monotube Dryer) Series | Single-tube dryer with high drying capacity for laboratory and CEMS. | Flow up to 4 l/min · 100 °C · 80 psig · Dew point down to –40 °C |
| PD (Polytube Dryer) Series | Parallel tubes for higher gas flows. Short residence time and high efficiency. | Flow up to 40 l/min · 100 °C · 30 psig · Dew point down to –40 °C |
| BE-HP (High Pressure) Series | For high-pressure systems up to 17 bar. Same operation as the BE series. | Flow up to 4 l/min · 50 °C · 250 psig |
| MDH (Heated Monotube Dryer) | Heated version of the MD series, prevents condensation with humid samples. | Flow up to 1.5 l/min · 80 °C sample · 30 psig |
| DM (Desiccant Membrane Dryer) | Compact, portable dryer for mobile measurement setups. | Flow up to 4 l/min · 80 °C · 80 psig |
| MRD (Monotube Rotating Dryer) | Adaptable design with various purge and connection options. | Flow up to 4 l/min · 100 °C · 80 psig |
BE series: braided exchangers
Principle: Nafion® tubing is woven and placed in a housing that exposes the gas stream to the ambient air.
Purge gas: No external purge gas source needed; the water vapour diffuses directly into the ambient atmosphere.
Use: Simple and low-maintenance drying solution for low to medium flow rates and applications where fast, passive drying is sufficient.
Advantages: No extra hardware or purge gas; extremely fast equilibration (typically within ~100–200 ms thanks to the first-order kinetic behaviour).
Typical for: gas detection systems, analytical instruments and applications where space and utilities are limited.
MD series: monotube dryers
Principle: A single Nafion® tube forms the drying section.
Purge gas: Requires an external dry purge gas stream flowing counter-current around the Nafion® tubing to remove moisture effectively.
Use: Reliable drying down to low dew points (down to approx. −40 °C) for laboratory, CEMS and process monitors.
Advantages: Very efficient drying with controlled purge gas flow; suitable for standardised gas analyses.
Typical for: analytical systems, emission and process monitoring where condensing moisture must be minimised.
PD series: polytube dryers
Principle: Several Nafion® tubes are placed in parallel in one housing; this increases the membrane surface area.
Purge gas: external purge gas stream as with the MD, but the larger membrane surface makes it particularly suitable for higher flow rates.
Use: High-capacity drying with low pressure drop and more efficient drying with larger gas flows.
Advantages: Up to tens of litres per minute possible, faster response thanks to a shorter sample path and more surface area.
Typical for: industrial gas conditioning, continuous emission monitoring and use cases with higher flow rates than standard monotube applications.
| Model series | Max. Flow (L/min) | Typical dew point achieved | Purge gas needed? | Application |
|---|---|---|---|---|
| BE (Braided Exchanger) | Up to approx. 4 L/min (passive release to ambient air) | ~ -20 °C to -40 °C (depending on environment & purge) | No | Compact systems, laboratory, OEM |
| MD (Monotube Dryer) | Up to 4 L/min (for monotube models) | Down to approx. -40 °C dew point (with sufficient purge gas) | Yes | Analytical gas conditioning, CEMS |
| PD (Polytube Dryer) | Up to 40 L/min (depending on model: 10/20/40) | Down to approx. -40 °C dew point (with sufficient purge gas) | Yes | High flow rates & industrial applications |
Frequently asked questions (FAQ) about Nafion® dryers
1. What is a Nafion® dryer?
A Nafion® dryer is a gas conditioning module that selectively removes water vapour from a gas stream without affecting the other gas components. The technology is based on an ionic membrane that only lets water molecules through.
2. How exactly does a Nafion® dryer work?
Nafion® removes water via first-order kinetic permeation, in which water molecules diffuse through the membranes extremely quickly. This means equilibrium is reached within milliseconds, even with varying moisture loads. The other gas components remain unchanged.
3. What is the difference between BE, MD and PD Nafion® dryers?
- BE series: passive drying to ambient air, no purge gas needed, up to approx. 4 L/min.
- MD series: monotube dryer with external purge gas stream, dew points down to −40 °C, up to approx. 4 L/min.
- PD series: multitube dryer for high flow rates, up to 40 L/min, also down to −40 °C dew points.
4. Do I need purge gas for my Nafion® dryer?
Only the BE series works without purge gas.
The MD and PD series require a dry purge gas stream to remove moisture effectively.
5. What dew points can Nafion® dryers reach?
With a correct purge gas configuration, MD and PD dryers can reach dew points down to approx. −40 °C.
BE dryers depend on the environment, but usually achieve −20 to −40 °C.
6. Are Nafion® dryers suitable for corrosive or acidic gases?
Yes. Nafion® is highly chemically resistant and suitable for many industrial and emission applications where gases such as SO₂, HCl, H₂S and NOx occur. Only ammonia can cause clogging or damage.
7. Can I integrate a Nafion® dryer into an OEM system?
Yes, Nafion® dryers are often used in OEM gas analysers, measuring instruments and compact analysis cabinets.
8. How do I choose the right Nafion® dryer?
Selection is based on:
- gewenste flow (L/min)
- required dew point reduction
- availability of purge gas
- available installation space
- chemicals and temperatures in the gas stream
Inacom Instruments helps with complete selection and sizing.
9. Are Nafion® dryers low-maintenance?
Yes. They contain no moving parts, do not need replacing like adsorption materials and only require cleaning of connections or housing if contaminated.
10. Which industries use Nafion® dryers?
Common applications include:
- emission measurements (CEMS)
- hydrogen and energy industry
- chemicals and petrochemicals
- laboratoria & R&D
- medical gas analysis
- OEM measuring systems
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