How to remove moisture from a gas?

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Discussion Overview

The discussion revolves around methods for removing moisture from gases such as hydrogen (H2) and nitrogen (N2) that contain water vapor. Participants explore various techniques, including cooling, absorption, and the use of desiccants, while considering practical applications and limitations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests cooling the gas below zero to condense water vapor, but questions the practicality of this method.
  • Another participant mentions using a liquid nitrogen (LN2) trap or an absorber like a Linde Molecular Sieve, noting that the sieve works best when kept cool.
  • A different viewpoint introduces the use of coalescers to remove gross water contamination from compressed gas systems.
  • Desiccants are proposed as a solution for removing water vapor, with specific mention of molecular sieve desiccants that can achieve low dew points.
  • One participant shares their application involving an electrolyzer, indicating the need for very dry gases for storage in hydrides and accumulators.
  • Another participant recommends zeolite or molecular sieves over silica gel for better moisture removal, emphasizing the importance of keeping the sieve cool.
  • Desiccant dryers are noted to be effective for achieving low dew points, although they can be expensive and may not be available in small units.
  • A participant shares their experience with a refrigeration unit that effectively removes water from their shop air system.

Areas of Agreement / Disagreement

Participants express a range of methods for moisture removal, with no consensus on a single best approach. Various techniques are discussed, each with its own advantages and limitations, indicating that multiple competing views remain.

Contextual Notes

Some methods depend on specific conditions, such as temperature and the presence of contaminants like oil, which may affect the performance of certain drying techniques.

Who May Find This Useful

This discussion may be useful for individuals involved in gas storage, industrial applications, or anyone seeking to understand moisture removal techniques in gas systems.

Topher925
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Whats a simple and easy way to remove moisture from a gas, for example H2 or N2 with some water vapor mixed in it. Do those dryers that you often find on industrial air compressors remove almost all the humidity from the air? The only thing that I can think of is to cool the air below zero, let all the water condense, and then reheat the gas. But this method doesn't seem very practical and I'm wondering there is a better way.
 
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Usual way is cooling, eg LN2 trap if you have some LN2 lying around.
Or an absorber, ( eg Linde Molecular Sieve) the sieve material works best if you can keep it cool and ultimately will saturate and need drying out.
 
Hi Topher. Is this to remove moisture from a flow inside a piping system? If so, you could start with a http://www.velcon.com/cartridges/coalescer.html" . They'll remove gross water contamination. When a gas such as air is compressed, it can't hold as much water (per unit mass) so water often comes out downstream of air compressors and is removed with a coelescer.

You could also use a desiccant which removes water vapor from either a piping system or could be used to remove water from a stationary volume of air. I've also seen http://www.google.com/search?hl=en&q=molecular+sieve+desiccant&aq=f&aqi=g2&aql=&oq=" used in piping systems to bring dew points down to very low levels.

If this is for a house or enclosed volume of air, a dehumidifier will do the job.
 
Last edited by a moderator:
Q_Goest said:
Hi Topher. Is this to remove moisture from a flow inside a piping system?

I guess you could say that. The application is an electrolyzer where I am trying to store H2 in a hydride and O2 in an accumulator. For both gases, the storage mechanisms require the gases to be as dry as possible. I'm thinking of putting some trap inline with the outlet that contains some silica decant which I can periodically remove to dry out.
 
You should get zeolite/mol sieve rather than just silica gel, 5nm power size if normal for water.
It works a lot better if you can keep it cool, doesn't have to be refrigerated but you don't want it just above the compressor motor.

You might want a simpler filter first if you think you will have oil from the compressor - oil kills mol sieve.
Drying it out is just a case of putting it in a regular warm oven (>100c) for an hour and putting it back in while still hot.
 
Desiccant dryers will get air down to a -40 dew point. They do work but are expensive. I don't know of any small units.
 
we have a refridgeration unit on our shop air
it works very well
the compressors are outside and we never have any water in the system in house(houston always has high RH, so that is saying something)

dr
 
lot of dryers at mcmaster -carr
ttp://www.mcmaster.com/#air-dryers/=60xozw
 

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