Author
Bruce Peat

Published
21st July 2016

Choosing laboratory gas generators: How to decide

When it comes to deciding which gas generator is best for your lab there are some considerations lab managers must make. There are two main technologies used to generate nitrogen from air: membrane and Pressure Swing Adsorption (PSA).

As a result of selective permeation across the membrane wall, nitrogen is separated from atmospheric air. Gases that are "fast" (oxygen, carbon dioxide, and water vapour) permeate the membrane wall much faster than gases that are "slow" (nitrogen).

In the selective permeation process across the membrane wall, nitrogen is separated from the atmospheric air source. The original gas mixture is separated into two streams: the permeate and the product. As a result of the permeation process, oxygen, carbon dioxide, and water vapour are combined and vented.

 

 

 

Membrane gas generator

Membrane technology illustration

The lower the flow rate passing through the membrane the higher the purity of nitrogen is achieved. The purity can be further enhanced by increasing the temperature.

The other option, Pressure Swing Adsorption, cycles gas at high and low pressure, flushing compressed air through a bed of carbon beads, also known as a Carbon Molecular Sieve. Nitrogen molecules are allowed to pass through the carbon bed but the oxygen and carbon dioxide molecules are too large to pass through and are vented off. PSA generators can be scaled up to provide very large quantities of nitrogen gas for entire labs or for manufacturing and process industries.

PSA-nitrogen generator Peak Scientific

PSA technology illustration

So which generator should you choose? The decision comes down to the purity required. For labs needing 99.5% purity and above, PSA is the optimum choice but for labs with lower purity requirements membrane generators are far more cost effective. When it comes to choosing your gas generator the cost is directly correlated to the purity, the more purity required, the more the generator will cost.

The final consideration a lab must make is whether they require a compressor based system or not. If a lab has an in-house supply of high quality compressed air a compressor less generator will be suitable, if not a compressor based system will be needed.

Compressor based systems feature moving parts and are therefore subject to general wear and tear over time and will require servicing at regular intervals. A service contract comes highly recommended for labs with this equipment in order to avoid unplanned costs should a breakdown occur. Generators without compressors do not contain moving parts and therefore their service requirements are dramatically reduced in cost and frequency.

Still unsure?    

 

Source: Lab manager

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