How nitrogen and oxygen purity affect costs

Before we explore how nitrogen (N₂) and oxygen (O₂) purity levels influence their costs, it’s important to clarify a common misconception: gas purity and gas quality are not the same. 

• Gas purity refers to the concentration of the main gas (e.g., nitrogen at 95% purity contains 5% oxygen). 
• Gas quality refers to the presence of contaminants such as moisture or hydrocarbons.

Managing nitrogen and oxygen purity levels directly impacts gas costs and allows companies to optimize expenses. Higher purity gases cost more to produce because they need more compressed air, more energy, and larger equipment. By tailoring the purity to your actual application needs, you can save significantly on investment, maintenance, and operating costs.

There are two main ways to acquire industrial nitrogen and oxygen:

Read more about the different ways of getting nitrogen gas.

There are two common technologies for generating nitrogen and oxygen on-site:

• Pressure Swing Adsorption (PSA): Compressed air passes through molecular sieves to produce nitrogen up to 99.999% purity and oxygen up to 95% purity.

• Membrane technology: Compressed air is filtered through semi-permeable membranes, generating nitrogen purity between 95% and 99.5%.

Although the difference between 99.9% and 99.999% purity may seem small, it has a significant effect on costs.

Energy consumption and equipment scaling

Producing higher-purity gas requires more energy-intensive processes. For example, nitrogen generation at 95% purity via membrane technology may consume 2 SCFM of air per 1 SCFM nitrogen, whereas achieving 99.999% purity with PSA can require up to 12 SCFM air per 1 SCFM nitrogen. Higher purity also demands larger compressors and more advanced equipment.

To optimize your gas costs, you can conduct a cost-benefit analysis considering:

• Your application’s minimum purity requirements.
• Investment and operating costs for different purity levels.
• Potential savings from using lower-purity gas without compromising quality.
• Energy consumption and maintenance expenses.

This analysis helps identify the ideal balance between purity and cost for your specific needs.

For companies that purchase their nitrogen or oxygen, the cost of gas is determined by these factors:

• Investment costs: Infrastructure for safe storage, such as secure cylinder areas or concrete foundations for bulk tanks, including compliance with fire safety regulations.

• Price per unit: The price you pay for each cubic meter of gas.

• Operating costs: Expenses like cylinder or tank rental, delivery fees, and environmental taxes.

• Investment costs: Purchase of the gas generator, compressor, air treatment equipment, and storage tanks.

• Operating costs: Electricity for running compressors and routine maintenance.

Key takeaway

Purchased gases are almost always supplied at ultra-high purity due to cryogenic production methods. This means many users pay for more purity than they need — with no option to adjust costs. On-site generation avoids this by letting you match purity to the application.

Most on-site gas generators use one of two technologies, which are summarized belowbut are described in greater detail in these articles about PSA and membrane echnology.  

• Air separation through Pressure Swing Adsorption: By running compressed air through a bed of molecular sieves, nitrogen purities of up to 99.999% and oxygen purities of up to 95% can be achieved.
• Air separation through membrane technology: By running compressed air through semi-permeable membranes, nitrogen purities between 95% and 99.5% can be generated.

While it may not seem like a big step between, for example, 99.9% and 99.999% purity, the difference is quite large with regard to costs. Let’s break down that equation…

Two factors make up the cost of on-site generators:

• Investment costs: Users must buy a gas generator as well as a compressor to supply the generator with feed air. The compressed air installation must include the required air treatment equipment and storage tanks.
• Operating costs: These costs consist of the electricity needed to run the compressor and maintaining the entire installation.

By matching the gas purity to the specifications of an application, companies that generate their own gas on-site can improve their bottom line in two ways:

• They can lower their investment costs by buying a smaller generator and compressor.
• As a result, they will also reduce their operating costs because using a smaller compressor uses less energy, which also leads to a lower carbon footprint.

Let’s examine two nitrogen applications to illustrate how purity impacts the cost of generating your own gas. In our example, wave soldering and coffee packaging both require a nitrogen flow of 50 Nm³/h. However, wave soldering necessitates a purity of 99.999%, while coffee packaging requires a more moderate purity of 99.9%.

This results in a difference in gas generation costs of 37%. This savings is achieved by matching the nitrogen purity for coffee packaging to its actual needs, which is well above major food standard requirements, rather than opting for the maximum purity level.

First, not overspecifying purity has a huge effect on investment costs as companies can meet their needs with a smaller generator and a smaller air compressor. In turn, this smaller system comes with lower maintenance costs. It also needs less compressed air to produce 1 unit of gas, which means lower energy costs.

Choosing the right purity level means:

• Lower investment: Smaller generators and compressors cost less upfront.
• Reduced maintenance: Smaller systems require less upkeep.
• Energy savings: Less compressed air is needed per unit of gas, lowering electricity bills and carbon footprint.