How nitrogen or oxygen purity affect their cost
Before examining the impact that the purity of a gas, such as nitrogen (N2) or oxygen (O2), has on its cost, it is important to first clear up a common misconception, which is that gas purity and gas quality are the same thing. They are not. The purity of a gas only refers to its concentration, for example nitrogen with a purity of 95% contains a residual 5% oxygen. Gas quality refers to the additional presence of contaminants. You can read all about gas purity (and quality) in this article.
There are two main ways of obtaining an industrial gas, regardless of whether it is nitrogen or oxygen: Companies can buy it or make their own using a compressor and a gas generator. Purchased gas is always of a very high purity. If gas is self-generated, however, then its purity can be freely chosen.
The cost of purchased gas
For companies that purchase their nitrogen or oxygen, the cost of gas is determined by three main factors:
- Investment costs: Both liquid gas and cylinders require investments in logistics. For example, gas cylinders must have a safe space for storage and installation, and they must comply with local fire safety regulations. Liquid bulk storage on the other hand needs a concrete foundation with fencing.
- Price per unit of gas: Of course, users must pay for the gas they purchase.
- Operating costs: Other operating costs might include cylinder or bulk tank rental, delivery charges, and environmental taxes.
Note that gas purity is not mentioned in the list above. That is because the cryogenic production of nitrogen and oxygen leaves little to no room for flexibility in purity. Purchased gas is always of very high purity, whether or not an application requires it. That means that a large section of users gets (and over-spends for) a purity level for which their application has no use. At the very least, they don’t have the option to lower their cost of gas by tailoring the purity to their needs.
The cost of on-site nitrogen- and oxygen generation
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.
How purity affects gas cost: a comparison
Let's look at two nitrogen applications to illustrate how purity affects the cost of generating your own gas. In our example, wave soldering and coffee packaging need a nitrogen flow of 50 Nm³/h. However, wave soldering requires a purity of 99.999%; coffee packaging a more moderate 99.9%.
Using generic values, this is how much both installations cost over a period of 7 years:
- Soldering with a purity of 99.999%: 30 investment + 50 electricity + 20 maintenance = 100
- Coffee packaging with a purity of 99.9%: 18 investment + 30 electricity + 15 maintenance = 63
That is a difference in gas generation costs of almost 40%! It’s achieved entirely by matching the nitrogen purity for coffee packaging to what it actually needs (a level well above the major food standard requirements), rather than going for the maximum purity.
Investment
Maintenance
Electricity
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.
It pays to get it right
The issue of gas purity most likely affects you too. The vast majority of professional nitrogen and oxygen applications do not require gas with an extreme purity (i.e. the type of purity offered by purchased gas), which makes this an area in which businesses can realize substantial savings. Because tailoring gas purity to your needs is always the optimal and most-efficient solution.
