Purity Specified in Industrial Applications

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Purity Specified in Industrial Applications

Although on site nitrogen generation can produce N2 purities of up to 99.999%, users can realize significant financial and energy savings if they match the purity of the nitrogen to the purity required by the application. Indeed, for many applications, a purity of 99.9% or above is not required.

Nitrogen serves to extend shelf life and preserve flavor, color and aroma in food and beverage products ranging from snack food packaging, coffee packaging and wine bottling. A purity level between 98-99.5% is specified for most products. Packaging of many products is filled with nitrogen, an odorless and tasteless addition. Products can undergo longer shipping distances without a loss of flavor when the oxygen is replaced with nitrogen in the packaging. Nitrogen is occasionally mixed with CO2 or small amounts of O2 to create a modified atmosphere packaging to inhibit specific bacterial growth in meats, fish or poultry. Other products, such as edible oils are blanketed with nitrogen to prevent oxygen from inducing rancidity. In wine production, nitrogen is used both in the blanketing of the fermenting stock and in bottling. Bottles are purged with nitrogen, filled with wine and topped with more nitrogen before corked.

The metals industry values nitrogen for a wide variety of purposes. In aluminum degassing, the molten metal is sparged with nitrogen, pushing out hydrogen which can cause gaseous occlusions. In aluminum extrusion, the inert nitrogen prevents the formation of oxides. Laser cutting employs nitrogen to blow off dross and minimize oxidation at the cut, while a laser bellow is purged so the dust is removed from the mirrors and H2O and CO2 is cleared, preventing the absorption of laser energy and blurring the cut. Heat treating metal needs an inert atmosphere such as nitrogen. Purities range from 97% for aluminium degassing to 99.5% or higher for heat treating and aluminium extrusion. For laser cutting, purities of nitrogen can be as low as 99.95% or lower depending on the material and thickness being cut.

Oil and gas and the petrochemical industries face safety concerns, well served by the inert properties of nitrogen. Levels of purity in these industries are usually between 95-99%. Fire prevention and explosion blanketing successfully removes the oxygen with the introduction of nitrogen. Chemical tanks are often blanketed with nitrogen to prevent fire or explosion. In upstream and midstream areas of the oil and gas industry there are multiple uses, from the cleaning and inspection of pipes to the pressurization of riser tensioners, used to maintain stability in a floating or tethered rig. Within a pipeline, gas seal turbines are often sealed using a cushion of nitrogen. The nitrogen prevents natural gas leakage and suppresses the risk of fire should any slight leak occur.

The pharmaceutical industry relies on the inert properties of nitrogen to assure safety and sterility in the chemicals and packaging, with an average purity level of 97-99.99%. In product transfer, nitrogen is used to purge receptacles to eliminate contamination.

Chemical blanketing, with nitrogen, assists with the stability of the final pharmaceutical product. Sealed packaging is infused with nitrogen to maintain freshness of the drugs. Deionized water, used throughout pharmaceutical processes, is blanketed to assure a constant pH by preventing exposure to CO2.

The development of plastics requires both the low dew point drying and inert properties of nitrogen for molding and extrusion processes. Nitrogen purities range from 95-99.5% in this industry. In injection molding, purging of the pellet hoppers and the prevention of carburization on the screw is achieved with nitrogen introduction. In gas-assist injection molding, pressurized nitrogen assists in packing out the part and eliminates shrinkage.

Blown film extrusion uses nitrogen for both purging and spray drying products.

The Power generation industry is highly safety and maintenance conscious. Nitrogen assists in removing oxygen and preventing corrosion. During boiler cycling, the proper layup of the Heat Recovery Steam Generator (HRSG) includes nitrogen to avoid corrosion and pitting of the boiler, following ASME guidelines. A boiler that has been powered down is both blanketed and sparged with nitrogen to prevent corrosion. Nitrogen is often used to blanket and sparge demineralized water tanks to prevent CO2 contamination of demineralized water. Purging natural gas lines with nitrogen allows repairs or valve installations without fire concerns. Across the field of power generation, nitrogen purity is usually between 95- 98%, with up to 99.6% in boiler layup.

In the Electronics Assembly industry, nitrogen is used to keep solder clean and soot free especially in the selective solder and wave solder processes. Purities in this industry can be as high as 99.999%.

Other applications for nitrogen use are in diverse fields where its inert properties and purging of oxygen is needed. Coal or other mines can be partitioned off and filled with nitrogen to purge oxygen and prevent explosions. Automotive paint blanketing and paint spraying with nitrogen speeds drying and improves product finish. Museum artifacts and antiquities are often stored in a nitrogen atmosphere to preserve and protect their surfaces.

Conclusion

In the majority of industrial applications, a nitrogen purity of 99.9% or above is not needed to achieve the benefits nitrogen provides. Specifying a purity of that level may unnecessarily add to the cost of production, and the amount of energy needed to create and transport the nitrogen which impacts CO2 emissions. In the purchase of bulk nitrogen, manufacturers must consider safety in handling cylinders, the potential of delivery delays, additional truck traffic to and from the manufacturing site, as well as the environmental impact.

On-site PSA and membrane systems are energy efficient and cost effective, requiring only enough energy to power the air compressor that supplies air to the system. Gas industry sources indicate that an air separation plant uses 1976 kJ of electricity per kilogram of nitrogen at 99.9% purities. At a purity of 98 percent, the energy required for on-site nitrogen plant consumes 62 percent less energy. Even for those applications requiring 99.9% purity, generating nitrogen on-site on-demand with a PSA system will use 28 percent less electricity compared to supplied bulk nitrogen.

The table below list the typical Nitrogen Purity Levels by the different industries

Nitrogen concentration or purity is defined in a percentage. The percentage represents 100% minus the oxygen content. The specified nitrogen is the inert gas content and will include Argon. For example, 98% nitrogen represents 2 % oxygen and the balance inert gases, i.e. nitrogen and argon.

Note : Each customer should determine the nitrogen purity which best suits their applications
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