Due to its inertness, gaseous nitrogen can be used for various blowing, covering, and flushing operations. Depending on the type of process involved, different levels of nitrogen purity are required to meet unique manufacturing needs.
What is nitrogen purity?
Nitrogen purity refers to the proportion of nitrogen present in the sample taken from its flow compared to the impurities present. According to the ratio of pure gas to pollutants such as oxygen, water vapor, carbon monoxide, and carbon dioxide, nitrogen can be classified as high purity or low purity.
This classification based on nitrogen concentration plays a crucial role in determining the applicability of nitrogen to any industrial process.
High purity and low purity nitrogen gas
The purity of nitrogen samples is determined by the percentage/concentration of pure nitrogen present. For gases classified as high-purity, they must contain at least 99.998% nitrogen, while lower purity nitrogen typically contains a higher proportion of impurities.
High-purity nitrogen
Gaseous nitrogen with a concentration higher than 99.998% is considered a high-purity fraction. High purity nitrogen can be classified in different ways by different manufacturers, but they are mostly considered as “zero grade” fractions. Zero grade high-purity nitrogen is classified as such because it contains hydrocarbon impurities below 0.5 parts per million.
The other main characteristics of high-purity nitrogen are:
- Oxygen concentration ≤ 0.5ppm
- Carbon monoxide/carbon dioxide not exceeding 1.0 parts per million
- Moisture content not exceeding 3 parts per million
- Low purity nitrogen gas
- Nitrogen with a purity of 90% to slightly less than 99.9% is considered low purity.
Nitrogen purity classification
The classification of pure nitrogen is achieved through a grading system using the numbers within each lowest purity level. The first number of each level refers to the number of “nine” that appear in it, while the second number represents the number after the last nine numbers.
The pure nitrogen classification includes N2.0, N3.0, N4.0, N5.0, N6.0, and N7.0.
What is ultra-high purity nitrogen?
Ultra high purity nitrogen refers to nitrogen gas with a concentration of 99.999% and negligible impurities. The nitrogen specifications are strict, and changes result in invalid classification.
The oxygen content of the gas shall not exceed 2 parts per million by volume (ppmv), the total hydrocarbons shall not exceed 0.5 parts per million by volume, and the moisture shall not exceed 1 part per million by volume. Nitrogen is commonly used for scientific applications.
What is anaerobic nitrogen?
Anaerobic nitrogen is defined as gaseous nitrogen with an oxygen content not exceeding 0.5 parts per million. The purity of OFN gas is usually maintained at 99.998%. This level of nitrogen can be used for scientific research and calibration processes, during which oxygen impurities may alter the results or lead to incorrect outcomes.
Nitrogen purity levels classified by industry/application
As mentioned above, the nitrogen concentration required for different industrial processes varies greatly. The key consideration for selecting nitrogen grade is the impact of impurities on the selected application. Sensitivity to moisture, oxygen, and other pollutants is a key factor to consider.
Food grade nitrogen/beverage grade nitrogen
Nitrogen is commonly used in different steps of food/beverage production, packaging, and storage. Nitrogen in food packaging and processing is used to maintain the shelf life of processed foods/beverages by eliminating food oxidants, preserving flavor, and preventing spoilage. The purity required for food grade nitrogen is usually between 98-99.5%.
Pharmaceutical grade nitrogen
The pharmaceutical manufacturing process requires high purity to prevent contamination and alteration of the final product. Many drugs require high-grade nitrogen gas with a purity between 97-99.99%. This high to ultra-high purity nitrogen is used to cover storage tanks, containers, and other pharmaceutical manufacturing equipment with nitrogen.
High purity nitrogen is also used in drug packaging to help maintain freshness and prevent active ingredients from spoiling.
Gas nitrogen with a purity of 95-99% can be used in the oil and gas industry to reduce the risk of fire and explosion during related processes. Inerting chemical storage tanks and purging pipelines with gaseous nitrogen can help minimize the risk of sudden combustion of their contents.
Pipeline maintenance services often use pressurized nitrogen for pipeline cleaning and pipeline decommissioning processes.
Industrial nitrogen grade purity
Below is an overview of some industrial applications and their nitrogen level requirements.
Electronic and semiconductor manufacturing grade nitrogen gas
The typical nitrogen content requirement in electronic and semiconductor production is usually at least 99.99% to 99.999%. Some processes such as part cleaning and adhesive covering use lower concentrations of nitrogen gas (95-99.5%).
Plastic manufacturing grade nitrogen
The nitrogen grade requirements for plastic synthesis are 95-98% for injection molding process, 99.5% for gas assisted injection molding process, and 98-99.5% for blown film extrusion process.
Metal processing grade nitrogen gas
The nitrogen content of metal processing grade varies greatly, ranging from 95-99% for heat treatment to 99-99.999% for laser cutting processes.
Power generation grade nitrogen
The power generation processes such as gas seal blowing, boiler laying, natural gas pipeline blowing, and softened water covering require nitrogen with a purity between 95-99.6%.