How is Nitrogen Gas (N2) Produced for Industrial Purposes?

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Nitrogen gas (N2) is a colorless, odorless gas which makes up roughly 78% of the earth&#;s atmosphere.  It is used in industry as a simple asphyxiant with inerting quality making it useful in many applications where oxidation is not desired.

N2 as an industrial gas is produced (generated) by one of the following means:

• Fractional distillation of liquid air (from companies such as Praxair, Air Liquide, Linde, etc)
• By mechanical means using gaseous air:
  • Polymeric Membrane
  • Pressure Swing Adsorption or PSA

 Fractional Distillation (99.999%): Pure gases can be separated from air by first cooling it until it liquefies, then selectively distilling the components at their various boiling temperatures. The process can produce high purity gases but is very energy-intensive.

 Polymeric Membrane (90 &#; 99.9%): Membrane Technology utilizes a permeable fiber which selectively separates the air depending on the speeds of the molecules of the constituents.  This process requires a conditioning of the Feed air due to the clearances in the fiber which are the size of a human hair.

Pressure Swing Adsorption (99 &#; 99.999%): Pressure swing adsorption (PSA) is a technology used to separate some gas species from a mixture of gases under pressure according to the species&#; molecular characteristics and affinity for an adsorbent material. It operates at near-ambient temperatures and differs significantly from cryogenic distillation techniques of gas separation. Specific adsorptive materials (e.g., zeolites, activated carbon, molecular sieves, etc.) are used as a trap, preferentially adsorbing the target gas species at high pressure.

The technology that IFS specializes in is polymeric membrane separation of gaseous air.

Membrane N2 Generation: Feed Air Conditioning

 Feed Filter Coalescers: In every Nitrogen Generation package it is critical that the system be provided with a filtration system that will protect the Nitrogen Membrane from damage and increase its efficiency.  The first two coalescer filters remove incoming moisture up to 0.01 Micron.

Immersion Heater: An Immersion Heater is an essential component due to any liquids that may have migrated past the Coalescer filters.  This heater provides roughly 10°F of superheat to the air, thus insuring no liquids will enter the nitrogen membranes.

Activated Carbon Vessel: Once heated the air will then flow through an activated carbon bed or filter to remove any additional hydrocarbon vapors prior to entering the membranes.

Particulate Filter: A  .01 Micron filter is located downstream the carbon bed as a final step to condition the air prior to entering the membranes.

Nitrogen Membranes

At the heart of the technology are polymeric membrane materials that allow for the rapid passage of one gas while minimizing the passage of others when applying a pressure gradient across the membrane. In this way, the membrane separates O2 and other &#;fast gases&#; from compressed air and generates to generate a high purity N2 stream.

Membrane materials are formed into hollow (tubular) fibers to provide high surface area for high volumetric gas processing rates.

The filters used by IFS have a high operating temperature (up to 180°F) and are PED and DNV certified. N1 or P3 membrane fibers are available with P3 offering the highest recovery of any membrane on the market.

N2 Generation Control Systems

Efficiency is the amount of N2 produced vs. the amount of Feed Air supplied to the Membrane.

Efficiency can be controlled by adjusting following process variables:

• Feed air temperature (produce more at higher temps)
• Feed air pressure (produce more at higher pressure)
• Product oxygen content (more efficient at higher O2 content)

You can monitor the purity of the N2 you are generating by using Oxygen Analyzers (Zirconium Oxide Type or Galvanic Fuel Cell Type). Purity valves work with the Oxygen Analyzer to maintain your set Nitrogen purity. Off-Spec/Product Valve are automated valves that direct flow of N2 product to process or vent.

Although IFS typically uses an Allen Bradley CompactLogix as the central brain for control, IFS has the capability to meet any Project specifications (Siemens, etc.) and HMI (Human Machine Interface) configuration.

 Generated N2 Products & Applications

 Nitrogen Generation

• General Inerting in Oil & Gas Industry
• Food storage & transportation
• OBIGGS (inerting on airplanes)
• Tire filling
• Beverage dispensing
• Marine inerting systems
• Oxygen Enriched Air

Process Gas Separations

• H2 purification in refineries
• Ammonia plant purge recovery
• Syn Gas ratio adjustment
• Helium purification

Dehydration

If you are looking for more details, kindly visit nitrogen compressor manufacturers.

• Low pressure clean dry air
• High pressure inter-stage air dehydration applications
• Natural gas dehydration

More from IFS relating to Nitrogen Generation:

Download: &#;How is Nitrogen Gas Produced&#;  Presentation PDF

Download: Process Flow Diagram (P&ID) Nitrogen Generation Membrane Package PDF

Read about our Skid-Mounted Packages:

Membrane Nitrogen Generation Systems: Modular, Engineered-to-Order, Shipped Ready to Plug In

Nitrogen (N2) makes up 78% of ambient air (20.95% of air is oxygen). N2 is an inert (non-flammable) gas used in industrial plants to prevent undesirable chemical reactions from occurring. Nitrogen is the most common inert gas used in the chemical process industries, due to its high natural abundance and low relative cost.

Major uses of N2 include several in metallurgy: for heat treatments; as an alloy constituent; for scavenging; and as a protective gas; as well as in heat treatment. N2 is also used as an inert gas in shielding and firefighting, in food storage and in processing. Nitrogen can be used in the manufacture of other products, including ammonia.

Most N2 is produced onsite at industrial facilities, for local consumption. However, it may be stored and transported as a gas or a liquid, at cryogenic temperatures. High-pressure cylinders or cylinder clusters can be used for storage and shipping of small quantities of nitrogen gas. Liquid nitrogen can be transported and shipped in specially insulated storage vessels (small quantities) or by road and rail tankers (large quantities).

Production process

The process of recovering N2 from air comprises three major sections: (1) purification; (2) refrigeration; and (3) rectification (Figure 1).

Purification. Initially, the air is purified from dust particles, carbon dioxide and water. This is accomplished by compressing the air, passing it through a heat exchanger (causing water condensation) and then through an adsorbent bed of molecular sieve for the removal of water, carbon dioxide and traces of other impurities.

Refrigeration. At this point, the purified air is cooled down/liquefied, as required for rectification steps downstream. This step is conducted in a plate-fin heat exchanger, using refrigeration values contained in the products (oxygen, nitrogen) and waste (nitrogen) streams.

Rectification. The last step in the process consists in submitting the cooled/liquified air to a fractional distillation carried out in two columns for nitrogen-oxygen separation, operating at different pressures, in such a way that nitrogen is distilled as a vapor and oxygen is obtained as a liquid. In addition, while oxygen and argon have close boiling points, a third column is used exclusively for the removal of that contaminant, vented to the atmosphere.

The main product obtained in the process under analysis here is gaseous, high-purity N2 (the product gas is greater than 99.7% N2), at 60 bars absolute.

Production pathways

Millions of tons of N2 are isolated from atmospheric air every year, through different separation processes that are selected according to the production scale and purity required (Figure 2). The production of large quantities of relatively pure nitrogen is carried out, mostly, through cryogenic distillation. On the other hand, moderate volumes of low-purity nitrogen are commonly produced via pressure-swing adsorption and membrane permeation.

In addition to nitrogen, oxygen (O2) and argon (Ar) can also be generated commercially in air-separation processes using cryogenic distillation and argon recovery units. Oxygen is also produced by vacuum-swing adsorption (VSA).

Edited by Scott Jenkins

Editor&#;s note: Content for this column was originally developed by Intratec Solutions LLC (Houston; www.intratec.us) and is edited by Chemical Engineering. The analyses presented are based on publicly available and non-confidential information. The content represents the opinions of Intratec only. More information about the methodology for preparing the analyses can be found, along with terms of use, at www.intratec.us/che.

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