How is Nitrogen Gas (N2) Produced for Industrial Purposes?
July 22, 2015 leem0
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.
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
- 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
- Low pressure clean dry air
- High pressure inter-stage air dehydration applications
- Natural gas dehydration
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