Nitrogen Purging Systems (NEPS) Theory & Characteristics

NITROGEN CHARACTERISTICS

Nitrogen is colorless, odorless, tasteless and inert gas and presents a particular danger of asphyxiation.

HOW IS DRY NITROGEN USED FOR PURGING?

Dry nitrogen can be supplied to equipment for through purging (venting of purge gas) or the more effective single point pressure purging (NEPS).

WHY USE NITROGEN?

Nitrogen is generally a reliable dry gas, which is economic, safe (when handled properly) and chemically inert with most metals and materials.

WHAT IS NITROGEN PURGING?

A method of means of removing the moisture/water vapor and oxygen to create a dry environment within equipment or a system.

SOURCES OF NITROGEN

Dry nitrogen can be supplied from bottles, cryogenic factories or nitrogen generators.

USES FOR NITROGEN

In the early years of air separation, oxygen was the most sought after component for use in the steel industry. This situation began to change when nitrogen was no longer considered a waste product and its inert properties could be exploited as a blanketing gas. Today, nitrogen is used in a host of applications, including:

  • Blanketing of tanks with flammable or toxic materials
  • Blanketing of metal reduction processes
  • Purging process equipment
  • Medical applications
  • Soil freezing prior to excavation
  • Food freezing
  • Finishing of rubber goods
  • Cooling in helium or hydrogen plants
  • Freeze grinding
  • Fragmentation of scrap metal
  • Electronics Industry


Purging and blanketing are probably the most popular uses of nitrogen gas. Tanks filled with hydrocarbon liquids have vapor space in the top of the tank, which collects hydrocarbon vapors. In atmospheric tanks, air can be drawn in when emptying the tank and it would be easy to ignite this by static electricity or friction. Purging the vapor space with nitrogen prevents this.

HOW DRY IS DRY NITROGEN?

Bottled nitrogen is often specified as dryer than 2 ppm (parts per million) equivalent to a dew point of -94°F (-70°C). The gas source for drying should always be validated before use. As a rule of thumb the gas must be at least 10°C lower than required purge dryness.

Molecular Weight 28.01
Boiling Point -319.9°F (-195.5°C ) at 14.7 psi (101.3 kPa)
Specific Volume 13.72 ft.3 lbs.-1 (0.855 m3 kg-1 at 68°F (20°C), 14.7 psi (101.3 kPa)
Critical Temperature -232.5°F (-146.95°C)
Critical Pressure 493 psi (3,400 kPa)
Heat Capacity .249 BTU lbs.-1 °F-1 (1,040 Jkg-1 K-1) at 77°F (25°C), 14.7 psi (101.3 kPa)

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