Nitrogen Enhanced Purging Systems (NEPS) Technical Information



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)

 



NEPS 1000 Leak Testing

Leak testing can be carried out to ensure the suitability of the equipment for pressurized purging. The default pressure test setting is 2.5 psi.

Leak testing with the NEPS nitrogen purge system is a simple operation and has a sensitivity which is related to pressure degradation against time. The NEPS nitrogen purge system has a display resolution of 0.01 psi allowing users to achieve high sensitivities depending on the monitored time for the equipment under test to degrade from the initial test pressure.

The equipment volume must be considered when calculating actual leak rate.

Pressure Degradation GraphTypical sensitivities for NEPS 1000 are:

60 Minutes to degrade by 0.01 psi
1,000 cc volume = 1.9 x 10-4 cc/second
10,000 cc volume = 1.9 cc x 10-3 cc/second


Caution: Leak testing must be conducted with a stable/constant ambient/equipment temperature.  A variation of 3.6°F (2°C) can cause up to a 0.1 psi change in pressure.




NEPS Frequently Asked Questions

Why is it called an "enhanced" purging system?
The single point purge of the NEPS 1000 is superior to a standard two point purge as it uses the nitrogen, or dry gas, more efficiently, thereby purging the equipment more quickly and sparing the additional expense of wasted gas. The single point feature of the NEPS 1000 also provides a dew point temperature measurement for the gas stream leaving the equipment.

Is this available in a rack mounted version?
Yes. It is available in a 19" rack mounted version ("NEPS 1900 Racked") for use in automated test situations.

What types of connectors are available?
The NEPS 1000 comes standard with male and female quick disconnect. The female will need to be adapted to your nitrogen line and has a 1/4" NPT female thread to connect to.

Do I need a nitrogen source for this unit to dry out my enclosure?
The standard NEPS 1000 and NEPS 1900 Rack Mount models require nitrogen or other dry air source. The "NEPS 1000 Pumped" has a bed of molecular sieve desiccant that dries the incoming air prior to sending it into your enclosure, and does not require a dry air source. This is particularly useful in field use where it might be cumbersome to have a bottle of high pressure nitrogen on hand. However, periodically, the molecular sieve desiccant will need to be replaced. AGM carries a full line of desiccant products and can supply replacement desiccant for NEPS units.

Do I need to use nitrogen gas with NEPS 1000?
No. The NEPS 1000 can be used with nitrogen, dry air, argon, and SF6 gases. It should be noted that dry gases are available in varying qualities and levels of dryness. (No flammable gases should be used)

What is the dew point display range of the NEPS?
The NEPS will display a dew point range of +20°C (+68°F) to -80°C (-112°F).

Does the NEPS 1000 require an operator to turn the equipment on and off?
No. After initial setup, the NEPS 1000 will automatically stop the dry gas cycling when the air stream leaving the equipment reaches a preset dew point temperature. With the addition of a remote sensor, the dew point stat feature of the NEPS 1000 will then resume dry gas cycling after the dew point temperature has degraded to a predetermined amount.

Is this cycling important?
Yes. After repeated cycles it will become apparent when the moisture has been removed from the hygroscopic materials in the equipment. It is a common misconception that the majority of the moisture in sealed equipment is contained in the empty volume of air. In fact, the majority of the moisture is contained in the hygroscopic materials, such as electrical boards and plastic components.

Can I lease a NEPS unit?
Yes. You can lease a NEPS unit so you can test it for your specific applications, contact AGM for more information.