NEWS | Nov. 29, 2015

A Bunch Of “Air” Heads – O2N2 Plant

By Mass Communication Specialist Seaman Matthew Riggs

WATERS SOUTH OF JAPAN – Got gas? No, not that kind of gas! Nitrogen (N2) and oxygen (O2) are the two most prominent elements in our atmosphere. N2 comprises 70 percent of air and O2 accounts for 20 percent. Aside from providing the essential molecules needed to breathe, these two gases have many uses aboard a forward-deployed aircraft carrier. In fact, there’s a whole shop dedicated to working with both gases. 

Engineering Department’s A division operates the Oxygen Nitrogen (O2N2) plants aboard the U.S. Navy’s only forward-deployed aircraft carrier USS Ronald Reagan (CVN 76) to provide O2 and N2 services for her more than 5,000 Sailors and 70 aircraft from the embarked air wing, Carrier Air Wing (CVW) 5.    

“Our products are used by a wide variety of departments throughout the ship,” said Machinist’s Mate 2nd Class Javan Millwood, from Antigua, Guatemala. “It is used by AIMD [Aviation Intermediate Maintenance Department], Medical, Dental, as well as the other divisions of Engineering.”      

The O2N2 plant operators use a machine called a producer unit to produce liquid oxygen (LOX) and liquid nitrogen (LIN) from ambient air. They use a process called cryogenic liquefaction to chill the air until the O2 and N2 become liquid and separate due to their differing liquefaction points. 

“We use an air compressor to gather the air that will eventually become LOX or LIN,” said Millwood. “That air is then sent to one of our producer units where it is taken though a reverse exchanger to begin the cooling process. Several absorbers remove the impurities as it is then sent through a turbo expander to cool the air even more. Finally, it is sent through two columns, one at low pressure (LP) and one at high pressure (HP). LOX is generated out of the LP column and LIN from the HP column.”  

According to Millwood, O2 liquefies at negative 297 degrees Fahrenheit and N2 at negative 320 degrees Fahrenheit. He added, once the two have been separated they are transferred to one of two holding tanks.

“We have two plants, forward and aft, with their own holding tanks,” said Millwood. “Once a plant starts to get low, we shut it down so we can start filling it. The other plant is then opened for business until the process repeats.” 

Working with such high quantities of gas at such low temperatures creates a unique hazard for plant operators.

“LOX acts as an accelerant to the combustion process, creating an explosion hazard,” said Millwood. “It’s volatile enough that the heat of compression, such as from stepping in a puddle of it, is enough to trigger an explosion. LIN is an asphyxiation danger because N2 displaces O2 in the air. We work with a lot of LIN in a very small space, so it is very dangerous.” 

“Due to these hazards, we are sent to a “C” school for three months to become cryogenic technicians,” said Machinist Mate 3rd Class Bryan Martinez, from <st1:City w:st="on"><st1:place w:st="on">Los Angeles. “Cryogenics is the study of production and effects of very low temperatures. At school we focus on learning how to operate and maintain the producer units, and familiarizing ourselves with the dangers and safety procedures of working with our equipment.” 

To minimize and control hazards of extremely low temperatures and dangerous gases, plant operators follow a set of rules and guidelines. 

“Whenever we are working with cryogenic liquids, we must obey the two-man rule,” said Martinez. “This means nobody can work alone. We also have special personal protective equipment to keep ourselves safe: gloves, boots and face shields to protect us from the cold, as well as special coveralls. These coveralls don’t have a zipper to negate the spark hazard, and have a single pocket to prevent the gases from being trapped in our clothing.” 

The plant operators transport LOX, LIN, or gaseous O2 or N2 to departments that need it. Their transportation equipment, like their safety equipment, is also highly specialized. 

“We have two methods of transporting our products,” said Martinez. “LOX is moved with an IMU-70, better known as the LOX cart. It’s a large machine built to withstand and maintain the cold that LOX requires, and holds about 50 gallons. We deliver LIN in buckets and supervise the entire process. Gaseous N2 and O2 are pumped into 3,500 psi bottles and stacked in a NAN cart, which holds six bottles at a time.” 

Finally, the O2 or N2 is used by other departments to perform their duties for the ship. 

“LOX and gaseous O2 is generally used as aviation breathing oxygen for pilots,” said Martinez. “O2 is also used by the Medical Department for medical procedures. LIN is used by Engineering to work as freeze sealants or to operate machinery. Gaseous N2 is used for aircraft and tractor tires, or for the welding machines the hull maintenance technicians use.”  

Sailors can breathe easy knowing that the O2N2 plants are gassed up and ready to help anyone who needs to put on airs – oxygen and nitrogen specifically!

Ronald Reagan and CVW-5 provide a combat-ready force that protects and defends the collective maritime interests of the U.S. and its allies and partners in the Indo-Asia-Pacific region.