Nitrogen Generation in an Environmental Testing Laboratory

Belmont Labs, located in Englewood, OH, is an environmental testing facility offering analytical services to clients in industry, civil/environmental engineering, and state and local governments. The laboratory, accredited by both the U.S. EPA and Ohio VAP (Voluntary Action Program), analyzes drinking water, wastewater, soils, and sludge for a variety of compounds including polychlorinated biphenyls (PCBs), pesticides, herbicides, semivolatile and volatile organics, as well as diesel- and gasoline-range organics.

The laboratory prepares samples using two RapidVap extraction systems (Labconco, Kansas City, MO). The evaporation units operate on a steady stream of purified nitrogen, which Belmont Labs was providing with LN2 (liquid nitrogen), dewar cylinders, and smaller compressed nitrogen cylinders. Nitrogen dewars and cylinders took up a lot of space and required constant monitoring so that they could be replaced when running low. In addition, it was inconvenient to switch tanks in and out, especially while in the middle of sample preparation. A good deal of time was spent checking to make sure that tanks were not empty, and changing out those that were.

Another problem was waste, which Belmont wanted to eliminate. Liquid nitrogen is volatile, and as it sits in cylinders or tanks it boils at room temperature. Tanks are vented to release gas and prevent explosions. Belmont was losing about 25% of each 200-gallon cylinder to routine venting, with one dewar lasting about a month.

Replacing tanks

The laboratory began looking for a more effective way to generate the nitrogen necessary for the operation of its two evaporation units. After looking at a number of  nitrogen generators and performing a return-on-investment (ROI) analysis, they settled on a Balston NitroVap-1LV generator (Parker Hannifin Corp., Filtration and Separation Division, Haverhill, MA) obtained from Summit Industries (Dayton, OH) (Figure 1). The ROI analysis indicated that the one NitroVap unit and two Zero Air generators (Parker Hannifin) (purchased to run gas chromatographs) would pay for themselves in less than two years. The annual savings to Belmont Labs by switching to the gas generators is estimated to be $7800.

Figure 1 - Two models of Balston nitrogen generator are available: the NitroVap-1LV, with a flow rate of 180 standard liters per minute (slpm), and the NitroVap-2LV, with a flow rate of 320 slpm.

In addition, generating nitrogen eliminated the safety concerns that accompany storage and movement of compressed gas cylinders. A liquid nitrogen cylinder can explode if not properly vented, and compressed cylinders may become projectiles if the inlet valve is damaged or knocked off.

The compact size and advanced filtering technology of the NitroVap nitrogen generator was also considered during the selection process. The generator provides a steady stream of up to 95% pure nitrogen at between 0 and 150 pounds per square inch, gauge.

One important feature of the generator is the sleep/economy mode, which eliminates compressed air consumption when the evaporators are not in use. In addition, because of their small size (about 10.5 × 14 × 16.5 in. and 53 lb), NitroVap generators can be easily placed on a benchtop or stored beneath a counter (Figure 2). The units are very easy to set up and connect directly to the instruments.

Figure 2 - NitroVap-1LV generator at Belmont Labs installed in an under-counter cabinet.

Instrument operation

Balston NitroVap nitrogen generators employ proprietary technology that uses hollow-fiber membranes to separate compressed air into concentrated nitrogen output and oxygen-enriched permeate streams. The generator connects via a 1⁄4-in. female inlet to the compressed air supply, while the output is attached directly by a 1⁄4-in. outlet to the nitrogen-using equipment. The self-contained unit includes all the controls necessary to perform prefiltration, air separation, and final filtration, as well as inlet and outlet pressure gauges and an outlet pressure regulator for the nitrogen stream.

A coalescing filter located behind the filter access panel prefilters the compressed air, removing contaminants such as liquids and particulate from the air supply, thus protecting the membrane module. A float drain automatically discharges any liquids that accumulate inside the filter housing.

Oxygen and water pass through the hollow fibers of the membrane module at a higher rate than nitrogen; thus the nitrogen that passes through the membrane is extremely pure and dry. A 0.01-μm membrane filter performs final filtration, ensuring clean and commercially sterile nitrogen. The oxygen-enriched permeates exit the membrane module through side ports.

Conclusion

In the Balston NitroVap-1LV generator, Belmont Labs has discovered an efficient way to generate nitrogen in the laboratory. The annual savings in both cost and operator time has been significant, and the generator’s advanced technology and small size make it a valuable addition to the laboratory.

Mr. Allison is Global Product Manager, Filtration and Separation Division, Parker Hannifin Corp., 242 Neck Rd., Haverhill, MA 01835-0723, U.S.A.; tel.: 978-858-0505; fax: 978-858-0625; e-mail: [email protected].

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