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Cost Effective Low Purity Nitrogen for Aluminum Degassing

16-May-2016

Gas companies typically supply nitrogen at a purity of 99.9%+. In many instances this purity is too high for the application. By over-specifying nitrogen purity, the customer is paying for more than he needs and that leads to a waste of energy and resources.

Aluminum degassing is a great example of where nitrogen at 97% to 98% is ideal. Nitrogen is bubbled through molten aluminum to remove hydrogen. Hydrogen becomes present in liquid aluminum due to humidity in the air. The more humid the air, the more hydrogen gets included.

Aluminum is becoming more and more used due to its strength and low weight. Ford recently introduced high strength, military grade, aluminum body panels on its F-150 pickup trucks, reducing the weight 700 pounds and improving performance. As needs for high grade aluminum increases, the need to remove hydrogen inclusions increases. Fortunately, nitrogen sparging effectively eliminates hydrogen.

Nitrogen is sparged or bubbled through the molten aluminum, usually with a rotating impeller or a static lance. Since hydrogen is much more soluble in gaseous nitrogen than molten aluminum, the hydrogen is drawn from the aluminum to the nitrogen bubbles. When the nitrogen comes to the surface, the hydrogen is released.

Nitrogen can be supplied either from the gas company or through the use of a membrane nitrogen generator. Gas companies can supply nitrogen in high pressure cylinders or liquid dewars. Reliance on a gas company typically involves signing an “Evergreen” contract with terms that only guarantee supply not price. These contracts auto-renew unless the buyer gives a one-year advance notice of cancelation. High pressure cylinders and dewars are hard to handle, incur fees for delivery like taxes, surcharges for fuel, hazmat fees and extra space for storage. Usually there is a rotation of three cylinders or dewars needed. One is empty, one is full and the other is in use. Dewars have the added disadvantage of constant outgassing. That means that nitrogen is being wasted even when the dewar is not in use.

An on-site gas generator can produce nitrogen typically with a cost payback of less than 24 months. Since the nitrogen is produced on-site and on demand, there is no need for reliance on a third party supplier, nor the associated delivery fees. Nitrogen generators are easy to install and maintain. Simply replace the existing source of nitrogen and supply the generator with compressed air. The generator comes complete with prefiltration, a hollow fiber membrane that separates oxygen in the compressed air and creates nitrogen. The generator does this without electricity so there is no need to even have an electrical outlet nearby. Maintenance involves replacing the prefilters every six months.

If you are degassing aluminum, nitrogen generation can streamline your process and reduce costs. Contact us for one of our factory trained specialists to make a specific recommendation for your on-site nitrogen needs.



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Parker Hannifin Corporation
Gas Separation and Filtration Division
4087 Walden Ave.
Lancaster, NY 14086
1-800-343-4048 (US and Canada)
1-978-858-0505
Fax: 978-478-2501