Nitrogen delivery system slashes cost for automotive metalcaster.
AEP was using 72 million cu. ft. of nitrogen per year from an 18,000-gallon liquid tank, which was filled three times a week. The annual cost of this liquid nitrogen system--including tank rentals, hazardous material charges, delivery fees and the cost of liquid nitrogen--exceeded $250,000.
Recently, engineers began investigating possible upgrades to the nitrogen delivery system to improve performance, reduce consumption and minimize maintenance. First, the team had to choose between the two types of commercial nitrogen generating systems:
* Membrane separation mechanically separates nitrogen from oxygen and other molecules without a chemical process with a system including an air compressor, dryer, filters, pre-storage tank, nitrogen membrane and nitrogen storage tank.
* Pressure swing adsorption (PSA) systems are vessels filled with a carbon molecular sieve that is pressurized with air. Oxygen, carbon dioxide and other molecules are captured while nitrogen is drawn into a receiving tank. Depressurizing the sieve bed then flushes the trapped gases and regenerates the sieve.
Honda engineers chose to pursue the installment of a PSA system because of its longer life expectancy, increased flow rates and a potential return on investment of two years. Honda selected to partner with its vendor based on its two-year system warranty; 24-hour technical support; performance certification of the system purity flow and pressure requirements; and the quality of the sieves in its systems.
A review of Honda's compressed air system determined there was enough open capacity for the nitrogen generator's needs. An investment in a compressor system wasn't necessary, which reduced overall costs and maintenance concerns. The project then was quoted utilizing Honda's shop air system, though a filter and refrigerate drying system needed to be added to ensure air quality. The nitrogen quality verification was integrated into the system via an oxygen analyzer.
The final consideration was achieving 100% uptime because the PSA system would shut down in the instance of a power outage and the compressed air feed would be too much for a back-up generator. Engineers retained the liquid nitrogen tank as a backup system. The PSA system then was placed in line between the liquid nitrogen tank and the nitrogen users.
If the nitrogen generator went offline or failed to meet the nitrogen supply needs, the pressure would drop and an inline pressure regulator would supply nitrogen from the liquid nitrogen tank to provide 100% uptime reliability.
The last step prior to installation was evaluating the business case for a change to the nitrogen system. The case would be evaluated against a SEQCDM model:
* Safety: The back-up system functioned correctly 100% of the time with no nitrogen outages experienced.
* Environmental: The average daily tank draw dropped from 18.8% to 0.5%. Liquid nitrogen deliveries went from three times a week to once or twice a year.
* Quality: Gas quality goal was met and maintained.
* Cost: Compressed air usage was monitored and was found to meet the 4:1 ratio that was expected. The cost reduction was determined to be 76%.
* Deliverables: All purity, flow and pressure requirements were met and maintained in service.
* Morale: No maintenance was added. Monitoring of the system is performed once a day and recorded on a check sheet by Honda associates.
This article is based on the paper, "Industrial Applications for Generated Nitrogen Gas at Honda of America, Mfg. Inc." by Aaron Flesher, Honda of America, and Daniel H. Herring, The Herring Group Inc.
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|Title Annotation:||CASTING INNOVATIONS|
|Date:||Sep 1, 2015|
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