For many industrial and analytical applications, using an in-house generator to supply nitrogen (N2) offers multiple advantages over receiving the gas in tanks from a supplier. Those advantages include:
- Continuous supply - A typical system produces N2 of greater than 99.5 percent purity at a flow rate of hundreds of cubic feet per minute at an outlet pressure of 100 psig.
- Lower cost - The in-house system uses far less energy to produce a kilogram of nitrogen compared to the use of bottled nitrogen. In addition, administrative costs are reduced and shipping costs are avoided.
- Less waste - The in-house system generates nitrogen at a pressure and flow rate required for the application, on demand, so no gas is wasted.
- Improved plant safety - The danger of handling high-pressure cylinders is eliminated.
- Greater security of supply. Users don’t need to depend on outside vendors which eliminates delivery delays, long-term contracts, and uncontrollable price increases.
Although situations vary, most users can expect a payback period of slightly more than one year when switching from bottled nitrogen to generating nitrogen in-house. That’s assuming conservatively that a facility uses a flow of 20 L/min (slpm) of N2 for four hours per day. Over the period of one year (250) days), 1,200,000 L of N2 will be consumed, equivalent to 186 standard 9x56 inch cylinders.
In addition to the direct benefits, there is also an environmental benefit to consider. Gas distillation is a highly energy intensive process. The use of a hollow fiber membrane for the generation of nitrogen uses significantly less energy and hence produces much less greenhouse gas than does fractional distillation. Not only does the distillation process itself use significant energy, but so does transporting the gas cylinders from where the N2 is produced to where it is used, as well as transporting the empty cylinders back to the plant.
A Low-Energy Process
How does the in-house generator achieve these benefits?
Rather than distill the N2 from the air, a process that requires significant cooling, a hollow fiber membrane separates oxygen and water vapor from the nitrogen at room temperature. First, compressed air flows through a high-efficiency coalescing filter to remove water vapor and particulate matter and then through an activated carbon scrubber to remove hydrocarbons. The air then passes through hollow fiber membranes that preferentially allow the oxygen and any remaining water vapor to escape while the N2 continues passing through the tube. From there, the nitrogen passes through a final filter containing activated sterile nitrogen filtration media. Finally, the purified nitrogen passes directly to the application via the system’s output port.
For many applications, an in-house hollow fiber membrane system is a more convenient, safer, lower cost, more reliable and more energy-efficient way to generate a continuous supply of pure nitrogen. And it’s better for the environment.
This is Part 2 of a 3 part series on a sustainable approach to the supply of nitrogen. Following are links to the rest of the series:
This series was written by Peter Froehlich, PhD, Peak Media, Inc.; David Connaughton, Product Manager Membrane Systems, Parker Hannifin; Joshua Benz, Development Engineer, Parker Hannifin; and Kim Myers, Global Product Manager, Analytical Gas Systems, Parker Hannifin.