[labnetwork] LN2 vs N2 generation on site

[Nibarger, John]

We also found our LN2 to be an expensive proposition. We have a 6000 gallon LN2 tank shared with an MBE. Cleanroom use was about 900 gallons per day while the MBE was about 200 gallons per day. The N2 generator we purchased system consists of a large compressor with filters and dryers to make CDA (-40 C dew point and very low hydrocarbons) which feed a PSA type N2 generator. We provide 110 psi N2 at 99.5% purity at ~ 2000 scfh. We've had the system online now for only 6 months. We expect a cost recovery on the system in less than two years. Maintenance is mostly keeping the compressor working well and following it's proper PM schedule. We'll need to replace the dryer material every 3 years or so and expect to replace the PSA carbon molecular sieve every 5-10 years.

It's one thing to get some cheaper low quality N2, the hard part is where to use it. Our fab is relativity new (~ 18,000 sqft which we moved into the summer of 2012) so our tooling hasn't migrated too far and all of the toxic gas tools and furnaces are in the same quadrant of the fab. We've kept our high purity LN2 evaporate plumbed to that quadrant (and used filters to improve quality further). We've used the low quality N2 generator gas in the rest of the fab as our N2 generator capacity allows. Any tools that need high purity N2 (99.999%) for processing have gas from dedicated cylinders. We also made provisions for intended or unintended shutdowns of the N2 generator by installing an automatic switchover to the LN2 evaporate so the fab stays up.

Overall, we're pretty happy with our system and is has made an noticeable savings on our LN2 costs. Users have not reported any issues. I'd say it's too early to put an operating cost on the system since we don't fully know the PM costs (largely driven by how long our PSA carbon molecular sieves last for). From a cost perspective we spent about $130,000 for the system including new piping and staff time over 5 years at 2000 scfh (93.11 standard cubic feet (scfh) of gaseous N2 = 1 gallon LN2) gives about $0.14/gallon LN2. The saving will be larger over longer times too. If you have access to large amounts of CDA from facilities services, which we didn't at the time of installation, you can forgo the cost of the compressor/dryer/filter part of the system and save even more.

Cheers,
John

John P. Nibarger, Ph.D.
Manager, Boulder Micro-Fabrication Facility
National Institute of Standards and Technology
325 Broadway, MS 817.03
Boulder, CO  80305
303-497-4575 (phone)
303-497-3042 (fax)
john.nibarger at nist.gov<mailto:john.nibarger at nist.gov>

From: <Morrison>, "<Richard H.>", "Jr." <rmorrison at draper.com<mailto:rmorrison at draper.com>>
Date: Tuesday, March 24, 2015 at 10:03 AM
To: "labnetwork at mtl.mit.edu<mailto:labnetwork at mtl.mit.edu>" <labnetwork at mtl.mit.edu<mailto:labnetwork at mtl.mit.edu>>
Subject: [labnetwork] LN2 vs N2 generation on site

Hi everyone,

I am paying >$220K per year for LN2 to generate Nitrogen for my fab. Have any of you guys switched to onsite Nitrogen generator?

Looking for ideas on:
Cost of system
Maintenance cost of system
 Quality of the Nitrogen.
Operating cost per CuFt of Nitrogen

Rick


Draper Laboratory
Principal  Member of the Technical Staff
Group Leader Microfabrication Operations
555 Technology Square
Cambridge Ma, 02139-3563

www.draper.com
rmorrison at draper.com<mailto:rmorrison at draper.com>
W 617-258-3420
C 508-930-3461

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