[labnetwork] Specification for clean dry air (CDA)

[Kuhn, Jeffrey G]

Hello Bob,

At the Birck Nanotechnology Center, the CDA design spec is 100 psi with a -80F dewpoint, but in reality we supply 120 psi. When this facility was built, the CDA system was purchased from a nearby photomask shop that was being closed, so it was not spec’d specifically for Birck. That system included one Kobelco oil-free compressor rated for 173 cfm @ 150 psi, the receiver tank, an Airtek twin tower desiccant dryer, and the filtration system. The system is oversized for this facility, so as a result we see a dewpoint of less than – 140F. At first I didn’t believe it was accurate, but several tests and calibrations proved that it is real. We supply CDA to approximately 21,000 sq. ft. of lab space and to our 24,000 sq. ft. ISO 3 to ISO 5 cleanroom. Not all labs or cleanroom bays use CDA so we have considerable future capacity.

A few years ago, we purchased a second identical Kobelco compressor so we could run them in lead/lag mode and reduce the impact of a compressor failure. They swap duty on a weekly basis, and each compressor is easily capable of supporting this facility. I estimate that the lead unit is loaded no more than 35% of the time. Part of that may be because we run our compressor at well under its maximum rated pressure, and also because the supply pressure is high compared to what the users actually need. Our highest pressure demand is around 90 psi and the cfm use there is quite low. There are some laser lithography tools that require relatively high CDA pressures, so that’s an important consideration when choosing a compressor system. Such was the case in the photomask facility from who we purchased the initial compressor, which is why it is rated to 150 psi.

Like you, we are converting as many N2 users as practical over to CDA in order to reduce N2 costs. This is an ongoing process and we continue to monitor the CDA demand, but so far the increased load on the compressors has been negligible.

I am responsible for the overall care and feeding of the CDA system but the trades do much of the actual work, especially the annual preventative maintenance. We had the local Kobelco service folks do the first few PM’s with the trades in attendance for training purposes, then the trades took over. If we have a component failure that we can’t repair ourselves I will call in the local service rep, but using our in-house folks for PM saves us quite a bit of money. Fortunately, component failures have been fairly rare.

I imagine you are already aware of this, but I would avoid being lured into using oil flooded compressors to save money. I’m sure your facility is sensitive to hydrocarbons like we are, and to me the risk of possible contamination outweighs the additional cost of buying an oil-free unit. If oil somehow gets into your distribution loop, the loop will likely have to be replaced since I know of no way to adequately clean it after contamination occurs. Besides, purchasing all of the filtration and hydrocarbon monitoring equipment needed to keep your processes and infrastructure safe offsets a lot of the higher cost of the oil-free compressor.

Lastly, ISO 8573.1 provides the specifications for the various grades of CDA in case you are interested in meeting a particular ISO spec.

I hope this information was helpful. Feel free to email me directly if you have any questions and best of luck with your new facility.

Regards,

Jeff Kuhn
Facility Engineer
Birck Nanotechnology Center
Purdue University
1205 West State St.
West Lafayette, IN 47906
Ph: 765-496-8329
kuhn1 at purdue.edu<mailto:kuhn1 at purdue.edu>


From: labnetwork-bounces at mtl.mit.edu [mailto:labnetwork-bounces at mtl.mit.edu] On Behalf Of Robert M. HAMILTON
Sent: Thursday, June 09, 2016 5:43 PM
To: Labnetwork <labnetwork at mtl.mit.edu>
Subject: [labnetwork] Specification for clean dry air (CDA)

Labnetwork Colleagues,

I recently contacted Dennis Grimard eho is helping design and build MIT's new lab to learn their specification for their compressed dry air (CDA). Dennis is terrific with numbers and engineering data. Dennis suggested it might be useful to broaden my query to the labnetwork. This begs the questions, how do other facilities specify their CDA and who supports their systems?

At the outset I’ll comment many university labs use their campus engineering maintenance support to service utilities and specs may not be at one’s finger tips. And, some universities have central plants for utilities which serve a broad number of facilities. In the case of the Marvell NanoLab we have virtually all our utilities contained within our sub-fab and we have chosen to maintain most utilities e.g. our acid waste neutralization system, air handlers CDA, DI water, LN and process cooling water system because we are so dependent on them.

My question is what are reasonable specifications for CDA? I realize this is a difficult question to answer because CDA usage will be based on an equipment load.  Perhaps adding a labs square footage helps to scale an answer?

The UC Berkeley Marvell NanoFabrication lab’s CDA is derived from two Atlas Copco 117 cfm (3,32M^3/min) screw compressors operating in a lead/lag configuration which deliver to a 200 gallon storage vessel, then to an Air-Tak brand dryer and Zander particle filters before delivery to the lab. Our CDA delivery specification is 90 psi at a dewpoint of -70F (~16 ppm H2O). We began with a dewpoint spec of -90F; however, we relaxed this spec. to reduce the work of the air dryer with wearable, moving parts. As backup, to facilitate the orderly shutdown of equipment and for brief periods to do CDA system maintenance our delivery is configured to automatically cross over to the lab’s cryogenically derived process N2 when the pressure falls below 70 psi. Such a crossover can support the lab for several hours using N2; however, the associated LN vessel vaporizers do not have sufficient capacity to run on cryogenically-derived N2 for extended periods of time – they ice over.

As has been previously noted, a few years ago we substituted CDA for N2 purging on a select number of dry pumps to reduce our N2 costs. The pumps switched to CDA were pumps which service equipment that does not pump acid-gases, flammables or pyrophorics. This has been a great success. The downside; however, is we are now peaking our CDA demands to greater than a single compressor can sustain. This makes us vulnerable should we lose a compressor.

Comparing how various research fabs spec CDA has value.

Regards,
Bob Hamilton


Robert Hamilton
University of CA, Berkeley
Marvell NanoLab Equipment Manager
Rm 520 Sutardja Dai Hall, MC 1754
Berkeley, CA 94720
Phone 510-809-8618 (desk - preferred)
Mobile 510-325-7557 (my personal mobile)
E-mail preferred: bob at eecs.berkeley.edu<mailto:bob at eecs.berkeley.edu>
http://nanolab.berkeley.edu/


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