[labnetwork] Fwd: Requesting expertise/ experience with Scrubber by-products in Fab.

[Kuhn, Jeffrey G]

Robert,

Based on your description of the airstream entering your scrubber, you should not have this problem - but obviously you do. I have a few questions and comments:


*         Your conductivity setpoint of 5000 uS concerns me for two reasons:

o   Assuming your make-up water conductivity is around 750 uS (typical for the Midwest), then you are running between six and seven cycles of concentration. That creates a lot of nutrients in the scrubber sump that bacteria can use to grow and multiply. The 7.5 to 9.5 pH you mention is a good operating range, but is also ideal for bacteria growth under those conditions.

o   If you are using high-hardness potable water for sump make-up (again, typical for the Midwest), then you will almost certainly create scaling on the scrubber packing as the calcium and magnesium precipitate out. This scale will eventually decrease the airflow through the packing by clogging the air paths and will result in a gradual increase in your exhaust fan speed as it tries to maintain your static pressure requirements.

*         My biggest curiosity lies in where the bacteria are coming from. Are there any BSL hoods tied into the scrubber, or are there any other biological agents that could be "seeding" the sump?

*         Is there any way that free acids, bases, etc. could be getting into the sump? Typically, the small amount of fumes from lab hoods should not cause a rapid change in pH or conductivity.

*         Is your pH and conductivity instrumentation calibrated routinely? Conductivity instruments tend to be relatively stable but pH instrumentation should be calibrated monthly - even more often if history indicates that it is necessary. pH electrodes should be replaced at least annually.

*         When you drain and refill your sump, what conductivity and pH numbers do you see initially and how rapidly do they change?

*         Are you certain that the scrubber is of sufficient size to handle the load (CFM, static pressure, face velocity, etc)?

I'd like to make the following recommendations as a starting point:


*         Measure the conductivity of your make-up water, then set your blow down to maintain the sump at 3X that value initially. Run that way for a while and see how it impacts the problem.

*         Verify that your pH and conductivity instrumentation has been calibrated and replace the pH sensor if it has aged beyond a year or so.

*         Audit your system for the possible introduction of liquids or other materials from sources other than the fume hoods.

*         If you do data collection through Siemens, Johnson Controls, etc., trend the fan operation to see if it is speeding up over time with no additional demands being placed on the exhaust (an indication that fouling is occurring).

If you try these things, please let us know if there are any improvements.

Good luck!

Jeff Kuhn
Facility Engineer
Birck Nanotechnology Center
Purdue University
1205 W. State St.
West Lafayette, IN 47907
Ph:  (765) 496-8329
Fax: (765) 496-2018



From: labnetwork-bounces at mtl.mit.edu [mailto:labnetwork-bounces at mtl.mit.edu] On Behalf Of Robert Pollina
Sent: Tuesday, November 27, 2012 7:37 AM
To: labnetwork at mtl.mit.edu
Subject: [labnetwork] Fwd: Requesting expertise/ experience with Scrubber by-products in Fab.

Struggling with Scrubber equipment and sending e-mails!  Hope you saw this e-mail Michael and Jeff.
---------- Forwarded message ----------
From: Robert Pollina <rpollina at umich.edu<mailto:rpollina at umich.edu>>
Date: Mon, Nov 26, 2012 at 7:50 AM
Subject: Re: [labnetwork] Requesting expertise/ experience with Scrubber by-products in Fab.
To: Rizik <rizik at intengr.com<mailto:rizik at intengr.com>>


Michael,
Thanks for the reply.
I will provide some details of our operation.
  The five gallons of by-product I mentioned refers to a yellow-brown skin of Fusarium fungus and Negative Rod bacteria that forms on the surface of the recirculating tank.  This material forms, grows and clogs the spray heads and pumps in the system.  This material is removed by hand each day.
  The ph of the water in the recirculating tank is maintained between 7.5 and 9.5.  The ph is controlled with a ph sensor in the tank and an automated Sodium Hydroxide (50% solution) feed pump system.  A constant flow of fresh "city provided" water is maintained at 1/2 gallon per minute to make up for evaporation.
  We use this Scrubber system to scrub the acidic fume hood exhaust air from our labs.
  A conductivity sensor helps to maintain a solution that can efficiently deliver the desired result.
  A manual "blow-down" valve adds fresh water to the system while ejecting old tank water to the drain to assist in maintaining a conductivity reading below 5000u.
The Scrubber tank is completely drained and refilled each week as total dissolved solids always exceeds the ability for a quick blow-down to lower conductivity to a good level after 5-7 days of lab operation.
An in-line strainer  collects the same material and is cleaned daily.
  I hope this furthers your understanding of our equipment (Harrington Scrubber)  and procedures.   Looking forward to hearing from you, let me know if more info is needed
-Robert.

On Sun, Nov 25, 2012 at 9:44 AM, Rizik <rizik at intengr.com<mailto:rizik at intengr.com>> wrote:
Please try to answer the following questions before we provide our recommendation:


1.      Daily removal of 5-gallons of concentrated solution - Do you mean caustic solution? If yes, what is the concentration?

2.      Is NaOH injection to the recirculating water stream being controlled by a pH Controller to maintained a predetermined pH level?

3.      What are you trying to scrub?

4.      What is the makeup water flow rate?

5.      Doe you control Total Dissolved Solids in the recirculating water? If yes, is it controlled by a TDS sensor & controller?

6.      Does the recirc water go through a periodic purge cycle or does it continue to circulate and water is replenished only when water level in the basin drops?



Rizik Michael, PE
Principal
Integrated Engineering Services
Office: +408 261 3500, Ext. 201
Cell:      +408 718 0927


From: labnetwork-bounces at mtl.mit.edu<mailto:labnetwork-bounces at mtl.mit.edu> [mailto:labnetwork-bounces at mtl.mit.edu<mailto:labnetwork-bounces at mtl.mit.edu>] On Behalf Of Robert Pollina
Sent: Wednesday, November 21, 2012 5:32 AM
To: labnetwork at mtl.mit.edu<mailto:labnetwork at mtl.mit.edu>
Subject: [labnetwork] Requesting expertise/ experience with Scrubber by-products in Fab.

Good morning,

  I maintain the exhaust Scrubbers serving our wet-benches and fumehoods here at the Nanofabrication Lab at the University of Michigan.
Exhaust air passes through our Harrington Scrubber where Sodium Hydroxide solution is sprayed over a "whiffle-ball-like" material, and a favorable PH is reached before the air is vented to atmosphere.  The NaOH solution is collected in a lower tank and recirculated to the spray heads. PH sensors and Conductivity sensors call for more NaOH and city supplied fresh water as needed.

  Problem: Large amounts of Fusarium , Negative rod and Rototurula bacterias and fungi are created in the tank and must be removed to keep the Scrubber operating properly. This by-product is removed almost daily, often exceeding five gallons of concentrated solution.

  I'm hoping someone has experience with this same equipment and unwanted Fusarium growth.
How do we better control production of this by-product?   What are the proper safety procedures for maintenance staff?
Are there other issues I am not aware of concerning this equipment,  its operation, maintenance and safety?

  Any assistance in this matter would be greatly appreciated.

Robert Pollina
University of Michigan
Electrical Engineering and Computer Science
Nanofabrication lab


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://mtl.mit.edu/pipermail/labnetwork/attachments/20121127/c1fcae89/attachment.html>