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

Mon Nov 26 18:48:18 EST 2012

Hi Jeff,

Excellent analysis. Our company's (IES) standard scrubbed exhaust system
design is to provide  not only caustic injection controlled by a pH probe &
Controller but a Conductivity meter to monitor water conductivity which
opens a purge solenoid valve to allow releasing about 5 gpm of scrubber
water, which will be replenished when the float valve drops below the high
limit or in the case of a controlled makeup water, when the LIT senses a
drop in water level, then a 2" control valve would open to replenish the
discharged water fast enough to prevent a vortex from forming and cavitating
the pumps. In addition, in a lot of cases we introduce a biocide injection
system to keep bacteria in check. In the old days when I used to work as a
Semiconductor Facility Engineer, we used to shock each scrubber with a
gallon or two of bleach. I agree with you that NOT ADDING FRESH water period
will increase the cycles of concentration and therefore TDS concentration. 

We recommend the following:

1.       Add an automatic purge system using a conductivity monitor and
controller

2.      Add a continuous SOFT water makeup of about 1 to 2 gpm.

3.      Add an automatic biocide injection system

4.      Provide semiannual basin cleaning using a wet vac / Pool vacuum
cleaner

Then, enjoy a nice running scrubber.

Take care,

Rizik Michael, PE

Principal

Integrated Engineering Services

Office: +408 261 3500, Ext. 201

Cell:      +408 718 0927

From: Kuhn, Jeffrey G [mailto:kuhn1 at purdue.edu] 
Sent: Monday, November 26, 2012 1:32 PM
To: 'Rizik'; 'Robert Pollina'; labnetwork at mtl.mit.edu
Subject: RE: [labnetwork] Requesting expertise/ experience with Scrubber
by-products in Fab.

Robert,

We have a large Harrington scrubber here at Birck, but it operates in a
somewhat different way than what you describe. The "scrubbing agent" in our
case is circulated water - not NaOH. Caustic is used only as needed to
maintain the pH within the desired range. Ideally, you would want your
circulating water to have an approximately neutral pH and not add caustic
until it drops below at least 7.0. What I believe you are referring to when
you mention the "lower tank" is actually the sump itself. Perhaps your
design is different??? Just for reference, our scrubber is rated for 42,000
cfm and our circulation rate is about 400 GPM.

We perform monthly bacteria testing using dip slides and, when needed, add a
measured amount of isothazilinone-based biocide to kill the bacteria. This
is only needed once or twice per year, usually in the summer months. We have
never had to shut down for removal of the types of biological material you
mention. Our fouling issues were always related to lime scale due to hard
water make-up, but that issue has been mitigated by the introduction of
softened make-up water.

In my opinion, you should never need to deal with removal of biological
material if your scrubber is operating correctly. I totally agree with Rizik
in his response below as to the need for answers to his questions. I would
also add that you need to control both your conductivity via periodic
blow-down, and should minimize your cycles of concentration (depending on
the make-up water parameters) to around 2-3 cycles. You should not let the
pH get too high. Around pH = 9.5 is the upper limit I'd like to see. It is
not so much the pH of the water that does the scrubbing, but rather the
water itself. The addition of caustic is simply to keep the pH within
certain limits so it can be discharged to your POTW (or WWT system if you
have it), and to protect internal components from corrosion.

Regards,

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 Rizik
Sent: Sunday, November 25, 2012 9:44 AM
To: 'Robert Pollina'; labnetwork at mtl.mit.edu
Subject: Re: [labnetwork] Requesting expertise/ experience with Scrubber
by-products in Fab.

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]
On Behalf Of Robert Pollina
Sent: Wednesday, November 21, 2012 5:32 AM
To: 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

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