[labnetwork] Fume Scrubber pH Drift

[Siva Penmetsa]

Hi,

We have a new wet scrubber that has a similar issue.

When ever we run a process that has HCl as by product the pH reduces
drastically(pH< 4 from idle of 8)

Maintenance
1. We drain and fill water once every week, and set the pH between 9 and 10
by adding few drops of NaOH solution
2. We monitor the pH periodically (morning and afternoon everyday) and when
pH<4 , few drops of NaOH(Sodium Hydroxide) is added so that the pH > 9(pH=
10 is the upper limit)
3. Clean pH probe with water when any deposites on it

Hope the above informations helps.

Regards,
Siva Prasad Raju Penmetsa
Senior Facility Technologist
Nantional Nano Fabrication Center
Indian Institute of Science(IISc)
Bangalore, India
siva at cense.iisc.ernet.in


On Tue, Jul 24, 2012 at 1:29 PM, Michael Khbeis <khbeis at uw.edu> wrote:

> Dear Colleagues,
>
> I was wondering if any of you had experience in pH swings on fume
> scrubbers.  We inherited the facility and associated scrubber that is
> attached to all our gas cabinets, GRC, and fume hoods.  We have little
> documentation on the PM schedule and no Operating and Maintenance manuals.
> Basically, we are neutralizing or raising pH to 10, but then over the
> course of a few minutes up to several hours the system will drop to pH of
> <5.  Acceptable range in our AOP is 5.5 - 11. We see this swing even when
> tools are idle - there does not appear to be an operational indicator that
> tracks the system response.
>
> System description at a high level: Age of system is 15 years.  Last media
> change - unknown, but plastic media looks mostly normal. Manual fill/drain,
> system recirculates with addition of caustic soda to balance out
> acidification - also manual dispense when pH is out of range.  We started a
> bacterial kill that was recommended in the weekly PM schedule about 3 weeks
> ago and starting seeing this instability in pH a week later.  We halted the
> PM schedule to see what impact there is, if any.
>
> Remedies attempted:
> 1) Added sodium bicarbonate to increase buffering of system.  Minimal
> impact.
> 2) Multiple drain/flush cycles - pH was normal (7) for few minutes then
> dropped to 4 shortly after.
> 3) pH probes were recalibrated and verified to be operational
> independently.
>
> Any recommendations or anecdotal experience would be appreciated. I thank
> you for participating in this community.
>
> Gratefully,
>
>   Dr. Michael Khbeis
> Associate Director
> Microfabrication Facility (MFF)
> University of Washington
> Fluke Hall, Box 352143
> (O) 206.543.5101
> (C) 443.254.5192
> khbeis at uw.edu
>
>
>
>
> _______________________________________________
> labnetwork mailing list
> labnetwork at mtl.mit.edu
> https://www-mtl.mit.edu/mailman/listinfo.cgi/labnetwork
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://mtl.mit.edu/pipermail/labnetwork/attachments/20120725/cc5654af/attachment.html>