Problems controlling pH

[Shooter81]

Could someone give me a brief description of any problems I will encounter when controlling the pH of industrial effluent through neutralisation?

Thanks in advance

 

[bimr]

There are a number of things that could wrong, but it is difficult to anticipate them without knowing details of your application.

Investigate the site below and if you still have any questions on pH control, post again.

http://www.phadjustment.com/index.html

 

[25362]

Factors that come to mind which may affect the viability of pH control could be:

-pH adjustment is batch-wise or continuous
-Presence of buffers
-Variation in flow rates and peaks to be shaved
-The effluent may alternate between acidic and basic
-The range of acidity or basicity may cover several decades.
-Present acids or bases may be strong or weak affecting the slope of the pH curve differently
-Instruments and pumps used (rangeability, linearity, turndown, type of control, etc.)
-The neutralizing chemical used, and the efficiency of mixing this chemical with the effluent stream

The following threads may give you an idea of what is involved:

thread127-111743
thread127-140520
thread164-117715
thread338-121617
thread830-111921

 

[Zoobie]

25362 has given a lot of good starting info. You need to remember that pH versus acid/base is a logarithmic function. This isn't too big a deal but you to ensure that the controller that you select can handle this. I have seen in the past where a notch gain controller was used to handle this but nowadays there are algorithms that take care of the non-linearity.

 

[m777182]

Presence of colloids, precipitates, hydrophobic substances, long chain polyelectrolytes or a large amount of dissolved gas will make your task even harder.
m777182