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Jun
14

If I had Just 12 Wishes for pH Control Systems

If I had just 12 wishes for practices to improve pH control systems they would be:

1. Review and improve electrode design (glass thickness, shape, and formulation and reference type and electrolyte)

2. Check and improve electrode location for dead time (transport delay) and velocity

3. Review and improve calibration practices

4. Check and improve upstream loop tuning and valve resolution to reduce size and speed of pH disturbances

5. Verify valve resolution by small step tests

6. Improve valve resolution (add digital positioner, reduce seating and packing friction, and verify positioner feedback mechanism to ascertain it actually tracks internal trim position)

7. For great reliability, maintainability, and onstream time, consider middle signal selection of 3 electrodes

8. Check dip tube and injector design for time delay for emptying and refilling upon closure of reagent valve (consider reagent injection into recirculation line)

9. Check for fully filled reagent pipeline downstream of valve

10. For flow disturbances and startup, consider flow feedforward

11. For steep titration curves, consider linear reagent demand control

12. If tank is not mixed well enough for pH, consider adding inline system upstream or in a recirculation line

I originally considered the first item further down on the list because it takes time for a plant trial to confirm improvements for radical changes in electrode construction but then I considered the system is only as good as the measurement and the trial could be started while the other items are pursued. Electrode construction is particularly important for high temperature, high ionic strength, low water content, high pH, and low pH streams.