When the correct electrode installation has been made using the Powell ORP electrodes, the silver/platinum electrode pair produce a millivoltage signal output according to the following formula: Where Eo is the standard oxidation potential for the reaction.
When the correct electrode installation has been made using the Powell ORP electrodes, the silver/platinum electrode pair produce a millivoltage signal output according to the following formula:
Where Eo is the standard oxidation potential for the reaction.
Since the electrode potential is primarily a function of the hydrogen ion concentration, a sharp inflection is noted at the reaction end point similar to that obtained by pH measurements.
Experience has shown that typical millivoltages in a chlorine scrubber starting with a typical 21% sodium hydroxide and reacting with chlorine will produce the following approximate mVDC signals with respect to the remaining sodium hydroxide versus the weight percent sodium hypochlorite. Data is show in Table 1.
Table 1: Remaining Sodium Hydroxide vs. Weight Percent Sodium Hypochlorite |
Wt % NaOH |
Wt % NaOCl |
ORP mVDC |
21.34 |
0.00 |
0 |
19.90 |
1.12 |
288 |
18.47 |
2.31 |
311 |
16.93 |
3.45 |
330 |
15.49 |
3.50 |
345 |
14.22 |
5.54 |
358 |
12.88 |
6.81 |
372 |
11.44 |
8.01 |
384 |
9.90 |
8.88 |
396 |
8.49 |
10.25 |
410 |
7.00 |
11.27 |
424 |
5.38 |
12.67 |
441 |
3.95 |
13.59 |
460 |
2.31 |
15.13 |
488 |
1.48 |
15.58 |
507 |
0.81 |
15.99 |
535 |
0.42 |
16.44 |
561 |
| *MilliVoltage Direct Current |
ORP vs Wt% NaOH
Using the data in Table 1, the Oxidation Reduction Potential Curve with the 21% by weight sodium hydroxide starting point can be represented as a graph, as shown in Figure 1 below. Using the proprietary Powell ORP electrodes any chlorine scrubber can be continuously or batch controlled at high sodium hydroxide levels as required by individual design of the scrubber.
Powell’s customers have successfully controlled by using continuous and automatic control sodium hydroxide levels at typical levels such as 12% by weight with excellent results. Many customers chose to operate the scrubbers at much lower levels of sodium hydroxide such as 1.5% using Powell ORP electrodes either by batch or continuous. If the system is automated with the application of automatic sodium hydroxide supply valves in conjunction with the Powell ORP electrodes, process upsets can be easily and quickly managed On batch chlorine scrubbers, the Powell ORP electrodes are used to provide information and alarms to inform the operators when to change batch sodium hypochlorite tanks in the scrubbing operation.
For More Information
Contact Powell today and find out why companies such as Olin and Occidental can now operate their emergency chlorine scrubbers automatically and continuously with the confidence necessary in today’s environmental standards.
ORP Electrodes
Chlorine Scrubber System |