Reasons for poor vacuum dechlorination efficiency: Where is the measurement point for the vacuum dechlorination temperature?
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This post was last edited by sunjl1981 on 2013-1-6 at 23:31. Sometimes the dechlorination effect is poor, even though the vacuum level, temperature, and saltwater flow rate are all normal. There was a period during which more sulfurous acid was used – I’m not sure what the reason for that is I would like to ask where the temperature measurement point for vacuum dechlorination is installed in your company? What other factors affect the dechlorination effect? # + + .
Possible reasons for poor dechlorination efficiency: 1. Vacuum dechlorination: (1) The amount of acid added was not properly controlled, and the pH value was not maintained between 1.5 and 2.0; since a high pH value results in a high concentration of hypochlorite ions, vacuum dechlorination cannot remove these ions. (2) There is a problem with the brine distributor in the dechlorination tower, resulting in uneven distribution of brine within the tower and poor dechlorination efficiency. An excessive flow rate of saline or a too short residence time in the dechlorination tower can also affect the dechlorination efficiency. 2. Chemical dechlorination: (1) Insufficient amount of alkali was used, and the pH was not maintained between 8 and 11; under acidic conditions, sodium sulfite tends to decompose, which affects the efficiency of dechlorination. (2) The sampling point is too close to the sodium hyposulfite inlet, resulting in inaccurate data. Of course, there are also reasons such as uneven mixing and incorrect readings on the instruments; with a careful inspection, the problem should be solvable
Where are the temperature measurement points for the vacuum-dechlorinated brackish water?
In chlor-alkali production, dechlorinated brine often contains sulfates and chlorates. Changes in their concentrations and changes in operating temperature have a significant impact on the ORP value. At the beginning of operation as well as later in the operation of a new system, the amount of sodium sulfite solution added increases substantially while the pH value remains unchanged. As the current efficiency decreases, the concentration of dissolved chlorine in brackish water increases significantly, resulting in a poorer dechlorination effect; more sodium sulfite is required to eliminate residual free chlorine. The calibration of the pH value and ORP measurement temperature also plays a significant role in the stability of the system. The measurement temperature for pH and ORP must be controlled, as the pH value changes with the temperature of the liquid being measured, meaning its zero point shifts. Therefore, the measured values of pH and ORP must be taken at a constant temperature (the temperature of the pH and ORP sensors should normally be maintained at 50°C); otherwise, the system will become unstable. Measurement instruments need to be calibrated regularly.
The original poster is asking about the temperature of the brine, whether it is before or after dechlorination, not about the temperature of the brine as measured by a gauge.
I wonder if the owner’s setup uses an additional heat exchanger to raise the temperature of the chlorinated brackish water; if so, this issue is quite significant. If not, this question doesn’t make much sense. At this time, the heat for the dechlorination tower comes from the electrolyzer, and the heat lost during transmission remains roughly the same under identical operating conditions. The dechlorination efficiency fluctuates; as you said, this is mainly due to 1: the pH value at the inlet of the tower needs to be controlled between 1 and 1.3 ； 2. The vacuum level is controlled at -68 to -78 KPa ； 3. The pH value of the brine exiting the tower should be controlled between 10 and 11 ； 4. The amount of sodium sulfite added shall be no less than 0.1 liters per unit tank. Even if the ORP value is within the controlled range, an appropriate additional amount should be added, followed by sampling and analysis for verification, in order to establish one’s own empirical values. 5. To control the pH value of the brine fed into the tower at as low a level as possible helps to keep the chlorate concentration at a stable level. It can be analyzed and verified.
Check the issue with the instrument; it should be easy to verify
The main reasons for poor dechlorination efficiency are: 1. Whether the vacuum level is stable, and the performance of the condenser before the feedwater circulation pump; the vacuum level should be monitored simultaneously using a pressure transducer and an on-site pressure gauge. 2. Verify whether the pH value is within the acceptable range of 1.0–1.5, using both a pH meter and laboratory tests. 3. The consumption of sodium hypochlorite is controlled properly; since sodium hypochlorite removes free chlorine primarily by reacting with hypochlorite ions, the pH value must be alkaline, between 9 and 11. 4. It could also be due to equipment issues: an insufficient packing layer in the dechlorination tower, or problems with the distributor, such as broken titanium bolts or uneven flow ； Or it’s a problem with the water ring pump; it’s unstable.
We are using 140,000 tons of ion exchange membranes, and the amount of sulfurous acid required is 160 L/H; I’m not sure what the situation is