Regarding the issue of pure water circulation in the electrolyzer after a power failure of all power sources

This post was last edited by nanren2 on 2015-12-1 14:04. Regarding this issue, the following points need to be determined: 1. After a complete power outage, it is not possible to operate the pumps; when using pure water for circulation in the electrolyzer, should it be applied to both the anode and the cathode, or only to the anode or only to the cathode? 2. In the case of a complete power outage, pure water is used for circulating in the cells. Where should the electrolyte that comes out of these cells be stored? Will it be sufficient if the brackish water flows from D-260 to the D-280 overflow pipe? Is the capacity of D-280 sufficient? If the cathode also circulates out of the catholyte tank, where is it stored? At this point, P-264 and P-274 have no power and cannot be started. 3. Since there is no electricity, the pure water pump cannot operate either; where does the pure water come from and by what force is it supplied to the electrolytic cell? Of course, some manufacturers use vertical pure water storage tanks that allow water to flow into the electrolyzer by gravity, but the storage capacity is limited! 4. What should be the flow rate of pure water circulating into the tank? How long does the cycle need to last? Will the capacity of the pure water pump be sufficient? 5. Does the polarization rectifier still need to be activated during pure water circulation? In my opinion, adding a high-level tank for diluted saline would completely solve the problem! For the shutdown and replacement of a caustic soda production plant with a capacity of 100,000 tons per year, approximately 130 cubic meters of diluted brine are required; for a plant with a capacity of 200,000 tons per year, that amount rises to 260 cubic meters of diluted brine! In the event of a power outage, this saltwater can be used directly to replace the electrolyte in the cell!

Personal opinion: 1. Only cycle the anode; chlorine has a high solubility in brine, which generates a strong driving force for the reverse current, so it needs to be replaced as soon as possible. Hydrogen has low solubility in alkalis, and the dissolution of a certain amount of hydrogen can slow down layer discharge. 2. Go to D-280 or the circulation tank, if P-264 and P-274 cannot be activated. The anode solution in the electrolytic cell is about 14 cubic meters per cell. D-280, 100 cubic meters to 150 cubic meters. 3. It can be supplied from a pure water tank; the pure water pump must be able to start quickly (using backup power sources such as UPS), and these requirements can be met during the design phase. 4. Approximately 0.25 cubic meters/h per tank (flow rate after normal shutdown polarization). The duration is determined by the liquid level controlled by two tanks. 5. Do not use polarization to avoid water electrolysis, as well as uneven electric fields that may arise due to temperature differences and resistance, thereby affecting membrane quality. Restore power as soon as possible. The idea of adding a high-level tank is mainly driven by cost considerations, and accidents of this kind are not very common, so a comprehensive evaluation is necessary.

Thank you for the replies and guidance from above, but the operating procedures require that both the anode and cathode be replaced with pure water, and a polarization power supply must be used!

This post was last edited by guitarpro0724 on 2015-12-2 at 14:49. After some consideration, if a polarized rectifier is used as a backup UPS power source, it might be better to keep it turned on; the chlorine concentration in the anode chamber remains relatively high at that time. However, it remains to be determined whether 15 minutes will cause some water to be electrolyzed, as after all, there is no saltwater circulation (which could lead to serious consequences, such as a mixture of oxygen and hydrogen in the anode chamber). For the cathode pure water circulation, it must be circulated if polarization is applied. It’s not necessary to use it if it’s not applied, as alkalinity helps protect the cathodic coating. Regarding pure water circulation, each process engineer likely has different opinions.

It should be discussed separately for the shutdown of direct current, alternating current, as well as the complete shutdown of both types of current along with the failure of the emergency power supply; I look forward to experts’ analysis. Process and safety are equally important; safety should come first

When using pure water for circulation, the polarization rectifier should not be used; once the level at 280 is full, it should be discharged directly to the ground, as there is little chlorine present at this point

The most extreme situation occurs during a complete power outage. We currently have a power distribution room, namely the MCC, equipped with two high-power generators. Our pure water pumps, as well as the important circulation pumps, are connected to the emergency bus bar, that is, to the generator set. As for where the liquid is discharged, as you mentioned, it is all discharged into the waste liquid tanks at the anode and cathode.