Ion membrane electrolyzer
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This post was last edited by sunjl1981 on 2013-1-6 at 20:09. Hello everyone: Our facility uses Wood’s ion exchange membrane electrolyzers with N3020 ion membranes. A few days ago, when the current was at 13.8 KA, nothing happened; the cell voltage dropped by 10 V, and the cell temperature decreased by 2 degrees. The groove voltage measured at the groove was also normal; the purity of chlorine, the hydrogen content in chlorine, the purity of hydrogen, the alkali concentration, the salt content in the alkali, and the pH of the anode solution were all within normal ranges. What was observed on-site was that the cell voltage of the electrolyzer cell in question was lower than that of the other cells, while the concentration of brine exiting that cell was higher than in the other cells. The cell voltage dropped first, followed by the cell temperature, but the current level remained unchanged; it only decreased after a few minutes. Could everyone please help analyze what the reason for this is? Thank you! # hcbbs
It is estimated that the actual current has dropped significantly; the current shown on the meter is not accurate. The actual current decreases, and the total impedance of the cells changes very little; as a result, the total voltage drops. For cells with 100 units or more, the total voltage drop of 10V results in a voltage decrease per cell of less than 0.01V. So when the person mentioned that there was no change in the voltage of individual cells, it’s not that there really is no change – it’s just that such changes are difficult to detect. But the original poster later said that the voltage in the unit slots at the site was lower than that in the other slots. There’s some contradiction between the beginning and the end; I don’t know what it means. The actual current has decreased, but the displayed value remains unchanged; as a result, the saltwater flow rate set by the DCS system does not change. Consequently, the rate of saltwater decomposition decreases, and the concentration of the saltwater exiting the tank increases. A decrease in current is certainly accompanied by a decrease in slot temperature; due to the lag effect of temperature, it is normal for the voltage to drop first and then the temperature. Gas parameters have no relation to current fluctuations, so there is no need to study them. The concentration of the alkaline solution remains unchanged, which is also easy to explain: all the alkaline solution that enters the tank is distributed evenly, while the amount of water that moves from the anode chamber to the cathode chamber changes depending on the current level. Therefore, the concentration of the alkaline solution does not change. It is estimated that this fault is caused by a problem with the current sensor or the wiring for the sensor signals; of course, the rectification control cabinet should also be inspected. It is necessary to compare the changes in the conduction angle (or control angle) before and after the voltage drop in order to make a comprehensive assessment.
1. The analysis by Electric Tiger is very thorough； 2. It is more likely that the problem lies in the corresponding rectifier cabinet, as there are no obvious changes in the slots of other units ； Therefore, factors such as changes in the external voltage can be ruled out ； A voltage change of 10V is not a small amount; if it were due to process-related reasons, it wouldn’t be so sudden and drastic. 3. Thyristors ensure the output of direct current by adjusting the voltage levels and control angles; current sensors serve as control elements for both the processing process and rectification, and are quite important – it is necessary to check for any signs of drift ； If the phenomenon described by the original poster occurs, it is likely to be short-lived and may recover ； 4. It’s estimated that the reason behind this, as identified by the original poster, has now been found; we’re just making assumptions, and we hope the original poster will reveal the truth.
Indeed, we haven’t been able to determine it yet. We suspect that there is a decrease in current, but we are not able to confirm this yet. We are using Wood electrolyzers, with a total of 162 cells. By saying that the voltage of these cells is normal, I mean that the measured voltage falls within the normal range; however, it is still lower compared to the voltage of the other cells. How can it be determined that the actual current has decreased? Thank you!
To determine the reduction in current, it is possible to carry out calculations using electrical power. For the 164-slot unit, the total voltage should be around 500 volts; by calculating the total DC power and then converting it to AC power, one can check whether the efficiency of the rectification and transformation process is higher than that of other systems of similar type. This can help in verifying the accuracy of the current value. This can be used to calculate the secondary output power of the rectifier transformer, based on the data transmitted by the current transformer in its secondary coil. Also, check whether the currents in cabinets A and B are balanced. If a thorough investigation is really necessary, an external high-current sensor can be used for comparative testing, but it is very dangerous and its use is not recommended. Under the same transformer setting, the conduction angle determines the DC current; carefully examining the records of the conduction angle should be a method for analyzing the problem. If the current is low due to one or several thyristors not being conducting, the system will automatically increase the conduction angle to stabilize the current.
We’re checking on it too! Thank you
I hope the truth behind the reasons will be revealed soon, so that we can all communicate better! ! !
I’m so sorry! We don’t know the specific reason yet. But last night it suddenly reverted to its previous state. Our full load is 13.8 KA; the normal range for the total voltage across the slots is between 530V and 545V, while the slot temperature ranges from 87.5 to 89 degrees. It dropped on the afternoon of May 1st, but suddenly rose again after 10 p.m. the previous night, returning to its previous level. Last night, the slot voltage increased by 10V, and the slot temperature rose by 2 degrees. Our current slot voltage is 538V, and the slot temperature is 87.5. When these values increase, the slot voltage rises first followed by the slot temperature. At our facility, a slot voltage and temperature of 13.8KA under full load is considered normal. Could the moderators please analyze what might be the cause of this? Thank you!
The old version is correct; it’s probably caused by drift in the high-current sensor. I’m not sure if the original poster has checked the changes in the conduction angle (or control angle); if there are significant changes before and after, it’s a problem with the current signal. It could be a drift issue within the high-current sensor itself, such as the effect of external temperatures, or it could be problems with the wiring, such as poor connections. All of these factors can lead to malfunctions, and such malfunctions inevitably result in a decrease in the conduction angle (or an increase in the control angle). The person asking the question really should pay close attention to the details.