Two issues that occur when restarting the electrolyzer after it has been shut down
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This post was last edited by sunjl1981 on 2013-1-6 at 23:39. The electrolyzers in our factory are six low current density forced circulation polarized electrolyzers produced in the early days by Beihua Machinery; the maximum operating current density is 4.0 KA/M3, with a typical operating value of 3.3 KA/M3. Recently, after a period of parking (about three days), when power was supplied again, it was observed through the hoses at the inlet and outlet of the catholyte that the catholyte turned black immediately upon power application. Additionally, it was seen on the DCS that the total voltage of the cell was very high, but the cell voltage dropped rapidly as well. Therefore, when increasing the current, it can only be raised gradually based on the slot voltage. This phenomenon occurred only in slot D of the six slots; in the other 5 slots, only darkening of the cathode solution was observed during operation, with the cell voltage not being high. I hope the experts here can offer some help! ! # ， ， &
1. The blackening of the catholyte is due to partial shedding of the cathodic coating at the beginning of operation； 2. A balance will be reached after normal driving, thereby achieving stability ； 3. If the voltage in certain slots is high, it is necessary to check the condition during shutdown to determine whether there has been any damage to the cathode coating ； 4. As the original poster said, a galvanic cell effect may have occurred during parking.
The cathode inlet hose turns black due to the coating peeling off; its main component is nickel oxide, which is why it appears black
In the early models of Beihua Machinery, the cathodes were made using the stainless steel etching method; as a result, coating loss occurred after each start-up and shutdown. Although this did not affect the quality of the products, it reduced the lifespan of the coatings. More attention needs to be paid to voltage changes
Due to the dissolution of the cathode coating caused by the galvanic cell reaction, it is recommended to install a polarization power supply; otherwise, it will have a significant impact on the electrode coating.
Stainless steel alkali etching involves a coating-free process that utilizes an increased surface area to reduce the actual current density.
Well, to put it that way, the alkaline etching of stainless steel doesn’t exactly result in an increase in surface area as you mentioned; rather, through alkaline etching, a porous nickel layer forms on the surface of the stainless steel, which lowers the hydrogen evolution potential. But this porous nickel layer tends to peel off easily, and the potential rises rapidly.
Can anyone tell me what alkali etched cathodes actually are????
The blackening of the catholyte is caused by the peeling off of the coating on the cathode side. The total voltage of the cell is very high, and the cell voltage drops rapidly – this is a galvanic cell phenomenon. A design like that used by Beihua Machinery is a bit like trying to pull a cart with an old ox; haha, as long as it can still produce products, that’s fine. .
For devices on the 9th floor, the galvanic cell effect is at its maximum, which corresponds to the theoretical decomposition voltage; however, this is not the case in our situation. As the current increases, the cell voltage also rises, but once the current stops increasing, the cell voltage begins to drop.
Another point is why it doesn’t turn black during cyclic heating, but only starts to turn black when power is applied. We are using forced circulation!!
The cathode solution turns black; sometimes it’s not just a coating issue, but it could also be due to the loss of iron elements in certain parts of the cathode system. If you have the chance, you can try using a magnet to see if that’s the cause