On the control of the alkali temperature in the tank
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Currently, the chlor-alkali market is weak, with many manufacturers operating at partial or reduced capacity. As a zero-gap electrolyzer of the Beihua model, especially when operating at low load in winter, steam heating is often required to maintain the cell temperature. I have two questions for everyone here! 1. In Asahi Kasei’s operating procedures, the original requirement for high electric density was that the temperature should be below 90°C, while the subsequent requirement regarding zero electrode distance was that the temperature should be below 87°C. Based on this, can it be assumed that it is possible to maintain a high operating temperature even when the electrolyzer is operating at low load? For example, is it possible to keep the electrolyzer’s temperature between 86–87°C when it is operating at 6KA? If not, is there a table showing the optimal operating temperature corresponding to the operating current to guide operational control? 2. If it is necessary to control the high temperature of the electrolyzer under low-load operation, achieve a lower operating voltage to save energy consumption, then it is essential to use the E-273 heat exchanger for steam heating in order to increase the temperature of the alkali fed into the electrolyzer (this is often the choice made by manufacturers that produce by-product steam). For a new zero-gap electrolyzer operating at 6KA in winter, to keep the electrolyzer’s temperature at 86 degrees Celsius, it is likely that raising the temperature of the alkali fed into the electrolyzer to 92°C will still not be sufficient! So, what is the highest temperature that can be controlled for the alkali entering the tank? It’s not covered in the operating procedures! Please give me some advice!
The temperature of the alkali fed into the tank is controlled based on the tank temperature; there are no specific requirements regarding the temperature of the material fed in, but when operating at 6KA, it is recommended to keep the tank temperature around 82 degrees.
It mainly affects current efficiency. What was said upstairs is correct; the main factor to consider is the cell temperature, as it directly affects current efficiency. If the inlet voltage is too low, it becomes difficult to maintain an appropriate cell temperature. However, when an electrolyzer is started up and the current is increased gradually from a low level, the temperature also rises accordingly. In my understanding, at a zero pole distance (or more precisely, a membrane pole distance), when the temperature is too high, too much water evaporates, which leads to an increase in bubbles in the electrolyte and an increase in internal resistance; this directly affects the cell voltage.
At each current density, there is a temperature at which the best current efficiency is achieved; as the current density decreases, the temperature at which the highest current efficiency is attained also decreases. When the electrolysis temperature drops below 65 degrees, the current efficiency declines rapidly, and even if the temperature rises later on, it is difficult for the current efficiency to return to its original level. It is recommended that the slot temperature remain at least 80 degrees when operating at 6KA.
The last edit to this post was made by nanren2 on 2016-9-24 at 09:01. Manufacturers currently using Beihua and Asahi’s cell types generally adopt two approaches to controlling the cell temperature: ① In accordance with the operating procedures, which specify that the cell temperature should be below 87°C (and below 90°C for cells with high current densities), during normal operation, regardless of the current level, efforts are made to keep the cell temperature as high as possible, as close to 87°C as feasible! Such an operation can reduce the operating voltage of the electrolyzer, and the voltage changes can be observed directly during operation. ②At temperatures below 87°C, high current and high tank temperature are used alongside low current and low tank temperature; this approach helps improve current efficiency, but the changes in efficiency during operation are not displayed online. It is impossible to compare whether the economic benefits resulting from improved current efficiency are greater or those resulting from voltage rise losses! Currently, Asahi Glass has very strict requirements regarding operating current and temperature; different current densities correspond to different temperature ranges, with generally higher current densities resulting in corresponding higher temperature ranges. For example, when the current density is 2 KA/㎡, the highest temperature is 80°C, the lowest is 68°C, and the optimal value is 76°C; whereas at 6 KA/㎡, the highest temperature is 89°C, the lowest is 78°C, and the optimal value is 85.5°C. It has a detailed correspondence table to guide production. Asahi Kasei requires a value of less than 90 degrees (with a zero electrode distance of less than 87 degrees and a high electric density of less than 90 degrees in the case of electrolyzers); no specific requirements are set for temperatures at other current levels. Is it possible to operate at high cell temperatures at low currents? Can high current achieve low groove temperature? If possible, what is the range? (There might be information on this topic, but I haven’t seen it personally; I hope someone who does have such information can share it.) The recommended conditions for the normal operation of DuPont are as follows: the optimal temperature range is between 80 and 87°C, and it functions well at a current density of 0 to 6 KA/㎡ ； The allowable temperature range is 75–95°C; it is suitable for a current density of 1.5–4 KA/㎡ ； The allowable temperature range is 70–95°C, and it is suitable for a current density of 1.5–2 KA/㎡. Overall, for DuPont, the lower limit temperature can be appropriately reduced when operating at low currents, while the upper limit temperature can reach its maximum value, thus expanding the range accordingly! However, the optimal operating temperature ranges from 80 to 87°C, and manufacturers generally maintain the operation within this optimal range. Therefore, overall, I still favor the second control scheme for groove temperature! The above is merely a summary and personal opinion based on limited information; there are certainly errors in it! It doesn’t represent anything else; it’s just for discussion with everyone! I look forward to your corrections!