Overview of sodium hypochlorite electrolytic systems
When the whole system is operating normally, the dilute brine enters the sodium hypochlorite generator for electrolysis to produce sodium hypochlorite solution. There is no flow switch at the entrance of the sodium hypochlorite generator. When the flow reaches the set value, the rectifier starts to output direct current for electrolysis, and produces sodium hypochlorite solution and by-product hydrogen into the sodium hypochlorite storage tank. After the hydrogen is diluted to less than 1% through the blow dryer, it is safely discharged into the atmosphere through the hydrogen outlet at the top of the sodium hypochlorite storage tank. The sodium hypochlorite solution enters the dosing pump for dosing.
After the reaction of the electrolytic cell inside the generator, due to the presence of calcium and magnesium ions in the water, these ions will form calcium and magnesium sediments on the cathode during electrolysis, increasing the consumption of electric energy, so these sediments must be eliminated regularly by pickling method.
Preparation before pickling
Stop the rectifier, in the case of the electrolytic cell power failure, continue to water for about 5 minutes, wash the residual sodium hypochlorite solution in the electrolytic cell. Stop the dilute salt pump, close the valves before and after the electrolyzer, open the drain valve of the electrolyzer, and drain the water. The sampling valve can be opened to exhaust air. After empting, open the pickling inlet and outlet valve, close the blowdown valve, and close the pressure sensor instrument valve. Prepare 35% industrial hydrochloric acid.
Pickling of electrolytic cell
Configuration of dilute hydrochloric acid: open the clean water inlet valve, observe the pickling tank level height reaches 1000mm, close the clean water inlet valve. Open the concentrated acid valve and inject about 31% of the industrial hydrochloric acid into the pickling tank to a height of 1500. At this time a dilute solution of hydrochloric acid with a concentration of 10% has been prepared.
Start the pickling pump and circulate the extracted hydrochloric acid in the electrolyzer and pickling tank for 3 hours to stop the pickling pump.
Flush the electrolytic cell, open the electrolytic cell valve and pressure sensor instrument valve, close the blowdown valve and pickling inlet and outlet valve, until the dilute salt pump flush the electrolytic cell for 3 minutes.
Discharge of pickling solution
Most common pickling solutions are citric acid, hydrochloric acid, nitric acid, and phosphoric acid. The PH value of the pickling waste liquid produced after cleaning is usually below 1.5, which is strongly acidic. If such waste water is discharged directly, it will cause great pollution to the soil and rivers, and directly affect the growth of animals and plants, so the pickling waste liquid must be treated before it can be discharged.
01 For hydrochloric acid, nitric acid and sulfuric acid strong acid lotion, industrial sodium hydroxide can be used for neutralization. However, this method can easily lead to residual acid in the pickling wastewater, so the PH value needs to be determined and then further residual acid treatment is carried out.
02 Before discharge, add appropriate amount of lime (about 2% quick lime, hydrated lime can be) precipitation, PH value reaches 7, filter out various impurities in rust remover, water dilution more than 3 times discharge, can be used as green water.
This scheme takes environmental protection rust remover as an example (the stock solution is a variety of complex organic acids, PH value is 2.5±0.8), and phosphoric acid pickling can also refer to this method, but the specific usage needs to be judged according to the actual situation.
03 For lemon pickling waste water, can be mixed with coal combustion treatment. Because citric acid is a fairly stable organic acid, the above two methods are difficult to break it down, because it is a hydrocarbon oxygen compound. Therefore, it can be oxidized and decomposed at high temperatures by burning.
The above three are commonly used pickling waste liquid treatment methods, and the specific use should be selected according to local environmental protection requirements and actual treatment conditions.
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