Selection and material choice for diaphragm caustic soda electrolyte preheaters
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This post was last edited by sunjl1981 on 2013-1-6 at 22:08. In our company, the preheaters for diaphragm caustic soda electrolyte solutions, as well as the pipes, evaporation feeding pipes, reflux pipes, etc., suffer from alkali embrittlement frequently; welding is required repeatedly, and leaks occur constantly. Especially the electrolyte preheater: the temperature can reach 160 degrees Celsius, it contains 10-12% caustic soda, and the salt content is 190 g/l. Three spiral plate heat exchangers have already been replaced (one made of carbon steel lasted 2-3 months; one made of 304 stainless steel developed cracks in the spiral welds on both sides after 15 days, with the cracks being more severe in the innermost layer; another one developed internal leakage after 13 days). I’m not sure what to do. I would appreciate your advice. Later, we replaced the original 304 stainless steel feed pipes, return pipes, and other components with carbon steel materials; the performance has been good, but it’s unclear how long this will last. So far, it has been in use for almost a month without any obvious leaks. For the electrolyte spiral plate heat exchanger, we would like to replace it with a plate heat exchanger; we’re not sure whether to use 310S, TA1, or nickel material. The reliability of plate heat exchangers is also uncertain. I would be grateful if teachers with expertise in this area could provide some guidance and specific advice. Thank you very much. # + + . hcbbs
This post was last edited by tclvjian on 2011-11-20 at 10:46. The main reason for frequent leaks in spiral plate heat exchangers is electrochemical corrosion. It is necessary to eliminate the leakage current in diaphragm electrolyzers; this can be achieved by cutting off power at the outlet funnel of the electrolyzer and grounding the outlet pipes, thereby preventing corrosion caused by leakage current. Nickel is the best material for this purpose, but it is also the most expensive.
This post was last edited by tclvjian on 2011-11-20 at 15:59. The leakage situation seems quite abnormal; an analysis of the chlorate content is necessary, and attention should be paid to the side reactions in the diaphragm cell.
Check the power-off effect of the saline circuit breaker; the corrosion of the heat exchanger is mainly caused by stray currents