What materials are used for containers for producing high-concentration alkali in the chlor-alkali industry?
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Our company operates in the chemical industry; we use rising-film evaporation to produce a mixture of potassium hydroxide and sodium hydroxide with a concentration of around 60%. This mixture is then poured into a tank with a diameter of 2.6 meters and a height of about 4.5 meters, where it is heated until it is completely dehydrated. Due to limitations related to production volume and time, the final temperature currently reaches around 550 degrees. The process used by some caustic soda manufacturers, which involves heating to 440 degrees and leaving the material there for 12 hours, cannot be adopted by us. Currently, the materials used for stainless steel end caps include 321, 316L, duplex steel, and 2205; the service life of each of these materials is no more than 3–4 months. The thickness of the end caps is 20 mm, and they need to be replaced frequently, which results in high costs. How do other companies in this industry handle this issue?
Have seen 625 pure material—from Huaibei； Or consider a double-layer composite material (carbon steel base layer on the outside + 625 deposited on the inside, which is cheaper than using pure material)
In our chlor-alkali industries, the ion exchange membranes produce alkali with a concentration of 32%; for producing caustic soda in tablet form, alkali with a concentration of 48% is obtained. Evaporators for this purpose are made of pure nickel, and as far as I know, those used for over a decade have not failed at all.
Only nickel-based alloys can be used, with NI201 being a good choice. Check the corrosion manual and you’ll know. A large number of corrosion coupon tests have shown that, under the operating conditions you described, nickel-based alloys meet the requirements.
Resistant to strong alkali corrosion; previously cast iron was used, but nickel is now more commonly employed.
I have a report on the corrosion resistance of special materials here; it’s quite large, so I can send it to you privately
The current boiling method has been largely phased out; nowadays, the falling film evaporation process is mostly used, with nickel being the material chosen for the falling film tubes.