Afaik the process of refining brine is also known as “brine graduation” and from that point of view “graduation” has well something to do with brine refining. You will find this term also in Wikipedia EN (graduation tower) as well as several dictionaries (Leo, Pons and others) where the precise german term “Gradierwerk” is translated as graduation works or graduation house (see #6).

I am very much sure that a majority of people in Germany don’t know what is meant by the term “Gradierwerk”. They would probably have some vague idea about a “Verdunstungsbauwerk” but the correct term nevertheless is “Gradierwerk”. I understand it is better to tag objects with the correct term instead of using some “easy to understand description”, as we do with other objects as well. I am sure a lot of people do not know what a “heliostat” may be, but anyhow it is tagged as such and not as “solar tower mirror”.

It has to be added that this kind of object is disappearing step by step. Most of them have been closed down within the past 100 years and those still in use have become more touristic objects instead of production plants. Apparently not much more than 200 may still be operated in Europe, most of them in just 4 countries. From that point of view I do not see much reason to change the actual tagging which is “graduation_tower” for most of them. We should just leave it like that.

More information about brine graduation here.