I'm always a bit suspicious of translations from Linguee, but it looks as though this one is probably right:

"A la hora de diseñar instalaciones de clasificación con los internacionalmente conocidos cilindros de triarbejón (los antiguos MCK), nos atrevemos con todo tipo de arroz"
"Whether you're processing risotto rice, basmati rice or Thai rice, short-grain or long-grain rice - we plan and design your grading systems with world-renowned trieur cylinders (formerly by MCK) for fractioning in any number of length categories, all the way to brown rice."
https://www.linguee.es/espanol-ingles/search?source=auto&que...

Triage means sorting, so it makes sense.

"Basic operating elements of the trieur block are the trieur cylinders which can operate both as a whole and separately."
http://www.agriexpo.online/prod/melinvest/product-169705-559...

"In Trieur cylinders (half-corn cylinders, cylinder separators) grain is slowly fed into the upper end of a rotating, inclined metal cylinder"
https://books.google.es/books?id=s9tf70Wk3bYC&pg=PA319&lpg=P...

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Note added at 31 mins (2019-01-11 09:19:32 GMT)
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Here's an old illustrated description of a "triarbejón", on pp. 52-53 of this book (Tratado práctico de la molinería, 1895).
https://archive.org/details/TratadoPrcticoDeLaMolineraConoci...

I think you can also call them "cylinder separators":
http://www.cimbria.com/products/seed-processing/indent-cylin...

Or "(cylindrical) trieur separators":
https://www.hampshiremills.org/Newsletters/118 Autumn 17 New...


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Note added at 53 mins (2019-01-11 09:41:06 GMT)
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I think the cylinder part needs to be mentioned because there are other types of separator/sorter. Indeed, they're distinguished here (another old text):

"Como se ve en la Fig. 19, un electromotor de 1/2 caballo acciona simultáneamente un triarbejón y una separadora." (figure 19 is not present, unfortunately):
http://hemerotecadigital.bne.es/pdf.raw?query=parent:0005231...

I think my final (?) recommendation might be "indented cylinder separator", because a key feature of the "triarbejón" is the cells (alvéolos) in the cylinder. You can see how they work in my archive.org source above.

"El triarvejón o cilindro con alvéolos para semillas finas MSA730 permite configurar cualquier tipo de diagrama de elaboración"
http://www.mazzettisas.com/?p=99&lang=es

"Triarvejón (Separador por alveolos)
El triarvejón separa las semillas cortas y rotas del producto que estamos seleccionando. Mientras el grano ya limpio por aire y cribas va através de la máquina, los granos cortos son separados. Estos se depositan en los alveolos y son echados a la canal interior para su separación."
https://www.interempresas.net/FeriaVirtual/Catalogos_y_docum...
Note here that the "triarvejón" is part of the seleccionador, not the whole of it.

"The PETKUS Indented Cylinder Separators ZK / ZL are used for the sorting and separating of seed, grain, fine and vegetable seeds, and similar agricultural, grained and free flowing granular products. The product is separated according to its length. [...]
The grain settles down in the cell pockets, and the rotation of the cylinder distributes it into the trough."
http://www.petkus.com/products/-/info/sorting/indented-cylin...