Industrial plant gave off stench: years, on and off (7)

I believe the answer is:

smelter

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'industrial plant' is the definition.
(I know that smelter is a type of industrial plant)

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for smelter that I've seen before include "Place where metal is extracted from ore by heating" , "Extractor of metal from ore" , "One processing ore" , "Metal works" , "Industrial plant for extracting metal by heat" .)

I've seen this clue in The Times.

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