Student or Learner
"To the West, in Langzhuo steelworks, No. 5 furnace comes on line."
I don't understand this sentence. Can somebody help me? Thank you!
To "come on line" means that something which was not working, for whatever reason (deliberate, or because of maintenence), is now working.
It usually also means that the item is one of a series -- thus the "on line" part.
A steel factory might have ten furnaces, of which six are working. They are probably also lined up along a specific wall (or wherever). If another is fired-up, a seventh furnace "comes [or goes] on line."