Industrial fuel (4)
I believe the answer is:
coke
'industrial fuel' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for coke that I've seen before include "Substance left after gas and tar have been extracted from coal" , "Drink - drug - solid-fuel product" , "Fuel derived from coal" , "something for heating" , "Furnace fuel" .)