Discharges quantities of coal, say (5)
I believe the answer is:
sacks
This might be a double definition.
'discharges' is the first definition.
('sack' can be a synonym of 'discharge')
'quantities of coal say' is the second definition.
'sacks' can be an answer for 'quantities' (sack is a kind of quantity). I'm not certain of the 'of coal say' bit.
Can you help me to learn more?
(Other definitions for sacks that I've seen before include "Plunders; fires" , "Discharges" , "Plunders; bags" , "Large strong bags" , "sends up in flames" .)