That's what was called 'Duff' and its not the coal we used for our home fires.
That duff could be destined for a Power Station but not sure.
'Hard up locals in the old days used to go down to the coal staiths with their old bikes and shovel up 'duff' waste into sacks then sit the sack on the bike and push it home.

For the benefit of younger people who haven't seen a piece of coal, here is a photo of a pile of it.