McCready wrote:
I have an open fire that's producing a lot of fine ash.
I burn smokeless coal, household coal and wood.

What can I use the ash for and how much of it can I put in my compost bin.

When you are burning more or less pure wood then no problem the ash it
potash fertiliser. Fruit trees and bushes respond well to a potash feed
in autumn. It is mild caustic so will burn leaves.

Otherwise the coal or smokeless fuel contains trace elements (lead,
copper, cadmium etc) massively concentrated in the ash that you really
don't want to add it to your garden soil. It probably won't do
ornamental plants any harm, but you don't want to add much coal ash to
your vegetable patch.

Regards,
Martin Brown