I live in the shamokin Pa. area. We take it to the township and they use it on the roads as nonskid. Greatest traction grabber for ice and snow you ever saw. It's not compost material, it is acidic, it does not breakdown.
put it this way--a couple of times last year I damn sure wasen't going off the porch--snowin & blowin like a bastard--soooo,I just dumped a couple of 5 gall.. pails of ash on top of one of the flower gardens & everything came back up just fine in the spring---I did rake it around & smoothed it out after the snow got gone
coal ash is slightly acidic depending on the particular coal you're burning, but no it won't harm anything. The trace elements and minerals in coal ash are comparable to the soil in general; unlike wood ash, it's basically coarse sand so it won't do much to help your compost.
I once had an old house that burned coal for many years and the previous owners just dumped the ash in the back yard. I wanted to plant a hedge of Arborvitae but when I dug a trench I found almost all coal ash. The hedge grew fine.