Why 2 water sprays? - Usually it gets the top layer of coal wetted to the optimum, too much water too quickly will form a hardened crust that will then vibrate apart over the rail journey and produce dust. Ideally they want the top layer of coal - about 6 inches to remain damp for the entire journey. On long rail journeys its not uncommon for wetting to occur again just prior to entering the unloading facility.

Pretty old system as nowadays the coal loaders usually have a vibrating screen to separate the dust from the coal, dust is then sold for BBQ briquettes.