@Number 90 posted:In my experience it has always been solid consists of rotary dump cars or bottom door cars. Maybe they do mix them, but I have never seen a dumper that could unload both kinds. But there may be other practices.
Tom,
There are plants that only rotary dump one or two cars at a time, such as the Belews Creek plant near Walnut Cove, NC. and of course Pier 6 in Norfolk, VA. (They may be able to handle two cars at a time, it's been a while since I have watched the operation there.). So, to the OP, it doesn't matter what type of car they are dumping.
I have never heard the term "porter" used before. Coal cars are either "hoppers" or "gons" around here.