If you can get the coal away from the pipe inlet at the bin, you can try to hand crank the auger to either bring the coal in or reverse it back to the bin side. Put the feed pawl up and hold the check pawl and crank away.
Removing the pipe coupler will expose the worm coupling and allow you to separate the pipes. The solid couplings can make pipe removal difficult, which is why I would use the split coupling. Whatever you do, be sure to butt the two pipes tight together inside the coupling when you're done. You may have to break the pipe coupling with a hammer if it wasn't never-seized. While you're at it, check the short worm for sharp edges on the flytes. That will also cause grinding.