There are feeders under the pile that feed coal from holes spaced under the pile onto a conveyor. This conveyor carries the coal up to the surface and into the power plant.
Alternateley a front end loader can be used to dig up coal and dump it into a hopper feeding a conveyor on the surface or underground.
Be aware that real conveyors take up a lot of space. The maximum slope is around 20 degrees from horizontal, more likely 12 to 15 degrees.
I'm not a fan of the tubular conveyor galleries, they are hard to ventilate and hard to inspect for corrosion on the bottom. Still some people like them. They are cheap to fabricate. I would think some plastic pipe could be used for a start. Depending on the size of the conveyor, they might be 10 to 20 feet in diameter, 1 1/4 inch to 2 1/2 inch diameter in HO. Bigger than they look from a distance.
The vertical pipe you saw is to control dust as the pile is built. It also may support the end of the conveyor. The coal falls through the center and out the nearest window above the pile surface.
Large coal piles have to be worked almost constantly with bulldozers and scrapers to extend and reclaim the pile, pack down the surface of the pile to shed water, and occasionally dig out a hot spot before it can start burning. Coal is tricky to store because it can spontaneously combust.
I am interested in building a large modern HO scale power plant, but had some questions regarding the conveyor systems. I can see from pictures how the coal moves from rail unloading structures via conveyor which starts underground, to a stockpile area. Some plants appear to have a large cylindrical column at the end of the conveyor that has openings and appears to form the coal stockpile, and in some cases the conveyor continues from this point to the plant. What I am confused about is how the coal gets from the stockpile to the plant. There appear to be conveyors which start underground from the stockpile area to the plant. Any help from those more versed in plant operations would be greatly appreciated.
Second, does anyone have a good method for modeling the cylindrical enclosed conveyors seen at some modern plants?
Thanks