I have been racking my brains out to come up with some of the tricks we have used in the past to get material moving in a silo/hopper, and to do it cheaply and easily. From the sound of what the guys are saying, the opening is more then enough to discount particule binding/lodging in the opening. But, it's happening, so considerations are:
Moisture (As Greg says) and possibly exotheric (spelling is terrible, but basicaly, builds up heat): Since this material is hydroscopic, it's going to attract moisture, like lime does. Moisture is going to expand the particule and really increase the surface tension. This allows the material to actually hold it's self up.
Wall friction: When we work with difficult to move material, we do two things, (1) line the hopper walls with Stainless Steel, (2) Provide minimum 60 degree slope to the come. These two things effectivily prevent the material from sticking to hopper walls, along with the steep slope, prevents bridging.
We use vibrators and air cannons to also help us when necessary.
Corrictive actions for moisture are to make sure that internal temperature of hopper is the same as outside temperature. Make sure you have air circulation in the hopper, that is critical. Drill holes (which is what I did on my little moultries) in the underside. If this material is somewhat exotheric, heat will build up, and the cool outside temperature will create moisture in the hopper. You'll never get the material out if that happens. Ok, I'm done for a while.
