hard rice coal fusing together into "black concrete"

I had some bagged rice coal left over from a previous season. I let these remaining bags sit stacked on a pallet all summer exposed to both rain and sun. When fall came I began using the coal in a Pioneer stove. As I used it I noticed the coal did not fall into the feeder and fall away from the sides of the hopper like the coal from the same pallet did the previous year. The Pioneer hopper has no angles on it so the coal normally falls into the feeder leaving coal in the bottom where it is angled from the feed opening up to the side of the hopper on all sides. This coal that sat in bags all summer exposed to the sun did not flow into the feeder "normally". Only the coal directly above the feed opening would fall creating a hopper full of coal with a hole in the center just above the feed opening. The coal was sticking "fusing" together which is why it would not fall into the feeder "normally". I had to push it over and fill up the hole that was created in the center of the full hopper with my hand. It did not take much effort to break it apart and push it into the center of the hopper. I continued doing this all winter. When spring came and I emptied the hopper to clean it out, the bottome of the hopper (remember this is a box without angles) where coal had sat all winter the coal was stuck to the bottom and sides and fused together like black concrete and it was just as hard to remove. I had to get a chisel and hammer to break it loose.

This must be due to the sun?

Anyone else experience this?

Is there anything you can use to cover it with if it is being stored outside all summer to prevent this?

i use the anthracite super vibrater available from leisure time products i think larry flint had the same problem with his rice coal

Just a guess, were the bags (assuming they are plastic here) breaking down from the sun? If so, perhaps particles of plastic from the bags went into the hopper with the coal. As it warmed getting closer to the fire it melted leaving a gooey mess that hardened like rock once the fire went out? When chipping it out, did it seem consistent with what you would expect from a plastic?
Anthracite is the Chuck Norris of coals, I doubt the sun could hurt it.

That's usually the result of dirty coal. What will happen is all the fines migrate down on the sides. As you add more coal the amount will build on the sides and it allows it to get more of an angle. I'm assuming the coal is probably still a little wet when you load the hopper? When that dries it acts like glue.

One reason you might have dirty coal is for the same reason. As the pile grows outside the sizing plant the coal will slide down from the top, the center of the pile will have the most fines especially with nut and pea. If you ever get to breaker if the pile is nice and large take a good look at it. The outside of edges of the pile will have all nice rounder pieces. When you start digging and get near the center you'll start getting flatter and dirty coal. If you get it delivered you'll find this same flatter and fines wherever the end of the chute was.

The bags have sat all summer in the sun and rain. I realize the bags will eventually disintegrate if left in the sun for a long time however in this instance they were still in great shape. The rice coal inside them was also still wet, the bags actually got more water in them from sitting out than they had initially since the water would not evaporated out very easily.

Richard S., what do you mean by "dirty coal"? Are you saying the "fines" have less coal in them and more "something else" meaning the dirty part?
My thinking was that the fines are just tiny bits of coal that have broken off. Are they not the same composition as the larger pieces of coal or are you saying the "dirty" stuff in coal breaks off easy thus these fines are not really coal but something else and this something else fusing together with itself is what I had to chisel away? Also does your suggestion apply to the large rice coal chunks themselves "sticking" together in the top of the hopper thereby preventing them from falling towards the center?

I wonder about the sun being a contributing factor because since that incident I have always stored the bags in my garage. I buy two years worth, use one year of coal and store the second years worth all summer. The bags are kept in the garage on a concrete floor. These bags will form some small whiteish/yellowish looking dirt/formations on the outside of the bags and on the floor which I assume is something leaching out of the coal however they have never given me the solidifying black concrete situation or the "sticking" together situation. They have always flowed through the hopper like you would expet, like stones and pebbles would if you filled the hopper with them.

I am from western PA so I have never been to a coal breaker or coal mine but I have noticed when I buy a pallet of bagged coal the stack has a piece of plastic covering the it. When I started burning coal I assumed this was to keep bags from filling up with rain. Now I wonder if it is two fold, to keep both rain and sun out. I know most dealers will not but some stove dealers at one time or another will have left over pallets of bagged coal sitting around all summer. Maybe the layer of plastic is so that there customers will not have the black concrete experience I had (if my sun theory is correct). This would also mean that this additonal plastic covering is not your typical plastic bag material. It actually feels a little different and it is kind of a light blue color also.

Am I crazy about this?