When I use eggs I put them straight in a cake pan that I use strictly for drying eggs. When I have the oven on for whatever reason I place the pan in there and after about 10-20 minutes. (I usually try to do this after I'm finished cooking and after I turn the oven off cause I'm bad about forgetting them and they will start to stink if you leave them in there too long!) When their cool I take a few pieces of paper towel lay it over the top and just smash them up. That's it.
I do it the same way that Barred Babies does when I feed the eggshells back to the hens. I don't do it very often though, mostly I just put oyster shell out for them free choice.
Chickens will eat eggshells just about any way that you give it to them. I crush the shells a little bit and toss them in with any other kitchen scraps I might have. The shells keep disappearing so I figure that they must be eating them. I also have oyster shell available all the time for them. I think that they like the shells better than the oyster shell.
Let them dry a bit, crush them up some so they don't look like a complete egg and toss them in. There is no need or reason to process them in any other way--if there are any germs on them they came from your birds in the first place so they can't harm them. Some people worry too much and, consequently, make more work for themselves--IMHO.
I have a ziplock under the sink that I put the egg shells in. They dry on their own - I will crush them down when it gets real full. Once the bag is very full, I grind them in the food processor and store them in an empty peanut butter jar back by the coop. I have a tuna can - had to snag from a friend since we can our own, that I keep filled in the coop. They eat a little here and there. I agree with woodmort - don't need to spend to much energy on it. I don't think they will ever eat all the shells that I could grind anyway.
i give them raw eggs and eggshells as a treat & they love it i wash them off with a hose beforehand just so there is no poop on them. crushing the shells so they dont look like eggs is a good idea so that they dont start pecking holes in the ones you want to eat for breakfast
My incredibly spoiled girls get scrambled eggs complete with shells & plain yogurt every morning.
I keep a feeder of free-choice oyster shell that is largely untouched.
Their eggshells are tough to crumble so it appears they are getting enough calcium from their breakfast.
I use a 3# margarine tub to save the eggshells, when full I dump them in a ziplock baggie and beat them...great way to take out frustrations, have even used a rolling pin on them.
When they no longer resemble an egg, I take the baggie out to the coop/run and use to fill the oyster shell/eggshell container (a tuna can screwed to the wall). I'm cheap...this is simple with no power tools or energy needed other than my own and I can always afford to get rid of some calories.