All of my egg shells are put on a napkin & microwaved for 2 minutes no matter if there's one or several. When you take them out they are dry so bacterial won't form & won't spoil; just fold napkin around them, crush with your hands, & save them in a container till there's enough to powder in a blender. This egg shell powder is good for gardens as a topping around plants, if you don't over blender it or just crush it, then it makes a good rough surface topping that keeps the slugs away from strawberries & adds nutrition to the soil. This powder makes excellent bedding/food (along with wheat bran, etc.) for raising mealworms to feed the chickens a "clean" protien.
Personally, I no longer feed chicken egg shell "byproducts" back to chickens, after a bad experience with a hen or two getting ideas after feed shells & breaking eggs, in a prior flock years ago. The "egg breaker" made a mess & who needs that. Besides crushed oyster shell (for calcium) for layers works very well, leave it out free feed for layers at all times (under a roof) & they will eat it when they want & need it. Non-layers (not producing eggs) don't usually need that much calcium & too much calcium can be bad for kidneys. There's good calcium along with other nutrition in alfalfa meal too as a additional supplement, or water soaked alfalfa pellets, or alfalfa hay. But, crushed oyster shell is a good primary source.