My soil test indicated low soil calcium. Lime is a perfectly good calcium supplement, as is good wood ash. So is ground eggshell.
I dry the eggshells until ready to grind up. I store them in an open container so they dry quickly and done become gross. I used to crush them in my hands but the food processor does a better job. I don't know if they will dull the blade over time. I have t noticed any issues.
I scatter the ground eggshell and, when the soil is cultivated, it disappears into the soil. The main mineral in eggshell is calcium and a fair amount of phosphorus, but they also contain small to trace amounts of magnesium, sodium, aluminum, boron, copper, manganese, iron, potassium, sulfur, and zinc. Eggshells are 5% protein, so there is a fair amount of nitrogen as well. Research varies as to the pH altering effects.. I think that is due to, the eggshells are slower release than lime so the effect is spread out over a longer time.
Considering the high cost of things, it seems like it's a good idea to make use of the eggshells' nutritional benefits rather than disposing of them in landfill where they serve no purpose. Combined with coffee grounds and bone ash, this is a replacement for much of the fertilizer needs of my vegetable garden.