Pagancat - I'm glad you mentioned that. It didn't make sense to me that charcoal ash would be bad in a compost pile, so I looked it up. Here's what a University of Colorado website says:
"Charcoal is most commonly made from burned wood. It is highly alkaline (high pH) and also rich in potassium salts. Colorado soils are already highly alkaline and rich in potassium. Adding charcoal ashes to gardens here only adds to soil characteristics already in excess.
Some gardeners may have applied ashes to eastern U.S. soils that are acid and low in potassium. In Colorado, soil circumstances are different and the practice is not recommended."
If you recall, I'm composting a bunch of oak sawdust, cornstalks, and grass clippings. The sawdust is acidic and low in potassium, so some charcoal ashes ought to be just the thing.
Good to know - I have nearly neutral soils, so I'd best not... but yeah, sounds like the perfect amendment for yours.
I think part of what folks were saying was the additives in commercial briquets were harmful, but like I said, it wasn't really completely explored... with as large as the project you're handling is, it's probably going to be somewhat safer to use - unless you barbecue in the same quantities that you compost!
There might be some confusion between charcoal ashes and coal ashes also.
I found one strong warning against ever using COAL ashes in compost because it has levels of sulfur and iron that are lethal to plants. That makes sense, because coal is just another form of petroleum - not something you'd want in the garden.
But I'll take my chances with the charcoal ashes - there may be some additives in small amounts, but the stuff is made from hardwood.
As said before, the ashes are going to sweeten your soil...and are going to give a lot of Potassium. Unless you are growing bananas...or other fruit, unless your soil is lacking the K, you may not need it. We take our burn pile ash and put it directly on the bananas...which love K. Our soil is slighly acidic...so it wouldn't hurt in the compost... Guess it all depends on your soil NPK...
But...would ash have anything to break down in the compost...? Would it smother the process going on? I just throw ashes directly on the stuff that needs to use it up!
I think I've read that those charcoal briquettes are chemically treated to make them ignite and burn. Don't remember what's used, maybe gasoline or kerosene, anyway some kind of petroleum product. It's not something I'd want in my garden.