I messed around for years with steel plates, weights, clay, dirt, rocks, and every once in a while got a barrel that stayed warm overnight which wasted some of the charcoal. After accumulating hundreds of containers of ground, sorted, dry engine grade charcoal, I realized I could quench the barrel with about 20 gallons of pond water, and the next day, dump it out into a pile. Eventually the contents of that pile would make it to the screening table, the grinder, and back to the screening table. This August (last month) we had about 25 days over 100° F, lots near 110° F, and any charcoal on the screening table was guaranteed DRY. All my extra drums and plastic barrels with lids are in use, so now I just transfer the charcoal to a feed sack or dog food bag and put it in the barn. If I ever get around to using it, it will have the same water content as any of the hundreds of bags in storage. I used to label the bags as to type of wood, and put the date on the tag, but now I just try to find a place to put it. Last week while out shredding pastures, I found two dead trees and used a front-end loader to move the wood to my charcoal making area. The wife asks why I keep making charcoal, and the answer is that I am attempting to slow global warming. (She buys that!)
So, just make a whole bunch of engine grade charcoal, and use the stuff you made years ago. Quenching with rain water works well, because as soon as mosquitoes appear in the collected water, it needs to be covered or dumped. Because of our coal-fired power plants, the rainwater has a pH of 3. (Carbon Dioxide to Carbolic Acid makes acid rain?) The acid water washed fines under the screening table go into the compost and end up in the garden. Good Stuff!