can I put my old charcoal briquets in my compost?

You may want to check to see if the binder used is a petroleum product. Some of the briquets are bound together using these. However, if in a small amount I believe a good hot compost pile can handle. You may want to repost this into the composting forum and ask the same question to those guys, they are real good and may have better answers. Also add your location to your profile, it helps when you ask other question.