I have to write a figure like 18 million 192 thousand tons.
If I use commas, how shall I write that?
For example: 18,192 million tons OR 18.192 million tons?
If you were referring to "18,000,000 tons," you could write this as "18 million tons." I don't know of any way that you could shorten "18,192,000 tons," though. (At least, not in a style that we use in English.)
Do you want to shorten it even if it means using just an approximation?
Then you can say 18.2 million tons.
Otherwise you are pretty much obliged to do the whole thing:
18,492,000 tons.