Originally Posted by Mo-Dave
I am no chemist but I don't think density would play much of a factor as you say unless you were burning something like rocks or steel that would require a very high heat so more oxygen would be needed.
Yes if the proper amount of intake/oxygen with the proper amount of exhaust/carbon monoxide is applied then lump should burn very close to the same rate as charcoal. I always have leftover lump in my uds for the next cook. You can have all the exhaust you need but lack of oxygen/intake and the fire will still smolder.
And if you have all the intake you need with limited amount of exhaust you will still smolder the fire.