Using Favor item Staff of Renewal, which grants a 20% cooldown reduction bonus.
Ring of Fire has a length of 7 seconds and a cooldown of 7 seconds.
However, you can't cast the second Ring of Fire while the first one is still active. You see the animation, the ring flares up, then douses again. The spell fizzled but the cooldown timer resets, making wait again for 7 seconds. And I think you still pay the mana.