Radak: Just like something that burns, it is consumed in smoke and is totally eradicated, so my days were evil, and it is as if they were consumed in smoke. And so it says "Kalu ve'Ashan Kalu" (37:20).

Malbim: He reached the ultimate termination and depicts the affliction like fire, and the body of the Klal of the nation as if it is placed on fire in the hearth. The fire melts it and separates it into parts, and they rise like smoke in the air. These are the days of his life; the bones that remained dried like in a hearth.

Radak: It is where fire is always kindled. It dries and is burned; so my bones dried.

Rashi: It is an expression of dryness, like "v'Atzmi Charah Mini Chorev" (Iyov 30:30). The Nun is due to the conjugation, like Na'asu and Niknu.