A fluidized bed combustor is $2 \mathrm{~m}$ in diameter and is fed with air at $250^{\circ} \mathrm{F}, 10 \mathrm{psig}$, at a rate of $2000 \mathrm{scfm}$. The coal has a density of $1.6 \mathrm{~g} / \mathrm{cm}^{3}$, and a shape factor of 0.85 . The flue gas from the combustor has an average MW of 35 and leaves the combustor at a rate of $2100 \mathrm{scfm}$ at $2500^{\circ} \mathrm{F}$ and $1 \mathrm{~atm}$. What is the size range of the coal particles that can be fluidized in this system.