Stack Height/Limits of Thermal Power Plants
Generation Capacity	Recommended Stack Height for Optimum Dispersion of Sulphur Dioxide
500MW and above	275
200 MW/210 MW and above to less than 500 MW	220
Less than 200 MW/210 MW	H=14 (Q) 0.3 where Q is emission rate of SO2 in kg/hr, and H is stack height in metres.
Source : Environmental Standards for Ambient Air, Automobiles, Fuels, Industries