In the present paper, an incinerator of waste liquids is developed so that atomization takes place upwards on the centerline of the burner in a riser. Waste liquids are modeled by using three liquids, namely, water, water-ethanol and a solution of water-ethanol-ammonium sulfate. The stable combustion region of a methane-air diffusion name with the atomization of liquids, and the behavior of the droplets and NOx emission in the riser are studied. The stable combustion region expands somewhat to a higher equivalence ratio when material with heat generation like ethanol is contained in the liquid. Conversion from nitrogen in ammonium sulfate (fuel-N) into NOx falls with increasing atomization rate. Preferable fittings between the data in the present work and Fenimore＇s correlation are obtained. It is found that almost all evaporation of droplets occurs in the flame, and the behavior of the evaporation rate of atomized droplets is described well by the behavior of the NOx emission rate.