Evaluation of the effects of selective lime slurry preparation on spray dryer efficiency in flue gas desulfurization

This study discusses the effects of various methods of lime slaking and the effects of lime (CaO) processing on spray dryer efficiency in flue gas desulfurization (FGD). The efficiency data were obtained at a pilot spray dryer facility. Particle diameter of the discrete lime slurry (Ca(OH)₂) particles was measured by the settling method using Stokes' law and a Coulter Counter particle size analyzer. Photographs of dried Ca(OH)₂ slurry particles were taken by a scanning electron microscope (SEM).

The findings of this report indicate that lower slake ratios (pounds of water per pound of CaO) with hotter water produced smaller Ca(OH)₂ particles with more surface area available for reaction with sulfur dioxide (SO₂) and, therefore, a higher spray dryer efficiency. CaO that had minimal exposure to air gave, when slaked, the smallest Ca(OH)₂ particles with highest surface area, shown by SEM photographs, and the highest spray dryer efficiency.

Higher spray dryer efficiency, on a per unit basis, means higher lime utilization which lowers the cost of flue gas desulfurization and reduces the volume of solid waste produced.