Effect of Ammonium Compounds as Additives on the Dissolution Rate of Limestone Samples Sourced from Tirunelveli District, Tamil Nadu, India

Sulphur dioxide (SO₂) represents one of the most important air pollution generators. The rate of CaCO₃ dissolution in slurry scrubbers for flue gas desulphurization affects SO₂ absorption, CaSO₃/CaSO₄ scaling and ultimate CaCO₃ utilization. Limestone is the low cost naturally occurring chemical which is the preferred reagent in many conventional WFGD systems. However, under normal system operating conditions, the limestone dissolves slowly. Therefore, in order to increase the alkalinity of the limestone slurry used in conventional WFGD systems and hence increase the system's SO₂ removal efficiency, the use of ammonium compounds as the possible additives has been examined in this study. Under normal operating conditions, once the slurry containing the dissolved limestone is sprayed into the SO₂ absorber, the dissolved limestone is quickly depleted making the slurry ineffective in removing more SO₂ and requiring a high rate of slurry recycle. As a result, high capital and operating costs are required when low cost limestone is employed as the reagent in WFGD systems. Increasing the limestone dissolution rate in WFGD systems allows courser limestone particles; lower limestone stoichiometry and lower slurry recycle rates to be employed, thereby saving capital and operating costs. Marginal grade limestone samples collected from Tirunelveli district, Tamil Nadu have been taken up for this particular study under conditions similar to those encountered in wet FGD processes.