Transient simulation of lime softening process

Hardness in water is due of existence of some cations that are mainly calcium and magnesium. In lime softening process calcium is removed from water by addition of lime and precipitation of Calcium in the form of Calcium Carbonate and separation of this precipitate by sedimentation process. Performance of lime softening process, a physicochemical process, depends on many factors that are fluid flow pattern, chemical reaction kinetics and thermodynamic equilibrium, coagulation, flocculation and breakage rates and sedimentation mechanism. In this research work it is attempted to simulate this process by deriving the governing equations considering all these factors and numerically solving these equations in order to predict performance of this process under transient and steady state conditions. The case study presented in this article is for a rectangular lime softening sedimentation basin. Discretized particle size population balance in the range of 2.5-201 μm is incorporated in governing equations. Transient profiles of chemical species concentration, particle size distribution and hydrodynamics are outcomes of simulated case study that are presented for some specific time instant as an example.

Keywords:

lime softening process , simulation , coagulation , flocculation , sedimentation Introduction: