Dynamic modelling and simulation of eutectic freeze crystallization process for recovery of ammonium sulphate from aqueous solutions

The advancement of industrial sectors generates large amount of wastewater containing ammonium sulphate (AS) ions, yet the current AS recovery technologies are energy-extensive and produce excessive sludge. In this study, a dynamic model for a batch crystallizer was developed to investigate the eutectic freeze crystallization process of AS in aqueous solutions using the method of moment (MoM). The variables affecting the crystal size distribution of AS and ice were described in terms of zeroth moment (& mu;0), first moment (& mu;1), second moment (& mu;2) and third moment (& mu;3). The & mu;0 of ice crystals increased significantly until 2 s and slowed down thereafter while & mu;0 of AS crystal increased steadily and reached a constant value of 1/m3s after 1 s. The & mu;1 , & mu;2 , and & mu;3 of the AS and ice crystals depicted a similar increasing trend. Through process optimization using a 3-D plot on the initial concentration of the system and initial temperature of cooling fluid which had been identified as the significant parameters via iterative plot using MATLAB software, the AS and ice reached maximum crystallization at 255 K which was close to the eutectic point of AS-water system at 254 K. The dynamic model which comprised of population, mass and energy balance equations established in this study demonstrated effectiveness in the prediction of crystallization of AS in aqueous solutions.

Automated summary

In this study, a dynamic model for batch crystallizer was developed to investigate the eutectic freeze crystallization process of ammonium sulphate (AS) in aqueous solutions. Through process optimization, the significant parameters were identified as initial concentration and initial temperature of cooling fluid, and it was found that AS and ice reached maximum crystallization at 255 K which was close to the eutectic point of AS-water system at 254 K. The dynamic model established in this study demonstrated effectiveness in predicting the crystallization of AS in aqueous solutions.