Study On The Carbonation And Crystallization In Soda Industry

The present paper deals with the problem of crystal growth kinetics of sodium bicarbonate and carbonation process simulation in soda industry.The crystallization experiments have been carried out in a batch ( seeded and unseeded ) crystallizer with two systems: NaHCO₃-H₂O and NH₃-CO₂-NaCl-H₂O. The crystal growth kinetics model equations are determined byanalysing seed size distribution and crystal size distribution. Model parameters were obtained with the methods of moments and optimization by solving the equations of mass balance of Na⁺ and crystal population of NaHCO₃.A mechanistic model, incorporating CO₂ chemical absorption, crystal growth, reversible reactions and crystal size distribution to simulate and optimize carbonation process and crystallization is developed. Model equations were solved with the methods of Tearnor, Lax-Wendoff and finite difference. This model is applicable to other Gas-Liquid reaction crystallization system.Some factors affected crystal quality such as: temperature, supersaturation, stirrer speed and batch time, were investigated. The results showed that crystal size distribution of sodium bicarbonate is mainly determined by nucleation rate in the critical zone of precipitation, which is controlled by the homogeneous nucleation rate. Crystal growth rate was independent of crystal size. The variation of optinum temperature during carbonation should produce reasonable number of nuclei and supersaturation for crystal growth. The whole carbonation process is controlled first by the CO₂ absorption in the critical zoneof precipitation, which are accelerated by the crystallization of NaHCO₃, and then by the reaction between CO₂ and OH^- in the liquid phase.