(47b) Process Intensification of Multi-Effect Evaporation and Crystallization

Multi-effect evaporation and crystallization are key separation processes for concentrating and purifying inorganic and organic solid products.  They are second only next to distillation in their consumption of energy with estimated energy consumption of greater than 660 trillion Btu/yr, or the equivalent of 110 million barrels of oil per year.  A small improvement in the energy efficiency can have major impact on overall energy savings and reducing the C-Footprint.  The objective of this DOE SBIR Phase I project focused on two specific aims: 1) to evaluate enhanced-tube performance for process intensification; and 2) to characterize fouling propensity of enhanced tubes in multi-effect evaporation and crystallization.  The process analysis was performed for the triple-effect and mechanical vapor recompression (MVR) crystallizers of the soda ash process.  Once a benchmark analysis was performed, the impact of enhanced tubes was evaluated in terms of reduced power in MVR and reducing the primary-steam pressure in the triple effect crystallizer.  The potential of energy efficiency in the MVR is direct and significant.  The primary steam in triple-effect is generally derived from power generation; therefore, by reducing the steam pressure increases the power generation.  Optimally designed enhanced tubes have shown to reduce fouling propensity in other applications.  The interactive effects of wall temperature, wall shear stress, and secondary flows in the vicinity of the heated wall surface are the governing factors associated with fouling.   Two types of enhanced tube were evaluated for applications in soda ash process.  This study also evaluated application of enhanced tubes in vertical or horizontal forced convective evaporator as well as falling-film evaporators.