Evaluation of percrystallization for zero liquid discharge in the pulp industry = Evaluación de percristalización para cero descarga líquida en la industria de la celulosa.

Abstract

Percrystallization was evaluated at laboratory scale to determine the suitability of the technique as the core evaporation technology for achieving Zero Liquid Discharge (ZLD) of a Kraft pulping effluent. Compared with conventional evaporation/crystallization, percrystallization allows to operate at room temperature, using relatively unexpensive membranes and vacuum to allow evaporation of aqueous brine solutions. This suggests that it could be an efficient alternative to evaporate the concentrated brine from an upstream desalination stage (electrodialysis), as less energy would be required to heat the solution and allow evaporation. Percrystallization of electrodialysis brine was successfully achieved at laboratory scale, but high energy consumptions over 3,000 kWh/ton were measured. After this, the energy consumption of an optimized industrial system (with an efficient vacuum pump) was computed based on theoretical equations, indicating energy consumptions between 110-150 kWh/ton, still higher than those of traditional ZLD systems based on brine crystallizers (around 90 kWh/ton). Percrystallization could be an efficient alternative for low scale applications where the temperature of the solution must remain low (e.g., less than 40°C).