Evaporator Scaling at a Zero-effluent BCTMP Mill

Over the last few decades, many pulp mills have implemented measures to reduce water consumption and maximize effluent reuse. With increasing closure of the effluent cycle, species can accumulate in the process streams and deposit in equipment and piping which negatively impacts the mill operations and product quality. This work focuses on scale formation in the evaporators of a zero-effluent bleached chemi-thermo-mechanical pulp (BCTMP) mill in Canada. The evaporators are used to concentrate the effluent and recover water for process use. In this work, the liquor-side scale deposits were characterized, and a mass balance study was carried out to identify the sources of scaling components in the streams to the evaporators. The third part of this work involved solubility experiments to determine the effects of temperature, degree of concentration, and pH on the solubility of the scaling components. The mass balance and solubility data provide information the mill can use to develop mitigation strategies.M.A.S