Effect of resin and fatty acids on sodium salt fouling

Abstract

The evaporation of black liquor is an important, energy intensive unit operation in the kraft chemical recovery process. Between 50 and 85% dry solids, black liquor evaporators are susceptible to heavy sodium salt fouling leading to reduced heat transfer efficiency and in extreme cases, plugging. Recent mill experiences indicate that the addition of small amounts of resin and fatty acids containing streams (tall oil soap, tall oil, tall oil brine) to the concentrators can reduce sodium salt fouling. The underlying mechanism for this is unknown, which limits broader application and control. In this work we use model solutions of sodium salts in a bench-top scaling setup to investigate the impact of resin and fatty acids on sodium salt fouling. The results show that low concentrations of abietic acid and oleic acid can inhibit sodium salt fouling during nucleation and in the presence of a stable crystal population.