Preliminary Investigation into Factors Affecting Second Critical Solids Black Liquor Scaling, 2000 Pulping / Process & Product Quality Conference Proceedings

J. B. Smith, J. S. Hsieh--Black liquor evaporators continue to be a key bottleneck to improving the operational efficiency of the typical pulp mill. As the evaporators are being pushed to higher and higher product solids levels scaling issues have again become an area of intense study. Higher solids concentrators currently operating in pulp mills are now experiencing sodium carbonate, or second critical solids, scales that pose different problems than their burkeite predecessors. This work has expanded on a previous effort directed at examining the onset and magnitude of second critical solids scaling.

A previously published batch evaporation technique was used in conjunction with a dimple plate falling evaporator to measure scaling in several kraft black liquors. Liquor was concentrated in the evaporator under varying conditions to examine how compositional and operational variables affect second critical solids scaling in black liquor. In this study increasing steam pressure and decreasing second critical solids increased the scaling rate observed in several kraft black liquors. These initial insights into higher solids scaling are the first steps in a continuing effort focused on elucidating this area of kraft chemical recovery operations.