Experience of low lime mud solids problems at a kraft pulp mill

An investigation was conducted to examine the causes of a low lime mud solids problem at a Brazilian kraft pulp mill. The results show that the problem was likely due to two main factors: the high SiO2 content in the lime mud and operation with high causticizing efficiencies during high sulfidity periods. High silica leads to the formation of gel-like calcium silicate hydrate, which makes lime mud more difficult to dewater. Variability in liquor sulphidity leads to operating conditions in the causticizing plant that are more susceptible to overliming, resulting in lime mud that is difficult to settle and to dewater.