Scaling During Evaporation of Acidic Bleach Plant Filtrates

Abstract

The potential danger of heat surface scaling during the evaporation of acidic bleach plant filtrates is discussed. The results of ECF and TCF filtrate evaporation tests are presented. The purity of condensates is analyzed and their potential use to replace fresh raw water in bleached pulp washing is evaluated. No severe scaling was observed on the heat surfaces. The precipitation seems to happen for the most part in situ in the liquid phase. This means, however that the evaporator should be designed so that it tolerates suspended matter in the evaporated liquid. When the pH of the filtrate is properly adjusted the purity of the condensates meets, after slight stripping, the requirements set for the wash water of bleached pulp.

Inhibitive effect of calcium on the primary nucleation of sodium carbonate in the evaporation process of the caustic liquor

“…Many evaporators suffer from scaling of their heat transfer surfaces and the type of scaling varies for different industries. [3][4][5][6][7] In the alumina industry, the scaling by sodium carbonate is the major problem due to its high content in caustic liquor. The presence of sodium carbonate in caustic liquor is unavoidable and originates from three main sources: 1) transformation of calcium and magnesium compounds in bauxite during alumina extraction; 2) absorption of CO 2 in the air by caustic liquor, especially during the precipitation process; 3) undecomposed lime after lime is added to the caustic liquor.…”

Pulp and paper effluent management

“…The project demonstrated a chloride removal efficiency of 90% with simultaneous 80% sodium return to recovery cycle. Trials revealed almost no scaling symptoms on heat transfer surfaces and overall the heat transfer coefficient was maintained Jarvinen (1999). described the potential danger of heat surface scaling during the evaporation of acidic bleach plant filtrates.…”