Application of a Solids Deposition Model to Control Falling Film Evaporator 'Crashing', 1997 Pulping Conference Proceedings

One of the most prevalent problems in pulp and paper industry is fouling in the evaporator train. Burkeite, a double salt of sodium carbonate and sodium sulfate, is one of the most common forms of scale found in the industry. This salt precipitates out of the black liquor stream after the liquor has been raised beyond the critical solids level. The precipitated burkeite can attach itself to the heat transfer surface and degrade the overall capacity of the evaporator. In this work the rate at which burkeite and other scales attach themselves to the evaporator’s heat transfer surface has been modeled in two ways. The first model addresses the assumed and experimentally determined impact of circulation rate, liquor level, sodium carbonate concentration of the black liquor, and steam pressure on this deposition rate. The second model determined the impact of these variables on a synthetic liquor solution. The development of a viable synthetic solution was undertaken in order to simplify experimentatal work on black liquor scaling. Both of these models were applied to actual mill data to determine if their predictive capability could be extended beyond the laboratory.