Scheduling for efficient reduction of fiber industrial evaporative lagoons

In a hardboard plant, the black liquor produced during the panel's pressing is treated in a new evaporation unit, to concentrate the solids up to 25%. Currently the concentrated black liquor from the evaporation plant goes to the evaporative lagoons to concentrate the solids up to 45%, by natural evaporation with subsequent burning in the furnace. The aim of this study is to develop an integrated system that improves the natural evaporation in the lagoons, by increasing the black liquor's temperature. To achieve this goal two artificial ponds were built, where the black liquor is heated with the hot water from the condensers, avoiding also the intensive use of the cooling towers. Therefore, two scenarios were studied for the heating of the black liquor. In the scenario 1 the two artificial ponds are used to heat the black liquor currently in the lagoons and during that period the effluent of black liquor from the evaporation plant goes to the lagoons. In the scenario 2 just one pond receives black liquor from the lagoons and the other one receives the effluent from the evaporation unit. The comparison of these two scenarios with the present situation enabled us to conclude that the scenario 1 is the best choice, because it allows us to obtain 45% of solids in the lagoons in less time than the current scenario and the operation period of the forced cooling towers is lower than the one corresponding to scenario 2. Therefore it is possible, with an integrated system, to achieve the solid content of 45% in the lagoons in 20 months, with the additional advantage of reducing the operational cost of the cooling towers. Copyright © 2009, AIDIC Servizi S.r.l.