Thesis for the Degree of Master of Science


Year 1996
Nina Bergman

Calculation of black liquor material properties and reactions in dynamic simulation

The aim of this work was to develop the Advanced Process Simulation software (APROS) so that the dynamic models of a black liquor evaporation plant and a kraft recovery boiler can be combined. In order to do this, new software modules for calculation of black liquor material properties and composition were designed, programmed and implemented. Also, the existing programs for the calculation of Arrhenius reaction kinetics were updated.

First, models for black liquor properties found in the literature are presented as well as a description of the physical and chemical processes in the recovery boiler. After this, the database structure related to the material properties calculation in APROS software is described and finally, the new data structures required for the calculation of black liquor properties and composition are developed. The procedure of adding chemical reactions to an APROS simulation model is also presented.

The programs for calculation of black liquor properties were tested with a rising film evaporator model developed earlier, and in order to test the reaction kinetics calculation, a simple model of the smelt bed was built. The simulation results indicate that the programs work properly. Also, the calculation speed of the evaporator model was increased markedly.

The parameters o the material properties correlations may vary a lot depending on the pulp process and the raw materials used. In this work these parameters were not identified according to an existing process. Instead, the parameters used in the test runs were adapted from various literature sources. The numerous reduction reactions of sodium sulphate in the smelt bed were combined into one simple test reaction. Therefore, the results from test runs can not be directly compared to real plant behaviour. However, the new programs allow the examination plant by means of simulation.

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