Chemical recovery at the kraft mill is the process whereby the valuable inorganic elements are extracted from spent kraft liquors and regenerated under their form effective to the cooking of the wood and energy is produced from the dissolved organic fraction. Many unit operations are involved and sometimes insufficiently described in terms of chemical engineering and thermodynamics.
In the general framework of the conversion of kraft pulp mills into wood biorefineries, this thesis aims at developing mathematical models of the overall kraft recovery process for implementation in a decision tool.
A comprehensive literature review was made regarding the models of the unit operations and the properties of the constituents. A database of the thermodynamic, physical and chemical properties of the constituents was created. The existing models were analysed and a new modelling approach for the evaporators was developed. The models were implemented in a C/C++ library which was called in an object oriented simulation platform using the Modelica language (OpenModelica/Dymola) and were validated against literature results.
Several simulation scenarii have put forward the main issues for global energy gains and the directions for possible improvements of some operations. More particularly the high refinement of the evaporator model in terms of thermodynamics and chemical engineering, above the published literature on the topic, opens novel perspectives in terms of strategy for process control of the evaporator train.
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