Object-oriented simulation of hydrometallurgical processes: Part II. Application to the bayer process
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I.
INTRODUCTION
BAUXITE is the most important raw material for the production of alumina. Currently, the Bayer process is the most common hydrometallurgical method for the production of pure alumina. In the Bayer process, ground bauxite is digested with caustic solution in steam-agitated autoclaves at high temperatures. The resulting sodium aluminate solution is separated from the mud residue and cooled before entering the precipitation tanks of the crystallization section. The solution is also seeded with recycled fine alumina trihydrate, which results in additional precipitation. The larger particles are recovered, washed, and calcined to the alumina product. Due to the obvious significance as well as the inevitable complexity of the entire flowsheet of the Bayer process, its simulation and flowsheeting play an important role in the successful design and analysis procedure. Hydrometallurgical processes are included in many commercial process simulators. However, the simplified mathematical models used, the limited thermophysical properties database involved, and inadequate representation of the industrial flowsheet make the use of such general-purpose computer tools less suitable for detailed simulation efforts. Muller and Johnson[2] proposed a mathematical model suitable for the dynamic simulation of the precipitation section of the Bayer process. Chen et al.[3] used ASPEN to simulate the digestor/flash system of the Bayer process. The models employed for simulation purposes were quite simple and could be used for preliminary design purposes. Steemson et al.[4] developed a mathematical model for the precipitation secC.T. KIRANOUDIS, N.G. VOROS, T. KRITIKOS, Research Assistants, Z.B. MAROULIS, Associate Professor, and D. MARINOSKOURIS, Professor, Department of Chemical Engineering, and N. PAPASSIOPI and O. DIMITROPOULOU, Research Assistants, I. PASPALIARIS, Assistant Professor, and A. KONTOPOULOS, Professor, Department of Mining and Metallurgical Engineering, are with the National Technical University, GR-15780, Athens, Greece. Manuscript submitted October 29, 1996. METALLURGICAL AND MATERIALS TRANSACTIONS B
tion of a Bayer plant. Kiranoudis et al.[1] developed an object-oriented process simulator to meet the needs of flowsheeting of complex hydrometallurgical processes. In the current work, the developed simulator[1] has been used for the detailed simulation of the entire Bayer process flowsheet, including the digestor/flash section as well as the precipitation and washing circuits. The simulator is of a modular type regarding solution of mass and energy balance equations, while user input is carried out interactively through a specialized graphical user interface. The models used for each process unit involved in the flowsheet are appropriately described. In this way, the overall effect on the entire plant efficiency of certain design parameters could be studied and analyzed in detail. The operational parameters involved are typical for the operation of such a plant (original performance data were provided b
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