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Thermodynamic process modeling and simulation of a diaspore bauxite digestion process
Mälardalen University, School of Business, Society and Engineering.
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Bauxite ores which originated from separate mines have different characteristics, i.e. each bauxite ore has its own individual specifications. Jajarm bauxite is of the diaspore-chamosite type and its alumina to silica mass ratio is lower than other diaspore ores. Diaspore bauxite digestion in comparison with other bauxite types has more complicated operational conditions and requires higher temperature, pressure and caustic concentration.

 The present study was thus performed on the above mentioned digestion process and include two parts. First, the behavior of some key parameters of the process was experimentally investigated. Second, a simulation model was developed to predict the performance of the process, particularly thermal energy consumption.  The model was validated with several sets of the industrial data and close agreement was found.

 The effects of various trends in pressure drops of the flash tanks on the slurry preheating were analyzed. The results showed that the proposed pressure profile can lead to an increase in the furnace inlet slurry temperature. Alternatively, it can lead to an appreciable decrease in the furnace fuel consumption, which is required for having the existing operating temperature.

 The generated vapor in different stages of the process was determined. A considerable amount of the generated water vapor and thermal energy were lost. The model was further developed to study the effect of using a part of these vapors on heat recovery. The simulation results showed that in the new design, the pre-heater sections can gain 5.71GJ/h additional heat and the fresh slurry temperature increases by 11°C. Therefore, the furnace required energy is reduced by 11.9%.  The new design was implemented in the refinery and according to the energy department report, it has reduced the furnace fuel consumption by 8%, which is around 200kg of natural gas /h less than the earlier condition for every digestion line.

Place, publisher, year, edition, pages
Västerås: Mälardalen University , 2013.
Series
Mälardalen University Press Licentiate Theses, ISSN 1651-9256 ; 170
National Category
Engineering and Technology Materials Engineering
Identifiers
URN: urn:nbn:se:mdh:diva-19001ISBN: 978-91-7485-113-7 (print)OAI: oai:DiVA.org:mdh-19001DiVA, id: diva2:621425
Presentation
2013-06-12, Lambda, Västerås, 13:00 (English)
Opponent
Supervisors
Available from: 2013-05-16 Created: 2013-05-14 Last updated: 2013-05-31Bibliographically approved
List of papers
1. THERMODYNAMIC PROCESS SIMULATION OF THE DIGESTION UNIT IN IRAN ALUMINA REFINERY
Open this publication in new window or tab >>THERMODYNAMIC PROCESS SIMULATION OF THE DIGESTION UNIT IN IRAN ALUMINA REFINERY
2009 (English)In: Proceedings of SIMS 50, Modeling of Energy Technology / [ed] Brian Elmegaard, Christian Veje, Mads Pagh Nielsen, Tommy Mølbak, 2009, p. 173-178Conference paper, Published paper (Refereed)
Abstract [en]

Jajarm bauxite is of the chamosite-diasporic type, one of the hardest types of bauxite for alumina production. The Iran Alumina Refinery uses Jajarm deposits and currently operates at 65-70% of its nameplate capacity. Digestion is one of the most important processes in the refinery and has become the main bottleneck in the production. In this paper we study the effect of selected parameters on the behavior of this important section of the refinery using thermodynamic simulation of the digestion unit. The ASTM tables property method was used for vapor streams and the Elec-NRTL property model was used for the global digestion process. The digestion process was simulated with Aspen plus software. The results show good agreement with experimental data. The relationship between the incoming slurry temperature in the first flash tank and the preheater cold stream (slurry into the furnace) temperature and energy consumption is discussed.

Keywords
Bauxite, Diaspore, Bayer process, Slurry, Alumina digestion, Simulation, Electrolyte NRTL property model
National Category
Materials Engineering
Identifiers
urn:nbn:se:mdh:diva-19009 (URN)978-87-89502-88-5 (ISBN)
Conference
The 50th International Conference of Scandinavian Simulation Society,SIMS 50-Modelling and Simulation of Energy Technology, Fredericia, Denmark, October 7–8, 2009
Available from: 2013-05-15 Created: 2013-05-15 Last updated: 2013-05-31Bibliographically approved
2. DIASPORIC BAUXITE DIGESTION PROCESS SIMULATION
Open this publication in new window or tab >>DIASPORIC BAUXITE DIGESTION PROCESS SIMULATION
2010 (English)Conference paper, Oral presentation with published abstract (Other academic)
Abstract [en]

The alumina digestion process in the Bayer overall process like the other hydrometallurgical processes is under the effect of various factors and the control and optimization of quality and efficiency of the process and also reducing the energy consumption are of prime importance. Process simulation provides the possibility to investigate the impact of various factors and study the optimum conditions for obtaining the desired quality and reducing the energy consumption and environmental impact. In the digestion unit, the high pressure diasporic bauxite slurry, a mixture of ground bauxite, lime and caustic liquor, is decomposed.  The bauxite slurry is preheated in the high pressure tube pre-heater and then is heated up to the decomposition temperature in the furnace. The dissolution takes place in the tubular digesters and resulting product, aluminate slurry, passes through the expanding stage, including 11 flash tanks to recover the thermal energy. 

In this paper the thermodynamic simulation consecutive stages of the digestion unit process including the property methods and the evaluation and verifying the simulation results against their accordance with the real conditions are studied. The obtained results showed that the outputs of the simulation have good and acceptable accordance with the empirical data. Using the simulation program; the results of some case studies showed that in the current situation, less than 70% of the energy generated in the dissolution process is directed to the pre-heaters. Also more than 30% of vapor generated in the dissolution process is dissipated and wasted. By using the vapor generated in the last two flash tanks, the efficiency of energy recycling will be increased and thus the water waste and environmental pollution will be decreased considerably.

Keywords
Bauxite, Diaspore, Slurry, Alumina digestion, Process Simulation, Electrolyte NRTL
National Category
Materials Engineering
Identifiers
urn:nbn:se:mdh:diva-19014 (URN)
Conference
51st SIMS Conference on Simulation and Modelling, SIMS 2010 October 14 to 15, 2010, Oulu, Finland
Available from: 2013-05-15 Created: 2013-05-15 Last updated: 2013-05-31Bibliographically approved
3. Modeling and Simulation of a DiasporeTubular Digestion Process
Open this publication in new window or tab >>Modeling and Simulation of a DiasporeTubular Digestion Process
2013 (English)In: International Journal of Simulation and Process Modelling, ISSN 1740-2123, E-ISSN 1740-2131, Vol. 33, no 2, p. 126-133Article in journal (Refereed) Published
Abstract [en]

A simulation model is developed to predict the performance of a tubular digestion process of a low alumina/silica ratio diaspore bauxite type. The electrolyte - NRTL property method is used to calculate the equilibrium and thermodynamic properties of the slurry. The Aspen Plus simulator has been employed to solve the reaction and thermodynamic submodels. The model was validated with several sets of the industrial experimental data in terms of the flash tanks temperatures and close agreement was found. The simulation model has been utilized by the R&D department to predict the digestion process behaviour at various operation conditions. One practical output of this work is suggestion for a new design to increase the vapour and thermal energy recovery in the digestion process unit. As a result, the exhaust vapour from the last flash tank was directed to a new pre-heater section. The industrial output has been confirmed by the energy department that has decreased 8% in the furnace fuel consumption and leads to an increase of water recovery in the digestion unit.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:mdh:diva-19076 (URN)10.2316/Journal.205.2013.2.205-5798 (DOI)2-s2.0-84880843143 (Scopus ID)
Available from: 2013-05-31 Created: 2013-05-31 Last updated: 2017-12-06Bibliographically approved

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