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This is the published version of a paper presented at 4th International Symposium for Gasification
(I-SGA 4), 2nd Sep, 2014 - 4th Sep, 2014, Schönbrunn Palace Conference Centre, Vienna, Austria.
Citation for the original published paper:
Mirmoshtaghi, G., Li, H., Thorin, E., Dahlquist, E. (2014)
THE EFFECT OF INCLUDING HYDRODYNAMICS FOR MODELING ATMOSPHERIC BUBBLING FLUIDIZED BED GASIFIERS.
In: Västerås
N.B. When citing this work, cite the original published paper.
Permanent link to this version:
The effect of including hydrodynamics for modeling atmospheric
bubbling fluidized bed gasifiers
G. Mirmoshtaghi1. D. Andersson1. M. Karlsson1. H. Li1.R. B. Fdhila1,2. E. Dahlquist1
1. School of Business, Society & Engineering. Mälardalen University. Box 883. SE-721 23 Västerås. Sweden 2. Automation Technologies. ABB corporate research.SE-722 26Västerås. Sweden
Abstract:
One of the approaches to model the fluidized bed gasifiers is to combine the reaction kinetics and bed hydrodynamics. The kinetic part of the model deals with main operating parameters such as temperature and pressure while the hydrodynamics consider the fluidization effect on the performance of the gasifier and consequently gas composition.
In this paper three major and one reference scenario in modeling the fluidized bed gasifiers have been studied and compared to each other. The indexes in evaluating each scenario are a) accuracy b) complexity c) flexibility to different input data. The reference scenario (S-0) is based on only using a kinetic model. First scenario (S-1) is the combination of kinetic and hydrodynamic models with the approach of “two phase theory”. Second scenario (S-2) is based on reaction kinetics and counter current back mixing approach in hydrodynamics of the bed. Finally the third scenario (S-3) is based on kinetics and hydrodynamics with the approach of bubble assemblage. The results would show the effect of including hydrodynamics as a part of modeling the biomass gasifier.
1. Introduction:
Several studies on investigating and modeling the fluidization phenomena in bubbling and circulating fluidized bed gasifiers can be found[1][2][3]. One of the developed theories was based on the idea of “bubble assemblage” which considers the bubble size growth along the bed height [4].The other theory which is used by different researchers in modeling fluidized bed gasifiers is “two-phase theory”. The basis of this model is to divide the bed in the bubble and emulsion phase [5]. The third hydrodynamic model studied in this paper is “Counter current back mixing” which has similarities with “two-phase theory”, but it focuses more on the solid phase (char) dynamic in the bed [3]
2. Concept and methodology:
This paper is based on comparing different scenarios to investigate: 1. If including the hydrodynamic model will increase the accuracy of the model in predicting the product gas composition and 2. How including different hydrodynamic modeling approaches influences the model complexity, flexibility and accuracy.
The reference scenario (S-0) is based on kinetic model without any hydrodynamic models. First scenario (S-1) is the combination of kinetic and “two phase theory” models while the second scenario (S-2) includes reaction kinetics and counter current back mixing model. Finally, the third scenario (S-3) is based on kinetics and bubble assemblage model.
Investigating the effect of including hydrodynamic models in modeling the bubbling fluidized bed gasifiers is the objective of this paper. The models are taken from literature and implemented in ASPEN plus. External FORTRAN subroutines are developed for each case
to combine reaction kinetics and bed hydrodynamics. Further the subroutines are used in ASPEN plus to model the bubbling fluidized bed gasifier.
3. Acknowledgements
The authors express their gratitude to the Swedish energy agency for major financing of this project.
4. References
[1] K. Daizo, L. Octave, I&EC Fundamentals., Vol 7(1968) p446
[2] K. Kato, C.Y. Wen, Chemical Engineering Science, Vol. 24 (1969) p1351
[3] F. Colin, P. Owen, Ind. Eng. Chem. Fundam., Vol. 11 (1972) p338
[4] Y. Wen-Ching, Handbook of Fluidization and Fluid-particle systems, Marcel Deker Inc., USA(2003)p246
