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Item type:Publication, Access status: without files , Modeling and flowsheet simulation of continuous fluidized bed dryersIn the current paper a simulation tool based on previous work of Burgschweiger and Tsotsas [1] is implemented within the framework of the flowsheet simulation program SolidSim [4]. The implementation within the flowsheet simulation program allows the simulation of the drying process for many different liquids and solids. It can also simulate the drying of mixtures of different solids. The module computes the vapor loading and temperature of the out flowing gas and the moisture and temperature distribution of the solids at the outlet taking into account their residence time distribution, their particle size and their moisture distribution at the inlet. Furthermore the model has been extended by a simple approach to simulate the drying in an elongated fluidized bed dryer. After validation the model has been used to study the influence of residence time, particle size and inlet moisture distribution in addition to drying of mixture of different types of solid. For the modeling it is assumed, that there is no classification occurring within the bed. This assumption is commonly fulfilled as long as the particle size distribution is not too wide and the fluidization velocity is sufficiently high. In this case the mixing action of the bubbles is dominating the segregation tendencies.Publicationtype: Journal Article160 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Fluidized bed spray granulation: Analysis of the system behaviour by means of dynamic flowsheet simulation(2010-12); ; Werther, JoachimNowadays, software tools for the flowsheet simulation of industrial processes are commonly used for design, simulation, balancing, troubleshooting and optimization purposes. Most of the tools are applicable to fluid processes only and cannot be effectively used for processes which involve solids.In this contribution we want to present the conceptual design of a new system applicable for the dynamic flowsheet simulation of complex solids processes. This system is developed as an enhancement to the existing simulation program.The novel software is able to simulate the unsteady behaviour of complex circuits of granulation processes. The transient behaviour during the start-up and changing of the process or material parameters can also be examined.As flowsheet examples, a typical spray granulation process with different schemes consisting of fluidized bed granulators, screens, mill and splitters was used. The mathematical model of the fluidized bed granulator is described by a one-dimensional population balance equation and coupled with heat and mass transfer and simple fluid dynamics.Received simulation results have shown that the proposed concept of the dynamic flowsheet simulation of granulation processes can be used effectively and has the potential to be generalized for other types of solids processes.Publicationtype: Journal Article23 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , The cell average technique for solving multi-dimensional aggregation population balance equations(2008-08-22); ; ; In this paper, the cell average discretization [Kumar, J., Peglow, M., Warnecke, G., Heinrich, S., & Mörl, 2006a. Improved accuracy and convergence of discretized population balance for aggregation: The cell average technique. Chemical Engineering Science, 61, 3327-3342] is extended to solving multi-dimensional population balance equations. Similar to the one-dimensional case, the scheme is based on an accurate prediction of certain moments of the population. The formulation is quite simple to implement, computationally not expensive and highly accurate. Numerical diffusion is a common problem with many numerical methods when applied on coarse grids. The presented technique nearly eliminates numerical diffusion and predicts four moments (zeroth, first, first cross and second) of the distribution function with high accuracy. The technique may be implemented on any type of grid. The accuracy of the scheme has been analyzed by comparing analytical and numerical solutions of three test problems. The numerical results are in excellent agreement with the analytical results and show the ability to predict higher moments very precisely. Additionally, an extension of the proposed technique to higher dimensional problems is discussed.Publicationtype: Journal Article23 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , An efficient numerical technique for solving population balance equation involving aggregation, breakage, growth and nucleation(2008-02-15); ; ; A new discretization for simultaneous aggregation, breakage, growth and nucleation is presented. The new discretization is an extension of the cell average technique developed by the authors [J. Kumar, M. Peglow, G. Warnecke, S. Heinrich, and L. Mörl. Improved accuracy and convergence of discretized population balance for aggregation: The cell average technique. Chemical Engineering Science 61 (2006) 3327-3342.]. It is shown that the cell average scheme enjoys the major advantage of simplicity for solving combined problems over other existing schemes. This is done by a special coupling of the different processes that treats all processes in a similar fashion as it handles the individual process. It is demonstrated that the new coupling makes the technique more useful by being not only more accurate but also computationally less expensive. At first, the coupling is performed for combined aggregation and breakage problems. Furthermore, a new idea that considers the growth process as aggregation of existing particle with new small nuclei is presented. In that way the resulting discretization of the growth process becomes very simple and consistent with first two moments. Additionally, it becomes easy to combine the growth discretization with other processes. The new discretization of pure growth is a little diffusive but it predicts the first two moments exactly without any computational difficulties like appearance of negative values or instability etc. The numerical scheme proposed in this work is consistent only with the first two moments but it can easily be extended to the consistency with any two or more than two moments. Finally, the discretization of pure and coupled problems is tasted on several analytically solvable problems.Publicationtype: Journal Article26 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Towards a complete population balance model for fluidized-bed spray agglomerationThis article concerns the simultaneous processes of agglomeration and drying. In order to predict temperatures and moisture content in gas and particle phase, heat and mass transfer mechanism and particle size enlargement has been considered in one model. The model takes heat and mass transfer phenomena between particle phase, suspension gas, and bypass gas into account. The disperse phase is modeled by a three-dimensional population balance (PBE), which can be reduced to a set of three one-dimensional PBEs. The latter are coupled with heat and mass transfer balances of the gas phase. Furthermore, some simulation and experimental results are presented.Publicationtype: Journal Article12 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , A generic population balance model for simultaneous agglomeration and drying in fluidized bedsFluidized bed spray agglomeration is a common process of particle size enlargement in process engineering. The objective of this study is to derive a general fluidized bed model, which takes the particle size enlargement by agglomeration and the simultaneous drying of particles into account. Therefore, a population balance approach is used to predict the size distribution, the moisture content and the temperature of the particles. The interaction of solid and gas phases is described by means of a heterogeneous fluidization model with active bypass. Selected simulation results are presented and discussed. The model is validated by various comparisons of simulations and batch agglomeration experiments.Publicationtype: Journal Article16 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , A numerical bifurcation analysis of continuous fluidized bed spray granulation with external product classification(2006-10); ; ; ; Nonlinear oscillations in continuous fluidized bed spray granulation with external product classification are analyzed. Using methods from numerical bifurcation analysis the size and location of the instability regions in the space of the design parameters and the adjustable operating parameters are predicted and discussed. The analysis is based on a new relatively simple population balance model, which is formulated on a mass basis, and provides first qualitative insights into the nonlinear dynamic behavior of continuous fluidized bed spray granulation processes.Publicationtype: Journal Article17 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , A discretized model for tracer population balance equation: Improved accuracy and convergence(2006-06-15); ; ; ; A new discretization for tracer population balance equation is developed. It is compared to the modified discretized tracer population balance equation of Peglow et al. [Peglow, M., Kumar, J., Warnecke, G., Heinrich, S., Mörl, L., Hounslow, M. J. (2006). Improved discretized tracer mass distribution of Hounslow et al. American Institute of Chemical Engineers, 52, 1326-1332]. The new formulation provides excellent prediction of the tracer mass distribution in all test cases. Furthermore, the new formulation is more efficient from a computational point of view, it takes less computational effort and is able to give a very good prediction for a coarser grid. Additionally, it is independent of the type of grid chosen for computation. For finer grids, both formulations tend to produce the same results. The performance of the new formulation is illustrated by the comparison with various analytically tractable problems. Moreover, the new formulation preserves all the advantages of the modified discretized tracer population balance equation of Peglow et al. [Peglow, M., Kumar, J., Warnecke, G., Heinrich, S., Mörl, L., Hounslow, M. J. (2005). Improved discretized tracer mass distribution of Hounslow et al. American Institute of Chemical Engineering (published online: 29 December 2005)] and provides a significant improvement in predicting tracer mass distribution and tracer-weighted mean particle volume during aggregation process.Publicationtype: Journal Article23 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Improved accuracy and convergence of discretized population balance for aggregation: The cell average techniqueA new discretization method for aggregation equations is developed. It is compared to the fixed pivot technique proposed by Kumar and Ramkrishna (1996a. On the solution of population balance equations by discretization - I. A fixed pivot technique. Chemical Engineering Science 51, 1311-1332). The numerical results for aggregation problems by discretized population balances are consistently overpredicting and diverge before the gelling point in the case of a gelling kernel. The present work establishes a new technique which assigns the particles within the cells more precisely. This is achieved by taking first the average of the newborn particles within the cell and then assigning them to the neighboring nodes such that pre-chosen properties are exactly preserved. The new technique preserves all the advantages of the conventional discretized methods and provides a significant improvement in predicting the particle size distribution (PSD). In addition, it is found that the technique is a powerful tool for the computation of gelling problems. The effectiveness of the technique is illustrated by application to several aggregation problems for suitably selected aggregation kernels including physically relevant kernels.Publicationtype: Journal Article19 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , An improved discretized tracer mass distribution of Hounslow et alThe discretized tracer population balance equations (DTPBE) for aggregation problems is discussed and modified. It is shown that the original version was not entirely consistent with the associated discretized population balance equation (DPBE). These inconsistencies are remedied in a new formulation that retains the advantages of the original DTPBE, such as conservation of total tracer mass, prediction of tracer-weighted mean particle volume, and so on. Furthermore, the DTBE has been extended to an adjustable discretization. Numerous comparisons are made of the validity of the extended and modified formulation.Publicationtype: Review Article13