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Item type:Publication, Access status: with files , Influence of spray parameters on injected droplets and product properties in fluidized bed spray granulationLiquid injection is one of the, if not the most, critical steps in fluidized bed spray granulation as the product quality as well as the overall process stability can be massively influenced by the associated parameters. Therefore, this study aims to correlate spray parameters to the spray pattern and droplets produced from the nozzle and the resulting granule properties. First, the effect of spray variables on spray angle and droplet size and velocity was analyzed, revealing the spray air pressure as crucial parameter. Afterwards, spray agglomeration experiments were conducted according to a statistical experimental plan varying several process-related parameters in addition to the nozzle set-up. The product particle size distribution was shown to be impacted by a complex combination of the investigated variables with the liquid spray rate, spray and protection air pressure, and fluidization air flow as main influences.Publicationtype: Journal Article62 50 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Dynamic bubble tracking in fluidized beds via electrical capacitance volume tomography(Elsevier, 2024-05-01); ; ; 23 90 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Mixing evolution behavior of raw and gasified biomass pellets in a fluidized bed reactor(2022-12-31); ; ; ; Due to a large particle size and a small specific surface, a homogeneous mixing of biomass pellets with bed materials during gasification plays a critical role in the devolatilization and carbon conversion. In this work, the mixing evolution behavior of biomass pellets at different gasification stages is investigated for the first time. Two bubbling fluidized beds are established to perform the preparation of biomass samples undergoing different gasification times and visualized mixing experiments, respectively. An image processing technique is introduced for the determination of the real-time distribution of biomass pellets. The vertical and lateral migration paths of biomass pellets at different gasification stages are revealed. The improvement of binary mixing by adjusting the operating conditions as well as the adaptability to different biomass loadings are discussed. A convolutional neural network is developed to validate the influence of fluidization velocity on the resulting flow and classify the fluidization behavior.Publicationtype: Journal Article43 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Process design of a multistage drying process via flowsheet simulation(Wiley-VCH, 2021-08); ; ; ; Abstract Multistage drying processes including spray drying and fluidized bed unit operations are challenging to design due to the dependencies of the preceding process steps. Flowsheet simulation offers the possibility to simulate a complete process by the application of suitable short‐cut models. In this contribution a novel model for a spray dryer based on a population balance approach is presented. Furthermore, a dynamic model for a fluidized bed dryer is introduced. Experimental data is used for validation and parameter optimization. The calibrated models are then used to design an industrial drying process of multiple drying stages.Publicationtype: Journal ArticleScopus© Citations 2 233 362 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Influences on the transition from bubbling to turbulent fluidization for Geldart's group B particles(2020-09-20); ; ; A detailed study of parameters influencing the transition from bubbling to turbulent fluidization was done. The transition velocity Uc was determined by pressure fluctuation analysis for different size fractions of sand and ilmenite particles (Geldart's group B). Four different plants (laboratory and pilot scale) were used having diameters ranging from 0.05 m to 0.4 m. The static bed height was varied, resulting in aspect ratios (static bed height/bed diameter) from 1 to 4. The results of Uc show a clear dependency of aspect ratio, bed diameter, temperature and particle size. The diameter of the bed was found to influence the transition velocity especially in small fluidized beds. The static bed height has a significant influence on the transition velocity which has to be considered in scale-up. As a further parameter, the temperature influence was investigated up to 800 °C. No correlation in literature was found to predict satisfactorily the influences of the parameters investigated.Publicationtype: Journal Article77 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Increasing the efficiency of chemical looping combustion of biomass by a dual-stage fuel reactor design to reduce carbon capture costsThis paper analyzes the capabilities of a pilot-scale chemical looping combustion plant firing wood biomass in two stages to efficiently achieve negative carbon dioxide emissions. The utilized in situ gasification-chemical looping combustion (iG-CLC) process isolates the oxygen supply via air from the fuel conversion itself with the help of two separate fluidized bed reactors and an oxygen carrier to supply the necessary oxygen for the combustion. As a result, a relatively pure stream of carbon dioxide and steam is generated. Thus, the process makes capturing carbon emissions more feasible since it eliminates the need for the cost- and energy-intensive separation of the produced gases. A major issue when using biomass in a chemical looping plant is the high amount of the volatiles exiting unconverted. This problem was mitigated by using a two-stage fuel reactor system. Two bubbling fluidized beds were arranged one upon the other. The lower stage, where the fuel is introduced, is used to release the volatiles and partly convert them. The remaining volatiles rise up into the second stage and are further converted to a high degree. A series of experiments were carried out with a 25-kWth pilot plant located at the Hamburg University of Technology. Gas concentrations were continuously measured after both stages of the fuel reactor to see the gradual conversion of the fuel gases. Additionally, carbon slip at the exhaust was measured to show the effectiveness. The experiments with the reactor concept showed promising results since already at a reactor temperature of 850 °C, the total oxygen demand needed to oxidize the combustible component in the exhaust gas was well below 2%. The carbon dioxide (CO2) capture efficiency when using German hardwood slightly decreased to 93–96% compared to 97% for German lignite. In the future, the reactor design must prove that it scales and that the efficiency can be further increased. Nevertheless, firing biomass with a two-stage iG-CLC process might allow a cost-efficient negative carbon dioxide emission while generating heat with relatively high efficiency. Therefore, it might be a sustainable alternative to generate heat in the future.Publicationtype: Journal Article143 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Continuous fluidized bed drying: Advanced modeling and experimental investigationsFluidized bed drying is a technology which is widely applied in industry for the drying of particulate solids. One of the major advantages of fluidized bed system results from the fact that due to high heat, mass and momentum transfer, and intensive solids, mixing a good temperature control is possible, which allows an effective drying of heat-sensitive materials as, for example, food or pharmaceutical products, which are very often also porous and hygroscopic. A disadvantage of the nearly perfect solids mixing in the fluidized bed is the wide residence time distribution of the solids, that is, some particle will leave the dryer already a few seconds after they have been fed to it, while other particles stay for very long times inside the dryer, which may result in a wide moisture distribution of the solids at the outlet of the dryer. Based on numerous works from the literature, a drying model for continuous fluidized bed drying has been developed and implemented as a module within the framework of the stationary flowsheet simulation program SolidSim, which allows the simulation of the drying process for many different solids, liquids, and gases. In addition to the residence time distribution described by a population model, the influence of particle size distribution and the moisture distribution of the feed material was taken into account. The module computes the humidity and temperature of the gas versus the bed height and the moisture and temperature distribution of the solids by taking into account their distributed properties such as for the residence time distribution, particle size and initial moisture. Additionally, also the drying of mixtures of particles with different types of sorptive behavior and drying kinetics is possible while assuming that no particle segregation occurs. Furthermore, the model has been extended by a simple approach to simulate the drying in an elongated fluidized bed dryer. For the validation of the model, the main operating parameters were varied and compared with experiments. The model can calculate the moisture distribution at the dryer outlet, but due to technical restriction, only the average moisture of the particles was measured and compared with the model prediction.Publicationtype: Book Part128 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Multiscale Analysis of a Coating Process in a Wurster Fluidized Bed ApparatusThis contribution outlines a multiscale simulation approach for analysis of a Wurster coating process occurring in a fluidized bed. The processes occurring in the apparatus are described on four different time and length scales: The Discrete Element Method coupled with Computational Fluid Dynamics, where each particle is considered as a separate entity and its motion in fluid field is calculated, play a central role in the modeling framework. On the macroscale, the Population Balance Model describes the particle growth. The nozzle zone model calculates the wetting and overspray rate on the mesoscale. The model on the lowest scale predicts the impact behavior of wetted particles. The influence of key processing parameters, such as gap distance or atomization air flow, on the particle-fluid dynamics during coating process is analyzed. In order to get material parameters, such as coefficient of restitution and friction, a set of experimental investigations of a model material is performed.Publicationtype: Book Part81 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Modeling of the spray zone for particle wetting in a fluidized bed(Wiley-VCH, 2013-01-29); ; ; ; In a spray agglomeration process the particle wetting influences the agglomerate growth and particle dynamics in the granulator. The mass of binder liquid that is deposited on single particles affects the amount of energy dissipation during particle contacts. For the agglomeration of colliding particles the whole impact energy has to be dissipated due to viscous and capillary adhesion forces in the liquid film and plastic deformation of the material. Therefore, a detailed knowledge of the particle wetting is necessary to model the agglomeration process. This contribution uses a coupled DEM-CFD approach to describe the spray zone of a two-fluid nozzle in a fluidized bed agglomerator. Droplets modeled as discrete elements showed the formation of a spray zone with a conical shape. Simulations of the spray zone and the wetting of single particles are in good agreement with experimental results. A coupled DEM-CFD approach is used to describe the spray generation of a two-fluid nozzle and the wetting of single particles. Valuable information to describe particle collisions of wetted particles is generated that are necessary to simulate fluidized bed processes, i.e. agglomeration and granulation.Publicationtype: Journal Article94 - 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