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Abstract
Cyclone preheaters are important components in cement and stone wool production plants. They are used to preheat the raw material by recovering the thermal energy of the hightemperature flue gas produced in a kiln or a melting reactor. Despite their deceptive simplicity, the complicated multiphase flow field within cyclone preheaters makes their design and optimization challenging. Conventionally, the design of cyclones is based on empirical approaches developed for simplified, generic, and smallscale cyclones which are not reliable for industrialscale cases. Therefore, Computational Fluid Dynamics (CFD) has become, in recent years, an essential tool in the analysis, design, and evaluation of cyclones by providing a detailed picture and understanding of the flow field inside these devices.
The present study aimed to develop a wellvalidated and comprehensive CFD model for simulation of highly loaded largescale cyclone preheaters. The model should be capable of predicting important performance parameters such as pressure drop, separation efficiency, heat transfer rate, as well as flow pattern and erosion pattern. For this purpose, an Eulerian–Lagrangian multiphase model, i.e., Dense Discrete Phase Model (DDPM) coupled with a robust turbulence model was developed.
The developed model was first validated against experimental measurements of pressure drop in an isothermal highly loaded labscale cyclone (diameter of 0.2 m) operating with coarse particles (diameter of 2 mm). The results indicated that the model is promising for the simulation of this complex case. The model was further implemented to simulate an isothermal, highly loaded pilotscale (1.6 m in diameter) cement cyclone operating with relatively fine particles, i.e., Sauter mean diameter of 5 μm. However, preliminary simulations showed that the model highly underpredicted separation efficiency and overpredicted pressure drop. It turned out that this was because the agglomeration phenomenon, which plays a vital role in the case of fine particles, was missing. Therefore, an agglomeration model based on a stochastic Lagrangian interparticle collision model was then implemented into the CFD model. The new model significantly improved predictions in terms of both pressure drop and separation efficiency.
The performance of the developed model may be influenced by submodels (e.g., turbulence models, drag models, etc.), model parameters (e.g., particleparticle restitution coefficient and particlewall rebound coefficient), and numerical parameters (e.g., parcel/grain size, time step size and order of discretization), to different extents. An extensive investigation was performed to suggest a set of submodels, model parameters, and numerical parameters providing the best prediction of the hydrodynamics of largescale highly loaded cyclones. The investigation showed that the turbulence model and particleparticle restitution coefficient have the strongest influence on the performance of the developed model.
In the next step, heat transfer modeling was added to the developed model, and an industrialscale (1.6 m in diameter), nonisothermal, highly loaded cyclone preheater with relatively coarse particles, i.e., Sauter mean diameter of 375 μm, was studied. The studied cyclone operates at Integrate Melting Furnace (IMF) system of a stone wool production plant. Plant operating parameters, i.e., pressure drop and global heat transfer rate and the data from a measurement campaign, i.e., local measurements of gas velocity profiles, using LDA, and gas temperature profiles, using thermocouple and FTIR were used for further validation of the CFD model.
In all these cases, reasonable agreements between the measurements and simulation predictions were obtained. In addition, the developed model was accurate enough to capture the major observed trends caused by the changes in the operating parameters; for example, the improvement in separation efficiency of cyclones due to an increase in particle load is well captured by the developed model.
Lastly, to conduct erosion investigation in highly loaded cyclones, the wellknown erosion model of Oka et al. was implemented into the developed CFD model. After successfully testing the model on a labscale cyclone, in which erosion was measured experimentally, the model was used to investigate erosion in the industrial cyclone preheater. The predicted erosion pattern and locations with severe erosion were qualitatively matched with observations.
Furthermore, throughout this study, parametric studies on operating conditions including gas and solid flow rates, particle size distribution, and gas inlet temperature were performed and the impacts on pressure drop, separation efficiency, heat transfer rate, and erosion, considered as key performance parameters of cyclone preheaters, were evaluated.
In essence, a CFD model has been developed that is computationally affordable and provides validated predictions of key performance parameters of cyclone preheaters, such as pressure drop, separation efficiency, and heat transfer rate. Additionally, by properly representing critical present physical phenomena, including turbulence, gasparticle interactions, particleparticle interactions, agglomeration, etc., the developed model provides valid predictions of flow patterns, temperature profiles and erosion patterns. Therefore, the developed model can probably also be used for other industrial applications to troubleshoot, redesign, and optimize industrial cyclone preheaters.
The present study aimed to develop a wellvalidated and comprehensive CFD model for simulation of highly loaded largescale cyclone preheaters. The model should be capable of predicting important performance parameters such as pressure drop, separation efficiency, heat transfer rate, as well as flow pattern and erosion pattern. For this purpose, an Eulerian–Lagrangian multiphase model, i.e., Dense Discrete Phase Model (DDPM) coupled with a robust turbulence model was developed.
The developed model was first validated against experimental measurements of pressure drop in an isothermal highly loaded labscale cyclone (diameter of 0.2 m) operating with coarse particles (diameter of 2 mm). The results indicated that the model is promising for the simulation of this complex case. The model was further implemented to simulate an isothermal, highly loaded pilotscale (1.6 m in diameter) cement cyclone operating with relatively fine particles, i.e., Sauter mean diameter of 5 μm. However, preliminary simulations showed that the model highly underpredicted separation efficiency and overpredicted pressure drop. It turned out that this was because the agglomeration phenomenon, which plays a vital role in the case of fine particles, was missing. Therefore, an agglomeration model based on a stochastic Lagrangian interparticle collision model was then implemented into the CFD model. The new model significantly improved predictions in terms of both pressure drop and separation efficiency.
The performance of the developed model may be influenced by submodels (e.g., turbulence models, drag models, etc.), model parameters (e.g., particleparticle restitution coefficient and particlewall rebound coefficient), and numerical parameters (e.g., parcel/grain size, time step size and order of discretization), to different extents. An extensive investigation was performed to suggest a set of submodels, model parameters, and numerical parameters providing the best prediction of the hydrodynamics of largescale highly loaded cyclones. The investigation showed that the turbulence model and particleparticle restitution coefficient have the strongest influence on the performance of the developed model.
In the next step, heat transfer modeling was added to the developed model, and an industrialscale (1.6 m in diameter), nonisothermal, highly loaded cyclone preheater with relatively coarse particles, i.e., Sauter mean diameter of 375 μm, was studied. The studied cyclone operates at Integrate Melting Furnace (IMF) system of a stone wool production plant. Plant operating parameters, i.e., pressure drop and global heat transfer rate and the data from a measurement campaign, i.e., local measurements of gas velocity profiles, using LDA, and gas temperature profiles, using thermocouple and FTIR were used for further validation of the CFD model.
In all these cases, reasonable agreements between the measurements and simulation predictions were obtained. In addition, the developed model was accurate enough to capture the major observed trends caused by the changes in the operating parameters; for example, the improvement in separation efficiency of cyclones due to an increase in particle load is well captured by the developed model.
Lastly, to conduct erosion investigation in highly loaded cyclones, the wellknown erosion model of Oka et al. was implemented into the developed CFD model. After successfully testing the model on a labscale cyclone, in which erosion was measured experimentally, the model was used to investigate erosion in the industrial cyclone preheater. The predicted erosion pattern and locations with severe erosion were qualitatively matched with observations.
Furthermore, throughout this study, parametric studies on operating conditions including gas and solid flow rates, particle size distribution, and gas inlet temperature were performed and the impacts on pressure drop, separation efficiency, heat transfer rate, and erosion, considered as key performance parameters of cyclone preheaters, were evaluated.
In essence, a CFD model has been developed that is computationally affordable and provides validated predictions of key performance parameters of cyclone preheaters, such as pressure drop, separation efficiency, and heat transfer rate. Additionally, by properly representing critical present physical phenomena, including turbulence, gasparticle interactions, particleparticle interactions, agglomeration, etc., the developed model provides valid predictions of flow patterns, temperature profiles and erosion patterns. Therefore, the developed model can probably also be used for other industrial applications to troubleshoot, redesign, and optimize industrial cyclone preheaters.
Original language  English 

Publisher  DTU Chemical Engineering 

Number of pages  248 
Publication status  Published  2023 
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 1 Finished

A numerical and experimental investigation of industrial cyclones
Mirzaei, M., Bai, X., Larsen, M. B., Lin, W., Jensen, P. A., Nakhaei, M. & Zhou, H.
01/12/2019 → 10/07/2023
Project: PhD