Gas-solid Flow Field Research Articles

A Numerical Study on the Flow Field and Classification Performance of an Industrial-Scale Micron Air Classifier under Various Outlet Mass Airflow Rates

In this study, the gas−particle flow field in a real-size industrial-scale micron air classifier manufactured by Phenikaa Group using 3D transient simulations with the FWC-RSM–DPM (Four-Way Coupling-Reynold Stress Model-Discrete Phase Model) in ANSYS Fluent 2022 R2 and with the assistance of High-Performance Computing (HPC) systems is explored. A comparison among three coupling models is carried out, highlighting the significant influence of the interactions between solid and gas phases on the flow field. The complex two-phase flow, characterized by the formation of multiple vortices with different sizes, positions, and rotation directions, is successfully captured on the real-size model of the classifier. Additionally, analyzing the effects of the vortices on the flow field provides a comprehensive understanding of the gas–solid flow field and the classification mechanism. The effect of the outlet mass airflow rate is also investigated. The classifier’s Key Performance Indicators (KPIs: d50, K, η, ΔP) and the constrained condition of the particle size distribution curve of the final product are used to evaluate the classification efficiency. The contributions of this work are as follows: (i) a simulation analysis of a real-size industrial-scale classifier is conducted that highlights its advantages over a lab-scale one; (ii) a comparison is conducted among three coupling models, showing the advancement of four-way coupling in providing accurate results for simulations of interactions between the gas phase and particles; and (iii) the particle size distribution curve performances of a classified product under different simulation models and outlet airflow rates are addressed, from which optimal parameters can be selected in the design and operation processes to achieve the required efficiency of an air classifier.

Effect of the Injection Structure on Gas Velocity Distribution in a 3D Vertical Oven

Gas injection structures were designed for a vertical oven to improve the gas–solid flow countercurrent structure. This work measured the wall temperature distribution of the vertical oven to reflect gas velocity distribution, and simulated the basic gas–solid flow field. The effects of the number of gas orifice layers and the injection angle on the gas velocity distribution were examined. The results showed that number of gas injection layers had a significant effect on the gas velocity distribution in the lower zone. Compared with the distributions with one or three injection layers, two injection layers produce more uniform gas flow. A small particle size of 6–15 mm increased the bed resistance and solid fraction standard deviation. A nozzle angle of 45° was conducive to increase the gas velocity in the upper zone and forming a more uniform gas distribution.

Study on Gas-solid Two-phase Flow Field of Ramon Mill Classifier

To reveal the working principle and internal flow field law of the grading machine, the numerical simulation of the gas-solid two-phase flow field was carried out. In this paper, the numerical simulation method based on Fluent is used to obtain the internal velocity distribution and pressure distribution of the grading machine. The flow field of gas-solid two-phase was studied based on the CFD-DEM coupling, and the particle motion trajectory in the grading machine and the particle motion law in the flow field at different times were obtained; The influence of the operating parameters of the internal flow field on the force of particles in the grading machine was analyzed, and combined with the change of particle number, the particle collection efficiency of the grading machine under different operating parameters was further given. It is of guiding significance to adjust the parameters of the grading machine, improve the output and the product quality of the longitudinal mill, and reduce the energy consumption of the longitudinal mill.

The Effects of Vaporisation Models on the FCC Riser Reactor

This work presents a steady-state one-dimensional model of the FCC riser considering the vaporisation of the gas oil feed and subsequent cracking reactions. The evaporation of droplets is studied using three models: the classical homogeneous model and the heterogeneous vaporisation models from the literature. Droplets are modelled using the Lagrangian framework model for particles moving through a fluid. This was coupled with the gas–solid flow field describing the catalyst particulate transport in the riser. Cracking reaction kinetics are modelled using a four-lumped model. The model was then validated against published plant data. The model performed well in terms of gas oil conversion, gasoline yield, pressure drop, and phase temperature profiles. Therefore, it is suitable for use in the design and optimisation of new and existing FCC unit risers, particularly in cost–benefit analysis considering the current push away from petroleum energy sources. It was found that vaporisation models are largely insignificant in terms of gas oil conversion profiles and gasoline yield for usual operation conditions of FCC risers, which is a finding that had yet to be proven in the literature. Vaporisation models are shown to only affect conversion and yield when the initial droplet exceeds 2000 μm.

Numerical simulation study on gas-solid flow characteristics and SO2 removal characteristics in circulating fluidized bed desulfurization tower

Circulating fluidized bed flue gas desulfurization technology is widely used in the world. The computational particle fluid dynamics (CPFD) numerical simulation method was used to study the gas-solid two-phase flow and desulfurization characteristics in the circulating fluidized bed desulfurization tower. The CPFD method is based on the MP-PIC method, which uses the stochastic particle method for the particle phase and the Euler method for the fluid phase to solve the dense particle flow. The established model was firstly verified by the experimental results of gas-solid flow field and desulfurization efficiency. Then, the effects of flue gas parameters on the flow field in the desulfurization tower and the effects of flue gas parameters, SO2 inlet concentration, and Ca/S on desulfurization efficiency were numerically simulated. An effective optimization scheme was also proposed to improve the desulfurization efficiency. The research results showed that the CPFD simulation results were in good agreement with the experimental results, which proved the reliability of the method. The particle motion state in the bed of the desulfurization tower presents a core-annular flow. As the flue gas inlet flow increased, the distribution of flue gas and particles has a serious deviation, and the desulfurization efficiency also decreased. The desulfurization efficiency will decrease with the increased of SO2 inlet concentration and increased with the increased of Ca/S. According to the distribution of SO2 concentration in the bed, three characteristic desulfurization zones can be proposed, namely, the initial mixing process zone, the high-efficiency desulfurization process zone, and the low-efficiency desulfurization process zone. Installing a baffle at the bottom of the desulfurization tower can optimize the distribution of gas-solid two-phase flow in the bed and the desulfurization efficiency.

Interaction and influence of a flow field and particleboard particles in an airflow forming machine with a coupled Euler-DPM model.

Particleboards are widely used in the artificial board market, which can be constructed from a variety of raw materials and require small amounts of energy to be produced. In the particleboard production process, forming machines play an important role as the key equipment for achieving continuous production. In recent years, airflow forming machines have received increasing attention in particleboard production lines because of their strong separation ability and low price. However, the internal flow field is complex and difficult to control, which affects the surface quality and strength of the particleboard. The most pressing technical difficulty is controlling the flow field characteristics of the airflow paver. At present, the research on this subject is conducted primarily through repeated experiments, which entail long research periods and high processing costs. To reduce human and financial costs, in this study, Computational Fluid Dynamics (CFD) is employed to investigate the flow field and the gas-solid two-phase flow field coupled with particle movement of an airflow forming machine. The accuracy of the calculation model is verified by comparing characteristic point velocities obtained from experimental analysis and a simulation. The simulation results show that in practical production, the frequency of a negative pressure fan should be greater than 27 Hz. It is necessary to set the shoulder properly, and the slab smoothness can be improved by moving the shoulder back on the premise of meeting the strength requirements of the box. The distance between the shoulders of the box body should be less than 2570 mm, and particles with uniform diameter should be added to the paving box to reduce the turbulence effect, improve the quality of particle forming and provide actual particleboard production with a solid theoretical foundation.

Migration law of flax threshing materials in double channel air-and-screen separating cleaner

In order to further clarify and improve the working performance of separating cleaner for flax threshing materials, and study the migration law and characteristics of components of flax threshing materials during separating and cleaning, in this paper, a gas-solid coupling simulation model was established on the separation cleaner for flax threshing materials and a numerical simulation was carried out on the separating and cleaning process. Simulation results showed that, the separating and cleaning effect of the components of flax threshing materials was good under the air-and-screen gas-solid coupling flow field. Meanwhile, the form distribution and the vector distribution of air volume and velocity of flax threshing materials in the air-and-screen devices were obtained. By referring to the migration trajectories of the flax threshing materials in the vibration sieve device, double channel residue collection device and dust absorber, the volume variation, motion trajectories and variation of migration velocity of the components of flax threshing materials over time in different regions were explored. Verification test results showed that, the content impurity rate of the separation cleaner for flax threshing materials was 2.06%, and loss rate in cleaning was 3.08%. Compared with simulation results, the verification test results were 1.23% and 0.42% higher, showing that the established discrete element model on the flax threshing materials and parameter setting were basically feasible. The verification test also verified the correctness of the simulation results of the separating and cleaning process of the flax threshing materials based on gas-solid coupling theory and the feasibility of the research method. Keywords: flax threshing materials, separation cleaner, air-and-screen, gas-solid coupling, discrete element model, numerical simulation DOI: 10.25165/j.ijabe.20211403.6058 Citation: Dai F, Song X F, Shi R J, Zhao W Y, Guo W J, Zhang Y. Migration law of flax threshing materials in double channel air-and-screen separating cleaner. Int J Agric & Biol Eng, 2021; 14(3): 92–102.

Research Progress on Numerical Simulation of Two-phase Flow in the Gas-solid Fluidized Bed

It is difficult to accurately measure the parameters of solid particles in the experiment of the gas-solid fluidized bed. The numerical simulation plays an important role to accurately describe flow characteristics in the fluidized bed. Combined with the research work of the research group, this paper analyzes the application of numerical simulation of fluidized bed from the aspects of gas-solid coupling algorithm, drag model, flow characteristics, and reaction characteristics based on the previous studies. The specificity improvement of the gas-solid coupling algorithm and the regional application of the drag model is the trend of the recent development of numerical simulation. Previous studies mainly focus on the gas-solid two-phase flow field characteristics in the traditional fluidized bed, but few on the complex flow characteristics such as gas-solid reverse flow and the coupling with reaction characteristics. It is of great significance for designing a novel fluidized bed reactor to realize gas-solid continuous reaction to establish and improve the numerical simulation method of gas-solid non-catalytic reaction.

Electrostatic Charge Distribution-Based Direct Velocity Tomography Method for Gas–Solid Two-Phase Flow

Electrostatic direct velocity tomography method (EDVT) based on electrostatic tomography (EST) is a technology that uses the induced charge signal on the electrode surface through an image reconstruction algorithm to obtain the particle velocity distribution of gas-solid two-phase flow. To simplify the calculation, EDVT assumes that the charge in the imaging region is uniformly distributed. However, due to the complexity of gas–solid flow, this assumption cannot be satisfied, which often brings great measurement errors. To solve the problem, this article proposes an electrostatic charge distribution-based direct velocity tomography (ECDDVT) method by introducing charge distribution information to improve the cross-correlation sensitivity matrix. To evaluate the effect of the particle velocity distribution reconstruction method, this article established an evaluation platform based on a three-dimensional (3-D) simulation of gas–solid flow field and electrostatic field. By assigning the weight value of the number of particles in different pixel units, a more accurate method for measuring the average particle velocity can be obtained. The simulation results and the experiment results of the belt type electrostatic velocity measurement facility show that the performance of the proposed ECDDVT in terms of image correlation coefficient and absolute percentage error (APE) is better than EDVT. The experimental results of the gas–solid two-phase flow rig show that the ECDDVT method can better reflect the particle velocity in the center of the pipe.

Numerical simulation of a novel fluidized bed for gas-solid non-catalytic reactions (NRFB)

This study proposed a novel fluidized bed (NRFB) to realize gas-solid non-catalytic continuous reaction. Gas and solid flowed in reverse direction in NRFB, achieving high-efficiency contact between particles and gas to form particles. The discrete phase model was used to simulate the gas-solid two-phase flow in NRFB. Basis on an optimum operating gas velocity, the characteristics of the gas-solid two-phase flow field and sodium phenolate carboxylation in NRFB were analyzed. The equal-area torus method was proposed to explore the radial particle distribution. The results showed that the gas in NRFB could be in full contact with solid particles. The introduction of the grid trays could significantly improve radial distribution and increase the residence time of sodium phenolate particles in the dense phase section, thereby improving the reaction efficiency. The simulation results can provide guidance for the determination of the operation parameters in pilot and industrial production of gas-solid non-catalytic reactions.

Research on visualization technology for abrasion of flow guide device in denitrification system based on Tabakoff model

In order to obtain the abrasion condition of the internal guide device of denitration system reactor intuitively, based on the particle missing model and takeoff wear model, the gas-solid two-phase flow field in SCR reactor is simulated by ANSYS-CFX calculation software, and the fly ash movement track and wear rate distribution of guide plate are visualized. The simulation results show that through the combination of particle missing model and Tabakoff wear model with CFX software, we can directly see the general wear distribution of the guide device in the flue. The wear rate distribution is mainly affected by the particle size of fly ash, and the wear rate value is mainly affected by the mass concentration. By verifying the field flow field test data and checking the wear and ash accumulation of the guide plate, the technical effectiveness is verified, which provides a technical means for the guide device to prevent wear and blockage.

Analysis and simulation of erosion of sand control screens in deep water gas well and its practical application

The occurrence of sand production in deep water gas well leads to faster airflow carrying sands and more serious erosion of the sand control screen. Screen erosion is easy to cause sand control failure, reduce production and increase the cost of later workover. In present study, the erosion of screens in deep water gas well is simulated by computational fluid dynamics (CFD). Based on the structure and performance of premium quality screens, star-shaped screens and wire wrapped screens, the screen geometric models and the pore geometric models which can be modified in stages to match the pore size change during the erosion process is established. The multi-angle screen erosion model of discrete particles is established based on the empirical screen erosion model and the impact angle function. After that, combined with the gas-solid phase coupling flow model, considering the inlet, outlet and wall boundary conditions of the screen and the pore, introducing the spatial discretization scheme and the pressure velocity coupling method, the gas-solid two-phase flow field and the erosion rate of the screen are iteratively calculated by under-relaxation method. Therefore, the numerical simulation of screen erosion in deep-water gas well is formed and it is applied to the wear analysis and the sand control screen optimization for the XX deep water gas well in the South China Sea. The results show that the multi-angle erosion model of discrete particles and the numerical simulation of screen erosion can accurately describe the process of high-speed airflow carrying sand to erode the screen in deep water gas well, and the sand control screen can be optimized according to the simulation results to prolong service life.

Experimental and numerical predictions of ash particle erosion in SCR monolithic catalysts for coal-fired utility boilers

Erosion by particles in monolithic selective catalyst reduction (SCR) processes can reduce the operational life of a catalyst and threaten the performance of the SCR system. We present an integrated approach implemented in two stages to predict the erosion condition of SCR processes. First, a 3D computational fluid dynamics (CFD) model was established for a full-sized SCR reactor to obtain information on the flue gas and ash particles at the entrance of the catalyst layer. Second, the detailed inner catalyst structure layers were simulated using MATLAB and a catalyst erosion model was developed, according to the initial and boundary conditions obtained using the CFD models. Relative cold state tests and erosion measurements were conducted to validate the simulation results. The model was applied to investigate the relationship between the reactor installment, the gas-solid flow field and the catalyst erosion. Moreover, a series of retrofit schemes were implemented to confirm that this method can be used in engineering applications.

The Study of Performance in a Novel Gas–Solid Separator

The three slit-type separator is a new separator which can shorten the residence time of oil & gas and improve the separation efficiency. In this study, a critical validation was carried out to examine the separation performances of the three slit-type separator with different inlet velocity and inlet concentration. According to the experimental results, the separation efficiency and pressure drop of the three slit-type separator increase with the increase of inlet velocity and inlet concentration. Numerical simulation of the gas–solid flow field in the three slit-type separator was carried out by the use of Fluent 15.0 platform. The simulated results coincide with the experimental results. The particles move along the inside wall of the separator in the vaulted space, meanwhile, more gas enters into the exhaust pipe through slots, which can improve the separation efficiency. The study shows that the residence time of oil and gas is less than 0.6 and the separation efficiency is up to 99% in the separator, in addition, the pressure drop could be controlled in 4 kPa below.

Numerical study of particle deposition and scaling in dust exhaust of cyclone separator

The solid particles accumulation in the dust exhaust cone area of the cyclone separator can cause the wall wear. This undoubtedly prevents the flue gas turbine from long period and safe operation. So it is important to study the mechanism how the particles deposited and scale on dust exhaust cone area of the cyclone separator. Numerical simulations of gas-solid flow field have been carried out in a single tube in the third cyclone separator. The three-dimensionally coupled computational fluid dynamic (CFD) technology and the modified Discrete Phase Model (DPM) are adopted to model the gas-solid two-phase flow. The results show that with the increase of the operating temperature and processing capacity, the particle sticking possibility near the cone area will rise. The sticking rates will decrease when the particle diameter becomes bigger.

Simulation of a Gas-Solid Flow Field in a Two-Stage Rice Husk High-Temperature Pyrolysis and Gasification Cyclone Gasifier

A scheme for using a two-stage cyclone gasifier for high-temperature rice husk pyrolysis and gasification to reduce the tar content in biogas is presented in this study. The two-stage cyclone gasifier consisted of an upper cyclone high-temperature pyrolysis chamber and a lower steam spray gasifier. The staging pyrolysis and gasification process used in this study can increase the carbon conversion efficiency and reduce tar content by increasing the pyrolysis temperature. This process uses part of the produced gas for combustion in an external burner to generate high-temperature (1600 °C) anaerobic flue gas and to provide heat for pyrolysis and gasification. This study simulates the isothermal gas phase and the gas-solid flow field for the upper cyclone chamber, as well as the gas-solid flow field, with steam (heat transfer between the steam and the gas is considered), for the entire gasifier by varying the structural and operational parameters. The optimal parameters for the cyclone gasifier for good mixing and lengthy residence (2.3 to 4.8 s) of the rice husk particles were found to be inlet angles of 20° and 30° with inlet velocities between 40 and 80 m/s.

Multi-scale product property model of polypropylene produced in a FBR: From chemical process engineering to product engineering

A multi-scale product model has been built to characterize the polypropylene (PP) formation dynamics in a catalytic FBR. For the first time, the gas–solid flow field, the morphological and molecular properties of particles, as well as their dynamics can be simultaneously obtained by solving the unique model that couples a CFD model, a population balance model (PBM) and moment equations. The quantitative relationships between the operating conditions and the multi-scale particle properties have been further established. The results demonstrate that the product model can be used to guide a multi-scale generalization of the polymer product from chemical process to product engineering.

3D CFD-PBM modeling of the gas–solid flow field in a polydisperse polymerization FBR: The effect of drag model

This work investigated a coupled computational fluid dynamics and population balance modeling (CFD-PBM) approach to predict the hydrodynamic behavior of the complex gas–solid two-phase flow in a three-dimensional (3-D) polydisperse propylene polymerization fluidized bed reactors (FBRs). Four different drag models, namely Syamlal–O’Brien, Gidaspow, McKeen and EMMS, were incorporated into the CFD-PBM model for evaluating the different effect of drag force between the gas and solid phases. Simulation results revealed a significant effect of the drag model on gas–solid flow in polydisperse polymerization FBRs. It was found that (1) compared to Syamlal–O’Brien and Gidaspow drag models, McKeen and EMMS drag models could predict a lower bed height, a higher temperature and an obvious core-annulus structure in polymerization FBRs; (2) EMMS drag model outperforms the other three drag models with respect to pressure drop prediction; and (3) the drag coefficient had little influence on the evolution of Sauter number and particle-size distribution.

Direct concurrent multi-scale CFD modeling: The effect of intraparticle transfer on the flow field in a MTO FBR

In this study, a coupled model based on a direct concurrent multi-scale approach incorporating a single particle model and a two-phase CFD model was developed to predict the effects of intraparticle transfer on the flow field and main composition distributions of a catalytic reaction to convert methanol to olefins (MTO) in a fluidized bed reactor (FBR). A single particle model was first constructed to describe the individual intraparticle molecular diffusion and reaction kinetics, while a CFD model characterized the gas–solid flow field in the FBR. Because the grid cells generated in the CFD model were too small compared with the size of the FBR, no distributions were considered in a single grid. In this case, all catalyst particles inside each small computational cell for the CFD model experienced the same external conditions, thus ensuring the effective coupling of the two models. This was validated by comparing the above assumption with simulation results and with experiment results. On the basis of the coupled model, the intraparticle transfer limitation and the flow field in the FBR were predicted numerically. The simulated results indicated that the intraparticle transfer limitation did exist and had significant effects on the reactor flow field. This model is expected to be useful in predicting the intraparticle transfer limitation in FBRs.

Structural Modification and Airflow Optimization of Bag-Type Collector Based on Flue-Gas Rich-Lean Separation

With the computational fluid dynamics software FLUENT, three dimensional gas-solid two-phase flow field was simulated and analyzed for HMC-64 pulse-jet cleaned bag-type collector. The simulation data and the actual operating parameters were compared, and the airflow distribution of bag-type collector was comprehensively learned. On the basis of the original analysis, the reconstruction about flue-gas rich-lean separation combining lateral extension at the entrance of bag filter was put forward. The velocity distribution and the mass flow rate of all filter bags were compared. Results showed that through using rich-lean separation combining lateral extension, the airflow distribution of each filter bag was optimized. The integrated flow non-uniform amplitude and the relative root-mean-square value became lower than those of original model. These conclusions about the structural modification and the airflow optimization provide theoretical foundation for further research.