Investigation of gas–solids flow characteristics in a conical fluidized bed dryer by pressure fluctuation and electrical capacitance tomography

Chemical Engineering Science

Wang

et al. 2018

Fluidized beds are widely used in pharmaceutical industry for particles coating and granulation. Due to the complex gas solids flow process, it is extremely desirable that a real time monitoring and control system is used in the process in order to enable a bubbling stable fluidization and reduce the chance of defluidization due to agglomeration with high moisture contents particles. The microwave tomography (MWT) technology has been developed for more than twenty years and was mainly applied in medical sectors. MWT has a wide range of frequency (1~2.5 GHz) and can be used to measure materials with high permittivity and conductivity. Therefore, it is a good choice for the monitoring of fluidized bed coating and granulation processes. In this paper, a MWT system with 16 antennas was designed and applied for the monitoring of wetting and coating processes in a lab-scale fluidized bed with top-spray and bottom-spray system. The hydrodynamics characteristics of wet gas-solids flow with different moisture content were investigated by MWT technology. This is the first time that MWT was applied in a real dynamics gas-solids fluidized bed. Experiment result shows that the MWT is available for the online monitoring of the gas solids flow with different moisture content. Different flow regimes were revealed based on the MWT images combined with pressure signals. The results indicate that the MWT provides valuable information to identify the defluidization in the fluidized bed process with high moisture contents materials. It is evident that microwave tomography has clear advantages over single point based measurement technology for process fault diagnose.

Section: <Figs 4 and 5>supporting

confidence: 78%

Section: Introductionmentioning

confidence: 99%

Application of microwave tomography to investigation the wet gas-solids flow hydrodynamic characteristics in a fluidized bed

Chemical Engineering Science

Wang

et al. 2018

“…Moreover, u mf can be calculated theoretically, according to Kunii et al (1991), where w s is the sphericity, ε mf is the void fraction of under the minimal fluidization state, it is expressed as TFBs with three different inclination angles are considered. The prototype of the fluidized bed is a dryer which has been introduced in the previous publication (Wang et al, 2018;Ge et al, 2016), and the particle properties (shown in Table 2 and Table 4) are determined based on the cellulose particles in previous studies (Che et al, 2018(Che et al, , 2020.…”

Section: Minimal Fluidization Velocitymentioning

confidence: 99%

Numerical investigation of the particle circulation characteristics in a tapered fluidized bed

Chen

2022

PurposeThe objective of this study is to investigate several issues related to particle circulation within the TFB, including exploring an appropriate method to quantify particle circulation time, the effects of different operational parameters on particle circulation time, and the relationship between particle mixing and particle circulation.Design/methodology/approachThe computational fluid dynamics coupled with the discrete element method (CFD-DEM) is applied to investigate the particle circulation characteristics of a tapered fluidized bed (TFB). An approach for defining particle circulation, which accounts for the horizontal motion of each particle, is proposed to estimate particle circulation time.FindingsIt is found that the overall particle circulation in a TFB could be accelerated by increasing air velocity and wall inclination angle, while an increase in particle size and an increase in inter-particle cohesive forces decelerate particle circulation; the increase in the open area ratio of the central region of the air distributor would decelerate the particle circulation. Moreover, the particle circulation time and mixing rate are independent variables that describe the flow dynamics of particles from different perspectives.Practical implicationsA large part of fluidized beds in industrial applications can be classified as TFB. This study presents a numerical method to obtain detailed knowledge about particle circulation in a TFB, which is essential for the design, optimization, and control of related processes.Originality/valueThe particle circulation in a TFB is important but rarely investigated, and it is hard to be quantified using existing experimental approaches. The proposed numerical workflow reveals the characteristics of particle circulation from a particle-scale perspective.

“…Based on the reconstructed permittivity distribution, the average solids concentration in the cross section is linearly related to the grey level of ECT image by (Ge et al 2016…”

Section: Ect Image Reconstructionmentioning

confidence: 99%

Application of process tomography in gas–solid fluidised beds in different scales and structures

Wang

et al. 2018

Meas. Sci. Technol.

Gas-solids fluidised beds are commonly used in particle-related processes, e.g. for coal combustion and gasification in the power industry, and coating and granulation process in the pharmaceutical industry. Because the operation efficiency depends on the gas-solids flow characteristics, it is necessary to investigate the flow behaviour. This paper is about application of process tomography, including electrical capacitance tomography (ECT) and microwave tomography (MWT), in multi-scale gas-solids fluidisation processes in the pharmaceutical and power industries. This is the first time that both ECT and MWT are applied for this purpose with multi-scales and complex structure. To evaluate the sensor design and image reconstruction and to investigate the effects of sensor structure and dimension on the image quality, a normalised sensitivity coefficient is introduced. In the meanwhile, computational fluid dynamic (CFD) analysis based on a computational particle fluid dynamic (CPFD) model and a two-phase fluid model (TFM) is used. Part of the CPFD-TFM simulation results are compared and validated by experimental results from ECT and/or MWT. By both simulation and experiment, the complex flow hydrodynamic behaviour in different scales is analysed. Time-series capacitance data are analysed both in time and frequency domains to reveal the flow characteristics.