The Experts below are selected from a list of 37905 Experts worldwide ranked by ideXlab platform
Hongzhong Li - One of the best experts on this subject based on the ideXlab platform.
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a hydrodynamic model of loop seal with a fluidized standpipe for a circulating fluidized bed
Particuology, 2018Co-Authors: Changjin Li, Hongzhong LiAbstract:Abstract Loop seals are among the most common non-mechanical valves used in circulating fluidized bed systems. In the present work, a fundamental study is conducted of a fluidized loop seal, which consists of a fluidized standpipe, a fluidized supply chamber, and a fluidized recycling chamber. Based on the principles of momentum, mass, and energy conservation, a hydrodynamic model for a loop seal is established, consisting of 13 equations. The effects of operating conditions such as the bottom aeration rate, total solid inventory, and fluidizing gas velocity in the riser on the Solids Flow rate and the performance of the loop seal are studied by a combination of model analysis and experiments. The experiments are carried out in a circulating fluidized bed with silica gel particles (Geldart group A). The model predictions show good agreement with the experimental data.
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cfd simulation of Solids residence time distribution in a multi compartment fluidized bed
Chinese Journal of Chemical Engineering, 2017Co-Authors: Yunlong Zhao, Hu Zhao, Libo Zhang, Hongzhong LiAbstract:Abstract The present work focuses on a numerical investigation of the Solids residence time distribution (RTD) and the fluidized structure of a multi-compartment fluidized bed, in which the Flow pattern is proved to be close to plug Flow by using computational fluid dynamics (CFD) simulations. With the fluidizing gas velocity or the bed outlet height rising, the Solids Flow out of bed more quickly with a wider spread of residence time and a larger RTD variance ( σ 2 ). It is just the heterogeneous fluidized structure that being more prominent with the bed height increasing induces the widely non-uniform RTD. The division of the individual internal circulation into double ones improves the Flow pattern to be close to plug Flow.
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hydrodynamic and Solids residence time distribution in a binary bubbling fluidized bed 3d computational study coupled with the structure based drag model
Chemical Engineering Journal, 2017Co-Authors: Yunlong Zhao, Hu Zhao, Libo Zhang, Hongzhong LiAbstract:The simulation of bubbling fluidized beds (BFB) residence time distribution (RTD) based on the structure-based drag model are conducted for the single and binary gas-solid phases systems, a comparison of computed results with experimental data proves that our model is applicable to both systems with better accuracy. The revised drag coefficient (Hd) increases with decreasing the gas velocity or increasing the particle diameter. The increase of the feed rate could improve the Solids Flow pattern to be close to the plug Flow, while increasing gas velocity or bed height would lead to a wider RTD. The particles in the binary mixture are in more diffusion-oriented movement so as to have less MRT (mean residence time) than that of the single system. The coarse particles with longer MRT are simulated to accumulate into the bed bottom with a slower vertical velocity.
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study on the Flow of fine powders from hoppers connected to a moving bed standpipe with negative pressure gradient
Powder Technology, 1999Co-Authors: Shan Jing, Hongzhong LiAbstract:In this work, the four Flow regimes of powders, i.e., bubbleless regime, bubble regime, plug regime and Flow stopping regime, in hoppers connected to a moving-bed standpipe with negative pressure gradient were observed by analyzing the signal of instantaneous pressure fluctuation and measuring average Solids Flow rate. The effect of the size of the orifice of a hopper, the half-angle of conical hopper, and the properties of powders on the regime and average Solids Flow rate were discussed in detail. Based on the properties of fluidized powders, the boundary of regimes and a correlation to predict the average Solids Flow rate are presented.
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mechanics of arching in a moving bed standpipe with interstitial gas Flow
Powder Technology, 1994Co-Authors: Hongzhong LiAbstract:The mechanism of arching in a moving-bed standpipe with interstitial gas Flow has been studied using the theories of particulate media mechanics and non-fluidized gas-Solids Flow. In order to determine the critical arching radius, which marks the change from arching to Flow, a situation where all the powder is in a critical passive state of stress is considered, and the powder in the standpipe is assumed to be composed of arched layers. The differential equations of force balance for a elemental arched layer corresponding to conical, trapezoidal, cylindrical, and rectangular tube shapes were given, respectively. The solutions of these differential equations, which can be used to determine the critical arching span, were also given. The boundary condition for solving these differential equations are that minor principal stresses equal zero at bottom surface of the arched layers. The calculated results of the critical arching span agree well with experimental data and these equations for predicting the possibility of arching can therefore be applied to industrial operation and design to preclude moving-bed Flow from arching.
Haigang Wang - One of the best experts on this subject based on the ideXlab platform.
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investigation of gas Solids Flow hydrodynamics in a cold model of a dual fluidised bed gasifier using electrical capacitance tomography sensors
Particuology, 2020Co-Authors: Zhan Luo, Yonglei Lin, Wuqiang Yang, Haigang WangAbstract:Abstract The Flow characteristics of a dual fluidised bed gasifier (DFBG) are more complex than those of a single fluidised bed gasifier. For stable operation and appropriate control, a cold DFBG test facility with both an upper and a lower U-valve was built, and electrical capacitance tomography (ECT) sensors were installed with pressure transducers to investigate the effects of operating conditions on gas‒Solids Flow hydrodynamics. The operating parameters included gas velocities in the riser and in the bubbling fluidised bed, aeration velocity in the lower U-valve, bed material inventory, and particle size. This is the first time that ECT was applied in different Flow zones of a dual fluidised bed gasifier system. The experimental results indicated that ECT in the recycle chamber could monitor the performance of the lower U-valve under different operating conditions for early detection of gas shortcut from the riser to the bubbling bed. Three main Flow regimes in the riser and the differences between the reactors were identified by two sets of ECT sensors with pressure transducers. Finally, the effects of the operating conditions on the pressure drop in different parts of the DFBG was investigated.
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investigation of gas Solids Flow characteristics in a pressurised circulating fluidised bed by experiment and simulation
Powder Technology, 2020Co-Authors: Xiaoli Zhu, Wuqiang Yang, Pengfei Dong, Zhiping Zhu, Haigang WangAbstract:Abstract Pressurised circulating fluidised bed (PCFB) is a new technology for coal/biomass combustion and gasification. To design, optimise and scale-up of PCFBs, it is necessary to understand the complex gas-Solids Flow characteristics. In this research, electrical capacitance tomography (ECT) technique, pressure measurement, and computational particle fluid dynamic (CPFD) simulation were combined for the first time to investigate the hydrodynamic behaviour of a pilot-scale PCFB test rig. The custom single- and dual-plane ECT sensors in the riser bottom and cyclone dipleg, provided the real-time cross-sectional particle distribution and circulation flux in a non-intrusive way. Pressure measurements in low and high frequency, revealed the full-loop pressure distribution and local Flow regime respectively. In addition, CPFD simulations based on Wen-Yu/Ergun and EMMS (energy-minimization multi-scale) drag model, were performed and evaluated by the experiments. The results demonstrate that (i) gas-Solids Flow in the PCFB riser shows the non-uniform distribution both axially and radially; (ii) EMMS based simulation predicts Flow behaviour in agreement with the experiments, while Wen-Yu/Ergun model significantly over-estimates the particle dispersion and circulation flux; (iii) the elevated operating pressure enhances the gas-Solids mixing, by demonstrating the more uniform particles axial distribution and development of radial “core-annular” structure towards the riser bottom and (iv) the elevated operating pressure improves the particle circulation flux, with the improvement limited by the saturated carrying capacity of the PCFB test rig.
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monitoring a lab scale wurster type fluidized bed process by electrical capacitance tomography
Flow Measurement and Instrumentation, 2017Co-Authors: H Q Che, Wuqiang Yang, Haigang WangAbstract:Abstract In this research, two types of electrical capacitance tomography (ECT) sensors, i.e. 12-4-8 combined electrodes and 8-8 dual planes sensors, were designed and used to monitor the gas-Solids Flow inside a Wurster type fluidized bed. For the 12-4-8 combined electrodes sensor, the measurement was conducted synchronously both inside and outside of the tube, i.e. coating zone and annulus zone, to achieve a fully understand the gas-Solids Flow characteristics in the bed. For the dual planes ECT sensor, the Flow through the two cross-section areas inside the Wurster tube was measured and Solids velocity was calculated based on cross-correlation method. A series of test were carried out by varying the operational parameters including the gap between the Wurster tube and air distributor, fluidization air velocity and materials loading. Different Flow regimes as well as the Flow stability were evaluated based on the ECT measurement results. To evaluate the Flow characteristics inside the bed, power spectra density (PSD) and standard deviation (SD) were applied to investigate the fluctuation characteristics in the coating and annulus zones. Experiment results indicate that ECT technology is a powerful tool to monitor the Wurster type fluidized bed process and analysis the gas-Solids Flow characteristics inside the bed.
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investigation of gas Solids Flow characteristics in a conical fluidized bed dryer by pressure fluctuation and electrical capacitance tomography
Drying Technology, 2016Co-Authors: Haigang Wang, Wuqiang YangAbstract:ABSTRACTIt is important to investigate the gas–Solids Flow characteristics of fluidized bed drying processes to improve the operation efficiency and guarantee the product quality. This paper presents research into fluidized bed drying processes measured by high-frequency differential pressure fluctuation and electrical capacitance tomography (ECT). Power spectra analysis is combined with dynamic calibration for ECT to reveal the complex gas–Solids Flow behavior. Bubble characteristics are visualized by cross-sectional and quasi-3D ECT images. In addition, results by discrete wavelet transform analysis are given and compared with the analysis results of previous sections. It has been found that bubbles would coalesce in different ways under different operation conditions, and discrete wavelet transform sub-signals of ECT measurements are sensitive to particle moisture. This work reveals the complex hydrodynamic behavior in the fluidized bed dryer and provides valuable information for process control.
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investigation of gas Solids Flow characteristics in a circulating fluidized bed with annular combustion chamber by pressure measurements and cpfd simulation
Chemical Engineering Science, 2015Co-Authors: Guizhi Qiu, Haigang WangAbstract:Abstract For large scale circulating fluidized bed (CFB) boilers, a new type of annular combustion chamber was proposed to improve the secondary air penetration and provide adequate space to arrange the heat transfer surface. To investigate the gas–Solids Flow characteristics and optimize the structure of the annular combustion chamber, a “cold” test rig was built with a cross sectional area of 1.18 m 2 and a height of 8.0 m. High frequency pressure transducers were used to obtain the pressure fluctuations characteristics. CFD simulation based on computational particle fluid dynamic (CPFD) was used to obtain pressure fluctuations and particles concentration. The time domain analysis, power spectrum analysis and Hilbert–Huang transform were applied to the experimental and simulation data. Different Flow regimes including single bubble regime, exploding bubble regime and turbulent fluidization regime were identified. The Flow characteristics were investigated in terms of standard deviation and higher-order moments, auto-correlation, power spectrum, and EMD energy entropy. The results show that the gas–Solids Flow in the bottom region of the annular combustion chamber was relatively uniform. The gas–Solids Flow in annular combustion chamber was proved similar to that in a conventional CFB riser.
Wuqiang Yang - One of the best experts on this subject based on the ideXlab platform.
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investigation of gas Solids Flow hydrodynamics in a cold model of a dual fluidised bed gasifier using electrical capacitance tomography sensors
Particuology, 2020Co-Authors: Zhan Luo, Yonglei Lin, Wuqiang Yang, Haigang WangAbstract:Abstract The Flow characteristics of a dual fluidised bed gasifier (DFBG) are more complex than those of a single fluidised bed gasifier. For stable operation and appropriate control, a cold DFBG test facility with both an upper and a lower U-valve was built, and electrical capacitance tomography (ECT) sensors were installed with pressure transducers to investigate the effects of operating conditions on gas‒Solids Flow hydrodynamics. The operating parameters included gas velocities in the riser and in the bubbling fluidised bed, aeration velocity in the lower U-valve, bed material inventory, and particle size. This is the first time that ECT was applied in different Flow zones of a dual fluidised bed gasifier system. The experimental results indicated that ECT in the recycle chamber could monitor the performance of the lower U-valve under different operating conditions for early detection of gas shortcut from the riser to the bubbling bed. Three main Flow regimes in the riser and the differences between the reactors were identified by two sets of ECT sensors with pressure transducers. Finally, the effects of the operating conditions on the pressure drop in different parts of the DFBG was investigated.
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investigation of gas Solids Flow characteristics in a pressurised circulating fluidised bed by experiment and simulation
Powder Technology, 2020Co-Authors: Xiaoli Zhu, Wuqiang Yang, Pengfei Dong, Zhiping Zhu, Haigang WangAbstract:Abstract Pressurised circulating fluidised bed (PCFB) is a new technology for coal/biomass combustion and gasification. To design, optimise and scale-up of PCFBs, it is necessary to understand the complex gas-Solids Flow characteristics. In this research, electrical capacitance tomography (ECT) technique, pressure measurement, and computational particle fluid dynamic (CPFD) simulation were combined for the first time to investigate the hydrodynamic behaviour of a pilot-scale PCFB test rig. The custom single- and dual-plane ECT sensors in the riser bottom and cyclone dipleg, provided the real-time cross-sectional particle distribution and circulation flux in a non-intrusive way. Pressure measurements in low and high frequency, revealed the full-loop pressure distribution and local Flow regime respectively. In addition, CPFD simulations based on Wen-Yu/Ergun and EMMS (energy-minimization multi-scale) drag model, were performed and evaluated by the experiments. The results demonstrate that (i) gas-Solids Flow in the PCFB riser shows the non-uniform distribution both axially and radially; (ii) EMMS based simulation predicts Flow behaviour in agreement with the experiments, while Wen-Yu/Ergun model significantly over-estimates the particle dispersion and circulation flux; (iii) the elevated operating pressure enhances the gas-Solids mixing, by demonstrating the more uniform particles axial distribution and development of radial “core-annular” structure towards the riser bottom and (iv) the elevated operating pressure improves the particle circulation flux, with the improvement limited by the saturated carrying capacity of the PCFB test rig.
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investigation of coating process in wurster fluidised bed using electrical capacitance tomography
Chemical Engineering Research & Design, 2018Co-Authors: Hanqiao Che, Wuqiang Yang, Hong WangAbstract:Abstract Wurster fluidised beds are used in the pharmaceutical industry for pellet coating. Due to Wurster tube in the chamber, the Flow hydrodynamic characteristics are complex and difficult to measure. This paper presents a 12-4-8 electrode electrical capacitance tomography (ECT) sensor used for investigation of complex gas–Solids Flow characteristics in Wurster fluidised bed coating processes by visualising Solids concentration and distribution both inside and outside of Wurster tube synchronously. It was revealed that there exist seven Flow regimes, i.e. bubbling-core, intermittent-core, plug-core, plug-bubbling, bubbling-dispersed, intermittent-dispersed and defluidisation, in a coating process. Further analysis of capacitance and pressure drop signals using a continuous wavelet transform (CWT) method indicates that the characteristic frequencies for bubbling, intermittent and plug Flow in the annular region are 2, 0–1 and 0 Hz, respectively. The influence of different operating parameters and Flow regime on the coating quality, in particular agglomeration, is discussed. Experimental results indicate that ECT is an efficient process analytic technology (PAT) tool to monitor the pellets coating process in a Wurster fluidised bed.
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monitoring a lab scale wurster type fluidized bed process by electrical capacitance tomography
Flow Measurement and Instrumentation, 2017Co-Authors: H Q Che, Wuqiang Yang, Haigang WangAbstract:Abstract In this research, two types of electrical capacitance tomography (ECT) sensors, i.e. 12-4-8 combined electrodes and 8-8 dual planes sensors, were designed and used to monitor the gas-Solids Flow inside a Wurster type fluidized bed. For the 12-4-8 combined electrodes sensor, the measurement was conducted synchronously both inside and outside of the tube, i.e. coating zone and annulus zone, to achieve a fully understand the gas-Solids Flow characteristics in the bed. For the dual planes ECT sensor, the Flow through the two cross-section areas inside the Wurster tube was measured and Solids velocity was calculated based on cross-correlation method. A series of test were carried out by varying the operational parameters including the gap between the Wurster tube and air distributor, fluidization air velocity and materials loading. Different Flow regimes as well as the Flow stability were evaluated based on the ECT measurement results. To evaluate the Flow characteristics inside the bed, power spectra density (PSD) and standard deviation (SD) were applied to investigate the fluctuation characteristics in the coating and annulus zones. Experiment results indicate that ECT technology is a powerful tool to monitor the Wurster type fluidized bed process and analysis the gas-Solids Flow characteristics inside the bed.
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investigation of gas Solids Flow characteristics in a conical fluidized bed dryer by pressure fluctuation and electrical capacitance tomography
Drying Technology, 2016Co-Authors: Haigang Wang, Wuqiang YangAbstract:ABSTRACTIt is important to investigate the gas–Solids Flow characteristics of fluidized bed drying processes to improve the operation efficiency and guarantee the product quality. This paper presents research into fluidized bed drying processes measured by high-frequency differential pressure fluctuation and electrical capacitance tomography (ECT). Power spectra analysis is combined with dynamic calibration for ECT to reveal the complex gas–Solids Flow behavior. Bubble characteristics are visualized by cross-sectional and quasi-3D ECT images. In addition, results by discrete wavelet transform analysis are given and compared with the analysis results of previous sections. It has been found that bubbles would coalesce in different ways under different operation conditions, and discrete wavelet transform sub-signals of ECT measurements are sensitive to particle moisture. This work reveals the complex hydrodynamic behavior in the fluidized bed dryer and provides valuable information for process control.
J F Davidson - One of the best experts on this subject based on the ideXlab platform.
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vertical plug Flow pneumatic conveying from a fluidised bed
Powder Technology, 2012Co-Authors: Roger Watson, R B Thorpe, J F DavidsonAbstract:Abstract Experiments are described on the pneumatic conveying of 2.7 mm alumina particles up a vertical riser of internal diameter 46.4 mm or 71.4 mm. The particles entered the riser from a fluidised bed, via a short horizontal pipe and a bend of radius 75 mm. Measured variables included Solids Flow rates, air Flow rates, inlet and outlet air pressures P 1 and P 2 , and the pressure profile in the riser. The Solids Flow rate was consistent with some earlier models of similar systems, in which the plugs of packed Solids move up at a velocity of about U − U mf , where U = superficial air velocity and U mf = incipient fluidising velocity. Solids–wall friction is significant and suppresses fluidisation. To model the system approximately, a conveying efficiency = (power for air compression) / (rate of gain of potential energy of Solids) is defined and correlated against Solids flux. It was found that the conveying efficiency tended to an asymptote just above 20%. The correlation led to a tentative design formula, Eq. (6), for predicting P 1 − P 2 at a given Solids Flow rate. P 1 − P 2 is typically between 50% and 100% of the pressure drop needed to support a column of Solids of height equal to that of the riser. It was concluded that plug Flow pneumatic conveying is a satisfactory technology for transporting coarse particles which cannot be conveyed in leaner regimes due to the possibility of pipeline erosion or Solids attrition.
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Vertical plug-Flow pneumatic conveying from a fluidised bed
'Elsevier BV', 2012Co-Authors: Rj Watson, Thorpe Rex, J F DavidsonAbstract:Experiments are described on the pneumatic conveying of 2.7mm alumina particles up a vertical riser of internal diameter 46.4mm or 71.4mm. The particles entered the riser from a fluidised bed, via a short horizontal pipe and a bend of radius 75mm. Measured variables included Solids Flow rates, air Flow rates, inlet and outlet air pressures P 1 and P 2, and the pressure profile in the riser. The Solids Flow rate was consistent with some earlier models of similar systems, in which the plugs of packed Solids move up at a velocity of about U-U mf, where U=superficial air velocity and U mf=incipient fluidising velocity. Solids-wall friction is significant and suppresses fluidisation. To model the system approximately, a conveying efficiency=(power for air compression)/(rate of gain of potential energy of Solids) is defined and correlated against Solids flux. It was found that the conveying efficiency tended to an asymptote just above 20%. The correlation led to a tentative design formula, Eq. (6), for predicting P 1-P 2 at a given Solids Flow rate. P 1-P 2 is typically between 50% and 100% of the pressure drop needed to support a column of Solids of height equal to that of the riser.It was concluded that plug Flow pneumatic conveying is a satisfactory technology for transporting coarse particles which cannot be conveyed in leaner regimes due to the possibility of pipeline erosion or Solids attrition. © 2012 Elsevier B.V
Tomasz Dyakowski - One of the best experts on this subject based on the ideXlab platform.
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application of electrical capacitance tomography for measurement of gas Solids Flow characteristics in a pneumatic conveying system
Measurement Science and Technology, 2001Co-Authors: Artur J Jaworski, Tomasz DyakowskiAbstract:Transient three-dimensional multiphase Flows are a characteristic feature of many industrial processes. The experimental observations and measurements of such Flows are extremely difficult, and industrial process tomography has been developed over the last decade into a reliable method for investigating these complex phenomena. Gas-Solids Flows, such as those in pneumatic conveying systems, exhibit many interesting features and these can be successfully investigated by using electrical capacitance tomography. This paper discusses the current state of the art in this field, advantages and limitations of the technique and required future developments. Various levels of visualization and processing of tomographic data obtained in a pilot-plant-scale pneumatic conveying system are presented. A case study outlining the principles of measuring the mass Flow rate of Solids in a vertical channel is shown.
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Solids Flow imaging and attrition studies in a pneumatic conveyor
Powder Technology, 1995Co-Authors: S. L. Mckee, T. A. Bell, Tomasz Dyakowski, Richard A Williams, Terence AllenAbstract:Abstract This work describes the first application of a non-invasive capacitance tomographic technique to monitoring the behaviour of industrial-scale pneumatic conveyors. Dynamic images of the Solids distribution within a pipe have captured the movement of slugs in dense-phase Solids conveying, and the presence of saltation in dilute-phase conveying. It has also been possible to acquire images downstream of a pipe bend and to use this information to establish a suitable location for obtaining a representative sample of a material stream. The information provided by cross-sectional images facilitates the validation of theoretical models and ultimately will allow improved design as the sensitivity and resolution of the technique are enhanced. A study of particle (sea salt) attrition is reported using a conveying line 32 m in length. It is demonstrated that particle breakage can be described as a function of the conveying velocity and Solids-gas loading factor. Particle breakage is described in terms of the mass-specific surface area, and is seen to increase with conveying velocity. Particle breakage rates are found to be inversely related to the Solids loading factor.
