Wenbiao Zhang

Measurement of Flow Characteristics in a Bubbling Fluidized Bed Using Electrostatic Sensor Arrays

Fluidized beds are widely applied in a range of industrial processes. In order to maintain the efficient operation of a fluidized bed, the flow parameters in the bed should be monitored continuously. In this paper, electrostatic sensor arrays are used to measure the flow characteristics in a bubbling fluidized bed. In order to investigate the electrostatic charge distribution and the flow dynamics of solid particles in the dense region, time and frequency domain analysis of the electrostatic signals is conducted. In addition, the correlation velocities and weighted average velocity of Geldart A particles in the dense and transit regions are calculated, and the flow dynamics of Geldart A and D particles in the dense and transit regions are compared. Finally, the influence of liquid antistatic agents on the performance of the electrostatic sensor array is investigated. According to the experimental results, it is proved that the flow characteristics in the dense and transit regions of a bubbling fluidized bed can be measured using electrostatic sensor arrays.

Measurement of flow parameters in a bubbling fluidized bed using electrostatic sensor arrays

Fluidized beds are widely applied in a range of industrial processes. In order to maintain the efficient operation of a fluidized bed, the flow parameters in the bed should be monitored continuously. In this paper, electrostatic sensor arrays are used to measure the flow parameters in the dense and transit regions of a bubbling fluidized bed. Each electrostatic sensor array has three electrodes and can provide more information and more reliable results than the conventional two-electrode sensor. By correlating the signals from multiple electrodes, particle velocities and corresponding correlation coefficients are obtained. Based on the correlation results and the amplitudes of the electrostatic signals, the solids movement and charge distribution in the dense and transit regions of the bed are monitored.

Parameters selection in the cross-correlation based velocimetry using electrostatic sensors

Cross-correlation methods in combination with electrostatic sensing technology offer a promising solution to the on-line continuous measurement of velocity of particulate solids in pneumatic pipelines. The sampling frequency and integral time are two fundamental parameters in cross-correlation calculation. This paper describes the principles and steps of the selection of these two parameters. The measurement error of the transit time and the real application requirement are taken into account. Additionally, an experimental platform was built and the principles in selecting the parameters in the electrostatic correlation based velocity measurement were proven.

Charge distribution reconstruction in a bubbling fluidized bed using a wire-mesh electrostatic sensor

The presence of electrostatic charge in a bubbling fluidized bed influences the operation of the bed. In order to maintain an effective operation, the electrostatic charges in different positions of the bed should be monitored. In this paper a wire-mesh electrostatic sensor is introduced to reconstruct the charge distribution in a bubbling fluidized bed. The wire-mesh sensor is fabricated by two mutually perpendicular strands of insulated wires. A Finite Element Model is built to analyze the sensing characteristics of the sensor. The sensitivity distributions of each wire electrode and the whole sensor are obtained from the model, which proves that wire-mesh electrostatic sensor has a higher and more uniform sensitivity distribution than single wire sensors. Experiments were conducted in a gravity drop test rig to validate the reconstruction method. Experimental results show that the charge distribution can be reconstructed when sand particles pass through the cross section of the sensor.

Hilbert-Huang transform based electrostatic signal analysis for characterization of dilute gas-solid two-phase flow

Online measurement of the particulate flow plays a significant role in the monitoring and controlling process of the industrial application. Due to the simple structure and non-intrusive character, the electrostatic sensor is widely used in industrial applications. The electrostatic signal from ring-shape electrostatic sensor was used in this paper to investigate the flow dynamics. Because of the advantages of Hilbert-Huang Transform, it was utilized to characterize the flow dynamics from the electrostatic signal of dilute gas-solid two-phase flow in the horizontal pipeline. A new method was introduced to eliminate the noise component of the electrostatic signal. The filtered electrostatic signal was then analyzed to find the relationship between the average fluctuation frequency and air flow rate. Besides, it can be concluded that the energy of the selected intrinsic mode functions can be a useful parameter to characterize the solid-phase concentration.

Measurement of Charge Distributions in a Bubbling Fluidized Bed Using Wire-Mesh Electrostatic Sensors

In order to maintain safe and efficient operation of a fluidized bed, the electrostatic charges in the bed should be monitored continuously. Electrostatic sensors with wire-mesh electrodes are introduced in this paper to measure the charge distribution in the cross section of a fluidized bed. A finite element model is built to investigate the sensing characteristics of the wire-mesh sensors. In comparison with conventional electrostatic sensors, wire-mesh sensors have higher and more uniform sensitivity distribution. Based on the induced charges on the electrodes and the sensitivity distributions of the sensors, the charge distribution in the cross section of the fluidized bed is reconstructed. However, it is difficult to directly measure the induced charges on the electrodes. A charge calibration process is conducted to establish the relationship between the induced charge on the electrode and the electrostatic signal. Experimental studies of charge distribution measurement were conducted on a lab-scale bubbling fluidized bed. The electrostatic signals from the wire-mesh sensors in the dense phase and splash regions of the bed for different fluidization air flow rates were obtained. Based on the results obtained from the charge calibration process, the estimated induced charges on the electrodes are calculated from the root-mean-square values of the electrostatic signals. The characteristics of the induced charges on the electrodes and the charge distribution in the cross section under different flow conditions are investigated, which proves that wire-mesh electrostatic sensors are able to measure the charge distribution in the bubbling fluidized bed.

Predicting the amount of coke deposition on catalyst pellets through image analysis and soft computing

The amount of coke deposition on catalyst pellets is one of the most important indexes of catalytic property and service life. As a result, it is essential to measure this and analyze the active state of the catalysts during a continuous production process. This paper proposes a new method to predict the amount of coke deposition on catalyst pellets based on image analysis and soft computing. An image acquisition system consisting of a flatbed scanner and an opaque cover is used to obtain catalyst images. After imaging processing and feature extraction, twelve effective features are selected and two best feature sets are determined by the prediction tests. A neural network optimized by a particle swarm optimization algorithm is used to establish the prediction model of the coke amount based on various datasets. The root mean square error of the prediction values are all below 0.021 and the coefficient of determination R 2, for the model, are all above 78.71%. Therefore, a feasible, effective and precise method is demonstrated, which may be applied to realize the real-time measurement of coke deposition based on on-line sampling and fast image analysis.

Coke deposition detection through the analysis of catalyst images

Coke deposition on catalyst will not only reduce catalytic activity and selectivity, but also affect the product yield, the reaction residence time, the regenerator temperature and so on. As a result, it is necessary to measure the amount of coke deposition on catalyst. This paper proposes a new method based on image analysis. An image acquisition system consisting of a flatbed scanner and an opaque cover is used to obtain catalyst images. After imaging processing and analysis, the gray layer is selected to be the most effective colour layer for colour features extraction based on a discriminability index, D. Eight colour features (mean, variance, skewness, entropy, energy, H, S, V) are extracted from images with a good ability to classify the catalysts with different coke amount. Furthermore, the results show that there is a significant linear correlation between the H value and amount of coke deposition on catalyst, which could reflect the coke deposited state and coking progress effectively.

Optimization of the multi-electrode electrostatic sensor for velocity distribution measurement

Measuring the velocity distribution of dilute gas-solid two-phase flow is necessary for industrial process monitor and control. However, in order to get correct measurement of the velocity distribution, the effective correlation calculation by non-corresponding side electrode couples of the electrostatic sensor was needed. By introducing the principle of electrostatic correlation based velocity distribution measurement method, the importance of the effective correlation calculation by non-corresponding side electrode couples was emphasized in this paper. In order to ensure effective correlation calculation by non-corresponding side electrode couples was emphasized in this paper. In order to ensure effective correlation calculation by non-corresponding side electrode couples, effective correlation analysis of multi-electrode electrostatic sensor was carried out and effective correlation analysis method was proposed. According to this method, the structure of multi-electrode electrostatic sensor was optimiz...