Xiangchen Qian

Flow Measurement of Biomass and Blended Biomass Fuels in Pneumatic Conveying Pipelines Using Electrostatic Sensor-Arrays

Key parameters such as particle velocity, concentration of solid particles, and stability of pulverized fuel flow in fuel injection pipelines are useful to power plant operators to detect fuel supply problems at an early stage. This paper presents the use of a novel multichannel instrumentation system with circular and arc-shaped electrostatic sensor arrays for the online continuous measurement of “mean” and “local” characteristics of blended biomass flow. Experimental tests were conducted on a pneumatic conveying test rig under various flow conditions on both horizontal and vertical pipes. The biomass fuels tested include willow, wood, and bark. A ground grain (flour) was used to replicate a biomass of finer particles. The results suggest that, due to the physical differences between the constituent biomass fuels, the characteristics of the flow depend on the proportion of larger biomass particles in the blend. It is found that pure flour particles travel faster and carry more electrostatic charge than those of larger biomass particles. As more biomass particles are added to the flow, the overall velocity of the flow slows down, the electrostatic charge level decreases, and the flow becomes less stable compared to the pure flour flow. Particles in the vertical pipe are found to be more evenly distributed, and the particle velocity profile across the pipe cross section is more regular when compared to those in the horizontal pipe.

Rotational Speed Measurement Through Electrostatic Sensing and Correlation Signal Processing

Rotational speed is a key parameter for the condition monitoring and control of rotating machineries, such as generators, electromotors, and centrifugal and machine tool spindles. It is essential for precision machining and early warning of faults to measure rotational speed in real time. This paper presents the principle and application of electrostatic sensors and correlation signal processing techniques to real-time measurement of rotational speed. The electrostatic sensors and signal conditioning and processing units were designed and implemented. Experimental tests were conducted on a laboratory-scale test rig under a range of conditions including different diameters of the shaft. The results obtained suggest that the distance between the electrodes and the surface of the rotating object is a key factor affecting the performance of the measurement system. The system performs better in terms of accuracy and repeatability at a higher rotational speed as more electrostatic charge is produced on the rotating surface. High and stable correlation coefficients acquired during the tests suggest that the measurement system is capable of providing reliable measurement of rotational speed under realistic industrial conditions.

Rotational Speed Measurement Using Single and Dual Electrostatic Sensors

Rotational speed is a key parameter for condition monitoring and control of rotating devices in many industrial processes. This paper presents a technique for the rotational speed measurement using a single or dual electrostatic sensors coupled with correlation signal processing algorithms. In the case of a single sensor, autocorrelation algorithm is applied to process the signal and measure the period of the rotational motion. In the case of dual sensors, cross correlation algorithm is applied to obtain the time delay between the two signals and hence the measurement of rotational speed. The fundamental characteristics of the sensing techniques with single or dual sensors for different sized rotors are studied through finite-element modeling. Experimental tests were conducted on a purpose-built test rig to assess the performance of both techniques over the speed range of 100-3000 r/min. The rotors used in the experimental tests are made of polyvinyl chloride with a diameter of 60 and 120 mm, respectively. Experimental results suggest that the measurement system using a single sensor is capable of producing repeatable rotational speed measurement with a maximum error of ±1.2% over the speed range of 600-3000 r/min. However, the measurement system with dual electrostatic sensors is capable of achieving valid measurements over a wider range of speeds (100-2000 r/min), although the measurement error is larger than that of the single-sensor system. Both techniques perform better with a larger rotor under a higher rotational speed.

Online particle size measurement through acoustic emission detection and signal analysis

Accurate determination of particle size distribution is critical to achieving optimal combustion efficiency and minimum pollutant emissions in both biomass and coal fired power plants. This paper presents an instrumentation system for online continuous measurement of particle size distribution based on acoustic emission (AE) method. Impulsive AE signals arising from impacts of particles with a metallic waveguide protruding into the flow carry information about the particle size. The relationship between the particle size and the peak AE voltage has been established through physical modeling of particle impact. A particle sizing algorithm is developed using peak detection techniques. Experimental results obtained with glass beads demonstrate the capability of the system to discriminate particles of different sizes from the recorded AE signals. The system has several appealing features such as online measurement, high sensitivity, simple structure, minimum invasiveness and low cost, which make it well suited for industrial applications.

Simultaneous Measurement of Belt Speed and Vibration Through Electrostatic Sensing and Data Fusion

Accurate and reliable measurement of belt speed and vibration is of great importance in a range of industries. This paper presents a feasibility study of using an electrostatic sensor array and signal processing algorithms for the simultaneous measurement of belt speed and vibration in an online, continuous manner. The design, implementation, and assessment of an experimental system based on this concept are presented. In comparison with existing techniques, the electrostatic sensing method has the advantages of non-contact and simultaneous measurement, low cost, simple structure, and easy installation. The characteristics of electrostatic sensors are studied through finite-element modeling using a point charge moving in the sensing zone of the electrode. The sensor array is arranged in a 2 × 3 matrix, with the belt running between two rows of three identical sensing elements. The three signals in a row are cross correlated for speed calculation, and the results are then fused to give a final measurement. The vibration modes of the belt are identified by fusing the normalized spectra of vertically paired sensor signals. Experiments conducted on a two-pulley belt-driven rig show that the system can measure the belt speed with a relative error within ±2% over the range 2-10 m/s. More accurate and repeatable speed measurements are achieved for higher belt speeds and a shorter distance between the electrode and the belt. It is found that a stretched belt vibrates at the harmonics of the belt pass frequency and hence agrees the expected vibration characteristics.

An Evaluation Method for Reconstructed Images in Electrical Tomography

The quality of reconstructed images plays an important part in evaluating reconstruction algorithms in electrical tomography. Existing image evaluation methods have many limitations. A multi-parameter and quantitative evaluation method is presented in this paper, which is based on the analysis of the characteristics of reconstructed images and digital image processing methods. The new method has three types of evaluation parameters, i.e., area, position, and similarity parameters. In order to ensure the efficacy of the new method, some typical distribution models are built using electrical field simulation software. Simulation data derived from the finite element method are also given. The simulation data demonstrate that the method is suitable for comprehensive evaluation of reconstructed images and the results are consistent with visual perception.

Non-Contact Vibration Monitoring of Power Transmission Belts Through Electrostatic Sensing

On-line vibration monitoring plays an important role in the fault diagnosis and prognosis of industrial belt drive systems. This paper presents a novel measurement technique based on electrostatic sensing to monitor the transverse vibration of power transmission belts in an on-line, continuous, and non-contact manner. The measurement system works on the principle that variations in the distance between a strip-shaped electrode and the naturally electrified dielectric belt give rise to a fluctuating current output. The response of the sensor to a belt moving both axially and transversely is numerically calculated through finite-element modeling. Based on the sensing characteristics of the sensor, the transverse velocity of the belt is characterized through the spectral analysis of the sensor signal. Experiments were conducted on a two-pulley belt drive system to verify the validity of the sensing technique. The belt vibration at different axial speeds was measured and analyzed. The results show that the belt vibrates at well-separated modal frequencies that increase with the axial speed. A closer distance between the electrode and the belt makes higher order vibration modes identifiable, but also leads to severer signal distortion that produces higher order harmonics in the signal.

On-line Sizing of Pneumatically Conveyed Particles Through Acoustic Emission Detection and Signal Analysis

Accurate measurement of the particle size distribution of pneumatically conveyed pulverized fuel is critical to achieving optimal combustion efficiency and minimum pollutant emissions at coal and biomass-fired power plants. This paper presents a prototype instrumentation system for the on-line continuous measurement of particle size distribution through acoustic emission (AE) detection. The proposed method extracts particle size information from the impulsive AE signals arising from impacts of particles with a metallic waveguide protruding into the flow. The relationship between the particle size and the peak AE voltage is established through mathematical modeling of the particle impact process. Identification of the peak AE voltage is achieved with an energy-based peak detection algorithm. Experimental results obtained with glass beads demonstrate the capability of the system to discriminate particles of different sizes from the recorded AE signals. The system performs better in terms of accuracy for higher speed, lower concentration particles as the impact signals are stronger and better separated in the time domain.

Flow measurement of pneumatically conveyed biomass-coal particles using multi-channel electrostatic sensors

Key parameters such as particle velocity and concentration of biomass-coal flow in fuel injection pipelines are useful to power plant operators to detect fuel supply problems at an early stage. This paper presents the use of a multi-channel electrostatic sensor with circular and arc-shaped electrodes for the on-line, continuous measurement of “local” and “mean” characteristics of the biomass-coal mixture flow. Experimental tests were conducted on a laboratory-scale particle flow test rig under various flow conditions. The results suggest that, due to physical differences between biomass and coal particles, the characteristics of the flow depend on the biomass proportion in the mixture. It is found that pure coal particles travel faster and carry more electrostatic charge than those of pure biomass particles. As more biomass is added to the coal flow, the overall velocity of the flow slows down, the electrostatic charge level decreases, and the flow becomes less stable compared to the pure coal flow.

Measurement of the Mass Flow and Velocity Distributions of Pulverized Fuel in Primary Air Pipes Using Electrostatic Sensing Techniques

Online measurement of pulverized fuel (PF) distribution between primary air pipes on a coal-fired power plant is of great importance to achieve balanced fuel supply to the boiler for increased combustion efficiency and reduced pollutant emissions. An instrumentation system using multiple electrostatic sensing heads is developed and installed on 510-mm bore primary air pipes on the same mill of a 600-MW coal-fired boiler unit for the measurement of PF mass flow and velocity distributions. An array of electrostatic electrodes with different axial widths is housed in a sensing head. An electrode with a greater axial width and three narrower electrodes are used to derive the electrostatic signals for the determination of PF mass flow rate and velocity, respectively. The PF velocity is determined by multiple cross correlation of the electrostatic signals from the narrow electrodes. The measured PF velocity is applied on the root-mean-square magnitude of the measured electrostatic signal from the wide electrode for the calibration of PF mass flow rate. On-plant comparison trials of the developed system were conducted under five typical operating conditions after a system calibration test. Isokinetic sampling equipment is used to obtain reference data to evaluate the performance of the developed system. Experimental data demonstrate that the developed system is effective and reliable for the online continuous measurement of the mass flow and velocity distributions between the primary air pipes of the same mill.