PC-based gas-solids two-phase mass flowmeter for pneumatically conveying systems

The development and performance of a PC-based instrumentation system for measuring the mass flow rate of gas-solid flow in a pneumatically conveying system have been discussed in this paper. A laboratory scale pneumatic conveyor incorporating facilities for calibration has been fabricated for this purpose. The test section is a vertical plexiglass tube of diameter 12.7 mm with an upward flow direction and sand has been used as the solid phase. The principle of measurement is based on inferential technique. Instantaneous velocity and concentration of the bulk solids are measured using a pair of electrodynamic sensors and a capacitance sensor, respectively. Several modifications of the existing technique of measurement have been suggested.     

Study and industrial evaluation of mass flow measurement of pulverized coal for iron-making production

This paper described a measurement system for mass flow measurement of pulverized coal in a blast furnace coal injection system. The system mainly consists of a volumetric concentration sensor and a velocity sensor. The concentration sensor is a capacitance sensor which has two pairs of concave electrodes placed axially on a piece of pipe of oxide of aluminum with different orientation to get being less affected by flow regime; the velocity sensor is also based on capacitance sensing principle, but uses “passing time difference method” which records the time at which each flowing cloud of coal powder passes through upstream and downstream sensor and then calculates the time difference to get the transit time for the cloud to travel between the two sensors. Both of the experiments in the laboratory and on the spot showed the measurement system has industrially acceptable performance.     

In-line measurement of pneumatically conveyed particles by a light transmission fluctuation method

An optical method for particle sizing in two-phase flow, the so-called light transmission fluctuation method, is presented in this paper. On the basis of this method, a novel optical instrument capable of in-line measurement of pneumatically conveyed particles is introduced. Quite a few medium-term tests validate the reliability and the applicability of this technique. Some measurement results are shown and discussed, concerning real-time in-line continuous monitoring of pulverized coal flow at coal-fired power plants and relevant laboratory experiments.     

An instrumentation system for multi-parameter measurements of gas-solid two-phase flow based on Capacitance-Electrostatic sensor

In this paper, an instrumentation system for the measurements of local solid volumetric concentration, local solid velocity, local solid mass flowrate and solid mass flowrate in gas-solid two-phase flow system is developed. It is based on a new type of a Capacitance-Electrostatic sensor (CES). The CES sensor is mainly composed of a capacitance electrode array and two electrostatic electrode arrays. The optimum design of the sensor is achieved by finite element method. The capacitance electrode array is employed to detect the solid distribution over the cross-section of the pipe, and the local solid volumetric concentration measurement is further derived. The electrostatic electrode arrays are used to measure the local solid velocities in conjunction with cross-correlation method. From the local solid velocity and local volumetric concentration, the solid mass flowrate and the local solid mass flowrate can be achieved. The developed system for the local solid volumetric concentration measurement is verified through analogue simulation experiments and static experiments. Finally, the system is employed to measure the local solid volumetric concentration, local solid velocity, local solid mass flowrate and solid mass flowrate on a belt conveyor. The experimental results show that the measurement error of the local solid volumetric concentration measurement results are less than 10.43% for solid local volumetric concentration ranging from 0.02 to 0.56, the standard deviations of the local solid velocity measurement results are less than 0.42 for solid velocity ranging from 3.5 m/s to 15.0 m/s, and the relative error of the solid mass flowrate is within −19.6% to +14.9% for solid mass flowrate ranging from 0.006 kg/s to 0.103 kg/s, indicating that the system is capable of achieving multi-parameters measurement in gas-solid two-phase flow system.     

气固两相流质量流量测量的新方法

文提出了一种采用电容传感器测量气固两相流质量流量的新方法。通过电容传感器对固相浓度的测量,可以求出气固两相流的固气比,结合气固混合之前所测得的载气流量,便可测出固相的质量流量。实测结果显示,测量误差小于5     

气固两相流固相浓度电容式传感器优化设计

本文建立了一种螺旋式电容传感器的数学模型,并基于该模型对传感器结构进行了优化设计。优化后的结构可以产生较均匀的灵敏场分布,实测结果表明,优化后的传感器电容值与固相浓度具有良好的线性关系,测量点的线性相对偏差小于0.8%,适用于气固两相流固相浓度的测量。     

气固两相流超声过程层析成像系统研究

研究了一种应用于气固两相流过程监测的超声波层析成像系统。为利用少数传感器实现较精确成像,研制了一套测试系统:传感器阵列由8个扇形空气耦合传感器组成,每个传感器均为收发一体式并且发射扇形波束角度可达150°;设计了基于单片机的切换装置以改善系统实时性;发展了改进二值逻辑反投影图像重建算法,通过设置双阈值改善边缘效应提高了图像重建精度。对四氟乙烯棒进行的静态实验与对煤粉进行的动态测试实验中,系统获得了足够多的有效信号数据,实现了气固两相流横断面的二维图像重建。静态实验中重建图像的最小空间成像误差(SIE)为3.2%,表明系统具有较好成像精度,可实现气固两相流流动监测。     

矩形电容层析成像传感器仿真模拟和实验测量

常规电容层析成像传感器为规则对称方形或圆形结构,其测量和成像算法已相对成熟.由于受循环流化床旋风分离器入口结构段的限制,上述传感器结构已不能应用在旋风分离器入口段的测量,因此为了研究大型化循环流化床多旋风分离器并联布置入口段固体颗粒浓度分布,提出和设计了一种矩形非常规电容传感器,该传感器为12电极结构,在每个入口段的短边布置2个电极,长边布置4个电极,成像敏感场仿真计算基于Ansoft-Maxwell软件.对此传感器进行了静态仿真模拟研究和静态实验测量,对不同激励电压和频率测量结果进行分析,并对测量结果进行误差分析,得到矩形不规则电容传感器最佳测量参数(激励电压和频率),并对循环流化床分离器入口段进行了动态测量.结果表明,这种矩形非常规电容传感器可以用于循环流化床冷态试验台的旋风分离器入口段的直接测量,测量结果对改进旋风分离器的布置方式有参考意义.     

Concentration measurement with thermal probe for pulverized coal in the pneumatic pipeline of power plant

The concentration measurement of pulverized coal in a pneumatic pipeline is a challenging issue in power plant. A thermal probe manufactured with abrasion-proof steel was developed for coal concentration measurement in such a situation. The probe generates 15 W of heat. This method is based on the heat transfer between the thermal probe and the gas–solid two-phase flow. Experiments were conducted in a horizontal pneumatic pipeline to assess the accuracy of the thermal probe, where the gas was air and the solid was pulverized coal with mean diameter of 65 µm. The wall temperature of the thermal probe was found to be dependent on both coal powder concentration and air velocity. A new heat transfer correlation was proposed in terms of the modified Reynolds and Nusselt numbers for the gas–solid two-phase flow across the thermal probe. In the range of coal powder concentration from 0.1 to 0.65 kg/kg, the standard deviation is 0.01 kg/kg for the thermal probe. The thermal probe has potential application for concentration measurement of pulverized coal in the pneumatic pipelines of power plants.     

Design of a Conductance and Capacitance Combination Sensor for water holdup measurement in oil–water two-phase flow

Oil–water two-phase flow widely exists in the process of petroleum industry. The liquid holdup measurement in horizontal pipeline is very important and difficult. In this work, a Conductance and Capacitance Combination Sensor (CCCS) system with four conductance rings and two concave capacitance plates is designed and validated for its measurement performance of in situ water holdup through dynamic experiments. A set of fast electronic switches controls the conductance rings and the capacitance plates alternatively set up each own sensing field in the same sensing volume. This configuration ensures the water holdup estimation in the range from 0% to 100% regardless of flow direction. A set of quick closing valves was used to acquire the in situ holdup for the on-line calibration of the CCCS system. The theoretical correlations of conductance sensor and capacitance sensor were established to make the real-time measurement convenient. A real-time measurement method by CCCS system is provided based on the fusion of the conductance and the capacitance measurement without flow pattern recognition. This method delivers an average error of 1.06% for the CCCS system measuring the water holdup of oil–water two-phase flow, with a standard deviation of 0.038 and a relative error less than ±5%.     

基于单片机的电容传感器测量油箱油量方法的研究

介绍了一种基于单片机的电容传感器测量飞机油箱内油量的方法,利用电容式传感器的电容随油面高度的变化,构建了以单片机为核心的油量自动测试系统,给出了该油量测试系统的测量原理、硬件设计和软件设计。实际应用表明,该油量测量系统具有结构简单、测试精度高、可靠性好等优点。     

阵列式静电-电容传感器灵敏度特性研究

结合静电和电容传感技术各自的特点,提出了阵列式静电-电容传感器用于气固两相流中固相颗粒的局部速度、局部浓度以及局部流量测量。利用静电极片阵列与电容极片阵列获取管道内颗粒的速度分布与浓度分布,进而计算出颗粒的局部流量。该阵列式传感器参数测量的准确性直接取决于它的空间灵敏度分布特性。对静电极片阵列和电容极片阵列的灵敏度特性进行了研究。首先,建立了静电极片阵列的三维静电场模型,通过有限元法分析静电极片阵列的结构参数(电极长度、电极覆盖角等)对传感器灵敏度特性的影响;然后根据电磁场理论建立电容极片阵列的数学模型,并对其进行数值计算,研究管道厚度、管道介电常数、电极覆盖角等参数对传感器灵敏度特性的影响;最后搭建了传动带装置进行了实验研究,实验结果证实了模拟结果的准确性,为阵列式静电-电容传感器的优化设计提供理论依据。     

Fast Coriolis mass flow metering for monitoring diesel fuel injection

Prism signal processing is a new recursive FIR technique that facilitates the rapid tracking of sinusoidal signals, such as those used in a Coriolis Mass Flow Meter (CMFM). A Prism-based CMFM prototype has been developed using a commercial flowtube and a dual ARM processor-based transmitter, which is capable of generating flow measurement updates at 48 kHz. This has been applied in a feasibility study to the tracking of fast (e.g. 1.5 ms) injections of diesel fuel on a laboratory rig at engine speeds of up to 4000 rpm equivalent and at fuel pressures of up to 100 MPa. Due to the high level of vibration in the system, Prism-based notch filtering is used to suppress undesired modes of flowtube vibration in the sensor signal. Individual flow pulses can be detected by the system, but the relatively long period of oscillation of the flowtube compared to the fuel injection duration results in a spreading out over time of each flow pulse measurement. More precise measurement results may be obtained using a higher frequency resonant flowtube.     

Design of a micro floating element shear stress sensor

A silicon-based micro-machined, floating element sensor for wall shear-stress measurement has been developed. Sensor with the dimension of 4×3×0.5 mm³ has been fabricated by inductively coupled plasma (ICP) etching techniques with single mask. An optical system was designed to identify whether there is defect in the structure of the fabricated sensor. Detection of the floating element motion induced by shear stress of fluid is accomplished using differential capacitance measurement. A special package was used to reduce the parasitic capacitance and realize flush mounted between the sensor and the wall. Calibration tests were carried out in a laminar flow channel; the result indicates that the sensitivity of the sensor is measured to be 27 mv/Pa. The measured non-linearity is less than 3.4% while the repeatability is within 4.9% in the regime of 0–35 Pa.     

Investigation of two-phase flow mixing mechanism of a swirl burner using an electrostatic sensor array system

A novel electrostatic sensor array was designed to measure particle concentration downstream of a swirl burner. The fundamental mechanism and the primary constituent elements of the sensor array were described. The root-mean-square magnitude of the measured electrostatic voltage was determined as an indication of the particle concentration. The accuracy of the electrostatic sensor array was calibrated by the optical fluctuation method. Local particle concentrations at different cross-sections of the measuring chamber were measured to investigate the diffusion characteristic of the pulverized coal particles. Electrostatic sensor array showed its ability in the field measurement in this work. The measurements indicated that the velocity of the inner secondary air had a significant effect on the diffusion of the pulverized coal particles. The particles concentrated in the center of the cross-section after leaving the burner. With the development of the gas–solid two-phase flow, the particles distributed like a ring shape. The radius of the particle ring increased with the increase of the velocity of the inner secondary air. But the effect of the velocity of outer secondary air on the radius of the particle ring is very slight. The maximum radius occurred when the velocity of inner secondary air was 21 m/s, which was favorable for stable combustion.     

双层电容层析成像传感器及应用

电容层析成像在气力输送过程中具有十分重要的应用地位，可进行固相浓度分布测量，流型判断。利用双层电容层析成像传感器不仅可以进行浓度测量还可以进行相关测速。基于这种思想，设计了一种双层电容传感器，与电容测量系统结合，用于气力输送过程固相浓度和速度的测量。     

Pulverized coal flow metering on a full-scale power plant using electrostatic sensor arrays

On-line continuous monitoring of pulverized coal in fuel injection pipes will allow power plant operators to optimize fuel conveying conditions and ultimately to achieve higher combustion efficiency and lower atmospheric emissions. This paper presents the design, implementation and trials of a prototype instrumentation system for the on-line measurement of pulverized coal on a full-scale power plant. An array of three identical arc-shaped electrostatic electrodes is housed in a sensing head to derive particle flow signals. Pulverized coal flow parameters such as velocity, mass flow rate and fuel distribution among the injection pipes from the same pulverizing mill are obtained by processing the signals and fusing the resulting measurements. On-plant demonstration trials on 560 mm bore pneumatic conveying pipes feeding a 600 MW boiler were undertaken following system evaluation tests on a 50 mm bore laboratory test rig. Experimental results demonstrate that reliable monitoring of pulverized coal flow parameters is achieved and that the system is able to track both transient and long-term fluctuations of pulverized coal flow in fuel injection pipes under real power plant conditions.     

A theoretical model for a capacitance tool and its application to production logging

A new theoretical model for a capacitance sensor used for measuring water holdup in production logging is proposed in this paper. The model realizes that the capacitance sensor is sensitive to oil droplets that collide against the sensor's inner electrode coated with an insulator when the water is electrically conductive and is the continuous phase in an oil/water bubbly flow. The sensor still has the ability to distinguish between oil and water in this case, its sensitivity decreasing with fluid velocity. The experiments were performed in a multiphase flow loop, and the results strongly confirm the theory. On the basis of the model, the measuring principle of the sampling-type capacitance tool is discussed, and an attempt to evaluate average oil droplet size with the capacitance sensor in the case of oil in water is also made.     

两相流离散相浓度测量新方法的研究

本文提出了一种基于流动成像技术测量两相流离散相浓度的新方法。该法以阵列式电容传感器为信息获取手段。针对离散相浓度测量的自身特性和要求建立了一种新的图像重建模型。为克服图像重建过程中的不适定性问题,提出了一种正则化广义逆图像重建算法并引入修正滤波。相应的浓度检测系统具有简单、非侵入性、实时性能佳等优点。实验结果表明,该方法是可行的,浓度测量最大误差小于５％。     

Adaptive calibration of a capacitance tomography system for imaging water droplet distribution

A highly sensitive electrical capacitance tomography (ECT) system based on an HP4284 impedance analyser has been developed and used to quantify low concentration multi-phase flows in wet gas separation processes. The system hardware provides high accuracy (0.05%) and high resolution (10⁻¹⁷ F). The sensor was calibrated in an environmental chamber with solid samples of known permittivity over ranges of temperature and humidity. Adaptive calibration and adjacent electrode pair correction techniques were applied to image very low concentration profiles. This paper describes the techniques used and presents the experimental results obtained from a test flow rig called Twister, which has been designed to separate liquid droplets from wet gas streams. The test results over a range of operating conditions (20–95% humidity) demonstrate that the ECT system is capable of reconstructing clear images of the droplet distribution inside Twister. Changes as small as 1 gWater/kgAir in the form of liquid droplets were detectable. It has also been shown that the concentration of the condensable phase can be estimated quantitatively within 20% in comparison with the reference measurements.