Thread Content
Application of petroleum machinery technology: the use of insert-type electromagnetic flowmeters in the measurement and control of water treatment in mines. Considering factors such as cost-performance, plug-in electromagnetic flowmeters are selected for pipes with a length of over 250. It introduces the working principle and structural composition of this flow meter, as well as the measurement and control aspects related to the use of plug-in electromagnetic flow meters in petroleum machinery applications for mine water treatment. Considering factors such as cost-performance, plug-in electromagnetic flowmeters are selected for pipes with a length of over 250. It introduces the working principle and structural components of this flow meter, and puts forward the following requirements for its installation: ensuring sufficient straight pipe sections, maintaining perpendicularity between the fluid and the sensor’s magnetic field, minimizing interference sources, ensuring proper grounding, and ensuring the correct insertion depth of the sensor. The draw-in type electromagnetic flowmeter was installed under pressure, and after nearly 5 months of operational testing, it has performed well, providing relatively accurate flow measurement. To reduce pollution and conserve water while cutting emissions, strict measurement and control are necessary for domestic water, industrial water, recycled water, as well as the wastewater discharged. The measurement of flow rate plays an important role in the implementation of total volume control and quota management for water resources, as well as in petrochemical production and process control. The Tiebei Mine Water Treatment Plant of Huaneng Coal Chemical Co., Ltd. is the main water supply facility for the circulating water in the coal chemical plant area; the proper operation of its water supply systems is crucial for the production processes and environmental protection efforts of the entire plant. Wastewater treatment capacity and treatment quality are important indicators for this water supply system; if the treatment capacity is low, it will not be possible to meet the water needs of the entire plant, and if the treatment quality is poor, it will not satisfy the discharge requirements. When evaluating the discharge capacity and economic benefits of mine water, three flow rate indicators are primarily considered, namely the inflow of mine water, the outflow of clarified water, and the outflow of sludge. Taking factors such as cost-performance into account, the author chose plug-in electromagnetic flowmeters for pipes with a diameter of more than 250 mm and carried out pressure-mounted installation. After nearly 5 months of operational testing, the flowmeters performed well, providing relatively accurate flow measurement. Technical Analysis The working principle of the insert-type electromagnetic flowmeter is based on Faraday’s law of electromagnetic induction. When measuring flow, the liquid flows through a magnetic field perpendicular to the direction of flow, which generates a voltage that is proportional to the average flow velocity (volumetric flow rate). Its induced voltage signal is detected by 2 electrodes in direct contact with the liquid, and transmitted to an intelligent transmitter via a dedicated cable. The intelligent transmitter performs calculations based on the magnitude of the potential and mathematical models of electromagnetic flow measurement, converting it into flow signals (including instantaneous and cumulative values) for on-site display. It then outputs flow standard signals of 4–20 MA or 1–5 VDC to secondary flow meters or DCS systems. 1.2 The plug-in electromagnetic flowmeter consists mainly of a sensor, an intelligent transmitter, and a dedicated cable. The sensor consists of electrodes and an excitation coil; its function is to generate a corresponding induced potential (5~60 mV) at the electrodes based on the varying speed at which the conductive medium (fluid) flows through the excitation coil. The function of an intelligent transmitter is to amplify the potential signal generated by the sensor, and then to perform calculations using mathematical models and formulas related to potential-flow, in order to obtain the flow rate value as well as a standard flow signal. The adjustment of various flow parameters and the setting of calibration parameters are carried out on the intelligent transmitter. The function of the dedicated communication cable is to allow the sensor to transmit millivolt potential signals to the intelligent transmitter, which in turn supplies an oscillating voltage to the excitation coil. Since the potential signal is a weak signal ranging from 5 to 60 mV, and the excitation signal is an oscillating signal with high frequency but low amplitude, the cable must have excellent shielding and noise resistance. The length of the cable is proportional to its cross-sectional area as well as to the conductivity of the medium. The stronger the conductive properties, the greater the transmission distance; generally, this distance ranges from 20 to 1.3 units. Installation requirements: It is necessary to ensure sufficient straight sections of pipe. When there are changes in the flow direction, pipe diameter, or valve opening, eddies and flow field distortions can occur, which can affect the measurements taken by the sensor electrodes and thus impact the accuracy of the instrument. Therefore, it is necessary to keep a certain distance from components such as elbows, manual valves, and control valves as much as possible. The specific requirements for the straight pipe section are shown in Table 1. In this table, D represents the pipe diameter, while L represents the distance from the sensor to components such as valves or elbows. To ensure that the fluid is perpendicular to the magnetic field of the insert-type electromagnetic flowmeter sensor, when installing pressure tapping stubs through pipe openings, care must be taken regarding the vertical orientation during welding. It is required that the angle between the axis of the welded stub and the pipe axis be 90*, and that the extension line of the flanged stub pass vertically through the center of the pipe’s cross-section; this ensures that the fluid is perpendicular to the magnetic field. Specific requirements for straight pipe sections: mm. Standards for pipeline types – length of front straight pipe section, length of rear straight pipe section, horizontal pipes, elbows, flared pipes, valves, contraction sections downstream of pumps, and mixed fluids downstream of pumps. In petroleum machinery, 1.3.3 states that interference sources should be avoided as much as possible. To ensure measurement accuracy, sensors should not be installed in areas where vacuums, gases, eddies, etc. may occur; moreover, the communication cables between sensors and intelligent transmitters should be kept away from strong electrical equipment such as motors. It is recommended to install it at the indicated location. To ensure a good ground for the sensor’s output signal, the grounding point should be electrically connected to the medium being measured. When the fluid cuts through the magnetic field lines to generate a flow signal, with the fluid itself serving as the 0 potential, a positive potential is generated at one electrode while a negative potential is generated at the other electrode, with these potentials alternating continuously. Therefore, the midpoint of the converter’s input side (the shield of the signal cable) must be at the same 0 potential as the fluid and conductive, in order to form a symmetric input circuit. The midpoint of the converter’s input side is electrically connected to the fluid under test through the ground point of the sensor output signal. Since the output signal of the sensor is very small, only a few millivolts, in order to improve the instrument’s resistance to interference, the 0 voltage in the input circuit must be grounded. Since ordinary metal pipes are connected to the ground, and the flowing medium is electrically connected to the ground through these metal pipes, it is not necessary to provide a separate grounding device for electromagnetic flowmeters, especially for those with small diameters. If it is a non-metallic pipe, it must be connected to a separate grounding wire. Ensuring the correct insertion depth of the insert-type electromagnetic flowmeter sensor: due to the laminar flow of fluid in the pipe, the flow velocity is slower near the pipe wall and faster near the center of the pipe; based on calculations, the average flow velocity is closest at the D/8 point of the pipe. During installation, the wall thickness of the pipe and the length of the flanged nozzle must be calculated to ensure that the sensor’s electrodes are positioned at a depth of D/8. However, not all insert-type flow meter sensors are installed at the D/8 position of the pipe; a few are installed at the D/2 position. It is essential to carefully study the installation instructions before installing them. For more information, please visit the company’s official website at http://www.yb1518.com/. Please retain this link when reproducing the content! http://www.yb1518.com/UploadFiles/201412269333291.jpg