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Description of the selection of electromagnetic flowmeter at the production site

The selection of flowmeters used in many production sites in oil fields is not reasonable enough, and some installation errors, resulting in excessive measurement errors, and some can not meet the needs of production or crude oil transfer metering, flow meters are the most commonly used instruments for oil mining enterprises. Many forms of flowmeters can measure crude oil, but the choice is based on experience and simply considering the purchase cost for selection, which may lose the opportunity to choose the most suitable instrument. This shows that the correct choice and use of the flow meter is not easy. To properly and efficiently select a crude oil flow meter, the following five factors must be considered: performance requirements, crude oil properties, installation requirements, environmental conditions, and costs.

Flowmeter performance requirements

The choice of flowmeters in terms of performance requirements are: instantaneous flow, cumulative flow, accuracy, repeatability, linearity, flow range and range, pressure loss, output signal characteristics, and response time. There are different options for flowmeter performance for different measurement purposes. For example, crude oil trade settlement measurement requires high precision; continuous measurement process control usually requires good reliability and repeatability, and sometimes requires a wide range, and measurement accuracy requirements should be placed in a secondary position; oil field production site does not The flowmeter is required to have too high precision, but has good adaptability to crude oil properties and working conditions.

If it is necessary to measure the total flow, it must be applied in the flow control system. For example, the flowmeter is used as both the crude oil transfer metering port and the crude oil pipeline leakage alarm device signal acquisition. The accuracy of the flowmeter must be determined throughout the system control accuracy. The requirements are carried out, because the whole system not only has the error of flow detection, but also includes the error of signal transmission, control adjustment and other influencing factors. For example, the operation execution link often has certain error, and the measurement instrument is determined to be too high precision. Degree is unreasonable and uneconomical. The accuracy level determined by the flowmeter specification is within a certain flow range. If it is used within the specified range, the general accuracy is guaranteed. If the specified flow range is exceeded, the actual accuracy is lower than the nominal value, and the measured flow rate is lower than the flowmeter. At the minimum measurement value, the flowmeter may not start. Generally, the flowmeter should be used within 30% to 80% of the nominal range. For trade settlement requirements, higher accuracy, generally should not be less than 0.2, should also consider the relationship between the durability of the accuracy and the verification cycle, can guarantee to pass the entire verification cycle. The pressure rating of the flowmeter should be one order of magnitude higher than the pressure rating required by the process. For example, the process flow is 4 MPa, and the selected flowmeter should generally be 6.4 MPa. Crude oil flowmeters should be equipped with explosion-proof functions, and the explosion-proof grade should meet the design specifications and safety requirements of oil and gas stations and reservoirs.

Repeatability is an important indicator in process control applications, which is determined by the principle and manufacturing quality of the flowmeter itself. However, in practical applications, the repeatability of the flowmeter is affected by many factors such as viscosity, density of the crude oil, and interference from surrounding electromagnetic fields. Therefore, where reproducibility is required, the environment, medium, and working conditions should not be selected to affect sensitive flowmeters.

Volumetric flowmeters are usually output at mechanical or pulse frequency, directly to obtain the cumulative flow, with high accuracy, suitable for the total amount of measurement, if you need to output instantaneous flow, you need to be equipped with the corresponding signaling device. Electromagnetic flowmeters, ultrasonic flowmeters, etc., in principle, derive flow by measuring the flow rate of the medium, and have a fast response, which is suitable for process control (such as leakage alarm), and the total flow can also be obtained by integrating. When selecting the flowmeter, the measurement accuracy required by the production process, the fluctuation range of the flow rate at the production site, the accuracy within which the measurement range is guaranteed, the verification period of the flowmeter required for production or management, and whether the on-line physical liquid verification is required should be considered. , the pressure level of the flow meter, the explosion-proof level, etc.

The diameter of the selected flow meter should be selected according to the flow range used by the pipeline to be tested and the upper and lower flow rates of the selected flow meter, and should not be simply selected according to the pipeline diameter. The maximum flow rate of a pipe fluid is usually designed to be determined by economic flow rate. Because the flow rate selection is too low, the crude pipe diameter is large; when the flow rate is too high, the transmission power is large, and the operating cost is increased. The flow rate of most flowmeter upper flow rate is close to or slightly higher than the economical flow rate of the pipeline. Therefore, the flowmeter diameter is the same as the diameter of the pipe diameter. The installation is convenient. If it is different, it should not be too different. The file size is connected by a reducer.

The flowmeter range is the ratio of the upper flow rate to the lower limit flow rate, and the larger the value, the wider the flow range. Linear instruments have a wide range, 0.5-stage volumetric flowmeters are generally 10:1; 0.2-stage volumetric flowmeters are generally 5:1; nonlinear gauges are smaller, usually only 3:1, and the flowmeter accuracy is higher. The smaller the range, the larger the range. The relationship between the two should be reasonably considered when selecting.

Installation considerations

Flowmeters with different principles have very different installation requirements. For example, differential pressure, turbine flowmeters require long upstream straight sections, and some flowmeters do not require this or require lower requirements. Some flowmeters need to consider the installation location and media flow direction, maintenance space, installation direction, and so on. The metering performance of the flowmeter is greatly affected by the installation condition. The reason for the large flowmeter error is caused by poor installation. The factors considered in the installation are: the installation direction of the flowmeter, the flow direction of the crude oil, the straight pipe section of the upstream and downstream, the valve position, vibration, electromagnetic interference and maintenance space.

Some flowmeters have different metering performances for horizontal and vertical installations. For example, the vertical downward flow of crude oil gives the flowmeter rotating elements extra force, which can significantly affect performance, linearity or repeatability. Most flowmeters are installed in accordance with the manufacturer's specifications and should be observed. The direction of installation also depends on the physical properties of the crude oil, such as horizontal installations that may precipitate solid particles that damage the flowmeter bearings. Some flowmeters can only work in one direction of flow, and incorrect installation into reverse flow can damage the flowmeter. The use of such flowmeters should also pay attention to whether there is a possibility of reverse flow under mis-operating conditions, and if necessary, a check valve is required to protect the flowmeter. Flowmeters that can operate in both directions may have some differences in measurement performance between forward and reverse. The importance of maintaining space is often overlooked. Generally speaking, it should be able to enter the flowmeter, easy to maintain, and have the position to replace the whole machine.

Some flow meters (such as Coriolis mass flow meters) are susceptible to vibration and should be considered for reliable support. There is always a control valve on the flow meter's line. The control valve should be installed downstream of the flowmeter to avoid any flow velocity distribution disturbances and cavitation from the valve, thus affecting measurement accuracy.

Some flow meters may require additional protection to ensure proper operation of the meter. For example, volumetric and turbine flow meters typically have suitable filters and getters installed upstream of them.

Considerations regarding crude oil properties and oil handling conditions

The operation of the crude oil flow meter is affected by factors such as crude oil temperature, oil pressure, crude oil density, crude oil viscosity, and flow rate. The physical properties of crude oil vary with temperature and pressure. When crude oil is metered by a flow meter, changes in temperature, pressure, viscosity, etc., all affect the volume of the crude oil. Temperature is one of the most influential parameters in flow metering. The change in temperature causes a series of parameter changes that cause the volume, density, viscosity of the crude oil, and the gap between the flowmeter housing and the internal components to change, resulting in a change in leakage flow. If the temperature is lowered, the paraffin and the coke in the crude oil adhere to the inner wall of the casing and the component, which changes the volume of the metering chamber of the flowmeter and directly affects the metering accuracy of the flowmeter. In the measurement of crude oil, the volumetric flowmeter is the most commonly used. Its metering principle is that there is a precise metering chamber in the flowmeter housing. The flowmeter measures the volume of crude oil delivered by recording the number of times the crude oil is filled in the measuring chamber. . Due to the certain gap between the flowmeter rotor and the metering chamber wall, plus the machining error of the rotor and the measuring chamber, the leakage of the measured medium will inevitably occur, but it is generally within the design allowable range, thus causing additional errors of the flowmeter. Caused by factors such as flow, viscosity, temperature, pressure, and operating time.

economic factors

In terms of economics, only the purchase cost of the instrument is not comprehensive. Other expenses, such as attachment purchase cost, installation fee, maintenance and flow meter verification fee, operation fee and spare parts fee, should also be considered. Trade settlement measurement should also compare the economic losses caused by measurement errors.

The operating cost of the flowmeter is mainly the energy consumption during operation, including the power consumption of the electrical components inside the electric instrument, and the energy consumed to push the fluid through the meter during the measurement process, that is, the pumping energy consumption cost of the flowmeter due to the measurement. Some flow meters are powered by dry batteries, and the battery consumption is also considerable. Pumping costs are a hidden cost and are often overlooked. For example, the differential pressure generated by the differential pressure gauge differential pressure device has considerable resistance. Electromagnetic flowmeters and ultrasonic flowmeters are neglected.

The flowmeter shall perform periodic verification. The verification period shall be determined according to the actual application frequency of the instrument, but shall not exceed the provisions of the verification procedure. The verification cost accounts for a large proportion of the flowmeter operating costs. The maintenance cost is the cost of maintaining the normal operation of the measuring system after the instrument is put into use, mainly including maintenance labor and spare parts. Instruments with moving parts generally require more maintenance work, such as regular replacement of wearable bearings, shafts, rotors, transmission gears, etc.

Environmental considerations

The surrounding conditions of the meter and its expected changes, including ambient temperature, humidity, safety and electrical interference, should be considered during the flowmeter selection process. The instrument's electronics and some meter flow detection sections are subject to changes in ambient temperature. For example, the size of the flowmeter housing changes, heat transfer through the meter housing changes fluid density and viscosity, etc.; affecting the display instrument electronics, will reduce the measurement performance. Sometimes the conversion display section and the flow sensor are separately installed in different places to ensure that the electronic components are protected from temperature. High humidity accelerates atmospheric and electrolytic corrosion and reduces electrical insulation. Low humidity tends to generate static electricity. These can have an effect on the circuit portion of the flowmeter and sometimes even cause a malfunction.

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