Brief introduction to the design and application of turbine flowmeter in oil pipeline

Oil pipelines are extremely important transmission equipment in the modern energy industry. The requirement for accurate measurement of fluids in oil pipelines is a goal pursued by relevant technicians, and it is also a technical problem that will never end. After all, the pursuit of technology in industrial production is endless. With the rapid progress of science and technology, this problem has been solved more and more perfectly. In view of this situation, through this article, the author combines the work practice of the unit to communicate with you about the design problems of turbine flowmeters in oil pipelines.

 


1. Working principle of turbine flowmeter The working principle of
　　turbine flowmeter is to install a turbine in the pipeline, supported by bearings on both sides. When the fluid passes through the pipeline, it impacts the blades of the turbine, and the impact force generates a driving torque on the turbine, causing the turbine to overcome the friction torque and rotate. Within a certain flow range, for a certain fluid medium viscosity, the rotational angular velocity of the turbine is proportional to the fluid flow rate. Therefore, the fluid flow rate can be obtained by the rotational angular velocity of the turbine, so that the fluid flow through the pipeline can be calculated.
 
　　The speed of the turbine is detected by a sensor coil installed outside the casing. When the turbine blades cut the magnetic lines of force generated by the permanent magnets in the casing, it will cause the magnetic flux in the sensor coil to change. The sensor coil sends the detected magnetic flux period change signal to the preamplifier, amplifies and shapes the signal, generates a pulse signal proportional to the flow rate, and sends it to the unit conversion and flow accumulation circuit to obtain and display the cumulative flow value; at the same time, the pulse signal is also sent to the frequency current conversion circuit to convert the pulse signal into an analog current, thereby indicating the instantaneous flow value.
　　
2. Design and application of turbine flowmeter in oil pipeline
　　1. Main performance of turbine flowmeter
　　Rated pressure: 4 MPa; Length: 600 mm; Flow range: 50 to 250 cubic meters per hour; Pressure drop: Pressure loss is less than 40 kPa at maximum flow (when water is used as the test medium); Total mass: less than 40 kg. It can work normally in an environment of -41 degrees Celsius to +46 degrees Celsius. The meter head displays instantaneous flow and cumulative flow at the same time, and can switch to display total cumulative flow, batch cumulative volume, instantaneous flow and medium temperature. The reading is convenient, clear and intuitive.
　　The communication interface equipped has a transmission distance of not less than 900 meters. The instrument coefficient uses multi-segment nonlinear correction, and the instrument coefficient of the flowmeter is calculated by interpolation according to the instrument coefficient corresponding to different flow points. Temperature compensation function: The reference temperature is 20 degrees Celsius, and different oil products use different temperature volume coefficients for compensation.
　　Measuring accuracy: zero point second level.
　　
       2. Design of turbine flowmeter
　　Liquid turbine flowmeter consists of turbine flow sensor and flow integrator.　　
         First, the design of turbine flow sensor. The turbine flow sensor is the basic unit of the turbine flowmeter, which is mainly composed of a rectifier, a flow guide, a turbine, an induction coil, a slotted joint, a handle, etc. It is based on the principle of dynamic torque balance. When the fluid flows through the sensor, it is rectified and accelerated by the rectifier and the flow guide. Because the turbine blades are at a certain angle to the flow direction of the fluid, the impeller generates a torque under the action of the accelerating fluid. After overcoming the friction torque and the fluid resistance torque, the turbine begins to rotate. Within a certain flow range, the turbine speed is proportional to the volume flow of the fluid. The impeller rotates and cuts the magnetic lines of force, periodically changing the magnetic flux in the coil, so that the two ends of the coil induce a pulse signal proportional to the volume flow of the fluid. The signal is amplified, filtered, and shaped and then sent to the flow integrator.
　　Turbine. The turbine is made of magnetic stainless steel and is equipped with spiral blades. The number of blades is six, the blade inclination angle is thirty-five degrees, and the gap between the blade and the inner shell is 0.8 mm. Rectifier
　　. The characteristics of the turbine flowmeter are closely related to the velocity distribution in the pipeline. Therefore, ensuring that the fluid entering the flowmeter has a uniform velocity distribution is an important prerequisite for improving the accuracy of measurement. Therefore, the turbine flowmeter developed has a built-in rectifier. The rectifier consists of a bundle of thin stainless steel tubes, and the length of the rectifier bundle is 100 mm: the number of rectifier bundle tubes is 42. By adding a rectifier, the length of the straight pipe section before and after the flowmeter can be reduced, the measurement accuracy can be improved, and the volume and weight can be reduced.　　
         Second, the design of the flow totalizer. As the calculation and display part of the flowmeter, the flow totalizer adopts a high-performance micro-power integrated chip, equipped with three output modes: pulse output, 4 mA to 20 mA analog signal output and YG-865 communication interface. It is powered by a high-capacity 3.6V lithium battery and has a built-in temperature sensor. The totalizer receives the signal from the sensor, performs calculations and processing, and displays it on the display window on the spot. Its main features are as follows:
　　It adopts a high-performance micro-power integrated chip, the whole machine is multifunctional, and the power consumption is low.
　　It can switch to display the total cumulative flow, batch cumulative volume, instantaneous flow and medium temperature, which is clear and intuitive, and easy to read.
　　Equipped with pulse output, 4 mA to 20 mA analog signal output, YG-865 communication interface.
　　Built-in high-capacity 3.6V lithium battery for power supply, long life, easy replacement, battery life can reach more than two years.
　　The software uses multi-segment nonlinear correction, and the instrument error caused by processing accuracy in the production process is corrected to within the standard value through software calculation.
　　The built-in temperature sensor can compensate the change caused by temperature online.
　　The volume expansion rate of gasoline, jet fuel and diesel is built into the software package. By setting the switch, temperature compensation can be performed on different oil products.
　　Temperature compensation. The volume of the fluid changes with the change of temperature. Generally speaking, the volume expands when the temperature rises. This property of the fluid is called thermal expansion, which is expressed by the thermal expansion rate. Different fluids have different thermal expansion rates.
　　The following example calculates the volume change rate of different media when the temperature rises by one degree Celsius. For diesel, when the density is 830 kilograms per cubic meter, the temperature volume coefficient is 0.00084. When the temperature rises by one degree Celsius, the volume change rate is 0.84 per thousand. If the temperature changes by ten degrees Celsius, it will cause a measurement error of 0.84 percent.
　　When transporting crude oil, temperature has a great influence on volume. When the temperature changes by ten degrees Celsius, it will cause a measurement error of 1.23 percent. The measurement accuracy of general flow meters can reach 0.5 percent. It is inaccurate to only improve the accuracy of the instrument without considering the change of the temperature of the measured medium, and it cannot meet the requirements of measurement transfer. The purpose of temperature compensation is to convert the flow value of the measured oil into the flow value under the standard temperature condition (based on 20 degrees Celsius) that can be used for measurement transfer.
　　

         3. Calibration of turbine flowmeter
　　Determine the flowmeter instrument coefficient and accuracy analysis. The turbine flowmeter belongs to the velocity flowmeter. Within a certain flow range, for a certain fluid medium viscosity, the rotational angular velocity of the turbine is proportional to the flow rate of the fluid.
　　The flowmeter is calibrated using a piston-type liquid volume tube. The volume tube model is JHYG-150, with a flow range of 0.56 cubic meters to 560 cubic meters per hour and an accuracy of 0.03%. According to the requirements of the regulations, the calibration is carried out within the flow range of 25 cubic meters to 250 cubic meters per hour, and each calibration point is calibrated nine times. The conditions of each calibration point are recorded during the calibration. The calibration results under different flow conditions are analyzed, and the linearity, repeatability, and accuracy of the flowmeter are 0.152 per thousand, 0.031 per thousand, and 0.0158 per thousand, respectively.
　　
3. Conclusion of this article
　　In summary, the author discussed the design and application of turbine flowmeters in terms of how to accurately measure flow in oil pipelines, and discussed the design and application issues from the perspective of their working principles, structural characteristics, and the work situation of the author's unit. I hope that this simple discussion can play a positive role in promoting and helping the accurate measurement of liquid in oil pipelines.