Measures to improve the accuracy of standard orifice flowmeter

njjnyb

Measures to improve the accuracy of standard orifice flowmeter [Copy link]

Measures to improve the accuracy of standard orifice flowmeters In order to improve the accuracy of standard orifice flowmeters, the following measures can be taken:

1. Manufacturing and installation of standard orifice throttling device
. The design, processing, manufacturing, inspection, installation and use of standard orifice throttling device must be strictly in accordance with the various technical indicators specified in the SY/T6143-2004 standard when using standard orifice flowmeter to measure natural gas flow. In particular, the processing and inspection of the sharpness of the edge of the orifice inlet and the roughness of the inner wall of the measuring tube; the guarantee of the length of the straight pipe section before and after the orifice, the roundness of the straight pipe section, the step and the coaxiality of the orifice and the measuring tube. In addition, the development of a unified design software for standard orifice flowmeters can improve the technical level of throttling device design and instrument selection.

2. Use of replaceable orifice plate device and fixed value throttling device The
replaceable orifice plate throttling device is a new type of throttling device. The throttling element is installed in a fixed seat body (the seat body is connected to the pipeline through a flange). Without dismantling the pipeline or stopping the fluid transportation, the orifice plate can be easily lifted for inspection, cleaning or replacement, thereby ensuring the measurement accuracy. The hydraulic lifting device is adopted, and the orifice plate is easy to lift, which is particularly suitable for large-diameter orifice plates. This throttling device is also equipped with a cleaning chamber and a cleaning mechanism, which provides an effective means to solve the problem of accurate measurement of dirty media, especially single-well natural gas. The
fixed value throttling device changes the existing method of processing the aperture of the throttling device according to the calculation results. A limited number of throttling parts are provided for each diameter measurement pipeline. The aperture series is selected according to the priority number system, and each diameter is equipped with 3 to 5 orifice plates with different aperture ratio β values. At present, the design of throttling devices is like tailoring clothes, while the fixed value throttling device becomes ready-made clothing selection. The use of fixed value throttling devices is conducive to mass production of products, reduces production costs, is convenient for selection and use, and is convenient for supervision of production. The combination of the replaceable orifice throttling device and the fixed value orifice plate will change the traditional production mode, realize the serialization, generalization and standardization of throttling device products, and help improve the measurement accuracy of the standard orifice plate device.
The disadvantage of the standard orifice plate is that the inlet sharpness is easily passivated under the scouring of the fluid. It is estimated that severe passivation may cause the outflow coefficient to shift by 1% to 2%. After passivation, its outflow coefficient is relatively stable, which brings great difficulties to the correction of the inlet sharpness of the orifice plate in the flow calculation. The outflow coefficient of the standard nozzle is stable. In addition, the pressure loss of the nozzle is only 30% of that of the orifice plate at the same flow rate and the same β value. The main reason affecting the promotion and use of standard nozzles is the high manufacturing cost of the nozzle. The uncertainty of the outflow coefficient of the nozzle in the standard is large (about 2%). The fixed value throttling parts and special processing equipment are used to achieve mass production and reduce production costs, while individual calibration can obtain a high outflow coefficient. The advantages of using nozzles instead of orifices in natural gas flow measurement are obvious.

3. Apply a reasonable flow integration scheme.
According to the natural gas metering working conditions and the user's requirements for metering accuracy, an integration scheme that automatically partially compensates or fully compensates for changes in pressure, temperature and natural gas components should be adopted. The selection of measuring instruments and accuracy of the metering system should comply with GB/T18603-2001 "Technical Requirements for Natural Gas Metering Systems". The online detection system composed of intelligent differential pressure transmitters, pressure transmitters, temperature transmitters and flow computers can compensate for temperature and pressure changes, improve measurement accuracy, and reduce additional flow measurement errors caused by flow pulsation (or fluctuations). The range ratio of the orifice flowmeter is generally 1:3, and the actual measurement of natural gas flow changes sometimes exceeds this range. In this case, its measurement accuracy is significantly reduced. If a fixed-value throttling device is used, a wide-range intelligent differential pressure transmitter can be used in conjunction with a flow computer to easily expand the flow range or migrate the range, thereby realizing the intelligence of the traditional standard orifice flowmeter.

4. Establish and improve various rules and regulations
Strengthening measurement management, establishing and improving various rules and regulations, and strictly implementing measurement regulations are the key to ensuring the accuracy of natural gas flow measurement by orifice flowmeter. According to GB/T18603-2001 "Technical Requirements for Natural Gas Metering System" standard, the unified orifice flowmeter measurement system is configured with secondary measuring instruments according to the measurement system of different scales. From the beginning of design, construction, acceptance, commissioning, operation and maintenance, they are all implemented according to unified technical requirements, so that natural gas flow measurement, flow integration method, flow calculation program software are all under strict technical requirements control, and comprehensive quality management is carried out to ensure the accuracy of flow measurement. In strict accordance with SY/T6143-2004 standard, the "Standard Procedure for Inspection of Flow Calculation Values" is compiled to strictly inspect the flow values calculated by various flow integration methods. The flow measurement uncertainty of the standard orifice flowmeter measurement system is evaluated, and the total flow measurement uncertainty of the measurement system should be lower than the maximum allowable error. Improve the measurement management system and formulate an orifice flowmeter operation, use and management procedure that is in line with the SY/T6143-2004 standard and meets actual needs. Its contents include establishing and improving measurement management responsibility systems at all levels, periodic inspection and maintenance systems for standard measuring instruments, inspection, adjustment and maintenance systems for working instruments, and data and archive management systems for measuring equipment and measuring instruments. While conscientiously implementing the SY/T6143-2004 standard and its related measurement standards, various measurement management procedures and management systems should be matched with it, and the training of measurement technicians should be strengthened to improve the technical management level of measurement personnel.


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