Flow meter structure requirement and improve the accuracy of orifice flowmeter metering several ways

Orifice flowmeter is a kind of process flow testing instrument a throttling device, through the three elements such as valve group, the differential pressure transmitter, constitute a complete measurement system, because with a long history of application of orifice flowmeter in use established the perfect design, selection of calculation, specifications, database tables, and formed a set of production and installation of standard specification. Engineering design as a kind of standard orifice throttling element has been widely used, in thermal power plants, heating gas transmission, municipal sewage measurement has many fields, such use, traffic detection is engineer design scheme of * *. By orifice flow timing, the orifice plate processing technical requirements are very strict, must conform to the state standards or the stipulations in the ministerial standard, otherwise, will bring error to natural gas flow measurement result. ( 1) Eccentric orifice plate: experiments show that the measurement error caused by the eccentric orifice plate is in commonly 2%, aperture ratio & beta; The higher the value, the greater the eccentricity influence, so, should avoid to use & beta; High value of the orifice plate. ( 2) Orifice plate bending: due to improper installation or maintenance, bending or deformation in the orifice plate, lead to the flow measurement error is bigger. On the orifice flange with test results, big errors caused by orifice plate bending is about 3. 5%. ( 3) Protruding out of the throttle device: throttling device inserted into the gasket, weld and so on also can make the flow measurement produce certain error, error of the size and the location of the protrusions, orifice plate and the distance of the protrusions, and the level of outstanding. The experiment proved that when & beta; = 0. 7, highlight the objects located in the upper orifice 2 times the pipe diameter, produce big error; If the protrusion is located at upstream orifice, the error is 16% ~ 50%, if the protrusion is located in the downstream of the orifice plate, the smaller the impact on the accuracy of measuring. Improve the accuracy of orifice flowmeter metering way ( 1) Pipeline requirements: national standards within the length of the measuring tube, straight tube, roundness and surface roughness has a strict technical requirements. When measuring small tube length can not meet the requirement of the standard, will bring the flow measurement result deviation, its size and aperture ratio & beta; And Reynolds number, so must be installed on the straight pipe in front of the orifice plate rectifier, to ensure the accuracy of measurement. ( 2) Installation requirements: orifice entrance end face must be perpendicular to the pipe axis, the deviation is no more than 1 degree. Installation should pay attention to the direction of the load pipeline orifice, it is strictly prohibited to the outfit, must conform to the standard requirement for not alignment tolerance. Between the flanges, orifice plate and take pressure device sealing gasket thickness shall not be greater than zero. 03D 。 The installation of the gasket may not penetrate in the straight pipe or inner cavity pressure device, shall not take blocking caused by pressure and change the position of pressure. New station must be in the pipeline purging and run a few days later, then install to the throttling orifice plate device, in order to avoid the orifice plate is in the gas liquid and solid impurity damage or pollution. To correctly choose and use differential pressure gauge, differential pressure measurement bout, flow is small, the differential gauge work under 30%, can greatly reduce the flow measurement accuracy, when measuring flow decrease, to timely replace the differential gauge range spring or orifice plate specification, otherwise, the differential error will be multiplied. When choosing instrument differential pressure value, both must consider aperture ratio & beta; After orifice pressure loss, and to make the pressure can meet the production needs. The flange to take pressure & beta; Value should be zero. 15 ~ 0. Between 7 so that can ensure the accuracy of measurement, and can reduce the pressure loss. ( 1) The cause of the pulsating flow. Sudden changes in the gas velocity and pressure in the pipeline, cause the pulsating flow, it can lead to differential pressure fluctuation, make record curve into a broadband. If (1) gas Wells for water to produce gas, these Wells measuring differential pressure change; Or (2) the transmission pipeline gas pipeline effusion caused by measuring the differential pressure fluctuation; (3) the use of natural gas compressor in the measuring differential pressure fluctuation; (4) between the gas well caused by the pressure differential pressure fluctuation; (5) the user gas uneven, gas, there was a sharp change in an instant gas supply pressure regulating valve suddenly up or down will lead to differential pressure fluctuation. ( 2) Inhibition of pulsating flow method. (1) to eliminate or from pulse source: adopt water control gas extraction; Adopt high efficiency separator, strengthen the gas water separation; To accumulate in the metering section, guide tube, flow meter high and low voltage ripple tube chamber and condensed liquid in the pipe should be timely purging or pigging. (2) control measurement section downstream valve: the practice proves that the control mean valve differential pressure fluctuation caused by all kinds of pulse source has inhibitory effect. (3) mounted to the buffer tank: can add buffer tank before measurement section, can store and release the energy of the gas, effectively reduces the differential pressure fluctuation caused by different kinds of pulse source, also can be set up special pulsation attenuator. (4) improve the differential pressure and aperture ratio & beta; : for the same pipeline measurement, to improve the differential pressure, will reduce the orifice diameter and the aperture ratio & beta; Reduce, in order to make the differential pressure and aperture all improve, must be the decrease of the diameter of the measurement accordingly. (5) : the pressure regulating valve is installed at the entrance of survey points before adding pressure regulating valve, stable output pressure, which can effectively reduce the pulsation phenomena influence on measurement accuracy. Which affect measurement accuracy of orifice flowmeter is driven by the throttle device geometry and flow state is deviating from the design standards. In actual use, therefore, should be in strict accordance with the design requirements of the throttle device regularly, orifice plate, double corrugated differential gauge for inspection and adjustment, so as to reduce the measurement error, ensure the accuracy of measuring.
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