On Line Calibration Method For Flowmeter Of Natural Gas

With the continuous promotion of energy-saving and emission-reduction policies in China,the domestic industrial energy structure is undergoing deep-seated adjustment.Natural gas,as a high-quality energy,is more and more widely used in chemical industry,electricity and life.The accurate measurement of the gas has become a task of great concern to all trades.The high pressure,large caliber and large flow flowmeters are used to measure natural gas,are difficult to make a cycle calibration in china,are difficult to use real media calibration and have the problems of high calibration cost and inconvenient assembly and disassembly.External clamped ultrasonic flowmeter,as a new type flowmeter,is more and more applied in the field of natural gas flow measurement,because of its high accuracy,good stability,less maintenance workload and convenient installation,etc.A great deal of research has been carried out in the world and the standards have been promulgated,in order to ensure the stability of the external clamped ultrasonic flowmeter and the accuracy of the measured data.with the current status of the measurement of natural gas flowmeter,an on-line calibration method using external clamped ultrasonic flowmeter as standard is put forward.In this paper,the principle and advantages of ultrasonic flowmeter and Lamb wave sensor are introduced,the factors affecting the measurement accuracy of the external clip ultrasonic flowmeter in the field application are mainly studied,combining theory with field test.And then,some pertinent solutions and countermeasures are put forward.As a key research content,the influence of noise on measurement during on-line calibration is introduced in detail.A method of noise reduction by special materials is proposed to improve the accuracy of measurement.In the application of ultrasonic flowmeter,sound speed test and distance correction method are put forward.At the same time,the accuracy of standard state flow measurement of natural gas with different pressure,temperature and composition is analyzed.According to the current detection method,the temperature & pressure compensation and automatic calibration device of natural gas flowmeter is developed.As a new on-line calibration method,The uncertainty evaluation method is introduced in detail in this paper.The relative expanded uncertainty of online calibration method is 0.5%,using ultrasonic flowmeter only.The relative expanded uncertainty of online calibration method is 0.9%,using ultrasonic flowmeter and temperature & pressure compensation and automatic calibration device.