Research On The Standard Facility Of Natural Gas Energy Measurement Based On The Verification Method Of Sound Velocity

With the rapid growth of domestic natural gas production and the acceleration of global integration,the current natural gas volume measurement method cannot meet the requirements of development,and the implementation of natural gas energy measurement cannot be delayed.At present,there is difference for the equipment and evaluation method on the natural gas energy measurement at different natural gas stations.So,it is imperative to establish and evaluate the uncertainty of natural gas energy measurement systems,which provides a useful reference to improve the implementation of natural gas energy measurement.The key to natural gas energy measurement is the accurate measurement of thermal properties such as calorific value and compressibility factor.Currently,the common method is to calculate the calorific value and compressibility factor by measuring gas components.Limited by the measurement method and measurement period of natural gas components,the measurement frequency of natural gas energy is generally in minutes and hours,and the measurement accuracy needs to be improved.To improve the measurement accuracy of natural gas energy measurement and solve the problem that the energy change during the measurement cycle cannot be checked due to the low measurement frequency of component data,a set of standard devices is established and the uncertainty is systematically evaluated.The main research contents of this paper are as follows:(1)Research on the verification method of sound velocity for natural gas energy measurement.Based on the thermodynamic relationship between sound velocity and gas molar mass,the relationship between the change of sound velocity and the change in molar mass is established.Within a certain range,the relationship between the change in molar mass and the change in calorific value and compressibility is developed.The model of natural gas energy measurement based on the verification method of sound velocity is presented,with the formula of natural gas energy calculation.(2)Verification on the accuracy of ultrasonic flowmeter sound velocity measurement.The experimental device is designed and built with the use of eight-channel ultrasonic flowmeter to measure the sound velocity for nitrogen,methane and two sets of natural gas with different components.The accuracy of the sound velocity and average sound velocity of each channel of the ultrasonic flowmeter are verified with the comparison of the deviation between the theoretical sound velocity and the measured sound velocity.Within the pressure range of 10MPa,the sound velocity measurement deviation between the channels of the ultrasonic flowmeter is better than 0.035%,and the uncertainty of the sound velocity measurement of the ultrasonic flowmeter is 0.18%(k=2).(3)Establishment a natural gas energy metering standard device.Based on the model of sound velocity verification method of natural gas energy and data acquisition control system,the natural gas energy metering standard device is built with the ultrasonic flowmeter as the main component,which can achieve the natural gas energy measurement within the pressure range of 10MPa and flow range of 2000m~3/h.The sound velocity information measured by the ultrasonic flowmeter can be used to check the change of natural gas energy flow in real time and accurately,and the frequency of energy measurement can be increased from the original minute level to the second level.(4)Evaluation on the uncertainty of the energy measurement standard device.With three sets of domestic high-pressure gas flow standard devices at different pressure ranges,the flow measurement accuracy of ultrasonic flowmeters is verified.The uncertainty of each component of natural gas energy based on the measurement results of the natural energy of the metering station by the energy metering standard device is evaluated.The relative expanded uncertainty of the energy measurement standard device is 0.33%(k=2).