Wu Shijie, Xu Jianhang, Zheng Chuanbo
Influence of Different Treatment Methods of Neopentane in Natural Gas Components on Measurement Accuracy
The main sources of domestic pipeline natural gas are central Asia, the Tarim Basin, the Sichuan Basin, and the Zhonghai Oil and Gas Field, etc. Due to the large geographical differences in gas sources, the components of natural gas are quite different. Therefore, accurate analysis of natural gas composition and calculation of the corresponding compression factor is an important part of the natural gas custody transfer process. There is a certain proportion of neopentane in current domestic natural gas, but there are no calculation parameters of neopentane in various corresponding calculation standards, including GB/T 17747/ISO 12213 and AGA 8 standards for compression factor calculation and GB/T 30491.1/ISO 20765-1 and AGA10 standards for sound velocity calculation. However, in theory, the treatment method of neopentane will directly affect the compression factor of natural gas, and then affect the measurement results. Therefore, how to deal with neopentane in natural gas and ensure the accuracy of natural gas measurement results is a problem worthy of study.
Generally, there are three ways to deal with neopentane in natural gas: (1) adding neopentane content to isopentane with similar properties; (2) adding neopentane content to n-pentane; (3) to normalize the neopentane content. In order to confirm the influence of the three different processing methods on the measurement accuracy of the flowmeter, the theoretical calculation and actual test verification are used for comparative analysis. The conclusions are as follows: The three treatment methods of neopentane have a certain influence on the calculation results of natural gas compression factor, but the overall influence is small. For the common components of domestic pipeline natural gas, the standard meter method and critical flow Venturi nozzle method standard devices are used to verify the tested flowmeter respectively. The maximum deviations of natural gas compression factor and indication error are 0.00001 and 0.00003 %, 0.00001 and 0.00301 %, respectively, namely, the different treatment methods of neopentane have little impact on the measurement results. Therefore, as an inherent component of natural gas, neopentane can be treated in the above three ways in trade measurement.