Gas loss during transportation is an important technical and economic indicator in assessing the level of production costs and economic benefits of natural gas enterprises. As the gas pipeline transmission trade continues to expand in China, the problems of gas losses have become increasingly prominent. Take one joint-stock gas pipeline of CNPC for example; the total output is about 24.2 billion cubic meters in 2012, while the amount of gas losses has reached about 60 million cubic meters, which brings significant economic losses to the enterprise, so it is necessary to carry out study on gas losses during transportation in gas transmission trunk line. For a trunk line system, gas losses generally refer to the flow quantities reduction during the process of gas purchase, transportation and sale, considering the variation of gas pipeline inventory, the amount of self-consumed gas and venting amount. Gas loss during transportation is mainly caused by measurement error of metering devices, but it is also related to the calculation deviation of gas pipeline inventory and venting amount.

In this paper, according to the flowmeter configuration in each station, the model of trunk line metering system is established, and the calculation method of flow measurement uncertainty of overall trunk line system is introduced. The early warning indicators of gas loss in different calculation cycle are obtained, by which the gas loss problems can be foud timely. A real case is introduced to evaluate its application of early warning indicators of gas loss. In the study of ultrasonic flowmeter, the influence of noise, gas component and dirty sediment on measurement error is analyzed. A transient simulation model of the trunk line has been built, based on the gas pipeline network simulation software TGNET, to analyze the influence of non-steady state on the calculation of gas pipeline inventory. Finally, some suggestions are made to lower gas losses during transportation from aspects of technical operations and management.

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