天然气在线分析系统性能评价标准现场应用

Field application of performance evaluation standard for natural gas online analytical system

关键词:  气相色谱仪  性能评价  气体标准物质

Key words:  gas chromatograph  performance evaluation  gas reference material

摘要:

天然气长输管道的A级以上贸易计量站一般均安装在线气相色谱仪测量天然气组成,用于计算发热量、压缩因子等物性参数,以作为贸易结算的依据,色谱仪检测结果的准确性对天然气贸易有重要意义。介绍了天然气在线分析系统性能评价标准在计量站现场的应用情况,说明了气体标准物质配备原则,给出了气相色谱仪有效性、重复性、分离度和一致性的判断方法和具体实例。从标准现场应用的情况来看,部分在线气相色谱仪存在少量组分不符合标准要求一致性的情况,对物性参数计算和体积计算的影响约为0.05%,在当前国内天然气贸易以体积计算为主的情况下,虽然对贸易计量的影响较小,但在未来转向能量计量结算的情况下,需提高组成分析设备的检测准确度。建议至少每2年对气相色谱仪开展一次性能评价,以确保仪器运行正常。

Abstract:

Natural gas on-line analytical systems are installed on most A-grade (classified according to GB/T 18603-2014) gas station of long distance transportation pipeline. They’re used to measure composition of natural gas, which is the basic data to calculate physical properties, such as calorific value and compression factor. The physical properties are very important for gas trade measurement. Hence, the precision of analytical systems measurement result is important too. Application of natural gas online analysis system performance evaluation standard for natural gas metering station is introduced in this paper. Determination method of composition for reference material is illustrated. Judgment method and example for the qualification of gas chromatograph’s effectiveness, repeatability, resolution and consistency are given. Viewing from the standard application result, some analytical system’s differences between test result and reference gas have exceed the limit of the standard requirement. The difference may introduce 0.05% error to physical property and gas volume. This amount of error can be ignored, since natural gas trade measurement is based on volume now. The precision of analytical system should be improved when energy measurement is adopted in the future. In order to keep the instrument running properly, performance evaluation should be carried out at least once every two years.