对国际标准ISO 10723:2012的认识与讨论

2012年修订发布的国际标准ISO 10723:2012《天然气分析系统的性能评价》与1995版有较大差异,了解和掌握该标准修订前后的技术差异和主要技术内容对于保障我国天然气能量测定的顺利实施具有重要的意义。为加快天然气大规模交接计量方式由传统的体积计量向能量计量过渡,我国已于2008年底发布了国家标准GB/T 22723—2008《天然气能量的测定》,但迄今未能对商品天然气管网系统中间接法测定天然气发热量的测量不确定度进行整体评估。为此,在了解ISO 10723:2012技术要点的基础上,对比分析ISO 10723:2012与ISO 10723:1995在推荐方法、仪器操作性能规定等方面的改进,探讨了平均校正系数的表达与计算,以及Monte—Carlo法(MCM)模拟的应用。结果表明:(1)与ISO 10723:1995相比,ISO 10723:2012在标准应用范围、MCM评估步骤、不确定度评估、误差设置等4个方面作出了重大改进;(2)根据ISO/IEC指南98-3阐明的原理提出平均校正系数计算式;(3)进入英国管网天然气的MCM模拟的平均误差介于-0.10~0.08 MJ/m~3,符合该国天然气准入协议规定。结论认为,应重视ISO 10723:2012附录B中以平均系数法评价气相色谱仪,并提出建议:(1)ISO 10723:2012对实施能量计量的A级计量系统MPE值规定为±1.0%;(2)在参比条件为15℃(燃烧)和15℃、101 325 Pa(计量)时,天然气组成中虚拟组分C6+按正己烷性质计算其发热量的工况条件下,最大允许误差为0.10MJ·m~(-3),最大允许偏差为0.025 MJ·m~(-3)。

Understanding and discussion on the international standard ISO 10723:2012

There is a big difference between the international standard ISO 10723:1995 of Performance Evaluation on Natural Gas Analysis System and the ISO 10723:2012 which was modified and issued in 2012. In order to ensure the smooth implementation of natural gas energy measurement in China, it is of great significant to understand and grasp the technological differences between ISO 10723:1995 and ISO 10723:2012 and the main technological content. In order to accelerate the transition of large-scale custody transfer metering mode of natural gas from the traditional volume metering to the energy metering, China issued national standard GB/T 22723 of Energy Measurement of Natural Gas at the end of 2008. So far, however, the metering uncertainty of Calorific value of natural gas in commercial natural gas pipeline networks by the indirect method has not been evaluated overall. In this paper, the key technological points of ISO 10723:2012 were understood. Then, ISO 10723:2012 and ISO 10723:1995 were compared from the aspects of recommendation method and instrument operational performance requirement. Finally, the expression and calculation of mean correction factor and the application of Monte–Carlo method (MCM) simulation were discussed. And the following research results were obtained. First, ISO 10723:2012 is much more advantageous than ISO 10723:1995 in terms of application scope, MCM assessment procedure, uncertainty assessment and error setting. Second, the computational formula of mean correction factor is set up according to the principles illustrated in ISO/IEC Guide 98-3. Third, the average error of MCM simulation on the natural gas flowing into the UK pipeline network is in the range of －0.010-0.08 MJ/m3, which is in accordance with UK's natural gas access agreement. It is concluded that attention shall be paid to the application of mean correction method to gas chromatograph evaluation described in Appendix B of ISO 10723:2012. It is recommended to set the Maximum Permissible Errors (MPE) of Level-A metering system for energy metering in ISO 10723:2012 as ±1.0%. Furthermore, when the reference condition is 15℃ (burning) and 15 ℃ and 101325 Pa (metering), the MPE and the Maximum Permissible Bias (MPB) are 0.1 MJ·m－3 and 0.025 MJ·m－3, respectively, in the working condition that the Calorific value of virtual composition C6+ of natural gas is calculated based on the property of n-hexane.