天然气标准物质中甲烷的不同定值方法对组成分析的影响

A study of influence on natural gas composition analysis by different means to determine the concentration of methane in reference gas

关键词:  气体标准物质  甲烷  差减法  不确定度

Key words:  gas reference material  methane  subtraction method  uncertainty

摘要:

通过对国内天然气标准物质现有的两种甲烷定值方式的探讨,结合实例对两种方法进行了说明。同时将两种不同方法与国际惯例相比较,充分说明了两种方法在法规和技术方面的优缺点。以甲烷作为平衡气,在使用时根据其他组分含量差减计算甲烷含量的方法,甲烷含量和不确定度与其他组分含量相关,甲烷含量越高,甲烷外其他组分不确定度越低,甲烷的相对不确定度更低,甲烷摩尔分数为80%左右时,甲烷相对不确定度为0.5%左右。但甲烷量值由间接方法获取,从法规和技术上不够完善。而直接对甲烷进行定值并给出不确定度的方法,在法规和技术上更完善,使用权威方法称量法进行定值,可实现向SI单位的直接溯源。 

Abstract:

There are two ways to determine the concentration of methane in natural gas reference gas, which is discussed and exhibited by examples. These two ways are compared with international convention to explain the advantages and disadvantages on regulation and technology. While methane is treated as balance gas, its concentration is determined by the difference between 100% and the summation of all the other components. With higher concentration of methane, the summation of other components as well as its uncertainty is lower, and the relative uncertainty of methane is more lower. With 80% of methane, the relative uncertainty of methane is about 0.5%. Because of the indirect calculation of methane concentration, there are some flaws regulation and technology. In the meantime, the direct way of given methane concentration and its uncertainty is a authoritative way and avoids the flaws, which gives the methane concentration direct traceability to SI unit.