摘要：
采用在线气相色谱仪实时监测管道中天然气组分的变化是目前大型输气场站保证天然气计量准确性的关键工艺,而在线气相色谱仪抽取样品的代表性则是保证分析检测结果准确可靠的关键因素,对于多气源汇合的输气场站,不同气源天然气的混合程度直接关系到在线气相色谱仪所取样品的代表性.为此,以中石化川气东送工程的普光首站为例,按照该站的工况条件,采用FLUENT软件对多气源天然气的混合规律进行了仿真模拟,探讨了多气源天然气混合距离与温度、压力、流速等因素的关系,以及多气源天然气混合均匀的最近位置.试验结果表明:①含两种不同摩尔分数值组分的天然气在汇管不同位置处混合的均匀程度不同——距汇管50 m处天然气各组分混合不均匀,具明显分层现象,距汇管150 m处天然气各组分的混合开始呈现均匀状态,但仍存在分层现象,距汇管280 m处天然气各组分混合完全呈现出均匀状态,其CH4摩尔分数为98.30％,CO2摩尔分数为0.95％;②在普光首站距混合点280 m以远处的位置安装在线气相色谱仪取样较为合适;③对于气源体积流量或气源的体积流量差别较大、压力较高或温度较低的工况条件,在线气相色谱仪的取样点可适当靠近混合点.%To perform real-time monitoring on the compositional change of natural gas in the pipelines by using an on-line gas chromatograph is the key process to ensure the accuracy of natural gas metering in large gas stations.And the representativeness of samples taken by the on-line gas chromatograph is crucial to guarantee the accuracy and reliability of the test analysis results.At the gas transportation stations with multiple gas sources,the representativeness of samples taken by the on-line gas chromatograph is directly dependent on the mixing degree of natural gas from different sources.In this paper,the Puguang Initial Station of the pipelines in the Sinopec's Sichuan-to-East China Gas Project was taken as an example.Based on its behaviors,the FLUENT software was used to simulate the mixing rules of multiple-source natural gas.Then,the relationships between the mixing distance of multiple-source natural gas and the temperature,pressure and flow rate were discussed,and the closest uniform mixing location of multiple-source natural gas was confirmed.It is indicated that natural gas composed of two compositions with different mole fractions is different in term of its mixing uniformity degree at different distances from the manifold;the compositions of the natural gas aren't mixed uniformly at the location 50 m away from the manifold,and the phenomenon of stratification is obvious;at the location 150 m away from the manifold,the uniform mixing of natural gas compositions emerges initially,but the phenomenon of stratification still exists;located about 280 m away from the manifold,the compositions of natural gas are completely in a homogeneous state with CH4 mole fraction of 98.30％ and CO2 mole fraction of 0.95％.Therefore,it is suggested that the on-line gas chromatograph should be placed at least 280 m away from the mixing point of the Puguang Station.In the working conditions of higher volume flow rates of the mixed gas or greater variations of volume flow rates between different gases,or gas under higher pressures or lower temperatures,the sampling point of the on-line gas chromatograph shall all be close to the mixing point properly.
