高酸性天然气流量测量的修正方法

由于高酸性天然气中含有较高浓度的H2S和CO2气体,对天然气的临界温度和临界压力有较大的影响,导致天然气的压缩因子增大。因此,当采用常规天然气流量测量仪表用于高酸性天然气的流量测量时,需要针对其测量结果进行必要的修正。通过查阅大量的文献资料,对各种天然气压缩因子计算方法进行分析、比较,提出采用Wichest-Aziz校正方法与Bumett关系式相结合的方法计算高酸性天然气的压缩因子,在其适用条件范围内(温度为-12.2~93.3℃,压力为0~13.789 6MPa,酸性组分H2S+CO2的摩尔分数不大于80%),计算得到的天然气压缩因子准确度较高,适于工程应用,也便于实现电算化,利用该方法计算的酸性天然气压缩因子与直接采用Bumett关系式计算的天然气压缩因子(替代常规天然气流量测量仪表内部计算的天然气压缩因子)相比,即可有效地求得天然气流量测量仪表的修正系数,从而提高了酸性天然气流量测量的准确度。

A modification method of high-sour gas flow measurement

Flow measurement of natural gas is one of the key control parameters in natural gas industry. The calculation model of a regular natural gas flow-measuring instrument is based on the AGA8-92 DC algorithm, by which the compressibility factor is calculated and the computing method of the natural gas's flow rate can be deduced. But this method mainly focuses on a certain kind of pipeline gas which contains no H₂S. However, with an increasing number of high-acid natural gas fields discovered in China, we found that higher contents of H₂S and CO₂ have a great effect on the critical pressure and critical temperature of the produced natural gas, which will result in the enlargement of the compressibility factor of the gas. Therefore, while using a regular flow measurement instrument, we need to correct the measurement results, which otherwise would be lower by more than 3%. Through reading a great amount of literatures, we analyzed and compared all kinds of methods for calculating the natural gas compressibility factor. As a result, we recommended a methodology combining the Wichest-Aziz correction method and the Bumett Relation. And within the application conditions (temperature: －12.2 ~ 93.3 ℃; pressure: 0 ~ 13.789 6 MPa; the mole fraction of H₂S＋CO₂:≤80%), this combination method will be practical and convenient for the electric data processing with a high accuracy of the calculated compressibility factor of natural gas. Compared to the other methods, this methodology will help engineers to effectively obtain the correction factor of regular flow instruments, thereby to improve the accuracy of the acid gas flow measurement.