基于气体组成的天然气压缩因子计算方法

Calculation methods of natural gas compressibility factor based on the gas composition

关键词:  压缩因子  状态方程计算法和经验公式法  Visual Basic 6.0  酸性贫气  计算误差 

Key words:  compressibility factor  equations of state law method and the empirical formulas method  Visual Basic 6.0  acidic lean gas  calculation error

摘要:

天然气压缩因子Z在天然气工程计算中是最重要的物性参数之一,其获取方法主要分为查Standing-Katz图法、实验法、状态方程计算法和经验公式法。前两种方法在使用上有很大的限制性,目前状态方程计算法和经验公式法的应用优势明显。对基于气体组成来求解压缩因子的AGA8-92DC、Piper-DAK、Piper-Mahmoud、Elsharkawy-DAK和Elsharkawy-Mahmoud方程进行了计算准确度评价。将这5个待评价的计算关系式写入Visual Basic 6.0,并使用113个酸性贫气压缩因子实测值对5个方程的计算值进行了对比分析。分析结果认为,对于低中压含碳贫气,AGA8-92DC方程的计算误差最小；对于低中压含硫含碳贫气,Piper-Mahmoud的计算误差较其他方程最小。此外还发现,当天然气温度升高时,5个方程的计算值误差较原来均有所减小。 

Abstract:

Natural gas compressibility factor Z is one of the most important physical parameters in the natural gas engineering calculations, and the determining methods mainly include Standing-Katz chart method, laboratory experiments method, equations of state law method and the empirical formulas method. Due to the usage limitations of the former two methods,the application advantages of equations of state law method and the empirical formulas method become increasingly evident. In this paper, the calculation accuracy of equations that calculate compressibility factor based gas composition was evaluated. The equations include AGA8-92DC, Piper-DAK, Piper-Mahmoud, Elsharkawy-DAK and Elsharkawy-Mahmoud. These five calculation formulas to be valuated were written into Visual Basic 6.0 and 113 measured values of acidic lean gas compressibility factor were used to compare with the calculated values of these five formulas. The comparison indicates that firstly for the lean gas with carbon dioxide at low pressure or medium pressure, the calculation error of AGA8-92DC is less than others；secondly, for the lean gas with hydrogen sulfide and carbon dioxide at low or medium pressure, the calculation error of Piper-Mahmoud is minimal compared to the other correlations. In addition, this study presents that when the temperature of natural gas increases, the errors of calculated values by these five formulas will all decrease compared with the original calculation errors.