Compressibility factor calculation from gross calorific value and relative density for natural gas energy measurement

Nowadays, the gas chromatography (GC) method is vastly used in natural gas energy measurement but suffers from slow analysis, high capital investment, and high maintenance costs. With the advent of commercial calorimeters using new principles, the calorimeter measurement (CM) method has the ability to overcome the shortcomings of the GC method and is hoping to be an alternative method for energy measurement. To realize accurate energy metering of natural gas by the CM method, the standard GERG-88 viral equation (denote hereafter as the SGERG-88 algorithm) is needed to calculate the compressibility factors (Z-factors). However, unlike the detailed characterization equation in American gas association report No.8 (denote hereafter as the AGA8-92 DC algorithm) used in the GC method, the SGERG-88 algorithm is seldom used since it was published in 1991, thus its applicability and accuracy is not so clear in the natural gas industry. In addition, the original SGERG-88 algorithm coupled hydrogen and carbon monoxide together with a fixed relation, which is not applicable to natural gas blended with hydrogen (NatualHy) that will be widely used anymore. This paper firstly improves the original SGERG-88 algorithm to make it applicable to NatualHy. Then, taking the Z-factor calculated by the AGA8-92 DC as references, the applicability of the improved SGERG-88 algorithm to different gases is assessed for natural gas and NatualHy measurement. Results and related conclusions or further study suggestions are drawn to prompt the accurate energy measurement of natural gas by the CM method.