Chromatographic data acquisition system for determination of natural-gas composition and properties

Abstract

A data acquisition system has been developed for the determination of natural-gas composition and properties, ensuring low cost of the system and a measurement error not exceeding 2 %. The architecture of the system, measurement methods, and investigation results are described.Data acquisition systems for determining physicochemical composition and properties of substances are used widely in various branches of the industry, including the oil and gas branch [1]. Development of these systems involves conforming the characteristics of the systems to the set requirements applying general principles of synthesis of the systems [1, 2]: determining methodological support, devising structural and functional schemes, evaluating technical and economic characteristics, and selecting construction (synthesis) version.In [1], an examination was made of the use of the principle of determination of the methodological support to the systems, namely, analysis and development of procedures for measurement (PFM) of the physicochemical composition of natural gas (NG), but not enough light was shed on the use of the other principles of synthesis of the systems.Let us analyze the use of general principles of synthesis in developing an automated system for measuring physicochemical composition and properties of NG [1], especially use of the principle of devising structural schemes and its relationship with the principles of determination of the methodological support and devising functional schemes as well as the interrelation of all principles of synthesis of the systems. Basic Requirements of the SystemThe developed system must perform the following functions: measurement of concentrations of NG components [1] and determination of density ρ and specific heat of combustion q of the NG:where ρ j and q j are the density and specific heat of combustion of the component j of the NG; X j is the volume proportion of the component j of the NG; and J is the number of components to be determined (J = 17). The system designed for laboratory research must consist of domestically made technical devices. In this case, the criterion of synthesis was the lowest cost of the system and the constraints were guarantying relative errors of not more than 2 % in the determination of density and specific heat of combustion of the NG [1]. Analysis of PFM Based on Principle of Determination of Methodological Support to the SystemsSynthesis of the developed system includes analysis of the PFM of the physicochemical composition of the NG. Standard [3] is one of the key documents regulating the order of determination of the NG composition. In experimental studies of PFM of concentrations of the C 1 −C 5 and C 6 −C 8 group hydrocarbons, separation of NG components by gas chromatography was found to be unsatisfactory [1].