THE INFLUENCE ON GAS CHROMATOGRAPHY ANALYSIS CAUSED BY THE JOULE-THOMSON COOLING EFFECT DURING THE NATURAL GAS SAMPLING

摘要

For obtaining representative samples of the natural gas to subsequent analysis by gas chromatography it's necessary an overview of principles that govern proper gas sampling and analysis, The incorrect sampling producers may cause poor natural gas samples and this sampling errors are due to thermodynamic changes that produce condensation when the gas reaches hydrocarbon dew point. If the natural gas has a dew point that is going to be reached during a pressure cut then pressure cut has to be isothermal. The Joule-Thomson cooling will cause the natural gas temperature to drop below of it's dew point during adiabatic throttling. This fact has an influence on the gas chromatography analysis, which it will show differences on the heat value of the sample, due the heavier compounds of the natural gas still or not into the sample cylinder. Many properties of natural gas will be change due this kind of distorted sampling. The Wobbe index, the density and the heat value are the most important parameters which will be different than the true, so the heating of pipings, tubings, probes, pressure regulators and devices are necessary to keep the original conditions of the natural gas. By this way, a number for that heating temperature will be fixed on a great value than the natural gas dew point to assurance the correct conditions and minimize the thermodynamic influences. To verify methods to accurately sample gas, the joule-Thomson effect on the repeatability and reproducibility of gas sampling and it's analysis are evaluating.