Determination of Hydrocarbon Dew Point Hdp of Natural Gas – Experimental and Theoretical

Abstract

Abstract Hydrocarbon dew point (HDP) temperature is defined as the temperature at which the first hydrocarbon liquid begins to condense in a natural gas cooled at constant pressure, which is an important qualitative parameter for pipeline operators. Hydrocarbon liquid drops-out along the gas pipeline will decrease the effective cross-sectional area of the pipes causing increased pressure drop, reduced line capacity as well as system shutdowns. It is therefore imperative that the gas pipelines be operated above the hydrocarbon dew point (HDP) temperature to ensure a trouble free line; this of course requires the knowledge of the HDP for the pipeline. In this work, onsite measurement of the HDP of 5 different natural gases from different flow stations and gas processing plants in the Niger-Delta region was done using an automatic optical condensation dew point meter. Subsequently, each of the gases was collected in stainless steel Proserv bottles and taken to the laboratory for compositional analysis using gas chromatographic technique with reference to GPA 2286. In addition, the Peng Robinson (PR) and Soave Redlich Kwong (SRK) Equations of state (EOS) were used to predict the hydrocarbon dew point temperature of the gases at the flow line pressures. The Average Absolute Error (AAE) for EOS PR was 9.33% while that for EOS SRK was 14.68%. Obviously, it showed that PR EOS gave better predictions than SRK EOS. The result of this work also showed that even a 50% variation in molar contributions of the non-hydrocarbon components had negligible effects on the predicted hydrocarbon dew point temperatures for all the gas samples tested.