On the retrograde condensation behavior of lean natural gas

Abstract

The occurrence of liquid dropout in natural gas pipelines may cause operational problems during storage, transport, and processing. Therefore, the availability of a model that accurately predicts the amount of liquid formed is of great importance for the natural gas industry. The objective of this study is to develop a thermodynamic model for the accurate prediction of the amount of liquid formed in natural gas pipelines at transportation conditions. As input, the model requires an accurate gas analysis. A modified Peng-Robinson equation of state was selected for the phase equilibrium calculations. Interaction parameters were optimized from experimental data at conditions of practical interest, i.e., at pressures 10 < p < 70 bar and at temperatures 250 < T< 290 K. For a number of "keysystems,'" the interaction parameters were calculated from new accurate solubility data of heavy hydrocarbons in some of the main constituents of natural gas like methane and nitrogen. Also, an extensive experimental program was carried out to study the influence of minute amounts of nitrogen, ethane and carbon dioxide in methane on the solubility behavior of decane in these gas mixtures. From a sensitivity analysis, it could be concluded that the liquid dropout is influenced mainly by the concentration and characterization of C7-C~3 fractions. In this work, two characterization procedures to represent these fractions are compared. For two types of lean natural gas, the model predictions are compared with field measurement data, recently supplied by the Dutch natural gas industry.

Extension of Cubic-Plus-Chain Equation of State: Incorporating Short-Range Soft Repulsion for Nonassociating Mixtures

“…Hydrocarbons are present in short-chain and long-chain molecules, and the ability to model their thermodynamic properties captures the interest of both academic and industrial fields. Modeling phase behavior accurately assists in avoiding potential flow assurance problems, including wax precipitation in pipelines caused by retrograde condensation, and enhancing process efficiency. For instance, the major products of the Fischer–Tropsch slurry reactor are mixtures of n -paraffins ranging from C 1 to more than C 200 , as well as side products of n -olefins and n -alcohols due to competing reactions and the types of catalysts used .…”

Measurement and Prediction of Hydrocarbon Dew Points of Synthetic Natural Gas Mixtures

“…As for the influence of each component in the samples on the cricondenbar, a similar variation tendency was observed. Voulgaris et al 41 investigated the relationship between the natural gas composition and the risk of condensation, and they believe that an increase in the CH 4 concentration in a natural gas can decrease the risk of condensation for a given pressure value because it increases the heavy component solubility in the vapor phase when the gas−liquid equilibrium was established.…”

The retrograde condensation problem in natural gas pipeline transportation system

“…The occurrence of the twophase system significantly worsens the pipeline transport conditions, causing significant pressure drops in the transported natural gas. The article examines cases where the phenomenon of retrograde (reverse) condensation occurred in the pipeline transportation of natural gas [1,2].…”