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

It is very important to predict the condensation of liquid hydrocarbons when transporting natural gas with pipelines in industry. Using a high-pressure transparent sapphire cell, the hydrocarbon dew points of eight synthetic natural gas mixtures were measured with the isothermal pressure search method. The test temperature ranges from 234.5 to 295.35 K and the pressure ranges from 1.706 to 11.495 MPa, and the results were used to evaluate the prediction performance of SRK and PR EOSs. The measured results showed that the cricondentherm and cricondenbar decrease with the increasing CH4 concentration; however, they present an increasing trend with the increasing concentration of other hydrocarbon components (C2H6 and C3+). It was found that 0.98 mol % changes in the n-C-5 concentration lead to the cricondentherm decreasing by 22 K, and 0.46 mol % changes in the n-C-6 concentration result in the cricondentherm reducing by 27 K. Correspondingly, the cricondenbar decreased by 1.9 and 2.7 MPa, respectively. In industry, a heavy hydrocarbon can be absorbed with low-volatility oil before proceeding with a pipeline, which can prevent the condensation of liquid hydrocarbons. For the dew point prediction by EOS, the PR calculation exhibited good agreement with the experimental data, and the average absolute deviations were within 0.791.53% while the SRK calculation evidently deviated from the measured values.