Supercritical pipelines are most commonly used in CO2 transportation. Liquid models are always utilized for design and hydraulic checking of those pipelines. However, supercritical CO2 may show significant characteristics of gaseous under certain operating condition. This phenomenon may increase pressure drop so that pressure values will be different from calculation results from liquid models. According to comparing the compression factor and density curve of liquid and supercritical CO2, the fact that when operation parameters of supercritical pipelines occupy in certain pressure and temperature regions, compressibility of CO2 cannot be neglectd is concluded. On the basis of density variation tendency, the method and its steps which are used to delimit compressible region of supercritical CO2 are proposed. Compared with this compressible region, operating parameters of supercritical pipelines can be checked. The application example calculates the pressure drop both by liquid model and gaseous model which considers copressibility. The results verified that delimited method of compressible region is accurate and reasonable.

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