Quasi-critical characteristics and safety control of CO₂ pipeline transportation

The physical parameters of CO₂ pipelining will exhibit quasi-critical characteristics of violent fluctuation around the critical point, which will seriously affect the safe and stable operation of pipeline. Using density as a reference parameter, the relationship of quasi-critical temperature has been fitted at the most dramatic fluctuation of the density in large-scale CO₂ pipelining. The influence of impurities on the quasi-critical temperature of CO₂ pipelining has been analyzed and an safety control program has been proposed. Exemplified with the first CO₂ pipeline demonstration project in China, suggestions on safe operation and transportation are put forward. The study shows that non-polar and weakly polar impurities make quasi-critical temperature line shift towards lower temperature while strong polar impurities and moisture cause quasi-critical temperature to shift to higher temperature. When piped CO₂ contains different impurities, different starting temperature and pressure should be adopted to avoid the pipe condition getting close to the quasi-critical temperature line or entering into two-phase region. The safe and stable flow of transported medium can be kept under the pressure higher than 14 MPa. When transporting flue gas of coal-fired power plants, the supercritical CO₂ pipeline, which is the first large-scale long-distance demonstration project in China, should adopt the corresponding safety control technologies for transporting CO₂ with non-polar impurities.