Effect of contaminants on the thermodynamic properties of CO2 -rich fluids and ramifications in the design of surface and injection facilities for geologic CO2 sequestration

Abstract

Abstract Geologic storage may involve injection of impure carbon dioxide (CO 2 ) streams in order to lower capture costs. The contaminants in the purified CO 2 stream depend on the type of power plant and the capture scheme. For on oxy-fuel based combustion cycle, we have previously evaluated the effect of presence of oxygen, nitrogen and argon on the CO 2 phase diagram and the critical properties of mixtures in these systems. For a 320 km pipeline, we established a base case for pure CO 2 , and evaluated the difference in compressor power requirements as each contaminant was added in fixed proportions. The key finding was that if the mixture encountered a two-phase region along the pipeline, the pressure drop becomes punitive. We proposed a minimal adjustment of operating conditions (or the temperature and pressure profile along the pipeline) to avoid the two-phase region and concomitant prohibitive pressure losses. In this paper, we consider the influence of hydrogen sulfide and water on the phase behavior of the CO 2 -rich captured stream. Specifically, we examine the phase equilibria and the PVT properties, and compare the GERG–2008 equation of state (EoS) computations with experimental data. In general, CO 2 -rich effluent mixtures from oxy-fuel plants may undergo phase separation at higher pressures than that for pure CO 2 for the temperature range likely to be encountered in surface and injection facilities designed for CO 2 sequestration. In addition, density, compressibility, and reactive properties of these mixtures may be significantly different from pure CO 2 . Consequently, operation of large geologic CO 2 storage sites must anticipate how these differences in the thermodynamic properties of the injected fluids may affect compressor power requirements, pipeline transport, well design, and wellbore and reservoir integrity.