Phase equilibrium properties aspects of CO₂ and acid gases transportation

Acid gases can be present in non-negligible quantity in natural gas. They are typically removed during gas processing operations and acid gases cleaning by chemical absorption with aqueous alkanolamine solution, for example. CO₂ and other impurities are also present in combustion products of power stations. Carbon dioxide Capture transport and storage (CCS) is one solution to reduce emission of CO₂ attributed to human activities. It exists in several technologies more or less mature which can be used for CO₂ capture. These technologies depend on the composition of the flue gas (the stream after combustion is mainly composed of N₂ and CO₂) and the processes used, (post-, pre- or oxy-combustion processes). CO₂ can be transported via ship or pipeline (mainly by pipelines for acid gases). The required compression pressure can be 100-300 bar, depending on the distance between the place of CO₂ removal and the place of its utilization but also the composition of CO₂ rich gas stream. The CO₂ rich stream can contain a lot of impurities which can modify the phase diagram. It is of great importance to know the phase behavior of CO₂ rich streams [1]. Indeed, along with carbon dioxide, a great number of compounds such as water, O₂, N₂, Ar, SOx, NOx, H₂, CO and H₂S can be present at different levels of concentration. The presence of these impurities combined with potentially long-distance transportation could lead to challenging engineering and flow assurance issues. During transportation by pipeline, if the pipe suffers a major fracture due to an accidental release or a failure, CO₂ can rapidly expand and cool: Vapor cloud followed by solid formation of CO₂ may appear. The impurities could change the characteristics of the leak and change the conditions and compositions of CO₂ clouds and solid. The presence of water in the stream may also result in corrosion, ice and/or gas hydrate formation and pipeline blockage, so the fluid system should meet certain dehydration requirements. Comparisons of the results obtained using different equations of state are also reported.