CO2/H2OPLUS: Understanding of hydrate formation, water deposition and water drop-out in CO2-streams - accurate dewatering specifications

Capture processes in most cases provide CO2, where apart from mutual solubility; water is present as a separate phase. In order to avoid water drop out during the transport of CO2 inside the pipeline, a transport specification for the maximum allowable wa ter contents is set. Normally a drying process is employed to remove the excess water from the captured CO2 stream to reach the specification. The basic concept for setting this maximum allowable water content is the avoidance of free water during pipelin e transmission in order to avoid both corrosion and hydrates. The resulting specification is often based upon best practice and set accordingly stringent. Several drawbacks with this current approach have been identified: - There is a lack of experimental data and models - The water dissolved in dense phase CO2 is not necessarily homogeneously distributed - Depressuration of pipeline can increase the concentration of the water phase - There are indications that hydrates may form in the CO2 stream or pipel ine surface at water concentrations below the solubility equilibrium - There is no current agreement in the necessary levels of dehydration of CO2 The challenges addressed in this project are the following: 1. Determining the phase behaviour of CO2/H2O m ixtures within the hydrate stable region and the effect of selected impurities upon this. 2. Determining the non-equilibrium conditions under which water drop out and hydrate formation occurs at water concentrations below equilibrium solubility levels. 3. Increasing the understanding of the conditions under which water adsorption on the pipeline wall is preferential and if subsequent hydrate formation occurs. 4. Increasing the understanding of the conditions under which hydrates may form without presence of free water. 5. Developing a thermodynamical model that can describe the phase behavior, water dropout, water deposition and hydrate formation as a function of pressure, temperature and composition.