Numerical Simulation of Non-Equilibrium Condensation in Supercritical CO2 Compressors

Abstract

There is increasing interest in supercritical CO2 processes, such as Carbon Capture and Storage, and electric power production, which require compressors to pressurize CO2 above the critical point. For supercritical compressor operation close to the critical point there is a concern that the working fluid could cross into the subcritical regime which could lead to issues with compressor performance if condensation was to occur in regions where the fluid dropped below the saturation point. Presently, the question of whether there is sufficient residence time at subcritical conditions for condensation onset in supercritical CO2 compressors is an unresolved issue. A methodology is presented towards providing a validated simulation capability for predicting condensation in supercritical CO2 compressors. The modeling framework involves the solution of a discrete droplet phase coupled to the continuum gas phase to track droplet nucleation and growth. The model is implemented in the CRUNCH CFD® Computational Fluid Dynamics code that has been extensively validated for simulation at near critical conditions with a real fluid framework for accurate predictions of trans-critical CO2 processes. Results of predictions using classical nucleation theory to model homogeneous nucleation of condensation sites in supersaturated vapor regions are presented. A non-equilibrium phase-change model is applied to predict condensation on the nuclei which grow in a dispersed-phase droplet framework. Model validation is provided against experimental data for condensation of supercritical CO2 in a De Laval nozzle including the Wilson line location. The model is then applied for prediction of condensation in the compressor of the Sandia test loop at mildly supercritical inlet conditions. The results suggest that there is sufficient residence time at the conditions analyzed to form localized nucleation sites, however, droplets are expected to be short lived as the model predicts they will rapidly vaporize.

Real Fluid Modeling and Simulation of the Structures and Dynamics of Condensation in CO2 Flows Shocked Inside a de Laval Nozzle, Considering the Effects of Impurities

“…The primary objective of the work is to show that this equilibrium real fluid approach is capable of accurately capturing the transient appearance of the condensation of the supercritical CO 2 observed experimentally in the divergent part of the de Laval nozzle. The second objective is to demonstrate the significant effects of impurities in CO 2 , which has been neglected in previous numerical simulations [8,11,12]. Indeed, as mentioned in the introduction, this can have a considerable impact on the phase diagram of mixtures (CO 2 -impurities), which, as we will show in this work, leads, in particular, to different quantities of condensed CO 2 .…”

“…Designing and establishing a working methodology for CO 2 compressors is a crucial step in the industrial scaling of the CO 2 compression process. The works of Brinckman [8], Baltadjiev [9] and Lettieri [10,11] provide insight into these challenges. The work of Romei et al [12] highlights the efficiency of power-cycles in pumps/compressors and the effect phase change has on them.…”

Effect detection of using a modified Redlich-Kwong-Aungier equation of state on the calculation of carbon dioxide flow in a centrifugal compressor

“…For compressor operation in the supercritical mode, close to the critical point, there is a hypothesis of the working fluid transitioning to the subcritical mode. This may lead to compressor performance issues if condensation occurs in regions where the liquid falls below the saturation point [5].…”

Effects of Near-Critical Condensation and Cavitation on the Performance of S-CO2 Compressor

“…The white region is the condensation place of CO 2 , the black region is the non-condensation region, and the red line indicates the throat. Figure 5b shows the contour of the predicted liquid CO 2 volume fraction by Brinckman [25]. When the relaxation time coefficient in the Lee model approaches infinity, the fluid-phase transition rate also approaches infinity.…”