Characterization of Non-Equilibrium Condensation of Supercritical Carbon Dioxide in a de Laval Nozzle

Abstract

On a ten-year timescale, Carbon Capture and Storage could significantly reduce carbon dioxide (CO2) emissions. One of the major limitations of this technology is the energy penalty for the compression of CO2 to supercritical conditions, which can require up to 15% of the plant’s gross power output. To reduce the power requirements supercritical carbon dioxide compressors must operate at reduced temperatures and near saturation where phase change effects are important. Non-equilibrium condensation can occur in the high-speed flow at the leading edge of the compressor, causing performance and stability issues. The characterization of the fluid at these conditions is vital to enable advanced compressor designs at enhanced efficiency levels but the analysis is challenging due to the lack of data on the metastable fluid properties. In this paper we assess the metastable behavior and nucleation characteristics of high-pressure subcooled carbon dioxide during the expansion in a Laval nozzle. The assessment is conducted with numerical calculations, supported and corroborated by experimental measurements. The Wilson line is determined via optical measurements in the range of 41 and 82 bar and near the critical point. The state of the metastable fluid is fully characterized through pressure and density measurements, with the latter obtained in a first of its kind laser interferometry set up. In a systematic analysis the inlet conditions of the nozzle are moved close to the critical point to allow for large gradients in fluid properties and reduced margin to condensation. The results of calculations using a direct extrapolation of the Span and Wagner equation of state model are compared with the experimental measurements. The analysis suggests that the direct extrapolation using the Span and Wagner model yields results within 2% of the experimental data, with improved accuracy at conditions away from the critical point. The results are applied in a pre-production supercritical carbon dioxide compressor and are used to define inlet conditions at reduced temperature but free of condensation. Full-scale compressor experiments demonstrate that the new inlet conditions can reduce the shaft power input by 16%.

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

“…The simulations are to test the reliability of the nonequilibrium phase-change model and the corresponding two-phase-flow simulation method. The characteristics of the nonequilibrium phase-change flow field have been analyzed, and the results have been compared to the experimental data of Lettieri [10]. The experimental test apparatus consists of a blowdown test rig filled with high-pressure CO 2 .…”

“…Condensation does not occur immediately when the saturation line is reached but continues to expand isentropically in the form of gas. The working fluid enters a metastable state until it arrives at the Wilson line (point D), where the spontaneous nucleation process will be triggered [10,11]. Finally, the fluid will return to equilibrium (point E).…”

Real Gas Simulation for High-pressure and Low-pressure Nonequilibrium Condensation in Transonic Flows

“…6, were simulated under high-pressure conditions in a computational grid consisting of 361 × 91 grid points. Lettieri et al (2017) experimentally measured the pressure and Wilson point in high-pressure CO 2 conditions. The computational conditions are summarized in Table 1.…”

Effects of Different CO2 equations of state on Condensation Position in Numerical Investigation

“…They also report flow visualization and pressure measurements for a series of supercritical CO2 blowdown tests, providing a valuable data set for condensation model assessment. High-speed imaging shows the onset of condensation at nozzle throat as "white fog" (Lettieri et al, 2017). Kevin W. Brinckman proposed a method for predicting condensation in supercritical CO2 compressors (Brinckman et al, 2019).…”