Liquid CO2 Formation, Impact, and Mitigation at the Inlet to a Supercritical CO2 Compressor

Abstract

Cycle efficiency is one of the critical parameters linked to the success of implementing a Supercritical Carbon Dioxide (sCO2) power cycle in a Concentrating Solar Power (CSP) plant application. Ambient conditions often change rapidly during operation, making it imperative that the efficiency of the plant cycle be optimized to obtain the maximum power production when sunlight is available. Past analyses have shown that operating the cycle at the critical point provides the optimum efficiency for dry operation. However, operation at this point is challenging due to the dramatic changes in thermophysical properties of CO2 near the critical point and the risk of the fluid having a two-phase, gas-liquid state. As a result, there is a high likelihood that liquid can form upstream of the primary compressor in the sCO2 power cycle. This paper explores the potential for liquid formation when operating near the critical point and looks at the influence of liquid on the compressor performance. The performance impact is based on industry experience with wet gas compression in power generation and oil and gas applications. Options for mitigating liquid effects are also investigated, such as upstream heating, separation, or compressor internal controls (blade surface gas ejection). The conclusions of the paper focus on the risk, estimated impact on performance, and summary of mitigation techniques for liquid CO2 entering a sCO2 compressor.

Design of a Centrifugal Compressor Stage and a Radial-Inflow Turbine Stage for a Supercritical CO2 Recompression Brayton Cycle by Using 3D Inverse Design Method

“…However, it is also widely reported that the very low cycle temperature will result in a condensation area near the compressor LE. The compressor efficiency will be very poor when its inlet flow is in the two-phase region according to Poerner et al [29]. It is also found that CFD (ANSYS CFX) becomes very difficult to converge for the given temperature range above.…”

Review of supercritical carbon dioxide (sCO2) technologies for high-grade waste heat to power conversion

“…A series of holes are placed at the blade inlet of the compressor impeller and used to eject a dry gas to break the liquid film formed on the airfoil. The result is the restored aerodynamic performance of the compressor and an improved lifetime of the component [58].…”

“…To overcome this limitation Poerner et al in [58] proposed to adopt the gas ejection technology, widely diffused in the oil and gas wet compressors. A series of holes are placed at the blade inlet of the compressor impeller and used to eject a dry gas to break the liquid film formed on the airfoil.…”

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

“…In a supercritical state, CO 2 has large specific heat capacity, large compressibility, large density, low viscosity and other qualities that can significantly reduce the compression work and then improve the cycle efficiency [3]. The closer the inlet condition is to the critical point, the greater the system performance is [4][5][6]. However, when the compressor inlet condition approaches the critical point, the thermophysical properties of CO 2 will change dramatically, deviate significantly from the ideal gas and show a strong real-gas effect [7,8].…”