Cycle Modeling and Optimization of an Integrally Geared sCO2 Compander

Abstract

This paper presents the selection of a system configuration and off-design control method for an integrally geared compander based on cycle modeling and optimization. The goal of the cycle modeling was to determine a cycle configuration that would reach an efficiency of 50% at design conditions and to optimize off-design control to maintain high efficiencies. The compander is being developed for use in a concentrated solar power supercritical carbon dioxide power plant with expected turbine inlet temperatures of 705°C and utilizing dry cooling leading to compressor inlet temperature varying between 35°C and 55°C. The compander is unique as it consists of eight turbomachinery stages on four pinions all being driven by a single bull gear. The separate stages offer the opportunity to consider a variety of flow splits and cycle configurations including intercooling and multiple stages of reheat. Cycle modeling was conducted in two stages: on-design and off-design. On-design modeling was simulated with all components operating at their design point. This was used to compare the performance of different cycle configurations and design temperatures. Off-design modeling was then performed to investigate the temperature dependence of the cycle efficiency and power output and to develop a control strategy. Strategies considered and discussed include: turbine bypass, compressor recycle, inlet guide vanes, and inventory control. To determine the best operating conditions for each configuration and control strategy, a genetic algorithm was implemented to optimize the cycle performance across the range of operating temperatures being considered. The final selection of cycle configuration, design temperature and control strategy is also presented.

Off-design and annual performance analysis of supercritical carbon dioxide cycle with thermal storage for CSP application

“…Nevertheless, it has been observed that the compressor inlet volumetric flow is higher than the design point volumetric flow at higher CIT when the cycle is optimised for maximum efficiency. This observation is in line with Bennett et al [53] and the trend is expected to depend on the shape of the compressor map.…”

“…18 shows these parameters when maximising the net power. A linear increase in the efficiency above the design value is observed when the CIT is lower than 42 °C, which is similar to the observations of Schmitt et al, and Bennett et al [42,53]. The maximum power optimisation reached 105% of the design value, which is set as the maximum bound for the power.…”

Design of a Wide-Range Centrifugal Compressor Stage for Supercritical CO2 Power Cycles

“…The study, which is described more fully in Refs. [1] and [2], was performed iteratively with turbomachinery aerodynamic design calculations, resulting in a four-stage reheated expander, twostage main compressor, and two-stage recompressor. The turbomachinery was incorporated into a single integrally geared machine with a main compressor first-stage design point inlet condition of 37 C and 85 barA.…”

Experimental Evaluation of Performance and Mechanical Reliability for High Pressure Co2 Integrally Geared Compressor

“…Temperature rise is suppressed in the former thus power consumption becomes smaller than in the latter. There are several key technologies such as (i) Rotordynamic design (ii) High pressure casing design (iii) High pressure gas seal (iv) Aerodynamic component design for high pressure operation including super critical area and (v) Impeller blade strength design, which has to be implemented in order to employ integrally geared compressors for high pressure gas compression usage, such as Carbon Capture and Storage (CCS), Urea plant and S-CO 2 Power Cycle (Bennett et al, 2017). The progress of these technologies is nowadays remarkable and enables integrally geared compressors to get into high pressure applications more than 20 MPaG.…”