In centrifugal compressors, the shaft seal clearance is critical to equipment efficiency and performance. Applications employing very small seal clearances must rely on abradable materials in the stator (housing) to prevent damage to rotating components in the case of rubs. An interaction (or rub) between the rotating seal geometry and stationary seal material can occur while traversing critical speeds or during upset conditions or transients outside the normal, designed operating range of the compressor such as thermal transients or excessive vibrations. The standard abradable seal material for compressor applications is mica-filled PTFE, but alternative materials are required in applications with elevated temperatures, elevated pressures, or harsh environments where chemical resistance is necessary. The behavior of these various abradable materials during a rub event is not well understood and needs to be further quantified to allow for proper material selection for each compressor design. In order to determine suitable alternative materials, a rub simulation test rig was developed to quantify the material wear characteristics and thermal stability of various seal samples. The test rig was designed with a 7.24-inch (184-mm) diameter rotating section with representative labyrinth seal teeth. The rotating shaft was coupled with a variable speed motor capable of operating up to 24,000 rpm, allowing for surface speeds up to 754 ft/s. A 180-degree abradable seal section was mounted concentric to the rotating shaft, which may be forced into the rotating seal teeth by a linear actuator to simulate the rub. The test rig was designed to accommodate various interaction rates, initially considering 0.1 and 1 mil/s (2.54 and 25.4 μm/s) to simulate a rub caused by thermal growth and a rub caused by vibration or bow, respectively. Furthermore, the test rig was equipped with an ambient heater and pressure enclosure to evaluate seal materials at elevated temperatures and with various gas compositions. This paper presents the design and capabilities of the abradable seal test rig as well as the initial rub test results for Fluorosint 500.

As the supercritical CO2 power cycle develops and the component technologies mature, there is still a need to reduce the associated capital and operating costs to maintain a competitive levelized cost of electricity (LCOE) in order to enter the market. When considering concentrating solar power (CSP) coupled with an sCO2 power block and sensible thermal storage, the technology presents a clean source for utility-scale power generation to support baseload or peak-load electrical demand. However, the LCOE of the technology is still considered higher than the competing technologies and should be reduced to better compete in the market; 2030 targets for dispatchable solar plants are 5¢/kWh for baseload CPS and 10¢/kWh for peaker plants, as set by the United States Department of Energy. In response to this need, this study is targeting improvements in the power cycle pre-cooler to reduce power block contribution to LCOE. This study considers a dry cooler, as CSP plants are sensitive to water consumption because many installations are slated for remote or arid locations where solar irradiance is very high, but water is scarce. Furthermore, the power block footprint for an sCO2 system is quite compact, especially as compared to a steam cycle. Therefore, there is interest in installing a more compact dry cooler that is proportional to the reduced footprint sCO2 power block, while conventional dry coolers are an order of magnitude larger. The competing goals of size, performance, and cost were considered in this study to develop a compact dry cooler that can easily be packaged with the power block, significantly reducing the installation and transport cost compared to the current state of the art, while maintaining or improving upon the heat transfer performance and impact on plant LCOE. This paper details the high-level findings of a large dry cooler sensitivity study for design point selection, design of the compact dry cooler, expected year-round performance for the dry cooler and the power cycle, and the predicted LCOE for a 30-year plant life. It was found that an aluminum heat exchanger core can be suitably designed to meet the pressure and temperature requirements for a pre-cooler in an sCO2 recompression Brayton cycle. The dry cooler assembly was found to have improved heat transfer performance, allowing for increased cycle efficiencies and a reduced plant LCOE. When coupled with a centrifugal blower and compact transition duct, the dry cooler assembly was able to reduce the installation footprint by over 50%.

As the supercritical CO2 power cycle develops and the component technologies mature, there is still a need to reduce the associated costs to maintain a competitive levelized cost of electricity (LCOE) in order to enter the market. When considering concentrating solar power (CSP) coupled with an sCO2 power block and sensible thermal storage, the technology presents a clean source for utility-scale power generation to support baseload or peak-load electrical demand. However, the LCOE of the technology is still considered high and should be reduced to better compete in the market; 2030 targets are 5¢/kWh for dispatchable baseload solar plants and 10¢/kWh for peaker plants, as set by the U.S. Department of Energy. In response to this need, this study is targeting improvements in the power cycle pre-cooler to reduce power block contribution to LCOE. This paper details the high-level findings of a large sensitivity study for design point selection, compact dry cooler design, expected year-round performance for the cooler and power cycle, and the predicted LCOE for a 30-year plant life. It was found that an aluminum heat exchanger core can suitably meet the pressure and temperature requirements for an sCO2 recompression Brayton cycle. The dry cooler assembly was found to have improved heat transfer performance, allowing for increased cycle efficiencies and a reduced plant LCOE. When coupled with a centrifugal blower and compact transition duct, the dry cooler assembly was able to reduce the installation footprint by over 50%.

In order to maintain viability as a future power-generating technology, concentrating solar power (CSP) must reduce its levelized cost of electricity (LCOE). One component of solving this problem is reducing the cost of the power block while simultaneously increasing the efficiency of the thermodynamic cycle. One disruptive technology that has the promise to accomplish this is supercritical CO2 based power cycles. These cycles are conceptually similar to steam cycles; however, they have substantially smaller turbomachinery at equivalent power while also delivering more efficiency at turbine inlet temperatures of 500–700°C. This paper will summarize the current status of a US Department of Energy project to develop machinery to support a 10 MW sCO2 power cycle. The team of Southwest Research Institute® (SwRI®) and Hanwha Power Systems America, proposed to develop an integrally-geared (IG) compressor-expander (compander) for use in a nominal 10 MW-scale CSP supercritical carbon dioxide (sCO2) plant application. This integrally-geared compander (IGC) comprises multiple pinion shafts interconnected on a single bull gear to create a compact package, and utilizes a low-cost, low-speed driver. In addition, the integrally-geared architecture allows each pinion to operate at different rotational speeds to optimize performance and easily allow for inter-stage cooling and turbine re-heat to further enhance both stage and cycle efficiency. The close integration of all turbomachinery elements into a single integrally-geared (IG) machine creates a design that lends itself to power block modularization, which makes it suitable for waste heat recovery, fossil fuel power plants, and especially CSP applications. As part of the commercialization of this technology, it is necessary to reduce risk by validation testing of key components. In the current work, the focus is developing a test loop to enable safe testing of the main compressor stage across a wide range of operating conditions, and to validate the mechanical integrity of the turbine at full pressure, temperature, and speed. Developing a test loop for sCO2 requires balancing a number of design alternatives that impact cost, lead time, safety, and performance. The current work discusses the design process for the reduced flow test loop for the compander.

This research effort focused on identifying equipment and processes that can be applied at compressor and pump stations to improve station operating efficiency, thereby reducing greenhouse gas (GHG) emissions. The project approach included a literature review and a PRCI member-company survey followed by evaluation and analysis and reporting tasks. This report has a corresponding webinar.