Session: 11-19-01: Fluid Measurements and Instrumentation/Young Engineer Paper (YEP) Contest

Paper Number: 167066

A Self-Regulating Face Seal for sCO2 Power Generation 

This research addresses critical challenges in advancing supercritical carbon dioxide (sCO₂) power generation, a key technology for next-generation nuclear energy systems. As demand for microreactors grows, efficient power conversion systems below 10 MWe are essential. At these scales, rotating equipment operates at speeds exceeding 40,000 rpm, necessitating high-temperature seals for sCO₂ Brayton power cycles. To enable commercial adoption, axial shaft seals capable of withstanding 700 °C and 4,500 psi are required.

Supercritical CO₂ seals face significant challenges related to leakage, wear, and long-term reliability in power generation applications. Traditional sealing technologies, including labyrinth, brush, finger, compliant foil, and Hydrostatic Advanced Low Leakage (HALO) seals, each have compatibility issues when applied to sCO₂ systems. While labyrinth seals are contactless and eliminate wear, they suffer from high leakage and can introduce destabilizing forces, causing rotor eccentricity and reducing operational stability. Brush and finger seals, though capable of reducing leakage, experience high friction and wear due to direct contact with the rotating shaft. These issues are exacerbated in sCO₂ systems, where elevated pressures and temperatures accelerate degradation, leading to reduced service life.

Compliant foil seals, another alternative, face multiple challenges in sCO₂ applications, including increased leakage from secondary flow effects, thermal sensitivity, and wear under extreme conditions. Additionally, their complexity and cost make them less viable for widespread implementation. More recently, Pressure-Activated Leaf Seals (PALSs) have been explored for sCO₂ applications. PALSs utilize thin sheet metal leaves that close around the rotor when exposed to upstream pressure, reducing leakage. Compared to a four-toothed labyrinth seal, PALS demonstrated a leakage reduction of over 50%. However, PALS rely on pressure differences for activation, which may lead to inconsistent sealing performance under the variable operating conditions of sCO₂ power cycles. Furthermore, prolonged exposure to high-pressure sCO₂ can result in increased wear and leakage over time, negatively impacting system efficiency.

This study proposes a novel, self-regulating shaft seal designed to withstand extreme conditions while minimizing leakage and wear. Unlike conventional seals, this scalable, cost-effective solution is optimized for sCO₂ turbomachinery by leveraging advancements in air and hydrostatic bearings. A simulation methodology was developed to evaluate the proposed seal’s behavior. Results indicate a quadratic leakage trend: initially increasing with pressure differential up to 53 g/s at 4.3 MPa, then decreasing to 3 g/s at 9 MPa. This behavior contrasts with traditional clearance-type seals, where leakage increases linearly with pressure. Such a trend is advantageous for sCO₂ applications, as minimal leakage is desired at higher operating pressures.

sCO₂ power cycles have the potential to significantly improve energy efficiency and reduce environmental impact, with projections estimating a reduction of over 180 million metric tons of U.S. CO₂ emissions annually by 2050. By addressing key technological barriers and fostering collaboration across academia, national laboratories, and industry, this research aims to drive lasting innovation in clean, efficient, and cost-effective power generation.

Presenting Author: Mohammad Fuad Hassan Georgia Southern University

Presenting Author Biography: Mohammad Fuad Hassan is a first PhD student in the Department of Mechanical Engineering at Georgia Southern University.

Authors:

Mohammad Fuad Hassan Georgia Southern University
Sevki Cesmeci Georgia Southern University
David Dewis Sole Proprietor