Supercritical Carbon Dioxide Seals and Bearings

Film-riding seals and gas bearings are key enabling component technologies for supercritical carbon-dioxide (sCO₂) turbomachinery. Specifically, film-riding sCO₂ seals are needed to ensure high efficiencies for large scale sCO₂ power cycles, and sCO₂ gas bearings enable oil-free operation and improved rotordynamics for high-speed sCO₂ turbomachinery. sCO₂ Power cycles have the ability to revolutionize Waste Heat Recovery applications as well as Fossil (coal and natural gas), Nuclear, and Concentrated Solar powered electricity generation in the near future with a combination of reduced turbomachinery size, reduced operating expenses and step changes in plant efficiencies.  

The GE team is presently developing high-temperature and high-pressure capable dry gas seals (Figure A) for applications in utility-scale sCO₂ turbomachinery. These novel seals are expected to improve cycle efficiencies and enable turbine architectures leading to more robust turbine operation. The seals under development at GE are twice as large and capable of operating at an order of magnitude higher temperature compared to the state-of-the-art commercially available dry gas seals. 

                                                            Figure A: Typical seal cross section

The GE team is presently developing high-temperature and high-pressure capable gas film lubricated bearings for high performance sCO₂ turbomachinery drivetrains. These novel, additively built bearings are expected to improve cycle efficiencies and enable revolutionary turbine architectures leading to lower cost electricity production. The bearings under development at GE are additively built allowing for complex features enabling advanced functionality, which permit implementation into high power machines.

Technical Challenges

The key technical challenges for thin-film sCO₂ film-riding seals and gas bearings include (a) sCO₂ film physics, (b) windage and thermal stability, (c) expansion of sCO₂ through seal/bearing faces, and (d) system integration issues such as rotor dynamics & thrust management.

Technical Approach & Capabilities

The GE team uses a combination of in-house and commercial design tools to analyze thermal loads, mechanical deformations and fluid flows in sCO₂ seals and bearings. Typical design tools include coupled fluid-structure-thermal interaction tools (Figure C) for studying the deformation of thin-film seals under varying operating loads. Seals and bearings developed with these tools are fabricated and tested on experimental test rigs at GE (an example rig depicted in Figure D) . Experimental rigs include several high-speed, high-temperature, high-pressure rigs capable of quantifying the flow leakage in seals, high-speed non-contact operation in seals/bearings, windage temperature rise in seals/bearings and rotordynamic coefficients of gas bearings. Recently, GE also commissioned a sCO₂ flow loop for performing supercritical CO₂ tests on individual components, such as bearings and seals (Figure E).