SBIR-STTR Award

Supercritical CO2 (sCO2) power cycles are superior over traditional water based, air-breathing, direct-fired, open Brayton cycles or indirect-fired, closed Rankine cycles in terms of efficiency and equipment size. They hold great potential in fossil fuel power plants, nuclear power production, solar power, geothermal power, and ship propulsion. To unlock the potential of sCO2 power cycles, technology readiness must be demonstrated on the scale of 10 – 600 MWe and at sCO2temperatures and pressures of 350 – 700 ºC and 20 – 35 MPa for nuclear industries. Amongst many challenges at the component level, the lack of suitable shaft seals for sCO2 operating conditions needs to be addressed for DOE’s next generation nuclear turbine and compressor development. We propose a proprietary Elasto-Hydrodynamic (EHD) high-pressure, high temperature, and scalable shaft seal for sCO2 turbomachinery in this STTR Phase I. The EHD seal for aircraft engine sealing has the following benefits to the sCO2 turbomachinery: Low Leakage. The self-regulated minimum clearance throttles the sCO2 leaking flow and improves cycle efficiency. Minimum Wear. The primary EHD seal operates on non-contact conditions. The startup seal only contacts the rotor at the startup and disengages from the rotor after startup. Smoother and Faster Startup. Unlike clearance-type seals, the startup seal addition provides a smooth transition from cold start to operation condition. Low Cost. Simple structure results in low seal cost and minimal wear saves maintenance cost. No Stress Concentration. EHD seal design eliminates sharp angle and stress concentration. In this STTR Ultool will conduct the development of the EHD seal for sCO2 turbomachinery, which will advance sCO2 seal TRL for support DOE sCO2 Power Cycle Program. Phase I will establish the boundaries and opportunities of the proposed EHD seal for sCO2 turbomachinery; prove the feasibility of sCO2 EHD seal through tests; and prepare the design criteria to be implemented in the Phase II prototype and beyond for full-scale commercialization.

Supercritical CO2 (sCO2) power cycles are superior to traditional water based, air-breathing, direct- fired, open Brayton cycles or indirect-fired, closed Rankine cycles in terms of efficiency and equipment size. They hold great potential in nuclear power production, fossil fuel power plants, concentrated solar power, geothermal power, and ship propulsion. To unlock the potential of sCO2 power cycles, technology readiness must be demonstrated on the scale of 10 – 600 MWe and at the sCO2 temperatures and pressures of 350 – 700 ºC and 20 – 35 MPa for nuclear industries. The lack of suitable seals at sCO2 operating conditions is one of the main challenges at the component level. So far, conventional seals all suffer from the incapability of handling sCO2 pressure and temperature in one way or another. To this end, we propose a patented elasto-hydrodynamic (EHD) high-pressure, high temperature, and scalable shaft seal for sCO2 cycles. Under the EHD mechanism, the higher the pressures, the tighter the sealing, while still sustaining a continuous sCO2 film. A patented secondary seal will be integrated to the primary seal to provide sealing at startup, which will enable active sealing for the whole operating range (from cold start to operating conditions). To further promote the longevity of the EHD seal, a proprietary wear-resistant coating deposition method will be explored. In Phase I, the simulation strategies have been established to address the complexity of the EHD analysis. Two pending US patents were resulted from the Phase I Project and the Phase I simulations have been published at ASME POWER 2021 and ASME TURBO EXPO 2021. An extensive analysis of the EHD seal has been conducted for nuclear power generation turbomachinery and a test rigs has been designed to test the EHD seal internally. The test rig will be completed by the end of the Phase I (July 2021) for seal demonstration and optimization. The Team has identified potential partners for the EHD seal development, including four federal laboratories. Two energy-saving and emission-reducing applications have been identified for the EHD seal: sCO2 Power Generation Turbomachinery Seal – Operate at sCO2 Conditions and Scalable to 18” +. High Efficiency Aircraft Engine Seal – Cut Total Aircraft Fuel Consumption by 3-5%. The Phase II Project will begin with developing a prototype EHD seal and optimize it via in-house testing and application-specific simulations, followed by an EHD seal demonstration at SNL’s 2” sCO2 Seal Testing Facility. The system integration approach and manufacturing process will be investigated and established. A new on-shaft coating deposition system will be studied for coatings on large sCO2 turbomachinery shaft (18”+). A path to commercialization will be identified and presented.