5-kW Closed-Loop Brayton-Cycle Microturbine for

PowerPoint PresentationCopyright © 2021, Creare LLC. An unpublished work. All rights reserved. MTG-21-05-7938 / 1010243 - 1
5-kWe Closed-Loop Brayton-Cycle Microturbine for Residential-Scale Combined Cooling, Heat, and Power
ARPA-E Energy Innovation Summit 24-27 May 2021
Steve Walker Founder/CEO, IMBY Energy
[email protected]
[email protected]
Copyright © 2021, Creare LLC An unpublished work. All rights reserved. MTG-21-05-7938 / 1010243 - 2
Company Backgrounds IMBY and Creare form a complementary team IMBY (In My BackYard) is focused on decarbonizing building
energy consumption • Use high-volume manufacturing expertise to transition most promising
technologies out of the laboratory • Provide direct path to decarbonized energy
Creare is focused on developing innovative technologies • 60 years of successful invention, development, and transition • Core emphasis on thermodynamic components and systems • Over four decades devoted to miniature high-performance turbomachines
and closed-loop Brayton systems
Vacuum Pumps for Mars Curiosity RoverBrayton Cryocooler for Hubble Space Telescope
Turbomachine Technology
Rene 41 Turbine Rotor Inconel Nozzle Ring Shrouded and Unshrouded Compressor Impellers
Turboalternator for Organic Rankine CycleTurbomachine Assembly for Brayton Power System (Turbine, Compressor, and Internal Permanent Magnet)
Overview
IMBY evaluated numerous engine technologies for small- scale combined heat and power generation
Closed-loop Brayton-cycle microturbine (CBM) identified as the best technology
Creare has developed closed-loop Brayton systems for NASA and DoD applications
• High cost has limited use to critical missions IMBY and Creare partnered to prototype a CBM designed for
mass-production Development funded by ARPA-E, NASA, IMBY, and Creare
IMBY System
Problem • Antiquated HVAC appliances • Poor grid resiliency • High carbon emissions
Solution • Provide building with all heating, cooling,
hot water, and electricity • Integrate microturbine, heat pump, and
thermal storage Benefits
• Lower CapEx and OpEx • Fuel flexibility (including renewable fuels) • On-grid or off-grid operation • Demand-side grid management • Direct path to carbon-free energy
Sankey Diagram
*HP = heat pump (operating at a COP of 2 at -20°C ambient)
Building Building
Cold-Weather Operation
Warm-Weather Operation
Engine Technology Selection
Existing small engines are too inefficient, expensive, and/or unreliable for IMBY system
Conventional Brayton engines are not appropriate • Features and performance scale poorly down to 5 kWe
• Open-loop operation allows oxidation and contamination ingress CBM is ideal
• Closed-loop operation enables dense working fluid with exceptional thermodynamic properties
» High efficiency » Compact components that are inexpensive to manufacture
• Closed-loop operation prevents contamination ingress and internal oxidation
» High reliability » Long maintenance-free life
• Creare has addressed scaling challenges required to provide high efficiency for small sizes
Closed-loop Brayton engines are not available presently as commercial products
CBM Characteristics
High efficiency • Low fuel consumption
Compact size • Low material costs
Efficiency and power density scale favorably as power level increases High reliability
• One moving component with non-contact gas bearings and clearance seals • No wear mechanisms, lubrication, or maintenance requirements
Long life • Limiting factor is high-temperature material creep
Assembly can be packaged to utilize available space • Discrete components connected by tubing/ducting • Customizable heat exchanger dimensions
Continuous gas flow enhances thermal energy input and removal • High efficiency • Low material costs
Vibration-free operation • No need for vibration cancelling devices, control methods, or system configurations
CBM Schematic
Turndown Efficiency
Laboratory Prototype
Critical Technologies
Turbomachine assembly with specialized hydrodynamic gas bearings
• Extremely low radial displacement enables exceptionally tight clearance seals for high efficiency at small size
• High rotational speed enables compact size to limit material costs • Contact-free operation enables long, maintenance-free life
Binary working fluid mixture of krypton and helium • Enables high efficiency and compact, low-cost components
Recuperated flameless combustion • Provides low exhaust emissions
CBM Development Path
Preliminary design funded by IMBY and NASA SBIR Phase IIE project (Contract NNX14CC09C)
Detailed design, fabrication, and testing funded by ARPA-E, IMBY, and Creare
• DOE Contract DE-AR0001067 • Scaled from 340 We engine under development for NASA RPS Program
(Contract 80GRC17C0028) Component fabrication and testing under way Prototype system testing to begin in late 2021
IMBY-NASA Comparison
Critical Parameters for Converter Design Parameter NASA System IMBY CBM
Working Fluid (Molar Composition) 85% Xe, 15% He 70% Kr, 30% He Mass Flow Rate 44.6 g/s 201 g/s Compressor Inlet Temperature 100°C 22°C Turbine Inlet Temperature 730°C 780°C Compressor Inlet Pressure 441 kPa (63.9 psia) 1,015 kPa (147 psia) Compressor Pressure Ratio 1.63 1.66 Turbine Pressure Ratio 1.59 1.61 Rotor Speed 161,000 rpm 137,000 rpm Heat Source Radioisotope (Pu-238) Combustion Energy Input Rate 1,500 W 13.15 kW Heat Loss Rate from Combustion Exhaust NA 0.37 kW Heat Leak Rate to Environment 150 W 0.59 kW Heat Rejection Rate 1,013 W 7.04 kW Unregulated Electric Power 337 W 5.16 kW Regulated Electric Power 319 W 5.00 kW Engine Efficiency 25.0% 39.2% Overall Efficiency 21.3% 38.0%
Critical Parameters for Converter Design
Parameter
NA
150 W
0.59 kW
NASA Engine
Turbomachine
Compressor, turbine, and alternator are a single assembly • Turbine drives compressor and alternator directly with one set of bearings
Specialized features enable high efficiency at small size • Tilt-pad journal bearings and high precision enable tight clearance seals
to minimize bypass leakage • Shrouded impellers minimize bypass leakage and enhance aerodynamic
efficiency Impeller diameters are 1.1 inch and 1.2 inch Rotational speed is 137,000 RPM
NASA Turbomachine Assembly NASA Rotor Assembly
Recuperator
Low-cost recuperator is critical for a cost-effective system • Existing approaches are too expensive
Diffusion-bonded foil recuperator is a breakthrough innovation • Inexpensive foil stamping • Single-step bonding without braze material
Two subscale assemblies built to refine fabrication processes Full-scale recuperator bonded
• Manifold attachment progressing
Combustion System (1 of 2)
External heat source enables flexible fuel type Flameless oxidation (FLOX) chosen
• Limits peak temperature and associated NOx formation • Initial testing with commercial FLOX burner complete
Hot interface heat exchanger will ensure effective heat transfer Combustion recuperator will minimize waste heat discharge Burner integration with interface heat exchanger under way Subsystem testing planned during June
Combustion System (2 of 2)
Burner Testing Interface Heat Exchanger
Conclusions
CBM is attractive for combined heat and power generation Technology is based on specialized systems developed for
NASA and DoD Diffusion-bonded foil recuperator is a key breakthrough to
enable low-cost manufacturing and commercialization Component fabrication and testing are under way Prototype system testing to begin in late 2021
Creare and IMBY are grateful for support provided by ARPA-E, DOE, NASA, and DoD
5-kWe Closed-Loop Brayton-Cycle Microturbine for Residential-Scale Combined Cooling, Heat, and Power
Company Backgrounds
Turbomachine Technology
Conclusions

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5-kW Closed-Loop Brayton-Cycle Microturbine for