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Reversing Turbomachine to Enable Laughlin-Brayton Cyclefor Thermally-Pumped Electrical Energy Storage

Brayton Energy, LLCMassachusetts Institute of Technology, Gas Turbine Lab

Exploring new aero-mechanical regimes toward

turbomachinery efficiency improvement for a novel

Brayton cycle energy storage

Project Vision

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100 m

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Malta, Laughlin BatteryPumped thermal-electric storage

Generation Cycle Schematic p

100 MW, 1GWh

Generation Cycle Schematic p

Cold Hexane-68oC

Hot Salt565oC

BEARINGSALT C.C.G.C.

RECUP

CSHX

HSHX

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GOOGLE-X

Laughlin’s Invention* The Ideal Reversible Brayton Cycle:- Charging as a Brayton cycle heat

pump - Generation is a gas turbine engine

* Robert Laughlin is a Stanford professor and Nobel Laureate in Physics

Brayton’s Solution: An ideal turbomachine should surpass state-of-the-art gas turbine efficiencies due to the elimination of the normal design constraints; high temperatures, blade cooling, size, weight, stage-count and with tightened tip clearance.

Approach: Develop a single turbomachine which operates as both generator and heat pump. Other innovations to be developed include a novel mag-bearing rotor design, and compact heat exchanger integration. The resulting round trip efficiency to be improved from nominally 54% to 63%.

Technical Challenges and Risks:• The Round-Trip- Efficiency (RTE) is extremely sensitive to

turbomachinery component efficiencies. 1 point of turbine & compressor efficiency equates to 2.6 points of RTE.

• Past embodiments of this cycle have committed to separate Brayton heat pump and Brayton generator turbomachines. This results in unacceptable compromises:

1. Excessive cost 2. High losses due to valves and piping3. Poor transient response to loads 4. Reduced reliability

Reversible Counter-Rotating Turbomachine to Enable Brayton-Laughlin CycleObjective: Develop the Perfect Reversible Gas Turbine Engine.

Principal Investigators: Jim Kesseli (Brayton Energy) , Choon Tan (MIT)

US Department or Energy / ARPAe Award (2019-2021)

Robert LaughlinInventor, Noble Laureate

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56 m 52 m

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Malta, Laughlin Battery(Background work by Brayton for Google-X)

10 MW, 100MWh

100 MW, 1GWh

3 bar Pressure, Non-Reversible

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Brayton was hired by Google-X to design the Laughlin Battery• Detailed turbomachinery trade studies,

analysis, design, and cost modeling • Heat exchanger designs, cost modeling and

testing • System modeling and full system integration

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Google-X 1.6 MW “Conventional” Twin Machine Designed by Brayton

• Aero reviewed by four prominent teams: Final Detailed Design • PCA• Turbo Solutions • Brayton & ConceptNREC• MIT Gas Turbine Lab

• Thermal-structural • Rotor system

• Full rotor dynamic and structural design • Mag bearings complications

Alternator – a second generation product • with our sponsored structural design by OEM• Housing and Cooling – thru PDR• Brayton purchases only magnet sleeve and wound

stator. Add shaft & housing

Power electronics- a second gen product • highly customized – needs re-quote

Conclusion: Could not make cost target ($500/kW, $50/kWh) or round trip efficiency target

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The Concept: Pumped Thermal Electric Energy Storage

1. In generation mode, convert stored thermal energy to electricity. In charging mode, restore thermal reservoirs by motored heat-pump

2. Reversing turbomachine; acts as a gas turbine genset and a Brayton-cycle heat pump.

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Brg

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Motor-

Gen.Brg

QH,GEN

QC,GEN

Cold Sto.Cold Sto

TESHot TES

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QREJ

5a

REVERSIBLE

Gas Turbine Generator & Brayton Heat Pump

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ARPAe DAYS Project Objectives

• Develop single turbomachine to function as heat pump and gas turbine. To achieve this, the flow direction through the machine must reverse between generation and charging modes.

• >93% polytropic efficiency for turbine and compressor

• Risks• Many conventional empirical design tools are not calibrated for the unconventional aerodynamic principles

employed in the proposed design. • Optimize for compressor

• Targets: Validate novel aerodynamic and mechanical design principles: 1. Design a full-scale energy storage plant – sufficient to defend performance, cost, and life targets

• Test and refine the aerodynamic principles with CFD

2. Sub scale similitude testing to validate design efficiency

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Reversing Turbomachine to Enable Laughlin-Brayton Cycle for Thermally-Pumped Electrical Energy Storage

50 MW-e65% Round Trip Efficiency

Compressor Compressor

Turbine

Turbine

Blade Direction

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1 10 100C

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Advances in Aerodynamic Efficiency for

Turbomachines

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DAYS CONCEPT: A single, dual purpose turbomachine

Benefits:

1. Halves the cost of a major cost driver – the gas turbine motor-generator

2. Eliminates complexity, cost, and pressure losses associated with piping and valves, otherwise required.

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Challenges:1. Optimize the turbomachine for ultra

high efficiency in dual modes2. Achieve compressor and turbine

polytropic efficiency over 93%

Baseline pumped thermal electric storage requires two separate turbomachines machines

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The Team

• Prime: Brayton Energy, LLC • Engineering staff of 45 specializing in turbomachinery design, gas turbines, and

advanced energy systems • James Kesseli, PI, Thomas Wolf, Aero lead, Josh Antrim, Mechanical Lead

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‣ Sub-recipient: Gas Turbine Laboratory, Massachusetts Institute of Technology– Dr. Edward Greitzer, HN Salter Professor of Aeronautics and Astronautics

– Dr. Choon Tan, Senior Research Engineer

– Joseph Chiapperi, Grad Student

‣ Advisor: Dr. Robert Laughlin, Stanford Professor, Anne and Robert Bass Professor of Humanities and Science and

Nobel Laureate in Physics

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Exploring new directions in Turbomachinery aerodynamics.

Approach: • Counter-rotating axial compressor

and turbine. • Elimination of conventional stators

and associated losses.• Optimized blade shapes to

minimize compromises associated with reversing flow.

Design of a high efficiency, economical solution for the Laughlin-Brayton Battery

• Combine the Brayton cycle heat pump and the gas turbine generator into a single turbomachine –reducing cost and improving efficiency.

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50 MW Machine

• Curved diffuser/inlets at all locations, AR = 3:1

• Cold machine 9 stage flow path incorporated

• Waukesha active magnetic bearings

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Performance @ Tamb = 288K

hgen COPchg hoverall

56.1% 1.17 65.7%

parameters for 50MWe system

gen charge

mGAS 336.9 kg/s 220.2 kg/s

Generation Charge QH 89.1 MW 58.5 MW

QC 15.3 MW 10.0 MW

QREJ 22.2 MW -

turbomachinery & bearings

gen charge

PRcomp 3.00 2.46

ERturb 2.82 2.34

HX performance (prescribed) HX performance (calculated) gen Dp/p (prescribed) chg Dp/p (calculated) hpoly ,comp 92.3% 92.3%

(TS - TG)GEN,HS 15.0K (T5 - T2)GEN 11.0K HX duct net hpoly ,turb 87.8% 86.8%

(TG - TS)CHG,HS 15.0K (T6 - T1)CHG 10.2K HX,HS (6-3) 0.75% 0.35% HX,HS (2-6) 1.07% ML1 302.7 kW 343.7 kW

(TG - THEX)GEN,CS 2.5K (T3 - T5)CHG 11.3K HX,CS (5a-1) 0.75% 0.35% HX,CS (4-5) 1.01% ML2 151.6 kW 161.1 kW

(THEX - TG)CHG,CS 2.5K erecup,gen 98.1% rcp,cold (2-6) 1.00% 0.70% rcp,cold (5-1) 1.56%

(T4 - T6)GEN 10.0K erecup,chg 98.3% rcp,hot (4-5) 1.00% 0.70% rcp,hot (6-3) 1.65% electrical losses

(T5a - Tamb)GEN 4.0K heat rej (5-5a) gen / motor effy 98.0%

DtCHG / DtGEN 1.52 power conversion effy 100.0%

0.50%

CMP = compressor, TRB = turbineML = mechanical loss (bearings)CS = cold s torage, HS = hot storageG = gas , S = sand, HEX = hexane

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TC_HSTH_HS

QREJ53

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867K 1100

244K 290K

867K1100

244K290K

247K

347K 1085K

862K 872K

1115

242K

347K

852K

852K

287K

882K

882K

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298K

5a

292 358K

Exercise of Laughlin system model with projected efficiency levels applied for cold turbomachinery components, and for the hot compressor. For the hot turbine, an additional efficiency point has been added reflecting earlier CFD analysis and recognizing that incidence errors for this component will be lower.

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Results of Detailed Design Review at MIT, January 30, 2020

13Insert Presentation NameMay 12, 2021

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Cost TargetsGoal Status

Power <$500/kWe <$329 /kWeEnergy <$50/kWh <$43/kWh

Life (MTBO) > 100,000 hrsO&M < 0.005 $/kWh

Reference Design • 50 MW-e generation • 500 kWh• 65% RTE

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Technology-to-Market

1. Goal: Acquire funding for 10 MW Demonstration Project

2. Status: Performing model validation testing

3. Critical Milestone: Complete testing in 2021

4. Next Steps: Seeking inputs from prospective demo sites 1. Preparing cost to manufacture full scale turbomachine

2. Seeking a partner for the thermal storage, either molten salt or Brayton particle system

ARO Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1

Manufacturing processes

Fabrication

Test program

2022 2023

Contact Jim Kesseli at Kesseli@BraytonEnergy.com