sCO2 Recuperators Application Notes and Testing Issues Echogen Power Systems Timothy J. Held, CTO sCO2 Power Cycles . Competitor to steam cycles . Offer advantages in efficiency, footprint, simplicity and water- free operation . Flexible power cycle . Nuclear, CSP, primary power applications . Waste heat recovery / combined cycle applications . Echogen’s strategy: Start with WHR/CC for near-term market availability, branch to other areas from there Echogen Power Systems 2 Echogen Background 2007 Echogen founded 2011 Partnership with Dresser-Rand (now Siemens) for oil & gas market; development of EPS100 7.5 MW engine begins 2013 Partnership with GE Marine; development of Akron, OH EPS30 1.35 MW engine begins 2014 EPS100 completes factory testing Echogen Power Systems is the 2016 EPS30 testing commences with high-speed industry leader in development alternator subsystem test of supercritical CO heat recovery 2 2018 Started energy storage project with ARPA-E systems. DAYS funding, developing 10MW primary Founded in 2007, EPS has power project progressed from small multi-kW 2019 First EPS100 commercial announcement demonstration units to the recent multi-MW heat recovery package, the EPS100. Echogen Power Systems Echogen EPS100 EPS100 process skid EPS100 power skid • 7.5 MWe net power output • Gas turbine combined cycle application (22 MWe target application) • Successfully completed factory testing • First commercial sale to TransCanada (through Siemens licensee) Echogen Power Systems Foreshadowing… . Recuperators have a significant impact on sCO2 power cycle performance and cost . Understanding the sCO2 application… counterflow, high effectiveness, Cr=1 . Materials issues: Strength at temperature, creep-rupture life, cyclic operation impacts on life, CO2 corrosion compatibility, non-CO2 corrosion compatibility . Importance of developing cost models (and our preferred form) . Testing of high-temperature recuperators Echogen Power Systems 5 100 Recompression Cycle recuperators 100 Recycled Heat source PHX 10 Low-temp recuperator High-temp recuperator Primary heat exchanger HTT HTR 10 HTC Cooler Low-temp High-temp LTR recuperator recuperator 1 100 300 500 700 900 1100 1300 LTC Recuperator inlet temperature ~ 150°C lower than turbine inlet temperature QRX Turbine inlet temperature limited by primary heat exchanger materials to ~700-730°C 1 Echogen Power Systems 6 100 300 500 700 900 1100 1300 Waste Heat Recovery architecture example PHX2 PHX1 100 Once-through Heat source Primary heat exchanger Recuperator Turbine 10 Recuperator Recuperator Pressure(MPa) Compr 1 100 200 300 400 500 600 700 800 900 1000 Enthalpy (kJ/kg) ACC WHR applications tend to be lower temperature (< 550°C) due to nature of heat sources Cycle design emphasizes wide temperature range for heat extraction Echogen Power Systems 7 Glide-matching Recompression cycle . Cycle design always trends towards glide-matched heat exchangers (Cr=1) to minimize exergy destruction / maximize cycle efficiency . Drives design flow mismatch in low- temperature recuperator 3 P=8.5 MPa 2.5 P=30 MPa 2 1.5 [kJ/(kg·K)] p c 1 0.5 0 0 100 200 300 400 500 600 700 800 Temperature (°C) Echogen Power Systems 8 Allam cycle recuperator Fuel + O2 100 Burner Turbine Recuperator Combustor H2O Recuperator Cooler CO2 10 Compr Pump Pressure(MPa) Intercooler Recuperator Compr 1 0 250 500 750 1000 1250 1500 1750 2000 Enthalpy (kJ/kg) Intercooler Turbine inlet temperature limited by recuperator inlet temp (750°C today) Echogen Power Systems 9 Extra challenges with the Allam cycle • Composition is more complex than pure CO2 • Water ~ 7% (molar) • Inert carryover from gas (primarily N2) • Trace materials, like sulfur, minor issue with natural gas, huge issue with coal-derived syngas • Composition changes rapidly between oxidizing and reducing over a very narrow equivalence ratio range • Not sure whether NetPower is biasing their control system on the rich or lean side Echogen Power Systems 10 Balancing cost and performance . Techno-Economic Optimization major part of Echogen’s focus . Requires coupled models of component performance and cost . Mostly means heat exchangers! . Turbomachinery efficiency is critical, but largely insensitive to investment cost Echogen Power Systems 11 Cycle implications on recuperator design . Design pressure is toward high effectiveness with Cr → 1.0 푈퐴 휀 휀 = or 푈퐴 = 퐶푚푛 퐶푚푖푛+푈퐴 1−휀 . Cycle performance is strongly influenced by recuperator performance . System cost is strongly influenced by heat exchanger cost . Recuperators typically 10-30% of equipment cost . Other heat exchangers comparable Echogen Power Systems 12 Representing heat exchanger cost . Until someone tells us otherwise, we represent heat exchanger cost as: Design study on WHR cycle Baseline: RC effectiveness = 95% 퐶 = 푓 푈퐴, ∆푝ℎ, ∆푝푐 ΔPh= ΔPl=0.1 MPa or in a slightly more detailed form UA-10% 퐶 = 퐴 + 퐵 푈퐴α · 푔 ∆푝 , ∆푝 ℎ 푐 UA+10% ΔPh x 2 Baseline High dP ΔPh / 2 Low dP ΔPl x 2 Cost ΔPl / 2 -1.0% -0.5% 0.0% 0.5% 1.0% 1.5% Impact on output power UA Echogen Power Systems 13 Other design issues . Don’t go nuts on passage size! . PCHEs have diameters ~ 1-3 mm . Less than that and we will have a serious plugging / filtration issue. CO2 systems are not that clean . Some applications are by nature cyclic (e.g. CSP) . Thought needs to be given to managing / designing / analyzing impact of thermal ramp rates . Less concerned about the core. Headers and connections usually the weak points . Non-counterflow features need to be evaluated for impact on limiting effectiveness (e.g. cross-flow in entry/exit regions) Echogen Power Systems 14 Testing high-temperature recuperators . Echogen is providing testing services for multiple HITEMMP awardees – open to others . Facility capable of 700°C, 20 MPa, 0.28 kg/s CO2 flow rate (demonstrated) . Inconel 740H heater . By moving heater to low-pressure side of system, can reach 800°C at 8 MPa Echogen Power Systems 15 Test facility for 800°C / 8 MPa Heater Heat input ~ 16 kW 674°C Designed for 60 kW 8.1 MPa Fixed 800°C orifice 8.0 MPa 680°C 24.5 MPa Recuperator design: 50 kWth 800°C / 8 MPa Test recuperator 300°C / 25 MPa Flow rate ε=80% 0.104 kg/s 300°C 408°C 25.1 MPa 7.8 MPa Recuperator ACC53°C (existing) 7.75 MPa 25°C 49°C 7.7 MPa 25.2 MPa Pump Echogen Power Systems 16 1100°C plan . No materials code-qualified to full pressure at > 800°C . Will need to encase final-stage heater and unit under test inside insulated pressure vessel Echogen Power Systems 17 1100°C / 8 MPa test conditions Heater 676°C . Lower effectiveness Heat input ~ 56 kW 8.1 MPa Designed for > 100 kW Fixed target increases Orifice 1100°C Recuperator design: heater duty 8.0 MPa 682°C 50 kWth 24.6 MPa requirements and 1100°C / 8 MPa 726°C 300°C / 25 MPa Test recuperator 7.8 MPa flow rate ε=50% . Dashed line = internal Test flow rate 300°C 0.104 kg/s 25.1 MPa to pressure vessel 324°C 7.8 MPa Low-T 53°C recuperator 7.75 MPa FCV 25°C 49°C 7.7 MPa Pump 25.2 MPa Echogen Power Systems 18 Other test issues . Test planning . Performance testing – steady-state evaluation of UA by inlet/outlet temperatures and pressures, CO2 flow rate at multiple operating conditions . Cyclic testing – Define min/max, number of cycles, duration . Practical issues . Fittings . Instrumentation Echogen Power Systems 19 How not to do fittings (and a potential better way) 1” fitting, 700°C, 25 MPa Inconel 740H Grayloc hubs Silver-plated Inconel 718 seal ring 347 clamp with HA230 studs/nuts $11.5K per connection 1” fitting Inconel 625 ~$1.5K Need to complete thermal and stress analysis at intended design conditions Preliminary scaling from room temperature design conditions to operating conditions favorable Echogen Power Systems 20 Instrumentation . External to heat exchanger – inlet/outlet pressures and temperatures, total flow rate . Pressure: Rosemount 3051 (±0.04% of span, ~ 0.1 bar) . Temperature: Type R special limit TC’s (±greater of 0.6°C or 0.1% of reading) . Flow: Micromotion CMF Coriolis mass flow meter (±0.25% of reading) . Can accommodate internal instrumentation, will be provider’s responsibility to provide Echogen Power Systems 21 Summary . Recuperators (and heat exchangers in general) are critical components of sCO2 power cycles . High temperatures mostly driven by Allam cycle today, but other applications may follow once limitations are moved . Cost vs. performance trades need good cost models . Test facility available for 800°C testing . 1100°C facility design and execution in very preliminary stages Echogen Power Systems 22 Thank you! Echogen Power Systems 23.