Hoffschmidt, Bernhard

Institute of Transport Research:Publications

Receivers for Solar Tower Systems   Prof. Dr. Bernhard Hoffschmidt  June 25-27, 2014 Font Romeu, France CSP Characteristics  Solar tower systems:  ⇒ higher concentration ⇒ higher process temperature ⇒ higher solar-to-electric efficiency ⇒ reduced collector area ⇒ lower cost (Tabsorber = Tprocess) [K] ηmax Flat Plate Collector Parabolic Trough Solar Tower Parabolic Dish ηmax= ηth,Carnot* ηabsorber C ∼ 𝟖𝟖𝟖𝟖 C ∼ 𝟐𝟐𝟖𝟖𝟖𝟖𝟖𝟖 C ∼ 𝟓𝟓𝟖𝟖𝟖𝟖 C = 1 Solar Tower Technology: • ascending renewable power technology • high conversion efficiency • added value: • high capacity factor (storage) • firm capacity • significant cost reductions expected • technological development • improved manufacturing • increased maturity (financing) • high local content achievable • also suitable for HT process heat Introduction: Solar Tower Technology Classification by  Heat Transfer Medium: • molten salt • water/steam • Air open/closed • liquid metals • solid particles • other gases   Receiver Classification Classification by maturity  State of the art technology: • molten salt • water/steam  First of its kind technology • Open volumetric air receiver  Technology in pilot phase • Pressurized Air Receivers  Technology under development: • liquid metals • solid particles   Receiver/Heat Transfer Medium is relevant for selection of storage system Storage type: • sensible • latent • (thermochemical)  Storage concepts: • direct: receiver HTM is also used as storage medium • molten salt, particles, (water) • indirect: a different storage medium is used • air/gases, liquid metals Combination of Receiver and Storage • „solar salt“: 60% NaNO3 / 40% KNO3  • low salt cost allow use as heat transfer and storage medium • salt temperatures up to 565°C for superheated steam generation • good heat transfer characteristics • critical: salt freezing below 220°C • heat tracing required, draining of receiver and other system components during night • salt degradation at temperatures higher than 600°C • corrosion issues on metallic components (depends on salt quality) www.DLRde  •  Chart 6 State of the Art: Molten Salt Receivers Molten Salt Systems Molten Salt Systems - GEMASOLAR: • 20MW el. • External tube receiver • operation since 2011 • 290°C – 565°C • 120 MWth @DP • etarec,DP ~88%  www.DLRde  •  Chart 8 - Crescent Dunes (SolarReserve) • Molten salt  • 110MWel • External tube receiver • Receiver outlet temperature: 565°C Molten Salt Systems Strategies improving Molten Salt Systems - Higher temperature molten salt: • Higher steam parameters • Smaller heat exchanger • Smaller storage • Less critical operation (over temperature receiver)  - Higher receiver efficiency by: • Reduction of thermal losses  • Cavity arrangement • Face down (can design) • Using standard vacuum absorber for first temperature step • Higher absorption of solar radiation ((selective) coatings)  - Optimization of operation  • Real time aim point strategy for homogenous receiver temperature (life time!) • Solar pre-heating of receiver  • Faster start-up  • Avoiding draining of receiver during clouds  - PS10/PS20  • direct irradiated absorber tubes (250°C@40Bar) • 11/20 MWel • cavity receiver State of the Art: Saturated Steam PS10 PS20 - Brightsource: • Ivanpah 377MW • direct Steam (550°C) • external tube receiver www.DLRde  •  Chart 12 Superheated Steam Systems - Higher steam temperatures and pressures for higher efficiency at the power block  - Higher loads for absorber tubes (pressure and temperature) - Three zones in receiver with different heat transfer coefficients: • pre-heating • evaporation • superheating  Strategies improving Superheated Steam Volumetric Receiver Principle First-of-its-Kind: Open Volumetric Air Receivers drastic increase of heat  transfer surface area First-of-its-Kind: Open Volumetric Air Receivers 140mm 140mm 2mm 0.02 m² Absorber 0.57 m² Submodul 5.7 m² Solair Receiver (PSA) 22.7m² Receiver (Jülich) Power Plant Jülich (DLR)  process parameters: • pressure: ambient • return air: 120°C • receiver air outlet: 680°C  material load parameters: • max. temp.:  1100°C (front) • max. load:  1000kW/m² • temp. gradient:  ~100K/cm • average mass flow: 0.55 kg/m²-s  dynamic operation: • air outlet temp. of single cup: max. temp. change ≈3.3K/sec First-of-its-Kind: Open Volumetric Air Receivers 00.250.50.7511.250 50 100 150 200 250 300 350 400 450 500cell density (cpsi)relative temp. diff. (wall-fluid) status quochannel width d=2.0mmd=1.5mmd=1.0mmd=1.25mmwall thickness w=0.8mmw=0.6mmw=0.4mmw=0.2mm Improve of Absorber • Higher Porosity • Higher heat transfer  surface per volume  • Stable mass flow • Extension of durability  Improve of System: • Less auxiliary energy • Decrease of pressure drop • Online aiming point strategy • Cavity receiver • Increase of air return ratio • Operator assistence system   First-of-its-Kind: Open Volumetric Air Receivers Strategies for Improving Technology in Pilot-Phase: Pressurized Air Receivers • pre-heating of the compressed air of a Brighton cycle  • currently two power levels are under development: large systems: • 5-150 MW el.  • combined with steam cycle  small systems: • 0.1-5 MW el. (recuperated turbine) • combined with cooling/heating (desalination)  volumetric receivers   tube receivers   ceramic plate receiver  Ceramic receiver Metallic tube receiver • air outlet temperature: 800-1000°C • pressure:   4-16 Barabs. • pressure drop:  100-400mBar • materials:  high temperature alloy, ceramics, fused silica Technology in Pilot-Phase: Receiver Development  • EU- project under leadership of ABENGOA SOLAR NT • Test of a 3MWth metallic tubular receiver • Inlet temperature: 330°C • Outlet temperature: 800°C • Pressure: 10Barabs • Since summer 2012: more then 700h of solar operation • Design values reached and simulation models validated • Next step: Integration of Volumetric Pressurized receiver (1MWth /1000°C)     Technology in Pilot-Phase: First Pilot (SOLUGAS) • high efficiency (>80%) caused by… • „volumetric“ absorption of radiation • relatively low absorber temperatures • low thermal reradiating • low pressure drop (< 30mbar) • high possible outlet temperatures  (>1000°C) • proven technology   Technology in Pilot-Phase: Receiver Development Closed Volumetric Receiver Folie 22 • using commercial FEM/CFD codes for the thermal and mechanical layout • using the raytracing code SPRAY  • thermal field can be used for mechanical simulation (strain, stresses) • parametric approach allows easy variations (geometry, load cases) and optimization Technology in Pilot-Phase: Receiver Development Tube Receiver and Design methods Folie 23 • mass flow is distributed to several parallel absorber tubes by a tubular header • absorber tubes should have small diameters for best heat transfer. • the thermal strain of each absorber tube has to be compensated. • tubular collector collects the heated fluid. • design of receiver has to fulfil thermodynamic, hydraulic and economic needs. Folie 23 Different Panel Arrangements Technology in Pilot-Phase: Receiver Development Ceramic Plate Receiver Material benefits of SiC ceramic • High thermal conductivity  • Very low thermal expansion coefficient • Temperature stability up to 1500°C (in air)   • Gas-tight  • High strength • “Black without coating” • Design of inner structure   Technology in Pilot-Phase: Receiver Development Ceramic Plate Receiver Technology under development: Liquid Metal Receivers  large temperature range high heat transfer coefficients  temperature [°C] temperature [°C] heat transfer coefficient [kW/m²K] NaK K Na Pb-Bi Pb Sn Receiver test in the USA: Sandia CRTF - 750 litres, 70 hours  Plant test in Spain: PSA - 70,000 litres, 5 years Folie 26 First receivers tested in the 80‘s with sodium as HTF achieved high efficiencies After a sodium  fire in 1986 in Almeria, investigation of liquid metals in solar power systems was stopped! Technology under development: Liquid Metal Receivers Experiences in solar power systems  Folie 27 Conventional technologies • Steam turbine (η ≈ 45%) • Gas turbine (η ≈ 40%) • Gas- and steam turbine (η ≈ 55%)  Innovative technologies • Thermo-electrical Generator (TEG: Seeback-Effect) (η ≈ 5%) • Thermionic Power Generator (Edison-Richard-Effect) (η < 5%) • Alkali-Metal Thermal Electric Converter (AMTEC), Electrochemical device for direct conversion of heat to electricity (η ≈ 15...40%) • Liquid Metal Magneto-hydrodynamic Generator (LM MHD), energy conversion: heat  kinetic energy  electricity (η ≈ 20...60%)  Technology under development: Liquid Metal Receivers Ongoing Research  Folie 28 Technology under development: Liquid Metal Receivers Conceptual study   direct absorbing of solar radiation at small ceramic particles  ceramic particles as heat transfer and storage medium  high temperature capability (>900°C) for power generation and process heat  no limits in flux densities (no wall between heat absorption and heat transfer medium)      Technology under development: Direct Absorbing Particle Receiver  • optically dense particle film near the inner surface of a cylinder/box • gravitation forces give falling speed and duration of particle in solar radiation • re- circulating of the particles necessary to obtain design outlet temperature • concentrated solar radiation through the opening at the bottom • high level models developed (coupling of CFD, raytracing and particle movement)         Technology under development: Direct Absorbing Particle Receiver: 1. Approach – Falling Particle Curtain  • optically dense moving particle film on the inner surface of a rotating cylinder • gravitation and centrifugal forces  particle retention time can be controlled by rotation speed • Prototype (10kW) successfully tested up to 900°C      Technology under development: Direct Absorbing Particle Receiver: 2. Approach – Centrifugal Particle Receiver R&D Outlook on Technologies (plus Trough Tech.)  DLR.de  •  Folie 32 > Vortrag > Autor  •  Dokumentname > Datum - State of the art technologies • Trough with thermo oil • Tower with steam • Tower with salt  • Fresnel with steam  - First-of-its-Kind technologies • DSG in trough • Open vol. Receiver • Industrial process heat  - Technology in pilot phase • Salt in Trough/Fresnel • GT + Tower  - Technology under development • Particle (Tower) • Liquid metal (Tower) • Development of new HTF (Tower/Trough/Fresnel) • Solar Fuels   Field of R&D  Methods on qualification, operation optimization, degradation, side evaluation    Optimization of components Adaptation of conventional components for solar applications   Pilot plants and Development      Prototype testing (lab scale) / Scale-up / Modeling / materials and properties / system evaluation / basic research on effects, kinetics, conversion rates …. 33 Thank you for your attention! 

Receivers for Solar Tower Systems

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Institute of Transport Research:Publications