Integrated Solar Combined Cycle Using Particles as Heat Transfer Fluid and Thermal Energy Storage Medium for Flexible Electricity Dispatch M. A. Reyes-Belmonte, M. Romero & J. González-Aguilar
Objectives § Solar plant concept being investigated under NEXT-CSP project § Dedicated modelling of Integrated Solar Combined Cycle ( ISCC ) pure-solar plant that uses particles as heat transfer fluid and storage medium § Plant components optimization (solar field, receiver, Brayton topping cycle, Rankine bottoming cycle, particles-based heat exchangers network) to maximize ISCC efficiency (design-point conditions) § Multi-tower solar plant arrangement for commercial scaling-up (150 MW e ) § Dispatch strategies definition to maximize electricity power output (annual performance) 25 th SolarPACES Conference, Daegu, South Korea, October 2, 2019 3 / 17
Plant Layout Description § Solar particles receiver was designed to reach 825 ºC § Double-reheated Brayton & reheated Rankine cycles to maximize ISCC efficiency § Dedicated design of particles-based heat exchanger network connecting solar loop & power cycle Particles T DPS = 825 ºC receiver Particles HOT Particles COLD tank tank T in = 800 ºC Heliostat field DPS-air DPS-air Compressor DPS-air HX Turbine reheater reheater Heat Recovery T in = 575 ºC m live reheater MP - LP Heat Recovery TURBINE Steam Generator m exh HP T in = 585 ºC m reh TURBINE HP LP Condenser pump pump deareator 25 th SolarPACES Conference, Daegu, South Korea, October 2, 2019 4 / 17
Boundary conditions ( design point ) Ouarzazate, Morocco Solar plant location 30.9 ° N, 6.93 ° W 900 W/m 2 @ noon 21 st March Design DNI 49 m 2 (Stellio heliostat) Heliostats area 2,000 kW/m 2 Aperture incident flux Thermal power onto aperture 55 MW Particles maximum temperature (at receiver 825 ºC outlet) Preferred commercial size (electrical power 150 MW e output) Multi-tower (& solar fields) configuration is required to achieve design- point dispatch power (150 MW e – pure solar) 25 th SolarPACES Conference, Daegu, South Korea, October 2, 2019 5 / 17
Boundary conditions ( annual performance ) § Annual DNI (15-min based) from Ourzazate § Typical electric grid demand curve from Mediterranean area DNI (W/m 2 ) W net (MW) 25 th SolarPACES Conference, Daegu, South Korea, October 2, 2019 6 / 17
Plant Layout Description § Multiple solar-fields & towers feeding single Combined Cycle Power Block § Particles transportation system between multi-solar fields units & common particles TES & heat exchangers network Unit 4 Unit 5 Unit 6 25 th SolarPACES Conference, Daegu, South Korea, October 2, 2019 7 / 17
Design-point optimization Solar plant & receiver Solar Field Solar Receiver Power incident on field 75.5 MW Power onto aperture 55 MW Absorbed thermal Number of heliostats 1731 44 MW power Heliostats area 49 m 2 Thermal efficiency 79.4 % noon 21 st March Design day Tubes height 7 m Design DNI 900 W/m 2 Number of tubes 240 Particles inlet Tower optical height 110 m 606 ºC temperature Aperture tilt angle 30º Particles mass flow 165 kg/s Aperture incident flux 2,000 kW/m 2 Receiver average flux 500 kW/m 2 Power cycle Topping cycle Bottoming cycle HP inlet pressure 14.3 bar HP inlet pressure 160 bar MP inlet pressure 6.1 bar MP inlet pressure 20 bar LP inlet pressure 2.5 bar HP inlet temperature 585 ºC HP – MP – LP inlet 800 ºC MP inlet temperature 575 ºC temperature 25 th SolarPACES Conference, Daegu, South Korea, October 2, 2019 8 / 17
Particle-based heat exchanger network Very regenerative configuration (double turbine reheating of the Brayton cycle) leading to reduced temperature difference across heat exchangers à high particles mass flow From particles Air (Brayton cycle) receiver 800 ° C Hot particles Cold particles Main heat 600 ° C addition Hot First Second particles reheating reheating Cold in air in 600 ° C 600 ° C 600 ° C 800 ° C 800 ° C 800 ° C 407 ° C IP DPS-HX HP DPS-HX1 HP DPS-HX2 LP DPS-HX Cold Hot C T1 T2 T3 particles out particles in m 2 m 3 m 1 600 ° C from ambient m total = m 1 + m 2 + m 3 to HRSG To particles (Rankine cycle) receiver Cold TANK 25 th SolarPACES Conference, Daegu, South Korea, October 2, 2019 9 / 17
Particles-based heat exchanger network Very regenerative configuration also leading to high temperature of “cold” particles sent back to the tanks and receiver à higher particles receiver area and storage tanks capacity Double reheating (higher pressure ratio) Temperature (C) 12 9 800 ºC 800 ºC 6 600 ºC 4 8 10 13 407 ºC T steam,live + ΔT 7 1 Specific entropy (J/kgK) Mass flow distribution: § m air (HP hot DPS-HX) = m air (IP DPS-HX) = m air (LP DPS-HX) = m air (HP cold DPS-HX) § m DPS (HP hot DPS-HX) ≈ m DPS (IP DPS-HX) ≈ m DPS (LP DPS-HX) ≈ 3 · m DPS (HP cold DPS-HX) 25 th SolarPACES Conference, Daegu, South Korea, October 2, 2019 10 / 17
Dispatch strategies (plant operation) Strategy A Constant power output (nominal power) from 17h – 22h 30 minutes ramp-up & ramp-down Strategy B Following grid demand during morning-peak (9h – 11h) and evening- peak (17h – 21h) Thermal energy surplus to be stored as hot particles (tanks sizing) 25 th SolarPACES Conference, Daegu, South Korea, October 2, 2019 11 / 17
Results Analysis: Daily Operation Thermal power reaching the solar field Thermal power reaching particles receiver Thermal power absorbed by particles Thermal power absorbed by particles September Electricity production 3 rd § Energy harvesting and electricity Strategy A production are decoupled. Power cycle runs taking thermal energy from storage tanks § Tanks sizing according to dispatch Grid demand strategy and electricity demand § Depending on DNI, grid demand and existing TES capacity, Strategy B dispatch electricity could not be enough to cover the demand Particles stored from previous day 25 th SolarPACES Conference, Daegu, South Korea, October 2, 2019 12 / 17
Results analysis: Annual performance Electricity annual production (MWe) § Winter months: not enough thermal power to dispatch 5 hours @ full load Turbine ramp-down Turbine ramp-up Strategy A Particles stored at tanks (tons) Maximum amount of particles stored during central months of the year and before power cycle Strategy A operation (before 17 h) 25 th SolarPACES Conference, Daegu, South Korea, October 2, 2019 13 / 17
Results analysis: Annual performance • Exceeding thermal power stored as hot particles by the end of the day (during those months when the solar resource is higher but the electricity demand is lower) Strategy B Strategy B 25 th SolarPACES Conference, Daegu, South Korea, October 2, 2019 14 / 17
Results analysis: Annual performance Strategy A Strategy B Surplus of thermal energy to be stored as hot particles (TES tanks oversized) Power cycle operation hours Ø Strategy A: operation hours depending on DNI evolution Ø Strategy B: operation hours depending on grid demand curve & DNI 25 th SolarPACES Conference, Daegu, South Korea, October 2, 2019 15 / 17
Conclusions § Pure-solar Integrated Solar Combined Cycle (ISCC) optimized at design-point conditions 2 dispatch strategies analyzed: § § Constant nominal power output (17h – 22h) Flexible dispatch power output to cover morning & evening peaks § Thermal storage sizing largely depends on dispatching scenario, so that a case- § by-case analysis (dispatching, resource, demand) is necessary Solar-to-electricity efficiency is not a good figure when similar times of full load § plant operation and turbine ramp up/shut off penalizes solar-to-electricity efficiency. More detailed analysis on operation modes based on dynamic modelling of § transients and economic analysis are absolutely needed to support power plant viability 25 th SolarPACES Conference, Daegu, South Korea, October 2, 2019 16 / 17
Integrated Solar Combined Cycle Using Particles as Heat Transfer Fluid and Thermal Energy Storage Medium for Flexible Electricity Dispatch THANKS FOR YOUR ATTENTION ! The research leading to these results has received funding from European Union’s Horizon 2020 research and innovation program under grant agreement No 727762, Next-CSP project. jose.gonzalez@imdea.org
Motivation v Novel heat transfer fluid based on Dense Particles Suspension ( DPS ) to be used at central solar receiver and for direct Thermal Energy Storage (TES) v Excellent thermophysical properties of DPS DPS HTF advantages ü High Temperature (> 650 ºC) ü Cheap and abundant ü No freezing risk ü High energy density ü High heat transfer coefficient (> 2,000 W/m 2 K) ü No hazardous CSP plant layout suitable to be coupled with several power blocks Plant layout proposal: A high-efficiency solar thermal power plant using a dense particle suspension as the heat transfer fluid, J. Spelling, A. Gallo, M. Romero, J. González-Aguilar. SolarPACES 2014
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