Comparison between s-CO2 and other supercritical working Fluids (s-Ethane, s-SF6, s-Xe, s-CH4, s-N2) in Line-Focusing Solar Power Plants with supercritical Brayton power cycles

Thermosolar power plants with linear solar collectors and Rankine or Brayton power cycles are maturing as a competitive solution for reducing CO2 emissions in power plants as an alternative to traditional fossil and nuclear fuels. In this context, nowadays a great effort is being invested in supercritical Carbon Dioxide Brayton (s-CO2) power cycles for optimizing the line-focusing solar plants performance and reducing the cost of renewable energy. However, there are other working fluids with similar properties as s-CO2 near critical point. This researching study was focused on assessing the solar plants performance with alternative supercritical working fluids in the Balance Of Plant (BOP): Ethane, Sulfur Hexafluoride, Xenon, Methane and Nitrogen, see [1, 2, 3]. The integration between linear solar collectors (Parabolic or Fresnel), Direct Moten Salt (MS) as Heat Transfer Fluids (HTF) and a Simple Brayton cycle with Recuperation and ReHeating were studied in this paper. Main innovation in this researching study is the Brayton power cycle parameters optimization at Design-Point via the Subplex algorithm as proposed in John Dyreby Thesis [4]. After obtaining the optimum reheating pressure, compressor inlet pressure, recompression fraction, and other optimized variables, the solar power plants performances were simulated and detail designed with Thermoflow software [5], providing a first approach about the Solar Fields (SF) effective areas and investment costs. As main conclusion, we deducted the importance of heat exchangers conductance (UA) for increasing the Brayton power plants efficiency and reducing the SF effective area and investment cost. The pinch point at recuperators exit is the main constrain for increasing the UA in s-CO2 cycles. This limitation is overcome with the other working fluids proposed in this study providing higher plant efficiency but requiring higher UA in the recuperators. In future studies the heat exchangers detailed design constitute a great challenge for increasing the UA and optimizing these equipments cost. The material corrosion and equipments dimensions and cost is another key issue discussed for selecting the optimum energy transfer fluid in Brayton power cycles

Hibridación biomasa-termosolar con batería de CARNOT para ciclos BRAYTON de s-CO2

CIES2020 - XVII Congresso Ibérico e XIII Congresso Ibero-americano de Energia SolarRESUMEN: Las baterías de Carnot son tecnología de vanguardia basadas en el almacenamiento de energía térmica y la gestionabilidad de la generación de electricidad. El presente estudio analiza y optimiza una central híbrida biomasa-solar térmica de torre central acoplada a un ciclo Brayton de dióxido de carbono en estado supercrítico (s-CO2) mediante almacenamiento térmico de sales fundidas, configurando una batería Carnot. Se ha realizado la optimización térmica y económica de los principales parámetros del ciclo de potencia, almacenamiento térmico, biomasa y planta termosolar para obtener el Payback Period mínimo disponible actual. La planta óptima presenta un Payback Period de 8.08 años con una capacidad de almacenamiento de 14 horas aplicando el escenario de ingresos relativo a la Ley Española.ABSTRACT: Carnot Batteries are state-of-the-art technology based on thermal energy storage and dispatchable electricity generation. The present study analyzes and optimizes a hybrid biomass-solar thermal central tower power plant coupled to a carbon dioxide Brayton cycle at supercritical state (s- CO2) through a molten salt thermal storage, configuring a Carnot battery. A thermal and economic optimization was carried out for the power cycle, thermal storage, and biomass and solar thermal power plant main parameters to obtain the current available minimum Payback Period. The optimum plant presents a Payback Period of 8.08 years with a storage capacity of 14 hours applying the Spanish Law revenue scenario.info:eu-repo/semantics/publishedVersio

Sandy coastlines under threat of erosion

Sandy beaches occupy more than one-third of the global coastline(1) and have high socioeconomic value related to recreation, tourism and ecosystem services(2). Beaches are the interface between land and ocean, providing coastal protection from marine storms and cyclones(3). However the presence of sandy beaches cannot be taken for granted, as they are under constant change, driven by meteorological(4,5), geological(6) and anthropogenic factors(1,7). A substantial proportion of the world's sandy coastline is already eroding(1,7), a situation that could be exacerbated by climate change(8,9). Here, we show that ambient trends in shoreline dynamics, combined with coastal recession driven by sea level rise, could result in the near extinction of almost half of the world's sandy beaches by the end of the century. Moderate GHG emission mitigation could prevent 40% of shoreline retreat. Projected shoreline dynamics are dominated by sea level rise for the majority of sandy beaches, but in certain regions the erosive trend is counteracted by accretive ambient shoreline changes; for example, in the Amazon, East and Southeast Asia and the north tropical Pacific. A substantial proportion of the threatened sandy shorelines are in densely populated areas, underlining the need for the design and implementation of effective adaptive measures. Erosion is a major problem facing sandy beaches that will probably worsen with climate change and sea-level rise. Half the world's beaches, many of which are in densely populated areas, could disappear by the end of the century under current trends; mitigation could lessen retreat by 40%.info:eu-repo/semantics/publishedVersio

Integration between direct steam generation in linear solar collectors and supercritical carbon dioxide Brayton power cycles

Direct Steam Generation in Parabolic Troughs or Linear Fresnel solar collectors is a technology under development since beginning of nineties (1990's) for replacing thermal oils and molten salts as heat transfer fluids in concentrated solar power plants, avoiding environmental impacts. In parallel to the direct steam generation technology development, supercritical Carbon Dioxide Brayton power cycles are maturing as an alternative to traditional Rankine cycles for increasing net plant efficiency and reducing balance of plant equipments dimensions and cots. For gaining synergies between these two innovative technologies, in this paper, Direct Steam Generation and Brayton power cycles are integrated in line-focusing solar power plants. Four configurations are studied: Configuration 1 consists on installing a condenser between solar field and power cycle; condensing the heat transfer fluid (steam water) with the balance of plant working fluid (carbon dioxide). The condenser would be a shell & tubes type. Along tubes carbon dioxide flows, and steam water condensates at shell-side. Main advantage of the condenser equipment is the high heat transfer coefficient at water condensing-side, reducing condenser dimension and weight. The main disadvantage of this configuration is the high operating pressure required in solar field for condensing steam into liquid water. This pressure should be between 150 bar and 175 bar for obtaining 400°C at turbine inlet. In the Configuration 2, the superheated steam delivered by solar collectors transfers the heat energy in a primary heat exchanger to the balance of plant working fluid. In this configuration the steam not condensate into liquid water, and only reduces the temperature from 550°C–560°C to 420°C. The steam pressure drops in solar field along receivers, headers and heat exchangers are compensated by means of steam compressors. This second solution is compatible with higher turbine inlet temperatures, up to 550°C. The keystones of this second configuration are the steam conditions at compressor inlet, pressure ∼175 bars and temperature ∼420°C, for minimizing steam compressor electrical consumption. The third design solution (Configuration 3) includes a solar field with direct steam generation in solar collectors with boiling recirculation mode, but the balance of plant is integrated by two Brayton power cycles in cascade. The first power cycle operating at 550 °C turbine inlet, and the second cycle at 410°C turbine inlet. Main advantage is the integration between a validated direct steam generation technology (recirculation boiling mode) with the Brayton power cycles avoiding steam compressors, a technology not yet commercially available, and main drawback of this design is the increasing number of balance of plant equipments. The Configuration 4 is very similar to the Configuration 2, with the same direct steam generation solar field with superheated steam without condensing, and a single reheating stage solar field with molten salt as heat transfer fluid. The Configuration 1 provides similar efficiency and net power output, for similar solar field effective aperture area, as obtained with molten salt solar collectors with supercritical carbon dioxide power cycle (recompression with main compression intercooling cycle provides 36.6% net efficiency, for a maximum 400°C turbine inlet). The second design solution (Configuration 2) net efficiency is not very much impacted for steam compressor electrical consumption recompression cycle net efficiency is 43.6% with steam solar field, versus 45.16% with molten salt solar field, in both cases with 550°C turbine inlet. The Configuration 3 performance is ∼39.7% with two cascade Brayton power cycles with recompression and main compression intercooling. Finally, the Configuration 4 optimum plant performance is obtained for the recompression cycle with a net efficiency ∼45.77%, and is constrained by the molten salt drawbacks (material corrosion, material cost, environmental impact, etc)

Supercritical CO2mixtures for Brayton power cycles complex configurations with concentrating solar power

An evaluation of the impact of using supercritical carbon dioxide mixtures (s-CO2/C2H6, s-CO2/CH4, s-CO2/Kr, and s-CO2/SF6) as a working fluid is made here for Brayton s-CO2 power cycles. The considered complex configurations include recompression with two reheating (RCC-2RH), recompression with three reheating (RCC-3RH), recompression with main compressor intercooling and two reheating (RCMCI-2RH), and recompression with main compressor intercooling and three reheating (RCMCI-3RH), which were coupled to a linear-focus solar system with Solar Salt (60% NaNO3/40% KNO3) as the heat transfer fluid (HTF). The design parameters evaluated the solar plant performance at the design point, the aperture area of the solar field, and variations in costs regarding the plant's total conductance (UAtotal). The methodology used to calculate the performance established the total conductance values of the heat recuperator (UAtotal) to between 5 and 25 MW/K. The main conclusion is that the cycle efficiency has a considerable improvement compared with that obtained using pure s-CO2. The s-CO2/Kr mixture with a molar fraction ratio of 30/70 increases the cycle efficiency between 7-11% relative to pure s-CO2 and as a function of the UAtotal. The s-CO2/CH4 mixture with a molar fraction of 45/55 increases between 3-7%, and the s-CO2/C2H6 and s-CO2/SF6 mixtures only increase between 1- 2%. For the solar field unitary costs, the s-CO2/Kr mixture has the lowest cost at $29-34 million USD, which depends on the solar field aperture area and the UAtotal for the RCC-2RH and RCMCI-2RH configurations. Finally, the results demonstrate that variations in the working fluid properties play a significant role due to the positive impact on the increased thermal efficiency of the s-CO2 Brayton cycle when using the RCC and RCMCI configurations

Biomass-solar thermal hybridization using Carnot batteries for s-CO2Brayton cycles

Carnot batteries represent state-of-the-art technology in the fields of thermal energy storage and dispatchable electricity generation. The thermal energy usually comes from solar thermal power plants. The present study analyzes and optimizes a hybrid biomass-solar thermal central tower power plant coupled with a carbon dioxide cycle in a supercritical state and thermal energy storage, known as a Carnot battery system. Thermal and economic optimization were carried out for the power cycle, thermal storage, biomass, and the power plant's main parameters to obtain the current available minimum levelized cost of energy, LCOE

Supercritical CO2 Binary Mixtures for Recompression Brayton s-CO2 Power Cycles Coupled to Solar Thermal Energy Plants

In this work, an evaluation and quantification of the impact of using mixtures based on supercritical carbon dioxide “s-CO2” (s-CO2/COS, s-CO2/H2S, s-CO2/NH3, s-CO2/SO2) are made as a working fluid in simple and complex recompression Brayton s-CO2 power cycle configurations that have pressure drops in their components. These cycles are coupled with a solar thermal plant with parabolic-trough collector (PTC) technology. The methodology used in the calculation performance is to establish values of the heat recuperator total conductance (UAtotal) between 5 and 25 MW/K. The main conclusion of this work is that the cycle’s efficiency has improved due to using s-CO2 mixtures as working fluid; this is significant compared to the results obtained using the standard fluid (pure s-CO2). Furthermore, a techno-economic analysis is carried out that compares each configuration’s costs using pure s-CO2 and a mixture of s-CO2/COS with a molar fraction (70/30), respectively, as working fluid where relevant results are obtained. These results show that the best configuration in terms of thermal efficiency and cost is the RCC-RH for pure sCO2 with values of 41.25% and 2811 $/kWe, while for the mixture sCO2/COS, the RCC-2RH configuration with values of 45.05$/kWe is optimal. Using the mixture costs 6.75% less than if it is used the standard fluid (s-CO2)