Comparison between SAM and Thermoflow for Linear Fresnel Solar Power Plants design

System Advisor Model is a software tool develped by National Renewable Laboratory (NREL), Department Of Energy, USA to design Solar Power Plants

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

Thermodynamic optimisation of supercritical CO2 Brayton power cycles coupled to Direct Steam Generation Line-Focusing solar fields

In this paper a new generation line-focusing solar plants coupled to a s-CO2 Brayton power cycles are studied. These innovative CSP will increase the plant energy efficiency, and subsequently optimizing the SF effective aperture area and SF investment cost for a fixed power output. Two SF configurations were assessed: the Configuration 1 with a condenser between the SF and the Balance Of Plant (BOP), for Turbine Inlet Temperatures (TIT) up to 400oC, and the Configuration 2, for higher TIT up to 550oC, with steam compressors in SF for pressure drop compensation. Both alternatives are interchangeable in the same CSP, and boosting with a backing boiler to warranty the plant performance. In relation to the BOP three configurations were studied the Recompression cycle (RC), the Partial Cooling with Recompression cycle (PCRC), and the Recompression with Main Compression Intercooling cycle (RCMCI), all these solutions without ReHeating. The methodology considered the thesis developed by Dyreby [1] as starting point, fixing the Brayton cycles recuperator conductance (UA), and optimizing the power cycles performance by means of the SUBPLEX [2] algorithm. The cycles optimal operating parameters were calculated with a “Windows” desktop application, called Supercritical_CSP (SCSP), calling the supercritical fluids properties database REFPROP, developed in C#, calling Fortran compiled dynamic linked libraries. The results obtained from the Brayton cycles optimizations were exported to Thermoflow [3] for SF simulation and design. The mathematical algorithms UOBYQA [4] and NEWOUA [5] were also integrated in the SCSP tool, for validating the SUBPLEX results. The HTF studied was Direct Steam Generation (DSG) in the SF, and the solar collectors simulated were PTC and LF. The plant net power output, the net efficiency, the SF effective aperture, were computed at DesignPoint. As main conclusion obtained it is confirmed minimum Pinch Point in heat exchangers is the main constrain, reaching a threshold in the net plant efficiency, when increasing the Low Temperatura Recuperator (LTR) and High Temperature Recuperator (HT) conductances UA. The shell-tubes heat exchanger types are the most suitable solution to couple the Balance Of Plant (BOP) and the SF. The target of future works will be aligned with the analysis of innovative linear solar collectors, as the Norwich Technologies company solution, for getting higher TIT as provided by Central Tower CSP. The s-CO2 BOP equipments detail design and detailed cost estimation are pending items under industrial development. Finally, the annual plant performance calculation, considering the variable ambient temperature and Direct Normal Irradiance (DNI), and the TES integration, are future researching works for calculating the Levelized Cost Of Energy (LCOE) in this new generation line-focusing solar power plants

Dual Loop Line-Focusing Solar Power Plants with Supercritical Brayton Power cycles

Most of the deployed commercial line-focusing solar power plants with Parabolic Troughs (PTC) or Linear Fresnel (LF) solar collectors and Rankine power cycles use a Single Loop Solar Field (SF), Configuration 1 illustrated in Fig. 2, with synthetic oil as Heat Transfer Fluid (HTF) [1, 2]. However, thermal oils maximum operating temperature should be below ~400ºC for assuring no oil degradation, hence limiting the power cycle gross efficiency up to ~38%. For overcoming this limitation Molten Salts (MS) as HTF in linear solar collectors (PTC and LF) were recently experimented in pilot facilities [3, 4]. Direct MS main drawbacks are the equipments and components material corrosion and the salts freezing temperature, requiring heat tracing to avoid any sald solidification, hence increasing the Solar Field (SF) capital investment cost and parasitic energy looses. Concentrated Solar Power plants (CSP) with Dual Loop SF are being studied since 2012 [5] for gaining the synergies between thermal oils and MS properties. In the Dual Loop SF the HTF in the primary loop is thermal oil (Dowtherm A) [6] for heating the Balance Of Plant (BOP) working fluid from ~300ºC up to ~400ºC, and a secondary loop with Solar Salt (60% NaNO3, 40% KNO3) as HTF, for boosting the working fluid temperature from ~400ºC up to 550ºC [7, 8, 9]. The CSP Dual Loop state of the art technology includes Rankine power cycles, the main innovation of this paper is the integration between Dual Loop SF and the supercritical Carbon Dioxide (s-CO2) Brayton power cycles [10], see Configurations 2 and 3 illustrated in Fig. 3a, Fig 3b. A secondary innovation studied in this paper is the integration between thermal oil HTF (Dowtherm A) in linear solar collectors, a widely validated and mature technology, with the s-CO2 Brayton power cycles. This technical solution is very cost competitive with carbon steel receiver pipes, low SF operating pressure, and no requiring any heat tracing. Two main conclusions are deducted from this researching study. Firstly we demonstrated the higher gross plant efficiency ~44.4%, with 550ºC Turbine Inlet Temperature (TIT), provided by the Dual Loop with the Simple recuperated s-CO2 Brayton cycle with reheating, in comparison with 41.8% obtained from the Dual Loop SF and subcritical water Rankine power cycle. And finally the second conclusion obtained is the selection of the most cost competitive plant configuration with a Single loop SF with Dowtherma A and a s-CO2 Brayton power cycle due to the receiver material low cost and no heat tracing for the thermal oil

New generation Line-Focusing Solar Power Plants with Molten Salts and Supercritical Carbon Dioxide Joule-Brayton Cycles

Nowadays there is no dominant technology for the concentrated solar power plants that means there is still a way to go. Within this context, new concepts for solar fields and power cycles are being studied. One of them is the proposed on this paper: the integration of line-focusing solar field, with parabolic trough or linear Fresnel solar collectors, with molten salts as heat transfer fluid and supercritical carbon dioxide Joule-Brayton power cycles. This concept works as a feasible design solution to increase efficiency and reduce final energy cost in solar electricity production. In this work, four Joule-Brayton cycles configurations were assessed and compared with the considered reference, a concentrated solar power plant with direct steam generation in the solar field and a Rankine power cycle. The studied Joule-Brayton cycles are: simple cycle, recompression cycle, partial cooling with recompression cycle and recompression with main compression intercooling cycle. The common operation conditions for all the configurations are that at design-point the high pressure turbine inlet temperature value is 550ºC, this limit was established considering maximum temperature allowed by selective coating material in linear receivers. Also is analyzed the hypothetical scenario of increasing the turbine inlet temperature to 650ºC, extrapolating the receivers heat losses regressions. The innovative configurations of solar field and supercritical carbon dioxide power cycles increase plant efficiency, for recompression cycle configuration, up to 46.84% (550ºC turbine inlet) and 50.85% (650ºC turbine inlet), and reduces required solar field effective aperture area and land area for a fixed plant power output. Proposed configurations, parabolic trough collector and linear Fresnel coupled with a Joule-Brayton cycle decreases the solar field required for the same net power. Relating to power block, the supercritical carbon dioxide higher density in comparison with water steam, reduces turbines and compressors dimensions, footprint and final cost, but is a technology nowadays under industrial development and final turbo machines cost could not be assessed in this study. Another important keystone in JouleBrayton cycle costs are the heavy duty heat exchangers required. Printed circuit heat exchangers are the most advisable solution proposed for supercritical carbon dioxide recuperators, mainly due to higher compactness and better heat transfer coefficient inside channels. However, in this paper it is demonstrated how common shell & tube heat exchangers, with AISI 347 (austenitic) stainless steels, are competitive and feasible solutions for the primary and reheating molten salts – carbon dioxide heat exchangers

Supercritical Steam power cycle for Line-Focus Solar Power Plants

The supercritical Rankine power cycle offers a net improvement in plant efficiency compared with a subcritical Rankine cycle. For fossil power plants the minimum supercritical steam turbine size is about 450MW. A recent study between Sandia National Laboratories and Siemens Energy, Inc., published on March 2013, confirmed the feasibility of adapting the Siemens turbine SST-900 for supercritical steam in concentrated solar power plants, with a live steam conditions 230-260 bar and output range between 140-200 MWe. In this context, this analysis is focused on integrating a line-focus solar field with a supercritical Rankine power cycle. For this purpose two heat transfer fluids were assessed: direct steam generation and molten salt Hitec XL. To isolate solar field from high pressure supercritical water power cycle, an intermediate heat exchanger was installed between linear solar collectors and balance of plant. Due to receiver selective coating temperature limitations, turbine inlet temperature was fixed 550ºC. The design-point conditions were 550ºC and 260 bar at turbine inlet, and 165 MWe Gross power output. Plant performance was assessed at design-point in the supercritical power plant (between 43-45% net plant efficiency depending on balance of plantconfiguration), and in the subcritical plant configuration (~40% net plant efficiency). Regarding the balance of plant configuration, direct reheating was adopted as the optimum solution to avoid any intermediate heat exchanger. One direct reheating stage between high pressure turbine and intermediate pressure turbine is the common practice; however, General Electric ultrasupercritical(350 bar) fossil power plants also considered doubled-reheat applications. In this study were analyzed heat balances with single-reheat, double-reheat and even three reheating stages. In all cases were adopted the proper reheating solar field configurations to limit solar collectors pressure drops. As main conclusion, it was confirmed net plant efficiency improvements in supercritical Rankine line-focus (parabolic or linear Fresnel) solar plant configurations are mainly due to the following two reasons: higher number of feed-water preheaters (up to seven)delivering hotter water at solar field inlet, and two or even three direct reheating stages (550ºC reheating temperature) in high or intermediate pressure turbines. However, the turbine manufacturer should confirm the equipment constrains regarding reheating stages and number of steam extractions to feed-water heaters

Viabilidad de Mezclas Supercríticas en Ciclos Brayton Acoplados a Plantas de Energía Solar Concentrada

In this work it is promoted to study the viability of the use of mixtures based on supercritical CO2 that can lead to thermal yields in Brayton cycles higher than those obtained with the standard fluid (pure s-CO2). The recommended settings to analyze are Recompression and Recompression with intercooling in the main compressor, which may include more than one superheat. These configurations are very transcendental because in terms of efficiency they are the ones with the highest values and, in addition, their total costs per net installed capacity are the lowest compared to other configurations.En este trabajo se promueve estudiar la viabilidad del uso de mezclas basadas en CO2 supercrítico que pueda conducir a rendimientos térmicos en los ciclos Brayton más altos que los obtenidos con el fluido estándar (s-CO2 puro). Las configuraciones que se recomienda analizar son las de Recompresión y Recompresión con enfriamiento intermedio en el compresor principal que pueden incluir más de un recalentamiento. Estas configuraciones son muy transcendentales debido a que en términos de eficiencia son las que mayores valores presentan y, además, sus costos totales por capacidad neta instalada son los más bajos en comparación con otras configuraciones

Modulating Organic/Inorganic Segregation in Columnar Mesophases

This work reports an uncommon modulation of columnar segregation of metal–organic triphenylene liquid crystals by blending two structurally dissimilar metallomesogens that can self-associate through complementary electron donor–acceptor interactions. The constituent molecules are cis-[PtCl2(CNR)2] (CNR = 2-(6-(4-isocyanophenoxy)hexyloxy)-3,6,7,10,11-pentakisdodecyloxytriphenylene) that displays an organic/inorganic segregated columnar mesophase and [PtCl2(Bipy)] (Bipy = didodecyl 2,2′-bipyridyl-4,4′-dicarboxylate) that shows a lamellar mesomorphism. The phase diagram of this system was constructed using polarized optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray scattering data. The phase diagram corresponds to a typical binary system with an intermediate compound (in this case a supramolecular aggregate) of stoichiometry [PtCl2(CNR)2]/2[PtCl2(Bipy)], which is maintained in solution. This species shows an unusual columnar mesophase formed by the stacking of alternating organic/inorganic fragments. Quantum chemical calculations show that the columnar structure is mainly supported by complementary π electron donor–acceptor interactions between each triphenylene group of the isocyanide complex and a platinum-bipyridine molecule. This induces the elimination of the organic/inorganic columnar segregation of the isocyano parent component and constitutes an unconventional example of modulation of organic/inorganic segregation in columnar mesophases by the intercalation of metal complexes into hexaalkoxytriphenylene stacks.This work was sponsored by the Ministerio de Ciencia e Innovación (Project PID2020-118547GB-I00), the Junta de Castilla y León (Project VA224P20), and the Basque Government (Project IT1458-22). E.D. thanks MECD for a FPU grant. The authors thankfully acknowledge the computer resources at Lusitania II and CIERZO-CAESARAUGUSTA III and the Technical support provided by Cénits-COMPUTAEX (FI-2022-1-0009, FI-2022-3-0008), Centro de Supercomputación de Aragón (QHS-2023-3-0005, QH-2023-1-0002) and Red Española de Supercomputación. We thank Dr. S. Ferrero (University of Valladolid) for his help in the NMR titration experiments

SolarPaces 2013: Innovations on direct steam generation in linear fresnel collectors

Direct Steam Generation (DSG) in Linear Fresnel (LF) solar collectors is being consolidated as a feasible technology for Concentrating Solar Power (CSP) plants. The competitiveness of this technology relies on the following main features: water as heat transfer fluid (HTF) in Solar Field (SF), obtaining high superheated steam temperatures and pressures at turbine inlet (500ºC and 90 bar), no heat tracing required to avoid HTF freezing, no HTF degradation, no environmental impacts, any heat exchanger between SF and Balance Of Plant (BOP), and low cost installation and maintenance. Regarding to LF solar collectors, were recently developed as an alternative to Parabolic Trough Collector (PTC) technology. The main advantages of LF are: the reduced collector manufacturing cost and maintenance, linear mirrors shapes versus parabolic mirror, fixed receiver pipes (no ball joints reducing leaking for high pressures), lower susceptibility to wind damages, and light supporting structures allowing reduced driving devices. Companies as Novatec, Areva, Solar Euromed, etc., are investing in LF DSG technology and constructing different pilot plants to demonstrate the benefits and feasibility of this solution for defined locations and conditions (Puerto Errado 1 and 2 in Murcia Spain, Lidellin Newcastle Australia, Kogran Creek in South West Queensland Australia, Kimberlina in Bakersfield California USA, Llo Solar in Pyrénées France,Dhursar in India,etc). There are several critical decisions that must be taken in order to obtain a compromise and optimization between plant performance, cost, and durability. Some of these decisions go through the SF design: proper thermodynamic operational parameters, receiver material selection for high pressures, phase separators and recirculation pumps number and location, pipes distribution to reduce the amount of tubes (reducing possible leaks points and transient time, etc.), etc. Attending to these aspects, the correct design parameters selection and its correct assessment are the main target for designing DSG LF power plants. For this purpose in the recent few years some commercial software tools were developed to simulatesolar thermal power plants, the most focused on LF DSG design are Thermoflex and System Advisor Model (SAM). Once the simulation tool is selected,it is made the study of the proposed SFconfiguration that constitutes the main innovation of this work, and also a comparison with one of the most typical state-of-the-art configuration. The transient analysis must be simulated with high detail level, mainly in the BOP during start up, shut down, stand by, and partial loads are crucial, to obtain the annual plant performance. An innovative SF configurationwas proposed and analyzed to improve plant performance. Finally it was demonstrated thermal inertia and BOP regulation mode are critical points in low sun irradiation day plant behavior, impacting in annual performance depending on power plant location

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