A comprehensive techno-economic analysis of destabilized Li hydrides, used as thermal energy storage systems in concentrating solar power plants, is presented and discussed. Two systems, operating at ...temperatures on the order of 550–650 °C, are selected as thermal energy storage units for steam power plants, namely the Si-destabilized Li hydride (LiSi) and the Al-destabilized Li hydride (LiAl). Two thermal energy storage systems, operating at temperatures on the order of 700–750 °C, are selected for integration in supercritical CO2 power plants, namely the Si-destabilized Li hydride (LiSi) and the Sn-destabilized Li hydride (LiSn). Each storage system demonstrates excellent volumetric capacity, achieving values between 100 and 250 kWhth/m3. The LiSi-based thermal energy storage systems can be integrated with steam and supercritical CO2 plants at a specific cost between 107 US$/kWhth and 109 US$/kWhth, with potential to achieve costs on the order of 74 US$/kWhth under enhanced configurations and scenarios. The LiAl-based storage system has the highest potential for large scale applications. The specific cost of the LiAl system, integrated in solar steam power plants, is equal to approximately 74 US$/kWhth, with potential to reach values on the order of 51 US$/kWhth under enhanced performance configurations and scenarios.
Traditional high-pressure mechanical compressors account for over half of the car station’s cost, have insufficient reliability, and are not feasible for a large-scale fuel cell market. An ...alternative technology, employing a two-stage, hybrid system based on electrochemical and metal hydride compression technologies, represents an excellent alternative to conventional compressors. The high-pressure stage, operating at 100–875 bar, is based on a metal hydride thermal system. A techno-economic analysis of the metal hydride system is presented and discussed. A model of the metal hydride system was developed, integrating a lumped parameter mass and energy balance model with an economic model. A novel metal hydride heat exchanger configuration is also presented, based on minichannel heat transfer systems, allowing for effective high-pressure compression. Several metal hydrides were analyzed and screened, demonstrating that one selected material, namely (Ti0.97Zr0.03)1.1Cr1.6Mn0.4, is likely the best candidate material to be employed for high-pressure compressors under the specific conditions. System efficiency and costs were assessed based on the properties of currently available materials at industrial levels. Results show that the system can reach pressures on the order of 875 bar with thermal power provided at approximately 150 °C. The system cost is comparable with the current mechanical compressors and can be reduced in several ways as discussed in the paper.
The use of Ti1.1CrMn metal hydride material in a thermal hydrogen compression system is investigated. The thermodynamic properties of the material, initially synthesized and annealed at 900 °C for 48 ...h (for quantities on the order of 10 kg), are assessed performing pressure-concentration-temperature equilibrium tests for hydrogen absorption and desorption at pressure up to about 900 bar. Results show flat plateaus and reduced hysteresis. The calculated absorption enthalpy and entropy are 20.55 0.13 kJ mol H 2 − 1 and 102.16 3.00 J mol H 2 − 1 K−1 respectively. The desorption enthalpy and entropy are 22.89 0.45 kJ mol H 2 − 1 and 107.80 10.45 J mol H 2 − 1 K−1, respectively. The metal hydride achieves a weight capacity of approximately 1.8% at room temperature and maintain an approximately constant weight capacity during the cycling testing. This makes the material a suitable candidate for high pressure hydrogen compressors, achieving pressures on the order of 450 bar at temperatures of approximately 140 °C. The same material composition is synthesized at laboratory scale quantities (on the order of 50 g), applying a modified annealing procedure (1200 °C for 240 h). This allows higher operating pressures to be achieved, but the modified annealing process also produces (at least) an additional phase, namely the C15 Laves phase, present in the material along with the C14 Laves phase. Consequently, two pressure plateaus are present at each operating temperature, reducing the effective material weight capacity available for the compression application. A two-stage hybrid compressor concept is also presented, with the thermal hydride compressor paired with a lower pressure electrochemical unit. In principle, the system can compress hydrogen with a compression ratio of 45 from 10 to 450 bar without any external thermal input and recovering the electrochemical unit waste heat to drive the thermal stage.
Hydrogen production thermochemical cycles, based on the recirculation of sulfur-based compounds, are among the best suited processes to produce hydrogen using concentrated solar power. The sulfuric ...acid decomposition section is common to each sulfur-based cycle and represents one of the fundamental steps. A novel direct solar receiver-reactor concept is conceived, conceptually designed and simulated. A detailed transport phenomena model, including mass, energy and momentum balance expressions as well as suitable decomposition kinetics, is described adopting a finite volume approach. A single unit reactor is simulated with an inlet flow rate of 0.28 kg/s (corresponding to a production of approximately 11 kgH2/h in a Hybrid Sulfur process) and a direct solar irradiation at a constant power of 143 kW/m2. Results, obtained for the high temperature catalytic decomposition of SO3 into SO2 and O2, demonstrate the effectiveness of the proposed concept, operating at pressures of 14 bar. A maximum temperature of 879 °C is achieved in the reactor body, with a corresponding average SO2 mass fraction of 27.8%. The overall pressure drop value is 1.7 bar. The reactor allows the SO3 decomposition into SO2 and O2 to be realized effectively, requiring an external high temperature solar power input of 123.6 kJ/molSO2 (i.e. 123.6 kJ/molH2).
•A novel direct solar receiver-reactor concept for sulfuric acid decomposition is described.•A detailed transport model for sulfuric acid decomposition is described.•Effective SO3 decomposition into SO2 and O2 is achieved.•Effective direct heat exchange between external concentrated solar radiation and reactive mixture is achieved.•Effective internal heat recovery between the reactive and the reacted sulfur mixtures is obtained.
A methodology was developed to determine the range of coupled material parameters and operating conditions that allow an adsorbent based hydrogen storage system to meet performance targets. The range ...of acceptable parameters forms a multi-dimensional volume, or envelope. For this reason, the methodology is referred to as the Adsorbent Acceptability Envelope. The model evaluates the performance of the overall storage tank, comprised of the adsorbent material, the heat transfer system and the pressure vessel. Two cases were analyzed, both based on the flow-through cooling approach providing the cooling power required to charge hydrogen, with results presented and discussed. The first application (the forward problem) analyzed the gravimetric and volumetric performance of MOF-5® based hydrogen storage beds, under various operating conditions. Results demonstrated that the system can reach a gravimetric capacity of approximately 4 wt% and volumetric capacity of about 20 g/L within 200 s during the absorption process. The second application (the inverse problem) identified the range of selected material parameters, required to meet the U.S. Department of Energy targets for gravimetric and volumetric capacity. Results showed that the most important parameters are the maximum capacity and the density of the material. Adsorbents having a density on the order of twice that of nominal powder form MOF-5® can meet the 2020 DOE targets (i.e. system gravimetric capacity of 0.045 kgH2/kgSystem and system volumetric capacity of 0.030 kgH2/LSystem). A density of about 3–4.5 times the nominal value is required to meet the DOE 2025 targets (i.e. system gravimetric capacity of 0.055 kgH2/kgSystem and system volumetric capacity of 0.040 kgH2/LSystem). Likewise, a material with a maximum adsorption capacity approximately equal to three times that of nominal MOF-5® can meet the 2020 DOE targets, while a maximum capacity about 4.5 times the nominal value is required to meet the 2025 DOE targets.
•Acceptability of adsorbents for H2 storage depends on relative parameter values.•Parameters are for both material characteristics and the storage system interface.•Trade-off between parameters precludes simple application of a table of values.•Methodology can be modified to suit range of system operations and isotherms.•Specific application to MOF-5 for DAR isotherm is used as a demonstration.
Concentrating solar power plants can achieve low cost and efficient renewable electricity production if equipped with adequate thermal energy storage systems. Metal hydride based thermal energy ...storage systems are appealing candidates due to their demonstrated potential for very high volumetric energy densities, high exergetic efficiencies, and low costs. The feasibility and performance of a thermal energy storage system based on NaMgH2F hydride paired with TiCr1.6Mn0.2 is examined, discussing its integration with a solar-driven ultra-supercritical steam power plant. The simulated storage system is based on a laboratory-scale experimental apparatus. It is analyzed using a detailed transport model accounting for the thermochemical hydrogen absorption and desorption reactions, including kinetics expressions adequate for the current metal hydride system. The results show that the proposed metal hydride pair can suitably be integrated with a high temperature steam power plant. The thermal energy storage system achieves output energy densities of 226 kWh/m3, 9 times the DOE SunShot target, with moderate temperature and pressure swings. In addition, simulations indicate that there is significant scope for performance improvement via heat-transfer enhancement strategies.
•A metal hydride storage system identified for supercritical steam power plant.•A laboratory scale thermal energy storage system modeled.•Technical feasibility of the system demonstrated, with recovery of waste heat.•Achieved temperatures of 600–650 °C, energy densities 9 times the DOE target.•Heat transfer system enhancements identified.
High temperature concentrating solar power plants require suitable thermal energy storage systems to produce electric power efficiently. Thermochemical energy storage based on metal hydrides ...represents a very appealing prospect for low cost and high efficient solar storage systems. The objective of the paper is to assess the properties required by the metal hydride systems to achieve the U.S. Department of Energy's SunShot techno-economic targets. A simplified model has been developed to evaluate the cost and the exergetic efficiency of hydride-based storage systems. Results demonstrate that metal hydride materials, operating at temperatures higher than 650 °C, with reaction enthalpy on the order of 95–110 kJ/molH2, raw material cost on the order of 1.4–2 $/kg, weight capacities on the order of 3–4% and operating pressures on the order of tens of bars have the potential to closely approach the targets. Selected sensitivity analyses have also been carried out showing that the raw material cost, the material weight capacity and the metal hydride reaction enthalpy are the properties that strongly affect the performance of the storage system.
•Metal hydride based thermal energy storage systems have been modeled, by techno-economic models.•Ideal metal hydride material properties have been identified, to meet the DOE targets.•Selected sensitivity analyses have been carried out for the selected metal hydrides.•Performance gap between the ideal metal hydrides and the existing candidate materials has been identified.•The materials having the highest potential to meet the targets have been identified.
•A two-liter MOF-5 adsorbent tank built and instrumented.•A finite element detailed transport phenomena model developed.•Hydrogen charging tests (flow-through cooling) carried out with model ...validation.•Hydrogen discharging tests (electrically heated finned heat exchanger) performed with model validation.•High gravimetric and volumetric capacities achieved using the proposed approaches.
A two-liter prototype hydrogen adsorbent tank, filled with MOF-5 material, was built, tested and modeled as part of the work carried out within the U.S. Department of Energy Hydrogen Storage Engineering Center of Excellence. The hydrogen was stored adopting the flow-through cooling concept. This approach exploits the characteristics of low temperature recirculating hydrogen to provide the cooling power required to adsorb the gas. The heating power, required to discharge hydrogen, was provided adopting a honeycomb finned heat transfer system, powered with a resistive heater. The system demonstrated the ability to achieve excess adsorption capacities on the order of 6.5 wt% at 77 K and at pressures between 40 bar and 80 bar. Adopting the flow-through cooling charging approach, gravimetric and volumetric capacities of 12 wt% and 31 g/L (on a material basis) were achieved, respectively, in approximately 10 min, at temperatures of about 90 K and pressures of 80 bar. The hydrogen discharging tests were carried out at pressures between 80 bar and 2.5 bar with a single resistive rod operating at an electric power on the order of 40 W. The prototype system demonstrated the ability to drive continuously a fuel cell of approximately 1 kW (corresponding to the prototype scale), at its nominal power for about 1 h 10 min.
•A honeycomb finned heat exchanger used for hydrogen desorption in adsorbent systems.•A bench scale system tested at room temperature and cryogenic temperatures.•The bench scale system modeled with ...validation against the experimental results.•The experiments and modeling results demonstrated proper desorption.•Additional model results showed proper hydrogen discharge to drive fuel cells.
One of the main technical hurdles associated with adsorbent based hydrogen storage systems is relative to their ability to discharge hydrogen effectively, as dictated by fuel cell requirements. A new honeycomb finned heat exchanger concept was examined to evaluate its potential as a heat transfer system for hydrogen desorption. A bench scale 0.5 L vessel was equipped with the proposed heat exchanger, filled with MOF-5® adsorbent material. The heating power, required to desorb hydrogen, was provided by a 100 W electric heater placed in the center of the honeycomb structure. Two desorption tests, at room temperature and under cryogenic temperatures, were carried out to evaluate the hydrogen desorption performance of the proposed system under different operating conditions. The bench scale vessel performance was verified from both an experimental and a modeling point of view, demonstrating the ability to desorb about 45% of the adsorbed hydrogen in reduced time and applying low heating power. Further modeling analyses were also carried out showing the potential of the proposed system to reach high hydrogen discharging rates at cryogenic temperature conditions and operating pressures between 100 bar and 5 bar. The proposed adsorption system also demonstrated to be able to discharge all the available hydrogen in less than 500 s operating at cryogenic conditions and with a nominal heating power of 100 W.
Concentrating solar power plants represent a competitive option to produce electric power only if equipped with suitable thermal energy storage. Metal hydride material-based thermochemical hydrogen ...storage is a very attractive solution to store high temperature solar thermal energy. A literature review of some of the past and more recent investigations on using metal hydrides for thermal energy storage has been carried out. Based on findings from this review and new material property data, a preliminary material techno-economic analysis was performed to select the most promising candidate metal hydrides as well as to examine their behavior under different operating conditions. The performance was evaluated adopting simplified system models and the results were compared against the US Department of Energy targets including installed cost, exergetic efficiency, operating temperature and volumetric energy density. Selected sensitivity analyses for the most promising materials have also been carried out in order to evaluate the influence of solar plant and material properties on the overall system installed cost. Results demonstrated that the selected storage systems, based on currently available metal hydride high temperature materials (i.e. NaMgH3, TiH2 and CaH2), are able to achieve and exceed many of the targets such as volumetric energy density (25kWhth/m3) and operating temperature (600°C). Material modifications as well as heat exchange system improvements are also discussed in the paper, with the aim of reducing the overall thermal energy storage specific cost and helping to meet and exceed all of the targets.
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