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This paper presents an overview of the activities carried out during the first half of the SOL2HY2 project. In particular, this paper is focused on the activities carried out by ENEA within the consortium, namely: elaboration of general plant concepts, integration of the hydrogen production plant with a concentrated solar power (CSP) plant, development of the catalyst for SO3 decomposition and selection and design of balance of plant (BoP) units. Copyright © 2015, AIDIC Servizi S.r.l.

A two-dimensional axial-symmetric isothermal model, based on full coupling between mass and momentum transport, has been developed to describe the separation of a binary gaseous mixture in a packed bed membrane module. Steady-state conditions have been studied. The gaseous mixture to be separated enters an annular gap between two co-axial cylinders. The inner wall of the outer cylinder is impermeable to both components, whereas a membrane, with infinite selectivity towards one of the components, is supported onto the outer wall of the inner cylinder. A radial flux of the permeating components is therefore present. The main focus was on the determination of the influence of radial convection on the performance of the separator, which has been analysed in terms of three dimensionless groups. Different transport regimes could be identified, corresponding to different values of the dimensionless groups. The impact of radial convection has been assessed by comparing model predictions with those of a fully uncoupled one-dimensional model. A discrepancy up to 20% of the recovery has been observed in industrially relevant ranges of the parameters.

This paper presents 7FP project named CoMETHy (Compact Multifuel-Energy to Hydrogen converter) cofunded by the European Commission under the Fuel Cells and Hydrogen Joint Undertaking (FCH JU). The project is developing an innovative steam reformer for pure hydrogen production to be powered by Concentrating Solar Power (CSP) plants using molten salts as heat transfer fluid. Due to the limitations in the molten salts maximum operating temperature of 550 °C, the reformer should operate at lower temperatures than conventional steam reforming processes. This implies the development of an innovative system, involving different R and D topics presented in this paper. © 2013, AIDIC Servizi S.r.l.

Time-on-stream stability of six different steam reforming catalysts has been tested at 500 °C under a simulated biogas feed. The catalysts are based on different combinations of Ni, Pt and Rh as active species, and CeO 2, ZrO2 and La2O2 as support. In order to perform a conservative analysis, biogas was simulated with a 50 % v/v CO2-CH4 mixture; furthermore a steam to methane ratio as low as 2.5 has also been used. All the samples containing CeO2 in the support proved fairly stable up to 50 h on stream. Therefore, these catalysts are worth being further investigated to assess their activity and determine appropriate reaction rate expressions. Copyright © 2013, AIDIC Servizi S.r.l.

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An innovative steam reformer for hydrogen production at temperatures lower than 550 °C has been developed in the EU project CoMETHy (Compact Multifuel-Energy To Hydrogen converter). The steam reforming process has been specifically tailored and re-designed to be combined with Concentrating Solar plants using “solar salts”: a low-temperature steam reforming reactor was developed, operating at temperatures up to 550 °C, much lower than the traditional process (usually > 850 °C). This result was obtained after extensive research, going from the development of basic components (catalysts and membranes) to their integration in an innovative membrane reformer heated with molten salts, where both hydrogen production and purification occur in a single stage. The reduction of process temperatures is achieved by applying advanced catalyst systems and hydrogen selective Pd-based membranes. Process heat is supplied by using a low-cost and environmentally friendly binary NaNO3/KNO3 liquid mixture (60/40 w/w) as heat transfer fluid; such mixture is commonly used for the same purpose in the concentrating solar industry, so that the process can easily be coupled with concentrating solar power (CSP) plants for the supply of renewable process heat. This paper deals with the successful operation and validation of a pilot scale reactor with a nominal capacity of 2 Nm3/h of pure hydrogen from methane. The plant was operated with molten salt circulation for about 700 h, while continuous operation of the reactor was achieved for about 150 h with several switches of operating conditions such as molten salts inlet temperature, sweep steam flow rate and steam-to-carbon feed ratio. The results obtained show that the membrane reformer allows to achieve twice as high a conversion compared to a conventional reformer operating at thermodynamic equilibrium under the same conditions considered in this paper. A highly pure hydrogen permeate stream was obtained (>99.8%), while the outlet retentate stream had low CO concentration (

The development of low-melting mixtures is crucial for the diffusion of sustainable and green alternative energy sources, namely, CSP. Ternary mixtures containing sodium, potassium, and calcium are extremely promising as thermal fluids due to their good thermophysical properties, low toxicity and cost. Most literature studies on ternary mQ4ixtures refer to a particular commercial composition and there are few data regarding ternary phase diagrams. Thus, for improving the current understanding on this topic, further theoretical and experimental investigation on ternary mixtures is of utmost interest. An experimental campaign was conducted to study the binary subsystems of the ternary mixtures and develop a regular solution model for simulating the ternary phase diagram. To validate the model, several data were determined using an innovative experimental rheometric method. The results showed that a ternary contribution in the regular solution model is necessary and an empirical expression for this ternary parameter was proposed and validated.

The NEXTOWER H2020 EU project investigates the possibility of using liquid lead as heat storage medium for high-temperature Thermal Energy Storage (TES) in concentrated solar power plants. To that end, within such project, a demonstration TES unit named SOLEAD (SOlar LEAd Demonstrator) is being developed to be coupled with an open volumetric air receiver in a solar tower CSP system. The SOLEAD demonstrator will use pure lead as working fluid and will be tested stand-alone, to address structural material behaviour at very high temperature, without coupling with air receiver. The tests are planned by the ENEA Brasimone R.C. in Italy. The introduction of the paper provides a general summary of the TES and CSP technology. Then a section is devoted to the conceptual design of SOLEAD. In the lead stand-alone experiment, the focus is on the materials corrosion in lead environment. Although the thermal stratification in the main vessel cannot be reproduced in a stand-alone experiment, the thermal cycle of the facility in the range 600-750°C will be properly reproduced in the experimental test. To this aim, external heating cables will heat up the system from 600°C to 750°C, while a proper Air Cooling System (ACS) will cool down the lead pool. A section of the paper contains the design criteria and calculation of the ACS with the air flowing on an annular gap between the vessel and the insulation. The power provided and extracted by the two systems (heating cables and ACS) is around 30 kW, so that the temperature range 600-750°C can be covered in about 8 hours and a complete cycle can be carried out in one day. Finally, a brief summary of the operational procedures needed from lead melting to the materials inspection is provided. The plan is to test the vessel for 4 months with daily thermal cycles to assess the resistance of FeCrAl materials exposed to very high temperature lead.

When designing a concentrating solar power (CSP) system, selection of a proper heat transfer fluid (HTF) material is a key, especially when employed in parabolic trough CSP plants. In particular, the use of low melting mixtures as an alternative to the widely commonly used “solar salt” can increase the CSP manageably and, as a result, several innovative nitrite/nitrate mixtures have been proposed. However, very few thermodynamics data are available for these compounds, especially regarding ternary compositions. One of the most interesting low freezing mixture is prepared with sodium and potassium nitrate together with sodium nitrite. The aim of this work is to investigate the thermodynamics properties of this ternary system, starting from its binary subunits, studying the phase diagram of this compound both experimentally and by a regular solution model. At this purpose, the literature phase diagrams of the binary subsystem were simulated in order to obtain the fitting parameters necessary for the employed semi-predictive tool. Then, the ternary system was modeled and the results showed very good agreement with the experimental points. It is quite interesting to note that both the theoretical and experimental results showed a low melting zone presenting greater sodium nitrate molar fractions with respect to sodium nitrite than previously reported in literature. This would lead to a decrease in the HTF price and an improvement regarding the fluid toxicity.

The possibility of storing solar thermal energy to decouple electricity production from the availability of the solar resource is a key factor in development of concentrating solar power (CSP) technologies. In this context, a challenging perspective is the storage of solar energy on a seasonal basis through thermochemical storage (TCS) systems, as well as the use of excess summer solar energy for stabilizing the annual electricity production, thus increasing the capacity factor of the CSP plant. In this paper, we report the experimental characterization of a material initially developed within the context of CO2 capture technologies, namely calcium oxide supported on mayenite, which in previous investigations shown good sorption capacity and substantial cycling stability. The objective of this new experimental campaign is to test the performance of this material when adopted for thermochemical storage purposes. The tests confirmed that the material, synthesized through a SolGel method, remains stable over long term cycling, with a carbonation conversion higher than 80%. Furthermore, no physical/chemical interaction of the mayenite support with CO2 was observed, confirming its inertia and suitability for TCS purposes.

The blast furnace slags are a by-product of the production process of cast iron, during which large amounts of liquid slags are formed. The composition of the blast furnace slags depends on the actual quality and proportion of the minerals and fluxes present in the blast furnace charge. Every year the steel industry in Europe produces 2900 tons of slags that, if left untreated, represent an industrial waste to be sent to landfills with serious environmental impact. In the RESLAG (Turning waste from steel industry into valuable low cost feedstock for energy intensive industry) project, the use of waste products deriving from iron and steel plants as new feedstock in different fields is considered: recovery of precious metals, thermal energy storage systems for steel-making and CSP industry, production of innovative refractory ceramic compounds. Within this framework, ENEA is investigating the possibility of using pebbles made with slags produced by the steel industry as a filler in high-temperature packed-bed thermocline TES systems, using a binary mixture of molten salts (60% NaNO3 40% KNO3) as HTF. More specifically, the pebbles are obtained by processing and sintering Electric Arc Furnace (EAF) slags produced during the manufacture of crude steel. Here, the lessons learned and the first experimental results collected during the commissioning phases of the PBTTES pilot plant developed within the RESLAG project are reported. In particular, the paper firstly reports about a preliminary set of tests carried out to check the chemical compatibility of the slags with the molten salts. Subsequently, the pilot plant is described and the results of the first commissioning tests, which were aimed at flooding the packed-bed with molten salts and checking the installed instrumentation, are reported.

Water splitting through the Hybrid Sulfur (HyS) process powered by solar energy is a promising pathway to the production of green hydrogen. The main challenges to the development of this process are related to the intrinsic variability of the solar resource, which, besides requiring the deployment of innovative process solutions, introduces significant elements of uncertainty in the plant design. In this paper, the Polynomial Chaos Expansion (PCE) method is applied for the uncertainty quantification (UQ) in this kind of systems. In particular, a forward analysis dealing with the evaluation of the output probability distributions is performed. This is carried out in terms of the input probability distributions, and the analysis is focused on how uncertainty is propagated from the input to the output. Moreover, a comparison between the PCE method and the standard Monte Carlo analysis (using the Latin Hypercube Sampling method) is performed. The obtained results show the advantage of the PCE approach in terms of convergence rate and the number of function evaluations. Finally, a sensitivity analysis through Sobol’ indices has been carried out, which highlighted the influence of each variation in the input on the output.

One of the most interesting perspectives for the development of concentrated solar power (CSP) is the storage of solar energy on a seasonal basis, intending to exploit the summer solar radiation in excess and use it in the winter months, thus stabilizing the yearly production and increasing the capacity factor of the plant. By using materials subject to reversible chemical reactions, and thus storing the thermal energy in the form of chemical energy, thermochemical storage systems can potentially serve to this purpose. The present work focuses on the identification of possible integration solutions between CSP plants and thermochemical systems for long-term energy storage, particularly for high-temperature systems such as central receiver plants. The analysis is restricted to storage systems potentially compatible with temperatures ranging from 700 to 1000 &deg, C and using gases as heat transfer fluids. On the basis of the solar plant specifications, suitable reactive systems are identified and the process interfaces for the integration of solar plant/storage system/power block are discussed. The main operating conditions of the storage unit are defined for each considered case through process simulation.

In this work, different tubular solid-foam packed-beds were experimentally investigated under air flow in order to determine the effective conductivity and wall-to-bed heat transfer coefficient. Several foam types with different material, namely silicon carbide and alumina, and cell density were tested. Foam samples were experimentally studied using different air flow rates and wall temperatures ranging between 200 and 500 °C. Axial and radial steady-state temperatures in the bed were experimentally measured and analysed with a two-dimensional, one-equation model. A Chilton–Colburn-type correlation based on the reactor diameter as characteristic dimension was proposed for the wall-to-bed heat transfer coefficient, which proved good to describe the behaviour of all tested foams. Effective radial thermal conductivity and pressure drop in the foams were also characterized.