Integration assessment of the hybrid sulphur cycle with a copper production plant

Copper is the third-most widely-used metal worldwide. However, copper processing is an energy-intensive process consuming large quantities of fossil fuels, both as the reducing agent and for energy which contributes significantly to anthropogenic carbon dioxide emissions. The hybrid sulphur cycle combines concentrating solar thermal energy with electrolysis to offer strong potential for low-cost green hydrogen production. A preliminary evaluation is reported of the techno-economic potential of this cycle to displace current fossil-based energy sources in an integrated copper mine and refinery (cradle-to-gate approach) at a remote location in Australia with an excellent solar resource. The effect of ore composition on the integration of the hybrid sulphur cycle and copper processing plant is evaluated using models developed in Aspen Plus. The evaluations show that sizing the hybrid sulphur cycle cycle to meet the oxygen demand of the copper refining process is more technoeconomically viable than sizing the hybrid sulphur cycle to meet the hydrogen required to replace the fossil fuel demand of the copper processing process. Moreover, it has been found that the integration of the hybrid sulphur cycle with the copper process plant has the potential to decrease both the carbon dixoide emissions and the operational expenditure of copper refineries for ores with a sufficiently high sulphide content (~50% mass fraction)

Operating Characteristics of Metal Hydride-Based Solar Energy Storage Systems

Thermochemical energy storage systems, based on a high-temperature metal hydride coupled with a low-temperature metal hydride, represent a valid option to store thermal energy for concentrating solar power plant applications. The operating characteristics are investigated for a tandem hydride bed energy storage system, using a transient lumped parameter model developed to identify the technical performance of the proposed system. The results show that, without operational control, the system undergoes a thermal ratcheting process, causing the metal hydride concentrations to accumulate hydrogen in the high-temperature bed over time, and deplete hydrogen in the low temperature. This unbalanced system is compared with a ’thermally balanced’ system, where the thermal ratcheting is mitigated by thermally balancing the overall system. The analysis indicates that thermally balanced systems stabilize after the first few cycles and remain so for long-term operation, demonstrating their potential for practical thermal energy storage system applications

Solar thermochemical hydrogen (STCH) Processes

There is a significant opportunity to store solar energy using hydrogen if a suitable thermochemical process can be developed. Although there are literally hundreds of cycles to choose from, there are only two real ones. One, the direct thermochemical cycle based on zinc oxide, has garnered significant attention in recent years, and development has proceeded far enough that a pilot-scale reactor has been developed. However, extremely high temperatures required present significant materials challenges that may not be solvable in the near-term, and the rapid quenching step limits process efficiency.The second, the hybrid thermochemical cycle based on sulfur dioxide, combines a low-temperature electrolysis step with a higher temperature decomposition step. Recent techno-economic studies demonstrate solar to hydrogen efficiencies on the order of 15-20% and costs on the order $4.80/kg with potential to reach values of$2.00/kg for large scale solar hydrogen production using the HyS cycle. In the future, additional advances in materials and operating parameters for all feasible thermochemical cycles will need to be demonstrated for commercial adoption of these processes

PROCESS DESIGN FOR SOLAR THERMO-CHEMICAL HYDROGEN PRODUCTION AND ITS ECONOMIC EVALUATION

The search for a sustainable long term massive hydrogen production route is a strong need, considering increasing energy demand, the diminishing fossil fuel reserves and global warming. One important objective of the EU project HYTHEC (HYdrogen THErmo-chemical Cycles) was to evaluate and to improve the potential for hydrogen production using the Hybrid-Sulfur cycle (HyS) driven by solar energy. This cycle comprises two main steps: at 850°C to 1200°C sulfuric acid is decomposed to H2O, O2 and SO2. The oxygen is separated from the gas stream and the SO2 (solved in water) is electrolyzed to produce hydrogen and sulfuric acid, thus closing the cycle. The technical feasibility and the economic potential of solar operation of the HyS process are being analyzed. Plant concepts have been created including the solar supply of heat for the thermo-chemical step and for electric power for the electrolysis step. The cycle is modeled using flow sheet techniques and will allow further optimization of the cycle efficiency. The high temperature heat is assumed to be provided by a heliostat field arranged around a central tower bearing the receiver reactor. Two systems sizes were analyzed: one central receiver system (CRS) with an annual average power of 50 MWth (equal to 140 MWth in peak), the second one six times larger. Both systems are considered to be feasible. The latter case leads to higher hydrogen production costs (HPC), mainly because of exponentially increasing costs of the high tower. Depending on the plant layout HPC of 4.9 €/kg seem achievable at locations with high solar irradiation

Technical challenges and future direction for high-efficiency metal hydride thermal energy storage systems

© 2016. Springer-Verlag Berlin Heidelberg. Recently, there has been increasing interest in thermal energy storage (TES) systems for concentrated solar power (CSP) plants, which allow for continuous operation when sunlight is unavailable. Thermochemical energy storage materials have the advantage of much higher energy densities than latent or sensible heat materials. Furthermore, thermochemical energy storage systems based on metal hydrides have been gaining great interest for having the advantage of higher energy densities, better reversibility, and high enthalpies. However, in order to achieve higher efficiencies desired of a thermal storage system by the US Department of Energy, the system is required to operate at temperatures >600 °C. Operation at temperatures >600 °C presents challenges including material selection, hydrogen embrittlement and permeation of containment vessels, appropriate selection of heat transfer fluids, and cost. Herein, the technical difficulties and proposed solutions associated with the use of metal hydrides as TES materials in CSP applications are discussed and evaluated