Toward a new method for the design of combined sensible/latent thermal-energy storage using non-dimensional analysis

Placing an encapsulated phase-change material (PCM) on top of a packed bed of sensible filler material is an effective way of reducing the drop in the heat-transfer fluid (HTF) outflow temperature during discharging associated with a sensible thermal-energy storage (TES). So far, the literature lacks guidelines for the design of a combined sensible/latent TES. This study aims at developing a new method for the design of combined TES based on non-dimensional analysis. The method will provide a designer with non-dimensional plots, produced from quasi-steady-state results of simulations with a one-dimensional model, that relate performance parameters to geometrical, thermophysical, and operational parameters of the combined TES. In this paper, a simplified version of the method is demonstrated that allows the selection of a metallic PCM and its amount such that a specified drop in the HTF outflow temperature is attained during discharging, assuming a fixed sensible section of natural rocks and air as HTF. The plots show that the drop in the outflow temperature during discharging is minimized by selecting a PCM with a melting temperature equal to 98% of the HTF inflow temperature during charging. The plots also show that the heat of fusion, provided it exceeds a threshold, has a subordinate effect on the drop in the outflow temperature. Finally, the plots show that a smaller heat of fusion can be compensated with a larger height of the latent section. The method is illustrated with a specific example.ISSN:0306-2619ISSN:1872-911

The Role of Carbon Capture, Storage and Utilization to Enable a Net-Zero-Co2-Emissions Aviation Sector

This contribution presents a techno-economic analysis of feasible pathways for the aviation industry to achieve netzero CO2 emissions. These pathways are based (i) on carbon capture and storage (CCS), where conventional fossil jet fuel is produced and the corresponding emissions are offset by capturing CO2, either via direct air capture (DAC-CCS route) or via point-source capture (PSC-CCS route), and permanently storing it underground; and (ii) on carbon capture and utilization (CCU), where synthetic jet fuel is produced by using CO2 as feedstock, which is either captured from air (DAC-CCU route) or from a point-source emitter (PSC-CCU route). To ensure net-zero CO2 emissions, the feedstock of the point-source emitter, both for CCS- and CCU-based routes, must be of biogenic nature. A comparative quantitative assessment of these scenarios and of a business-as-usual (BAU) scenario, where aviation emissions are subjected to a carbon tax, is performed based on jet fuel cost and carbon price projections until 2050. Cost reductions due to economy of scale of current low-maturity technologies are accounted for. An uncertainty analysis based on Monte Carlo simulations is performed to assess the effects of the uncertainty associated with the most relevant technoeconomic quantities on the observed trends. Findings show that CCS-based scenarios consistently lead to lower jet fuel costs than CCU-based scenarios across the considered time scenarios and sensitivity analyses. This is mainly due to the fact that CCU-based routes result in an energy consumption more than 20 times higher than CCS-based routes, which also implies higher CO2 emissions when considering the carbon intensity of current electricity grids. Overall, the PSC-CCS route represents the most cost-effective solution for decarbonizing the aviation industry and it is costcompetitive with BAU already today

Role of Carbon Capture, Storage, and Utilization to Enable a Net-Zero-CO2-Emissions Aviation Sector

A techno-economic analysis of viable scenarios for the aviation industry to achieve net-zero CO2 emissions is presented. These scenarios are based (i) on carbon capture and storage (CCS), where conventional fossil jet fuel is produced, and the corresponding emissions are offset by capturing CO2, either via direct air capture (DAC-CCS route) or via point-source capture (PSC-CCS route), and permanently storing it underground, and (ii) on carbon capture and utilization (CCU), where synthetic jet fuel is produced by using CO2 as feedstock, which is either captured from air (DAC-CCU route) or from a point-source emitter (PSC-CCU route). All routes are feasible and have their advantages and shortcomings. To ensure net-zero CO2 emissions, the feedstock of the point-source emitter, both for CCS- and CCU-based routes, must be of biogenic nature. A quantitative assessment of these scenarios and of a business-as-usual (BAU) scenario, where aviation emissions are subjected to a carbon tax, is performed based on jet fuel cost and carbon price projections until 2050. Cost reductions due to wide deployment and economy of scale of current low-maturity technologies are accounted for. Parametric and Monte Carlo sensitivity analyses are performed to assess the effects of uncertainty associated with the most relevant techno-economic quantities on the observed trends. Findings show that CCS-based scenarios consistently lead to lower jet fuel costs than CCU-based scenarios across the considered time scenarios and sensitivity analyses. This is mainly due to the fact that CCU-based routes result in an energy consumption more than 20 times higher than CCS-based routes, which also implies higher CO2 emissions when considering the carbon intensity of current electricity grids. Overall, the PSC-CCS route represents the most cost-effective solution for decarbonizing the aviation industry, and it is costcompetitive with BAU already today.ISSN:1520-5045ISSN:0888-588

A two-step carbon pricing scheme enabling a net-zero and net-negative CO2-emissions world

This contribution introduces a novel carbon pricing system and illustrates its benefits. The system is based on two related but distinct ideas. First, we group the global pools of carbon into three aggregate pools, and we tax or credit human-caused carbon fluxes across the boundaries of the pools. Second, we base the tax or credit solely on physical movements of carbon between pools; hence, the system uses a physical baseline instead of a behavioral baseline based on the hypothetical emissions levels that would have arisen absent the carbon price. The proposed system goes beyond the limitations of current carbon pricing schemes for a number of reasons: it is designed to capture all positive and negative emissions based purely on their climate impact, allowing a broader scope and more appropriate incentives than current systems; it avoids creating bad incentives, particularly those caused by additionality requirements found in carbon offset systems; it captures the complexity of carbon movements through human and natural systems; it reduces measurement errors; and it provides transparent and easily observed price signals. Though this manuscript is conceptual in nature and refrains from discussing the technicalities related to the implementation of the proposed carbon pricing system, we trust that it may contribute to the development of policies enabling a net-zero and net-negative CO2-emissions world.ISSN:0165-0009ISSN:1573-148

Constrained multi-objective optimization of thermocline packed-bed thermal-energy storage

A constrained multi-objective optimization approach is applied to optimize the exergy efficiency and material costs of thermocline packed-bed thermal-energy storage systems using air as the heat-transfer fluid. The axisymmetric packed-bed’s height, top and bottom radii, insulation-layer thicknesses, and particle diameter were chosen as design variables. The competing objectives of maximizing the exergy efficiency and minimizing the material costs were treated by a Pareto front. The Pareto front allows identifying the most efficient design for a given cost or the cheapest design for a given efficiency and is an important tool to find the best overall design of storage systems for a specific application. Constraints were imposed to obtain storage systems with specified capacities and limits on the air outflow temperatures during charging and discharging. The results showed that a storage shaped as a truncated cone with the smallest cross-section at the top has a higher exergy efficiency than storages shaped as cylinders or truncated cones with the largest cross-section at the top. The higher efficiency is attributed to the axial temperature distribution in the packed bed and the associated conduction heat losses across the insulated walls. The optimization of an industrial-scale storage allowed identifying a design with an exergy efficiency that was only 4.8% below that of the most efficient design, but a cost that was 81.3% lower than the cost of the most efficient design. Compared to brute-force design approaches, the optimization procedure can reduce the computational time by 91–99%.ISSN:0306-2619ISSN:1872-911

Optimization and assessment of carbon capture, transport and storage supply chains for industrial sectors: The cost of resilience

This study investigates the optimal design of carbon capture, transport and storage (CCTS) supply chains for decarbonizing industrial emitters. It builds upon previous analyses, which determine the cost-optimal design of CCTS supply chains while complying with specified emissions reduction scenarios, and determines optimal designs in terms of minimum cost and maximum resilience. The resilience of a supply chain is defined as its ability to permanently store the captured CO2 during the time horizon of interest, and it is quantified in terms of expected amount of carbon not stored under a fixed number of possible simultaneous failures. A mixed-integer linear program is developed to design CCTS supply chains that ensure a specified level of resilience while minimizing total system costs and CO2 emissions. The model is illustrated by determining the optimal decarbonization strategy in terms of costs and level of resilience for the Swiss waste-to-energy sector from 2025 to 2050. Overall, resilience is achieved with a cost increase with respect to the cost-optimal solution ranging from about 5% (backup truck connections to minimize the cost of the supply chain) to about 70% (backup pipeline connections to minimize the emissions of the supply chain) when the storage site is in the North Sea. When the storage site is available in Switzerland, the cost increase is much reduced and ranges from about 1% to 10% with respect to the cost-optimal solution.ISSN:1750-5836ISSN:1878-014

Carbon dioxide mineralization in recycled concrete aggregates can contribute immediately to carbon-neutrality

Bioenergy with carbon capture and storage (BECCS) is a carbon dioxide removal (CDR) solution necessary to achieve net-zero-carbon-emissions goals. While the BECCS potential from large industrial emitters has been quantified, the BECCS potential of small emitters, such as biogas facilities, has not been investigated. Moreover, most BECCS solutions rely on the expected availability of large geological storage capacity for future CDR implementation, although the deployment of CO2 transport and storage supply chains is still a barrier for geological carbon storage ambitions. An alternative opportunity for permanent sequestration of CO2 is concrete, in which captured CO2 can be permanently fixed through carbon dioxide mineralization technologies. We describe and discuss this solution by quantifying the potential of a European bioenergy with carbon capture, utilization, and storage (BECCUS) supply chain, which relies on biogenic CO2 from biogas facilities as a CO2 source, and on carbon dioxide mineralization in concrete as a permanent CO2 sink. This solution is available today, can be adopted seamlessly, and does not need economies of scale for its deployment. We find that European biogas facilities produce 24 Mtons of biogenic CO2 per year, of which 4 Mtons of CO2 per year are emitted from facilities already upgrading biogas into bio-methane. We estimate that carbon dioxide mineralization in recycled concrete aggregates in Europe could permanently store up to 8 Mtons of CO2 per year. Despite the limited storage potential, BECCUS supply chains would reduce CO2 transportation distance and system complexity compared to BECCS supply chains, and would result in a marketable product, namely concrete. Overall, carbon dioxide mineralization in recycled concrete aggregates combines carbon utilization with permanent sequestration, hence contributing to carbon-neutrality goals.ISSN:0921-3449ISSN:1879-065

Process performance maps for membrane-based CO2 separation using artificial neural networks

Membrane-based gas separation processes are currently being implemented at different scales for several industrial applications. The optimal design of such processes, which is of key importance for their large-scale commercial deployment, has been extensively studied through parametric analyses and optimisation procedures. Nevertheless, the applicability of such design methodologies is generally limited by the large computational time and effort they require. In this work, surrogate models based on artificial neural networks are developed to circumvent the lengthy optimisation of a one-stage and two-stage cascade membrane-based gas separation process. In 200 ms, the surrogate model generates a Pareto front that describes the optimal trade-off between the process specific electricity consumption and productivity based on given input data, i.e., membrane material properties, feed composition and separation target. Whereas the surrogate model is applicable to any binary gas mixture, here its features are illustrated by creating process performance maps for post-combustion CO2 capture. Such maps provide valuable insights on: (i) attainable gas separation regions in term of CO2 recovery and CO2 purity, and (ii) the impact of membrane material, feed composition and separation target on the Pareto fronts and the optimal operating conditions.ISSN:1750-5836ISSN:1878-014

Pilot-scale demonstration of advanced adiabatic compressed air energy storage, Part 2: Tests with combined sensible/latent thermal-energy storage

Experimental and numerical results from the world’s first pilot-scale advanced adiabatic compressed air energy storage plant with combined sensible/latent thermal-energy storage are presented. The combined thermal-energy storage was composed of sensible and latent units with maximum capacities of 11.6 MWhth and 171.5 kWhth, respectively. The latent thermal-energy storage consisted of a steel tank with 296 stainless-steel tubes encapsulating an Al–Cu–Si alloy as phase-change material. The combined thermal-energy storage was investigated using four charging/discharging cycles with durations of about 3 h each and air inflow temperatures of up to 566 °C. The experimental results showed that the latent thermal-energy storage reduced the drop in the air outflow temperature during discharging. Minor leaks of the phase-change material were traced to the welding seams in the encapsulation as well as to holes required to insert resistance temperature detectors. Analysis of the leaked phase-change material revealed degradation and/or phase separation, which were attributed to the initial off-eutectic composition of and impurities in the phase-change material and resulted in a reduced heat of fusion. Simulations predicted the performance of the combined thermal-energy storage with good overall accuracy. Discrepancies were put down to changes in the thermophysical properties