External Tank Research Articles

Evaluating the Performance of an All-Aqueous Copper Trab through 200 Hours of Discharge Cycling

Thermally regenerative ammonia batteries (TRABs) have the potential to serve as a viable solution for energy storage and electricity generation by harnessing low-grade heat. A TRAB discharge closely resembles that of a conventional flow battery, where electrochemical reactions are used to produce electrical power and aqueous electrolytes are stored in external tanks. However, the key distinction of a TRAB from a conventional flow battery lies in the recharging process, where thermal energy is used to separate ammonia from the negolyte, referred to as thermal recharging. During thermal recharging, the exhausted negolyte is converted into a fresh posolyte through the thermal separation of ammonia that was dissolved into the solution. This separated ammonia is subsequently added into the depleted posolyte, turning it into a fresh negolyte thereby completing the recharging process. Although there are many types of TRABs, the all-aqueous copper TRAB (Cuaq-TRAB) has produced some of the largest power densities and energy storage densities observed from a TRAB discharge. Building on these recent successes with Cuaq-TRABs, our investigation seeks to assess the performance of the Cuaq-TRAB during prolonged operation. Previous investigations with TRABs have typically lasted 0.5-7 hours, with the longest lasting 20 hours, which does not provide sufficient data to demonstrate the stability of the technology as thousands of hours of operation will be required. To address this gap, we operated an Cuaq-TRAB for 200 hours with a constant discharge current density of 10 mA cm-2 to examine battery performance and material degradation over time. Throughout the 200-hour test period, we measured an average power density of 7.2 mW cm⁻², which increased by 0.01% during the test. Additionally, the average energy density was 2.7 Wh L⁻¹, with a degradation of only 0.03% over the 200-hour timeframe. These results are the first to provide valuable information about the stability of the Cuaq-TRAB system during extended operation.

Functionalization of Organic Redox Mediators to Mitigate Crossover in Chemically Regenerative Redox Fuel Cells

Chemically regenerative redox fuel cells are promising alternatives to conventional PEMFCs as stationary energy conversion devices since they avoid platinum-based catalyst at the cathode for the oxygen reduction reaction thanks to the chemical oxidation of the mediators in an external tank[1]. The requirements for the mediator are a high standard redox potential (0.6 V vs. SHE), high diffusion coefficient and fast electron transfer kinetic to reach high power density. Furthermore, the mediator must be stable in acidic medium (pH<1) and at the operating temperature of the system (40 to 80°C). The durability of the system will depend on the physico-chemical properties as well as on the chemical reactivity with oxygen in order to regenerate the reduced redox mediator. Loss of performance over time can be attributed to the crossover of the solubilized species from the cathode to the anode side and to the chemical instability over redox reaction. Crossover phenomena are commonly observed in aqueous organic redox flow battery using (2,2,6,6-Tetramethylpiperidin-1-yl)oxyl (TEMPO) as reactive species[2].In this study, several mediators based on TEMPO with different PEG chain length are synthesized and characterized. The goal of the functionalization is to mitigate the crossover rate of the mediator through the membrane. Fuel cell tests were performed giving access to performance and power decrease over time. For a deeper understanding of the origin of performance losses, an ex situ electrochemical setup was developed to assess the impact of functionalization toward crossover.[1] Singh R, Shah AA, Potter A, Clarkson B, Creeth A, Downs C, et al. Performance and analysis of a novel polymer electrolyte membrane fuel cell using a solution based redox mediator. J Power Sources 2012;201:159–63. https://doi.org/10.1016/j.jpowsour.2011.10.078.[2] Small LJ, Pratt HD, Anderson TM. Crossover in Membranes for Aqueous Soluble Organic Redox Flow Batteries. J Electrochem Soc 2019;166:A2536–42. https://doi.org/10.1149/2.0681912jes. Figure 1

Green Hydrogen Production Using Manganese – Vanadium Redox Flow Batteries

The redox flow batteries (RFBs) can be tuned to allow mining of surplus energy capacity and supplement green hydrogen economy as a one-stop station [1, 2].With this concept, an RFB can undergo two sequential discharging modes: i) electrochemical discharge of redox active species, and ii) chemical discharge to produce hydrogen gas, when surplus electricity is available, on the surface of electrocatalysts contained in additional external tanks (i.e., dual circuit RFB) [3, 4]. Herein, electrolytes with Mn3+/Mn2+ (RFB catholyte ~ 1.5 V vs. SHE) and V3+/V2+ (RFB anolyte ~ −0.26 V vs. SHE) redox species are flown to spatially separated external catalytic reactors to drive redox mediated water electrolysis. The fully charged V2+ redox mediator in the anolyte provides electrons to achieve hydrogen evolution reaction (HER) and thereby itself gets discharged to V3+ redox state before circulating back to flow battery tanks.Considering the additional layer of redox-mediated water electrolysis, it is imperative to identify benchmark cycling performance for a robust dual circuit RFB operation. In the first phase of our study, electrochemical behavior of Mn3+/Mn2+ redox couple in the favorable presence of V5+ as an additive was elucidated using ultramicroelectrode voltammograms. Despite significant performance enhancement, capacity fade during galvanostatic cycling could not be fully eliminated owing to Mn3+ disproportionation reaction and manganese crossover. Also, charge/discharge cycling profiles suggest that the inevitable Mn3+ disproportionation affects the true state-of-charge in electrolytes which in turn hinders their potential to generate hydrogen gas. Working towards hydrogen generation, our recent efforts have been to evaluate kinetics for hydrogen evolution reaction (HER) on different carbon substrate – electrocatalyst combinations in acidic V3+/V2+ environment. Overall, this study aims to provide a profound understanding of reliable operating conditions to establish a synergy between Mn3+ disproportionation during the conventional energy storage mode and the total volume of hydrogen gas produced during the secondary mode. References Reynard, D. and H. Girault, Combined hydrogen production and electricity storage using a vanadium-manganese redox dual-flow battery. Cell Reports Physical Science, 2021. 2(9): p. 100556. Amstutz, V., et al., Renewable hydrogen generation from a dual-circuit redox flow battery. Energy & Environmental Science, 2014. 7(7): p. 2350-2358. Peljo, P., et al., All-vanadium dual circuit redox flow battery for renewable hydrogen generation and desulfurisation. Green Chemistry, 2016. 18(6): p. 1785-1797. Piwek, J., et al., Vanadium-oxygen cell for positive electrolyte discharge in dual-circuit vanadium redox flow battery. Journal of Power Sources, 2019. 439: p. 227075.

Experimental Study on Mechanical Properties of Reinforcement under Low-Temperature Impact

Abstract Ammonia is an important carrier of hydrogen energy, and the large-scale storage of liquid ammonia is the next trend of cryogenic energy storage. At present, the international mainstream liquid ammonia tank is generally about 50, 000 m3. The outer storage tanks generally adopt a metal structure, and the material applied for larger concrete full-capacity tanks is worth doing further research. Steel reinforcement bars (rebar) are an important construction material for full-capacity cryogenic energy storage tanks. The performance of rebar is an important index in the process of designing the strength of building structures. The factors affecting the properties of rebar are diverse, and reasonable control of each influencing factor can improve the performance of rebar used for liquid ammonia storage tanks. This paper carries out the study on the mechanical properties of the steel reinforcement bars from the concrete of the main container under low temperatures for storing liquid ammonia. Through experimental research on the failure of steel used in external tanks, it has been shown that temperature has a significant impact on the ductile-brittle transition. Further treatment can effectively prevent the brittleness of steel bars, improve the safety and reliability of storage tanks at low temperatures, and is of great significance for the design and construction of subsequent large liquid ammonia storage tanks.

The response characteristics and damage effects of large LNG storage tanks subject to the coupled effects of explosion shock waves and fire

As the demand and import of liquefied natural gas (LNG) increase, large LNG receiving stations are being constructed. LNG leakage can lead to fire or explosion accidents. The simultaneous occurrence of explosions and fires, often inevitable, is more damaging than the effect of a single load. This study utilizes finite element analysis software LS-DYNA and the ALE algorithm to examine the response characteristics and damage effects on large LNG storage tanks under the combined impact of explosion shock waves and high-temperature loads (with the explosion preceding the fire). The findings indicate that post-explosion, the concrete outer tank's compressive strength diminishes as temperatures rise. The dome deflection of the storage tank's external tank surpasses the standard limit at 400 °C and fails at 600 °C. This research identifies the critical failure mode of the concrete storage tank's outer tank under the joint impact of explosion shock waves and fire. It provides a foundation for the anti-explosion design of such storage tanks.

Multi-{Physics, Phase, Scale} Computational Modeling of Interface-Coupled Problems in Redox Flow Battery Design

Motivated by an urgent need to deploy large-scale energy storage technologies to integrate intermittent renewables, redox flow batteries (RFBs) are gaining prominent attention due to their interesting features including higher durability and power-energy decoupling. RFBs are rechargeable electrochemical systems in which an electrolyte solution containing dissolved or suspended active species is stored in external tanks and pumped through the electrochemical stack - consisting of flow fields, porous electrodes, and membranes - where the active species undergo electrochemical reactions to charge/discharge the battery. However, large-scale deployment of RFBs has feasibility issues regarding costs and efficiency, which can be tackled by tuning their multi-scale design parameters [1].Developing a coupled multi-scale computational model for RFBs can facilitate our understanding of the interplay between intricate phenomena occurring at several length and time scales (depicted schematically in the figure), ranging from transport phenomena, i.e., mass, charge, momentum, and heat, on the cell level (macro and meso scales) to microstructure effects and wettability behavior on the pore-scale (micro and nano scales). Furthermore, the modeling framework should capture the reaction kinetics and multi-phase chemistry of emerging flow battery concepts (e.g. metal-air) including plating and stripping reactions [2].In this research, we are developing a multi-{physics, phase, scale} model for the optimization of next-generation RFBs in the cell-, electrode-, and pore-scale. The model includes free fluid flow (representing flow field channels) over a porous medium (porous electrode) and solves the transport mechanisms over the entire computational domain with a focus on the electrolyte-electrode interface. The model is developed using finite element/volume methods combined with pore network modeling techniques, implemented using various open-source modeling frameworks including OpenFOAM [3], FEniCS [4], and OpenPNM [5].In this presentation, I will first discuss the structure of the modeling framework including the continuum transport models, the pore network model, and the employed numerical schemes. Then, I will present the coupling between continuum and porous medium models. Finally, I will highlight some initial results focused on the efficiency of the coupling of the electrolyte fluid transport with the porous medium and pore network representation of the electrode [6]. We hope that the developed model can be a functional tool to assess and optimize RFB materials and operating conditions and can be broadly adopted to model emerging flow battery chemistries. References K. Chakrabarti et al., Sustainable Energy & Fuels. 4, 5433–5468 (2020).Hein et al., ACS Applied Energy Materials. 3, 8519–8531 (2020).G. Weller et al., Computers in Physics. 12, 620 (1998).Alnæs et al., Archive of Numerical Software, in press, doi:10.11588/ANS.2015.100.20553.Gostick et al., Computing in Science & Engineering. 18, 60–74 (2016).van der Heijden et al., Journal of The Electrochemical Society. 169, 040505 (2022). Figure 1

Performance of Hybrid Mesh Filter Bioreactor For Textile Wastewater Treatment

The rapid growth of the textile industry, while bringing positive impacts, also brings negative effects related to the increasing amount of wastewater generated. Poorly managed wastewater can potentially create adverse effects on human health and the environment. This study evaluates the hybrid mesh filter bioreactor (MFBR) performance for textile wastewater treatment. The bioreactor was operated with a nylon mesh filter having 37 µm pore size under intermittent aeration with aeration on/off durations of 1/1 hour. Wastewater influent was degraded by microorganisms attached to biofilm carriers and filtered by an external filtration tank. The process performance was evaluated under varying concentrations of COD (600–1200 mg/L). The stable operation was achieved for around 60 days with 88.4-94.8% turbidity removal and a flux value of 102±15 L/m2·hour. Although high COD removal was observed (89.4-92.1%), only 14.3-25.2% color removal was achieved in hybrid MFBR under hydraulic retention time (HRT) of 4-8 hours.

Modeling Improved Li-Ion Cell Capacity through Suppression of Temperature with Internal Electrolyte Flow

Lithium-ion cells are ubiquitous in portable electronic applications and are growing in popularity for electric vehicles including passenger cars. Yet, a dramatic reduction in global emissions to combat climate change calls for significantly broader adoption of carbon neutral technologies in electric vehicles and in stationary energy storage to complement variable renewable sources and growing electricity demand.1 For lithium-ion batteries, a critical barrier to such broader adoption is the inability to sustain high rate while also accessing the full capacity of cells. In addition to mass transport effects, overheating commonly limits the duration of high-rate discharge or charge due to excessive heat generation and inadequate heat removal.Here, we provide a brief illustrative tutorial of these coupled effects in a pseudo two-dimensional electrochemical model and build on our previous modeling and dimensional analyses2-4 of how internal electrolyte flow across Li-ion cells reduces both mass and thermal transport limitations.First, we describe the intentional and sudden onset of internal electrolyte convection to curb or to avert further temperature rise in a Li-ion cell during high-rate discharge. We examine two modes for introducing electrolyte flow: temperature-triggered (“reactive”) and discharge-rate triggered (“proactive”) modes. In the reactive case, flow is introduced in the simulation when a cell under high-rate discharge reaches a high safety cutoff temperature. In the proactive case, flow begins as the discharge rate is step changed from midrate to high rate. A practical application of proactive mode is that a battery thermal management system could be programmed to initiate electrolyte flow in anticipation of greater heat generation at a higher rate.Next, using the aforementioned continuum modeling with circulation through an external tank, we compare and contrast Li-ion cell thermal responses to the onset of flow in reactive mode versus in proactive mode. In both cases, the threshold flow rate (~μm/s) to suppress temperature rise agrees in order of magnitude with dimensionless group estimates reported in our previous work.4 Namely, temperature rise is suppressed when the heat generation rate becomes lower than the heat removal rate. At the highest electrolyte flow rates simulated (>>μm /s), the heat removal by internal electrolyte flow dominates, and the cell achieves nearly full discharge capacity without prematurely crossing temperature or voltage cutoffs. For low flow rates (<μm /s), the proactive and reactive cases show quantitatively different transient temperature trajectories due to the temperature dependences of heat generation and removal. Heat generation rate decreases with elevated cell temperature due to facile mass transfer and resultant concentration uniformity, optimal electrolyte conductivity, and ease of charge transfer kinetics. Also, heat removal using internal electrolyte flow becomes more effective with high cell temperature relative to ambient inlet temperature. Hence, the flow rate needed to cool a cell that has reached a high safety cutoff temperature (in reactive mode) is lower than the flow rate required to curb temperature rise in a cell just above ambient temperature (in proactive mode) as high-rate discharge starts.

Technology and implementation of fermentative units for bioprotein production from natural gas

Objectives. To conduct a comparative analysis of the features of a fermentation unit design for obtaining bioprotein from natural gas and determine the main technical and structural solutions used in the development of fermentation apparatus, which vary according to the method of organizing hydraulic and mass transfer processes.Results. An analysis of publications devoted to the problem of developing technological equipment for conducting the process of obtaining a bioprotein from natural gas is presented. Using the comparative analysis, the key features of bioreactors and their internal elements are indicated according to the method of organizing the hydrodynamic regime. The main approaches to the technological development of fermentation units for obtaining bioprotein from natural gas are described and technical solutions used in the implementation of these structures are identified.Conclusions. Fermenter designs for the cultivation of methane-oxidizing microorganisms vary according to the main approaches for implementing the hydraulic regime inside the apparatus. While one class of fermentation systems is based on the principle of volumetric mixing in the working space of the apparatus, with the possibility of including external circulation circuits, additional tanks, and auxiliary bioreactors in the system, the other main class relies on the principle of flow (displacement) in the tube space with subsequent release of the gas phase from the circulating culture liquid.

CG Based Design Optimization of Aircraft Drop Tanks

A new method is introduced to locate the partitions in external fuel tanks, a.k.a. drop tanks of combat aircraft. Using operational requirements to simplify the fuel transfer sequence, an optimization algorithm is developed to reduce the variation in aircraft Centre of Gravity (CG). A conservative limit on the CG effect of fuel slosh is introduced. This method results in locating the tank partitions such that dynamic effects on CG-variation are minimized. The method can be generalized and used in the design of any external drop tank. This ab-initio method is developed based on the experience gained in the development of a legacy fighter aircraft fuel system.

An energy autonomous and portable pilot unit for the photocatalytic treatment of wastewater

An energy-autonomous and portable pilot unit was designed and manufactured. The unit was placed on a wheeled support consisting of a photovoltaic panel, four (4) metallic photo-reactors, each equipped with 6 W UV-A lamps, two (2) peristaltic pumps of 5 W, and an external recirculation tank. The annular space of reactors was packed with ZnO-coated Duranit spheres. The pilot unit was assessed with regard to the degradation capacity of phenol solution and effluents collected from wastewater treatment plant (WWTP). Measurements of the UV-light intensity were combined with the 2-flux radiation model to determine the radial profile of UV-radiant flux across the annular photoreactor. The experimentally measured transient responses of phenol concentration, total organic, and inorganic carbon were fitted with one-dimensional (1D) numerical models to estimate the apparent 1st order kinetic constant of photo-degradation processes. On average, the energy demand of the unit was counterbalanced by the electric power generated by the photovoltaic panel. The repeated use of the same photocatalysts in all experiments confirmed the long-term energy efficiency of the unit. The apparent kinetic constants of phenol, intermediates species, and total organic carbon (TOC) degradation were found to be governed by the corresponding mass-transfer coefficients of relevant species from the bulk liquid to the active catalyst surface. At early times, the total inorganic carbonates (TIC) concentration increases, and at late times the fast mass-transfer of dissolved CO2 to gas phase compensates for the production of inorganic carbon. Preliminary tests showed that the photocatalytic unit is capable of reducing the COD and TOC of WWTP effluents and occasionally, the concentration of nitrates and ammonia may also decrease.

Optimization control of the double‐capacity water tank‐level system using the deep deterministic policy gradient algorithm

AbstractProcess control systems are subject to external factors such as changes in working conditions and perturbation interference, which can significantly affect the system's stability and overall performance. The application and promotion of intelligent control algorithms with self‐learning, self‐optimization, and self‐adaption characteristics have thus become a challenging yet meaningful research topic. In this article, we propose a novel approach that incorporates the deep deterministic policy gradient (DDPG) algorithm into the control of double‐capacity water tanklevel system. Specifically, we introduce a fully connected layer on the observer side of the critic network to enhance its expression capability and processing efficiency, allowing for the extraction of important features for water‐level control. Additionally, we optimize the node parameters of the neural network and use the RELU activation function to ensure the network's ability to continuously observe and learn from the external water tank environment while avoiding the issue of vanishing gradients. We enhance the system's feedback regulation ability by adding the PID controller output to the observer input based on the liquid level deviation and height. This integration with the DDPG control method effectively leverages the benefits of both, resulting in improved robustness and adaptability of the system. Experimental results show that our proposed model outperforms traditional control methods in terms of convergence, tracking, anti‐disturbance and robustness performances, highlighting its effectiveness in improving the stability and precision of double‐capacity water tank systems.

Clean energy by proven new energy technology

Extended dependence on fossil fuels and other consumable resources to meet the energy requirements of the modern world and to provide the high living standards required by modern society; have been driving mankind toward the exhaustion of current fuel and energy resources. Hence, this article provides an infinite energy device that can be used to produce energy constantly by using buoyancy and gravitational force. The infinite energy device comprises a positive buoyant stable vessel body (the vessel is attached to an external tank with bars) having at its base (inside) an extendable/retractable chamber with the lock to open and close the intake valve for incoming water through the valve's hole from the lower end of the vessel. The water exits the chamber via a pipe due to the external pressure from a weight plate. The continuous flow of water from the pipe can be further used to generate energy. This device is not a completely isolated system from the rest of the universe; we do not know the far future so it is not a perpetual motion device and thus does not violate physics principles. I have a working prototype, and I have included as much information as possible about the device so that the experiment can be reproduced. Therefore, I included supporting photos. In layman's terms, this device has the advantage of a sequence of five systems. Lateral water displacement reduces the depth distance to send water above; buoyant force (75.40 kgf) acts as an upward force to expand a chamber of the device's vessel (inside) to store energy in the form of the gravitational potential energy of a weight plate (21.5 kgf). The buoyant force (75.40 kgf) is greater than gravitational force (21.5 kgf) due to which a steady state is reached with a net force equal to 53.9 kgf. Incoming water enters the chamber through an intake valve underneath. This is a float valve system. The valve is used to close by the buoyant force. It is initially locked by hand before automatic locking systems enclose the chamber. The hydraulic lift principle (system) is used to pressurize the chamber via the weight plate (gravity). Pascal's principle and gravity thus bring the chamber water outside the vessel and above the surrounding water level through a pipe. The (falling) water generates electricity in the water turbine generator and distributes electrical energy for the automatic locking of the intake valve and the rest, for our use. This is the main benefit of the device. The objective of the device is to bring the surrounding (chamber) water above water level by using buoyant force and gravity. And, I have demonstrated the prototype.

Development and Experimental Characterization of an Innovative Tank-in-Tank Hybrid Sensible–Latent Thermal Energy Storage System

This study focuses on the development and testing under lab-controlled conditions of a hybrid sensible–latent thermal energy storage (TES) system for domestic hot water (DHW) provision in residential buildings. The TES system’s design is based, for the first time in the literature, on a commercial tank-in-tank architecture integrating a macro-encapsulated commercial phase change material (PCM) inside the external tank to guarantee the safe provision of DHW and increase overall energy storage density at a reasonable cost. The PCM is a salt hydrate with a nominal melting temperature of 58 °C. The overall tank-in-tank TES volume is about 540 dm3. Almost one tenth of this volume is occupied by the PCM macro-capsules. The developed TES system was comparatively tested against the same configuration operated as a sensible TES. The obtained results showed the ability of the PCM to increase the thermal inertia inside the external tank, thus guaranteeing the quite stable provision of heat to the integral DHW tank during the stand-by periods. This effect was confirmed by the PCM’s ability to achieve an energy storage capacity up to 16% higher than the reference sensible TES system.

Acidification of slurry to reduce ammonia and methane emissions: Deployment of a retrofittable system in fattening pig barns

Livestock farming, and in particular slurry management, is a major contributor to ammonia (NH3) and methane (CH4) emissions in Europe. Furthermore, reduced NH3 and CH4 emissions are also relevant in licensing procedures and the management of livestock buildings. Therefore, the aim is to keep emissions from the barn as low as possible. Acidification of slurry in the barn can reduce these environmental and climate-relevant emissions by a pH value of 5.5. In this study, an acidification technology was retrofitted in an existing fattening pig barn equipped with a partially slatted floor. The slurry in a compartment with 32 animals was acidified. An identical compartment was used for reference investigations (case-control approach). Several times a week slurry was pumped for acidification in a process tank outside the barn compartment in a central corridor, where sulphuric acid (H2SO4) was added. Then the slurry was pumped back into the barn. In contrast to other systems, where acidified slurry was stored mainly in external storage tanks, in this study the slurry was completely stored in the slurry channels under the slatted floor, during the entire fattening period. The emission mass flow of NH3 and CH4 was measured continuously over three fattening periods, with one period in spring and two periods in summer. On average 17.1 kg H2SO4 (96%) (m³ slurry)−1 were used for acidification during the three fattening periods. NH3 and CH4 emissions were reduced by 39 and 67%, respectively. The hydrogen sulphide (H2S) concentration in the barn air of the acidification compartment was harmlessly low (0.02 ppm). Thus, despite the storage of the acidified slurry in the barn, the system leads to a lower concentration of detrimental gases, which is beneficial for the animals' as well as for the workers’ health. The study shows that it is possible to retrofit acidification technology into existing pig barns. Further investigations shall identify possible measures to reduce the amount of H2SO4 used and thus minimise the sulphur input into the slurry.

New Developments in the High-Energy-Density Solid-Liquid Storage Technology for Redox Flow Batteries

The environmental impact of the use of fossil fuels for energy can be reduced if electricity, which represents one-third of all energy uses, can be generated totally from renewable/sustainable sources such as wind and solar. However, this is only possible if cost-effective long-duration storage technologies are available to allow the highly variable and unpredictable wind and solar energy sources to become reliable baseline energy sources like coal, nuclear or natural gases. Redox flow battery (RFB) energy storage systems are highly suitable for this large-scale, long-duration storage application because while their power output scales with the size of the battery, their energy content resides in the amount of active materials that are stored in external tanks and can be easily scaled up for longer duration.1 The conventional redox flow batteries store electrical energy in the form of some aqueous or non-aqueous soluble ions or compounds in the electrolyte solution. Because of the low solubility (< 2M) of most ions and compounds in aqueous and non-aqueous solvents, these redox flow battery systems have low energy density.2–4 For example, the commercialized all-vanadium RFB system has an average energy density of 20 Wh/kg while that of the lithium-ion battery system is 100-265 Wh/kg.5 To store enough energy for 3-5 days in these RFBs requires a very large volume of solution in a large number of tanks, making these RFB systems expensive due to the cost of tanks and the fluid distribution system and floor space. Our group recently developed a new storage approach that can greatly increase the energy storage density while still enabling the flow battery concept.6 In this approach, the reactants are stored as both soluble ions and their undissolved solid forms and only the liquid containing the soluble ions is circulated through the batteries. This approach potentially enables >4X increase in the storage energy density. This technology was recently demonstrated in a hydrogen-vanadium (VI/V) system, and new test results and findings in this area will be presented in this talk.References H. Zhang, W. Lu, and X. Li, Electrochemical Energy Reviews, 1–15 (2019).D. G. Kwabi et al., Joule, 2, 1894–1906 (2018).M. Wu, T. Zhao, H. Jiang, Y. Zeng, and Y. Ren, Journal of Power Sources, 355, 62–68 (2017).C. Ding, H. Zhang, X. Li, T. Liu, and F. Xing, The Journal of Physical Chemistry Letters, 4, 1281–1294 (2013).A. Manthiram, ACS Central Science, 3, 1063–1069 (2017).Y. Li and T.V. Nguyen, “A Solid-Liquid High-Energy-Density Storage Concept for Redox Flow Batteries and Its Demonstration in an H2-V System,” Paper ID APEN-MIT-2021_023, Applied Energy Symposium: MIT A+B, Aug. 11-13, 2021, Cambridge, MA, USA.

Close Contact without Mixing: All-Aqueous Membrane-Free Flow Battery

The accumulation of energy produced by renewable sources to be used when demand is high is a key aspect of a truly decarbonized grid. Among all energy accumulation technologies, Redox Flow Batteries (RFBs) are specially promising due to its safety, flexibility of design and the ability to decouple capacity and power of the system. In a standard configuration, both redox electrolytes that are stored in external tanks are pumped in the electrochemical reactor separated only by an ion-selective membrane. This membrane is a critical part of the battery as it allows the selective pass of certain ions that compensate the charge imbalances while maintaining separated the active species in their respective compartments. Membranes used in RFB are expensive (up to 25% of the total cost in vanadium RFB), contribute greatly to the ohmic resistance of the battery, and the undesired crossover through it is never fully avoided which produces a performance decay of the battery over time. These issues are addressed by membrane-free RFB designs developed in our group.The idea behind MFreeB ERC project is to take advantage of the immiscibility of certain liquids to naturally separate redox active species in a membrane-free battery design [1]. Aqueous Biphasic Systems (ABSs) are a special example of all-aqueous natural occurring immiscible phases made by mixing water with two compounds that can be either polymers, inorganic salts or both. The two redox active species added to the biphasic system can be rationally selected and optimized so that they partition specifically to one of the two phases used as anolyte and catholyte [2]. These types of batteries have been proposed by several groups, including us, mostly as “static batteries” because filter-press reactors, typically used in conventional RFB, cannot be easily adapted to this membrane-free concept. In order to develop truly flowing systems, a totally different electrochemical reactor should be designed.Here, we report on the development of an electrochemical reactor that allows the formation of the two immiscible phases making possible the testing of immiscible batteries under flowing conditions for the first time. A counterflow flow-through configuration was used since it reduces flow instabilities while at the same time it allows high conversion rates in the carbon felt electrodes avoiding mass transport issues [3]. Several tests were performed in the battery; e.g. polarization curves, charge and discharge cycling and efficiency over time were measured. Moreover, the self-discharge phenomena, occurring near the interface when charged species enter in contact and provoking a loss of efficiency, was evaluated as a function of operating conditions. Special attention was given to the study of the different processes occurring in the region near the interface in order to mitigate losses and further optimize the design. Acknowledgments This work has been partially funded by project MFreeB which have received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (Grant Agreement No. 726217).

Improving Anaerobic Digestion of Brewery and Distillery Spent Grains through Aeration across a Silicone Membrane

An increase in the number of independent breweries and distilleries has led to an increase in the amount of spent grains with inadequate means of disposal. One option for disposal is as feedstock for anaerobic digestion if digester stability is ensured. In this study, brewers’ spent grain and distillers’ spent grain were used as substrate for anaerobic digestion for 32 weeks. The digestate was treated by recirculation through a silicone hose located in an external tank filled with saline solution. The hose served as a permeable membrane allowing for the passage of gases. The recirculation tanks were fitted with check valves to maintain three pressure/gas regimes: 26 mm Hg N2, 26 mm Hg aeration or 100 mm Hg aeration. A fourth digester was operated with no recirculation as the control. These treatments were chosen to determine if differences in digester stability, wastewater treatment efficiency, and biogas production could be detected. A combination of dairy and swine manure was used as seeding to provide a methanogenic consortium and bicarbonate buffering. However, despite trying to provide for adequate initial bicarbonate buffering, all four digesters had low initial buffering and consequently low pH as short-chain fatty acids accumulated. After six weeks, bicarbonate buffering and pH increased as methane production increased, and short-chain fatty acids decreased. Later, despite the fluxes of O2 and N2 across the silicone membrane being very low, differences between the various treatments were noted. The pH of the digestate treated by N2 recirculation was lower than the other digesters and decreased further after distillers’ spent grain was substituted for brewers’ spent grain. Aeration at a pressure of 26 mm Hg and 100 mg Hg increased biogas production compared to other treatments but only significantly so at 100 mm Hg. These results suggest that partial purging of dissolved gases in anaerobic digestate by the small fluxes of N2 or O2 across a permeable membrane may affect digester performance.

New operating strategy for all-vanadium redox flow batteries to mitigate electrolyte imbalance

Despite the major advantage of an all-vanadium redox flow battery (VRFB) associated with the absence of cross-contamination between the anolyte and catholyte, VRFB systems still suffer from the issue of electrolyte imbalance. This is due mainly to the asymmetric water crossover between the charge and discharge operations, which is rectified only by costly periodic electrolyte rebalancing procedures during long-term usage. In this study, we attempt to mitigate the degree of electrolyte imbalance by designing different initial supporting electrolyte concentrations between the anolyte and catholyte. The new VRFB operating strategy is successfully verified using both 3-D numerical simulations and experimental tests at various charge/discharge current densities. With the same initial anolyte and catholyte compositions, the amount of catholyte and anolyte imbalance during a single charge-discharge cycle at 20 mA/cm2 is measured to be ±5.80ml based on a 50 ml external electrolyte tank. On the other hand, the amount of catholyte and anolyte imbalance is successfully reduced to ±0.70ml using appropriate control of the initial anolyte and catholyte compositions.

Ground effect aerodynamics of twin fuselage aircraft

The paper presents experimental study results of ground effect influence on the aerodynamic characteristics of the twin fuselage transport airplane in a low-speed wind tunnel. The aerodynamic configuration has the two fuselages distributed under high-wing, and a “TT”–shaped tail. The twin fuselage transport airplane model consists of two fuselages, wing, empennage and external tank. The analysis includes studying the ground effect on the longitudinal and lateral aerodynamic characteristics and horizontal tail effectiveness. The effect of installing an external cryogenic fuel tank under the wing between the fuselages of the model was considered too. The obtained data shows the typical behaviour of the aerodynamic characteristics near the ground plate for aircraft model with high-wing and high placed horizontal tail. Ground proximity significantly increases the maximum lift-to-drag ratio and slightly changes the longitudinal moment characteristics. Horizontal tail effectiveness is maintained for all tailplane angles near the ground plate. The longitudinal and lateral stability of the twin fuselage transport airplane model is maintained in all considered modes near the ground plate.