Packed Bed Thermal Energy Storage Research Articles

Numerical study of high-temperature cascaded packed bed thermal energy storage system

The thermal energy storage system (TES) in the form of packed bed with encapsulated phase change materials (EPCMs) can further improve the thermal performance of ordinary TES. This study presents a numerical model for a three-dimensional cascaded packed bed thermal energy storage system (PBTES), in which an effective thermal conductivity model is used by consisering the natural convection effects in each EPCM based on its volume average liquid fraction. To examine the system-storage thermal energy and exergy in PBTES accurately, a thermodynamic analysis approach is also given. The high-temperature PCMs are grouped as KNO3, NaNO3, and NaNO2 according to the phase transition temperature from high to low in the packed bed stage. The effects of element stages on the thermal performance of PBTES are studied. Results show that the total thermal energy storage of cascaded-PBTES is 38.5% higher than that of single-PBTES (KNO3), and the total thermal exergy storage is 30.8% higher than single-PBTES. The average exergy efficiency possessed by cascaded-PBTES is 5% higher than that of single-PBTES. Furthermore, the effects of heat transfer fluid (HTF) inlet temperature and mass flow rate on the thermal performance of cascaded-PBTES are discussed. The increase of inlet temperature and mass flow rate can promote the charging process and influence the exergy efficiency. However, increasing the inlet mass flow rate will not lead to an increase in maximum thermal energy and exergy storage capacity.

Influence of geometrical dimensions and particle diameter on exergy performance of packed-bed thermal energy storage

Expansion of infrastructure acquiring electricity from renewable sources determines the necessity of energy storage technology development. For highly urbanized areas specializing in the exploitation of underground coal deposits, due to the progressive decarbonization process, an adiabatic compressed air energy storage system using post-mining mine shafts has been proposed. The adiabatic character of the system is provided using Thermal Energy Storage (TES) tank, which is designed to be installed in a mine shaft volume. The solution determines unique geometrical dimensions compared to the studied and applied heat storage tanks, which affect both the heat transfer intensity and pressure drop of the flowing medium. This paper presents an exergy analysis of the performance of heat storage tanks on a laboratory scale, which was based on a numerical analysis validated on experimental data. It is shown that as the slenderness of the storage tank increases, the exergy efficiency of the heat storage process increases from 90.7% to 98.5% depending on the geometry studied. For the full cycle of the heat storage performance, exergy efficiency values ranging from 56.2% to 69.0% were obtained depending on the studied geometry.

Non-Stoichiometric Redox Thermochemical Energy Storage Analysis for High Temperature Applications

Concentrated solar power is capable of providing high-temperature process streams to different applications. One promising application is the high-temperature electrolysis process demanding steam and air above 800 °C. To overcome the intermittence of solar energy, energy storage is required. Currently, thermal energy at such temperatures can be stored predominately as sensible heat in packed beds. However, such storage suffers from a loss of usable storage capacity after several cycles. To improve such storage, a one-dimensional packed bed thermal energy storage model using air as a heat transfer medium is set up and used to investigate and quantify the benefit of the incorporation of different thermochemical materials from the class of perovskites. Perovskites undergo a non-stoichiometric reaction extension which offers the utilization of thermochemical heat over a larger temperature range. Three different perovskites were considered: SrFeO3, CaMnO3 and Ca0.8Sr0.2MnO3. In total, 15 vol% of sensible energy storage has been replaced by one perovskite and different positions of the reactive material are analyzed. The effect of reactive heat on storage performance and thermal degradation over 15 consecutive charging and discharging cycles is studied. Based on the selected variation and reactive material, storage capacity and useful energy capacity are increased. The partial replacement close to the cold inlet/outlet of the storage system can increase the overall storage capacity by 10.42%. To fully utilize the advantages of thermochemical material, suitable operation conditions and a fitting placement of the material are vital.

Coupled Thermal and Mechanical Dynamic Performances of the Molten Salt Packed-Bed Thermal Energy Storage System

Coupled Thermal and Mechanical Dynamic Performances of the Molten Salt Packed-Bed Thermal Energy Storage System

Experimental and computational analysis of packed-bed thermal energy storage tank designed for adiabatic compressed air energy storage system

The growing importance of decarbonization and renewable energy sources to national power systems has brought about a need to implement large-scale energy storage technology. Adiabatic Compressed Air Energy Storage (A-CAES) systems comport with the environmental requirements of renewable energy storage better than traditional CAES systems because they eliminate the combustion of auxiliary fuel during discharge. This benefit is achieved with a Thermal Energy Storage (TES) tank that heats up during the air compression step, stores the thermal energy, and then releases it during discharge by heating the expanding air. This process increases the overall energy efficiency of the A-CAES system since a large portion of the heat of compression is used rather than lost. The subject of this paper is an experimental and numerical study of a slender basalt-filled TES tank designed for installation in decommissioned mine shafts. Storing energy in such otherwise unused, already depreciated infrastructure represents a unique application and economic opportunity for highly urbanized industrial areas. Situating A-CAES systems in mine shafts also significantly reduces their cost due to natural stress compensation from high air pressure. The slenderness of the reservoir compared to existing and previously studied systems has a positive effect on the efficiency of heat storage in the basalt due to the reduced heat conduction field, but results in a greater pressure drop of the flowing air. To investigate the performance of the TES storage tank, a laboratory bench was constructed with basalt grit as the accumulation material. The experimental results obtained were used to verify the numerical model used in ANSYS Fluent. The numerical model showed a theory–experiment discrepancy in the basalt temperature rise results of only 1.91% for the entire curves and 2.29% for the most intense temperature rise phase, and the difference between the pressure drop results did not exceed 4%. The flexibility of the numerical model was tested for various input parameters. A high level of model validation was achieved by selecting an accurate correlation for the Nusselt number, as well as implementation of temperature-dependent thermodynamic parameters for the storage material.

Thermal performance of the packed bed thermal energy storage system with encapsulated phase change material

The thermal performance of the packed bed thermal energy storage (PBTES) system used in waste heat recovery and utilization is studied experimentally and theoretically. The experiments are conducted to test the thermal performances of the PBTES system at various charging temperatures and mass flow rates. In addition, a one-dimensional concentric dispersion model considering heat loss is established and validated by the experimental results. Furthermore, the non-dimensionalized model is developed, and the heat transfer processes inside the PBTES system at various Pe, Nuloss,vol and Ste numbers are simulated. The results show that the time durations of the charging and discharging processes are significantly decreased with the increases of the Pe and Ste numbers, e.g., reduced by 44.7% of charging duration as the Pe number increases from 188 to 338, and the time durations are indistinctively affected by the Nuloss,vol number, i.e., increased by 7.1% of charging duration as the Nuloss,vol number increases from 19.9 to 46.5. The thermal efficiency is significantly increased from 65.6% to 80.1% as the Pe number increases from 188 to 338, and from 59.2% to 77.6% as the Ste number increases from 0.479 to 0.799. The novel dimensionless parameter Nuloss,vol number shows great effect on the thermal performance and the thermal efficiency is significantly decreased from 91.3% to 72.6% when the Nuloss,vol number increases from 19.9 to 46.5. Besides, a new dimensionless parameter Nr¯ number which is a monotonic function of instantaneous thermal efficiency is proposed and can be used for estimating the heat transfer performance of the PBTES system.

Experimental evaluation of a high-temperature radial-flow packed bed thermal energy storage under dynamic mass flow rate

High-temperature thermal energy storage is recognized to be a key technology to ensure future sustainable energy generation. Packed bed thermal energy storage is a cost-competitive large-scale energy storage solution. The present work introduces the experimental investigation of an innovative 49.7 kWhth radial-flow type high-temperature packed bed thermal energy storage under dynamic mass flow rates. Various dynamic air flow rate profiles, representative of different potential applications, have been tested during the charging process to investigate their influence on the thermodynamic performance of the storage. The outlet thermal power during the discharge has been controlled by managing the air flow rate. Short operational cycles have also been performed. The results show that dynamic mass flow rates can lead to a thermal efficiency reduction between 0.5 % and 5 % with respect to static conditions. Controlling the air mass flow rate could be an efficient strategy to stabilize the thermal power output during the discharge while minimizing peaks in the pressure drop. This work testifies that specific dynamic boundary conditions should be included during the thermal storage design process since they could largely affect the unit thermodynamic performance and potential scale-up. If no specific dynamic profiles are available during the packed bed storage design stage, it is suggested to consider typical dynamic profiles of the air mass flow rate to guarantee limited efficiency reduction during operation.

Performance analysis and optimization of packed-bed TES systems based on ensemble learning method

Most existing studies that focused on the performance analysis and optimization of packed bed thermal energy storage systems (PBTESS) have ignored some impact factors, which decreased the accuracy of the system performance prediction. In this work, the Latin Hypercube Sampling (LHS) and numerical simulation were used to construct the training database, and a full-parameter prediction model of PBTESS was constructed with the help of the LightGBM (LGBM), the naive Bayes optimization algorithm was then used to further optimize the performance of PBTESS. The prediction model considered all parameters of the system and the rationality was verified through the numerical simulation. The results showed that LGBM was effective in predicting actual heat release time, actual heat storage, and actual utilization rate of the material with R-square of 0.960, 0.962, 0.956. Meanwhile, the trained prediction model could analyze the effects of all parameters on the performance of PBTESS by the characteristic importance method. The optimization results showed that actual heat release time, actual heat storage, and actual utilization rate of the material of PBTESS were improved by 410%, 14.11%, and 39.86%.

The Thermal Response of a Packed Bed Thermal Energy Storage System upon Saturated Steam Injection Using Distributed Temperature Sensing

The effectiveness of a thermal energy storage (TES) system is typically characterized with the help of thermal stratification or temperature gradients along the direction of heat injection, which is typically the flow direction of heat transfer fluid. The steepness of temperature gradients are a direct indicator of the effectiveness or efficiency of the heat storage or dispatch process. The temperature gradient evolution along the packed bed of ceramic particles upon saturated steam injection is presented in this work. Distributed temperature sensing based on optical frequency domain reflectometry was deployed in a packed bed of ceramic particles to capture the thermal front evolution in the axial direction. The physical processes accompanying steam injection in packed beds are complex due to phase change, transitioning two-phase flow, and changes in condensate accumulation. Therefore, the variation of thermal response of the TES system for various steam injection flow rates was experimentally studied using a high-resolution distributed temperature sensing system in a chemically inert alumina particle-packed bed. Distinct zones of different heat transfer modes were observed during the steam injection experiments. A distinct conduction zone, evident from diffuse thermal fronts, was observed at low flow rates, and these thermal gradients became sharper as the flow rate increased. The diffuse thermal fronts in the heat storage media suggest a low exergy efficiency of the TES system, as energy losses started initiating before a significant fraction of the bed was saturated with steam.

Design and investigation of solar cogeneration system with packed bed thermal energy storage for ceramic industry

A novel cogeneration system was designed with three different configurations integrating cogeneration system with solar-aided (Configuration-1), solar-aided with packed bed thermal energy storage (Configuration-2), solar-aided with packed bed thermal energy storage and auxiliary unit (Configuration-3). Thermo-economic-environmental analyses were performed for three designed configurations under Indian climatic conditions (20°C–50 °C).The maximum energetic and exergetic efficiencies of the three configurations were found as 44.96% and 23.14%, 51.84% and 31.22%, and 58.67% and 36.21%, respectively. Configuration-3 was best among others, and the sustainability index was 1.57. The maximum irreversibility rate has occurred for the combustion chamber, ground and wall tile dryer. The payback period for Configuration-3 was found as 4.91 years. Due to various unfavourable conditions, the payback period for Configuration-2 is 27% higher than Configuration-3. The economic optimization was performed for the higher payback period configuration, and the payback period was finally reduced to 4.88 years. The cost of the product from the cogeneration system, such as electricity and ground-wall tile was found as Rs.6.29/unit and Rs.16.11/piece for ceramic tile size of 0.10 × 0.10 × 0.007 m. The CO2/SO2/NOx emission from the three configurations was found as 1,54,090/119/230 ton/year, 1,31,341/102/196 ton/year, and 1,47,961/114/221 ton/year, respectively. Furthermore, the carbon emission saving for three configurations was obtained as 21%, 24%, and 32%, which is imperative for the environment.

Applicability of coal slag for application as packed bed thermal energy storage materials

Refractory materials are considered as the most suitable high-temperature sensible heat storage materials due to their excellent thermo-mechanical resistance and superior thermophysical properties. Unfortunately, refractories are usually too expensive. To reduce the cost of energy storage materials, the recycling of refractory industrial solid wastes into storage materials is becoming increasingly prevalent. The paper innovatively proposes to use the slags from a liquid slagging furnace of a coal-fired power plant in China as packed bed sensible heat energy storage materials. This paper characterizes the chemical compositions and thermophysical properties of three typical coal slags (Fukang coal slag, Fukang coal granulated slag, Hongshaquan coal granulated slag) and evaluates their potentials as storage materials. The results show that the three kinds of coal slags have good thermophysical properties. At 380 °C, the energy storage densities per unit volume of the three materials are 1037 MJ/m3, 986 MJ/m3 and 920 MJ/m3, respectively. Fukang coal slag has good thermal stability and durability and can be directly used for ultra-high temperature energy storage at 1000 °C. Due to the low crystallization degree, the two granulated slags have poor thermal durabilities and need to be processed at high temperatures before using them for energy storage applications.

A performance analysis of the spray-type packed bed thermal energy storage for concentrating solar power generation

The concept of spray-type packed bed thermal energy storage (medium and high temperature thermal energy storage, from 200 °C to 350 °C, Alumina pellets+T66 fluid) has been proposed in our previous investigation. Its low-cost and high-efficiency shows its promising application prospect. Further investigation of the new concept is carried out both numerically and experimentally in this paper. First, the “charging-standby-discharging” cycle of a pilot spray-type packed bed is investigated experimentally. Second, the dynamic liquid holdup of the spray-type packed bed is correlated with the experiment data and is applied to build the mass balance equations. Based on the energy balance equations and mass balance equations, a three-phase one-dimensional transient model for the spray-type packed bed is established. Results from the experiment confirms the correctness of the numerical model. Based on the model, the liquid holdup of the packed bed during the “charging-standby-discharging” cycle is studied. At last, sensitivity analysis was carried out to study the influence of the parameters of the “charging-standby-discharging” process on the thermal performance of the spray-type packed bed. Values of these parameters can be found to achieve the best thermal performance of a spray-type packed bed.

Economic and environmental assessment of a CO2 solar-powered plant with packed-bed thermal energy storage

Investigating supercritical natural fluids for efficient and clean energy production has become a trending research topic due to their technical and environmental advantages. However, on account of the supercritical operational conditions, using specially-developed components increases manufacturing prices, especially when dealing with solar-powered plants assisted by thermal energy storage (TES) systems. This paper assesses the economic and environmental trends of an integrated supercritical carbon dioxide (s-CO2) solar-powered plant. The system is composed of a packed-bed TES system, a solar field, and a power block while considering conventional backup heating. Transient year-around numerical simulations explore several operational conditions relying on detailed cost and typical meteorological year (TMY) data. Also, the modeling accounts for the system’s environmental sustainability through a penalization cost regarding CO2 emissions due to auxiliary heating. With parametric analyses, the study assesses the compromise solutions minimizing the levelized cost of energy (LCOE). The results revealed the possible feasibility of the integrated system using such a TES technology for s-CO2 and evidenced several venues for further examination. In the end, a sensitivity analysis investigates the influence of the specific costs and TMY data on the LCOE.

Design optimization on characteristics of packed-bed thermal energy storage system coupled with high temperature gas-cooled reactor pebble-bed module

The packed-bed thermal energy storage (PBTES) coupled with the high temperature gas-cooled reactor pebble-bed module (HTR-PM) system is of emerging interest which can ensure the economy, safety and reliability operation of the HTR-PM. For the coupled PBTES system, multi-parameters need to be considered and there is a need to propose an integral method to help the design and optimization. In this work, firstly, the numerical results are compared and validated with the experiment data. Then, the thermal characteristics of the coupled PBTES system including the overall heat storage quantity, heat release quantity, average charging power, average discharging power, charging/discharging/total enthalpy efficiency and charging/discharging/total exergy efficiency are systematically evaluated with the orthogonal design optimization. At last, the typical non-dimensional numbers including the ReP number, Nu number and Pr number of the high temperature fluid (HTF) are illustrated for the optimal scheme. The results indicate that the calculation results agree well (relative error within 7.0%) with the experiment data. Additionally, the most optimal scheme is determined as 26 mm of the capsule diameter, “K2CO3-Li2CO3 (65–35 wt%)”+“LiF-NaF-KF (29–12–59 wt%)” of the phase change materials (PCMs), 0.229 m3·s−1 of the inlet HTF flow rate and 850℃ of the inlet HTF temperature or initial PCMs temperature. It demonstrates an integral method including the numerical model calculation, orthogonal design optimization, thermal characteristics evaluation, range and variance analysis, enthalpy and exergy efficiency and dimensionless number for the design of the coupled PBTES system.

Dynamic simulation and techno-economic analysis of liquid air energy storage with cascade phase change materials as a cold storage system

Liquid air energy storage (LAES) is a promising solution for overcoming the challenge of intermittency in renewable-based energy systems. Cold recovery is the most important part of the LAES and plays a vital role in the performance of the system. In this study, the LAES system which utilizes a packed bed thermal energy storage (PBTES) comprising three-layer phase change materials (PCM) is investigated from a thermodynamic and economic point of view. As a result of the transient nature of PBTES the dynamic modeling is applied to analyze the performance of the system. The designed LAES system with ideal condition consumes 4.42 MWh for compressing the air and generates 1.8 MWh of electricity during the peak time. The payback period of the system for the case study of San Fransico is 6.7 years with 0.66 M$ total profit. As a dynamic behavior of the system liquid yield, the mass flow rate of liquid air, the specific work of the compressors, and the cryo turbine vary during different cycles. After about 22 cycles system with a total efficiency of 42.5% reaches the equilibrium and the performance of the system decrease about 5.9% because of transient behavior in comparison with the ideal cycle.

Experimental evaluation of an innovative radial-flow high-temperature packed bed thermal energy storage

High-temperature packed-bed thermal energy storage represents an economically viable large-scale energy storage solution for a future fossil-free energy scenario. The present work introduces first-of-a-kind experimental setup of a radial packed-bed TES, and its performance assessment based on experimental investigations. The storage performance is analyzed based on a set of dimensionless criteria and indicators. The laboratory-scale prototype has an energy capacity of 49.7 kWhth and working temperatures between 25 °C and 700 °C with a non-pressurized dry airflow. The influence of different working fluid mass flow rates and inlet temperatures during charge and discharge is assessed. The proposed storage design ensures limited pressure drop, lower than 1 mbar, and thermal losses, about 1.11 % during dwell after charging at 700 °C until a state of charge of 55.8 %. A maximum overall thermal efficiency of 71.8 % has been recorded and trade-offs between efficiency, thermal uniformity, and thermocline thickness are highlighted. This work testifies that reduced pressure drops are the key advantage of radial-flow packed-bed designs. Thermocline degradation is shown to be the main weak point of this thermal energy storage design.

Numerical modelling and optimization of packed-bed thermal-energy storage system

In this work, numerical modelling (including convection and radiation heat transfer) of Packed-bed storage systems (PBSS) is carried out and the effect of various system parameters affecting the efficiency and temperature is studied. One dimensional forms of the time-dependent, coupled partial differential equations for energy conservation of the heat transfer fluid (HTF) and the packing materials are solved using the finite difference method to design a PBSS for a given mass flow rate for 0.125 MWh (0.45 GJ). The packed-bed material is assumed to be spherical with an average diameter, and the mass flow rate, void fraction, packed bed material diameter, heat transfer fluid (HTF), and the packed-bed materials are varied for optimal efficiency during charging (i.e. when the temperature of HTF is greater than that of the packed bed). The results are compared with the analytical solutions for validation. Present solutions (considering only convection) are found to be matching reasonably well with the analytical data. With the validated model, the radiation heat transfer effect on the packed-bed is modelled (along with the convection) and void fraction, mass flow rate of HTF, a diameter of the packed-bed material, different HTF, various packed-bed materials are compared for maximum efficiency. From the present work, a PBSS design with void fraction =0.45, mass flow rate =1.8 kg/s, the average diameter of the packed-bed material = 0.02 m, water as HTF, and brick as packed-bed material is found to give the maximum efficiency along the length of the packed-bed.

Thermal and structural characterizations of packed bed thermal energy storage with cylindrical micro-encapsulated phase change materials

This work evaluates the circumferential thermal stress developed in the tank wall due to the restricted contraction during discharging operation, exergy efficiency, and stratification behaviour of a cylindrical micro-encapsulated packed bed latent heat thermal energy storage (PBTES) systems. A numerical model employing the enthalpy-porosity technique and the non-equilibrium energy equations for heat transfer fluid (HTF), phase change material (PCM) and wall of the storage tank is developed. The effect of PCM melting is incorporated in the energy equation by estimating the thermal resistance that arises from the radial shifting of the solid-liquid interface inside the cylindrical capsule. Hytherm 600 is HTF that flows through the pores between cylindrical particles filled with a commercial PCM, A164. A parametric investigation is conducted to examine the effects of varied charging and discharging HTF inlet temperatures, tank wall material, and arrangement of the cylindrical capsule. The higher charging HTF inlet temperature shows better thermal stratification. The thermal stress increases on decreasing the discharging HTF inlet temperature. The HTF flow over the capsules axially shows better thermal stratification and exergy efficiency. The thermal stress in the TES wall is found higher for cross-flow arrangement over the capsules than axial flow arrangement.

Thermal energy storage characteristics of packed bed encapsulating spherical capsules with composite phase change materials

• Experiments were conducted on a solar heating system with a PBTESD. • The PA/EG/CF composite phase change material were prepared. • Models were developed for the dynamic processes of the packed bed. • Temperature field and dimensionless parameter analysis was conducted. Packed bed thermal energy storage technology is one of the valid methods to coordinate the balance of energy sources supply and demand and settle the matter of the time and space mismatching of renewable energy in the future. In this paper, the thermal energy storage characteristics of a packed bed thermal energy storage device (PBTESD) filled with spherical phase change capsules are analyzed. The PA/EG/CF composite phase change material (CPCM) was used as an encapsulation material, and water was used as heat transfer fluid (HTF). Based on Schumann’s model, a one-dimensional two-energy equation two-phase mathematical model of PBTESD was established. The heat transfer resistance between the spherical phase change capsules and HTF and the heat loss between the heat storage tank and the surrounding environment were considered in the model. MATLAB was used for numerical simulation calculation of the equation, and the results obtained were compared with the experimental results and literature results. The effects of Reynolds number, Stefan number, dimensionless diameter and effective thermal conductivity of phase change material (PCM) on the temperature evolution trend and thermal performance of PBTESD were investigated by single factor analysis. The results showed that the increase of Stefan number leaded to the increase of thermal energy storage density in the charging process. Increasing Reynolds number and Stefan number and decreasing dimensionless diameter increased the average energy storage rate and average exergy storage rate. The reduction of Stefan number and dimensionless diameter could improve exergy efficiency, while the effective thermal conductivity of PCM had little effect on the thermal characteristics of PBTESD. This paper elaborated on the transient thermal characteristics of PBTESD, which laid a foundation for subsequent research.

A study of metallic coatings on ceramic particles for thermal emissivity control and effective thermal conductivity enhancement in packed bed thermal energy storage

Ceramic particles based packed bed systems are attracting the interesting from various high-temperature applications such as thermal energy storage, nuclear cooling reactors, and catalytic support structures. Considering that these systems work above 600 °C, thermal radiation becomes significant or even the major heat transfer mechanism. The use of coatings with different thermal and optical properties could represent a way to tune and enhance the thermodynamic performances of the packed bed systems. In this study, the thermal stability of several metallic (Inconel, Nitinol, and Stainless Steel) based coatings is investigated at both high temperature and cyclic thermal conditions. Consequently, the optical properties and their temperature dependence are measured. The results show that both Nitinol and Stainless Steel coatings have excellent thermal stability at temperature as high as 1000 °C and after multiple thermal cycles. Contrarily, Inconel (particularly 625) based coatings shows abundant coating degradation. The investigated coatings also offer a wide range of thermal emissivity (between 0.6 and 0.9 in the temperature range of 400–1000 °C), and variable trends against increasing temperature. This work is a stepping-stone towards further detailed experimental and modelling studies on the heat transfer enhancement in different ceramic-based packed bed applications through using metallic coatings. • Thermal stability of nine metallic coatings on ceramics is tested up to 1000 °C. • Inconel 738 shows excellent thermal stability after long residency at 1000 °C. • Nitinol and Stainless Steel 304 present oxidation but not coating loss under cycles. • Thermal emissivity are between 0.6 and 0.9 in the temperature range of 400–1000 °C. • Effective thermal conductivity increases of 17% at 1000 °C can be attained.