Industrial Waste Heat Recovery Research Articles

Modification of steel slag to prepare chlorides based composite phase change materials with shape stability for high-temperature thermal energy storage

Using steel slag to prepare high-temperature (>500 °C) PCMs was an effective way to achieve its high value-added utilization as a potential heat storage medium in a variety of applications, such as solar energy storage, power peak shaving, and industrial waste heat recovery. However, the complex solid waste of steel slag might be corrosive to salt-based PCMs at high temperature. To address this issue, steel slag was firstly modified with another solid waste (i.e., CFA), which was then used to microencapsulate NaCl-KCl to prepare shape-stabilized C-PCMs in this work. Thermophysical and mechanical properties of C-PCMs were analyzed. Results showed that CFA modification greatly improved chemical compatibility between steel slag and eutectic salt through phase reconstruction. Steel slag modified with 30 wt% CFA at 1100 °C was identified as the optimum skeleton. The prepared C-PCMs containing 50 wt% salt showed a phase transition temperature of 653 °C with a high latent heat of 139 J/g and an excellent cycling stability. Additionally, its thermal conductivity reached 1.46 W/(m·K), 180 % higher than of pure salt. Compressive strength of the composite could be as high as 119 MPa, superior to other salt-based C-PCMs. A heat storage device was further designed to allow the numerical investigation of thermal performance of the prepared C-PCMs in practical conditions. Attributed by reasonable arrangement of bricks, the heat storage device possessed a uniform temperature distribution over the vertical cross-section of HTF, which contributed to a quick completion of charging and discharging process. This work could potentially lay a foundation for application of steel slag in the field of high-temperature thermal energy storage.

Hybridization of heat recovery from exhaust gas of boilers using thermoelectric generators

This study investigates the possibilities for energy recovery and environmental effect reduction of waste heat, a consequence of industrial activities. The main objective of the work is to integrate thermoelectric generators (TEGs) into industrial hybrid waste heat recovery system. The study consists of combining TEGs modules with a boiler waste heat recovery system with Rockwool insulation, taking into consideration variables like thermal resistance, power output, water temperature, and energy conversion efficiency. The results show that TEG placement has a major impact on system performance. One of the promising configuration is TEGs placed close to heat source, especially outside exhaust pipe outer walls, where electrical power up to 27 W can be generated and heat of 4215 W can be recovered from the exhaust gas.

Experimental study on flow characteristics of falling film over horizontal tubes under countercurrent gas flow

Open-absorption heat pump serves as an important means of industrial waste heat recovery, and the overall performance of the heat pump system depends on the absorber’s performance. Horizontal-tube–falling-film absorption refers to a complex process involving the coupling of fluid flow, heat transfer, and mass transfer. For the complete understanding of the intertube flow characteristics of horizontal-tube falling film under countercurrent gas flow (We), Visual experimental studies on falling-film flow were conducted using high-speed photography. The critical Reynolds number (Re) was quantitatively characterized to represent the transition of different flow patterns between tubes. The experiment was conducted to investigate the variation in the critical Re under the coupling effects of various factors and establish an experimental prediction correlation formula for the critical Re and solution properties, We, s, and d with an error margin of less than 10%.The influence of single factors was characterized qualitatively and then subjected to sensitivity analysis. The factors affecting the critical Re in descending order of magnitude were as follows: solution mass fraction > s > d > countercurrent gas flow (We). A reduction of approximately 50% in the critical Re for every 10% increase in the solution mass fraction.

Multi-Stakeholder Decision Support Based on Multicriteria Assessment: Application to Industrial Waste Heat Recovery for a District Heating Network in Grenoble, France

The decarbonization and decentralization of district heating networks lead to the shared use of on-site resources by multiple stakeholders. The optimal design of prospective equipment in such contexts should take into account the preferences and objectives of each stakeholder. This article focuses on the adaptation of a 4E multicriteria model (the criteria being energy, exergy, economic, and exergoeconomic) to include and compare the stakeholders’ performance criteria around the technical design. In addition, two graphical supports are proposed that represent and cross-analyze the different stakeholders’ preferred optima. A preliminary implementation of the methodology is illustrated through a study case in France, which features waste heat recovery for district heating utilization. After presenting the results, a discussion is offered on how to complete the methodology with an iterative negotiation procedure to determine the most suitable design. It was concluded, among other considerations, that the relaxation of the stakeholders’ optimality requirements can greatly enable the project’s feasibility. Such a relaxation could be implemented in the form of a joint consortium. In addition, the results showed that stakeholder relaxations of requirements can lead to new solutions that may outperform the best solutions pre-relaxation. Lastly, perspectives are suggested toward verifying whether relaxed requirements from upstream stakeholders might be more impactful than those of downstream stakeholders.

Case study on combined heat and water system for district heating in Beijing through recovery of industrial waste heat in Tangshan

With the proposal of China's dual-carbon goal, the recovery of industrial waste heat (IWH) for district heating has gained increasing attention. Recently, some scholars have proposed that combined heat and water (CHW) systems are more economical compared with separate heat and water supplies. Beijing lacks desalinated water (DW) and clean low-carbon heat, whereas Tangshan in Hebei Province is rich in IWH. By combining CHW with seasonal thermal energy storage, a case of long-distance transport of hot DW from Tangshan to Beijing was planned, and the costs, energy consumption, and feasibility were analyzed. As a result, under the optimal heat source temperature and effect number of 70 °C and 10 for seawater desalination, the heat from various IWH sources of the three costal steel plants is recovered maximally to produce about 35000 t/h of 95 °C DW. Then, the hot DW is transported to Beijing with a long-distance heat loss ratio controlled below 3 %. Annually, 271.2 million tons of DW and 91.5 million GJ of heat is supplied. The introduction of IWH can save 2.68 billion Nm3 of natural gas per year and the discounted payback period is about 10 years, which has obvious energy-saving, environmental, and economic benefits.

Impedance spectroscopy analysis of thermoelectric modules under actual energy harvesting operating conditions and a small temperature difference

Thermoelectric (TE) devices can convert heat into electricity and have gained great interest as energy harvesters in many applications, such as self-powered sensors, solar TE generators and industrial waste heat recovery. Not many techniques are usually available for their characterization under operating conditions. Consequently, only current-voltage (power output) curves are typically reported to account for their performance, which provide limited information. Impedance spectroscopy, which has been mainly applied to the study of TE modules suspended in air or vacuum, has the advantage to be used under operating conditions. Here, we exploit this advantage and provide an in-depth analysis of the impedance response of standard TE devices when they operate under a small temperature difference. First, we derive the physical models (equivalent circuits) for the two most common operating conditions: (i) constant temperature difference and (ii) constant heat power input. Then, we use the obtained equivalent circuit to successfully fit experimental impedance measurements in both operating modes, which show significant differences. From the fittings, it is possible to obtain the thermal contact resistance between the TE device and the heat exchangers (heat source and heat sink) among other key parameters. In addition, we analyze the variations found in the impedance spectra for different current output levels. Moreover, we show how different electrical resistances, extracted from the impedance results, directly relate to the slope of the I-V curve (power output), and can provide very valuable information about the different processes that determine its value. All these results establish impedance spectroscopy as a very powerful tool to characterize TE devices under operating conditions and as a method that can provide highly valuable insights into their performance.

Form-stable Na2CO3-NaCl/mullite phase change composite with SiC enhanced thermal conductivity for high temperature thermal storage

High-temperature energy storage technologies are gaining prominence to meet the needs of concentrating solar power plants and industrial waste heat recovery. In this study a series of form-stable phase change materials are prepared by a simple and efficient cold compression sintering method. In this method, Na2CO3-NaCl will be mixed with mullite ceramic powder; simultaneously, SiC nanoparticles are introduced to improve the thermal conductivity of the material. The leakage, microstructure, chemical compatibility and thermal physical properties of the prepared composites are systematically analyzed using Fourier-transform infrared spectroscopy, X-ray powder diffraction, Scanning electron microscope, Differential Scanning Calorimetry and Thermogravimetric. The results of the study show that good chemical compatibility of the components in the composites, and the latent heat of melting of the encapsulated composites as well as the sample with added SiC are 266.97 J/g and 217.63 J/g, respectively, while the latent heat of crystallization is 197.37 J/g and 151.13 J/g, respectively. Compared to the thermal conductivity of PCMs (0.41 W/(m·K)), the thermal conductivity of the sample with 20 % SiC added is 1.83 W/(m·K), an increase of 8.7 times. Thermal cycling and reliability tests show that even after 300 cycles, good chemical compatibility is maintained between the components in composites, and the phase change properties and quality remain stable. In addition, the thermal storage cost of FSPCM-M40-S20 is 1.90 $/MJ. Therefore, we believe that the prepared Na2CO3-NaCl/mullite/SiC FSPCM has promising applications in high-temperature thermal energy storage, especially in solar power generation and industrial waste heat recovery.

Multi-layered composite coatings with enhanced corrosion and abrasion resistance for industrial flue gas waste heat recovery

The corrosion and abrasion performance of flue gas heat exchangers is a prominent research focus in the field of industrial flue gas waste heat recovery. In this study, we have developed a multi-layered composite coating containing fluorographene and carborundum fillers, which exhibits excellent anti-corrosion and wear-resistant properties. Electrochemical and abrasion experiments demonstrate that the multi-layered composite coating effectively improves both the corrosion resistance and the mechanical properties of the material. The structure and preparation of this multi-layered composite coating provide a novel approach for design and application of advanced coatings for highly corrosive and dusty flue gas waste heat recovery.

Performance simulation study of multi-stage compression-throttle water working medium high-temperature heat pump system

In order to meet the demands of industrial high temperature heat and waste heat recovery in an economical and low-carbon manner, there has been a growing interest in the high-temperature heat pump using water as working medium. The study aims to address the issue of higher exhaust temperature in water working medium heat pumps resulting from a substantial increase in temperature, especially for the large temperature difference system which needs to adopt multi-stage compression. This will be accomplished by proposing a new and energy-efficient high-temperature heat pump system that utilizes water as the working medium. The optimized system combining with self-circulating water spraying and multi-stage compression, which can significantly reduce exhaust superheat and steadily improve system performance. A thermodynamic analysis was conducted on both two-stage and three-stage high-temperature heat pumps, taking into account the improved structure. The results indicate that the three-stage compression-throttle type can achieve the highest maximum water spraying ratio and the lowest exergy loss. This can effectively decrease the superheat of the compressor exhaust and enhance the overall system performance. Furthermore, in the three-stage compression-throttle system, when the evaporation temperature is set at 100 °C with a temperature increase of 40 °C, a mere 0.01 % augmentation in the water spraying ratio results in approximately a 0.0776 uplift in the COP of the water working medium system. This notable observation suggests that the implementation of self-circulating water spraying considerably enhances the system’s overall performance. Subsequently, an analysis of the corresponding design and operating parameters was conducted. It is important to note that the temperature of the waste heat source and the rotational speed of the compressor are the two key parameters that significantly impact the operation of the system. By this study, it provides some theoretical guidance for practical engineering applications.

Numerical simulation of a combined thermochemical-latent energy storage system based on paired metal hydrides and phase change material

The main goal of this paper is to assess the operating performance of a thermal energy storage system that combines latent and thermochemical heat storage for their utilization in industrial waste heat recovery as well as in solar power plants. Thermal energy is stored and released through endothermic desorption and exothermic absorption processes, thereby cycling hydrogen between two paired metal hydrides (MHs). The thermal performance of the dynamically coupled Mg2Fe/LaNi5 pair, which has never been investigated before, is presented in this study. Sodium acetate trihydrate is used as a PCM for the LaNi5-tank thermal management. Moreover, during the heat charging stage, the Mg2Fe-tank was subjected to a typical solar heat flux. A mathematical model has been established and utilized to simulate how the storage system would operate in practical situations. The impacts of the operating conditions, which are the efficiency of the supplied heat system, the HTF temperature, the heat transfer coefficient, and the initial temperature of the MH beds, on the storage system's performance are studied and discussed in detail. The findings from this investigation revealed that the pairing of Mg2Fe with LaNi5 at suitable operating conditions enabled the storage system to achieve a specific energy storage capacity of 2 MJ/kg of Mg2Fe and an efficiency of 87.1 %. The results of this study reveal the excellent performance of a potential and viable metal hydride pair (Mg2Fe/LaNi5) for its usage in thermal energy storage systems.

Novel value-add recycling route of industry solid waste for acting as supporting skeleton of NaNO3 phase change materials (PCMs)

This study provided a value-added utilization route for industrial solid waste by converting them into porous ceramics to act as supporting skeleton for PCMs. Steel slag (SS), ferronickel-slag (FNS) and Fly ash (FA) was used as main raw material to prepared anorthite-cordierite (AC) porous ceramics. Five groups of formula with different phase content were designed by adjusting the amount of SS and FNS addition. FactSage 8.0 software was applied to calculate the equilibrium phase composition of AC at high temperature, which provided guidance for the actual high temperature synthesis process. The prepared AC porous ceramics were found to have good mechanical strength and high porosity. Good chemical compatibility between AC and NaNO3 was demonstrated and the infiltration ratio was varied from 42% to 45%. In addition to high thermal storage capacity, AC has been found to help reduce the supercooling of NaNO3 and helps to improve the thermal storage performance. After 100 thermal cycles of melting and freezing, NaNO3/AC C-PCMs could maintained high than 97% of latent heat. Thermal transfer properties of AC were significantly enhanced after molten NaNO3 infiltrated. The thermal conductivity of NaNO3/AC40 C-PCMs at 25 °C reached 1.60 W·(m·K)−1, which is more than three times that of pure NaNO3. The good thermal storage performance of NaNO3/AC C-PCMs makes it potential candidate in high-temperature thermal storage fields like industrial waste heat recovery and solar energy storage. In a word, the application potential of metallurgical slag in the field of energy saving was well demonstrated by this study.

Novel high thermal conductivity alumina/salt composites for thermal energy storage: Effect of wettability on microstructure and properties

In this work, alumina foam ceramics (AFC) were prepared by foaming method, and AFC/salt composite phase change materials were prepared by melt infiltration method using AFC as skeleton materials. The results showed that AFC had good chemical compatibility with Na2SO4 and NaCl. The salt contents of AFC/Na2SO4 and AFC/NaCl were 37.8 wt% and 31.7 wt%, respectively, with compressive strength of 100.1 MPa and 72.8 MPa, thermal conductivity of 5.53 W/m·K and 6.40 W/m·K, and energy density of 1129 J/g and 1019 J/g, respectively. Due to the better wettability, AFC and Na2SO4 form a chimeric structure, which has better binding and bonding strength, and is not prone to molten salt leakage. AFC/ Na2SO4 is expected to be applied to industrial waste heat recovery and solar thermal power generation with periodic temperature changes.

Numerical investigation of latent heat storage unit with dual helical tube

The application of latent heat storage systems in waste heat recovery has become a promising solution for energy storage. This study proposes a configuration using dual helical tube, specifically designed for industrial waste heat recovery applications. This study investigates the thermal performance of a horizontal dual helical energy storage unit under natural gravity. It considers various parameters, including helical diameter, the number of helical turns, and eccentricity. When an eccentricity of 5 mm is used, the overall energy storage time is reduced by 30.86 %, and the energy storage density is at its highest (3.11 × 10−4 kW/cm2). Adjusting the outer helical tube to 9 turns produces the highest energy storage efficiency (0.9252). Additionally, the heat transfer characteristics during simultaneous energy storage and release processes have been studied. The results indicate that as the temperature difference or velocity ratio between the heat transfer fluids increases, the liquid fraction at steady state decreases. This decrease in liquid fraction requires a longer time to reach the steady state. When the outer helical tube is filled with the hot fluid and counter flow configuration is adopted, it achieves higher levels of absorption and release power at steady state. The influence of velocity on absorption and release power is more significant than that of temperature difference.

Research on the low-temperature waste heat storage performance of a novel microencapsulated phase change material with a double-shell encapsulation of hexadecylamine

Phase change materials (PCMs) have the advantages of high energy storage density and the temperature can be kept stable when the phase change process occurs, so they can be widely applied to the recovery of industrial waste heat. In this paper, hexadecylamine (HDA) was selected as PCMs, polystyrene (PS) and calcium carbonate (CaCO3) as wall materials, and PS/CaCO3/HDA microencapsulated phase change materials (MEPCMs) were prepared by ultrasonic emulsification. Then the prepared PCMs were characterized and their properties were tested by using transmission electron microscopy, scanning electron microscopy, X-ray diffraction analyzer, X-ray photoelectron spectrometer, Fourier infrared spectrometer, thermogravimetry, differential scanning calorimetry and other characterization methods. The results showed that PS/CaCO3/HDA MEPCMs with microcapsule structure were successfully prepared with a diameter of about 1.5 μm. The thermal conductivity of PS/ CaCO3/HDA MEPCMs was 0.491 W/(m·K), which was 3.41 times of the thermal conductivity of pure HDA. The highest latent heat of PS/CaCO3/HDA MEPCMs was 33.96 kJ/kg, and no leakage problems occurred. The above results indicate that PS/CaCO3/HDA MEPCMs have good stability and high thermal conductivity, and they have good thermal storage performance at low temperatures.

Adsorption behavior of H2O on the strontium bromide surface: first-principles and molecular dynamics calculations.

Thermochemical adsorption heat storage based on gas-solid interaction is an energy storage technology for the effective recovery of industrial waste heat and renewable energy sources such as solar energy. Currently, hygroscopic salts and water are commonly used as the working pairs in thermochemical thermal storage systems. Strontium bromide (SrBr2) is a highly potential material for low-grade thermal energy storage and building applications due to its high sorption capacity and reaction enthalpy. In order to better understand the microscopic mechanism of adsorption, the water adsorption behavior of strontium bromide surfaces on the atomic scale is investigated in this study by using density functional theory (DFT). The effects of doping Ca or Mg into strontium bromide on water adsorption are analyzed by the comparison of the energy barrier, density of states (DOS) and crystal orbital Hamilton population (COHP) obtained before and after metal atom doping. The energy barrier of the SrBr2/H2O reaction system is 5.916 kcal mol-1, and the energy barrier of Ca-doped SrBr2 reduces to 3.432 kcal mol-1, whereas the energy barrier of Mg-doped SrBr2 increases to 13.394 kcal mol-1. The thermodynamic properties of strontium bromide are significantly improved by doping with calcium atoms. The absolute value of the COHP for Ca-doped SrBr2 decreases, which indicates that Ca-doped SrBr2 can adsorb the H2O molecules more easily at the same temperature. The doping of Ca atoms has a positive effect on the adsorption heat storage process. This study provides insight into the adsorption mechanism of water molecules on strontium bromide and could facilitate the design of efficient composite adsorbents.

Effect of orientation and nanoparticle addition of a encapsulated phase change material on heat transfer in a packed bed thermal energy storage system – A numerical analysis

Thermal energy storage technology research is growing globally due to the increased awareness of the clean energy demand and limitations of fossil fuel commodities. The packed bed latent heat thermal energy storage (PBLHTES) system is one among it promising a greater number of applications like solar water heating, industrial waste heat recovery process, thermal power generations, thermal comfort of buildings etc., Due to the high latent heat capacities, available in wide temperature ranges and minimal volume change, solid-to-liquid phase change materials (PCMs) are more attractive than any other latent heat materials to use in the PBLHTES system. Although, the low conductivity of PCM restricts the heat transfer while the charging and discharging periods. Therefore, it is necessary to incorporate thermal enhancement techniques in a PBLHTES system to improve the melting rate of the PCM. In this work, it is attempted to carry the 2-D numerical analysis of PBLHTES system provided with encapsulated PCM staggered in the flow direction of heat transfer fluid. The numerical results are validated with the experimental work. The effect of the inclination of PCM capsules with the flow direction (0°, 2.5°, 5°, 7.5°, and 10°), the addition of Multi-walled carbon nanotubes (MWCNT) nanoparticles (0 %, 1 %, 2 %, 3 %, 4 %, and 5 %) on energy absorbed by the PCM are studied. Also, the contours of temperature distribution and liquid fraction of the PCM with time are presented. The results revealed that the temperature distribution of HTF rises when PCM spheres orientated to the HTF shifted from 0 to 2.5° later it reduces. Though HTF temperature rises, the PCM temperature, liquid Fraction and energy absorbed decline when the capsules inclined to the flow direction. This is mainly due to the reason that the HTF moves outwards from the flow direction and towards the edges of the container, which makes the HTF carry a more amount of heat without sharing with the PCM capsules. Therefore, these arrangements will be helpful to switch over the ideal high-temperature HTF at the outlet without charging the TES system and vice versa. An improvement of 13.16 % melting rate is observed from 0 to 3 % of a nanoparticle addition and only 4 % enhancement is noted from 3 to 5 % MWCNT deposition. The effect of nanoparticles on energy absorbed by the PCM is nearly constant after 3 % of Multi-walled carbon nanotubes (MWCNT) addition. Therefore, this is the optimum MWCNT volume concentration to be added. The maximum energy absorbed with 3 % MWCNT for 60 min of time is 98.7 kJ and 97 kJ which are 3.5 % and 3.65 % more than the pure PCM for the standard case (0°) and 2.5° angle of attack of EPCMs with the flow direction.

Surrogate empowered Sim2Real transfer of deep reinforcement learning for ORC superheat control

The Organic Rankine Cycle (ORC) is widely used in industrial waste heat recovery due to its simple structure and easy maintenance. However, in the context of smart manufacturing in the process industry, traditional model-based optimization control methods are unable to adapt to the varying operating conditions of the ORC system or sudden changes in operating modes. Deep reinforcement learning (DRL) has significant advantages in situations with uncertainty as it directly achieves control objectives by interacting with the environment without requiring an explicit model of the controlled plant. Nevertheless, direct application of DRL to physical ORC systems presents unacceptable safety risks, and its generalization performance under model-plant mismatch is insufficient to support ORC control requirements. Therefore, this paper proposes a Sim2Real transfer learning-based DRL control method for ORC superheat control, which aims to provide a new simple, feasible, and user-friendly solution for energy system optimization control. Experimental results show that the proposed method greatly improves the training speed of DRL in ORC control problems and solves the generalization performance issue of the agent under multiple operating conditions through Sim2Real transfer.

Macroencapsulation of sodium chloride by a double layer strategy for high temperature phase change thermal storage over 800 °C

To solve the key problems of high corrosiveness, easy leakage and low thermal conductivity of sodium chloride as phase change material (PCM) for high-temperature heat storage, this study reports a double-shell coating method to prepare centimeter-sized macrocapsules. The capsules are made of powder raw materials with the help of organic adhesives such as polyvinyl pyrrolidone and carboxymethyl cellulose for shape formation, in which the inner expanded graphite (EG) layer and the outer Al2O3 layer are coated on the salt core spheres and finally are sintered formed at high temperatures. The double-shell capsules can prevent salt from leakage because the inner EG layer is repellent to liquid salt, in contrast, the single Al2O3 shell is penetrated by liquid salt due to their wettability. After 100 cyclic tests, the double-shell capsules have good stability and high durability for long-term use. In order to improve the heat storage density of the capsules, the method of isostatically pressing the cores to increase the compactness is studied. At 200 MPa, the capsules in size of 20@2@2 show a high heat storage capacity of 1024.54 J/cm3 and 551.56 J/g from 600 to 900 °C. The double-shell encapsulated salt PCM can be widely used in high-temperature heat storage over 800 °C in solar thermal power plants and industrial waste heat recovery.

Advancements in Phase Change Materials: A Path to Sustainable Energy Solutions in China

With the rapid development of China, the country's demand for energy has significantly increased. According to the "World Energy Outlook 2020," China's annual average growth rate of primary energy consumption is 1.9%, and it is predicted that China's energy consumption will account for over 20% of global energy consumption by 2050. In the energy budget, 90% is allocated to thermal energy conversion, transmission, and storage. Facing an impending energy crisis, enhancing energy production while minimizing energy loss has become a matter of widespread concern. Phase Change Materials (PCMs), also called phase change energy storage materials, have garnered attention as a novel energy-efficient and environmentally friendly material. PCMs refer to substances that undergo a change in state and provide latent heat without changing their temperature. Phase change thermal storage materials utilize phase transitions during heat exchange processes to store energy by means of these phase changes. Compared to chemical energy storage materials, PCMs offer high thermal efficiency and energy storage density, maintain constant temperature, and are more easily controllable. They hold great potential as a promising material in the field of thermal energy storage and have been widely applied in areas such as solar energy, lithium batteries, building insulation, and medical applications. This article offers a comprehensive overview of the principles and classification of Phase Change Material (PCM), including organic PCM, inorganic PCM, and composite PCM. It discusses their applications in solar thermal energy storage, cooling of photovoltaic panels, building materials, and industrial waste heat recovery. The article also highlights China's research and development efforts in these areas, emphasizing the country's significant contributions to advancing PCM technology.

Packed bed thermal energy storage for waste heat recovery in the iron and steel industry: A cold model study on powder hold-up and pressure drop

Waste heat recovery in the energy intensive industry is one of the most important measures for the mitigation of climate change. The present study examines the integration of a packed bed thermal energy storage for waste heat recovery in the iron and steel industry. Along with the highly fluctuating availability of excess heat the main difficulty of waste heat recovery in industrial processes is the high amount of powder that is transported by the hot exhaust gases. Therefore, the experimental investigations in this study focus on the powder hold-up and pressure drop in a packed bed thermal energy storage that is operated with a gas-powder two phase exhaust gas as heat transfer fluid. The ultimate goal is, to assess its suitability and robustness under such challenging operational conditions. The results indicate, that 98% of the powder that is introduced into the system with the heat transfer fluid during charging accumulates in the packed bed. Remarkably, most of the powder hold-up in the packed bed is concentrated near the surface at which the heat transfer fluid enters the packed bed. When reversing the flow direction of the heat transfer fluid to discharge the storage with a clean single phase gas, this gas is not contaminated with the powder that has been accumulated in previous charging periods. The entirety of these findings reinforces the suitability of packed bed thermal energy storage systems for waste heat recovery in the energy intensive industry.