Industrial Waste Heat Recovery Research Articles

Macro encapsulated Cu-based phase change material for high temperature heat storage with characteristic of self-sealing and high durability

The objective of this research is to develop encapsulated phase change materials with applications exceeding 1000 °C that can be applied to concentrated solar power systems and industrial waste heat recovery. In this study, a macro-encapsulation phase change storage material with a copper-based core and an alumina-based shell was developed by slip-casting method and filling mixture of copper beads and Cu-40 %Al powder. The capsule was able to achieve self-sealing by local oxidation reaction at the entrance without leakage. After aging tests at 1100 °C for up to 1000 h, no leakage or damage was found and mass increase of the encapsulate phase change material was only 4.5 %, confirming the superior durability and oxidation resistance of the encapsulated phase change material. The heat storage density of the copper-based phase change material was evaluated as high as 147 J/g. The heat storage capacity did not decrease after 1000 h and ten cycles of aging. The mechanism of its high durability was explored by morphological observations and Raman spectroscopy. In the original material, a small amount of aluminum was oxidized with priority to alumina which significantly enhanced the durability of the capsules. This macro-encapsulated phase change material exhibits excellent thermal storage performance, as well as self-sealing and durability properties, which are of great significance for improving the efficiency of thermal energy recovery above 1000 °C.

Investigations on a bubble-pump-aided diffusion absorption heat transformer using deep eutectic solvent for harvesting and upgrading thermal energy

Absorption heat transformer shows promising potential in thermal energy harvesting and upgrading, while the corrosion and crystallization risks of existing working substance restrict its promotion. A bubble-pump-aided diffusion absorption heat transformer using deep eutectic solvent is proposed in this study. The influence of operating parameters of bubble pump is analyzed, indicating that motive head should be as large as possible while diffusion gas flow rate has the optimum. Because of worse pumping ability, deep eutectic solvent has narrower normal operating range compared with LiBr, but the optimal energy performance shows little difference. Ethaline exhibits the best performance among deep eutectic solvents. With heat source of 90 ℃, COP and ηEX of 0.401 and 48.9% can be reached to output thermal energy of 120 ℃, leading to a CO2 emission reduction of 20.1 Mt per year. Parametric analysis demonstrates that single-stage diffusion absorption heat transformer using ethaline can realize temperature lift up to 50 ℃, which delivers comparative performance against existing AHT systems, except for operating range. Approaches are discussed to enlarge its operating range and further improve its performance as well. The results in this paper contribute to: 1) providing a promising absorption heat transformer configuration for large-scale and long-term use; 2) quantitatively demonstrating the prospect of deep eutectic solvent; 3) enlightening insights in the recovery of industrial waste heat, the upgrading of thermal energy and the reduction of CO2 emission.

Spent Yeast-Derived 3D Porous Carbon Skeleton as Low-Cost D-Mannitol Supporting Material for Medium Temperature Thermal Energy Storage.

Shape-stable phase change materials (ss-PCMs) are extensively applied in renewable energy storage. The core for realizing high latent heat and good thermal stability of ss-PCMs is the designation of suitable supporting skeletons that can effectively preserve the PCMs from leaking out. In this study, ss-PCMs impregnated by D-mannitol were prepared using a waste yeast-derived carbon (YC) as the support material. YC possesses a large surface area (669.90 m2/g), which can provide sufficient phase transition space and nucleation sites for D-mannitol. The results indicated that a reduced supercooling of 44.76 °C for YC/D-mannitol ss-PCMs can be realized. The ss-PCMs also exhibited good cycling stability, with latent heat loss rates of 4.00% and 2.15% after 200 thermal cycles. We further demonstrate that YC provides restricted space for mannitol to inhibit the supercooling mechanism. The YC/D-mannitol ss-PCMs exhibited great promise for solar heat storage and industrial waste heat recovery in the medium temperature domain.

First experimental characterization of CaCl2 coated heat exchanger for thermochemical heat transformer applications in industrial waste heat recovery

This study aims at evaluating the performance of a heat exchanger coated with CaCl2 (PVA polyvinyl alcohol used as binder) for Thermochemical Heat Transformers (THT) applications in industrial waste heat recovery.For this purpose, an experimental test bench has been built allowing to test operating temperatures up to 160 °C. A model heat exchanger plate is used to test two configurations: a thick layer of CaCl2 to model a packed bed reactor (used as reference) and a CaCl2-PVA deposit to model a coated reactor.For the packed bed configuration, results comparable to that of the literature are obtained with a specific power of 180 W/kg obtained for a temperature lift of 60 K. A high sensitivity to temperature lift is identified with a decrease of the specific power down to 38 W/kg for a lift of 77 K. The coated heat exchanger configuration achieves significantly higher performance with a specific power up to 341 W/kg for a temperature lift of 63 K. However, the analysis of the repeatability tests highlights a rapid change in temperature profiles highlighting a change in properties of the CaCl2/PVA compound material. Next steps will consist in enhanced material formulation and change in deposit protocol and to move to work at small reactor scale to assess system performance.

Macro-encapsulation of metal balls prepared by waste aluminum cans in ceramic capsules with reserved space

Phase change materials (PCMs) form the core of thermal energy storage (TES) for enhancing solar and industrial waste heat recovery. Metals have attracted growing attention due to their unique advantages, including high latent heat storage and high thermal conductivity. The application of metallic PCMs in TES is limited by the absence of appropriate packaging technology. Volume expansion during the solid-liquid phase can cause breakage of the protective coatings. This study proposes a “double-layer coating, recycling inner layer” method for the encapsulation of metallic PCMs. Waste aluminum cans (WACs) were selected as the PCM for cost reasons. The alloy balls prepared using the WACs were sequentially coated with an alkane mixture and ceramic slurry. The alkane mixture melts and discharges during the baking process, leaving a void for the phase-change volume expansion. The shell was gradually densified, and the metallic PCM was completely encapsulated after the heat treatment. The prepared MAEPCMs heat-treated at 1200 °C showed excellent mechanical properties, high heat storage capacity, and thermal cycle stability. The force required for compressive failure was approximately 2623 N. In addition, the total heat storage capacity reached approximately 198.6 kJ/kg at the temperature range of 600–700 °C, of which the latent heat accounted for more than 98.5%. There was no erosion between the alloy and the shell material, and the cumulative mass change was less than 8 wt. % after 600 thermal cycles. This study provides a structurally stable and low-cost technique for the preparation of durable macro-encapsulated PCMs with a high heat storage capacity and high thermal conductivity.

Design and modelling of a small-scale reversible high-temperature heat pump—organic Rankine cycle system for industrial waste heat recovery

Abstract Organic Rankine cycle (ORC) and heat pump (HP) are two well-established technologies for industrial waste heat recovery. Given the similarity between ORC and HP configurations, a system that can switch between HP and ORC modes with minimal modification is feasible. The reversible system according to the requirement of the industry can exploit waste heat in lower temperature bands operating as a high-temperature heat pump (HTHP) to provide useful process heat or as an ORC system generating power and thus increasing the efficiency of waste heat exploitation. This study discusses the design aspects of a small-scale reversible HTHP—ORC system, including the system layout, component selection, selection of an appropriate working fluid, the operating conditions for both modes and equipment sizing. R1233zd(E) was selected as the refrigerant for the reversible system and an automotive open-drive scroll compressor was found to be suitable, which can also be used as an expander for ORC with minimum modifications. The study also presents the modelling of the reversible system in ORC and HTHP modes including performance analysis of the scroll machine in expander and compressor roles attaining isentropic efficiency values up to 62.4 and 75.4%, respectively. The modelling results show a cycle efficiency of 5.9% (Tev = 102°C, $ \dot{m} $r = 0.064 kg/s) in ORC mode and a coefficient of performance of 4.19 in HTHP mode (for a temperature lift of 49 K with Tsource: 85°C, Ncomp: 2000 rpm).

Advanced Heat Exchangers for Waste Heat Recovery Applications

The incentive for industrial waste heat recovery, which has attracted much research interest in recent years, has been twofold: the obligation to reduce greenhouse gas emissions in line with climate change targets and the need for processes to reduce overall energy consumption in order to remain commercially competitive [...]

Experimental study on high temperature heat pump system with a double heat source cascade

In order to improve the thermal performance of a high temperature heat pump system, to realize the efficient heat recovery of industrial waste heat, and to make the combined utilization of low and medium temperature heat sources, a high temperature heat pump system with a double heat source cascade is proposed, which can absorb heat from industrial waste heat and the system is capable of heating water up to the required high temperature. The performance of the system is tested and analyzed. It is found that the inlet temperature of the medium temperature heat source has a significant impact on the performance of the heat pump system under working mode of the medium and low temperature heat sources. When the inlet temperature of the intermediate temperature heat source rises from 42?C to 53?C, the heating capacity of the cascade heat pump increases by 18.6%, and its performance coefficient increases by 8.9%. This paper provides a reference for the high efficiency of the cascade high temperature heat pump technology.

Low-Temperature Industrial Waste Heat (IWH) Recovery Using a New Design for Fast-Charging Thermal Energy Storage Units

The dynamic melting of CuO–coconut oil was addressed in a latent-heat thermal energy storage unit loaded with copper foam. In a new design, the thermal storage unit is made of a shell-tube-shaped chamber, in which a liquid flow of hot phase-change material (PCM) is allowed to enter the chamber from a port at the bottom and exit at the top. A fin is mounted in the chamber to forward the entrance PCM liquid toward the solid regions. The control equations were solved using the finite element method. The impact of foam porosity, inlet pressure, fin length, and the concentrations of CuO nanoparticles on the thermal charging time of the chamber was investigated. A fast-charging time of 15 min with a foam porosity of 0.95 was achieved. A porosity of 0.95 can provide a maximum thermal charging power of 15.1 kW/kg. The inlet pressure was a significant parameter, and increasing the inlet pressure from 0.5 kPa to 4 kPa reduced the melting time by 2.6 times. The presence of the fin is not advantageous, and even a long fin could extend the thermal charging time. Moreover, dispersed nanoparticles were not beneficial to dynamic melting and extended the thermal charging time.

Preparation and characterization of steel slag-based low, medium, and high-temperature composite phase change energy storage materials

In this study, industrial solid waste steel slag was used as supporting material for the first time, and polyethylene glycol (PEG), sodium nitrate (NaNO3), and sodium sulfate (Na2SO4) were used as low, medium, and high-temperature phase change materials (PCMs). A series of shape-stable composite phase change materials (C-PCMs) were prepared by vacuum impregnation and mixing-sintering methods. The morphology, thermal properties, and thermal reliability of C-PCMs were characterized by scanning electron microscopy (SEM), Fourier transforms infrared spectroscopy (FT-IR), and differential scanning calorimetry (DSC). The results show that the three PCMs are uniformly dispersed in the pores of steel slag, and the maximum loading is 35 %, 40 %, and 50 %, respectively, and they have good chemical compatibility with steel slag. Compared with their pure PCMs, the three prepared C-PCMs showed a reduction in subcooling of 2.64 °C, 4.53 °C and 0.79 °C, respectively, and an increase in thermal conductivity of 172 %, 54.9 % and 82.4 %, respectively, all with good phase change thermal storage properties. Even after 100 thermal cycles, the latent heat retention rate was more than 97 %, which had good thermal reliability. Therefore, it can be concluded that the three kinds of low, medium, and high-temperature C-PCMs have considerable application potential in different temperature areas, such as building latent heat storage, solar energy storage systems, and industrial waste heat recovery system.

A novel cascade latent heat thermal energy storage system consisting of erythritol and paraffin wax for deep recovery of medium-temperature industrial waste heat

Recovering medium-temperature (e.g., 150–180 °C) industrial waste heat through latent heat thermal energy storage (LHTES) can effectively attenuate the consumption of fossil fuels. However, the LHTES system containing a single medium-temperature phase change material (PCM), e.g., erythritol, cannot absorb the part of heat below the PCM's melting point (∼118 °C) during the charging process. Meanwhile, a single low-temperature PCM, e.g., paraffin wax, is unable to supply a significant amount of heat at temperatures higher than its melting point upon discharging. Therefore, a cascade LHTES system combining one erythritol unit and two paraffin wax units (melting point of ∼60 °C) was proposed to deeply recover the waste heat during charging and increase the heat supply temperature during discharging. Through prototype testing, the performance of such a cascade system was examined under various working conditions. It was shown that the cascade system could improve the efficiency of the waste heat recovery from 15.8% to 63.4% under the charging condition of 100 L/h and 160 °C, as compared to a single-stage erythritol-based system. The average heat supply temperature of the cascade system was also increased from 37 °C (at a constant flow rate) to 53.6 °C via an active discharging strategy (by tuning the flow rate). This highly efficient cascade LHTES system has great potential for recovery of medium-temperature waste heat towards a decarbonized future of space heating for buildings.

Numerical study on stratification performance of cascaded three-layered packed-bed in the thermal storage process

Packed-bed thermal storage tank (PBTST) has broad application prospects in solar water heating systems, thermoelectric decoupling in power plants, and industrial waste heat recovery. In the present work, a three-dimensional PBTST model with three-stage phase change material (PCM) and three-layered diameter capsules was proposed, its thermal energy storage behavior and thermal stratification performance were studied by numerical simulation. The effects of PCM bed height ratio, fluid flow rate, and inlet temperature on the stratification performance of the new tank were investigated. The results reported that due to the increased heat transfer area and expanded heat-transfer temperature difference: (1) Compared with the conventional non-cascaded single-layered diameter capsule PBTST, the charging efficiency of the cascaded three-layered diameter capsule PBTST increased from 24% to 61% at the end of charging; (2) the cascaded three-layered diameter capsule PBTST shows significantly improved stratification properties compared to the conventional ones, with the Richardson number increased from 20.78 to 49.47; (3) increasing the height of the bottom PCM bed, raising the inlet temperature, and reducing the flow rate all can improve the stratification performance.

Comparison study of conventional and advanced exergy analysis on cascade high temperature heat pump system based on experiment

Cascade high temperature heat pump (CHTHP) has shown remarkable application potential for industrial waste heat recovery owing to its superiority of large temperature lift. Great efforts have been made to optimize the performance of CHTHP by means of conventional exergy analysis (CEA), which was not qualified to uncover the thermodynamic interactions among components. Thus, advanced exergy analysis (AEA) has been adopted to comparatively evaluate the relationships of reversibility among the CHTHP components. Herein, both CEA and AEA were based on the experiment results from a prototype which could realize maximum temperature lift of 100 °C.The CEA results show that total exergy efficiency is 43.23%, while AEA results indicate that endogenous part accounts for 98.27% of the total exergy destruction and 67.69% of it is avoidable. The AEA reveals that the highest improvement priority belongs to low temperature compressor (LTCOM), followed by cascade heat exchanger (CHE) and high temperature compressor (HTCOM) and that low temperature expansion valve (LTEV) and high temperature expansion valve (HTEV) has no improvement potential which is different from the results of CEA theory. Conclusively, AEA can give more detailed guidance about the potential for improvement.

Thermal decomposition and interaction mechanism of HFC-134a/HFC-32 mixture in Organic Rankine Cycle

Organic Rankine Cycle (ORC) is an effective technology for the recovery of industrial waste heat and the utilization of renewable energy to produce electricity. Hydrofluorocarbon mixtures are more attractive used in ORC systems than pure working fluids due to the advantages of higher work outputs, higher cycle efficiencies, and lower exergy losses. For the supercritical ORC system, thermal stability is one of the main factors to screen the working fluids. In the present work, ReaxFF reactive molecular dynamic simulations and density functional theory calculations are performed to investigate the thermal decomposition and interaction mechanism of HFC-134a/HFC-32 mixture. The thermal decomposition process, the effects of temperature, and HFC-134a to HFC-32 ratio on the thermal decomposition of HFC-134a/HFC-32 mixture, and the interaction between HFC-134a and HFC-32 are investigated. The results showed that the hydrogen bond formed between HFC-134a and HFC-32 in HFC-134a/HFC-32 mixture, which inhibits the decomposition of HFC-134a. The HFC-134a/HFC-32 mixture used in ORC system has a better thermal stability than pure HFC-134a. The results of this study are beneficial to the screening of ORC working fluid and the safe operation of the ORC system.

Life cycle techno-enviro-economic assessment of dual-temperature evaporation transcritical CO2 high-temperature heat pump systems for industrial waste heat recovery

Replacing fuel-fired boilers by using efficient heat pump plants to recover industrial waste heat is an effective solution to achieve the “dual carbon” target. Three novel transcritical CO2 high-temperature heat pump systems (Ej-Evap2-A, Ej-Evap2-B, and Ej-Evap2-C) are proposed in this study, by introducing the technique of dual-temperature evaporation realized with an ejector for cascade heat absorption from the heat source. Considering the application in the scenario of industry requirement of hot water heating, the life cycle performances of the new proposed heat pump systems and fuel-fired boilers are comprehensively studied from the perspectives of energetic, emissions, and economic. A sensitivity analysis about the new configuration heat pump system is also conducted considering the variation in electricity and coal price. The results demonstrate there exists an optimum discharge pressure that maximizes the coefficient of performance (COP). Ej-Evap2-C shows a maximum COP of 4.85, which is 14.40% higher than the baseline CO2 heat pump system (Base), and the exergy efficiency of Ej-Evap2-C is 7.86–15.19% higher than that of Base. Among the eight heating methods including coal-fired boilers (CFB), gas-fired boilers (GFB), electric heating boiler (EHB) and five kinds of CO2 heat pump systems, Ej-Evap2-C shows the least pollutant emissions and life cycle cost. Furthermore, Ej-Evap2-C has the shortest payback period of fewer than 7 years compared with the CFB. The dual-temperature evaporation CO2 high-temperature heat pump is promising to substitute traditional fuel-fired boilers to generate high-temperature fluid in the future.

Simulation and assessment of an integrated thermal processes and Organic Rankine Cycle (ORC) system with Modelica

Waste heat recovery (WHR) has been regarded as a viable method to improve energy efficiency and promote sustainability in industry. The operation of high energy consuming thermal processes in industry generates high quantities of thermal losses, thus being associated to a great waste heat potential. In this sequence, several technologies have emerged to reuse this industrial waste heat. The implementation of these technologies within the operation of plants results in the project of different WHR strategies. This work presents a simulation model developed in Modelica language for an industrial waste heat recovery (WHR) installation. Such installation involves several industrial processes, which integrate system of thermal processes and an Organic Rankine Cycle (ORC). Based on the specific data from a case-study of a ceramic industry plant, namely two tunnel kilns, a WHR strategy is conceptualised,​ simulated and assessed in terms of economic viability and environmental impacts. The simulation results demonstrated the validity of the developed model (deviation values for key variables were calculated with a maximal value of 0.94% having been obtained for one of the variables, which is a considerably negligible deviation). The economic and environmental assessment revealed that the WHR project is overall viable, considering a 1.1 years payback period and 2.36 kton CO2,eq reduction (corresponding to 32.8% of natural gas savings and 11.3% of electric energy savings).

Application of Exergy Analysis in Flue Gas Condensation Waste Heat Recovery System Evaluation

Flue gas condensation heat recovery technology has a good technical and economic performance in industrial exhaust gas waste heat recovery. Thermal efficiency analysis is the traditional analysis method for the flue gas condensation heat recovery system but it cannot reflect the recovered heat degree. Exergy analysis, which can reflect the recovered energy heat degree, was first applied to the evaluation of a flue gas condensation waste heat recovery system in this paper. The calculation method of wet flue gas exergy is more complex as both a heat and mass transfer is presented. Flue gas waste heat exergy efficiency (EE) and the flue gas waste heat exergy utilization rate (EUR) were proposed as the evaluation indexes for exergy analysis. The exergy analysis method was applied to the comparative evaluation of three recovery schemes in a practical project. The results show that when the water vapor content of wet flue gas is less than 10%, the condensed water exergy can be neglected when calculating EE. The EUR could be used as a comprehensive index for comparing different waste heat recovery schemes, and EE could be used to judge whether the energy grade of heat exchange equipment was seriously decreased. Exergy analysis could effectively make up for the deficiency of thermal efficiency analysis that could not reflect the waste heat grade utilization. Exergy analysis and thermal efficiency analysis are recommended to be used simultaneously to make a more comprehensive analysis and evaluation of the system.

Heat transfer performance of a phase-change material in a rectangular shell-tube energy storage tank

Rectangular shell-tube thermal storage systems have a wide range of applications in both industrial waste heat recovery and solar power plants. Mastering the heat transfer mechanism and improving the heat transfer efficiency can considerably enhance the energy-utilization. In this study, we experimentally investigated the dynamic thermal behavior of a visualized rectangular shell-tube type phase-change heat storage device containing natural convection, using paraffin wax as the phase-change material. Subsequently, the corresponding numerical simulation was completed. The two results agreed well, within a maximum error of ± 5%. In addition, the theoretical parameters of paraffin wax were examined experimentally. The impact of inlet temperature, flow rate of the heat transfer fluid, and the length-to-diameter ratio of the heat flow tube on the efficiency of the system was studied. It was observed that a rise in inlet temperature from 353 K to 363 K increased the melting rate by 21.43%. When the inlet flow rate was increased from 2 L/min to 5 L/min, the melting rate was raised by 16%. However, reduction in tube length-to-diameter ratio from G = 14 to G = 12 shortened the melting time of the PCM by 6.64%. The equation for the liquid phase fraction of the PCM with dimensionless Ste and Ra numbers was fitted. The research results have a specific guiding significance for utilizing rectangular shell-tube energy storage systems.

Performance of A Plate-Finned Thermoelectric Generator (TEG) Module for Industrial Waste Heat Recovery

A thermoelectric generator (TEG) cell is a solid-state semi-conductor capable of converting thermal energy directly into electrical energy. Studies on specific designs for TEG modules are needed for an effective industrial waste heat recovery. Typical TEG systems apply direct heating or cooling without being assisted by heat transfer devices which makes it difficult to maintain high temperature difference between TEG cells surfaces for higher electrical power generation. To suit the TEG system with the industrial condition, a waste heat recovery (WHR) module was developed consisting of a Bismuth Telluride TEG cell and another module consisting of two TEG cells in a stacked configuration. The TEG cells were sandwiched between two copper blocks and connected to two plate-finned heat sinks and eight heat pipes. The two modules were tested on a dedicated test bench to study its performance based on an industrial WHR setup. The hot stream waste heat temperature was constant at 80 ℃ while the cooling air streams were set based on ambient conditions between 22 ℃ to 30 °C. The maximum power performance (MPP) varied from 10 mW to 153 mW where the effect of cooling is very significant on the power outputs. Under forced cooling condition, the MPP generated from the double stacking TEG configuration is significantly higher compared to single cell configuration, by approximately 250%.

Review on bio-based shape-stable phase change materials for thermal energy storage and utilization

Thermal energy storage using phase change materials (PCMs) plays a significant role in energy efficiency improvement and renewable energy utilization. However, pristine PCMs suffer from liquid leakage, low thermal conductivity, and single function. Bio-based porous materials are low-cost, environmentally friendly, and widely available, which can be used as support materials to prepare shape-stable PCMs effectively. In this article, the sources of bio-based porous materials are divided into plant-based porous materials and animal-based porous materials. To make full use of bio-based porous materials, their processing methods are systematically reviewed, including direct carbonization, hydrothermal carbonization, and activation. In addition, bio-based shape-stable PCMs in various fields, including solar energy storage, building thermal management, industrial waste heat recovery and storage, electromagnetic interference shielding, and other applications, have been summarized. Finally, the challenges and future potential of bio-based shape-stable PCMs are discussed. The utilization of bio-based PCMs may carry thermal energy storage to a new realm and prosperity with more significant economic and environmental benefits.