Industrial Waste Heat Recovery Research Articles

Constructing heat conduction path and flexible support skeleton for PEG-based phase change composites through salt template method

Phase change materials (PCMs) have been widely applied to various occasions for their merit of constant temperature during energy storage process. However, the risks of leakage, low thermal conductivity, and brittleness severely limit the applications of PCMs. In this work, the shape-stabilized phase change composites (PCCs) with high thermal conductivity and heat storage density were fabricated by vacuum impregnation of natural rubber (NR)-expanded graphite (EG) skeleton material in polyethylene glycol (PEG) above phase change temperature, and the NR-EG skeleton was prepared by salt template method. In detail, the obtained NR-EG85@PEG exhibits high thermal conductivity of 1.05 W/(m·K) and high phase change enthalpy of 144.11 J/g. Benefiting from high thermal conductivity and enthalpy, the PCCs show remarkably rapid energy storage and thermoelectric conversion efficiency to drive windmill. In addition, the PCCs exhibit excellent reusability and flexibility in which the enthalpy shows negligible reduction after 500 thermal cycles and the porous skeleton of NR-EG can be compressed and recover under high pressure. The results indicate that the NR-EG85@PEG PCC displays huge application prospects in the field of industrial waste heat recovery.

Physicochemical Characterization of Phase Change Materials for Industrial Waste Heat Recovery Applications

The recovery and storage of process heat in industrial applications are some of the key factors to improve the sustainability and reliability of high temperature applications. In this sense, one of the main drawbacks is focused on the selection of proper thermal energy storage (TES) materials. This paper performs a full characterization of four phase change storage materials (PCM), KOH, LiOH, NaNO3 and KNO3, which are proposed for storage applications between 270 and 500 °C, according to the results obtained through differential scanning calorimeter and thermogravimetric analysis. One of the main innovations includes the corrosive evaluation of these materials in a promising alumina forming alloy (OC4), close to their corresponding phase change temperature during 500 h. The physicochemical properties obtained confirm the optimal use of NaNO3 and KNO3 and recommend the use, with caution, of KOH, due to its higher corrosive potential. FeCr2O4, NiCr2O4 and FeAl2O4 were the main protective spinels formed in the alloy surface, however, the cross-section study in the alloy immersed in KOH, revealed a non-uniform behavior, presenting some cracks and spallation in the surface. On the other hand, the proposal of LiOH was disregarded since it presents a narrow operation temperature range between melting and solidification point.

Waste Heat Recovery From The Hot Water Boiling Plant Analysis using CFD

To fulfil the world's growing need for fossil fuel energy, renewable energy harvesting is required, and the rate of depletion of non-renewable energy sources must be slowed. Currently, many of these techniques are available, but with less effectiveness than before. These techniques result in a long payback period of investment. The goal of this research is to look at many elements of convective heat transfer enhancement using finned heat pipes, as well as the recovery of industrial waste heat. To validate these new energy-saving concepts, ANSYS 2020 R1 is used, including control strategies and simulation techniques. An integrated waste heat recovery system using finned heat pipes is having a significant effect on overall efficiency. The efficiency is increased by 10.5%–18.8% for various load conditions.

Experimental analysis of a novel device for accelerating the energy storage rate of phase change materials

Phase change materials (PCMs) are widely used in new energy storage fields such as industrial waste heat recovery and solar heat recovery. However, the low thermal conductivity of PCMs causes the slow heat storage efficiency of PCMs, resulting in a large waste of waste heat. For the sake of increasing the heat storage rate of PCMs, a new type of pulsating heat pipe (PHP) phase change heat storage device is designed, which couples PHP with PCMs. For sake of further improve the heat storage efficiency of the novel device, a different filling working medium was used in the experiment. The results show that methanol is the best charging working fluid compared with water and ethanol, the corresponding heat storage time of methanol was reduced by 2500 seconds and 900 seconds, respectively. Therefore, methanol is the best charging medium, followed by water and ethanol.

Experimental investigation of the rheological and phase change behavior of adipic acid as a phase change material (PCM) for thermal energy storage at 150 °C

Phase change materials (PCM) can store and release thermal energy mostly through a transition from solid to liquid and vice versa. This transition and its related parameters such as melting point, enthalpy and heat capacity were most often studied from a thermodynamic point aspect. Investigating the phase transition from a rheological point of view can provide us with important information such as viscosity change during the transition and in the melt. Considering the importance of natural convection during the melting of a PCM, the rheological knowledge can improve the estimations resulting from the numerical analysis of a phase change transition. However, there are a few studies on rheological behavior of PCMs. Here, the rheological behavior of an organic PCM, adipic acid, is studied. This PCM melts at 150 °C which corresponds to a medium temperature range for application in industrial waste heat recovery. Rotational and oscillatory tests under thermal insulation have been performed using a controlled stress rheometer and a plate geometry. Finally, the heat flow measured by Differential Scanning Calorimetry (DSC) is compared to the rheological oscillatory test results to provide a detailed information of phase transition range. To the authors best knowledge, this study is the first study in the rheology of a PCM at medium to high temperature (150 °C).

Exceptionally Heavy Doping Boosts the Performance of Iron Silicide for Refractory Thermoelectrics

AbstractThermoelectric (TE) power generation is expected to be one of the most effective solutions to convert industrial exhaust heat to electricity for conserving fossil energy and reducing carbon emissions. However, its real application is obstructed decisively by the weakness of the service stability of state‐of‐the‐art TE materials at high temperatures in air. Refractory iron silicide (β‐FeSi2) used to be widely investigated as TE materials, but the low zT has restricted its practical application and even made it almost vanish from TE research in recent years. Here, guided by theoretical calculation, ultrahigh solubility of Ir on the Fe sites of β‐FeSi2 is successfully realized. Doping 16% Ir elicits multi‐valley electrical conduction and phonon‐electron scattering, doubling the previous zT record of β‐FeSi2 to ≈0.6 at 1000 K. The TE properties of the obtained β‐FeSi2 are practically unchanged after thermal aging in air at 1173 K. The new conceptual electrode‐less β‐FeSi2‐based refractory module demonstrates considerable power density and stable power generation when it is burned by a gas flame in air. These results mark a step toward developing practical TE power generation technology for the recovery of industrial waste heat.

Development of an electric arc furnace steel slag-based ceramic material for high temperature thermal energy storage applications

This paper details the development process of ceramics made out of 100% electric arc furnace (EAF) steel slag, to be used as a shaped homogenous thermal energy storage (TES) media in packed-bed thermocline systems for high-temperatures industrial waste heat recovery, concentrated solar power (CSP), and Carnot batteries applications, among others. The main objective of this study was to investigate the influence of different process parameters on the properties of the resulting ceramics. The samples have been characterized in terms of bulk density, apparent solid density, and water absorption to identify the best values for different process parameter. The best properties were obtained for samples prepared with heat-treated slag powders, pressed at 300 MPa and fired at 1300 °C for 8 h under a static air atmosphere. The optimal bulk density was 3.1 g/cm3, and the water absorption was 1.2%wt. The measured specific heat capacity was 1026, 1181 and 1216 J/(kg.K) at 200, 400 and 600 °C, respectively, while the thermal conductivity values were 1.53, 1.50 and 1.37 W/(m.K) at the same temperatures. This work confirms the feasibility of manufacturing TES ceramics out of EAF steel slags, using equipment and techniques well-known in the refractory industry.

A structured procedure for the selection of thermal energy storage options for utilization and conversion of industrial waste heat

Thermal energy storage is a key enabling technology for the recovery and valorisation of industrial waste heat. Nevertheless, there is a wide gap between the variety of heat storage options investigated and the recurrent few types virtually implemented in the industries. To take advantage of a wider spectrum of solutions, a structured procedure is proposed in this work for the selection of storage material and layout. The algorithm developed consists of a preliminary storage design followed by a performance estimation of the overall system where the heat storage is integrated. The preliminary design allows a first screening and ranking of sensible, latent or thermochemical materials using a quasi-stationary approach. The performance estimation leads to the final selection of the heat storage system, which is based on the analysis of the dynamic thermal response of the heat storage along with physically based or input-output models for the load. The algorithm is applied to improve the heat recovery of a discontinuous and fluctuating flue gas at medium temperature from a steel industry, targeting the production of process steam or electricity. The results show that the integration of a packed bed heat storage, either of the sensible or latent type, allows the highest amount of steam to be generated in the discharging. Moreover, the combination of the same heat storage with an organic Rankine cycle or the Kalina cycle results in the highest amount of generated electricity. The investment in a packed bed rock storage was found to result in payback times of about seven years, whereas tank-based storage units appear not profitable due to the high cost of the silicone oil.

Incorporating machine learning for thermal engines modeling in industrial waste heat recovery

This paper proposes a methodology for efficient, accurate, and sustainable waste heat recovery, where the energy needs of an industrial plant allow the installation of thermal engines. In this methodology, pinch analysis, mathematical equations, machine learning models, and an optimization algorithm are combined for the first time. To satisfy the industrial requirements, the selected thermal engines are the steam Rankine cycle, the organic Rankine cycle, and the absorption refrigeration cycle, which are modeled by using multilayer perceptron neural networks. The Non-dominated Sorting Genetic Algorithm-III is used to solve the optimization problem. Moreover, multi-objective trade-offs between economic, environmental, and social aspects are studied. A case study is presented to show the applicability of the proposed methodology. The multilayer perceptron models of the thermal engines were created with high accuracy. Furthermore, the results show that with this methodology it is possible to find the optimal operating conditions of thermal engines and solutions that allow the use of different fuels to fulfill the three objective functions.

Combined energetic, economic and climate change assessment of heat pumps for industrial waste heat recovery

The recovery of waste heat represents a promising opportunity to reduce greenhouse gas (GHG) emissions from industrial sectors. The current development of heat recovery technologies can provide industries with several options for retrofitting their heat generation systems. Although past studies estimated the resulting savings in GHG emissions for specific industries or facilities, work is still needed to fully substantiate the expected benefit and the competitiveness of these alternatives, taking into account data at country scale (e.g. long-term reduction targets, energy cost, etc.). Hence, in this study, a new methodology is developed to determine the minimum conditions for waste heat recovery solutions to enable compliance with the targets from the Paris Agreement, taking 2030 and 2050 as reference years. It is applied to several industrial sectors for 24 EU countries, focusing on mechanical heat pump solutions (MHPs). Results indicate that all countries are compliant in 2050 for MHP integration with low temperature lift (like ammonia production) and 21 countries are compliant for high temperature lift (like food industry). The main constraint to the development of the MHP technology in 2030 is found to be economic, while in 2050, the main barrier for countries that do not reach the reduction targets is a too high carbon intensity of electricity generation. To accommodate the relatively long lifetime of the heat production system, the future MHP roadmap should therefore anticipate these potential barriers including carbon footprint of electricity network, working fluids and gas to electricity price ratio. In addition to meeting the 2030 requirements by a large margin, this strategy would factor in constraints associated with the long-term investments in MHPs. To further expand such foresight analysis, our methodology can be duplicated to other technologies than MHPs, so it can help industry decision-makers select the most suitable waste heat recovery options for a given industrial process in a specific country.

Output prediction of alpha-type Stirling engines using gradient boosted regression trees and corresponding heat recovery system optimization based on improved NSGA-II

Climate change is becoming a pressing global concern, and the search for new energy and energy recovery technologies is becoming a worldwide research imperative. The broad adaptability of the Stirling engine to a wide variety of heat sources makes it a promising technology for industrial waste heat recovery and solar thermal generation. The operation of the Stirling engine involves a multi-physical coupled process of heat transfer and mechanics as well as non-linear losses due to mechanical friction and gas charge leaking. Therefore, accurate prediction of Stirling engine power output through theoretical analysis is complex and costly. Emerging machine learning algorithms like Gradient Boosted Regression Trees (GBRT) can offer new approaches to solve this problem. The GBRT model consists of multiple decision trees that branch by exhausting thresholds for all features under study to find the best split structure for data regression, and the principle of GBRT gives it the natural advantage of finding a wide range of distinguishing features and combinations, and a powerful generalization capability. A GBRT forecasting model is thus constructed to model the output power of Alpha-type Stirling engines. Test data from the General Motors 4L23 Stirling Engine are applied as the training and test set. Results from the random test set accounting for 25% of the total samples indicate that the GBRT model has a prediction accuracy of 96.23%. Furthermore, a regional microgrid containing Stirling engines, photovoltaic panels and batteries for industrial waste heat recovery is constructed and an evaluation system for energy supply performance is also established. Finally, based on the proposed power output model, multi-objective optimization based on improved NSGA-II is implemented, providing guidance for industrial application of Stirling engines.

Modeling and analysis of a dual-acoustic-driver thermoacoustic heat pump

Thermoacoustic heat pumps (TAHPs) can be used for heating and/or cooling purposes. Current designs of travelling-wave TAHPs normally employ a single acoustic driver and rely on a looped pipe to establish and maintain the required acoustic field. The resultant system is thereby bulky and expensive, detracting from the structure simplicity and low-cost advantages of thermoacoustic technology. To address this issue, this paper investigates the dual-acoustic-driver concept that can significantly increase the system’s compactness. Theoretical analyses are conducted for the dual-acoustic-driver TAHP, and the acoustic and temperature fields in the thermoacoustic core are examined. Parametric studies are undertaken to investigate the effects of acoustic drivers on the acoustic and thermal characteristics of the TAHP. It is found that, as the frequency of acoustic drivers changes, the acoustic field in the thermoacoustic (TA) core could be dominated by a standing, traveling, or hybrid standing-traveling wave. The temperature distribution within the TA core and temperature difference between the core ends will change accordingly. Results show that the temperature difference is non-zero only when the acoustic field contains a traveling-wave component. To obtain a large temperature difference, the acoustic drivers should be driven near resonance frequencies at which the acoustic field is hybrid and the pressure amplitude is large. This study gains new insights into the working mechanisms behind the dual-acoustic-driver TAHP concept, paving the way for developing compact, efficient, and high-power-density TAHPs for industrial waste heat recovery.

Industrial waste heat recovery: A helix-weaved convection-radiation converter for heat transfer enhancement in gas heat exchanger

Waste heat from industrial hot flue gas is worth to be recovered for energy conservation. While due to the poor heat transfer performance in gas side, heat recovery coefficient of conventional heat exchanger is restricted. Herein, a novel “Convection-radiation converter” (CRC) created with helix-weaved wire, possessing large specific area (1000∼10,000 m2/m3) and randomly wire-nested structure, is proposed. Helix-weaved CRC is placed in gas side, in which heat convection between flue gas and the Heat exchange wall (HEW) is converted to coupled convection-radiation among flue gas, CRC and the HEW. Comprehensive emissivity (εcomp) of the CRC is governed by heat transmitting thickness (H) rather than the CRC porosity (φ), helix wire diameter (d) and original surface emissivity (ε0). εcomp would approach to ∼1 with H getting large enough. The relation of εcomp and H, φ, d is proposed for helix-weaved CRC design. Numerical analysis of heat transfer process with & without CRC is carried out, which indicates that the apparent heat convective coefficient can be enhanced to 4∼5 times by the coupled heat convection and radiation of CRC. The helix-weaved CRC is further applied for industrial application, and its enhancing effect on heat transfer in gas side is verified.

Microencapsulation of high temperature metallic phase change materials with SiCN shell

Metallic phase change materials (PCMs) have the advantages of large phase change latent heat, high heat storage density and broad application prospects in various high temperature industrial waste heat recovery and utilization. However, due to the strong corrosion of molten metal at high temperature, appropriate packaging technology is the prerequisite for the promotion and application of metallic PCMs. In this research, a high temperature PCM microencapsulating technology with SiCN shell and a new microencapsulation method was proposed. The high temperature microencapsulated phase change materials (MEPCMs) with the core–shell mass ratios of 5:1, 4:1 and 3:1 were prepared by “solvent evaporation-heating curing” method, using SiCN cured by organic polysilazane (OPSZ) as heat resistant shell material and Al-Si particles as core PCMs. The mechanisms of shell formation and coating of OPSZ were studied experimentally, as well as the material properties and thermal performance of MEPCMs. With the increase of temperature, OPSZ gradually formed a dense SiCN shell on the surface of Al-Si particles. The experimental results showed that MEPCMs with the core–shell mass ratio of 4:1 had a high phase change temperature (571.9 °C-573.7 °C) and good heat storage capability (281.2 J/g-282.9 J/g). SiCN shell was conducive to maintain a complete core–shell structure, and exhibited excellent thermal resistance and oxidation resistance to protect inner core materials during thermal cycles. Therefore, the prepared microcapsule was a potential heat storage material, which provided a new idea for developing microencapsulation method of high temperature PCMs.

Practice of Waste Heat Recovery in Iron and Steel Industry for Urban Central Heating

Practice of Waste Heat Recovery in Iron and Steel Industry for Urban Central Heating

Experimental Flow Boiling Study of R245a at High Reduced Pressures in a Large Diameter Horizontal Tube

Evaporators used in organic Rankine cycles (ORC) are designed using existing flow boiling correlations that are mainly based on HVAC&R data. However, the ORC evaporators employed in the industry typically have larger diameters and operational conditions at higher reduced pressures compared to the HVAC&R applications. The present study presents the results of flow boiling heat transfer experiments in operational conditions that are representative for an industrial waste heat recovery low-temperature ORC’s evaporator tube, by being performed at high reduced pressures and in a large-diameter horizontal tube with R245fa as working fluid. The measurements are performed within a range of mass flux, saturation temperature and heat flux at 83–283 kg/m2s, 85–120 °C (8.9–19.2 bar) and 17–29 kW/m2, respectively. Test section is a round and plain horizontal carbon steel tube with 21 mm I.D., 2.5 m length. 513 local two-phase heat transfer coefficients are recorded. The experimental results are compared with each other to reveal heat transfer coefficient trends with respect to varying experimental conditions. Four distinctive heat transfer zones are observed, namely, the nucleate boiling dominant (NBD) zone, weakening nucleate boiling dominance (WNBD) zone, flow boiling zone (FBZ) and the dry-out zone (DOZ). Heat transfer coefficient vs vapor quality trends partly resembled CO2 flow boiling results reported in the literature. Two flow boiling correlations moderately predicted the data.

A Low-to-Medium Temperature Cascade Latent Heat Thermal Energy Storage System Consisting of Paraffin Wax and Erythritol for Deep Recovery of Industrial Waste Heat

A Low-to-Medium Temperature Cascade Latent Heat Thermal Energy Storage System Consisting of Paraffin Wax and Erythritol for Deep Recovery of Industrial Waste Heat

Influence of thermal stability on organic Rankine cycle systems using siloxanes as working fluids

• An off-design model with fluid decomposition parameters was established. • The influence of MM thermal decomposition on the ORC system was evaluated. • MM decomposition reduced the net power and efficiency of ORC system obviously. • MM decomposition may lead to incomplete evaporation and evaporator acid corrosion. The organic Rankine cycle (ORC) is an efficient power generation technology that has been widely used in renewable energy utilization and industrial waste heat recovery. The thermal stability of working fluids has a significant effect on the fluid selection and system design of ORC systems. In this study, an off-design model of an ORC system was established with hexamethyldisiloxane (MM) as the working fluid, and the effects of the MM thermal stability on the system were analyzed. The results showed that the effect of MM thermal decomposition on the cold source and working fluid pump was limited. The outlet temperature of the evaporator decreased with MM decomposition, which might lead to incomplete evaporation of working fluids and possible damage to the expander. The outlet temperature of the heat source also decreased with MM decomposition, which led to lower outlet temperatures than the acid dew point limit temperature. Both of these results can affect the safe operation of ORC systems. The net power and thermal efficiency of the system decreased with increasing thermal decomposition ratios of MM. The net power and thermal efficiency decreased by 7.48% and 10.72% respectively in the model of this study with a 10% decomposition ratio.

Waste heat recovery in steel industry for steam production to feed carbon capture process

Waste heat recovery in steel industry for steam production to feed carbon capture process

Energy performance assessment of a novel zeolite-water direct contact adsorptive heat pump for waste heat recovery

• The low-grade industrial waste heat can be recovered using adsorption heat pumps. • The direct contact adsorption heat pumps guarantee simple configurations. • The water inlet downward flow configuration shows excellent thermal performances. The adsorption heat pumps are a promising technology suitable for the industrial waste heat recovery. In particular, the direct contact configuration can be used to generate high pressure steam for industrial applications limiting the design complexities. In this paper, a numerical simulation of the adsorption phase of an original configuration of a direct contact water/zeolite heat pump is presented and discussed. Two different models have been developed and compared using experimental data. Different sensitivity analyses were carried out with the aim of understanding the process of steam generation. The mass flow inlet results to be one of the most relevant parameters of the process and, consequently, an innovative process configuration is proposed. A descendent inlet water flow is implemented and compared with the classical ascendent process. The simulations on this configuration demonstrated that it is possible to obtain higher steam production and better process performances doubling the generated steam mass flow.