Low Temperature Waste Heat Recovery Research Articles

Aerodynamic design and optimization analysis of a 200 kW radial-inflow turbine

Abstract In low-temperature waste heat recovery for organic Rankine cycle (ORC) power generation, the radial-inflow turbine (RIT) plays a crucial role. This study focuses on the preliminary design, three-dimensional simulations, and optimization of a 200 kW RIT for R245fa working fluid. The turbine’s preliminary design relies on selected empirical coefficients, leading to performance uncertainty. The performance of the turbine obtained from the initial design was evaluated using computer simulations, indicating that achieving outstanding isentropic efficiency and power targets solely relying on the design of empirical coefficients can sometimes be challenging. Design of Experiments (DOE) on five variables was performed using the Isight platform, highlighting rotor inlet blade height as crucial for turbine performance. The optimized RIT showed a 10.5% efficiency increase and 45.6 kW power gain. Entropy production analysis confirmed substantial improvement. Systematic theoretical calculations followed by DOE optimization effectively enhance turbine efficiency, providing valuable and innovative insights for satisfactory design solutions.

Process design, performance comparison and operating test of the multi-stage vertical absorption heat exchanger realizing independent heating in three zones

Absorption heat exchangers applied in district heating systems can significantly reduce the outlet water temperature of the primary network, thereby expanding the heating scale and promoting low-temperature waste heat recovery. However, nearly 50% of the existing heating systems in high-rise buildings are divided into three independent zones. At present, there is a lack of research for absorption heat exchangers in this scenario. The main task of this paper is to address this issue to expand the application range of absorption heat exchangers. Firstly, two different processes are designed in this paper. The first process is to add a plate heat exchanger in the existing two-stage process, while the second process is a novel three-stage vertical process, consisting of three absorption heat pumps with different pressures and three sets of plate heat exchangers. Then, the operating performance, self-adjustment ability and the system cost of different processes are compared based on the simulation method. Although the price of Process 2 is 26.4% higher than that of Process 1, the efficiency of Process 2 is 20.3%-27.7% higher, and the self-regulation ability is significantly better. Thus, Process 2 has better overall performance. Moreover, the system development and operating test of Process 2 are conducted. Throughout the whole heating season, the overall efficiency of the system is 1.17–1.23. Without manual intervention, the relative standard deviations of the inlet water temperature of the secondary network and the actual heat supply rate ratio are less than 5% and 16% respectively, which proves that the system has great self-adjustment ability. The conclusions in this paper can guide the design and application of the absorption heat exchanger in three-zone independent heating scenarios.

Advanced Exergy and Exergoeconomic Analysis of Cascade High-Temperature Heat Pump System for Recovery of Low-Temperature Waste Heat

Cascade high-temperature heat pumps (CHTHPs) are often applied to recover low-temperature industrial waste heat owing to their large temperature lift. Through a comprehensive consideration of thermodynamic and economic performance, conventional and advanced exergy and exergoeconomic analyses are employed in this study to evaluate the potential for the improvement in CHTHP systems. The results show that the avoidable endogenous exergy destruction in a CHTHP system accounts for 62.26% of its total exergy destruction, indicating that most of the exergy destruction comes from the components. This suggests that CHTHP systems still have significant potential for improvement. The very low exergoeconomic factor of the total system (only 0.75%) implies that the exergy destruction cost has a great influence on the economic performance of a CHTHP system. The high- and low-temperature compressors are the two components with the highest exergy destruction, accounting for 34.14% and 26.79% of the total exergy destruction in the system, respectively. Moreover, their exergy destruction cost is much larger than that of the other components. Thus, the priorities for improvement should be the high- and low-temperature compressors. The decrease in exergy destruction in compressors produces a reduction in carbon emissions. This comprehensive analysis of thermodynamic and economic performance supplies guidance for the engineering application of CHTHPs in low-temperature waste heat recovery.

Greening the organic Rankine cycles: low-global warming potential working fluids for low-temperature waste heat recovery

Greening the organic Rankine cycles: low-global warming potential working fluids for low-temperature waste heat recovery

Study on the performance of oil fume heat recovery heat exchanger based on micro heat pipe array

In China, the utilization of high-temperature flue gas waste heat recovery has been widely studied and developed, while the large number of low-temperature flue gas waste heat recovery has not been fully developed. Therefore, research has been conducted on the heat transfer characteristics of plate heat exchangers for low-temperature oil fume. The heat exchanger were 28–44 ℃ at the hot end and − 10 to 5 ℃ at the cold end. The outlet temperature, wind speed, etcetera were measured and recorded by changing indoor and outdoor temperature, variable flow rate and variable fin size. The impact of different working conditions on heat transfer and heat transfer efficiency of the heat exchanger was analyzed. The result showed that within the range of effective experimental test temperature, the variation trend of Nu and h was the same for heat exchangers with different finned fins and heat pipes with a different liquid-filled working medium The Nu value increased linearly with the increase of the Reynolds coefficient (Re), and the heat transfer coefficient presented a quadratic curve and increased with the increase of Re. Smaller fins had a higher efficiency and higher heat transfer. The heat exchange efficiency was stable between 0.75 and 0.97, which was higher than the value required by the national standard. At the same time, the heat exchanger also met the demand for high-efficiency heat recovery at low outdoor temperature, which has a wide application prospect.

Research of the thermal storage properties of thermally conductive carbon fiber-reinforced paraffin/olefin block copolymer composite phase change materials with thermotropic flexibility

This study focuses on the fabrication and evaluation of paraffin (PA)/olefin block copolymer (OBC)/carbon fiber (CF) composite phase change materials (CPCMs) prepared using the melt impregnation process. The resultant PA/OBC/CF CPCMs exhibit superior thermal stability below 200 °C and maintain excellent shape stability at 60 °C. These characteristics are attributed to the alternating soft and hard segments of OBC, wherein the hard segments prevent liquid leakage from PA. The distinct structure of OBC further lends flexibility and recyclability to the PA/OBC/CF CPCMs. The latent heat of these CPCMs ranges from 169.1 to 197.6 J/g. Notably, the CPCMs variant (PA/OBC/CF-1) with 2 wt% CF addition retains 95 % of its initial latent heat even after 100 thermal cycles, thereby demonstrating superior cycling stability. The thermal conductivity of CPCMs with 10 wt% CF is 1.3 times that of pure PA. This significant improvement in thermal conductivity is attributed to the heat conduction pathways provided by the fibrous CF. These results indicate that the fabricated CPCMs offer substantial promise for utilization in low-temperature waste heat recovery applications.

Numerical and experimental study of a non-frosting thermoelectric generation device for low temperature waste heat recovery

Liquefied natural gas (LNG) has great potential for power generation using thermoelectric generators (TEG) due to the large amount of cold energy released during LNG gasification, but frosting is a major issue which slows the heat transfer between the TEG and the environment and reduces the power generation efficiency. This study describes a non-frosting cryogenic thermoelectric generator for cold energy recovery. This device uses natural gas vapor on the hot side of the TEG to avoid frosting caused by direct contact of the TEG with air. The device characteristics were modeled using a thermodynamic analysis with the predictions verified by experiments to predict the output characteristics. The results show an optimal channel length for the selected design conditions that maximizes the power generation. Increasing the flow rate and enhancing the heat transfer on the hot side significantly increases the power output. For the design conditions of 1000 Nm3/h gasification capacity and 0.4 MPa working pressure, the optimum channel length is 9.8 m with 350 pairs of thermoelectric modules that gives the maximum power generation of 593.94 W with a 1.36% efficiency.

High-performance tellurium-free thermoelectric module for moderate temperatures using α-MgAgSb/Mg2(Si,Sn)

α-MgAgSb is a promising thermoelectric material with an average figure of merit above unity between room temperature and 573 K, making it attractive for low temperature waste heat recovery or temperature regulation applications. We demonstrate here the first α-MgAgSb/Mg2(Si,Sn)-based thermoelectric module, where Mg2(Si,Sn) was chosen as n-type counterpart due to its excellent thermoelectric properties, low weight, abundant, and eco-friendly constituents. By using this new material combination, a maximum conversion efficiency of 6.4% and maximum power of 0.68 W were achieved for a temperature difference of 275 K, superior to commercially available (Bi,Te,Sb)-based thermoelectric modules. The Constant Property Model was used to check the validity of the measurement results and to identify room for further improvement. The characterization of the prototype shows a relatively good match between measurement and calculation for most of the thermoelectric module performance parameters; however, the measured internal electrical resistance is around 10% higher than the predicted values, indicating opportunities for further enhancement.

Thermoelectric Properties of Polyaniline/Bismuth Antimony Telluride Composite Materials Prepared via Mechanical Mixing

Organic-based thermoelectric composites are highly promising for low-temperature heat-to-electrical energy conversion applications due to their low toxicity, cost-effectiveness, facile synthesis and easy processing. Potential applications of such materials include, among others, low-temperature waste heat recovery and body heat use, such as wearable thermoelectric devices and sensors. Due to the lack of studies on organic (matrix)–inorganic (additive) thermoelectric composites prepared via mechanical mixing with respect to the processing parameters and thermoelectric performance, this work aims to contribute in this direction. More precisely, composite pellets were prepared starting from polyaniline (PANI)/bismuth antimony telluride mixed powders using a mechanical press. The processing parameters investigated included temperature, pressure and processing time, along with the inorganic additive (bismuth antimony telluride) content introduced within the composites. The experimental data revealed that the processing temperature and the additive content had the most significant effect, since their increase led to an enhancement in the composites’ thermoelectric performance. The optimal ZT (2.93 × 10−3) recorded at 130 ∘C corresponded to PANI-BST composites with a 30 wt.% BST content, prepared at a processing temperature of 80 ∘C, a processing time of 75 min and under 2 tons of pressure.

On-Site Experimental Study on Low-Temperature Deep Waste Heat Recovery of Actual Flue Gas from the Reformer of Hydrogen Production

Improving the energy-saving efficiency of flue gas deep waste heat and reducing the emission of carbon dioxide and other pollutants have been two issues that need to be paid attention to in petrochemical heating furnaces. A hydrogen production reformer with high energy consumption and high carbon emissions in the petroleum refining process affects the thermal and productive efficiency of the hydrogen production, amounts of heat from flue gas are wasted with the exhausted corrosive gas of the reformer, and latent heat is not recovered. To recover the sensible and latent heat from the exhausted gas, a new anti-corrosion, high-efficiency, and low-pressure-drop flue gas condensing heat exchanger (FGCHE) with low consumption and pressure drop was developed. The energy-saving performance was evaluated through on-site measurements and theoretical analysis. The results show that the exhausted gas temperature was reduced from 161.3~175.9 °C to 33.9~38.9 °C after using the new FGCHE to recover waste heat. The energy-saving efficiency and the utilization ratio of flue gas waste heat were 12~16.1% and 74~81.9%, respectively. The latent heat accounted for 41.3~48.1% of the total recovered heat. The exergy efficiency and the total thermal efficiency of the reformer reached 73~86.8% and 95.2~96.6%, respectively. The condensation in the flue gas reduced pollutant emissions (SO2 and NOx). This paper provides a practical application reference for the technology development of waste heat recovery and the application of an FGCHE for petrochemical heating furnaces.

Modeling and Multi-Stage Planning of Cement-IIES Considering Carbon-Green Certificate Trading

The cement industry is an important industrial entity responsible for implementing carbon emission reduction targets. Considering the carbon trading and green certificate trading mechanisms, this paper presents a multi-stage planning approach for the constructed Cement-Industrial Integrated Energy System (Cement-IIES). Carbon reduction technologies represented by low-temperature waste heat recovery, as well as phased changes in economic and technical parameters, are considered in the model. The case study shows that the proposed method not only optimizes the design economy of the Cement-IIES but also achieves a substantial carbon emission reduction in the cement production process and energy supply system. Compared with the traditional single-stage planning, the proposed method improves the system’s economic efficiency by 13.88% and flexibly adapts to changes in policies such as “coal reform”, green certificate trading and carbon quotas. The low-temperature waste heat recovery technology helps the system energy utilization efficiency in the two stages increase by 0.45% and 0.86%, respectively, whilst oxygen-enriched combustion and carbon capture technologies can reduce the total carbon emissions by about 83%. In addition, the negative carbon emission effect of biomass gives the system access to annual benefits of CNY 3.10 × 107 and CNY 7.89 × 107 in the two stages, respectively.

A techno-economic survey on high- to low-temperature waste heat recovery cycles for UK glass sector

ABSTRACT Three heat recovery cycles are studied to recover the waste heat from the exhaust gas outlet of a glass-melting furnace. To determine the viability and potential dangers based on techno-economic aspects, three fundamental recovery cycles for the exhaust gas from UK glass melting furnaces are examined. The parametric thermodynamic and techno-economic study reveals the effects of the key parameters: The condenser temperature of the ORC cycle, the pressure ratio of the s cycle, and the flash pressure of the Kalina cycle. Three thermodynamic parameters (Power production, energy, and exergy efficiency), as well as five techno-economic parameters (LCOE, NPV, PP, IRR, and MOIC), have been studied with varying key factors. The results showed that ORC is the best possible option for low-temperature waste exhaust gases as it is not as expensive as other ones, while super-critical has the highest power production to produce power from high-temperature waste heat sources. Even though ORC’s payback period is 10% longer than ‘s, Comparing the IRR, NPV, and MOIC of the ORC cycle to those of the cycle, the differences are just 8.3%, 5.3%, and 8.2% lower.

Design of Bi2Te3-based thermoelectric generator in a widely applicable system

A Bi2Te3-based thermoelectric generator (TEG) system cooled by heat radiation fin (HRF) applies to most scenarios of low-temperature power generation and waste heat recovery, while the high performance of the TEG system requires the precise design of the structure. Here we developed a theoretical model to simulate the thermal-electric coupling of the TEG system and analyzed the Bi2Te3-based TEG system with the aid of numerical and experimental methods. Results show that the increase in height of TEG not only improves the conversion efficiency but leads to a peak value of output power, which is much different from the traditional view that the output power solely decreases with the increase of height of TEG. Compared to the thickness of the fin, the height of the fin plays an essential role in optimizing the performance of TEG. By adding an electrical fan to improve the heat exchange coefficient, the net output power is doubled and the net conversion efficiency is improved by more than 80%. Besides, the structure of the TEG system is designed for different material parameters via the theoretical method. We anticipate that our results will guide the design and optimization of the TEG system.

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.

Low-temperature waste heat recovery from internal combustion engines and power output improvement through dual-expander organic Rankine cycle technology

Energy, being the driving force behind the economic development, there has been continued efforts to develop alternative energy-utilisation strategies. Due to lower heat utilisation efficiency of internal combustion engines, they provide a huge potential of waste heat recovery by organic Rankine cycle technology. The present work is devoted towards the waste heat recovery from engine coolant. This study provides the complete thermodynamic analyses, cycle configuration, system size design and selection of working fluid for the development of the stand-alone engine-coolant based ORC. The system performance at fluctuating flow of jacket cooling water with engine speed and load is investigated. The effect of changing mass flow rate of heat source, which leads to varying heat input available to be recovered from the engine coolant is considered with fixed temperature of 90°C. Methodology has been presented to enhance the cycle thermal efficiency with the use of dual expander at part load conditions, by parallelising the flow to attain the favourable input conditions for the expanders over wider variation of heat input. R245fa showed the highest performance characteristics giving cycle efficiency and work output of 4.72% and 0.97 kW, respectively at dual expander operating mode. The control strategy to switch to the dual expander is based upon its evaluation of actual isentropic efficiency and optimum working range. The present study establishes the importance of considering the continually varying heat-input conditions and its effect on the key components, unlikely assuming its performance to be constant. And to capture their varying characteristics and integrate its effect on the overall system to provide operational controlling at off-design conditions to attain flatter efficiency at wider operating conditions for system optimisation.

Modeling of a transient low-temperature waste heat recovery in the plate heat exchanger in Flownex Simulation Environment

The paper analyses the feasibility of determining the parameters of a heat exchanger operating in the crop production and realising low-temperature heat recovery from biological processes. For the first time, the Flownex 8.7 Simulation Environment has been used for this purpose. The temperature of the waste water was between 20 and 30°C. On the basis of the simulations, the power of the heat exchanger is determined to be 1 MW. The heat exchanger can efficiently heat up cold water from a deep well (7-10°C) to an assumed temperature of 19.7°C. The results from the simulation calculations correspond to the results obtained under actual conditions within a range of up to 2%.

Compact Thermal Storage with Phase Change Material for Low-Temperature Waste Heat Recovery—Advances and Perspectives

The current interest in thermal energy storage is connected with increasing the efficiency of conventional fuel-dependent systems by storing the waste heat in low consumption periods, as well as with harvesting renewable energy sources with intermittent character. Many of the studies are directed towards compact solutions requiring less space than the commonly used hot water tanks. This is especially important for small capacity thermal systems in buildings, in family houses or small communities. There are many examples of thermal energy storage (TES) in the literature using the latent heat of phase change, but only a few are commercially available. There are no distinct generally accepted requirements for such TES systems. The present work fills that gap on the basis of the state of the art in the field. It reviews the most prospective designs among the available compact latent heat storage (LHS) systems in residential applications for hot water, heating and cooling and the methods for their investigation and optimization. It indicates the important characteristics of the most cost- and energy-efficient compact design of an LHS for waste heat utilization. The proper design provides the chosen targets at a reasonable cost, with a high heat transfer rate and effective insulation. It allows connection to multiple heat sources, coupling with a heat pump and integration into existing technologies and expected future scenarios for residential heating and cooling. Compact shell-tube type is distinguished for its advantages and commercial application.

Comparing and optimizing the potential advantages of a salinity-gradient solar pond for either absorption-based or ejector-based refrigeration cycles combined with thermoelectric generators

This study compares the applicability of two popular refrigeration cycles for air-conditioning, i.e., absorption-based (Model 1) and ejector-based (Model 2), combined with a salinity-gradient solar pond. Indeed, there exists a gap in comparing the performance of solar pond-based refrigeration cycles to which this study intends to respond. In addition, utilizing zeotropic mixtures in an ejector refrigeration cycle integrated with a solar pond and selecting the most suitable zeotropic for such a framework has not been regarded in the literature. Both models are boosted using thermoelectric generators for low-temperature waste heat recovery and electricity generation. Energy, exergy, economic, and environmental investigations with a net present value analysis are implemented, and multi-objective optimization using non-dominated sorting genetic algorithm-II is conducted. As another principal point, this paper performs a case study to illustrate the performance of models regarding an actual climate condition. Results show that using Butane-R143a zeotropic increases the advantages of Model 1; however, Model 2 is the most suitable selection for the solar pond. According to the optimum state, Model 1 possesses exergy efficiency and Levelized cost of products of 17.93% and 0.12 $/kWh, which are 0.84 percentage points and 83% better than Model 2. But Model 2 has a better environmental performance by mitigating 22% further carbon dioxide than Model 1.

Thermal–economic optimization and working fluid selection of subcritical organic Rankine system for low-temperature waste heat recovery based on NSGA-II and TOPSIS

Thermal–economic optimization and working fluid selection of subcritical organic Rankine system for low-temperature waste heat recovery based on NSGA-II and TOPSIS

Decarbonization of Heat through Low-Temperature Waste Heat Recovery: Proposal of a Tool for the Preliminary Evaluation of Technologies in the Industrial Sector

In an industrial energy scenario increasingly focused on decarbonization and energy cost containment, waste heat is a resource that is no longer negligible. Despite the great abundance of waste heat, its recognized potential, and numerous technologies available for its use, the rate of waste heat recovery (WHR) is still low, especially at low temperatures (<230 °C). Non-technological barriers, such as the lack of knowledge and support tools, strongly limit the diffusion of WHR technologies. The work presented in this paper aims to overcome non-technological gaps by developing a simple and operational tool that can support companies in the preliminary stages of evaluating a WHR application. The methodology followed involved the development of specific data-based models for WHR technology sizing by correlating waste heat input characteristics with dimensional and economic parameters of the technologies evaluated. We considered the most representative technologies in the WHR scenario: organic Rankine cycles for electric power generation, heat pumps for thermal power generation, absorption chillers for cooling generation, and plate heat exchangers for low-temperature heat exchange applications. One of the significant strengths of the tool is that it was developed using real and hard-to-find technologies performance and cost data mainly collected through continuous interactions with WHR technology providers. Moreover, the interaction with the technology providers allowed contextualization and validation of the tool in the field. In addition, the tool was applied to three large companies operating in the Italian industrial sector to test its effectiveness. The tool applications made it possible to propose cost-effective solutions that the companies had not considered before, despite the high level of attention with which they were already approaching energy efficiency improvements. The result obtained demonstrates the applicability and innovativeness of the tool.