High Temperature Waste Heat Recovery Research Articles

Liquid metal-enhanced thermoelectric generator for high-temperature thermal harvesting

It is a challenge to achieve high output power of the thermoelectric generator (TEG) for high-temperature waste heat recovery due to the working fluids with low thermal conductivity (such as air) or low tolerance of temperature (water or oil). In this paper, the gallium-based liquid metal (LM) with a high boiling point (>1000 ℃) and thermal conductivity (>20 W/mK) are introduced to significantly enhance heat charging and discharging at the hot/cold sides of TEG. We also developed an electromagnetic induction pumping method for the effective LM-driven flow at high temperatures. A three-dimensional coupling multi-parameter optimization simulation model of LM-based TEG was developed to reveal the internal heat transfer and power generation mechanism for clarifying the impact factors of the performance. The results have shown that the power generation capacity can be effectively improved by increasing the inlet temperature (Thot-in). It is worth noting that the temperature difference (ΔT) of the TEG module is severely limited by the thermal resistance (Rcapacity) of the LM heat capacity, such as, when the flow rate of 2 L/min, the Rcapacity accounts for 90.6 % (0.020 ℃/W). It is easier to achieve a larger open circuit voltage by increasing the height of the thermoelectric leg, but the Pmax is constantly weakened. Compared with Xceltherm 600 and Solar salt, LM heat transfer fluid has more obvious advantages in enhancing the power generation performance of the system. The LM-based TEG experiment platform was established to study heat transfer and power generation characteristics. The results have demonstrated that good consistency was proved by comparing experimental and numerical data. And the Pmax of the LM-based TEG system is 0.16 W/cm2 at ΔT of 136 ℃. LM-based TEG can open new perspectives for broad applications in high-temperature 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.

Steam Storage Rankine Cycle for Unutilized Applications in Distributed High-Temperature Waste Heat Recovery

In the light of increasingly valuable resources and a trend towards more efficient processes pushed by climate change, distributed Waste Heat Recovery (WHR) is an important element in the transformation of the energy supply. In recent years, however, WHR systems have often been optimized and implemented for steady-state applications. In this paper, dynamic system modeling and a Steam Rankine Cycle (SRC) pilot plant with 40 kWel are used to investigate applications unutilized thus far for the conversion of high-temperature waste heat into electricity using a shell boiler with 1.27 m3 of liquid water for short-term energy storage. In addition to experimental investigations of the storage system as an Uninterruptible Power Supply (UPS) and the input and output of +/−100% electrical power peaks for grid-assistive operation, a control concept for the use of volatile waste heat is developed from a model-based controller design up to a Model Predictive Control (MPC) with the help of a dynamic system simulation. Based on the validated model and experimental measurement data, outlooks for concrete applications with higher storage capacity and power are provided.

Multi-fidelity robust design optimization of an ORC turbine for high temperature waste heat recovery

The ORC technology is subject to manifold sources of uncertainty that can have a severe impact on the thermodynamic and economic efficiency of plant components, particularly when the system is operated at off-design conditions. In this contribution we focus on the development of ORC turbines with stable performance under uncertainty: a novel multi-fidelity robust design optimization (RDO) strategy is used to design the first nozzle of an ORC turbine for high temperature waste-heat recovery. For this kind of application, the turbine inlet and outlet conditions may vary randomly over a large range. The RDO strategy combines parsimonious uncertainty quantification techniques with a multi-objective genetic algorithm optimizer based on surrogate models. The multi-fidelity approach allows to estimate with high accuracy and with a low computational cost the statistical moments of the probability distribution function of the quantity of interest, which here is the entropy generation within the cascade. To improve the accuracy of the surrogate model coupled with the optimizer, the multi-objective expected improvement criterion is adopted. The optimization converges to an efficient optimum solution, ensuring improved and stable performance over the whole considered range of uncertain operating conditions and with a computational cost that is significantly lower than other RDO approaches proposed in literature.

First principle studies on electronic and thermoelectric properties of Fe2TiSn based multinary Heusler alloys

The alloys with 8/18/24 valence electron count (VEC) are promising candidates for efficient energy conversion and refrigeration applications at low as well as high temperatures. Recently Fe-based Heusler alloys attracted researchers due to their compelling electronic band structure i.e flat band along one direction of the Brillouin zone and highly dispersive bands along the other directions. Here we focus on the thermoelectric (TE) transport properties of isovalent/aliovalent substituted Fe2TiSn systems those may be potential TE materials. The multinary substitution has been done in such a way that it preserves the 24 VEC and hence the semiconducting nature. The calculated total energies with VASP-PAW potential within density functional theory with PBE-GGA functional were used to determine the ground state properties such as equilibrium lattice parameters, bulk modulus etc. We have also investigated the structural, electronic, lattice dynamic and TE transport properties by using PBE-GGA and TB-mBJ exchange–correlation functional. The full potential linearized augmented plane wave method as implemented in WIEN2k code was used to investigate electronic structure and TE transport properties with the PBE-GGA and TB-mBJ exchange potentials and Boltzmann transport theory. The calculated single crystal elastic constants, phonon dispersion and phonon density of states confirm that these systems are mechanically and dynamically stable. The TE transport properties is calculated by including the lattice part of thermal conductivity (κL) obtained from two methods one from the calculated elastic properties calculation (κLelastic) and the other from phonon dispersion curve (κLphonon). The strong phonon–phonon scattering by large mass difference/strain fluctuation of isovalent/aliovalent substitution at Ti/Sn sites of Fe2TiSn reduces the lattice thermal conductivity which results in high thermoelectric figure-of-merit (ZT) value of 0.81 at 900K for Fe2Sc0.25Ti0.5Ta0.25Al0.5Bi0.5. The comparative analysis of TE transport properties using the band structures calculated with the PBE-GGA and TB-mBJ functional shows that the ZT value obtained from TB-mBJ scheme is found to be significantly higher than that based on PBE-GGA. The calculated relatively low lattice thermal conductivity and high ZT values suggest that isovalent/aliovalent substituted Fe2TiSn are promising candidates for medium to high temperature waste heat recovery.

Thermal Investigation of Solid Oxide Fuel Cell Ni-YSZ Anode supported with Cooling System: A FEM Approach

Solid oxide fuel cell (SOFC) is preferred for power generation owing to its high-temperature waste heat recovery and low pollutant emissions. Nevertheless, SOFC operation is highly dependent on an effective cooling system, and the temperature gradient (ΔT) causes the distribution of thermal stress. The trade-off between meeting the SOFC requirement to operate at elevated temperature and minimizing thermal stress by reducing ΔT in the SOFC stack is required. Therefore, a cooling system for the SOFC stack is required to control the temperature homogeneity in the stack. In this study, a 3D finite element method containing heat transfer and energy charge equations was developed and then applied to investigate the effects of the (i) cooling plate and (ii) cooling fin on temperature distribution. The conventional stack orientation (i) parallel flow and (ii) counter flow were considered and compared with the adiabatic model in Ansys thermal analysis. The analysis was carried out under steady-state conditions. Considering that the temperature distribution varies according to the operating temperature and environment, the ambient temperature was set at 800 °C, 750 °C, 700 °C, and 650 °C. The study showed that the steepness of ΔT for a fin with the parallel flow is 1.5% better than for counterflow in the same operating scenario. Notably, the contribution of the cooling plate can minimize ΔT by 10% more than the fin. In addition, cooling measures are required to ensure the long-term stability of the cell during prolonged operation.

Choosing Thermos chemical Storage Materials for High Temperatures Using a MCDM Methodology

Because of its inherent variability, intermittency, and technological and economic difficulties, currently, manufacturing waste heat is underutilized. One of the best methods for removing obstacles, lowering greenhouse gas emissions, and safeguarding the ecosystem at large is energy recovery. The process of choosing materials is crucial to the design of heat storage devices. Complex interactions between a number of variables and parameters are necessary to produce the finest candidate material for a particular appli-cation. The selection of high-temperature thermo chemical storage (TCS) materials is addressed in this re-search using a matrix-based multi-criteria decision-making (MCDM) approach. The Port Talbot Steelworks also utilized the suggested method to select suitable components for high temperature waste heat recovery (above 500 C). In this article, a COPRAS set theory-based multi-criteria decision-making (MCDM) model is proposed. Alternatives include MgH2, MgH2/Composite, Mg2FeH6, Mg2NiH4, MgO/Mg(OH)2, and Heat Release Temperature. Evaluation criteria also include Reaction Enthalpy, Volumetric Energy Densi-ty, Mass Energy Density, and Heat Charge Temperature. Because of this, remanufacturing is ranked first and refurbishing is ranked last. Compared to other options, Mg2FeH6 is superior.

A decision support model for waste heat recovery systems design in Data Center and High-Performance Computing clusters utilizing liquid cooling and Phase Change Materials

The Data Center (DC) and High-Performance Computing (HPC) sector is increasingly becoming one of the single largest energy consuming sectors in the energy system and the demand for new DCs is growing with the rising use of cloud-based services, social media and internet usage in general. DCs and HPC clusters employ energy intensive cooling in order to dissipate the generated heat from the Information Technology (IT) equipment. Conventionally, the cooling is almost exclusively done by air-based systems; however, the use of liquid based cooling has shown potential to increase computational efficiency of the systems and decrease cooling needs by operation above the free cooling limit. Furthermore, the liquid coolant can operate at higher temperatures allowing high temperature waste heat recovery. In addition, load shifting through Latent Thermal Energy Storage (LTES) will allow the non-controllable waste heat resource to be stored seasonally, thereby granting the ability to cover larger District Heating (DH) loads. In this work, a decision support model is developed that will take basic information regarding a HPC cluster or DC as inputs. The decision support model will provide a parameterized output that shows different configurations and design parameters that can be utilized for the system. The main outputs includes yearly energy savings, yearly cost savings and efficiency gains through the Power Usage Efficiency and the Energy Reuse Efficiency. The decision support model is demonstrated in a Danish case study. Electricity savings between 8.14 % and 10.8 % of the total cluster electricity consumption and a waste heat recovery potential of 85 MWh/year to 576 MWh/year are obtained. It is shown that if the DH covered is needed to be self-sufficient the configuration would require an LTES with PCM mass of 500 kg, but system configurations that operate as an addition to an existing local heating source shows increases in yearly energy savings of 332 % compared to self-sufficient configurations. The goal of the decision support model is to assist the design of future waste heat recovery applications through selection of system parameters including coolant temperatures, energy storage design parameters, DH supply temperatures and DH load coverage from the DC or HPC cluster.

A thermodynamic configuration method of combined supercritical CO2 power system for marine engine waste heat recovery based on recuperative effects

Supercritical CO2 Brayton cycle (SCBC) is widely used in high-temperature waste heat recovery combined systems with sequential or cascade configurations due to its compact structure and high efficiency. However, since the heat source conditions of these systems are not clearly defined, there is no practicable design approach to comprehensively adapt the waste heat with different temperatures, especially for the ships. This paper aims to propose an effective thermodynamic configuration method to facilitate the design and application of recuperative SCBC combined systems for the high-temperature waste heat recovery of marine engines. To this end, the factors that may affect the system configuration are investigated, and it reveals that the recuperator effectiveness can not only influence its own performance but also determine the heat source conditions, which will finally affect the performance of the entire system. Therefore, a new system configuration method is proposed based on the recuperative effects, and a novel combined system is designed as a case study for further illustration and multi-objective optimization. The results indicate that an optimal value of the recuperator effectiveness exists in the preliminarily determined range, 0.56–0.8. Under the system optimal operating conditions, the total energy output and electricity production cost are 538.97 kW and 5.34 cent/kWh, respectively, and the corresponding thermal and exergy efficiencies research up to 33.17 % and 61.93 %, respectively. It proves that the configuration method proposed in this paper can realize an efficient design of recuperative SCBC combined system, and provide a reference for other relevant systems.

Electromagnetic self-encapsulation strategy to develop Al-matrix composite phase change material for thermal energy storage

How to break through the corrosion rupture limit of eutectic Al-Si phase change material (PCM) in iron-based encapsulation container has been a major challenge for realizing the high temperature waste heat recovery in metallurgical industry. Herein, we proposed a self-encapsulation strategy of eutectic Al-Si PCM with no need of container via constructing the 3D-honeycomb-SiC reinforced Al matrix composite with Si-rich◎Si-poor cladding structure ([SiC&Si-rich]◎EAl-Si), which can fundamentally address the corrosion issue. Strikingly, such a structure feature delivers the excellent structural stability and superior energy storage capacity with a high thermal conductivity of 96 ~ 62 W·m−1·°C−1 at 75 ~ 550 °C (increased by ~ 10% after 1000 cycles), and giant discharge energy density of 490 J·g−1 (with the capacity retention of over 98.9% after 1000 cycles). Compared with the Al-Si@Al2O3 microcapsule with core–shell architecture, the discharge energy density of the [SiC&Si-rich]◎EAl-Si was enhanced by 19.3%~105.7%. In comparison with conventional iron-based container encapsulation, the [SiC&Si-rich]◎EAl-Si demonstrates a 10.7% and 16.2% improvement in efficiency of charge and discharge process. More importantly, this self-encapsulation strategy of eutectic Al-Si PCM can be further constructed continuously by the electromagnetic continuous separation technology, which can potentially pave the way to achieve the large scale production of the [SiC&Si-rich]◎EAl-Si, thus providing technological support for accelerating the application process of eutectic Al-Si PCM in metallurgical industry.

Correlation analysis based multi-parameter optimization of the organic Rankine cycle for medium- and high-temperature waste heat recovery

The present paper established a multi-parameter optimization model of the organic Rankine cycle (ORC) to recover medium- and high-temperature waste heat. The preliminary screening of 42 pure working fluids is completed according to the limitations of environment and safety requirements. Afterwards, the relationship between heat source temperature, working fluid physical properties, and system net output power are analyzed. It can be found that there is a parabola variation relationship between working fluid critical temperature and system net power output. When the net power output reaches its peak value, a further increase of working fluid critical temperature will causes the opposite effect. Furthermore, correlation analysis is introduce to investigate the variation relationship between system net output power and working fluid critical temperature, system evaporating temperature/pressure, and condensing temperature/pressure by different heat source temperatures is investigated in detail. Results show that it is not much effective to use a working fluid with great pressure ratio for the design of a high-efficiency ORC system. On the contrary, using working fluid with a high temperature ratio can always improve the system net power output. Besides, the working fluid specific heat difference/ratio, and the latent heat difference/ratio during the evaporation and condensation processes jointly influence the ORC output performance. As a result, the influence order of working fluid key properties to the system net power output is: temperature ratio＞pressure ratio＞latent heat＞specific heat.

Deep insight into phase transition and crystallization of high temperature molten slag during cooling: A review

High temperature molten slags, such as blast furnace slag, mold flux, coal slag, etc., exist widely in the metal manufacturing and energy power industries and play important roles in equipment operation, energy saving and emissions reduction as well as resource reuse. The treatment of high temperature molten slag usually involves a phase change cooling process coupled with crystallization behavior, which is a very challenging process and will significantly affect the high-temperature waste heat recovery, the vitreous content in slag, the quality of the as-cast slab, and the stable operation of the integrated coal gasification combined cycle system. This paper firstly reviews the main methods to explore the crystallization behaviors of molten slag. Then, the crystallization behaviors of molten slag are discussed under different cooling rates and main components. In what follows, the attempts on the prediction of molten slag crystallization behaviors are summarized. The major conclusions and future research priorities are as follows: The critical cooling rate of molten slag decreases gradually when it undergoes the isothermal temperature, continuous cooling and variable cooling condition. Moreover, the variation of the precipitated crystal phase is the essential reason that affects the crystallization behaviors of molten slag. To better guide the practical process, it has a long way to go in predicting the crystallization behavior of molten slag using the easy-to-obtain parameters.

Optimal Design of Combined Two-Tank Latent and Metal Hydrides-Based Thermochemical Heat Storage Systems for High-Temperature Waste Heat Recovery

The integration of thermal energy storage systems (TES) in waste-heat recovery applications shows great potential for energy efficiency improvement. In this study, a 2D mathematical model is formulated to analyze the performance of a two-tank thermochemical heat storage system using metal hydrides pair (Mg2Ni/LaNi5), for high-temperature waste heat recovery. Moreover, the system integrates a phase change material (PCM) to store and restore the heat of reaction of LaNi5. The effects of key properties of the PCM on the dynamics of the heat storage system were analyzed. Then, the TES was optimized using a genetic algorithm-based multi-objective optimization tool (NSGA-II), to maximize the power density, the energy density and storage efficiency simultaneously. The results indicate that the melting point Tm and the effective thermal conductivity of the PCM greatly affect the energy storage density and power output. For the range of melting point Tm = 30–50 °C used in this study, it was shown that a PCM with Tm = 47–49 °C leads to a maximum heat storage performance. Indeed, at that melting point narrow range, the thermodynamic driving force of reaction between metal hydrides during the heat charging and discharging processes is almost equal. The increase in the effective thermal conductivity by the addition of graphite brings about a tradeoff between increasing power output and decreasing the energy storage density. Finally, the hysteresis behavior (the difference between the melting and freezing point) only negatively impacts energy storage and power density during the heat discharging process by up to 9%. This study paves the way for the selection of PCMs for such combined thermochemical-latent heat storage systems.

Carbon Dioxide Mixtures as Working Fluid for High-Temperature Heat Recovery: A Thermodynamic Comparison with Transcritical Organic Rankine Cycles

This study aims to provide a thermodynamic comparison between supercritical CO2 cycles and ORC cycles utilizing flue gases as waste heat source. Moreover, the possibility of using CO2 mixtures as working fluids in transcritical cycles to enhance the performance of the thermodynamic cycle is explored. ORCs operating with pure working fluids show higher cyclic thermal and total efficiencies compared to supercritical CO2 cycles; thus, they represent a better option for high-temperature waste heat recovery provided that the thermal stability at a higher temperature has been assessed. Based on the improved global thermodynamic performance and good thermal stability of R134a, CO2-R134a is investigated as an illustrative, promising working fluid mixture for transcritical power cycles. The results show that a total efficiency of 0.1476 is obtained for the CO2-R134a mixture (0.3 mole fraction of R134a) at a maximum cycle pressure of 200 bars, which is 15.86% higher than the supercritical carbon dioxide cycle efficiency of 0.1274, obtained at the comparatively high maximum pressure of 300 bars. Steam cycles, owing to their larger number of required turbine stages and lower power output, did not prove to be a suitable option in this application.

Extensive techno-economic assessment of combined inverted Brayton – Organic Rankine cycle for high-temperature waste heat recovery

This work is a techno-economic study of the combination of inverted Brayton cycle, and organic Rankine cycle (combined IBC-ORC) applied for high-temperature waste heat recovery (WHR) of the engine exhaust energy. In IBC, exhaust gases expand to subatmospheric pressure in the turbine, transmit heat residuals to ORC, and restore pressure to 1 atm in the compressor. The system is analysed in the Aspen Hysys software in design conditions at the case study of 1.4 MW gas-fueled internal combustion engine as a high-temperature waste heat source (470–570 °C). Firstly, the paper shows the performance of the system optimised for different ambient temperatures. The role of water condensation contained in flue gas is emphasised for these bounds. Then, the paper presents a multi-objective optimisation illustrated by Pareto fronts for the objective functions of system electric efficiency and levelized cost of energy (LCOE) in the mentioned range of exhaust temperatures. TOPSIS-based Pareto-front analysis results in recommendations of the best sets of cycle parameters in this trade-off. For exhaust temperatures 470 °C, 520 °C, and 570 °C, optimal configurations identified via TOPSIS methodology demonstrate 10.8%, 12.1%, 13.3% efficiencies with LCOE equal to 185.5 $/MWh, 162.4 $/MWh and 146.1 $/MWh correspondingly.

Understanding Oxidation Resistance of Half-Heusler Alloys for in-Air High Temperature Sustainable Thermoelectric Generators.

High temperature waste heat recovery has gained tremendous interest to generate useful electricity while reducing the harmful impact on the environment. Thermoelectric (TE) solid-state materials enable direct conversion of heat into electricity with high efficiency, thereby offering a practical solution for waste heat recovery. Half-Heusler (hH) alloys are the leading TE materials for medium to high temperature applications, as they exhibit a high figure of merit and mechanical strength at temperatures as high as 973 K. Here we investigate the most promising hH alloys represented as MNiSn, MCoSb, and NbFeSb systems (M = Hf, Zr, and Ti) and provide fundamental understanding of their in-air thermal stability at high temperatures under realistic operating conditions required for energy generation. The understanding of oxidation resistance of TE materials is crucial for their practical deployment in extreme environments without vacuum sealing. The n-type MNiSn and p-type NbFeSb compounds are found to exhibit excellent oxidation resistance at a high temperature of 873 K. The oxidation resistance is enhanced through the presence of an intermetallic Ni-Sn layer for MNiSn and Nb-TiO2 double layer for (Nb,Ti)FeSb. A unicouple thermoelectric generator (TEG) fabricated from thermally stable materials demonstrated consistent performance for more than 150 h at 873 K in air. These results demonstrate the significance of TE materials in waste heat recovery systems.

Experimental study on heat pipe thermoelectric generator for industrial high temperature waste heat recovery

The recovery of high-temperature waste heat is important for improving energy efficiency and environmental sustainability. In this paper, a novel high-temperature waste heat recovery system with heat pipe and thermoelectric generator (TEG) is proposed to resolve the mismatch between energy supply and demand. A Heat Pipe Thermoelectric Generator (HPTEG) experimental setup with potassium heat pipes and skutterudite TEGs is designed and fabricated to achieve passive thermal management and electricity generation. The passive heat transfer and thermoelectric performances are investigated. The effective thermal conductivity of the heat pipe is proposed to assess the heat pipe heat transfer performance. When the heat pipe temperature reaches 630 °C, the effective thermal conductivity reaches 35831 W/(m•K), which is practically 100 times that of copper. An effective Seebeck coefficient and an effective thermal conductivity of the TEGs are proposed to evaluate the TEG system-level performances. The simulation accuracy of HPTEG system performances is significantly improved when the effective Seebeck coefficient and effective thermal conductivity are employed. Moreover, they can be utilized to accurately predict the HPTEG performance in actual engineering fields.

Techno-economic analysis of combined inverted Brayton – Organic Rankine cycle for high-temperature waste heat recovery

Many practical cases with waste heat recovery potential such as exhaust gases of reciprocating engines, cement kilns or heat-treating furnaces, are nowadays often integrated with organic Rankine cycle to convert waste heat to the mechanical power. However, when dealing with high-temperature waste heat, organic Rankine cycle faces efficiency limit due to the physical properties of the working and thermal fluids. That gives room for further enhancement of the waste heat recovery technologies via the investigation of different non-conventional schemes as one of the possible ways. In the present work, a system introducing the combined inverted Brayton plus organic Rankine cycle is under investigation. Aspen Hysys models of both conventional organic Rankine cycle and combined cycle were designed, orienting on waste heat recovery from the heavy-load gas-fueled reciprocating engine exhaust. In this way, the performance of the combined scheme was benchmarked versus the conventional organic Rankine cycle. An assessment of the organic Rankine cycle working fluids was provided, and pentane has shown the best thermodynamic performance. The study on inverted Brayton cycle defined the remarkable effect of the water condensation in the gas duct on the inverted Brayton cycle performance. Finally, both thermodynamic and economic optimizations of the models were conducted, setting the stage for the comparison of solutions. Results have shown the 10% advantage of the combined scheme over organic Rankine cycle in generated power and system efficiency. The levelized-cost-of-energy-based optimization for variable capacity factors has highlighted above 6% advantage of the investigated solution. The analysis of the sensitivity from machines’ efficiencies and heat exchangers’ pinches has shown that with some sets of parameters, the studied scheme may concede to the organic Rankine cycle.

WITHDRAWN: Techno-economic analysis of combined inverted Brayton - Organic Rankine cycle for high-temperature waste heat recovery

Abstract Many practical cases with waste heat recovery potential such as exhaust gases of reciprocating engines, cement kilns or heat-treating furnaces, are nowadays often integrated with organic Rankine cycle to convert waste heat to the mechanical power. However, when dealing with high-temperature waste heat, organic Rankine cycle faces efficiency limit due to the physical properties of the working and thermal fluids. That gives room for further enhancement of the waste heat recovery technologies via the investigation of different non-conventional schemes as one of the possible ways. In the present work, a system introducing the combined inverted Brayton plus organic Rankine cycle is under investigation. Aspen Hysys models of both conventional organic Rankine cycle and combined cycle were designed, orienting on waste heat recovery from the heavy-load gas-fueled reciprocating engine exhaust. In this way, the performance of the combined scheme was benchmarked versus the conventional organic Rankine cycle. An assessment of the organic Rankine cycle working fluids was provided, and pentane has shown the best thermodynamic performance. The study on inverted Brayton cycle defined the remarkable effect of the water condensation in the gas duct on the inverted Brayton cycle performance. Finally, both thermodynamic and economic optimizations of the models were conducted, setting the stage for the comparison of solutions. Results have shown the 10% advantage of the combined scheme over organic Rankine cycle in generated power and system efficiency. The levelized-cost-of-energy-based optimization for variable capacity factors has highlighted above 6% advantage of the investigated solution. The analysis of the sensitivity from machines’ efficiencies and heat exchangers’ pinches has shown that with some sets of parameters, the studied scheme may concede to the organic Rankine cycle.

Design of a high-temperature heat to power conversion facility for testing supercritical CO2 equipment and packaged power units

This paper addresses the need of bridging between fundamental energy research and industrial exploitation of technologies by presenting a state of the art experimental facility to investigate pilot heat exchangers and plants dealing with high temperature waste heat recovery and conversion. The facility comprises a 830 kW process air heater with an exhaust mass flow rate of 1.0 kg/s at 70 mbarg and maximum temperature of 780 °C. The heater has a 2.0 m long test section for the installation and characterization of waste heat recovery heat exchangers. The heat sink is a 500 kW water dry cooler with full control of flow rate and temperature of the cooling stream. The high-temperature heat to power conversion facility hosts a 50 kWe power conversion unit based on the simple recuperated Joule-Brayton cycle with supercritical CO2 (sCO2) as working fluid. The packaged, plug and play sCO2 system utilizes a single-shaft Compressor-Generator-Turbine unit. The paper discusses the main design features of the test facility as well as operation and safety considerations.