Recycling Waste Heat Research Articles

Numerical analysis on the performance of sodium chloride solution evaporative crystallization system driven by high-temperature heat pump

In the context of sustainable development, heat pump technology is increasingly recognized as a key method for enhancing the efficiency of evaporative crystallization processes. In this study, we propose a high-temperature heat pump evaporative crystallization system to facilitate the recycling of waste heat from secondary steam in low-vacuum and low-temperature evaporative crystallization, thereby achieving the cyclic utilization of condensation heat from secondary steam. The primary objective of this research is to develop a comprehensive mathematical model for the HPC system that investigate its operating performance under varying conditions, with the aim of promoting its practical application. The results demonstrate that by adjusting operating pressures, the temperature of the secondary steam can be controlled, allowing for regulation of the main particle size of the product. Specially, when maintaining the flow rate of the raw material liquid at 90 % of design condition, it is possible to achieve a maximum main particle size of 2.8 mm. Additionally, fluctuations in the flow rate of the raw material liquid significantly impact the cycle rate, with the optimum operating flow rate range identified as 75 % to 110 % of the rated value. The coefficient of performance of the system can achieve 5.85 under design conditions with a concentration of 4 % and flow rate of 310 kg/h. This research provides a theoretical foundation for the practical operation and commissioning of the HPC units.

Reduction of carbon emission in iron sintering process based on hot air sintering technology

Reducing carbon dioxide (CO2) emissions in the iron and steel industry plays a crucial role in addressing global climate change. One significant technological solution for reducing CO2 emissions in iron and steel production is the recycling of waste heat. Hot air sintering has the potential to decrease CO2 emissions from flue gas by reusing hot flue gas in the production process. This can result in a reduction in the consumption of fossil fuels. Usually, the relationship between the hot air temperature and the carbon content determines the CO2 emission reduction effect. In order to meet the demand for reducing CO2 emissions, this paper thoroughly investigates the mechanism of CO2 reduction by hot air sintering through sintering pot experiments. It precisely establishes the correlation between hot air temperature and carbon content, and suggests strategies for effectively managing hot air sintering based on scientific principles. The results show that hot air sintering achieves a reduction in CO2 emissions by enhancing fuel combustion heat utilization and heat substitution. On the one hand, the heat of the sinter bed surface layer is increased, which improves the mineralization conditions and increases the sintered mineral quantity and quality, thus reducing the CO2 emission by 4.4%; on the other hand, the waste heat is returned to the sinter bed to replace part of the fuel combustion heat, thus reducing the CO2 emission by 17.7%. The experimental results show that the best carbon reduction effect is achieved at a hot air temperature of 300 °C and a solid fuel ratio of 4.7% (labelled T300-C47), which reduces carbon emissions by 17.7% and improves the quality of the sintered minerals. Combined with the actual production, in the range of 200–300 °C hot air, by increasing the hot air temperature to replace the solid fuel with equal heat can realize the hot air sintering to reduce CO2 emissions and improve the sintering production. The research provides theoretical guidance for the clean production of iron and steel sintering and energy saving and carbon reduction.

Electronic cooling and energy harvesting using ferroelectric polymer composites

Thermal management emerges as a grand challenge of next-generation electronics. Efforts to develop compact, solid-state cooling devices have led to the exploration of the electrocaloric effect of ferroelectric polymers. Despite recent advances, the applications of electrocaloric polymers on electronics operating at elevated temperatures remain essentially unexplored. Here, we report that the ferroelectric polymer composite composed of highly-polarized barium strontium titanate nanofibers and electron-accepting [6,6] phenyl-C61-butyric acid methyl ester retains fast electrocaloric responses and stable cyclability at elevated temperatures. We demonstrate the effectiveness of electrocaloric cooling in a polymer composite for a pyroelectric energy harvesting device. The device utilizes a simulated central processing unit (CPU) as the heat source. Our results show that the device remains operational even when the CPU is overheated. Furthermore, we show that the composite functions simultaneously as a pyroelectric energy converter to harvest thermal energy from an overheated chip into electricity in the electrocaloric process. This work suggests a distinct approach for overheating protection and recycling waste heat of microelectronics.

Dynamic performance of a polygonal thermoelectric generator using sickle-shaped fins for automotive application

About 40 % of automotive fuel energy is lost in the form of heat through exhaust gas, the utilization of thermoelectric power generation technology presents a direct conversion of thermal to electric energy. A thermoelectric generator (TEG) system was designed in this study, comprising a polygonal heat exchanger using sickle-shaped fins to enhance waste heat recycling. Additionally, a transient Computational Fluid Dynamics (CFD)-analysis model was introduced to investigate its dynamic response utilizing the instantaneous variations of exhaust gas and coolant under the China Light-Duty Vehicle Test Cycle (CLTC) as transient inputs. The TEG system exhibits an average power output of 24.48 W and a conversion efficiency of 1.12 % throughout the CLTC. After heating from ambient temperature to normal operating temperature, the power rises to 34.48 W and efficiency to 1.57 %, showing enhanced output performance. A comparison of the transient and steady-state analysis results indicates that the transient analysis reflects the hysteresis effect of heat transfer more accurately. Through experimental verification, the mean absolute percentage errors of the transient model are calculated to be 5.57 % and 8.28 % respectively, proving the credibility of the simulated results. The proposed dynamic model allows for evaluating the actual behavior of the TEG system under intricate driving cycles and offers a robust reference for TEG system optimization and its automotive applications in future.

A new strategy to produce calcium carbide-acetylene from integrated multi-level low carbon construction driven by biomass

A highly efficient and clean biomass energy-based calcium carbide-acetylene production system, including low-carbon energy supply, solid waste recycling and cascade utilization of waste heat, has been developed for the conventional energy-intensive and highly polluting fossil fuel-dependent calcium carbide industry. This system supplies the carbide-acetylene production plant with energy from the gasification of biomass and converts the plant's solid waste carbide slag into the calcium feedstock required by the plant. The waste heat from the plant's high-temperature exhaust gases is recycled and used via the multi-stage heat exchange, so that the energy cascade conversion and utilization is achieved. A simulation model of the plant is created in Aspen Plus, and a mathematical model for the biomass gasification process and cycle compensation of the calcium source through the Fortran language is written and embedded. When calculating the carbon consumption and CO2e emissions of the system, it was found that the carbon consumption and CO2e emissions of the conventional process were 5.43 t Coal·t−1C2H2 and 2.25 t CO2e·t−1C2H2, respectively. However, the carbon consumption of the new process was reduced by 65.19%, and carbon emissions by 27.24% in comparison. The energy analysis shows that the energy efficiency of the system is 36.21% for the conventional process and 44.82% for the new processes. The exergy analysis of the effective energy shows that the exergy efficiency of the new process is 73.20%, which is 52.98% better than that of the conventional process. Introduction of an index, the levelized income of acetylene product (LIOA), to characterize the product income of the system. When the price of acetylene is between 2.23 $/kg and 4.19 $/kg, the LIOA for the conventional and the new processes are 1.41 $/kg to 3.38 $/kg and − 1.28 $/kg to 0.68 $/kg, respectively. It is worth noting that the critical price (PCC2H2) for products generating net revenue from the new process is 3.17 $/kg. This study is of great importance for the development of a low-carbon biomass-coupled calcium carbide-acetylene process.

Cascade utilization of full spectrum solar energy for achieving simultaneous hydrogen production and all-day thermoelectric conversion

Solar-driven photocatalytic water/seawater splitting holds great potential for green hydrogen production. However, the practical application is hindered by the relatively low conversion efficiency resulting from the inadequate utilization of solar spectrum with significant waste in the form of heat. Moreover, current equipment struggles to maintain all-day operation subjected to the lack of light during nighttime. Herein, a novel hybrid system integrating photothermal catalytic (PTC) reactor, thermoelectric generator (TEG), and phase change materials (PCM) was proposed and designed (named as PTC-TEG-PCM) to address these challenges and enable simultaneous overall seawater splitting and 24-hour power generation. The PTC system effectively maintains in an optimal temperature range to maximize photothermal-assisted photocatalytic hydrogen production. The TEG component recycles the low-grade waste heat for power generation, complementing the shortcoming of photocatalytic conversion and achieving cascade utilization of full-spectrum solar energy. Furthermore, exceptional thermal storage capability of PCM allow for the conversion of released heat into electricity during nighttime, contributing significantly to the overall power output and enabling PTC-TEG-PCM to operate for more than 12 h under the actual condition. Compared to traditional PTC system, the overall energy conversion efficiency of the PTC-TEG-PCM system can be increased by ∼500%, while maintaining the solar-to-hydrogen efficiency. The advancement of this novel system demonstrated that recycling waste heat from the PTC system and utilizing heat absorption/release capability of PCM for thermoelectric application are effective strategies to improve solar energy conversion. With flexible parameter designing, PTC-TEG-PCM can be applied in various scenarios, offering high efficiency, stability, and sustainability.

Multi-functional microparticles constructed by steerable phase separation process for synchronous uranium selective extraction and heat storage

Nuclear wastewater contains large amounts of uranium and waste heat, and hence synchronous uranium selective extraction and heat storage from nuclear wastewater are of prime importance. Herein, a series of distinctive dual-functional absorbents, such as P(St-VA)-1, P(St-VA)-2, P(St-VA)-3, were developed through photoinitiated interfacial polymerization via emulsion templates, using styrene and ethylene phosphate as co-monomers. The P(St-VA) has dual-functions, i.e., waste heat storage and uranium extraction. The uranium extraction feature is derived from the phosphoric acid group, while paraffin was encapsulated inside the P(St-VA). The concentration of sodium dodecyl sulfate (SDS) determines the rate and extent of phase separation between styrene and paraffin via tuning the size and stability of the emulsion, and hence the morphology and functionality of the P(St-VA). The P(St-VA) demonstrates excellent uranium adsorption performance with prominent selectivity. Furthermore, the P(St-VA) underwent multiple phase transitions between 25℃ and 70℃, displaying endothermic and exothermic behaviours and great heat storage potential. This study has provided an innovative path for the synchronous recycling of uranyl ions and waste heat from nuclear wastewater for practical applications.

Process development and multi-criteria optimization of a biomass gasification unit combined with a novel CCHP model using helium gas turbine, kalina cycles, and dual-loop organic flash cycle

The non-renewable nature of conventional power plants and the challenges associated with fuel costs and environmental impact highlight the need for innovative solutions. This research proposes a biomass-based combined system designed to produce multiple products, including electric power, coolant, and heat, addressing the drawbacks associated with conventional power generation. The proposed system integrates a biomass gasification unit with a helium gas turbine and a Kalina power unit. Additionally, a domestic water heater is incorporated into the Kalina cycle for heat generation, and the heat loss from the helium gas turbine is utilized in a modified Kalina cycle with a refrigeration unit. To further enhance efficiency, a dual-loop organic flash cycle is employed to recycle waste heat from the modified Kalina cycle. The analysis of this framework encompasses technical aspects, including energy, exergy, and economic considerations. The system is optimized using the multiple-objective particle swarm optimization method. Two scenarios are explored based on the desired product capacities: heat-electric power and coolant-electric power. In the first scenario, the system demonstrates an optimal electric power generation capacity of 6239.56 kW, along with favorable exergetic and economic outcomes. The optimal exergetic efficiency, net present value, and payback period are determined as 35.57 %, 15.07 M$, and 3.97 years, respectively. This research presents a comprehensive approach to biomass-based power generation, considering both technical and economic aspects, and provides valuable insights for sustainable energy solutions.

An urban energy recycling system that recycles the waste heat from industry for deicing on urban road in winter-taking Harbin as an example.

Northern cities in China have frequently suffered from ice and snow disasters. On the other hand, Harbin mainly relies on coal-fired plants for heating during the winter time. However, coal-fired plants produce a significant amount of air pollution through the production of numerous hazardous gases. This thesis proposed an urban energy recycling system that uses waste gas from heating facilities to recycle waste heat and reduce air pollution in northern cities during the winter. This research made a hypothesis that wintertime ice and snow on city streets could be melted by using waste heat of waste gases from heating industries. The methodology of this research can be divided into three parts: Firstly, the principle of theenergy recycling system is designed based on investigation. Secondly, a simulation experiment is used to analyze the system's difficulties. According to the experiment, when anicy road is far away from the heating industry, ice melting efficiency is low. Finally, this research proposed a method for system improvement based on the findings of the experiment. The system's environmental and social benefits will likely lead to its future application in northern Chinese cities even if there are many application-related difficulties, such as the high cost of construction.

Effects of bipolar plate flow channel configuration on thermal-electric performance of direct ammonia solid oxide fuel cell: Part Ⅱ- Promoting in-cell ammonia endothermic decomposition via a novel parallel S-type channel arrangement

This study explores impact of novel parallel S-type flow channels on ammonia decomposition and thermal-electric performance of direct ammonia solid oxide fuel cells (DA-SOFC). Four channel arrangements were numerically studied using single cell models: conventional unbent channels (UC–SOFC) and proposed single S-type channels (SSC–SOFC), double S-type channels (DSC-SOFC), triple S-type channels (TSC-SOFC). Cells with parallel S-type channel configurations outperformed unbent channel. Particularly, TSC-SOFC demonstrated the highest electrical performance, followed by DSC-SOFC, SSC-SOFC, and UC-SOFC, with power density improvements of 33.6%, 28.9%, and 28.9%, respectively, compared to UC-SOFC. Further results show that S-type channels exhibit self-heating effects, namely heat released from electrochemical reactions in the rear supplies ammonia decomposition in the front part of channel, enhancing H2 concentration and electrochemical reactions. Quantitatively, back-heat supplied to primary ammonia decomposition region increases by 33.3% in TSC-SOFC compared to UC-SOFC. Moreover, higher velocities in S-type channels enhance species diffusion towards rib underside, finally reducing concentration polarization and, improving power density. Besides of electrical performance, recycling waste heat from exhaust gases also improve the temperature uniformity cell, potentially benefiting the stability and lifetime of cell.

Innovative process integrating high temperature heat pump and direct air capture

Direct air capture (DAC) technology plays a crucial role in mitigating the effects of global warming by capturing carbon dioxide (CO2) directly from the atmosphere. A significant technical challenge for DAC is its high thermal energy consumption, which results in an unacceptable overall cost (600$tCO2–1). The combination of a high-temperature heat pump (HTHP) and DAC system offers a substantial reduction in thermal energy consumption, decreased reliance on renewable energy sources, and enhanced DAC system flexibility. This study presents three distinct thermal integration strategies that combine an HTHP with solid adsorbent-based DAC and verifies their effectiveness in reducing energy consumption and CO2 emissions compared to a traditional DAC system. Among them, the deeply integrated DAC-HTHP system (I-DAC) exploits low-grade adsorption heat and waste heat, providing direct heating and cooling energy to the DAC system via refrigerant condensation and evaporation processes. Simulation results indicate that the I-DAC system achieves an extremely low operating energy consumption of 2.77 GJtCO2–1, representing a 69.5% reduction than traditional DAC under the same conditions. Consequently, the I-DAC offers a cost-effective (32.0–46.2 $tCO2–1) negative emission solution. We also demonstrate that the I-DAC is promising for wide application in cities to recycle waste heat and remove CO2 from the air. The comprehensive implementation of the I-DAC in 105 cities could yield a net annual productivity of 980 MtCO2.

Estimation of industrial waste heat recovery potential in China: Based on energy consumption

Waste heat is a major source of recoverable losses in societal energy use, and the recycling of waste heat offers great potential for reducing greenhouse gas emissions. To estimate the potential of waste heat recycling in China, a combined gray relational analysis and bi-directional long- and short-term memory (GRA-BiLSTM) forecasting model is proposed to forecast China's energy consumption under the 1.5 °C scenario and 2 °C scenario, respectively. The results show that the proposed prediction model has high performance with a Mean Absolute Percentage Error value of only 4.21%. Energy consumption peaks at 7015 mtec in 2040 for the 1.5 °C scenario, and continues to increase to 7965 mtec in 2050 for the 2 °C scenario with a peak trend. Energy consumption peaks in 2040 under the 1.5 °C scenario. Energy consumption in the 2 °C scenario continues to increase and peak by 2050. In addition, the potential of waste heat recycling is estimated based on the prediction results and the organic Rankine cycle. The results show that there is a huge potential for waste heat recycling in China, with a minimum of 3.6 TWh. And the economic metrics, such as payback period(Pt), net present value(NPV), and Levelized Cost of Electricity (LCOE) were used to show the economic feasibility of the method. The results show that the payback period for different scenarios is less than 5 years, and the lowest NPV is $2597.8 million. The cost consumed for each kWh produced is much lower than the average feed-in tariff in China, and we believe that the method is economically feasible.

Thermal Effect on Algae, Biofilm and Their Composition Towards Membrane Distillation Unit: A Mini-review.

Membrane distillation (MD) has lower operating temperature and potential to recycle waste heat for desalination which catches much attention of the researchers in the recent years. However, the biofouling is still a challenging hurdle to be overcome for such applications. The microbial growth rate, secretion and biofilm formation are sensitive to heat. Membrane distillation is a thermally driven separation, so the increase of temperature in the seawater feed could influence the extent of biofouling on the unit parts. In this review, we present the effect of temperature on algal growth, the range of temperature the microbes, marine algae and planktons able to survive and the changes to those planktons once exceed the critical temperature. Thermal effect on the biofilm, its composition and properties are discussed as well, with association of the biofilm secreting microbes, but the study related to membrane distillation unit seems to be lacking and MD biofouling factors are not fully understood. Characterization of the algae, biofilm and EPS that govern biofouling are discussed. This information not only will help in designing future studies to fill up the knowledge gaps in biofouling of membrane distillation, but also to some extent, assist in pointing out possible fouling factors and predicting the degree of biofouling in the membrane distillation unit.

Waste polyvinyl chloride derived latent thermal energy storage composites for waste heat recovery via packed bed system

Latent thermal energy storage (TES) techniques utilizing phase change materials (PCMs) provide a promising way to mitigate the discrepancy between the intermittent nature of solar energy supply and consistent demand for human society. However, the development is hindered by the slow charging/discharging rates of the low thermal conductivity PCMs. Meanwhile, the high value-added utilization of waste plastic is receiving increasing attention as an environmentally sustainable strategy. In this regard, waste polyvinyl chloride (PVC) is recovered as SiC skeletons to obtain green phase change composites (PCCs) for waste heat recovery. After being infiltrated with paraffin wax (OP44E), proposed PCCs demonstrate a high retention ratio of latent heat up to 91.1% and a thermal conductivity of 2.4 W·m−1·K−1, which is benefitted from limited expansion and impurity remove process, respectively. With the elevated thermal conductivity and spectral absorptance, proposed PCCs exhibit superior solar-thermal energy storage rates. Furthermore, numerical simulation of the thermal charging/discharging performance and flow characteristics is carried out for the packed bed TES system. The results reveal a reduction in charging and discharging time by 21% and 41.1% for proposed PCCs, respectively. This work introduces a novel strategy for recycling waste heat via high-performance TES and repurposing waste plastics simultaneously.

Optimal Energy Integration and Off-Design Analysis of an Amine-Based Natural Gas Sweetening Unit

The present paper focuses on the efficiency enhancement of the energy-intensive natural gas (NG) sweetening process in the context of upstream natural gas production. A bi-level heat integration scheme is proposed including direct recycling of available high-temperature waste heat and harnessing the excess low-temperature waste heat in an optimized organic Rankine cycle (ORC) for power production. The energy performance of the whole model was studied under a range of possible reservoir conditions. A particle swarm optimization (PSO) algorithm was adopted to simultaneously optimize the parameters of the heat recovery network as well as the ORC cycle parameters. Finally, in order to account for the impact of perturbations of the heat source and sink, an off-design performance analysis was conducted using real-time data from an industrial plant. The proposed integration methodology was found to be effective across most of the reservoir conditions covered in this study. At optimal integration, a reduction of 40% up to 100% in heating requirements of the amine process was reported, as well as a net electricity production of 30% up to 190% of the electrical demand of the background process. The use of propane (R290) as a working fluid resulted in the highest energy output, whereas higher carbon number fluids allowed a better energy/working pressure trade-off. The off-design analysis allowed for the quantification of the impact of operational fluctuations of the background process on integration performance. Energy savings resulting from direct heat integration were found to range from 68% up to 103% of the expected design value, whereas the ORC net energy output respective to the use of R290, R600a, and R601a was found to range from 60% to 132%, 47% to 142%, and 52% to 135%.

Atomic‐Molecular Engineering Tailoring Graphene Microlaminates to Tune Multifunctional Antennas

AbstractAtomic‐molecular engineering is an effective way to accurately tailor the microstructures and components of materials at the micro‐nano scale, which can be applied to flexibly manipulate their electromagnetic (EM) response. Herein, graphene microlaminates with multi‐layer structure are fabricated by atomic cluster engineering and oxidative molecular layer deposition for the first time. The microlaminates enable a tunable EM loss (from 0.93 to 3.94 for imaginary permittivity and from 0.17 to 0.25 for imaginary permeability) by changing poly(3,4‐ethylenedioxythiophene) cycles, and the attenuation constant reaches 160. On this basis, multifunctional antennas are conceived, achieving frequency‐selective response that enables steady harvest of > 90% of EM energy from signal source, and tactfully recycling waste heat energy and mechanical energy. This study will furnish a new horizon for information transmission and artificial intelligence in the future.

Organic thermoelectric generators: working principles, materials, and fabrication techniques.

Organic thermoelectricity is a blooming field of research that employs organic (semi)conductors to recycle waste heat through its partial conversion to electrical power. Such a conversion occurs by means of organic thermoelectric generator (OTEG) devices. The recent process on the synthesis of novel materials and on the understanding of doping mechanisms to increase conductivity has tremendously narrowed the gap between laboratory research and their application in actual applications. This Feature Article intends to highlight the impressive progress in materials and fabrication techniques for OTEGs made in recent years.

Graphene thermionic energy converter combined with an absorption heat transformer for electricity generation and thermal upgrading

To improve energy utilization by recycling waste heat, a novel hybrid system composed of a graphene-based thermionic energy converter (GTEC) and an absorption heat transformer (AHT) is presented, where the GTEC anode waste heat is absorbed by the AHT for thermal upgrading. Considering major irreversible losses, the mathematical expressions for the equivalent power density, energy efficiency and exergy efficiency of the hybrid system are derived using thermionic emission and nonequilibrium thermodynamic theory. The hybrid system's general performance characteristics are also discussed in detail. Additionally, according to numerical calculation, the hybrid system's maximum energy efficiency (MEE), maximum power density (MPOD), and maximum exergy efficiency are 54.53 %, 7.73 W/cm2 and 68.16 % respectively, at the high-temperature heat source temperature of 1500 K. The hybrid system MPOD and MEE have risen by 17.97 % and 17.96 %, respectively, and maximum exergy efficiency has increased by 17.97 % as compared to a single GTEC. Furthermore, the impacts of the high-temperature heat source temperature, the Fermi energy level of graphene, cathode work function, ambient temperature, heat transfer coefficients of AHT, and the temperature of heated space on the hybrid system are investigated in depth. This study provides a new avenue for waste heat utilization in GTEC.

Energy, conventional and advanced exergy analysis for the organic Rankine cycle-vapor compression refrigeration combined system driven by low-grade waste heat

Global issues such as energy crisis and environmental pollution have driven the development of waste heat recovery technology. The organic Rankine cycle (ORC)-vapor compression refrigeration (VCR) combined system is a promising solution to achieve refrigeration requirements by recycling waste heat. How to determine the irreversible losses of the system and the improvement priority of the components is of great significance to enhance the system performance. Firstly, the energy and conventional exergy analysis of the ORC-VCR combined system is carried out to obtain thermodynamic performance of the system. Then, the advanced exergy analysis of the system is conducted and the exergy destruction distribution characteristics and improvement potential of the components are obtained. In addition, the interactions between the components are investigated in detail to achieve the improvement priority of the components. Finally, the improvement strategies for each component are proposed based on the influence of the components on the system. The results show that the coefficient of performance (COP) and exergy efficiency of the system are 0.44 and 14.97 %, respectively. The condenser contributes the most (44148 W) to the exergy destruction of the system. The largest endogenous (32935 W), avoidable (28530 W) and endogenous-avoidable (21577 W) exergy destruction also belong to the condenser. The condenser is determined as the most important component to promote system performance. The turbine and compressor have dominant influence on the system and the improvement depends on themselves. While the generator, condenser and evaporator only affect themselves and the improvement depends on all the components of the system. The results can provide theoretical guidance for further improving system performance.

Thermodynamic analysis and optimisation of a novel transcritical CO2 cycle

Transcritical and supercritical CO2 cycles are simple, low-cost, environmentally friendly, and compact solutions for harnessing a wide range of thermal energy sources such as waste heat, solar-thermal, geothermal, and nuclear reactors. In a supercritical CO2 cycle, compression begins near the critical-state (30.98 °C and 7.3773 MPa), whereas CO2 condensation occurs below the critical-state in a transcritical CO2 cycle, and the required sink temperatures are difficult to attain in the hot arid climates. The current study presents and optimises a novel transcritical CO2 power cycle that can be used in hot climates and offers very compact system which is vital for engine waste heat recovery. The proposed system achieves CO2 condensation by expanding pre-cooled CO2 from some intermediate pressure. It uses phase-wise CO2 separation in the separator and two recuperators to recycle waste heat from the hot CO2 stream leaving the turbine, reducing heat input into the heater and heat rejection by the pre-cooler. To achieve the best thermal efficiency, a differential evolution optimisation is used, and the phase-wise split of CO2 is tuned to provide excellent matching of temperature profiles while achieving the required pinch-point conditions in both the recuperators, resulting in a minimal low exergy destruction. The maximum thermal efficiency of the proposed cycle is 39.82%, while the optimal supercritical recuperative-Brayton cycle offers efficiency of 37.77%, under the same initial conditions. Under optimal current cycle conditions, thermodynamic processes avoid operating close to the CO2 critical point, necessitating less demanding and simpler turbomachinery designs.