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In order to reduce the environmental impact of conventional sludge treatment methods and to utilize the energy in sludge more effectively, a coupled system based on sewage sludge gasifier (SSG), solid oxide fuel cells (SOFC), supercritical CO2 cycle (S-CO2), and organic Rankine cycle (ORC) is proposed. The clean syngas obtained from sludge gasification is mixed with CH4 and then first utilized by the fuel cell. The exhaust gas from the fuel cell is fully combusted in the afterburning chamber and then enters the bottom cycle system consisting of S-CO2 & ORC to generate electricity. To understand the performance of the system, thermodynamic and economic analyses were conducted to examine the project's performance. The thermodynamics as well as the economics of the coupled system were analyzed to arrive at the following conclusions, the power production of the system is 37.34 MW; the exergy efficiency is 55.62%, and the net electrical efficiency is 61.48%. The main exergy destruction is the gasifier and SOFC, accounting for 62.45% of the total exergy destruction. It takes only 6.13 years to repay the construction investment in the novel system, and the project obtains a NPV of 17 723 820 USD during 20 years lifetime. The above findings indicate that the new coupled system has a better performance in terms of energy utilization and economy. [ABSTRACT FROM AUTHOR]

In this research, two different structures of the combined system of supercritical Brayton cycle of carbon dioxide with regenerator along with organic Rankine cycle and also the combined system of supercritical Brayton cycle recondensation with organic Rankine cycle with heliostat collector from the point of view of energy and economic-exergy simulated and compared. R123 fluid has been used in organic cycle due to its suitable thermophysical and environmental properties. The results indicate that with the change of the influencing parameters such as the compressor pressure ratio and the turbine inlet temperature, the work output of the system with the regenerator has been higher in all the examined efficiencies, but the exergy efficiency of the recompression system is higher in the ratio of low pressures in the compressor. Also, despite the higher overall cost rate of the system with the regenerator, this system creates a lower electricity production cost. Other simulation results indicate that the highest amount of exergy destruction occurs in the solar collector that is about 9726 kW. And the solar collector, having the highest cost rate, should be examined more than other components from an exergy-economic point of view. Finally, a parametric analysis has been done the effects of the change in compressor pressure ratio with 3485$/h, turbine inlet temperature, and low pressure, on the performance of the system, from the perspective of energy and exergy-economics. [ABSTRACT FROM AUTHOR]

A partial cooling supercritical carbon dioxide cycle is used in this study for the application of a solar power tower. Additionally, the organic Rankine cycle (ORC) is considered as a bottoming cycle in the process of recovering wasted heat. Moreover, fluids with zero ozone depletion potential and low global warming potential are considered as operating fluids for bottoming ORC. Exergy, energy and exergoenvironmental analyses were performed in order to evaluate the usefulness of the proposed system to generate electrical power and driven by solar energy. The effect of various independent parameters on system performance is investigated. It is concluded that as direct normal irradiation (DNI) changes from 0.4 to 0.95 kW m−2, the combined cycle's thermal efficiency, exergy efficiency, and power output increase from 35.16% to 55.43%, 37.73% to 59.42%, and 188 kW to 298.5 kW, respectively for R1224yd(Z) fluid. However, exergoenvironmental impact index falls by 58.79% as DNI rises, while the exergetic stability factor rises by 57.79%. The system's optimized thermal efficiency is found to be 53.45%. Furthermore, the performance of the combined system can be improved by decreasing the incidence angle of the sun while simultaneously increasing the concentration ratio. The fluid R1224yd(Z) is recommended as the best-performing fluid as compared to the other fluids due to its superior thermal performance. [ABSTRACT FROM AUTHOR]

Based on a constructal theory, the structure design of a printed circuit recuperator with a semicircular heat transfer channel for supercritical CO2 cycle is carried out. First, a complex function composed of weighted sum of the reciprocal of total heat transfer rate and total pumping power consumption is regarded as an optimization objective, and total volumes of the recuperator and heat transfer channel are regarded as constraints. The optimal heat transfer channel radius and minimum complex function of the recuperator are obtained. It turns out that heat transfer rate, pumping power consumption, and complex function under the optimal construct of recuperator are reduced by 15.10%, 82.44%, and 32.33%, respectively. There exists the optimal single plate channel number which results in the double minimum complex function. Second, for the purpose of minimizing the reciprocal of heat transfer rate and pumping power consumption, NSGA-II algorithm is used to achieve multi-objective optimization, and the minimum deviation index derived by the decision-making methods is 0.076, which can be taken as multi-objective optimal design scheme for printed circuit recuperator with semicircular heat transfer channels. The findings presented here can serve as theoretical recommendations for the structure design of printed circuit recuperator. [ABSTRACT FROM AUTHOR]

Using the efficient, space-saving, and flexible supercritical carbon dioxide (sCO2) Brayton cycle is a promising approach for improving the performance of nuclear-powered ships. The purpose of this paper is to design and compare sCO2 cycle power systems suitable for nuclear-powered ships. Considering the characteristics of nuclear-powered ships, this paper uses different indicators to comprehensively evaluate the efficiency, cost, volume, and partial load performance of several nuclear-powered sCO2 cycles. Four load-following strategies are also designed and compared. The results show that the partial cooling cycle is most suitable for nuclear-powered ships because it offers both high thermal efficiency and low volume and cost, and can maintain relatively high thermal efficiency at partial loads. Additionally, the new load-following strategy that adjusts the turbine speed can keep the compressor away from the surge line, making the cycle more flexible and efficient compared to traditional inventory and turbine bypass strategies. [ABSTRACT FROM AUTHOR]

In this study, a new cogeneration system is presented that can make optimal use of the waste heat from the sCO2 power cycle using a double-effect parallel absorption refrigeration cycle (DEARC), generating electricity and refrigeration simultaneously. A comparative study between the proposed (sCO2/DEARC) system and the stand-alone sCO2 power system is conducted to show its advantages and potential. The performances of the sCO2 and sCO2/DEARC systems are evaluated from the energetic and exergetic points of view using an in-house developed thermodynamic simulation platform via Engineering Equation Solver (EES) software. Variables such as pressure ratio, turbine inlet temperature, and evaporator temperature are also used for parametric analysis. The results indicate that the proposed system can generate of 132.72 MW cooling capacity. Also, the results show that the proposed sCO2/DEARC system can achieve a 55.8% and 5.2% improvement in thermal efficiency and exergy efficiency, respectively, with a negligible decrease in net power output (Wnet) compared to the stand-alone sCO2 power plant.

In this paper, a novel polygeneration system involving plasma gasifier, pyrolysis reactor, gas turbine (GT), supercritical CO2 (S-CO2) cycle, and organic Rankine cycle (ORC) has been developed. In the proposed scheme, the syngas is obtained by the gasification and the pyrolysis is first burned and drives the gas turbine for power generation, and then the resulting hot exhaust gas is applied to heat the working fluid for the supercritical CO2 cycle and the working fluid for the bottom organic Rankine cycle. In addition to the electrical output, the pyrolysis subsystem also produces pyrolysis oil and char. Accordingly, energy recovery is achieved while treating waste in a non-hazardous manner. The performance of the new scheme was examined by numerous methods, containing energy analysis, exergy analysis, and economic analysis. It is found that the net total energy output of the polygeneration system could attain 19.89 MW with a net total energy efficiency of 52.77%, and the total exergy efficiency of 50.14%. Besides, the dynamic payback period for the restoration of the proposed project is only 3.31 years, and the relative net present value of 77 552 640 USD can be achieved during its 20-year lifetime. [ABSTRACT FROM AUTHOR]

The printed circuit heat exchanger (PCHE) plays a vital role in the supercritical CO2 cooling system for hypersonic aircraft, which significantly affects the efficiency and stability of the cooling system. In this study, a novel structure is proposed to improve the overall performance of airfoil fin PCHE. The RP-3 aviation kerosene and SCO2 are used as working fluids to study the thermal-hydraulic performance and the enhancement mechanism. The results indicate that the overall performance of the PCHE can be improved by slotting the airfoil fin. With the increase in groove thickness, the thermal performance of the new airfoil fin PCHE first improves and then worsens, while the hydraulic performance of the PCHE first worsens and then improves. Compared with the original airfoil fin, the fin with a groove thickness of 0.6 mm reduces the pressure drop by up to 15% without affecting the thermal performance, while the fin with a groove thickness of 0.1 mm increases the heat transfer by 4%-5%. In addition, the optimal mass-flow ratio of SCO2 to kerosene is obtained by thermal resistance matching under different working conditions, which is helpful for the design and optimization of airfoil fin PCHE based on the SCO2 cycle cooling system for scramjets. [ABSTRACT FROM AUTHOR]

Low-temperature seawater is far away from CO 2 critical temperature, which has significant impacts on the performance of CO 2 closed cycle in the marine environment. The temperature adaptability of CO 2 closed cycle to the marine environment and its performance remain open issues. In this paper, we compare performance advantages of transcritical/supercritical CO 2 cycle based on thermodynamic and dynamic models. Compared with supercritical CO 2 Brayton cycle, transcritical gas-phase CO 2 Brayton cycle exhibits higher thermal efficiency and specific power at low cycle maximum pressure, and its reduced heat load and thermal inertia of regenerator facilitate cycle rapid response. However, transcritical liquid-phase CO 2 Brayton cycle and transcritical CO 2 Rankine cycle demonstrate higher thermal efficiency and specific power at high cycle maximum pressure. Lower compressor inlet temperature causes CO 2 pseudo-critical point to migrate into regenerator, and the intersection point of c p curves of CO 2 on both sides is located within regenerator. This can lead to pinch point and non-physical design within regenerator that inhibits cycle response. It can be avoided by adjusting cycle matching parameters so that the temperature corresponding to intersection point is lower than regenerator hot side outlet temperature. This study provides insights into performance advantages of transcritical CO 2 cycles in marine environments. [Display omitted] • Compare the performance of trans/supercritical CO 2 cycles in marine environments. • Performance analysis based on the cycle thermodynamic and dynamic simulation model. • Transcritical CO 2 cycle performance is more advantageous in marine environments. • Migration of pseudo-critical point to regenerator can inhibit the cycle response. • Avoid pseudo-critical point migration by adjusting cycle matching parameters. [ABSTRACT FROM AUTHOR]

Supercritical CO2 cycle can be used in the low temperature scenario to reduce the end temperature of the cycle and increase the cycle pressure ratio, which can well match with the coal-fired boiler to form a high-efficiency coal-fired power plant. Considering the climate and coal mine distribution, the coal mine bases in northern China, such as eastern Inner Mongolia and northern Xinjiang, have low atmospheric temperature conditions for more than four months in winter and spring, which is good for the constrution of high-efficiency supercritical CO2 coal-fired power plants. For the end temperature condition of 3-15 ℃, the thermodynamic calculation of supercritical CO2 cycle was carried out, and the economic and social benefits of the unit were analyzed. The results show that the supercritical CO2 cycle generator with 620 ℃/30 MPa initial parameters can obtain more than 48% of the net plant power generation efficiency in the low temperature scenario below 9 ℃, which is expected to surpass the efficiency of double-reheat ultra supercritical steam turbine unit. Supercritical CO2 cycle coal-fired power plants can supplement the power generation gap of renewable energy generation in winter and spring, and realize the efficient utilization of coal resources in the north through “North to South Power Transmission”.

As a part of the change towards a higher usage of renewable energy sources, which naturally deliver the energy intermittently, the need for energy storage systems is increasing. For the compensation of the disturbance in power production due to inter-day to seasonal weather changes, a long-term energy storage is required. In the spectrum of storage systems, one out of a few geographically independent possibilities is the use of heat to store electricity, so-called Carnot-batteries. This paper presents a Pumped Thermal Energy Storage (PTES) system based on a recuperated and recompressed supercritical CO2 Brayton cycle. It is analysed if this configuration of a Brayton cycle, which is most advantageous for supercritical CO2 Brayton cycles, can be favourably integrated into a Carnot-battery and if a similar high efficiency can be achieved, despite the constraints caused by the integration. The modelled PTES operates at a pressure ratio of 3 with a low nominal pressure of 8 MPa, in a temperature range between 16 °C and 513 °C. The modelled system provides a round-trip efficiency of 38.9 % and was designed for a maximum of 3.5 MW electric power output. The research shows that an acceptable round-trip efficiency can be achieved with a recuperated and recompressed Brayton Cycle employing supercritical CO2 as the working fluid. However, a higher efficiency would be expected to justify the complexity of the configuration.

Summary: When the supercritical CO2 power cycle is employed in confined spaces, such as nuclear‐powered ships and spacecraft, its size should be given priority. To estimate the component size, the one‐dimensional heat exchanger model developed in this study is used in a recompression supercritical CO2 cycle integrated on a small‐scale lead‐cooled fast reactor. A parameter analysis was performed to study the influence of several key parameters on the levelized cost of electricity, thermal efficiency, and system size. Moreover, four types of multi‐objective optimizations were conducted to provide optimization schemes for different scenarios. Results indicated that the increased turbine inlet temperature improved the thermoeconomic but augmented the system volume. The size of the low‐temperature recuperator was observably enlarged near the optimal flow split ratio, thereby increasing the system volume. Pareto optimal solution of bi‐objective optimization based on the levelized cost of electricity and system size reached the lowest system volume of 3.71 m3. Additionally, the best trade‐off result of three‐objective optimization was a thermal efficiency of 42.14%, a levelized cost of electricity of 56.30 $∙MWh−1, and a system volume of 4.43 m3. Meanwhile, maximal and minimal pressure drops of CO2 appeared in the cooler and intermediate heat exchanger, respectively. [ABSTRACT FROM AUTHOR]

This paper presents a cogeneration supercritical CO2 recompression Brayton cycle (SCRBC) integrated with an ejector refrigeration cycle (ERC). The system uses the waste heat of SCRBC to drive ERC to produce both electricity and cooling effect. The generator of ERC cools the hot CO2 before entering the compressor and simultaneously heats the ERC refrigerant. Ammonia is selected as a working refrigerant in the ERC. A comprehensive thermodynamic and exergoeconomic study examines a base case of the SCRBC/ERC plant. A sensitivity study is conducted to identify the substantial parameters needed for multi-objective optimization (MOO), which balances cost-saving and energy efficiency. Because the proposed plant produces two useful outputs, electricity and cooling effect, three MOO cases are investigated to enhance the plant performance. Case (1) maximizes the energy utilization factor and minimizes the total product unit cost. Case (2) provides a compromise between the cost of exergy destruction per unit product exergy and the plant investment cost per product exergy unit. Finally, case (3) focuses on finding the best trade-off between the proposed plant's electricity cost and second-law efficiency. The optimization study indicates that case (3) provides the lowest cost of products at the maximum energy and exergy efficiencies. According to it, 13.45 MW for electric power and 4.47 MW for cooling effect are delivered at an evaporator temperature of 5 °C, which is more suitable for cooling applications. [ABSTRACT FROM AUTHOR]

The supercritical carbon dioxide (sCO 2) Brayton cycle demonstrates special advantages for the high temperature gas-cooled reactor (HTGR) delivered into commercial operation recently in China, with its high efficiency, compactness, flexibility, and safety compared to the conventional steam Rankine cycle. However, the large temperature rise of 500 °C for the HTGR brings new challenges for the design of sCO 2 cycle. Here, we present the first study on the thermodynamic, economic, and environmental performance of the HTGR-sCO 2 system using the energy, exergy, economic, and environmental (4E) evaluation method. The cascaded sCO 2 cycle made up of two independent sCO 2 cycles is proposed, which are arranged in series on the cold side of reactor heat exchanger. We show that the cascaded sCO 2 cycle can utilize the heat absorption from HTGR effectively by optimizing the cycle configurations of top and bottom sub-cycles. The improved cascaded sCO 2 cycle minimizes the exergy loss, and increases the thermal efficiency to 43.2% when compared to the steam Rankine cycle of HTGR demonstration power plant and the single recompression cycle. By balancing the fixed-capital investment cost with the net power, the levelized cost of electricity can be reduced to 0.0283$/kWh. The life-cycle GHG emission intensity of HTGR-sCO 2 systems is about 6.5gCO 2,eq /kWh, which is much smaller than that of coal-fired power plants, suggesting a great potential for decarbonization of the HTGR-sCO 2 system. Our study may find implications for the advancement of the sCO 2 Brayton cycle in next-generation nuclear power plant. • Cascaded supercritical CO 2 cycles are investigated for high temperature gas-cooled reactor. • System performances are assessed by energy, exergy, economic, and environmental analyses. • Four cycle configurations are compared for improving thermodynamic performance. • Greenhouse gas emission is little affected by supercritical CO 2 cycles. • Turbomachinery parameters are significant for thermo-economic performance. [ABSTRACT FROM AUTHOR]

• A new arrangement of the reheating Allam cycle is proposed and simulated. • A comparative thermodynamic analysis is carried out on the proposed cycle. • The proposed cycle generates more power compared to other oxy-combustion cycles. • The net specific work of the optimized reheating Allam cycle is evaluated at up to 596.3 kJ/kg. • The optimum values of η th and η ex were obtained at 52.37 % and 46.70 %, respectively. This study presents a new arrangement of the reheating Allam cycle and investigates the efficacies of key parameters on the net specific work and thermal and exergy efficiencies of the proposed cycle. The performance of the optimized reheating Allam cycle is compared to several oxy-combustion cycles, and the results show that the inlet temperature of the low-pressure turbine, followed by the inlet temperature of the high-pressure turbine, has a remarkable efficacy on the thermodynamic performance of the reheating Allam cycle. In contrast, the minimum temperature of the proposed system has the lowest impact on its performance. The study identifies that the low-pressure combustion chamber accounts for the biggest share of the exergy destruction of the proposed reheating Allam cycle, representing 20.68 % of the overall input exergy. The net specific work of the optimized reheating Allam cycle is evaluated at up to 596.3 kJ/kg, with thermal and exergy efficiencies obtained at 52.37 % and 46.70 %, respectively. These values indicate significant performance improvements compared to other oxy-combustion cycles. This study supplies valuable perceptions into the design of the reheating Allam cycle and suggests that this configuration has the potential to be a promising alternative to other cycles in terms of its high efficiency and low environmental impact. [ABSTRACT FROM AUTHOR]

To clarify the importance degree and assess the effect of key parameters on comprehensive performance during operational adjustment, the artificial neural network (ANN) method is employed to quantitatively analyze the supercritical CO 2 (sCO 2) cycle performance for the advantage of accurate prediction and regression capabilities. The effects of seven operating parameters on the performance of the simple sCO 2 cycle, recompression sCO 2 cycle, and partial cooling sCO 2 cycle are discussed. The test results obtained through the ANN method depict that the key parameters are turbine inlet temperature (T TIT) and pressure ratio (P r) according to importance degree ranking. The maximum relative errors observed in the quantitative analysis of thermal efficiency and input heat are 2.48% and 3.47%, respectively. Additionally, the performance comparison of the quantitative analysis shows that the R2 values of thermal efficiency, output work, and input heat in this research are 0.057025, 0.0001381, and 0.019063 higher than those in the MATLAB software. Furthermore, the recommended operating parameters for T TIT and P r are 500/900/500 °C and 2.266/3.378/2.276 in the three sCO 2 cycles to achieve multi-objective optimization. The corresponding values for thermal efficiency, output work, and input heat are 44.91%/57.7%/44.05%, 104.8761/278.3495/109.5893 kJ/kg, and 190.3585/198.9562/198.8478 kJ/kg, respectively. This research can contribute to expanding future investigations on adjusting experimental parameters to enhance the performance of sCO 2 cycles. [Display omitted] • The ANN method is employed to quantitatively analyze the sCO 2 cycle performance. • The key parameters for sCO 2 cycles are turbine inlet temperature and pressure ratio. • The R2 values of η th , w tur , and q in are larger than 0.986 in the simple sCO 2 cycle. • The recommended values for T TIT and P r are 500/900/500 °C and 2.266/3.378/2.276. [ABSTRACT FROM AUTHOR]

Printed circuit heat exchangers (PCHEs) are considered as the most promising heat exchangers for use of the supercritical carbon dioxide (S-CO2) Brayton cycle. As crucial components operating at high pressure and thermal load at the same time, PCHE structural integrity evaluations are essential. In this study, to assess the structural strength of PCHEs serving as recuperators and precoolers in the S-CO2 Brayton cycle as a waste heat recovery system for marine engines, the finite element method (FEM) is used and compared with a currently used method from ASME codes. The effects of temperature and pressure on the hot and cold sides are studied in terms of the temperature and pressure differences between the two sides and the main factors affecting its strength discussed. Then, detailed stress intensities of a PCHE under design conditions are investigated, and the results indicate that the highest stress appears at the middle of the semicircular arc of the channel, except for a concentration near the channel tip regions. Stresses of the PCHE are mainly caused by both pressure and temperature differences, with the minimum effect from temperature. The synthesis of the temperature and pressure fields exhibits a complicated action on the total stress under the design conditions. FEM was a more comprehensive means for structural assessment than the method from ASME codes. Further structural optimization of PCHE is conducted to ensure a maximum life span. This research work can provide theoretical guidance for structural integrity assessment of PCHE for the S-CO2 Brayton cycle. [ABSTRACT FROM AUTHOR]

Waste-to-energy is considered as an effective way to simultaneously digest the municipal waste and generate useful power. Steam Rankine cycle is conventionally adopted for solid-waste incineration energy harvesting. To further improve the energy conversion efficiency, cascade systems consisting of a supercritical CO2 cycle and an organic Rankine cycle were proposed, where both the subcritical and transcritical organic Rankine cycle systems using R1233zd(E) as the working fluid were considered. Thermodynamic and the environmental analysis were evaluated comprehensively, with a follow-up comparison with the state-of-the-art technologies. The results show that compared with the original waste-to-energy plant, the turbine output (2.55 × 107 W) and waste-to-energy efficiency (42.61%) of the supercritical CO2 cycle/subcritical organic Rankine cycle power plant are increased by 9.50 × 106 W and 59.41%, respectively. If changing to the supercritical CO2 cycle/transcritical organic Rankine cycle system, the improvement will be greater, i.e., 10.19 × 106 W and 63.71% respectively. The comparison with the state-of-the-art power plants also shows the new waste-to-energy plant has higher efficiency and better environmental performance. The ecological efficiency and sustainability index of supercritical CO2 cycle/subcritical organic Rankine cycle system power plant are 88.82% and 1.54, while 89.14% and 1.57 with the supercritical CO2 cycle/transcritical organic Rankine cycle system. The proposed cascade system demonstrated its potential in performance improvement in the field of waste-to-energy incineration. The study provides insights into the next-generation power plants for solid-waste disposal. [ABSTRACT FROM AUTHOR]

This study presents an innovative multigeneration for power, cooling load, distilled water, and hydrogen production from solar energy. The proposed system is comprised of a supercritical carbon dioxide (sCO2) ejector refrigeration cycle, a solar still desalination unit (SSDU), and a solid oxide steam electrolyzer (SOSE), integrated with parabolic dish collectors (PDCs) field. Exergoeconomic, carbon footprint (CF), and water footprint (WF) analyses are performed to assess the comprehensive performance of the system using seven inorganic and metal high-temperature PCMs, namely MgCl2, NaCl, LiF-MgF2, NaF-CaF2-MgF2, Zn-Cu-Mg, Cu-Si-Mg, and Cu-Si. It is found that Cu-Si delivers superior thermodynamic performance enhancement, and NaF-CaF2-MgF2 leads to the lowest economic, carbon, and water footprint performances among the desired PCMs. Moreover, multi-objective antlion optimization (MOALO) is conducted to ascertain and compare the maximum exergy efficiency and the minimum product cost, CO2 emission, and water consumption rates of Cu-Si and NaF-CaF2-MgF2. Under optimal conditions, Cu-Si gives an exergy efficiency of 31.27% with hydrogen, net power, cooling capacity, and distilled water production of 44.56 kg/h, 1508 kW, 74.03 kW, and 15.48 kg/h, respectively, and NaF-CaF2-MgF2 yields the lowest cost, CO2 emission, and water consumption rates of 73.55 $/h, 86.338 CO2e/h, and 180.73 kg H2O/h, respectively indicating 11.01%, 5.20% and 7.88% improvements with an 8.98% decrement in exergy efficiency compared with Cu-Si. [ABSTRACT FROM AUTHOR]

This study presents an innovative multigeneration for power, cooling load, distilled water, and hydrogen production from solar energy. The proposed system is comprised of a supercritical carbon dioxide (sCO 2) ejector refrigeration cycle, a solar still desalination unit (SSDU), and a solid oxide steam electrolyzer (SOSE), integrated with parabolic dish collectors (PDCs) field. Exergoeconomic, carbon footprint (CF), and water footprint (WF) analyses are performed to assess the comprehensive performance of the system using seven inorganic and metal high-temperature PCMs, namely MgCl 2 , NaCl, LiF-MgF 2 , NaF-CaF 2 -MgF 2 , Zn-Cu-Mg, Cu-Si-Mg, and Cu-Si. It is found that Cu-Si delivers superior thermodynamic performance enhancement, and NaF-CaF 2 -MgF 2 leads to the lowest economic, carbon, and water footprint performances among the desired PCMs. Moreover, multi-objective antlion optimization (MOALO) is conducted to ascertain and compare the maximum exergy efficiency and the minimum product cost, CO 2 emission, and water consumption rates of Cu-Si and NaF-CaF 2 -MgF 2. Under optimal conditions, Cu-Si gives an exergy efficiency of 31.27% with hydrogen, net power, cooling capacity, and distilled water production of 44.56 kg/h, 1508 kW, 74.03 kW, and 15.48 kg/h, respectively, and NaF-CaF 2 -MgF 2 yields the lowest cost, CO 2 emission, and water consumption rates of 73.55 $/h, 86.338 CO 2 e/h, and 180.73 kg H 2 O/h, respectively indicating 11.01%, 5.20% and 7.88% improvements with an 8.98% decrement in exergy efficiency compared with Cu-Si. [ABSTRACT FROM AUTHOR]

Solar thermal power plants for electricity production include, at least, two main systems: the solar field and the power block. Regarding this last one, the particular thermodynamic cycle layout and the working fluid employed, have a decisive influence in the plant performance. In turn, this selection depends on the solar technology employed. Currently, the steam Rankine cycle is the most widespread and commercially available option, usually coupled to a parabolic trough solar field. However, other configurations have been implemented in solar thermal plants worldwide. Most of them are based on other solar technologies also coupled to a steam Rankine cycle, although integrated solar combined cycles have a significant level of implementation. In the first place, power block configurations based on conventional thermodynamic cycles—Rankine, Brayton, and combined Brayton–Rankine—are described. The achievements and challenges of each proposal are highlighted, for example, the benefits involved in hybrid solar source/fossil fuel plants. In the second place, proposals of advanced power block configurations are analyzed, standing out: supercritical CO2 Brayton cycles, advanced organic Rankine cycles, and innovative integrated solar combined cycles. Each of these proposals shows some advantages compared to the conventional layouts in certain power or source temperature ranges and hence they could be considered attractive options in the medium term. At last, a brief review of proposals of solar thermal integration with other renewable heat sources is also included. This article is categorized under:Concentrating Solar Power > Systems and InfrastructureEnergy Efficiency > Systems and InfrastructureEnergy Research & Innovation > Systems and Infrastructure [ABSTRACT FROM AUTHOR]

Supercritical CO2 (sCO2) power cycles play an important role in energy production as they are more efficient and more compact than conventional energy production systems. Therefore, they are widely used in different systems such as nuclear systems, renewable energy systems, heat recovery systems, fossil power plants, submarines, and some commercial and navy ships that produce a wide range of power operating in different temperature ranges. It has become very popular especially in recent years due to its widespread use and technical capabilities. This study analyses the effects of some design parameters (pressure ratio and temperature ratio) on the performance criteria (net work, thermal efficiency, back work ratio, and total entropy generation) and draws some optimum working conditions by means of the purpose of using. Results show that to obtain an optimum system according to maximum thermal efficiency or maximum net work the design range for the compression ratio for temperature ratio (a) 2, is between 5.224 and 6.449, for a=2.75, 8.408 and 12.57, and for a=3.5, the design range is between 11.35 and 16. [ABSTRACT FROM AUTHOR]

• The atmosphere CLC is integrated with the combined sCO 2 -ORC for power generation. • The energy efficiency can reach 51.79% in the natural gas fired system. • The detailed technology and exergy analysis is conducted, and improvement strategies in off-design conditions are put forward. • The whole system performance is not sensitive to the CLC operating temperature, reducing the requirements for oxygen carriers and CLC reactors. Chemical looping combustion (CLC) has attracted wide interests with high-efficiency and near-zero energy penalty carbon capture. However, the low-pressure operation of the most adopted circulating fluidized-bed reactors restricts the application of the downstream combined (gas-steam turbines) cycle, leading to an unsatisfying system efficiency. For this reason, this paper integrates atmosphere CLC with the combined recompression supercritical CO 2 Brayton cycle and organic Rankine cycle (CLC-sCO 2 -ORC) for power generation. The proposed system was modeled and simulated with Aspen Plus to manifest its tech-economic feasibility. The sensitive analysis suggests that the optimal sCO 2 turbine inlet temperature and pressure are 700 °C and 280 bar, respectively, and the recompression split fraction is 0.72. Under the optimal condition, the energy efficiency of 51.79% is superior to the conventional natural gas combined cycle (NGCC) (49.38%) and other CLC-based power generation technology (50.13%). Exergy analysis was also performed to put forward some improvement strategies. Importantly, CLC operating temperature imposes nearly no impact on exergy loss. Besides, the economic indicator, levelized cost of electricity (LCOE) is supposed to be profitable at 79.17 $/MWh, which is lower than that of other CLC-based power generation system (83.12 $/MWh). [Display omitted] [ABSTRACT FROM AUTHOR]

The modification of printed circuit heat exchangers through extended surface areas is a relatively underexplored topic, especially when considering their application in conjunction with precoolers in supercritical CO 2 cycles. This study evaluates the response of a precooler by incorporating various configurations of integral and interrupted ribs, with the primary objective of identifying an optimized ribs combination under different operating conditions. The results demonstrate that ribs enhance secondary swirl flows, contributing to an increase in heat transfer levels in the supercritical CO 2 flow. However, ribs do increase flow resistance, necessitating the careful selection of the optimal rib combination. The use of non-uniform patterns of interrupted ribs has been identified as the most feasible approach. By reducing the rib length and the distance between ribs at the upstream of supercritical CO 2 and water flows, the performance of the precooler is notably enhanced. No matter the operating condition, cases with shorter rib lengths or smaller rib-to-rib distances at the beginning of both fluid paths consistently yield the best performance. Implementing these configurations in the precooler, the comprehensive performance index can reach approximately 1.2. This study contributes to enhancing efficiency and improving the compactness of large-scale solar power plants utilizing the supercritical CO 2 cycle. • Non-uniform interrupted ribbed plates for printed circuit heat exchangers are designed. • Heat transfer and flow of supercritical CO 2 in the new-type plates are investigated. • The utilization of non-uniform interrupted ribs enhances thermal performance by 3.4–29.8 %. • Overall performance indexes of up to 1.28 for hot-side and 1.61 for cold-side are observed. • Effects of ribs are more pronounced under operating conditions far from the critical point. [ABSTRACT FROM AUTHOR]

Solar energy stands out as one of the most abundant and cost-effective resources for energy conversion systems, playing a pivotal role in addressing the world's growing energy demands and environmental concerns. This study focuses on a power generation system that integrates multiple technologies for efficient energy conversion, including a parabolic solar trough collector unit, a supercritical carbon dioxide Brayton cycle, and two dual-pressure organic Rankine cycles. The goal is to assess this system from various angles, including energy, exergy, exergoeconomic, and exergoenvironmental aspects. The base mode study results reveal an overall energy efficiency of 16.66 %, exergy efficiency of 17.88 %, a total net power generation of 17.32 MW, a payback period of 4.38 years, and a total exergoenvironmental impact rate of 126.75 Pt/h. Additionally, the study conducts a parametric investigation to analyze how the system performs under different conditions and how changes in design parameters affect its main outputs. Furthermore, the study utilizes a multi-objective particle swarm optimization algorithm and a decision-maker method to identify the most desirable condition for the system's performance. Three optimization scenarios are considered, and various specific costs for electricity are evaluated to determine the payback period and net present value. • Designing and scrutinizing a solar power system with high efficiency. • Inclusion of parabolic solar collector and supercritical CO 2 cycle. • Comprehensive evaluation, including energy, exergy, economics, and environmental. • Obtaining net power of 17.32 MW with a payback period of 4.38 years. • Optimal design of the system using multi-objective optimization. [ABSTRACT FROM AUTHOR]

[Introduction] The high exhaust temperature of gas turbine can increase the bottom cycle and generate electricity by using the waste heat of exhaust gas, so as to improve the total energy utilization rate of fuel. In view of its high thermal efficiency, simple system, compact structure, flexible operation and other potential advantages, supercritical CO2 cycle can be combined with gas turbine to form a new type of gas-supercritical CO2 combined cycle. [Method] In order to make full use of the exhaust heat of the gas turbine, a simple regenerative supercritical CO2 cycle was constructed on the basis of a simple regenerative supercritical CO2 cycle, and the thermal efficiency of the PG9351 (FA) gas turbine was calculated and analyzed. At the same time, by adding waste heat utilization device in the system, the residual heat could be used for heating, converting into cold energy or generating electricity. [Result] The results show that for the selected gas turbine, the maximum temperature of supercritical CO2 cycle can reach 600 C, the cycle power generation efficiency is about 32%, the heat recovery temperature is above 170 ℃, the heat recovery accounts for 9% of the exhaust heat of gas turbine, and the combined cycle power generation efficiency is about 54%. [Conclusion] The gas-supercritical CO2 combined cycle power generation system has high thermal efficiency and retains some high-grade waste heat, which can be further used in power plant operation.

[Introduction] Because of the low temperature parameter, the power generation efficiency of the small modular PWR nuclear power plant is less than 30%. [Method] In order to improve the efficiency of the nuclear energy utilization, the small modular reactor can be combined with the renewable energy and the advanced supercritical CO2 cycle was used as the thermal energy conversion device. Based on a supercritical CO2 cycle with a simple regenerative mode, adding one intercooling and one reheating, a new hybrid power generation system was integrated with a small reactor and a solar energy source and a biomass energy source, and the efficiency of the power generation was analyzed. [Result] The results show that the power generation efficiency is 34.13% and 41.22% for the system with the inlet temperature of the high pressure turbine at 390 ℃ and 550 ℃, respectively. In addition, the analysis of the safety of the system shows that the CO2 itself has the nuclear safety property, and the supercritical CO2 cycle can also be used as the passive waste heat discharge system of the reactor to ensure that the reactor continuously exhaust the decay heat under the severe accident condition. [Conclusion] Supercritical CO2 cycle power system integrated with small modular reactor and renewable energy source has good power generation efficiency and nuclear safety.

Summary: The paper proposes a novel combined heating and power (CHP) system integrated with solid oxide fuel cell (SOFC) and supercritical CO2 (SCO2) partial preheating cycle to improve the energy utilization rate by employing the SCO2 cycle to recover the waste heat from the SOFC. The SCO2 partial preheating cycle can not only improve the net output power but also preheat the air supplied to the SOFC for enhancing the system efficiency. Sensitivity analysis is implemented to study the influences of six key parameters (ie, fuel flow rate, excess air ratio, fuel utilization factor, CO2 turbine inlet temperature, CO2 compressor pressure ratio, and CO2 split ratio) on the proposed system in terms of thermodynamic behaviors. And then the optimal operating conditions for the different objectives are determined by parametric optimization. The results indicate that the optimal overall electrical efficiency and CHP efficiency of the proposed system are 72.84% and 83.83% respectively, while the exergy efficiency can achieve 70.84%. Furthermore, the best trade‐off result is obtained with the energy output of 434.71 kW and the exergy efficiency of 64.28%. Finally, the investigation demonstrates the fuel flow rate is the most sensitive parameter which should be determined with the comprehensive consideration of the efficiency and energy output, and the lower excess air ratio and higher CO2 turbine inlet temperature are preferred for power generation. [ABSTRACT FROM AUTHOR]

The reconstruction of ageing thermal power plants with the possibility of their increased efficiency, prolonged service and decreased environmental impact is an intensely debated and researched topic nowadays. Among various concepts, the replacement of the steam cycle by a supercritical CO2 cycle is proposed with the prospect of reaching higher efficiencies at the same working fluid inlet parameters as the ultra-supercritical steam cycles. A paper published previously by Rogalev et al. (2021) analyzed the variants of supercritical coal power plant reconstruction to a supercritical CO2 cycle and ranked them according to the cycle efficiency. This contribution comments on the scope and applied method in that paper aiming to provide additional input relevant to the decision-making process on thermal power plant reconstruction to such a cycle.

The turbomachinery used in the sCO2 power cycle requires a high stable rotor-bearing system because they are usually designed to operate in extremely high-pressure and temperature conditions. In this paper, we present a pump-drive turbine module applying hydrostatic bearing using liquid CO2 as the lubricant for a 250 kW supercritical CO2 power cycle. This design is quite favorable because stable operation is possible due to the high stiffness and damping of the hydrostatic bearing, and the oil purity system is not necessary when using liquid CO2 as the lubricant. The pump-drive turbine module was designed to operate at 21,000 rpm with the rated power of 143 kW. The high-pressure liquid CO2 was supplied to the bearing, and the orifice restrictor was used for the flow control device. We selected the orifice diameter providing the maximum bearing stiffness and also conducted a rotordynamic performance prediction based on the designed pump-drive turbine module. The predicted Campbell diagram indicates that a wide range of operation is possible because there is no critical speed below the rated speed. In addition, an operation test was conducted for the manufactured pump-drive turbine module in the supercritical CO2 cycle test loop. During the operation, the pressurized CO2 of the 70 bar was supplied to the bearing for the lubrication and the shaft vibration was monitored. The successful operation was possible up to the rated speed and the test results showed that shaft vibration is controlled at the level of 2 μm for the entire speed range. [ABSTRACT FROM AUTHOR]

The utilization of sensible waste heat such as flue gas and industrial surplus heat is essential for energy saving. Supercritical CO2 power generation cycle is a promising way to be used in this field. In this paper, a new supercritical CO2 Rankine cycle coupled with an absorption refrigeration cycle is proposed, which consists of a reheating supercritical CO2 cycle, a mixed-effect LiBr-H2O absorption refrigeration cycle and solar subsystem including evacuated-tube collector and a hot water storage tank. The system has four variants according to the presence or absence of solar subsystem and net cooling energy output. The thermodynamic model of the proposed system was established and its performance was evaluated. The proposed system is able to realize cascade utilization of flue gas waste heat and efficient conversion of solar energy. It has much higher thermodynamic efficiency than the reference system (i.e., the conventional supercritical CO2 Brayton cycle). Taking combined power and cooling system driven by flue gas waste heat and solar energy as an example, its thermal efficiency and exergy efficiency are 20.37% and 54.18% respectively, compared with the 14.74% and 35.96% of the reference system. Energy Utilization Diagrams (EUD) are implemented to investigate the irreversible losses and variation of the exergy destruction in the energy conversion process. Parametric analysis in two key parameters is conducted to provide guidance for the system optimal design. [ABSTRACT FROM AUTHOR]

Summary: In this article, the performance improvement of supercritical carbon dioxide (sCO2) Brayton cycles through heat recovery and advanced heat exchanger (HX) design is reviewed. The configuration of sCO2 cycles and the bottleneck of the design of an efficient sCO2 cycle is first evaluated. It was found that heat rejected in the precooler is a large waste that could potentially enhance the overall sCO2 system performance. Then integration of the absorption cycle, organic Rankine cycle, and thermal desalination plant to the sCO2 cycle to recover the waste thermal energy is reviewed and discussed. Results showed that these bottoming heat recovery cycles could substantially improve the overall sCO2 system efficiency. The combined system of sCO2/absorption chiller, sCO2/ORC increases the cycle efficiency to about 78% and 79%, respectively. Also, a combined system of sCO2/desalination produces about 200 000 m3/day with a cost of less than $1.0/m3. Based on the review, the evaluation criteria are proposed for decision‐makers. Another bottleneck of the design of the sCO2 system is the HXs (recuperators) used in the sCO2 cycle which are relatively large and negatively affect the cycle compactness and performance. Therefore, various types of recuperators proposed and designed for sCO2 cycles are reviewed and evaluated. This review highlights the need for further research to enhance heat recovery, reduce the cost of bottoming cycles, and improve the design of HXs. [ABSTRACT FROM AUTHOR]

Summary: In recent years, to overcome the challenges of nuclear power plants due to their large scale, numerous types of small modular reactors are being designed worldwide. Small modular reactors are required to have a capability to operate in environmentally challenging regions with long refueling time. Supercritical CO2 (S‐CO2)‐cooled direct‐cycle reactor is one of the candidates that can meet these requirements. In order to evaluate if the design achieves this goal, transport of generated radionuclides from the long‐term operation has to be evaluated in order to estimate the radioactivity accumulation in the system. However, existing radionuclide transport evaluation method does not reflect the characteristics of supercritical fluids properly. In this paper, the fission product plate‐out behavior of Korea Advanced Institute of Science and Technology Micro Modular Reactor (KAIST‐MMR), a 10‐MWe class S‐CO2‐cooled fast reactor with direct S‐CO2 power conversion system, is studied. The evaluation methodology was developed via integrating suitable models while considering the shape of the nuclear fuel, component geometries, characteristics of a working fluid in supercritical state, and the fast reactor design. As a result of the analysis, the degree of plate‐out of KAIST‐MMR is not expected to have serious radioactivity accumulation within the components. Most of the sorption occurred at the turbine and recuperator hot‐side inlet region. In particular, the dose rate of the turbine was quite low, because the size of the turbine is very small. Highlights: Plate‐out behavior of a 10‐MWe scale S‐CO2‐cooled direct‐cycle GFR was evaluated. Plate‐out evaluation method for S‐CO2 direct‐cycle reactor was developed. Most of the sorption occurred at the turbine and recuperator hot‐side inlet sides. Degree of plate‐out was not expected to have serious radiation risk. [ABSTRACT FROM AUTHOR]

The supercritical CO2 (s-CO2) power cycle has been taking into account as one of the most effective alternatives for energy conversion because of its higher efficiency and smaller compressor and turbine sizes for many years. A plenty number of parametric and experimental studies for the different type of s-CO2 cycles have been accomplished in the literature. In this paper, a performance analysis based on a power density criterion has been carried out for a simple s-CO2 Brayton power cycle. The parameters which are obtained from analyzes were compared with those of a power performance criterion that is shown that design parameters at maximum power density give a chance to smaller cycle components and more efficient s-CO2 Brayton power cycle. Due to loses in the cycle, the power and thermal efficiency will reduce by a certain amount, however, the maximum power density conditions will still give a better performance than at the maximum power output conditions. The analysis exemplified in this paper may provide a reference for the finding of optimal operating conditions and the design parameters for real s-CO2 Brayton power cycles. [ABSTRACT FROM AUTHOR]

In this paper, a novel combined heat and power (CHP) system is proposed in which the waste heat from a supercritical CO2 recompression Brayton cycle (sCO2) is recovered by a LiBr-H2O absorption heat pump (AHP). Thermodynamic and exergoeconomic models are established on the basis of the mass, energy, and cost balance equations. The proposed sCO2/LiBr-H2O AHP system is examined and compared with a stand-alone sCO2 system, a sCO2/DH system (sCO2/direct heating system), and a sCO2/ammonia-water AHP system from the viewpoints of energy, exergy, and exergoeconomics. Parametric studies are performed to reveal the influences of decision variables on the performances of these systems, and the particle swarm optimization (PSO) algorithm is utilized to optimize the system performances. Results show that the sCO2/LiBr-H2O AHP system can obtain an improvement of 13.39% in exergy efficiency and a reduction of 8.66% in total product unit cost compared with the stand-alone sCO2 system. In addition, the sCO2/LiBr-H2O AHP system performs better than sCO2/DH system and sCO2/ammonia-water AHP system do, indicating that the LiBr-H2O AHP is a preferable bottoming cycle for heat production. The detailed parametric analysis, optimization, and comparison results may provide some references in the design and operation of sCO2/AHP system to save energy consumption and provide considerable economic benefits. [ABSTRACT FROM AUTHOR]

• The coal-based Allam cycle with full water quench syngas cooling is designed. • Complete thermodynamic analysis and optimization are conducted. • The optimal cycle features a low turbine inlet temperature and pressure. • An improved cycle layout is proposed with a simplified heat integration. • The net efficiency of the improved cycle reaches 40.22% (HHV basis). The coal-based Allam cycle is an efficient oxy-fuel combustion semi-closed supercritical carbon dioxide (sCO 2) cycle coupled to coal gasification and stands out for its capability to achieve zero carbon emissions. The main goals of this study are to systematically optimize the cycle employing full water quench syngas cooling for maximum efficiency. Detailed analytical models based on energy and material balance are developed to assess the thermodynamic performance of the system. The influences of cycle variables are evaluated through sensitivity analyses, and the optimal parameters are determined using a combined black box and PSO-GA approach. Results show that the turbine inlet temperature is the main factor influencing the net cycle efficiency, while higher efficiency is achieved at a relatively low turbine inlet temperature with the increased recovery of syngas heat; the maximum cycle efficiency of the conventional cycle layout is equal to 40.04 %, featuring the turbine inlet temperature of 1031.7 °C and pressure of 268.9 bar. Furthermore, an improved cycle with a simplified heat integration process is proposed, featuring a higher net efficiency of 40.22 % and specific work of 252.7 kJ/kg, which demonstrates that the adoption of adiabatic compression in the air separation unit (ASU) is a non-essential measure for efficiency improvement. This study indicates that the availability and grade of syngas heat play a pivotal role in determining the optimal parameters. [ABSTRACT FROM AUTHOR]

• Systems of medium temperature fluegas energy utilization are compared and optimized. • Influence of reheat stages on power plant efficiency are calculated. • Cold end systems including intercooling and waste heat recovery are compared. • Efficiencies of complex and simple optimized systems achieve 49.32% and 48.52%. The integration of supercritical CO2 (SCO2) cycle instead of steam Rankine cycle may be a revolutionary technique to increase the efficiency of coal-fired power plants. To effectively extract exergy from the fluegas and convert exergy to power, the characteristics of hot end (heat reservoir) and cold end (heat sink) should be fully considered, and the system multi-parameters should be optimized. In this study, based on a benchmark coal-fired power plant integrated with a recompression SCO2 power cycle, quantitative efficiency enhancements of system improvements of the hot end and cold end for SCO2 power cycle are calculated and compared. The optimized efficiency of benchmark coal-fired plant integrated with recompression SCO2 power cycle is 45.43%. When the fluegas at the economizer outlet is effectively used, the power plant efficiency can be increased by 1.32%. With single and double reheats to decrease the heat transfer irreversibility of the hot end, the power plant efficiency can be increased by 1.77% and 2.24%, respectively. Cold end optimization with single intercooling and cold air preheating can increase the power plant efficiency by 0.32% and 0.33%, respectively. Finally, a simple structure system and a complex structure system are proposed. With optimal system parameters, the power plant efficiencies of the complex and simple systems are 49.32% and 48.52%, respectively. [ABSTRACT FROM AUTHOR]

The Allam Cycle is a semi-closed, oxy-fuel, supercritical carbon dioxide (sCO 2) Brayton power cycle fueled with natural gas or syngas derived from coal, biomass or other carbonaceous fuels, offering advantages over simple cycle and combined cycle arrangements. For the coal based Allam Cycle, a gasification system is required to convert coal to clean syngas for downstream power generation. These systems require heat input to dry as-delivered coal to certain specifications. Produced steam is typically used for this purpose, but since the Allam Cycle is based on use of sCO 2 , and not steam, it is preferable to utilize alternative methods for coal drying. An experimental study was carried out at Energy & Environmental Research Center (EERC) to determine the heat energy required for drying lignite coal down to moisture levels acceptable for the operation of different gasifiers (range of moisture levels inserted here), and to investigate the effect of the heat transfer medium (steam and/or N 2) and heat transfer type (direct or indirect) on the lignite drying performance. The results show that optimal operating temperature of coal drying is 90 °C. For direct heating system, the result shows a relatively linear trend of drying energy versus the coal's moisture content, and the drying data suggests that individual parameters of velocity, residence time, and bed temperature are of secondary importance compared to how they combine to determine energy transfer to the coal. When the results of the direct heating tests using different heat transfer medium were compared, they were in good agreement, in that they indicate an approximate heat of evaporation around 2791.2 kJ/kg moisture removed. The energy consumption of the indirect heating steam coil tests is about 4652–5815 kJ/kg moisture removed, which is much higher than direct heating test data since not all the steam can condense at the exit of the steam coil. All the test results are important for designing the lignite drying process for the Allam Cycle. In the coal based Allam Cycle power generation system, low grade energy at the temperature of 70–100 °C from the turbine exhaust stream is sufficient for the coal drying process. Nitrogen from air separation unit can be used via direct heating and coal fluidization medium. For an indirect heating coal dryer system, a closed loop high pressure water system can be designed to transfer low grade heat from turbine exhaust stream to the dryer to remove moisture from coal. [ABSTRACT FROM AUTHOR]

• Dynamic model development in Matlab/Simulink proposed. • Analysis of control strategy for the WHR system. • Dynamic performance evaluation under varying heat source condition. • Supercritical CO 2 power cycle is promising for WHR application. Large amount of waste heat is available for recovery in industrial processes worldwide. However, significant proportion (up to 50%) of this thermal energy is released directly to the environment. Application of waste heat to power (WHP) technologies can increase the energy efficiency and cut CO 2 emissions from these facilities. Steam Rankine cycle (SRC) and organic Rankine cycle (ORC) are commonly deployed for this purpose. The main drawback of SRC and ORC is the high irreversibility in the heat exchangers. In addition, ORC has limited temperature range and low efficiency while SRC has a large footprint. Supercritical CO 2 (sCO 2) power cycle is considered an attractive option, which provides better matching of waste heat temperature in the main heater (i.e. low irreversibility). It offers compact design, improved performance and it is applicable to a wide range of waste heat source temperature. The conditions of industrial waste heat sources are highly variable due to continuous fluctuations in the operation of the process. This is likely to significantly affect the dynamic performance and operation of the sCO 2 power cycle. In this work, dynamic model in Matlab/Simulink was developed to assess the dynamic performance and control of the sCO 2 power cycle for waste heat recovery from cement industry. The case of waste heat at 380 °C utilized to deliver 5 MWe of power was considered. Steady state simulation was performed to determine the design point values. Open loop simulation was performed to show the inherent dynamic response to step change in the temperature of the waste heat. The dynamic performance and control of the system under varying exhaust gas flow rate between 100% and 50% of the design value were studied. Similar study was done for varying exhaust gas temperature between 380 °C and 300 °C. The results showed that the thermal efficiency of proposed single recuperator recompression sCO 2 is about 33%. Stable operation of the system can achieved by using cooling water control and throttle valve to maintain constant precooler outlet condition. Dynamic simulation result showed that it is best to allow the turbine inlet temperature to vary according to the fluctuation in the waste heat source. These findings indicated that dynamic modelling and simulation of WHP system could contribute to understanding of the behaviour and control system development under fluctuating waste heat source conditions. [ABSTRACT FROM AUTHOR]

This study energetically, exergetically and economically analyses a hybrid electricity generation system. The proposed system is a combination of a biomass gasifier, a solid oxide fuel cell module, an indirectly heated air turbine and a supercritical carbon dioxide power cycle. Influences of major designing and operating plant parameters, viz. current density of the solid oxide fuel cell, pressure ratio of the air compressor, turbine inlet temperature of the CO2 gas turbine, on the performance of the proposed system have been examined. The proposed system exhibits the highest first law efficiency of 51% at the current density of 2000 A/m2 and cell temperature of 1123 K, air compressor pressure ratio of 4.4, CO2 gas turbine inlet pressure and temperature of 10.14 MPa and 423 K. At this aforesaid condition, the proposed system exhibits a second law efficiency of 45%. It is found that the highest amount (40.70%) of exergy destruction takes place at the biomass gasifier, followed by the solid oxide fuel cell (20.05%). The economic analysis predicts that the minimum achievable levelized unit cost of electricity is 0.095 $/kWh. [ABSTRACT FROM AUTHOR]