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For realizing efficient utilization of liquified natural gas cold energy and high‐temperature flue gas waste heat, herein, a combined cooling, heating, and power system using Peng–Robinson property package in Aspen HYSYS software, which includes a three‐stage parallel Rankine cycle (RC) in series with single‐stage RC and a supercritical CO2 (S‐CO2) Brayton cycle, is proposed. The system performance is evaluated using the first law of thermodynamics, second law of thermodynamics, specific energy costing method, and exergoenvironment analysis method. The influences of the pump 1 outlet pressure, turbine 3 inlet temperature, working fluid R23 mass flow rate, compressor 1 outlet pressure, CO2 liquefaction pressure, and ambient temperature on system performance are investigated. The nondominated sorting whale optimization algorithm and technique for order preference by similarity to ideal situation are applied to optimize the multiobjective system performance, and the payback periods of system before and after optimization are calculated. The analysis indicates that under the initial conditions, the thermal efficiency, exergy efficiency, total product unit cost, and sustainability index of the system are 41.68%, 48.50%, 112.293 $ GJ−1, and 1.75, respectively. After optimization, exergy efficiency increases by 2.4% and exergoeconomy decreases by 8.277 $ GJ−1. [ABSTRACT FROM AUTHOR]

Organic Rankine cycle (ORC) and supercritical CO 2 (sCO 2) Brayton cycle are two key and competition technology routes as the power cycle of Lead–Bismuth micro-reactor (LBMR). However, few studies focus on the comparison of thermodynamic and economic performance between ORCs and sCO 2 cycles in nuclear micro-reactor. The objectives in this study are to perform parameters analysis and techno-economic comparison in ORCs and sCO 2 cycles with various configurations as the power cycle of LBMR, so as to provide the technical support for the selection of power cycle and its operating conditions in different scenarios. Several high/low-temperature working fluids are screened for ORCs in view to achieve high net efficiency (η th) and low electricity production cost (EPC). Multi-objective optimization is performed to solve the trade-off between η th and EPC , and then to compare the comprehensive performance of various cycles from thermodynamic, compact and economic aspects. Results show that, the η th and EPC of ORCs are comparable or superior to that in sCO 2 cycles when the two cycles have similar structures (simple/regenerative). Among the ORCs, the cascade ORC with two-side regeneration using N -Dodecane/Pentane as working fluid pair has the best performance. In all cycles, recompression sCO 2 cycle performs best, but only when the heat source temperature is higher than 460 °C, the performance of the recompression sCO 2 cycle are overall better than the cascade ORC. • Techno-economic comparison of various power cycles for LBR are conducted. • Several high/low-temperature fluids are screened in different configurations of ORC. • N -Dodecane/Pentane is the best working fluid pair for the cascade ORC2. • The η net and EPC of ORCs are slight superior to sCO 2 cycles with similar structures. • The η net and EPC of recompression sCO 2 cycle are both better than ORC when t s > 460 °C. [ABSTRACT FROM AUTHOR]

CO 2 capture from coal-fired power plants (CFPP) with low cost is crucial for China to achieve carbon peaks in 2030. The manuscript proposes a novel combined cycle of supercritical CO 2 Brayton cycle (SCBC) and organic Rankine cycle (ORC) in CFPP with CO 2 capture. The novelty of the proposed scheme lies on its high-level thermal integration which can efficiently complete the conversion of heat to electricity, waste heat recovery, and CO 2 capture. Exergy analysis and levelized cost of electricity (LCOE) are employed to respectively evaluate the thermodynamic and economic performance. The simulation results show that the exergy efficiency of the combined cycle is 39.74% as considering CO 2 capture, resulting in a 3.41% of efficiency penalty. The introduction of ORC improves the exergy efficiency by 1.05%. The LCOE of the combined cycle is 79.03$/MWh, almost 19.3$/MWh (32.29%) more expensive than the base plant, and the costs of CO 2 captured and avoided are respectively 21.81$/tCO 2 and 26.25$/tCO 2. The results indicate that the proposed combined cycle has the potential to compete with other carbon capture technologies from the views of exergy efficiency and cost. Coal combustion in the S–CO 2 boiler and the calciner is responsible for the maximum internal exergy destructions, and increasing the cycle maximum temperature may reduce the exergy destruction. The largest cost contributor to LCOE is associated with capital expenditures (41.55%), and the cost reduction efforts should be aimed at capital expenditures. • The highly integrated combined cycle of SCBC and ORC is proposed for power generation with CO 2 capture. • The exergy efficiency penalty arising from CO 2 capture is 3.41% for the proposed scheme. • The introduction of ORC for heat recovery improves exergy efficiency by 1.05%. • The CO 2 capture cost of the proposed combined cycle is 21.81$/t. • The largest cost contributor to LCOE is associated with capital expenditures (41.55%). [ABSTRACT FROM AUTHOR]

• A novel waste heat recovery system is proposed based on WTE plant. • A comprehensive thermodynamic analysis of the system is conducted. • Based on NPV, the dynamic payback period of new WTE plant is studied. • Sensitivity analysis as well as multi-objective optimization are employed. • The system levelized cost of electricity and ecological efficiency are studied. Owning to its advantage in waste reuse, waste-to-energy technology, has become the most popular way to deal with the increasingly municipal solid waste. However, the energy efficiency of waste-to-energy plant is limited because of the huge heat loss. In this study, a novel waste heat recovery system, consisting of a supercritical CO 2 cycle, an organic Rankine cycle, and an absorption refrigeration cycle, is proposed to improve both the thermal efficiency and economic performance of the waste-to-energy plant. A comprehensive thermodynamic analysis is performed to study the energy and exergy efficiency of the system by establishing a reliable mathematical model. Net present value analysis is carried out to study the final net profit and dynamic investment payback period. Besides, the levelized cost of electricity and ecological efficiency of the waste-to-energy plant are investigated. Based on the results of parameter sensitivity analysis of the system, multiple objective optimizations is carried out by using non-dominated sorting genetic algorithm-II. The results show that the combined system obtains the highest economic benefit in winter. The energy efficiency of the waste-to-energy plant can be up to 75.07% after adding the waste heat recovery system, with an increment of 54.58%. And the maximum net present value and minimum dynamic payback period are 23.22 M$ and 4.11 years, separately. Compared with the original waste-to-energy plant, the levelized cost of electricity and ecological efficiency are decreased by 68% and increased by 16%, respectively. From the results of sensitivity analysis, the isentropic efficiency of turbine of supercritical CO 2 cycle, the evaporator pressure of organic Rankine cycle, and the generator temperature of absorption refrigeration cycle are the most sensitive factors for the thermal efficiency and economic performance of the system. The exergy destruction analysis shows that the exergy destruction rate of the boiler declines to 48.41% after adding the waste heat recovery system, but the condensers need further improvement for their lowest exergy efficiency. In conclusion, the waste-to-energy plant can provide electricity, heating and cooling simultaneously after adding the waste heat recovery system and the proposed system is theoretically feasible from the results of thermodynamic, economic and environmental analysis. [ABSTRACT FROM AUTHOR]

• A novel IGCC with negative CO 2 emission is proposed. • An improved transcritical CO 2 Rankine cycle is put forward. • Net electric efficiency of the proposed system can reach 51%. • 0.6 kg CO 2 can be removed from air per 1 kWh electricity generation by this system. • The price of electricity produced by the system can be 0.63$/kWh. A novel carbon-negative integrated gasification combined cycle (NIGCC) is proposed. The chemical looping air separation technology, the supercritical CO 2 Brayton cycle and an improved transcritical CO 2 Rankine cycle are employed for efficient bio-power generation. The NIGCC system is then systematically modeled, with all the subunit models elaborated and validated against the reported data in literature. Thereafter, the effects of different key operation parameters on the system essential performance indicators are studied in terms of thermodynamics and economics. The exergy analyses for the NIGCC system are also implemented and the corresponding exergy Grassmann diagram are drawn. The net electric efficiency, CO 2 emission rate and the levelized cost of electricity of the NIGCC system can reach 51%, −0.6 kg/kWh and 0.63$/kWh, respectively. The exergy efficiencies of the gasifier and gas turbine can be potentially improved so that the NIGCC performance can be further promoted. [ABSTRACT FROM AUTHOR]

This paper addresses the simultaneous optimization of a novel combined supercritical CO 2 Brayton cycle-organic Rankine cycle integrated with molten salt solar power tower plant. The supercritical CO 2 Brayton cycle adopts a two-stage compression intercooling design. The organic Rankine cycle is added as a bottoming cycle to recover the waste heat of the Brayton cycle to generate extra power. Due to its complexity, the integrated system involves many degrees of freedom, which make it challenging to optimize using metaheuristic methods. To tackle this issue, we develop an equation-based model that simultaneously optimizes stream thermodynamic properties and flowsheet mass/heat equilibrium of the integrated system. The problem is formulated as a nonlinear programming model, and a tailored two-step solution strategy is developed to improve its solution efficiency. Several numerical studies are carried out to demonstrate the effectiveness of the proposed optimization method, as well as the efficiency of the integrated system. Solution time of the model is less than 224 CPU seconds. Results show that the method obtains an increase up to 3.6% in thermal efficiency compared with literature results; the optimal intercooling design increases net power output by 2.7% comparing with recompression cycle; the recompression cycle-organic Rankine cycle design obtains a 3.5% increase; and the combined intercooling cycle-organic Rankine cycle design achieves a total 4.4% increase. • A novel concentrated solar power-sCO 2 Brayton cycle-ORC integrated system is proposed. • An NLP model is formulated for simultaneous optimization of the integrated system. • High accuracy thermodynamics module is embedded to estimate physical properties. • Four types of system design are optimized and compared for energy performance. [ABSTRACT FROM AUTHOR]

• S-CO 2 Brayton cycle has the highest efficiency for 500–1000 °C solar temperatures. • The lowest P tur_in of the cycle for ' η max -1%' is much lower than P tur_in for η max. • S-CO 2 Brayton cycle is severely undervalued if P tur_in is restricted to 30 MPa. • Air Brayton cycle does not need high P tur_in but 6% lower than s-CO 2 efficiency. • Sensitivity to η tur is air Brayton cycle > steam Rankine cycle > s-CO 2 Brayton cycle. Concentrated solar power (CSP) is an important way for solar energy utilization, and the efficient solar energy utilization is closely related to a reasonable power cycle. The comparative analysis of the steam Rankine cycle, supercritical CO 2 (s-CO 2) Brayton cycle and air Brayton cycle is always with a particular heat source, working parameter and working condition. However, the solar energy for CSP has a wide temperature range from 250 to 1000 °C and the energy conversion potential of the cycles varies obviously under different heat source temperatures. The maximum pressure of the working condition restricts the cycle energy conversion potential especially for s-CO 2 Brayton cycle. The isentropic efficiency settings severely influence on the cycle comparison results. Therefore, in this work, the energy conversion mechanism and potential of the three types of cycles under a wide solar energy temperature ranges are revealed by optimized with multi-operating conditions. The sensitivity of each cycle to the high working pressure and irreversible processes are analyzed. Results show that, achieving the highest efficiency η max often means an extremely high working pressure. However, the lowest P tur_in to keep relatively high efficiency (higher than ' η max -1%') can be much lower than that of the maximum efficiency. S-CO 2 Brayton cycle has the absolutely highest cycle thermal efficiency when the turbine inlet temperature is higher than 500 °C and the least sensitive to the turbine isentropic efficiency. However, s-CO 2 Brayton cycle is the most dependent on high turbine inlet pressure and the energy conversion potential of s-CO 2 Brayton cycle is severely undervalued if the working pressure is restricted to 20 MPa or 30 MPa. The air Brayton cycle efficiency keeps around 6% lower than the s-CO 2 Brayton cycle at the same turbine inlet temperature and exceed the steam Rankine cycle when the turbine inlet temperature is higher than 750 °C. The air Brayton cycle has the least dependence on high working pressure, however, it is most affected by the non-ideality of expansion and compression processes. [ABSTRACT FROM AUTHOR]

This study presents an investigation of a CO 2 plume geothermal and supercritical CO 2 Brayton (CPG-sCO 2) combined cycle using solar energy as auxiliary heat source. This combined cycle may help solve the problems of CO 2 sequestration and geothermal energy utilization simultaneously. The CPG production is heated by a solar power generation system with solar tower and molten salt. Then a recompression sCO 2 cycle utilizes geothermal energy and solar energy directly. A solution procedure is performed to analyze the thermoeconomic performance of the CPG-sCO 2 combined cycle. Results show that the combined cycle has an optimal main compressor inlet pressure and split ratio for maximum combined cycle efficiency. It can achieve 19.57% by genetic algorithm (GA) optimization, which is 5.65% and 4.07% higher than CPG systems with indirect sCO 2 cycle and organic Rankine cycle, respectively. Moreover, it indicates that the combined cycle efficiency and total capital cost have opposite variation trends with the increase of parameters, including main compressor inlet pressure (p 5), split ratio (sr), well distance (d 8,11) and injection temperature (T 8). Based on multi-objective GA optimization and optimal solution selection, it is concluded that the most thermoeconomic CPG-sCO 2 combined cycle has a combined cycle efficiency of 18.09% and a total capital cost of $5.959 × 107, respectively. Findings suggest that the CPG-sCO 2 combined cycle has potential to combine CO 2 sequestration with geothermal energy utilization. • A CPG-sCO 2 combined cycle with auxiliary solar energy source was studied. • This combined cycle coupled CO 2 sequestration with geothermal energy utilization. • The CPG-sCO 2 combined cycle had a maximum efficiency of 19.57%. • Its efficiency is 5.65% and 4.07% higher than CPG with indirect sCO 2 cycle and ORC. • Most thermoeconomic combined cycle had η cc of 18.09% and C cur,cc of $5.959 × 107. [ABSTRACT FROM AUTHOR]

• The novel CO 2 transcritical power cycle operates with conventional water cooling. • Theoretical study was executed on the relationships among the cycle's parameters. • The novel cycle simplifies the development of the pressurizing component. Compared with the conventional Rankine cycle, the CO 2 transcritical power cycle gives a higher thermal efficiency because of its high average heat absorbing temperature and is suitable for driving a compact system. The self-condensing CO 2 transcritical power cycle can solve the problem that CO 2 is difficult to condense in a conventional CO 2 transcritical power cycle using conventional water cooling. Based on solar thermal energy, a theoretical analysis model was established to study the relationship between the cycle performance and the operating parameters. The results showed that the thermal efficiency increases with increasing the cooled pressure with a low final cooled temperature. By increasing the final cooled temperature, a peak appears on the thermal efficiency curve. The outlet temperature of the cooling water is affected by a shift of the pinch point position in the cooler. According to the variation of the outlet temperature of the cooling water and the proportion of the mass flow rate of CO 2 in the power sub-cycle and that in the whole cycle, it can be concluded that conditions with a very low cooled pressure are uncontrollable. In these conditions, the maximum thermal efficiency of the self-condensing CO 2 transcritical cycle is 0.3463, which is 0.0313 a little lower than that of the supercritical CO 2 Brayton cycle. However, the novel cycle simplifies the development of the pressurizing component and avoids the liquid hammer in the pressurizing process. [ABSTRACT FROM AUTHOR]