The expansion device is considered the crucial equipment in Organic Rankine cycle (ORC). Due to the structure limitation, the scroll expander would be critical affected by the external load ...characteristics. In this work, to fit the development trend of small-scale ORC and fill the research blank of load resistance, the ORC system with rated power of 300 We was experimentally studied, the dynamic operation characteristics, the direct and indirect influence on each device, and the overall system performance with rated load of 175 We, 200 We and 225 We were evaluated. By adjusting the frequency of the pump, the system dynamic operation characteristics are developed, and the behaviors of the devices are analyzed. According to the system analyses, despite the system with a rated load of 225 We could reach the highest output of 707 Wnet, the system with the lower rated load has the favorable performance, caused by the superior expander and generator behaviors with lower Ampere force. The overall system performance shows that the thermal efficiencies exhibits an increase trend of about 6.67 %, 7.01 %, and 7.27 % sequentially for the system with rated load of 225 We, 200 We, and 175 We.
•The ORC system with rated power of 300 We was experimentally studied.•Effect of resistive load with 175 We, 200 We and 225 We on system behaviors were evaluated.•The coordination of the rated load, system capacity and operating parameters is highlighted.•Thermal efficiencies are about 7.27 %, 7.01 %, 6.67 % for system with 175 We, 200 We, and 225 We.
Gas-fired power generation, characterized by high efficiency, low carbon emissions, and flexibility, contributes significantly to the global energy transition. In the present work, a novel dual-stage ...intercooled and recuperative gas turbine system integrated with transcritical organic Rankine cycle (dICR-GT-tORC) was proposed. System modeling was carried out based on Thermoflex software for different configurations to evaluate the energetic and exergetic performances. It was found that the dICR-GT-tORC exhibited improved thermodynamic performance compared to the gas turbine simple cycle and dICR-GT system, with the system net energy efficiency/exergy efficiency/specific work increasing from 43.88%/41.80%/567 kJ·kgair−1 and 57.21%/54.49%/684 kJ·kgair−1 to 62.48%/59.52%/745 kJ·kgair−1, respectively. An energy utilization diagram analysis revealed that the energy cascade utilization was achieved by coupling a bottoming tORC to fully utilize the waste heat from intercoolers and the exhaust gas. Furthermore, the dICR-GT-tORC demonstrated enhanced environmental performance, reducing the CO2 emission rate by a maximum value of 29.8%. Additionally, the impacts of key parameters, including the organic working fluid selection, the minimum temperature difference at the pinch point of recuperators and the terminal exhaust gas temperature on the system performance were investigated. It was indicated that the proposed system could be applicable in various practical scenarios from thermodynamic and environmental perspectives.
•Dual-stage intercooled and recuperative gas turbine system integrated with transcritical ORC was proposed.•System modeling was conducted for energetic and exergetic performances evaluation.•The energy efficiency of the proposed gas-fired power system reached up to 62.48%.•Influence of key parameters on the system performance was analyzed quantitatively.
This paper presents a review of the organic Rankine cycle and supercritical Rankine cycle for the conversion of low-grade heat into electrical power, as well as selection criteria of potential ...working fluids, screening of 35 working fluids for the two cycles and analyses of the influence of fluid properties on cycle performance. The thermodynamic and physical properties, stability, environmental impacts, safety and compatibility, and availability and cost are among the important considerations when selecting a working fluid. The paper discusses the types of working fluids, influence of latent heat, density and specific heat, and the effectiveness of superheating. A discussion of the 35 screened working fluids is also presented.
▸ We conduct the thermodynamic and economic performance comparison of the fluids in both subcritical ORC and transcritical power cycle. ▸ We perform parameter optimization based on five indicators. ▸ ...The optimum operation parameters and working fluids are not the same for different indicators. ▸ The LEC value is used as the determining factor for fluids screening. ▸ The transcritical power cycle with R125 as the working fluid was a cost-effective approach.
Organic Rankine Cycle (ORC) is a promising technology for converting the low-grade energy to electricity. This paper presents an investigation on the parameter optimization and performance comparison of the fluids in subcritical ORC and transcritical power cycle in low-temperature (i.e. 80–100°C) binary geothermal power system. The optimization procedure was conducted with a simulation program written in Matlab using five indicators: thermal efficiency, exergy efficiency, recovery efficiency, heat exchanger area per unit power output (APR) and the levelized energy cost (LEC). With the given heat source and heat sink conditions, performances of the working fluids were evaluated and compared under their optimized internal operation parameters. The optimum cycle design and the corresponding operation parameters were provided simultaneously. The results indicate that the choice of working fluid varies the objective function and the value of the optimized operation parameters are not all the same for different indicators. R123 in subcritical ORC system yields the highest thermal efficiency and exergy efficiency of 11.1% and 54.1%, respectively. Although the thermal efficiency and exergy efficiency of R125 in transcritical cycle is 46.4% and 20% lower than that of R123 in subcritical ORC, it provides 20.7% larger recovery efficiency. And the LEC value is relatively low. Moreover, 22032L petroleum is saved and 74,019kg CO2 is reduced per year when the LEC value is used as the objective function. In conclusion, R125 in transcritical power cycle shows excellent economic and environmental performance and can maximize utilization of the geothermal. It is preferable for the low-temperature geothermal ORC system. R41 also exhibits favorable performance except for its flammability.
•We introduced partially curved, composite U-bend (CU) into supercritical vapor generator of ORC.•Larger curvature in the bending section of CU dramatically improves heat transfer.•The straight ...section of CU can thermally outperform the corresponding curved section of typical U-bend (TU).•The overall performance of CU is superior to TU when Grq/Grth ≥ 25.•The critical factor determining the overall enhancement of CU is the thermal redevelopment.
This study explores the introduction of partially curved, composite U-bends into a supercritical vapor generator of Organic Rankine Cycle. The curved section of composite U-bends is decomposed into two bends with larger curvature, and its thermal performance was numerically studied over a wide range of heat flux, mass flux, and inlet temperature. Results reveal a dual-peak heat transfer pattern that notably improves local heat transfer. Meanwhile in the straight section between two bends, the strong secondary flows induced completely disrupt the original buoyancy-stratified flow, which have almost an identical effect as the thermal development at the tube entrance. The enhancement of heat transfer resulting from the ‘thermal re-development’ is more significant than that caused by the relatively small curvature in typical U-bends. Consequently, the straight section of composite U-bends can thermally outperform the corresponding curved section of typical U-bends, ultimately determining the overall enhancement effect of composite U-bends. Moreover, as buoyancy effect becomes stronger, the re-development effect is also more remarkable. When buoyancy parameter Grq/Grth ≥ 25, composite U-bends demonstrates superior overall performance compared to typical U-bends. Within the scope of this research, the heat transfer enhancement of composite U-bends can reach up to 20 % without increasing material costs or assembly space.
A novel cascade energy utilization system with Solid Oxide Fuel Cell (SOFC) as the prime mover is designed and analyzed. The upper loop contains SOFC and Gas Turbine (GT), and the bottom loop ...includes Supercritical CO2 (SCO2) power cycle - Organic Rankine Cycle (ORC) combined cycle, single - effect Absorption Refrigeration Cycle (ARC), and heating subsystem. Based on simulation data and mathematical models of the system, energy analysis, conventional and graphical exergy analysis, and sensitivity analysis are conducted. The simulation result demonstrates that the net power efficiency, overall energy efficiency, exergy efficiency and SOFC electrical generation efficiency are 59.62%, 77.61%, 59.08% and 43.18%, respectively. The exergy analysis reveals that the system exergy losses obtained from conventional exergy and graphical exergy analysis are 383.29 kW and 372.46 kW, respectively, a relative error of 2.91%. However, the SOFC subsystem has the greatest exergy destruction, reaching 65.77% (graphical exergy analysis) or 65.06% (conventional exergy analysis) of the total system exergy loss. The system with favorable energy efficiency provides a reference direction for the future research and optimization of Solid Oxide Fuel Cell (SOFC) - Combined Cooling, Heating and Power (CCHP) system.
•A new type of SOFC–CCHP system integrating SCO2-ORC and ARC is presented.•The condensation heat of SCO2 cycle is recovered by ORC.•The energy level change and exergy loss of components are clearly shown by EUD.•Sensitivity analysis of parameters affecting the system performance is performed.
•A SOFC cogeneration system with an ORC waste heat recovery system is proposed.•The performance of the dual-loop ORC system with 20 working fluids is explored.•Thermodynamic and economic ...multi-objective optimisations are performed.•Exergy efficiency of 52% with 969 kW electricity and 564 kW cooling is achieved.•The system LCoE is up to 74% lower than those of traditional SOFC configurations.
A novel combined-cycle system is proposed for the cogeneration of electricity and cooling, in which a dual-loop organic Rankine cycle (ORC) engine is used for waste-heat recovery from a solid oxide fuel cell system equipped with a gas turbine (SOFC-GT). Electricity is generated by the SOFC, its associated gas turbine, the two ORC turbines and a liquefied natural gas (LNG) turbine; the LNG supply to the fuel cell is also used as the heat sink to the ORC engines and as a cooling medium for domestic applications. The performance of the system with 20 different combinations of ORC working fluids is investigated by multi-objective optimisation of its capital cost rate and exergy efficiency, using an integration of a genetic algorithm and a neural network. The combination of R601 (top cycle) and Ethane (bottom cycle) is proposed for the dual-loop ORC system, due to the satisfaction of the optimisation goals, i.e., an optimal trade-off between efficiency and cost. With these working fluids, the overall system achieves an exergy efficiency of 51.6%, a total electrical power generation of 1040 kW, with the ORC waste-heat recovery system supplying 20.7% of this power, and a cooling capacity of 567 kW. In addition, an economic analysis of the proposed SOFC-GT-ORC system shows that the cost of production of an electrical unit amounts to $33.2perMWh, which is 12.9% and 73.9% lower than the levelized cost of electricity of separate SOFC-GT and SOFC systems, respectively. Exergy flow diagrams are used to determine the flow rate of the exergy and the value of exergy destruction in each component. In the waste-heat recovery system, exergy destruction mainly occurs within theheat exchangers, the highest of which is in the LNG cooling unit followed by the LNG vaporiser and the evaporator of the bottom-cycle ORC system, highlighting the importance of these components’ design in maximising the performance of the overall system.
Present study deals with the comparative assessment of three different configurations of ORC (Organic Rankine Cycle) system including basic ORC, recuperated ORC, and regenerative ORC system for low ...temperature geothermal heat source. The comparison of the performance of each cycle is carried out at their optimum operating condition using Non-dominated Sorting Genetic Algorithm-II for minimum specific investment cost and maximum exergy efficiency under logical bounds of evaporation temperature, pinch point temperature difference and superheat. Objective functions are conflicting, therefore, optimization results are presented in the form of a Pareto Front Solution. Thermal efficiency and the exergy efficiency for recuperated and regenerative are higher than basic ORC but with an additional average specific investment cost of 3% for basic and 7% for regenerative cycle. Working fluids with critical temperature in the same range of heat source results in better thermal performance. R245fa has highest Exergy efficiency of 51.3% corresponding to minimum specific cost of 2423$/kW for basic cycle, 53.74% corresponding to 2475$/kW for recuperated, and 55.93% corresponding to 2567$/kW for regenerative cycle.
•Comparative assessment of different configurations of Organic Rankine Cycle.•System Optimization for minimum specific cost and maximum exergy efficiency.•System Optimization was performed using multi objective genetic algorithm.•Parametric analysis for specific cost and exergy efficiency for each configuration.
•Recuperative ORC (RORC) presents a higher efficiency (+20 %) and power (+18 %) than ORC.•RORC works with a lower mass flow rate than ORC for a given evaporating temperature.•RORC needs a lower heat ...input thus increasing the operating time in absence of solar radiation.•The higher operating time involves a higher yearly electricity energy production (+37 %).•Hot water and coolant temperature play the most important effect on RORC performance.
Organic Rankine Cycle -based microcogeneration systems that exploit solar sources to generate electricity and domestic hot water simultaneously are promising solutions for reducing CO2 emissions in the residential energy-intensive sector. Such systems can be assisted by thermal energy storage reservoirs in which water is heated by solar energy and cooled by the direct use of thermal energy for domestic hot water production and acting as heat source of the power plant. An interesting plant layout optimisation involves the adoption of a recuperative heat exchanger to preheat the working fluid before it enters the heat recovery vapour generator, which is fed with the same working fluid leaving the expander. Despite the positive effect of recuperative heat exchanger adoption on the efficiency of the entire plant, the impact on electrical energy production at this microscale is not straightforward to assess as the heat source is represented by the water inside the reservoir and it is not a continuous high- or medium-temperature stream. The lack of experimental analyses in the literature on these applications makes this a debatable question.
Thus, to fill this gap and quantitatively assess the benefits introduced by the adoption of a recuperative stage, a wide experimental comparison between recuperative and not-recuperative Organic Rankine Cycle-based power unit layout was performed. To support the experimental analysis, a comprehensive theoretical model of the Organic Rankine Cycle-based plant was developed and validated against experimental data.
The experimental campaign demonstrated that the recuperative Organic Rankine Cycle-based unit required a lower working fluid flow rate for a given expander inlet temperature and pressure ratio. Consequently, a higher electrical power can be produced, requiring lower thermal power from a heat source. The reduction in the thermal power absorbed from the heat source, produced by a higher temperature incoming working fluid entering the Heat Recovery Vapor Generator, had a positive effect, allowing a longer-in-time working condition with a higher conversion efficiency intrinsically produced by the recuperative heat exchanger. Considering the annual electricity consumption of 2700 kWh of a family living in a city in central Italy, the contribution given by the recuperative Organic Rankine Cycle plant operating with a reservoir fed by 15 m2 of flat solar panels was 330 kWh, whereas without the recuperative stage, the production was 240 kWh. The cost of electricity saved justified the adoption of a recuperative heat exchanger.
Organic Rankine Cycles (ORCs) are particularly suitable for recovering energy from low-grade heat sources. This paper describes the behavior of a small-scale ORC used to recover energy from a ...variable flow rate and temperature waste heat source. A traditional static model is unable to predict transient behavior in a cycle with a varying thermal source, whereas this capability is essential for simulating an appropriate cycle control strategy during part-load operation and start and stop procedures. A dynamic model of the ORC is therefore proposed focusing specifically on the time-varying performance of the heat exchangers, the dynamics of the other components being of minor importance. Three different control strategies are proposed and compared. The simulation results show that a model predictive control strategy based on the steady-state optimization of the cycle under various conditions is the one showing the best results.
