COGENERACIÓN CON UN SISTEMA TERMOSOLAR TIPO FRESNEL ACOPLADO A UN CICLO RANKINE ORGÁNICO PARA APLICACIONES RURALES

This study was aimed at quantifying the net electrical power producible from an abandoned oil well in Nigeria using different organic Rankine cycle (ORC) configurations and working fluids. The geological features of a typical Nigerian oil well were employed in the study and a borehole heat exchanger was used for simulating the thermodynamic parameters of the heat source. Specifically, a subcritical ORC without a recuperator (SBC), a subcritical ORC with a recuperator (SBC-R), a supercritical ORC without a recuperator (SPC), and a supercritical ORC with a recuperator (SPC-R) were analyzed, using R115, R236fa, and R1234yf as working fluids. Results showed that between 272 kW and 875 kW of electrical power could be produced from the abandoned oil well using the most basic ORC configuration (SBC). Furthermore, it was obtained that the introduction of a recuperator would increase the ORC net power by about 13% for R236fa, 33% for R1234yf, and 107% for R115. Similarly, a switch from a subcritical ORC to a supercritical ORC configuration would increase net power for all the working fluids. Specifically, an increase in net power was estimated at 3.6% for R236fa, 46% for R1234yf, and 152% for R115 regarding a switch from the SBC to the SPC. Moreover, decreasing the condensation pressure of the ORC plants was observed to improve net power in all cases.

Comparative assessment of four novel solar based triple effect absorption refrigeration systems integrated with organic Rankine and Kalina cycles

Organic Rankine Cycle (ORC) is named for its use of an organic, high molecular mass fluid that boils at a lower temperature than the water. Among many well-proven technologies, the ORC is one of the most favorable and promising ways for low-temperature applications. In comparison to water, organic fluids are advantageous when the plant runs at low temperature or low power. The ORC is scalable to smaller unit sizes and higher efficiencies during cooler ambient temperatures, immune from freezing at cold winter nighttime temperatures, and adaptable for conducting semi-attended or unattended operations [1]. Simpler and cheaper turbine can be used due to the limited volume ratio of organic fluid at the turbine outlet and inlet [2]. In the case of a dry fluid, ORC can be employed at lower temperatures without requiring superheating. This results in a practical increase in efficiency over the use of the cycle with water as the working fluid [3]. ORC can be easily modularized and utilized in conjunction with various heat sources. The success of the ORC technology is reinforced by high technological maturity of majority of its components, spurred by extensive use in refrigeration applications [4]. Moreover, electricity generation near the point of use will lead to smaller-scale power plants, and thus the ORC is particularly suitable for off-grid generation. The selection of the working fluid is of key importance in ORC applications. This is because the fluid must have not only thermophysical properties that match the application but also adequate chemical stability at the desired working temperature. There are several optimal characteristics of the working fluid: 1. Dry or isentropic fluid to avoid superheating at the turbine inlet, for the sake of an acceptable cycle efficiency; 2. Chemical stability to prevent deteriorations and decomposition at operating temperatures; 3. Non-fouling, non-corrosiveness, non-toxicity and non-flammability; 4. Good availability and low cost. However, not all the desired general requirements can be satisfied in a practical ORC. In the previous research, numerous theoretical and experimental studies have focused on ORC fluid selection with special respect to thermodynamic properties. Hung et al. studied waste

Diesel engines are widely used in agricultural tractors. During field operations, the tractors operate at low speed and high load for a long time, the fuel efficiency is only about 15% to 35%, and the exhaust waste heat accounts for 38% to 45% of the energy released from the fuel. The use of tractor exhaust waste heat can effectively reduce fuel consumption and pollutant emissions, of which the organic Rankine cycle (ORC)-based waste heat recovery conversion efficiency is the highest. First, the diesel engine map is achieved through the test rig, a plate-fin evaporator is trial-produced based on the tractor size, and the thermodynamic and economic performance model of the ORC are established. Then, taking the thermal efficiency of ORC and the specific investment cost (SIC) as the objective function, the particle swarm optimization (PSO) algorithm and the technique for order of preference by similarity to ideal solution (TOPSIS) decision method were used to obtain the optimal operating parameter set under all working conditions. Finally, the results showed that the ORC thermal efficiency could reach a maximum of 12.76% and the corresponding SIC value was 8539.66 $/kW; the ORC net output power could be up to 8.31 kW compared with the system without ORC; and the maximum brake specific fuel consumption (BSFC) could be reduced by 8.3%. The improvement in the thermodynamic performance will lead to a sacrifice in economic performance, and at high speeds, the economic benefits and thermal efficiency reach a balance and show a better thermal economic performance. Recovering exhaust heat energy through ORC can reduce tractor fuel consumption and pollution emissions, which is one of the effective technical means to achieve “carbon neutrality” in agricultural production. At the same time, through the PSO algorithm, the optimal combination of ORC operating parameters is obtained, which ensures that the exhaust heat energy can be effectively recovered during the tractor field operation, and provides a basis for the adjustment of real-time work strategies for future research.

Organic Rankine Cycle (ORC) power systems offer a high potential for utilizing solar power for electricity generation. Inherently, the heat supply by solar power is time-dependent, and significant fluctuations occur during the day. Although some time-averaging of the heat input by thermal storage systems might be employed, the off-design performance of turbines is highly relevant for the mean thermal efficiency of such cycles. This study aims to analyze the effect of a hybrid power plant system obtained by combining an Organic Rankine Cycle (ORC) and a Linear Fresnel system (LFR) on the ORC turbine efficiency under part-load. The performance data of the LFR system is taken from an installed system designed to produce 20 kW of heat. The LFR-ORC system was modeled in detail, and thermodynamic calculations were performed using the cycle simulation program EBSILON. The local Direct Normal Irradiation (DNI) values for the selected day, the thermal efficiency of the system, and the temperature and mass flow rate of the thermal oil entering the system were used as inputs for ORC cycle. The ORC power plant was designed as a subcritical cycle with Novec 649 as the working fluid. The off-design performance of the ORC turbine used is compared with the nominal design operating performance using the Kroon and Tobiasz approach. The turbine efficiency as a function of the part-load operation was discussed within the framework of selected loss correlation. The analysis examined the thermal efficiency obtained from the turbine on the ORC side for varying thermal efficiency on the solar field side.

Transient simulation of hybridized system: Waste heat recovery system integrated to ORC and Linear Fresnel collectors from energy and exergy viewpoint

This study evaluates the exergetic performance of a novel combined thermoelectric generator (TEG), an organic Rankine cycle (ORC), and an absorption refrigeration cycle (ARC) run by engine exhaust heat. Further, this study investigates the effect of TEG columns on system performance and provides complete information lacking in previous studies related to engine exhaust-driven TEG-ORC systems. It was found that the net TEG and ORC power increases with the number of TEG columns while the ARC’s cold energy decreases. The organic fluid flow rate requires adjustment with the number of TEG columns to heat it up to the saturation temperature at the TEG outlet. Considering R123, R245ca, and R245fa as working fluids in the ORC, R123 and R245ca are found superior to R245fa. From parametric variation, it was found that the TEG and net ORC power decrease as ORC evaporation pressure increases for both R123 and R245ca, though R245ca performs better at lower pressures, while R123 excels at higher pressures. Meanwhile, ARC’s cooling output increases with evaporation pressure, with R123 consistently providing more cooling energy than R245ca. The cooling output surpasses the combined TEG and net ORC power, especially for R123. Consequently, the total energy output increases with evaporation pressure, with R123 outperforming R245ca in all conditions. The overall system energy and exergy efficiencies for R123 were 49.97% and 40.83% with 5 columns and 10 rows of TEG modules at the recommended ORC evaporation pressure of 32 bar.

High-performance Organic Rankine Cycle (ORC) systems are extensively utilized across various industrial sectors. In some applications, radial flow turbines are crucial for low-temperature heat sources. This study aims to enhance the energy and electrical efficiency of small radial turbines in Organic Rankine Cycle (ORC) ORC systems using n-pentane as the working fluid through numerical analysis. Micro-turbines are proposed to maximize performance for ORC applications. To assess the electrical, hydrodynamic and thermodynamic performance, 3D RANS simulations are conducted for five different mass flow rates with an inlet temperature of 450 K. The findings underscore the potential of radial turbines in ORC systems for utilizing low-temperature heat sources effectively. The results conducted on the entropy resulting from the irreversibility of heat transport and the irreversibility of friction. The following ranges contain the significant parameters for which this work has been completed: mass flow rates (0.1–0.5 kg.s-1), 450 k at the inflow.

Possibilities of electricity generation in the Republic of Croatia from medium-temperature geothermal sources

In this study, the organic Rankine cycle (ORC) and hybrid absorption recompression cycle have been modified by the addition of turbine bleeding with regeneration and ejector, making it a unique solar-powered trigeneration system. With this modification, the useful electric power increases by 65 kW due to increased mass flowrate and overall efficiency nearly by 0.7%, and this difference grows as direct normal irradiation (DNI) rises. After identifying these improvements, a parametric study was conducted to determine the optimum value of these operating variables, such as direct normal irradiation, condenser pressure, turbine inlet temperature, and pressure ratio based on the desired outputs and efficiencies of the proposed modified systems. The results indicate that the proposed system is capable of simultaneously generating 315.3 kW of electric power, 1588 kW of heating output, and 501.6 kW of cooling at energy and exergy efficiencies of 80.8% and 25.36%, respectively. Further, in terms of energy one could conclude that only 19.2% of total available energy is getting wasted, but in reality, around 75% of the work potential of the input exergy is getting wasted. The maximum exergy is lost at the solar collector and destructed at heat recovery vapor generator (HRVG), hence requiring careful design to improve their performance. Lastly, an economic analysis of the proposed system has also been conducted, and the payback period is found to be 2.33 years, which ensures its economic viability.

Dual-pressure Organic Rankine Cycles (ORCs) driven by the low temperature heat source usually work under part-load conditions, and it is therefore essential to predict the off-design performance of such ORCs. This paper presents the off-design performance prediction of the dual-pressure ORC on the basis of the model including plate heat exchangers, axial turbines and a centrifugal pump. Pure working fluid R600a and the mixture R245fa/R600a are compared. The sliding pressure operation strategy is considered under off-design conditions. The results indicate that under the design hot water parameters (hot water 140 °C, 64.87 kg/s), compared with the single-pressure ORC using R600a, the dual-pressure ORC using R600a shows a 9.57% higher net power and a 17.32% higher heat transfer area. Furthermore, the dual-pressure ORC with the mixture R245fa/R600a (0.42/0.58 mass fraction) shows a 1.04% higher net power and a 3.87% higher heat transfer area than the dual-pressure ORC using R600a under the design hot water parameters. In the dual-pressure ORC, the rotational speed of the high-pressure pump is more strongly influenced by the inlet temperature of hot water than that of the low-pressure pump. In addition, when the mass flow rate ratio of hot water or the inlet temperature of hot water increases, the difference of the net power between the dual-pressure ORC using the proposed mixture R245fa/R600a (0.42/0.58 mass fraction) and that using pure R600a increases.

Off-design performance comparative analysis between basic and parallel dual-pressure organic Rankine cycles using radial inflow turbines

Assessment and optimization of a novel solar driven natural gas liquefaction based on cascade ORC integrated with linear Fresnel collectors

The Organic Rankine Cycle (ORC) is commonly accepted as a viable technology to convert from low to medium temperature geothermal energy into electrical energy. In practice, the reference technology for converting geothermal energy to electricity is the subcritical simple ORC system. Over time, geothermal ORC plants with more complex configurations (architectures) have been developed. In the open literature, a large number of advanced architectures or configurations have been introduced. An analysis of the scientific literature indicates that there is some confusion regarding the terminology of certain advanced ORC system architectures. A new categorization of advanced configurations has been proposed, with a special emphasis on the application of geothermal energy. The basic division of advanced plant configurations is into dual-pressure and dual-stage ORC systems. In this study, the real potential of advanced ORC architectures or configurations to improve performance as compared with the simple ORC configuration was explored. The research was conducted for a wide range of geothermal heat source temperatures (from 120 °C to 180 °C) and working fluids. Net power output improvements as compared with the basic subcritical simple ORC (SORC) configuration were examined. The ability to produce net power with different ORC configurations depends on the magnitude of the geothermal fluid temperature and the type of working fluid. At a lower value of geothermal fluid temperature (120 °C), the most net power of 18.71 (kW/(kg/s)) was realized by the dual-pressure ORC (DP ORC configuration) with working fluid R1234yf, while the double stage serial-parallel ORC configuration with a low-temperature preheater in a high-temperature stage ORC (DS parHTS LTPH ORC) generated 18.51 (kW/(kg/s)) with the working fluid combination R1234yf/R1234yf. At 140 °C, three ORC configurations achieved similar net power values, namely the simple ORC configuration (SORC), the DP ORC configuration, and the DS parHTS LTPH ORC configuration, which generated 31.03 (kW/(kg/s)) with R1234yf, 31.07 (kW/(kg/s)) with R1234ze(E), and 30.96 (kW/(kg/s)) with R1234ze(E)/R1234yf, respectively. At higher values of geothermal fluid temperatures (160 °C and 180 °C) both the SORC and DP ORC configurations produced the highest net power values, namely 48.58 (kW/(kg/s)) with R1234ze(E), 67.23 (kW/(kg/s)) with isobutene for the SORC configuration, and 50.0 (kW/(kg/s)) with isobutane and 69.67 (kW/(kg/s)) with n-butane for the the DP ORC configuration.

The organic Rankine cycle (ORC) presents a great potential in the efficient heat–power conversion of low and medium temperature (<350°C) thermal energy. Dual-pressure evaporation ORCs can significantly reduce the exergy loss in the endothermic process. While, variations of optimal cycle parameters and the superiority in the thermodynamic performance compared with the single-pressure evaporation ORC remain indeterminate for various heat source temperatures. This paper focuses on the dual-pressure evaporation ORC using R1234ze(E) driven by the 100–200°C heat sources without the outlet temperature limit. Two-stage evaporation pressures and the high-pressure evaporator outlet temperature were optimized, and the system thermodynamic performance was compared with that of the single-pressure evaporation ORC. Results show that the maximum net power output of the dual-pressure evaporation ORC system is generally larger than that of the single-pressure evaporation ORC system for the heat source temperature below 150°C. The heat source temperature is lower, the increment of the maximum net power output is generally larger; and the maximum increment is 24.3%. When the endothermic process minimal temperature difference of the single-pressure evaporation ORC occurs at the evaporation bubble point, the dual-pressure evaporation ORC generally can further increase the system net power output.