Regenerative Organic Rankine Cycle Research Articles

Thermodynamic, Economic and Sustainability Analysis of Solar Organic Rankine Cycle System with Zeotropic Working Fluid Mixtures for Micro-Cogeneration in Buildings

Globally there are several viable sources of renewable, low-temperature heat (below 130 °C), particularly solar energy, geothermal energy, and energy generated from industrial wastes. Increased exploitation of these low-temperature options has the definite potential of reducing fossil fuel consumption with its attendant very harmful greenhouse gas emissions. Researchers have universally identified the organic Rankine cycle (ORC) as a practicable and suitable system to generate electrical power from renewable sources based on its beneficial usage of volatile organic fluids as working fluids (WFs). In recent times, researchers have also shown a preference towards deployment of zeotropic mixtures as ORC WFs because of their capacity to improve thermodynamic performance of ORC systems, a feat enabled through the greater matching of the temperature profiles of the WF and the heat source/sink. This paper demonstrates the thermodynamic, economic and sustainability feasibility, and the notable advantages of using zeotropic mixtures as WFs through a simulation study of an ORC system. The study examines first the thermodynamic performance of ORC systems using zeotropic mixtures to generate electricity powered by a low-temperature solar heat source for building applications. A thermodynamic model is developed with a solar-driven ORC system both with and excluding a regenerator. Twelve zeotropic mixtures with varying compositions are evaluated and compared to identify the best combinations of mixtures that can yield high performance and high efficiency in their system cycles. The study also examines the effects of the volume flow ratio, and evaporation and condensation temperature glides on the ORC’s thermodynamic performance. Following a detailed analysis of each mixture, R245fa/propane and butane/propane are selected for parametric study to investigate the influence of operating parameters on the system’s efficiency and sustainability index. For zeotropic mixtures, results disclosed that there is an optimal composition range within which binary mixtures are inclined to perform more efficiently than the component pure fluids. In addition, a substantial enhancement in cycle efficiency can be obtained by a regenerative ORC, with cycle efficiency ranging between 3.1–9.8% and 8.6–17.4% for ORC both without and with regeneration, respectively. Results also revealed that exploiting zeotropic mixtures could enlarge the limitation experienced in selecting WFs for low-temperature solar ORCs. Moreover, a detailed economic with a sensitivity analysis of the solar ORC system was performed to evaluate the cost of the electricity and other economic criteria. The outcome of this investigation should be useful in the thermo-economic feasibility assessments of solar-driven ORC systems using working fluid mixtures to find the optimum operating range for maximum performance and minimum cost.

Thermodynamic analysis and multi-objective optimization of a transcritical CO2 waste heat recovery system for cruise ship application

To develop the energy-efficient and flexible waste heat recovery process for cruise ship application, a novel combined system with transcritical CO2 Rankine cycle and ejector refrigeration cycle (ETCRC) is presented. The proposed system driven by main engine exhaust gas can be selectively operated in a specific mode with adjustable capacities of heating, cooling and power to satisfy shipboard demands. The simulation model is developed for performance analysis from the thermodynamic aspect. Moreover, a typical transcritical CO2 Rankine cycle coupled with valve-expansion refrigeration process (VTRCR) and a conventional regenerative organic Rankine cycle (RORC) using R123 are considered as reference systems. Parametric investigation and performance comparison between the present system and each considered reference system in different operation modes are respectively conducted. Furthermore, based on artificial bee colony (ABC) algorithm and fast-non-dominated sorting technique, multi-objective optimization for the proposed system is performed to maximize useful energy productions. According to the results, the proposed combined cycle is found to be more efficient than the reference cycle in each of the specified operation mode. Under the optimal conditions, the maximum cooling effect and net power of the ETCRC in Mode-S operation are 863.3 kW and 202.9 kW, respectively. And the maximum high-temperature heating output and net power of the ETCRC for Mode-SAW operation are 960.5 kW and 272.7 kW, respectively. The performance characteristics of the proposed cycle theoretically demonstrate its advantages for application in cruise ships.

Performance enhancement and multi-objective optimization of a solar-driven setup with storage process using an innovative modification

The main objective of this study is to propose and design a novel modification process of a combined cooling, heating, and power production setup using parabolic trough solar collectors, contributing a higher performance. The base setup consists of a solar subsystem, an organic Rankine cycle for electricity generation, a heat exchanger and a single-effect absorption chiller that produce heating and cooling utilizing the organic Rankine cycle waste heat. The base setup is modified by adding two regenerative organic Rankine cycles, three heating process heat exchangers, and a double-effect absorption chiller. Both systems are studied and compared in three different modes, embracing solar mode (low radiation), solar and storage mode (high radiation), and storage mode (no radiation). Compared to the base setup, for the modified system, electricity production improves by 10.4%, 18.4% and 3.0% in the aforementioned operational modes, respectively. Also, for these modes, the electrical efficiency of the modified system is found to be 1.4 percent-point, 0.9 percent-point, and 0.3 percent-point higher than those of the base one, correspondingly. Eventually, a multi-objective optimization is conducted to optimize the modified system using a genetic algorithm.

Experimental comparison of the performance of basic and regenerative organic Rankine cycles

Adding the regenerator to recover extra heat from the exhaust can improve the system overall performance. Based on a 10 kW organic Rankine cycle (ORC) experimental prototype, a comparison between the basic and regenerative organic Rankine cycle is investigated. The heat input is in range of 30–90 kW and R245fa is used as working fluid. The heat source temperature utilization rate is defined to appraise the heat source utilization. The detailed behaviors for heat source loop, ORC loop and cooling water loop are examined. Research demonstrates that the BORC has a better heat source temperature utilization than the RORC. RORC has a maximum thermal efficiency of 5.5%, which is 25.5% higher than BORC of 4.1%. The maximum condenser heat transfer coefficients for BORC and RORC are 501.4 W/m2 K and 1701.4 W/m2 K, respectively. The BORC has higher electrical power and generating efficiency than the RORC. The maximum generating efficiency for BORC is 3.4%, while that for RORC is 2.5%. Besides, the exergy destructions of the main components are addressed, and the evaporator has a very large percentage of exergy destruction for BORC and RORC. Therefore, system performance can be heightened by improving the temperature difference matching of the heat sources.

Waste heat recovery in an intercooled gas turbine system: Exergo-economic analysis, triple objective optimization, and optimum state selection

The development of heat and power generation systems has a major step towards sustainable development, reducing fossil energy consumption and reducing environmental pollution. Integrated energy systems are considered widely due to their high efficiency. In the present paper, an intercooled gas turbine system is developed to achieve a system with high thermal efficiency as well as better economic performance and cleaner production. The main goals of the suggested system is improvement of thermodynamic and exergo-economic performance beside multi-criteria optimization, which lead to improve the system sustainability. The intercooled gas turbine in the current work integrated with hot water system and thermoelectric generator unit to develop an advanced combined heat and power system. A comprehensive energy, exergy, and exergo-economic analyses are employed to price assessment of the new introduced system. A comparative analysis with conventional intercooled gas turbine system is presented. The results of thermodynamic modeling indicate that an improvement about 613.3 kW, 8.21 kW, and 12.3 kW can be obtained in the gas turbine, Kalina cycle, and regenerative organic Rankine cycle subsystems. The results of energy and exergy analysis show that the values of both energy and exergy efficiencies for all subsystems experience increment in the new introduced. Parametric analysis based on thermodynamic and exergo-economic criteria is done and a triple objective optimization conducted to determine the best system configurations. The Technique for Order of Preference by Similarity to Ideal Solution is employed to choose the final optimal state of the system. The result of optimum selection among non-dominant solutions suggested by Pareto points indicates that the energy efficiency, total exergy destruction rate and electricity cost rate are 53.91%, 2392.01 kW, and 52.29 $/h.

Open feed organic heater pressure analysis on single-stage regenerative organic Rankine cycle performance

Single-stage regenerative organic Rankine cycle (SSRORC) is a system that is used for increasing the simple organic Rankine cycle (ORC) performance. Open feed organic heater (OFOH) addition in the ORC system increase power and efficiency of the system. This paper analyzes the SSRORC performance with a variation of P6/P1 ranges from 1.25 to 3.75 with an increment of 0.25, where P6 is the OFOH pressure at the inlet side and P1 is the pressure at the inlet pump 1, respectively. Hot water was used as the heat source with 100 °C and 100 l/min of temperature and volume flow rate as the initial data. R227ea, R245fa, and R141b were chosen as working fluids for performance analysis. The analysis was performed by calculating the heat input, heat loss, pump and turbine power, net power, and thermal efficiency through energy balance. Exergy input, exergy output, and exergy efficiency were analyzed through exergy balance. The results show that P6/P1 = 2 obtains the highest performance than the other pressure ratios for R227ea, while R245fa and R141b obtain the highest performance at P6/P1 = 2.25. R141b has better performance than the other two fluids with 10.97 % and 11.96 % for thermal and exergy efficiency. The results show that the ratio of OFOH pressure at the inlet side to the pressure at inlet pump 1 (P6/P1) in the middle value obtains the best performance.

Analysis of organic Rankine cycle based on thermal and exergy efficiency

The binary power plant is a geothermal power generation system used at low to medium temperature levels and used indirect system. In this system, the heat generated from the reservoir is channelled to the secondary working fluid which has a lower boiling point than water using a heat exchanger. In this case, the Organic Rankine Cycle (ORC) is a suitable system for use. This improves the performance and efficiency of the plants. However, in this system, the installation configuration of the ORC model is an important factor that can affect its performance. The selection of an improper ORC design reduces the thermal efficiency of the system. Therefore, it cannot utilize heat optimally. In this study, Engineering Equation Solution (EES) simulation program is used to run the system as in operation conditions. A comparative analysis is conducted using ORC, Regenerative ORC (RORC), and RORC with Internal Heat Exchanger (IHE). The results indicate that RORC with IHE has the greatest value for both energy (21.74%) and exergy efficiency (25.26%) while net power produced 5479 kW. This shows the addition of OFOH and IHE can increase these factors, improve performance and reduce energy degradation from the cycle.

Regenerative Organic Rankine Cycle as Bottoming Cycle of an Industrial Gas Engine: Traditional and Advanced Exergetic Analysis

This investigation shows a traditional and advanced exergetic assessment of a waste heat recovery system based on recuperative ORC (organic Rankine cycle) as bottoming cycle of a 2 MW natural gas internal combustion engine. The advanced exergetic evaluation divides the study into two groups, the avoidable and unavoidable group and the endogenous and exogenous group. The first group provides information on the efficiency improvement potential of the components, and the second group determines the interaction between the components. A sensitivity analysis was achieved to assess the effect of condensing temperature, evaporator pinch, and pressure ratio with net power, thermal efficiencies, and exergetic efficiency for pentane, hexane, and octane as organic working fluids, where pentane obtained better energy and exergetic results. Furthermore, an advanced exergetic analysis showed that the components that had possibilities of improvement were the evaporator (19.14 kW) and the turbine (8.35 kW). Therefore, through the application of advanced exergetic analysis, strategies and opportunities for growth in the thermodynamic performance of the system can be identified through the avoidable percentage of destruction of exergy in components.

Power and efficiency optimizations of an irreversible regenerative organic Rankine cycle

Rational and efficient uses of low temperature waste heats have become an important research topic, and organic Rankine cycle is one of effectual methods for the recoveries of waste heats. The performances of simple and regenerative organic Rankine cycles have been analyzed and optimized by using classical thermodynamics and finite thermodynamics. Based on finite time thermodynamics, an irreversible regenerative organic Rankine cycle model is built in this paper. With the fixed total heat transfer area of all heat exchangers (evaporator, condenser and regenerator) in the cycle, the power output and thermal efficiency of the cycle are maximized with the changes of heat transfer area ratios of the heat exchangers, mass flow rate of the working fluid and superheat. The influences of the internal irreversible losses on the power output and thermal efficiency of the cycle are analyzed. The results illustrate that there exist an optimal evaporator heat transfer area, an optimal mass flow rate and an optimal superheat to make the power output reach its triple maximum. There also exist an optimal evaporator heat transfer area ratio, an optimal regenerator heat transfer area ratio and an optimal superheat to make the thermal efficiency reach its triple maximum. The power output and thermal efficiency after triple optimizations are increased by 25.22% and 12.16%, respectively. Moreover, the internal irreversible losses have similar effects on the power output and thermal efficiency. Useful guidelines for the designs of the practical regenerative organic Rankine cycles can be offered from the gained results of this paper.

Thermo-Economic Study of a Regenerative Dual-Loop ORC System Coupled to the Main Diesel Engines of a General Support Vessel

A thermo-economic analysis of a regenerative dual-loop organic Rankine cycle (ORC) is conducted, which will be coupled with the main diesel engines of a general support vessel. An energy and exergy analysis of the regenerative dual-loop ORC is conducted. The energy and exergy analysis results of the regenerative dual-loop ORC are compared with pertinent results for a simple dual-loop ORC without regeneration. A mission analysis that was based on a vessel speed profile with the proposed ORC was conducted. A heat transfer analysis was performed for dimensioning the heat exchangers of both ORC loops. Finally, an economic analysis is conducted to calculate the total capital cost and the payback period of the proposed ORC. The results showed that the proposed ORC is thermodynamically superior in both energetic and exergetic terms compared to the simple dual-loop ORC. The total fuel cost saving is 337,493 Euros, the total CO2 emission saving is 1,153,416.4 kg, and the SO2 emission saving is 36,044.3 kg. The total capital cost of the proposed ORC is 2,546,000 Euros. Finally, the installation of the proposed ORC in the examined vessel is economically feasible because it results in a reasonable payback period, which is less than nine years.

Comparison of Exergy and Advanced Exergy Analysis in Three Different Organic Rankine Cycles

Three types of organic Rankine cycles (ORCs): basic ORC (BORC), ORC with single regeneration (SRORC) and ORC with double regeneration (DRORC) under the same heat source have been simulated in this study. In the following, the energy and exergy analysis and the advanced exergy analysis of these three cycles have been performed and compared. With a conventional exergy analysis, researchers can just evaluate the performance of components separately to find the one with the highest amount of exergy destruction. Advanced analysis divides the exergy destruction rate into unavoidable and avoidable, as well as endogenous and exogenous, parts. This helps designers find more data about the effect of each component on other components and the real potential of each component to improve its efficiency. The results of the advanced exergy analysis illustrate that regenerative ORCs have high potential for reducing irreversibilities compared with BORC. Total exergy destruction rates of 4.13 kW (47%) and 5.25 kW (45%) happen in avoidable/endogenous parts for SRORC and DRORC, respectively. Additionally, from an advanced exergy analysis viewpoint, the priority of improvement for system components is given to turbines, evaporators, condensers and feed-water heaters, respectively.

LNG 냉열과 재생 유기 랭킨 사이클을 이용한 복합 사이클의 성능 특성 해석

LNG 냉열과 재생 유기 랭킨 사이클을 이용한 복합 사이클의 성능 특성 해석

Economic and Exergo-Advance Analysis of a Waste Heat Recovery System Based on Regenerative Organic Rankine Cycle under Organic Fluids with Low Global Warming Potential

The waste heat recovery system (WHRS) is a good alternative to provide a solution to the waste energy emanated in the exhaust gases of the internal combustion engine (ICE). Therefore, it is useful to carry out research to improve the thermal efficiency of the ICE through a WHRS based on the organic Rankine cycle (ORC), since this type of system takes advantage of the heat of the exhaust gases to generate electrical energy. The organic working fluid selection was developed according to environmental criteria, operational parameters, thermodynamic conditions of the gas engine, and investment costs. An economic analysis is presented for the systems operating with three selected working fluids: toluene, acetone, and heptane, considering the main costs involved in the design and operation of the thermal system. Furthermore, an exergo-advanced study is presented on the WHRS based on ORC integrated to the ICE, which is a Jenbacher JMS 612 GS-N of 2 MW power fueled with natural gas. This advanced exergetic analysis allowed us to know the opportunities for improvement of the equipment and the increase in the thermodynamic performance of the ICE. The results show that when using acetone as the organic working fluid, there is a greater tendency of improvement of endogenous character in Pump 2 of around 80%. When using heptane it was manifested that for the turbine there are near to 77% opportunities for improvement, and the use of toluene in the turbine gave a rate of improvement of 70%. Finally, some case studies are presented to study the effect of condensation temperature, the pinch point temperature in the evaporator, and the pressure ratio on the direct, indirect, and fixed investment costs, where the higher investment costs were presented with the acetone, and lower costs when using the toluene as working fluid.

A comparative assessment of SPECO and MOPSA on costing of exergy destruction

This paper presents the comparison of specific exergy costing (SPECO) and modified productive structure analysis (MOPSA) method to test their abilities on costing of exergy destruction. MOPSA method is applied to a combined supercritical CO2 regenerative cycle and organic Rankine cycle using zeotropic mixtures for gas turbine waste heat recovery system. The results obtained with applying SPECO method to the system are taken from literature. The exergy destruction cost rate of overall system is obtained to be $86.08/h and $1,113.13/h for MOPSA and SPECO methods, respectively. The exergoeconomic factor of overall system is found to be 31.88% for SPECO method, while this value is found to be 85.82% for MOPSA method. The obtained results with applying MOPSA method for exergy destruction cost rate are significantly lower and more consistent compared to the results obtained by SPECO method.

A comparative assessment of SPECO and MOPSA on costing of exergy destruction

This paper presents the comparison of specific exergy costing (SPECO) and modified productive structure analysis (MOPSA) method to test their abilities on costing of exergy destruction. MOPSA method is applied to a combined supercritical CO2 regenerative cycle and organic Rankine cycle using zeotropic mixtures for gas turbine waste heat recovery system. The results obtained with applying SPECO method to the system are taken from literature. The exergy destruction cost rate of overall system is obtained to be $86.08/h and $1,113.13/h for MOPSA and SPECO methods, respectively. The exergoeconomic factor of overall system is found to be 31.88% for SPECO method, while this value is found to be 85.82% for MOPSA method. The obtained results with applying MOPSA method for exergy destruction cost rate are significantly lower and more consistent compared to the results obtained by SPECO method.

Thermodynamic and economic investigation of an ionic liquid as a new proposed geothermal fluid in different organic Rankine cycles for energy production

Organic Rankine cycle (ORC) is a promising technology for electricity generation by utilizing heat sources at low to moderate temperatures. In the present work, an ionic liquid (1-butylpyridinium tetrafluoroborate, C9H14NBF4), a known green chemical and non-volatile compound with good thermal and chemical stability, and significant heat capacity are utilized as a geothermal fluid. Simulation and optimization were conducted for a basic ORC, a regenerative organic Rankine cycle (RORC) and a two-stage evaporative organic Rankine cycle (TSORC) by maximizing exergy efficiency and minimizing specific investment cost. The operating parameters considered in the optimization exercise were evaporative and regenerative temperatures, pinch point temperature difference of evaporators and the degree of superheat. Peng Robinson equation of state was used and isobutane (R-600a) and butane (R-600) were selected as working fluids. Comparisons were made between the performance of ORCs when C9H14NBF4 and water were individually used as a geothermal fluid. Utilization of an ionic liquid improved the performance of the three ORC configurations with the best performance generated from a basic ORC with exergy efficiency of 82.35% (R-600) and 87.70% (R-600a). From an economic viewpoint, the amount of specific investment cost (SIC) is comparatively lower when ionic liquid is used as a geothermal fluid.

Thermoeconomic Optimization with PSO Algorithm of Waste Heat Recovery Systems Based on Organic Rankine Cycle System for a Natural Gas Engine

To contribute to the economic viability of waste heat recovery systems application based on the organic Rankine cycle (ORC) under real operation condition of natural gas engines, this article presents a thermoeconomic optimization results using the particle swarm optimization (PSO) algorithm of a simple ORC (SORC), regenerative ORC (RORC), and double-stage ORC (DORC) integrated to a GE Jenbacher engine type 6, which have not been reported in the literature. Thermoeconomic modeling was proposed for the studied configurations to integrate the exergetic analysis with economic considerations, allowing to reduce the thermoeconomic indicators that most influence the cash flow of the project. The greatest opportunities for improvement were obtained for the DORC, where the results for maximizing net power allowed the maximum value of 99.52 kW, with 85% and 80% efficiencies in the pump and turbine, respectively, while the pinch point temperatures of the evaporator and condenser must be 35 and 16 °C. This study serves as a guide for future research focused on the thermoeconomic performance optimization of an ORC integrated into a natural gas engine.

Thermal and economic assessment of organic Rankine cycles for waste heat recovery in cement plants

This work aimed to investigate the thermodynamic and economic performance of simple and regenerative organic Rankine cycles (ORCs) working under subcritical and subcritical conditions, with superheating operating conditions. These were used in waste heat recovery (WHR) in Brazilian cement factories with clinker productive capacities from (3000 to 6300) ton/d. After selecting the most appropriate organic fluids, the cycles were modelled in terms of their thermodynamic and economic properties using Engineering Equation Solver (EES) software. The key operating parameters of the cycles were optimized using the same software via the genetic algorithm method. The results show that the organic fluids with highest performance from the point of view of their net power output, thermal and exergy efficiencies were R141b, R11, and R123. For all the cycles analysed, the payback period was less than two years, the net present value varied from 130 to 170 million reais, and the internal rate of return exceeded 80%/year. In addition, the proposed ORCs were able to produce around (4000–9000) kW (or ~80 MW for the cement sector of the Minas Gerais state in Brazil, thus eliminating the production of 221,069 kgCO2/year), and had to reach specific costs of investment and specific electricity generation costs ranging from (2250 to 4300) R$/kW and (0.09–0.11) R$/kWh, respectively. Based on the obtained results, we can conclude that the proposed ORCs for WHR in the Brazilian cement industry are environmentally interesting and extremely competitive in terms of their financial and technical properties.

Identification of key affecting parameters of zeotropic working fluid on subcritical organic Rankine cycle according limiting thermodynamic cycle

Attributing to the research on key parameters analysis and working fluid selection, this paper attempted to propose a quantitative method for the performance of zeotropic working fluids used in subcritical organic Rankine cycle. Based on the graphical analysis method in temperature-entropy diagram, the limiting performances, which could be measured using limiting thermal efficiency and limiting thermodynamics perfection, of 4 typical zeotropic working fluids used in simple and regenerative organic Rankine cycle were proposed and calculated. The key affecting parameters and variation mechanism were analyzed as well. The results show that the limiting thermal efficiency of simple organic Rankine cycle increases with the increasing of latent heat of vaporization in both evaporation and condensation process, slope of working fluid saturated liquid line and the decreasing of temperature glide in both evaporation and condensation process, specific heat capacity of liquid working fluid at constant pressure. In addition to the impact of temperature glide in condensation process on limiting thermal efficiency of regenerative organic Rankine cycle, which should be determined according to specific working fluid, the impact of other parameters on limiting thermal efficiency of regenerative organic Rankine cycle is the same as that of simple organic Rankine cycle. The quantitative description of the limiting performance of zeotropic working fluid is of great significance to the analysis and improvement of cycle performance with an in-depth understanding on mechanism and could guide the selection or design of zeotropic working fluid.

Preliminary experimental comparison and feasibility analysis of CO2/R134a mixture in Organic Rankine Cycle for waste heat recovery from diesel engines

This paper presents results of a preliminary experimental study of the Organic Rankine Cycle (ORC) using CO2/R134a mixture based on an expansion valve. The goal of the research was to examine the feasibility and effectiveness of using CO2 mixtures to improve system performance and expand the range of condensation temperature for ORC system. The mixture of CO2/R134a (0.6/0.4) on a mass basis was selected for comparison with pure CO2 in both the preheating ORC (P-ORC) and the preheating regenerative ORC (PR-ORC). Then, the feasibility and application potential of CO2/R134a (0.6/0.4) mixture for waste heat recovery from engines was tested under ambient cooling conditions. Preliminary experimental results using an expansion valve indicate that CO2/R134a (0.6/0.4) mixture exhibits better system performance than pure CO2. For PR-ORC using CO2/R134a (0.6/0.4) mixture, assuming a turbine isentropic efficiency of 0.7, the net power output estimation, thermal efficiency and exergy efficiency reached up to 5.30 kW, 10.14% and 24.34%, respectively. For the fitting value at an expansion inlet pressure of 10 MPa, the net power output estimation, thermal efficiency and exergy efficiency using CO2/R134a (0.6/0.4) mixture achieved increases of 23.3%, 16.4% and 23.7%, respectively, versus results using pure CO2 as the working fluid. Finally, experiments showed that the ORC system using CO2/R134a (0.6/0.4) mixture is capable of operating stably under ambient cooling conditions (25.2–31.5 °C), demonstrating that CO2/R134a mixture can expand the range of condensation temperature and alleviate the low-temperature condensation issue encountered with CO2. Under the ambient cooling source, it is expected that ORC using CO2/R134a (0.6/0.4) mixture will improve the thermal efficiency of a diesel engine by 1.9%.