Fluid In Organic Rankine Cycle Research Articles

Exergo-economic analysis of different power-cycle configurations driven by heat recovery of a gas engine

In the present work a 34.3 kW stationary gas engine considered as prime-mover of bottoming thermodynamic cycles. The waste heat recovery cycles of engine exhaust gas consist of several configurations of organic Rankine cycle and combination of Rankine/Kalina cycles, also the engine jacket water heat is recovered by trilateral flash cycle. The performance of bottoming cycles was investigated from thermodynamic and thermo-economic points of view. For the organic Rankine cycle, three fluids including Benzene, Toluene and Cyclohexane have been compared. Also, considering that the trilateral flash cycle is a suitable cycle for heat recovery from a low temperature heat source due to its better matching between the temperature profiles of cycle working fluid and heat source fluid, this cycle is considered as bottoming waste heat recovery cycle for engine jacket water. In order to compare different working fluids and cycle configurations, three objective functions including energy efficiency, exergy efficiency and specific investment cost for the 18 studied cases are compared. The results reveal that, energy, exergy efficiency and specific investment cost of all configurations with toluene as working fluid of organic Rankine cycle is the highest and least compared to the other working fluids, respectively. But for configuration Rankine with Open Feed Heater-Kalina-Trilateral Flash Cycle, benzene fluid is better in terms of specific investment cost, however the energy and exergy efficiency of this cycle is also maximal with toluene fluid. Also, the results depict that configurations Rankine with Internal Heat exchanger – Trilateral Flash Cycle and Rankine with Open Feed Heater_Kalina_Trilateral Flash Cycle thermodynamically, and configurations Rankine with Internal Heat exchanger – Trilateral Flash Cycle and Rankine with Open Feed Heater – Trilateral Flash Cycle exergo-economically show the better performance. In this regard, employing configurations Rankine with Internal Heat exchanger – Trilateral Flash Cycle, Rankine with Open Feed Heater-Kalina – Trilateral Flash Cycle and Rankine with Open Feed Heater – Trilateral Flash Cycle in base mode leads to 6.85 kW, 6.48 kW and 6.54 kW increment in net power produced imposing 3318 $/kW, 4090 $/kW and 3377 $/kW specific investment cost, respectively.

Design of steam condensation temperature for an innovative solar thermal power generation system using cascade Rankine cycle and two-stage accumulators

An innovative solar thermal power generation system using cascade steam-organic Rankine cycle (SORC) and two-stage accumulators has recently been proposed. This system offers a significantly higher heat storage capacity than conventional direct steam generation (DSG) solar power plants. The steam condensation temperature (T2) in the proposed system is a crucial parameter because it affects the SORC efficiency (ηSORC) in normal operations and the power conversion of the bottoming organic Rankine cycle (ORC) in the unique heat discharge process. The present study develops a methodology for the design of T2 with respect to a new indicator, that is, the equivalent heat-to-power efficiency (ηeq). ηeq is a compromise between the efficiencies in different operation modes. The effects of main steam temperature (T1), Baumann factor (a), mass of storage water (Mw), and ORC working fluid on T2 are investigated. Results show that ηeq is a better indicator than ηSORC. The optimum steam condensation temperature (T2,opt) that corresponds to the maximum ηeq (ηeq,max) is generally higher than that based on the maximum ηSORC. T2,opt reduces as T1, a, and Mw decrease. ηeq,max rises with the increment of T1 and the decrement of a and Mw. Pentane is a more preferable ORC fluid than benzene and R245fa. The T2,opt and ηeq,max of pentane are, respectively, 139–190 °C and 20.93%-24.24%, provided that T1 ranges between 250 °C and 270 °C, a varies from 0.5 to 1.5, and Mw changes from 500 ton to 1500 ton.

Second-law-based screening of working fluids for medium-low temperature organic Rankine cycles (ORCs): Effects of physical and chemical properties

Abstract The diversity of both organic fluids and performance criteria makes the selection and evaluation of working fluids for organic Rankine cycles (ORCs) full of challenge. To overcome this challenge, this paper first reports on second-law-based analytical expressions for thermal efficiency and a turbine size parameter, which reveal key dimensionless parameters relating to operating temperatures and thermodynamic properties of organic fluids. This paper systematically screens more than 70 working fluids involving a wide range of physical and chemical properties. This study shows that specific turbine size generally increases with critical temperature, reduced ideal gas heat capacity, and the atom number of working fluids. Different-family fluids may lead to ten-fold relative differences in specific turbine size even though they have the same atom numbers. The thermal efficiency of ORCs appears to be independent of critical temperature, or at most, a weak function of critical temperature for low boiling point wet fluids and other halocarbons. This is a result of Jacob number being independent of or dependent weakly on the critical temperature of organic fluids such as alkanes, alkenes, and benzenes.

How to give a full play to the advantages of zeotropic working fluids in organic Rankine cycle (ORC)

Improving the efficiency of organic Rankine cycle (ORC) is the ultimate goal of the researchers with thermodynamic background. As the “blood” of ORC, the working fluid plays a vital role to the improvement of the performance. The thermos-physical properties parameters, transport parameters and other parameters of working fluids could directly affect the efficiency, safety, stability and economy of ORC. With the increasing requirements on working fluids, it is difficult to find a pure working fluid not only with satisfied thermodynamic performance but also permissible enverimental protection and safety. In contrast, zeotropic working fluid, which is mixed with two or more pure working fluids, is easier to meet the requirements of thermos-physical properties, environmental and safety. But at the present stage, the application of zeotropic working fluids in ORC still adapted or employed the methodology originated from what we learn from pure working fluids. Under such circumstances, the temperature glide of zeotropic working fluids improves system efficiency while the composition shift would in turn reduce system efficiency. Thus, 3D-ORC is proposed in this paper to provide zeotropic working fluids a full play on performance improvement of energy conversion. The performance of 3D-ORC is calculated for the recovery of waste heat of internal combustion engines and compared with the simple ORC using pure and zeotropic working fluids. The results show that the performance of 3D-ORC is better than simple ORC under the same conditions.

A Simple Method of Finding New Dry and Isentropic Working Fluids for Organic Rankine Cycle

One of the most crucial challenges of sustainable development is the use of low-temperature heat sources (60–200 °C), such as thermal solar, geothermal, biomass, or waste heat, for electricity production. Since conventional water-based thermodynamic cycles are not suitable in this temperature range or at least operate with very low efficiency, other working fluids need to be applied. Organic Rankine Cycle (ORC) uses organic working fluids, which results in higher thermal efficiency for low-temperature heat sources. Traditionally, new working fluids are found using a trial-and-error procedure through experience among chemically similar materials. This approach, however, carries a high risk of excluding the ideal working fluid. Therefore, a new method and a simple rule of thumb—based on a correlation related to molar isochoric specific heat capacity of saturated vapor states—were developed. With the application of this thumb rule, novel isentropic and dry working fluids can be found applicable for given low-temperature heat sources. Additionally, the importance of molar quantities—usually ignored by energy engineers—was demonstrated.

Thermo-economic performance comparison of two configurations of combined steam and organic Rankine cycle with steam Rankine cycle driven by Al2O3-therminol VP-1 based PTSC

The main goal of this study is to compare thermo-economic performance of three configurations of power generation system driven by solar heat source in which nanofluid based PTSC is used. Configuration 1 presents simple steam Rankine cycle (SRC) and configuration 2 and 3 show combined SRC with organic Rankine cycle (ORC) in two different conditions. In second configuration, ORC absorbs heat from SRC condenser and in third one, ORC absorbs heat in ORC evaporator from remain heat of SRC evaporator exiting nanofluid. The effects of various parameters such as concentration of nanoparticles, SRC evaporation temperature and SRC condensation temperature are investigated on output parameters and each configuration is optimized by using 4 different organic fluids (R113, n-hexane, cyclohexane, toluene) in ORC. After parametric analysis and performance comparison in base case, components performance and comparison of various configurations are examined at optimal point. Comparison of applying organic fluids in ORC related to configurations 2 and 3 shows that toluene has the best performance. Nanoparticles concentration for all 3 configurations is equal to zero at the selected optimal point and configurations 1 and 2 have relatively similar thermo-economic performance. Configuration 3 has the most net power output (4293 kW); however, it has the weakest thermo-economic performance due to the highest total cost rate (1434 $/h) and less energy and exergy efficiencies.

Energy and exergy analysis of solar energy-integrated, geothermal energy-powered Organic Rankine Cycle

In this study, the energy and exergy analysis of the solar- and geothermal energy-powered Organic Rankine Cycle was made for different system configurations and Simav geothermal field was taken into consideration for system designs. The solar collectors were integrated into the system with thermal energy storage tank. The R-600a, Therminol VP-1, and molten salt were used as a working fluid in Organic Rankine Cycle, solar field, and thermal energy storage, respectively. As a result of this study, the energy and exergy efficiencies of the geothermal-powered ORC were decreased with the integration of solar energy. But the net power output of the system was increased. The energy and exergy efficiencies of the solar energy-aided, geothermal-powered Organic Rankine Cycle increase by the decrease in the solar collector area. The energy generation of the proposed system was calculated up to 305,713.5 kWh.

A thermodynamic assessment of working fluids in ORC systems

ORC (Organic Rankine Cycle) is widely used to convert low temperature heat into electricity using organic working fluid. The performance of an ORC installation is influenced deeply by selected working fluid and operation conditions. Recently has been presented a new generation of working fluids dedicated to ORC systems. They are characterized by near zero ODP (Ozone Depletion Potential) coefficient and significantly smaller GWP (Global Warming Potential) in comparison with currently used refrigerants. This paper presents preliminary research on selected dry and isentropic ORC fluids and some peculiarities in their behaviour.

A preliminary approach to the 3D construction of thermodynamic cycle based on zeotropic working fluids

Thermodynamic cycle is one of the important ways to convert energy. Improving the efficiency of thermodynamic cycle is still an important way to promote the efficient use of energy at the present stage, and it is also the efficient way to solve the energy crisis. Organic Rankine cycle (ORC), with advantages of simple structure, less maintenance and possibility of small scales, has been widely applied for various types of source in recent years. In exiting researches, the working fluid, as the blood of ORC, is commonly considered to play a vital role in the cycle: (1) relative to ideal cycle, the actual power cycles in the engineering field cannot operate without working fluid; (2) energy efficiency, considering the analysis of second-law efficiency, of actual cycle has a significant decrease due to the introduction of working fluid. The thermos-physical properties parameters, transport parameters and other parameters of working fluid could directly affect the efficiency, safety, stability and economy of ORC. With the increasing requirements on working fluids, it is difficult to find a pure working fluid not only with satisfied thermodynamic performance but also permissible environmental protection and safety. In contrast, zeotropic working fluid, which is mixed with two or more pure working fluids, is easier to meet the requirements of thermos-physical properties, environmental and safety. But at the present stage, the application of zeotropic working fluids in ORC still adapts or employs the methodology originated from what we learn from pure working fluids, which leads to the fact that the efficiency of the ORC using zeotropic working fluids is still low. This paper takes the working fluid as the starting point and uses the characteristics of the component shift to break the limitation of the thermodynamic cycle performance of the single circulating working fluids by adding the mixing and separation processes of zeotropic working fluids. Firstly, the 3D construction method of ORC is proposed by adding the dimensionality of the zeotropic component on the basis of the transmission temperature entropy analysis. Subsequently, the 3D ORC is compared with the traditional 2D ORC, and the advantages of 3D construction of thermodynamic cycle are clearly defined: (a) analysis of variable mass system; (b) reveal the thermodynamic process of composition regulation; (c) explore new ways to reduce the loss of exergy. At last, in view of the utilization of waste heat of internal combustion engine, a component adjustable ORC is proposed, and the application and function of the 3D construction method are expounded. The preliminary exploration results are given for the advantages of the thermodynamic cycle in 3D space relative to the traditional 2D construction method.

Mixed refrigerant as working fluid in Organic Rankine Cycle for hydrogen production driven by geothermal energy

The possibility of utilizing low temperature heat source systems for producing electricity has been significant due to increasing energy demand. In this study, the Organic Rankine Cycle (ORC) integrated with proton exchange membrane (PEM) electrolyzer is analyzed thermodynamically and economically. A mixture of butane, pentane and iso-pentane is selected as working fluid. The results show that utilizing the mixed refrigerant enhances the performance of the system and results in a higher hydrogen production rate because of a glide match of temperature profiles in the heat exchangers. Economic analysis results which are helpful in designing entire the system show that the highest cost component is electrolyzer, followed by the turbine and condenser.

Thermal stability of hexamethyldisiloxane (MM) as a working fluid for organic Rankine cycle

Thermal stability of hexamethyldisiloxane (MM) as a working fluid for organic Rankine cycle

A study of working fluids for Organic Rankine Cycles (ORCs) operating across and below ambient temperature to utilize Liquefied Natural Gas (LNG) cold energy

Liquefied Natural Gas (LNG) contains significant amounts of cold exergy, which is normally wasted during regasification at receiving terminals. This paper addresses working fluid screening for Organic Rankine Cycles (ORCs) utilizing LNG cold energy. Due to the cryogenic temperature of LNG, the condensation temperature of an ORC should be far below ambient temperature, and the working fluid should be totally different from conventional ORCs operating above ambient temperature. However, the working fluids also depend on the cycle configuration and the natural gas target pressure. In this study, a simulation-based optimization framework is proposed to compare the performance of 22 candidate working fluids. The Particle Swarm Optimization (PSO) algorithm is adopted to optimize 5 and 7 dimensional search spaces for the combined systems operated across and below ambient temperature. Promising working fluids for ORCs considering the effect of natural gas target pressure are suggested based on the optimization results. The most energy efficient working fluids are R125, R143a, R290 and R1270 for ORCs operated below ambient temperature without waste heat utilization. For ORCs operated across ambient temperature utilizing flue gas waste heat from a natural gas fired power plant, R170, R134a and R290 perform better than other working fluids.

Heat recovery of nano-fluid based concentrating Photovoltaic Thermal (CPV/T) Collector with Organic Rankine Cycle

This study proposed a novel configuration of solar concentrating receivers that utilize Nano-fluids for spectral splitting and coupled with Organic Rankine Cycle (ORC) for heat recovery. 1-D modelling of a conventional Parabolic Trough Collector was performed for validation and results were in the range of ±5% of experimental data. Model was further advanced for 1-D thermal modelling of Concentrating Photovoltaic Thermal (CPV/T) and Nano-fluid Filter based CPV/T (NFCPV/T) Collectors that were coupled with ORC. Highly efficient triple-junction InGaP/InGaAs/Ge was selected as PV cells for concentrating solar system while R1233zd was chosen as working fluid for ORC. Optical modelling of water/Ag solution as Nano-fluid was integrated with overall system and performance results of CPV/T and NFCPV/T combined with ORC were compared. Comparative study of electrical (ηelectrical), thermal (ηthermal) and overall (ηoverall) efficiencies demonstrated that NFCPV/T outperformed CPV/T especially at concentration ratios greater than 7 with values of 1.8%, 3.3% and 5.1% respectively. Parametric study of input variables were conducted to identify those inputs that have most considerable influence on key outputs. DIRECT optimization of system performance (ηsystem) demonstrated that NFCPV/T coupled with ORC has markedly higher ηsystem of about 2.71% compared to CPV/T. These results highlight effectiveness of proposed NFCPV/T configuration.

Exergy and exergoeconomic evaluation of hydrogen and distilled water production via combination of PEM electrolyzer, RO desalination unit and geothermal driven dual fluid ORC

Exergy and Exergoeconomic analysis are carried out for a new hydrogen and distilled water producing system. The presented cogeneration system is the combination of geothermal driven dual fluid organic Rankine cycle (ORC), proton exchange membrane (PEM) electrolyzer and reverse osmosis (RO) desalination unit. In fact, hot geothermal water is the system input energy, which turns into power and runs the PEM electrolyzer and RO unit. Exergy analysis revealed that the ORC has the highest exergy destruction among the all main units and causes 59% of the total exergy destruction. Also, within the ORC, low pressure evaporator has the highest exergy destruction compared with other components. An increase in the geothermal water temperature resulted in a reduction in system overall exergy efficiency. Furthermore, exergoeconomic analysis showed that 56% of the total investment cost refers to the ORC. Based on the exergoeconomic analysis and considering the unit exergy cost of 1.3 $/GJ for geothermal hot water, produced hydrogen and distilled water have costs of 4.257 $/kg and 32.73 cent/m3, respectively. Moreover, the annual payback period of 5.6 years indicates that the presented system can be of interest from the viewpoint of initial investment.

A Review of Working Fluids for Organic Rankine Cycle (ORC) Applications

The organic Rankine cycle (ORC) systems are commercially employed for small scale and large scale thermal conversion to electricity of a large variety of abundant heat sources such as exhaust waste heat and some renewable energy sources where conventional steam Rankine and open-gas cycle turbine cycles cannot provide any viable, sustainable, techno-economic solution for power generation. The ORC operates the conventional steam Rankine cycle in subcritical level but can as well operate trans critical cycle while employing heavy molecular organic fluids in place of steam which makes the ORC suitable for medium and low grade heat conversion into electricity. No singular ideal fluid exists for any application and hence over 600 pure and zeotropic mixtures have been investigated by various researches for their best suitability for different applications and operating conditions based on performance characteristics such as efficiency, cost and environmental impacts. In this study a review of working fluids selection for different applications has been conducted. This study helps in identifying the possible most suitable organic fluids for various ORC applications depending on the operating conditions.

Theoretical analysis and experimental investigation of material compatibility between refrigerants and polymers

A new generation of refrigerants, the hydrofluoroolefines, has been introduced within the last years. These fluids have a significantly smaller Global Warming Potential compared to the state-of-the-art fluids, which are within the class of hydrofluorocarbons. The hydrofluoroolefines are unsaturated molecules consisting of double-bonded carbon atoms. Especially, compared to hydrofluorocarbons, which are saturated molecules, the interaction with polymers might differ. Therefore, this study investigates the compatibility between polymers and refrigerants, which are commonly used as working fluids in Organic Rankine Cycles or refrigeration units. The compatibility is evaluated due to a theoretical analysis of the relevant mechanisms of the fluid-polymer interaction and an experimental study. The investigated refrigerants are two state-of-the-art fluids, namely R245fa and R134a, as well as three next-generation refrigerants R1233zd-E, R1234yf and R1234ze-E. In addition, two blends, namely R450a and R513a, as well as a lubricant polyolester are investigated. The polymers comprise six elastomers and two thermoplastics, more specifically, two different compositions of ethylene-propylene-diene rubber, two compositions of fluororubber, chlorobutadiene rubber, nitrile-butadiene rubber, polytetrafluoroethylene and polypropylene. The material compatibility is evaluated by changes in volume, weight, Shore hardness as well as in small load hardness. Summing up, 64 different fluid-polymer combinations are tested at two different temperature levels.

Thermo-economic analysis and optimization of combined PERC - ORC - LNG power system for diesel engine waste heat recovery

In order to recover diesel engine exhaust gas waste heat, a new configuration consisting of screw expander based Partial Evaporation Rankine Cycle (PERC) combined with Organic Rankine Cycle (ORC) and Liquefied Natural Gas (LNG) power system is proposed and its performance is investigated from thermo-economic viewpoint. In studied system, a heat exchanger preparing domestic hot water is considered to recover the residual waste heat after PERC evaporator and thermo-economic performance of the system is investigated for 6 various organic fluids in ORC. Also, parametric analysis is performed to assess the effects of PERC evaporation temperature, PERC expander inlet steam quality and ORC condensation temperature on system performance. Finally, multi objective optimization is used to find the favorable performance point of system. LNG and PERC systems have a proper operation respectively from energy and exergoeconomic viewpoints. Also, ORC condenser has the highest total cost rate. System optimization results show that using isopentane fluid leads to the highest net power output and total cost rate respectively equal to 178.6 kW and 19.3 $/h and using toluene fluid leads to the lowest net power output and total cost rate that are respectively equal to 154.7 kw and 17.36 $/h.

Multi-objective optimization and exergoeconomic analysis of waste heat recovery from Tehran's waste-to-energy plant integrated with an ORC unit

Recovery of waste heat in large industrial plants is nowadays an important topic of thermal optimization. In the present study, energy, exergy, and exergoeconomic analysis of an integrated system, Tehran's waste-to-energy power plant coupled with an organic Rankine cycle (ORC), is analyzed. Parametric study of essential parameters (moisture content, pinch point temperature differences of the HROG, steam generator's superheat temperature difference, and steam turbine inlet pressure) is performed thermodynamically. The best system performance achieved using R123 as the working fluid of ORC. After implementation of the waste-heat-recovery system into the WtE plant, with R123 the energy and exergy efficiencies increase from 17.27% to 19.51% and 14.49%–16.36%, respectively. Exergy analysis reveals that the gasifier and steam generator are the main source of exergy destruction in the overall system. Additionally, the results of single-objective optimization based on maximum exergy efficiency and minimum total product unit cost were calculated. Furthermore, multi-objective optimization based on genetic algorithm using MATLAB software is implemented to find the optimum point with respect to exergy efficiency and total product unit cost as the objective functions. The exergy efficiency and total product unit cost at the optimum point, considering multi-objective optimization, are 19.61% and 24.65 $/GJ, respectively.

Process integration of organic Rankine cycle (ORC) and heat pump for low temperature waste heat recovery

Organic Rankine cycles (ORCs) have been a mature technology for low temperature waste heat utilization. However, the relatively low thermal efficiency and incomplete waste heat recovery limit the power output of ORC systems. The reason for the above two problems is that the temperature-enthalpy (T-H) profile of waste heat sources does not match well with the organic working fluid in an ORC system. Heat pumps may reinforce the match between the waste heat carrier and the organic working fluid of the ORC. The condensation heat released by a heat pump can be used to evaporate the organic working fluid during phase change. Thus, a better thermal match between waste heat and the organic working fluid in the ORC can be obtained. Due to the possibility to improve power output, the integration of an ORC and a heat pump is investigated in this study. Proper working fluids in ORCs and heat pumps are chosen simultaneously. The integration between ORCs and heat pumps presents significant power output increases for special cases and deserves to be popularized in practical applications. However, the integrated system does not always lead to an increase in power output. The integration is profitable only when the following pre-conditions are satisfied simultaneously: (a) poor thermal match between working fluid and waste heat for standalone ORC; (b) the evaporation temperature of the ORC is set appropriately; (c) the working fluid of the ORC has a small ratio of latent to sensible heat; (d) the COP of the heat pump is satisfactory. A systematic procedure to determine the optimal operating conditions of the system is proposed in this study. A case study adopted from literature demonstrates the potential benefits of the integration of heat pumps and ORCs. The results show that the net power output and the amount of waste heat recovered increase by 9.37% and 12.04% respectively.

Thermodynamic modeling and optimization of a combined biogas steam reforming system and organic Rankine cycle for coproduction of power and hydrogen

Abstract This paper aims to use waste heat of the biogas steam reforming (BSR) system for organic Rankine cycle (ORC) for simultaneous power and hydrogen production. A comprehensive thermodynamic modeling of the proposed combined system is carried out. In addition, optimization of the proposed system is conducted, using genetic algorithm (GA). Four different working fluids of R600, R245fa, R123, and R113 are used in ORC, where among all of them R600 is recommended due to its high performance and environment benefits. Using R600 as working fluid in ORC, results of the optimization demonstrated that the proposed system performs in an optimum state based on the selected objective functions when steam to carbon molar ratio, carbon dioxide to methane molar ratio, reaction pressure, reactor temperature, pump pressure ratio and pinch point temperature difference of the internal heat exchanger (IHE) are set in 2.99, 0.502, 1.004 bar, 998.85 K, 7.21 K, and 5.44 K, respectively. In this case, the optimum net output power, hydrogen production rate, energy efficiency and exergy efficiency are obtained 15.9 kW, 0.02529 kg s−1, 45.63%, and 74.89%, respectively. Moreover, the results of exergy analysis indicated that among all components, recuperator and reactor are accountable for the highest exergy destruction through the system. To better understand the effect of various parameters on performance of the system, a comprehensive parametric study of some key thermodynamic parameters on the main performance criteria is performed. It is concluded that the energy and exergy efficiencies of the combined BSR-ORC system can be increased by increasing steam to carbon molar ratio and pump pressure ratio or decreasing reaction pressure, carbon dioxide to methane molar ratio and pinch point temperature difference of the IHE.