Analysis Of Organic Rankine Cycle Research Articles

Analysis of the Properties of Working Substances for the Organic Rankine Cycle based Database “REFPROP”

The object of the study are substances that are used as a working fluid in systems operating on the basis of an organic Rankine cycle. The purpose of research is to find substances with the best thermodynamic, thermal and environmental properties. Research conducted on the basis of the analysis of thermodynamic and thermal properties of substances from the base “REFPROP” and with the help of numerical simulation of combined-cycle plant utilization triple cycle, where the lower cycle is an organic Rankine cycle. Base “REFPROP” describes and allows to calculate the thermodynamic and thermophysical parameters of most of the main substances used in production processes. On the basis of scientific publications on the use of working fluids in an organic Rankine cycle analysis were selected ozone-friendly low-boiling substances: ammonia, butane, pentane and Freon: R134a, R152a, R236fa and R245fa. For these substances have been identified and tabulated molecular weight, temperature of the triple point, boiling point, at atmospheric pressure, the parameters of the critical point, the value of the derivative of the temperature on the entropy of the saturated vapor line and the potential ozone depletion and global warming. It was also identified and tabulated thermodynamic and thermophysical parameters of the steam and liquid substances in a state of saturation at a temperature of 15 °C. This temperature is adopted as the minimum temperature of heat removal in the Rankine cycle when working on the water. Studies have shown that the best thermodynamic, thermal and environmental properties of the considered substances are pentane, butane and R245fa. For a more thorough analysis based on a gas turbine plant NK-36ST it has developed a mathematical model of combined cycle gas turbine (CCGT) triple cycle, where the lower cycle is an organic Rankine cycle, and is used as the air cooler condenser. Air condenser allows stating material at a temperature below 0 °C. Calculation of the parameters of all substances in the model are based on a base “REFPROP”. Numerical investigations on this model showed that the highest net efficiency will be at work on pentane. Butane and R245fa have the same net efficiency, for 0.8% lower than pentane. Ammonia has a net efficiency of 2.5% is lower than pentane. CCP net efficiency strongly depends on the condensation temperature of the substance, as for pentane at lower temperature of condensation at 10 °C it is increased by 1%.

Efficiency analysis of organic Rankine cycle with internal heat exchanger using neural network

In this study, artificial neural network (ANN) has been used for efficiency analysis of the organic Rankine cycle with internal heat exchanger (IHEORC) using refrigerants R410a, R407c which do not damage to ozone layer. It is well known that the evaporator temperature, condenser temperature, subcooling temperature and superheating temperature affect the thermal efficiency of IHEORC. In this study, thermal efficiency is estimated depending on the above temperatures. The results of ANN are compared with actual results. The coefficient of determination values obtained when the test set were used to the networks were 0.99946 and 0.999943 for the R410a and R407c respectively which is very satisfactory.

Performance analysis of organic Rankine cycles using different working fluids

Low-grade heat from renewable or waste energy sources can be effectively recovered to generate power by an organic Rankine cycle (ORC) in which the working fluid has an important impact on its performance. The thermodynamic processes of ORCs using different types of organic fluids were analyzed in this paper. The relationships between the ORC?s performance parameters (including evaporation pressure, condensing pressure, outlet temperature of hot fluid, net power, thermal efficiency, exergy efficiency, total cycle irreversible loss, and total heat-recovery efficiency) and the critical temperatures of organic fluids were established based on the property of the hot fluid through the evaporator in a specific working condition, and then were verified at varied evaporation temperatures and inlet temperatures of the hot fluid. Here we find that the performance parameters vary monotonically with the critical temperatures of organic fluids. The values of the performance parameters of the ORC using wet fluids are distributed more dispersedly with the critical temperatures, compared with those of using dry/isentropic fluids. The inlet temperature of the hot fluid affects the relative distribution of the exergy efficiency, whereas the evaporation temperature only has an impact on the performance parameters using wet fluid.

Energy analysis of Organic Rankine Cycles for biomass applications

The present paper aims at analysing the performances of Organic Rankine Cycles (ORCs) adopted for the exploitation of the biomass resulting from the pruning residues in a 3000 hectares district in Southern Italy. A parametric energy analysis has been carried out to define the influence of the main plant operating conditions. To this purpose, both subcritical and transcritical power plants have been examined and saturated and superheated conditions at the turbine inlet have been imposed. Moreover, the effect of the working fluid, condensation temperature, and internal regeneration on system performances has been investigated. The results show that ORC plants represent an interesting and sustainable solution for decentralised and small-scale power production. Furthermore, the analysis highlights the significant impact of the maximum temperature and the noticeable effect of internal regeneration on the performances of the biomass power plants.

Minimisation of exergy losses in mono high pressure nitric acid process

Nitric acid production plant is self-sufficient in energy. It is a net exporter of energy. But its exergy efficiency is very low. Turbocompressor, which utilises work produced by recovered heat, is used to maintain pressure in the process. Large amount of heat is taken out from cooler condenser by using cooling tower water. In this paper, energy and exergy analysis of mono high pressure nitric acid process is carried out. Both turbocompressor and cooler condenser are accounting to 33.28% of total exergy destruction. An attempt has been made to reduce exergy losses in both equipments by using a practical approach. Heat available in cooler condenser is recovered by using the organic Rankine cycle (ORC) within available practical limits of the plant. Exergy analysis of ORC shows that 42% of the losses in cooler condenser are reduced.

LNG 냉열을 열싱크로 이용하는 유기랭킨사이클(ORC)의 작동유체에 따른 성능 특성

This paper presents thermodynamic performance analysis of organic Rankine cycle (ORC) using low temperature heat source in the form of sensible energy and using liquefied natural gas (LNG) as heat sink to recover the cryogenic energy of LNG. LNG is able to condense the working fluid at a very low condensing temperature in a heat exchanger, which leads to an increased power output. Based on the mathematical model, a parametric analysis is conducted to examine the effects of eight different working fluids, the turbine inlet pressure and the condensation temperature on the system performance. The results indicate that the thermodynamic performance of ORC such as net work production or thermal efficiency can be significantly improved by the LNG cold energy.

Preliminary analysis of organic Rankine cycles to improve vehicle efficiency

This paper presents the background rationale and key findings for a model-based study of supercritical waste heat recovery organic Rankine cycles. The paper’s objective is to cover the necessary groundwork to facilitate the future operation of a thermodynamic organic Rankine cycle model under realistic thermodynamic boundary conditions for performance optimisation of organic Rankine cycles. This involves determining the type of power cycle for organic Rankine cycles, the circuit configuration and suitable boundary conditions. The study focuses on multiple heat sources from vehicles but the findings are generally applicable, with careful consideration, to any waste heat recovery system. This paper introduces waste heat recovery and discusses the general merits of organic fluids versus water and supercritical operation versus subcritical operation from a theoretical perspective and, where possible, from a practical perspective. The benefits of regeneration are investigated from an efficiency perspective for selected subcritical and supercritical conditions. A simulation model is described with an introduction to some general Rankine cycle boundary conditions. The paper describes the analysis of real hybrid vehicle data from several driving cycles and its manipulation to represent the thermal inertia for model heat input boundary conditions. Basic theory suggests that selecting the operating pressures and temperatures to maximise the Rankine cycle performance is relatively straightforward. However, it was found that this may not be the case for an organic Rankine cycle operating in a vehicle. When operating in a driving cycle, the available heat and its quality can vary with the power output and between heat sources. For example, the available coolant heat does not vary much with the load, whereas the quantity and quality of the exhaust heat varies considerably. The key objective for operation in the vehicle is optimum utilisation of the available heat by delivering the maximum work out. The fluid selection process and the presentation and analysis of the final results of the simulation work on organic Rankine cycles are the subjects of two future publications.

Parametric optimization and range analysis of Organic Rankine Cycle for binary-cycle geothermal plant

In this study, a thermodynamic model of Organic Rankine Cycle (ORC) system combined with orthogonal design is proposed. The comprehensive scoring method was adopted to obtain a comprehensive index to evaluate both of the thermodynamic performance and economic performance. The optimal level constitution of system parameters which improves the thermodynamic and economic performance of ORC system is provided by analyzing the result of orthogonal design. The range analysis based on orthogonal design is adopted to determine the sensitivity of system parameters to the net power output of ORC system, thermal efficiency, the SP factor of radial inflow turbine, the power decrease factor of the pump and the total heat transfer capacity. The results show that the optimal level constitution of system parameters is determined as the working fluid of R245fa, the super heating temperature of 10°C, the pinch temperature difference in evaporator and condenser of 5°C, the evaporating temperature of 65°C, the isentropic efficiency for the pump of 0.75 and the isentropic efficiency of radial inflow turbine of 0.85. The order of system parameters’ sensitivity to the comprehensive index of orthogonal design is evaporating temperature>isentropic efficiency of radial inflow turbine>the working fluid>the pinch temperature difference of the evaporator and the condenser>isentropic efficiency of cycle pump>the super heating temperature. This study provides useful references for selecting main controlled parameters in the optimal design of ORC system.

Thermodynamic Analysis of ORC for Energy Production from Geothermal Resources

This study concerns a thermodynamic analysis of Organic Rankine Cycles for energy conversion from geothermal resources. A numerical flow-chart tool based on a lumped parameters approach is adopted to compute values of thermodynamic variables during each transformation composing the cycle. The equation of state is expressed by the Peng-Robinson formulation. The different plant components are outlined by single blocks, linked each other by connections through balance equations. Analyses are carried-out considering two working fluids (isopentane and isobutane). Results are obtained for several sets of operating parameters, such as the evaporation and condensation pressure for the working fluid, the mass flow rate of the geothermal fluid and the cooling water temperature. From results, thermodynamic cycles are built-up in the T-s plan, allowing to quantify effectiveness and energy benefit related to the investigated functional scenarios.

Performance analysis of organic Rankine cycle based on location of heat transfer pinch point in evaporator

The location of heat transfer pinch point in evaporator is the base of determining operating parameters of organic Rankine cycle (ORC). The physical mathematical model seeking the location of pinch point is established, by which, the temperature variations both of heat source and working fluid with UA can be obtained. Taking heat source with inlet temperature of 160 °C as example, the matching potentials between heat source and working fluid are revealed for subcritical and supercritical cycles with the determined temperature difference of pinch point. Thermal efficiency, exergy efficiency, work output per unit area and maximum work outputs are compared and analyzed based on the locations of heat transfer pinch point either. The results indicate that supercritical ORC has a better performance in thermal efficiency, exergy efficiency and work output while outlet temperature of heat source is low. Otherwise, subcritical performs better. Small heat transfer coefficient results in low value of work output per unit area for supercritical ORC. Introduction of IHX may reduce the optimal evaporating pressure, which has a great influence on heat source outlet temperature and superheat degree. The analysis may benefit the selection of operating parameters and control strategy of ORC.

Performance Analysis of Organic Rankine Cycle With Preliminary Design of Radial Turbo Expander for Binary-Cycle Geothermal Plants

In order to produce less emission of greenhouse gases, many studies have been done on the binary-cycle geothermal power plant to obtain better performance. The radial turbo expanders play an important role in the performance of the organic rankine cycle (ORC) for binary-cycle geothermal plants. However, few studies have investigated the effect of parameters of radial turbo expanders on the performance of the ORC. In this paper, a new thermodynamic model of the ORC coupled with the preliminary design of radial turbo expanders is developed. The effects of geothermal water temperature on the ORC performance parameters, such as power output and thermal efficiency are investigated by using the proposed thermodynamic model. The variation of radial turbo expanders’ parameters, such as specific rotational speed with geothermal water temperature is revealed. In the present study, the reasonable efficiency of radial turbo expanders by using the preliminary design is adopted to analyze the performance of the ORC, and an accurate reference about the effect of geothermal source on the parameters of radial turbo expanders is obtained.

Improved analysis of Organic Rankine Cycle based on radial flow turbine

With attention to the drawback of specifying isentropic efficiency of expander (or turbine) in Organic Rankine Cycle (ORC) analysis, in order to enhance reliability of analysis results, this article replaces the constant isentropic efficiency by internal efficiency of optimal radial flow turbine for each condition. With both analysis methods, namely internal efficiency analysis method and conventional analysis method, 14 subcritical ORC working fluids are studied with hot water of 90 °C, pinch point temperature of 5 °C and condensing temperature of 30 °C. Results with both analysis methods are compared. The results show that turbine internal efficiency is determined by expansion ratio in rotor and decreases with the rise of expansion ratio in rotor. There are differences between cycle net power output with internal efficiency analysis method and that with conventional analysis method. The differences can change the results in optimizing fluid. It is significant to apply computational optimal efficiency instead of constant isentropic efficiency in ORC analysis.

Cost-effectiveness performance analysis of organic Rankine cycle for low grade heat utilization coupling with operation condition

This paper analyzed the influence of working fluids selection and operation conditions on the cost-effectiveness performance and net power output of an ORC for low grade heat utilization. A net power output model has been proposed theoretically and compared with the theoretical data calculated from thermodynamic analysis, exhibiting excellent agreements with the theoretical data. The proposed net power output model theoretically indicates that Jacob number and the ratio of evaporating temperature and heat rejected temperature play essential roles in discriminating the net power output among various working fluids at the same operation condition. For a given condensing and evaporating temperature, it can be concluded theoretically that fluid with low Jacob number will show attractive performance in an ORC. The maximum net power output is determined by the heat source rather than working fluids with a low inlet temperature of heat source. Cost-effectiveness performance analysis reveals that the maximum net power output and the best CEP cannot be achieved at the same time and compromise must be made when choosing the most suitable organic working fluids in different ORC designs.

Construction and preliminary test of a low-temperature regenerative Organic Rankine Cycle (ORC) using R123

Higher efficiencies and optimal utilization of geothermal energy require a careful analysis of Organic Rankine Cycle (ORC) which is suitable for converting electric power from low-temperature heat sources. The objective of this study is to experimentally analyze the effect of varying working fluid mass flow rate and the regenerator on the efficiency of the regenerative ORC operating on R123. As R123 presents a low boiling point temperature (27.82 °C), a technology was invented to address the leakage issue when transferring R123 between the inside and outside of the regenerative ORC system. A specially manufactured throttle valve was adopted in the bypass subsystem to protect the turbine during the starting and closing processes and a novel phenomenon was discovered during the test. A preliminary test of the system was conducted with a geothermal source temperature of 130 °C. The experimental results show that the power output is 6 kW and the regenerative ORC efficiency is 7.98%, which is higher than that of the basic ORC by 1.83%.

Exergy Analysis of Organic Rankine Cycle with Internal Heat Exchanger

 Abstract—In recent years Organic Rankine Cycle (ORC) has become a field of intense research and appears a promising technology for conversion of heat into useful work or electricity. In this work thermodynamic performance of ORC with internal heat exchanger is comparatively assessed for various working fluids based on the second law of thermodynamics. Special attention is paid to the effect of turbine inlet pressure on the exergy destructions (anergies) at various system components and the exergy efficiency of system. Results show that for a given source the component at which the greatest anergy occurs differs with working fluid. As turbine inlet pressure increases, exergy efficiency increases for working fluid such as ammonia or R22, but decreases for working fluid with low critical pressure such as iso-pentane or n-pentane.

Energy and exergy-based working fluid selection for organic Rankine cycle recovering waste heat from high temperature solid oxide fuel cell and gas turbine hybrid systems

SUMMARY This paper performed a comparative analysis of organic Rankine cycle (ORC) using different working fluids, in order to recover waste heat from a solid oxide fuel cell-gas turbine hybrid power cycle. Depending on operating parameters, criteria for the choice of the working fluid were identified. Results reveal that due to a significant temperature glide of the exhaust gas, the actual ORC cycle thermal efficiency strongly depends on the turbine inlet temperature, exhaust gas temperature, and fluid's critical point temperature. When exhaust gas temperature varies in the range of 500 K to 600 K, R123 is preferred among the nine dry typical organic fluids because of the highest and most stabilized mean thermal efficiency under wide operating conditions and its reasonable condensing pressure and turbine outlet specific volume, which in turn results in a feasible ORC cycle for practical concerns. Copyright © 2012 John Wiley & Sons, Ltd.

Non-conventional combined cycle for intermediate temperature systems

SUMMARY This work presents a non-conventional combined cycle comprising a topping supercritical Brayton cycle working with carbon dioxide (S-CO2) and a bottoming organic Rankine cycle (ORC). As shown by previous authors in the field of nuclear energy, carbon dioxide cycles are characterised by lower turbine inlet temperatures (around 1100 K) than conventional gas turbines, and they usually incorporate a highly efficient recuperative heat exchanger in order to increase system efficiency. Accordingly, temperatures of around 200 °C are achieved at the outlet of the recuperator, hence leaving a certain amount of heat at the disposal of a bottoming cycle. Presently, ORCs are the most appropriate commercially available technology for such low temperature heat recovery. In this paper, an analysis of ORCs with different organic fluids is presented. Initially, only pure substances are considered. Then, the performance of the same cycle working with mixtures of hydrocarbons is assessed finding a 7 percentage point improvement in global efficiency with respect to the stand-alone topping cycle when the bottoming system (heat recovery unit and ORC) is incorporated. Following this interesting result, the performance of a S-CO2-ORC, a conventional gas turbine and ORC and an ORC–ORC combined cycles are evaluated for a tower-type central receiver Concentrating Solar Plant. Isopentane (the optimum pure substance obtained in the analysis mentioned earlier) is used in all cases for the bottoming system, showing favourable results for the proposed combined cycle configuration. Additionally, a discussion about the most relevant techno-economic concerns is presented at the end of the work showing that complementary economic benefits must be expected because of the lower footprint of the heat transfer equipments when carbon dioxide is used. These positive features derive from the more interesting transport properties of carbon dioxide when it is used at very high pressure, what also contributes to reducing the size of turbomachinery by decreasing their volumetric flows. In summary, the work presents a very interesting proposal, both thermodynamically and economically, to be used in intermediate temperature systems even if this technology is not mature yet. Copyright © 2012 John Wiley & Sons, Ltd.

Thermodynamic analysis of Organic Rankine Cycle with Ejector

The low efficiency of Organic Rankine Cycle (ORC) with low-grade heat source (LGHS) has limited its use in industry. In order to increase the power output capacity and its efficiency, an Organic Rankine Cycle with Ejector (EORC) was proposed in this paper. In the EORC, an ejector and a second-stage evaporator were added to the ORC. The vapor from the second-stage evaporator worked as the primary fluid for the ejector, to suck the exhaust from the expander so as to decrease the expander backpressure and increase the pressure difference through the expander, which resulted in an increase of the power output capacity. A Double Organic Rankine Cycle (DORC) was also introduced in order to analyze and compare the EORC with the ORC and DORC in the thermal performance. The output capacity was increased by EORC and DORC compared to the ORC. The thermal performance of DORC was superior to EORC, but another expander-generator and its auxiliary equipments were required for the DORC led to increase the investment and operation management compared to the EORC.

Energy efficiency analysis of Organic Rankine Cycles with scroll expanders for cogenerative applications

Small scale Organic Rankine Cycle (ORC) systems has been the object of a large number of studies in the last decade, because of their suitability for energy recovery and cogenerative applications.The paper presents an ORC numerical model and its applications to two different case studies; the code has been obtained by combining a one-dimensional model of a scroll machine and a thermodynamic model of a whole ORC system. Series production components, such as scroll compressors, from HVAC field, have been first considered in order to reduce costs, because this is a critical issue for small scale energy recovery and cogeneration systems. The detailed model of the scroll machine is capable to calculate the performances of both a compressor and an expander, as function of the geometry of the device and of the working fluid. The model has been first tested and validated by comparing its outputs with experimental tests on a commercial scroll compressor, then used to calculate the working curves of commercial scroll machines originally designed as compressors in the HVAC field, but operating as expanders. The model of the expander has been then integrated in the thermodynamic model of the ORC system.A series of comparisons have been carried out in order to evaluate how the performances are influenced by cycle parameters, scroll geometry and working fluid for different applications. The results confirm the feasibility of small scale CHP systems with acceptable electrical efficiency, taking into account the low-temperature thermal source, the small power output and the low-cost series production components employed.

Optimization design and exergy analysis of organic rankine cycle in ocean thermal energy conversion

Performance analytical function and exergy efficiency of organic rankine cycle (ORC) in ocean thermal energy conversion (OTEC) are derived and optimized in this paper. Firstly, the state function corresponding to every point in ORC and depending strongly on the temperature of the evaporator and condenser is successfully achieved, where the suitable working fluids include, but not limited to, ammonia, r134a, etc. And then the system net power output function is achieved based on the characteristics of the ORC, which is mainly decided by the warm seawater temperature, warm seawater mass flow rate, evaporator temperature, condenser temperature, etc. After that, a further optimization is carried out to maximize the net power output of ORC. Results show that ammonia is a good choice for ORC utilized in OTEC from net power output viewpoint. In addition, thermal efficiency and exergy efficiency at maximum net power output are also given as reference. Finally, the preliminary design criteria of ORC in OTEC illustrates that the design of the ORC in a certain scale should choose its corresponding reasonable heat exchanger since it is a choke point for the larger maximum net power output.