Design Of Organic Rankine Cycle Research Articles

Optimizing waste heat recovery with organic Rankine cycles: A novel graphical approach based on Exergy-Enthalpy diagrams

The Organic Rankine Cycle (ORC) is a widely-used waste heat recovery approach, that converts low-grade heat into shaft work. This paper introduces a graphical methodology using Exergy-Enthalpy (Ex-H) diagrams, for evaluating and designing ORCs. ORC thermodynamics can be represented by approximate triangular exergy profiles without compromising accuracy. The exergy profile of the heat-absorbing process is crucial to ORC performance. Approximate triangular exergy profiles can be constructed for any ORC configuration to predict ORC performances, such as work output, exergy loss, and thermal efficiency. Furthermore, a systematic graphical approach is developed for integrating waste heat streams and ORCs, with step-by-step procedures outlined. The evolution procedure of the ORC exergy profile can determine working fluid selection and operating conditions. This visually intuitive yet scientifically rigorous tool clarifies the complex relationships between fluids, parameters, and system performance. Two case studies demonstrate the method's effectiveness, confirming it as a valuable tool for ORC design.

An Investigation of Organic Rankine Cycle (ORC) System Application for Energy Efficiency of Smart Agriculture

Organic rankine cycle (ORC) system application on smart agriculture is rather energy efficient in terms of waste heat recovery supplied by ORC. The recovered waste heat, such as from agricultural wastes, changes into the electrical energy produced by the generator of ORC cycle. This energy efficiency supplied by ORC system is crucial for smart agriculture as being not only efficient but also environment friendly which is good for green world and nature. In this study, biogas based regenerative ORC system design is explained as more efficient than simple ORC design due to its better regenerator efficiency.

Design of the Organic Rankine Cycle for High-Efficiency Diesel Engines in Marine Applications

Over the past few years, fuel prices have increased dramatically, and emissions regulations have become stricter in maritime applications. In order to take these factors into consideration, improvements in fuel consumption have become a mandatory factor and a main task of research and development departments in this area. Internal combustion engines (ICEs) can exploit only about 15–40% of chemical energy to produce work effectively, while most of the fuel energy is wasted through exhaust gases and coolant. Although there is a significant amount of wasted energy in thermal processes, the quality of that energy is low owing to its low temperature and provides limited potential for power generation consequently. Waste heat recovery (WHR) systems take advantage of the available waste heat for producing power by utilizing heat energy lost to the surroundings at no additional fuel costs. Among all available waste heat sources in the engine, exhaust gas is the most potent candidate for WHR due to its high level of exergy. Regarding WHR technologies, the well-known Rankine cycles are considered the most promising candidate for improving ICE thermal efficiency. This study is carried out for a six-cylinder marine diesel engine model operating with a WHR organic Rankine cycle (ORC) model that utilizes engine exhaust energy as input. Using expander inlet conditions in the ORC model, preliminary turbine design characteristics are calculated. For this mean-line model, a MATLAB code has been developed. In off-design expander analysis, performance maps are created for different speed and pressure ratios. Results are produced by integrating the polynomial correlations between all of these parameters into the ORC model. ORC efficiency varies in design and off-design conditions which are due to changes in expander input conditions and, consequently, net power output. In this study, ORC efficiency varies from a minimum of 6% to a maximum of 12.7%. ORC efficiency performance is also affected by certain variables such as the coolant flow rate, heat exchanger’s performance etc. It is calculated that with the increase of coolant flow rate, ORC efficiency increases due to the higher turbine work output that is made possible, and the condensing pressure decreases. It is calculated that ORC can improve engine Brake Specific Fuel Consumption (BSFC) from a minimum of 2.9% to a maximum of 5.1%, corresponding to different engine operating points. Thus, decreasing overall fuel consumption shows a positive effect on engine performance. It can also increase engine power output by up to 5.42% if so required for applications where this may be deemed necessary and where an appropriate mechanical connection is made between the engine shaft and the expander shaft. The ORC analysis uses a bespoke expander design methodology and couples it to an ORC design architecture method to provide an important methodology for high-efficiency marine diesel engine systems that can extend well beyond the marine sector and into the broader ORC WHR field and are applicable to many industries (as detailed in the Introduction section of this paper).

Compost Waste Heat to Power Organic Rankine Cycle Design and Analysis

Abstract This paper presents a feasibility study of a hybrid compost waste heat to power/Concentrating Solar Panel (CSP) green energy Organic Rankine Cycle (ORC). The power plant is baselined to operate with a duty of 24/7 on compost waste heat and utilize solar thermal energy to boost power output during the day. This paper discusses the design of the power plant, the design of a compost driven heat exchanger/boiler, compost pile thermal analysis, CSP analysis, and simulated power plant output analysis The selection of isobutane as ORC working fluid is justified herein. A Levelized Cost of Energy (LCOE) analysis was performed to ensure that the energy produced by this hybrid power plant would come at a reasonable and competitive cost. The results herein show that the hybrid power plant affords an LCOE of 4 ¢/kWh for compost operation alone and an LCOE of 10.7 ¢/kWh for compost and CSP solar energy operation. The hybrid compost/ORC power plant presented herein affords an average energy conversion efficiency of 4.3%. Centric to the operation of the compost waste heat to power plant presented herein is the correct design and selection of the heat exchanger which interfaces the compost waste heat stream to the isobutane ORC. The design and analysis of this heat exchanger as well as commercially off-the-shelf hardware to meet the specifications is given in detail herein

Machine learning for design and optimization of organic Rankine cycle plants: A review of current status and future perspectives

AbstractThe organic Rankine cycle (ORC) is widely acknowledged as a sustainable power cycle. However, the traditional approach commonly adopted for its optimal design involves sequential consideration of working fluid selection, plant configuration, and component types, before the optimization of state parameters. This way, the design process fails to achieve an optimal design in most cases, since the process relies heavily on empirical judgments. To improve the design process, researchers have been exploring lately the suitability of machine learning techniques. It is however not clear yet if data‐driven designs of ORC plants are practically viable and accurate. To bridge this gap, this article reviews literature studies in the field. Overviews were first presented on the ORC technology and machine learning modeling approaches. Next, studies that applied machine‐learning methods for the design and performance prediction of ORC plants were discussed. Furthermore, studies that focused on ORC machine learning optimizations were discussed. The artificial neural network (ANN) approach was observed as the technique most frequently applied for ORC design and optimization. Additionally, researchers agree in general that machine‐learning methods can achieve accurate results, with significant reductions of computational time and cost. However, there is the risk of using inadequate data size in the machine learning design approach, or insufficient data set training time, all of which can affect accuracy. It is hoped that this effort would spur the practical implementation of machine learning techniques in the future design and optimization of ORC plants, toward the achievement of more sustainable energy technology.This article is categorized under: Sustainable Energy > Energy Efficiency Sustainable Energy > Other Renewables

Cogeneration system based on large temperature difference heat transfer with stepwise utilization

Organic Rankine cycle (ORC) plays a critical role in systems such as waste heat recovery, cogeneration, renewable energy generation and energy storage. No matter which field ORC is applied in, the evaporator side of ORC has an extremely poor utilization of the thermal energy from heat source, resulting in the outlet temperature of hot side fluid being much higher than the inlet temperature of cold side fluid. In order to fully capitalize on the thermal energy, this study introduces the two-stage absorption heat exchanger (AHE) and integrates it into ORC to obtain an original high-efficiency cogeneration system (AHEORC-CHP), which is parametrically analyzed by constructing and operating thermo-economic model in terms of the expansion pressure ratio and working fluid of ORC, the type and flow rate of heat source, and the inlet temperature of generator in AHE. Due to the existence of pinch point temperature difference, conventional ORC design can only reduce the outlet temperature of the heat source with an inlet temperature of 130 °C to about 70 °C under the condition of ideal heat transfer. The AHEORC-CHP configuration proposed in this work can achieve a significant reduction in the final outlet temperature of waste heat source (as low as 24.69 °C) and realize heat exchange with large temperature difference and efficient utilization of the heat source. Besides, the thermoelectric efficiency and temperature effectiveness can reach 90.9% and 1.2 respectively, while the profit ratio of investment rises to 8.46. Further improving the performance of AHEORC-CHP system requires optimizing the design of the pressure in absorption heat pump (AHP) cycle as well as the concentration and flow rate of LiBr-H2O solution. This study can provide a simulation pathway for the application of two-stage AHE in ORC, and likewise for future experimental investigations.

Definition of a general performance map for single stage radial inflow turbines and analysis of the impact of expander performance on the optimal ORC design in on-board waste heat recovery applications

Small-scale Organic Rankine Cycles (ORCs) represent a promising technology for on-board waste heat recovery (WHR) from internal combustion engines (ICEs) especially in innovative long-haul trucks transport applications. Despite market leader companies have already proved its effectiveness, detailed system design procedures are scarcely available in the open literature and proposed solutions are often more simplified with respect to current industrial state-of-art. The present work describes a methodology to include within the ORC design and optimization procedure an efficiency map of the turbo-expander, retrieved exploiting a reduced-order method developed in-house. The proposed approach allows therefore to design the thermodynamic cycle considering a realistic performance of the expander and to retrieve the best cycle architectures and turbine geometry depending on heat source characteristics and active constraints. First the turbine performance is defined in general terms and investigation of its applicability to different fluids and to expansions characterized by various degrees of non-ideality is provided. Then, the methodology is applied to different WHR applications highlighting for several potential working fluids the impact of adopting turbine performance maps within the cycle optimization procedure rather than assuming constant efficiency values. Results show that the cycle configuration and the main design parameters are strongly affected by the plant size and the working fluid selection, and that the adoption of a turbine performance map is particularly valuable when dealing with small size power plants adopting high density fluids. In particular, the assumption of constant turbine efficiency may lead to the definition of thermodynamic cycles extremely far from the optimal ones (e.g. adoption of supercritical cycles rather than subcritical ones) that in turn can result in an unfeasible design of the turboexpander. Moreover, this assumption may also lead to an incorrect comparison between different candidate working fluids lacking in identify those more suitable for a specific plant size. Both those limits can be solved with the adoption of the expander performance map proposed in this work. Final results show that on board WHR ORC can reach an efficiency of at least 20% in a relatively large range of internal combustion engine size. On the contrary, the choice of the best working fluid is affected by engine size and chosen hot sources: for small available thermal power the use of complex and flammable hydrocarbons (cyclopentane, cyclohexane, toluene) is the most efficient choice while the use of low GWP non-flammable halogenated hydrocarbons (R1233zd and R245fa) becomes promising only for relatively large available thermal power.

Effects of working fluid mixtures on the exergetic sustainability of a solar-biomass organic Rankine cycle power plant

This study assessed the effects of working fluid mixtures on the exergetic sustainability of a solar-biomass organic Rankine cycle (ORC) plant. The design features of a real ORC plant operational at Ottana (Italy) were employed for analyses. Although a lot of studies exist in the literature on thermo-economic implications of mixture working fluids in ORC plants, the aspect of sustainability is often left out. The desire to bridge this gap is the key motivation for this study. Zero-dimensional models were implemented in MATLAB for the design of all the hybrid plant units. The ORC design considered as working fluids the existing pure MM, and mixtures 0.1MM/0.9MDM, 0.8MM/0.2MDM, and 0.9MM/0.1MDMselected actively from the REFPROP database. Furthermore, established off-design models were incorporated into the ORC simulations. The exergetic sustainability index (ESI), the environmental effect factor (EEF), the exergetic improvement potential rate (IP), and the exergetic recoverability ratio (RECR) were adopted as sustainability performance indicators. Additionally, the destruction factor (DF) was used to assess the effects of a working fluid mixture on the sustainability performance of the ORC at the component level. Results showed that under design conditions, the mixture 0.1MM/0.9MDM had worse ESI than pure MM by about 1.5%, while the mixtures 0.8MM/0.2MDM and 0.9MM/0.1MDM improved ESI by about 1.6% and 2%, respectively. At off-design conditions, the optimum HTF mass flow rate with the highest ESI was obtained as about 7 kg/s for all the fluids. For the HTF temperature, 260 o C was obtained as the optimum for the mixture 0.8MM/0.2MDM, and 250 o C for all the other fluids. Also, decreasing the heat sink temperature in all fluids increases linearly the system ESI. Moreover, the ORC condenser showed the highest DF of over 70% for all the fluids, and the use of the best mixture (0.9MM/0.1MDM) as the ORC working fluid would increase the condenser DF by about 2 percentage points relative to pure MM. Future studies should seek to derive a set of general criteria that would aid the selection of cycle and working fluid mixture designs in favor of sustainability.

Experimental and simulation investigation on the heat exchangers in an ORC under various heat source/sink conditions

Investigation on the operation behavior of heat exchanger under various operation conditions is essential in improving the life-span performance of an organic Rankine cycle (ORC). In the present study, the experimental study on an ORC under different heat source/sink combination conditions is conducted. A numerical simulation model and a solution procedure for the evaporator and condenser are developed and validated. Through the combination of simulation and experimental investigation, the heat transfer characteristics of the heat exchangers under various off-design conditions are achieved. The variation of heat source heat transfer coefficient (HTC), working fluid HTC, heat sink HTC, overall HTC, equivalent overall HTC, and area allocation of heat exchanger are achieved zone by zone from the developed simulation model. The correlation for the evaporation pressure and condensation pressure are developed and the simulation on the heat exchangers under conditions different to the experimental conditions are conducted. Exergy analysis is conducted to study the exergy construction allocation of heat exchangers under off-design conditions. The findings of the present study are beneficial to understand the operation behavior of the heat exchanger in the context of ORC and aid the design of ORC under varying operation conditions.

Optimal coupling design for organic Rankine cycle and radial turbine rotor using CFD modeling, machine learning and genetic algorithm

The organic Rankine cycle (ORC) as a potential technology can be used to recover low-grade waste heat. This study provides a rapid and systematic methodology to design ORC system coupling with the radial turbine rotor. Firstly, the coupled model of ORC and the radial turbine is established, and the thermodynamic and economic performance is obtained to optimize the preliminary design parameters. Then, the CFD analysis for the turbine rotor is performed to generate the databases, and the machine learning algorithms (random forest, XGBoost, decision tree, and support vector machine) are used to train the surrogate models. And finally, the optimal shape of the meridional surface is obtained to improve ORC’ power output. The results indicated that the system net power output and the cost rate at the decision point achieved 393.06 kW and 13.59 $/h, respectively. The support vector machine exhibited the highest value of R2 (coefficient of determination) among the regression algorithms. The optimized results showed a more uniform pressure distribution is founding on the suction surface of the optimized structure compared with the basic structure’s, leading to the power output was increased by 7.5 %. The findings can provide references for the rapid coupling design and optimization of ORC and the turbine.

Performance Prediction and Working Fluid Active Design of Organic Rankine Cycle Based on Molecular Structure

Working fluid selection is crucial for organic Rankine cycles (ORC). In this study, the relationship between molecular structure and ORC performance was established based on the quantitative structure–property relationship (QSPR) and working fluid parameterized model (WFPM), from which an ORC working fluid was actively designed. First, the QSPR model with four properties, namely, critical temperature (Tc), boiling point (Tb), critical pressure (pc), and isobaric heat capacity (cp0), was built. Second, the evaporation enthalpy (hvap), evaporation entropy (svap), and thermal efficiency (η) were estimated by WFPM, and the results were compared with those using REFPROP to verify the calculation accuracy of the “QSPR+WFPM” coupling model. The average absolute relative deviations of evaporation enthalpy and entropy are below 8.44%. The maximum relative error of thermal efficiency is 6%. Then, the thermodynamic performance limit of ORC and corresponding thermophysical properties of the ideal working fluid were calculated at typical geothermal source conditions. Finally, the active design of the working fluid was conducted with the ideal working fluid Tc and pc as the target. The research shows that C3H4F2 and C4H3F5 are optimal working fluids at 473.15 and 523.15 K heat sources, respectively.

Effect of cooling water flow on heat transfer performance of horizontal tube spray falling film evaporator in ORC system

Organic Rankine cycle (ORC) uses low-temperature heat source to realize thermoelectric conversion, which is an important way to realize the effective recovery and utilization of waste heat. Based on the horizontal tube spray falling film evaporator, an orc power generation system with R245fa as the circulating working medium is built to study the influence of the change of cooling water flow on the heat transfer performance of the evaporator. The results show that under the condition of constant heat source temperature, the evaporation pressure and condensation pressure first decrease and then increase with the increase of cooling water flow, while the total heat transfer coefficient outside the evaporator tube first increases and then decreases. When the cooling water flow is greater than 3100 L/h, it has little effect on the heat exchange system of the evaporator, and it is more appropriate to keep the cooling water flow at about 3100 L/h. By studying the influence of cooling water flow on the heat transfer performance of evaporator, an important experimental basis is provided for the design and optimization of ORC cooling system.

An Effective Method for Working Fluid Design of Organic Rankine Cycle

This paper addresses an effective method for the selection and design of optimal working fluids of organic Rankine cycle (ORC) based on quantitative working fluid selection rules, aiming to reduce the complexity and improve the calculation efficiency of the working fluid design model. In the proposed method, the critical properties of the optimal working fluids for the given heat sources are first explored and summarized based on the quantitative relationship obtained by existing research and simulations. Based on the concept of working fluid substitution, the critical properties of the optimal pure working fluid are then adopted to target the optimal mixture working fluid by solving a modified computer-aided molecular-mixture design (CAMD) model and the ratio r of critical pressure to critical temperature is also strictly constrained to ensure a better working fluid. The component and the composition of the mixture working fluid are, thus, determined simultaneously. Results showed that both the designed pure and mixture working fluids have better performance than the existing ones determined by the selection and design rules. The targeted mixture working fluid enables one to achieve at least similar systematic efficiency and a better exergy efficiency in ORC than pure working fluid featuring similar critical properties. The application of the proposed method and model is finally verified via a practical case study.

Waste Heat Source Profiles for Marine Application of Organic Rankine Cycle

The maritime industry will continue to see increasing regulatory requirements to reduce carbon emissions from ships’ operations. Improving the energy efficiency of ships with waste heat recovery systems based on the organic Rankine cycle (ORC) is an attractive way to meet these tightening requirements. The operational profile of a ship has a huge influence on the feasibility of installing ORC onboard as it affects the waste heat source profile from the diesel engines. However, to date, scant attention has been paid to examining the effects that the operational profile has on the marine application of ORC as it is both difficult and expensive to obtain. The present paper aims to describe a methodology that can overcome this problem by developing a generic ship speed profile that defines the ship’s operational profile. This speed profile works together with a fit-for-purpose diesel engine waste heat model to derive a waste heat source profile that is used as the input to a thermoeconomic analysis that can justify the installation of ORC. The proposed methodology allows for an objective comparison of the feasibility of ORC subjected to variations in the operational profile. Furthermore, the optimum ORC design can be identified to meet payback time expectations of different shipowners.

A comprehensive performance analysis of meta-heuristic optimization techniques for effective organic rankine cycle design

Optimizing the operating parameters is of great importance to improve Organic Rankine Cycle (ORC) system efficiency. Nowadays, meta-heuristic algorithms are widely used to obtain fast and effective solutions. However, it is a difficult task to determine the most effective algorithm among dozens of available algorithms to solve the ORC design problem like many other real-world optimization problems. Moreover, defining a feasible solution and determining a method that can find this solution quickly and decisively is a major challenge. To overcome these challenges, a well-planned and comprehensive research is essential. In this article, a research consisting of two stages was conducted to determine the most effective meta-heuristic optimization methods that can find the optimum and feasible solutions of the ORC design problem in a stable and fast way. 31 algorithms selected among the most up-to-date and powerful meta-heuristic search algorithms in the literature were used in simulation studies. The data obtained were analyzed by using the non-parametric statistical test methods. The results show that TLABC, DE, and PSO algorithms are very successful in finding a feasible solution. In addition, the TLABC algorithm can find a feasible solution in a shorter time than its alternatives. The maximum net power output and the total cost of the system were calculated as 74.593 kW and 692,452 $, respectively for optimum design. Thus, the total cost per net power output of the ORC system was determined as 9283.066 $/kW.

Part-load efficiency boost in offshore organic Rankine cycles with a cooling water flow rate control strategy

Global concerns regarding greenhouse gas emissions and global warming have necessitated the speed up in using renewable energies and more efficient use of fossil fuels in the oil and gas industry. Harvesting gas turbine heat by organic Rankine bottoming cycles has raised as a potential solution to cut carbon dioxide emissions in offshore oil and gas installations. Offshore power cycles are expected to operate most of their operational life at part-loads where they suffer from poor efficiency. The purpose of this article is to boost the part-load efficiency of offshore organic Rankine cycles and keep it as close as possible to the design value. Here an operational strategy based on cooling water flow control is developed and added to a sliding pressure control logic and a variable area nozzle turbine control strategy. An in-house tool is developed for the design of organic Rankine cycles and the simulation of off-design control strategies. A design methodology is presented to optimize the cycle power output while minimizing the cycle footprint offshore. The proposed control strategy was successful in keeping the part-load efficiency close to design value and achieving a 5% reduction of annual carbon dioxide emissions.

Preliminary Design of Organic Rankine Cycle using Solar Thermal in Hungary

Renewable energy sources have grown in popularity in a variety of applications over the last century, particularly in solar power generation. Exploiting solar energy in low-medium temperature systems via the organic Rankine cycle (ORC) is a prospective idea for producing clean energy in remote areas at a low cost. The amount of solar energy available in Hungary is sufficient to power the ORC system. In this study, a parabolic through collector (PTC) solar collector is used to convert solar thermal energy into a heat stream that is used to boil the working fluid of R134a, which was chosen as a good ORC working fluid because it has a low boiling point as well as a low ODP and GWP value. Many recent studies have studied solar-ORC both from a theoretical and experimental point of view in various areas, especially in design system. In this study, the preliminary design that overcomes the need for solar-ORC, including an analysis of energy, the efficiency of the system, and turboexpander characteristics using different pinch temperatures (10 °C and 5 °C) will be elaborated. The weather data in June is used for initial data input, for calculations in the PTC solar collector. The result shows that the ORC system with 5 °C has a better result in view of the energy from the turbine and the thermal efficiency, compared to the ORC system with 10 °C.

Parametric optimization and comparative study of an organic Rankine cycle power plant for two-phase geothermal sources

For two-phase geothermal sources, Organic Rankine Cycle (ORC) based binary plant is often applied for power production. In this work, a network topology is designed with the open-source Thermal Engineering Systems in Python (TESPy) software to simulate the stationary operation of the ORC plant. With this topology, the performance of six different working fluids are compared. From the thermodynamic perspective, the gross and net power output are optimized respectively. Results show that R600 has the highest gross power output of 17.55 MW, while R245fa has the highest net power output of 12.93 MW. However, the turbine inlet temperatures for these two working fluids need to be designed at the upper theoretical limit. R245ca and R601a require the heat exchange rates of internal heat exchanger to be larger than 1.51 MW and 0.99 MW to satisfy the re-injection temperature limit, which are smaller than the R600 (6.7 MW) and R245fa (6.0 MW) cases. Besides, the working fluid with lower critical state is preferred for a geothermal source with smaller steam fraction to establish a stable ORC plant. The workflow for the ORC design and optimization in this work is generic, and can be further applied to thermo-economic investigation.

A new indicator for minimizing size of an ORC power plant based on heat exchanger and turbine design parameters

• System size index SSI – a novel indicator for minimizing size of the ORC is proposed. • SSI is defined based on heat exchanger area and turbine rotor diameter. • By using heat transfer indicators, the turbine may be oversized by up to 70%. • With the use of turbine indices, the heat exchanger may be oversized by up to 40% . • By applying the SSI index, the ORC components are sized optimally. The increasing interest in mobile applications and modular structures of an organic Rankine cycle (ORC) has resulted in growing importance of the optimal sizing of the ORC installation. Most of the existing works were focused on reducing dimensions of the ORC by applying indicators estimating size of a single type of the ORC component. This study aims to define an indicator which comprehensively evaluates the size of the ORC power plant. The proposed indicator, specified as System Size Index SSI , is formulated based on two key ORC design parameters, namely the total heat transfer area of the heat exchangers and the rotor diameter of the turbine. To examine the versatility of SSI , the analysis was conducted considering different ORC applications scenarios, including modular geothermal power plants and mobile waste heat recovery units. The findings of single-objective optimization procedures have shown that by applying indicators evaluating size of the heat exchangers, the turbine rotor diameter may deviate from its smallest possible dimension by up to 70%. Similarly, by utilizing indices evaluating size of the turbine, the heat exchangers area may differ from its optimal size by up to 40%. Meanwhile, by using the SSI indicator, both the total heat transfer area and turbine rotor diameter did not differ from their smallest possible dimensions by more than 1% for each scenario considered. Finally, based on a bi-objective analysis with SSI and net power output as the criteria, it was concluded that by applying such indicators as APR parameter or performance factor PF , the designer is left with a single design solution, while the adoption of the bi-objective approach gives much more flexibility in finding a compromise between the system size and power output of the installation.

Superstructure-based mixed-integer nonlinear programming framework for hybrid heat sources driven organic Rankine cycle optimization

Organic Rankine cycle (ORC) is a promising technology capable of harnessing low-grade energy, e.g. renewable energy and waste heat, and converting it into electricity. Conventional ORC often operates with single heat source, which can be unfavorable to its efficiency due to the poor matching between its working fluid and heat source. Implementing hybrid heat sources is generally more energy-efficient as multiple heat sources can effectively match with the working fluid, however, the design can be a challenging task. This study proposes a superstructure-based method for the ORC design that simultaneously synthesizes heat exchanger network for hybrid heat sources and working fluid, and optimizes the ORC and heat sources' parameters. A mixed-integer nonlinear programming model is formulated to achieve the simultaneous optimization. We also develop a tailored multi-step initialization algorithm to facilitate the optimization. The model is applied to the design and analysis of ORCs driven by solar energy and waste heat with four different working fluids. Results demonstrate that the hybrid heat source-driven ORC improves the system performance. Cyclohexane is found to be the optimal working fluid for the proposed ORC system with a 48.19% increase in net power output compared with the single heat source-driven ORCs running separately.