Organic Rankine Cycle Process Research Articles

Reverse design of molecule‐process‐process networks: A case study from HEN‐ORC system

AbstractThe integrated design of the heat exchanger network (HEN) and organic Rankine cycle (ORC) system with new working fluids is a complex optimization problem. It involves navigating a vast design space across working fluid molecules, ORC processes, and networks. In this article, a new two‐stage reverse strategy is developed. The optimal HEN‐ORC configurations and operating conditions, and the thermodynamic properties of the hypothetical working fluid are identified by an equation of state (EOS) free HEN‐ORC model in the first stage. With two developed group contribution‐artificial neural network thermodynamic property prediction models, working fluid molecules are screened out in the second stage from a database containing more than 430,000 hydrofluoroolefins (HFOs). The presented method is employed in two cases, where new working fluids are found. The total annual cost of Case 1 is 12%–22% lower than the literature, and the power output of Case 2 is 5%–8% higher than the literature.

Efficient predictive control method for ORC waste heat recovery system based on recurrent neural network

The model predictive control performs well in regulating operating parameters and ensuring system safety when the organic Rankine cycles are operating with variable heat sources. However, traditional nonlinear predictive control based on the organic Rankine cycle mechanism model involves significant computational complexity, making it challenging to quickly find a control solution. This limitation hinders its application in the organic Rankine cycle for rapid response control. To address this issue, a fast model predictive control method is proposed in this work. A recurrent neural network model is well-trained using the input–output data of the organic Rankine cycle process, and it is used as a surrogate model in the design of the model predictive controller for the control of organic Rankine cycle operating parameters. The formulated optimal control problem is then transformed into a mixed integer linear programming problem, which can obtain high-quality and fast solutions during the control process. Through comparison with recurrent neural network-based nonlinear predictive control and pseudo-sequential method-based fast nonlinear predictive control, the results show that the designed controller can effectively accomplish the control of organic Rankine cycle operating parameters with smaller overshoot. Moreover, its average control solution time is shorter by 89.59% and 93.27% respectively while the total net output power of the system during the control process is 0.54% and 1.3% higher than that of the other two controllers. It exhibits superior control performance, even under variable waste heat conditions.

4E analysis of the cryogenic CO2 separation process integrated with waste heat recovery

Carbon dioxide capture, utilization, and storage (CCUS) is an attractive method to reduce carbon dioxide (CO2) emissions originating from fossil fuels burned from large single-point sources. CO2 separation from a CO2-laden gas stream is the first stage of CCUS. In this investigation, a cryogenic distillation-based CO2 separation process (CCSP) is developed. CCSP is modified to utilize waste heat obtained in the process for reducing the energy consumption of CO2 separation. Two modifications are carried out in the process which include (i) heat integration (HI) with CCSP (CCSP + HI) of the reboiler with the heat from hot streams available in the process and further, (ii) energy recovery by using the organic Rankine cycle (ORC) operating between gas compressor temperature and ambient temperature (CCSP + HI + ORC). The parametric and 4 E (energy, exergy, economic, and environmental) analysis results obtained for the CCSP + HI, CCSP + ORC, and CCSP + HI + ORC processes are compared with those of CCSP. The net electrical energy required to operate the compressor for CCSP is 2.7%, 7%, and 21.8% higher than that for CCSP + HI, CCSP + ORC, and CCSP + HI + ORC, respectively.

Mechanical vapor recompression coupling organic rankine cycle process for purification of crude biodiesel obtained by solid base-catalyzed transesterification

In this study, an effective method of mechanical vapor recompression coupling Organic Rankine Cycle process is introduced to purify crude biodiesel obtained by solid base-catalyzed transesterification. Mechanical vapor recompression is used for recovering the waste heat of the methanol, while the Organic Rankine Cycle is applied for converting the waste heat of biodiesel into electric energy. Pinch technology is proposed to guide the coupling of mechanical vapor recompression and Organic Rankine Cycle process, the electric energy and waste heat generated by Organic Rankine Cycle are supplied to the mechanical vapor recompression system. Compared with conventional purification process, the total annual cost of proposed process decreases by 55.40% and the greenhouse gas emissions decrease by 76.31% for CO2, 76.41% for SO2, and 76.42% for NOx, respectively. In addition, the parameters of the proposed process are optimized to achieve a coefficient of performance of 16.03 for mechanical vapor recompression and 14.06% thermal efficiency for Organic Rankine Cycle.

Thermodynamic simulation and optimization of natural gas liquefaction cycle based on the common structure of organic rankine cycle

In this paper, using Aspen HYSYS and two different structures of an organic Rankine cycle (ORC), thermodynamic and environmental improvements are made in the common process of a natural gas liquefaction process based on the PRICO method. According to the analyses, in the PRICO process, the total exergy efficiency, power consumption, and carbon dioxide (CO2) emission are 43.9%, 278.47 kWh/ton, and 0.17 kgCO2/kgLNG, respectively. Results showed that heat recovery by the ORC cycle results in decreasing the exergy loss, increasing the exergy efficiency, lowering the power consumption, and reduction in the CO2 emission. The total exergy efficiency of the PRICO process coupled with the modified ORC and ORC increases to 54.1% and 53.68%, respectively. Besides, the amount of consumed power is reduced to 225.42 kWh/ton and 227.26 kWh/ton, respectively. From the environmental aspect, it is demonstrated that the CO2 emission of the PRICO plus modified ORC process in comparison with PRICO and PRICO plus ORC is lower by 23.53% and 7.14%, respectively. Finally, comparing the results with previous papers revealed that the proposed scheme in this paper (PRICO plus modified ORC), regarding the energy and exergy efficiencies, has a better performance than technologies such as SMR, DMR, C3MR, and PRICO.

Characteristics and trends in geothermal development and use, 1995 to 2020

Production of electricity using geothermal energy started in 1904 at Larderello, Italy with an experimental 10 kWe generator. This was followed by a 250 kWe commercial unit in 1913. Italy was the world's only industrial generator of geothermally fueled electricity until 1958 when New Zealand came on-line with a 11.2 MWe unit built at Wairakei. By 1967, power plants were constructed in Mexico, the United States and Russia, where the first binary cycle power plant was installed in Kamchatka. Other countries followed: by 1970, Japan, Iceland, and China. Since WWII geothermal power has grown at an average rate of 6.2% annually. Electric power from geothermal energy, originally using steam from resources above 150 °C, is now being produced from resources with temperatures as low as 90 °C using the organic Rankine cycle process in binary power units sometimes in combination with district heating projects. Geothermal energy capacity has grown to 15,950 MWe, and 95,098 GWh of electricity produced in 29 countries. These power plants operate with an average capacity factor of 73%, many of them “on-line” over 95% of the time, providing almost continuous base-load power. The geothermally fueled electricity currently being produced serves the equivalent of 63 million people throughout the world.Direct uses of geothermal energy are traditional and well established world-wide. The people of Japan have lived in harmony with the earth's heat for centuries, using it mainly for bathing. Other nations have similarly taken advantage of hot springs for bathing and agriculture/aquaculture uses. There are now many large-scale uses of geothermal energy including district heating in Iceland and China, greenhouse heating in Hungary, and process heating with steam in New Zealand. One of the main advantages of the direct use of geothermal energy is that it can use low-to-moderate resource temperatures. The other advantage is that it can be found, often at shallow depths, almost anywhere in the world. Using ground-source heat pumps extends the use of geothermal energy to temperatures as low as 10 °C. As of 2021, 88 countries have reported some direct applications of geothermal energy with at least 10 others suspected of using this resource. Thermal energy for direct use is used 58.5% for geothermal heat pumps, 18.0% for bathing and swimming, 16.0% for space heating, 3.5% for greenhouse and covered ground heating, 1.6% for industrial applications, 1.3% for aquacultural pond and raceway heating, 0.4% for agricultural drying, 0.2% for snow melting and cooling, and 0.2% for miscellaneous applications. The installed capacity and thermal energy available worldwide today are 107,727 MWt and 1,020,887 TJ/yr. (283,580 GWh/yr.), respectively.

Thermodynamic Analysis on the Reversibility of Compressor-expander

ABSTRACT Expander is the most important component for Organic Rankine Cycle (ORC) especially to convert low-temperature heat to power in remote areas. However, most of developing countries are still far from capability in fabricating the required expander. Thermodynamically, the expander’s function can be obtained by reversing the operation of the compressor. The purpose of this study is to test the performance of a compressor reversed expander and to study its thermodynamic reversibility. The compression cycle and the expansion cycle were performed by using a scroll-type compressor, and the working fluid used for the performance test was R134a. Based on the test results, it was found that the pressure ratio, in terms of maximum-to-minimum ratio, increased in line with the increase of the evaporator temperature both in the compression and expansion cycle. The average isentropic efficiency of the expansion cycle was 77.66%, with an entropy generation rate of 0.06 W/K. It was relatively higher than that of the compression cycle, which was 30.34% of average isentropic efficiency with 1.11 W/K of entropy production rate. The results showed that the scroll-type compressor reversed expander can be used for ORC process with considerable effectiveness.

Advanced exergy and exergoeconomic analysis of an integrated system combining CO2 capture-storage and waste heat utilization processes

To solve the problem regarding the purification of coal syngas, a system that integrates the CO2 capture and storage process and the waste heat utilization processes is proposed herein and analyzed using advanced exergy and exergoeconomic analysis methods. The purpose is to obtain the distribution of the exergy destruction rate and the cost rate of each block in the integrated process. The total exergy efficiency of the system was found to be 17.56%. Moreover, the total exergy destruction was 36424 kW, of which the CO2 capture and storage process accounted for 43.15%, the organic Rankine cycle process accounted for 32.35%, and the absorption refrigeration cycle process accounted for 24.50%. The exergy destruction ratio of the whole system was 82.44%. In this process, the optimization of the blocks such as the distillation column, absorber, and Evaporator 2 is to be considered a priority. Advanced exergy and energy efficiency analysis can provide guidance for the optimization of system irreversibility and help to determine the improvement potential of each block. In addition, certain strategies are proposed for the improvement of each block on the basis of the results, which can provide a theoretical flowchart for the efficient operation of the integration process.

Energy-saving technology of styrene unit based on mechanical vapor recompression coupled with organic Rankine cycle process

ABSTRACT The conventional four columns styrene distillation unit for separating benzene, toluene and ethylbenzene etc. required high energy consumption. Numerical simulations were performed by Aspen Plus software(version 7.3) environment under the Peng-Rob thermodynamic model. In order to improve the energetic efficiency, the multi-effect distillation (MED), mechanical vapor recompression (MVR) heat pump technology and organic Rankine cycle (ORC) generation power technology were suggested as competitive improvements on conventional distillation process. The economy of the double-effect distillation (DED) process was performed and the MVR heat pump distillation process was compared based on total annual cost (TAC). To further protect the environment friendly, the MVR heat pump distillation process coupled with ORC generation power technology was developed. The results show that compared with the conventional four columns distillation process, the DED process, MVR heat pump process, and MVR heat pump process coupled with ORC generation power technology can reduce energy by 21.3%, 40.3%, and 50.5%, save TAC by 19.4%, 37.3%, and 41.0% respectively. In all examples, the MVR heat pump distillation process coupled with ORC methodology is able to outperform previous studies regarding TAC, proving a practicable alternative to methods that are currently applied in the literature.

Toward the Integrated Design of Organic Rankine Cycle Power Plants: A Method for the Simultaneous Optimization of Working Fluid, Thermodynamic Cycle, and Turbine

Abstract The conventional design of organic Rankine cycle (ORC) power systems starts with the selection of the working fluid and the subsequent optimization of the corresponding thermodynamic cycle. More recently, systematic methods have been proposed integrating the selection of the working fluid into the optimization of the thermodynamic cycle. However, in both cases, the turbine is designed subsequently. This procedure can lead to a suboptimal design, especially in the case of mini- and small-scale ORC systems, since the preselected combination of working fluid and operating conditions may lead to infeasible turbine designs. The resulting iterative design procedure may end in conservative solutions after multiple trial-and-error attempts due to the strong interdependence of the many design variables and constraints involved. In this work, we therefore present a new design and optimization method integrating working fluid selection, thermodynamic cycle design, and preliminary turbine design. To this purpose, our recent 1-stage continuous-molecular targeting (CoMT)-computer-aided molecular design (CAMD) method for the integrated design of the ORC process and working fluid is expanded by a turbine meanline design procedure. Thereby, the search space of the optimization is bounded to regions where the design of the turbine is feasible. The resulting method has been tested for the design of a small-scale high-temperature ORC unit adopting a radial-inflow turbo-expander. The results confirm the potential of the proposed method over the conventional iterative design practice for the design of small-scale ORC turbogenerators.

Multi-objective optimization of organic Rankine cycle system for the waste heat recovery in the heat pump assisted reactive dividing wall column

The application of heat pump (HP) technique to reactive dividing wall column (RDWC) achieving energy-saving has received more and more attention, however, massive low-temperature (<100 °C) waste heat would be hereby produced. Therefore, in this work, the organic Rankine cycle (ORC) is adopted to effectively convert the produced waste heat of the compressed stream to clean energy (i.e., electricity). The HP assisted RDWC (HP-RDWC) of diethyl carbonate process is taken as an example, the ORC system with five working fluids candidates are explored. The operating parameters of the ORC system (e.g., flow rate of working fluid and inlet pressure of evaporator) are optimized based upon the maximum net revenue and ORC thermal efficiency through the improved multi-objective genetic algorithm. The optimal ORC system is determined by considering the economic (i.e., net revenue) and thermodynamic efficiency (i.e., ORC efficiency) performances. The results illustrated that the net revenue of the ORC system with R123 and R600a could achieve 175,807.2 US$ and 133,665.5 US$ with ORC efficiency of 15.57 and 16.19%. In addition, total annual cost of the HP-RDWC integrated ORC processes with working fluids R123 and R600a could be reduced by 11.78% and 10.30%, respectively.

Working fluid selection for organic rankine cycles via deterministic global optimization of design and operation

The performance of an organic Rankine cycle (ORC) relies on process design and operation. Simultaneous optimization of design and operation for a range of working fluids (WFs) is therefore a promising approach for WF selection. For this, deterministic global process optimization can guarantee to identify a global optimum, in contrast to local or stochastic global solution approaches. However, providing accurate thermodynamic models for a large number of WFs while maintaining computational tractability of the resulting optimization problems are open research questions. We integrate accurate thermodynamic and transport properties via artificial neural networks (ANNs) and solve the design problems with MAiNGO in a reduced-space formulation. We illustrate the approach for an ORC process for waste heat recovery of a diesel truck. After an automated preselection of 122 WFs, ANNs are automatically trained for the 37 selected WFs based on data retrieved from the thermodynamic library CoolProp. Then, we perform deterministic global optimization of design and operation for every WF individually. Therein, the trade-off between net power generation and investment cost is investigated by multiobjective optimization. Further, a thermoeconomic optimization finds a compromise between both objectives. The results show that, for the given conditions, monoaromatic hydrocarbons are a promising group of WFs. In future work, the proposed method and the trained ANNs can be applied to the design of a variety of energy processes.

Energy analysis and multi-objective optimization of waste heat and cold energy recovery process in LNG-fueled vessels based on a triple organic Rankine cycle

Due to the high level of pollutant emissions from traditional marine diesel engines, Liquefied Natural Gas (LNG) as clean energy is becoming a better choice for main engines to replace the traditional fuels. Meanwhile, in order to improve the energy efficiency of the marine power system, the Organic Rankine Cycle (ORC) has been regarded as the most suitable solution to recover the waste heat for the power generation of vessels. In this paper, both the waste heat of the main engine and the cold energy of LNG have been fully considered, and a novel triple ORC process has been proposed for the waste heat and cold energy recovery of LNG-fueled vessels. It adopts the exhaust gas of the main engine and the cooling water from the engine jacket as heat sources, and uses the cold energy of LNG and the sea water as cold sources. Based on the 15 optional working fluid conditions, the heat source utilization rate, system exergy efficiency, net output power, and system cost are, respectively, combined as two objectives, and the multi-objective adaptive firefly algorithm is used to optimize the thermodynamic performance of the system. The optimization results of different heat and cold sources as well as the design parameters have been discussed. Finally, the system's exergy loss has been analyzed to make suggestions for further improvement. The results show that this novel ORC system can better meet the energy recovery requirements of LNG-fueled vessels, with higher net output power, lower cost, and greater energy recovery efficiency. The largest exergy loss of the system exists in the condensers of the stages 2 and 3, and the expanders in the various stages. Therefore, subsequent cooling energy recovery and the use of Stirling engines can be considered to further improve the system efficiency.

Multi-objective optimization of Organic Rankine Cycle (ORC) design considering exergy efficiency and inherent safety for LNG cold energy utilization

Natural gas (NG) is an environment-friendly energy source with low CO2 and SOx emission. NG is usually liquefied during processing for transportation and storage, and then vaporized before consumption for multiple purposes. Usually, cold energy from the vaporization process is not utilized and hence wasted. One of the means of utilizing the cold energy is Organic Rankine Cycle (ORC), through which electricity can be generated from any grade of heat sources. Accordingly, ORC has been extensively investigated with the aim of increasing efficiency. However, although the ORC process has high potential risk of fatality, the safety aspect has not been previously studied.In this study, ORC design considering the thermodynamic and safety aspects is explored with a multi-objective optimization methodology. Exergy efficiency is used for the thermodynamic aspect, and risk distance is used for the safety aspect, with inherent safety techniques for designing safer processes in the conceptual design. Considering the working fluid as the main factor for optimal ORC design, six working fluids in three categories (pure component, binary components, ternary components) are investigated. Pareto optimal solutions are obtained from the multi-objective optimization method with two objectives based on working fluids for ORC design. Optimization variables include working condition (pressure), working fluid conditions (components). Moreover, the final optimal solution is selected using decision techniques, such as LINMAP and TOPSIS.

Process optimization and working fluid mixture design for organic Rankine cycles (ORCs) recovering compression heat in oxy-combustion power plants

In this study, an Organic Rankine Cycle (ORC) is proposed to be integrated with the flue gas pre-compression process to reduce the energy cost resulting from Carbon Capture and Storage (CCS). An equation-based flowsheet optimization model is developed considering the mixture working fluid design, ORC operating conditions and the compression process simultaneously. The optimal number of stages of CO2 compression, the working fluid composition and the optimal operating conditions of ORCs and the compression train can be determined simultaneously using the proposed mathematical model. Proper heat integration can boost the power output of the ORC system significantly. The heat integration model considering variable process streams is extended to the integrated ORC and flue gas compression train process. The results show that the optimal number of stages is 4 and a pure working fluid could perform better than a mixture working fluid if operating conditions are chosen properly. The integration of ORCs can reduce the energy penalty by 7.9% compared with the original optimal design that did not include ORCs. In addition, one compressor stage is avoided.

Reversible Heat Pump–Organic Rankine Cycle Systems for the Storage of Renewable Electricity

Storage of electricity from fluctuating renewable energy sources has become one of the predominant challenges in future energy systems. A novel system comprises the combination of a heat pump and an Organic Rankine Cycle (ORC) with a simple hot water storage tank. The heat pump upgrades low temperature heat with excess power. The upgraded heat can drive an Organic Rankine Process using the heat pump in reverse operation mode. This approach allows a comparably efficient storage of excess electricity. Waste heat sources usually do not qualify for electricity production even with ORC processes due to low temperatures. Upgrading the temperature of the waste heat by means of excess electricity makes the use of an ORC feasible in order to recover the electricity input. Thermodynamic cycle simulations with IPSEpro software outline that the process provides power-to-power efficiencies in a range of 50% for small-scale applications based on commercially available heat pump components. The isentropic efficiency of compressors/expanders plays a crucial role on the system performance. Applications of the proposed cycle in the megawatt range with more efficient turbines and dynamic compressors will therefore increase the power-to-power efficiency to above 70%.

Data‐Driven Superheating Control of Organic Rankine Cycle Processes

In this paper, a data‐driven superheating control strategy is developed for organic Rankine cycle (ORC) processes. Due to non‐Gaussian stochastic disturbances imposed on heat sources, the quantized minimum error entropy (QMEE) is adopted to construct the performance index of superheating control systems. Furthermore, particle swarm optimization (PSO) algorithm is applied to obtain optimal control law by minimizing the performance index. The implementation procedures of the presented superheating control system in an ORC‐based waste heat recovery process are presented. The simulation results testify the effectiveness of the presented control algorithm.

MVR heat pump distillation coupled with ORC process for separating a benzene-toluene mixture

In this work, a process consisting of Mechanical Vapor Recompression (MVR) heat pump distillation coupled with Organic Rankine Cycle (ORC) was proposed to separate the benzene-toluene mixture. Aspen Plus (version 7.3) was used to study the steady state simulations of the process. An optimized ORC system was applied to recover waste heat from the MVR heat pump system. In addition, the optimized parameters of ORC waste-heat power generation process were obtained based upon the net power output and cycle’s thermal efficiency. All other parameters, including operating and equipment parameters for the whole process were based upon the total annual cost (TAC). The results showed that the MVR heat pump distillation coupled with ORC process was more competitive than the conventional distillation process. Additionally, the proposed process was found to be more economical than the MVR heat pump distillation process.

Working Fluid Selection and Optimal Power-to-Weight Ratio for ORC in Long-Haul Trucks

In 2013, about 82% of the total CO2 emissions from transportation systems in the U.S. were caused by road transportation, highly based on internal combustion engines (ICE). Organic Rankine Cycles (ORC) are a waste heat recovery (WHR) technology that can contribute significantly to reduce environmental impact of road transportation. A trade-off has to be found between the improved fuel energy utilization and the weight and volume of the ORC, which increase the vehicle load and reduce the available space for transportation. In the present work, 17 working fluids are analyzed as possible candidates for WHR with direct-evaporation ORC in long-haul trucks. The preheater/evaporator is modelled as a finned shell-and-tube heat exchanger, while the condenser is an air-cooled finned flat-tube heat exchanger, as in common truck radiators. The ORC process is optimized for each fluid in terms of maximum power output, taking into account the impact of the working fluid on the heat exchanger weight and volume. The heat exchangers are modelled in MATLAB®. The results show that acetone and ethanol can recover more than 6 kW of mechanical power, but the system would present large weight and required space. Isobutane shows the highest power-to-weight and power-to-volume ratio (234 W/kg and 277 W/dm3 resp.), but the net power output is lower. Cyclopentane and pentane allow a good trade-off between power output and space requirement. The discussed procedure can be also applied to other transportation systems, where the condenser might have to be adapted to different boundary conditions.

Integrated design of ORC process and working fluid using process flowsheeting software and PC-SAFT

Organic Rankine Cycles (ORC) transform low-temperature heat into electrical power. To make best use of a heat source, ORC process and working fluid have to be optimized simultaneously. Thus, integrated design approaches of fluids and processes have been developed. However, integrated design approaches are usually complex and based on specific software tools which prevents fast and easy development of the ORC models. In this work, we have integrated the so-called 1-stage CoMT-CAMD approach into the process flowsheeting software gPROMS ProcessBuilder allowing for integrated design of process and working fluid. In 1-stage CoMT-CAMD, thermodynamic properties are modeled by the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) equation of state, which we use directly from the gSAFT physical property package. To introduce the molecular structure of the working fluid as an additional degree of freedom within the process optimization, we implemented the homosegmented group contribution approach of PC-SAFT and the Computer-aided Molecular Design (CAMD) formulation of 1-stage CoMT-CAMD in ProcessBuilder. Existing model libraries of ProcessBuilder were adapted to employ the Variable Molecular Structure Compound feature (VMSC) of gSAFT during process optimization. The resulting mixed integer nonlinear program (MINLP) optimization problem is solved by the standard MINLP solver integrated in ProcessBuilder. Thereby, the optimal working fluid and the corresponding optimal process are identified in one single optimization. The resulting tool enables the easy definition of integrated design problems based on the drag-and-drop feature of a process flowsheeting software for ORCs and beyond.