Utilizing Computational Methods to Identify Low GWP Working Fluids for ORC Systems

Parametric optimization of regenerative organic Rankine cycle (ORC) for low grade waste heat recovery using genetic algorithm

The performance of Organic Rankine cycle (ORC) systems is defined by the system design as well as working fluid selection. Integrated thermo-economic optimisation of both can unlock maximum system potential in terms of power generation at a minimal cost. However, such optimisation is associated with uncertainties related to the underlying thermodynamic fluid models, ORC system models, and equipment cost correlations. In this paper, the main sources of uncertainty are quantified and their impact on optimal system design and working fluid selection is analysed. A computer-aided molecular and process design (CAMPD) optimisation framework based on first-law system design models is developed and validated with experimental data. Results reveal that the developed framework can identify promising working fluid candidates with high probabilities, even considering the most important sources of uncertainty. In a case study of industrial waste-heat utilisation, it was found that while uncertainties challenge the strict discrimination of the most promising working fluids, they mainly affect absolute performance values, rather than the overall ranking of working fluids. Propane was identified as having a 94-% probability of being among the best 3 working fluids. Furthermore, although the overall specific investment costs are highly uncertain (mean: 3810 £/kW, standard deviation: 720 £/kW), the results are less sensitive to uncertainties in fluid equilibrium and transport properties (standard deviation: 160 £/kW), with the impact of equipment cost uncertainties being dominant. The analysis of uncertainties in working fluid selection also applies to other CAMPD problems, and other applications of group-contribution-based equations of state.

Organic Rankine cycle systems for engine waste-heat recovery: Heat exchanger design in space-constrained applications

A feasibility study has been conducted for an organic Rankine cycle (ORC) system coupled to the exhaust of a Diesel engine generator. The objective of this study was to determine the possible electrical generation of the ORC using the exhaust gas of a 78 kW diesel engine as its energy input. A thermodynamic model was developed to predict the possible electricity generation of the ORC. Using this model it was determined that the preferred working fluid for the ORC was R245ca. The calculated maximum ORC thermal efficiency was 14.3%. The net electrical power generated from the ORC was 5.36 kWe. The ORC would require no additional fuel and would not generate any additional emissions. The most cost-effective and simple means to develop a small packaged ORC system is to high volume production HVAC system components. An ORC system consisting of air conditioning system components, including a scroll expander, yielded a projected ORC efficiency of 10.7%, and a net electrical power of 4.02 kWe. The total capital cost of the ORC system was $2,140 CAD. Three engine usage scenarios were developed, with the time to payback of the initial capital cost of the ORC ranging from 12.8 to 0.58 years, depending on low or high usage.

Energy harvesting using solar ORC system and Archimedes Screw Turbine (AST) combination with different refrigerant working fluids

The Organic Rankine Cycle (ORC) is a thermodynamic cycle that converts heat into mechanical energy to produce electrical power in a closed system using organic working fluids. It is also a heat recovery technology that can use heat at low temperatures and makes it a promising thermodynamic cycle with cost-effectiveness and more energy efficiency. However, the ORC system's total efficiency is determined by the compatibility of the expander characteristics and working fluid properties with the system's thermodynamic cycle parameters. This study aims to analyze using an integrative review method regarding the development of the ORC system as a heat recovery technology. The purpose of the integrative review method is to review the knowledge base, where the review is carried out critically and has the potential to conceptualize and expand the theoretical foundation developed. In this case, the first analysis is about the literature study on the parameters of the ORC system. Furthermore, the development and optimization of the ORC system are discussed further to analyze its capabilities in various applications. Work fluids, component optimizations, and system configurations have been reported for possible improvements. In addition, this ORC system can be used as a technology in developing various renewable energy sources, including solar, biomass, geothermal, and waste heat. Furthermore, this system is assessed for its environmental and economic benefits to developing its capabilities and potential. The results show that integrating the ORC system in various renewable energy sources can provide proper operation, better efficiency, and advantages such as increased power and reduced pollution.

Enhancing sustainable energy conversion: Comparative study of superheated and recuperative ORC systems for waste heat recovery and geothermal applications, with focus on 4E performance

Influence of the radial-inflow turbine efficiency prediction on the design and analysis of the Organic Rankine Cycle (ORC) system

Small-scale Organic Rankine Cycle (ORC) systems have emerged as promising technologies for waste heat recovery and distributed power generation. The selection of an appropriate working fluid is critical to system performance, as it directly impacts thermal efficiency, safety, environmental impact, and economic viability. This paper presents a comprehensive comparative analysis of various organic working fluids including hydrofluorocarbons (HFCs), hydrofluoroolefins (HFOs), hydrocarbons, and siloxanes for small-scale ORC applications. The analysis evaluates thermodynamic properties, environmental characteristics, safety parameters, and system performance across different heat source temperatures ranging from 100°C to 200°C. Results demonstrate that HFO-1234yf and HFO-1234ze(E) offer superior environmental profiles with Global Warming Potential (GWP) <1, while cyclopentane and R-245fa provide balanced thermodynamic efficiency. This study provides practical guidance for engineers in selecting optimal working fluids for specific ORC system designs and operating conditions.

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

Life cycle assessment of Organic Rankine Cycles for geothermal power generation considering low-GWP working fluids

Combined heat and power (CHP) coal-fired plants and heat-only boilers are still working as main heat sources in North China. These provide high temperature water on the primary side of district heating (DH) systems. There can be large temperature differences between the primary side and secondary side deployed in low temperature district heating (LTDH) of buildings. In this paper, a LTDH system, integrated with an organic Rankine cycle (ORC) system, is presented and evaluated on how to utilize the limited temperature difference between the primary and secondary sides in a substation. Two cases are illustrated of the performance of two modes (series or parallel connection) and energy efficiencies of the configurations with or without an ORC system. The results showed that the integrated ORC system could provide sufficient power for the circulating pumps in the DH system. The integration of the ORC leads to only a very slight decrement on the supply water temperature. Generally, the series mode can generate the maximum output power from an integrated ORC system. The parallel mode showed more flexibility on the adjustment of output power from the ORC system, especially where domestic hot water is needed. When the cold tap water was used as a cooling stream in the condenser of an ORC system before preparing to be the domestic hot water, it is very helpful in improving the performance of the ORC and increasing the energy efficiency of the DH system.

Analysis of ORC (Organic Rankine Cycle) systems with pure hydrocarbons and mixtures of hydrocarbon and retardant for engine waste heat recovery

A significant improvement in the economy-of-scale of small-scale organic Rankine cycle (ORC) systems can arise from the appropriate design of components that can be manufactured in large volumes and implemented flexibly into a wide range of systems and potential applications. This, in turn, requires accurate predictions of component performance that can capture variations in the cycle conditions, parameters or changes to the working fluid. In this paper previous work investigating a modified similitude theory used to predict the performance of subsonic ORC turbines is extended to analyse the supersonic flow of organic fluids within 2D converging-diverging nozzles. Two nozzles are developed using a minimum length method of characteristics design model coupled to REFPROP. These are designed for R245fa and Toluene as working fluids with nozzle exit Mach numbers of 1.4 and 1.7 respectively. First, the nozzle performance is confirmed using CFD simulations, and then further CFD simulations are performed to evaluate the performance of the same nozzles over a range of different inlet conditions and with different working fluids. The CFD simulations are compared to predictions made using the original and modified similitude theories, and also to predictions made by conserving the Prandtl-Meyer function for the different operating conditions. The results indicate that whilst the modified similitude model does not accurately predict nozzle performance, conserving the Prandtl-Meyer function allows to predict the nozzle outlet Mach number to within 2% providing there is not a significant change in the polytropic index. Finally, the effect of working fluid replacement on the ORC system is discussed, and preliminary results demonstrate the possibility of matching a particular turbine to a heat source through optimal working fluid selection.

Transient thermal waste heat sources, such as solar energy, industrial waste heat, and ship exhaust heat, pose significant challenges in terms of their reuse in other processes. Therefore, ensuring the safe and efficient design and operation of the organic Rankine cycle (ORC) system for these heat sources is imperative. Comprehending the ORC system's dynamic characteristics is necessary to formulate suitable control strategies. This article undertakes a comprehensive review of previous studies on dynamic modeling and control of the ORC system and discusses the prevalent dynamic modeling methodologies, the challenges frequently encountered in dynamic simulations, and a range of control strategies. This article comprehensively analyzes the overall control strategies used by ORC systems. Additionally, the energy conversion systems utilized in ORC are depicted in detail. Furthermore, using model predictive control in a simulation study allows for investigating various components’ disturbance and dynamic characteristics within the ORC system. These components include the expander, pump, condenser, and evaporator using setpoint tracking. Ultimately, this analysis aims to optimize the performance of the ORC cycle. The findings indicate that the utilization of superheating in the working fluid is the most effective method for achieving maximum power generation in an ORC system.