Fluid In Organic Rankine Cycle Research Articles

Combustion and interaction mechanism of 2,3,3,3-tetrafluoropropene/1,1,1,2-tetrafluoroethane as an environmentally friendly mixed working fluid

Organic Rankine cycle (ORC) is an effective way to improve energy efficiency, and 2,3,3,3-tetrafluoropropene (R1234yf) is considered as a promising working fluid for ORC. However, the development of R1234yf in ORC is limited by its flammability, and the addition of 1,1,1,2-tetrafluoroethane (R134a) is an effective method to inhibit its flammability. In this paper, the combustion and interaction mechanism of R1234yf/R134a were investigated. Firstly, the combustion products of R1234yf/R134a were measured using an improved experimental device, the results showed a substantial reduction in the concentrations of CO, CO2, and HF with an increasing proportion of R134a. Then, the combustion mechanism of R1234yf/R134a was studied by ReaxFF-MD simulation. The initial decomposition time of R134a was found to be later than that of R1234yf, and a reduction in the production rate of combustion products was achieved with the addition of R134a. Furthermore, the combustion reaction was promoted by the increase in temperature. Finally, the main reaction pathways of working fluids were analyzed. The abstraction reaction of R134a with radicals and the scavenging of active radicals by flame retardant radicals were the key to inhibit the combustion reaction. The results have universal guiding significance for the safe application of R1234yf/R134a.

Simultaneous working fluid and expander selection method for reaching low‐threshold technology organic Rankine cycle (ORC) design

AbstractMaximizing the utilization of an available source serves as the ideal approach, provided that only technical factors are considered. For sources with low heat flux, however, cost‐effective solutions are more suitable due to the minimal net power generated, regardless of the effectiveness of the energy conversion. In such cases, utilizing low‐threshold technology may be the most fitting solution, the layout of these cycles should be simple and inexpensive. In the case of organic Rankine cycles (ORCs)‐based power cycles, this means the omission of superheaters or recuperative heat exchangers and the use of simple expanders and small heat exchangers. Simplifying the design, however, requires additional considerations about the elementary steps of the cycle. This work presents a procedure to select favorable working fluids for ORC while considering the expander's internal efficiency. The criteria for favourability is to have a nonideal expansion process starting and ending in (or very near) saturated vapor states to avoid problems related to wetness/dryness between the given maximal and minimal expansion temperatures. It is demonstrated that the design can be simplified under the simultaneous working fluid and expander selection method presented in this study, regardless of the type and isentropic efficiency of the expander. The resulting methodology applies the novel classification of working fluids using the sequences of their characteristic points on temperature‐entropy space. The proposed approach is illustrated with a case study finding optimal working fluid for an ORC system fitted to industrial waste heat, a low‐temperature geothermal, and a cryogenic heat source.

Combustion mechanism and product characteristics of 2,3,3,3-tetrafluoropropene as an environmentally friendly working fluid for organic Rankine cycle

Combustion mechanism and product characteristics of 2,3,3,3-tetrafluoropropene as an environmentally friendly working fluid for organic Rankine cycle

Pyrolysis mechanism of HFO-1234yf/iso-butane mixture: ReaxFF reactive molecular dynamic simulation study

HFO-1234yf/iso-butane mixture is a promising working fluid of organic Rankine cycle, but the working fluid will be pyrolyzed under the high temperature heat source. In this study, the pyrolysis mechanism of HFO-1234yf/iso-butane mixture was studied by using density functional theory method and ReaxFF reactive force field. The initial pyrolysis reactions of HFO-1234yf and iso-butane, the pyrolysis process, the effects of HFO-1234yf to iso-butane ratio and temperature on the pyrolysis of HFO-1234yf/iso-butane mixture were investigated. The results indicated that the iso-butane of the HFO-1234yf/iso-butane mixture inhibited the pyrolysis of HFO-1234yf, the thermal stability of HFO-1234yf/iso-butane mixture was better than that of pure HFO-1234yf. Therefore, HFO-1234yf/iso-butane mixture has better thermal stability than HFO-1234yf and can match higher temperature heat source.

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.

Technical assessment of novel organic Rankine cycle driven cascade refrigeration system using environmental friendly refrigerants: 4E and optimization approaches.

Hydrocarbons are a promising working fluid for organic Rankine cycles and refrigeration systems that have gained increasing attention in recent decades as a replacement for the currently used higher global warming potential fluids. A novel standalone cascade refrigeration system (CRS) has been developed in this study for simultaneous ultra-low temperature cooling and heating production to medical applications most suitable for rural and power outages. Using the energy utilization factor (EUF) metrics, neopentane was chosen as the working fluid for the organic Rankine cycle (ORC) system among the selected hydrocarbon (HC) refrigerants. The standalone ORC-CRS system performance was investigated in terms of cooling and heating capacity, EUF, exergy, and environmental metrics by varying both ORC and CRS key temperature parameters. The exergy destruction of individual components was evaluated, and it was found that the ORC evaporator has the highest exergy destruction, followed by the expander. The highest EUF and exergy efficiency for a combined ORC-CRS system was about 0.64 and 38%. The maximum cooling and heating capacity of novel standalone CRS system was achieved by 70kW and 225kW respectively at a typical operating condition. At a higher ORC evaporation temperature, the exergy efficiency of the ORC-CRS system is decreased, leading to reduction in SI. The standalone ORC-CRS system at ORC evaporator temperature of 150°C achieved the maximum CO2 emission tax savings of $ 6.4 × 107 over a 15-year lifetime period. The total annualized cost index of the combined cooling heating system is in the range between 35 and 60 $/h for the variable operating condition. Non-dominated sorting genetic algorithm II (NSGA-II) method was used to conduct the multi-objective optimization analysis, and the technique for order of preference by similarity to ideal solution (TOPSIS) method used to found the optimal point, which had the following values of TAC 42.22 $/h and exergy efficiency was around 46.10%.

Effect of ignition energy on combustion characteristics of flammable working fluids

Working fluids with low global warming potential (GWP) will play an important role in the research and development of alternative working fluids for organic Rankine cycles and refrigeration cycles. However, the flammability of low GWP working fluid limits their development, and the energy of typical fire sources has a significant impact on their safe application. At present, there is a lack of relevant research on the effect of ignition energy on their flammability. In this paper, the effect of ignition energy on the combustion characteristics for propane (R290), fluoroethane (R161), 1,1-Difluoroethane (R152a), and 3,3,3-Trifluoropropene (R1243zf) was studied using a variable ignition energy system. The initial flame propagation process, flammability limit, and burning velocity were tested and analyzed in the range of 50 mJ to 20 J. The results showed that with the increase of ignition energy, the lower flammability limit (LFL) decreased and the upper flammability limit (UFL) increased, but their rate of change decreased with the increasing ignition energy. The effect of ignition energy on the flammability limit of R1243zf was significantly greater than that of the other three working fluids. In addition, the effect of ignition energy on flame propagation was mainly limited to the initial stage, and the burning velocity was independent of ignition energy. The mechanism of ignition energy on combustion characteristics was obtained. The research results have guiding significance for the safe application of flammable working fluids.

Analysis of Different Organic Rankine and Kalina Cycles for Waste Heat Recovery in the Iron and Steel Industry.

This study analyzed waste heat of two sections including the rolling section and electric arc furnace with low and medium temperature ranges, respectively. Organic Rankine cycles (ORCs) and Kalina cycles are the best technologies for the conversion of low-quality and medium-quality thermal energy to electrical power. The ORC applies the principle of the steam Rankine cycle, but it uses organic working fluids with low boiling points to recover heat from lower temperature heat sources. Also, in the Kalina cycle, ammonia water is selected as the working fluid because of its variable boiling point and thermodynamic properties. This study employs the thermo-economic method using the genetic algorithm to optimize the performance of three different ORC systems including a basic ORC (BORC) system, a single-stage regenerative ORC (SRORC) system, and a double-stage regenerative ORC (DRORC) system using five different working fluids and a basic Kalina cycle with KCS34 and complex cycle under the same waste heat conditions. Based on the energy and exergy analysis, the complex Kalina cycle shows the best performance among all studied cycles. The next best performance was exhibited by KCS34 and DROC, respectively. In general, Kalina cycles and ORCs are suitable for low-temperature and medium-temperature heat sources, respectively. According to the thermo-economic analysis, KCS34 in the rolling section and DRORC in EAF show optimum performance for heat recovery. R11 and R113 are selected as the best working fluids for ORCs, and ammonia with a concentration of 0.9 in the mixture is the optimal solution for Kalina cycles.

Thermal stability of a mixed working fluid (R513A) for organic Rankine cycle

Organic Rankine cycle (ORC) is an effective way to utilize low-grade energy, with R1234yf being considered a promising working fluid for ORC for its low global warming potential (GWP). Nevertheless, the weak thermal stability has limited the application R1234yf in ORC, emphasizing the necessity to find a way preventing the its pyrolysis in ORC. In this connection, a systematic study on the mechanism of R134a affecting the thermal stability of R1234yf in ORC was conducted in this work. Our experimental results indicate that the pyrolysis temperature of R513A (R1234yf/R134a) is in the range of 190–210 °C. Further, ReaxFF simulations and density functional theory (DFT) calculations were performed on the pyrolysis process of R1234yf, R134a and R513A. It is revealed that the main pyrolysis reaction pathways of working fluids can be divided into three types: the reactions of working fluid molecules collision with F radical (FCR) or H radical (HCR), and the self-decomposition reactions of working fluid molecules (SDR). In R513A, F and H radicals are the origin for the affected thermal stability of R1234yf. The results are of great significance to guide the selection of additive species to enhance the thermal stability of HFO working fluid.

Thermodynamic analysis and optimization of a multi-stage Rankine cycle power system combining with hydrate energy storage for liquefied natural gas cold energy utilization

Natural gas (NG) as a primary energy source plays an important in industrial systems. Natural gas generally needs to be converted into liquified natural gas (LNG) during transportation and stored at a low temperature (around-162 °C), which contains a large amount of cold energy that can be used. The discharge of cold energy into the ocean or atmosphere will cause not only energy waste but also environmental pollution. In order to recover LNG cold energy more efficiently, a novel LNG cold energy utilization system integrating Organic Rankine cycle (ORC), transcritical CO2 cycle (TRCC), CO2 energy storage and seawater ice-making cycle and combustion power system is proposed and investigated in this study. Energy analysis and exergy analysis were studied in details. The exergy efficiency and net electric generation (NEG) were analyzed and optimized using the optimizer in Aspen HYSYS. The results reveal that, exergy loss ratio of combustion power system and CO2 energy storage system are relatively larger than that of other subsystems. In addition, The ORC performance of six working fluids was analyzed. The NEG of R290 and R1270 as working fluid of ORC is significantly higher than that of the other four working fluids. Under the condition of basic process simulation, the NEG of ORC and TRCC is 223.7 kW and 216.4 kW, respectively. The total exergy efficiency reaches 39.01 %. After parameter optimization in the optimizer, the total NEG of ORC and TRCC increases by 6.9 % from 440.1 kW to 470.6 kW and the exergy efficiency can reach 39.8 %.

An examination of super dry working fluids used in regenerative organic Rankine cycles

Thermodynamic and economic performance of an Organic Rankine Cycle (ORC) system is closely related to the thermophysical properties of its organic working fluid. Super dry working fluids are especially suitable for regenerative ORC. Setting a recuperator in an ORC not only improves its thermodynamic performance, but also increases the investment cost of heat exchanger that accounts for the highest proportion in the whole ORC system. Based on the above consideration, this paper presents an examination of super dry working fluids used in regenerative ORC. The suitable super dry working fluid used in a regenerative ORC is determined and selected for common medium/low-temperature heat sources. Based on different types of heat sources, the optimal single-stage extraction pressure and extraction temperature of each super dry working fluid in regenerative ORC is determined according to the net power output and thermal efficiency of regenerative ORC, respectively. The results show that heptane may match the closed heat source best with an optimal extraction condition at 0.45 MPa and 478.64 K. While pentane, hexane, propylcyclohexane, undecane and o-xylene may match five different open heat sources. Their corresponding optimal extraction conditions are 0.85 MPa/408.78 K, 0.6 MPa/445.33 K, 0.35 MPa/570.22 K, 0.175 MPa/584.25 K and 0.4 MPa/544.32 K.

Numerical simulation of flow boiling heat transfer characteristics of R134a/Ethane binary mixture in horizontal micro-tube

The cryogenic organic Rankine cycle (ORC) is appropriate for recovering the cold energy of liquefied natural gas (LNG) for power generation. However, pure working fluids in ORC are challenging to match the evaporation curve of LNG appropriately, which causes a large amount of exergy loss. Thus, adopting mixture working fluid is a good option due to their temperature-varying evaporation and condensation process. This study investigates the heat transfer characteristic of R134a/ethane (widely adopted in cryogenic ORC as pure working fluid) binary mixture in the horizontal micro-tube through numerical simulation. The law of boiling heat transfer characteristics with vapor quality, heat flux, mass flow, ethane mole fraction, and other factors are obtained. The simulation illustrated that the boiling heat transfer coefficient increases with the heat flux and mass flow. Furthermore, compared with R134a, ethane has higher thermal conductivity, lower vapor density, and latent heat of vaporization. Hence, the heat transfer coefficient of the R134a/ethane mixture increases with the ethane’s mole fraction. The fluid disturbance mainly influences the pressure drop and the turbulence intensity significantly when the fluid is transformed into a gas–liquid flow. This study could provide insights into boiling heat transfer improvement of binary mixtures for ORC power generation applications.

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.

Dynamic performance and control strategy of a combined heat and power system driven by geothermal energy considering the building multi-load requirements

The combined heat and power (CHP) system driven by geothermal energy has been confirmed as a promising technology due to its high energy conversion efficiency and environmental benefits. However, the operation of the geothermal CHP system is affected by the external disturbances and energy demand of users. In this paper, a geothermal CHP system coupling the organic Rankine cycle (ORC)with heat pump cycle was developed to supply heat and electricity simultaneously. Meanwhile, a model of the building multi-load based on back propagation neural network was established to acquire the energy demand of users. The dynamic models of the geothermal CHP system were established to explore the effect of external disturbances on the system dynamic performance. Besides, a prediction-feedback control strategy was developed to improve the stability of the geothermal CHP system under fluctuant energy demands. Results show that the heat output of the geothermal CHP system can be improved by increasing the mass flow rate of working fluid in heat pump cycle, and the electrical output can be improved by increasing the mass flow rate of working fluid in ORC and geothermal water simultaneously. Moreover, the shorter settling time indicates that the prediction-feedback control strategy can enable the geothermal CHP system to match the energy demand quickly.

Insight into the pyrolysis of R32 and R32/CO2 as working fluid for organic Rankine cycle

Organic Rankine cycle(ORC) is one of the effective ways to improve energy utilization and develop renewable energy. R32/CO2 is a mixture working fluid with outstanding comprehensive performance in ORC. However, organic working fluids may undergo pyrolysis in ORC. Therefore, it is necessary to study the thermal stability and pyrolysis mechanism of mixture fluid R32/CO2. Firstly, the thermal stability of R32 and R32/CO2(70/30 mol%) was studied using high-temperature and high-pressure experiments. The results showed that the pyrolysis temperatures of both R32 and R32/CO2 were 270–290 ℃, and the main gas product of R32 and R32/CO2 were HF. Then, the pyrolysis mechanism of R32 and R32/CO2 was investigated using ReaxFF MD. In ReaxFF MD, the pyrolysis mainly occurred in R32, CO2 mainly acted as an inert gas in the pyrolysis of R32/CO2, so the pyrolysis mechanism of R32 was mainly analyzed. The main fragments of pure R32 pyrolysis were HF, F, H, CH2F, CHF2, CF, CH and C2. The pyrolysis pathways of working fluids can be divided into two types: abstraction reaction and self-decomposition reaction. The self-decomposition reaction mainly occurred in the former stage, and the abstraction reaction mainly occurred in the latter stage of pyrolysis.

Selecting working fluids in organic Rankine cycle (ORC) for waste heat applications and optimal cycle parameters for different hot source temperatures

Selecting working fluids in organic Rankine cycle (ORC) for waste heat applications and optimal cycle parameters for different hot source temperatures

Thermal stability and pyrolysis mechanism of working fluids for organic Rankine cycle: A review

Thermal stability and pyrolysis mechanism of working fluids for organic Rankine cycle: A review

An effective and simplified method to select the working fluid for waste heat recovery based Organic Rankine Cycle

Organic Rankine Cycle (ORC) is an attractive option to utilize the low-grade waste heat for power generation. The selection of working fluid for ORC is a challenging task because of environmental constraints as most of the organic fluids has the capacity to damage the environment. In this research, a method for the selection of an optimum working fluid for the operation low grade waste heat is determined. The selection of the optimum working fluids depends upon the thermal efficiency, Global Warming Potential (GWP), Ozone Depletion Potential (ODP) and Atmospheric Lifetime of the fluid. Twelve different organic fluids including R134a, butene, R22, R152a, R245fa, R290, R161a, isobutene, isobutane, dimethyl ether, R600 and R124 are selected for the study. The ORC is analyzed by using EES at 2 MPa, 2.5 MPa and 3 MPa. The thermal efficiency of ORC is determined and is found that high operating pressure is favorable for the operation of ORC. At 2.5 MPa, the top three working fluids are R-245fa, R-600 and Iso-butene with an efficiency of 12.7%, 12% and 11.3% respectively. On the basis of thermal efficiency, R-245fa is the best but it has the highest GWP and atmospheric life of 1050 and 7.7 years. R-600 has GWP and atmospheric life of just 20 and 0.018 years. On the basis of environmental constraints, R-600 is found to be more beneficial than R-245fa. It is concluded that R-600 is the optimum working fluid for the operation of low-grade waste heat ORC.

Experimental investigation of combustion engine with novel jacket and flue gas heat recovery

Internal combustion engines (ICE) are utilized in a number of energy and transportation systems and with the prospect of synthetic green fuels have also secured a place in the future low emission systems. Still, aiming at the effective utilization of the fuel suggests an addition of waste heat recovery systems such as organic Rankine cycle (ORC) to boost electric efficiency. Greater widespread of the ORC integration into the ICE systems is however limited from multiple aspects. Furthermore, when these systems are employed, they are typically applied only for flue gas waste heat utilization, while the large amounts of lower temperature jacket cooling heat remain unutilized, or at the cost of high system complexity. Direct cooling of the ICE jacket by the ORC working fluid has been previously theoretically proposed to tackle some of them. Complexity of the system can be reduced while more waste heat can be effectively transferred from the ICE jacket cooling to the ORC. Here we propose further configuration of ICE waste heat sources integration into a biomass fired ORC unit, creating a multi-fuel system. Such system offers the possibility to increase the electricity demand while reducing biomass consumption. This system has been experimentally explored on a case of a 3 kWe/50 kWth micro-cogeneration ORC and an 8 kWeICE. The experimental data are evaluated in comparison to the theoretically predicted operation. A specific control system has been developed for this system to be easily operated. The results, experience and operation verification from the ICE jacket cooling with the ORC fluid can be also utilized in the construction for waste heat recovery ORC integrated to ICE for higher electrical efficiency. Integration of combined direct jacket and flue gas heat recovery increased the overall electrical efficiency of the system from about 5% for operation of standalone ORC to over 20% for full ICE power.

Comparative study, working fluid selection, and optimal design of three systems for electricity and freshwater based on solid oxide fuel cell mover cycle

In this paper, a novel electricity and freshwater cogeneration system is proposed in which an organic Rankine cycle (ORC) is utilized for recovering the wasted heat of a Solid Oxide Fuel Cell (SOFC). The electricity generated in the recovery unit is used to derive a Reverse Osmosis (RO) water desalination unit. Also, three different configurations are considered for the ORC unit. At the first step, a robust three-objective genetic optimization is applied for all three configurations and the best one is selected to have the maximum generated power, minimum total productions cost, and minimum pollutant emissions, simultaneously. The second step is focused on selecting the best working fluid of the optimal ORC (among five different working fluids). The results demonstrated that the regenerative configuration with the R123 working fluid has the best performance. For this optimal layout, the outputs are included 649.2 kW of the net generated power and 34.5 m3/h of freshwater At this condition, the optimal exergy efficiency, product unit cost, and pollutant emission factor are 46.29%, 28.59 US$/GJ, 0.2587 kg/kWh, respectively.