Exergy Analysis of Organic Rankine Cycles with Zeotropic Working Fluids

Waste heat recovery is one of the possible solutions to improve the efficiency of internal combustion engines.Instead of wasting the exhaust stream of an energy conversion system into the environment,its residual energy content can be usefully recovered,for example in Organic Rankine Cycles(ORC).This technology has been largely consolidated in stationary power plants but not yet for mobile applications,such as road transport,due to the limitations in the layout and to the constraints on the size and weight of the ORC system.An ORC system installed on the exhaust line of a bus powered by a natural gas spark ignition engine has been investigated.The thermal power available at engine exhaust has been evaluated by measuring gas temperature and mass flow rate during real driving operation.The waste thermal power has been considered as heat input for the ORC plant simulation.A detailed heat exchanger model has been developed because it is a crucial component for the ORC performance.The exergy analysis of the ORC was performed comparing different working fluids:R601,R1233zd(E)and two zeotropic blends of the two organic pure fluids.The model allowed the evaluation of the ORC produced energy over the driving cycle and the potential benefit on the engine efficiency.

Life Cycle Assessment Introduced by Using Nanorefrigerant of Organic Rankine Cycle System for Waste Heat Recovery

The use of nanorefrigerants in Organic Rankine Cycle(ORC)units is believed to affect the cycle environment performance,but backed with very few relevant studies.For this purpose,a life cycle assessment(LCA)has been performed for the ORC system using nanorefrigerant,the material and energy input,characteristic indicators and comprehensive index of environmental impact,total energy consumption and energy payback time(BPBT)of the whole life cycle of ORC system using Al_(2)O_(3)/R141b nanorefrigerant were calculated.Total environmental comprehensive indexes reveal that ECER-135 index decrease by 1.5%after adding 0.2%Al_(2)O_(3)nanoparticles to R141b.Based on the contribution analysis and sensitivity analysis,it can be found out ORC system manufacturing is of the most critical stage,where,the ECER-135 index of ORC component production is the greatest,followed by the preparation process of R141b,transportation phase,and that of Al_(2)O_(3)nanoparticles preparation is small.The retirement phase which has good environmental benefits affects the result significantly by recycling important materials.Meanwhile,the main cause and relevant suggestion for improvement were traced respectively.Finally,the environmental impacts of various power generations were compared,and results show that the power route is of obvious advantage.Among the renewable energy,ORC system using Al_(2)O_(3)/R141b nanorefrigerant with minimal environmental impact is only 0.67%of coal-fired power generation.The environmental impact of current work is about 14.34%of other nations’PV results.

BP-PID Control Applied in Evaporator of Organic Rankine Cycle System

According to the problem that the selection of traditional PID control parameters is too complicated in evaporator of Organic Rankine Cycle system(ORC),an evaporator PID controller based on BP neural netw ork optimization is designed. Based on the control theory,the model of ORC evaporator is set up. The BP algorithm is used to control the Kp,Kiand Kdparameters of the evaporator PID controller,so that the evaporator temperature can reach the optimal state quickly and steadily. The M ATLAB softw are is used to simulate the traditional PID controller and the BP neural netw ork PID controller. The experimental results show that the Kp,Kiand Kdparameters of the BP neural netw ork PID controller are 0. 5677,0. 2970,and 0. 1353,respectively.Therefore,the evaporator PID controller based on BP neural netw ork optimization not only satisfies the requirements of the system performance,but also has better control parameters than the traditional PID controller.

Thermodynamic and Techno-economic Analysis of a Triple-pressure Organic Rankine Cycle: Comparison with Dual-pressure and Single-pressure ORCs

Investigation of a triple-pressure organic Rankine cycle(TPORC) using geothermal energy for power generation with the net power output of the TPORC analyzed by varying the evaporation pressures, pinch temperature differences(tpp) and degrees of superheat(tsup) aimed to find the optimum operation conditions of the system. The thermodynamic performance of the TPORC was compared with a dual-pressure organic Rankine cycle(DPORC) and a single-pressure ORC(SPORC) for geofluid temperatures ranging from 100°C to 200°C, with particular reference to the utilization of a hot dry rock(HDR) geothermal resource. Thermodynamic performances of the TPORC system using eight different organic working fluids have also been investigated in terms of the net power outputs. Results show that a higher geofluid mass flow rate can make a considerable contribution to shortening the payback period(PBP) as well as to decreasing the levelized electricity cost(LEC), especially when the geofluid temperature is low. For the temperature range investigated, the order from high to low based on thermodynamic and techno-economic performances is found to be TPORC > DPORC > SPORC. In terms of using geothermal resources within the given temperatures range(100°C–200°C), the TPORC system can be a better choice for geothermal power generation so long as the wellhead geofluid temperature is between 140°C and 180°C.

Thermo-economic Investigation of an Enhanced Geothermal System Organic Rankine Cycle and Combined Heating and Power System

As a potentially viable renewable energy, Enhanced Geothermal Systems(EGSs) extract heat from hot dry rock(HDR) reservoirs to produce electricity and heat, which promotes the progress towards carbon peaking and carbon neutralization. The main challenge for EGSs is to reduce the investment cost. In the present study, thermo-economic investigations of EGS projects are conducted. The effects of geofluid mass flow rate, wellhead temperature and loss rate on the thermo-economic performance of the EGS organic Rankine cycle(ORC) are studied. A performance comparison between EGS-ORC and the EGS combined heating and power system(CHP) is presented. Considering the CO_(2)emission reduction benefits, the influence of carbon emission trading price on the levelized cost of energy(LCOE) is also presented. It is indicated that the geofluid mass flow rate is a critical parameter in dictating the success of a project. Under the assumed typical working conditions, the LCOE of EGS-ORC and EGS-CHP systems are 24.72 and 16.1 cents/k Wh, respectively. Compared with the EGS-ORC system, the LCOE of the EGS-CHP system is reduced by 35%. EGS-CHP systems have the potential to be economically viable in the future. With carbon emission trading prices of 12.76 USD/ton, the LCOE can be reduced by approximately 8.5%.

Performance Analysis of an Organic Rankine Cycle with a Preheated Ejector

The so-called organic Rankine cycle(ORC)is an effective technology allowing heat recovery from lower temperature sources.In the present study,to improve its thermal efficiency,a preheated ejector using exhaust steam coming from the expander is integrated in the cycle(EPORC).Considering net power output,pump power,and thermal efficiency,the proposed system is compared with the basic ORC.The influence of the ejector ratio(ER)of the preheated ejector on the system performances is also investigated.Results show that the net power output of the EPORC is higher than that of the basic ORC due to the decreasing pump power.Under given working conditions,the average thermal efficiency of EPORC is 29%higher than that of ORC.The ER has a great impact on the performance of EPORC by adjusting the working fluid fed to the pump,leading to significant variations of the pump work Moreover,the ER has a remarkable effect on the working fluid temperature lift(TL)at the evaporator inlet,thus reducing the evaporator heat load.According to the results,the thermal efficiency of EPORC increases by 30%,when the ER increases from 0.05 to 0.4.

Experimental Investigation of Organic Rankine Cycle (ORC) for Low Temperature Geothermal Fluid: Effect of Pump Rotation and R-134 Working Fluid in Scroll-Expander

Organic Rankine Cycle(ORC)is one of the solutions to utilize a low temperature geothermal fluid for power generation.The ORC system can be placed at the exit of the separator to extract energy from brine.Furthermore,one of the main components of the system and very important is the pump.Therefore,in this research,the pump rotation is examined to investigate the effect on power output and energy efficiency for low temperature geothermal fluid.The rotation is determined by using an inverter with the following frequencies:7.5,10,12.5,15 and 17.5 Hz,respectively.R-134 working fluid is employed with 373.15 K evaporator temperature in relation to the low temperature of the geothermal fluid.Furthermore,the condenser temperature and fluid pressure were set up to 293.15 K and 5×10^(5) Pa,respectively.This research uses a DC generator with a maximum power of 750 Watt and the piping system is made from copper alloy C12200 ASTM B280 with size 1.905×10^(−2) m and a thickness of 8×10^(−4) m.The results showed that there is an increase in mass flow rate,enthalpy and generator power output along with increasing pump rotation.In addition,it showed that the maximum generator output power was 377.31 Watt at the highest pump rotation with a frequency of 17.5 Hz.

Analysis of Solar Direct-Driven Organic Rankine Cycle Powered Vapor Compression Cooling System Combined with Electric Motor for Office Building Air-Conditioning

Solar energy powered organic Rankine cycle vapor compression cycle(ORC-VCC)is a good alternative to convert solar heat into a cooling effect.In this study,an ORC-VCC system driven by solar energy combined with electric motor is proposed to ensure smooth operation under the conditions that solar radiation is unstable and discontinuous,and an office building located in Guangzhou,China is selected as a case study.The results show that beam solar radiation and generation temperature have considerable effects on the system performance.There is an optimal generation temperature at which the system achieves optimum performance.Also,as a key indicator,the cooling power per square meter collector should be considered in the hybrid solar cooling system in design process.Compared to the vapor compression cooling system,the hybrid cooling system can save almost 68.23%of electricity consumption.

A Steady-State Evaluation of Simple Organic Rankine Cycle (SORC) with Low-Temperature Grade Waste Heat Source

The low-grade heat source recovery is usually constrained by the physical characteristics of the hot fluid medium. The present work focuses on the importance of energy recovery from low-temperature waste energy sources and its conversion to useful electrical power. The thermal performance analysis is based on the utilization of R-123, R-134a, R-290, R-245fa, R-1234ze-E, and R-1233zd-E fluids in a simple organic Rankine cycle (SORC). A waste energy source from an industrial sector is suggested to be available at a temperature greater than 110 °C. A hypothetical organic Rankine cycle of 10 kW nominal heat recovery was implemented to evaluate the cycle performance. It operates at evaporation and condensation temperatures of 90 °C and 45 °C, respectively. The selected vapor superheat degree at the expander entrance was 5 °C - 15 °C, and the liquid was subcooled by 5 °C at the discharge port of condenser. The estimated first law cycle thermal efficiency fell in the range of 6.4% - 7.7%. The results showed that the thermal efficiencies of R-134a, R-123, R-245fa, R-1233zd-E, and R-1234ze-E were higher than that of R-290 by 10% - 14%, 11% - 12%, 9% - 12%, 4% - 7% and 1% - 3%, respectively. R-1233zd-E, R-1234ze-E, and R-290 showed close thermal efficiency values, and it fell in the range of 6.7% - 7% for the (SORC) at a superheat degree of 15 °C. At the same superheat degree, the corresponding range of thermal efficiency for R-134a, R-123 and R-245fa fell within 7.5% - 7.7%. R-134a possessed the highest net power output of the (SORC);it reached a value of 0.91 kW as predicted at 15 °C superheat degree. Increasing the expander volumetric efficiency value by 10% improved the cycle thermal efficiency by 10% - 12%.

Design and Blade Number Ratio Analysis of Organic Rankine Cycle Radial-Inflow Turbine on Vehicle

The organic Rankine cycle is widely used in industrial waste heat, engine waste heat and other waste heat recovery applications, and as a key component of the system, it affects the efficiency and output power of the system. In this paper, a centripetal turbine is designed for the organic Rankine cycle, using vehicle exhaust gas as the heat source. Numerical simulations are performed to analyze the effect of the ratio of the number of guide vane blades to the number of impeller blades (vane number ratio) on the turbine performance and flow field. The results show that the effect of the number of impeller blades on the turbine entropy efficiency, the average exit velocity and the temperature of the guiding grate becomes less and less as the ratio of the number of blades increases. The optimum turbine performance is obtained when the number of impeller blades and the ratio of the number of blades are 17 and 1.5882, respectively, and the expansion performance of the guide impeller is improved and the isentropic efficiency of the turbine is improved by 3.84% compared with the preliminary number of blades.

Exergoeconomic Evaluation and Optimization of Dual Pressure Organic Rankine Cycle (ORC) for Geothermal Heat Source Utilization

In the present study, a dual-pressure organic Rankine cycle (DORC) driven by geothermal hot water for electricity production is developed, investigated and optimized from the energy, exergy and exergoeconomic viewpoint. A parametric study is conducted to determine the effect of high-stage pressure and low-stage pressure variation on the system thermodynamic and exergoeconomic performance. The DORC is further optimized to obtain maximum exergy efficiency optimized design (EEOD case) and minimum product cost optimized design (PCOD case). The exergy efficiency and unit cost of power produced for the optimization of EEOD case and PCOD case are 33.03% and 3.059 cent/kWh, which are 0.3% and 17.4% improvement over base case, respectively. The PCOD case proved to be the best, with respect to minimum unit cost of power produced and net power output over the base case and EEOD case.

Working Fluid Distribution and Charge Regulation Control in Organic Rankine Cycle

Charge-based studies,in particular investigations of mass distribution,are still almost absent,although the efficiency of the organic Rankine cycle(ORC)has attracted a great deal of scholarly attention.This paper aims to provide a new perspective on the intrinsic relationship among the mass distribution,phase-zone distribution in the heat exchanger(HEX),charge of working fuid(WF),rotation speed of the pump(RSP),and system performance.A comprehensive ORC simulation model is presented by linking each component's sub-models,including the independent models for HEX,pump,and expander in an object-oriented fashion.The visualization study of mass distribution of the WF in the system is investigated under different working conditions.Furthermore,the volume and mass of the gas phase,two-phase and liquid phase of WF in the HEX and their variation rules are analyzed in-depth.Finally,the strategies of charge reduction considering HEX areas and pipe sizes are investigated.The results show that the model based on the interior-point method provides high levels of accuracy and robustness.The mass ratio of the WF is concentrated in the liquid receiver,especially in the regenerator,which is 32.9%and 21.9%of the total mass,respectively.Furthermore,2.4 kg(6.9%)WF in the system gradually migrates to the high-temperature side as the RSP increases while 6.1 kg(17.4%)WF migrates to the low-temperature side,especially to the condenser,as the charge in the system increases.Output power and efficiency both decrease gradually after the peak due to changes in RSP and charge.Last,reducing heat transfer areas of the condenser and regenerator is the most effective way to reduce WF charge.

Performance Assessment of a Novel Polygeneration System Based on the Integration of Waste Plasma Gasification,Tire Pyrolysis,Gas Turbine,Supercritical CO_(2)Cycle and Organic Rankine Cycle

In this paper,a novel polygeneration system involving plasma gasifier,pyrolysis reactor,gas turbine(GT),supercritical CO_(2)(S-CO_(2))cycle,and organic Rankine cycle(ORC)has been developed.In the proposed scheme,the syngas is obtained by the gasification and the pyrolysis is first burned and drives the gas turbine for power generation,and then the resulting hot exhaust gas is applied to heat the working fluid for the supercritical CO_(2)cycle and the working fluid for the bottom organic Rankine cycle.In addition to the electrical output,the pyrolysis subsystem also produces pyrolysis oil and char.Accordingly,energy recovery is achieved while treating waste in a non-hazardous manner.The performance of the new scheme was examined by numerous methods,containing energy analysis,exergy analysis,and economic analysis.It is found that the net total energy output of the polygeneration system could attain 19.89 MW with a net total energy efficiency of 52.77%,and the total exergy efficiency of 50.14%.Besides,the dynamic payback period for the restoration of the proposed project is only 3.31 years,and the relative net present value of 77552640 USD can be achieved during its 20-year lifetime.

A Method for Determining the Operable Ideal Condensation Temperature of Dry and Isentropic Fluids Used in Organic Rankine Cycle(ORC)Based on Temperature-Entropy(T-s)Diagram

Condensation temperature is one of the crucial parameters determining the performance of an organic Rankine cycle.It is necessary to consider the differences in the working fluids themselves when setting the condensation temperature of organic Rankine cycle.In current study,temperature-entropy(T-s)diagram is employed to describe the difference in working fluids.Three areas of dry and isentropic fluids in a temperature-entropy(T-s)diagram,which are the area denoting net output work of cycle(A_(1),the area denoting net output work of the Carnot cycle(A),and the curved triangle in superheated region denoting condensation characteristics(A_(2)),are defined.On this basis,the ratio of A_(2)to A_(1)and the ratio of A_(1)to A are calculated.Logarithmic Mean Difference of the above two ratios is obtained to determine the operable ideal condensation temperature of 66 dry and isentropic fluids employed in Organic Rankine Cycle.The findings indicate that the operable ideal condensation temperatures for the majority of dry and isentropic fluids are in the range of 305 K to 310 K.The work presented in this study may be useful for designing and establishing an Organic Rankine Cycle system.

Effect of flue gas outlet temperature in evaporator on thermal economic performance of organic Rankine cycle system for sinter waste heat recovery

In order to improve the recovery and utilization rates of sinter waste heat effectively,the organic Rankine cycle(ORC)system with subcritical cycle was designed to recover the low-temperature sinter cooling flue gas waste heat in an annular cooler for power generation.The thermodynamic,economic and multi-objective optimization models of ORC system were established,and R600a was selected as the ORC working medium.Subsequently,the variations in system thermodynamic performance and economic performance with the ORC thermal parameters were discussed in detail,and the optimal ORC thermal parameters were determined.The results show that the system net output power increases with increasing the evaporation temperature and decreasing the condensation temperature and increases first and then,decreases with the increase in superheat degree for a given flue gas outlet temperature in the evaporator,while the heat transfer area per unit net output power appears different variation trends in various ranges of flue gas outlet temperature.Taking the sinter cooling flue gas waste heat of 160℃as the ORC heat source,the optimal thermal parameters of ORC system were the flue gas outlet temperature of 90℃,the evaporation temperature of 95℃,the superheat degree of 10℃,and the condensation temperature of 28℃.

Analysis of a 1 kW organic Rankine cycle using a scroll expander for engine coolant and exhaust heat recovery

The development of engine waste heat recov- ery technologies attracts ever increasing interests due to the rising strict policy requirements and environmental con- cerns. This paper presented the study of engine coolant and exhaust heat recovery using organic Rankine cycle （ORC）. Eight working fluids were selected to evaluate and compare the performance of the integrated waste heat recovery system. Rather than the conventional engine ORC system mainly focusing on the utilization of exhaust energy, this work proposed to fully use the engine coolant energy by changing the designed parameters of the ORC system. The case study selected a small engine as the heat source to drive the ORC system using a scroll expander for power production. The evaluation results suggest that under the engine rated condition, the solution to fully recover the engine coolant energy can achieve a higher power generation performance than that of the conven- tional engine ORC system. The results suggest that adding a recuperator to the ORC system can potentially improve the system performance when the working fluids are dry and the overall dumped heat demand of the system can be reduced by 12% under optimal conditions. When the ORC evaporating and condensing temperature are respectivelyset at 85℃ and 30℃, the integrated engine waste heat recovery system can improve the overall system efficiency by 9.3% with R600, R600a or n-Pentane as the working fluid.

Optimization of Low-Temperature Exhaust Gas Waste Heat Fueled Organic Rankine Cycle

Low temperature exhaust gases carrying large amount of waste heat are released by steel-making process and many other industries, Organic Rankine Cycles （ORCs） are proven to be the most promising technology to re- cover the low-temperature waste heat, thereby to get more financial benefits for these industries. The exergy analysis of ORC units driven by low-temperature exhaust gas waste heat and charged with dry and isentropic fluid was per- formed, and an intuitive approach with simple impressions was developed to calculate the performances of the ORC unit. Parameter optimization was conducted with turbine inlet temperature simplified as the variable and exergy effi- ciency or power output as the objective function by means of Penalty Function and Golden Section Searching algo- rithm based on the formulation of the optimization problem. The power generated by the optimized ORC unit can be nearly as twice as that generated by a non-optimized ORC unit. In addition, cycle parametric analysis was performed to examine the effects of thermodynamic parameters on the cycle performances such as thermal efficiency and exergy efficiency. It is proven that performance of ORC unit is mainly affected by the thermodynamic property of working fluid, the waste heat temperature, the pinch point temperature of the evaporator, the specific heat capacity of the heat carrier and the turbine inlet temperature under a given environment temperature.

Analysis of the thermodynamic performance limits of the organic Rankine cycle in low and medium temperature heat source applications

In this paper,an exploration of the practical thermodynamic performance limits of the organic Rankine cycle(ORC)under working fluid and cycle parameter restrictions is presented.These performance limits are more realistic benchmarks for the thermodynamic cycle than the efficiency of the Carnot cycle.Subcritical ORC configuration with four typical case studies that are related to temperature ranging from 373.15 to 673.15 K is taken into account.The ORC is defined by its cycle parameters and working fluid characteristic properties.The cycle parameters involve evaporation temperature(T_(eva)),condensation temperature(T_(con))and superheat degree(ΔT_(sup)),while the working fluids are represented by the characteristic properties including critical temperature(T_(c)),critical pressure(p_(c)),acentric factor(ω),and molar ideal gas isobaric heat capacity based on the principle of corresponding states.Subsequently,Pareto optimum solutions for obtained hypothetical working fluids and cycle parameters are achieved using multi-objective optimization method with the consideration of both thermal efficiency(η_(th))and volumetric power output(VPO).Finally,sensitivity analysis of the working fluid characteristic properties is conducted,and the second law of thermodynamics analysis,especially the applicability of entropy generation minimization,is performed.The results show that the current commonly used working fluids are widely scattered below the Pareto front that represents the tradeoff betweenη_(th) and VPO for obtained hypothetical fluids.T_(eva) and T_(con) are the most dominant cycle parameters,while T_(c) and ωtend to be the most dominant characteristic property parameters.The entropy generation minimization does not give the same optimal results.

Performance Evaluation and Optimization of a Novel System Combining a Photovoltaic/Thermal Subsystem&an Organic Rankine Cycle Driven by Solar Parabolic Trough Collector

A novel coupling system that combines a photovoltaic/thermal(PV/T)subsystem and an Organic Rankine Cycle(ORC)driven by solar parabolic trough collector(PTC)is presented in this paper.The mathematical model is initially built.On the basis,the influence of area ratio of two collectors(PV/T and PTC)on the performance of system is discussed.The results show that the optimal area ratio of PV/T to PTC is 8:2,which can achieve the maximum energy output.Moreover,the performance of the coupling system and two independent systems(PV/T and ORC system)are compared and analyzed.The results show that the coupling system is more reliable and its total output energy(heat and electricity)is the highest,compared with the other two independent systems.The solar energy utilization efficiency of the coupling system is 40%higher than that of the other two independent systems in the steady-state simulation.Moreover,the annual output energy per unit area collector of the coupling system is 13%higher than that of the other two independent systems in the dynamic simulation.Furthermore,in the dynamic simulation of a typical day,the PV panels’temperature of the coupling system is 5℃–7℃ lower than that of the independent PV/T system.It means that the power generation efficiency of PV panels can be increased by 1.5%–3.5%.This study aims to explore the operation characteristics of the novel solar energy utilization coupling system and promote the development of renewable energy utilization models,which provides a reference for the design and optimization of related energy systems.

Comparison of Conventional and Advanced Exergy Analysis for Dual-Loop Organic Rankine Cycle used in Engine Waste Heat Recovery

At present,the dual-loop organic Rankine cycle(DORC)is regarded as an important solution to engine waste heat recovery(WHR).Compared with the conventional exergy analysis,the advanced exergy analysis can better describe the interactions between system components and the irreversibility caused by economic or technical limitations.In order to systematically study the thermodynamic performance of DORC,the conventional and advanced exergy analyses are compared using an inline 6-cylinder 4-stroke turbocharged diesel engine.Meanwhile,the sensitivity analysis is implemented to further investigate the influence of operating parameters on avoidable-endogenous exergy destruction.The analysis result of conventional exergy analysis demonstrates that the priorities for the components that should be improved are in order of the high-temperature evaporator,the low-temperature turbine,the first low-temperature evaporator and the high-temperature condenser.The advanced exergy analysis result suggests that the avoidable exergy destruction values are the highest in the low-temperature turbine,the high-temperature evaporator and the high-temperature turbine because they have considerable endogenous-avoidable exergy destruction.The sensitivity analysis indicates that reducing the evaporation pinch point and raising the turbine efficiency can decrease the avoidable exergy destruction.