Thermodynamic Performance Analysis of Geothermal Power Plant Based on Organic Rankine Cycle (ORC) Using Mixture of Pure Working Fluids

The selection of working fluid significantly impacts the geothermal ORC’s Efficiency.Using a mixture as a working fluid is a strategy to improve the output of geothermal ORC.In the current study,modelling and thermodynamic analysis of ORC,using geothermal as a heat source,is carried out at fixed operating conditions.The model is simulated in the Engineering Equation Solver(EES).An environment-friendly mixture of fluids,i.e.,R245fa/R600a,with a suitable mole fraction,is used as the operating fluid.The mixture provided the most convenient results compared to the pure working fluid under fixed operating conditions.The impact of varying the evaporator pressure on the performance parameters,including energy efficiency,exergy efficiency and net power output is investigated.The system provided the optimal performance once the evaporator pressure reached the maximum value.The efficiencies:Energy and Exergy,and Net Power output of the system are 16.62%,64.08%and 2199 kW for the basic cycle and 20.72%,67.76%and 2326 kW respectively for the regenerative cycle.

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.

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.

Evaluation of working fluids for organic Rankine cycles using group-contribution methods and second-law-based models

The group-contribution (GC) methods suffer from a limitation concerning to the prediction of process-related indexes, e.g., thermal efficiency. Recently developed analytical models for thermal efficiency of organic Rankine cycles (ORCs) provide a possibility of overcoming the limitation of the GC methods because these models formulate thermal efficiency as functions of key thermal properties. Using these analytical relations together with GC methods, more than 60 organic fluids are screened for medium-low temperature ORCs. The results indicate that the GC methods can estimate thermal properties with acceptable accuracy (mean relative errors are 4.45%-11.50%);the precision, however, is low because the relative errors can vary from less than 0.1% to 45.0%. By contrast, the GC-based estimation of thermal efficiency has better accuracy and precision. The relative errors in thermal efficiency have an arithmetic mean of about 2.9% and fall within the range of 0-24.0%. These findings suggest that the analytical equations provide not only a direct way of estimating thermal efficiency but an accurate and precise approach to evaluating working fluids and guiding computer-aided molecular design of new fluids for ORCs using GC methods.

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.

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%.

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.

Thermodynamic optimization and fluid selection of organic Rankine cycle driven by a latent heat source

Organic Rankine cycle(ORC) is applicable for the heat-work conversion. Whereas, there also exist a lot issues that influence the efficiency and the cost of the system. In this work, eleven pure working fluids(as categorized into alkanes, and fluorinated alkanes) are investigated based on the first and second law of thermodynamics. The major objective is to obtain the most suitable working fluid for the latent heat source. The results show that the working fluid is an important factor of the system performance. The heat absorption of the working fluid in the evaporator is inversely proportional to the evaporating temperature, but the thermal and exergetic efficiencies are just the opposite. RC318 has the highest net power output and the lowest outlet temperature of the heat source, but its global warming potential(GWP) value is too high. The cyclohexane shows the highest thermal efficiency among the fluids investigated. Moreover, the figure of merit(FOM) of the isobutane is higher than that of other working fluids. Overall, the cyclohexane shows that the optimal comprehensive performance is more feasible for medium grade heat source in engineering applications.

Energy and exergy recovery from exhaust hot water using organic Rankine cycle and a retrofitted configuration

Exhaust hot water （EHW） is widely used for various industrial processes. However, the excess heat carried by EHW is typically ignored and discharged into the environment, resulting in heat loss and heat pollution. An organic Rankine cycle （ORC） is an attractive technology to recycle heat from low-temperature energy carriers. Herein, ORC was used to recycle the heat carried by EHW. To investigate the energy and exergy recovery effects of EHW, a mathematical model was developed and a parametric study was conducted. The energy efficiency and exergy efficiency of the EHW-driven ORC system were modeled with R245fa, Rl13 and R123 as the working fluids. The results demonstrate that the EHW and evaporation temperatures have significant effects on the energy and exergy efficiencies of the EHW-driven ORC system. Under given EHW conditions, an optimum evaporation temperature exists corresponding to the highest exergy efficiency. To further use the low-temperature EHW, a configuration retrofitted to the ORC by combining with flash evaporation （FE） was conducted. For an EHW at 120 ~C and 0.2 MPa, the maximum exergy efficiency of the FE-ORC system is 45.91% at a flash pressure of 0.088 MPa. The FE-ORC performs better in exergy efficiency than the basic FE and basic EHW-driven ORC.

Simulation and performance analysis of organic Rankine cycle combined heat and power system

To improve the overall thermal efficiency of the organic Rankine cycle（ ORC）, a simulation study was carried out for a combined heat and power（ CHP） system, using the Redlich-Kuang-Soave（ RKS） equation of state. In the system,R245 fa was selected as the working fluid. A scroll expander was modeled with empirical isentropic expansion efficiency.Plate heat exchangers were selected as the evaporator and the condenser, and detailed heat transfer models were programmed for both one-phase and two-phase regions. Simulations were carried out at seven different heat source temperatures（ 80,90, 100, 110, 120, 130, 140 ℃） in combination with eight different heat sink temperatures（ 20, 25, 30, 35, 40, 45, 50,55 ℃）. Results showthat in the ORC without an internal heat exchanger（ IHE）, the optimum cycle efficiencies are in the range of 7. 0% to 7. 3% when the temperature differences between the heat source and heat sink are in the range of 70 to90 ℃. Simulations on CHP reveal that domestic hot water can be produced when the heat sink inlet temperature is higher than40 ℃, and the corresponding exergy efficiency and overall thermal efficiency are 29% to 56% and 87% to 90% higher than those in the non-CHP ORC, respectively. It is found that the IHE has little effect on the improvement of work output and efficiencies for the CHP ORC.

Coupling effect of evaporation and condensation processes of organic Rankine cycle for geothermal power generation improvement

Organic Rankine cycle(ORC)is widely used for the low grade geothermal power generation.However,a large amount of irreversible loss results in poor technical and economic performance due to its poor matching between the heat source/sink and the working medium in the condenser and the evaporator.The condensing temperature,cooling water temperature difference and pinch point temperature difference are often fixed according to engineering experience.In order to optimize the ORC system comprehensively,the coupling effect of evaporation and condensation process was proposed in this paper.Based on the laws of thermodynamics,the energy analysis,exergy analysis and entropy analysis were adopted to investigate the ORC performance including net output power,thermal efficiency,exergy efficiency,thermal conductivity,irreversible loss,etc.,using geothermal water at a temperature of 120℃as the heat source and isobutane as the working fluid.The results show that there exists a pair of optimal evaporating temperature and condensing temperatures to maximize the system performance.The net power output and the system comprehensive performance achieve their highest values at the same evaporating temperature,but the system comprehensive performance corresponds to a lower condensing temperature than the net power output.

Parametric optimization and performance comparison of organic Rankine cycle with simulated annealing algorithm

Taking the ratio of heat transfer area to net power and heat recovery efficiency into account, a multi-objective mathematical model was developed for organic Rankine cycle （ORC）. Working fluids considered were R123, R134a, R141b, R227ea and R245fa. Under the given conditions, the parameters including evaporating and condensing pressures, working fluid and cooling water velocities were optimized by simulated annealing algorithm. The results show that the optimal evaporating pressure increases with the heat source temperature increasing. Compared with other working fluids, R123 is the best choice for the temperature range of 100--180℃ and R141 b shows better performance when the temperature is higher than 180 ℃. Economic characteristic of system decreases rapidly with the decrease of heat source temperature. ORC system is uneconomical for the heat source temperature lower than 100℃.

Slag-washing water of blast furnace power station with supercritical organic Rankine cycle

Organic Rankine cycle(ORC) power plant operating with supercritical parameters supplied by low temperature slag-washing water(SWW) of blast furnace was investigated.A schematic of such installation was presented with a description of its operation and the algorithm of calculations of a supercritical power plant.Two typical organic fluids with sufficiently low critical parameters were selected as candidate working fluids in the plant to study the efficiency of the system with different organic fluids.An analysis of the influence on the effectiveness of operation of a plant was carried out.With the same temperature of slag-washing water,the specific work in turbine of fluid R143a is 45% higher than that obtained for the fluid R125,however,the specific work in pump of fluid R143a is approximate equal into that one of the fluid R125.

Performance comparison and analysis of a combined power and cooling system based on organic Rankine cycle

A novel power and cooling system combined system which coupled organic Rankine cycle(ORC) with vapor compression refrigeration cycle(VCRC) was proposed. R245 fa and butane were selected as the working fluid for the power and refrigeration cycle, respectively. A performance comparison and analysis for the combined system was presented. The results show that dual-pressure ORC-VCRC system can achieve an increase of 7.1% in thermal efficiency and 6.7% in exergy efficiency than that of basic ORC-VCRC. Intermediate pressure is a key parameter to both net power and exergy efficiency of dual-pressure ORC-VCRC system. Combined system can produce maximum net power and exergy efficiency at 0.85 MPa for intermediate pressure and 2.4 MPa for high pressure, respectively. However, superheated temperature at expander inlet has little impact on the two indicators. It can achieve higher overall COP, net power and exergy efficiency at smaller difference between condensation temperature and evaporation temperature of VCRC.

Power Generation Systems Using Continuous Blowdown Waste Heat from Drum Boilers Driving an Organic Rankine Cycle

提出了一种利用汽包锅炉排污系统余热的有机朗肯循环发电系统,有机工质回收扩容器疏水的热量,并通过气轮机发电。建立了系统的热力性能分析模型,并对R227ea、RC318、R236ea、R245fa、R245ca、R123和R113等7种工质的热力性能进行了优化。结果表明,临界温度高的工质,其o2循环的最佳主气温度（蒸发温度）反而低；亚临界循环采用干流体时,过热不利于余热的利用；超临界循环可以改善热源与工质间的温度匹配,有利于增大系统输出功,但是其运行压力高、大比热区的传热恶化等问题是实际运行和设计需要考虑的因素；R236ea的热力性能优于其余6种工质。

An approach for IC engine coolant energy recovery based on low-temperature organic Rankine cycle

To promote the fuel utilization efficiency of IC engine, an approach was proposed for IC engine coolant energy recovery based on low-temperature organic Rankine cycle(ORC). The ORC system uses IC engine coolant as heat source, and it is coupled to the IC engine cooling system. After various kinds of organic working media were compared, R124 was selected as the ORC working medium. According to IC engine operating conditions and coolant energy characteristics, the major parameters of ORC system were preliminary designed. Then, the effects of various parameters on cycle performance and recovery potential of coolant energy were analyzed via cycle process calculation. The results indicate that cycle efficiency is mainly influenced by the working pressure of ORC, while the maximum working pressure is limited by IC engine coolant temperature. At the same working pressure, cycle efficiency is hardly affected by both the mass flow rate and temperature of working medium. When the bottom cycle working pressure arrives at the maximum allowable value of 1.6 MPa, the fuel utilization efficiency of IC engine could be improved by 12.1%.All these demonstrate that this low-temperature ORC is a useful energy-saving technology for IC engine.

Dynamic test on waste heat recovery system with organic Rankine cycle

Dynamic performance is important to the controlling and monitoring of the organic Rankine cycle(ORC) system so to avoid the occurrence of unwanted conditions. A small scale waste heat recovery system with organic Rankine cycle was constructed and the dynamic behavior was presented. In the dynamic test, the pump was stopped and then started. In addition, there was a step change of the flue gas volume flow rate and the converter frequency of multistage pump, respectively. The results indicate that the working fluid flow rate has the shortest response time, followed by the expander inlet pressure and the expander inlet temperature.The operation frequency of pump is a key parameter for the ORC system. Due to a step change of pump frequency(39.49-35.24 Hz),the expander efficiency and thermal efficiency drop by 16% and 21% within 2 min, respectively. Besides, the saturated mixture can lead to an increase of the expander rotation speed.

Parametric Optimization of Organic Rankine Cycle with R245fa/R601a as Working Fluid

In order to select the appropriate working fluids and optimize parameters for medium-temperature geothermally-powered organic Rankine cycle(ORC), R245 fa is mixed with R601 a at geothermal water temperature of 110 ℃. Based on thermodynamics, the characteristics of mixture and its influence on the performance of ORC under different evaporating temperatures and composition proportions are analyzed. Results show that the zeotropic mixture R245fa/R601a(0.4/0.6) has the highest performance. When the evaporating temperature reaches 67 ℃, the outlet temperature of geothermal water is 61 ℃, the net power output is the highest and the thermal efficiency is about 9%.

Selection of organic Rankine cycle working fluid based on unit-heat-exchange-area net power

To improve energy conversion efficiency, optimization of the working fluids in organic Rankine cycles(ORCs) was explored in the range of low-temperature heat sources. The concept of unit-heat-exchange-area(UHEA) net power, embodying the cost/performance ratio of an ORC system, was proposed as a new indicator to judge the suitability of ORC working fluids on a given condition. The heat exchange area was computed by an improved evaporator model without fixing the minimum temperature difference between working fluid and hot fluid, and the flow pattern transition during heat exchange was also taken into account. The maximum UHEA net powers obtained show that dry organic fluids are more suitable for ORCs than wet organic fluids to recover low-temperature heat. The organic fluid 1-butene is recommended if the inlet temperature of hot fluid is 353.15-363.15 K or443.15-453.15 K, heptane is more suitable at 373.15-423.15 K, and R245 ca is a good option at 483.15-503.15 K.