Pinch Point Temperature Difference Research Articles

Novel combined desalination, heating and power system: Energy, exergy, economic and environmental assessments

Current research proposes and investigates a novel small-scale solar-driven sustainable combined desalination, heating and power (CDHP) system for a house in cold remote locations and hill stations. Latent heat storage integrated evacuated tube solar collector, organic Rankine's cycle, active solar still and water heater are main subsystems of the proposed system to generate power, potable water and hot water simultaneously. Therminol-66 and eco-friendly organic substance (n-butane) are selected as working fluids for the collector system and organic Rankine's cycle, respectively. Heating oil flow is divided after vapor generator to get best temperature glide and hence exergetic performance. The system is assessed based on multi-objective functions like power output, heating output, water productivity, component irreversibility, subsystems and overall system energy and exergy efficiencies, economic and environmental criterion. Generator temperature, condenser temperature, preheater mass fraction and pinch point temperature difference cases are selected decision variables for the parametric studies. The CDHP system energy efficiency, exergy efficiency, cost rate and CO2 reduction are obtained as 17.89%, 3.915%, 1784 $/yr and 10.806 tonnes, respectively, at mean operating conditions. Furthermore, the maximum exergy efficiency of organic Rankine's cycle is found as 57.46% at optimum generator temperature of 119 °C for 50% preheater mass fraction. Overall, the current CDHP system is recommended to produce power, potable water and hot water to meet energy demands, especially at cold remote locations.

Exergoeconomic investigation and multi-objective optimization of different ORC configurations for waste heat recovery: A comparative study

This paper compares four different architectures of organic Rankine cycle (ORC) namely the Basic ORC, Recuperative ORC, Regenerative ORC, and Recuperative-Regenerative ORC (RR-ORC) from the exergoeconomy viewpoint. First, a parametric analysis is performed to understand the effect of evaporator temperature, condenser temperature, and pinch point temperature difference on the performance of each system configuration. Next, a multi-objective optimization is performed to optimize the performance of the four configurations using Pareto Envelope-based Selection Algorithm-II (PESA-II) with exergy efficiency and the system cost rate as the objective functions. Pareto fronts, representing the set of optimal solutions, are obtained for each configuration, and multi-criteria decision analysis is done using the Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS) to select the best optimal solution. Next, the exergetic and exergoeconomic performance of the four ORC configurations is evaluated at their corresponding optimal conditions in order to provide a comparative assessment. It was found that, under optimal conditions, the RR-ORC performs superiorly to the other three configurations. Compared to the Basic ORC, the net power and exergy efficiency of the RR-ORC are 16.19% and 15.33% higher, while the system cost rate is 1.68 % low. After, the RR-ORC, the Regenerative, and the Recuperative ORCs are the second and the third-best configurations. It was also found that in all four configurations, the cost rate of exergy loss accounts for approximately 60 % of the total system cost rate.

Machine learning prediction of ORC performance based on properties of working fluid

In order to develop machine learning methods for performance prediction of basic ORC (BORC) and regenerative ORC (RORC), thermodynamic properties of working fluids are used to separately model thermodynamic processes including compression, expansion, evaporation and regeneration by artificial neural network (ANN), based on REFPROP calculation data of 106 working fluids. These properties include critical temperature, critical pressure, acentric factor and ideal gas heat capacity. Other cycle performances can be derived from the predictions of established ANNs. Furthermore, for RORC, considering that dry or isentropic working fluid is usually preferred, vapor slope of temperature-entropy saturation curve is modeled by ANN to determine the working fluid behavior. Meanwhile, for ensuring occurrence of heat exchange in regenerator, temperature difference between outlets of turbine and pump is modeled to judge whether temperature difference is larger than the assumed pinch point temperature difference. Based on the obtained predictions for BORC, average absolute deviations (AADs) of net work and thermal efficiency are 1.3928% and 1.5461%, respectively. As for RORC, AADs of vapor slope, temperature difference, net work and thermal efficiency are 2.3659%, 1.2020% 1.8277% and 2.1047%, respectively. Based on the above models, cycle performances of BORC and RORC can be accurately predicted from thermodynamic properties of any working fluid.

Multi-objective optimization of an innovative power-cooling integrated system based on gas turbine cycle with compressor inlet air precooling, Kalina cycle and ejector refrigeration cycle

In this paper, an innovative power-cooling integrated system based on gas turbine, Kalina cycle system, ejector refrigeration cycle (GT-KCS-ERC) is proposed. The ERC driven by GT flue gas and KCS low concentration liquid waste heat is utilized to precool GT inlet air for producing extra power from GT and provide some cooling capacity for users, simultaneously. The comprehensive thermodynamic and thermo-economic analyses are conducted to demonstrate the feasibility of novel GT-KCS-ERC hybrid system by comparing with standalone GT-KCS system. Furthermore, the effects of seven key operation parameters on the system performances are investigated. The multi-objective optimization of GT-KCS-ERC hybrid system and standalone GT-KCS system is carried out through Non-dominated Sorting Genetic Algorithm-II, in which the objectives are maximum total energy efficiency and minimum levelized cost of energy (LCOE). The results show that the total energy efficiency of GT-KCS-ERC increases with increasing pinch point temperature difference of boiler ΔTKCS,boi and decreasing ammonia concentration of working solution in KCS, while that of standalone GT-KCS shows opposite trends. The LCOE of GT-KCS-ERC is lower than that of standalone GT-KCS as ΔTKCS,boi is larger than 21℃ or turbine inlet pressure of KCS is higher than 6.6 MPa. The optimal saturated evaporator temperature and pressure ratio of vapor generator to condenser in ERC with optimal refrigerant of R290 are 0℃ and 4, respectively. Under the optimal condition, the GT-KCS-ERC with an ERC secondary flow split ratio of 0.162 for precooling GT inlet air presents 219.4 kW more net power and 764.2 kW more cooling capacity than standalone GT-KCS system. The LCOE decreases by 0.802% and total energy efficiency increases by 5.347% in novel GT-KCS-ERC system comparing with standalone GT-KCS system.

Waste heat management of direct carbon fuel cell with advanced supercritical carbon dioxide power cycle – A thermodynamic-electrochemical modeling approach

This study evaluates the performance of a hybrid supercritical carbon dioxide (SCO2) power cycle, which uses the waste heat of a direct carbon fuel cell (DCFC). Three different configurations including a standalone DCFC, an integrated system consisting of a DCFC coupled with a simple SCO2, and another hybrid system consisting of a DCFC and a partial cooling SCO2 are examined and characterized. In the proposed systems, the effects of the electric current density, operating temperature, anode dimensions, and the pinch point temperature difference in the SCO2 evaporator are then discussed. Considering the optimum operational region of the supercritical cycle, the partial cooling SCO2 was found to be a very promising power cycle for coupling with DCFC. Integrating a supercritical CO2 cycle with DCFC can compensate for the loss of efficiency and power density caused by decrease in fuel cell temperature. There is even an operating window in which the performance of the introduced integrated systems is practically independent of the fuel cell temperature. Results show that at the current density of 1000 A/m2, the rate of change in power density and efficiency of the standalone DCFC system is 0.47 W/m2 and 0.058% per unit of fuel cell temperature, respectively. For the integrated DCFC and partial cooling SCO2 system, however, those rates reduce to 0.13 W/m2 and 0.02% per unit of temperature.

Performance characteristics and working fluid selection for high-temperature organic Rankine cycle driven by solar parabolic trough collector

Abstract In present paper, thermodynamic analysis and techno-economic assessment of an organic Rankine cycle (ORC) coupled with solar parabolic trough collector (PTC) are investigated. The thermodynamic and economic models, based on the principles of thermodynamics and heat transfer, as well as dynamic economic analysis, are developed for the components of the combined system. By performing a parametric study, the effects of outlet temperature (TPTC,out) and temperature difference between inlet and outlet of PTC (ΔT) and pinch point temperature difference of heat exchangers on the thermo-economic performance are evaluated. Moreover, under reasonable thermodynamic boundary conditions, the optimal operational parameters are obtained via a Pareto frontier solution. It is indicated that the improving TPTC,out is beneficial to the thermo-economic performance. Among the fluid candidates, toluene yields the best energy, exergetic and economic performance. There exists an optimal ΔT at which the thermal and exergy efficiency achieve the maximum. The optimal ΔT is 19–26°C for the screened working fluids. The pinch point temperature difference of evaporator has different impact on the system performance compared with that of condenser. The evaporator pinch point temperature difference has slight influence on the economic performance when it is larger than 10°C. While there is optimized condenser pinch point temperature difference (7–8°C), the economic performance is the optimal. The PTC and heat exchanger are the main source of total investment cost, account for more than 75%. The Pareto frontier solutions can provide a design guide for the decision maker.

Multi-objective optimization of a proposed multi-generation cycle based on Pareto diagrams: Performance improvement, cost reduction, and CO2 emissions

Energy system optimization is a significant task aimed at optimizing system operations and reducing costs and emissions. In this paper, an energy system is presented for multi-energy generation of power, heating/cooling, and desalination. First, the cycle’s exergy, exergoeconomics, and environmental impact are analyzed. Then, optimization is performed using MATLAB software by applying a genetic algorithm (GA) and adopting 10 design parameters with two objective functions. The goal of optimization is to find the design variable values based on a Pareto plot that will increase the exergy efficiency while reducing cost and CO2 emissions. Scatter plots of the decision variables for the population indicate that objective functions can be optimized. Optimal values for the objective functions can be found by selecting lower values for the heat exchanger and evaporator’s pinch-point temperature differences and higher values for the compressor pressure ratio, inlet temperature of the gas turbine (GT), isentropic efficiencies of air compressor (AC) and GT, and temperature of Rankine cycle evaporator. After optimization, exergy efficiency increased around 8.4%, cost dropped 14.8%, CO2 emissions were reduced by 1.2%, and the production of desalinated water increased about 7.6% using the proposed cycle. At the end of work, the influences of design variables on CO2 emissions as well as the total cycle cost are investigated in a parametric study.

Thermo-economic analysis of the pumped thermal energy storage with thermal integration in different application scenarios

Pumped thermal energy storage (PTES) refers to a promising electricity storage technology that converts electricity into heat using the heat pump for cheaper storage, and then converts it back into electricity through a heat engine. The integration of an additional low-grade heat source can increase the coefficient of performance (COP) of the heat pump and thus significantly improve the storage efficiency. To evaluate the economic impact of different heat sources including waste heat, solar, or district heating network, this paper constructs the thermodynamic and economic model of thermally integrated PTES (TI-PTES), evaluates the round-trip efficiency and storage cost in five typical scenarios, and explores the effects of key system parameters (storage temperature, temperature difference, component efficiency) and heat source conditions (flow rate, temperature). Results indicate that the storage efficiency competes with the storage cost and capacity for a fixed heat source condition. As the power-to-power efficiency increases from 50% to 120%, the cost could increase by 47%, while the storage capacity could decrease from 1544 kW to 163 kW with a heat source flow rate of 50 kg·s−1. Detailed parameter analysis indicates that a higher heat source flow rate/temperature leads to higher component efficiency. A smaller pinch point temperature difference results in higher efficiency or lower costs. In particular, the energy storage cost is more sensitive to the turbine's efficiency than that of compressor, so it is necessary to prioritize improving the turbine. In terms of typical heat source scenarios, TI-PTES is more suitable to couple with waste heat rather than district heating network or solar thermal scenarios, resulting in a minimum Levelized cost of storage (LCOS) of 0.23 $·kWh−1.

Optimization of an Organic Rankine Cycle-Based Waste Heat Recovery System Using a Novel Target-Temperature-Line Approach

Abstract Organic Rankine cycle (ORC)-based waste heat recovery (WHR) systems are simple, flexible, economical, and environment-friendly. Many working fluids and cycle configurations are available for WHR systems, and the diversity of working fluid properties complicates the synergistic integration of the efficient heat exchange in the evaporator and net output work. Unique guidelines to select a proper working fluid, cycle configuration and optimum operating parameters are not readily available. In the present study, a simple target-temperature-line approach is introduced to get the optimum operating parameters for the subcritical ORC system. The target-line is the locus of temperatures satisfying the pinch-point temperature difference along the length of the heat exchanger. Employing the approach, study is carried out with 38 pre-selected working fluids to get the optimum operating parameters and suitable fluid for heat source temperatures ranging from 100 °C to 300 °C. Results obtained are analyzed to get cross-correlations between key operating and performance parameters using a heat-map diagram. At the optimum condition, optimal working fluid’s critical temperature and pressure, evaporator saturation temperature, effectivenesses of the heat exchange in the evaporator, cycle, and overall WHR system exhibit strong linear correlations with the heat source temperature.

A Sustainable model for the integration of solar and geothermal energy boosted with thermoelectric generators (TEGs) for electricity, cooling and desalination purpose

In this research paper, an integrated energy system for the production of cooling, hot water, and electricity along with desalinated water is proposed, simulated, assessed, and optimized. This integrated energy system is composed of a geothermal well, a single-effect Li/Br and water absorption chiller, parabolic trough collectors (PTCs), a steam Rankine cycle (SRC) and, a reverse osmosis desalination unit. Instead of the condenser, thermoelectric generators (TEGs) are used to increase the generated electricity by the SRC. The system's performance is evaluated in terms of energy, exergy, and exergoeconomic, and the cases with the TEG is compared to the system with the condenser, and results are discussed and investigated. Using the TEG instead of a condenser, results in reducing the total cost rate and enhancing the system's exergy efficiency. Also, the performance of the system was evaluated for four different days in Shiraz city. For the selected days in spring, summer, fall, and winter, the highest generated electricity of the system with the thermoelectric generator is 1087 kW, 1158 kW, 1133 kW, and 766.5 kW, respectively. Thus, the system with thermoelectric is selected for optimization. To optimize the system, seven decision variables are selected namel, the geothermal fluid temperature, the total solar aperture area, the collector outlet temperature, the inlet pressure of the turbines, the TEG figure of merit, the turbine outlet pressure, and the evaporator pinch point temperature difference. Total cost rate and system exergy efficiency are considered as two objective functions. To determine optimum values of the objective functions, a multi-objective genetic algorithm is applied, and also the Pareto frontier figure is obtained. In this figure, the best point is chosen from the technique for order of preference by similarity to ideal solution (TOPSIS) decision-making criterion, where the cost rate is 10.41 ($ / GJ), and the exergy efficiency is 20.52%.

Experimental study of two cascaded organic Rankine cycles with varying working fluids

Organic Rankine cycles convert low-temperature heat from different sources, like solar, geothermal or biomass, into electricity and may thus help to meet the energy demand in an environmentally friendly way. While single ORC systems have been studied extensively, there are only very few experimental works on systems consisting of two cascaded organic Rankine cycles (two-ORC). In this work, an experimental study is carried out on the performance of a two-ORC system that consists of a high temperature (HT) cycle and a low temperature (LT) cycle. Each cycle is composed of the four significant components, i.e. expander, evaporator, condenser and pump, while the LT cycle is equipped with a throttle as expansion device. The HT cycle utilized heat from electrical heaters, while the LT cycle was driven by the waste heat from the HT cycle. The test rig utilizes Therminol 66 as a source that is heated up by electrical heaters with a power of 158 kW. Propane, butane, pentane and cyclopentane are chosen as working fluids for the present experiments. Parameter variations are carried out to study the thermodynamic characteristics of each cycle. The aim is to investigate the HT cycle performance considering turbine power output, thermal efficiency and exergy efficiency. The effect of the HT cycle on the LT cycle is examined by studying the heat transfer rate between the two cycles, characteristics of heat exchangers and pinch point temperature difference. A further goal is to explore the system performance under different conditions to maximize the exergetic utilization of the heat source. The results confirm that turbine power output and thermal efficiency increase with heat source temperature and turbine inlet pressure in the HT cycle. The maximum achieved thermal and exergy efficiencies are 5.5% and 20.2%, respectively, while the maximum turbine power output is 4.92 kW. Heat transfer measurements show that the maximum transferred heat flow from the HT cycle to the LT cycle is 23 kW when pentane is used as a working fluid. Temperature profiles and the pinch point temperature difference in the heat exchangers of both cycles are assessed under conditions where the highest turbine power is obtained. The experimental tests are promising and show that the two-ORC system is suitable to utilize heat sources in various temperature ranges.

Performance investigation of a novel hybrid system for simultaneous production of cooling, heating, and electricity

A novel hybrid system (a regenerative gas turbine cycle with a heat exchanger integrated with Kalina and ejector refrigeration cycles) is developed for the simultaneous production of cooling, heating, and electricity. The laws of thermodynamics are applied to investigate the system performance from energetic and exergetic standpoints. A parametric study is presented for studying the effects of some key parameters on four criteria of electrical efficiency (ηelec), thermal efficiency (ηth), primary energy ratio (PER), and exergetic efficiency (ηex). The key parameters include compressor pressure ratio, gas turbine inlet temperature, ammonia mass fraction in basic ammonia/water mixture, vapor generator pressure, the pinch-point temperature difference of the heat exchanger (which connects Kalina and ejector sub-cycles), and evaporator temperature. Results of the modeling procedure at the base conditions areηelec = 37.87%, ηth=36.55%, PER=74.42% andηex = 38.85%; also, the produced cooling, heating, and power are 164.7 kW, 836.85 kW, and 1038 kW, respectively. The combustion chamber and evaporator has also the highest and lowest contribution in total exergy destruction (with exergy destruction rates of 939.2 kW and 0.034 kW), respectively. The parametric study shows that compressor pressure ratio and heat exchanger pinch-point temperature difference have the highest and lowest impacts on the performance criteria, respectively.

Energy, exergy, and economic (3E) analysis of an organic Rankine cycle using zeotropic mixtures based on marine engine waste heat and LNG cold energy

In this paper, thermo-economic performance comparisons between zeotropic mixtures and pure fluids are conducted via simulation for a parallel two-stage organic Rankine cycle (PTORC) driven by waste heat from LNG-fueled ship. The exhaust gas and jacket water of the marine engine work as heat sources, and the LNG fuel is considered as heat sink. R1150/R170 and R170/R1270 are employed as the working fluids in the first stage while R600a/R601a and R600/R601 are used in the second stage. The effects of working fluids and pinch point temperature difference (PPTD) on the PTORC performances are studied from the viewpoint of the first and the second law of thermodynamics. It concludes that the zeotropic mixtures do not always exhibit an advantage over the pure fluids. The highest net power of the PTORC is 146.9 kW obtained with R1150-R600a. The results of PPTD indicate that LNG regasification should occur in the first-stage condenser. The maximum energy efficiency and exergy efficiency of the PTORC are 22.09% and 23.28%, respectively. The best economic performances of the PTORC are achieved with R170/R1270 (0.9/0.1, mass fraction)-R600. The total cost, payback period, and levelized energy cost vary in the range of 5.98–8.08 × 105 $, 4.58–5.18 years, and 0.065–0.074 $/kWh, respectively.

Optimal design of organic Rankine cycle recovering LNG cold energy with finite heat exchanger size

An optimization study, under a size constraint, was carried out for an organic Rankine cycle (ORC) combined with an LNG regasification plant for recovering LNG cold energy. Typically, many researchers approached to an optimization problem by assuming pinch point or minimum approach temperature difference. As a different point of view, the size constraint was considered in that resources such as thermal energy and equipment size are limited in a real problem. Given this situation, adequate allocation of finite resources is an important issue for the system to maximize performance. Thus, the aim of this study is to understand how to properly utilize the resources when LNG cold energy and total conductance of heat exchangers are limited. Accordingly, the influences of heat duty allocation, UA allocation, and superheating a turbine’s intake on net power were mainly taken into account. Results indicate that, when total conductance for system design increases, the ORC should take more heat duty and total conductance should be weighted to an evaporator. In most cases, the size of heat exchangers should be weighted in the order of evaporator, condenser, and trim heater, provided that total conductance for system design is sufficiently available.

Design and multi-criteria optimisation of a trigeneration district energy system based on gas turbine, Kalina, and ejector cycles: Exergoeconomic and exergoenvironmental evaluation

A novel trigeneration district energy system (TDES) is designed and evaluated from energy, exergy, exergoeconomic, and exergoenvironmental points-of-view. By recovering the wasted heat of a regenerative gas turbine cycle, a heat exchanger is utilized for heating applications, a Kalina cycle is run for generating some additional power, and an ejector refrigeration cycle is used for producing some cold. The problem is firstly modeled through developing a precise code in Engineering Equation Solver program and then optimal conditions are sought by coupling the outputs of modeling procedure with Artificial Neural Network, and Non-dominated Sorting Genetic Algorithm II approaches. Three new functions of integrated weighted efficiency, exergoeconomic criterion, and exergoenvironmental criterion are defined as the system’s evaluation criteria. From a robust parametric study, it is demonstrated that the system’s evaluation criteria have the highest and lowest sensitivity on the variation of pressure ratio of compressor and pinch-point temperature difference of heat exchanger 2, respectively. From the optimisation procedure, the optimum values of the system’s primary energy ratio, exergetic efficiency, exergoeconomic criterion, and exergoenvironmental criterion are 76.9%, 30.8%, 58.4 $/GJ, and 42.7 kg/GJ, respectively. At these conditions, the capacity of the TDES is 1025.9 kW, 1642.3 kW, and 304.9 kW with the associated cost of production of 149.6 $/GJ, 7.8 $/GJ, and 60.1 $/GJ for power, heat, and cold, respectively.

Thermodynamic, economic and environmental analyses of a novel solar energy driven small-scale combined cooling, heating and power system

A novel solar-driven compact and sustainable combined cooling, heating and power system is proposed to fulfill the energy demands of small buildings at remote locations and exergy, economic and environmental assessments are carried out. This system consists of evacuated tube collectors coupled with thermal energy storage, organic Rankine cycle, ejector refrigeration cycle and water heater to generate combined power, cooling and heating outputs. Exergy efficiency, cooling cost, heating cost, power cost, total cost per total output and equivalent carbon dioxide emission are selected as objective functions. Parametric studies are performed to observe the effect on objective functions by considering generator temperature, evaporator temperature, condenser temperature, pinch point temperature difference and turbine mass fraction as decision variables. The overall exergy efficiency, total cost rate and equivalent carbon dioxide emission are evaluated as 3.159%, 2023 $/yr and 13.10 tonnes, respectively. Increasing generator temperature or evaporator temperature increases exergy efficiency, CO2 emission and heating cost while decreases the cooling and power costs. Increasing condenser temperature decreases exergy efficiency, cooling and power costs while increases heating cost and CO2 emission. Increasing turbine mass fraction increases exergy efficiency, power cost and equivalent carbon dioxide emission, while decreases cooling cost and cooling-power cost ratio. Overall, the proposed CCHP system seems to be fit for cooling, heating and power production to meet the future generation energy demands.

The performance assessment of a refrigeration system which exists on a cargo vessel influenced by seawater-intake temperature

The effects of the seawater-intake temperature on the performance of the refrigeration system which exists on a cargo vessel were introduced in this study. The performance of the real refrigeration system was analysed by using both conventional and advanced exergy analyses and exergoeconomic evaluation. First, a parametric study with different seawater-intake temperatures was carried out by applying conventional exergy and advanced exergy analyses to the refrigeration system considered to identify the pinch point components and processes with high irreversibilities. Then, advanced exergy analyses were applied to overcome technological and physical limitations to increase the knowledge about the refrigeration system. The exergetic efficiency of the refrigeration system was calculated based on varying seawater-intake temperature which enters the condenser while other operating parameters are kept constant. Seawater-intake temperatures were selected in terms of regional seawater temperatures which are assumed to be in the vessel route. As a result of the study, it was determined that the hot entry of the seawater into the condenser causes a reduction in the exergetic efficiency of the refrigeration system. The gap between real system exergetic efficiency and the unavoidable cycle exergetic efficiency increased as the pinch point temperature differences increased in the condenser by approximately 16%. Some of the exergy destruction in the refrigeration system components was unavoidable and constrained by technological and physical limitations. Based on the findings in this study, it has been shown that the greatest improvement in the exergetic efficiency of the cooling system can be achieved by improving the condenser and compressor.

FIRST AND SECOND LAW EVALUATION OF COMBINED BRAYTON-ORGANIC RANKINE POWER CYCLE

In the present work, we have conducted thermodynamic analysis of an organic Rankine cycle (ORC) using waste heat from intercooler and regenerator in Brayton cycle with intercooling, reheating, and regeneration (BCIRR). First of all, the first law analysis is used in this combined cycle. Several outputs are revealed in this study such as the cycle efficiencies in Brayton cycle which is dependent on turbine inlet temperature, intercooler pressure ratios, and pinch point temperature difference. For all cycles, produced net power is increased because of increasing turbine inlet temperature. Since heat input to the cycles takes place at high temperatures, the produced net power is increased because of increasing turbine inlet temperature for all cycles. The thermal efficiency of combined cycle is higher about 11.7% than thermal efficiency of Brayton cycle alone. Moreover, the net power produced by ORC has contributed nearly 28650 kW. The percentage losses of exergy for pump, turbine, condenser, preheater I, preheater II, and evaporator are 0.33%, 33%, 22%, 23%, 6%, and16% respectively. The differences of pinch point temperature on ORC net power and efficiencies of ORC are investigated. In addition, exergy efficiencies of components with respect to intercooling pressure ratio and evaporator effectiveness is presented. Exergy destructions are calculated for all the components in ORC.

Thermo-economic analyses and evaluations of small-scale dual-pressure evaporation organic Rankine cycle system using pure fluids

Thermo-economic performance of small-scale (<1 MW) dual-pressure evaporation organic Rankine cycle (DPORC) system using pure fluids was studied. The effects of heat source conditions (flow rate and temperature), pinch point temperature differences (PPTDs), and heat sink condition on the thermo-economic performance of DPORC system were analyzed. The distribution characteristics of component costs were given. Traditional single-pressure evaporation ORC (SPORC) system was selected as the compared object to evaluate the thermo-economic performance of DPORC system. Results show that the minimized specific investment cost (SIC) of DPORC system substantially decreases with increasing flow rate and temperature of heat source. The DPORC system can obtain a better thermo-economic performance compared with SPORC system. For R245fa, the minimized SIC of DPORC system can be 0.6% lower than that of SPORC system, meanwhile its net power output also increases by 21.9%. The substantial increase of heat absorbers cost generally results in the minimized SIC of DPORC system is higher. Furthermore, the DPORC system has a larger application potential at the working conditions of the large flow rate of heat source and PPTD during heat absorption process. The working fluid with a high critical temperature is more suitable to adopt the DPORC system.

Influence of heat exchanger pinch point on the control strategy of Organic Rankine cycle (ORC)

The pinch point of organic Rankine cycle (ORC) heat exchangers affects the thermal efficiency and total heat absorbed by the working fluid. The pinch point variation with operating condition is associated with the control mode. However, few studies pay attention to the influence of pinch point on ORC control strategy. In order to obtain the ORC control strategy adapting to pinch point, pinch point models are built and a case study of subcritical ORC applied to recover waste heat from boiler exhaust flue gas is conducted in this paper. The results show that pinch point temperature difference (PPTD) of the evaporator and the condenser are affected by evaporation temperature and parameters of heat and cold source in conventional control. When maintaining PPTDs, there appears a turning point (TP) of cooling water mass flow rate. At TP, the slight increase of mass flow rate with evaporation temperature changes into a sharp rise. The evaporation temperature where TP happens varies with the inlet temperature of both cooling water and gas. A control strategy of maintaining PPTDs is proposed and simulated. The evaporation temperature is regulated to maximize the thermal efficiency and to avoid the sharp rise of cooling water mass flow rate.