Organic Rankine Cycle Evaporator Research Articles

Methodical thermodynamic analysis and regression models of organic Rankine cycle architectures for waste heat recovery

The ORC (organic Rankine cycle) is an established technology for converting low temperature heat to electricity. Knowing that most of the commercially available ORCs are of the subcritical type, there is potential for improvement by implementing new cycle architectures. The cycles under consideration are: the SCORC (subcritical ORC), the TCORC (transcritical ORC) and the PEORC (partial evaporation ORC). Care is taken to develop an optimization strategy considering various boundary conditions. The analysis and comparison is based on an exergy approach. Initially 67 possible working fluids are investigated. In successive stages design constraints are added. First, only environmentally friendly working fluids are retained. Next, the turbine outlet is constrained to a superheated state. Finally, the heat carrier exit temperature is restricted and addition of a recuperator is considered. Regression models with low computational cost are provided to quickly evaluate each design implications. The results indicate that the PEORC clearly outperforms the TCORC by up to 25.6% in second law efficiency, while the TCORC outperforms the SCORC by up to 10.8%. For high waste heat carrier inlet temperatures the performance gain becomes small. Additionally, a high performing environmentally friendly working fluid for the TCORC is missing at low heat carrier temperatures (100 °C).

3D numerical analysis of exhaust flow inside a fin-and-tube evaporator used in engine waste heat recovery

A fin-and-tube evaporator can be used for an ORC (organic Rankine cycle) to collect waste heat of the exhaust gas of an internal combustion engine. In this paper, the thermal-hydraulic characteristics of an ORC evaporator are analyzed using a CFD method. A 3D numerical model is derived from an engineering diagram of the fin-and-tube evaporator, and the boundary conditions are specified according to the measured data obtained by the engine test. The simulation results show that the exhaust on the shell side flows primarily parallel with the fin layers. Alternating high and low temperatures appear on the middle planes of the adjacent tube rows. The shapes of the front-end and the rear-end parts connecting the main body to the exhaust pipes are important factors on the flow field. The maximum exhaust pressure decrease in the fin-and-tube evaporator is significantly less than the backpressure limit required by the engine exhaust pipe. The simulation results are verified by an engine experiment, and there exists a correlation between the numerical results and the actual heat transfer process.

Energy and economic analysis of geothermal–solar trigeneration systems: A case study for a hotel building in Ischia

This paper presents the design, simulation and optimisation of a small trigeneration plant supplied by geothermal and solar energies. Different technologies are implemented in a dynamic simulation model purposely developed for research scope: a 6kWe micro Organic Rankine Cycle (ORC); a 30kWf single stage H2O/LiBr absorption chiller; a geothermal well; a solar field obtained by new prototypal flat-plate evacuated solar collectors. The ORC is supplied by heat obtained by a geothermal well in which geothermal brine is about at 95°C. In order to improve system performance, additional heat is provided by solar energy obtained through a 25m2 solar field. Diathermic oil (up to 130°C) is adopted as working fluid in order to supply heat to the ORC evaporator. A suitable oil storage tank is modelled in order to mitigate the temperature fluctuations due to the variability of solar energy availability. The output power of the ORC depends on the availability of solar energy. The absorption chiller is switched-on in summer time and it is fed by geothermal energy only. This simulation model is implemented in TRNSYS environment. The ORC is modelled by zero-dimensional energy and mass balances implemented in Engineering Equation Solver (EES).A case study is developed in order to test the energy and economic performance of this innovative micro-trigeneration plant. In particular, the above mentioned model is applied to the Regina Isabella hotel in Ischia (Naples, South Italy), famous for its geothermal sources. Currently, such hotel is already equipped by a geothermal system (by several hot water wells) for thermal cares, domestic hot water production and space heating. By TRNSYS the optimisation of the system design parameters and the calculation of the thermo-economic conditions were performed. The system showed excellent energy performance indexes. In fact, the average yearly efficiency of the solar thermal collectors is close to 60%, whereas the average yearly ORC electric efficiency is about 6%, which is a good achievement considering the system driving temperature. Results also show that the system performance is more dependent on the availability of the geothermal energy than the solar one. From the economic point of view, good results are also obtained. In fact, in the worst operating conditions the Simple Pay Back Period is 7.6years, decreasing to 2.5years in the most convenient considered scenario (public funding and full utilisation of the produced thermal energy).

Waste heat recovery in CO2 compression

Carbon capture and storage (CCS) is a strategically important approach for achieving significant reductions in greenhouse gas emissions from large stationary emission sources, and ensures the availability of a reliable global energy supply for the future. Carbon dioxide (CO2) compression accounts for a significant amount of the capital and operating costs, and energy penalties associated with the CCS system. In this paper, different CO2 compression strategies were reviewed, and the opportunities of recovering waste heat as an effort to reduce their energy consumption were examined. Models of an intercooling compression chain and a 2-stage shockwave compression chain were built to investigate their respective energy consumption and potential waste heat recovery. An organic Rankine cycle (ORC) model was employed to recover waste heat. An exergy analysis was applied to assess the performance of the system. The results indicated that, without waste heat recovery, the shockwave compression chain had a higher specific energy requirement than the intercooling option. With waste heat recovery, the compression energy requirement in both cases dropped as expected, and the shockwave option required a lower specific compression energy with respect to the intercooling option. Within the ORC system, thermal efficiency, exergy efficiency, and exergy destruction rates decreased as turbine inlet temperature (TIT) increased. The ORC's evaporator was found to be the largest contributor to exergy destruction. These results demonstrate opportunities to optimize the CCS configuration and improve the overall economics of the plant.

Analysis of the integrated characteristics of the CPS (combined power system) of a bottoming organic Rankine cycle and a diesel engine

This study analyses the integrated characteristics of a CPS (combined power system) consisting of a topping diesel engine and a bottoming ORC (organic Rankine cycle). Two models (an integrated and a cascaded CPS model) for the same CPS have been developed based on the experimental data. The results show that the process of integrating the ORC causes a substantial decrease in the power output of the ICE subsystem, this integration outweighs the corresponding power output increasing from the ORC subsystem, and the overall thermal efficiency of the integrated CPS model is higher than that of the standalone ICE system model but lower than that of the cascaded CPS model, which can be determined from the pressure drop on the exhaust gas side of the ORC evaporator and is reflected in the overall thermodynamic performance. Moreover, the matching characteristics of the heat-transfer and fluid flow conditions in a fixed sized evaporator are analysed in the integrated CPS model. The results show that when the intake airflow rate decreases, the temperature of the exhaust gas exiting the evaporator decreases to the minimum allowed temperature, which is below the dew point, and this low-temperature might cause corrosion problems in the subsequent components.

A thermodynamic analysis of waste heat recovery from reciprocating engine power plants by means of Organic Rankine Cycles

Organic Rankine Cycle (ORC) is a Rankine cycle using organic fluid as the working fluid instead of water and steam. The ORC process is a feasible choice in waste heat recovery applications producing electricity from relatively low-temperature waste heat sources or in applications having a rather low power output. Utilizing waste heat from a large high-efficiency reciprocating engine power plant with ORC processes is studied by means of computations. In addition to exhaust gas heat recovery, this study represents and discusses an idea of directly replacing the charge air cooler (CAC) of a large turbocharged engine with an ORC evaporator to utilize the charge air heat in additional power production. A thermodynamic analysis for ORCs was carried out with working fluids toluene, n-pentane, R245fa and cyclohexane. The effect of different ORC process parameters on the process performance are presented and analyzed in order to investigate the heat recovery potential from the exhaust gas and charge air. A simplified feasibility consideration is included by comparing the ratio of the theoretical heat transfer areas needed and the obtained power output from ORC processes. The greatest potential is related to the exhaust gas heat recovery, but in addition also the lower temperature waste heat streams could be utilized to boost the electrical power of the engine power plant. A case study for a large-scale gas-fired engine was carried out showing that the maximum power increase of 11.4% was obtained from the exhaust gas and 2.4% from the charge air heat.

Analytical method for calculation of heat source temperature drop for the Organic Rankine Cycle application

In the paper presented are considerations on the cooperation of the limited capacity heat source with the Organic Rankine Cycle unit. Usually the heat source providing thermal energy to the Organic Rankine Cycle (ORC) may have twofold characteristics. It can be in the form of a single phase fluid, i.e. as hot exhaust gas or hot liquid, or in some cases it may be available as a phase changing fluid, as for example, technological or geothermal steam. Such fluid will be condensed whilst supplying heat to the ORC evaporator. In case of the heat source in the form of a single phase fluid flow its temperature is decreasing in the course of heating of the ORC. In the paper a simple analytical method, based on the energy balance of evaporator, is presented for evaluation of the final temperature of the heat source for ORC installation for two cases, namely single phase fluid and phase changing fluid heat supply. Additionally, the ratio of the heating fluid to the ORC working fluid is presented in function of the minimum temperature difference between the heat source and working fluid.

Energy and exergy analyses of a biomass trigeneration system using an organic Rankine cycle

In this study, energy and exergy analyses of a biomass trigeneration system using an organic Rankine cycle (ORC) are presented. Four cases are considered for analysis: electrical-power, cooling-cogeneration, heating-cogeneration and trigeneration cases. The results obtained reveal that the best performance of the trigeneration system considered can be obtained with the lowest ORC evaporator pinch temperature considered, Tpp = 20 K, and the lowest ORC minimum temperature, T9 = 345 K. In addition, this study reveals that there is a significant improvement when trigeneration is used as compared to only electrical power production. This study demonstrates that the fuel utilization efficiency increases, in average, from 12% for electrical power to 88% for trigeneration. Moreover, the maximum exergy efficiency of the ORC is 13% and, when trigeneration is used, it increases to 28%. Furthermore, this study reveals that the electrical to cooling ratio can be controlled through changing the ORC evaporator pinch point temperature and/or the pump inlet temperature. In addition, the study reveals that the biomass burner and the ORC evaporator are the main two sources of exergy destruction. The biomass burner contributes to 55% of the total destructed exergy whereas the ORC evaporator contributes to 38% of the total destructed exergy.

Energetic and exergetic analysis of waste heat recovery from a microturbine using organic Rankine cycles

SUMMARY This article examines the exhaust waste heat recovery potential of a microturbine (MT) using an organic Rankine cycle (ORC). Possible improvements in electric and exergy efficiencies as well as specific emissions by recovering waste heat from the MT exhaust gases are determined. Different dry organic working fluids are considered during the evaluation (R113, R123, R245fa, and R236fa). In general, it has been found that the use of an ORC to recover waste heat from MTs improves the combined electric and exergy efficiencies for all the evaluated fluids, obtaining increases of an average of 27% when the ORC was operated using R113 as the working fluid. It has also been found that higher ORC evaporator effectiveness values correspond to lower pinch point temperature differences and higher exergy efficiencies. Three different MT sizes were evaluated, and the results indicate that the energetic and exergetic performance as well as the reduction of specific emissions of a combined MT-ORC is better for small MT power outputs than for larger MTs. This article also shows how the electric efficiency can be used to ascertain under which circumstances the use of a combined MT-ORC will result in better cost, primary energy consumption, or emission reduction when compared with buying electricity directly from electric utilities. Copyright © 2012 John Wiley & Sons, Ltd.

Exergy modeling of a new solar driven trigeneration system

Abstract In this paper, exergy modeling is used to assess the exergetic performance of a novel trigeneration system using parabolic trough solar collectors (PTSC) and an organic Rankine cycle (ORC). Four cases are considered: electrical-power, cooling-cogeneration, heating-cogeneration, and trigeneration. In this trigeneration system a single-effect absorption chiller is utilized to provide the necessary cooling energy and a heat exchanger is utilized to provide the necessary heating energy. The trigeneration system considered is examined using three modes of operation. They are: solar mode during the low-solar radiation time of the day, solar and storage mode during the high-solar radiation time of the day, and storage mode during night time. The storage mode is operated through the heat collected in a thermal storage tank during the solar and storage mode. The exergy efficiencies and exergy destruction rates are examined under the variation of the ORC evaporator pinch point temperature, ORC pump inlet temperature, and turbine inlet pressure. This study reveals that the maximum electrical-exergy efficiency for the solar mode is 7%, for the solar and storage mode is 3.5%, and for the storage mode is 3%. Alternatively, when trigeneration is used, the exergy efficiency increases noticeably. The maximum trigeneration-exergy efficiency for the solar mode is 20%, for solar and storage mode is 8%, and for the storage mode is 7%. Moreover, this study shows that the main sources of exergy destruction rate are the solar collectors and ORC evaporators. Therefore, careful selection and design of these two components are essential to reduce the exergy destructed by them and, thus, increase the exergy efficiencies of the system.

Greenhouse gas emission and exergy assessments of an integrated organic Rankine cycle with a biomass combustor for combined cooling, heating and power production

Abstract In this study, greenhouse gas emission and exergy assessments of an integrated organic Rankine cycle (ORC) with a biomass combustor for combined cooling, heating, and power production as a trigeneration system are conducted. This trigeneration system consists of a biomass combustor, an ORC, a single-effect absorption chiller, and a heat exchanger. Four special cases are considered in this comprehensive study, namely, electrical power, cooling-cogeneration, heating-cogeneration, and trigeneration cases. Various exergetic and environmental output performance parameters, namely, exergy efficiency, exergy destruction rate, and greenhouse gas emissions, are examined under varying ORC evaporator pinch point temperature, pump inlet temperature, and turbine inlet pressure. This study shows that using trigeneration considerably increases both energy and exergy efficiencies and decreases the greenhouse gas emissions as compared to the electrical power case. This study reveals that the heating-cogeneration and trigeneration cases are less sensitive to the considered temperature and pressure variations as compared with the electrical power and cooling-cogeneration cases. In addition, the results show that when the trigeneration case is used, the exergy efficiency increases significantly to 27% as compared with the exergy efficiency of the electrical power case, which is around 11%. It is also found that the main two sources of exergy destruction are the biomass combustor and ORC evaporator. Moreover, this study shows that the emissions of CO2 in kg/MWh are significantly high for the electrical power case while for the trigeneration case, the emissions per MWh of trigeneration drop significantly to relatively low level. Specifically, the emissions drop to around one seventh per MWh produced when trigeneration is used as compared with only electrical power production case.

Optimization of low temperature solar thermal electric generation with Organic Rankine Cycle in different areas

The presented low temperature solar thermal electric generation system mainly consists of compound parabolic concentrators (CPC) and the Organic Rankine Cycle (ORC) working with HCFC-123. A novel design is proposed to reduce heat transfer irreversibility between conduction oil and HCFC-123 in the heat exchangers while maintaining the stability of electricity output. Mathematical formulations are developed to study the heat transfer and energy conversion processes and the numerical simulation is carried out based on distributed parameters. Annual performances of the proposed system in different areas of Canberra, Singapore, Bombay, Lhasa, Sacramento and Berlin are simulated. The influences of the collector tilt angle adjustment, the connection between the heat exchangers and the CPC collectors, and the ORC evaporation temperature on the system performance are investigated. The results indicate that the three factors have a major impact on the annual electricity output and should be the key points of optimization. And the optimized system shows that: (1) The annual received direct irradiance can be significantly increased by two or three times optimal adjustments even when the CPC concentration ratio is smaller than 3.0. (2) Compared with the traditional single-stage collectors, two-stage collectors connected with the heat exchangers by two thermal oil cycles can improve the collector efficiency by 8.1–20.9% in the simultaneous processes of heat collection and power generation. (3) On the use of the market available collectors the optimal ORC evaporation temperatures in most of the simulated areas are around 120 °C.

Analysis of exhaust waste heat recovery from a dual fuel low temperature combustion engine using an Organic Rankine Cycle

Abstract This paper examines the exhaust waste heat recovery potential of a high-efficiency, low-emissions dual fuel low temperature combustion engine using an Organic Rankine Cycle (ORC). Potential improvements in fuel conversion efficiency (FCE) and specific emissions (NO x and CO 2 ) with hot exhaust gas recirculation (EGR) and ORC turbocompounding were quantified over a range of injection timings and engine loads. With hot EGR and ORC turbocompounding, FCE improved by an average of 7 percentage points for all injection timings and loads while NO x and CO 2 emissions recorded an 18 percent (average) decrease. From pinch-point analysis of the ORC evaporator, ORC heat exchanger effectiveness ( ɛ ), percent EGR, and exhaust manifold pressure were identified as important design parameters. Higher pinch point temperature differences (PPTD) uniformly yielded greater exergy destruction in the ORC evaporator, irrespective of engine operating conditions. Increasing percent EGR yielded higher FCEs and stable engine operation but also increased exergy destruction in the ORC evaporator. It was observed that hot EGR can prevent water condensation in the ORC evaporator, thereby reducing corrosion potential in the exhaust piping. Higher ɛ values yielded lower PPTD and higher exergy efficiencies while lower ɛ values decreased post-evaporator exhaust temperatures below water condensation temperatures and reduced exergy efficiencies.

Exergy analysis of an integrated solid oxide fuel cell and organic Rankine cycle for cooling, heating and power production

The study examines a novel system that combined a solid oxide fuel cell (SOFC) and an organic Rankine cycle (ORC) for cooling, heating and power production (trigeneration) through exergy analysis. The system consists of an SOFC, an ORC, a heat exchanger and a single-effect absorption chiller. The system is modeled to produce a net electricity of around 500 kW. The study reveals that there is 3–25% gain on exergy efficiency when trigeneration is used compared with the power cycle only. Also, the study shows that as the current density of the SOFC increases, the exergy efficiencies of power cycle, cooling cogeneration, heating cogeneration and trigeneration decreases. In addition, it was shown that the effect of changing the turbine inlet pressure and ORC pump inlet temperature are insignificant on the exergy efficiencies of the power cycle, cooling cogeneration, heating cogeneration and trigeneration. Also, the study reveals that the significant sources of exergy destruction are the ORC evaporator, air heat exchanger at the SOFC inlet and heating process heat exchanger.