Organic Rankine Cycle Engine Research Articles

Experimental Investigation of Power Generation from Salinity Gradient Solar Pond Using Thermoelectric Generators for Renewable Energy Application

Low grade heat (<100°C) is currently converted into electricity by organic rankine cycle (ORC) engines. ORC engines require certain threshold to operate as the organic fluid generally boils at more than 50°C, and fails to operate at lower temperature. Thermoelectric generators (TEGs) can operate at very low temperature differences and can be good candidate to replace ORC for power generation at low temperatures. In this paper, the potential of power generation from TEG and salinity-gradient solar pond (SGSP) was investigated. SGSP is capable of storing heat at temperature up to 80°C. The temperature difference between the upper convective zone (UCZ) and lower convective zone (LCZ) of a SGSP can be in the range of 40°C 60°C. This temperature difference can be used to power thermoelectric generators (TEG) for electricity production. This paper present result of a TEG system designed to be powered by the hot and cold water from the SGSP. The system is capable of producing electricity even on cloudy days or at night as the SGSP acts as a thermal storage system. The results obtained have indicated significant prospects of such system to generate power from a low grade heat for remote area power supply.

Thermal energy storage for solar-powered organic Rankine cycle engines

The feasibility of energy storage is of paramount importance for solar power systems, to the point that it can be the technology enabler. Regarding concentrated solar power (CSP) systems, the implementation of thermal energy storage (TES) is arguably a key advantage over systems based on photovoltaic (PV) technologies. The interest for highly efficient and modular CSP plants of small to medium capacity (5kWE–5MWE) is growing: organic Rankine cycle (ORC) power systems stand out in terms of efficiency, reliability and cost-effectiveness in such power-range. In this paper a thorough investigation on thermal storage systems tailored to high-temperature (≈300°C) ORC power plants is addressed first, stemming from the observation that the direct storage of the ORC working fluid is effective thanks to its favourable thermodynamic properties. The concept of complete flashing cycle (CFC) is then introduced as a mean of achieving an unmatched system layout simplification, while preserving conversion efficiency. This is a new variant of the Rankine cycle, whereby the vapour is produced by throttling the organic working fluid from liquid to saturated vapour conditions. The presentation and discussion of a case study follows: a 100kWE CFC system with direct thermal energy storage, coupled with state-of-the-art parabolic trough collectors. The proposed turbogenerator achieves an estimated 25% efficiency, which corresponds to a value of 18% in design conditions for the complete system. Considering siloxanes as working fluids, the estimated values of storage density are around 10kWeh/mstorage3.

Electricity generation from low-temperature industrial excess heat—an opportunity for the steel industry

Awareness of climate change and the threat of rising energy prices have resulted in increased attention being paid to energy issues and industry seeing a cost benefit in using more energy-efficient production processes. One energy-efficient measure is the recovery of industrial excess heat. However, this option has not been fully investigated and some of the technologies for recovery of excess heat are not yet commercially available. This paper proposes three technologies for the generation of electricity from low-temperature industrial excess heat. The technologies are thermoelectric generation, organic Rankine cycle and phase change material engine system. The technologies are evaluated in relation to each other, with regard to temperature range of the heat source, conversion efficiency, capacity and economy. Because the technologies use heat of different temperature ranges, there is potential for concurrent implementation of two or more of these technologies. Even if the conversion efficiency of a technology is low, it could be worthwhile to utilise if there is no other use for the excess heat. The iron and steel industry is energy intensive and its production processes are often conducted at high temperatures. As a consequence, large amounts of excess heat are generated. The potential electricity production from low-temperature excess heat at a steel plant was calculated together with the corresponding reduction in global CO2 emissions.

Design of a small-scale organic Rankine cycle engine used in a solar power plant

Under the economic and political pressure due to the depletion of fossil fuels and global warming concerns, it is necessary to develop more sustainable techniques to provide electrical power. In this context, the present study aims at designing, building and testing a small-scale organic Rankine cycle (ORC) solar power plant (∼3 kWe) in order to define and optimize control strategies that could be applied to larger systems. This paper presents a first step of the design of the solar power plant and focuses more specifically on the ORC engine. This design is defined on the basis of simulation models of the ORC engine and takes into account some technical limitations such as the allowed operating ranges and the technical maturity of the components. The final configuration includes a diaphragm pump, two plate heat exchangers for the regenerator and the evaporator, an air-cooled condenser, two hermetic scroll expanders in series and R245fa as the working fluid. Simulations indicate that an efficiency close to 12% for the ORC engine can be reached for evaporating and condensing temperatures of 140 and 35°C, respectively. Copyright , Oxford University Press.

Evaluation of the Energy Performance of an Organic Rankine Cycle-Based Micro Combined Heat and Power System Involving a Hermetic Scroll Expander

This paper evaluates the performance of an organic Rankine cycle (ORC) based micro- combined heat and power (CHP) unit using a scroll expander. The considered system consists of a fuel boiler coupled with an ORC engine. As a preliminary step, the results of an experimental campaign and the modeling of a hermetic, lubricated scroll compressor used as an expander are presented. Then, a fluid comparison based on several criteria is conducted, leading to the selection of R245fa as working fluid for the ORC. A simulation model is then built to evaluate the performance of the system. The model associates an ORC model and a boiler model, both experimentally validated. This model is used to optimize and size the system. The optimization is performed considering two degrees of freedom: the evaporating temperature and the heat transfer fluid (HTF) mass flow rate. Seasonal simulation is finally performed with a bin method according to the standard PrEN14825 for an average European climate and for four heat emitter heating curves. Simulation results show that the electrical efficiency of the system varies from 6.35% for hot water at 65 °C (high temperature application) to 8.6% for a hot water temperature of 22 °C (low temperature application). Over one entire year, the system exhibits an overall electrical efficiency of about 8% and an overall thermal efficiency around 87% without significant difference between the four heat emitter heating curves. Finally, some improvements of the scroll expander are evaluated. It is shown that by increasing the maximum inlet temperature (limited to 140 °C due to technical reasons) and using two scroll expanders in series, the overall electrical efficiency reaches 12.5%.

A performance analysis of a novel system of a dual loop bottoming organic Rankine cycle (ORC) with a light-duty diesel engine

A small-scale organic Rankine cycle (ORC) can be used to harness the waste heat from an internal combustion engine. In this paper, the characteristic of a novel system combining a vehicular light-duty diesel engine with a dual loop ORC, which recovers waste heat from the engine exhaust, intake air, and coolant, is analyzed. A high temperature loop recovers the exhaust heat, whereas a low temperature loop recovers the residual heat from the high temperature loop and the waste heat from both the intake air and the coolant. A performance map of the light-duty diesel engine is created using an engine test bench. The heat waste from the exhaust, the intake air, and the coolant are calculated and compared throughout the engine’s entire operating region. Based on these data, the working parameters of the dual loop ORC are defined, and the performance of the combined engine–ORC system is evaluated across this entire region. The results show that the net power of the low temperature loop is higher than that of the high temperature loop, and the relative output power improves from 14% to 16% in the peak effective thermal efficiency region and from 38% to 43% in the small load region. In addition, the brake specific fuel consumption (bsfc) of the combined system decreases significantly throughout the engine’s operating region.

Optimal Collector Type and Temperature in a Solar Organic Rankine Cycle System for Building-Scale Power Generation in Hot and Humid Climate

The objective of this paper is to determine the optimal solar collector type and temperature of a building-scale power generation system employing solar organic Rankine cycle (ORC) engine for a geothermal air-conditioned net zero-energy building (NZEB) in a hot and humid climate. In the authors' previous work, 11 fluids have been suggested to be employed in solar ORCs that use low-temperature or medium-temperature solar collectors. In this paper, the system requirements needed to maintain the electricity demand of a commercial building have been compared for the 11 suggested fluids. The solar collector loop, building, and geothermal air conditioning system are modeled using TRNSYS with the required input for the ORC system derived from the previous study. The commercial building is located in Pensacola of Florida and is served by grid power. The building has been equipped with two geothermal heat pump units and a vertical closed loop system. The performance of the geothermal system has been monitored for 3 weeks. Monitoring data and available electricity bills of the building have been employed to calibrate the building and geothermal air conditioning system simulation. Simulation has been repeated for Miami and Houston in order to evaluate the effect of the different solar radiations on the system requirements.

Expander Modelling in Binary Cycle Utilizing Geothermal Resources for Generating Green Energy in Victoria, Australia

This paper investigates the computational modeling of a binary organic Rankine power cycle. The computer model has been generated to aid the design and manufacture of apparatus that will be utilized during experimentation on the geothermal resources in Victoria, Australia. A review of Australia's geothermal prospects is also presented here. Suitable technology to utilize the low grade heat from the available geo-fluids has been explained to connect the recent technology with the new approached design. The paper involves the design of the heat engine with the reaction turbine. In addition, theoretical analysis and performance predictions have been presented briefly in the paper to compare between different diameters for the reaction turbine in the organic Rankine cycle engine with power and efficiency. In this paper, realistic recommendations will be discussed to the best of the geothermal energy as sustainable energy resources to be useful for achieving the Australian target.The binary cycle is modeled to evaluate the output power and the efficiency. A computer model for binary cycle is presented in this paper. Thermal-mechanical energy conversion efficiency is predicted using the computer modeling and presented in the analysis.

Assessment of high temperature organic Rankine cycle engine for polygeneration with MED desalination: A preliminary approach

The objective of this paper is to assess a proposed simultaneous energy and water generation system through a main combination of technologies: organic Rankine cycle (ORC) for heat and power generation, multi-effect distillation (MED) water desalination and a cold generation thermally activated technology (TAT). It is also a primary objective the performance evaluation of the ORC subsystem applied to the use of high temperature renewable energy sources to activate the proposed configuration. This study is divided into three main sections. First of all, the energy feasibility of the proposed configuration is analysed through the Fuel Energy Saving Ratio (FESR) in order to determine the optimal distribution of the heat generated by the prime mover, i.e. the ORC, obtaining that the highest savings correspond to the complete use of heat for domestic hot water (DHW) or heating, which limits the amount of heat used for the activation of MED and TAT subsystems only up to 40%, when the polygeneration system is compared with a high performance stand-alone one. In addition, the ORC subsystem was modelled using the Aspen Plus process simulator, while heat to MED unit was simulated as an input of the model. This part of the paper analyzes a comprehensive list of candidate working fluids for the ORC polygeneration application, and a selection was made of the most interesting according to the preliminary conclusions extracted from the first section of this paper: fluorobenzene and octamethyltrisiloxane could be the most suitable organic fluids for the proposed system. The third main section of this paper deals with the liability of the proposed polygeneration configuration activated by biomass thermal oil boilers through a techno-economic evaluation, revealing that approximate payback periods between 4 and 20 years might be obtained for biomass prices and MED engine specific investment cost in the range of 0–200 €/t and 0–15,000 €/m 3/day, respectively. The main conclusions extracted from the paper results reveal that the amount of heat generated in the ORC condenser used for desalination severely limits the primary energy savings in comparison to conventional systems, as well as the electric efficiency obtained with every single fluid. In consequence, the working fluids that might be used in order to obtain a valid FESR and an assumable economic performance for investors are limited. The importance of the proposed configuration activated by biomass combustion lies in the well-known environmental advantages of this renewable resource, plus the energy advantages from the efficiency point of view (despite the lower efficiency of the subsystems in comparison with internal combustion engines or compression chillers) proving that it is possible to achieve small scale water desalination and electricity, cold and heat generation with energy savings in comparison with conventional systems.

Performance and design optimization of a low-cost solar organic Rankine cycle for remote power generation

Recent interest in small-scale solar thermal combined heat and power (CHP) power systems has coincided with demand growth for distributed electricity supplies in areas poorly served by centralized power stations. One potential technical approach to meeting this demand is the parabolic trough solar thermal collector coupled with an organic Rankine cycle (ORC) heat engine. The paper describes the design of a solar organic Rankine cycle being installed in Lesotho for rural electrification purpose. The system consists of parabolic though collectors, a storages tank, and a small-scale ORC engine using scroll expanders. A model of each component is developed taking into account the main physical and mechanical phenomena occurring in the cycle and based on experimental data for the main key components. The model allows sizing the different components of the cycle and evaluates the performance of the system. Different working fluids are compared, and two different expansion machine configurations are simulated (single and double stage).

A review on “Experimental investigation of a low-temperature organic Rankine cycle (ORC) engine under variable heat input operating at both subcritical and supercritical conditions”

The research paper citied, involves detailed experimental investigation of an organic Rankine cycle (ORC), which is designed to operate at supercritical conditions. The tests are conducted at the laboratory and the heat source is a controllable electric heater, which can keep the hot water temperature constant, by switching on/off its electrical resistances. The expansion machine is a modified scroll compressor with major conversions, in order to be able to operate with safety at high pressure (or even supercritical at some conditions). The ORC engine is equipped with a dedicated heat exchanger of helical coil design, suitable for such applications. The speeds of the expander and ORC pump are regulated with frequency inverters, in order to control the cycle top pressure and heat input. The performance of all components is evaluated, while special attention is given on the supercritical heat exchanger and the scroll expander.

Performance Analysis of a Solar-Powered Organic Rankine Cycle Engine

ABSTRACT This paper presents the performance analysis of a power plant with the Organic Rankine Cycle (ORC). The power plant is supplied by thermal energy utilized from a solar energy collector. R245fa was the working fluid in the thermodynamic cycle. The organic cycle with heat regeneration was built and tested experimentally. The ORC with a heat regenerator obtained the maximum thermodynamic efficiency of approximately 9%. IMPLICATIONS The ORC engine can cooperate with any low-temperature waste heat source. Hence, the waste heat can be used for electricity or mechanical work production.

Identification of behaviour and evaluation of performance of small scale, low-temperature Organic Rankine Cycle system coupled with a RO desalination unit

Abstract This paper presents the detailed laboratory experimental results of a low-temperature Organic Rankine Cycle (ORC) engine coupled with a Reverse Osmosis (RO) desalination unit. In a previous work, the identification of performance of the scroll type expander was presented. At that primary experimental phase an electric brake was co-axially connected to the expander to act as the mechanical load of the ORC engine. The identification of behaviour of the integrated ORC–RO system is a research step ahead since the electric brake is replaced by the RO desalination unit representing the actual system's mechanical load. Several characteristic quantities of both energy supply (ORC) and demand (RO) side have been measured and are illustrated in the current paper. The results show that ORC can be effectively used to exploit low-temperature thermal sources (i.e. in the range from 40 to 70 °C) for desalination of sea or brackish water through the RO process. Such low-temperature values can be available from excess industrial heat, solar collectors and geothermal fields making the ORC–RO process an alternative desalination variant. However, it becomes clear that the system performance strongly depends on the corresponding operation point.

Exergy analysis of a combined engine-organic Rankine cycle configuration

This article presents an exergy analysis of a combined engine-organic Rankine cycle configuration (E-ORC) using the exergy topological method. A detailed roadmap of exergy flow is presented using an exergy destruction chart to clearly depict the exergy accounting associated with each thermodynamic process. The analysis indicates that an ORC combined with an engine not only improves the engine thermal efficiency but also increases the exergy efficiency. Different organic fluids are evaluated in this article. Depending on the organic fluid employed, the thermal and exergy efficiencies could be increased by approximately 10 per cent. Parameters such as the thermodynamic influence coefficient and degree of thermodynamic perfection are identified as useful design metrics to assist exergy-based design of devices. This article also examines the effect of the pinch-point temperature difference (PPTD) on the E-ORC performance. Results show that the lower the PPTD the higher the thermal and exergy efficiencies.

Modelling and optimisation of solar organic rankine cycle engines for reverse osmosis desalination

The objective of this paper is to model and optimise solar organic rankine cycle (ORC) engines for reverse osmosis (RO) desalination using currently available solar thermal collectors. The proposed systems are intended to be potentially attractive for remote areas without (or with very high cost) access to the public electricity grid. In this study the ORC system is modelled using the Aspen Plus process simulator, with the required inputs from other programmes to model Reverse osmosis and thermal solar plants in the same modelling platform. The first part of this paper analyzes a comprehensive list of candidate working fluids for the ORC desalination application, and a selection is made of the most interesting fluids according to the type of solar collectors used in each case. The optimal operating temperature is calculated for the solar ORC integrated with the RO plant that optimises the global ORC-thermal solar plant efficiency. The second part of the paper deals with the applicability of the system obtained. Two case studies were examined from Almería and Barcelona that can be considered representative of two different levels of solar radiation characteristic of the Mediterranean area of Spain. In these case studies the area of the solar field collectors was calculated, considering both brackish and sea water desalting applications for a handling capacity of 15 m 3/day. An economic estimation is also reported comparing the present results with those of an equivalent photovoltaic-RO plant. The technical-economic results obtained for the two locations suggested the adequate thermal solar technology to be that represented by the PTC collector system. The use of an equivalent photovoltaic system to generate electricity to drive the RO desalination system had a higher cost than the optimised solar ORC–RO system specially when using the best solar thermal technology.

Advances in solar thermal electricity technology

Various advanced solar thermal electricity technologies are reviewed with an emphasis on new technology and new market approaches. In single-axis tracking technology, the conventional parabolic trough collector is the mainstream established technology and is under continued development but is soon to face competition from two linear Fresnel reflector (LFR) technologies, the CLFR and Solarmundo. A Solarmundo prototype has been built in Belgium, and a CLFR prototype is awaiting presale of electricity as a commercial plant before it can be constructed in Queensland. In two-axis tracking technologies, dish/Stirling technologies are faced with high Stirling engine costs and emphasism may shift to solarised gas micro-turbines, which are adapted from the small stationary gas turbine market and will be available shortly at a price in the US$1 ppW range. ANU dish technology, in which steam is collected across the field and run through large steam turbines, has not been commercialised. Emphasis in solar thermal electricity applications in two-axis tracking systems seems to be shifting to tower technology. Two central receiver towers are planned for Spain, and one for Israel. Our own multi-tower solar array (MTSA) technology has gained Australian Research Council funding for an initial single tower prototype in Australia of approximately 150 kW(e) and will use combined microturbine and PV receivers. Non-tracking systems are described of two diverse types, Chimney and evacuated tubes. Solar chimney technology is being proposed for Australia based upon German technology. Air is heated underneath a large glass structure of about 5 km in diameter, and passes up a large chimney through a wind turbine near the base as it rises. A company Enviromission Ltd. has been listed in Australia to commercialise the concept. Evacuated tubes are growing rapidly for domestic hot water heating in Europe and organic rankine cycle engines such as the Freepower 6 kW are being considered for operation with thermal energy developed by evacuated tube and trough systems. These may replace some PV in medium sized applications as they offer potential for inexpensive pressurised water storage for 24 h operation, and backup by fuels instead of generators. In the medium term there is a clear trend to creation of smaller sized systems which can operate on a retail electricity cost offset basis near urban and industrial installations. In the longer term large low cost plants will be necessary for large scale electricity and fuels production. Retrofit central generation solar plants offer a cost effective transition market which allows increased production rates and gradual cost reduction for large solar thermal plant. In the paper the author describes current funding systems in Europe, Australia, and the USA, and makes suggestions for more effective programmes of support.

Application of Bethe-Zel'dovich-Thompson Fluids in Organic Rankine Cycle Engines

Thenovel concept ofimproving organicRankinecycleengines (ORCEs)by exploiting the unusual e uid dynamic behaviorofaspecialclassofworkinge uidsknownasBethe ‐Zel’dovich‐Thompson(BZT)e uidsisexplored.ORCEs are currently manufactured and used for numerous remote terrestrial applications requiring reliable, unattended power.OneofthemajorlossmechanismsinORCEsisshockwavesgenerated intheturbinestage.Operatingunder theproperthermodynamicconditions, a BZT working e uid can potentially weaken oreliminate shock waves. This would reduce losses due to both the wave drag from shocks as well as losses from boundary-layer separation due to shock ree ections on the turbine blades. Two-dimensional e owe elds through realistic symmetric impulse turbinecascades arecompared using a e ux-limited, e nite differencenumerical schemeto assess differences in e ow efe ciencies. Resultsshowsignie cantimprovementsin turbineefe cienciesforBZTworkinge uidsoverconventional ORCE working e uids.

Thermophysical capability of ozone-safe working fluids for an organic rankine cycle system

The thermodynamic performance of a variety fluids circulated in an ideal organic Rankine cycle (ORC) engine has been evaluated with the aid of the Iwai-Margerum-Lu equation of state. Two merit number indices were also calculated to represent the inherent heat-transfer capability of the working media at evaporation and condensation, respectively. The result indicated that the thermophysical capability of compounds correlates with the fluid's normal boiling point, critical pressure and molecular weight. It also showed that HCFC-123 could be one of the most favourable ozone-safe working fluids for the ORC energy-recovery system.

The Nuclear Battery: a very small reactor power supply for remote locations

The Nuclear Battery is a small reactor power supply being developed by Atomic Energy of Canada Limited for use in locations that are remote from utility grids and natural gas pipelines. Key technical features of the Nuclear Battery reactor core include a heat-pipe primary heat transport system, graphite neutron moderator, low enriched uranium TRISO coated-particle fuel and the use of burnable poisons for long-term reactivity control. An external secondary heat transport system extracts useful heat energy that may be converted into electricity in an organic Rankine cycle engine, or used to produce high-pressure steam. The reference design is capable of producing about 2400 kW(t) (about 600 kW(e) net) for 15 full-power years without refuelling.

The nuclear battery: A very small reactor power supply for remote locations

The Nuclear Battery is a small reactor power supply being developed by Atomic Energy of Canada Limited for use in locations that are remote from utility grids and natural gas pipelines. Key technical features of the Nuclear Battery reactor core include a heat-pipe primary heat transport system, graphite neutron moderator, low-enriched uranium TRISO coatedparticle fuel, and the use of burnable poisons for long-term reactivity control. An external secondary heat transport system extracts useful heat energy that may be converted into electricity in an organic Rankine cycle engine, or used to produce a high-pressure steam. The reference design is capable of producing about 2400 kW(t) [about 600 kW(e) net for 15 full-power years without refueling.