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

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.     

Design recommendations for solar organic Rankine cycle (ORC)-powered reverse osmosis (RO) desalination

This paper deals with the design recommendations for solar reverse osmosis (RO) desalination based on solar organic Rankine cycles (SORC). This technology can be the most energy-efficient technology for seawater and brackish water desalination within the small to medium power output range (up to 500 kW) of the power cycle if the system is properly designed. However, theoretical studies, design proposals and experimental works are very scarce and only very few solar reverse osmosis systems driven by ORC has been either implemented or analysed in the past. In this paper, those systems are outlined and general design recommendations from previous detailed analysis already publish are given for future RO desalination system to be designed based on SORC. Useful information is given about the selection of the working fluid and boundary conditions of the ORC, operation temperature and configuration of the solar field, suited solar collector and thermal energy storage technology, etc. Recommendations are exemplified with well selected numerical cases based on recommended working fluids and solar cycle configuration with proper values of design point parameters. Recommendations given in this paper could be helpful in future initiatives regarding the research and development of this promising solar desalination technology.     

Assessment of different configurations for combined parabolic-trough (PT) solar power and desalination plants in arid regions

The combination of desalination technology into concentrating solar power (CSP) plants needs to be considered for the planned installation of CSP plants in arid regions. There are interesting synergies between the two technologies, like the possibility of substituting the condenser of the power cycle for a thermal desalination unit. This paper presents a thermodynamic evaluation of different configurations for coupling parabolic-trough (PT) solar power plants and desalination facilities in a dry location representing the Middle East and North Africa (MENA) region. The integration of a low-temperature multi-effect distillation (LT-MED) plant fed by the steam at the outlet of the turbine replacing the condenser of the power cycle has been simulated and compared with the combination of CSP with a reverse osmosis (RO) plant. Furthermore, an additional novel concept of concentrating solar power and desalination (CSP+D) has been evaluated: a LT-MED powered by the steam obtained from a thermal vapour compressor (TVC) using the exhaust steam of the CSP plant as entrained vapour and steam extracted from the turbine as the motive vapour of the ejector. This new concept (LT-MED-TVC) has been analyzed and compared with the others, evaluating its optimization for the integration into a CSP plant by considering different extractions of the turbine.     

An iterative method for modelling the air‐cooled organic Rankine cycle geothermal power plant

This work presents an iterative method for modelling the effect of ambient air temperature on the air‐cooled organic Rankine cycle. The ambient temperature affects the condenser performance, and hence the performance of the whole cycle, in two ways. First, changing the equilibrium pressure inside the condenser, the turbine outlet pressure and the turbine pressure ratio vary. Since the turbine pressure ratio is a major parameter in determining the power generated by a turbine, the plant output is directly affected. Second, changing the condenser outlet temperature with ambient temperature, the pump inlet and outlet conditions are changed. Thus, the vapourizer equilibrium temperature and pressure are influenced. The developed method iteratively seeks the equilibrium conditions for both the condenser and vapourizer. Two case studies based on a real plant performance have been carried out to demonstrate the validity of the method. The developed method demonstrates robustness and converges regardless of the initial conditions allowed by the physical properties of the working fluid. This method is effective for cycles that use saturated vapour as well as superheated vapour under static or dynamic conditions with appropriate initial conditions and constraints. The developed method may be applied to any Rankine cycle with closed cycle operation. Copyright © 2010 John Wiley & Sons, Ltd.     

Combined solar organic Rankine cycle with reverse osmosis desalination process: Energy,exergy, and cost evaluations

Organic Rankine cycles (ORC) have unique properties that are well suited to solar power generation. In this work design and performance calculations are performed using MatLab/SimuLink computational environment. The cycle consists of thermal solar collectors (Flat Plate Solar Collector (FPC), or Parabolic Trough Collector (PTC), or Compound Parabolic Concentrator (CPC)) for heat input, expansion turbine for work output, condenser unit for heat rejection, pump unit, and Reverse Osmosis (RO) unit. Reverse osmosis unit specifications used in this work is based on Sharm El-Shiekh RO desalination plant. Different working fluids such as: butane, isobutane, propane, R134a, R152a, R245ca, and R245fa are examined for FPC. R113, R123, hexane, and pentane are investigated for CPC. Dodecane, nonane, octane, and toluene are allocated for PTC. The proposed process units are modeled and show a good validity with literatures. Exergy and cost analysis are performed for saturation and superheated operating conditions. Exergy efficiency, total exergy destruction, thermal efficiency, and specific capital cost are evaluated for direct vapor generation (DVG) process. Toluene and Water achieved minimum results for total solar collector area, specific total cost and the rate of exergy destruction.     

Economic assessment of a two-stage solar organic Rankine cycle for reverse osmosis desalination

The current paper presents the economic evaluation of a two-stage Solar Organic Rankine Cycle (SORC) for using the mechanical energy produced during the thermodynamic process to drive a Reverse Osmosis (RO) desalination unit. The developed integrated system is briefly analysed and the specific fresh water cost, as well as the cost of energy is calculated. The economic assessment results are compared with those obtained from a low-temperature SORC-RO and two alternative variants of PhotoVoltaic RO (PV–RO) systems (with and without batteries). It is found that the critical fresh water cost for the system under consideration is 7.48 €/m³ of permeate water and the cost of energy equals to 2.74 €/kWh, when the water cost is slightly higher than the critical one (meaning 8 €/m³). These values are considered satisfactory enough, in comparison to the other autonomous desalination technologies. Additionally, the specific fresh water cost of the developed technology was calculated to be 6.85 €/m³, being very close to the values of the PV–RO systems. The variant of two-stage SORC significantly improves the efficiency and reduces the cost of the already developed prototype system (single-stage low-temperature SORC for RO desalination), because the specific cost is found to be much lower and taking into consideration its reliability, this technology can constitute an alternative desalination method competitive to the PV–RO on the basis of techno-economic feasibility.     

Wind effect on the performance of a solar organic Rankine cycle

The effects of wind, ambient temperature and solar radiation on the simultaneous productions of mechanical work and heat by a solar Rankine cycle are studied. The on site experimental study uses the pentafluorobutane R365mfc as working fluid in a system consisting of a small-scale single glazed flat plate collector, a micro turbine, a condenser and a pump. The theoretical study focuses on the prediction of the optimum operating temperature of the collector according to the solar radiation, the temperature of air and the wind speed. Then, the total production of mechanical and thermal energy is calculated during a sunny day for which various wind speeds are simulated. The results highlight the effect of wind on the corresponding production and they also establish the value of the recommended evaporating temperature according to weather conditions.     

A novel auto-cascade low-temperature solar Rankine cycle system for power generation

A novel auto-cascade low-temperature solar Rankine cycle (ALSRC) system is proposed. Compared to the single stage low-temperature solar Rankine cycle (SSLSRC) system, the ALSRC system is different because it consists of two solar collectors, two expanders, a regenerator, and an internal heat exchanger (IHE). The working fluid for the ALSRC is the zeotropic mixture Isopentane/R245fa. The main advantages of the ALSRC system is that heat from the exhaust stream of the expanders are reclaimed twice, once using an IHE and another time using a regenerator. System parameters such as regeneration, mixture composition, the outlet temperature of the low temperature solar collector, and the inlet temperature of two expanders are investigated to determine their effects on thermal efficiency. Results showed that with a regenerator, the thermal efficiency of the ALSRC system using a mixture of 0.32 R245fa by mass was significantly higher than that of the SSLSRC system. It was determined that regeneration, the mixture composition, and the outlet temperature of the low temperature solar collector are all important factors that affect the system’s thermal efficiency.     

A study of organic working fluids on system efficiency of an ORC using low-grade energy sources

Rankine cycles using organic fluids (as categorized into three groups: wet, dry, and isentropic fluids) as working fluids in converting low-grade energy are investigated in this study. The main purpose is to identify suitable working fluids which may yield high system efficiencies in an organic Rankine cycle (ORC) system. Efficiencies of ORC systems are calculated based on an assumption that the inlet condition of the working fluid entering turbine is in saturated vapor phase. Parameters under investigation are turbine inlet temperature, turbine inlet pressure, condenser exit temperature, turbine exit quality, overall irrversibility, and system efficiency. The low-grade energy source can be obtained from a solar pond or/and an ocean thermal energy conversion (OTEC) system. Results indicate that wet fluids with very steep saturated vapor curves in T-s diagram have a better overall performance in energy conversion efficiencies than that of dry fluids. It can also be shown that all the working fluids have a similar behavior of the efficiency-condenser exit temperature relationship. Furthermore, an appropriate combination of solar energy and an ORC system with a higher turbine inlet temperature and a lower condenser temperature (as operated deeply under sea level) would provide an economically feasible and environment-friendly renewable energy conversion system.     

Exergetic utilization of solar energy for feed water preheating in a conventional thermal power plant

This communication is based on exergy concept for the utilization of solar thermal energy in a Rankine cycle‐based fuel‐fired thermal power plant (FFTPP). It has been shown that solar thermal energy as an aided source for feed water preheating helps to reduce the exergy loss in feed water heater (FWH) of Rankine cycle and develops more work than that could have been produced in a solar thermal power plant (STPP). It has been found that this enhancement in work increases for low‐pressure FWHs. For further illustration, a case study has been carried out of a typical 50 kW STPP and a 220 MW FFTPP. The effect of utilizing the same input solar thermal energy of typical STPP, if used as an aided source in a 220 MW FFTPP for feed water preheating is investigated. The work output of STPP is 59.312 kW, while the extra work output of FFTPP by using solar thermal energy of STPP is 90.27 kW. It has been found that the efficiency of work conversion of aided solar thermal energy in FFTPP is higher than the efficiency of work conversion in STPP. Copyright © 2009 John Wiley & Sons, Ltd.     

海水淡化与火力发电厂现状

针对国内水资源的日益匮乏的现状,结合火力发电厂能源的回收利用,在传统的海水淡化技术系统基础上提出了蒸馏法和反渗透膜法相结合的海水淡化系统——MSF-RO联合海水淡化系统。通过与传统单一海水淡化技术相比较,指出联合海水淡化系统经济性和优越性,并对今后海水淡化核心和发展方向做出展望。     

Solar energy powered Rankine cycle using supercritical CO2

A solar energy powered Rankine cycle using supercritical CO₂ for combined production of electricity and thermal energy is proposed. The proposed system consists of evacuated solar collectors, power generating turbine, high-temperature heat recovery system, low-temperature heat recovery system, and feed pump. The system utilizes evacuated solar collectors to convert CO₂ into high-temperature supercritical state, used to drive a turbine and thereby produce mechanical energy and hence electricity. The system also recovers heat (high-temperature heat and low-temperature heat), which could be used for refrigeration, air conditioning, hot water supply, etc. in domestic or commercial buildings. An experimental prototype has been designed and constructed. The prototype system has been tested under typical summer conditions in Kyoto, Japan; It was found that CO₂ is efficiently converted into high-temperature supercritical state, of while electricity and hot water can be generated. The experimental results show that the solar energy powered Rankine cycle using CO₂ works stably in a trans-critical region. The estimated power generation efficiency is 0.25 and heat recovery efficiency is 0.65. This study shows the potential of the application of the solar-powered Rankine cycle using supercritical CO₂.     

Feasibilty study of renewable energy powered seawater desalination technology using natural vacuum technique

With an ever-increasing population and rapid growth of industrialization, there is great demand for fresh water. Desalination has been a key proponent to meet the future challenges due to decreasing availability of fresh water. However, desalination uses significant amount of energy, today mostly from fossil fuels. It is, therefore, reasonable to rely on renewable energy sources such as solar energy, wind energy, ocean thermal energy, waste heat from the industry and other renewable sources. The present study deals with the energy-efficient seawater desalination system utilizing renewable energy sources and natural vacuum technique. A new desalination technology named Natural Vacuum Desalination is proposed. The novel desalination technique achieve remarkable energy efficiency through the evaporation of seawater under vacuum and will be described in sufficient detail to demonstrate that it requires much less electric energy compared to any conventional desalination plant of fresh water production of similar capacity. The discussion will highlight the main operative and maintenance features of the proposed natural vacuum seawater desalination technology which seems to have promising techno-economic potential providing also advantageous coupling with renewable energy sources.     

Parametric theoretical study of a two-stage solar organic Rankine cycle for RO desalination

The present work concerns the parametric study of an autonomous, two-stage solar organic Rankine cycle for RO desalination. The main goal of the current simulation is to estimate the efficiency, as well as to calculate the annual mechanical energy available for desalination in the considered cases, in order to evaluate the influence of various parameters on the performance of the system. The parametric study concerns the variation of different parameters, without changing actually the baseline case. The effect of the collectors' slope and the total number of evacuated tube collectors used, have been extensively examined. The total cost is also taken into consideration and is calculated for the different cases examined, along with the specific fresh water cost (€/m³).     

Advancement in solar photovoltaic/thermal (PV/T) hybrid collector technology

This article presents an overview on the research and development and application aspects for the hybrid photovoltaic/thermal (PV/T) collector systems. A major research and development work on the photovoltaic/thermal (PVT) hybrid technology has been done since last 30 years. Different types of solar thermal collector and new materials for PV cells have been developed for efficient solar energy utilization. The solar energy conversion into electricity and heat with a single device (called hybrid photovoltaic thermal (PV/T) collector) is a good advancement for future energy demand. This review presents the trend of research and development of technological advancement in photovoltaic thermal (PV/T) solar collectors and its useful applications like as solar heating, water desalination, solar greenhouse, solar still, photovoltaic-thermal solar heat pump/air-conditioning system, building integrated photovoltaic/thermal (BIPVT) and solar power co-generation.     

Simulation and economic analysis of a CPV/thermal system coupled with an organic Rankine cycle for increased power generation

In concentrating photovoltaic (CPV) systems the incident solar radiation is multiplied by a factor equal to the concentration ratio, with the use of lenses or reflectors. This is implemented, in order to increase the electric power production, since this value has a linear dependence from the incident radiation. Therefore, the specific energy production of the cells (kWh/m²) radically increases, but due to this high intensity CPVs consequently operate at elevated temperatures, because heat dissipation to the environment is not so intense and heat produced cannot naturally convected. This temperature increase not only leads to a reduction of their electric efficiency, but also it must be dissipated, since issues regarding their degradation and reduction of their lifetime might arise. There are many reported ways of removing this heat, either by adding a cooling unit on the back side of the CPV module, or by recovering with possible uses in buildings, industry, additional power production or even desalination of seawater.The current work is actually a feasibility study, concerning a concentrating photovoltaic/thermal (CPV/T) system, where the heat produced is recovered by an organic Rankine cycle (ORC) for additional power production. A pump drives the organic fluid of the cycle, which is evaporated in the tubes of the CPV/T and driven to an expander for mechanical power production. For the condensation of the organic fluid several possible alternatives can be applied. That way, the PV cells can be cooled effectively and increase their electrical efficiency, while the recovered heat is designated to produce additional electric energy through the organic Rankine process, when the expander of the Rankine engine is coupled to a generator.The scope of the present work is to investigate an alternative application of concentrating PV modules through exploiting the generated heat by the ORC process and combining both technologies into an integrated system. The design of the system is presented in details, along with an optimization of some main parameters. The performance of the system will also be examined and compared with an equivalent conventional CPV system, referring to their design points. Finally, the annual and daily performance will be studied, which is a more realistic indicator, concerning the increased efficiency this integrated system is expected to have, followed by a cost analysis, in order to examine its economic feasibility as well.     

Impact of solar energy cost on water production cost of seawater desalination plants in Egypt

Many countries in North Africa and the Middle East are experiencing localized water shortages and are now using desalination technologies with either reverse osmosis (RO) or thermal desalination to overcome part of this shortage. Desalination is performed using electricity, mostly generated from fossil fuels with associated greenhouse gas emissions. Increased fuel prices and concern over climate change are causing a push to shift to alternative sources of energy, such as solar energy, since solar radiation is abundant in this region all year round.     

Economic evaluation of reverse osmosis desalination system coupled with tidal energy

A reverse osmosis (RO) desalination system coupled with tidal energy is proposed. The mechanical energy produced by the tidal energy through hydraulic turbine is directly used to drive the RO unit. The system performances and the water cost of the conventional and tidal energy RO systems are compared. It is found that the proposed tidal energy RO system can save water cost in the range of 31.0%-41.7% in comparison with the conventional RO system. There is an optimum feed pressure that leads to the lowest water cost. The tidal RO system can save more costs at a high feed pressure or a high water recovery rate. The optimum feed pressure of the tidal energy RO system is higher than that of the conventional RO system. The longer lifetime of the tidal energy RO system can save even more water cost. When the site development cost rate is lower than 40%, the water cost of the tidal energy RO system will be lower than that of the conventional RO system. The proposed technology will be an effective alternative desalination method in the future.     

Analysis of the power cycle utilizing the cold energy of LNG

The aim of this study is to analyse the performance of the Rankine power cycles operating with the LNG as the heat sink and with the seawater as the heat source. A model for the power cycle utilizing the cold energy of the LNG is established and a cycle simulation is carried out to analyse the performance characteristics. The analysis reveals that there exist optimum values in the condenser-outlet temperatures of the LNG and the ratio of heat transfer capacity of the condenser to the total capacity of the condenser and the vapour generator. An additional finding of this study is that near the point of maximum net work, the heat transfer capacity of the vapour generator becomes larger than that of the condenser, as opposed to the cases of a general Rankine cycle. Also the results of this study illuminate several advantages of using binary mixtures as working fluids over the use of pure substances.     

A comprehensive techno-economical review of indirect solar desalination

Solar powered desalination has been the focus of great interest recently worldwide. In the past, majority of the experimental investigations focused on solar coupled thermally driven conventional desalination technologies such as Multi-Stage Flash (MSF) and Multi-Effect Distillation (MED). With the advancement in membrane technology and its advantages such as high Recovery Ratios (RR) and low specific energy requirements Reverse Osmosis (RO) desalination has gained popularity. Currently, 52% of the indirect solar desalination plants are RO based with MED and MSF having a 13% and 9% share respectively. Membrane Distillation (MD) based plants represent 16% of the total and have been a focus of recent research efforts. This paper aims to provide a comprehensive review of all the indirect solar desalination technologies along with plant specific technical details. Efforts assessing the economic feasibility and cost affecting parameters for each desalination technology are also reviewed.