Multi-stage Flash Desalination Units Research Articles

Performance optimization of an integrated solar combined cycle for the cogeneration of electricity and fresh water

Many Arabic countries suffer water scarcity while having an energy surplus. The present work investigates and optimizes a proposed plant for the cogeneration of electricity and fresh water. This plant comprises an Integrated Solar Combined Cycle (ISCC) power plant and a Multi Stage Flash (MSF) desalination unit. The steam condenser of the ISCC acts as a brine heater of the MSF desalination unit. Thus, the waste thermal energy from the ISCC is used to desalinate the seawater. The proposed cycle produces fresh water during its part load operating conditions. Simulation programs were developed and validated using real data from the ISCC power plant in Kuraymat-Egypt. The present results show that the proposed plant is very promising for the cogeneration of electricity and fresh water. An optimum top brine temperature (To) of 80 °C was estimated based on the amount of fuel required to desalinate the seawater. The proposed plant produces up to 1140 m3/h of fresh water under the typical operating conditions of Hurghada-Egypt, 50 % of the rated output power, and To = 80 °C. It saves up to 84.7 % of the fuel required for desalination compared to a standalone MSF desalination unit that operates under the same conditions.

Thermo-Economic Analysis of Gas Turbine Combined Multistage Flash (MSF) Desalination Cycle

Over the past few decades, the growth of the earth’s population has increasingly contributed to global warming, and increased demand for fresh water on top of a need for a greater power supply. This paper will analyze the integration of a combined- gas turbine with intercooler and a multi-stage flash (MSF) desalination plant for the simultaneous generation of electricity and supply of water and improved performance. The paper will also examine the calculation of the production cost and the capital cost of the MSF desalination plant. The thermo-economic analysis of the study was conducted using the IPSEpro software system. Also, exergy losses of the gas turbine and MSF desalination unit were also calculated. The desalination plant uses the exhaust gases from the gas turbine, as a form of thermal energy, and discharges to feed the seawater heater. A portion of the desalinated water is used to cool the compressed air in the intercooler heat exchanger. Results indicate the improvement in the gas turbine’s performance when desalinated water is used for the intercooler between compressor stages, as the power output increased by 59% over the the simple gas cycle and found decrease with an increase in the ambient temperature. The desalinated water cost was calculated to be $1.7 per cubic meter after determining the optimal configuration and operating conditions. A decrease in steam cost by 36% was observed when the waste heat from the gas turbine was used as the source of thermal energy. Part of this reduction can be explained by the observation that the desalination plant’s pumps consume part of the power generated by the gas turbine.

Part load operation of an integrated solar combined cycle using the brine heater of a MSF desalination unit as a steam condenser

Hot-climate countries, like Egypt, have an energy surplus while suffering water scarcity. Energy surplus causes frequent part load operation of Integrated Solar Combined Cycle (ISCC) power plants. The present work proposes a cycle that combines an ISCC with a Multi Stage Flash (MSF) desalination unit. The brine heater of the MSF desalination unit acts as a steam condenser for the ISCC. The condenser pressure/top brine temperature of the MSF desalination unit controls the ISCC part load operation. A simulation model for an actual ISCC in Kuryamat-Egypt was developed and validated. A validated model for the MSF unit was integrated with the developed ISCC model. The proposed cycle (ISCC-MSF) was simulated under different operating and geometric conditions. The simulation results were used to optimize the MSF desalination unit and achieve a performance ratio of 11.65 and a 7.7% reduction in the stage area. Cost analysis was performed for the unit production cost of fresh water (UPCMSF), where a reduction of UPCMSF to 0.77$/m3 was achieved. Further reduction of UPCMSF down to 0.54$/m3 can be attained by reducing the interest rate from 5% to 1%. Detailed part load performance investigation of the proposed cycle is recommended for future work.

Experimental Validation of a Solar Powered Multistage Flash Desalination Unit with Alternate Storage Tanks

The fossil fuels that power conventional desalination systems cause substantial environmental impact. Solar desalination can satisfy critical water needs with only a minimal contribution to global warming. The current work presents an attractive new design suitable for regions with limited water resources and high solar radiation rates. This work is an experimental study of a newly designed, solar-powered, multi-stage flash (MSF) desalination plant. The design could address the need to increase the limited water resources in solar energy-rich areas. The prototype consists of a solar collector, an MSF unit, and a novel dual thermal storage tank design. In this prototype, preheated brine is directly heated by circulation through the solar collector. Two tanks serve the MSF unit; one tank feeds the MSF unit while the other receives the preheated feed water. The two tanks alternate roles every 24 h. The study was conducted in Taif, Saudi Arabia, throughout the month of September 2020. The results of the experiment showed that 1.92 square meters of solar collector area is needed for an average daily production of 19.7 kg of fresh water, at a cost of approximately $0.015 per liter.

Dynamic R-Curve analysis and optimization of steam power plant solar repowering

Installing solar collectors to preheat boiler feedwater is one of the most economical methods of repowering steam power plants. The production of freshwater in repowered plants can increase their productivity. The present study aimed at integrating the Bandar Abbas steam power plant's repowered cycles with desalination units and subsequently analyzing the cycles using the R-Curve tool. Three scenarios are were considered for repowering: In the first scenario, parallel collectors were used instead of the low-pressure feedwater heaters, while in the second and third scenarios, parallel solar collectors were used instead of low-pressure feedwater heaters integrated with multi-effect and multi-stage flash desalination units, respectively. The dynamic development of the R-Curve, as well as the use of a combination of artificial intelligence and genetic algorithm programming to optimize the complex cycles of the multi-generation of power, heat, and freshwater, are the most important issues presented in this study. Results show that the Bandar Abbas steam power plant in operation has an R-ratio equal to 1.21 and a cogeneration efficiency of 36.5 percent. In the first scenario of repowering, the R-ratio is equal to 1.21, and in most months, the cogeneration efficiency varies between 35 and 45 percent. In the second and third scenarios, however, cogeneration efficiency is 50 percent at its lowest level. Moreover, with the introduction of the new conceptual graphical curves, it was found that using more solar energy and adding desalination units increase the cogeneration efficiency throughout the year. Optimization of repowered cycles integrated with multi-effect and multi-stage flash desalination units increased freshwater production by 178 and 42 percent, respectively.

Design and thermodynamic assessment of a solar powered energy–food–water nexus driven multigeneration system

Decentralized food production can lead to the optimum and resilient utilization of resources while increasing the system performance, which can be made possible with the implementation of renewables. This study demonstrates a solar-powered multigeneration system designed to produce electrical power, freshwater from seawater, oxygen, hydrogen, and space cooling for a greenhouse application. The system’s main components include a Parabolic trough collector, organic Rankine cycle, multi-stage flash desalination unit, water electrolyzer, hydrogen-oxy combustor, thermal energy storage, absorption cooling system, and a greenhouse structure. For the system’s continuous operation, thermal energy storage and hydrogen-oxy combustor are used as a backup energy utilizing the hydrogen and oxygen produced from the electrolyzer. The integrated system is thermodynamically analyzed using mass, energy, entropy, and exergy balance equations. Furthermore, specified system outputs are evaluated by conducting parametric studies related to solar radiation, ambient temperature, and greenhouse area. The results of the analysis demonstrate that by installing a parabolic trough collector on an area of 80,000 m2, the integrated system delivers an electrical power of 2.70 MW, approximately 72.2 m3/day of freshwater, 796 kW of space cooling, 6420 kg/day of oxygen, and 802.3 kg/day of hydrogen. The overall system energy and exergy efficiencies are 41.0% and 28.4%, respectively. The system is designed in a way that it can be scaled up or down as a part of a decentralized food production system.

Comparative life cycle cost analysis of various solar energy-based integrated systems for self-sufficient greenhouses

This study provides a life cycle cost comparison of four different integrated systems powered by solar energy to provide electricity, water, and cooling for a self-sufficient greenhouse complex. System-1 and System-2 have a vapor absorption cooling system, while System-3 and System-4 have a vapor compression cooling system to provide the required cooling. All the systems have a multi-stage flash desalination unit driven by solar thermal energy to provide freshwater. PV or PV/T modules are installed to meet the electricity demands of the greenhouses. A new greenhouse roof concept is introduced in System-2 and System-4, where there are spectrum selective nanofluids as the working fluid of the PV/T units. This spectrum selective nanofluid absorbs solar radiations having wavelength greater than 1400 nm while flowing through the roof of the greenhouse, and thus reducing the cooling load of greenhouses. The thermal energy of PV/T is utilized to pre-heat the sea water entering the desalination unit for improved process efficiencies. The life cycle cost analysis indicates that the systems employing nanofluid are less costly than the regular systems due to better efficiency and lower energy requirements, especially in cooling. The reductions in life cycle cost of 22.3% and 12.8% are obtained for System-2 and System-4 as compared to System-1 and System-3, respectively. The evacuated tube collectors constitute more than 60% share of the life cycle cost of System-1 and System-3, while PV and PV/T modules have more than 50% share in the life cycle cost for System-2 and System-4. The ambient temperature and solar irradiance have a significant impact on the life cycle cost of all systems. The minimum values for the levelized cost of electricity and cooling are found to be 0.033 $/kWh and 0.015 $/kWh, respectively, for the System-3. System-2 has a minimum cost value of 1.45 $/m3 for the levelized cost of freshwater.

Energy, exergy and exergo-environmental assessment of a novel solar powered Kalina cycle incorporated with micro-CCHP for poly-generation

In this study, a solar parabolic trough collector combined with a Kalina cycle, multi-stage flash desalination unit, a proton exchange membrane electrolyser for hydrogen production, and a micro-combined cooling, heating, and power system is presented. Systematic energy, exergy, and exergo-environmental evaluation are used to analyse the viability of the integrated systems as the most effective approach for performance assessment of integrated systems. The energy and exergy efficiencies of the overall system is observed to be 50.51% and 3.27% respectively. The rate of exergy destruction of each component and the overall cycle is determined where the parabolic trough collector is shown to have an exergy destruction rate of 234.4 kW, which is the highest among all the components. The performance of the proposed systems is also checked through a parametric study of the different key parameters.

Experimental study of high-performance hybrid NF-MSF desalination pilot test unit driven by renewable energy

This study presents the experimental results of a renewable energy (RE) driven, high-performance multi-stage flash (MSF) desalination unit integrated with nanofiltration (NF) membrane. The desalination pilot test is built to evaluate, the performance of the novel De-aeration and brine Mix (MSF-DBM) configuration. The NF pilot is build in order to enable MSF desalination unit the operation at high top brine temperature (TBT). The capacity of the desalination pilot plant is 1.0 m3/day of water. The whole pilot plant is installed at Wadi El-Natroun (Egypt). This study presents the first phase of the project, including the pilot test description, and experiments of concentrated solar trough, steam generator, NF and MSF units. Comparison between the simulation and the experimental results of the pilot unit’ subsystems are relatively satisfactory. The newly developed NF-MSF-DBM (de-aerator and brine mix) configuration is tested at TBT = 100°C and the gain output ratio (GOR) is calculated as 15 which almost twice of traditional MSF under the same operating conditions. The newly high-performance NF-MSF-DBM and unit’s input thermal energy which make the integration with (the relatively expensive) RE as a desalination plant driver is a viable option.

Factors Affecting MSF Evaporator Life Expectancy

AbstractWith proper design and operation—particularly materials selection and corrosion control—multistage flash (MSF) evaporators can last 40–50 years. Such lifetimes parallel the obtainable operational life spans of the power units in which MSF desalination units are used in dual-purpose setups. The propositions set forth in this article are founded on use of sound corrosion engineering principles and application of information and experiences accruing from more than 45 years of operating an MSF plant in Saudi Arabia. The article also highlights the roles of local seawater chemistry and low-oxygen concentrations in feed and recirculating brine, as well as procedures to extend periods between acid cleans.

Performance study of enhanced and smooth surface tubes in a system condenser of a multistage flash desalination unit

Fouling of the multistage flash (MSF) system condenser tubes used for water desalination reduces the system overall heat transfer coefficient very rapidly. Consequently, hearts the system efficiency and increases the cost of distillate water. In this study, a comparison between enhanced and plain tube performance characteristics is investigated experimentally in the MSF system. The study is performed for aluminium-brass tubes with inside diameters of 19.05, 23, and 29.5 mm. A three different flow velocity of 0.1, 0.1645, and 0.2398 m/s are examined with these three tubes. The study is carried over for two different coolants fresh and brine water. In this paper, the results for fresh water are presented. The results indicated that the overall heat transfer coefficient ( U) varies with both coolant flow velocity and tube diameter. For both smooth and enhanced tubes, the higher the coolant speed or/and pipe diameter the larger the overall heat transfer coefficient. However, the effect of these two parameters is more significant with enhanced tubes. A gain in overall heat transfer coefficient by factor of 2.13 over smooth tubes can be achieved. Results also, showed that for certain tube diameter there is an optimum flow speed for maximum value of U. For a certain flow speed there is an optimum pipe diameter size. The results proved that the heat transfer coefficients of corrugated tubes are superior to plain tubes for most flow speeds and diameters investigated in the present study.

Dynamic modeling of multistage flash desalination plants

A model for the dynamic simulation of multistage flash desalination units has been developed, based on a detailed description of the fundamental elementary phenomena involved in the process. It takes into account stage geometry, physico-chemical and transport properties of water, vapor and brine and the different non-idealities of the process. In this work the model is used to describe the behavior of the MSF plant under different kinds of process disturbances, thus showing some of its nonlinear dynamic features. Further applications of the model may deal with the analysis of steady-state stability and the development of optimal control strategies and start-up/shut-down procedures.

Fuel efficiency concept for a dual-purpose power plant

A modified heat rate concept to evaluate the performance of dual-purpose power plants (DPPP) is proposed. This concept is specifically developed for co-generation power plants that employ thermal steam turbines and multi-stage flash desalination units to produce electricity and water. The conventional heat rate concept, normally used to assess the performance of single-purpose electric power plants, is found to be unsuitable for co-generation power plants. Alternatively, the proposed concept combines the two types of output to provide a single realistic indicator of the DPPP performance. The results of the analysis are finally applied to evaluate the performance of a power station in Kuwait.

Present trends in materials selection and performance in multi-stage flash desalination units

This paper utilizes data from a series of worldwide surveys conducted from 1968 to 1980 for the U.S. Department of the Interior, Office of Saline Water and Office of Water Research and Technology as well as the recent literature to illustrate the improvements made in the materials selection process over the last several years. Trends in materials used for heat exchange tubing, flash chambers and components, pumps, water boxes, etc., are enumerated and evaluated with respect to likely service life as a function of the severity of operating conditions. Plant factor (percent of time operating at rated capacity) is correlated with design and to gain perspective is compared to plant factors achieved in the chemical processing industry generally. Present trade-off decisions with respect to materials, operating temperatures and conditions, performance factors, electrical energy consumption, and use of chemicals are summarized and commented upon.