Multi-stage Flash Research Articles

Estimation of pressure drop in a demister for multi-stage flash desalination process based on stacked long short-term memory (LSTM) neural networks

The thermal desalination process such as a multi-stage flash desalination process (MSF) uses demisters as the separator between the flashed off vapor and the brine droplets in the flashing stage. The performance of the MSF plant depends on the quantity of fresh water produced. The separation efficiency depends on the pressure drops in the demister that influences the plant performance. This study proposes the application of Long Short-Term Memory (LSTM) neural networks for estimating pressure drop across demisters. The stacked LSTM algorithm is effective in estimating the pressure drop for experiment and real plant data. The superiority of stacked LSTM algorithm above reference benchmarks is evident. The Root Mean Square Error (RMSE) of the estimation from stacked LSTM algorithm is less than the estimation from the work of Al-Fulaij et al CFD model Al-Fulaij H, et al 2016, Desalination, 385: 148–157 by 40%.

Application of directional freezing for seawater desalination: Parametric analysis using experimental and computational methods

Directional freezing is valuable due to their capability to provide excellent relocation of impurities away from ice crystals and thus produce higher desalination efficiency. In this work, desalination of surrogate seawater using directional freezing in radial and vertical directions of a cylindrical crystallizer was assessed experimentally and numerically. Experiments on the effect of different brine concentration and freezing direction on the salinity at various spatial locations was conducted. Moreover, a transient computational fluid dynamics model of multispecies flow which allows for solidification and melting was developed in order to simulate the experimental set-up. Subsequently, a modified model was developed to investigate the role of stirring on the solutes distribution during the directional ice growth. The developed model showed good agreement with the experimental results. The model also showed a successful directional freezing by obtaining the anticipated salinity gradient due to salt diffusion away from the ice growth layer. Performance metrics such as effective partition coefficient, removal efficiency and energy consumption of the desalination process were evaluated. Results showed that better partition and removal efficiency were achieved under lower salinity brine, top freezing instead of bottom or radial freezing, and with stirred flow versus stagnant configurations. Freeze desalination (FD) consumed less energy as compared to multi-stage flash distillation (MSH), humidification-dehumidification (HDH). The FD consumed 11.34 kWh/m3 as compared to MSH and HDH which require 24.6kWh/m3 and 123kWh/m3, respectively. Although the energy consumed in FD (11.34 kWh/m3) was more that of reverse osmosis (RO) (8.2 kWh/m3), it was relatively close.

Brine reject dilution with treated wastewater for indirect desalination

The forward osmosis (FO) process was suggested as a pretreatment to a multi-stage flashing (MSF) plant to reduce the environmental impact of brine discharge and the chemicals used. Yet, there is no study investigating the performance of the FO process pretreatment to the MSF plant using tertiary sewage effluent (TSE) as a feed solution. Combining MSF brine with the TSE generates a considerable permeation flux, reducing the membrane area and capital cost. This study evaluated the performance of the FO process for indirect desalination of the MSF brine, considering membrane fouling, cleaning, required membrane area and the specific power consumption. The FO process used a thin-film composite (TFC) membrane to dilute the brine reject from the MSF plant by the TSE and hence converting waste solutions into a feasible water resource. A considerable high water flux (±35 L/m2h) was generated and slightly decreased throughout each experiment's 4 cycles. An enhancement in the water permeability was observed in the FO tests with a prefiltration of the brine reject and the wastewater with 20 μm and an osmotic backwash cleaning of the used membrane. The prefiltration of the draw and feed solutions was effective in minimizing the impact of fouling. Maximum power consumption of 0.007 kWh/m³ was consumed in the forward osmosis process without prefiltration and decreased to 0.006 kWh/m³ in the FO process. The proposed FO system successfully diluted the brine reject’ divalent ions, reducing their concentration to 43% in some cases. Depending on the FO membrane orientation, the TSE feed solution resulted in a 276%–473% reduction in the number of FO elements required in the FO process compared to the seawater feed solution.

Dynamic simulation of once-through multistage flash (MSF-OT) desalination process: Effect of seawater temperature on the fouling mechanism in the heat exchangers

Scale formation of carbonates and sulphates is one of the most well-known types of crystallization fouling in heat exchangers. Tackling crystallization fouling in Once-Through Multistage Flash Desalination (MSF-OT) is one of the most challenging tasks in the desalination industry. In this paper, a fouling model is developed and then incorporated into a MSF model to investigate the fouling behaviour under variable seawater temperature. The proposed dynamic model investigates the crystallization of calcium carbonate and magnesium hydroxide at the inside tube surface areas by considering the attachment and removal mechanisms. The results show that the fouling rate is higher at high constant seawater temperature. Overall, the fouling rate is lower at the seasonal variation of the seawater temperature, resulting in a higher performance ratio (PR). The results also show that although the brine heater duty increases in winter due to low seawater temperature, the drop of fouling rate in cold months may save some energy.

Research on Key Technologies of Ocean Thermal Desalination

Due to the process of urbanization and industrialization, the crisis of freshwater resources has become a problem to be solved by mankind. Although the traditional low-temperature multi-effect distillation method, multi-stage flash evaporation method and reverse osmosis membrane method seawater desalination currently occupy the mainstream position [1], Low-temperature multi-effect distillation method brine evaporation temperature cannot exceed 70 °C, reverse osmosis membrane method has the characteristics of high requirements for seawater pretreatment, and multi-stage flash evaporation method has the defect of high energy consumption. Therefore, ocean temperature difference can be used as a renewable energy source. Due to the huge reserves, about 10TW (10x1012W) that can be developed and utilized in the world is recognized by the international community as one of the most potential energy sources[2]. This article first describes the significance of the development of ocean temperature difference energy and the current research status of ocean temperature difference energy seawater desalination; secondly, it takes the ocean temperature difference energy seawater desalination method as the research object, based on the technical difficulties of ocean temperature difference energy seawater desalination and the process of the seawater desalination method that reduces the temperature difference. Four aspects put forward the main factors to improve the performance of the system; finally, it is concluded that the transformation of the key technological achievements of the ocean temperature difference energy seawater desalination method will provide more energy-saving, environmentally friendly, and more efficient for the comprehensive development and utilization of marine engineering, offshore oil drilling platforms, and islands. High-quality freshwater resources.

Development of S22053+12MnNiVR rolled clad steel plate for multi-stage flash desalination evaporator shell

This paper describes the development process of S22053+12MnNiVR composite steel plate using vacuum electron beam welding technology and double-sided symmetrical billet assembly method in ANSTEEL Co., Ltd., which has a product thickness of 2+12mm and is used in multi-stage flash seawater desalination evaporator shell. The stainless-steel clad steel plate has excellent comprehensive mechanical properties, good resistance to intergranular corrosion and seawater corrosion. The bonding rate of its composite interface meets the requirements of GB/T 8165-2008 Class I, and the bonding rate between atoms is 100%. As a new generation of green composite material, the successful development of S22053+12MnNiVR stainless steel-clad steel plate is of great significance in reducing the cost of seawater desalination, increasing the life of seawater desalination equipment, and realizing the localization of equipment, which provides an important way for China to solve the shortage of fresh water resources and lays a solid foundation for China to realize the green recycling of seawater resources.

Development and assessment of a solar driven trigeneration system with storage for electricity, ammonia and fresh water production

This research paper designs and analyzes a novel integrated solar-driven system for ammonia synthesis, freshwater production and power generation. The trigeneration system contains a solar thermal subsystem, a thermal energy storage system where the molten salt is used as a heat transfer fluid and storage medium, a solar energy-driven Rankine cycle, a multistage flash distillation, a proton exchange membrane electrolyser array, and an ammonia synthesis unit. The proposed integrated system uses solar energy to charge the molten salt, which flows through a heat exchanger and generates steam for the topping cycle. The exhaust stream of the steam turbine provides heat for the multistage flash distillation (MFD) process. A 20 stage MFD unit is proposed where the seawater is utilized as the feedwater in this study. A portion of the produced freshwater is sent to the PEM electroylzer array for hydrogen production, which is used for ammonia production via the Haber-Bosch process. The thermodynamic analysis of the solar driven multigeneration system is analyzed through the Engineering Equation Solver (EES) and Aspen Plus software packages. The novelty of this study relies on the development of a new solar energy-based integrated system and its application for a selected community with over 10,000 residents to meet all of their needs to be self-sufficient and sustainable. Ammonia (for multiple purposes, such as fuel, energy carrier and feedstock), freshwater and electricity are the useful outputs as targeted in this paper. The study incorporates the phase change materials into the system for thermal energy storage purposes. The performance assessments based on energy and exergy efficiencies are carried out for the overall system and its components. Furthermore, the power, freshwater and ammonia production capacities are studied for better demand coverage. The overall exergy efficiency of the system is determined as 12.1 %, where the ammonia synthesis, power generation, and freshwater production capacities are 0.85 kg/s, 17.6 MW, and 143.97 kg/h respectively. Moreover, the study investigates the energy and exergy efficiencies with and without the presence of an air separation unit. The study results show that the air separation unit has less than 0.3% effect on the overall energy and exergy efficiencies.

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.

Fresh Water Generator: A Review

This search presents a study for some types of fresh water generators FWGs, giving an overview of each type and comparing them with other types, and knowing the design criteria for different designs, as well as studying their advantages and disadvantages, including thermal desalting which types are vapor compression (VC), multi stage flash distillation (MSF), multiple effect distillation (MED), and multiple effecte evaporator, adsorption desalination, membrane distillation (MD), freezing desalination, and hydrate desalination. Then we studied the non-thermal desalination process, which includes electro-dialysis (ED), ion exchange desalination (IX), extraction desalination process, and additional types of fresh water generators FWGs.

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.

Techno-economic analysis of sustainability and externality costs of water desalination production

Increase in economic activities and population growth have resulted in the high energy and water demands which made them top priorities for many countries around the globe. This led to exploring new sources for producing fresh water including desalination. Estimating the true cost of desalinated water production should include both internal and externality costs. The objective of this paper is to calculate the externality costs that are associated with desalination water production in United Arab Emirates. The study examines and quantifies the environmental, economical and social costs of thermal desalination plants for both Multi-Effect Distillation (MED) and Multi-Stage Flash (MSF) technologies using Analytical Hierarchy Process model. For this purpose, various desalination sustainability criteria that are considered include CO2 emissions, brine discharge, chemicals pollutants, land area, employment rate, desalinated water quality and water availability. Results show that the true cost of desalinated water production almost doubled when the externality costs are included. Results indicated that the externality costs for the MED technology ranged between 0.297$/m3 and 0.702 $/m3 leading to an average increase of 65.8%. For the MSF technology, the externality costs ranged between 0.548$/m3 and 1.174$/m3 leading to an average increase is of 81.9%.

Hybrid modelling for combined design optimization of CO2 removal and compression in raw natural gas treatment complexes

CO2 removal in raw natural gas is required to meet the sale gas specifications. The chemical solvent absorption method is one of the most commonly used technologies. The absorption-based processes, however, require an enormous amount of energy to regenerate the solvent, and are designed to discharge the captured CO2 into the atmosphere directly. The energy efficiency and greenhouse gas emissions should be considered in the gas treatment process. In this study, a new process, combining CO2 removal and compression, is proposed for raw natural gas treatment complexes. Compared with the conventional absorption-based processes, in the new process CO2 is not stripped from rich solvent in one distillation column but through multi-stage flash separators operating under different pressures and temperatures. The CO2 removed from each stage is then compressed separately to the proper pressure for carbon transportation and storage. A mathematical model is then developed to determine the optimum process configuration and operating conditions. A surrogate-based optimization framework is presented in order to strike a good balance between computational efficiency and model accuracy. The complex units are replaced by Kriging surrogate models. Aspen HYSYS is used to generated sampling points for the construction of surrogates. A method of dimension reduction is introduced to compact the surrogate models by selecting essential variables. Finally, a hybrid optimization model comprising of the surrogate models for “complex” units and explicit models for the rest of the process is formulated. The cases show the total annual cost of the CO2 removal and compression can be reduced by 20.6%–28.8% for different sweet gas purity specifications.

Dynamic simulation and life cycle cost analysis of a MSF desalination system driven by solar parabolic trough collectors using TRNSYS software: A comparative study in different world regions

In the present work, water desalination by solar energy is investigated based on life cycle cost. In the first step, regions under consideration are prioritized for solar energy utilization applying an appropriate ranking method based on desalinated water demand, saline water availability, annual average solar irradiation, and local water tensions. TRNSYS software is used for simulation and a multi-stage flash desalination system is defined in this software as a new component type by employing the Fortran program. Solar troughs and natural gas are used for solar energy extraction and heater, respectively. The considered system is investigated in seven different cities with high solar potential from the economic point of view. Also, an economic comparison is conducted in order to assess the multi-stage flash desalination system utilizing solar collector, auxiliary heater, and the system using natural gas without solar system. In this regard, the life cycle cost method is applied. The results of the study showed that using solar energy is more economical in comparison with natural gas for all of the case studies and the highest saving is obtained for Port Hedland in Australia. The lowest cycle cost of the system, utilizing solar energy and natural gas, is observed in Hurghada. In Hurghada, 88% of the energy required by the system is supplied by sun, and this city benefits the most from solar energy compared to other cities. Los Angeles and Manzanillo had the lowest share of solar energy at 59% and 57%, respectively.

Process optimization and revamping of combined-cycle heat and power plants integrated with thermal desalination processes

Optimal revamping, sizing, and operation of an existing gas-turbine combined-cycle dual-purpose power/desalination plant – simultaneous electricity and freshwater generation – which operates with a heat recovery steam generation with one-pressure level (1P-HRSG) and a multi-stage flash desalination process, is addressed. The sizes and configurations of the gas turbine and desalination unit are kept the same as in the existing plant through the study. However, the 1P-HRSG is conveniently extended to two- or three-pressure levels with different exchanger arrangements, including steam reheating. To this end, a superstructure-based representation of the HRSG simultaneously embedding several candidate structures was proposed and a mixed-integer nonlinear programming model was derived from it.One revamping case consisted in maximizing the ratio between the freshwater production rate and the heat transfer area of HRSG, keeping unchanged the electricity generation rate (around 73 MW). It was found that the inclusion of a 3P-HRSG resulted in an increase of 13.782 kg⋅s−1 in the freshwater production, requiring 22753 m2 of heat transfer area less in the HRSG. Another revamping case consisted in maximizing the profit, contemplating the possibility to sell extra amounts of electricity and freshwater. Sale prices, for which producing extra electricity and freshwater is beneficial, were determined.

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.

On The Thermodynamics of Dual Purpose Power Desalting Plants with Gas Turbine.(Dept.M)

Recent advances in gas turbine cycles and combined gas/steam turbine cycles are presented. First and second law analysis of gas turbine cycles is presented and shows that substantial available energy (up to 30% of fuel availability) is carried out by gas turbine exhaust gases. This available energy can be utilized for further heat to work conversion or for direct process heating. Heat recoverd from gas turbine exhaust gases in heat recovery steam generator (HRSG) can generate relatively high pressure steam to be supplied to Rankine steam power cycle to form gas/steam power cycle of high efficiency (40-45%). Steam can be generated at low pressure in the HRSG for direct supply to the brine heater of a multistage flash (MSF) desalting system. Possible combination of simple gas turbine cycle or combined gas/steam cycle with reverse osmosis or MSF sea water desalting systems are presented and evaluated. The evaluation indicates that most of these combination are more superior than combination with steam power plants from energy view points.

Design, evaluation, and optimization of an efficient solar-based multi-generation system with an energy storage option for Iran’s summer peak demand

In summer, the coastal areas of southern Iran suffer from the freshwater shortage and electricity instability. Meanwhile, this region benefits from the high intensity of solar radiation and the huge potential of brackish water resources. Hence, this paper designs a novel cooling, power and pure water trigeneration system for application in this area to mitigate its energy and water crisis. The proposed system is composed of a solar-based Goswami power and cooling production cycle and a multistage flash seawater desalination process. Moreover, a molten salt heating energy storage unit is used to prove its steady operation under uncertain sunlight condition. A comprehensive parametric study is provided to evaluate the system performance by changing the key variables. The numerical results demonstrate that increasing the pressure ratio from 6 to18 causes 3.3% leads to an increase in system efficiencies and minimum total products cost experiences at the pressure ratio of 12.6. Additionally, as the superheating degree increases from 0 to 10 K, the energy efficiency decreases but the exergy efficiency increases. When the ammonia concentration at the rectifier exit is increased from 0.965 to 0.995, the energy efficiency increases 5%, the exergy efficiency has a decreasing trend from 28% to 25.9%, and the minimum total products cost is 131.2 $/GJ. Furthermore, the exergy efficiency gains its maximum, the energy efficiency has a minimum value, and the total products cost grows with higher values of the minimum approach temperature. Finally, the system is optimized under four different scenarios to identify its best operating condition in each condition: three single-objective and one multi-objective optimization cases. The results of the multi-objective optimization are trade-offs between the ones for single-objective optimization cases. In this case, the net power of 12 MW, cooling capacity of 15.74 kW, and the freshwater of 4.72 kg/s are attainable.

Design and behaviour estimate of a novel concentrated solar-driven power and desalination system using S–CO2 Brayton cycle and MSF technology

Solar-based power and desalination system using super-critical carbon dioxide (S–CO2) Brayton cycle can be considered as one of the most promising development directions of future energy. This study presents the design and behaviour estimate of a novel concentrated solar-driven power and desalination (CSPD) system using S–CO2 Brayton cycle and multi-stage flash (MSF) desalination technology. Operation simulations and exergic analysis of the CSPD system are conducted by utilizing the Ebsilon software. Operation behaviour estimate results of the CSPD system show that the efficiency of S–CO2 Brayton cycle is 36.6%. The electric power and freshwater daily output of the CSPD system are 50.1 MW and 4050.8 t. The CSPD system can perform the solar-driven electricity production and solar-driven desalination simultaneously according to the pre-set operation strategy. The exergic analysis results indicate that the solar tower receiver and heat exchanger of desalination system have the two maximum energy destructions as well as the two lowest exergy efficiencies. The economic analysis results reveal that the CSPD system has an equivalent LCOE (levelized cost of electricity) of 0.059 $∙kWh−1 and an LCOW (levelized cost of water) of 1.15 $∙t−1, which means the CSPD system is economically feasible.

Recent Desalination Technologies by Hybridization and Integration with Reverse Osmosis: A Review

Reverse osmosis is the leading technology for desalination of brackish water and seawater, important for solving the growing problems of fresh water supply. Thermal technologies such as multi-effect distillation and multi-stage flash distillation still comprise an important portion of the world’s desalination capacity. They consume substantial amounts of energy, generally obtained from fossil fuels, due to their low efficiency. Hybridization is a strategy that seeks to reduce the weaknesses and enhance the advantages of each element that makes it up. This paper introduces a review of the most recent publications on hybridizations between reverse osmosis and thermal desalination technologies, as well as their integration with renewable energies as a requirement to decarbonize desalination processes. Different configurations provide improvements in key elements of the system to reduce energy consumption, brine production, and contamination, while improving product quality and production rate. A combination of renewable sources and use of energy and water storage systems allow for improving the reliability of hybrid systems.

Performance of the Pressure Assisted Forward Osmosis-MSF Hybrid Desalination Plant

An osmotically driven membrane process was proposed for seawater pretreatment in a multi-stage flashing (MSF) thermal plant. Brine reject from the MSF plant was the draw solution (DS) in the forward osmosis (FO) process in order to reduce chemical use. The purpose of FO is the removal of divalent ions from seawater prior the thermal desalination. In this study, seawater at 80 g/L and 45 g/L concentrations were used as the brine reject and seawater, respectively. The temperature of the brine reject was 40 °C and of seawater was 25 °C. Commercial thin-film composite (TFC) and cellulose triacetate (CTA) membranes were evaluated for the pretreatment of seawater in the FO and the pressure-assisted FO (PAFO) processes. Experimental results showed 50% more permeation flux by increasing the feed pressure from 1 to 4 bar, and permeation flux reached 16.7 L/m2h in the PAFO process with a TFC membrane compared to 8.3 L/m2h in the PAFO process with CTA membrane. TFC membrane experienced up to 15% reduction in permeation flux after cleaning with DI water while permeation flux reduction in the CTA membrane was >6%. The maximum recovery rate was 11.5% and 8.8% in the PAFO process with TFC and CTA membrane, respectively. The maximum power consumption for the pretreatment of seawater was 0.06 kWh/m3 and 0.1 kWh/m3 for the PAFO process with a TFC and CTA membrane, respectively.