Multi-stage Flash System Research Articles

Exergy and economic analysis of a novel integration of compressed air energy storage with multi-effect distillation and multi-stage flash systems

Potable water and power shortage are major concerns for the world community. Large-scale energy storage systems (ESSs) are a suitable solution for grid-scale energy storage, among which Compressed air energy storage (CAES) is a lead technology. Hybrid CAES-Desalination was introduced in previous investigations. The system can supply power and potable water simultaneously which can be a strategic system for dry and warm climates. Multi-stage flash (MSF) and multi-effect distillation (MED) are modeled and thoroughly investigated in this paper. The CAES system's exhaust hot air is the drive power of the distillation systems. Therefore, not only the CAES system's performance is improved but also a large amount of drinkable water is generated. The compressors and turbine's dissipated heat play as the main sources in the distillation unit in charging and discharging periods, respectively. This paper has mainly focused on the exergy and economic analyses of this integration and has worked on the optimum arrangement considering exergy and economic investigation. This paper has also studied the exergy and economic analyses of the CAES system's recuperator removal. The exergy analysis declares that the majority of the exergy destruction in desalination units happens at the first stage where the heat exchange occurs. It also shows that pressure regulator, HTES, and turbine are responsible for significant shares of exergy destruction in the CAES system. The economic assessment expresses 5.1 years for the payback time of the integrated system.

An innovative rearrangement and comprehensive comparison of the combination of compressed air energy storage (CAES) with multi stage flash (MSF) desalination and multi effect distillation (MED) systems

Energy and drinkable water are the two critical resources for the world population. Compressed air energy storage (CAES) is one of the best solutions for grid-scale electricity power storage. Besides different technologies of desalination have been proposed until now. Comprehensive scrutiny of an integrated CAES-Desalination has been proposed in this study. This system can produce drinkable water and electricity power at the same time which makes it an ideal system in dry and warm environments. Multi-effect distillation and Multi-stage flash have been simulated and compared as desalination units. CAES system's dissipated heat is consumed as the input heat power of the desalination unit. In this way not only a large amount of potable water is produced but also the CAES performance is improved. The desalination required heat power is supplied in both charging and discharging mode from the compressors' heat exchanger secondary stream and turbine exhaust hot air respectively. The novelty of this paper is in the simulation of the CAES, MED, and MSF systems separately and thoroughly Comparing MED-CAES and MSF-CAES systems and also proposing a new arrangement for CAES-Desalination systems, and analyzing the effect of omitting the CAES system's recuperator and its consequence on system total outputs. The results for this case showed an almost 3 % improvement in roundtrip efficiency in comparison to the one with a recuperator. Also, the distilled water rate is almost 2.5 times of the normal CAES-Desalination system.

Dynamic Modelling and Simulation of a Multistage Flash Desalination System

As the leading thermal desalination method, multistage flash (MSF) desalination plays an important role in obtaining freshwater. Its dynamic modeling and dynamic performance prediction are quite important for the optimal control, real-time optimal operation, maintenance, and fault diagnosis of MSF plants. In this study, a detailed mathematical model of the MSF system, based on the first principle and its treatment strategy, was established to obtain transient performance change quickly. Firstly, the whole MSF system was divided into four parts, which are brine heat exchanger, flashing stage room, mixed and split modulate, and physical parameter modulate. Secondly, based on mass, energy, and momentum conservation laws, the dynamic correlation equations were formulated and then put together for a simultaneous solution. Next, with the established model, the performance of a brine-recirculation (BR)-MSF plant with 16-stage flash chambers was simulated and compared for validation. Finally, with the validated model and the simultaneous solution method, dynamic simulation and analysis were carried out to respond to the dynamic change of feed seawater temperature, feed seawater concentration, recycle stream mass flow rate, and steam temperature. The dynamic response curves of TBT (top brine temperature), BBT (bottom brine temperature), the temperature of flashing brine at previous stages, and distillate mass flow rate at previous stages were obtained, which specifically reflect the dynamic characteristics of the system. The presented dynamic model and its treatment can provide better analysis for the real-time optimal operation and control of the MSF system to achieve lower operational cost and more stable freshwater quality.

Mode-Based Analysis and Optimal Operation of MSF Desalination System

Multi-stage flash (MSF) desalination plays an important role in achieving large-scale fresh water driven by thermal energy. In this paper, based on first-principle modeling of a typical multi-stage flash desalination system, the effects of different operational parameters on system performance and operational optimization for cost saving were extensively studied. Firstly, the modelled desalination system was divided into flash chamber modules, brine heater modules, mixed modules and split modules, and based on energy and mass conservation laws the equations were formulated and put together to describe the whole process model. Then, with physical parameter calculation the whole process was simulated and analyzed on the platform of MATLAB, and the water production performance effected by operational parameters such as the feed temperature of seawater, the recycle brine from the discharge section, steam temperature and flowrate of recycled brine were discussed and analyzed. Then, the optimal operation to achieve maximize GOR (gained output ratio) with fixed freshwater demand was considered and performed, and thus the optimal flowrate of recycled brine, steam temperature, and seawater output flowrate from rejection section were obtained based on the established model. Finally, considering that minimizing the daily operational cost is a more rational objective, the operational cost equations were formulated and the optimal problem to minimize the daily operational cost was solved and the optimal manipulated variables at different hours were obtained. The study results can be used for guideline of real time optimization of the MSF system.

Sustainable desalination process selection: Decision support framework under hybrid information

Desalination technology has been recognized as a promising solution for mitigating the pressure caused by water shortage. In order to help the decision-makers to select the most sustainable desalination process/technology, a multi-criteria decision analysis method under hybrid information was proposed for sustainability ranking of alternative desalination processes. The interval AHP (Analytic Hierarchy Process) method was employed to determine the weights of the evaluation, and the TOPSIS (Technique for Order Preference by Similarity to an Ideal Solution) under hybrid information was employed to determine the sustainability ranking of the alternative desalination processes. Comparing with the previous studies about desalination process selection, the proposed method can achieve desalination selection based on the decision-making matrix composed by multiple types of data (i.e. crisp numbers, interval numbers and fuzzy numbers). Accordingly, the challenges of uncertainties and the quantification on the soft criteria can be successfully solved. The results based on the developed model can facilitate the decision-makers to select the most sustainability desalination technology with the considerations of economic, environmental. Technological and social pillars simultaneously. Four alternative desalination processes including multi-stage flash system (MSF), low temperature multi-effect distillation (LT-MED), reverse osmosis (RO), and vapor compression distillation (VCD) were studied by the proposed method in this study, and the closeness degree (CD) of LT-MED which represents its integrated sustainability performance is 0.6984, followed by the CDs of MSF (0.5602), VCD (0.5381) and RO (0.4116), respectively. Thus, the sustainability ranking from the best to the worst is LT-MED, MSF, VCD and RO. The results were validated by the sum weighted method, and sensitivity analysis was also carried out. The results reveal that the selection of LT-MED as the most sustainable is robust.

EXERGY OF A HYBRID SOLAR-WIND REVERSE OSMOSIS-MSF DESALINATION SYSTEM

Новая гибридная система многостадийной опреснительной (MSF) ректификационной опреснительной установки с использованием солнечного ветра (RO) была изготовлена ​​и испытана в реальных условиях в Иране. Энергия ветра была необходима для обеспечения электрической энергии. Эксергетический анализ может быть использован для разработки более эффективных энергетических систем. Эксергия, задействованная в гибридной системе опреснения RO-MSF солнечного ветра, проанализирована ниже с использованием данных, полученных в результате теоретических и экспериментальных исследований.Системы RO и MSF, работающие от энергии ветра и солнца, гарантируют повышение надежности и гибкости системы. Согласно эксергетическому анализу, необратимые потери от гибридной установки RO-MSF с солнечным ветром сосредоточены в солнечном коллекторе и многоступенчатой ​​испарительной камере. Эти параметры могут быть уменьшены за счет изоляции коллектора, покрытия труб и стен MSF, а также улучшения процесса вспышки. Оптимизирующая производительность гибридной системы RO-MSF мощность солнечного ветра должна увеличиваться, а потребление энергии должно снизиться, что должно повысить общую эффективность системы. и улучшение процесса прошивки.Оптимизирующая производительность гибридной системы RO-MSF мощность солнечного ветра должна увеличиваться, а потребление энергии должно снизиться, что должно повысить общую эффективность системы. и улучшение процесса прошивки. Оптимизирующая производительность гибридной системы RO-MSF мощность солнечного ветра должна увеличиваться, а потребление энергии должно снизиться, что должно повысить общую эффективность системы.

EXERGY OF A HYBRID SOLAR-WIND REVERSE OSMOSIS-MSF DESALINATION SYSTEM

A novel hybrid solar-wind reverse-osmosis (RO) multistage flash (MSF) distillation desalination system was manufactured and tested in actual conditions in Iran. Solar energy was used to provide both thermal and electrical power and wind energy was used to provide electrical power. Exergy analysis can be used to design more efficient energy systems by reducing inefficien-cies, and indicates opportunities for improving performance in existing systems. The exergy involved in the hybrid solar-wind RO-MSF desalination system is analyzed below using data obtained from theoretical and experimental studies. The RO and MSF systems, powered by wind and solar energy, achieved increases in the reliability and flexibility of the system and in the quality of the resulting drinking water. According to the exergy analysis, the irreversible losses from the hybrid solar-wind RO-MSF plant are concentrated in the solar collector and the multistage flash chamber. These exergy losses can be reduced by isolating the collector, coating the pipes and MSF walls, selecting the parameters for the vapor compressor and RO membrane and pumps, and improving the flash process. By optimizing the performance of the hybrid solar-wind RO-MSF system, the amount of water recovery should increase, and the energy consumption should decrease, which should improve the overall efficiency of the system.

Examining the life-cycle environmental impacts of desalination: A case study in the State of Qatar

Comprehensive environmental impact of thermal desalination is poorly understood in Middle Eastern and North African region, especially for multistage flash (MSF) desalination. Nearly 75% of Qatar's municipal water supply is being produced by MSF due to process reliability and other advantages, which is highly energy-intensive and creates an enormous environmental burden. Hence, this paper aimed to develop a multi-faceted, life-cycle based framework that quantifies the overall environmental and human health impacts of MSF desalination in Qatar. Three different MSF systems were examined by varying the gain ratio (GOR) through life cycle assessment. Different environmental loads were examined and evaluated, including climate change, freshwater eutrophication, fossil fuel depletion, ozone depletion, and human toxicity. The results showed that the modified MSF configuration with higher GOR released 7.32 kg CO2 for 1 m3 of water production while the plant with lowest GOR released 12.6 kg. Quantitative analysis of the environmental degradation caused by desalination reflects the reality of water use in Qatar and can motivate users to reduce their water consumption as part of the Qatar's national vision 2030. The implication of this study is particularly important at a regional level as it serves as a preliminary baseline for a more efficient water strategy.

Steady state optimization of design and operation of desalination systems using Aspen Custom Modeler

In this paper Multistage flash (MSF), Reverse Osmosis (RO) and hybrid MSF/RO desalination systems are optimized. A superstructure is set up for analyzing various process configurations in a single flowsheet. Detailed steady state models for MSF and RO sections of the superstructure are developed incorporating comprehensive physio-chemical properties and design characteristics. The model for the hybrid system combines individual models of MSF and RO systems and additional separators and mixers. The optimization variables consist of the operating and design variables, and the objective function is developed on the basis of economic and technical performance indicators. Primary results show that the hybridization of MSF and RO systems sharing common intake-outfall facilities presents lower cost with the additional benefits of higher overall recovery than MSF system and higher product quality than RO system. The sensitivity analysis of the cost parameters is performed to realize their effects on the selection of process configuration.

Retrofitting the combined-cycle producing electric power and desalted seawater to include district cooling in GCC

Recent installed power plants (PP) in Qatar and other Gulf Co-operation Countries (GCC) are using combined cycle (CC). The CC cycle consists of gas turbine (GT), heat recovery steam generators (HRSG), and steam turbine (ST). In these plants, GTs produce electric power (EP) and its exhaust hot gasses operate the HRSG to generate steam. The steam is supplied to ST that generates more EP, and its extracted (or discharged) steam is directed to thermally operated desalting plant (DP), e.g. multi stage flash (MSF) or multi-effect thermal vapor compression (ME-TVC) producing desalted seawater (DW). A plant producing both EP and DW is called co-generation power desalting plant (CPDP). The used ST type is either extraction condensing steam turbine or back-pressure steam turbine. The MSF or ME-TVC consumes about 280 MJ/m3 thermal energy, besides pumping energy of 4 kWh/m3 for MSF or 2 kWh/m3 for ME-TVC systems. Because of high consumed energy, the MSF and ME-TVC systems have to be substituted by the much more energy-efficient seawater reverse osmosis (SWRO) desalting system, which consumes 4–5 kWh/m3 only as pumping energy. Replacement of the MSF (or ME-TVC) with the SWRO system will ban the use of steam extracted (discharged) to the DP; the plants produce only EP, and become single-purpose PP. This reduces the plant overall efficiency unless major retrofitting is done by adding low pressure (LP) ST and condenser to expand the steam that was supplied to the DP in the turbine to produce more work. In this paper, it is suggested that the CPDP widely used in the GCC to become a tri-generation plant producing EP, DW (by SWRO), and chilled water for district cooling (DC). An analysis is presented for the newly suggested configuration. It showed that a reference plant can be fitted with SWRO to replace the DP of MSF or ME-TVC and gives almost the same DW production capacity for the identical consumed EP by the MSF units. The process heat that was supplied to the thermal desalting units would be utilized for DC system using an absorption cooling unit(s). Comparisons of absorption cooling with the EP driven mechanical vapor compression refrigeration; and SWRO with the MSF desalting systems are illustrated in this article. The benefits of using DC in the GCC are also presented.

Realistic power and desalted water production costs in Qatar

Water security in Qatar is of main concern. Low water pricing in Qatar does reflect the real value of water. The high cost of desalted seawater (DW) calculated in this paper calls for the use of more energy efficient desalting system such as the SWRO system in place of the multistage flash (MSF) and multieffect thermal vapor compression (METVC) methods presently used. Both MSF and METVC use thermal energy of about 270 kJ/m3 and pumping energy of 2–4 kWh/m3. In this paper, the mechanical energy equivalent to the thermal energy supplied to the MSF (or METVC) systems is calculated. When added to the pumping energy, it gives the specific consumed energy of more than 20 kWh/m3, compared to 4–5 kWh/m3 for SWRO system. Qatar’s ground water (GW) is overexploited, depleted, and quality deteriorated, and thus the demand for DW is on the rise, with the more financial burden. Moreover, DW productions mean more air and marine environment deterioration. The water subsidization by the government should be reviewed, and water demand management should be applied. Wastewater should be treated for reuse to decrease the demand on both GW and DW. The calculated costs of DW at different natural gas price are calculated, and compared with the underestimated cost reported by the government.

Optimum numerical approach of a MSF desalination plant to be supplied by a new specific 650 MW power plant located on the Red Sea in Egypt

Nowadays, desalination of salt water is considered as an important industrial process. In many regions of the world, the multi-stage flash (MSF) water desalination technique has an essential contribution in the production of freshwater. In this study, a (MSF) model is used to design a MSF desalination system and, the feasibility of using the MSF desalination process in proximity of a 650MW power plant is investigated. This power plant can provide 385.03kg/s superheated steam from low pressure (LP) section of heat recovery steam generator (HRSG) for thermal desalting system. Three modules were tested with different numbers of heat rejection sections. The optimum design was 25 stages in the heat recovery section and 3 stages in heat rejection section. The designed MSF system with gained output ratio (GOR) of 8.76 has 28 flashing stages and can produce 2229kg/s of freshwater. The expected performance characteristics of the designed MSF desalination plant are determined.

Structural optimization of seawater desalination: I. A flexible superstructure and novel MED–MSF configurations

A methodology is proposed to identify improved thermal-based desalination structures. It is based on the notion of superstructure, allowing for the simultaneous representation of numerous feed, brine and vapor routing schemes. By adjusting the flow routings, the superstructure is capable of representing the common thermal desalination structures, as well as an extremely large number of alternate structures, some of which might exhibit advantageous behavior. The superstructure is built around a repeating unit which is a generalization of an effect in a multi-effect distillation system (MED) and a stage in a multi-stage flash system (MSF). The superstructure is proposed as an improved tool for the structural optimization of thermal desalination systems, whereby the optimal selection of components making up the final system, the optimal routing of the vapors as well as the optimal operating conditions are all variables simultaneously determined during the optimization problem. The proposed methodology is applicable to both stand-alone desalination plants and dual purpose (water and power) plants wherein the heat source to the desalination plant is fixed. It can be extended to also consider hybrid thermal–mechanical desalination structures, as well as dual purpose plants where the interface of power cycle and desalination is also optimized for.

New anti-scalant performance evaluation for MSF technology

The desalination industries are looking for the reduction in the unit cost of desalinated water through developments in the technologies, process optimization, etc.; multi stage flash (MSF) technology has a proven track record for high reliability in the tough seawater condition. One of the technical barriers to improve the MSF system performance is the scale formation phenomena. This phenomenon can be manipulated by nanofiltration or by chemical treatment (anti-scalant). A pilot plant was constructed to evaluate the performance of a novel anti-scalant, under high top brine temperature (TBT) condition. Techniques such as atomic absorption spectroscopy and X-ray diffraction are used to measure the scale deposition in the test sections. Different operation parameters such as TBT, salinity, dosing rate, and operation with/without ball cleaning are considered. The experimental results indicate that the scale inhibition shows good performance after 72 h even for a low dosing rate of 2.5 ppm.

Multi stage flash desalination plant with brine–feed mixing and cooling

Improving the performance of Multi Stage Flash (MSF) desalination plants is a major objective in the seawater desalination industry. Fresh water production rates from MSF plants depend on the evaporation range defined as the difference between the top brine temperature (TBT) and the bottom stage temperature. Lowering the temperature of the plant bottom stage elongates the evaporation range and increases the yield. A modified multi stage flash plant with brine mixing and cooling (MSF-MC) is presented in this paper. Part of the brine leaving the plant is mixed with fresh seawater feed then cooled to low temperature before it enters the bottom stage feed heater. This MSF-MC features several advantages such as expanded evaporation range at the conventional TBT levels, reduced feed pumping power, moderate levels of chemical treatment requirements and fixed fresh water production rates independent of seasonal seawater conditions. Operating with low feed mass fraction minimizes the cooling load and reduces the cooler size. An improvement in the yield by 1.18%–1.4% for every 1 °C reduction in the plant bottom temperature can be achieved with MSF-MC compared to conventional MSF systems.

Optimal Design of Multistage Flash Desalination Process Based on the Modified Genetic Algorithm (MGA)

In this paper, a rigorous mathematical model of multistage flash system (MSF) is presented based on a detailed physicochemical representation of the process, including all the fundamental elementary phenomena. In particular, Comparison to the mathematical model of reference, two integer variables, which are the number of recovery stage (NR) and the number of rejection stage (NJ), are introduced to the model. Additionally, two special variables, which are the ratio of recirculation brine water flow rate and distillation flow rate and the ratio of make-up flow rate and the distillation flow rate, are introduced to the model as the continuous variables too. Then, the MSF system is described as a mixed-integer nonlinear programming (MINLP). The objective is to minimize the total annual cost (TAC), which is mainly composed of the operating costs and investment cost. Here the modified genetic algorithm (MGA), which is characterized as mixing coding way, is adopted for the system optimization. A case study and a discussion of the results are presented.

Fuel cell operated reverse osmosis desalination system

Kuwait has limited natural water resources and the non-conventional source of desalted seawater is used to satisfy the demand for potable water. Co-generation power-desalting plants (CPDP) are used to produce both electric power and desalted water, with steam extracted from steam turbines to supply desalting units, usually multi-stage flash (MSF) desalting units, with its thermal energy requirements. The MSF system is known for its high rate of energy consumption. The Ministry of electricity and water (MEW) was forced to install gas turbines (GT) to satisfy the increase in the peak load and to carry a good share of the base load. This resulted in a shortage in the availability of steam turbines for future use of the MSF units. Both alternative energy sources (other than steam extracted from turbines) and more energy-efficient desalting systems are needed to meet the rising demands for water and electricity. This paper discusses the feasibility of using reliable and commercially available fuel cells (FC), ...

Superstructure of Alternative Configurations of the Multistage Flash Desalination Process

This paper addresses the optimal synthesis and design of multistage flash (MSF) evaporator systems. A detailed nonlinear programming (NLP) model based on a superstructure developed previously by Mussati et al. [Ind. Eng. Chem. Res. 2003, 42, 4828-4829] has been appropriately reformulated to include more alternative configurations for the process. The new superstructure includes the number of stages and the stream flow patterns (distillate, feed and discharge brine, extraction points, and recycle flow patterns). Therefore, the superstructure simultaneously embeds an enormous number of alternatives, including, of course, the three commonly operating modes for the evaporator: MSF-BR, MSF-M, and MSF-OT systems and their combinations, which, to date, have not been analyzed systematically. In addition, a rigorous mathematical model by stage and component, which also includes the geometric design of each stage (length, height, and width), number of tubes in the preheaters, fluid-dynamic equations for the streams among others, is applied. An attractive configuration for the MSF system resulted from the proposed superstructure. This structure differs from the conventional structure, because it considers distillate extractions, two recycle streams, and new allocations for the cooling seawater, blow-down brine, and recycle. The mathematical model and the solution procedure have been implemented in GAMS [Brooke et al., CAMS: A User's Guide; Scientific Press: 1992]. Two study cases are presented, to illustrate the model and solution procedure capabilities. A complete description of the novel configuration, detailed comparison between different sub-optimal structures, and a sensitivity analysis on the main process variables are summarized.

The release of CO 2 in MSF and ME distillers and its use for the recarbonation of the distillate: a comparison

The knowledge of the CO 2 release from the evaporating brine in multi-stage flash (MSF) and multiple-effect (ME) distillers is very important for the design, the operation, and the cost of desalination distillers as well as for the recarbonation of the distillate. The CO 2 released in MSF plants can be used for the recarbonation of the distillate. The recarbonation method using CO 2 from the vent gases of MSF plants has gained importance, since the post-treatment of potable water can be effected without additional CO 2 production by combustion processes. The paper discusses if this approach may also be applied to ME distillers. The amounts of CO 2 required for the recarbonation are compared with the amounts released. To this end, the CO 2 release rates were calculated on the basis of two previously developed models. One consequence of the differences between MSF and ME systems regarding evaporation mechanisms, fluid flow, operating temperatures, and concentrations is that in MSF distillers the specific phase interface areas are lower and the mass transfer coefficients are higher compared to ME distillers. Consequently, the specific CO 2 release in MSF plants is significantly higher than in ME plants. The total CO 2 release in MSF recycle distillers amounts to about 82 g CO 2 per ton of distillate at a top brine temperature of 100°C. The calculations show that, for the limestone/carbon dioxide method, MSF recycle distillers produce sufficient CO 2 to allow recarbonation of the distillate up to an alkalinity of 187 ppm as CaCO 3 at a top brine temperature of 100°C. The total CO 2 release in ME distillers amounts to about 55 g CO 2 per ton of distillate at a top brine temperature of 64°C. Utilizing the CO 2 for the limestone recarbonation process would result in an alkalinity in the distillate of 124 ppm as CaCO 3. Provided that the alkalinity values aimed at in the distillate range from 50 to 80 ppm as CaCO 3, the calculations suggest that the CO 2 release in ME distillers may be just sufficient in terms of stoichiometric consumption to allow for recarbonation using the limestone method.

Integrating hybrid systems with existing thermal desalinationplants

In Gulf countries, most power plants are co-generation power desalting plants (CPDP) that generate electric energy and also produce fresh water through the desalination of seawater. This paper provides detailed technical and economical analyses to evaluate a new generation of dual purpose technology that includes the integration of reverse osmosis (RO) processes with existing thermal desalination processes and power generation (triple hybrid system) at Layyah plant, Sharjah, UAE. Hybridization of sweater reverse osmosis (SWRO) and the multi-stage flash (MSF) technology was considered to improve the performance of latter and reduce the cost of the produced water. Moreover, “idle” power in winter (seasonal surplus of unused power) was mainly utilized by RO to further reduce the cost of the hybrid system for six months of the year. Spinning reserve was also used to further reduce the cost of the proposed hybrid system. Integration ofthe three processes of MSF, MED, and RO desalination technologies could be made at different levels through which the resulting of water cost will depend on the selected configuration and the cost of materials of construction, equipment, membrane, energy, etc. Thus, the capital and annual operating costs were calculated for all potential alternatives for various plant capacities. It was found that for all plant capacities, integrated hybrid systems resulted in most cost effective solution. For example, at a capacity of 50 MIGD, the present worth of the cost was calculated to be 588.7, 443.2, and 380 million US$ for MSF, MED, and hybrid RO systems, respectively.