Multi-effect Desalination System Research Articles

A techno-economic review of multi effect desalination systems integrated with different solar thermal sources

The scarcity of fresh water resources and the need for additional water supplies is already critical in many arid regions of the world and will be increasingly important in the future. The solar thermal/Multi Effect Desalination (MED) is a candidate to tackle water scarcity. A comprehensive review of the technical and economic aspects of the technology and the state-of-the-art investigations in terms of integration of various MED configurations with different solar thermal sources was provided. Based on the results, the unit cost of the fresh water varies depending on the solar thermal technology and cost, solar radiation level, water production rate, seawater temperature and salinity. Based on the review, the integration of the MED with low temperature (60 °C–95 °C), medium temperature (165 °C–200 °C) and high temperature (370 °C–530 °C) solar collectors leads to water production costs of 2$/m3–3.6$/m3, 1.4$/m3–3.1$/m3 and 1.8$/m3−2.2$/m3, respectively, with a payback period of 4 to 16 years. The directions for the future research include localization of the solar collector industry, the MED brine management, the improvement of the MED and solar collector thermal efficiencies as well as the integration schemes. Useful information is provided to choose the most appropriate combinations of solar/MED technology for small or large applications.

Exergoeconomic optimization of a forward feed multi-effect desalination system with and without energy recovery

The escalating freshwater demand is stimulating the researchers to optimize the performance of desalination technologies. The current study presents the exergoeconomic optimization of a forward feed multi-effect desalination (FF-MED) system under two configurations i.e., conventional MED and MED with energy recovery (MED-ER). A detailed numerical model concerning energy, exergy, and a component-based exergoeconomic analysis is employed to estimate the energy consumption, exergy destruction, and water production cost. Thereafter, the FF-MED-ER system is optimized using a Genetic Algorithm for four different objective functions i.e., maximum gain output ratio (GOR), and minimum specific energy consumption (SEC), exergy destruction, and water production cost. The constraint variables included steam temperature, brine salinity, and the last effect brine temperature. The analysis showed that the incorporation of an energy recovery section increased GOR by 17.9% and decreased SEC and water production cost by 14%, and 10.5%, respectively. Moreover, the optimization improved GOR by 9.26%, decreased SEC by 12.86%, exergy destruction by 12.59%, and the water production cost by 8.25% compared to the standard nonoptimal system.

Performance Analysis of a New Electricity and Freshwater Production System Based on an Integrated Gasification Combined Cycle and Multi-Effect Desalination

Integrated biomass gasification combined cycles can be advantageous for providing multiple products simultaneously. A new electricity and freshwater generation system is proposed based on the integrated gasification and gas turbine cycle as the main system, and a steam Rankine cycle and multi-effect desalination system as the waste heat recovery units. To evaluate the performance of the system, energy, exergy, and economic analyses were performed. Also, a parametric analysis was performed to assess the effects of various parameters on the system’s performance criteria. The economic feasibility of the plant was analyzed in terms of net present value. For the base case, the performance metrics are evaluated as W.net=8.347 MW, ε=46.22%, SUCP=14.07 $/GJ, and m.fw=11.7 kg/s. Among all components of the system, the combustion chamber is the greatest contributor to the exergy destruction rate, at 3250 kW. It is shown with the parametric analysis that raising the combustion temperature leads to higher electricity and freshwater production capacity. For a fuel cost of 2 $/GJ and an electricity price of 0.07 $/kWh, the total net present value at the end of plant’s lifespan is 6.547×106 $, and the payback period is 6.75 years. Thus, the plant is feasible from an economic perspective.

Development, evaluation, and multi-objective optimization of a multi-effect desalination unit integrated with a gas turbine plant

In this research study, a 40 MW gas turbine power plant, which is coupled with a multi-effect desalination system with thermal vapor compression, is investigated. The energy, exergy and exergoeconomic analyses of the integrated plant are presented. As the number of effects in a desalination system is a key parameter, the effect of number of effects on the system performance is investigated. The genetic algorithm-based multi-objective optimization is applied to determine the best decision variables.To achieve the best optimization states, different scenarios of multi objective optimization based on the total exergy destruction rate, unit electricity price, total cost rate, gain output ratio, distilled water cost, and total exergy efficiency are examined. Additionally, seven decision variables are compressor pressure ratio (rp), combustion temperature (T3), compressor isentropic efficiency (ηc), gas turbine isentropic efficiency (ηGT), top brain temperature (TBT), last effect temperature (LET), and ejector compression ratio (Cr). The parametric analysis results indicated that although increasing the number of effect enhance the distilled water production rate, it increases the total cost rate of the system. With motive steam flow rate of 14 kg/s, results showed that distilled water production rate is 12294m3/day. Additionally, with three different scenarios the optimal states of integrated system are introduced. The results of optimization scenarios suggested different optimal states that are best guide for designer to select the best system configuration.

Heat recovery from sulfuric acid plants for seawater desalination using RO and MED systems

Conforming to the factor characteristics of electricity–water cogeneration power plants, an improved multieffect desalination (MED) and reverse osmosis (RO) are the most current techniques for seawater desalination. A principal change between these operations consists of their various energy requirements, thermal energy for MED and mechanical energy for RO plants. The main improvement ideas of RO and MED are the recovery of large quantities of heat produced during the production of sulfuric acid, which exhibits an exothermic reaction where a part of this heat will be used for the thermal power plant and subsequently reverse osmosis and another amount of heat recovery system will be used to desalinate seawater by the MED system. In this work, the sulfuric acid is used to recover heat energy; this energy is used in a hybrid system of RO–MED in order to desalinate the seawater. A thermodynamic steady-state study of this system is investigated to select the optimum cogeneration system. These improvements could make the benefits of cogeneration to the energy consumption of an RO and MED which will be remarkably reduced.

Conventional and advanced exergoeconomic assessments of a CCHP and MED system based on solid oxide fuel cell and micro gas turbine

This paper presents an assessment of a combined cooling, heating and power (CCHP) and multi-effect desalination (MED) system based on SOFC/MGT by conventional and advanced exergoeconomic analyses. The conventional exergy analysis can reveal the sources of irreversibility in the system. The largest exergy destruction occurs in after burner followed by SOFC and MED, accounting for 20.079%, 12.986%, 12.907%, respectively. In the advanced analysis, the exergy destruction, exergy destruction cost and investment cost are split into avoidable/unavoidable and endogenous/exogenous parts to investigate the real potentials of exergy and economic performances. The advanced analysis results indicate that the major exergy destructions of most components are endogenous parts with inverter, MGT and air compressor owning the most potentials to reduce exergy destructions. The modified exergy efficiency of each component in the advanced analysis is higher than the conventional one. Finally, three possible strategies are suggested to reduce the avoidable exergy destruction cost rates.

Solar driven polygeneration system for power, desalination and cooling

This paper presents a thermodynamic study of a polygeneration system combining Solar Power System (SPS), Multi Effect Desalination (MED) system and Absorption Refrigeration System (ARS). The plant is powered by solar energy with a backup natural gas heater. SPS includes a parabolic Trough Collector (PTC) field with thermal oil working fluid and steam Rankine cycle. A detailed simulation of a plant that can serve 1000 residential houses is developed. The analysis is performed using MATLAB package and its graphical user interface (GUI) tool. A parametric study is carried out to investigate effects of the different design and operating parameters on the plant energetic and exergetic parameters. Moreover, an economic evaluation is conducted to evaluate CAPEX, OPEX and unit product water/cooling costs. Results reveal that the highest exergy loss was found to occur in PTC solar field with about 82.42% of the plant exergy destruction. Moreover, the minimum PTC area can be achieved through the selection of the units (ARS, MED and SPS) capacities depending on steam condenser flow rate. In addition, the highest OPEX and total costs percentage (87.68% and 54.83%) are due to the natural gas heater. The proposed integrated system provides the lowest unit water price (1.247 $/m3), unit cooling price (0.003 $/kW hr) and the highest exergetic efficiency (23.95%) compared to the single and dual-purpose ARS/MED systems.

Design and optimization of an energy hub based on combined cycle power plant to improve economic and exergy objectives

This paper uses the energy hub concept to meet the water, heat and electricity demand of a power plant in the Qeshm island in south of Iran. Given the power plant’s high potential for waste heat recovery and some scenarios were considered using the hub energy concept based on energy, exergy, environmental and economic analyzes in terms of meeting the demands of the hub and purchasing/selling energy carriers including electricity, heating, freshwater as well as its production using gas turbine, steam turbine, boiler, Reverse Osmosis (RO) and Multi-Effect Desalination (MED) system. Energy hubs are optimized based on the Genetic Algorithm (GA) with the goal of supplying demand, as well as reducing costs and pollutants and increasing the exergy efficiency which ultimately will be selected using the concept of an energy hub at its optimal capacity. By comparing the two energy supplying systems of the current case study and optimal energy hub, results showed that the Total Annual Cost (TAC) level decreased by about 257904 $/year and exergy efficiency increased by 34.31%. CO2 emission will also decrease by about 471 tons/year.

Exergoeconomic analysis and optimization of an integrated system of supercritical CO2 Brayton cycle and multi-effect desalination

A cogeneration system is proposed for power and fresh water production in which the waste heat from a supercritical CO2 recompression Brayton cycle is utilized to power a conventional multi-effect desalination system. Energy, exergy and exergoeconomic analyses are performed for the proposed system and compared to a stand-alone supercritical CO2 recompression Brayton cycle. Under the same operating conditions, the results show that the energy utilization factor and exergy efficiency of the proposed system increase by 6.3% and 0.15%, respectively, compared to the stand-alone supercritical CO2 recompression Brayton cycle. A parametric analysis is conducted to investigate the influence of design parameters on the key performance parameters for the proposed system. Furthermore, single- and multi-objective optimizations are performed to find the optimal design using a genetic algorithm method. The energy utilization factor, exergy efficiency and total product unit cost of the proposed system from exergoeconomic optimization are 54.8%, 67.7% and 7.42 $/GJ, respectively which are 6.2%, 0.52% and 2.1% higher than the corresponding values for a base case. Also, the fresh water and net power productions are increased by 103% and 0.19%, respectively. From exergoeconomic optimization, the water and electricity prices are 0.72 $/m3 and 0.029 $/kWh, respectively.

Performance enhancement of a conventional multi-effect desalination (MED) system by heat pump cycles

Multi-effect desalination (MED) systems are highly promising for high salinity seawaters at large scales, and hence are used broadly in desalination plants. Despite the fact that the MED systems can be driven by various renewable or waste heat energies, many of the available renewable technologies are expensive in some parts of the globe. Hence, proposing and developing high-efficient mechanical-based MED units can be an encouraging alternative. In pursuance of this objective, two innovative mechanical-driven MED units are devised, simulated and the results are compared with those of the conventional MED-MVC (mechanical vapor compression) unit. For this aim, absorption-compression heat pump (ACHP) and vapor compression heat pump (VCHP) systems are used for integrating with the MED unit. Under a constant input power of 1845 kW it is found that proposing the MED-VCHP system instead of the conventional MED-MVC system improves gain-output-ratio (GOR), performance ratio (PR), freshwater rate, specific work consumption (SWC), exergy efficiency, exergy destruction rate, and exergy of loss by 1%, 12.86%, 12.64%, 11.45%, 10.78%, 3.3%, and 10.86% respectively. However, the unit cost of distilled water (UCDW) of the MED-VCHP system is around 6.7% higher than that of the MED-MVC system. Also, the MED-VCHP system uses less exergy of fuel than the MED-MVC system due to its high seawater exergy. Furthermore, it is found that one can decrease the overall exergy loss rate from 145.4 kW to 129.6 kW when the MED-VCHP system is used instead of the MED-MVC system.

Development of an innovative cogeneration system for fresh water and power production by renewable energy using thermal energy storage system

In this paper, solar dish collectors incorporated with phase change material storage are used for providing the required thermal energy of a steam power plant with a net production capacity of 1063 MW. The storage of phase-change material is employed during the night and in the absence of solar thermal sources. In order to prevent heat losses in the condenser, a large part of the dissipated heat is given to a multi-effect desalination system. The desalination system generates 8321 kg/s of fresh water by utilizing 2571 MW of waste heat from the steam power plant. This hybrid system has a total electrical efficiency of 28.84%, and total thermal efficiency of 97.18%. Exergy analysis is used to examine the integrated structure by means of the second law of thermodynamic. The exergy efficiency of the whole integrated structure is 52.23%, and the highest share of exergy destruction among equipment is related to heat exchangers and collectors with 46.83% and 40.93%, respectively. Hysys, Transys, and Matlab software are used in order to simulate the hybrid system by means of the weather input data of the case study, i.e. the city of Bushehr. Sensitivity analysis of the vital indicators of the system is conducted, and suitable solutions for improving the model and determining the amount of decision making parameters are made.

Impact of Cumulative Fouling Characteristics on Full-cycle Operation Optimisation of Multi-effect Distillation Desalination System

Cumulative fouling characteristics are often overlooked by researchers when optimising the operation of multi-effect distillation seawater desalination system. In order to analyse the influence of fouling cumulation on the optimisation operation, an eight-effect dynamic model for multi-effect distillation with thermal vapour compression (MED-TVC) seawater desalination system has been established and the cumulation of fouling has been considered in this model. Operation parameters of the eight-effect MED-TVC desalination system have been optimised repeatedly at different times (namely at different levels of fouling cumulation) throughout the full-cycle. Results indicate that the cumulation of fouling will gradually let the system deviate from the optimal operation condition, resulting in decrease in fresh water production, and operation re-optimisation at different times gets different results, which can efficiently reduce the influence of fouling and obtain better operational benefits. This work concludes that fouling cumulation has a big impact on operation optimisation of MED-TVC systems, and it is necessary to timely re-optimise operation parameters.

Design and thermoeconomic analysis of a multi-effect desalination unit equipped with a cryogenic refrigeration system

In this paper, a hybrid tri-generation system is designed to produce LNG and freshwater simultaneously based on a multi-effect desalination system and analyzed using energy and exergy analyses. For natural gas liquefaction, the initially required cooling of the cycle is supplied by ammonia-water absorption system, and the required intermediate cooling load and liquefaction process are provided by a refrigeration system with mixed fluid. Two alternatives for providing power generation to the system and the required heat for driving the absorption cycle have been considered and compared. The first alternative relies on a natural-gas-fired power plant, while the second is based on steam-solar power plant with dish collectors. The former results in the total energy efficiency of 85.8% (LHV). The highest thermodynamic irreversibilities occur in the heat exchangers (61%), even if they have the highest exergy efficiency compared to the other plant equipment. On the other hand, using solar dish collectors enables to decrease carbon dioxide emissions by 40%, and increases freshwater and LNG production by 95% and 4.7% respectively. The power obtained per kg of LNG produced is about 0.19 kWh, which is less than or equal to the other similar patents. The results of the economic analysis with the annualized cost method of the system show that the products prime cost of both structures 1 and 2 are equal to 0.2580 and 0.1784 US$ per kg of LNG, respectively. A suitable strategy for modelling enhancement of system’s parameters is suggested by expanding of sensitivity analysis on the important parameters of the developed system.

Introducing a hybrid renewable energy system for production of power and fresh water using parabolic trough solar collectors and LNG cold energy recovery

In order to solve the water and energy crisis problem, the thermal water desalination and parabolic trough solar collectors are used at the cogeneration plants. In this paper, an integrated structure for cogeneration of fresh water and power has been developed using a multi-stage thermal water desalination system and organic Rankine cycle. In order to supply the input heat, an integrated structure of parabolic trough solar collectors, and to supply the condenser cooling of organic Rankine cycle, the re-gasification operations have been used. This integrated structure is capable of fresh water generation of 3628 kgmol/h and electrical power of 459.9 MW. In this integrated structure, the efficiency of the organic Rankine cycle power plant and gain output ratio of the multi effect desalination system is 12.47% and 2.918, respectively. Exergy analysis has been used to examine the second law of thermodynamics and the quality of the integrated structure. The total exergy efficiency of the integrated structure is 87.11%, and also, the highest share of equipment exergy destruction is related to the heat exchangers and collectors by 50.23% and 38.18%, respectively. In order to simulate the dynamics of the integrated structure, according to the input climatic information of the studied location in Tehran, Iran. Furthermore, decisions are made upon the sensitivity analysis on economic important indicators within an integrated structure.

Thermodynamic analysis of compressed air energy storage (CAES) hybridized with a multi-effect desalination (MED) system

Compressed air energy storage is one of two existing grid-scale energy storage technologies. It can be efficiently used in dry and warm climates, where providing both electricity and potable water is indispensable. A novel integration of compressed air energy storage and multi-effect desalination system is proposed to reduce energy dissipation, exergy destruction and provide power and potable water. Compression heat in the charging period is conveyed to the desalination unit; during discharging, the remaining energy in the turbine exhaust is reassigned to the desalination unit after passing through the recuperator. Round trip efficiency is thereby improved while providing peaking power and pure water. Besides, the effect of the maximum to minimum pressure ratio of the compressed air vessel on efficiency and the operational period of the system is studied for a particular set of circumstances. Results indicate that 38 kg/s potable water is produced during charging, whereas 80 MW electricity and 62.5 kg/s distilled water are concurrently generated during peak demand periods. As a result, 69.95% round trip efficiency and 9.47 performance ratio are obtained for the proposed hybrid system.

Multi objective optimization of using the surplus low pressure steam from natural gas refinery in the thermal desalination process

Abstract The production of a large amount of wastewater in the process of natural gas refining, which cannot even be released into the environment in many cases, has become the major problem of the natural gas refineries. However, the existence of rich waste heat sources in gas refineries allows the use of thermal methods to desalinate the refinery wastewater. In this paper, the feasibility of using the surplus low pressure steam from Khangiran refinery to turn wastewater into drinking water was studied. In the first step, the changes in the important parameters of the thermal vapor compression section of the multi effect desalination system were examined and the Pareto method, as a multi-objective optimization technique, was employed to optimize the operating conditions of the thermal vapor compressor. As a result, the optimum values for the output steam pressure of thermal vapor compressor and the flow rate ejected from the final effect of the multi effect desalination unit were obtained 712.7 kPa and 0.1 kg/s, respectively. In the second step, the Pareto front for top effect temperature was calculated 82.73 °C, based on the exergy efficiency and useful exergy of multi effect desalination system. Finally, the optimal number of effects and the flow rate of the desalinated water were nine effects and 38.5 kg/s, respectively.

Performance assessment of a CCHP and multi-effect desalination system based on GT/ORC with inlet air precooling

This paper proposes a combined cooling, heating and power (CCHP), and multi-effect desalination system to supply cooling, heating, power and freshwater. The proposed system mainly includes a gas turbine (GT), a multi-effect desalination unit with a thermal vapor compressor (MED-TVC), an organic Rankine cycle (ORC) integrated with a steam ejector refrigerator (SER), and heat exchangers. The mathematical model is developed to thermodynamically conduct energy-exergy analysis, and a parametric study is performed to explore the effects of key design parameters such as air compressor pressure ratio, inlet air temperature of air compressor, pinch point temperature difference of waste heat boiler, motive steam pressure of MED-TVC unit, TVC compression ratio and working medium flow rate of ORC on the system performance. The proposed system can provide power, heating, cooling and freshwater at loads of 31.25 MW, 1.108 MW, 4.203 MW and 85.89 kg/s under the design conditions. The electrical, the exergy, and the overall energy efficiencies of the present system are 36.44%, 41.26% and 46.70%, respectively. The results indicate that the power output of GT can be increased by precooling the inlet air of air compressor, and the integration of GT with MED-TVC unit, ORC and heat exchangers can efficiently recover the waste heat from exhaust gas based on the principle of “energy cascade utilization”. In addition, the largest exergy destruction occurs in the combustion chamber followed by regenerator 1 and the MED-TVC unit.

Thermodynamic diagnosis of a novel solar-biomass based multi-generation system including potable water and hydrogen production

In this study, a new proposed multi-generation system as a promising integrated energy conversion system is studied, and its performance is investigated thermodynamically. The system equipped with parabolic trough collectors and biomass combustor to generate electricity, heating and cooling loads, hydrogen and potable water. A double effect absorption chiller to provide cooling demand, a proton exchange membrane electrolyzer to split water into hydrogen and oxygen and a multi-effect desalination system to provide potable water by recovering the waste heat of biomass combustion is combined with a steam Rankine cycle. The results of the thermodynamic analysis indicate that thermal efficiency of 82.5% and exergy efficiency of 14.6% is achievable for the proposed system. Hydrogen and potable water production rates are 88.1 kg/h and 3.9 m3/h, respectively. The proposed system generates 26.3 MW electricity, 26.3 MW heating load, and 137.2 MW cooling load. Parabolic trough solar collector, double effect absorption chiller and biomass combustor are the primary sources of thermodynamic irreversibilities in comparison to other components. The mass flow rate of biomass fed to the system and aperture area of parabolic trough solar collector is calculated to be 6.2 ton/h and 188,000 m2. Besides conventional analyses, to conclude the concept of multiplicity six different cases for the studied multi-generation system are modeled and evaluated regarding thermal and exergy efficiencies. Finally, the parametric study is performed to identify the consequential parameters on the thermodynamic performance of the system.

Developing of an integrated hybrid power generation system combined with a multi-effect desalination unit

An integrated hybrid power generation system combined with a water multi-effect desalination system is herein developed for simultaneous power generation and thermal waste recovery. A heat recovery steam generator is employed for steam generation using outlet thermal energy from the system. Next the generated steam enters into a multi-stage desalination system for producing fresh water. The fuel cell over-potential and gained voltage are obtained using operating conditions, flow rate and electrochemical modeling of the fuel cell. By adding a Stirling engine, the power output is increased to 2.63 kW and the system efficiency is increased by 11.7%. Fresh water is produced by 143.64 kg/h using the recovered energy of the system. In the following, the performance of the system is being analyzed in terms of important variables of the system. The results show that by increasing the temperature of the fuel cell up to 100 °C, the power and efficiency of the fuel cell increase by 2 kW and 1.8%, respectively. Additionally, the amount of produced fresh water is increased up to 65% with the number of desalination stages from 4 to 6 stages.

Multigeneration system exergy analysis and thermal management of an industrial glassmaking process linked with a Cu–Cl cycle for hydrogen production

A multigeneration system for hydrogen production linked with a glassmaking process via thermal management is examined in this study. The exhaust gas is interconnected with a Rankine cycle and the copper-chlorine (Cu–Cl) cycle for hydrogen production. The present system consists of a steam Rankine cycle, Cu–Cl cycle with multistage compression, double-stage organic Rankine cycle, and multi-effect desalination system. A Cu–Cl cycle based on the four-step model is employed with the proposed system. The useful system outputs are electricity, hydrogen, and fresh water. The simulation software packages utilized in the analysis and modeling are Engineering Equation Solver and Aspen Plus. The energy efficiency of the overall system is 36.5% while 38.1% is the exergy efficiency. The parametric studies are conducted to investigate the system performance. In addition, the effects of exhaust gas variables, such as flow rate, temperature, and pressure are examined to investigate the system performance.