Multi-effect Distillation Process Research Articles

Technical-economic analysis and optimization of multiple effect distillation system by solar energy conversion as the heat source

The utilization of multi-effect distillation (MED) in thermal desalination processes is more widespread owing to lower energy consumption. The focus of this paper is to optimize the performance of MED through process optimization. It aims to identify the optimal operating conditions that result in maximum water and power production. Additionally, it investigates the potential of using solar renewable energy as a substitute for the current fossil energy source. Subsequently, a switch to solar energy was made with a focus on an economically viable approach. The research explored the best-suited collector and fluid for heat transfer among the 8 types of molten salt for use in the collector. Subsequently, an economic and sensitivity analysis was conducted using this procedure. The outcomes indicated that by enhancing the stated procedure, it was found that 27.93 Megawatt (MW) of heat would be required when 6938 ton/h of natural gas are burned. Additionally, the 4-effect MED process produced 6.123 MW of electricity and 116.5 cubic meters per hour (m3/h) of freshwater. The gain output ratio (GOR) of the process saw an uptick from 2.75 to 3.328, whereas MED efficiency showed progress from 13.76 to 49.218 %. The parabolic trough collector (PTC) collector outperforms the linear Fresnel collector (LFC) and solar dish (SD) collector in terms of efficiency among other results. To store heat for the rest of the day and night and supply thermal energy for the entire process, 155,542 square meters (m2) of this collector are necessary. Additionally, in regards to the thermal fluid of the PTC collector, coastal chemical registered heat transfer salt (HITEC salt), a commercial mixture of solar salt, has exhibited superior performance over other molten salts (for a total expenditure of 50 million dollars over two decades). In addition, the economic analysis has indicated a return rate of 32.46 % for the investment and a capital recovery period of 3.08 years for the process. The implementation of the mentioned process in renewable mode results in the avoidance of 18.5 tons per hour (ton/h) of carbon dioxide (CO2) emissions.

Desalinated Water Costs from Steam, Combined, and Nuclear Cogeneration Plants Using Power and Heat Allocation Methods

This work presents a detailed thermo-economic analysis of unit water costs from dual-purpose cogeneration plants. The power levelized cost was first calculated for stand-alone steam, nuclear, and combined-cycle power plants. The cost of energy needed to operate the desalination systems connected to power plants was evaluated based on two different approaches: power- and heat-allocated methods. Numerical models based on the heat and mass balances of the power and desalination plants’ components were developed and validated. Comprehensive and updated data generated using Desaldata libraries were correlated to estimate the capital, labor, overhead, and maintenance costs for different desalination systems. The levelized water cost produced by multi-effect distillation, multi-effect distillation with vapor compression, multi-stage flash, and reverse osmosis systems connected to different power plants was estimated. The impact of various controlling parameters, including the price of natural gas, nuclear power plant installation cost, and the desalination capacity on water cost, was investigated. For all simulated cases, the levelized water cost evaluated using the heat-allocated method was found to be lower by 25–30% compared to that estimated using the power-allocated method. The cost of water produced using reverse osmosis remains below that produced by other desalination technologies. However, using the heat-allocated method to estimate the levelized water cost narrows the gap between the costs of water produced by multi-effect distillation and that produced by seawater reverse osmosis. The results also show that the use of the multi-effect distillation process in a cogeneration configuration rather than multi-effect distillation with vapor compression can result in a lower water cost. The profit analysis shows slight differences between the profit of a power plant connected to a reverse osmosis system and the profit of a power plant connected to a plain multi-effect distillation system.

Water-renewable energy Nexus: Optimization of geothermal energy-powered seawater desalination systems

This paper addresses the optimization of geothermal energy-powered seawater desalination systems. A nonlinear optimization mathematical model was implemented into General Algebraic Modelling System (GAMS). The model embeds many candidate configurations for optimization, which result from the combination of the following subsystems: a single flash (SFGP) or double flash (DFGP) geothermal power plants, a multi-effect distillation (MED) process or a reverse osmosis (RO) system for freshwater production. Also, an energy recovery turbine (ERT) is embedded. The minimization of the total annual cost of the process represents the objective function. The proposed model is a powerful decision-making tool for selecting the optimal configuration of the integrated process, sizes, and operating conditions to meet the demands of electricity and freshwater desired by users. It was found that for fixed 70 MW electricity generation and low freshwater demands (720–2880 m3/h), the optimal configuration is SFGP/MED. For high freshwater demands (4320–5040 m3/h), the optimal configuration is DFGP/MED/RO. For intermediate freshwater demand (3600 m3/h), an optimal transition configuration is in between the two previous configurations, i.e., SFGP/MED/RO/ERT. It is highlighted that the model can be used to simulate fixed configurations if no degrees of freedom are available.

Optimisation of hybrid MED-TVC and double reverse osmosis processes for producing different grades of water in a smart city

The integration of two or more processes in a hybrid system is one of the most desirable options to provide flexibility, interoperability and data sharing between the connected processes. Various examples of hybrid systems have been developed with seawater desalination systems such as the combination of thermal and membrane technologies. This paper focuses on the simulation and optimisation of an integrated (hybrid) system of multi effect distillation and double Reverse Osmosis (RO) processes to produce different grades of water needed in a smart city from seawater resources. The optimisation-based model investigates five scenarios to obtain the highest productivity of drinking water, irrigation water, livestock water and power plant water at the lowest specific energy consumption and with the product water salinities within the required standards. For this purpose, multi objective optimisation problem was formulated using the gPROMS (general Process Modelling System) software. The results confirm the superiority of the developed hybrid system to sustain different grades of water in a smart city.

Techno-economic optimization of coupling a cascaded MED system to a CSP-sCO2 power plant

Integrating a multi-effect distillation (MED) process with a concentrated solar power (CSP) plant can enable a sustainable solution to meet our global society’s increasing energy and freshwater demands. This integration makes possible the ‘free’ reuse of waste heat from an advanced power block, albeit at slightly reduced thermal efficiency. As such, this study can be considered a pioneering analysis of the potential of integrating a cascaded MED system with a supercritical CO2 (sCO2) cycle, which provides two main innovations: (a) a highly efficient sCO2 cycle is proposed to mitigate the energy efficiency penalty of the more traditional (Rankine Cycle) in CSP-Desalination (CSP-D) coupling, and (b) a cascaded MED system is proposed to recover much more of the rejected waste heat than a single MED configuration. These two innovations were explored in detail by employing an in-house thermo-economic numerical model, which was validated using literature data. It was found that 4-MED systems maximized the distillate production, with 57% waste heat energy recovery compared to 26% energy recovery using a single-MED system. Encouraged by this positive performance boost, an economic feasibility analysis was conducted by considering the installation site (i.e., pipeline distance from the coastline and the direct normal irradiance (DNI) resource) and the potential revenue from a power purchasing agreement (PPA) and a water purchasing agreement (WPA). It was found that the desalination process has a negligible effect on the payback due to the limited water production (i.e., ∼1 million m3/yr) compared to the high electricity generation (i.e., ∼190 GWh/yr). Thus, reducing the power block’s investment cost and installing the plant in high PPA markets (i.e., above 20 UScents/kWh) represent the two most significant factors for improving the plant’s feasibility. It was also found that a 0.6 kWh/m2day of additional DNI is required to offset each 100 km of pumping energy consumption (for a PPA of 20 UScents/kWh and WPA of 1.5 USD/m3) for a payback period of less than 20 years. Furthermore, a non-linear regression model was applied to develop a correlation that researchers can use to explore any potential sites that could benefit from this technology. This correlation was tested on water-stressed countries with access to the sea and high solar resources. It was found that countries with high electricity prices (i.e., above 20 UScents/kWh), such as Australia, Chile, Jordan, Somalia, Spain, and the Southwest region of the USA, could benefit most from using this cogeneration plant, but (unfortunately) the gulf states, where fossil-fuel desalination is dominant, are unlikely to see an immediate economic benefit from the proposed plant. Thus, this study provides deeper insights on how CSP-sCO2-MED cogeneration plants can help ‘green-terraform’ arid lands and help water-stressed countries.

Minimisation of energy consumption via optimisation of a simple hybrid system of multi effect distillation and permeate reprocessing reverse osmosis processes for seawater desalination

Multi Effect Distillation (MED) and Reverse Osmosis (RO) processes have been extensively used to produce freshwater from seawater resources. amongst many performance indicators, energy consumption of different configuration of hybrid system of MED and RO processes have been analysed in the past. Hybrid MED-RO system is energy intensive and use of fossil fuel can significantly increase the carbon footprint, unless stable renewable energy sources are used. In this work specific energy consumption of a simple hybrid MED-RO system with permeate reprocessing is minimised while optimising a number of operating decision variables using model based optimisation technique. A detailed process model developed earlier by the authors is embedded in the optimisation framework resulting in a constrained Non-linear Programming (NLP) problem. The minimum specific energy consumption achieved in this work is about 18% lower than what is reported in the literature resulting in a significant energy saving and thus carbon footprint.

Feasibility study of multi-effect distillation dealing with high-salinity organic RO concentrates: Experiment and theoretical analysis

Feasibility of the multi-effect distillation (MED) process was investigated experimentally and theoretically in present work to deal with the high-salinity organic reverse osmosis concentrates (ROCs) generated by the double membrane process for the treatment of wastewater from the refining and chemical enterprises. Two key problems involving the behaviors of organic and inorganic impurities in the ROCs during evaporation and process optimization of MED thermally and economically were highlighted. The experimental results indicated that about 6% and 8% of organic impurities volatilized during evaporation and entered into the produced water and the tail gas, respectively. The produced water and the tail gas which met the related China National standards could be reused or vented directly without further treatment. However, scaling of calcium sulfate was drastically occurred in the evaporator when about 30% water was recovered, indicating the necessity of removal of the hardness in ROCs before evaporation. A forward flow MED model established on Aspen Plus platform was employed to perform the thermal and economic analysis for the ROCs treatment. Performance analysis including the Gained Output Ratio (GOR), fresh steam flow and specific heat transfer area as functions of the effect number and the heating steam temperature were conducted. The results showed that the performance of the MED system was significantly influenced by effect number over the heating steam temperature. An increase in the effect number would improve the thermodynamic performance of MED system but increased the capital costs. The model established in this work could provide a theoretical guidance for the development of MED process dealing with ROCs.

Embodied water consumption between typical desalination projects: Reverse osmosis versus low-temperature multi-effect distillation

At present, there are more than 20 kinds of seawater desalination technologies utilized worldwide including Reverse Osmosis and Low-Temperature Multi-effect Distillation. To compare the embodied water consumption of the main seawater desalination technologies, this study assesses the water consumption of Reverse Osmosis and Low-Temperature Multi-effect Distillation desalination projects in China based on the system analysis method. Taking full account of the direct and indirect water consumption in the desalination projects, the embodied water consumption of the Reverse Osmosis desalination project is 3.96E+04 m3 in the construction stage, whereas that of the Low-Temperature Multi-effect Distillation project is 7.22E+05 m3 at the same daily water production capacity. In the operation stage, the Low-Temperature Multi-effect Distillation process has the potential to utilize waste heat generated by the thermal power plant for hydropower cogeneration, while the Reverse Osmosis process requires regular maintenance and replacement of reverse osmosis membranes. With respect to the embodied water consumption, the Reverse Osmosis desalination project presents more advantages than the Low-Temperature Multi-effect Distillation desalination project in terms of water savings and economic costs during the construction stage, but relevant departments should also take actual local requirements and water resources conditions into consideration. On the basis of providing comparisons between different projects, this study attempts to play a vital role in the rational allocation of desalination projects, the promotion of reasonable water-saving policies, and sustainable economic and social development from a macro perspective.

Scope and Limitations of the Mathematical Models Developed for the Forward Feed Multi-Effect Distillation Process—A Review

Desalination has become one of the obvious solutions for the global water crisis due to affording high-quality water from seawater and brackish water resources. As a result, there are continuing efforts being made to improve desalination technologies, especially the one producing high-quantity freshwater, i.e., thermal desalination. This improvement must be accomplished via enhancement of process design through optimization which is implicitly dependent on providing a generic process model. Due to the scarcity of a comprehensive review paper for modeling multi-effect distillation (MED) process, this topic is becoming more important. Therefore, this paper intends to capture the evolution of modeling the forward feed MED (most common type) and shed a light on its branches of steady-state and dynamic modeling. The maturity of the models developed for MED will be thoroughly reviewed to clarify the general efforts made highlighting the advantages and disadvantages. Depending on the outputs of this review, the requirements of process development and emerging challengeable matters of modeling will be specified. This, in turn, would afford a possible improvement strategy to gain a reliable and sustainable thermal desalination process.

An Innovative Design of an Integrated MED-TVC and Reverse Osmosis System for Seawater Desalination: Process Explanation and Performance Evaluation

In recent times two or more desalination processes have been combined to form integrated systems that have been widely used to resolve the limitations of individual processes as well as producing high performance systems. In this regard, a simple integrated system of the Multi Effect Distillation (MED)/Thermal Vapour Compression (TVC) and Permeate Reprocessing Reverse Osmosis (PRRO) process was developed by the same authors and confirmed its validity after a comparison study against other developed configurations. However, this design has a considerable amount of retentate flowrate and low productivity. To resolve this issue, two novel designs of MED and double reverse osmosis (RO) processes including Permeate and Retentate Reprocessing designs (PRRP and RRRO) are developed and modelled in this paper. To systematically assess the consistency of the presented designs, the performance indicators of the novel designs are compared against previous simple designs of MED and PRRO processes at a specified set of operating conditions. Results show the superiority of the integrated MED and double permeate reprocessing design. This has specifically achieved both economic and environmental advantages where total productivity is increased by around 9% and total retentate flowrate (disposed to water bodies) is reduced by 5% with a marginally reduced energy consumption.

Experimental study of a novel solar multi-effect distillation unit using alternate storage tanks

Abstract In recent years, the use of solar energy has been growing exponentially and applied in a wider range of applications; one of the important applications for using solar energy is water desalination. The current work investigates the proof of concept experimental setup for a novel solar multi-effect distillation (MED) using alternate storage tanks. The experimental setup consists of a MED unit, two thermal storage tanks, and a solar collector. One storage tank is used as a charging tank while the other tank is used as a discharging tank. This unique dual-tank system stores the thermal energy to be used later in the MED unit, which improves the control of the water mass flow rate and water temperature throughout the MED process. The peak temperature achieved every day in the charging tank determines the MED production capacity. This system is designed for the tanks to alternate roles every 24 hours. The testing of this design was carried out during May 2019 in Saudi Arabia. The experimental results prove the novel concept design to work efficiently providing an average production rate of about 21 kg/day with total solar collector area of 2.7 m2 and average daily performance ratio of 2.5.

Pilot studies on synergetic impacts of energy utilization in hybrid desalination system: Multi-effect distillation and adsorption cycle (MED-AD)

The hybridization of desalination processes is one of the most promising technologies to overcome the current limitations of desalination technologies while maximizing the advantages of individual processes in practice. Multi-effect distillation (MED) and adsorption desalination (AD) hybrid desalination process has been investigated in this study to maximize the utilization of energy input in desalination. Two different thermal desalination technologies have been integrated, and the synergetic impact of utilizing energy enhanced the performance of the hybrid system. The synergetic thermodynamic model has been developed in this study and the experimental results from the pilot unit, with a nominal production capacity of 10 m3/day, installed at KAUST, KSA have been affirmed the proposed model. Both the water production and the universal performance ratio (UPR) have been improved 2–5 times in different quality of the heat source (40–60 °C) to the MED. Moreover, the MED-AD hybrid process is enabled to scavenge the energy from the ambient temperature below 30 °C for the desalination. The utilized energy of both thermal and flash evaporation in all operation conditions, and individual effects has been inventoried to analyze the thermodynamic synergy of the hybridization. In the sole MED operations, the energy input in the first effect is carried over to the following effects, and part of it is used for thermal evaporation. However, due to the AD driven flash evaporation, the energy used in evaporation of the following effect is shown greater than the previous effect. The developed synergetic model of MED-AD hybrid system and its experiment with 4-effects MED pilot have demonstrated the potential of the hybrid system and its application to the industrial processes.

Multi-effect distillation plants for small-scale seawater desalination: thermodynamic and economic improvement

The growing global demand for fresh water coupled to the increasing interest in renewable energies and waste heat recovery has resulted in flourishing attention to the multi-effect distillation process for seawater desalination. The low operating temperature makes this technology attractive in the case of low temperature heat sources such as geothermal, solar or waste heat recovery. The low energy density of these heat sources requires small-scale desalination systems whose layout and operation may differ from large-scale plant. In this work, new plant configurations for a small-scale multi-effect distillation system are proposed and analyzed from a thermodynamic and economic point of view. Each configuration tends to better exploit the energy content of the various streams by improving heat recovery, according to an increasing layout complexity. These configurations were studied in two layouts, differing in the way seawater and brine fed the various effect. The feed mass flow in each effect was varied to maximize the recovery ratio by imposing the maximum salt concentration in the brine related to calcium sulphate precipitation. Numerical simulations were conducted in Aspen Plus environment by varying the top brine temperature with a fixed bottom brine temperature of 40 °C. The electrolyte non-random two liquid equation of state was adopted to evaluate saltwater properties and an inter-model comparison with a validated algebraic model was carried out. The configurations implementing seawater preheating increased the performance ratio up to 10% due to the better exploitation of the energy content of distillate streams. The proposed solutions with the maximization of the recovery ratio demonstrated to be cost-effective with respect to the base multi-effect distillation configuration when thermal energy cost became relevant. In the case of negligible thermal energy cost (waste heat recovery) the base configuration was the preferable solution in terms of water cost, despite the lower performance ratio.

An enumeration-based synthesis framework for multi-effect distillation processes

Heat integration, such as multi-effect distillation (MED), can often help save considerable energy in distillation processes. With the increasing level of heat integration and consequent flowsheet complexity, the chemical industry calls for systematic design procedures. Usually, MED synthesis is followed by heuristic rules, such as arbitrarily set pressure level based on temperature-pressure relationship. No systematic design procedure driven by economic criterion has been established so far. As a solution, an enumeration-based MED process synthesis framework is therefore suggested for optimization using column pressure as an independent decision variable. The framework firstly includes 43 potentially useful MED configurations to generate a search space, followed by mathematical formulation of a shortcut nonlinear programming for each configuration. Then rapid screening is performed to evaluate all the design variants in the search space. The solution provides a rank-list of all feasible configurations in total annualized cost (TAC) criterion, from which top preferred candidates are verified through a genetic algorithm (GA) based rigorous optimization in the third step. The validity of this framework is illustrated with three case studies. Results show the MED can generally save approximately 50% of energy and up to 30% of TAC, compared to a conventional distillation column.

Cost evaluation and optimisation of hybrid multi effect distillation and reverse osmosis system for seawater desalination

In this research, the effect of operating parameters on the fresh water production cost of hybrid Multi Effect Distillation (MED) and Reverse Osmosis (RO) system is investigated. To achieve this, an earlier comprehensive model developed by the authors for MED + RO system is combined with two full-scale cost models of MED and RO processes collected from the literature. Using the economic model, the variation of the overall fresh water cost with respect to some operating conditions, namely steam temperature and steam flow rate for the MED process and inlet pressure and flow rate for the RO process, is accurately investigated. Then, the hybrid process model is incorporated into a single-objective non-linear optimisation framework to minimise the fresh water cost by finding the optimal values of the above operating conditions. The optimisation results confirm the economic feasibility of the proposed hybrid seawater desalination plant.

Techno-economic assessment of multi-effect distillation process for the treatment and recycling of ion exchange resin spent brines

A treatment chain including nanofiltration, crystallization and multi-effect distillation (MED) is for the first time proposed for the treatment of an effluent produced during the regeneration of Ion Exchange resins employed for water softening. The goal is to recover the minerals and to restore the regenerant solution to be reused in the next regeneration cycle. MED is the most crucial unit of the treatment chain from an economic point of view. A techno-economic analysis on the MED unit was performed and a novel performance indicator, named Levelized Brine Cost, was introduced as a measure of the economic feasibility of the process. Different scenarios were analysed, assuming different thermal energy sources and configurations (plane-MED or MED-TVC). It was found that the plane-MED fed by waste-heat at 1 bar is very competitive, leading to a reduction of 50% of the fresh regenerant current cost. Moreover, the thermal energy cost of 20US$/MWhth was identified as the threshold value below which producing regenerant solution in the MED is economically more advantageous than buying a fresh one. Overall, MED allows reducing the environmental impact of the industrial process and it results competitive with the state of the art for a wide range of operating conditions.

Design and optimization of multi-effect-evaporation-assisted distillation configuration for recovery of 2,3-butanediol from fermentation broth

2,3-butanediol (2,3-BDO) is a precious chemical owing to its extensive industry applications. In addition to the traditional chemical synthesis, the production of 2,3-BDO from biomass-based feedstock is an attractive alternative. Nevertheless, this production way consumes considerable energy because the concentration of product from the conversion of biomass is low. In this study, several novel multi-effect-evaporation-assisted distillation (MEED) configurations are proposed to improve the energy efficiency of 2,3-BDO production from a fermentation broth. The binary interaction parameters between 2,3-BDO and water were determined through regression using experimental data. All configurations were designed and optimized using the sequential quadratic programming methodology. The results indicate that the proposed MEED configurations can create the synergistic effect by combining the multi-effect evaporator and distillation processes, which is able to increase substantial energy efficiency as compared the conventional distillation column. Notably, the total annual cost (TAC) of the MEED configurations with double effect, triple effect, quadruple effect, quintuple effect, and sextuple effect can be reduced by up to 12.3%, 16.9%, 20.1%, 21.7%, and 17.5%, respectively. The proposed MEED configuration with heat integration significantly reduced the TAC by up to 38.9%. Furthermore, CO2 emissions were estimated and compared between a conventional column and the suggested configurations.

Energy, environmental and economic assessment of a polygeneration system of local desalination and CCHP

In this investigation, a polygeneration scheme integrating local desalination units with CCHP systems, providing cold, heat and power for Kish twin towers as well as providing a portion of the fresh water demand of the island, is proposed and evaluated in terms of energy, environment, and economy aspects. The proposed system is compared to the conventional CCHP and desalination system adopting the separate production system as the reference. Here, two types of desalination technologies, namely multi-effect distillation (MED) and reverse osmosis (RO) processes, are used to provide desalinated water. A genetic algorithm is implemented to determine the optimal operating parameters. It results in that in the polygeneration system the yearly average power generation efficiency, the annual primary energy saving ratio (APESR) and the annual total cost saving ratio (ATCSR) of the whole system increase by 3.45%, 9.73%, and 6.49%, respectively, compared to the conventional system. Using the MED process can increase the ATCSR from 9.8% to 16.0%, depending on the fresh water market price. Moreover, the carbon dioxide emission (CDE) decreases by 1460.5 tons each year, compared to the reference. It is also indicated that 93.87% of the MED input heat can be recovered for domestic hot water (DHW) provision.

Performance analysis of hybrid system of multi effect distillation and reverse osmosis for seawater desalination via modelling and simulation

The coupling of thermal (multi stage flash, MSF) and membrane processes (reverse osmosis, RO) in desalination systems has been widely presented in the literature to achieve an improvement of performance compared to an individual process. However, very little study has been made to the combined multi effect distillation (MED) and reverse osmosis (RO) processes. Therefore, this research investigates several design options of MED with thermal vapor compression (MED_TVC) coupled with RO system. To achieve this aim, detailed mathematical models for the two processes are developed, which are independently validated against the literature. Then, the integrated model is used to investigate the performance of several configurations of the MED_TVC and RO processes in the hybrid system. The performance indicators include the fresh water productivity, energy consumption, fresh water purity, and recovery ratio. Basically, the sensitivity analysis for each configuration is conducted with respect to seawater conditions and steam supply variation. Most importantly, placing the RO membrane process upstream in the hybrid system generates the overall best configuration in terms of the quantity and quality of fresh water produced. This is attributed to acquiring the best recovery ratio and lower energy consumption over a wide range of seawater salinity.

Thermo-economic analysis of low-grade heat driven multi-effect distillation based desalination processes

We examine the economic viability of three multi-effect distillation (MED) based processes against the MED as a benchmark, when they are driven by low grade heat. We model and compare the Boosted MED (BMED), Flash Boosted MED (FBMED) and Distributed Boosted MED (DBMED) processes with the MED in terms of waste heat performance ratio, specific capex and opex. All three new configurations generate significantly higher productions than MED with higher capex and opex investment. We provide the corresponding cash-flow analyses using such financial metrics as the Net Present Value (NPV) and Internal Rate of Return (IRR). This study leads to the conclusion that the DBMED process is the superior scenario up to an interest rate of 12.5% at 65 °C heat source supply temperature which then drops to 8.4% at 90 °C heat source supply temperature. Also, the analysis shows for the high interest rates (above 8.4% at 90 °C), MED has higher NPV compared to other MED based processes.