Multi-effect Distillation Plant Research Articles

Exergy cost and thermoeconomic analysis of a Rankine Cycle + Multi-Effect Distillation plant considering time-varying conditions

A detailed exergy cost and thermoeconomic analysis applied to a Rankine Cycle (RC) coupled to a Multi-Effect Distillation (MED) plant was performed. The aim of this work is to identify the impact of design and operating conditions on the exergy and thermoeconomic costs of the final products, electricity, and freshwater, and to assess the distribution of the destroyed exergy, the fuel, and the plant costs. The plant model considers a high disaggregation model, which includes MED plant and condenser parasitic losses, a seawater pumping system and a brine energy recovery system. It also considers solar molten salts as the RC fuel, which is the typical fluid used in solar tower plants. The impact of RC + MED plant part-load operation, ambient temperature, MED plant size, and location plant’s altitude was evaluated and an analysis of operational day of the RC + MED plant was carried out. Results indicate that the plant part-load operation has a significant influence on the unit exergy and thermoeconomic product costs, while the ambient temperature evidences only a minor effect on the water costs. As well, the largest MED plant sizes (above 50,000 m3/day) offer the lowest electric and water costs, while the altitude strongly increases the water costs.

A Spatially Resolved Thermodynamic Assessment of Geothermal Powered Multi-Effect Brackish Water Distillation in Texas

Brackish groundwater desalination is increasingly being considered as a means to supplement drinking water in regions facing scarce freshwater supplies. Desalination is more energy intensive and expensive than traditional freshwater sources. One method of offsetting carbon emissions is to pair desalination technology with renewable energy sources. This research assesses the geographical feasibility of using a geothermal multi-effect distillation (MED) plant to produce freshwater from brackish aquifers in Texas. The system is analyzed using a thermodynamic model of a binary cycle MED plant. The thermodynamic model is integrated with spatially resolved information of Texas’ geothermal gradient and existing brackish well data (such as depth, salinity, and temperature) to quantify production potential. The results from this study allow for a comparison of potential geothermal desalination plant implementation across all of Texas, rather than a single site assessment. Although this water treatment approach is technologically viable across much of Texas, the system proves to be very energy intensive in all areas except for two hot geopressured fairways in Southeast Texas, the Frio and the Wilcox. In both locations, our research concludes the binary cycle-MED plant can operate self-sufficiently, producing both freshwater and electricity. One well in the fairways can produce 121–1132 m3 of water per day, enough for 232–2133 people. The framework outlined in this paper can be useful to policymakers and water planners considering where to build desalination facilities.

Determination of the Criteria for Comparative Analysis of Desalination Plant

The problem of fresh water lack can be solved my desalination of the seawater. Desalination of the seawater can be accomplished by several methods. Distillation of the seawater is one of the most promising among them. Comparative analysis of distillation desalination plant requires certain criteria. This criterion must take into account both energy consumption and seawater salinity. Relation of the minimal work required for seawater desalination to energy consumption was selected as such criterion. Four types of the distillation plants were considered: Multi-effect distillation plants (MED), multi-effect distillation plants with mechanical vapor compression (MVC) plants, MVC desalination plants have the best multi-effect distillation plant with thermal vapor compression (TVC) plants and Multistage flash distillation plants (MSF). MSF plants gave dependency that their efficiency rise along the gain ratio. That may be explained by the fact that its steam consumption does not depend on seawater consumption. TVC plants have slightly higher efficiency than MED plants. Thus, MVC plants can be recommended to use if there is no heat source, MSF plants - if there is heat source and plant must have a high gain ratio and TVC plant in the rest cases.

Environmental assessment of sustainable energy options for multi-effect distillation of brackish water in isolated communities

Access to sufficient quantities of fresh water is becoming increasingly difficult, especially in dry regions. Moreover, high levels of salinity, arsenic and boron are further limiting the access to quality fresh water in many isolated communities worldwide. This paper evaluates the life cycle environmental impacts of a small multi-effect distillation (MED) plant, treating brackish water with high levels of these metalloids in an isolated location in Northern Chile. The facility currently operates solely with electricity from a diesel generator and heat from a biomass boiler. In order to evaluate the environmental impacts of more sustainable energy options, the implications of the use of solar fields and grid electricity as potential alternatives have been analysed. The results demonstrate that coupling solar fields and grid electricity is the best option, sharply decreasing impact in most categories in comparison to the current operating mode of the plant. This was attributed to the impact savings from reducing/eliminating onsite diesel and biomass combustion, and their associated transportation to the plant. For MED desalination in off-the-grid areas, the use of solar energy is highly recommended as an alternative to complement the use of diesel and biomass, especially if the latter is not nearby the unit. The concentration of arsenic and boron was reduced to below the required standards for irrigation and livestock consumption. The article concludes that the use of solar energy and grid electricity are environmentally beneficial for the production of quality fresh water from brackish water using MED at isolated communities.

Exergy cost assessment of CSP driven multi-generation schemes: Integrating seawater desalination, refrigeration, and process heat plants

An exergy cost assessment of integrated solar multi-generation schemes, which includes cogeneration, trigeneration, and polygeneration schemes, for the joint production of electricity, fresh water, cooling, and process heat, is carried out. This evaluation process allows finding out the key equipment to improve the design, detect potential energy savings, and establish the best configurations of these schemes, in terms of unit exergy cost, total exergy cost, and exergy efficiency. The methodology includes modelling and evaluating the performance of solar multi-generation schemes and stand-alone systems, by applying the symbolic exergoeconomic methodology. The solar multi-generation schemes consider a concentrated solar power as the prime mover, which is coupled to a multi-effect distillation, an absorption refrigeration, and a process heat plant. Twenty-one configurations were investigated, twenty of them regarding solar multi-generation plants: eight of cogeneration, eight of trigeneration, four polygeneration schemes, and the other one considering stand-alone systems. This study reveals that the recommended configurations for the solar multigeneration schemes are those in which the desalination plant replaces the condenser of the power cycle, and the refrigeration plant, as well as the process heat module are coupled to turbine extractions. Furthermore, the main components contributing to the cost formation of electricity are, in this order, solar collectors, evaporator, and reheater. In the case of by-products generated, the main components are dissipative systems, solar collectors, and productive subsystems (multi-effect distillation, refrigeration, and process heat plants). In consequence, they constitute the key equipment that could be improved. Finally, solar multi-generation schemes are more cost effective than stand-alone systems. For instance, the best option within the polygeneration schemes analyzed allowed reducing the unit exergy cost about 6.8%, 59.2%, 45.6%, and 32.2% for electricity, water, cooling, and process heat respectively. Therefore, solar multi-generation schemes are identified as a promising alternative for zones with high irradiation conditions and scarcity of water, where the CSP technology can be the prime mover.

Correlations for estimating the specific capital cost of multi-effect distillation plants considering the main design trends and operating conditions

This work proposes a correlation for the specific capital cost of multi-effect distillation (MED) plants, considering their main design options and parameters, such as the number of effects, size/capacity, and heat source temperature. These parameters are varied within a large range to cover as many different cases as possible. The cost correlation decouples the evaporator cost and includes in the expression the ratio of the heat exchanger area to a reference one. This area is calculated using a validated MED numerical model, with the results then processed to produce fitted expressions. Two versions of this correlation with different levels of complexity are proposed, which provide similar results. The results of the improved correlation have been compared with the actual specific cost of a limited number of MED plants for validation purposes. It has been shown that this correlation provides more accurate results in most of the cases, although the sample is small due to limited availability of data from other plants. The specific capital cost of typical MED plants is then examined, presenting the cost when the number of effects and heat source temperature change. These calculations capture the expected trend of the plant cost under different main design options.

An efficient integrated trigeneration system for the production of dual temperature cooling and fresh water: Thermoeconomic analysis and optimization

This paper describes and analyzes an integrated trigeneration system for the production of air conditioning, fresh water and refrigeration at different temperatures. A single effect steam driven H2O-LiBr absorption cooling (ABC) cycle is integrated with a multi effect distillation (MED) unit and a CO2 based parallel compression economization-vapor compression refrigeration (PCE-VCR) cycle. The thermo-economic analysis is performed to identify how the integration can improve the energy utilization and annual costs. A detailed parametric study of several key design and operating parameters and an economic optimization are also conducted. The analysis shows that the MED plant can produce a significant amount of fresh water using the free steam supplied by the ABC cycle. Changes in the number of effects, top and last effect brine temperatures, size of the VCR cycle and number of operating hours significantly impact the MED plant productivity and unit production cost of water (UPCW). The integrated ABC-MED-VCR system, in a base case analysis, reduces the unit production cost of cooling (UPCC) for combined cooling and refrigeration and the UPCW by 25% and 27%, respectively compared to separate use of the three systems. Due to integration, substantial improvements in the fuel energy utilization and reductions in the annual capital cost (ACC) and annual operating cost (AOC) are achieved. Also, the AOC and ACC decrease 38% and 13%, respectively. At the optimized conditions, utilization of exhaust waste gas to drive the integrated ABC-MED-VCR system leads to additional 52%, 41% and 0.13% reductions in the AOC, UPCC and UPCW, respectively.

Reducing electric energy consumption in linear Fresnel collector solar fields coupled to thermal desalination plants by optimal mirror defocusing

In many parts of the world, desalination is the only viable and economic solution to the problem of fresh water shortage. The current commercial desalination technologies rely on fossil fuels and are thus associated with high greenhouse gas emissions that are a major cause of climatic changes. Solar thermal-driven multi-effect distillation with thermal vapor compression is a clean alternative to conventional desalination technologies. To comprehend this process, as well as its features and limitations, extensive modeling is required. In this work, we proposed a plant design based on a solar field with a linear Fresnel collector that supplies heat to a multi-effect distillation plant with thermal vapor compression. The solar desalination plant model is implemented in the Engineering Equation Solver (EES). The system performance is investigated and a control strategy for reducing electric pumping is proposed. Results showed that 1 m2 of the solar field produces 8.5 m3 of distillate per year. The proposed control strategy resulted in a 40% reduction in electric pumping energy. Our results highlight the versatility of the linear Fresnel collector when coupled with thermal desalination.

Computational analysis for a multi-effect distillation (MED) plant driven by solar energy in Chile

Abstract This study presents a numerical model for a multi-effect distillation (MED) plant driven by solar energy. The model is based on mass, energy, and heat transfer equations applicable to the coupled MED and steam generation plants. The MED plant model has been validated with experimental data from the multi-effect distillation plant of the Plataforma Solar de Almeria (PSA) in Spain [1]. Additionally, the model of the solar steam generation plant is validated using experimental data acquired from the parabolic trough collector (PTC) at the SANDIA National Laboratory, USA [2]. Both validations show good agreement between model and measurements, with a relative error smaller than 3%. Additionally, the heat transfer processes that occur in evaporators and preheaters are studied herein, and several heat transfer correlations are tested. The heat transfer model used in evaporators appears to be a key factor for performance predictions and may require further studies. Finally, the validated model is used to assess the technical feasibility of the installation of a solar MED plant in Valparaiso, Chile. The main results are analyzed under variable weather conditions. In addition, the MED plant is evaluated in different Chilean cities, and a linear dependence between fresh water production and solar radiation is established. In conclusion, a powerful computational tool is developed that may be useful for the design, optimization, and assessment of the technical feasibility of installation of future solar MED plants.

Energetic evaluation of a double-effect LiBr-H2O absorption heat pump coupled to a multi-effect distillation plant at nominal and off-design conditions

This paper presents the experimental characterization of a double-effect absorption heat pump (DEAHP) using lithium bromide-water (LiBr-H2O) which recovers the low-energy latent heat from the last effect of a multi-effect distillation (MED) plant. The experimental facility is located at the Plataforma Solar de Almería (PSA) and the test campaign has been performed with the aim to find the best operating strategies that minimize the energy consumption and maximize the energetic efficiency of the DEAHP-MED system taking also into account the distillate production of the MED unit. For this purpose, the impact of the variation of the input variables by which the DEAHP-MED system can be controlled (MED inlet hot water flow rate, MED inlet hot water temperature, the live steam flow rate and the DEAHP cooling water flow rate) on the coefficient of performance (COP), the performance ratio (PR) and on the total distillate production, has been analysed in two different coupling schemes between the DEAHP and the MED unit (indirect and direct). The results revealed that in direct mode, the rise in the live steam flow rate has the greatest impact on the distillate production and the increase of the MED inlet hot water flow rate and the DEAHP cooling flow rate on the COP. In the indirect mode, the rise in the MED inlet hot water temperature was the most influential in both parameters. The maximum COP, distillate production and PR was 2.08 ± 0.34, 2.42 ± 0.07 m3/h, and 18.53 ± 1.94, respectively in the direct mode and 2.04 ± 0.39, 1.92 ± 0.11 m3/h, 16.67 ± 3.42, respectively in the indirect mode. Moreover, empirical correlations that forecast the PR and the distillate production as a function of the COP were developed from the characterization results and were validated statistically by the coefficient of determination (R2) and the adjusted R2Radj2.

Techno-economic assessment of a multi-effect distillation plant installed for the production of irrigation water in Arica (Chile)

In the context of a regional Chilean project (FIC Taltape project, BIP code 30158422-0), a multi-effect distillation (MED) pilot plant has been built and installed in a small community in the north of Chile (Taltape, Arica) in order to supply treated water for agricultural and domestic purposes. The aim of this paper is to assess the techno-economic feasibility of this system for supplying water with the required quality to the population. The characterization of the feed water and the effluents from the MED pilot plant (distillate and brine), obtained during five months of operation, has been firstly performed. Then, the prediction of the operation of the water treatment system with solar energy has been carried out using a typical meteorological year and the design of a static solar field that cover the thermal energy needs of the water treatment plant.The annual simulations of the MED pilot plant operating with solar energy showed that the water needs can be mostly covered using a static solar thermal field with a total area of 113.2 m2, which would generate roughly 46% of the total heat required by the water treatment plant. The technical analysis has been completed with an exhaustive economic assessment. The specific water costs have been determined for the MED pilot plant and the scale factor when the productivity is increased up to 5000 m3/day has been evaluated. The cost of distillated water produced by the MED plant varied from 15.0 USD$/m3 for the 10 m3/day production capacity to 1.25 USD$/m3 when this variable is increased to 5000 m3/day.

Comparison of the levelized cost and thermoeconomic methodologies – Cost allocation in a solar polygeneration plant to produce power, desalted water, cooling and process heat

The present work shows a comparison between the levelized cost and the thermoeconomic methods in their application to assess the performance of a solar polygeneration plant. The aim is to analyze the costs allocation process, the unit specific costs of each product, as well as the energy and exergy efficiencies, which allows to identify the main advantages of both the evaluated methods. The methodology is applied in a case study configured by a concentrated solar power with thermal energy storage and backup system, combined to a multi-effect distillation plant, an absorption refrigeration plant, and a process heat module. The present study reveals that through the levelized cost method, the cost associated to the electricity generation is higher than it is by applying the thermoeconomic method, whereas the costs of water, cooling and process heat are significantly lower. Those differences represent an increase of about 35.1% in the case of the electricity, and a reduction in the cost associated to the water, cooling, and heat production by around 34.4%, 78.1%, and 97.6%, respectively. Results show that the thermoeconomic method is an equitable and rational cost allocation method which is suitable for a solar polygeneration plant. This method is recommended when a more precise analysis is required to assess the proper costs of different products, and for assessing the benefits of a polygeneration plant, when compared to stand-alone plants. However, the levelized cost method is a simple and fast method, and a deep knowledge of thermodynamics is not required, being recommended when in need to perform a first approach of the costs of each product.

An Integrated Approach to Water-Energy Nexus in Shale-Gas Production

Shale gas production is associated with significant usage of fresh water and discharge of wastewater. Consequently, there is a necessity to create proper management strategies for water resources in shale gas production and to integrate conventional energy sources (e.g., shale gas) with renewables (e.g., solar energy). The objective of this study is to develop a design framework for integrating water and energy systems including multiple energy sources, the cogeneration process and desalination technologies in treating wastewater and providing fresh water for shale gas production. Solar energy is included to provide thermal power directly to a multi-effect distillation plant (MED) exclusively (to be more feasible economically) or indirect supply through a thermal energy storage system. Thus, MED is driven by direct or indirect solar energy and excess or direct cogeneration process heat. The proposed thermal energy storage along with the fossil fuel boiler will allow for the dual-purpose system to operate at steady-state by managing the dynamic variability of solar energy. Additionally, electric production is considered to supply a reverse osmosis plant (RO) without connecting to the local electric grid. A multi-period mixed integer nonlinear program (MINLP) is developed and applied to discretize the operation period to track the diurnal fluctuations of solar energy. The solution of the optimization program determines the optimal mix of solar energy, thermal storage and fossil fuel to attain the maximum annual profit of the entire system. A case study is solved for water treatment and energy management for Eagle Ford Basin in Texas.

Multi-Effect Vacuum Membrane Distillation systems: Model derivation and calibration

Vacuum Membrane Distillation (VMD) has been shown to be a promising desalination approach when going beyond the application range of Reverse Osmosis. Multi-stage arrangements in particular benefit from system-inherent heat recovery and thus yield low specific energy demand. Nevertheless, these systems show a complex behavior and therefore require a careful design, especially for higher salt concentrations which provide significant vapor pressure reduction. Previous experimental studies showed a need for a reliable system simulation tool, which we derived and calibrated in this work. The focus was on accurate modeling of the physical behavior, especially the multi-staging, polarization effects and different salt solutions up to their solubility limit. The model calibration and verification were based on results yielded by a novel triple channel VMD bench scale test cell, as well as technical scale system results from experiments with a memsys 2/4-stage Multi-Effect Vacuum Membrane Distillation (MEVMD) plant. The developed model was able to reproduce the system behavior and provides a tool for system optimization while providing insight into channel coupling, pressure staging, and phenomena like self-reduction of the number of working stages with rising feed salt concentration.

Optimal operating conditions analysis for a multi-effect distillation plant according to energetic and exergetic criteria.

In order to reduce the energy cost while improving the process operation, a study which aims to analyze the influence of the operational parameters variations and determine the optimal operating conditions of a pilot multi-effect desalination system (MED) at CIEMAT-Plataforma Solar de Almerıía (PSA) has been performed. An equation-based object-oriented mathematical model of the experimental MED plant, implemented using the modeling language Modelica and previously developed, calibrated and validated, has been adapted to carry out this study. Firstly, an energetic and exergetic analysis of the process under nominal conditions has been carried out, revealing the key sources of energy and exergy consumption. On the one hand, the thermal energy contained in the mass outflows are the main responsible source of the high energy consumption, on the other hand the entropy generation and the heat exchanged with the environment are the responsible of the exergy degradation. Secondly, a study on the influence of the operational parameters shows that the production of the real plant under nominal conditions is far from the maximum simulated values and some operational parameters have not a great influence in the process with respect to the rest. Finally, using a genetic optimization algorithm implemented in the modeling tool, a optimization process taking into account different energy and exergy performance criteria, sets optimal operational set points.

P.2.b.013 - The change of suicidal ideation over a 12- week naturalistic treatment of depression: comparison between young people and older adults

This work proposes an analysis of conventional (single stage) and dual stage Closed-Loop Pressure Retarded Osmosis (CLPRO) for power generation from a salinity gradient resource. Model calculations were performed taking into account the influence of operating parameters such as the draw solution concentration, membrane area, and draw solution pressure on the performance of the CLPRO process. Modeling results showed that the dual stage CLPRO process outperformed the conventional CLPRO process and power generation increased 18% by adding a second stage of PRO membrane. Multi-Effect Distillation (MED) was selected for the regeneration of the draw solution taking advantage of an available source of waste heat energy. The performance of MED process has been assessed by investigating two key parameters: the specific thermal consumption and the specific heat transfer area. The model calculations showed that the power generation by the single and dual stage CLPRO was higher than the electrical power consumption by the MED plant. In the case of the power generation obtained by the dual stage CLPRO, it was 95% higher than the electrical power consumption by the MED plant, proving the possibility of using low-grade heat for producing electricity from a salinity gradient resource.

Integrating desalination with concentrating solar thermal power: A Namibian case study

This paper reports on a feasibility study into the integration of a multi-effect distillation plant with a central receiver plant to generate electricity for the Namibian grid, and fresh water for the community and mining operations at Arandis. Arandis receives on average 2528 kWh/m2/year of solar irradiation, is only 48 km from the coast and 580 m above sea level, making it attractive for a cogeneration plant. Desalination is energy intensive, but the required energy is freely available from the waste heat rejected at the condenser of a Rankine cycle. In this study, high level thermodynamic models of a multi-effect distillation and central receiver plant were developed to better understand the economics of such a cogeneration plant. Results indicate that a 100 MWe central receiver plant combined with a multi-effect distillation plant, is capable of servicing the current water demand in the region. Despite the high capital costs of central receiver plant, as well as pumping seawater inland, the plant is economically viable within the proposed tariff structure for renewable energy in Namibia, and existing water tariffs. Profit parity between a cogeneration plant and a stand-alone, dry-cooled central receiver plant is reached for top brine temperatures above 65 °C. Under these conditions, water sales would subsidize electricity production. However, it is not price competitive with a grid-powered reverse osmosis plant on the coast. The most significant barriers in making cogeneration plant competitive against more conventional desalination methods such as reverse osmosis are the high capital cost of the cogeneration plant, and pumping seawater inland.

Experimental characterization of a multi-effect distillation system coupled to a flat plate solar collector field: Empirical correlations

In the last three decades, developments in desalination plants have been focused on the minimization of its energetic consumption and cost. Advancements include emerging technologies that make use of low grade thermal energy, like Multi-Effect Distillation (MED). The energy optimization of MED systems and their coupling with solar thermal technologies have been deeply investigated by the Solar Desalination Unit of the Plataforma Solar de Almería (PSA) through a solar desalination test facility consisting of a MED plant coupled to a static solar field. Recently, the previous solar field composed of compound parabolic concentrators (CPC) has been replaced by a new one with large-aperture flat plate collectors (FPC). In this work, an experimental characterization of the solar MED system under off-design conditions is presented and discussed. The efficiency of the FPCs’ solar field at several temperature levels for different climate conditions has been determined. Also, the influence of the variation of key parameters by which the MED plant is controlled (the inlet hot water flow rate (mhot) and temperature (Thot), the feed water flow rate (mf) and the condenser vapor temperature (Tc)) on the freshwater production and performance ratio (PR), were analyzed with an experimental campaign of 82experiments. The results obtained were used to fit polynomial expressions, validated statistically, that predict the distillate yield and the PR for different operation strategies. The experimental characterization of the desalination plant revealed that the rise in the Tc has the highest impact in the thermal efficiency of the MED unit, and the rise in the mf has the greatest influence on the distillation production. Moreover, from the analysis of the coupling of the MED plant with the solar field it was found that the thermal storage has an autonomy of up to 6h when the MED works with hot water at 65°C, which allows the plant to continue the operation even in transient periods (presence of clouds). Also, from a theoretical annual study for the solar MED system, it was found that the annual solar fraction ranges from 30.7% to 42.4%, which leads to an annual distillate production between 6701m3 and 11,314m3, respectively.

Single and dual stage closed-loop pressure retarded osmosis for power generation: Feasibility and performance

This work proposes an analysis of conventional (single stage) and dual stage Closed-Loop Pressure Retarded Osmosis (CLPRO) for power generation from a salinity gradient resource. Model calculations were performed taking into account the influence of operating parameters such as the draw solution concentration, membrane area, and draw solution pressure on the performance of the CLPRO process. Modeling results showed that the dual stage CLPRO process outperformed the conventional CLPRO process and power generation increased 18% by adding a second stage of PRO membrane. Multi-Effect Distillation (MED) was selected for the regeneration of the draw solution taking advantage of an available source of waste heat energy. The performance of MED process has been assessed by investigating two key parameters: the specific thermal consumption and the specific heat transfer area. The model calculations showed that the power generation by the single and dual stage CLPRO was higher than the electrical power consumption by the MED plant. In the case of the power generation obtained by the dual stage CLPRO, it was 95% higher than the electrical power consumption by the MED plant, proving the possibility of using low-grade heat for producing electricity from a salinity gradient resource.

Optimal operating conditions analysis of a multi-effect distillation plant

Optimal operating conditions analysis of a multi-effect distillation plant