Multi-effect Desalination Plant Research Articles

A novel renewable energy system designed with Mg–Cl thermochemical cycle, desalination and heat storage options

In this paper, a novel multigenerational integrated system that is able to produce five useful commodities, such as freshwater, space heating, hot water, power and hydrogen for a community, is proposed and investigated. The system uniquely covers heat storage by molten salt heat storage along with hydrogen production by magnesium-chlorine (Mg–Cl) based thermochemical cycle. Additionally, the present system has a multi-effect desalination plant to provide freshwater community needs. A solar power tower is offered due to its capability of harvesting high energy levels. The heat recovered by the solar power receiver is passed through an organic Rankine cycle (ORC) to meet the need for the high-temperature level that is required for the thermochemical cycle. The molten salt storage tanks are used to offset the mismatch between demand and supply for the necessary energy to run the system in case of the absence of solar irradiation. The suggested system is intended to leverage solar and geothermal energy sources to generate practical necessities like power, heat, and hot water for residential applications of a projected community. The system is then analyzed in detail thermodynamically in the context of exergy and energy approaches. In addition, the subsystems are analyzed parametrically to study the performance of the overall system to observe how the ambient and working conditions change the system efficiencies. The city of Vancouver in Canada is selected as the potential location where the system performance assessment is carried out accordingly. As a result of the present thermodynamic analysis, the energetic and exergetic efficiencies for the system are obtained as 45.45% and 52.32%. The total exergy destruction rate is another exergy metric to compare both versions, where the rate of 163967.39 kW exergy destruction is obtained for the overall system.

A dynamic optimization approach for a multi-effect desalination (MED) integrated with thermosolar storage system

This work aims to propose a more robust and realistic dynamic optimization (DO) approach to maximize the profit of distilled water production in a multi-effect desalination (MED) plant integrated with thermosolar storage system. Unlike the literature, the underlying model comprehends the integrated system composed of solar collectors, thermal energy storage (TES) tanks and MED. To carry out this study, a non-linear phenomenological model representative of these conjugated systems was developed and validated with dynamic data from the literature, with maximum relative deviations below 5%. A sensitivity analysis identified irradiance, ambient temperature, and the water flow to the solar collectors and to the first MED’s evaporator as the main variables. These last two variables were used as decision variables in the optimization problem, which was solved using the orthogonal collocations on finite elements. This method proved to be stable and computationally efficient, with a simulation time of 54 s. The results demonstrate that the consideration of two decision variables, instead of just one in the objective function, provides a 5% gain in profitability and almost 24% in distillate production. Simulations over longer time horizon (48 h) confirm that the TES can supply the heat demand for desalination even after sunset, yet a receding horizon architecture is required to prevent tank’s drying or overflow. The optimal profiles obtained for the water flow to the solar collectors and to the MED’s first effect can be used for implementing control schemes.

Exergoeconomic Analysis of the Cycle of Cogeneration of Power, Cooling and Freshwater for a Residential Complex in Iran

This research presents a system to use natural gas to meet electricity, freshwater and cooling needs for a residential building in Bandar Abbas. The system includes a gas turbine, absorption chiller and multi-effect desalination (MED) plant. The energy produced in the gas turbine is used to generate electricity, and the excess energy is used to produce cooling and freshwater. Finally, an exergoeconomic evaluation of the system is performed. The effects of ambient temperature on the output power as well as the exergy current have been investigated. The COP of the absorption cycle has been investigated, and the results show that at an operating temperature of 150∘C compared to 90∘C, the efficiency rate increases to 20%. The highest exergoeconomic cost rate is related to absorption chiller, and the lowest is related to heat recovery steam generation. The results show that if the ambient temperature increases, the production capacity decreases. Increasing the fuel flow rate increases the power. Evaluation of two different solutions to reduce the ambient temperature and increase the fuel flow shows that increasing the fuel flow is a better solution, considering the exergy cost of the absorption chiller, which is 10 times higher than that of the gas turbine.

Influence of operating temperature range on the performance of multi-effect desalination (MED) plant

Desalination technology provides a long-term option for supplying freshwater to water-scarce coastal areas, such as the region between Karachi and Gwadar in Pakistan. Desalination through reverse osmosis (RO) is a low-energy process. Recent advancements in multi-effect desalination (MED) technology, such as integrating adsorption/absorption vapor compression systems and the synthesis of novel antiscalants, have made it a viable option. The current top brine temperature (TBT) for the MED unit is 65 °C (due to salt precipitation in the evaporators), which may accommodate 8 – 10 falling film evaporators. However, with to advancements in antiscalants, the TBT can now be extended to 85 °C, indicating the inclusion of more evaporators and hence increased freshwater yield. A mathematical model of the MED unit is created in Engineering Equation Solver (EES) for this purpose, and the MED unit's performance is evaluated at increased TBT. The mathematical model is validated using a literature-based empirical model as well as a commercial desalination facility in Qatar. This work presents and discusses the influence of the number of effects, TBT on performance ratio, specific heat transfer area, and specific cooling water requirement.

CFD analysis of evaporation heat transfer for falling films application

Multi-effect desalination (MED) uses less energy and has a smaller footprint than other thermal desalination systems. The MED plant consists of cascaded horizontal-tube falling film exchangers (HFFE), offering improved heat transfer at lower liquid loads. The MED plant’s current working temperature range is 40 °C–65 °C, for which 6–8 HFFE can be used. However, this limit can be extended to 5 °C–85 °C by using new antiscalants and an adsorption vapor compression system. Thus, more HFFE can provide enhanced water production. Furthermore, the heat transfer studies for this range are limited. Therefore, this work presents a 2-D computational fluid dynamics (CFD) model in Ansys fluent v19.0 to examine the film thickness, the temperature distribution, and the heat transfer coefficient for working temperatures of 5 °C, 65 °C, and 85 °C at various liquid loads. It is found that the heat transfer is improved at higher temperatures and liquid loads by 21 %–37 %, which indicates lower energy requirements and better distillate productivity.

Life-cycle environmental assessment of solar-driven Multi-Effect Desalination (MED) plant

Seawater desalination supplies 97 million m3 of freshwater daily to more than 300 million people worldwide. The global desalination market is dominated by two technologies, thermal and membrane desalination. These processes have adverse impacts on the environment in the form of harmful emissions into the air and water and also on human health. Therefore, our main research questions are: to what extent can we minimize the life cycle environmental impact of conventional thermal desalination processes through the integration of concentered solar power collectors, and how do various collectors compare in this regard? We answered these questions by conducting a life-cycle assessment (LCA) study on an optimized solar-driven multi-effect desalination (MED) process. The LCA results revealed that most of the life-cycle impact in the climate change, fossil depletion, and water depletion categories occurs during the operation phase based on electric pumping energy. The solar-driven process reduces climate change impact by 10 kg-CO2 eq., for every 1 m3 of freshwater as compared to the conventional one. We also found that the linear Fresnel collector has a better LCA rating than the parabolic trough collector. The broader implications of this work pertain to renewable energy and water resources policymaking and resource conservation.

Sea Level Rise Mitigation by Global Sea Water Desalination Using Renewable-Energy-Powered Plants

This work suggests a solution for preventing/eliminating the predicted Sea Level Rise (SLR) by seawater desalination and storage through a large number of desalination plants distributed worldwide; it also comprises that the desalinated seawater can resolve the global water scarcity by complete coverage for global water demand. Sea level rise can be prevented by desalinating the additional water accumulated into oceans annually for human consumption, while the excess amount of water can be stored in dams and lakes. It is predicted that SLR can be prevented by desalination plants. The chosen desalination plants for the study were Multi-Effect Desalination (MED) and Reverse Osmosis (RO) plants that are powered by renewable energy using wind and solar technologies. It is observed that the two main goals of the study are fulfilled when preventing an SLR between 1.0 m and 1.3 m by 2100 through seawater desalination, as the amount of desalinated water within that range can cover the global water demand while being economically viable.

Heat Transfer Coefficient Estimation of Falling Film for Horizontal Tube Multi-Effect Desalination Evaporator Using CFD

The multi effect desalination (MED) plant comprises of horizontal tube falling evaporators with the operational range of 40°C – 65°C, and can accommodate 8 – 10 evaporators/effects. The operating temperature range is limited by scale formation and condenser temperature. With the recent advances in antiscalants and vapor compression systems, the higher limit can be increased up to 85°C, and the lower limit can be reduced to 5°C. Therefore, more evaporators can be used to augment the amount of desalinated water, and the thermal performance of evaporators for a broader range needs to be assessed. In this study, the heat transfer coefficient at inlet temperatures of 85°C and 5°C, and different liquid loads, are numerically estimated. For this purpose, a two-dimensional CFD model is developed and validated. The computed results demonstrate that the heat transfer coefficient at the impact point is the highest that decreases with the angular position of the tube. The recirculations in the impingement zone enhance the heat transfer because of better mixing. At Ti = 85°C, the heat transfer performance is better due to lower film thickness, recirculations, and broad thermal developing region. For a liquid load of Γ1/2 = 0.09 kg/(m•s), the heat transfer coefficient at Ti = 85°C is 43.5 % higher as compared to that of at Ti = 5°C. Furthermore, the higher operating temperature limit should be increased instead of decreasing operating temperature for improved heat transfer performance.

The influence of fresh water production rate on the economics of two dual-purpose power/water plants: a case study

ABSTRACT The technical and economic analysis of the dual-purpose power/water Solar Rankine Cycle (SRC) coupled with Multi-Effect Desalination (MED) system was investigated. The influence of using Thermal Vapor Compression (TVC) on the unit costs of the generated power and water was also studied. Due to the population increase in the southern touristic coastal region of Iran and decreasing trend of the fuel price subsidy over the recent years, the government interest is shifting to the use of solar thermal energy and integrating the MED or MED-TVC desalination units with the conventional Rankine cycles, and to apply the solar thermal energy to reduce the fuel consumption. The water production rate of the MED or MED-TVC plants integrated into the SRC can significantly affect the electrical performance and consequently the fresh water and electricity unit of costs which has been rarely reported in the literature. In this regard, a comparison was made between the SRC-MED and SRC-MED-TVC configurations under two different scenarios of 6 and 12 hours of thermal energy storage. The output temperature of the LF solar field was considered to be regulated by defocusing the field mirrors and changing the working fluid mass flow rate. The unit costs of electricity (COE) and fresh water (COW) for both plants were determined under different scenarios of the water production capacities. Based on the results, COE and COW range from 0.20$/kWh to 0.25$/kWh and from 1.25$/to 3$/, respectively, for different water production rates. Also, for water production rates of more than 80,000/day, the SRC-MED plant has lower COE and COW as compared to the S‌RC-MED-TVC plant. While the COE and COW of the SRC-MED-TVC plant are less than those of the other plant for water production rates of less and equal to 36,000/day.

Thermal Performance of MED-TVC Pilot at 95°C Elevated Temperature with Acid-anti-scalant Blend Treatment

Enhancing the efficiency of desalination plants and economics of desalinated water are the major goal to researchers. In desalination industry; Multi Effect Desalination (MED) has an economic potential which proves its maturity among different desalination technologies. Large MED plants were built and operated with satisfactory performance in the last decade. They have been operated at low temperature compared to MSF and competitive operation efficiency. The Desalination Technology Research Institute (DTRI) which belongs to the Saline Water Conversion Corporation (SWCC) of Saudi Arabia has tested MED pilot plant with hybrid acid and anti-scalant treatment to control the scale. The test was conducted under 95 °C compared to 65 TBT which the current commercial standard operational temperature and previously tested 85 TBT within DTRI-SWCC pilot plant. Increase in the TBT would allow to increase the number of effects which lead to more system efficiency (the performance ratio) and then reduce fuel consumption which reflected in water unit cost of the desalinated water. The results showed that the thermal performance including fouling factor and performance ratio was constant and have very minor degradation during the test. The good thermal performance was confirmed by the post-operation visual inspection, which revealed that the heat transfer tubes were maintained in a clean condition after testing.

Techno-economic analysis of a combined concentrated solar power and water desalination plant

The aim of this study is to model and highlight the capabilities of the cogeneration of electricity and water using a contemporary configuration employing a multi-effect desalination plant and a reverse osmosis plant integrated with a concentrated solar power plant using parabolic trough collectors, working on the basic principle of the Rankine cycle. Environmental data was collected at the selected location, and a mathematical model was established using the MATLAB/Simulink package to predict the amount of fresh water and electricity produced by the proposed system under the required operational constraints. Preliminary results showed that Ras Gharib is an ideal location for the implementation of the proposed system owing to its high solar irradiance, yielding freshwater production in July of 21,000 m3/day and 1775 m3/day from multi-effect desalination and reverse osmosis plants, respectively. In addition to generating a total of 22,775 m3/day freshwater, a total of 15.5 MWe was generated and supplied to the grid after meeting all the electricity requirements of the system. Monthly assessments were conducted to determine the amount of fresh water and electricity supplied by the system.

Small-Scale Desalination Plant Driven by Solar Energy for Isolated Communities

In the last years, an increasing number of countries has been affected by water shortage. Seawater desalination driven by solar energy, which is usually available in arid regions, might be a solution to satisfy the freshwater demand. In this study, the feasibility of a stand-alone multi-effect desalination (MED) plant driven by solar energy for an isolated community was studied. The system was made up of a solar field, a MED unit, and a thermal storage that mitigated solar energy fluctuations. Simulations with different top brine temperature and inclination and number of the solar panels were carried out in Matlab and Aspen Plus on an hourly basis by considering one typical meteorological year for ambient temperature and solar radiation. Two different sources of electrical energy were considered: A photovoltaic (PV) field and a diesel generator. The results were compared from an energetic and economic point of view, by considering the adoption of plastic as a material for MED heat exchangers. The maximum water production was obtained with December as the design month. Polytetrafluoroethylene heat exchangers allowed the cost of water to be reduced up to 9.5% compared to conventional exchangers. The lowest cost of water (7.09 $/m3) was obtained with September as the design month and a tilt angle of 45° with the PV field as the electrical power source.

Novel sea water desalination unit utilizing solar energy heating system

A conventional parallel cross feed flow multi-effect desalination plant was simulated and optimized by the use of multi-goal algorithm MATLAB language programming together with engineering equation solver. An analysis of the overall performance of the plant was executed. A new design of solar desalination plant inclusive of solar parabolic collectors, steam generator, and MED unit has been proposed to commute the conventional plant. Further, an implementing was carried out on the subject of oblique steam production true more than one thermal oil which include THERMINOL VP1, THERMINOL 66, THERMINOL 59, THERMINOL SP, THERMINOL 55 and DOWTHERM A in addition to water. Via the simulation, it became clear that THERMINOL VP1 had 1.025% greater desalinated water than others. Additionally, the operation cost of distillate production by the usage of mazut or natural gas is a lot extra than using solar energy.

Exergoenvironmental analysis and evaluation of coupling MSF, MED and RO desalination plants with a combined cycle plant

In this paper, freshwater production through multi-effect desalination (MED), multistage flash (MSF), reverse osmosis (RO), hybrid (MED-RO), and hybrid (MSF-RO) units have been investigated based on environmental impacts associated with life cycle assessment (LCA) modelling tool and exergoenvironmental analysis. The integration of Qom combined cycle as a real case study with selected desalination plants has been studied. In this regard, thermodynamic simulation has been performed in computer code with high accuracy. Furthermore, computer code has been developed to perform exergy, exergoeconomic, and exergoenvironmental analyses. Results show; the environmental impact rate associated with the integrated combined cycle with the MED unit decreased by 23% compared to the stand-alone power plant. Also, in the integration of combined cycle with MSF, RO, MED-RO, and MSF-RO, it has been found that 25%, 60%, 27%, and 25% decrease can be obtained in the environmental impact rates, respectively.

Optimised annual performance of hybrid solar energy MED-TVC desalination plants with and without preheating

In the current study, energy, exergy, economic and environmental (4E) analysis for a multi-effect desalination plant with and without feed brine preheater integrated with a steam boiler and solar hybrid system for three coastal cities of southern Iran during a year is investigated. Four main configurations of hybrid/MED-TVC, hybrid/MED-TVC.FH, boiler/MED-TVC and boiler/MED-TVC.FH are considered. By using artificial bee colony algorithm, systems were optimised. The results show that: using feed brine preheater, the unit cost reduced by 6.5% for the system with a boiler and 3.8% for the hybrid system.

Optimised annual performance of hybrid solar energy MED-TVC desalination plants with and without preheating

In the current study, energy, exergy, economic and environmental (4E) analysis for a multi-effect desalination plant with and without feed brine preheater integrated with a steam boiler and solar hybrid system for three coastal cities of southern Iran during a year is investigated. Four main configurations of hybrid/MED-TVC, hybrid/MED-TVC.FH, boiler/MED-TVC and boiler/MED-TVC.FH are considered. By using artificial bee colony algorithm, systems were optimised. The results show that: using feed brine preheater, the unit cost reduced by 6.5% for the system with a boiler and 3.8% for the hybrid system.

Performance enhancement of a multi-effect desalination plant: A thermodynamic investigation

In current work the multi-effect desalination (MED) plant scheme and operation have been studied based on thermodynamic optimization using mathematical calculation and modeling for the main equations related to mass, energy and salinity balance taking in account the synchronized consequence of several constraints on the system execution. The effects of irreversibilities and energy losses are integrated in the study which in turn the results obtained are very close to the real results more than previous studies. The results obtained show that the system performance is meaningfully influenced by heat source flux, stage number, heat exchangers efficiency and feed water temperature and flow rate Then the effects of involved parameters are performed and discussed. Moreover, various 3D results have been displayed involving the effect of more than two parameters in system performance. Therefore, the outputs of this work assist manufacturer for the optimization and design of MED plant. The authenticity and perfection of the numerical solution technique are proved and verified within real results.

Assessment of an Integrated Gasification Combined Cycle using waste tires for hydrogen and fresh water production

In this paper, an Integrated Gasification Combined Cycle (IGCC), which uses waste tires as a feedstock, for power, hydrogen and freshwater production is modeled using both EES and Aspen Plus software packages and assessed thermodynamically. During the study, it is found that tire gasification is a viable solution for leftover tire waste in the world. Furthermore, the novel integration of a multi effect desalination plant, driven by the excess heat from the combined cycle, further increases the systems plant efficiency. The hydrogen production to feed rate ratio is found to be 0.154, which is competitive to high-quality coals, such as Illinois No.6, making waste tires an excellent feedstock to produce hydrogen. The net power production output from the combined cycle is 14.5 MW which was driven by the excess thermal energy of the syngas. The water distillate production rate from the forward flow multi-effect desalination plant at the set conditions is found to be 0.99 kg/s. The systems overall energy and exergy efficiencies obtained are 58.9% and 57.4%, respectively.

Review on CFD analysis of horizontal falling film evaporators in multi effect desalination plants

Review on CFD analysis of horizontal falling film evaporators in multi effect desalination plants

Transient and thermo-economic analysis of MED-MVC desalination system

An exergo-economic model is used to assess the performance of a multi-effect desalination plant integrated to a mechanical vapor compressor unit (MED-MVC) with a water production capacity of 1500 m3/day. The results show that the second law efficiency (ηII) is 2.8%. The MVC and evaporator units are responsible for about 39 and 52% of the total exergy destruction, respectively. The total water price (TWP) is 1.70 $/m3 when calculated using a simple conventional economic model and 1.63 $/m3 when calculated using an exergy-based cost model. Increasing the number of effects from 1 to 6 results in a 39% reduction in the specific power consumption (SPC), a 70% increase in ηII and a 24% decrease in TWP. A dynamic model is developed to investigate the effect of fluctuations of compressor work (W˙c) and inlet seawater temperature (Tsw) on the plant behavior and performance. The dynamic model results show that the disturbance in W˙c has a significant effect on the plant transient behavior and may cause the plant to cease operation while a disturbance in Tsw has only a moderate impact. Increasing Tsw above a certain value of the steady-state condition without proper control on the plant response could lead to evaporator dry out. In term of performance, a reduction in W˙c causes a decrease in the plant production capacity and SPC, while it increases the plant performance ratio (PR). On the other hand, a reduction in the inlet Tsw causes a reduction in the plant production capacity and PR and an increase in SPC for the same compressor work. Furthermore, a comparison between a MED-MVC system and a MED integrated to a thermal vapor compressor system (MED-TVC) reveals that the latter system is rather sensitive to the reduction in Tsw due to the presence of the condenser unit in the MED-TVC. The response of the MED-MVC system is slower than the MED-TVC which is due to the high thermal capacity of the preheaters for the feed in the MED-MVC.