Low-temperature Multi-effect Distillation Research Articles

Corrosion behavior of AA5052 aluminum alloy in the presence of heavy metal ions in 3.5 % NaCl solution under negative pressure

Aluminum alloy heat exchange tube is attractive for the Low Temperature-Multi Effect Distillation (LT-MED) desalination device, for its low cost and excellent mechanical property. However, it is prone to galvanic coupling corrosion in presence of heavy metal ions. In this paper, the effect of Cu2+ and Fe3+ ions on the corrosion of aluminum alloy in 3.5 wt% NaCl solution under negative pressure is investigated by the weight-loss method and the electrochemical measurements. It shows that the operation pressure affects significantly the corrosion behavior of AA5052 aluminum alloy in presence of heavy metal ions. As the pressure decreases, the resistance of the aluminum alloy to corrosion increases markedly. The corrosion products formed under different operation pressure are detected by SEM, XRD analysis. It is found that the diffusion process of corrosion products from the aluminum alloy surface into the solution is prevented as the decrease of pressure, resulting in the formation of the passivation layer on the aluminum alloy surface. The decrease of pressure can effectively restrain the heavy metal ions to be adsorbed on the defects of the oxide layer and mitigate the corrosion of aluminum during the LT-MED desalination process.

Multi-effect distillation: a sustainable option to large-scale green hydrogen production using solar energy

Development of sustainable, gigawatt capacity green hydrogen will require both renewable energy and water inputs, along with careful management of the waste heat produced by these processes (i.e., 9.3–16.7 kWhth/kgH2 for a 70–80% stack efficiency, high heat value). Here we compare the water demands and operating costs for a solar-driven electrolyser facility (powered by solar PV) operating on desalinated seawater produced using reverse osmosis or low-temperature multi-effect distillation. The waste heat was managed via passive cooling, evaporative cooling or through thermal recovery. It was found that the costs for low-temperature multi-effect distillation were up to 85% lower than reverse osmosis and generated 50–270L/ kgH2 of surplus water for ancillary benefit. This work challenges conventional wisdom surrounding the use of membrane desalination for meeting the water demands, offering compelling reasons for thermal desalination to be employed in large-scale production of green hydrogen.

Fouling on aluminum-brass and titanium tube surface in environment of low-temperature multi-effect distillation for desalination

Fouling on aluminum-brass and titanium tube surface in environment of low-temperature multi-effect distillation for desalination

Behavior of calcium carbonate growth during low-temperature multi-effect distillation seawater desalination

Behavior of calcium carbonate growth during low-temperature multi-effect distillation seawater desalination

Study on the superhydrophilic modification and enhanced corrosion resistance method of aluminum alloy distillation desalination tubes

In low temperature multi-effect distillation (LT-MED) seawater desalination system, the (super-)hydrophilic surface modification of aluminum alloy distillation desalination tube is effective in improving the performance of the desalination system and reducing the cost. However, the poor corrosion resistance of desalination tubes under (super-)hydrophilic surface modification is a bottleneck that limits the application of desalination tubes. This research breaks this technical bottleneck and proposes a simple, economical and industrially applicable method that jointly enhances hydrophilicity and corrosion resistance on aluminum alloy distillation desalination tubes. This method combines a concentrated anodizing electrolyte, pyrophosphoric acid, with an eco-friendly corrosion inhibitor, Na2MoO4, and prepares a superhydrophilic anodic oxide film with substantially enhanced corrosion resistance. The research shows that the concentration of Na2MoO4 in electrolyte plays a crucial role in the corrosion resistance of the superhydrophilic anodic oxide films: under the condition of ensuring the superhydrophilic surface of aluminum alloy (contact angle <5°), as Na2MoO4 concentration (0– 0.5 mol/L) increases, the higher the concentration of Na2MoO4 in the electrolyte, the better the corrosion resistance of the prepared superhydrophilic anodic oxide film. When adding 0.5 mol/L Na2MoO4 to 70 wt% pyrophosphoric acid electrolyte, compared with the superhydrophilic anodic oxide film without the addition of Na2MoO4, the prepared superhydrophilic film has its corrosion potential increased by 0.451 V, corrosion current density reduced by nearly four times, and corrosion inhibition efficiency increased from 25 % to 80 %. This research reveals the mechanism by which the corrosion inhibitor Na2MoO4 enhances the corrosion resistance of superhydrophilic anodic oxide film through adsorption of the porous layer, thickening of the barrier layer and Mo(+VI) incorporating. This paper provides a new idea and method for developing aluminum alloy desalination tubes with both stable superhydrophilicity and excellent corrosion resistance.

A systematic construction of water-electricity cogeneration and thermal membrane coupling desalination technology using the waste heat in steel industry

The widespread use of fossil energy emits a large amount of carbon dioxide, leading to the greenhouse effect and global warming. The essence of reducing carbon emissions is to achieve higher-quality sustainable development. The recycling of waste heat in the iron and steel industry is of great significance to reducing carbon emissions. Aiming at the problem of insufficient utilization of gas in iron and steel industry and the development of seawater desalination industry, a water-electricity cogeneration and thermal membrane coupling technology is established. Low-temperature multi-effect distillation seawater desalination device is directly connected with steam turbine generator, which uses gas to generate electricity. After generating electricity, negative pressure exhaust at the end of steam turbine is used for seawater desalination. The thermal efficiency of the system is increased to over 80%, the waste heat is effectively utilized, and the carbon emission in the thermal desalination process is reduced. At the same time, the high-efficiency removal and resource utilization of salt in concentrated seawater are realized. The recovery ratio of freshwater is over 55%, the salt content of freshwater is below 500 mg/L, and the salt content of seawater concentrated by membrane method can reach 79,450 mg/L. A new comprehensive utilization and recycling system of seawater has been constructed to realize efficient recycling of energy resources and promote the development process of carbon emission reduction.

Capacity optimization of renewable energy microgrid considering hydropower cogeneration

This paper proposes a renewable energy system based on photovoltaic power generation, wind power generation and solar thermal power generation, combining thermal power plants with low-temperature multi-effect distillation. Through the electric heater and the thermal storage system photovoltaic and wind power will spare capacity in the form of heat energy, at the same time by thermal power generation system to maintain the stability of the power supply, run under constant output scheduling policy, to the levelling of the smallest energy cost and the design of power rate of maximum satisfaction as the goal, using multi-objective particle swarm optimization (PSO) algorithm to find the best combination of capacity, this system is established. At the same time, combined with low-temperature multi-effect distillation, compared with reverse osmosis seawater desalination cost is lower, reduce energy consumption, has a good application prospect.

Simulation investigation on performance of a power–water cogeneration system coupled with a two-stage thermal vapor compressor

The shortage of freshwater resources is becoming increasingly serious. A thermal power plant coupled with a low-temperature multi-effect distillation seawater desalination (single-stage thermal vapor compressor (TVC)) has been widely used. To reduce the water production cost effectively, a two-stage TVC is proposed in this study. The simulation work for the system performance under single- and two-stage TVC is analyzed. Results show that the performance of the system coupled with the two-stage TVC is superior under most conditions, and an optimal intermediate pressure (16 kPa) of the two-stage TVC is found for minimum coal consumption. When the power plant load is higher than 70% THA, the cogeneration system performs well, and the motive steam of the two-stage TVC comes from extraction point No. 5. Otherwise, the motive steam that comes from extraction point No. 4 is a suitable choice. The maximum coal consumption reduction value is 1.48 t/h. To deal with the low operation load of power plants in China, 60% THA load of power plant is a suitable choice for two-stage TVC of power-water cogeneration system.

Pilot testing of a novel Multi Effect Distillation (MED) technology for seawater desalination

This work presents an improved evaporator design of the Multi Effect Distillation (MED) to minimize the thermal losses and footprint of the evaporator. An advanced modular MED pilot plant has been installed with a nominal capacity of 25 m3/day to validate the concept under a seawater salinity of 57,500 ppm (Dukhan Coast, West of Qatar), at the top brine temperature of 65 °C. Both the pilot testing and the simulation results confirm the features of the novel design of the MED. By implementing this invention's design, the heat transfer area has been decreased and accordingly, the capital cost of the evaporator is reduced by 20%. The tube arrangement with new vapor route allows the removal of the traditional demister, which accordingly reduces the footprint of the desalination plant by 65%. The sieve tray for spraying the seawater over the rectangular and inline tube bundle creates a uniform wettability. The improved design also discloses the utilization of an online vent water-ejector, for vent out of the non-condensable gases (NCGs). The novel evaporator design based low temperature MED technology, shows a potential solution for the industrial applications of high salinity byproduct and solar desalination.

Research on Key Technologies of Ocean Thermal Desalination

Due to the process of urbanization and industrialization, the crisis of freshwater resources has become a problem to be solved by mankind. Although the traditional low-temperature multi-effect distillation method, multi-stage flash evaporation method and reverse osmosis membrane method seawater desalination currently occupy the mainstream position [1], Low-temperature multi-effect distillation method brine evaporation temperature cannot exceed 70 °C, reverse osmosis membrane method has the characteristics of high requirements for seawater pretreatment, and multi-stage flash evaporation method has the defect of high energy consumption. Therefore, ocean temperature difference can be used as a renewable energy source. Due to the huge reserves, about 10TW (10x1012W) that can be developed and utilized in the world is recognized by the international community as one of the most potential energy sources[2]. This article first describes the significance of the development of ocean temperature difference energy and the current research status of ocean temperature difference energy seawater desalination; secondly, it takes the ocean temperature difference energy seawater desalination method as the research object, based on the technical difficulties of ocean temperature difference energy seawater desalination and the process of the seawater desalination method that reduces the temperature difference. Four aspects put forward the main factors to improve the performance of the system; finally, it is concluded that the transformation of the key technological achievements of the ocean temperature difference energy seawater desalination method will provide more energy-saving, environmentally friendly, and more efficient for the comprehensive development and utilization of marine engineering, offshore oil drilling platforms, and islands. High-quality freshwater resources.

Assessment of organic Rankine cycle configurations for solar polygeneration orientated to electricity production and desalination

This work addresses the polygeneration concept integrating concentrating solar power (CSP) with an organic Rankine cycle (ORC) to produce electricity and drinking water by hybrid desalination process combining reverse osmosis (RO) and low-temperature multi-effect distillation (LTMED). Experiments carried out on a bench scale RO pilot led to determine optimal operating parameters as well as options to mitigate the main limiting factors of this technology by hybridizing with LTMED. These data helped to simulate a large scale solar polygeneration plant integrating parabolic trough collectors as CSP technology and a hybrid RO-LTMED system as desalination technology. Various ORC design proposals were simulated and the optimal configuration was pointed out on the basis of thermodynamic criteria (energy efficiency and exergy destruction) and an economic analysis by using two working fluids: an alkane commonly admitted as good candidate and an ester proposed here as green alternative. Results obtained in this work contribute positively to extending the solar polygeneration for desalination and production of energy leading to future sustainable plants.

Pitting and crevice corrosion evolution characteristics of 2205 duplex stainless steel in hot concentrated seawater

The pitting and crevice corrosion behaviors of 2205 stainless steel were studied in the concentrated seawater at 72 °C, i.e., the simulated low-temperature multi-effect distillation environments, during 11,550 h of immersion by using electrochemical measurement techniques and surface analysis methods. The corrosion evolution successively shows passive, transient, and active corrosion stages. In comparison with the non-creviced specimens, the creviced specimens show insignificant difference in the corrosion potential, but the much lower polarization resistance values in the whole immersion process and shorter induction time for the transition of passive to active state. Crevice corrosion is easier to occur than pitting corrosion in hot concentrated seawater. The corrosion depth is deeper for the crevice than the pits, but is still very shallow. The pitting and crevice corrosion changes from charge transfer control to mixed control of charge transfer and diffusion process in the long-term immersion conditions. The diffusion process dominates the crevice corrosion since about 10,200 h. The ferrite phase dissolves preferentially in the crevice.

Optimization of parallel/cross flow multi-effect desalination system with flue gas pre-heating considering thermo-vapor compression coupling

To reduce the energy consumption of low-temperature multi-effect distillation (LT-MED), a new scheme was proposed by combining the thermo-vapor compression (TVC) and utilizing the low-grade heat of flue gas in the thermal power generating unit for feed brine preheating. For further improvement, the concept of the mass fraction is especially proposed and considered. Taking the gained output ratio (GOR) and water production cost as the objective functions, the effects of temperature difference, TVC positions were investigated by thermodynamic and economic analysis. The optimal effect number was selected for the LT-MED system under the lowest investment. The results indicated that GOR increased and the water production cost decreased with the backward movement of TVC. The lowest water production cost was obtained under the conditions that N = 5 and TVC was at the 4th effect with the mass fraction Rmf is 0. Thermodynamic, economic, and exergy analysis was performed on the selected systems and the control group. It was concluded that the new proposed system was superior to the others in both the water production and the water production cost. GOR increased from 9.67 to 10.94 and the water production cost fell from 3.13 $/m3 to 2.84 $/m3.

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.

Technical assessment of LNG based polygeneration systems for non-interconnected island cases using SOFC

Liquefied Natural Gas (LNG) is one of the most promising fuels with high calorific value and low specific GHG emissions that offers several advantages as an energy carrier for power generation. In this paper, a novel polygeneration concept based on LNG fired plant for power, cooling and drinking water production in island systems is presented. Two Solid Oxide Fuel Cell based energy systems (one simple SOFC and another hybrid concept of SOFC combined with GT) are modelled in Aspen Plus and compared with two conventional combustion based technologies (internal combustion engine and Gas Turbine Combined Cycle) in terms of overall efficiency. Furthermore, a Low Temperature Multi-Effect Distillation (LT-MED) plant was modelled and coupled with the energy systems to evaluate the waste heat recovery potential for desalinated water production. Moreover, three concepts for cold recovery from the LNG regasification plant were presented and modelled. Process simulations results revealed that the hybrid SOFC-GT plant is the best solution in terms of energy efficiency and the heat recovery of the exhaust gas in a LT-MED unit is a promising option for drinking water production with almost no energy cost. Last, from exergetic point of view, the cryogenic energy storage (CES) via the production of liquid air was evaluated as the best option for waste cold utilization during LNG regasification.

Combined concentrated solar power plant with low-temperature multi-effect distillation

This study analyzes a technological concept for simultaneously generating power and desalinating water in a Middle East and North Africa country. An innovative, low-temperature, multi-effect desalination (LT-MED) process integrated with a concentrating solar power (CSP) plant was assessed and analyzed. A combined power and seawater desalination plant was modeled for the city of Aqaba by the Red Sea in Jordan. Parabolic-trough collectors using indirect steam generation with thermal energy storage connected with power and desalination blocks were designed. The designed plant was modeled and simulated using EBSILON Professional, a discrete energy balance simulation software, under several operating conditions, to analyze the results. An economic feasibility analysis of the combined CSP+LT-MED plant was also conducted. The simulation results showed the broad variability of the cogeneration system in terms of electricity generation and water production. The output power of the CSP plant without water production reached 58.7 MWel in June. The output power accompanied with distilled-water production with a mass flow rate of 170 m3/h was approximately 49.5 MWel. Furthermore, the number of desalination stages had the strongest influence on distillate production but limited the operational flexibility of the power plant due to the temperature gradients within the desalination stages. The distilled-water mass flow reached 498 m3/h for 10 stages. The research showed that the design successfully worked with up to €78.84 million, earned from selling the produced electricity. However, owing to highly subsidized water tariffs in Jordan (80% less than the actual cost), the integration of water desalination into the CSP plant was not economically feasible.

Pitting corrosion resistance of sensitized type 2205 duplex stainless steel in hot concentrated seawater

Pitting corrosion resistance of 2205 duplex stainless steel aged at 850 °C was investigated in the hot concentrated seawater (i.e., the simulated low-temperature multi-effect distillation environment) by optical microscopy (OM), scanning electronic microscopy (SEM), and electrochemical measurement techniques. The precipitation of the σ phase leads to sensitization in the specimens during the aging treatment. The degree of sensitization (DOS) presents a maximum value with the change of σ phase content. The pitting corrosion resistance of the specimens degrades markedly in the presence of very weak sensitization. The pitting potential decreases almost linearly with the logarithm of DOS. The pit propagation mainly takes place along the Cr-depleted region around the σ phase. The repassivation ability of the specimens changes insignificantly with the aging time.

Peak shaving performance of coal-fired power generating unit integrated with multi-effect distillation seawater desalination

The peak-load regulation of a coal-fired power plant is critical to promote renewable energy power generation in grid systems. A low-temperature multi-effect distillation (LT-MED) was proposed to improve the dispatchability of a 600 MW coal-fired power generating unit; here, an unsteady thermal system model was established using the Ebsilon software to study peak shaving capacities. The results show that the increased extraction amount and pressure will reduce the power generation and increase the coal consumption. The peak shaving capacity curve was obtained based on the extraction amount. It is indicated that the peak shaving capacity can reach a maximum of 477 MW when the amount of steam extraction is less than 238 ton/h. When the amount of extraction is sufficiently large, the exhaust steam from the low-pressure turbine attains the minimum allowable value, the peak shaving capacity of the unit then sharply decreases. The dynamic response of an LT-MED system to the step variation of the output load of the power generating unit was also revealed. Moreover, the power generation and coal consumption are slightly influenced by the steam consumption in a single LT-MED system. The maximum extraction of the unit can afford a maximum of 19 LT-MED systems. The results of this study will provide a useful reference for the peak shaving of coal-fired power generating units.

Sustainable desalination process selection: Decision support framework under hybrid information

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

Research on phenol wastewater treatment by low-temperature multi-effect distillation combining with super-critical water oxidation

Based on the mechanism of low-temperature multi-effect distillation combining with super-critical water oxidation (LT-MED&SCWO), a system that disposes phenol wastewater is introduced. Establishing a process of four-effect forward feed LT-MED concentrated phenol waste-water and a SCWO degradation of phenol by Aspen Plus software is essential to compare the effects of in-feed phenol mass concentration, system concentration ratio on phenol concentration ratio and mixing temperature of reaction required for degradation. The study shows that with the increase of in-feed phenol mass concentration, phenol concentration ratio keeps almost constant, 97.7%, but, preheating temperature of the concentrated water decreases when the final product mass phenol concentration is less than 0.5ppm; when system concentration ratio increases, phenol concentration ratio decreases from 99.5%to 96.7%and preheating temperature of the concentrated water also decreases when the final product mass phenol concentration is less than 0.5ppm.