Low Temperature Multi-effect Distillation Plants Research Articles

Comprehensive corrosion failure analysis of HAl77-2 alloy tubes serving in a low temperature multi-effect distillation plant: From feature analysis to corrosion mechanisms

Premature perforation and leakage of HAl77-2 alloy heat exchanger tubes occurs after 2.5 years of service in the largest low temperature multi-effect distillation (LT-MED) plant in China. The root reasons of perforation and leakage of tubes were investigated through macroscopic morphology, chemical composition, metallographic structure, seawater quality, flowing simulation and microstructure characterization. The results show that the HAl77-2 alloy tubes with perforation leakage meet the standard requirements. And the failure of the tubes was mainly attributed to the synergistic effect of serious pitting corrosion and stress cracking caused by the high fluid pressure and polluted seawater with Fe2+/Fe3+, sulfide and NH4+. Especially, the velocity and pressure spatial distribution of liquid film on the outside of horizontal tubes well verified the interesting observation that corrosion pits concentrating in one strip on the top of the tube. Moreover, corrosion mechanism was proposed that the loose corrosion products of Cu2S, FeS and Cu2(OH)3Cl lead to the formation of some defect points on the homogeneous protective Cu2O layer. For these defect points, the direct expose of the alloy matrix to corrosive substances such as Cl− and NH4+, significantly accelerates the dissolution of Cu in form of CuCl2− and Cu(NH3)2+ from the alloy. Finally, the tube occurs pitting corrosion and even perforates under the strong hydraulic erosion after long-terms of operation.

Flash recovery system analysis and flashing tank optimization in desalination plants

This study established and calculated the flash system model of 7-effects low-temperature multi-effect distillation (LT-MED) system with an installed capacity of 4500 m3/d. The calculation results showed that the brine and distillate flashing accounts for 6.0% of the total water production, which indicate the significant effect of such flashing heat recovery system. Furthermore, a three-dimensional simulation of water–vapor flow in the flashing tank of a LT-MED plant was conducted by using a FLUENT CFD code coupled with a user-defined function. The factors related to the flash efficiency, including flashing tank diameter, length, and internal platform height, were simulated and analyzed. Finally, an improved scheme for setting a platform inside the flashing tank was proposed. The simulation results revealed that the improved scheme ensures the sufficient flash of water inside the tank. These finds of the present study can serve as a reliable reference for the design of flashing tank in LT-MED plant.

Analysis and optimization of LT-MED system powered by an innovative CSP plant

The access to drinking water is an increasing problem in the World in many geographical areas. The desalination of seawater is the main source to provide fresh water. The thermal desalination systems such as Low Temperature Multi-Effect Distillation (LT-MED) have gone through many stages of development to increase the energy efficiency of this system: this technology uses steam as part of its process to produce fresh water. Some improvements on the thermal desalination processes have resulted in less energy consumption. In order to further increase the energy efficiency in the desalination plants, renewable energy sources should be considered and evaluated in order to satisfy the worldwide demand of this technology. This paper presents an LT-MED system integrated with a novel Parabolic Trough Concentrated Solar Power (PT-CSP) plant whose reference cycle is called DEC, Discrete Ericsson Cycle which uses air as heat transfer fluid. This study explores the use of the waste heat in CSP-DEC plant to feed an LT-MED technology. It also discusses the plant layouts and performances of CSP-DEC+LT-MED plant. Because CSP-DEC can perform steam supply for LT-MED with less affecting on the electricity generation efficiency, CSP-DEC can optimize to lower energy loss than conventional CSP, while still producing larger quantity of fresh water.

Integration between concentrated solar power plant and desalination

AbstractFresh water and electricity production in desert areas via the use of solar radiation represent examples of sustainability. The concentration of solar power by means of parabolic trough (PT-CSP) technology has a great potential not yet exploited in the realm of renewable energy production. A new technology for the solar energy section is being proposed by the authors which uses air as a working fluid. The use of air allows the cycle to be coupled with an inter-cooled compression section and a re-heated expansion section which is called Discrete Ericsson Cycle, (DEC-based plant). The paper presents an integration of such a CSP-DEC plant with desalination: where freshwater is produced according to a Low Temperature Multi Effect Distillation (LT-MED) technology. The LT-MED plant operates on the heat from the air coolers in the inter-stage cooling of the DEC-based plant. This heat is normally expelled to atmosphere. In fact, the heated air has the same temperature ranges required for the operation of ...

EFFECT OF TEMPERATURE AND CONCENTRATION RATIO ON PITTING RESISTANCE OF 316L STAINLESS STEEL IN SEAWATER

Due to a serious shortage of natural fresh water in many areas all over the world, the seawater desalination has emerged as an effective compensation way to meet the consumption requirements. Due to the good corrosion resistance and low cost, stainless steels have been used extensively to construct the multi effect distillation(MED) plants, especially type 316L stainless steel for the evaporation chambers. However, with the application and development of low temperature MED, there is increasingly need of higher temperature distillation and higher brine concentration in the desalinators to reduce the drainage of hot brine and increase the water production ratio, which may cause more serious corrosion on the stainless steel components in the plants. Pitting corrosion of 316L stainless steel was studied in the concentrated environments of seawater with different temperatures(25, 50, 63, 72, 85 and 95 ℃) and concentration ratios(1, 1.5, 2, 2.5 and 3 times) by using cyclic anodic polarization measurement and SEM surface observation. The results show that both pitting potential and repassivation potential of 316L stainless steel decrease linearly with temperature in the concentration ratio range of 1 to 3 times for seawater, but the change of pitting potential is very slight when the solution temperature is higher than 85 ℃ in the case of concentration ratio larger than 2 times. Both pitting potential and repassivation potential reduce linearly with the logarithm of the concentration ratio of seawater in the range of 25 to 95 ℃. It is apparent that increasing temperature and concentration ratio of seawater will deteriorate the pitting resistance of 316L stainless steel noticeably. The influence of temperature and concentration ratio is analyzed on the basis of the point defect model. Nevertheless, the concentration ratio of seawater has a weaker influence on pitting resistance of 316L stainless steel in comparison with temperature as revealed by the pitting potential changes resulted from the concentration ratio around 1.5 times and solution temperature around 72 ℃. Therefore, compared with temperature, the corrosion resistance of 316L stainless steel for low temperature MED plants may be relatively tolerant of the adjustment or fluctuation of seawater concentration.

Evaluation of cooling technologies of concentrated solar power plants and their combination with desalination in the mediterranean area

Different alternatives for the effective integration of desalination technologies in the cooling of concentrating solar power (CSP) plants in the Mediterranean area are discussed and evaluated. Two cases are considered where a low temperature multi-effect distillation (LT-MED) plant is integrated into a CSP plant replacing the condenser of the power cycle. In one case, a LT-MED plant is fed by steam at the outlet of the turbine expanded to 70 °C. In the other case a LT-MED is fed by the steam obtained from a thermal vapour compressor (TVC) which uses the exhaust steam of the CSP plant (at 37 °C, 0.063 bar) together with some from the high pressure turbine extraction (17 bar). The two cases are compared with that of a reverse osmosis (RO) unit powered by the electricity produced by the CSP plant. In this case, two different wet cooling technologies, once-through and evaporative water cooling, and a dry air cooling are considered for the CSP plant. Thermodynamic simulations are presented for all cases, together with an economic analysis.

Evaluation of technologies for a desalination operation and disposal in the Tularosa Basin, New Mexico

According to the United Nations Environment Programme, one-third of the world's population lives in a situation of water stress. In the case of New Mexico, about 90% of the 1.8 million inhabitants depend on ground brackish water as their only source of potable water in many areas of the state. This report presents a technically-supported, economically-feasible and environmentally friendly proposal to desalinate brackish water to supply potable water to inland, isolated communities in southwest New Mexico. Several existing technologies were reviewed to identify opportunities for optimization by combining them to provide potable water and reduce the waste stream. Alternatives were studied and experimentation was conducted for some of them. The alternatives proposed were the use of natural coagulants for pretreatment, various solar collectors' arrangements for energy supply, reverse osmosis (RO), low temperature multi-effect distillation (LT-MED), multi-stage flash distillation (MSF), solar distillation (SD), and electrodialysis for desalination process; Spirulina cultivation and SD for waste treatment, and deep well injection (DWI) for waste disposal. Some alternatives were eliminated because they are either technologically or economically not feasible for this case and present high environmental impact. Three plant configurations were analyzed. Option A involves using the linear Fresnel systems (LFS) to produce steam for the first effect of a nine-effect evaporation plant. The number of effects was determined to achieve the optimal relation between equipment investment costs and steam production cost. This plant operates 8 h per day with solar energy and the rest of the 24 hour operating time is provided with fossil fuels. The waste produced will be further evaporated with SD to minimize its flow and the concentrated brine will be injected into a deep well. Option B has the same elements as option A, except that it does not consider the SD, but direct brine injection into a deep well. Option C considers the use of SD as the only process for distillation with DWI as the waste disposal method. The selection criteria for the best configuration were optimal use of solar energy resources, minimization of fossil fuel consumption and waste stream generation and disposal. Operation requirements and economic analysis were considered to select a proposal easy to implement and operate in rural isolated communities. For the following reasons option A is the best configuration to cover the necessity of potable water in New Mexico: (A) the plant is easy to construct and operate. In addition, it can handle different ranges of brackish water flow. (B) The 76% water recovery of the system almost matches the recovery achieved in a RO plant (80%), with the advantage that maintenance costs are reduced and treatment flowrates cannot be matched by the RO plant. (C) Use of the LFS reduces the emission of combustion gases to the atmosphere by 33%. This manifests as a positive point in a LCA evaluation. (D) The minimum environmental impact of the process facilitates the public involvement plan (PIP) because it gives the plant an environmentally responsible image in terms of avoiding greenhouse gases emissions. (E) The return on investment (ROI) is 10.2% at a price of $5.00/m 3 of desalinated water, which is superior to the estimated minimum attractive rate of return (MARR) used for LT-MED plants as 9.5% annually.

Low temperature, multi-effect distillation for cogeneration yielding the most efficient sea water desalination system

IDE Technologies Ltd. (IDE) has commissioned in March 1988 and in July 1990, two 10,000 tons per day low temperature multi-effect distillation (LT-MED) plants each linked to a low pressure 3.1 MW turbine (as a replacement to an aging MSF plant), demonstrating a total specific energy consumption of below 5.0 kWh per ton of desalinated water. During the last four years IDE has also commissioned three smaller LT-MED plants, 1200 to 2200 t/d, utilizing exhaust waste heat of diesel generator power stations with a total net specific power consumption of only 2.5 kWh per ton of desalinated water. This paper describes the process principles of the LT-MED plants that made these achievements possible. Also, a description of the Curacao, 2×10,000 t/d and the Ebeye, 1,100 t/d MED plants will be given.