Sea water desalination by reverse osmosis in chigasaki laboratory

For the purpose of constructing a reverse osmosis [RO) sea water desalination plant of 800 m³/day capacity, a series of tests on the following themes have been carried out in the Chigasaki Laboratory:

1. Performance and durability of 8B modules made in Japan

2. Simplification of pretreatment system

3. Establishment of energy recovery system.

Domestic modules showed good and stable performance during long term operation, and water recovery ratio of these modules have been raised to 40%.

In-line coagulation and filtration system has been established for the pretreatment of feed sea water, instead of coagulation, sedimentation and filtration system.

The energy recovery equipment is consisted of a high-pressure pump, a motor and a hydraulic turbine on a common base. Recovered energy from pressurized brine is used for the auxiliary motive power of the high-pressure pump. The experimental data show that about 20% of required power for the pump was recovered.     

RO membrane autopsy of Zarzis brackish water desalination plant

Tunisia, located in a semi-arid zone, has limited water resources. The shortage of good water quality in particular at the south regions required a brackish water desalination to supply these regions with potable water. Zarzis desalination plant, working since 1999, has revealed difficulties related to the loss of membrane performances. In the aim to determine the reason of membrane fouling, foulant layer were analysed. The membrane autopsy has achieved by different methods, such as TOC (total organic carbon) measurement, SEM (scanning electron microscopy), AFM (atomic force microscopy), FTIR (fourier transform infrared spectroscopy) analysis, diffraction by X-ray. Results show that the foulant layer composed mostly of SiO₂, clay, organic matter (polysaccharide, protein), CaSiO₃, Fe₃O₄, AlPO₄, and CaSO₄. The characteristics bonds obtained by IR indicate the presence of polysaccharides and proteins that constitute a source for further microbiological growth; this is the problem of biofouling. The metallic elements results of corroded stainless steel and internal coating of cartridges filter that are damaged by the silica particle rejected by sand filters. The scale of CaSO₄ and CaSiO₃ deposition is owing to the bad antiscaling efficiency. The results are presented and discussed in the light of new trends in material.     

Characteristics of RO foulants in a brackish water desalination plant

This study identified the membrane fouling of a two-stage RO process of the Bai-sha brackish water desalination plant facing serious fouling problems. Two membrane modules, one from each stage, were autopsied and diagnosed for the cause for the failure of the RO system. Different morphologies were exhibited on the fouled membrane. Results suggested that the fouling on the first-stage membrane tended to be organic and biological, while that on the second-stage membrane appeared to be scaling. Higher than 85% of the foulants on the first stage membrane were organic substances in opposed to the 5 to 8% of those on the second stage membrane. However, the total organic matter on the second stage membrane was more than that on the first stage one. The thick layer of scalants on the surface of the second-stage membrane was identified to be calcium carbonate of which the crystal was clearly seen in the SEM images. The scaling was thickest at the outlet of the membrane. Huge amount of microbes were found on both membranes. The FTIR results also suggested the existence of extracellular polymeric substance (EPS) on the first stage membrane. This study recommended that the recovery rate, pH and the potential for bio-fouling should be defined at the real operation.     

反渗透海水淡化膜法预处理技术研究进展

简要论述了反渗透海水淡化的各种新型膜法预处理技术研究进展情况及其在国内外的具体运用情况,内容主要涵括连续微滤技术(CMF)、浸没式帘式膜过滤、超滤技术、纳滤技术以及陶瓷膜过滤.并指出膜法预处理将成为今后反渗透海水淡化预处理的主要发展方向.     

Reliability of the jeddah seawater RO desalination plant based upon operations experience

Demand on commercial RO seawater desalination plants can be assured with increase in reliability and with high levels of performance. Such improvements can best be achieved through “lessons learned” from experience gained in available RO systems such as the large Jeddah RO plant.In this study, critical components which affect plant performance have been identified and methods of improving the design have been recommended. Failure data has been extracted from operation and maintenance reports.An assessment is made of the impact of failures and outages on the availability of the RO desalination plant. The single largest influence on the effective capacity of a water supply system based on RO desalination of seawater is found to be plant availability and maintainability. The design configuration of the plant is also found to have an impact on the acceptability of water supply system performance.     

Long term experiments on sea water desalination at the Chigasaki Laboratory

The technology of producing fresh water from sea water by the reverse osmosis (RO) process has been developed since 1974 under the supervision of the Ministry of International Trade and Industry. Highly satisfactory and stable performances have been recorded for the two-stage desalination process using RO modules developed in Japan. Durability of the membranes under testing is expected to last more than three years. The quality of the product water can be kept below TDS 200 ppm that is suitable for potable consumption. Construction of a demonstration plant of 500 m³ /day using domestic modules is now being planned.     

Low-pressure RO membrane desalination of agricultural drainage water

Agricultural drainage water is a complex mixture of dissolved and suspended chemical species and may contain a wide variety of microorganisms. The application of membrane systems for desalination of agricultural drainage (AD) water requires careful consideration of feed water quality, suitable membrane selection and operating conditions. In order to evaluate the potential applicability of low-pressure reverse osmosis (RO) to the treatment of AD water, a diagnostic approach to membrane selection and process evaluation was undertaken in support of a pilot field study in the California San Joaquin Valley. Five candidate membranes were evaluated in a diagnostic laboratory membrane system which provided an initial selection based on salt rejection and product water flux performance for model salt solutions of univalent and divalent cations. Biofouling potential of the selected membranes was also evaluated using two standards strains of bacteria. Preliminary pilot plant performance, based on the selected membranes, was encouraging and has provided the basis for long-term pilot plant testing at higher recoveries to assess the impact of fluctuating AD water feed composition.     

Operating experience of desalination units in Schevchenko

The paper discusses the main disign and process features of desalination units of three types built at the largest in the USSR system in Schevchenko and operated at the atomic thermoelectric fast reactor plant. Data are also presented on the experience gained in operation of natural and forced circulation evaporators, adjustment of specially designed circulation pumps and initial sea water cleaeration, impronement of non-condensing gas removal system and method of preventing scale from depositing in regeneration heaters through carbon dioxide stabilization of sea water and in evaporators through the introduction of chalk.     

Control and instrumentation experience at Lok on pai MSF seawater desalination plant

Discusses most critical measurements in multistage flash seawater distillation plants; pH and dissolved oxygen in feed and their associated control systems and the continuing acquisition and evaluation of corrosion data. The use of central processor to aid evaluation of date is described and practices recommended to enhance performance and security are given.     

Operating experience of the Dhekelia seawater desalination plant using an innovative energy recovery system

Dhekelia Desalination Plant in Cyprus has been in operation for 7 years. It includes eight 5,000 m³/d seawaterreverse osmosis trains operating with Mediterranean seawater with a TDS content of 41,800 ppm, with water temperature ranging from 17°C to 32°C. The energy recovery system originally installed at the plant is the Francis turbine, which, at the time, was considered one of the most efficient and economical devices on the market. Since then, however, market forces to reduce operational costs, by cutting down energy consumption, led to the advent of new energy recovery systems. Today several systems are in operation which reduce the RO energy consumption. Apart from the versions of the Francis turbine and Pelton wheel they include the hydraulic turbocharger, work exchanger and pressure exchanger, all harnessing the pressure energy of the brine. In our effort to be competitive for the years to come we decided to convert our existing energy recovery system from Francis turbines to the pressure exchanger. This paper outlines how it was decided to go ahead with the pressure exchangers, and gives comparisons with other energy recovery methods, and describes our operating experience with the pressure exchangers.     

Investigation on sea water desalination plants in Spain

The main desalination research and development programs and the demand for fresh water on the Spanish coasts are outlined. The experimental plants of the Moncloa (Madrid) (MSF, vapor compression, reverse osmosis and others) and their computer programs are described as are also the pilot plants of Lanzarote (Canary Islands). The close collaboration between private enterprise and the Spanish Government is discussed.     

Operating experience and performance data of an advanced barge-mounted VTE/VC seawater desalination plant

The floating desalination demonstration plant “MEDA” presents an advanced concept to produce fresh water from seawater with low energy consumption. At first step of ts demonstration phase, MEDA was operated at Helgoland in the North-Sea at its design capacity of 5000 m³/day and a performance ratio of 22 to 1 kg/kg. The 24 effect VTE evaporator combined with two vapor compression topping effects operated at a max. feed temperature of 135 °C with sulphuric acid pretreatment. High heat transfer rates were obtained using foamy upflow in double-fluted evaporator tubes without inter-effect pumps. Data were obtained for an alternative pretreatment system for feed make-up using a fluidized bed ion exchanger system operating in the countercurrent mode. Calcium ion content in the feedwater was demonstrably reduced by more than 90 %. This paper presents and analyses the above performance results.     

Energy-saving electro dialyzer for sea water desalination

Tokuyama Soda Co. ltd. has developed an energy-saving skid mounted electrodialyzer for sea water desalination. This equipment is suitable for making fresh water for drinking and industrial use. To desalinate 25°C sea water and turn out one ton of product water. This equipment consumes only 8.5 KWH of electricity and 0.09 Kg of concentrated sulfuric acid. Low energy consumption is achieved by adoption of low electric resistance membranes, new spacer and new designed one pass type system. Low running cost, easy maintenance and low initial installment cost place the equipment good position in the desalination field. And also we applied high temperature electrodialysis up to 50°C of sea water and get figure 6.0 KWH for one ton of product water.     

Systems analysis of a multi-stage tubular module reverse osmosis plant for sea water desalination

A tubular reverse osmosis system for sea water has been analyzed based on current cellulose acetate membrane technology. The possibility of staging product water in two and three stages has been studied. A dynamic programming model is developed and solved to arrive at optimum operating parameters for the two-stage and three-stage designs.A variable membrane permeability model is used to simulate operating conditions along the tube length within a stage, to arrive at optimum membrane curing temperatures. Actual performance data from UCLA's experimental plant at La Jolla, California was used. Cost analysis and equations are derived from actual costs incurred at La Jolla.     

Operational water cost and productivity improvements for small-size RO desalination plants

This detailed study was carried out for the determination of the water cost in small size RO desalination plants in remote areas. Data from desalination plants in three Greek islands were used for a period of three years. The actual expenses for these plants were examined thoroughly and as a result the real cost per cubic meter was estimated. An evaluation of the efficiency of two different energy recovery systems was conducted by using factual operating data. The introduction of new technologies, automation, data acquisition and remote operation can be used to reduce the labor and maintenance cost for small size RO desalination plants. The increase in labor productivity has proved to be the direct result of the introduction of a low cost SCADA system to the RO plant.     

Exergy analysis of a combined RO, NF, andEDR desalination plant

A brackish water desalination plant in California that incorporates RO, NF, and EDR units was analyzedthermodynamically using actual plant operation data. Exergy flow rates were evaluated throughout the plant, and the exergy flow diagrams were prepared. The rates of exergy destruction and their percentage are indicated on the diagram so that the locations of highest exergy destruction can easily be identified. The analysis shows that most exergy destruction occurs in the pump/motor and the separation units. The fraction of exergy destruction in the pump/motor units is 39.7% for the RO unit, 23.6% for the NF unit, and 54.1 % for the EDR unit. Therefore, using high-efficiency pumps and motors equipped with VFD drives can reduce the cost of desalination significantly. The plant was determined to have a Second Law efficiency of 8.0% for the RO unit, 9.7% for the NF unit, and 6.3% for the EDR unit, which are very low. This indicates that there are major opportunities in the plant to improve thermodynamic: performance by reducing exergy destruction and thus the amount of electrical energy supplied, making the operation of the plant more cost effective.     

Seasonal fouling on seawater desalination RO membrane

A pilot study has been performed to investigate the seasonal characteristic of seawater reverse osmosis (RO) membrane fouling. Two batches of experiment during summer and winter were both performed 18 days to provide a clear picture on microbial population variability. The feed water of the pilot from seawater desalination plant has significant difference in temperature and silica content between the two seasons.In our experiments, scaling and biofouling are more serious in summer. And the permeate flux decline is closely related to the rise in microbial population, and it was dominated by cell multiplication rather than adhesion. In addition, the summer cell multiplication is much more abundant. Moreover, the extracellular polymeric substance (EPS) feature intensity detected by Fourier-transform infrared spectroscopy was also stronger in summer. The abundant EPS was one of the major reasons to cause the inorganic matter adsorption. Si, Al, Fe, Ca and Mg were found as the major inorganic foulants deposited on the Ro membranes. Silica and calcium in summer appeared obvious higher amounts than that in winter, which indicated that they should be affected by microbial action directly or indirectly more than other elements.In summary, there exists a seasonal effect on membrane scaling and fouling, and scaling is associated with biofouling in some degree. Further researches could be focus on actual association between microbial action and inorganic fouling.     

Investigation of heat exchange during sea water boiling in a horizontal thin film desalination plant

This paper describes the characteristic features of heat exchange during sea water boiling in a thin film on the heated surface of tubes with outer diameters of 16, 24, 32 mm over a wide range of heat fluxes, film loadings, pressures and initial sea water concentrations.On the basis of experimental data, we found two areas of flashing whose transient value is defined by q'. We obtained the equations for minimum and maximum film loadings and correlated the variables for heat transfer coefficient calculation.     

Thermal desalination of sea water in thin film-plants

The paper deals with several types of thin film desalination plants with vertical and horizontal heating surfaces. Data on the characteristic features of heat exchange during boiling of sea water in such plants are given. Some equations describing performance characteristics of the plants are provided.     

短流程反渗透海水淡化预处理试验研究

针对我国沿海水质的特点,开发了集浸没式超滤及絮凝反应为一体的短流程反渗透海水淡化预处理设备,并进行了中试试验。结果表明,处理后产水水质可达到后续反渗透进水要求,SDI15<1%,浊度<0.1 NTU,并可以在33⁴0 L/(m40 L/(m²·h)的高通量下保持6个月稳定运行,可以应用于反渗透海水淡化系统的预处理过程中。