浅除盐水处理技术的应用

从小氮肥厂的应用人手,介绍了浅除盐水处理技术特点.结果表明,该技术在工业锅炉上推广应用,具有安全、经济的效果.     

Enhanced water desalination performance through hierarchically-structured ceramic membranes

Developments of membrane water desalination are impeded by low water vapor flux across the membrane. We present an innovative membrane design to significantly enhance the water vapor flux. A bilayer zirconia-based membrane with a thick hierarchically-structured support and a thin functional layer is prepared using a combined freeze drying tape casting and screen printing method. The hierarchically-structured YSZ support has a porosity of 42.6%, pores of 4.5 μm or larger, and a relatively low tortuosity of 1.58 along the thickness direction. The bilayer membrane is then converted from naturally hydrophilic to hydrophobic via grafting with a fluoroalkylsilane. A water flux of 28.7 Lm⁻² h⁻¹ and a salt rejection of 99.5% are achieved by exposing the functional layer to 80 °C salt water of 2 wt.% NaCl and the support layer to 20 °C distilled water. These results are the best performing ones for ceramic membranes in direct contact membrane distillation operation.     

Continuous capacitive deionization-electrodialysis reversal through electrostatic shielding for desalination and deionization of water

We report a new concept for capacitive deionization with simple and cheap porous bipolar intermediate graphite electrodes which is operated continuously by constant or alternating polarity without any down time for electrode saturation, regeneration and rinsing steps and certainly without any permselective ion exchange membranes. The proposed process utilizes the advantages of the classical electrodeionization technologies combining them all to a unified continuous capacitive deionization-continuous electrodeionization-electrodialysis-electrodialysis reversal process. Separate and unchanged diluate and concentrate compartments are created in two modes, first by periodical charging/discharging the bipolar intermediate electrodes through a pulsating electric field and second by simultaneous charging/discharging them through a constant or pulsating electric field and electrostatic shielding. Because of coion permeation and the convenience of alternating the polarity without any negative impact on the deionization process, the new technique is less affected by the known membrane associated limitation, such as concentration polarization, limiting current density or scaling. The new electrochemical deionization technique is suitable for regeneration of ion exchange resins and production of high purity deionized water, removal of heavy metal ions from industrial effluents and desalination of brackish or seawater.     

Total desalination of brackish water

With desalination of brackish water far inland, the discharge of the concentrated brine which -is -inevitably produced as a by-product by all the desalination processes may pose a serious problem.

Deep well injection and discharge into rivers can be a solution in many cases. These methods however have serious disadvantages with respect to ecology and a pipeline to the sea can only be considered for shorter distances.

As an alternative, a hybrid plant consisting of a Reverse-Osmosis unit and a crystallization section has been studied. Such a combination converts brackish water into fresh water and a crystal sludge which can be either stored or treated for further use. Because of the scale-forming substances in brackish water, only modified crystallization processes can be employed as second stage of the hybrid plant. In this study, two versions are discussed: agitated thin-film evaporators and a modified MSF-process employing oil as a heat-carrier.

Cost figures for the total process will be given and the sensibility of the fresh-water-price to variations of the main parameters like capacity, fuel price etc. will be discussed.     

脱盐水系统问题初探

化肥厂脱盐水装置自建成投产后一直存在着质量、产量、成本等重大问题，生产被动。在对脱盐水系统存在的问题进行了分析后，进行了相应的技术改造，从而降低了生产成本，改善了水质，保障了化肥装置的稳产高产。     

Feed water pretreatment for desalination plants

Effective membrane pretreatment is a crucial requirement for trouble free and cost effective RO desalination. Pretreatment construction costs are significant and may reach as much as 10%-20% of the total desalination plant capital costs. This paper presents a general review of the central factors involved in assessing raw water quality. The main foulant categories are described and the various unit operations commonly applied are reviewed. Pretreatment aspects of desalination offer fertile grounds for advancing desalination technologies. Promising research directions are highlighted.     

Experiments with desalination of Arabian Gulf water

With the “plate-and-frame” reverse osmosis system and a new thin film composite membrane it has been possible to desalt very salty water (43.000 ppm). A minimum of pre-treatment has been necessary, because the membranes are very resistant to pH and temperature, and the flow rate in the plate-and-frame modules is very high. The raw water is pumped directly to the multi-media filter, followed by a 25 micron cartridge filter. The growth of algea and bacteria is prevented by irradiation with UV-light. After the pre-treatment the water is pumped into the modules and desalted. The economy of the process is good, thanks to the high capacity of the membranes and the small degree of pre-treatment.     

The role of desalination in water reuse

If reuse of water is being considered in an area where seawater desalination will be used to produce the basic water source, overall water resource development costs should be considered before selection of the basic desalination process. In cases where the system's wastewater is treated and used for artificial ground-water recharge and recovery, there are inherent benefits in utilizing a thermal rather than a membrane process to produce the basic water source from seawater.     

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.     

Investigation of water desalination by distillation technique

The information is given on the main large stationary desalination units of different types (evaporating, instantaneous boiling) developed in the USSR and used in the design of the largest plant in Shevchenko having the output of 100000 m³/day of distillate; it operates in close interrelation with an atomic thermoelectric БH-350 fast reactor plant and back pressure turbines. Some results are discussed of constantly performed studies into heat transfer, vapour separation, control of scale deposits and corrosion, search for new thermal systems and instruments to be used for the improvement of operating distillation desalination units and development of new ones. Further prospects of thermal desalination are associated with the use of multi-stage units equipped with horizontally-arranged-tube-film evaporators.     

Vertical tube foam evaporation for water desalination

Vertical tube foam evaporation (VTFE) provides a method of enhancing evaporator performance substantially by increasing the brine-side heat transfer coefficient. It reduces the temperature needed to drive evaporation and the energy required; consequently, the evaporation rate or evaporator capacity is increased under constant temperature conditions. VTFE applied to multiple effect evaporators, to evaporation with vapor compression to drive the process and to waste-heat evaporation of aqueous solutions are illustrated by test data obtained with pilot plants operated under realistic process conditions and utilizing full-size distillation tubes.     

Reverse osmosis in the desalination of brackish water and sea water

To make RO an economical process, plant and operating costs have been reduced by developing compact modules, led by polyamide hollow fibre modules which recover energy from the reject when desalinating highly saline brackish water and seawater. Such plants only start to pay their way at product rates of around 400m³ /d +. Energy costs for desalination systems with lower capacities can also be reduced considerably by operating the RO plants at conversion rates of more than 30%. To what extent the required higher conversion rates can be obtained for a particular application depends on concentration of scales-forming content matter (calcium sulphate, strontium sulphate, barium sulphate and calcium carbonate), salt content of the raw water, concentration of fouling substances such as iron, manganese, anorganic and organic matter, risk of biological growth due to algae, shells and bacteria. The scope and type of conditioning and pre-treatment are based on these factors.     

Sea water desalination using glass hollow fibre membranes

Hollow fibre membranes suitable for the two-stage desalination of sea water have been prepared from phase-separable Na₂O-SiO₂-B₂O₃ glasses. The hollow fibres had outside diameters in the range 20 to 200 microns and corresponding wall thicknesses of 5 to 40 microns. The production of fibres from two glasses by means of phase separation, leaching and sintering is described. Using a 3.5% NaCl solution at 120 bars, product fluxes of about 1.0 m³/m²/day at 88% rejection were obtained with fibres of one glass, and fibres of the other glass withstood hydraulic compressive pressures over 200 bars. There was no evidence of compaction or hydrolytic degradation.     

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.     

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.     

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.