Seawater desalination and reverse osmosis plant design

Plant site, water intake, pretreatment, choice of materials of construction, design alternatives and energy recovery are important variables to be considered in the design of seawater desalination plants employing “permasep” B-10 reverse osmosis modules. Techniques are outlined to permit custom design of seawater desalination plants which offer reliable long term performance as well as competitive economics.     

Seawater reverse osmosis—Statement of the art assessment

Considerable time and effort has been spent in developing new membranes and system configurations for Seawater Reverse Osmosis. This has led to reverse osmosis being accepted as a viable method for seawater desalination.     

Influence of temperature and permeate recovery on energy consumption of a reverse osmosis system

A model permits analysis of the influence of temperature on permeate recovery and energy consumption. The proposed model is based on the following assumptions: (1) membrane morphology is temperature-independent; (2) membrane rejection and other transport characteristics of membranes are position-independent; (3) specific water permeability of membranes was based on exponential dependence of viscosity vs. temperature; (4) temperature-dependence depembrane rejection is assumed to be linear. This allows for analyzing the influence of channel geometry, feed concentration, flow rate and temperature on permeate recovery and energy consumption. Calculated data are included. The solutionpresented can be segmented andbuilt into systems for comprehensive techno-economic evaluation of the RO-based process where temperature-dependence of process characteristics has to be considered.     

Distillation and reverse osmosis energy consumption and costs

The paper compares the energy requirements of single and dual purpose MSF distillation with seawater reverse osmosis plant. Energy consumptions are given both as heat and power consumptions for distillation and as power consumption for R.O. To enable a true comparison to be made these inputs are referred back to the heat inputs from fuel needed at the boiler plant or appropriate thermal power plant.Energy recovery is also considered for reverse osmosis and it is shown that the energy input can be expected to decrease by some 35% for a typical example.Although the prime energy input needed for reverse osmosis is shown to be substantially lower than for dual purpose distillation, the overall costs taking account Of capital charges, energy, replacements and other operating costs, are found to be in a band width of about 5% for plants in the range of 5000 to 15000 m³/day. Reverse osmosis plant water costs are significantly less than distillation if membrane life increases from 3 years to 5 years, particularly with small plant capacities.     

Seawater reverse osmosis system projects,a manufacturer's viewpoint

A reverse osmosis desalination system will provide excellent service if care is taken in the design, selection, installation and operation of the system. Precautions should be taken not to overly complicate the design and operation. The environment dictates that the highest quality components should be used. Satisfactory operation is highly dependent upon the experience of the manufacturer and the preparations taken prior to installation and commissioning of the system.     

Considerations of energy consumption in desalination by reverse osmosis

The primary factors affecting the energy consumption of a reverse osmosis plant are considered. These are the osmotic pressure of the feedwater, the feedwater temperature, the water recovery, and the relationship between the water flux and salt flux characteristics of the membrane. In addition, the required permeate quality may have several indirect effects on the energy consumption. Permeate quality standards may impose minimum operating pressures, limit the recovery, and/or require treatment with a full or partial second stage. As a general rule, the energy required increases with increasing feed salinity and increasing permeate quality.For any given recovery, a single stage system will require less energy than a partial two stage system. However, for a specified permeate quality, a partial two stage system can operate at a higher overall recovery and a lower energy consumption than a single stage systemEnergy recovery systems can recover between 50 and 90 percent of the available energy in a reverse osmosis unit, thus significantly lowering the energy consumption. Studies have shown that with an energy recovery system, the minimum energy consumption occurs at a first stage recovery of 30 to 35 percent. Currently, very few energy recovery systems are in use due to their high capital cost, but as energy recovery systems become more available and reliable, they will greatly increase the energy efficiency of reverse osmosis plants.     

Effect of recovery on desalination of the black sea water by reverse osmosis

The effect of fresh water recovery was studied during Black Sea water RO desalination with cellulose acetate tubular membranes. Two different schemes of brine pretreatment before RO were investigated.It was shown that ultrafiltration can be applied as an effective alternative method for Black Sea water pretreatment. Up to 30% recovery, the product flux as well as the salt and the specific ionic rejection are all fairly stable. Special experiments showed that in a stable turbulent regime Ca ions removal from Black Sea water before RO with tubular membranes hold out no technological advantages.     

Techniques for achieving high recovery from saturated water sources using reverse osmosis membranes

In water-short areas of the world there is a premium for extracting the largest fraction possible of usable water from limited water supplies. Likewise in the elimination of wastewater through recycling, there is also a premium for maximizing the recovery of good water from the waste stream.Reverse osmosis membranes are being utilized to accomplish both of these functions. This paper will discuss several approaches for maximizing the fresh water recovery from saturated water sources using reverse osmosis membranes.     

Arsenic removal by reverse osmosis

Arsenic is widely distributed in nature in air, water and soil. Acute and chronic arsenic exposure via drinking water has been reported in many countries, especially Argentina, Bangladesh, India, Mexico, Mongolia, Thailand and Taiwan, where a large proportion of ground water is contaminated with arsenic at levels from 100 to over 2,000 micrograms per liter (ppb). Public health standards of maximum of 50 ppb have been adopted by the US and World Health Organization in the 1970s and the 80s. Carcinogenicity and genotoxicity led to the WHO recommendation of 10 ppb maximum level in 1993, followed by the US adoption of the same in 2001, with the US estimate that 5% of all US community water systems will have to take corrective actions to lower the current levels of arsenic in their drinking water. In high arsenic areas of the world, the need for better water treatment and resulting economic impact would be even greater. In this article, we briefly review the geochemistry, natural distribution, regulation, anthropogenic sources and removal mechanisms of arsenic, pointing especially to the promise of reverse osmosis (RO) as a practical means of purification. We conclude that arsenic in the commonly high oxidation states of (V) is very effectively removed by RO. With further attention to the removal of the weakly acidic arsenic (III) species in waters by the operation of RO at sufficiently high pHs made possible by the newer antiscalants, practical processes can be developed with RO to remove all major species of arsenic from water. Further studies are needed in the characterization of the arsenic species being treated and in the design of the RO process to match the demands.     

反渗透膜的清洗

介绍了反渗透设备在应用中遇到的膜污染问题、清洗方案的制定及实施清洗后取得的良好效果。     

Industrial wastewater treatment for reuse with reverse osmosis

This paper discusses the use of RO for industrial wastewater reclamation for its reuse. The performance of RO pilot plants processing several industrial wastewaters is outlined. The operating problems and pretreatment requirements are described. The potential benefits resulting from reusing wastewaters from selected industrial processes are shown.     

High-temperature reverse osmosis membrane element

Polymeric thin-film composite (TFC) reverse osmosis (RO) membranes in a patented spiral-wound element configuration were evaluated at process temperatures to 90°C. The viability of the membrane elements operating at high temperature was successfully demonstrated. The high temperature RO (HT-RO) membrane elements are suitable for a variety of dewatering, concentrating and component separation applications in liquid food and beverage processes that operate at an elevated temperature.

In this paper, the performance of HT-RO elements for dewatering high temperature sugar solutions is highlighted. Also discussed are the special design features of the HT-RO element as well as its performance characteristics at high temperatures.     

Jeddah seawater reverse osmosis installation

The world's largest reverse osmosis system for seawater desalination was placed on-line in January 1979 to supply 12,000 cubic meters of desalted Red Sea water per day to the drinking water supplies of Jeddah, Saudi Arabia. This system is based on the newly developed spiral-wound TFC membrane elements. These elements exhibit the high water permeability, low salt permeability, thermal stability, resistance to micro-organisms, and chemical stability required for economic desalination of seawater.

The system consists of power generation, a seawater intake, dual media filtration, nine first-stage reverse osmosis units, three second-stage reverse osmosis units and product stabilization. Since each unit can be brought on or off line in a matter of minutes, the system is extremely flexible. Simplicity of installation and operation is a major advantage of reverse osmosis.

Cost data accrued to date has verified that reverse osmosis is more economical than multistage flash distillaion, both in terms of capital and operating costs. The short lead time from bid to operation, as compared to MSF is demonstrated by the fact that the plant was designed, constructed, and accepted within eighteen months of acceptance of bid.     

Efficiency,recovery and productivity of continuous reverse osmosis systems: new closed expressions

Numerical and approximate analytical solutions for salt concentration polarization in hyperfiltration with laminar flow in a flat sheet configuration are presented. The analysis accounts for the variation of the water flux in the longitudinal direction. Approximate solutions were obtained with an integral method which was found to provide good agreement with the numerical solution. The integral method allows one to obtain closed expressions for the productivity Q, the recovery R and the efficiency E of a reverse osmosis system which can be applied relatively quickly in design calculations.In this analysis the physical properties of the solution are taken to be constant.     

Reverse running centrifugal pumps as hydraulic power recovery turbines for seawater reverse osmosis systems

Because of the ever increasing energy demand and costs, different recovery systems are becoming more and more useful and economical.On the Reverse Osmosis (RO) Systems about 70% of the energy for pumping is wasted at pressures of 800–1000 psi. This paper will discuss the application of reverse running centrifugal pumps as power recovery turbines to recover up to 80% of that energy. The economics of Hydraulic Power Recovery Turbine (HPRT) systems are explored with respect to the equipment cost, operating costs and payouts for the different sizes of R.O. Systems.HPRT's come in various sizes and types and configurations with efficiencies being a function of specific design, flow rate, pressure and speed. Typical design features of HPRT's are described for use in the R.O. System.Different schemes and equipment arrangements are available and require the use of steam turbines, motors, electric generators, clutches, and speed controls or a combination of the above for optimum results. Recommendation of the most economical equipment arrangement for the R.O. System is discussed.Head vs. capacity and BHP vs. capacity relationships are an essential criteria for selection and operation of HPRT's. An overview of the performance characteristics is illustrated. The conclusions will point to the use of reverse running pumps as hydraulic turbines for economical, reliable and efficient recovery of energy from the waste brine circuits of reverse osmosis system.     

反渗透系统中难溶盐极限回收率的解析分析

基于反渗透系统给水三类难溶盐饱和度的解析计算,计及了温度、pH、回收率、阻垢剂及浓差极化等因素的影响,导出了用系统给水参数解析表达的反渗透系统浓水难溶盐饱和度,得出了反渗透系统给水参数决定的系统难溶盐极限回收率．从而为反渗透系统的极限收率指标提供一个简捷而清晰的求取方式。     

Hollow fiber composite reverse osmosis membrane

Progress is described on the adaptation of the NS-200 technology from a laboratory flat sheet RO membrane to a pilot process for the production of hollow fiber RO membranes. Changes in substrate manufacture were required to produce a self-supporting porous hollow fiber substrate. Modifications of the chemistry of the solute rejecting layer resulted in a practical production rate.

At the present time, modules of up to 50 gpd are being field-tested. Facilities to produce commercial sized modules are being designed and built. Research is being conducted towards a goal of producing more economical membranes and membranes of improved chemical stability.