膜法海水淡化系统在华能威海电厂的应用

随着我国水资源的日益匮乏,海水淡化技术不断应用于工业中。华能威海电厂三期海水淡化系统设备为笔者所在公司提供,海水作为该厂锅炉补给水水源,采用了超滤(UF)-海水反渗透(SWRO)-一级反渗透-二级反渗透-电去离子技术(EDI)全膜法制备。其中能量回收作为海水淡化系统的重要部分,本文将介绍几种常用的能量回收装置,并详细介绍膜法海水淡化系统在该厂中的应用。     

Recent advances in reverse osmosis and electrodialysis membrane desalting technology

The potential impact of recent developments in both reverse osmosis and electrodialysis membrane desalting technology are summarized.Particular emphasis is given to the status of advanced technology reverse osmosis membranes with chlorine resistance having single pass seawater desalination capability. Membranes capable of using low operating pressures for brackish water desalting are also reviewed.Results obtained with large prototype reverse osmosis modules and their potential effect on lowering plant capital costs are presented.Possible elimination of acid and use of ultrafiltration as the predominant pretreatment step in seawater desalination plants are also described.Recent developments in the high temperature electrodialysis program for seawater desalting and in the use of newly developed anion membranes for brackish water desalination are reviewed.Finally, the effect of recent budget cut-backs imposed on the office of Water Research and Technology (OWRT) and potential impacts on future membrane desalination R&D activity are discussed.     

Status of reverse osmosis desalination technology

Reverse osmosis (RO), a relatively new technology, is gradually becoming an established and economical method for demineralization of saline waters. Over 50 commercial plants ranging in size from 50,000 gpd to 2 million gpd (2 mgd) are producing fresh quality water for municipal and industrial uses from brackish water sources. The U.S. Congress has authorized construction of a 100 mgd plant in Yuma, Arizona to demineralize otherwise unusable high salinity irrigation return flows as part of the Colorado River Salinity Control. Engineering design and operation details together with cost information on some commercial plants and the planned 100 mgd plant will be presented.A review of the plant operation data indicates that is imperative for the plant owners and equipment suppliers to place due emphasis on providing adequate feed water pretreatment facilities and trained plant operation personnel to ensure trouble-free operation and to achieve furthur economy in desalting costs.Significant advances have been made in the development of RO process for sea water desalination. Soaring energy costs are providing incentive for plant owners to prefer RO plants (up to 100,000 gpd) over vapor compression distillation hardware. Results of the Federal Government Desalting R & D Programs clearly indicate that RO desalting costs will be at least 20–30% lower than distillation.     

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.     

Professor Joseph W. McCutchan, 1918-1982

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.     

Membrane processes for water supply and reuse - a question of energy consumption and cost

This paper is limited primarily to reverse osmosis which is the dominating membrane process in commercial plants. Desalination of brackish water and seawater with reverse osmosis, with special emphasis on costs and energy consumption, is the primary subject discussed in the paper. Some aspects of and development trends in industrial and domestic applications of membrane processes are also taken up, particularly with regard to by-product recovery and water reuse in connection with advanced wastewater treatment.The first RO plant to be brought into operation in Riyadh, Saudi Arabia, is located at Salbukh. The investment and total operation costs for this plant have been calculated in the paper. The water cost is at least twice as high as in a continental U.S. location. The main reason for this is the very high cost of civil and local works in Saudi Arabia. A similar calculation has been made for RO seawater desalination.Increased energy costs during the last decade have directed research and development work for all desalination methods towards reducing energy consumption. It is shown in the paper that energy recovery in connection with RO seawater desalination is particularly feasible. Different methods for energy recovery have been investigated and reported, the preferred methods depending on the size of the RO plant. A large underground RO plant for energy recovery, based on utilization of the static pressure instead of high pressure pumps, has also been studied.Another possible energy-saving, but also water quality improving method has been proposed, viz . a combined MSF-RO dual purpose plant. Excess power for reverse osmosis seems to be more and more available in Saudi Arabia due to the high power/water ratio in MSF dual purpose plants compared to the real demand for power and water.     

Comparative economics of current and advanced desalting systems

A comparative investigation of the economics of desalting based on current and projected technology has been made. Current operating cost of various plant types operating in Israel are reported. These costs range from less than $.4/m³ for membrane plants desalting brackish water to more than three times as much for thermal plants desalting seawater. For new systems, two plant sizes were evaluated: 4,000 m³/day plants applying current technology and 100,000 m³/day plants applying projected technology. The water costs obtained for the various plant types and applied economic parameters, especially energy prices, range between $.2/m³ and $.6/m³ for brackish water desalting and from $.5/m³ to $2.4/m³ for seawater desalting.     

Conceptual design and cost study for a dual-purpose nuclear-electric reverse osmosis seawater conversion plant

This paper presents the results of a study to develop a conceptual design, and cost estimate for a 25 million gallon per day seawater reverse osmosis desalting plant operating at both Caribbean and Persian Gulf sites. The plants operate in conjunction with a 1000 MWe nuclear power plant. Four seawater membrane manufacturers were supplied with feedwater analyses and a simplified cost estimating procedure so that they could recommend an optimum membrane system. From this information, plant designs and cost estimates were developed. For both sites, a two-stage system was selected for the conceptual cost estimate. The product water cost was determined, based- upon 1978 construction costs, for both the Caribbean, and Persian Gulf sites. In addition, areas of potential cost reduction were discussed.     

Cost analysis of seawater desalination with reverse osmosis in Turkey

Economically usable water resources per capita are decreasing due to excessive population increase each year in Turkey. For this reason, new water resources should be found in the near future. The potential water resources are seawater or well water both of which need removal of salinity. The most promising treatment method for salinity is reverse osmosis. While reverse osmosis becomes widespread, the cost of the process will decrease. There is no detailed information about cost of seawater desalination in Turkey. In this study, a cost analysis of seawater desalination in Turkey was performed for reverse osmosis systems. The basic parameters of cost analysis such as capacity, recovery, membrane life, energy, chemical costs and flux were evaluated based on the effects on capital, operating and total production costs.     

On the reduction of desalting energy and its cost in Kuwait

All seawater desalting processes, multi-stage flash (MSF), multi-effect boiling (MEB), mechanical vapor compression (MVC) and seawater reverse osmosis (SWRO) consume significant amounts of energy. The recent increase of fuel oil cost raises the cost of energy consumed for desalting water and the final water cost, and creates more interest in using more energy efficient desalting systems.

The most used desalting systems by distillation (MSF and MEB) are usually combined with power plants in what is called co-generation power desalting plants, CPDP. Fuel is supplied to the CPDP to produce both desalted water D and power W, and the fuel cost is shared between D and W. Exergy analysis and equivalent work are among the methods used to determine the fuel energy charged to each product. When desalting systems, such as SWRO and MVC, are not combined with a power plant, the fuel energy can be directly determined from its electrical power consumption.

In this paper, the fuel energy cost charged to desalting seawater in the presently used CPDP in Kuwait is calculated based on exergy analysis. The MSF, known by its high energy consumption, is the only desalting method used in Kuwait. The MSF units consume 258 kJ/kg thermal energy by steam supplied to the brine heater BH, 16 kJ/kg by steam supplied to steam ejectors, and 4 kWh/m3 mechanical energy for pumping. These MSF units are operated either by:

(1) Steam extracted from extraction/condensing steam turbines EC/ST as in as in Doha West, Azzour, and Sabbiya CPDP. This practice is used in most Gulf area.

(2) Steam supplied directly from boilers as occurred in single purpose desalting plants as Al Shuwaikh plant; or in winter time when no steam turbines are in operation in the CPDP to supply steam to the desalting units.

The CPDP have limited water to power production ratio. While they can cope with the increase of power demand, it cannot satisfy the water demand, which is increasing with higher pace than the power demand.

The case of steam CPDP used in Kuwait is presented in this paper as a reference plant to evaluate the amount of fuel energy consumed to desalt water in MJ/m3, its cost in $/m3. The resulted high fuel cost calls for some modifications in the reference CPDP to lower the energy cost, and to increase its water to power ratio. The modifications include the use of an auxiliary back-pressure steam turbine ABPST supplied with the steam presently extracted to the MSF units. The power output of the ABPST operates MVC or SWRO desalting units; while the ABPST discharged steam operates LT-MEB desalting unit. The desalting fuel energy costs when applying these modifications are also calculated by the exergy analysis and compared with that present situation.

It is also suggested to increase desalted water output by using separate SWRO desalting units operated by the existing power plants of typical η_c = 0.388, or by new combined gas/steam turbines power cycle GT/ST-CC of typical η_c = 0.54 under construction. The SWRO with energy recovery is assumed to consume typical 5.2 kWh/m³ electric energy.     

反渗透技术应用总结

结合辽宁华锦通达化工股份有限公司除盐水系统流程,介绍反渗透装置的主要技术参数、运行控制要点、装置消耗情况及出现的问题.通过采用反渗透技术取代石灰软化技术用于除盐水处理的应用实践,说明在除盐工艺中应用反渗透技术将取得节水、降耗的双重效益.     

液化天然气深冷-膜蒸馏海水淡化系统集成与分析

提出了一种PRICO天然气液化-膜蒸馏（MD）海水淡化系统集成方法,利用PRICO过程压缩机出口的余热驱动MD海水淡化。采用Aspen Plus和GAMS建立了集成系统的数学模型,综合考虑系统的结构、物流物性、设备规模、操作参数等系统设计问题,分析不同设计下系统的投资、能耗、运行费用以及MD单位产水成本。模型应用于一个处理量为1 kmol/s的PRICO天然气液化系统与MD集成的案例研究。计算结果表明,单位产水成本最小时,系统产水成本为1.98 USD/m³,淡水产量为5.78 m³/h,与反渗透等海水淡化技术相比,MD在经济性方面具有较强的竞争力。     

Integrating hybrid systems with existing thermal desalinationplants

In Gulf countries, most power plants are co-generation power desalting plants (CPDP) that generate electric energy and also produce fresh water through the desalination of seawater. This paper provides detailed technical and economical analyses to evaluate a new generation of dual purpose technology that includes the integration of reverse osmosis (RO) processes with existing thermal desalination processes and power generation (triple hybrid system) at Layyah plant, Sharjah, UAE. Hybridization of sweater reverse osmosis (SWRO) and the multi-stage flash (MSF) technology was considered to improve the performance of latter and reduce the cost of the produced water. Moreover, “idle” power in winter (seasonal surplus of unused power) was mainly utilized by RO to further reduce the cost of the hybrid system for six months of the year. Spinning reserve was also used to further reduce the cost of the proposed hybrid system. Integration ofthe three processes of MSF, MED, and RO desalination technologies could be made at different levels through which the resulting of water cost will depend on the selected configuration and the cost of materials of construction, equipment, membrane, energy, etc. Thus, the capital and annual operating costs were calculated for all potential alternatives for various plant capacities. It was found that for all plant capacities, integrated hybrid systems resulted in most cost effective solution. For example, at a capacity of 50 MIGD, the present worth of the cost was calculated to be 588.7, 443.2, and 380 million US$ for MSF, MED, and hybrid RO systems, respectively.     

Performance study of RO systems in Saudi Arabia

Desalination of water is one of the most important engineering tasks facing Saudi Arabia today. Lacking unlimited supplies of potable Water, the Kingdom must depend upon the desalination process of brackish well water or sea water to satisfy the ever increasing demands. These demands are expected to reach the 430 MGD figure in 1980 and 700 MGD in 1985.

Abstract

until quite recently, the reverse osmosis played a rather modest role in the country's desalination program and was almost exclusively limited to brackish water applications and plants not exceeding a capacity of 1 MGD. Within the last year, significant changes took place in favor of these processes. The estimated total output of RO units to be commissioned this year will be about 70 MGD. This figure includes the 3.2 MGD plant for desalting the sea water in Jeddah and the 55 MGD plant in Riyahd from brackish well water.

This paper deals primarily with the performance of RO systems, their cost of operation/maintenance and the factors affecting the cost. These factors may be divided into three groups as related to feed water, system design and system operation. The quality of feed water and good pretreatment plays an extremely important role in performance of a RO system. This study pays special attention to these parameters in expectation that more cost effectiveness will evolve in the future either through a better understanding of the processes or an improved process design match to materials employed.     

The Yuma Desalting Plant

The 96 million gallon per day Yuma desalting plant is part of a complex project intended to solve a long standing water quality problem between the United States and Mexico. Designed to treat up to 129,000 acre-feet of 3200 mg/l irrigation return flows, the plant will deliver 283 mg/l product water to maintain a 115 mg/l differential between water delivered to U.S. users and to Mexico .

Design of the plant was preceded by an extensive research program to determine pretreatment requirements, membrane performance, plant capacity and equipment and instrumentation performance. Two pretreatment systems were tested. Partial lime softening followed by multi-media filtration was chosen for the final design. Nine membrane systems (both reverse osmosis and electrodialysis) were tested. Two spiral wound reverse osmosis systems were chosen as most efficient from physical and economic viewpoint, and contracts for site preparation and construction of the intakes and sedimentation basin is scheduled for award summer 1979 with construction of the main plant and installation of desalting equipment scheduled for award summer of 1980.

Based on January 1979 prices, total cost of the desalting complex is approximately $190 million (including interest during construction). The investment cost per daily gallon of installed capacity is approximately $2. per 1000 gallons of desalted water (capital amortization plus operation and maintenance) is $0.77.     

Recent developments in thin-film composite reverse osmosis membrane systems

Desalination of seawater by reverse osmosis requires a membrane which approaches theoretical semipermeability and is sufficiently thin to provide transport of water at practical operating pressures and recovery rates. This objective has been achieved by the development of a family of thin-film composite membranes based on nitrogen-containing polymers supported on a fabric-reinforced porous supporting membrane. The membranes, packaged in the spiral-wound configuration, exhibit high water permeability, low salt permeability, thermal stability, resistance to micro-organisms, wet-dry, and chemical stability.Membranes of this type are currently employed for the conversion of seawater to potable water in the world's first large reverse osmosis plant in Jeddah, Saudi Arabia, trailer-mounted U.S. Army military units, off-shore drilling platforms, marine applications, and hand-powered emergency units. Reverse osmosis systems, employing thin-film composite membrane elements, are also in operation for the conversion of brackish to potable water and a variety of water-reuse applications for textile finishing, boiler water for electrical utilities, soft drink manufacturing, agricultural water, and reclamation of municipal waste water.     

Desalination costs in Australia: A survey of operating plants

A survey of desalination costs in Australia was conducted using data obtained from plant operators, and is reported in second quarter 1986 A$. Unit water costs range from $0.76/kL (for a precursor to deionisation for boiler feed) to $14/kL (for emergency supplies for an island resort).

However, an average figure for desalination of brackish water is $3–$4/kL, and for seawater, $5–10/kL in medium-sized installations.

Capital costs for brackish water plants have been correlated with plant design capacity ranging from 10 to 3400 kL/d.

There is insufficient information to allow a proper comparison between reverse osmosis and electrodialysis for brackish water desalination.