浅析热法海水淡化浓盐水对环境的影响及综合利用

热法海水淡化浓盐水具有温度高、盐度高和TDS浓度高等特点,其不合理排放会对环境造成一定的危害。文章简要介绍了热法海水淡化的各种工艺方法及特点,对热法海水淡化浓盐水排入环境中的影响进行评述,并讨论热法海水淡化浓盐水的处理方法,包括直接排放、综合利用及零排放技术等。     

海水淡化浓盐水排放与处理技术研究概况

文章分析了不同海水淡化方法浓盐水的主要特征,介绍了国外常用的浓盐水排放和利用技术,包括直接排放法(排入海洋、地表水、污水处理系统等)和浓盐水再利用(灌溉、考虑制盐、提取化工原料)两类。文章分析了上述浓盐水处理技术适用的条件及其优缺点,指出了我国加强相关技术研究和制定相关法规的紧迫性和必要性。     

反渗透浓水的管理与处置方法

反渗透(RO)系统被广泛的应用于海水淡化、地下水脱盐和污水再生利用,但RO浓水含盐量高且可能含有有毒物质,直接排放会对环境造成一定的影响。选择适宜的脱盐RO浓水管理方式直接关系到水厂的投资和运营成本,以及产生的环境影响。本文针对脱盐RO浓水的管理与处置,在综述传统处置方式的基础上,从零排放、末端处理和资源化三个方面详述了RO浓水处置方式的研究进展与现状。     

海水淡化浓盐水排海的环境影响与对策

目前虽未见海水淡化工程对其所在海域的生态环境造成严重破坏的相关报道,但由于浓盐水具有高盐度、高温的特点,且含有铝、重金属和杀菌剂余氯,会明显抑制部分浮游动植物的生长;而在浓盐水排放的相关海域中,鱼类丰度和物种丰富度有所提高。因此,需要进一步研究浓盐水排放对海洋生态环境的影响。综述了国内外海水淡化产生的浓盐水的排放现状和管理要求,重点分析了海水淡化工程浓盐水排放对海洋生态环境造成的影响,并提出减缓影响的相应对策与建议。通过梳理现有排放方式,发现通过优化浓盐水排放口设计,采用混合排放技术、综合利用与零排放技术等相应措施,可进一步减缓浓盐水排海的影响范围和程度。随着海水淡化产能的增加,建议在海水淡化工程取排水海域开展生态环境常规监测,以加强对海水淡化排放浓盐水的监测评估,对海水淡化管理的相关政策和标准进行研究和分析,以促进海水淡化产业健康、可持续发展。     

刍议工程总承包项目的招标模式

招标作为工程建设的常见行为,在工程建设中有着重要意义。因此,本文将三种常见的招标模式作为研究对象,包括评定分离法、综合评分法以及合理最低价评估法,分别分析这三种招标模式的优缺点以及应用范围。其中,评定分离法优点在于评标结果客观公平,缺点在于对自身内部控制机制要求较高,主要适用于施工难度较大的重点大型工程;综合评分法优点在于容易选取到有经验的中标方,缺点在于对评标专家业务能力要求较高,主要适用于技术条件较为复杂以及施工周期较为漫长的工程项目;合理最低价评标法优点在于节省项目成本,缺点在于项目施工风险较大,主要适用于技术要求一般以及施工难度一般的工程。     

热膜耦合方式下浓海水脱硬处理零排放实验研究

针对海水淡化副产高盐度浓海水直接排放会对生态环境造成破坏的问题,采用化学沉淀法与膜法相结合技术,从浓海水中提取70%以上有效碳酸钙,并控制透过液中Mg2+的质量浓度为15~20mg/L;浓海水硬度基本去除的同时,降低反渗透进水硬度,提高淡水回收率,降低药剂成本;反渗透产二次浓盐水可供给盐碱厂,可降低海水淡化成本、解决淡化后浓盐水的排放问题。     

福建省某小型海岛海水淡化工程设计初探

介绍我国海岛海水淡化发展现状及兼具取水口作用的码头取水方式,并针对小型海岛前期开发中用水量较小、可用陆地面积小、施工空间紧凑特点,采用集装箱式模块化海水淡化装置。该工程将取水构筑物与港池紧密结合,以利于减少海上取水工程量和降低工程费用;同时,充分考虑码头取水的污染风险和海水淡化站浓盐水、排泥对环境的影响。该工程对类似远海岛屿海水淡化工程建设具有良好的示范效应。     

膜蒸馏技术可望消除浓水排放

天津工业大学生物化工研究所在国内率先将膜蒸馏技术用于市政污水、工业废水净化以及海水淡化后的浓水处理,有望使废水排放量大大降低,甚至只有固形沉降物排出。该技术现已完成实验室规模实验,准备进行中试及工、皿化前期实验。目前国内多采用反渗透技术处理市政污水和工业废水,该技术虽然高效节能,但实际产水率一般在70％左右,仍有大量浓水排放,对环境十分不利。而针对淡水资源短缺开发的多种海水淡化技术,在应用中也只能实现约50％的淡水收率,另一半浓海水也需排海,会对近海海域的生态环境污染造成危害。     

粉煤灰空气输送斜槽透气层的选择及应用

目前, 电厂粉煤灰的输送排放分干法和湿法二种. 其中, 干法输送排放, 越来越显出它的优越性, 空气输送槽适用于水平输送, 是电厂粉煤灰输送配套的可靠设备, 与螺旋输送相比, 它具有易加工制造、成本低、省电、维护检修工作量少等优点.     

低温多效海水淡化副产浓盐水的再处置

低温多效海水淡化在产生高品质淡化水的同时也会产生含盐量约40000~46000 mg/L的浓盐水,直接排放至海洋会对生态环境、海洋水环境造成较严重的破坏。将富含化学矿物资源的低温多效海水淡化副产浓盐水进行再处置,经新型中空纤维反渗透膜后,电导率可稳定达到81200~86600μS/cm,继而通过一系列化学反应和超滤、反渗透手段去除二次浓盐水中的钙、镁等离子,制成有经济价值的碳酸钙、氢氧化镁等化学品外售。三次浓盐水可直接出售给盐化工厂进行提钾、提溴、制纯碱等。     

Overview of seawater concentrate disposal alternatives

This article discusses the available alternatives for ocean concentrate disposal, site specific factors involved in the selection of the most viable alternative for a given project, and the environmental permitting requirements and studies associated with their implementation. The article focuses on the three most widely used alternatives for ocean discharge of concentrate: direct discharge through new outfall; discharge through existing wastewater treatment plant outfall; and co-disposal with the cooling water of existing coastal power plant. Key advantages, disadvantages, environmental impact issues and possible solutions are presented for each discharge alternative. Results from recent salinity tolerance and toxicity study completed at the Carlsbad, California seawater desalination demonstration plant for a variety of sensitive marine organisms are presented. The practical implementation of this study along with other methods for analysis of the environmental impact of ocean discharges from large seawater reverse osmosis plants is illustrated with case study examples.     

Integration of seawater desalination with power generation

The economic benefits of integrating seawater desalination with power plants are discussed, starting from the first principles of thermodynamics. The concepts of the “fuel-use performance ratio” and the “power loss” method are described in the context of their usage for thermal cycle evaluation and desalination process selection, both with conventional steam cycles and with combined cycle power plants. A thermo-economic model is introduced to evaluate water and power costs and rates of return in dual-purpose power/desalination applications. The future of integrated power and desalination plants is discussed with reference to the growing role of seawater reverse osmosis (SWRO) in the desalination arena. A case study is presented to evaluate the benefits of integrating SWRO with existing power/desalination plants in the Middle East. Subject to the assumptions of the study, it is concluded that repowering and retrofitting would result in a nearly three-fold increase in the power generating capacity and an over six-fold increase in the water output, without requiring any expansion of the seawater intake system. Based on natural gas fuel, the repowered plant would also result in a 70% increase in the fuel efficiency of the station and a drastic reduction in the cost of water production. For a privatization scenario, an economic analysis is used to show that attractive rates of return would be obtained if a developer were to purchase and refurbish the existing plant, selling the products on a build own and operate (BOO) basis. In preparation for this promising application, the need for pilot plant testing at existing power/desalination stations, together with research and development work in membrane technology for high temperature operation, is emphasized.     

Solar barometric distillation for seawater desalting part I: Basic layout and operational/technical features

The report presents an innovative solar barometric distillation technology for seawater desalting (SW-SBD) which has several attractive features such as: (1) efficient vacuum solar collectors of simple construction; (2) a barometric layout for quasi-steady operation at subatmospheric pressure; (3) a demister system of simple mechanical construction; and (4) an electronic control system regulating plant productivity parameters on available solar radiation flux. The proposed seawater desalting technology consists of single-effect distillation with water vapor produced and heated at subatmospheric pressure in a solar collector loop; the basic layout, operational features, and energy efficiency are presented and analysed in detail. Subsequent reports will provide technico-economical data from prototype desalting plants in view of industrial implementation. A promising specific electric energy consumption,∼2 kWm³ offresh water produced, was found by estimating pumping power requirements of major SW-SBD plant pumps. A sizable reduction in produced water cost with respect to an existing solar seawater desalting plant in Abu Dhabi is expected on the basis of a preliminary economic evaluation for a ∼100 m³/d plant prototype.     

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.     

海水淡化浓盐水排放对环境的影响与零排放技术研究进展

回顾了目前常用的海水淡化技术及其应用现状,重点综述了海水淡化浓盐水排放对海洋环境的影响,分析了排放盐水的组分、盐度、热污染、腐蚀产物、化学清洗剂等对海洋环境和海洋生物的潜在影响,提出了相应的解决措施与解决方法,说明浓盐水零排放技术是解决环境问题的有效途径。     

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.     

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.     

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.     

火力发电厂废水处理的研究与进展

随着火力发电厂的快速发展以及水资源紧缺和环境保护要求,发电厂面临的废水处理技术日益突出.简述了火力发电厂废水的种类及特点,综述了各类废水处理方法的研究与进展.重点讨论了各种方法的优缺点,探讨了火电厂废水处理技术今后的发展方向,为火电厂废水处理技术的研究提供理论依据.     

Myth and reality of the hybrid desalination process

The paper discusses some misconceptions that have contributed to the continued use of thermal desalination processes and promotion of the hybrid desalination process for new plants being built or considered at Middle East locations. The misconceptions are examined both on the basis of fundamental thermodynamic principles and in terms of practical engineering parameters. The analysis shows that there is no economic or performance advantage in the installation of greenfield hybrid power/thermal desalination/ seawater reverse osmosis (SWRO) plants in preference to power/SWRO plants, because the latter would produce water more cheaply under all conditions and at all fuel costs, and would provide more operational flexibility than the former. The paper identifies situations where the hybrid desalination process can be fully justified: in existing power/desalination plants, where aging boilers and multistage flash (MSF) units need to be repaired or replaced, through retrofitting and repowering. In such situations, abandonment of the MSF process would result in a reduction in the power output of the plant. The paper refers to previous work which showed that the repowering of a typical existing power/desalination station with refurbishment/replacement of the MSF units, together with the addition of SWRO units, would result in a several-fold increase in the water and power output and a dramatic improvement in the fuel efficiency, without any additions to the existing seawater intake system. The paper emphasizes the importance of test stations/demonstration plants at existing power/desalination stations in the Middle East in order to obtain data and make improvements in the technology of higher temperature SWRO, with the feed obtained from the cooling water returning from the power plant condenser and the thermal desalination plant. The paper shows that the potential benefits would easily justify the investment in research and development required to validate this concept.