火电机组海水淡化系统能耗特性及其热力成本分析

以某电厂亚临界600MW火电机组及其海水淡化系统为例,基于热力学基本原理研究了机组热力系统以及海水淡化系统的能耗特性,构建了基于质量单元的电-水热耗分摊模型和海水淡化热力成本计算模型,并以机组运行负荷、海水淡化系统的造水比、煤价等作为敏感元素,进行了敏感性分析.结果表明:在联产抽汽量一定时,淡化水的成本随着机组负荷的降低而增加;在负荷一定时,淡化水的成本随着抽汽量的增加而降低,但变化幅度不大;海水淡化造水的总成本随着标准煤单价的提高而增加,且标准煤单价对造水成本的影响较大;造水比对淡化水的热力成本影响较大,不同负荷下淡化水热力成本随着造水比的增大而急剧降低.     

低温多效蒸馏海水淡化工艺的应用

海水淡化又称海水脱盐,是从海水中获取淡水的技术和过程。目前,广泛应用的海水淡化技术主要包括多级闪蒸(MSF)、压汽蒸馏(MVC)、多效蒸发(MED)和海水反渗透膜(SWRO)。MED方法中低温多效蒸馏(LT-MED)开发后在世界范围内得到了较广泛的应用,与RO和MSF成为最具发展前景的海水淡化技术。1海水淡化工艺选择首钢京唐钢铁联合有限责任公司为实现循环经济、节     

太阳能海水淡化动态仿真和生命周期成本分析

设计一种由槽式集热器和多级闪蒸装置构成的全天候太阳能海水淡化系统，日均淡水产量为3000 m³。应用上海市的气象数据，引入多级闪蒸简化算法，采用TRNSYS软件进行动态仿真，并利用生命周期成本分析法对设计系统和常规能源淡化系统进行经济性对比。结果表明：太阳能淡化系统的年平均太阳能保证率为41.11%；在整个生命周期中，位于上海市的太阳能淡化系统单位造水成本为18.48元/m³；当通货膨胀率低于8.5%或天然气价格高于2.09元/m³时，太阳能淡化系统相较于同等规模的常规能源淡化系统，具有更好的经济性。     

压汽闪蒸海水淡化方法的研究与进展

分析、比较、归纳出现有海水淡化方法中,多级闪蒸法和多效蒸馏法在开路热焓过程中,有二次蒸汽的凝结潜热损失问题、蒸馏法的结垢与腐蚀问题、反渗透法的海水前处理与产品水质不稳定问题.进而综合其优点,首次提出:由热功效率最高的压汽法,来驱动产品水质最好的闪蒸法,这样一种全新、最优、集成的压汽闪蒸法海水淡化工艺,兼具投资成本最低、独立闪蒸操作、模块化组合生产等技术优势.由于集成技术成熟而全面,装置运行安全而可靠,必将以卓越的技术性、经济性,逐步取代现有各种方法,统一海水淡化市场,引导海水淡化技术发展.     

供热机组-海水淡化联产系统的经济性分析

针对供热机组-海水淡化联产系统的特点,应用循环函数法、等效焓降法和汽轮机变工况分析理论,建立了计算分析矩阵模型,得出了用于海水淡化的抽汽对供热机组发电和供热两方面以及制水成本影响的计算分析方法.研究结果表明,增加夏季供热负荷用于海水淡化,能够增加供热机组的发电热效率和热能利用率,同时降低海水淡化的成本;采用制水电耗率（ELWP）比采用传统的造水比（GOR）指标更能够准确地评价海水淡化系统热性能;该水电联产系统能够提高热电机组的能源利用效率,有效解决沿海地区火电厂的缺水问题.图3表1参7     

水蒸气吸附/解吸海水淡化技术特点及优势

针对现有反渗透、多级闪蒸、多效蒸馏等传统海水淡化技术存在的热源温度要求高、产水率低、能耗和电耗高等问题,介绍了一种新型的海水淡化工艺和技术——水蒸气吸附/解吸海水淡化技术。该技术具有能量利用率高,所产淡水水质高,对驱动热源的适应性广,可利用太阳能、地热等可再生能源等优点,有利于技术推广和成果转化,是一种海水淡化领域的前沿技术,具有良好的节能效果、社会效益和海洋生态效益。     

太阳能海水淡化技术

太阳能海水淡化技术无污染、低能耗、生产规模可有机组合,是有效解决淡水危机的新途径.介绍了现有的海水淡化技术,分析了太阳能海水淡化,尤其是中高温槽式太阳能闪蒸法海水淡化系统.     

我国海水淡化日产淡水77.4万吨

正根据国家海洋局海洋科学技术司发布的《2012年全国海水利用报告》,截至2012年底,全国已建成海水淡化工程95个,日产淡化水总规模达到77.4万吨,其中最大的海水淡化工程规模达到日产20万吨。淡化水广泛应用于沿海电力、石化、钢铁等高耗水行业及海岛生产生活用水。海水淡化主要采用反渗透和低温多效蒸馏技术,每吨产水平均成本6~8元。海水直流冷却、海水循环冷却、大生活用海水技术得到不断应用,年利用海水作为冷却     

MSF多级闪蒸海水淡化系统的建模与仿真

通过对MSF多级闪蒸过程的机理分析,建立了完整的动态数学模型,与其它文献提供的模型比,考虑了蒸汽密度和级间闪蒸盐水流量变化的影响,仿真计算结果真实地反映了MSF系统动态过程的非线特性。     

海水淡化技术的研究进展

淡水资源的紧缺已成为一个世界性问题。我国水资源匮乏,海水淡化包括西北地区的苦咸水淡化,将成为解决我国沿海地区和岛屿、华北和西北部分干旱地区等缺水问题的重要手段。海水淡化技术在国外已得到广泛应用,在我国也日趋重视。分析了海水淡化不同技术的原理、特点及其应用情况,指出与热力发电厂余热利用相结合的多效蒸馏法、多级闪蒸法将体现其明显的经济性,而且可在掌握系统技术的基础上,开发相应的成套设备。     

A scheme for large scale desalination of sea water by solar energy

A scheme is proposed to desalinate sea water using solar energy for the Thar Desert of India. The scheme has been using solar energy for the Thar Desert of India. The scheme has been designed to produce about 5.25 × 10⁷ m³/yr (13860 MG/yr) of fresh water with 11.52 km² (4.5 miles²) of collector area. The solar collectors are rectangular concrete tubes, half buried in the ground, through which sea water flows and is heated by solar energy. The heated sea water is then flash evaporated in a multi-stage flash evaporator (MSF) unit to yield fresh water. Pumping of the sea water to the site and through the MSF unit is powered by 415 wind turbines each of 200 kW capacity. Economic analysis of the scheme shows that it compares favorably with the existing fossil fuel fired desalination plants of the equivalent capacity.     

THE THERMAL CHARACTERISTICS AND ECONOMIC ANALYSIS OF A SOLAR POND COUPLED LOW TEMPERATURE MULTI STAGE DESALINATION PLANT PART II: ECONOMIC ANALYSIS

This paper presents the thermal performance and economic feasibility of matching the SGSP with the MSF destilation plant with a daily product water output of 1000 m³/day. The analysis are based on the assumption that the solar pond is to be used as the sole heal source (thermal energy) for the distillation plant. The thermal simulation of the MSF desalination process was predicted by using a mathematical model based on stage by stage calculations taking into account the variations in fluid properties and flow conditions. The generated simultaneous equations of the mass and energy balances were combined and arranged in a matrix form and then translated into algorithm to predict process variables such as temperature and flash evaporation rates.

The paper discusses optimisation of the size of the pond and the number of stages for three different storage zone temperatures taking into account the large variation in quantity of energy supplied by the pond between summer and winter. One result is that oversizing the pond, leading to some rejection of the heat collected during the summer (which is referred to as peak clipping), will result in a higher utilisation factor of the desalination plant and a reduction in the summer/winter yield ratio. Optimum peak clipping days, leading to the minimum product water cost, for each storage zone temperature and performance ratio is presented.

The sensitivity analysis of the various factors affecting the overall water costs show that the capital costs comprise about two thirds (2/3) of the total desalinated water costs. This demonstrates and re-emphasises the inherent and basic fact that solar desalination is a capital intensive enterprise. Each 1% increase in interest rate increases solar pond thermal energy costs by about 13–15% and desalinated water costs from SP/MSF combination by about 10–13%.     

Proposal and analysis of a dual-purpose system integrating a chemically recuperated gas turbine cycle with thermal seawater desalination

A novel cogeneration system is proposed for power generation and seawater desalination. It combines the CRGT (chemically recuperated gas turbine) with the MED-TVC (multi-effect thermal vapor compression desalination) system. The CRGT contains a MSR (methane-steam reformer). The produced syngas includes plenty of steam and hydrogen, so the working medium flow increases and NO_x emissions can achieve 1 ppm low. However, the water consumption is large, ∼23 t/d water per MW power output. To solve this problem and produce water for sale, MED-TVC is introduced, driven by exhaust heat. Such a dual-purpose plant was analyzed to investigate its performance and parameter selection, and compared with four conventional cogeneration systems with the same methane input. Some main results are following: In the base case of the CRGT with a TIT of 1308 °C and a compression ratio of 15, the MED-TVC with 9 effects, the specific work output, performance ratio and CRGT-consumed water ratio are 491.5 kJ/kg, 11.3 and 18.2%, respectively. Compared with the backpressure ST (steam turbine)/CC (combined cycle) plus MED/MSF (multistage flash), the CRGT + MED has better thermal performance, lower product cost and shorter payback period, which indicates the CRGT + MED dual-purpose system is a feasible and attractive choice for power and water cogeneration.     

Multi stage flash desalination plant with brine-feed mixing and cooling

Improving the performance of Multi Stage Flash (MSF) desalination plants is a major objective in the seawater desalination industry. Fresh water production rates from MSF plants depend on the evaporation range defined as the difference between the top brine temperature (TBT) and the bottom stage temperature. Lowering the temperature of the plant bottom stage elongates the evaporation range and increases the yield. A modified multi stage flash plant with brine mixing and cooling (MSF-MC) is presented in this paper. Part of the brine leaving the plant is mixed with fresh seawater feed then cooled to low temperature before it enters the bottom stage feed heater. This MSF-MC features several advantages such as expanded evaporation range at the conventional TBT levels, reduced feed pumping power, moderate levels of chemical treatment requirements and fixed fresh water production rates independent of seasonal seawater conditions. Operating with low feed mass fraction minimizes the cooling load and reduces the cooler size. An improvement in the yield by 1.18%-1.4% for every 1 °C reduction in the plant bottom temperature can be achieved with MSF-MC compared to conventional MSF systems.     

Energy consumption by multi-stage flash and reverse osmosis desalters

Kuwait and most of the Gulf countries, depend mainly on desalted water from the sea for satisfying their fresh water needs. These countries are using the multi-stage flash (MSF) desalting system, as the ‘work horse’ for their water production. This system is less efficient in energy consumption as compared to the reverse osmosis (RO) system. Moreover, large units based on the MSF system have to be combined with steam or gas turbines power plants for better utilization of steam supplied to the MSF units at moderately low temperature and pressure (as compared to steam produced by large steam generators). The value and the cost of the thermal energy supplied to the MSF desalting system depends on the method of supplying this energy. This steam can be supplied directly from a fuel operated boiler or heat recovery steam generator associated with a gas turbine. It can also be supplied from the exhaust of a steam back pressure turbine or bled from condensed extraction steam turbine at a pressure suitable for the desalting process. Any energy comparison should be based on simple criteria, either how much fuel energy is consumed to produce this energy or how much mechanical energy is needed per unit product. The energy consumed in the light of the practice used in most Gulf countries are discussed here. In this study, reference desalting and power plants are used for comparison purposes. This study shows that shifting from MSF desalting system to the RO system can save up to 66% of the fuel energy used to desalt seawater.     

Application of the concept of a renewable energy based-polygeneration system for sustainable thermal desalination process—A thermodynamics' perspective

Fossil fuel-powered thermal desalination processes have many harmful environmental effects including greenhouse gas (GHG) emissions and high-salinity brine discharge resulting in biological damages, in addition to energy losses because of the high temperatures of the streams leaving the desalination unit. In this study, a solar energy-based polygeneration approach has been proposed to address these issues. In the proposed system, concentrated solar parabolic trough technology is used to drive a multi-stage flash (MSF) desalination unit for production of fresh water. To recover the waste heat carried by the produced clean water, an organic Rankine cycle is integrated to produce electricity. In addition, to recover the waste heat carried by brine, an absorption cooling system is employed to provide cooling. In order to mitigate the effects of high-salinity brine, a pressure retarded osmosis (PRO) unit is installed, which reduces the salinity of the discharge and produces additional electrical energy. To ensure stable nighttime operations, a thermal energy storage (TES) system is also added to the system. A comprehensive thermodynamic analysis is conducted through mass, energy, and entropy, as well as exergy balances along with energetic and exergetic efficiencies to assess the overall performance of the system. The attained results show that at reference conditions with an overall parabolic trough collectors (PTCs) area of 100 000 m², the system produces 583.3 kW of electricity, approximately 4284 kW of cooling, and 1140 m³ of freshwater daily. Furthermore, the effects of changing operational conditions on the overall performance of the system are investigated. At design conditions, the overall energetic and exergetic efficiencies of the system are found to be 34.54% and 14.55%, respectively.     

Theoretical study of multi-stage flash distillation using solar energy

Solar energy was utilized as a clean renewable heat source for operation of a multi-stage flash (MSF) distillation system in Benghazi to produce distilled water. The optimum T_h for operation of the MSF system with a typical flat-plate collector is 80°C; 1 m² of a flat-plate collector produces annually 8.2 m³ of distilled water at T_h = 80°C. When 1 m² of a compound parabolic collector (CPC) is used at T_h = 122°C, 13.1 m³ of distilled water are produced.     

Study of an incrementally loaded multistage flash desalination system for optimum use of sensible waste heat from nuclear power plant

Existing practice of nuclear desalination cogeneration incurs loss of nuclear plant power generation because it competes for live steam with nuclear plant steam turbine. Such loss is completely avoided with the nuclear desalination plant design proposed in the present study. The plant called GTHTR300 is based on a high‐temperature gas reactor rated at 600 MWt. Gas turbine is used to replace steam turbine as power generator. The gas turbine converts about a half of the reactor's thermal power to electricity while rejecting the balance as sensible waste heat to be utilized in a multistage flash (MSF) plant for seawater desalination. A new MSF process scheme is proposed and optimized to efficiently match the sensible waste heat source. The new scheme increments the thermal load of the multistage heat recovery section in a number of steps as opposed to keeping it constant in the traditional MSF process. As the number of steps increases, more waste heat is utilized, and top brine temperature for peak water production is increased. Both tend to increase water yield. Operating with a similar number of stages, the new process is shown to produce 45% more water than the traditional process operating over the same temperature range. As a result, the GTHTR300 yields 56,000 m³/d water and generates 280 MWe power at constant efficiency with and without water cogeneration. Copyright © 2012 John Wiley & Sons, Ltd.     

Development of a steady‐state mathematical model for multistage flash (MSF) desalination plant

In this paper, a mathematical model for multistage flash (MSF) desalination plants was developed. The model was based on basic principles of physics and chemistry that describe the stages occurring in the desalination process. The input plant parameters that are known to affect the operation of the MSF desalination plant and its performance was taken into account in the construction of the model. These parameters included make‐up flow, brine recycle flow, seawater flow, seawater temperature, seawater concentration, top brine temperature (TBT), steam temperature and the plant load. For each stage, the developed model was used for predicting the temperatures of the brine, distillate and cooling brine, and the flow rates of brine outlet and distillate production. The developed model was evaluated with the MSF plant vendor simulation results and its actual operating data. The evaluation indicated that model predictions matched well with the vendor simulation results and the plant operating data. The developed model is sufficiently accurate and model predictions can be relied upon. Therefore, it may be recommended for determining optimum set point of a running MSF desalination plant at different loads to maximize the water production or minimize energy consumption. It can also be used to calculate controller set points for different loads of the plant. Copyright © 2011 John Wiley & Sons, Ltd.