低温多效海水淡化混流效组系统优化与分析

建立了多个混流点的混流效组低温多效蒸发(LT-MED)海水淡化数学优化模型,将海水视为盐和水的混合物,其焓表达为温度的函数,降低优化模型的非线性程度,使其易于收敛。以比传热面积为优化目标分析了不同流程和参数对系统的影响。结果表明,在喷淋密度为30~80 g/(m·s)时,多混流点系统的造水比与单混流点系统相比提高了12.1%,比传热面积降低了8.4%,优化流程为5效+2效+2效组合;提高首效加热蒸汽温度可有效的减少换热面积,降低制水成本,对系统的造水比影响不大;增加系统效数,可以有效提高造水比。各效等面积蒸发方案造水比比不等面积方案略有下降,比传热面积略有增加。模拟结果与文献中相关数据吻合良好,可为低温多效蒸发海水淡化系统工程化设计提供技术支持。     

低温多效海水淡化系统的模拟计算

根据系统物料平衡、盐平衡、能量平衡、传热方程、热力学关系式及海水物性参数计算公式,建立了低温多效蒸馏海水淡化系统蒸汽喷射压缩器、蒸发器、淡水闪蒸罐及浓水闪蒸罐的数学模型。运用牛顿迭代法,确定了系统工艺参数计算的源程序。结合某电厂已投产四效平流低温多效蒸馏海水淡化装置,进行模拟计算,得出了系统造水比、比传热面积、比冷却海水流量等性能参数,且模拟计算结果与现场操作数据误差小于10%。     

低温多效蒸发海水淡化系统性能的实验研究

针对大型海水淡化工程设计关键技术,依托1 t·d-1低温多效蒸发海水淡化实验平台,考察了装置运行性能的稳定性,系统地研究了不同海水进料量及首效蒸汽温度对造水比、浓缩比和产品水质等关键参数的影响。结果表明:在实验条件范围内,随着首效蒸汽温度提高,海水的浓缩比先减小后增加,而首效温度对造水比的影响较小;在一定首效温度下,浓缩比随着海水进料量的增大而减小,而造水比随海水进料量的增大而增大。在实验范围内,产品水的固体总溶解浓度均低于5 ppm。小型海水淡化平台关键技术的实验研究为低温多效海水淡化系统在扩大化中的设计优化提供了参考和借鉴。     

低温多效蒸发海水淡化系统热力分析

建立了喷射器低温多效蒸发海水淡化系统的数学模型,计算分析了各种温度损失随温度的变化,并研究了顶值盐水温度、蒸发器效数和动力蒸汽等参数对系统的造水比和生产单位质量淡水所需传热面积的影响。结果表明各种温度损失在末效蒸发器内显著增加;喷射器低温多效蒸发系统的热力特性明显优于多效蒸发系统;通过增加顶值盐水温度、蒸发器效数和动力蒸汽温度,可以实现系统的优化运行。     

三倍浓缩低温多效海水淡化装置的工艺设计及验证

对三倍浓缩低温多效海水淡化技术的工艺流程、参数及运行效果进行了介绍。充分考虑高浓缩倍率的结垢风险,设计采用海水顺流流程,对蒸发器效数、效间传热温差、海水喷淋密度等进行了优化,并将一套二倍浓缩1 000 t/d低温多效海水淡化装置进行技术改造,对三倍浓缩工艺进行了试验验证,测试了蒸发器的抗结垢性能和耐腐蚀性能。运行结果显示,浓缩比、造水比等各项性能指标达到预期目标。     

不同流程下低温多效海水淡化系统热力性能研究

建立了串联无预热、串联预热、并联无预热、并联预热4种流程下的低温多效海水淡化系统数学模型,并利用MATLAB语言编制程序进行了求解,比较了不同流程对系统热力性能的影响。计算结果表明：当海水淡化系统为6效,在其他参数相同的情况下,与无预热流程相比,预热流程所需的加热蒸汽量较少,造水比较大,传热总面积较小,冷却海水量小。与串联流程相比,并联流程所需的加热蒸汽量较少,造水比较大,传热总面积较小,冷却海水量小。综合结果是并联预热流程的热力性能最优。     

基于全周期缓慢结垢的多效蒸发海水淡化慢时变系统优化设计

多效蒸发（MED）是最主要的海水淡化方法之一,作为典型的慢时变系统,该系统在长期运行的过程中,往往会由于结垢导致蒸发器传热效率降低,造成减产甚至停工。为避免出现这种问题,工艺设计者会采取冗余设计,增大传热面积,这会导致设备投资的显著增加。为保证MED系统能够全周期运行,且尽可能减少总传热面积,提出了一种全周期优化设计方法。该方法以总传热面积最小为目标,对决策变量在整个周期内进行分段优化,同时考虑结垢过程、工艺变化以及控制方面的需求,对各效传热面积进行裕量设计,通过一步优化求解得到最优操作条件与最小传热面积,实现对慢时变系统的优化设计。最后,以八效MED海水淡化装置为例,同时用等面积法、等温差法、稳态优化设计方法以及全周期优化设计方法对系统进行设计。结果表明,全周期优化设计方法能够最大限度减少传热面积,大大降低了系统的设备投资,是一种有着良好应用前景的多效蒸发海水淡化系统优化设计方法。     

吸收式热泵海水淡化系统性能与经济研究

提出了单效溴化锂吸收式热泵低温多效蒸发海水淡化系统,建立了系统数学模型。分析了不同溴化锂浓溶液浓度对系统的影响,并与不带吸收式热泵的低温多效蒸发海水淡化系统进行了性能与经济比较。计算结果表明:在本文的计算范围内,随LiBr浓溶液浓度的增加,发生器产生的饱和蒸汽温度降低,所需动力蒸汽量减少,造水比升高,海水淡化装置蒸发器总面积增加,综合效果是淡水成本增加。在相同条件下,与不带吸收式热泵的海水淡化系统相比,吸收式热泵海水淡化系统的淡水成本可节省16.5%。     

塔式多效蒸馏海水淡化装置的进料优化

基于全塔负荷均衡的原则，进行了塔式多效蒸馏海水淡化装置的进料优化。结果表明采用优化的三股进料可以使塔内的盐水流量趋于均匀，提高造水比，降低操作的运行费用(电耗和汽耗)，降低预热器的传热面积。而每效的淡化水产量和淡化水累积量几乎不受进料流股数的影响。     

海水淡化与水源热泵联合系统性能与成本研究

提出了低温多效海水淡化装置与水源热泵联合系统技术,建立了联合系统数学模型,并利用MATLAB编制程序进行了求解,分析了末效二次蒸汽温度对联合系统热力性能与成本的影响,并且与低温多效海水淡化系统进行了成本比较。计算结果表明:在文章的计算范围内,随着末效二次蒸汽温度的升高,加热蒸汽量减少,蒸发器总传热面积增大,驱动蒸汽量减少,供热水量减少,综合效果是淡水成本增加。其他参数相同的情况下,与低温多效海水淡化系统相比,联合系统的淡水成本节省11.68%。     

Energy and exergy analyses of seawater desalination system integrated in a solar heat transformer

Among the numerous options to improve the energy efficiency of desalination plants stands out the absorption heat transformer. A heat transformer is a device, which can deliver heat at a higher temperature than the temperature of the fluid by which it is fed. Solar thermal energy can be used as heat input for single effect heat transformer while the high grade thermal energy delivered by the heat transformer can be used as heat source for water desalination.In this paper, an attempt has been made to study the combination: flat plate solar collectors, a single effect heat transformer and desalination system (distillation process) used to provide a beach house located in Skikda (East of Algeria; Latitude 36.52°N, Longitude 6.57°E) with drinking water. This system produces about 500 l of drinking water per day in July.Mathematical models of the solar flat plate collectors (FPC), absorption heat transformer (AHT) operating with the water/lithium bromide solution and the overall desalination system (WP) were developed to simulate the performance of this combination system. The energy and exergy analyses are carried out for each component of the system. All exergy losses that exist in this solar desalination system are calculated. Energy and exergy efficiencies are estimated.     

Exergy analysis of humidification–dehumidification desalination systems using driving forces concept

In this paper, a new method for exergy analysis of humidification–dehumidification (HD) desalination systems is presented. It is based on the principle that there are exergy losses wherever the driving forces exist. A methodology was developed for investigating various parametric effects on exergy losses. The method involved developing a sink and source model as well as basic relations in the system. Results showed that the mass transfer phenomenon does not have any effect on the total exergy losses of the HD systems. Heater was the largest irreversibility resource. Flow rate of the Un-heated fluid and the maximum temperature of the system had key roles in the total exergy losses. An optimum point for the water-heated HD desalination system is also introduced. Finally, some comparisons are proposed between the water-heated and the air-heated HD desalination systems.     

An exergetic analysis of a membrane desalination system

In this paper, the exergetic analysis of a seawater membrane-based desalination plant has been carried out. The desalination plant has been described in detail, then the exergy of the various saline water streams has been determined and a comprehensive analysis towards the exergy distribution of the major process components has been conducted. The examination of the exergy losses throughout the plant revealed that exergy destruction was mainly due to pressure drops in the membrane modules, valves and brine lines. Moreover, 12.9% of the exergy input to the system was supplied by the heater. Therefore, the most reasonable way to reduce power input to the plant, thus improving its performance and cost, has been shown (i) to be replacing the valves on the reverse osmosis brine stream by an energy recovery system, and (ii) to have thermal energy available in the plant. With the identified technical changes, energy consumption decreased from 18.3 to 2.05 kWh/m³, resulting in an annual saving of 0.17$/m³.     

25000 t LNG燃料动力化学品船能量利用系统的设计及优化分析

以25000 t LNG燃料动力化学品船为研究对象,在分析及评估原船废气余热利用系统以及高温冷却水系统用能水平基础上,针对船舶发电、海水淡化、冷库及空调等需求,综合考虑原船余热资源及未加以利用的LNG冷能,以加装废气动力涡轮、LNG冷能ORC发电、冷冻法海水淡化及设置高低温冷库与空调系统等方式组合提出了五种能量系统梯级利用方案。通过HYSYS软件模拟计算和对比分析,从（火用）效率及经济性两个方面对各方案进行了评估。结果表明,诸方案中以低温冷库+高温冷库+空调系统经济性最好,所形成的新设计系统经优化后（火用）效率可提高至62.87%,每年经济收益可达1227.85万元。     

Comparative analysis of the efficiency of thermal desalination plants

In the desalination of sea water, exergy heat transfer losses are greatest. Thin film thermal desalination plants were found to have the best hydrodynamic, technical and economic properties.     

Exergy analysis of desalination by solar-powered membrane distillation units

There has been an increasing interest in using exergy as a potential tool for analysis and performance evaluation of desalination processes where the optimal use of energy is considered an important issue. Unlike energy, exergy is consumed or destroyed due to irreversibilies in any real process and thus provides deeper insight into process analysis. Exergy analysis method was employed to evaluate the exergy efficiency of the “compact” and “large” solardriven MD desalination units. The exergy efficiency of the compact and large units with reference to the exergy collected by the solar collector was about 0.3% and 0.5% but was 0.01% and 0.05%, respectively, when referenced to the exergy of solar irradiance. The exergy efficiency of the flat plate solar collectors in both units varied diurnally and the maxima was 6.5% ad 3% for the compact and large units, respectively. The highest exergy destruction was found to occur within the membrane distillation module.     

MSF海水淡化系统（火用）分析模型及其应用

为更好进行系统热力设计，性能评价、热经济学分析和优化。本文建立了完善的ＭＳＦ系统的火用分析模型。它可对系统中不同环节和过程进行详细的包括化学火用变化在内的火用分析。案例研究表明，本文建立的火用分析模型精度高，可广泛地应用于系统分析和评价     

Exergy analysis of a combined RO, NF, andEDR desalination plant

A brackish water desalination plant in California that incorporates RO, NF, and EDR units was analyzedthermodynamically using actual plant operation data. Exergy flow rates were evaluated throughout the plant, and the exergy flow diagrams were prepared. The rates of exergy destruction and their percentage are indicated on the diagram so that the locations of highest exergy destruction can easily be identified. The analysis shows that most exergy destruction occurs in the pump/motor and the separation units. The fraction of exergy destruction in the pump/motor units is 39.7% for the RO unit, 23.6% for the NF unit, and 54.1 % for the EDR unit. Therefore, using high-efficiency pumps and motors equipped with VFD drives can reduce the cost of desalination significantly. The plant was determined to have a Second Law efficiency of 8.0% for the RO unit, 9.7% for the NF unit, and 6.3% for the EDR unit, which are very low. This indicates that there are major opportunities in the plant to improve thermodynamic: performance by reducing exergy destruction and thus the amount of electrical energy supplied, making the operation of the plant more cost effective.     

Exergy analysis of a reverse osmosis desalination plant in California

The exergy analysis of a 7250 m³/d reverse osmosis (RO) desalination plant in California was conducted by using actual plant operation data, and an alternative design was investigated to improve its performance. The RO plant is described in detail, and the exergies across the major components of the plant are calculated and illustrated using exergy flow diagrams in an attempt to assess the exergy destruction distribution. The primary locations of exergy destruction were the membrane modules in which the saline water is separated into the brine and the permeate, and the throttling valves where the pressure of liquid is reduced, pressure drops through various process components, and the mixing chamber where the permeate and blend are mixed. The largest exergy destruction occurred in the membrane modules, and this amounted to 74.07% of the total exergy input. The smallest exergy destruction occurred in the mixing chamber. The mixing accounted for 0.67% of the total exergy input and presents a relatively small fraction. The second law of efficiency of the plant was calculated to be 4.3%, which seems to be low. The analysis of the alternative design was based on the exergy analysis. It is shown that the second law of efficiency can be increased to 4.9% by introducing a pressure exchanger with two throttling valves on the brine stream, and this saved 19.8 kW electricity by reducing the pumping power of the incoming saline water.     

Exergy analysis of a seawater reverse osmosis plant

Exergy analysis is a powerful tool to determine how inefficiencies of the processes influence system performance. The exergy analysis of a seawater reverse osmosis desalination plant with 21,000 m³/d of nominal capacity located in Tenerife (Canary Islands, Spain) was studied. Once defined, the flow chart of the process, the exergy rate and exergy cost of flows were determined as well as the exergy destruction rate in equipment. The main results indicate that 80% of the exergy destruction is placed on core processes (high pressure pumping and valve regulation, reverse osmosis separation and energy recovery), 29% extra exergy is necessary to obtain the unit of feed exergy from previous stages (seawater pumping and pretreatment) and extra exergy of 1.06 kJ is needed to generate 1 kJ of final product exergy (exergy performance about 50%). In addition, the moderate fluctuations of seawater environmental conditions in the Santa Cruz de Tenerife metropolitan area (and Canary Islands as a whole) establish that environmental parameters present a less important influence on exergy analysis.