注蒸汽燃机-热蒸馏海水淡化复合系统的环境负荷及其分摊

以注蒸汽燃机-热蒸馏海水淡化复合系统为例,基于火用经济学理论,建立了系统中电、水环境负荷的分摊模型,初步分析了系统的生命周期污染物排放,计算了系统中各火用流以及系统产品的环境负荷向量,得到了电、水的环境负荷分摊比。本文的研究虽然基于注蒸汽燃机-热蒸馏海水淡化系统而进行,但所探讨的方法同样适用于以干式燃机或其他湿式燃机为基础的电水联产系统。     

Analysis of a mechanical vapor compression desalination system

The mechanical vapor compression (MVC) desalination system is based on distillation of seawater. The system is basically a heat exchanger that is an evaporator/condenser. The heat required to evaporate water which flows on one side of a heat transfer surface is supplied through the simultaneous condensation of the distillate-producing vapor on the other side of the surface. That is, the latent heat is exchanged in the evaporation—condensation process within the system. A compressor is the driving force for this heat transfer and provides the energy required separating the solution and overcoming dynamic pressure losses and other irreversibilities. In this study, the operation characteristics of a low-temperature MVC desalination system are investigated. In the modeling, the overall energy balance and mass balance equations and LMTD method for heat transfer are used. The tube diameter and the tube length were taken at 0.025 m and 9 m, respectively. The main dependent parameters, the compressor work and the mass flow rate of the distilled water, were investigated against the independent parameters, the evaporation side pressure, the condensation side pressure, and the water inlet temperature.     

Economical study of a small-scale direct contact humidification-dehumidification desalination plant

Economical study of humidification-dehumidification desalination (HDD) pilot plant was made in order to estimate the economic benefits of the process in comparison with a small-scale reverse osmosis (RO) system. The energy recovery of the unit was investigated to be 75%. Some theoretical modifications were made to the HDD system in order to reduce the energy costs of the unit. Exact and clear economic analysis results were obtained using COMFAR ΙΙΙ software including fixed investment costs, production costs, internal rate of return on investment, operating costs, energy costs and some other economical parameters. Based on the energy prices in Iran, the total fresh water production cost was calculated to be $ 6.4/m³ that was nearly the same as produced by an imported RO plant. Finally some points were recommended whether to choose HDD or RO plant in different cases and capacities.     

Studies on a single-stage solar desalination system for domestic applications

In this paper, an attempt has been made to study a single stage solar desalination system to get a daily yield of 10 1 of potable water. The experimental system consists of a flat plate collector, an evaporator, a single stage vacuum pump and a condenser. The input parameters such as solar irradiance and vacuum pressure in the flash evaporator are varied to find its influence on the performance output viz., system efficiency and yield per day. Efficiency of this plant is found to vary from 15% to 26% for the variation in beam solar radiation from 400 W/m² to 900 W/m². A maximum distillate yield of 8.5 1/d is obtained with collector area of 2 m². The frequency of operation of the vacuum pump and the yield of desalinated water for various beam solar radiations is carried out from which the cost of water is determined. The cost of desalinated water is found to be 0.9 e/l. The desalinated water is tested for various parameters and the results indicate that the quality of water is satisfactory and well below the permissible limits.     

Characterization of a sulfonated pentablock copolymer for desalination applications

Water and salt transport properties were determined in a family of sulfonated pentablock copolymers to characterize their potential as chlorine-tolerant desalination membrane materials. The degree of sulfonation, block molecular weight, and casting conditions can be independently varied to tune the transport properties of these materials. Data for water uptake, water permeability, salt permeability, and apparent surface charge are presented. Apparent diffusion coefficients of water in these materials were calculated using the solution-diffusion theory. Generally speaking, water sorption, water diffusivity, water permeability, and salt permeability increase with increasing degree of sulfonation. As ion exchange capacity increases from 0.4 to 2.0 meq/g (dry polymer), water uptake values vary between 21% and 118%, and water permeability values, in units of cm² s⁻¹, vary over 4 orders of magnitude. Salt permeability depends on both the upstream sodium chloride concentration, between 0.01 and 1.0 mol L⁻¹, and the degree of sulfonation. Both water permeability and salt permeability are sensitive to the conditions used when casting the polymer films. Apparent surface charge, as characterized by zeta potential, has been shown to be related to the fouling tendency of several membrane materials. In these materials, zeta potential is most negative in samples with low levels of sulfonation and is near neutral in samples with the highest level of sulfonation.     

Measurements of dynamic behavior of a multistage flash water desalination system

This study focuses on measuring the process dynamics for the multistage flash desalination process (MSF) in an industrial unit with a capacity of 4546 m³/d. This is a novel addition to the literature because previous studies are limited to theoretical analysis of process dynamics or controller tuning, as well as conceptual design of conventional or advanced control systems. The measurements evaluate the performance of seven control loops, which include the pressure, temperature, and flow rate of the heating steam; the pressure of the vacuum ejector; and flow rates of the brine recycle, make-up seawater, and cooling seawater. All measurements start from steady-state conditions. The system is then set on manual where all control units are disengaged. Subsequently, only one control valve is adjusted by ± 15% of its steady-state setting. A total of 14 experiments were performed involving simultaneous measurements of the system variables. Measurements showed non-linear behavior where increasing or decreasing the valve settings did not provide similar trends. Analysis of results shows that one of the most sensitive variables is the distillate level in the last stage: the distillate trays either were flooded or became dry. The brine level in the last flashing stage was also found to be sensitive to valve settings where level increase resulted in higher product salinity. The results and analysis presented provide a better understanding in system fault analysis which could be caused by improper operating conditions. These data are essential to propose, design, and evaluate advanced/comprehensive control systems for the MSF process.     

Technical and economic analysis for the integration of small reverse osmosis desalination plants into MAST gas turbine cycles for power generation

A technical and economic analysis concerning the integration of small reverse osmosis (RO) desalination plants into mixed air steam turbine (MAST) technologies for power generation was carried out. The simulation tool used is the computer aid reverse osmosis calculations optimization algorithm. This user-friendly software takes into account the capital cost, fuel cost and operation and maintenance requirements of each candidate RO desalination plan scheme and calculates the least-cost configuration. The results indicate that the integration of a RO desalination plant into MAST gas turbines has a minor effect on the final operating cost of the power plant.     

Feasibility of reverse osmosis desalination of brackish agricultural drainage water in the San Joaquin Valley

The technical feasibility of reverse osmosis (RO) desalination of agricultural drainage (AD) water in California's San Joaquin Valley (SJV) was evaluated based on systematic analysis of water quality monitoring data and field water desalting tests in a laboratory plate-and-frame RO (PFRO) system. Thermodynamic solubility analysis and diagnostic PFRO desalting tests served to determine the feasible range of water recovery limits and to assess the mineral scaling potential. Analysis of the recovery limits imposed by scaling due to sparingly soluble salts (e.g. calcite, gypsum, silica) suggested feasible recoveries in the range of 46%-69%. Diagnostic PFRO desalting tests with five representative field water sources from the SJV (having gypsum and calcite saturation indices in the range of 0.12-1.03 and 2.9-9.5, respectively) confirmed the above recovery range. Mineral scale coverage was consistent with the observed flux decline. Deployment of RO technology for treatment of brackish SJV AD water would require site-specific process optimization given the geographic and temporal water quality variabilities. Therefore, RO operation with variable feed water quality (with respect to salinity and scaling propensity) and at sufficiently high recovery would require effective plant control, enabled by real-time mineral scale detection and adaptable process operation to mitigate mineral scaling.     

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.     

Characterization of uncertainties in the operation and economics of the proposed seawater desalination plant in the Gaza Strip

In the Gaza Strip, the available freshwater sources are severely polluted and overused. Desalination of seawater through reverse osmosis (RO) has become the most realistic option to meet a rapidly growing water demand. It is estimated that the Gaza Strip will need to develop a seawater desalination capacity of about 120,000 m³/d by the year 2008, and an additional 30,000 m³/d by the year 2016 in order to maintain a fresh water balance in the coastal aquifer and to fulfill the water demand for different uses in a sustainable manner. Cost and reliability of a large RO facility are still subject to much uncertainty. The cost of seawater desalination by RO systems varies with facility size and lifetime, financing conditions, intake type and pre-treatment requirements, power requirements, recovery rate, chemicals cost, spare parts cost, and membrane replacement cost. The permeate salinity is a function of feed water temperature, recovery rate, and permeate flux. The quantity of water produced depends mainly on plant size, recovery rate, and operating load factor. Many of these parameters are subject to a great deal of uncertainty. The objective of this work is to develop a probabilistic model for the simulation of seawater reverse osmosis processes using a Bayesian belief network (BBN) approach. This model represents a new application of probabilistic modeling tools to a large-scale complex system. The model is used to: (1) characterize the different uncertainties involved in the RO process; (2) optimize the RO process reliability and cost; and (3) study how uncertainty in unit capital cost, unit operation and maintenance (O&M) cost, and permeate quality is related to different input variables. The model utilizes information from journal articles, books, expert opinions, and technical reports related to the study area, and can be used to support operators and decision makers in the design of RO systems and formulation of operational policies. The structure of the model is not specific to the Gaza Strip and can be easily populated with data from any large-scale RO plant in any part of the world.     

Optimal design of hybrid RO/MSF desalination plants Part II: Results and discussion

This paper presents the results of an optimization study, based on minimum water cost, to explore the feasibility of the hybridization of RO and MSF processes. The study explores the possible improvement of MSF process economics. Nine different scenarios for the production of the same capacity of desalted water are presented and compared from the standpoint of minimum water cost, specific capital cost and water recovery. The process and cost models, formulation of the optimization problem and solution outlines were previously presented in the first part of this study. In this work, results show that RO technology is recommended when building new desalination plants. RO technology becomes preferable at low feed concentrations and for brackish water desalination. Although they come in second position after the RO process, some hybrid plants economically exceed by far the MSF process. Computations gave a water cost of 1.1 $/m³ for the brine recycle MSF process against 0.75 $/m³ for the two-stage RO process. Water cost of the MSF process can be reduced by 17 to 24% through hybridization with RO technology.     

化工矿山预可行性研究计算机辅助设计系统

概略介绍了该系统的功能、结构、运行方式及控制逻辑结构,以及测试结果。     

Once-through and brine recirculation MSF designs — a comparative study

This study investigated the feasibility of the once-through (OT) MSF design for constructing large-capacity desalting plants rather than the conventional brine recycle (BR) MSF configuration. This was to explore the possibility of improving MSF process economics through the application of a simpler process design. It is known that the OT design is characterized by its simplicity and elimination of the brine recirculation pump as well as the rejection section. These features are expected to reduce capital and maintenance costs. The current study is based on comparing the two MSF plant configurations, OT and BR, from the standpoint of minimum heat transfer area, which is a major element in capital investment. Alternative tube layouts, long-tube (LT) and cross-tube (CT) arrangements, were considered. Design calculations were based on a plant capacity of 20 MGD, a gained output ratio of 10, a top brine temperature of 120°C, a feed temperature and concentration of 35°C and 48,000 ppm, respectively. The total number of stages was varied stepwise between 20 and 40. A rigorous mathematical model was developed to solve the optimization problem taking into consideration the nonlinearity of the thermo-physical properties of seawater and steam. The Solver tool of Microsoft Excel was used to determine the optimal solutions. Substantial savings in the heat transfer area can be realized through the application of the LT-OT design when the number of stages goes up to 40. However, comparison of the different MSF designs with the optimal number of stages and minimum heat transfer area tells us that the use of the OT designs is not likely to save more than 1% in heat transfer area relative to the conventional CT-BR configuration. Findings related to the specific chemical consumption are not in favor of OT plants where the consumption ratio varies between 1.7 and 1.9 relative to the CT-BR plants. Of course, excessive chemical consumption penalizes the operating cost of the OT plants. However, the increase in operating costs has to be weighed against the savings in capital cost and lower power consumption due to the elimination of the recycle pump and the heat rejection section. This will determine the use of the OT configuration for building MSF plants in the future. In this event, a detailed cost analysis will be needed.     

海水淡化系统的性能优化与评价准则

可持续发展要求海水淡化系统不仅具有优良的经济性,还要具有优良的环境性能,目前综合考虑这二方面因素的研究还很少。文中从海水淡化系统的综合性能优化和评价出发,建立了统一性能指标(亦称淡水综合成本),该指标由淡水生产的经济成本和环境成本构成,以其为目标函数优化得到的系统具有最佳能源、经济、环境综合性能。淡水的综合成本、经济成本、环境成本还构成了海水淡化系统的多准则性能评价体系,据此可实现对不同海水淡化方法和装置的更全面、合理的评价。基于前面建立的性能准则,以近年来受到较多关注的低温多效蒸发海水淡化系统为例进行了计算、分析和讨论,研究结果验证了准则的合理性和有效性。     

Theoretical analysis of a single-stage and two-stage solar driven flash desalination system based on passive vacuum generation

An innovative solar driven flash desalination system is proposed. The system uses the natural forces of gravity and atmospheric pressure to create a vacuum. Single-stage and two-stage concepts have been outlined. The main components include evaporator(s), condenser(s), collection tanks, heat source and seawater circulation pump. Partial heat recovery is attained by first passing the feedwater through the condenser(s), followed by the heat source. Additional distillate output is obtained in the second stage of the two-stage system without any extra heat addition, since the high temperature brine from the first stage is passed and flashed in the second stage.Theoretical analysis of the single-stage and two-stage concepts is done for the system when coupled with constant temperature heat source and solar collector. When coupled with a solar collector of 1 m² area, a single-stage system produces 5.54 kg of water in 7.83 h, while the two-stage system produces 8.66 kg in 7.7 h. The performance ratios obtained, including the efficiency of solar collectors, are 0.48 and 0.75 for a single-stage and two-stage system respectively, or 0.748 and 1.350 if only the useful heat collected by the solar collector is considered.     

新建1000MW火电机组补给水系统可行性研究

通过对国华徐州电厂现有锅炉补给水处理系统的产水量标定、产水水质测定、设备状态评估以及经济性评价,全面论证了将它用于现有2×220MW机组和新建2×1000MW机组的可行性,并提出了设备改造和系统优化方案。     

新建1 000 MW火电机组补给水系统可行性研究

通过对国华徐州电厂现有锅炉补给水处理系统的产水量标定、产水水质测定、设备状态评估以及经济性评价,全面论证了将它用于现有2×220MW机组和新建2×1000MW机组的可行性,并提出了设备改造和系统优化方案。     

Numerical simulation and analysis of a patented desalination and power co-generation cycle

A patented cycle for water desalination and power generation was evaluated with regard to thermal efficiency and water production. The inventor of the patent claimed that the patented cycle provides a thermal efficiency of 41 %, which is higher than current combined water and power generation steam plants. A simulation program was developed to evaluate the thermal efficiency and water productivity of this cycle. Simulation parameters were selected from data provided by the patent as well as data generally used in the design of combined power and desalination plants. Results of the simulation were compared with a simulation of the Jubail-II combined plant. The simulation proved that the patented cycle is far inferior to current dual-purpose MSF desalination plants in terms ofwater production. In addition, the patent was found to have a much lower efficiency than what was claimed by the inventor.     

螺旋扭曲管用于燃气轮机进气温度调节换热器的可行性研究

对将螺旋扭曲管用于燃机进气温度调节换热器进行可行性分析,模拟燃机进气加热器实际运行的工况条件进行综合传热性能实验研究,得到了传热与流阻准则关系式;引入综合评价因子概念并与传统钢铝翅片管换热器进行对比发现,螺旋扭曲管换热器是钢铝翅片管换热器的1.31~1.52倍。以某建设项目采用的E级PG9171E型机组为例,对采用螺旋扭曲管和钢铝翅片管的两种进气温度调节换热器进行对比发现：当采用螺旋扭曲管换热器时,在同样换热能力下,换热器风侧阻力增大了14.7%;在同等质量下,换热器换热能力提高9.9%左右。     

Transient performance of a stepped solar still withbuilt-in latent heat thermal energy storage

The transient performance of a stepped solar still with built-in latent heat thermal energy storage was studied. Thestill was designed for heating and humidification of agriculture greenhouses (GH) in remote areas. The solar still consists of five stepped basins with an inclined glass cover and is insulated on the bottom. The basin was placed on a slab filled with a layer of paraffin wax (phase change material, PCM) that acts as a latent heat thermal energy storage system (LHTESS). Air from GH enters the still from the bottom, flows between the basins and glass cover where it is heated and humidified, and then flows back into the GH. The still performance parameters investigated were analyzed, and the results compared with the case of a still without the LHTESS. The results showed that the still with LHTESS has an efficiency of 57%, and the total daily yield is about 4.6 L/m². The still temperature as well as outlet air temperature and GH heat load are more uniform compared to the sinusoidal trends for the still without LHTESS. It was found that the relative humidity of circulating air increased along the still and always leaves at saturation conditions. The results indicated that decreasing the air flow rate has an insignificant influence on the still yield, while the GH heat load experiences a decrease. For a selected design and operational parameters, the still was able to provide heat for the GH for 24 h/d. This finding is important since heat could be provided to the GH at night and when it is most needed.