Solar stills made with tubes for sea water desalting

The report concerns basic technological features of simple solar stills utilizing tubes for sea water desalting. The evaporation section comprises horizontal transparent thin-walled plastic or glass tubes, of ~0.10–0.25 m inner diameter, half-filled with sea water which absorbs solar radiation. The condensation section is physically separated from the evaporation section, in a shaded space below it, and comprises horizontal plastic or metal tubes of ~0.01 m inner diameter. The wall thickness of condenser plastic tubes is rather small, ~50 μm.

Water vapour released by solar radiation in evaporator tubes flows into condenser tubes to be condensed into produced fresh water by delivering condensation latent heat to atmospheric air. Heat transfer by air convection may be helped by surface winds, often available in coastal areas. Enhanced fresh water productivity is expected with respect to conventional solar stills in which sea water evaporation and water vapour condensation occur in one confined space. Technological features of the proposed solar stills are analysed in some detail and specific experimental work is suggested on prototype solar stills in view of clarifying relevant aspects concerning transparent and opaque construction materials, assembling procedures, and the role of the various operative parameters vis-à-vis energy efficiency and fresh water productivity.     

Fertilizers and the environment

Soil fertility decline is occurring over large parts of the world, particularly the developing world. It occurs mainly through intensive cultivation and the inadequate application of replacement nutrients, and through deforestation and clearance of vegetation on sandy soils. Large amounts of soil nutrients are also lost to the terrestrial ecosystems through wind and water erosion. Low soil fertility is considered as one of the most important constraints on improved agricultural production. To sustain the future world population more fertilizers are required, which may become an environmental hazard, unless adequate technical and socio-economic measures are taken. It is estimated that, by the year 2020 at a global level, 70% of plant nutrients will have to come from fertilizers. Fertilizers are thus indispensable for sustained food production, but excessive use of mineral fertilizers has roused environmental concerns. Chief among these concerns are eutrophication of fresh water bodies, global warming and stratospheric ozone depletion, proliferation of algal blooms in coastal waters and contribution towards acid rain.     

Applicability of flashing desalination technique for small scale needs using a novel integrated system coupled with nanofluid-based solar collector

The present study introduces an attempt for the application of flash desalination technique for small scale needs. An integrated system uses a flashing desalination technique coupled with nano-fluid-based solar collector as a heat source has been made to investigate both the effect of different operating modes and that of the variation of functioning parameters and weather conditions on the fresh water production. The flashing unit is performed by similar construction design technique of commercial multi-stage flashing (MSF) plant. The thermal properties of working fluid in the solar collector have been improved by using different concentrated nano-particles. Cu nano-particle is used in the modeling to determine the proper nano-fluid volume fraction that gives higher fresh water productivity. An economic analysis was conducted, since it affects the final cost of produced water, to determine the cost of fresh water production. Although a system may be technically very efficient, it may not be economical. The effect of different feed water and inlet cooling water temperatures on the system performance was studied. The mathematical model is developed to calculate the productivity of the system under different operating conditions. The proposed system gives a reasonable production of fresh water up to 7.7 l/m²/day under the operation conditions. Based on the cost of energy in Egypt, the estimated cost of the generated potable water was 11.68 US$/m³. The efficiency of the system is measured by the gained output ratio (GOR) with day time. The gained output ratio (GOR) of the system reaches 1.058. The current study showed that the solar water heater collecting area is considered a significant factor for reducing the water production cost. Also, the produced water costs decrease with increasing the collecting area of the solar water heater. The volume fractions of nano-particle in solar collector working fluid have a significant impact on increasing the fresh water production and decreasing cost.     

新型闭式太阳能海水淡化装置及其性能模拟

本文提出了一种闭式海水淡化装置,阐述了系统的工作原理,建立了相应的数学模型。就冷却水流量、海水喷淋量、集热器面积、蒸发器尺寸等因素对系统淡水产量的影响情况进行了计算机模拟,根据实验测得的气象数据对一天内系统淡水产量随时间变化情况进行了模拟,并根据典型的月平均日气象数据对系统一年内每个月的系统性能进行了分析。分析表明,不计系统夜间运行时的淡水产量,在西安地区系统淡水产量可以达到4.6kg/d.m2。     

New experimental aspects of the carrier gas process (CGP)

The carrier gas process (CGP) based on humidification and dehumidification is a new interesting process (with respect to previous conventional processes such as multistage flash and reverse osmosis) for water desalination. The CGP contains several advantages such as flexibility in capacity, moderate installation and operating cost, possibility of using a wide range of thermal energies (geothermal, solar, recovered, direct fossil fuel, etc.) and simplicity (atmospheric pressure). The aim of this paper is to present the principal and characteristics of this technique based on experimental investigation. The present pilot plant unit consists of two packed columns, humidification and dehumidification, one heat exchanger and one air pre-heater. Most investigators have used solar thermal energy as the source for heating the saline water, but in this work electrical energy was used for heating the air stream. Besides this point most investigators have used a coil heat exchanger for condensation of fresh water but in the present work a packed column was used instead to do the same job. The experimental results of the work that was carried out at Bushehr Port, southern Iran, were: the effect of air pre-heater and coolant water temperatures, air, saline water, recirculating fresh water and coolant water flow rates on the amount of produced fresh water per unit of heat duty and fresh water production flow rate. It was found that the performance of the system strongly depended on the temperature and flow rate of the air pre-heater and the temperature and flow rate of the coolant water. However, it depended weakly on the flow rate of the saline water and fresh water re-circulation. It is expected that the unit would be of great potential for saline water desalination in arid areas and isolated islands.     

A small solar desalination plant for the production of drinking water in remote arid areas of southern Algeria

The common methods of desalination salt water for production of fresh water by distillation, reverse osmosis and electrodialysis are intensive energy techniques. However, in remote arid areas, the desalination needs not exceed a few cubic meters per day. This decentralised demand favours local water production by developing other desalination processes, especially those using renewable or recovered energy (solar, geothermal, etc.). Solar desalination process is one of these methods used to resolve the scarcity of fresh water. Several reviews have been published by different authors. Small production systems as solar stills can be used if fresh water demand is low and the land is available at low cost. To supply the population of remote arid lands of South Algeria with drinkable water, solar distillation of brackish waters is recommended. It satisfies some of theses demands. Solar stills are used to produce fresh water from brackish water by directly utilising sunshine. These stills represent the best technical solution to supply remote villages or settlements in South Algeria with fresh water without depending on high-tech and skills. The production capacity indicates a possible daily production of far more than 15 l/m²d. Therefore, the still has a place in the upper range of known comparable products with regards to production output. This depends on the material used and the price of the solar stills and their accessories. The best working temperature solves most problems. Small, modular high-performance stills with features like the possibility of decentralised use, less maintenance and robust construction can help to reduce fresh water scarcity. The recent development of stills based on new concepts and heat recovery has been successful. The technical optimization is still in process today, it aims to improvement of the efficiency of these distillers. In our research work, a plant for brackish water distillation by directly sunshine and heat recovery was constructed and investigated experimentally and theoretically in South Algeria. This study aims the improvement of the performance of this solar distillation plant, conducted under the actual insulation, for brackish underground geothermal water desalination.     

Comparison of classical solar chimney power system and combined solar chimney system for power generation and seawater desalination

An alternative method of heat and moisture extraction from seawater under the collector of a solar chimney system for power generation and seawater desalination is investigated with the aim of estimating the output of power and fresh water when used in seawater desalination using one-dimensional compressible flow model. It is found that the temperature and velocity of the airflow inside the chimney in the combined plant is less than that inside the chimney in the classic plant due to the release of vapor latent heat as the air rises up the chimney. Additionally, the power output from air turbine generators and water generators in the combined plant is less than that of the classic plant. Furthermore, a revenue analysis based on the price of fresh water and electric power in Dalian, China shows that the chimney less than 445 m high for the proposed combined solar chimney power plant having a collector 3000 m in radius is more economical than for the classic plant. The critical chimney height is found to depend on the local price of fresh water and electricity.     

An evaluation of the energy requirements of desalination processes on the basis of the fuel-use performance ratio

The fuel-use performance ratio is defined as the quantity of water produced, in kg, per 1000 kJ of the heat content of the fuel used for supplying thermal, mechanical and/or electrical energy to the desalination plant. The concept is used to evaluate the energy requirements of the major sea water conversion processes - reverse osmosis, multistage flash, multiple effect boiling (as exemplified in the vertical tube foam evaporation process), vapor compression and hybrids of the thermal processes - for three types of plants: (a) single-purpose (water only), (b) dual-purpose (power/water) involving “power loss” and (c) dual-purpose (power/water) utilizing waste heat. It is concluded that only distillation systems based on waste heat can compete with the low energy requirements of reverse osmosis.     

竖壁自储水式蒸馏器空腔自然对流换热及产水特性

引言利用太阳能进行海水淡化是解决淡水短缺的重要途径之一。世界范围内对此课题展开了多方面的研究,最具代表意义的是太阳能多效蒸馏技术以及露点蒸馏技术。太阳能多效蒸馏技术由于具有结     

有机热载体炉的安全使用

文章介绍了影响有机热载体炉安全使用的四个方面:有机热载体的选用原则是高热稳定性、环保性能和最高使用温度;有机热载体质量监测和控制的四个主要指标是运动粘度、闪点、残炭和酸值,应符合相应要求,以及防止有机热载体过热和氧化的方法;有机热载体炉的设计和安装应符合《有机热载体炉安全技术监察规程》要求;严格执行有机热载体炉的安全操作规程,预防事故发生。     

Design of a small solar-powered desalination system

A design is presented for a solar/thermal system configured to power a reverse osmosis (RO) desalination unit to produce 7000 gallons of fresh water in an eight hour period. A field of line-focus tracking solar collectors is used to heat a high pressure liquid-vapor water storage tank supplying two compound reciprocating steam engines, one direct-connected to the RO high-pressure pump and the other to an electric generator for auxiliary power. An auxiliary heating loop with an oil-fired boiler is also used to supply the steam engines.The system operates in either all-solar, all-oil, or mixed solar/oil modes. Primary operating mode is assumed to be a mixed solar/oil mode in which the oil-fired boiler is used only to prevent shutdown of the RO system during the course of a partly sunny day. In this mode, the RO system does not come on line in the morning until the solar collector field has brought the high-pressure storage tank to a point near maximum operating pressure. Thereafter, the oil-fired boiler comes on automatically whenever the storage tank is drawn down to a pressure near minimum full-power operation (due to inadequate or intermittent insolation) and remains on, supplying the steam engines, until the solar collectors have again brought the storage tank to the high-pressure cutoff.In the all-solar mode, the system continues to operate at reduced power as storage tank pressure drops below the point at which the oil-fired boiler would otherwise come on. A portion of the RO system is shut down to maintain pressure in the remainder.The all-oil mode is used whenever fresh water is required during non-sunny periods, or to increase fresh water production in sunny periods.     

The barium sulfate seeding process

The maximum brine temperatures in the final heaters of multistage flash evaporators, being limited by calcium sulfate scaling, in the case of acid decarbonized sea water, might be enhanced by seeding processes. Use of barium sulfate (barite) as seed has recently been proposed in a feasibility study and reported to have the advantage of recycling of a given amount of barite, and the special advantage of inherent diminution of the calcium concentration in the circulating brine. Using the MEWAK I closed loop system, experiments have shown that barite particles remain active as seed when the suspension system is alternatively heated and cooled several times. The “loading” and “unloading” velocity is satisfactory. Further experiments are concerned with the separation of barite from its suspension in sea water brine by hydrocyclones.     

考虑水需求的水电联产海水淡化系统的优化设计

水电联产不仅能缓解淡水资源不足的问题,而且可有效降低能耗和淡化成本。建立了水电联产系统数学模型,将优化设计描述为一个混合整数非线性规划(MINLP)问题,并采用混合编码的遗传算法进行求解,结果表明,以水定电模式下水电联产系统最优操作模式为发电、多级闪蒸(MSF)和反渗透(RO)三者的集成,且MSF和RO的产水比存在最优值,发电采用背压式蒸汽轮机。随着淡水需求量的增加,联产系统的淡水成本逐渐降低,MSF与RO的产水比呈现出逐渐降低的趋势。     

Sea water intake and its effect on heat rejection design and material for flash distillation plant

The suspended matter in sea water play a big role in the design of sea water intake and heat rejection section.The sea water intake usually depends on the shore nature and quality of sea water. Chemical treatment can handle marine growth and bacteria but the suspended matter in the sea water need further treatment usually by settling basin and screens, these are normally costly and need minimum plant size to prove its economical aspects. For relative small installation up to about 15 MIGPD Plant other solution can be adopted in the sea water design and choice of materials of heat rejection section.In case of sea water having suspended sand higher than certain sizes and quantity with large temperature differences between summer and winter and tubes of copper bases will lead to either over design of the heat rejection flash stages or providing recirculating sea water facilities between the outlet and inlet of the heat exchanger of the heat rejection section. Comparison has been carried out for cupro-nickel tubes and titanium tubes with and without settling basin respectively and comprehensive study and analysis has been done as well as discussion on cost, operation procedures, limit of parameters such as velocities, corrosion deposit, erosion and fouling etc.Recommendation and conclusion are given.     

Desalination in Australia operational experience and future prospects

To provide high quality fresh water to meet peak demands at times of drought in large population centres and to satisfy the requirements for water standards in industrial processes are perhaps the prime attractions of sea water desalination plants. Australia, the driest of earth's continents, will probably have a need for such water supply supplementation and industrial process application long before desalting is applied generally to agriculture or rural production. As the cost of fossil fuel gradually increases, it would also seem likely that the thermal energy required for desalting will come from nuclear fuels. In this paper the existing fresh water resources of the Australian continent are briefly surveyed. Present costs associated with supplying fresh water for industrial and domestic consumption to selected communities at representative locations of the Australian continent are assessed. The technology and economics of large scale sea water desalination plants operating on thermal cycles are discussed. In particular, the multi-stage flash evaporator principle is reviewed and its potential discussed. Consideration is given to the advantages and disadvantages of nuclear powered heat sources. Proposals are made for the control and conjunctive use of reservoirs and desalination plants. The optimisation of desalination plant size and its integration with reservoir storage schemes in two potential Australian locations is discussed.     

Alarm substance of the marine mud snail,Nassarius obsoletus: Biological characterization and possible evolution

The gastropod snailNassarius obsoletus shows a dramatic self-burial response to the presence of crushed conspecifics. After it was shown that this burial alarm response could be reliably replicated in laboratory tests, a further characterization of the alarm substance was undertaken. Dilution experiments showed a very high response threshold resulting in a short effective radius of the substance in agreement with earlier field reports. Longevity experiments showed that the substance had lost some activity after 16 hr standing over marsh mud in sea water at room temperature; it became inactive after 24 hr. Superthreshold concentration in sea water was not necessary to keep the snails buried: Mud apparently provides an adsorption surface which can remain a stimulus source for previously unalarmed snails, and snails tend to remain buried after a short exposure to alarm substance, even when given a fresh environment. The substance is present in the snail's blood and tissues and is passively released. A potential natural predator capable of such release isCarcinus maenas, the green crab. Predator odor alone did not cause burial alarm responses. Preliminary chemical analysis indicates that the substance is water soluble, heat stable, and of high apparent molecular weight (over 100,000). A comparison with fish alarm substance and response is made in a discussion of the possible evolution of chemically triggered alarm responses. It is argued thatN. obsoletus may have developed an alarm response to an existing nonspecific substance rather than a true alarm pheromone.This paper is based in part upon a thesis submitted by D.S. to Boston University for the degree of Master of Arts.     

Operational issues in isothermal calorimetry

Isothermal (heat conduction) calorimetry is a general technique to study processes through the thermal power they produce. This paper deals with operational issues concerning isothermal calorimeters. In this paper it is shown that steady-state and pulse calibrations give the same result; that the use of mobile heaters (placed in the reaction ampoule) give more accurate results than fixed heaters (placed in the ampoule holder); and that at least the tested calorimeter had calibration coefficients that were independent of the thermal power level. It is shown that well balanced references are necessary to get low noise and low drifts. It is discussed how baselines should be measured. The influence of temperature and sample size is also discussed and it is shown that large cement paste samples with high thermal powers will show an accelerated reaction. Finally, the thermal dynamics of a heat conduction calorimeter is discussed.     

Parametric analysis to improve the performance of a solar desalination unit with humidification and dehumidification

A solar desalination unit with humidification and dehumidification, characterized by reusing some of somewhat concentrated saline water after evaporation, recovering condensation heat, and forced air flow, was expected to produce more fresh water. A mathematical model of the unit is presented. The model was experimentally validated for numerical simulation. Parametric analysis was conducted in order to optimize the unit performance. The effect of some of the operating conditions such as flow rates, temperatures of feed water, air and cooling water, etc., was studied in detail. The daily solar productivity corresponding to unit square meter of collector area is about 6 kg/m²/d with 20 MJ solar energy input a day under given conditions. The unit has proven to be an efficient device to utilize solar energy for obtaining fresh water from saline water.     

Humidification-dehumidification desalination system driven by geothermal energy

The work presented in this paper focuses on desalinating sea water system using a humidification-dehumidification process as it is supplied with water heated by geothermal energy as clean and renewable natural resources of energy. Computer simulation of the behavior under various working conditions of the desalination system was carried out to predict the variations of key output. Such variables include the ratio of sea water mass flow rate related to air mass flow rate, cooling water temperature difference across the condenser, geothermal source inlet temperatures to the heat exchanger and the amount of produced distilled water. To validate the computer program, a comparison between the experimental and theoretical results was conducted, and a good agreement had been obtained. The result showed that, the optimum value of the ratio between sea water mass flow rate to air mass flow rate was found to be in the range of 1.5 to 2.5. Improvement in the fresh water productivity at the optimum ratio of sea water mass flow rate to the air flow rate was observed by increasing both the geothermal source inlet temperature and the cooling water temperature difference across the condenser.     

Desalinated water production at LNG-terminals

A process has been worked out to apply the laws of thermodynamics to sea water desalination making use of LNG.Ambient temperature heat is applied to LNG which evaporates and generates power.This power is employed to extract heat from sea water; part of the sea water is frozen and the heat is discharged to environment.The ice produced is melted at ambient temperature and desalted water is obtained.Detailed technical calculations have been developed by Nuovo Pignone in the past and cost estimations made for both investment and production costs. At present this is probably the cheapest method of producing desalted water.Conventional technology is used for every component of the resulting plant.This kind of plant may produce quite a substantial amount of desalted water, up to 30.2 tons of water per ton of LNG. Therefore a terminal capacity of 5.10⁹ Nm3/yr of natural gas may produce 10,000 t/d of water, equivalent to the needs of a town of 40,000 inhabitants.