Solar multistage flash evaporation (smsf) as a solar energy application on desalination processes

The application of solar energy on desalination constitutes one of the activities of the research and development program of digases. Within this philosophy a project is being developed in cooperation with the Federal Republic of Germany. The objective of the project is to test and prove the feasibility of the solar energy utilization as the source of the thermal energy required for a multistage flash evaporation plant.

The plant is composed of three systems:

1. Desalination system. Multistage flash evaporation plant with 10m³/d production capacity, 5.0 in performance ratio and 10 stages.

2. Solar energy captation. Composed of one low temperature subsystem of double pipe flat collectors with 670m² of effective captation surface, and a high temperature subsystem composed of parabolic concentrators with 320m² of captation surface.

3. Storage of energy. System designed with such capacity which allows continuous operation of desalination unit.

The poject is separated into two phases. The first includes the design manufacturing and tests for the three systems. The second phase comprises the installation and integration of the systems which compose the plant, the start-up operation and evaluation of plant performance.

At the present time, the first phase of the project is under development and it is expected to finish it at the end of June. The second phase will start in August with system start-up scheduled for the end of October.     

Operating experience on RO sea water desalination plant at chigasaki laboratory

A demonstration plant with a capacity of 800 m³/d has been operating satisfactorily in Chigasaki Laboratory since September 11, 1979. The plant has two sets of modules, namely hollow fiber and spiral wound types. These two types of modules have been operated alternately every other month, being supplied sea water from the same pretreatment facility and the same high pressure pump. The accumulated operation time of each module has exceeded 5,000 hours. The operation result shows high recovery ratio, low energy consumption and good quality of product water.     

Catalysis for fine chemicals: towards specificity with polyphasic media

Three examples of the work undertaken at the Institut de Recherches sur la Catalyse for the selective preparation of fine chemicals in polyphasic media are presented and discussed:

1. diastereoselective hydrogenation of 1,2-disubstituted arenes to cyclohexyl derivatives,

2. chemoselective oxidation of anilines, and

3. regioselective alkoxycarbonylation of styrene derivatives to 2-arylpropionic esters.

Factors influencing the selectivity of these reactions are discussed in the light of concepts from molecular chemistry.     

Hydrodenitrogenation of isoquinoline

To determine the formation and reactivity of addition compounds produced during hydrodenitrogenation (HDN), we investigated the HDN of isoquinoline for a sulfided Ni–Mo/Al₂O₃ catalyst operated under a hydrogen pressure of 12 MPa (cold charge) in the temperature range 300–375°C. The reaction products were classified into five groups of compounds:

1. hydrogenated derivatives of isoquinoline (tetrahydroisoquinolines, decahydroisoquinolines, and their isomers);

2. nitrogen-containing ring-opened products (1-amino-2-(2-methylphenyl)ethane and 1-amino-1-(2-ethylphenyl)methane);

3. denitrogenated products (1-ethyl-2-methylbenzene, 1-ethyl-2-methylcyclohexane, and their isomers);

4. addition products (hydrocarbons with molecular weights of 238, 244, and 250 and nitrogen-containing compounds with molecular weights of 249, 251, and 257); and

5. cracked products (toluene, ethylbenzene, dimethylbenzenes, and their hydrogenated derivatives).

Most of the nitrogen-containing addition compounds appear to be substituted on the nitrogen atom. The HDN of isoquinoline was more than 10 times faster than the HDN of quinoline, whereas the hydrogenation of isoquinoline was difficult compared to the hydrogenation of quinoline. The reaction network for the HDN of isoquinoline is also presented.     

Low-temperature methanol synthesis from carbon dioxide and hydrogen via formic ester

A new route of methanol synthesis, at 443 K and under pressurized conditions, from carbon dioxide and hydrogen through formic ester was investigated, by using Cu-based catalysts. This one-pot reaction consisted of three steps:

1. formic acid synthesis from CO₂ and H₂,

2. esterification of formic acid by ethanol to ethyl formate, and

3. hydrogenolysis of ethyl formate to methanol and ethanol.

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.     

Pilot filtration study to reduce fouling on Marbella seawater RO plant

The seawater RO plant at Marbella had operated intermittently, and at low flowrates, since its construction 10 years ago. This was because the plant had been designed to operate at times of water shortage, to provide water when the conventional supplies were not available.

During the early part of the 21st century, the mode of the plant changed, and it was expected to operate at design capacity for most of the time. This brought two facts to light — that during high abstraction rates the intake water quality deteriorated significantly, and that the filtration system that had been installed was not capable of adequately filtering the feed water to make it suitable for feeding to a reverse osmosis plant.

The plant was originally built using DuPont B10 permeators. Due to the unavailabilty of these permeators, the plant is currently being converted, stream by stream, to spiral wound membranes supplied by Hydranautics.

At design flowrates, the DuPont system fouled rapidly, and required cleaning every two weeks. The spiral trains fouled more slowly, but still required cleaning at a higher frequency than would be considered normal for this type of plant.

A pilot filtration plant was installed on site to attempt to find the following;

• An optimum coagulant for the water.

• An approximate dose rate for that coagulant.

• The effect of different media on the quality of filtered water.

• The length of run between backwashes using different media.

• The quality of water that can be achieved using this coagulant and media.

By installing pressure tapping points along the length of the filter, the area of differential pressure could be measured. This was used to ensure depth filtration was taking place, and the foulants were being removed through the length of the bed rather than surface filtration.

The trials lasted a total of three months and achieved all of the targets set. The SDI typically achieved by the main plant was approximately 5. The pilot filter showed that the SDI could be reduced to below 2 by modifying the filters and applying a coagulant. Filter runs achieved by the pilot filters were in excess of 48 h.

Following the trials, the plant commenced replacing the media in the filtration system, and is expected to install a coagulant dosing system once this was complete.

This paper describes the pilot plant built, the selection of the media, and the coagulants used, and presents the operating data produced from the trials.     

Reverse osmosis to achieve water control and recycle

A 648,000 GPD reverse osmosis (RO) facility at ERDA's Rocky Flats Plant near Golden, Colorado will convert tertiary sewage plant effluent for recycle as cooling tower makeup to reduce external water demand and achieve “zero discharge” off-site of tertiary sewage effluent.

Design parameters for the facility, determined by three years of pilot plant testing, include 98% feedwater recovery, 100 ppm T.D.S. product water, and minimum brine production for evaporation to dryness.

Pretreatment consists of RO feed attenuation in a large pond, chlorination, sand filtration, softening, diatomaceous earth filtration, feed-water heating and pH adjustment. The RO plant will have three 150 GPM trains, each with a combination of HFF modules producing about 90% of the permeate, followed by SW modules producing the final 10%. Permeate from the SW modules can be combined with permeate from the HFF modules or returned to the RO feed stream.

Unique design considerations include heating the 40–70°F fee to 77°F by means of heat recovery from the permeate and supplemental steam heating, recycling of pretreatment backwash streams wherever possible to reduce the volume of brine, and precautions to avoid silica scaling of the modules.     

反渗透海水淡化中差动式能量回收装置的研究

研究了一种应用于中小型反渗透海水淡化装置的新型差动式能量回收装置.结果表明,使用本能量回收装置的日产10m3反渗透海水淡化装置的单位淡水能耗只有3.6kWh/m^3,不考虑高压泵及电机自身损耗的影响时,单位淡水能耗为2.3～2.7kWh/m^3,装置能耗显著降低,能量回收效率达到97%.此能量回收装置不需要其它附加增压设备,并且能有效改进由于阀门开闭导致系统压力波动而造成的淡水产量不稳定的问题,保护了反渗透膜、高压泵等系统内的重要设备.     

冷却水流量对ORC系统性能影响的实验研究

采用自主研发的单螺杆膨胀机作为机械动力,实验研究了冷却水流量对ORC余热发电测试系统及单螺杆膨胀机性能的影响。实验结果表明：当冷却水流量从8 m³·h^-1升至19 m³·h^-1时,单螺杆膨胀机输出功和轴效率分别从4.31 kW、36.38%增至5.15 kW、41.1%,分别增加了19.5%、13%。针对本实验系统,在考虑润滑油泵、工质泵、冷却水泵和冷却塔风扇等所有系统辅机功耗之后,当冷却水流量为12 m³·h^-1时,系统净输出功和系统净效率达到最大值,分别为2.44 kW和2.47%。通过研究冷却水流量对ORC系统性能的影响,为ORC冷却系统的设计和优化系统性能提供重要的实验依据。     

Fractionation of partially stereoregular poly(propylene oxide)

Partially stereoregular poly(propylene oxide) samples were synthesized via reactions catalysed by a preformed analytically defined trimethylaluminium hydrolysate. These samples were fractionated into two contrastingly different fractions.

1. (i) D-polymers: This fraction constituted the major part (up to 90%). It mainly contained cyclic low molecular weight oligomers (MW < 1000). The linear chains found in D-polymers had hydroxyl end groups. No double bonds could be detected spectroscopically.

2. (ii) K-polymers: This fraction was high molecular weight stereoregular polymer. Stepwise thermal precipitation from dilute isooctane solution of K-polymers yielded a succession of fractions which differed in melting point. It appears that the phase equilibria during the thermal precipitations were not controlled by the molecular weights of species.

APPLICATION OF GASndashLIQUID TWO-PHASE CROSS-FLOW FILTRATION TO PILOT-SCALE METHANE FERMENTATION

As part of a national project, “Aqua-Renaissance '90,” by the MITI, a pilot-scale evaluation of membrane-enhanced anaerobic fermentation, has progressed for the wastewater from a pulp and paper mill. A novel membrane filtration system was newly proposed with the aim of saving energy. That is, a gas-liquid two-phase cross-flow filtration which was generated with liquid circulation by an air-lift pump effect, was combined in the anaerobic bioreactor. It was confirmed that the membrane filtration not only offered very stable and large permeate flux, but enhanced the processing efficiency by retaining the microorganisms in the bioreactor. Furthermore, the power consumption per unit permeate volume in the membrane system of 1.78 kWh/m³ was achieved. which was a very highperformance result from the viewpoint of saving energy, as compared with 3ndash;5 kWh/m³ of conventional liquid single-phase cross-flow filtration.     

A new look at dual purpose, water and power, plants - economy and design features

In light of rapidly rising equipment and fuel costs, recent studies have shown some important results in the economy and optimum designs for dual purpose power/desalting complexes. The desalination cycle chosen for- detailed comparisons in this study is the well known multistage flash (MSF) evaporator, which uses brine recirculation and polyphosphate scale prevention. The multi- stage flash evaporator has found wide spread application in large plants throughout the world. Single units of up to 1400 m3/hr (9.5 MGD), acid dosing, have been built and are now in operation. In general due to corrosion problems, polyphosphate plants are now preferred over the acid one.

A number of schemes for the combined production of power and. water were chosen, mainly a combination of MSF Unit with each of the following power cycle:

• 1- Automatic extraction steam turbine

• 2- Simple gas turbine with waste heat boiler

• 3- Back pressure steam turbineThis paper presents a study of the economic aspects, thermodynamic features and optimization analysis of each of these combined power and water production plants.

The optimum value of the performance ratio and its effect on reducing the cost of water in each of the above mentioned schemes would be discussed in this paper.     

Implementation of ISO 14001:2004 (environmental management system standard) for reverse osmosis desalination plants for the first time in Iran

Implementation of ISO 14001:2004 (environmental management system) has been executed for reverse osmosis desalination plants for the first time in Iran at Noor Vijeh Company (N.V. Co), a water and wastewater firm based in Tehran. The scope of work was the activities and product of company's BWRO desalination plant in the city of Qom (3000 m³ per day) and SWRO desalination plant in Assaluyeh, Pars Special Economic and Energy Zone, Iran. The aims of this project were in line with company’s approach to sustainable development and its direction towards conducting environmental friendly activities and production characteristics.

Initially the famous PDCA (Plan, Do, Check, Act) was used to identify the aspects and evaluate their effects. The significant aspects of each plant affecting the environment are then identified and preventive control measures and reducing their probabilities of loss are anticipated. These cover the normal activities within each plant and those aspects arising from emergency conditions such as earthquakes, fire, etc.

Elements of this system are

• Environmental policy and its targets and programmes

• Practical methods for environmental management system processes

• Executive manuals for implementing special activities

• Tables and indexes for environmental aspects for each plant

• Organizational charts, positions, qualifications, and necessary trainings for the involved personnel.

Environmental aspects are evaluated through their interaction with and effects over, releases to water, emissions to air, land contamination, waste management, energy use, and use of natural resources and raw material.     

双膜法处理高浓度含磷废水工艺研究

考察了钙基软化+曝气混凝+超滤+反渗透工艺处理高浓度含磷废水的可行性和可靠性。以钙基软化+曝气混凝+超滤作为反渗透预处理工艺,可有效去除Ca2+、F-、PO43-等会造成反渗透浓水侧结垢的离子,去除率可以达到80%左右,剧毒物质单质磷去除率可以达到85%以上,经超滤后保证出水浊度小于0.5 NTU,超滤产水SDI控制在3.2以下;当反渗透的回收率不大于60%时,反渗透运行稳定,没有出现明显污堵情况。     

Two detailed case studies of large Libyan desalination plants and their influence on development

Two large Libyan desalination plants are studied :

1. The Ganzour (Tripoli West) MSF plant with two units, each having a rated distillate output of 11,250 m³/day at full load, the distilla- te purity being 25 ppm. The reliability tests on this plant are just beginning and consequen- tly we shall stress on the erection problems.

2. The Zliten MSF plant with three units, each having a distillate production rate of 4525 m³/day, the distillate purity being 25 ppm. This plant being in operation, we shall stress on the occuring maintenance problems.

All difficulties encountered (during erection for Ganzour plant and during maintenance for Zliten plant) are studied in details. Also the influence of each plant on the development of surrounding regions is considered. Recommendations to both sides (Libyan government and foreign plant manufacturers) are made in order to avoid the future repetition of these problems and troubles.     

Field testing and economic evaluation of RO seawater technology

An experimental RO seawater system has been in operation for two years at Eilat on the Red-Sea shore. Simplified seawater pretreatment, comprising only sand filtration and acid dosing was applied. Hollow fiber and spiral wound membranes were tested. Evaluation of pretreatment effectiveness and comparative membrane performances are reported. Investment and water cost analysis of a 4,000 m³/day RO seawater desalting system under various operating conditions is given. The analysis is based on the results of experimental site operation, current technology development and updated industrial quotations. The resulting water production cost from a one-stage system, adequate to produce desalted water acceptable for local drinking water standards, is approximately $ 1.1/m³.     

An innovative trigeneration system using biogas as renewable energy

One of the ways to decrease the global primary energy consumption and the corresponding greenhouse gas emissions is the application of the combined cooling, heating and power generation technologies, known as trigeneration system. In this research an innovative trigeneration system, composed by an absorption heat pump, a mechanical compression heat pump, a steam plant, and a heat recovery plant is developed. The low temperature heat produced by absorption chiller is sent to a mechanical compression heat pump, that receives process water at low temperature from the heat recovery plant and bring it to higher temperatures. The trigeneration system is fed by biogas, a renewable energy. A design and a simulation of the system are developed by Chem Cad 6.3? software. The plant produces 925 kW of electrical energy, 2523 kW of thermal energy and 473 kW of cooling energy, by the combustion of 3280 kW of biogas. Primary energy rate(P.E.R.) is equal 1.04 and a sensitivity analysis is carried out to evaluate the effect of cooling capacity, produced electrical energy and process water temperature. The first has a negative effect, while other parameters have a positive effect on P.E.R. Compared to a cogeneration system, the trigeneration plant produces the 28% higher of power and the 40%lower of carbon dioxide emissions. An economic analysis shows that the plant is economically feasible only considering economic incentives obtained by the use of heat pumps and steam plant at high efficiency. Saving 6431 t·a~(-1) corresponding to 658000 EUR·a~(-1) of incentives, the plant has a net present value(N.P.V.) and a pay back period(P.B.P.) respectively equal to 371000 EUR and 4 year. Future works should optimize the process considering cost and energetic efficiency as the two objective functions.     

The Ebeye desalination project — total utilization of diesel waste heat

The Ebeye (Marshall Islands) sea water desalination project produces 300,000 US GPD (1100 m³/day) of pure distilled water utilizing as its prime energy input the waste heat discharged from an adjacent diesel generator station, operating at an average load of 3.2 MW. The only other energy requirement is electric power for process, heat recovery and seawater supply pumping - at about 9.5 KWH/1000 gal. (2.5 KWH/m³).The desalination plant consists of one 12 effect low temperature multi-effect distillation unit, operating at a top brine temperature of 158 degrees F (70 degrees C) with simple polyphosphate feed pretreatment.The diesel generator station consists of two 2.4 MW diesels, with provision for the addition of a third as demand increases.Heat is recovered from the diesel's exhaust gases, jacket cooling water, lube oil and compressed air after coolers.The paper describes the total water and power generating scheme (including the heat recovery system) uts performance and costs.     

Treatment of effluents from the regeneration of ion exchangers using the MD process

The membrane distillation (MD) process for the treatment of wastewater from ion-exchanger regeneration was proposed. The precipitation of salt deposits on the membrane surface was observed when such wastewater was directly used as a feed. A rapid decline of the permeate flux from 532 to 410 dm³/m²d was found. The problem of fouling was significantly diminished by the addition of Ca(OH)₂ to the wastewater followed by filtration. The improvement of MD module performance was achieved after such pretreatment. The degree of water recovery equal to 50% was obtained without significant variations of the permeate flux. However, when the pretreated feed was subjected to two-fold concentration, precipitation of the silicon compounds was observed. The deposit caused clogging of the inlets of capillary membranes and resulted in a gradual decline of the module efficiency. The two-fold concentrated feed was then treated by sedimentation and filtration, which permitted a further concentration of obtained retentate and enhanced the degree of water recovery to 75%.