Sunday, 12 June 2011
Mineral Water Reverse Osmosis Plant
PakWater Care Services Offers World Latest Technologies of Process for Mineral Water (Bottled Water) Production from Different Source of water Like Bore Hole, Deep Well, River Water, Sea Water etc. Water is passed through following different stages for process of filtration & separation in packaged drinking water plant process. Manufacturing Mineral Water i.e. water containing sufficient/required quantity of minerals which is required to human bodies.
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- Bottle Water Path to Market
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- Automatic Mineral Dosing System
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- Cartridge Filters
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- Post Treatment System
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- Pre Treatment System
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- Pre Treatment System
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- Finished Water Tanks
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- Filling Pump and Product Water Tanks
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- Double Pass Reverse Osmosis
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- Washing & Filling Station
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- Post Treatment System
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- Pre Treatment System
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- Pre Treatment & Reverse Osmosis
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- Poduct Water Tank
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- Revrese Osmosis Plant
Remove suspended matter from the water.
Activated Carbon Filter
Remove Color, Odor and Smell from the water. Remove Oil & Grease from the raw water. Control the BOD & COD in the raw water.
Antiscalant Dosing System
Remove Hardness Minerals from Feed Water which would otherwise cause Mineral Deposits [scale] within the Water Purification System.
Cartridge Filter/Micron Filtration
Remove 1-5 micron particles from the raw water.
High Pressure Pump
To create osmotic pressure in raw water.
Desalination System by Reverse Osmosis Membrane Element
To desalt the raw water i.e. to reduce total dissolve solids.
Ion Controlling System/Remineralization
To adjust the minerals contains in the Process water by means of mixing of raw water in the desalted Treated water, Due to proportionate mixing Required quantity of raw water, we can mix to get required Quantity of ions from the raw water to desalted water.
Storage of Treated Water
Remove back pressure in R. O. Membrane elements.
UV system
To kill the bacteria from fine water.
Ozonation
Prevent the biological & micro organism growth in the stagnant water.
Fine Polishing Filtration
To filter water from 1 micron to 0.2 micron rating & achieve the crystal clear filtered mineral water.
Rinsing Filling & Capping with Label shrinking
To rinse, Fill & capping of the bottle of mineral water.
Bottle Manufacturing Machine
To manufacture the PET bottle from Pet granules.
Reverse Osmosis Membrane Cleaning System
To clean the membrane when it comes in maintenance stage.
Packing of mineral water in Bottles, container or polypack
To pack the final production in the selected packing to sell it in the market.
The mineral water plant consisting following equipments for different process of filtration & separation during the manufacturing mineral water. The Equipments in the project of packaged drinking water manufacturing unit are as follows:
1. Raw Water Storage tank
2. Raw Water Feeding Pump
3. Multi Graded Sand Filter
4. Activated Carbon Filter
5. Antiscalant Dosing system
6. Ultra Violet Disinfection System
7. Micron Filtration System
8. High Pressure Pump
9. Reverse Osmosis Element
10. Pressure Vessel for elements
11. Electric Control Panel
12. Instruments and Instrument Panel
13. Micron Filtration for Minerals Controlling System
14. Treated Water Storage Tank
15. Treated Water Transfer Pump
16. Fine Polishing Micron Filtration System
17. Ultraviolet Disinfection System
18. Ozone Generating Set
19. Ozone Reacting Tank
20. Ozone Circulating Pump
21. R.O. Membrane Cleaning System
22. Injection molding Machine
23. Stretch Blow Moulding Machine
24. Rinsing Filling & Capping Machine
25. Label Shrinking Machine
26. In house Laboratory
Following are the requirement and it is managed by the Purchaser
1. Water Source (Bore Well)
2. Raw Water Storage
3. Power
4. Snap caps for 20 ltrs container
5. Food grade PVC caps for bottles
6. Pet granules for pet bottle manufacturing
7. Rappers for bottles & containers
8. Civil works for installation
9. Operating Staff
10. Legal Clearance.
PakWater Care Services, Complete turnkey Solution for Bottle Water or Dialysis Reverse Osmosis Treatment
Pakwater Care Services (PWC) designs, services and sells the PWC line of dialysis water treatment equipment throughout Pakistan.
PakWater Care Services can provide design of your central system using your center’s dimensional data and location of utilities: electric, water, sewer. A customized drawing will be prepared and upon final installation a P&ID will be provided.
Central Systems
Custom designed for your Dialysis Center.
- Multimedia filter removes particulates that may cause damage to the RO membrane
- Backwashing carbon tanks in worker/polisher configuration to assure chloramine removal
- Timer controlled water softener regenerates at a time convenient to your center
- Dual reverse osmosis systems keep you on-line continuously
- Holding tank with vent filter and spray ball assures endotoxin-free quality water
- Dual recirculation pumps
- Connection for deionized exchange hook-up
- Final ultrafilter
Ozone Disinfection
The dialysis disinfection system is a complete compact portable unit that easily connects to the bicarb mixing and distribution system and water system for effective disinfection. The ozone model has a unique gas-off and ozone gas destruct for operator comfort.
The ozone system provides a high dose of aqueous ozone, which is the best disinfectant available for dialysis bicarb and water systems. The system has all UL listed components with built-in safety features to prevent harm to the operator. The system is lightweight, yet has field integrity and durability for long life.
Benefits
- Disinfects more powerfully than chemicals.
- Leaves no chemicals or byproducts.
- Microorganisms cannot build up tolerance to ozone.
- Has no detrimental effect on bicarb and water system components including PVC.
- Provides ease of operation at low cost.
- Destroys: Bio-film, bacteria, endotoxins, viruses and algae.
Dialysis Water Treatment Maintenance
Typical applications include
- High Performance Liquid Chromatography (HPLC)
- Tissue culture research
- Atomic absorption
- Fluorescence spectrometry
- Mass spectroscopy
- Reagent grade chemical solution make up
- Gas chromatography
- Biotechnology
- Enzymology
- Biochemical assays
- Glassware rinsing
- Ultrapure water for trace metals analysis
Water Desalination - Textile Industries in Pakistan
| A number of processes within the textile industry involve water. For instance, water is produced for boiler water, humidification, and rinse water which are used in the treatment of textiles.Use of water in the wet processes Rinse water is used in wet treatment processes, e.g. pretreatment, colouring, printing, and subsequent treatment of textiles. During the pretreatment, the unwanted substances, which were added to the textiles in previous production processes, are washed out. When colouring and printing textiles, softened water should be used in order to gain the best result. Finally, the surplus substances from the colouring and printing are washed out. Minimizing the environmental impact The purpose of the water treatment is among other things to minimize the environmental impact, i.e. the use of chemicals, environmentally harmful substances, and the quantity of discharged waste water. |
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WATER DESALINATION FOR TEXTILE WET PROCESSING
| Abstract Textile wet processing is an all-encompassing term used for bleaching, dyeing, printing and finishing treatments for different types of textile goods like fibres, yarn, tows, woven and knitted fabrics, garments etc. made from both natural and man-made fibres. Wet processing is essential for making the textile materials comfortable and attractive. These embellishing treatments require large quantities of good quality water, a commodity that has acquired the status of a raw material for the textile industry. Unfortunately an important source i.e. sub-soil water is brackish in Pakistan in general and its textile centres of Karachi and Faisalabad in particular. This state of affairs is responsible for the unsatisfactory quality and increase in cost of production of the finished materials. Quality of brackish water can be improved by different methods but its desalination or demineralization, softening with the reverse-osmosis (R.O.) process is the most feasible. Many textile mills and other industrial units in Pakistan have installed the R.O. plants in the recent past and are very satisfied with the results. This paper discusses the difficulties faced by the industry by using poor quality water and advantages and savings incurred by using the desalinated water. Details about cost of the purifying process for water are also included. |
1. Profile of Textile Industry of Pakistan
Textile manufacturing is the major industry of Pakistan and it plays a key role in the economy of the country. The industry exports goods worth more than 6 billion U.S. dollars annually. This is about two thirds of the total foreign exchange earnings of the country. Textile industry also provides at least 40% of the industrial jobs, besides creating vast opportunities for relevant commercial enterprises. These include sales of different textile products, transport of raw materials and the finished goods, supplying of machinery and their spares, packing, forwarding, shipping trades etc. The cotton textile manufacturing consumes more than 9 million bales (1.5 million tonnes) of cotton in addition to 0.5 million tonnes of man-made fibres and 80 thousand tonnes of wool. The industry has not only impressive credentials within the country but is also a major force in the world trade as Pakistan is in the top 10 textile manufacturing and exporting countries.
2. Requirement of Water by Textile Industry
The present day product-mix and manufacturing techniques are a far cry from the pre 1980’s period when Pakistan was exporting raw cotton, yarn, grey cloth and T-shirts, the last named at a ridiculous price of $6 per dozen. Present emphasis is on manufacture of the high-value added finished products and average price of the knitted garments is now $ 45 per dozen. As the name suggests the finished goods need to be bleached, dyed and printed and these processes require plentiful quantities of the good quality water. On the average one Kg of the material requires at least 100 litres of water. Unfortunately the quality-water, found in our perennial rivers, is always in short supply because the first charge on this water is for human consumption and agriculture. The other source is sub-soil water but this is mostly brackish as happens in all semi-arid countries like Pakistan. The saline or brackish sub-soil waters are unfit for bio-consumption and are also unsuitable for most of the industrial uses, including the textile wet processing. The sub-soil waters of the two major textile centres of the country, Karachi and Faisalabad, are highly saline and as such are not suitable for producing high quality finished textile products.
About two decades back, setting up of a textile finishing plant was banned in Karachi only because quality water was not available. Now when the ban has been lifted, all the mills are using sub-soil water for wet processing of their products because water of the rivers ‘Sindh’ and ‘Hub’, that is supplied by the Karachi Water and Sewerage Board (K.W.S.B), hardly meets even 10% of their requirements. The precious KWSB water is, therefore, used mainly for boilers and drinking purposes.
Focussing on the water shortage dilemma of Karachi, it may be observed that this city is the biggest manufacturer of the textile wet processed goods in the country. Karachi has at least 300 registered processing mills that include 200 cloth (woven cotton and man-made fibres), 70 knitting and 30 towel mills. In addition to these about another 50-70 unregistered mills and a large number of factories processing garments, yarns, kitchen towels, mops, laces, jute goods, garment-accessories, etc. also exist that consume fairly large quantities of water. It has been estimated that the wet processing industry of Karachi consumes around 50 million gallons (British) of water every day. This huge supply is met by extracting the sub-soil water either by the mills directly or by the so-called “Tanker” water-suppliers, including the National Logistic Cell.
3. Quality of Sub-Soil Water
The sub-soil water of Karachi is of a poor quality and has high concentration of the dissolved salts or has a high TDS(Total Dissolved Solids). The TDS content varies from 1,500 to 30,000 ppm (parts per million) in different localities of the metropolis and follows no clear-cut pattern of TDS content within a locality. In many factories in the SITE area the TDS ranges between 1,500 to 3,000 ppm but it may go up to 15,000 or even to 25,000 in the nearby mills.
The same pattern of TDS variation exists in the sub-soil waters in Korangi, Landhi and the North Karachi areas. The KWSB water in comparison has a TDS ranging between 250-350 ppm depending on the time of the year, being low in the rainy season and high in winters.
4. Effect of Water Impurities on Wet Processing
High concentration of dissolved salts, especially the hardness-causing calcium and magnesium ones, creates lot of difficulties in wet processing. Nature of the impurities and their effect on the quality of the finished goods are briefly mentioned below.
(a) Organic matter, Turbidity and Color: Turbidity and colour are usually due to presence of organic matter in water and these detract from brightness of the bleached and purity of shade of the dyed goods. The organic matter, whether dissolved or suspended breeds micro-organisms that may develop mildew, fungi etc., which in turn produce coloured spots, foul smell and even holes in the material.
(b) Hardness: Hardness creates many undesirable effects in processing. On heating or coming in contact with alkalis, calcium and magnesium salts are precipitated on fabrics as whitish carbonate and hydroxide particles. Although concentration of these salts is small yet their overall reflection pattern lowers whiteness of the bleached goods and depth of shade of the dyed goods and mars purity and brightness of the hue. In package yarn dyeing, the precipitated particles hinder free-flow of liquor through the packages and tend to cause uneven dyeing. The precipitated salts also impart harshness to the fibres. Excessive presence of these salts also causes uneven dyeing and necessitates addition of expensive sequestering agents. Some processing mills of Karachi have resorted to soften the entire supply of the process water to get more uniform dyeings but softening does not reduce TDS of water and creates some other problems as mentioned in the following Para (c).
- In textile mills, including the spinning and the weaving sections, certain equipments are installed that require circulation of water through pipes. These include boiler, humidification plant and multi-tubular heaters/coolers of the dyeing machines. With passage of time the hardness producing salts in water accumulate to form a hard scale inside the pipes. The scale is a bad conductor of heat and causes wastage of fuel in boilers and lowers efficiency of the other equipment. Removal of the scale from inside the tubes is a time consuming and an expensive proposition and adds to the cost of processing.
(c) Total Dissolved Solids: In addition to the hardness causing calcium and magnesium salts, water contains other dissolved salts that are mainly sodium cations and chloride, sulphate and bicarbonate anions. These sodium salts create certain complications like precipitation of dyes of inherent low solubility.
Presence of excessive amount of sodium ions gives a damp and limp handle to the finished fabric due to their tendency to hold water. The materials dyed in such waters look dull and lack brightness.
High TDS in the boiler feed water causes foaming and carry-over problems that lower efficiency of the boilers and also create difficulties in processing. Further excessive sodium ions in boiler water accelerate corrosion of the iron plates due to their high electrical conductivity. Such waters also require more frequent blow-downs that result in fuel loss.
To sum up the goods processed in the high TDS waters have dull shades, a poor handle and in many cases uneven dyeing. To avoid uneven dyeing expensive sequestering agents are added in the dye bath but still brightness of dyed and printed goods is poor and handle unattractive. These shortcomings lower value of the finished goods.
5. Desalination of Brackish and Sea Water
As discussed above, it appears that the quality-water is going to be in short supply for the industry permanently and this shortage is likely to be progressive. It is, therefore, necessary to consider alternative processes to supplement the existing water sources and the most obvious choice is demineralisation or desalination of brackish sub-soil water and even seawater. There are three major methods that are being successfully used for desalination of water. These are based on the following principles:
1.Vaporization and Condensation.
2. Ion exchange.
3. Reverse Osmosis.
1.Vaporization and Condensation.
2. Ion exchange.
3. Reverse Osmosis.
5.1 Vaporization and condensation: In this system, saline water is heated preferably under reduced pressure to boiling point and the water vapours (steam) are cooled to condense to pure water. This process is expensive unless it is made synergistic with power generation. It is also capital intensive and needs high calibre and so expensive expertise to run and maintain the plants. The system has been used in oil producing low fuel-cost countries like Saudi Arabia and UAE but even there the R.O. process has replaced this.
5.2. Ion-exchange Demineralisation Process: This method of water purification is based on the principle of the Water Softening but differs in having two columns of different resins. In the one cations and in the other anions of the dissolved salts are replaced with hydrogen and hydroxyl ions respectively and water of a very high purity or zero conductivity is obtained. After exhaustion, the resins are regenerated: the cationic with a mineral acid and the anionic with caustic soda.
The capital cost of the equipment is lower than the other two systems but cost of the resins and their regeneration chemicals is high and so makes the process uneconomical for the textile industry. This process is mainly used by the pharmaceutical and certain chemical industries where water of ultra-high purity is needed.
5.3. Reverse osmosis process or Hyper Filtration: According to the well-known principle of osmosis when a salt solution is separated from water with a semi-permeable membrane, water molecules tend to move across the membrane towards the salt solution under the concentration gradient. In an enclosed vessel, transport of water molecules through the membrane creates pressure that is known as the “Osmotic Pressure” and is proportional to the difference in concentrations of salt on both sides of the membrane. If pressure is applied on the salt-solution side of the membrane, flow of water is stopped. If pressure exceeds the value of the osmotic pressure, water will start flowing in the opposite direction, i.e. from the salt solution to the waterside. This principle is used in the reverse osmosis process for reducing salt concentration in the brackish water or even the sea water.
The process was known for quite sometime but could become commercially feasible only after robust and long lasting synthetic semi-permeable membranes were developed and became available at competitive prices. The reverse osmosis method of demineralisation of water has now acquired a great commercial significance in the semi-arid countries.
5.3.1 Semi-Permeable Membranes: The semi-permeable membranes are mainly of two types, viz. the spiral and the hollow fibre. Former is a composite of polyamide polymer on polysulphone support membrane. The hollow-fibre module consists of polyamide or cellulose triacetate fibres of 25-250 mm diameter that are sealed on one end. A large number of the hollow fibres are bundled together and placed in a saline water-pressure vessel. Pressure required for making water flow across the membrane depends on salinity of the water, type of membrane and the desired salt removal and it varies from 100 to 400 psi. One square meter of the membrane, whose pore size is of the order of 10-20 Ao, is capable of demineralising about 500 litres or 110 (Br.) gallons of water per day. The pressure pump is usually a multistage type having a throttle valve to control the pressure to the desired level. Power consumption for treating seawater is about 5-9 KWh and for brackish water 2-3.5 KWh per m3 or 220 (Br.) gallons. Life of the membrane depends upon quality of the water and conditions of working. Acidic pH and presence of oxygen, oxidizing chemicals, soil and microbes in water deteriorate the membrane rapidly. The saline water is, therefore, thoroughly pre-treated before passing through the R.O. membrane.
In the following paragraphs information has been collected by a study of two leading textile wet processing mills that were pioneers in introducing the R.O. engineering in their mills. Both the mills use sub-soil water, having a TDS ranging from 3,000 to 6,000 ppm.
5.3.2 Filtration and Chemical Treatment:
The feed water is carefully filtered in 2 stages; in the first or multi-media system particles up to 40 mm are removed and in the second step particles above 5mm are removed in special cartridge filters. The filtering media in the former are gravel and sand and in the latter fine polypropylene fibres. The cartridge filters are replaced with the fresh ones after the filtration pressure reaches a level of 15 psi. Before the first filtration feed water is treated with an oxidizing agent like sodium hypochlorite to destroy any possible microbial growth. Any excess of the oxidizing agent and the dissolved oxygen is next removed by adding a reducing agent that is usually sodium metabisulphite. Before forcing water through the R.O. membranes, it is treated with an anti-scaling agent to minimise formation of scale on the membranes. Hydrochloric acid is also fed at the same time to decompose alkaline carbonates and bicarbonates and a pH of 6.5 is maintained. The R.O. water or the permeate is finally degassed to remove carbon dioxide and its pH is adjusted to 7.5 by adding alkali. The final product may have 2-5% of the TDS of the raw water while TDS of the waste-water is normally not allowed to go beyond 20,000 ppm.
The membranes are periodically back-washed with the R.O. water to which some proprietary cleansing chemicals are also added to remove scale and other impurities. If carefully maintained, the R.O. membranes may last for 4 years but it may be kept in mind that it is very easy to damage these.
6.3 R.O. Process for Sea water: This paper is mainly concerned with desalination of the sub-soil waters but it may be mentioned, for the sake of comparison, that cost of the R.O. plant for sea water is nearly three times and the running cost is higher of the sub-soil waters up to 6,000 ppm TDS.
7. Conclusion
The net cost of the R.O. water is higher than the KWSB water that is supplied in SITE area of Karachi @ Rs.73/1,000 (Br.) gallons. However, it is lower than the tanker water that is sold, on the average, @ Rs.120/1,000 gallons and has a TDS ranging anywhere from 1,200 to 2,000 ppm. Consideration of regular availability of good and uniform quality of this raw material has encouraged many textile mills in Karachi to install the R.O. Plants. An equally encouraging factor is saving in the cost by at least 30% of the sequestering agent and the printing thickener used in dyeing and printing processes, besides improving the general look and finish of the goods. Many textile mills have installed the R.O. plants and these include M/s Yunus Bros, Siddique Sons, Nakashbandi, Liberty, Afroze, Goodwell, Caravan East, Iqbal Silk, Standard etc. Some prominent non-textile users are M/s Proctor and Gambol, Candyland, Abbot and Knoll Pharmaceutical, Siddique Sons Tin-Plate factory, mineral waters and aerated-drinks manufacturers and many hospitals.
One of the major constraints in setting up of desalination plants in Karachi is insufficient availability of the sub-soil water of a TDS below 6,000 ppm. Some mills have installed as many as 6 pumping wells and still there is shortage of water for their R.O. plant. This situation discourages many mills management interested in the project. In my opinion we have two hitherto unexploited sources of water, i.e. the mills’ own effluent and the municipal sewerage. Effluent of the processing mills is highly colored and has a higher TDS than the sewerage that is about 800-1000 ppm. In case the mill effluent is to be treated arrangements should be made to collect the washings of the bleached and the dyed products separately from the spent bleach and dye liquors. This will reduce the organic constituents (BOD) and TDS of the effluent and make the pre-treatments and R.O. processes more efficient and economical.
The alternative source of the sewerage water has a volume of at least 300 million gallons per day in Karachi. If it is completely got rid of its dissolved and suspended organic impurities, as is done in all the developed countries of the World, it would be an excellent source for textile wet processing. But there is a big “IF” and the purification process can be entrusted only to a private organisation on a commercial basis whose performance be monitored by an independent controller appointed by the consumers. After the usual purification treatments, R.O. desalination should be carried out to bring the TDS of water down to a level of 200-300 ppm and also to ensure complete removal of the organic matter. This suggestion is for a serious consideration of KWSB and the Karachi textile entrepreneurs.
Energy Recovery Turbine - ERI
Breakthrough engineering is the core of ERI's Pressure Exchanger™ (PX™) energy recovery technology. It is no surprise that the PX is the most efficient energy recovery device (ERD) on the market. ERI has invested years in research and development as well as millions of dollars to build the most efficient ERD available today—up to 98% efficient, producing energy savings of over 60%.
Re-thinking SWRO
Though it has quickly become the benchmark ERD technology, ERI’s PX device was a new paradigm when first introduced to reverse osmosis (RO) systems. There are, consequently, fundamental differences between the way legacy Pelton and Francis turbine devices are designed and optimized and the modern approaches used with PX device-based desalination systems. Some of the new concepts and rules being driven by ERI are:
Though it has quickly become the benchmark ERD technology, ERI’s PX device was a new paradigm when first introduced to reverse osmosis (RO) systems. There are, consequently, fundamental differences between the way legacy Pelton and Francis turbine devices are designed and optimized and the modern approaches used with PX device-based desalination systems. Some of the new concepts and rules being driven by ERI are:
- Hydraulic efficiencies up to 98%
- PX device-equipped SWRO systems use less energy at lower recoveries (between 35% and 45%)
- The high-pressure pump flow equals the systems permeate flow recovery rate
- The high-pressure pump and permeate flows are independent of the reject flow
- PX device efficiency is essentially independent of system flow rate and pressure changes
These fundamental concepts reverse many of the traditional rules that have constrained the RO desalination designer for many years. PX technology opens up new avenues for RO design and optimization using larger train sizes. It also allows the designer or operator to select a recovery rate which is optimum for a given salinity, temperature, and membrane fouling performance. The papers below describe these ideas in detail:
- Development of a Fourth Generation ERD
- Low Energy Consumption in the Perth SDP
- Low Power Bill Makes SWRO Affordable
SWRO Plant Optimization
A major economical benefit of PX device technology is that the PX requires a much smaller high-pressure pump than typically used by conventional technology. Even more crucial, PX technology disassociates the high-pressure pump from the ERD. These two factors combine to give desalination plant designers much more flexibility in optimizing train sizes and selecting the best high-pressure pump for their project.
Design and Installation
ERI’s team of service professionals draws from its experience reviewing designs and supervising successful startups of hundreds of desalination plants around the world. Its people are not just experts in the application of PX technology, but bear comprehensive knowledge of reverse osmosis (RO) plant operation. ERI is dedicated to ensure successful PX device deployments by working closely with operators and partners to understanding each project’s unique needs.
Design
ERI’s expertise comes into play long before RO plant construction begins. Service professionals conduct thorough technical reviews of process and instrument designs and control logic. It is not unusual, for example, that during these reviews the ERI team identifies problems that were overlooked by the plant planner. By helping to address these problems proactively, ERI can help accelerate plant installation and start-up.
ERI’s website contains a wealth of technical information, including operations and service manuals, technical guidance documents, and the ERI Power Model™ to support the design process. The ERI-SIM™ SWRO process simulator and ERI’s Factory Training provide dynamic, hands-on training for designers and operators.
Ceramics
ERI’s PX devices have only one moving part. The heart of the PX device is a high purity aluminum oxide rotor, turning at up to 1,000 rpm in an almost frictionless hydrodynamic bearing. This ceramic material is unaffected by chemicals or aqueous corrosion, is three times harder than steel, and provides unmatched durability in the PX application.
ERI has developed manufacturing capabilities and expertise that range from working with high alloy stainless steels and exotic metals, such as super–austenitic and super duplex stainless steel and titanium, to the synthesis and precision machining of ceramics.
Creating advanced ceramics components requires specialized equipment, a fully equipped materials lab, and optimized processes. Custom formulated spray-dried powders are compacted at extreme pressures to create the machineable blocks that become rotors. The lengthy sintering process occurs at temperatures greater than 1600°C and eventually achieves a hardness of Mohs 9.0 in a material chemically identical to sapphire. Once the ceramics have been properly formed, they are cooled slowly and evenly to avoid cracking. This overall process is critical to achieve a smooth hard surface, which will sustain many years of operation in a harsh seawater environment.
Glossary
Acre-foot (AF). A unit for measuring the volume of water. One acre-foot equals 325,851 gallons (the volume of water that will cover one acre to a depth of one foot) or 1,233 cubic meters. One million gallons equals 3.07 acre-feet.
Bar. A unit for measuring pressure. 1 bar = 14.5 psi = 0.99 atm
Biocide. A chemical used to kill biological organisms (e.g., sodium bisulphite).
Brackish. Water that typically contains less than 10,000 ppm salt-more salt than freshwater but less than the open seawater.
Brine. Water that contains greater than 50,000 ppm salt. Brine discharges from desalination plants may also include constituents used in pretreatment processes. See also "Concentrate".
BTU (British Thermal Unit). A standard unit for measuring a quantity of energy. Electricity, natural gas or any other source of energy can be measured in BTUs. One BTU is the amount of energy required to raise the temperature on one pound of water one degree Fahrenheit at sea level. One thousand BTUs equals 0.29 kilowatt-hours.
Coagulation. A pretreatment process used in some desalination plants. A substance (e.g., ferric chloride) is added to a solution to cause suspended particles to agglomerate and form larger particles that are easier to remove from a solution than small particles.
Cogeneration. A power plant that is designed to conserve energy by using "waste heat" from generating electricity for another purpose, for example to thermal desalination or to warm SWRO feed water.
Concentrate. Water containing concentrated salts rejected by the membrane. See also "Brine".
Deaeration. Removal of oxygen. A pretreatment process in desalination plants to reduce corrosion and fouling.
Dissolved Air Flotation (DAF). A pretreatment process in desalination plants to remove solids and organics.
Distillation. A process of desalination where the water is heated to produce steam. The steam is then condensed to produce product water with low salt concentration.
Efficiency. Energy transfer efficiency expressed as the ratio of the sum of the energy leaving the PX unit (or array) divided by the sum of the energy entering, as calculated with the following equation:
| Efficiency = | ∑(Pressure x Flow)OUT | x100% |
| ∑(Pressure x Flow)IN |
Electrodialysis. Most impurities in water are present in an ionized (electrically charged) state. When an electric current is applied, the impurities migrate toward the positive and negative electrodes. The intermediate area becomes depleted of impurities and discharges a purified stream of product water. This technology is used primarily for brackish waters.
ERD. Energy recovery device.
Feedwater. Water fed to the desalination equipment. This can be source water with or without pretreatment.
Fouling. Contamination or biological growth on the reverse osmosis membranes or pretreatment filters.
Freshwater. Water that contains less than 1,000 milligrams per liter (mg/L) of dissolved solids; generally, more than 500 mg/L of dissolved solids is undesirable for drinking and many industrial uses.
High-Pressure Differential Pressure (HP DP). The pressure at the high-pressure inlet port of the PX device minus the pressure at the high-pressure outlet port of the PX device.
Infiltration Gallery. A method used for the area where seawater enters the SWRD process. Perforated pipes are arranged in a radial pattern in the sand onshore below the water level. Water in the saturated sand enters the perforated pipes.
Ion Exchange. A reversible water treatment process. A charged polymer exchanges Na+, H+, Cl-, or OH- for other ions in a solution.
Isobaric. Literally: same pressure. An isobaric energy recovery device, like the PX, includes chambers wherein the pressure of two volumes of water equalizes.
Low-Pressure Differential Pressure (LP DP). The pressure at the low-pressure inlet port of the PX device minus the pressure at the low-pressure outlet port of the PX device.
Lubrication Flow. The flow of high-pressure brine required to lubricate the PX device's hydrodynamic bearing, measured as a difference in any of the following flows:
- Low-pressure feedwater to the high-pressure pump minus the membrane permeate
- High-pressure brine to the PX unit minus the high-pressure feedwater from the PX device
- Low-pressure brine from the PX unit minus the low-pressure feedwater to the PX device
Kilowatt (kW). One thousand watts.
Kilowatts-hours per cubic meter (kWh/m³). A measure of the power require to produce a cubic meter of permeate.
Megawatt (MW). One million watts.
Minimum Discharge Pressure. The minimum allowable pressure at the low-pressure outlet port of the PX device.
Multiple Effect Distillation (MED). A form of distillation. Evaporators are placed in series, and vapor from one effect is used to evaporate water in the next lower pressure effect. There are several forms of this technology, one of the most common is the Vertical Tube Evaporator (VTE).
Multistage Flash (MSF). A form of distillation. Intake water is heated then discharged into a chamber maintained slightly below the saturation vapor pressure of the incoming water, so that a fraction of the water content flashes into steam. The steam condenses on the exterior surface of heat transfer tubing and becomes product water. The unflashed brine enters another chamber at a lower pressure, where a portion flashes to steam. Each evaporation and condensation chamber is called a stage.
Nanofiltration (NF). A lower pressure membrane filtration technology sometimes used for pretreating reverse osmosis feedwater.
Permeate. Water purified by reverse a osmosis membrane.
Pounds per square inch (psi). A unit for measuring pressure. 1 psi = 0.069 bar = 0.068 atm.
Product Water. The desalted, post-treated water (or permeate) delivered to the water distribution system.
Recovery. Ratio of permeate to membrane feed flows, typically expressed as a percentage.
Reverse Osmosis (RO). A process where pressure is applied continuously to feedwater, forcing water molecules through a semipermeable membrane. Water that passes through the membrane leaves the unit as permeate or product water; most of the dissolved impurities remain behind and are discharged in a concentrated brine or waste stream.
Salinity Increase. The increase in the salinity of the membrane feed stream caused by the energy recovery device. Salinity increase varies with the membrane recovery rate. It is typically expressed as a percentage increase of the membrane inlet stream above the salinity of the system feedwater according to the following equation:
| Salinity Increase = | membrane inlet salinity - system feedwater salinity | x100% |
| system feedwater salinity |
Seawater Reverse Osmosis (SWRO). Reverse osmosis desalination of seawater.
Scaling. Salt deposits on the surfaces of a membrane.
Total Dissolved Solids (TDS). Total salt and calcium carbonate concentration in a sample of water.
Vacuum Freezing (VF). A process of desalination where the temperature and pressure of the seawater is lowered so that the pure water forms ice crystals. The ice is then washed and melted to produce the product water. This technology is still being developed, and is not commercially viable.
Vapor Compression (VC). A form of distillation. A portion of feedwater is evaporated, and the vapor is sent to a compressor. Mechanical or thermal energy is used to compress the vapor, which increases its temperature. The vapor is then condensed to form product water and the released heat is used to evaporate the feedwater.
Volumetric Mixing. The percentage of the volume of concentrate that mixes into the feedwater inside the energy recovery device (ERD). It is expressed as a function of the salinities of the ERD high-pressure and low-pressure inlet and outlet streams according to the following equation:
| Volumetric Mixing = | HP outlet - LP inlet (TDS) | x100% |
| HP inlet - LP inlet (TDS) |
Watt (W). A measure of power used by electricity generating plants. One watt is equivalent to 1 Joule/second or 3.41 Btu/hour.
Saturday, 11 June 2011
What is UltraFiltration?
Ultrafiltration is a separation process using membranes with pore sizes in the range of 0.1 to 0.001 micron. Typically, ultrafiltration will remove high molecular-weight substances, colloidal materials, and organic and inorganic polymeric molecules. Low molecular-weight organics and ions such as sodium, calcium, magnesium chloride, and sulfate are not removed.
Because only high-molecular weight species are removed, the osmotic pressure differential across the membrane surface is negligible. Low applied pressures are therefore sufficient to achieve high flux rates from an ultrafiltration membrane. Flux of a membrane is defined as the amount of permeate produced per unit area of membrane surface per unit time. Generally flux is expressed as gallons per square foot per day (GFD) or as cubic meters per square meters per day.
Ultrafiltration membranes can have extremely high fluxes but in most practical applications the flux varies between 50 and 200 GFD at an operating pressure of about 50 psig in contrast, reverse osmosis membranes only produce between 10 to 30 GFD at 200 to 400 psig.
Ultrafiltration, like reverse osmosis, is a cross-flow separation process. Here liquid stream to be treated (feed) flows tangentially along the membrane surface, thereby producing two streams. The stream of liquid that comes through the membrane is called permeate. The type and amount of species left in the permeate will depend on the characteristics of the membrane, the operating conditions, and the quality of feed. The other liquid stream is called concentrate and gets progressively concentrated in those species removed by the membrane. In cross-flow separation, therefore, the membrane itself does not act as a collector of ions, molecules, or colloids but merely as a barrier to these species.
Conventional filters such as media filters or cartridge filters, on the other hand, only remove suspended solids by trapping these in the pores of the filter-media. These filters therefore act as depositories of suspended solids and have to be cleaned or replaced frequently. Conventional filters are used upstream from the membrane system to remove relatively large suspended solids and to let the membrane do the job of removing fine particles and dissolved solids. In ultrafiltration, for many applications, no prefilters are used and ultrafiltration modules concentrate all of the suspended and emulsified materials.
Ultrafiltration will find an increasing application in the production of high purity water. The basic principles outlined here should help in the understanding and use of this technology.
Advantages of Ultra-Filter Membrane
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