JP2006021110A - Method and apparatus for optimum high yield, energy efficient, double perfect total nano-filtration seawater reverse osmosis desalting - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optimum seawater desalting method and an apparatus therefor which solve problems of scale formation, energy consumption, and pollution. <P>SOLUTION: Salt water is made to pass through a two stage membrane nano filtration unit, where an energy recovering turbo-charger unit is disposed between stages, and if necessary, a booster pump is added. A first water product where the content of ionic species is reduced, and microorganisms, particulate matter and almost all of scale-forming hard ions are removed is made from an NF (nano-filtration) product obtained by mixing a first and second NF products. Subsequently, the first water product is made to pass through a two stage SWRO ((sewage reverse osmosis) SWRO<SB>2</SB>) where an energy recovering TC is disposed between stages and, if necessary, a booster pump is added. A final second water product (permeate), and a third SWRO water product brine waste where salinity as quality of drinking water is increased and scale-forming hard ions are drastically reduced are produced from a mixture of the products from the two SWRO stages. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a seawater reverse osmosis (SWRO) desalination process.

Typically, the process of the invention using a two-stage NF ₂ initial pretreatment step performs a semi-desalting step by reducing the feed TDS by about 35-50%, most importantly, Removes more than 80% of Ca ⁺⁺ and Mg ⁺⁺ scale-forming hardness ions that constrain water recovery, more than 95% of their sulfate covalent anions, and bicarbonate ions Remove to about 65%. Removal of scale-forming hard ions, especially SO ₄ ⁼ and bicarbonate ions, allows SWRO operation with high water recovery. As indicated in another patent application, the operation of the thermal desalination unit is much higher than the current top brine temperature (TBT) limit by a single conventional method of 120 ° C. Allows operation with TBT, operation of multistage flash distillation (MSFD) and multiple effect distillation (MED), or vapor compression distillation (VCD), or reheat distillation (RH) units at 65-70 ° C. This method allows for a much higher TBT than the current TBT limit and provides many advantages over conventional seawater desalination methods. The method of the present invention provides energy consumption per unit of product that is equal to or lower than many other conventional desalination processes, as well as water yield, product water recovery, and unit water costs. Efficiently superior to all conventional methods in that it is dramatically reduced. This method achieves NF product recovery rates of 75 and 80% or higher from high salinity Gulf seawater (TDS≈45,000 ppm) and ocean seawater (TDS≈35,000 ppm), respectively. From the SWRO unit, when operating it on NF product, approximately 71-80% nearly equal product recovery is also more than 53% over double water NF ₂ -SWRO ₂ total water recovery Has been obtained. Using the configuration of the method as shown in FIG. 3, high values from Gulf Seawater (TDS≈45,000 ppm) to 57% can be obtained. As shown in a separately filed patent, the scale-forming hard ions and their exclusion from SWRO with very little of their covalent anions can be removed from the heat of NF ₂ -SWRO ₂ -thermal triple hybrids. When used as a supplement to the formula unit, this recovery rate is further increased, bringing the total water recovery rate of the triple hybrid to the Gulf Seawater supply to about 60%, resulting in even greater values from the Ocean Seawater supply.

Optimal high recovery rate, energy efficient double and triple _NF 2 -SWRO _2, or _NF 2 -SWRO ₁ method and device.
FIELD OF THE INVENTION The present invention deals with an energy efficient NF ₂ -SWRO ₂ , or NF ₂ -SWRO ₁ (the term optimal will be used in the future to refer to the presently optimal seawater desalination method of the present invention). For the method with the highest possible water recovery currently available from a pre-treated seawater feed, seawater shore well feed, or other aqueous solution feed, where the feed is Large concentrations: (1) TDS on the order of 20,000 to 50,000 ppm, and (2) scale-forming hard ions (ie, SO ₄ ⁼ , Ca ⁺⁺ , Mg ⁺⁺ , and Not only has HCO ₃ ⁻ ), but (3) especially when the feed is taken from high sea water, it is characterized by containing some turbidity and bacteria.

  The NF unit, depending on the type of NF membrane, is lower than the pressure used to operate the SWRO unit, P = 25 ± 10 bar in the first NF stage, and about 35 ± 10 in the second NF stage. Operated at a relatively low feed pressure (P) of bar, in which case the first stage SWRO is operated with a conventional SWRO, usually set at P = 55 ± 10 bar, while the second stage SWRO unit is This second stage is operated using an energy recovery turbocharger mechanism to recover energy from the reject, which is used to increase the feed pressure to the second stage SWRO unit to P≈90 ± 10 bar. In newly developed commercial high-pressure tolerant SWRO membranes (Kurihara Masaru, et al., Desalination 125: 9-15 (1999)), or equivalently newly developed by other membrane manufacturers It is used WRO film.

Alternatively, as shown in FIGS. 2a and b, the SWRO unit is operated in one step at high pressure using a high pressure tolerant membrane up to 84 bar, such as Toyobo HB type membrane [Goto T. et al. Others, Progress in SWRO technology, The International D & WR IDA Quarterly, 2001, Vol. II / p. 31-36]. Furthermore, the third form, NF membrane assembly (two stage) -SWRO (one stage) double desalination system operation mixes a portion of the SWRO reject with the seawater feed and recirculates to the NF unit; The operation of the SWRO unit is performed at approximately P = 65 ± 5 bar (FIGS. 3a and b). However, the recirculated SWRO exclusion, which has a high salinity, its hard ion content, especially the content of SO ₄ ⁼ covalent anions, is dramatically reduced to a very small fraction in the case of seawater. Has decreased. With this optimal method, for example, a typical SWRO membrane recovery of about 25-35% of the conventional single SWRO method when applied to Gulf water or Red Sea water (TDS≈45,000 ppm). , 56-70% or more. This device configuration and dual hybrid NF ₂ -SWRO ₂ or NF ₂ -SWRO ₁ method allows total water recovery by NF and SWRO units, for example, on the order of 53% or more (up to 57%) from Gulf seawater Rate (Figures 1, 2 and 3) using triple hybrid NF-SWRO-thermal, when SWRO exclusion is used as a supplement to the thermal unit connected to it, either membrane or thermal Compared to only 25-35% with the conventional single SWRO desalination process, it rises above about 60%, giving an increase in water recovery in the range of 50-100%. This recovery is also greater than that of our fully developed NF-SWRO or NF-thermal method developed previously. In this case, each of NF and SWRO consisted of only one single stage without an energy recovery system. Hassan A. M.M. U.S. Pat. No. 6,508,936, Jan. 21, 2003. This optimal seawater desalination method reduces both the energy required per unit water volume and the water generation cost by 30% or more.

  In many countries, desalination of salt water, particularly sea water, has been considered as a fresh water source for dry coastal areas, or areas where the water source is salty or has excessive hardness. Typical areas where desalination is considered or used include the Gulf States and other Middle Eastern countries: Southern California in the United States; Mediterranean Arab countries in Libya, Algeria, and Egypt; Europe, primarily Spain, Includes Malta and Cyprus; Pacific countries in Mexico and South America. Similarly, islands with limited fresh water supplies, such as Malta, the Canary Islands, and the Caribbean, use and consider seawater desalination as a source of fresh water. Currently, fresh water from the sea accounts for over 70% of drinking water in Saudi Arabia and the Emirates. In both Kuwait and Qatar, almost 100% of drinking water is derived from desalted seawater.

  The conventional commercial SWRO desalination process pre-treats the feed, removes turbidity, primarily suspended matter and bacteria, adds a scale inhibitor, usually an acid, and then this pre-treated feed. Through a high pressure of 55-82 bar (800-1200 psi) and separating the feed stream into product (permeate) and reject (concentrate). In many older SWRO plants, another second stage salty water RO unit is deployed to reduce the salinity of the product from the first stage SWRO unit to standard drinking water salinity. However, this conventional method used in many of the plants built in the early days (until the mid-90s) requires a high energy per unit amount of desalted water product and a relatively low yield. , Typically using two-stage SWRO units from Gulf seawater and operating from 25% to 35%, based on the feed, lower using single-stage SWRO. Therefore, they were economically viable only for areas where freshwater shortages were serious, energy was available, and their costs were considered low (although artificial). This is also true for thermal methods such as MSFD and MED. Desalination plants have also been used in other areas, such as California, but they are commonly used as standby or supplemental freshwater sources during drought times or when other water sources are temporarily limited or unavailable. Has been. In many areas where there is not much natural water resources available, current desalination methods use other freshwater sources such as onshore pipelines or water pipes from distant rivers and reservoirs as in Southern California. Cannot compete effectively.

  However, because oceans and oceans have vast amounts of water and direct freshwater sources (eg, island rivers, lakes, and groundwater channels) are beginning to be depleted, polluted, and reaching capacity limits, All these factors overlap with the growth of the world's population without a significant increase in natural water resources, e.g. the removal of salt water, especially seawater, as in the case of Middle Eastern countries, especially GCC Gulf countries. Extensive research has been conducted around the world on economic methods for salting. In fact, this study is developing towards the ultimate goal of meeting the growing water demand for many countries experiencing severe water shortages in the present or future, and in a way to bring peace between nations. They are considered to be the main cause of their grace, otherwise there will be a great struggle for limited water resources between neighboring states within their boundaries.

  As previously mentioned, several commercial seawater desalination methods are currently available and in use. Thermal multistage flash distillation is one of the two main desalting methods currently used worldwide. Alone, it accounts for about 41% of the global desalination capacity, whereas about 44% is produced by the reverse osmosis (RO) process. The rest (15%) has been obtained by various methods, mainly electrodialysis (ED), multi-effect distillation (MED), and vapor compression distillation (VCD); Wangnick Klaus, 2000 IDA World Desalination Plant Inventory (2000 IDA World Desalting Plants Inventory), report no. 16. International Desalination Association (May 2000). Saudi Arabia is the primary user of MSFD and the United States is the largest user of RO law. The MSFD, MED, and VCD methods are all used exclusively in seawater desalination, but ED is mainly applied in salty water desalination and pure water production. However, the RO method is a diversified salt water desalination method. It applies to both seawater and salty water supplies, but in the past it has mainly been applied to the production of salty, drinking and pure water. Recently, however, SWRO desalination has become more common and has been used worldwide, with plants of 39-57 million liters / day (mld) [10-15 million gallons / day (mgd)] or more. A relatively large plant is used.

Seawater desalination must take into account the important properties of seawater itself: (1) species, concentration, and total hard ions, (2) salinity [ion content, total dissolved solids (TDS)], And (3) the presence of turbids, suspended particles and microorganisms as well as other large particles. These properties interfere with the desalination system and determine plant performance (product: yield, recovery, and quality). In particular, only slightly soluble scale-forming hard ions and their coanions are 25% to 35% of the freshwater yield values expected from conventional seawater desalination methods, such as Gulf and Red Sea seawater. % Limit is given. As shown in FIG. 4, the seawater desalination method is a separation / concentration method, whether it is a membrane type or a thermal type, and the fresh water product stream and pollutants with clean drinking water quality: TDS and hard ions Is separated into an exclusion stream containing a high concentration. This fraction / concentration method is responsible for four main problems that occur in seawater desalination. These are summarized in FIG. 5 along with their causes: (1) scale formation, (2) high energy consumption, (3) contamination, (4) increased corrosion. Since hard ions have very low solubility and CaSO ₄ solubility decreases with increasing processing temperature, increasing the concentration of hard ions in brine can be achieved by various conventional seawater desalination methods, whether thermal or membrane. Demineralized water recovery rate is severely limited (gulf seawater, TDS≈45,000 ppm, 25-35% or less).

  This application refers to water referred to as “saline”, which is seawater from the sea, such as seawater from the Gulf, Red Sea, Mediterranean, and oceans, water from various salt lakes and ponds. , Including water from very salty water sources, brines, other surface and ground water sources including ionic inclusions, which are classified as “salt water” as shown in Table 1. ing. Saline can generally be considered water having a salt content of TDS ≧ 20,000 ppm or more. Of course, sea water has the greatest potential as a source of drinking water, so this application focuses on sea water desalination. However, all sources of high salinity, especially hard water, should be considered within the scope of the present invention, and focusing on seawater is for simplicity and limitation. It should be understood that this should not be considered.

  As mentioned earlier, the performance and product recovery of seawater desalination plants (thermal and SWRO plants) are severely limited by the three problems mentioned earlier, all of which are the quality of seawater and its material content. (1) Turbidity, (2) TDS, and (3) Total hard ions in the water feed. If turbidity is present in the feed, it is particularly trapped on the membrane, leading to membrane contamination. Biological contamination occurs when bacteria are present in the feed along with turbidity, ie suspended solids that nourish the bacteria. In RO, the feed osmotic pressure increases with TDS. From the RO principle, the pressure applied is: (1) partial and needs to be used to exceed the osmotic pressure, and (2) only the remaining part of the applied pressure passes through the membrane through the permeate (product ) Is the true pressure to push out (Pnet). The lower the osmotic pressure by reducing the feed TDS, the greater the true pressure that pushes the water, and thus the greater the pressure used to push the permeate through the membrane (FIG. 6), This also provides the added benefit of producing higher quantities of higher quality products.

  A high content of hard ions that are only slightly soluble in the feed is the biggest obstacle limiting fresh water recovery. This is because increasing the recovery rate beyond the solubility limit of hard ions causes more severe scale formation effects and causes a sharp decline in plant performance.

  In short, the scale formation of seawater desalination plants, together with their large energy consumption and pollution, constitutes three main problems of seawater desalination. Corrosion is the fourth major problem of seawater desalination, and the occurrence of corrosion increases with increasing salinity and chloride content in seawater. The first main object of the present invention is not only to solve these problems, but also to develop an efficient seawater desalination treatment and method that will result in the establishment of an optimal high efficiency seawater desalination method and apparatus. is there.

Increasing the SWRO plant water recovery rate would reduce unit water generation costs. This is because this unit cost is calculated by dividing the total water production cost by the amount of product. As the water recovery rate increases, the amount of product increases and the unit water cost simply decreases. At the Water Cost Countermeasures Meeting of major Japanese desalination experts (scientists and engineers) held at the Japan Water Reuse Promotion Center, the highest reduction in water production costs is to the SWRO plant (TDS = 35,000 ppm). Can be achieved with a 60% SWRO water recovery rate (ie SWRO reject TDS = 88,000 ppm), and this TDS value with SWRO rejects from Gulf seawater (TDS≈45,000 ppm) It is concluded that the corresponding optimum water recovery rate from Gulf seawater should not exceed 48% in order to maintain The large water recovery rate will cause the calcium sulfate to adhere significantly on the membrane, and the gain in water cost reduction due to the increased water recovery rate is needed to eliminate the very large increase in osmotic pressure This is offset by an increase in the cost of the applied pressure (see the above-mentioned reference by Goto et al.). Due to the removal of hard scale-forming ions and the reduction of feed TDS caused by the NF ₂ -SWRO ₂ of the present invention, much larger SWRO recovery is achieved by a combination of NF (two-stage) and two-stage or one-stage high-pressure SWRO operation. Rate can be obtained. As previously mentioned, the increase in SWRO recovery according to the present invention is a major advantage of the system of the present invention. During this development, the optimum double NF ₂ -SWRO ₂ desalination method, which exceeds all conventional methods in terms of efficiency and water recovery rate, or one stage of NF ₂ -SWRO (Figs. 1, 2 and 3) was developed. Efforts have been made to make it critically possible to increase the optimal SWRO water recovery rate from ocean supplies to over 80%.

  The above description is clearly illustrated in FIG. 7, in which an 80% product water recovery is achieved at a pressure of 70 bar. Both the product stream from the SWRO unit operated for the NF product and the water recovery rate are the same if the same SWRO pilot plant is operated on the seawater feed without using NF pretreatment. It is twice that obtained. The permeate begins to flow at an applied pressure of about 15 bar and sometimes lower when the SWRO unit feed consists of NF product, which is 2 times this value when the feed to the SWRO unit consists of sea water. It is comparable to twice (Fig. 7). Furthermore, the quality of the product water is much better when the SWRO unit is operated with NF product than when it is operated with seawater, unlike the former case, the product water Requires further processing by the RO unit for salty water to bring its quality to the drinking water standard.

This method is equally applicable to the conventional thermal seawater desalination process and is discussed elsewhere in other patent applications, due to the formation of the following hybrids:
NF (2 stages) - thermal, and _NF 2 -SWRO ₂ (elimination thereof) - thermal,
Here, the exclusion from the one or two stage NF product feed SWRO unit constitutes a make-up to the thermal unit of the MSFD, or MED, or VCD, or RH unit. This is another major advantage of the NF ₂ -SWRO ₂ of the present invention, where there is very little hard material in the SWRO reject, and thus to the thermal plant without the use of scale inhibitors. It has already been demonstrated that it can be used as a supplement. US Pat. No. 6,508,936 (January 2003).

  Traditionally, various types of filtration or agglomeration and filtration systems for treating water and other liquid solutions and suspensions have been used to remove particulate matter (Table 2). The addition of scale inhibitors is used to prevent scale formation and thus help to increase water recovery to the limit. However, despite this conventional pretreatment of removing turbidity and adding scale inhibitors, fresh water recovery rates are still limited to 25-35% or less, for example, in conventional SWRO conventional desalination. .

  Recent work to remove fine particles with particle sizes smaller than 2 μm uses microfiltration (MF) or ultrafiltration (UF). Low pressure reverse osmosis (LPRO) or salty water RO (BWRO) membranes (see below) have also been used prior to SWRO pretreatment. MF membrane treatment is used to remove particles having a particle size in the range of 0.08 to 2.0 μm. The UF membrane method is more effective in removing finer particles having a particle size in the range of 0.01 to 0.2 μm and a molecular weight (MW) in the range of 10,000 g / mol or more. Both the MF and UF membrane methods are genuine filtration methods, and the separation of the particles is done only by particle size, not by their ionic properties. Furthermore, both MF and UF membranes have their own characteristic pore size and separation limit. These two membrane filtration methods are effective in keeping the feed clean by removing turbidity and bacteria, and as such, can eliminate membrane contamination, including biological contamination, during plant operation. They are very effective pretreatment methods to prevent. The pretreatment method by MF and UF filtration is significantly different from the RO pretreatment. As already mentioned, unlike the MF and UF membrane methods that do not separate or eliminate ions from solution or seawater, the RO method has a particle size of 0.001 μm or less and a molecular weight of 200 g / mol or less. This is a pressure difference method for separating all ionic particles having. In addition, these highly airtight SWRO membranes require operation at high pressures on the order of 50-80 bar, compared to operation at low pressures of only about 5-10 bar in the MF and UF processes. And

Compared to other membrane separation methods, the NF membrane method falls between the separation range of RO and UF, and has a particle size in the range of 0.01 to 0.001 μm and a molecular weight of 200 g / mol or more. Suitable for separation. However, unlike either UF or RO, NF works by three principles: elimination of neutral particles by particle size, elimination of ionic species by electrostatic interaction with negatively charged membranes; Rautenbach ) Other, Desalination, 77: 73-84 (1990). Third, the operation of the NF membrane is governed in part by the osmotic pressure principle. For these reasons, as will be shown in later sections, NF membranes are more or less covalently bound or all monovalent ions are excluded to the same extent as NF is Na ⁺ , Cl ⁻ etc. Rather than eliminating monovalent ions such as SO ₄ ⁼ , HCO ₃ ⁻ , Ca ⁺⁺ , and Mg ⁺⁺ scale-forming hard ions and having much greater exclusion to covalent and trivalent ions. Is different. NF has been used in Florida to process salty hard water to produce potable water. The NF method has also been used to remove colored turbids and dissolved organics from drinking water; Duran et al., Desalination, 102: 27-34 (1995) and Fu et al., Desalination. , 102: 24-56 (1995). NF has been used in other applications to treat salt solutions and landfill leachate; Linde et al., Desalination, 103: 223-232 (1995); injected into offshore oil wells Removal of sulfate from seawater; Ikeda et al., Desalination, 68: 109 (1988); Aksia Serch Baker, Filtration and Separation (June, 1997). As shown below, the NF seawater membrane pretreatment is performed at a much lower pressure, typically 10-25 bar, than the SWRO membrane operation (typically 55-82 bar, ie 800-1200 psi). .

In addition to the above use of the NF method, it has also been used in the treatment of various seawater and aqueous solutions. As mentioned above, the NF membrane of US Pat. No. 4,723,603 is used to remove sulfate from seawater, but it still has a high sodium chloride content and is Used to form a perforated slurry, this method prevents barium sulfate scale formation. US Pat. No. 5,458,781 discloses an aqueous solution containing bromide and one or more polyvalent anions in two streams, one bromide-rich stream and the second in a polyvalent anion. NF separation is described in a rich stream. Although further treatment with RO has been suggested to bring the bromide rich stream to bromide concentrations used in industrial applications, nothing has been done. EPO Notice No. 0914260 (03,06,97) passes seawater through three flat membrane cells of a polyvinyl alcohol polyamide nanofilter (NF membrane) to remove sulfate ions, and then passes the filtered water through an RO membrane. Thus, by removing SO ₄ ⁼ , a method has been proposed to solve the problem of improving the concentration rate while suppressing the deposition of scale (but no further details of the study are given).

  As shown in FIG. 8, the first person to apply NF pretreatment to SWRO and other seawater thermal (MSFD, MED, VCD) desalination methods, first in the pilot plant and demonstration desalination plant stages, In US Pat. No. 6,508,936, Hassan A. et al. M.M. Hassan et al., “Desalination and Water Reuse, Four Seasons”, published May-June (1998) Vol. 8/1, 54-59, and September-October (1998), Vol. 8/2, 35-45: Desalination, 118: 35-51 (1998); Desalination, 131: 157-171 (2000); Proceedings of the International Conference on Desalination and Water Reuse (San Diego) (1999) Best IDA thermal award for salt) and many other publications.

  This new NF-SWRO desalination process was first developed in a pilot plant and proved successful in solving the major problems previously mentioned for conventional seawater desalination processes by: (1) prevention of SWRO membrane contamination, (2) prevention of plant scale formation, and (3) not only significantly increasing plant productivity and improving SWRO product quality both in yield and recovery. Reduce both energy requirements and cost per unit water product. As shown in FIG. 8, the same advantage was obtained by connecting the NF membrane unit and the thermal desalting MSFD unit as a double hybrid desalting unit. Similarly, as shown in the same drawing, the SWRO reject is used as a supplemental feed to the MSFD unit because the hard material has been removed from the reject in the SWRO unit to which the NF product is supplied. Has been successful. In both the double NF-MSF hybrid and the NF-SWRO (exclusion) -MSF triple hybrid, the MSF unit is operated for the first time even at a maximum brine temperature (TBT) of 120 ° C. and later with scale inhibitors. Without being operated at higher yields with higher TBT up to 130 ° C. (see literature in previous paragraph).

This dual NF-SWRO desalination process is further illustrated in FIG. 9 in a commercial scale plant, an existing Umm Lujj SWRO plant commissioned in 1986, with one SWRO train 100, capacity 2203 m. ³ / d (582, 085 gpd). The plant was converted from a single SWRO desalination process to a new dual NF-SWRO desalination process by introducing NF pretreatment and semi-desalination units in front of existing SWRO units. See photo in FIG. The second line in the same plant, the train 200, is similar in design and manufacture to the train 100, but continued to operate in a single SWRO mode. Before establishing the operating parameters for a large NF-SWRO plant before changing the plant to the dual NF-SWRO method, the design and operation of the NF-SWRO plant using a demonstration unit similar to the new NF-SWRO plant. The method was tested. From the results of this experiment, the NF recovery rate in NF-SWRO was fixed to 65% (Fig. 11), and then successfully operated with the demonstration mobile pilot unit for 2 months with 70% NF product recovery rate. Hassan A. M.M. Others, Proceedings of IDA International Conference on Desalination (Bahrain) October 2001, Abstract, p. See 193-194.

The ion exclusion rate and the total hardness of scale-forming hard ions of SO ₄ ⁼ , Mg ⁺⁺ , Ca ⁺⁺ , HCO ₃ ⁻ of the NF unit of Train 100 are 99.9%, 98%, 92%, 56%, And 97% (FIG. 12). This very large hard ion rejection rate is compared to an exclusion rate of only 24% for monovalent Cl ⁻ ions and 38% rejection rate for TDS ions, and the TDS of about 45,460 seawater feed is , Reduced to 28,260 in the NF product (FIG. 12).

The results obtained from the operation of this commercial SWRO unit of a novel dual NF-SWRO desalting hybrid show a significantly improved product over that (SWRO unit) operation in the conventional commercial SWRO desalination process. The production rate and recovery rate are shown. The output of the train 100 operated in the NF-SWRO mode is 130 m ³ / hour from the supply of NF product at 234 m ³ / hour, which is one conventional SWRO operation. When operated with seawater at 360 m ³ / hour, the productivity is 91.8 m ³ / hour, increasing the train production rate by 42%. Furthermore, the 56% recovery rate of a SWRO unit in a double NF-SWRO operation is twice that of 28% when it (SWRO unit) is operated in a single mode. The same trend is also observed when the permeate production and recovery of NF-SWRO train 100 are compared to the results obtained from SWRO train 200, with 1.5: 1.0 and 56 for SWRO units, respectively. %: The ratio is 23.5%, and the former is better than the latter train operation (FIG. 13). The product flow ratio of train 100 to train 200 is almost on the order of about 160%: 100% (FIG. 13d). Train 100 productivity: Train 200 productivity is about 1.6- The ratio is 1.4: 1, clearly a dual NP-SWRO operation is more convenient than a single SWRO plant operation.

Also, compared to operation with the conventional SWRO method, train 100 operation as a dual NF-SWRO hybrid significantly reduces energy consumption and cost per unit production (m ³ ) by 23% and 46 or more, respectively. ing. Compared to the SWRO operation, the expected savings in both energy consumption / m ³ and cost per unit water produced by the NF-SWRO method are 39% and 68%, respectively. Furthermore, line conversion from SWRO to NF-SWRO operation could be done quickly and at a relatively low cost.

  US Pat. No. 6,190,556 B1 (February 20, 2001) describes a beverage from an aqueous supply such as seawater using a pressurized vessel designed for low pressure operation (250-350 psi). An apparatus and method for producing water is described, in which both NF and RO membranes are placed with an NF membrane member upstream of the RO membrane member. The seawater feed is first sent through the vessel and processed at this low pressure through NF to remove the hard material, but is only flushed unaffected through the RO membrane area. The NF product collected in a specially designed mechanism is later sent through the same vessel at the same pressure using the same pump, reducing its osmotic pressure and desalting through the RO membrane. Can do.

  Some other patents use an RO module prior to the SWRO module for SWRO desalination. U.S. Pat. No. 4,341,629 (July 1982) uses cellulose acetate with 90% ion rejection as the first stage unit, and then cellulose triacetate SWRO membrane with 98% ion rejection. A method using an attached second stage separation unit is described. The invention of US Pat. No. 4,156,645 (May 1979) uses a two-stage continuous separation unit and, as a second stage, uses a SWRO unit fitted with an airtight membrane, Process the product from another loose RO membrane unit, the latter having an ion exclusion rate of 50-75% and operating at a low pressure of P = 300-400 psi (21-28 bar) A collection method is proposed. The loose RO membrane is also used before the airtight membrane in EPO 6,120,810. U.S. Pat. No. 5,238,574 describes a method and apparatus for treating water with a plurality of RO membranes and then producing water and salts with an evaporation mechanism. U.S. Pat. No. 4,036,685 also produces high quality permeate removed from the first RO cartridge, while at the same time from the next two cartridges in series with the first RO cartridge. A method and apparatus for producing a low quality permeate by combining the products is described.

  From the discussions and results above, in addition to other pre-treatments, a very special and excellent pre-treatment function, i.e., out of hard ions and covalent ions, trivalent, rather than eliminating monovalent ions. The ability to reject ions to a much greater extent (see NF exclusion rate in Umm Lujj plant—FIG. 12) and, as previously mentioned, the ability to reject at a pressure much lower than that required by the SWRO or RO method. It can be emphasized that NF is designed to do so. Furthermore, the NF membrane is characterized by having much greater tolerance to fluxes and turbids than RO or SWRO membranes. These facts distinguish it and separate its function from the other previously shown water separation membrane methods, namely MF, UF and RO. Because of this quality, the nanofiltration, loose reverse osmosis, and low pressure reverse osmosis used in the above-mentioned patents, i.e., SWRO membranes that receive RO, loose RO, LPRO pretreatment feeds are considered the same in the art. It should be noted that not. In fact, the nanofiltration (NF) pretreatment of seawater feeds that allow those skilled in the art to remove hards and, as a result, produce drinking water from SWRO without forming scales with high recovery rates, This is not only an excellent pretreatment of the seawater feed to the seawater desalination plant, but also said that reverse osmosis (RO) or loose membrane reverse osmosis (LMRO) membranes are not operationally or functionally equivalent. I've acknowledged the fact and still admit it. The references cited below highlight the differences:

1. Bequet et al., Desalination, 131; 299-305 (2000).
2. Bisconer, “Explore the Capabilities of Nano- and Ultrafiltration”, Water Technology, March 1998, (2 pages; page numbers not stated).
3. Kodak, “Nanofiltration for Professional Motion Imaging”, On-Line Technical Support paper, pp, 1-6 (1994-2000).
4). Linde et al., Desalination, 130; 223-232 (1995) (abstract only).
5. Nicolaisen, “Nanofiltration-Where does it Belong in the Larger Picture”, pages 1-7, “Desal-5” membrane product Product technical bulletin for "Desal-5" membrane products; Desalination Systems, Inc. (December 1994).
6). Scott Handbook of Industrial Membrane, 1995 (page 46).

  As Vis Corner admits, in this field, RO and NF can be considered “cousins” and the membranes used look the same, but in practice they are “clearly different” "I have a separate function." Among the important differences between NF and RO (BWRO, loose RO, and LPRO), NF gives a significantly larger rejection rate of hard ionic species at a much larger total product stream bundle than RO. This has actually been observed in the Umm Lujj NF-SWRO experiment; see Hassan et al. And FIG. In particular, although Nicolaicen (1994) sometimes misrepresents various terms in the art, those skilled in the art will exclude di- and tri-anionic species at least particularly greater than the exclusion of NaCl. It also points out that it recognizes the clear superiority of NF to RO in that it has a much larger (NF membrane) flux than the flux of RO membranes. Please refer. Furthermore, it has greater tolerance to turbid contamination than SWRO membranes. Others make the same point by recognizing that the RO flux is low compared to the NF flux and that a much greater pressure with a much larger membrane surface area is required in the RO than in the NF membrane. ing. These facts have been observed in the above commercial experiment of NF-SWRO operation in the Umm Lujj plant train 100, where each NF module consists of almost three SWRO modules (one module contains six membrane members). A single pressure vessel fitted with a feed. In order to have a real effect, the RO unit requires a finer feed pretreatment than the NF membrane process in the removal of solid particles.

SWRO membranes are the most airtight desalination membranes and are characterized by their large salt (all ions) rejection. SWRO membranes are operated at a high pressure, 55-82 bar depending on the membrane type, and their flow rates are low, so the SWRO method requires a large number of SWRO membranes to produce a large amount of water. Because of all these factors, the cost of water production by the SWRO method is considered the highest among all other membrane desalination methods. On the other hand, the NF membrane is operated at a much lower pressure and has a large flow rate. Most importantly, however, as noted above, they are characterized by great specificity for the elimination of scale-forming hard ions (SO ₄ ⁻ , Ca ⁺⁺ , Mg ⁺⁺ , HCO ₃ ⁻ ). See literature given earlier by Hassan et al.

Not only their main different properties, quality, and characteristics between SWRO and NF membranes, but also the ability to distinguish NF from other RO membranes, including the above-mentioned loose RO or low pressure RO membranes, one dual NF -As a SWRO operation method, an advantage is surely obtained by completely integrating the NF and the SWRO membrane. M.M. U.S. Pat. No. 6,508,936 (January 21, 2003), first performed on a pilot plant scale (see FIG. 8) and then on a commercial plant scale (see FIGS. 9 and 10). As it has been successful. However, this is done by using each of the NF and SWRO units in one step. Operate each of the NF and SWRO units in a dual NF-SWRO set up in two stages with a turbocharger placed between the two stages to recover energy from the brine, as will be shown later A greater advantage is seen. This highly optimized and well-designed dual NF (two stage) -SWRO (two stage) configuration shown in FIG. 1 for the proposed Red Sea SWRO plant has a feed rate of 316 m ³ / hour and about 170 m ³ Per hour (1.08 mgd) yield, optimal seawater desalination process, increasing both plant productivity, yield and water recovery, energy requirements for unit freshwater production from the sea, and Not only does it provide an economically efficient SWRO desalination operation by lowering costs, but it effectively outperforms what can be predicted by conventional, conventional seawater desalination methods. This method is also applied to NF ₂ -SWRO ₂ (exclusion) -thermal triple hybrids with great advantages, as exemplified elsewhere in my other invention, in which case hard SWRO exclusions whose ion concentration has dropped dramatically have been supplemented to thermal units.

  This optimal NF (two-stage) -SWRO (two-stage) and triple hybrid SWRO desalination system is only quite different from conventional methods including those described in US Pat. No. 6,190,556 B1. It is far superior to them in terms of process efficiency and economy. For example, the NF-SWRO system described in US Pat. No. 6,190,556 B1 (February 20, 2001) has both NF and SWRO members placed in the same pressurized container. However, it is operated at the same but lower pressure of 17.24 to 24.05 bar (250 to 350 psi) using a single pressure pump. In this system, the operation is started by first collecting sufficient NF product, after which the collected NF product is specially designed, placed in a controlled holding tank, and under pressure (250-350 psi). Low pressure), which results in a product of questionable quality mainly due to the SWRO low pressure. More importantly, if the NF membrane is operated for some time, it can be left idle during the next SWRO operation, or vice versa, to partially utilize the NF or SWRO membrane. It is that. In contrast, all components according to the present application, NF (two-stage) -SWRO (two-stage), are used completely 100%, which results in a higher plant production rate. Further, the two-stage configuration provides sufficient high pressure for the second stage feed, in particular for the first and second stage SWRO units, again in the above-mentioned US Pat. No. 6,190,556 B1. Enabling a higher plant production rate with a much higher product quality than that obtained from the use of To produce the same amount of water on a commercial scale by the two methods, the latter method requires more capital investment and more equipment than the method given here (optimal method). And

  Therefore, it produces economically fresh water from salt water, especially sea water, in a good yield, effectively and efficiently addresses the problems mentioned above, ie removes hard substances and turbidity from such salt water, The ability to obtain optimal seawater desalination processes that reduce total dissolved solids with increased plant production rates and economic efficiencies, including low energy consumption per unit water product and low water costs, It will be a concern for humans, especially those who need fresh water from the sea, but cannot. Use of rejects from SWRO units fed with NF product, providing supplements to NF (two-stage) pre-treatment methods, or thermal MSFD, or MED plants also provides similar gains, seawater membrane or thermal This results in enormous improvements in the efficiency of the formula desalination plant.

SUMMARY OF THE INVENTION I have focused particularly on seawater by combining two substantially different water film methods represented by the configurations given in FIGS. 1, 2 and 3 in a manner not previously performed. A unit that is equivalent to or better than the conventional SWRO desalination method of much lower efficiency, producing a very high yield of high quality fresh water, including drinking water, Invented the optimal SWRO desalination method to produce with energy consumption per production. To achieve this goal, for example, each of the NF and SWRO units of FIG. 1 may be arranged in two stages, with an energy recovery turbocharger between them, or alternatively, NF in two stages. The energy recovery TC is arranged and used between the two stages. In this case, the SWRO is arranged in one stage, and the energy recovery TC or the pressure exchanger (PX) between the SWRO membrane unit and the high-pressure pump is also arranged. Then, using the configuration as shown in FIGS. 2a and b, or 3a and b, using NF and SWRO membrane selectivity for the method as described below and in the previous section. This method not only improves product quality and increases product yield and productivity from each step, but also reduces energy consumption per unit water production when using the PX system. Optimal method: reduced to 0.445: 1 as a ratio of conventional SWRO without NF pretreatment, with the net effect of reducing cost per unit water product. In my method, the two-stage nanofiltration as the first desalting process is synergistically combined with the subsequent two-stage seawater reverse osmosis process shown by the configuration as given in FIG. A desalination system, whereby salt water (especially seawater) can be efficiently and economically obtained into high quality fresh water with the conventional SWRO method alone or with previously known or described combinations Conversion can be achieved with a yield significantly greater than the yield. Thus, individual processes are known separately and such processes have been described individually in combination with other methods for different purposes, but are due to different stages and are discussed above. As described above, the method of the present invention has not been known or conceived by those skilled in the art, and compared with the method and apparatus of the conventional method, There was nothing in the prior art that suggested that all types (membrane or thermal) provide surprisingly unique and significant improvements and great system efficiency.

Thus, as a broad aspect, the present invention provides a solution of hard scale-forming ionic species, microorganisms, particulate matter, and brine containing a large amount of total dissolved solids to two-stage nanofiltration (NF ₂ ) An energy recovery turbocharger is placed between them, and a pressure increase pump is replenished as necessary, and the content of the first water product and the hard ionic species is drastically reduced at a high recovery rate. As well as a low energy consuming NF water product having a TDS content significantly lower than seawater and almost completely free of microorganisms or particulate matter, after which the first water product is A two-stage seawater reverse osmosis (SWRO ₂ ) is provided with an energy recovery turbocharger between these two SWRO stages as shown in FIG. The desalination process involves producing a second water product (permeate) having a reduced salinity equal to the salinity of water. This aspect constitutes the basis of the optimal membrane seawater desalination hybrid system NF (two-stage) -SWRO (two-stage) which is part of the subject matter of the present application.

  Even in the second and third broad aspects, the present invention passes a saline solution containing hard scale-forming ionic species, microorganisms, particulate matter, and total dissolved solids through a two-stage nanofiltration to produce the ionic Form a first water product with a reduced content of chemical species, microorganisms, and particulate matter, after which the first water product is subjected to energy recovery between those stages for the next one-stage seawater reverse osmosis TC or PX is placed and refilled with high pressure increase pump if necessary, in which case the SWRO stage has any form and configuration as shown in FIG. Includes a desalination process comprising producing a second water product (permeate) having a reduced salinity equal to salinity.

The three aspects form the basis of the optimal SWRO desalination method that is the subject of the present application, which consists of the following seawater membrane desalination hybrids: NF ₂ -SWRO ₂ (FIG. 1), NF ₂ -SWRO ₁ ( 2) and NF ₂ -SWRO ₁ (FIG. 3).

  Only these three hybrids and the above three aspects are discussed in this filed patent application and are filed concurrently with a second separate patent application that includes the thermal seawater desalination aspect of the present invention.

The method easily and economically produces a significant reduction in the properties of salt water (especially sea water) and produces good fresh water, including drinking water. Typically, in the process of the present invention, the two-stage NF ₂ is reduced in terms of seawater feed properties, containing calcium and magnesium cations on the order of 75% to 95% or more, 90 to 99.9% or more. On the order of sulfate reduction, pH reduction of about 0.4-0.5, and reduction of total dissolved solids content (TDS) of about 30% -50%. On the other hand, the product from SWRO ₂ or SWRO ₁ unit has drinking water quality. Similarly, as illustrated elsewhere, the distillate can be removed from MSFD, or MED, or VCD, or RH units, which are SWRO excluded from SWRO units fed with NF product or NF product. Product when operating with a replenisher consisting of material. For ocean water feed TDS≈32,000 ppm, a maximum water recovery of about 66% or more is achieved by the NF ₂ -SWRO ₂ (exclusion) -thermal triple process. Its value exceeds all values obtained by conventional seawater desalination.

  Drawings are graphs or process diagrams relating to data given in the text. A more detailed description of the drawings will be found in the discussion of data.

Detailed Description and Preferred Embodiments Optimal SWRO desalination of the present invention will be best understood by first considering the various components and properties of salt water, particularly sea water. As previously mentioned, seawater is high TDS, high hard substance concentration due to the presence of scale forming hard ions Ca ⁺⁺ , Mg ⁺⁺ , SO ₄ ⁼ , and HCO ₃ ⁻ , particulate matter, macro and micro. It is characterized by having a relatively high concentration of turbidity of varying degrees due to the presence of the organism and a pH of about 8.2. Many of the problems related to seawater desalination limitations and their effects are related to the quality of these seawaters. Seawater typically has a cation content on the order of 1.2% to 1.7%, of which about 900-2100 ppm is “hardness” cations, ie calcium and magnesium cations. The anion content of scale-forming hard ions, ie sulfates and bicarbonates, is on the order of 1.2% to 2.8%, and the pH is on the order of 7.9 to 8.2. Typically, there may be a wider range for one or more of these properties, on the order of 1.0% to 5.0%, generally 3.5% to 4.5%. May constitute total dissolved solids content. However, it will be appreciated that these components and properties vary throughout the world's oceans and oceans. For example, a small closed sea with a hot climate usually has a higher salinity (ion content) than the high seas region, for example, a bay-to-ocean seawater composition as shown in Table 1.

One major problem of seawater desalination is the high TDS of the seawater feed, especially in the case of the SWRO process. The osmotic pressure of the feed increases as the TDS of the feed increases. Given a given applied pressure P _appl , this increase in osmotic pressure (Pπ) about 0.7 bar per 1000 ppm TDS increase reduces the resulting pressure P _net :
P _net = P _appl −Pπ (1)
_Where P _net is the pressure that pushes water through the RO membrane to produce a permeate stream. In order to increase P _net and thus increase the permeate stream, a high applied pressure is required as long as the membrane strength can be tolerated. The effect of feed TDS variation on osmotic pressure and P _net pressure in the SWRO process at a temperature of 25 ° C. and an applied pressure of 60 bar and a final brine TDS of 66,615 ppm has been shown previously in FIG. Effective applied pressure to extrude the water through the membrane is represented by the area shaded in P _{net Non,} it decreases as the feed TDS increases. Since the permeate stream through the membrane is directly proportional to the water driving pressure P _net , the reduction of the seawater feed TDS by the method of the present invention not only reduces energy waste but also increases the fresh water permeate through the membrane. . As illustrated below, the reduction in energy requirements per unit water product due to the reduction in feed TDS in this case, which increases P _net and permeate streams, is the main advantage obtained by the process of the present invention. It is an effect.

Similarly, the turbidity (reflecting total suspended solids and microorganisms) of small areas such as the ocean or ocean, where the desalination plant draws its seawater feed, reflects the organism and particulate matter. Depending on local concentrations, such concentrations within the same sea can often change with weather, climate and / or topographical changes. Typical values are shown in Table 1 for typical high sea water, Mediterranean, and closed “bay sea” (sometimes referred to as “ocean water” and “gulf water”, respectively) in the future. The seawater fluctuation between water is illustrated. “Ocean water” is often taken as the basis for standard (usual) seawater properties, but for the purposes of the discussion here, the components and properties of oceans and seas around the world are substantially It will still be appreciated that it is the same everywhere. The main difference is in the concentration of salt, but not in their relative ratio, but it tends to be constant in different seas, for example, Na ⁺ and Cl ⁺ total salt The concentration ratio with respect to each remains approximately the same at about 30.7 to 55%. See Table 1. These local variations that may occur are well understood and understood by those skilled in the art. Thus, the present invention described herein is useful in virtually any map location, and the following description of operations relating to gulf water or ocean water is not intended to be limiting, but merely considered as examples. It should be.

  The presence of particulate matter (macroparticles), microorganisms (eg, bacteria), and macro-organisms (purple oysters, barnacles, seaweeds) will remove them from the feed to both SWRO and thermal desalination plants. I need. The removal of turbidity and microparticles, usually defined as total suspended solids (TSS), from the feed intended for the SWRO plant is essential, but the thermal process was not always required. It has become most necessary to remove chlorine from the feed to chlorine sensitive NF and SWRO membranes.

  As already shown repeatedly, the third major problem inherent in all conventional desalination methods is the high content of hard ions in seawater, which is more thermal than the membrane method. Has a major negative effect. Since all desalting processes are operated to extract fresh water from salt water, salt and hard ions are left in the brine, giving the effect of increasing both the brine TDS and the hard matter concentration. This is illustrated in FIG. Since hard ions are only slightly soluble in seawater, when they are concentrated in brine, they usually deposit in the form of scales in desalination equipment, such as tubes, membranes, etc. The water recovery rate is limited to a low value of, for example, 25 to 35% or less for desalted gulf seawater and 30 to 40% for ocean seawater. Depending on the conditions in which the desalting process is operated, two types of scale forms occur: an alkaline soft scale consisting mainly of CaCO〓 and Mg (OH) 〓 and mainly CaSO〓, CaSO〓 · H〓O, and CaSO〓. It is a non-alkaline hard scale composed of 2H〓O. The latter form becomes worse as the temperature increases. This is because the solubility of CaSO〓 decreases as the solution temperature increases. Traditionally, in thermal desalination plants such as MSFD or other MED plants, acids and other anti-scale additives are generally added to the feed water, and in the case of MSFD, at a brine temperature of 90-120 ° C, the MED In the case of a plant, the process operation is limited so as not to cause scale formation at a brine temperature of 65 ° C. However, nevertheless, freshwater product recovery was as low as 25% to 35% as a fraction of product to replenish the feed from Gulf seawater. At higher operating temperatures, ion exchange was required to remove SO soot or Ca soot and to obtain higher water recovery. Similarly, in SWRO operations, scale inhibitors have also been commonly added to prevent membrane or plant scale formation, but again, for example, in the case of Gulf seawater, the water recovery rate by conventional methods is still about It was limited to 25 to 35% or less. In addition, the scale inhibitor is usually returned to the marine environment, as part of a brine discard, or during a descaling operation. Such materials are usually pollutants in the marine environment and should be avoided as such.

  These problems during seawater desalination and the measures used to mitigate them, along with the quality requirements for the feed to the SWRO plant when taking the feed from the high seas (surface) intake, Table 2 has already been summarized and given. The two-stage NF feed pretreatment method used with or without a suitable scale inhibitor in the present invention can efficiently and economically remove turbids, hard ions and reduce TDS. The process of the present invention can be carried out with higher NF product recovery than would be expected with the conventional process, and therefore the process of the present invention is conventional and other conventional seawater desalination processes. It will be understood that this provides a significant improvement. In addition, the removal of hard ions helps to increase recovery in all types of seawater desalination methods (membrane or thermal).

  Briefly, the optimal seawater thermal desalination process of the present invention significantly reduces hards, lowers TDS and removes turbidity from the feed in the membrane process step, thereby eliminating energy and chemical consumption. Reduce the volume, increase the water recovery rate, and reduce the production cost of fresh water from seawater. This is achieved by a unique combination of NF and SWRO, each in two stages, with an energy recovery turbocharger between the stages, as shown in FIG. 1 as an example, given in FIG. As shown in the configuration, it has one SWRO stage (which may be NF and MSFD, MED, or VCD), which can be further improved by additional combinations with media filtration, It can be improved by the quality of the feeds without it, or by using underground water intake such as coastal wells to collect seawater.

  Nanofiltration and SWRO desalination are all widely described in the literature and have become a commercial facility for each source. Thus, a detailed description of each stage, equipment and materials used herein, and various operating parameters need not be given in detail here. As a typical example of a comprehensive description of the literature, ENCYCLOPEDIA OF CHEMICAL TECHNOLOGY for nanofiltration by Kirk-Othmer, 21: 327-328 (No. 4th edition: 1991); 303-327; and RO for McKetta et al., ENCYCLOPEDIA OF CHEMICAL PROCESSING AND DESIGN, 16: 198-224 (1982), and Corbitt. ), STANDARD HANDBOOK OF ENVIRNMENTAL ENGINEERING, 5-146 to 5-151.

By describing and understanding the basic concepts of NF and SWRO, NF is coupled to SWRO, so that two-stage NF and two-stage or one-stage SWRO (FIGS. 1, 2, and 3), SWRO or NF and MSFD. The details of the progress of the research conducted on the complete synthesis of the system can best be understood by referring to experimental research conducted on a pilot plant scale. A schematic process diagram formed as an NF-SWRO process with one single stage NF combined in one single stage SWRO is given in FIG. The method consists of a seawater supply system, a dual media filter, and a subsequent fine sand filter, a 5μ cartridge filter, a feed tank, an NF unit and a SWRO unit each consisting of one stage. The particle size of the sand in the sand filter can vary and is usually on the order of 0.3 to 1.0 mm. The pre-treatment part of this system is NF ₂ -SWRO ₂ (FIG. 1), or NF ₂ -SWRO ₂ -thermal triple hybrid, or only one stage SWRO is a high pressure membrane, eg Toyobo HB type (FIG. 2). using _NF 2 -SWRO _1, or NF (2 steps) -SWRO (one step) (FIG. 3) is maintained in the two-hybrid or triple hybrids of this new invention as, NF supplied SWRO reject Are recycled to the product or to one or more SWRO plants, but all have the same feed rate of 316 m ³ / hour, as illustrated by way of example in FIGS. In that case, the filtration process is not shown in each of FIGS.

  In commercial SWRO or NF plants, membrane members are usually arranged in series as six members per pressurized vessel. This type of membrane configuration has become a preferred configuration in many commercial NF and SWRO plants worldwide. This is also the array of NF and SWRO members used in the dual NF-SWRO operation in the commercial Umm Lujj SWRO plant shown in FIGS. In order to establish the performance of six members within one pressurized vessel, the demonstration unit can replace two members instead of six members (8 ″ × 40 ″) per pressurized vessel, as shown in FIG. It was constructed using three pressurized vessels each fitted with an NF member (8 ″ × 40 ″). The performance of each of the two members in the first: second: third pressurization vessel was as shown in the same figure and had the following ratio.

From a feed of 11.95 m ³ / h with an applied pressure of 25 bar and T = 30 ° C. and a TDS of 45,000 ppm:
Product logistics 4.61: 3.3: 1.32 Total: 9.28m ³ / hr Product recovery rate 38%: 28%: 11% Total recovery rate: 78%
Product TDS 28,000: 35,000: 40,000 Combined product: 32,270 ppm
For each vessel, product recovery was calculated as the ratio of NF product to total feed 11.95 m ³ / hour. As shown in the same figure, the two elements in the third container are highly stressed; they have a feed of only 3.99 m ³ / hour with TDS = 69,100 ppm, ie For the first two parts, for example, 1/3 of the feed at 11.95 m ³ / hour was received at P = 24 bar, which was supplied with TDS = 45,000 ppm seawater at P = 25 bar. . Higher pressures are required for operation of members in the third pressurized vessel to overcome the increase in feed osmotic pressure.

In order to remove this large stress on the last two members in the third container, or a part thereof, and increase the efficiency of the NF process, the configuration shown in FIG. 1 was used in the present invention. In this configuration, the NF process is performed in two stages, with an energy recovery turbocharger placed between them. This configuration has two functions: it increases the product stream and water recovery and reduces the energy consumption per unit water product, as will be shown later. The ratio of the number of members in the first: second NF stage is about 2: 1. Further, in this configuration, each member in the first stage has a recovery rate of about 50-60%, the first NF stage has a recovery rate of 50%, and the second NF stage is received by the first stage member. If the SWRO recovery rate for the latter (first stage) is less than 50%, the second stage member is more than the feed sent to the first stage member. Receive supplies. The first stage in which seawater was supplied at P = 25 ± 10 bar consists of two parallel NF blocks by way of example, where one block is a number arranged in parallel according to seawater feed quality (TDS). Each of the pressurized containers is provided with four NF members. If the feed TDS is sub-ocean quality, up to a total of 6 members could be used in one pressurized vessel. On the other hand, the second stage has one NF block having about half the number of modules in the first stage block. All modules are arranged in parallel, each consisting of one pressurized vessel fitted with four NF members. The first and second stage NF members may be of the same type as long as the membrane can withstand high pressures up to 35 ± 10 bar, or the second stage NF member may be replaced with the first stage NF member. Choose to have a higher pressure tolerance up to 45 bar, higher than the pressure allowed by the member. The second stage NF unit is fed with the combined reject from the first stage module after increasing its pressure from 25 ± 10 bar to about 35 ± 10 bar by a turbocharger. If necessary, the second stage pressure can be further increased (pressurized) by using a pressurized pump, as shown in FIGS. The high-pressure first stage reject can be received and further raised to the desired pressure value. The pressure increase (ΔP) due to the turbocharger is equal to the following (Pump Enguneering, Inc. Manual # 299910):
ΔP _tc = (nte) (R _r ) (P _r −P _c ) (2)
nte = hydraulic energy transfer efficiency R _r = ratio of brine flow to supply to turbocharger vs. feed stream P _r = brine pressure to turbocharger C _c = brine pressure exiting turbocharger

  In the case of SWRO shown in FIG. 1, the calculated ΔP is equal to 37.5 bar, and for the case of NF it is about 13 bar.

  The configuration of NF (two stages) -SWRO (two stages) is illustrated in FIG. The NF unit consists of a high-pressure pump so as to apply a pressure of up to 25 ± 10 bar to the first stage NF unit, which unit consists of two modules arranged in parallel. As previously mentioned, one module consists of one pressurized vessel with four 8 ″ × 40 ″ or other sized membrane members. While NF membranes may be in the form of spirals, hollow microfibers, tubes, or plates, almost all commercial NF membranes are thin film composites that are spirally shaped. Made from a nanocellulose polymer having a rolled form. The polymer is of the usually hydrophobic type with negatively charged groups, as described, for example, by Raman et al., Chem. Eng. Progress. 7 (1): 58 (1988). . Seawater feed is fed to the first stage module at ambient seawater temperature, and their combined pressure exclusion is illustrated in FIG. 1 to the next second stage module with four NF members per module. As shown, the pressure is increased by a turbocharger fixed between the two stages after increasing its pressure to 35 ± 5 bar. If necessary, a pressure pump can raise the pressure above 40 bar. The number of modules in the second NF stage is about 1/2 or approximately equal to their number in the first NF stage. The seawater feed pretreatment unit has the same parts and configuration as the feed pretreatment shown in FIG. Alternatively, direct feed from the coastal well is used without the need for a pretreatment unit.

  The combined NF product from the first and second NF stages is sent to a SWRO unit with one high-pressure pump giving a pressure of 55 ± 10 bar, the first stage SWRO consisting of one block of modules arranged in parallel The first stage comprising membranes of the type used in conventional SWRO plants, such as Toyobo or Toray or Hydranautics, or Filmmec or DuPont membranes The pressure exclusion collected from the SWRO module is passed through a turbocharger to increase its pressure to about 85 ± 5 bar, and then this pressure exclusion is the second stage SWRO unit, each module being high pressure tolerant SWRO member consisting of one pressurized vessel fitted with 4 or 6 Toray 820BMC or equivalent SWRO membranes O supplied from one block to have been unit configuration of the modules. By using a turbocharger, if necessary, the pressure can be increased to 90 bar by using a pressure pump. The combined products from the two SWRO stages are collected and become the final product with drinking water quality.

Field work on commercially available NF membranes conducted at our R & D illustrates that they differ significantly in performance and can be classified into more or less three groups: The “A” group is an NF membrane with an airtight structure characterized by having a high rejection rate but a low permeate flow (flux), whereas the “C” group is a large flow and mild The “B” group has good balanced performance in terms of permeate flow and ion exclusion (Hussan et al., Proceedings of IDA International Conference on Desalination, 1999 10). Moon). As a result of this study, the “B” group of membranes has been successfully used in the dual NF-SWRO operation of the Umm Lujj SWRO plant (Hussan et al. Moon). The same type of NF “B” group and / or selected NF membranes of “C” group are used in the present invention in the first stage vessel of the plant of the present invention, such as that shown in FIG. . “B” group type membranes with membranes with higher pressure tolerance are used in the second stage NF unit. By using a demonstration plant consisting of three pressurized vessels, each containing two NF8 ″ × 40 ″ membrane members, P = 25 bar, feed rate of about 12 m ³ / hr, and T = 30 ° C. And 66% product recovery from the second module member was achieved (FIG. 14). In repeated experiments, only about 62% recovery was achieved when operating the same four parts in two pressurized vessels at a feed rate of 8 m ³ / hour, P = 24 bar, and T = 28 ° C. (FIG. 15). About 5.1 + 05.2m ³ / NF product stream time is obtained from feed 8m ³ / time, NF supply amount, as long as the temperature and that the pressure is kept constant, approximately from the first stage NF unit 62% product recovery was maintained and they gave a constant product conductivity (FIG. 15). Control of the feed temperature up to about 35 ° C can be achieved by using some warm seawater (43 ° C) used to cool the MSF distillate in the heat rejection zone of the MSF unit to cool seawater portion (18-25 ° C). (See FIG. 8). The NF unit performance variation along with the feed temperature variation is clearly illustrated in FIG. 16 for the case where the NF unit is operated with a seawater feed (18-25 ° C.) without using this mixing step. As shown in FIG. 3, the removal rates of the scale-forming hard ions of SO ₄ ⁼ , Mg ⁺⁺ , Ca ⁺⁺ , and CHO ₃ ⁻ by the NF member of the first container are 99.9, 98.3, and 96, respectively. The hard ion rejection by the NF membrane member in the second container was 99.9, 98.3, 96, and 78%, while .8 and 84.4%. In some experiments, no SO ₄ ⁼ ions were detected in the product of the NF member in the first and second containers. The hard ion rejection rate of SO ₄ ⁼ , Mg ⁺⁺ , and the total hard material, which is 98% or more, is almost the same as that of the NF member product in the first and second containers, and the exclusion of Ca ⁺⁺ ions It is recognized that rates are similar. However, there is a difference in the rejection rate of HCO ₃ ⁻ between the NF members of containers 1 and 2 (Table 3). The NF hard ion exclusion rate established in this experiment is similar to that previously achieved in the Umm Lujj plant with six NF members arranged in one pressurized vessel (FIG. 12). The product water recovery compared to the feed at about 8 m ³ / hour is 36.3% and 25.6% for the front part of the first and second pressure vessels, and from the four parts The total was about 62%.

Compared to the excellent rejection of the NF membrane for hard ions, the rejection of monovalent Cl ^- ions is only 35.6 and 23.8% for the NF members of containers 1 and 2, respectively. The TDS ion rejection rates are 42.7 and 31.4%, respectively, and the exclusion by NF is much greater for covalent hard ions than for monovalent ions, but RO (BWRO, SWRO, LPRO, and Loose RO) supports the previous argument that more or less monovalent and covalent ions have the same exclusion rate.

From the above results, as shown in FIGS. 15 and 16, especially FIG. 16, the performance of NF depends on the operating conditions of applied pressure, operating temperature, supply flow (quantity) and quality (TDS). By controlling these operating conditions, as already established, recovering up to about 62% or more from the first NF stage in the NF pretreatment unit having the configuration as shown in FIGS. It can be concluded that the rate can be obtained. Furthermore, if it is supplied from the NF first stage reject to the second stage in the same figure, a recovery rate of about 35% can be easily obtained, and the total recovery rate from the two stages should be 75%. Can do. When the first stage was operated at 25 bar and a recovery rate of 62% and the second stage was operated at a recovery rate of 40%, a total recovery of 77% was achieved from the two-stage NF unit in the pilot plant. The feed consisted of Gulf seawater, TDS≈45,000 ppm. By increasing the pilot plant feed from 8 m ³ / h to 9 m ³ / h and maintaining the pressure at the same value of 25 bar, the NF product recovery increased to 80%. Higher recoveries can be achieved by testing different NF membranes with or without the addition of a suitable scale inhibitor to the seawater feed. Recovery rates higher than this value can be obtained from the NF (two stage) unit by adding a suitable scale inhibitor to the feed. As previously mentioned, this is to be compared to the NF product recovery of up to 70% obtained from six components placed in series in the same pressurized vessel at the Umm Lujj plant (Hussan A M. Others, Proceedings of IDA International Conference on Desalination, Bahrain, March 2002).

  As illustrated in the configuration shown in FIG. 1, the same benefits realized by the two-stage NF are due to the configuration of the SWRO unit shown in the same diagram, and the placement of a turbocharger between the dual NF-SWRO desalination systems. It has been obtained in two stages. This is extremely realistic and can be applied in consideration of using a SWRO high-pressure membrane developed later. For example, their use increases the seawater recovery rate in the ocean (Sea of Japan) from 40% to 60%, allowing an increase of 50%. See Goto et al. At the SWRO pilot plant level operated on our side, operating the plant for NF product from a single stage NF unit with an applied pressure of only 50 bar achieved a water recovery of 60% and 70 bar At the applied pressure, the recovery rate increases to 80% (FIG. 7). Similarly, water recoveries of 56-58% were achieved with the Umm Lujj SWRO train 100 operated on the NF product in one step (see previous literature by Hassan et al.).

As shown in FIG. 1, assuming a water recovery rate of 56% of the first stage SWRO, a total of 133 m ³ / hour is achieved by the first SWRO stage, while a water recovery rate of 36% and about 92%. little 37m ³ / when the second stage SWRO at a pressure of bar not achieved, the total product of 170m ³ / time from 238m ³ / time of NF product as feed, i.e., 71% or more by their two stages The overall recovery rate has been achieved. Because of the very low hard ion content and the high pressure applied to the second SWRO stage, a recovery rate higher than 71% is expected from the two-stage SWRO unit. This brings the total recovery of the total NF (two stage) -SWRO (two stage) desalted hybrid to about 54% (0.75 x 0.714).

In addition to the benefits of lowering the energy requirement and water cost per unit water product and increasing the plant production rate, which is both water flow rate and product recovery, this optimal dual of the present invention. NF (2 steps) -SWRO (two steps) (Figure 1), or _NF 2 -SWRO ₁ (FIG. 2), or _NF 2 -SWRO ₁ (FIG. 3) seawater desalination method has the following advantages:

  (1) Due to the significant reduction in hard material, resulting in reduced or eliminated scale formation, adding anti-scaling chemicals to the feed to the RO process or adding such chemicals to the conventional In this system, it is no longer necessary to enter the RO facility where scale formation occurred. Of course, this is an important advantage from an environmental point of view. This is because such chemicals are no longer discarded into the marine environment, or into landfill sludge or water tanks.

  (2) Furthermore, due to the high purity of the NF product in that it does not contain suspended solids or bacteria, the pressure differential (ΔP) through the SWRO membrane remains very low, thus the SWRO membrane. Is not contaminated. This not only extends the life of the SWRO membrane, but also maintains high efficiency membrane performance without frequent cleaning. In Umm Lujj's train 100, SWRO membranes have now been operated for 3 years and 6 months without any SWRO membrane cleaning or replacement, but for 8 months against seawater feed without NF pretreatment. After continuous use, the NF product was operated for over 34 months.

  (3) Due to the high quality of the SWRO product produced by this double NF-SWRO process, the second stage, the second stage RO unit as normally done in a conventionally operated SWRO plant is In this case, this second stage is required to produce good quality water with TDS <500 ppm.

(4) One major advantage of the dual NF-SWRO process of the present invention is the good quality of its SWRO reject, making it eligible as a supplement to a thermal seawater desalination plant. . As shown in Table 4, besides the high transparency due to the absence of suspended solids and bacteria, the scale-forming hard ions it contains, SO ₄ ⁼ , Mg ⁺⁺ , Ca ⁺⁺ , and HCO ₃ ⁻ The concentration of is dramatically lower.

Further utilization of this product in an NF ₂ -SWRO ₂ (exclusion) -thermal triple hybrid desalination system when each of NF and SWRO is operated in two stages will result in total water recovery for seawater desalination. The rate increases.

(5) Energy consumption / generation of the optimal methods of the present invention ^{m 3:} The energy consumption / ^{m 3} for conventional one million gallons SWRO plant shown in FIG. 17 is adapted to 4.269 On the other hand, for the conventional two-stage (SWRO and subsequent RO) method (FIG. 17), it is 9.326 kWh / m ³ , a ratio of 0.44: 1. The energy consumption of this method (KW h / m ³ ) is about 44% of the value required for a conventional one-stage SWRO followed by a second saltwater RO system. The energy requirement was calculated according to Equation 3:
Energy (KW at the time _{^{/ m 3) = [Q f}} .H f ρ / 366Q p e] (3)
In the formula:
- Q _f and _{Q p} is the amount of each feed and product (unit, ^{m 3} / h).
-H is the pressure head (unit, m).
-Ρ is the density of seawater (1.03).
-E is the pump efficiency (≈0.85).

  See Water Treatment Handbook, 5th Edition, 1979, Halsted Press Book, John Wiley & Sons Publisher. “Pump Handbook” 2nd edition, Igor J.M. Karassik Willian C.I. Krutzsch, Warren H. Franchen (Warren H. Franser) and Joseph P. See also Joseph P. Messina, McGraw Hill Publisher, International Publishing, Industrial Engineerirg Series.

  To further illustrate the advantages of the method of the present invention, a fully integrated optimal dual NF (two-stage) for the production of a Gulf Seawater feed, SWDS plant from TDS 45,000 ppm to 1 million US gallons per day (mgd) -A SWRO (two-stage) plant design was used to simulate a commercial plant and compare its performance with that of a conventional SWRO with the same production capacity (Figure 17). The NF recovery rate for Gulf water was set to 75%, and the SWRO unit recovery rate was set to 71%. In order to increase the recovery rate from 56% in the first stage SWRO to 71% in the second stage, it is necessary to add 15% to the total SWRO unit recovery rate in the second stage. In the above study at the pilot plant level, this was quite possible. This is because the second-stage high-pressure SWRO was able to recover 35% or more of the rejected products by the first-stage SWRO unit. Using the same ratio of 35%, the recovery of product from the Umm Lujj first stage exclusion of 44% of the total feed was 15.4% (ie 0.35 × 44 = 15.4%) The total recovery is 71.4% (56 + 15.4%). In fact, with high pressure and low feed TDS for the first and second SWRO stages, the SWRO unit is expected to have a total recovery of greater than 71% (see FIG. 7).

Table 5 shows that by applying the optimum NF (two-stage) -SWRO (two-stage) seawater desalination method of the present invention, not only the recovery rate, but also the reduction in feed amount and energy consumption (KW hour / m ³ ). It illustrates the many advantages obtained over the conventional SWRO method. The amount of reject (brine) is also small. Feed by conventional SWRO process to this Millions of US gallons / day plant, whereas it is only 322.45m ³ / time of the present invention, in the conventional SWRO process is when 602m ³ /, 1: 0 The ratio was .485. As shown in FIG. 9 and also shown in FIG. 17, the conventional SWRO plant has a recovery rate of 30% for the SWRO unit and in this case the second saltwater RO unit is 85% using the low pressure RO unit. The recovery was performed in two steps.

In summary, the optimal method of the present invention has a much higher efficiency than the conventional SWRO method. Furthermore, many of these advantages are not limited to application to the desalination of Gulf Seawater (TDS 45,000 ppm). Higher NF and SWRO recovery, as well as a total recovery of about 65% or more, can be achieved when the process is applied to desalination of ocean seawater (TDS 35,000 ppm). The amount of energy required, as well as the amount of feed and rejects, is expected to be significantly lower in the case of demineralization of the ocean seawater feed than in the case of desalination of the gulf seawater feed. In a lower TDS feed, higher recovery rates, a greater _yield, NF 2 -SWRO ₂ (elimination thereof) - when operating the SWRO plant as part of a thermal type can be obtained.

  Although not explicitly described above, it is clear that there are many aspects of the present invention that clearly fall within the spirit and scope of the present invention. Therefore, the above description should be considered as exemplary only, and the actual scope of the present invention should be determined only from the appended claims. As shown in FIG. 1, a similar claim can be made to form an NF product from a two-stage NF unit or to form a SWRO exclusion, in which case thermal seawater desalination (MSFD, MED, VCD) NF product is supplied to the SWRO unit as a supplement to the plant. The claims of the present invention include an optimal NF (two-stage) -SWRO (two-stage) and NF (two-stage) -SWRO (one-stage) seawater desalination process as shown in FIGS. Limited to only.

Citation 3,654,148 4/1972 Bradely
4,036,685 9/1977 Bray
4,156,645 5/1979 Bray 4,341,629 7/1982 Uhlinger
4,723,603 2/1998 Plummer
5,238,574 8/1993 Kawashima, others 5,458,781 10/1995 Lin
6,508,936 1/203 Hassan
PCT / US98 / 20213 25/9/1998
EPA No. 989858559 2/9/1999
6,190,556B1 20/2/2001 Erlinger JP 09141260 3/6/1997

FIG. 1 is a schematic process diagram of the optimum fully integrated seawater desalination method of the present invention having NF (two-stage) -SWRO (two-stage) in which a turbocharger is disposed between two stages in each of the NF and SWRO units. It is. FIG. 2a is similar to FIG. 1, but with a high pressure (P≈84 bar), high flow rate, large salt rejection rate membrane with an energy recovery turbocharger, 75 ± 10 bar high pressure pump. FIG. 5 is a process diagram in the case of using one-stage SWRO instead of two-stage. FIG. 2 b is a similar process diagram with a pressure exchanger (PX). FIG. 3a is similar to FIG. 2 with a single stage SWRO unit, but using a conventional SWRO membrane at high pressure (P≈55 ± 10 bar), using an energy recovery turbocharger system, FIG. 6 is a process diagram showing recycling a portion as feed to a two-stage NF unit. FIG. 3b is a similar process diagram using a further pressure exchanger configuration. FIG. 4 shows turbidity, bacteria, hard ions, and TDS in the seawater desalination process that separates the feed into product and reject, various seawater desalination (thermal or membrane) processes. It is a figure which shows the density | concentration about. FIG. 5 is a diagram showing the main problems of various seawater desalination methods. FIG. 6 is a graph showing the effect of seawater feed TDS on osmotic pressure and the true effective pressure (Pnet) that pushes permeate through the membrane. FIG. 7 shows NF seawater for SWRO unit performance, plotted by permeate, (a) flow rate, (b) recovery, and (c) conductivity plotted against seawater feed applied pressure. It is a graph shown about the case where it does not use with the case where pre-processing is used (each of NF and SWRO consists of only one stage). FIG. 8 is a schematic process diagram showing the complete overall configuration of double and triple hybrids with NF, SWRO, and MSF in an NF-seawater desalination (SWRO and MSF) pilot plant. Figure 9 shows a commercial Umm Lujj SWRO plant (a) SWRO configuration of a plant built in 1986 (Train 200), (b) Conversion to NF-SWRO system (NF and SWRO each in one stage) And is a schematic process diagram for an NF-SWRO configuration (train 100) operated in September 2000. FIG. FIG. 10 is a photograph showing a Umm Lujj NF-SWRO plant (train 100) constructed in September 2000, with the NF unit installed on the front side and the fully coupled SWRO unit on the rear side. Have FIG. 11 is a graph showing the performance (product flow rate, recovery rate, and conductivity) of the NF membrane unit in the Umm Lujj NF-SWRO train 100 with a fixed NF product recovery rate of 65% versus operating time. is there. FIG. 12 focuses on the composition of the seawater feed and the NF product with respect to their scale-forming hard ions (SO ₄ ⁼ , Ca ⁺⁺ , Mg ⁺⁺ , HCO ₃ ⁻ ), Cl ⁻ , and TDS content. Are shown together with their ion rejection rate (%) by the NF membrane. FIG. 13 shows the performance (product flow rate and recovery), the product flow ratio of train 100 to train 200, and operating conditions for the SWRO unit train 100 in the fully integrated NF-SWRO system shown in FIG. It is a graph. FIG. 14 is a process diagram showing the performance of an NF member using a pilot plant with three different pressurized vessel configurations, each of which is a pressurized vessel containing two NF8 ″ × 40 ″ members. FIG. 15 is a plot of NF performance as a first NF stage versus operating time (over 9000 hours) using two pressurized vessels arranged in series, each vessel containing two NF members. It is. FIG. 16 shows the NF unit performance measured for various operating conditions (pressure, temperature, feed flow rate, and feed TDS) for permeate (a) flow rate, (b) recovery, and (c) conductivity. FIG. FIG. 17 is a schematic showing the method of the present invention for only the desalted portion of each of the two methods, as compared to the conventional SWRO method, for the daily output of a million gallon plant. It is process drawing.

Claims (21)

Brine containing high concentrations of hard scale forming ionic species, microorganisms, particulate matter and high concentrations of total dissolved solids into a two-stage membrane nanofiltration (NF ₂ ) unit and energy recovery turbocharger between those stages The (TC) unit replenishes the pressure pump as necessary, and the content of the ionic species is reduced from the combined NF product of the first and second NF stages, and microorganisms, particulate matter and Forming a first water product from which almost all scale-forming hard ions have been removed, and then the first product is transferred to a two-stage SWRO (SWRO ₂ ) energy recovery between those stages The TC increases the final second water product (permeate) and salinity of the drinking water quality from the combined product of the two SWRO stages through the replenishment of the pressurization pump as required, and the scale Producing a third water product of SWRO brine waste with dramatically reduced formable hard ions;
An optimum desalting method and apparatus. Brine containing a high content of hard scale-forming ionic species, microorganisms, particulate matter and total dissolved solids is made into a two-stage membrane nanofiltration (NF ₂ ) unit by an energy recovery TC unit between those stages. , Replenish high pressure pressurization pump as needed, from the combined NF product of the first and second NF stages, the content of the ionic species (TDS) is reduced, microorganisms, particulate matter and most Forming a first water product from which all scale-forming hard ions have been removed, and then passing the first water product through a one-stage seawater reverse osmosis unit to provide a second water of drinking water quality. The product (permeate) and the salinity increase, but the hard substance forms a dramatically reduced third water product exclusion, in which case the one-stage SWRO unit is an energy recovery turbocharger. charge 2 and 3 is replenished with a high-pressure pressurizing pump if necessary, or a turbocharger energy recovery system or pressure exchanger (PX) is replenished and has the configuration and configuration as shown in FIG. Process,
A desalination process and apparatus. It has a double fully integrated NF ₂ unit with an energy recovery turbocharger in between, where the first NF stage has a high pressure pump and NF unit and produces NF under a pressure (P) of 25 ± 10 bar And NF reject, which is passed through a turbocharger unit or a pressurized pump or a combination thereof to increase its pressure to 35 ± 10 bar, and then the second stage According to claim 1 or 2, comprising a feed to NF and combining the product from this second stage NF unit with the NF product from said first NF stage to constitute a first water product. The optimum desalting method and apparatus as described. Large exclusion rates of medium to high product streams and scale-forming hard ions: use NF membranes with SO ₄ ⁼ higher than 90% and other hard ions with exclusion rates on the order of 60-98% On the other hand, the second stage NF membrane has a large elimination rate of scale-forming hard ions at moderate product flow rates: up to 90% for SO ₄ ⁼ , up to 60-98% or more for other hard ions The optimum desalination system according to any one of claims 1 to 3, characterized by an exclusion rate.   The first SWRO stage has a high pressure pump and sends feed to the SWRO unit at P = 55 ± 10 bar, from which it produces SWRO product and reject stream, which is either a turbocharger or a pressurized pump or Through their combination, the energy recovered from the second SWRO stage exclusion increases its pressure to 90 ± 10 bar, after which it is fed to the second stage SWRO unit, The optimal of claim 1, wherein the combined product of the second SWRO stage forms a drinking water quality SWRO product and the third stage SWRO reject water product forms from the brine of the second stage SWRO unit. Desalination method and apparatus.   First-stage SWRO, a commercially available SWRO membrane of the kind used in conventional one-stage SWRO plants, with a high salt rejection of over 99.0% and capable of withstanding pressures up to 70 bar The optimum desalination system according to claim 1, wherein a high pressure tolerant SWRO membrane up to 90 ± 10 bar is used in the second stage SWRO.   The optimal seawater desalination system according to claim 1, wherein the first and second stage SWRO use pressurized vessels capable of withstanding pressures up to 70 and 100 bar, respectively.   The optimum seawater desalination system according to claim 2, wherein the one-stage SWRO unit has the form and configuration shown in FIG.   9. The optimum seawater desalination system according to claim 8, wherein the SWRO membrane and the pressurized vessel can withstand pressures up to 85 bar.   The optimum seawater desalination system according to claim 2, wherein the one-stage SWRO has the form and configuration shown in FIG.   The optimal seawater desalination system according to claim 10, wherein the SWRO membrane and the pressurized vessel can withstand pressures up to 70 bar.   A portion of the SWRO reject (the third water product of the SWRO reject) is recycled back at its own pressure, mixed with the seawater feed, and fed to the NF unit as shown in FIG. The optimal seawater desalination system according to claim 10 or 11, wherein:   The optimal desalination system according to claim 1 or 2, wherein the salt water includes seawater.   14. The optimum desalination system according to claim 13, wherein the seawater has a total dissolved solids content on the order of 2.0% to 5.0%.   The seawater solution has a cation content of the order of 1.2% to 1.7%, an anion content of the order of 2.2% to 2.8%, and a pH of the order of 7.9 to 8.2. 14. An optimum desalination system according to claim 13, having a total dissolved solids content on the order of 2.0% to 5.0%.   16. The optimum desalination system of claim 15, further comprising a cation content comprising 700-2200 ppm calcium and magnesium cations. With regard to the properties of seawater, the calcium, magnesium, sulfate and bicarbonate ion content is reduced on the order of 63% to 99% by NF ₂ units and the total dissolved solids content is reduced by about 30% to 50%. The optimal desalination system according to claim 13 or 15.   The optimum desalination system according to claim 1 or 2, wherein the nanofiltration unit is operated at a temperature on the order of 15 ° C to 40 ° C.   The optimum desalination system according to claim 1 or 2, wherein the seawater reverse osmosis unit is operated at a temperature on the order of 15 ° C to 40 ° C.   3. A desalination process according to claim 1 or 2, wherein the second water product comprises drinking water (SWRO permeate) and its product recovery relative to the seawater feed is on the order of 50% or more. The third water product comprises a SWRO exclusion that has a high salinity but has dramatically reduced scale forming hard ions of SO ₄ ⁼ , HCO ₃ ⁻ , Mg ⁺⁺ and Ca ^++. Item 3. A desalting method according to Item 2.

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