WO2013091129A1

WO2013091129A1 - Membrane filtration process for industrial process water treatment and recovery

Info

Publication number: WO2013091129A1
Application number: PCT/CN2011/002122
Authority: WO
Inventors: Sijing Wang; Gaorong He; Guixi Zhang
Original assignee: General Electric Company
Priority date: 2011-12-19
Filing date: 2011-12-19
Publication date: 2013-06-27
Also published as: AR089227A1; TW201331131A

Abstract

Several methods for recovering industrial process water are provided. The first method is a method for recovering industrial process water comprising injecting CO₂ (7) into industrial process water to produce a conditioned solution (9); and filtering the conditioned solution (9) through a membrane filtration unit (13), producing a retentate solution (17) and a permeate solution (15). Another method discloses filtering the industrial process water through a membrane filtration unit (13), creating a retentate solution (17) and a permeate solution (15), and then routing the retentate solution (17) to a precipitation tank (19), wherein supernatant water (25) and precipitated solids are formed.

Description

MEMBRANE FILTRATION PROCESS FOR INDUSTRIAL PROCESS WATER TREATMENT AND RECOVERY

FIELD OF THE INVENTION

[0001] The invention pertains to reverse osmosis and nanofiltration processes for water purification and recovery. More particularly, processes for removing impurities from and recovering cooling tower blowdown.

BACKGROUND OF THE INVENTION

[0002] Cooling towers are widely used in industries to remove excess heat in processes, such as oil refining, chemical processing, and power generating plants.

Cooling towers are also used in the HVAC systems common in commercial, institutional, and hospital buildings. Water consumption in cooling tower operation constitutes the largest water withdrawal from natural water sources in many countries. The Department of Energy stated in its report on the Power-Plant R&D Program that power plants consume from 190 to 990 gallons of water per megawatt hour of electricity produced. Water scarcity has become an increasing concern worldwide. According to the data published by Global environment outlook, 5% of population was facing water scarcity problems in 2000, mainly in the Middle East. However, by year 2030, nearly half of world population will be water stressed.

[0003] In addition to the limited water resources, environmental regulation on industrial wastewater disposal is becoming increasingly restricted. Cost of treating wastewater before discharge to the environment is continually increasing.

[0004] Water shortage worldwide and stringent environment regulations have led to increasing water conservation effort in all industries. Inevitably, it has significant impact on industry water use, especially on huge water consumption industries. Cooling water system conservation efforts have focused on replacing fresh water with treated municipal effluent, reusing plant wastewater, and reducing water discharge by operating at higher cycles of concentration, such as greater than about 7 cycles. As a result, water in the cooling tower reservoir can become highly concentrated with solid contaminants that can cause fouling on cooling tower components. To reduce contaminant

concentration, a portion of the reservoir water is removed ("blowdown") and it is replaced with fresh water.

[0005] Water consumption and costs can be further reduced if cooling tower blowdown is treated to remove contaminants and recovered. High efficiency reverse osmosis processes ("HERO"; see, for example, United States Patent Nos. 5,925,255 and 6,537,456) can achieve higher water recovery rates compared to conventional reverse osmosis processes. HERO relies on a series of pretreatment steps prior to reverse osmosis filtration, which includes use of weak acid cation resin columns, degasification and pH adjustment.

[0006] Other processes may involve the use of microfiltration (MF), ultrafiltration (UF), ion exchange and chemical precipitation to achieve greater water recovery (see, for example, United States Patent Nos. 5,501 ,798, 6, 1 13,797 and 6,461 ,514). Briefly, microfiltration may utilize a membrane or other filtration device to separate particles from solutions. The materials retained by microfiltration typically range from about 0.2 μη to about several μιτι in size. Ultrafiltration utilizes membrane filters to retain soluble macromolecules and larger particles while allowing solvents, ions and other small soluble materials to pass through.

[0007] Reverse osmosis and nanofiltration are filtration methods that can be used to purify water by removing or reducing total dissolved solids (TDS) and residual organic compounds from various water sources, such as from natural water sources, municipal water supply or industrial effluents. Reverse osmosis (RO) relies on a diffusive mechanism to separate relatively large molecules and ions from a solution by applying pressure to the solution on one side of a semipermeable membrane. Nanofiltration (NF) is typically a cross-flow filtration technology which ranges somewhere between ultrafiltration (UF) and reverse osmosis. The filtration process takes place on a selective separation layer formed by a semipermeable membrane. Both reverse osmosis and nanofiltration are a pressure driven separation process. The driving force of the separation process is the pressure difference between the feed (retentate) and the filtrate (permeate) side at the separation layer of the membrane.

[0008] In reverse osmosis and nanofiltration processes, efficiency and water recovery is often limited by mineral scale formation from hardness compounds, such as calcium, magnesium, barium, iron, fluoride, sulfate, carbonate and silica or silicate salts on membrane surfaces. Residual organic compounds and biological proliferation can also cause membrane fouling. In a conventional RO or NF water purification process, the water recovery rate (referring to the percentage of the permeate recovery from the feed water) is often limited to the range of 65-80%, depending on the influent water quality. As such, a large amount of the membrane concentrate (or "reject") has to be further treated or disposed of at a high cost.

[0009] The complex chemistry of cooling tower blowdown, makes the purification process more difficult and less cost efficient compared to purification of other sources of water such as surface water. Most cooling blowdown waters are supersaturated inorganic solutions of CaC0₃, Ca₃(P0₄)₂ and/or silicate solution. To inhibit scaling in the cooling tower, anti-scalants are added to the cooling system. These chemicals are surface-active materials that interfere with precipitation reactions by inhibiting the precipitation threshold and modifying and dispersing crystals of inorganic deposits. When the cooling blowdown water is treated with RO/NF membranes, the membrane can be easily fouled by inorganic deposits, cooling water treatment chemicals, colloids, organics and their combinations in the cooling water. Additional causes of RO NF fouling include silica and silicates, total dissolved solids, corrosion inhibitors, and anti-biofouling agents. As a result, treating and purifying cooling blowdown water with RO/NF membranes for reuse can be much more challenging compared to other RO/NF treatment processes, such as for surface water purification. BRIEF DESCRIPTION OF THE INVENTION

[0010] In one embodiment, a method for recovering industrial process water is disclosed. The first method is a method for recovering industrial process water comprising injecting C0₂ into industrial process water to produce a conditioned solution; and filtering the conditioned solution through a membrane filtration unit, producing a retentate solution and a permeate solution.

[0011] In another embodiment, the industrial process water is treated with at least one anti-scalant. Suitable anti-scalants include organic phosphonic acid and salts and anionic polymers. Specific examples of organic phosphonic acid and salts include, but are not limited to, aminotrimethylene phosphonic acid and salts, 1-hydroxyethylidene- l , 1 -diphosphonic acid and salts, hexamethylene diamine tetra (methylene phosphonate), ethylenediamine tetra(methylene phosphonic acid and salts), bis (hexamethylene) triaminepentakis (methylene phosphonic acid and salts), diethylene triamine

pentamethylene phosphonic acid and salts, and 2-phosphono butane- 1 ,2,4-tricarboxylic acid and salts. Specific examples of anionic polymers include poly(meth)acrylic acid and salts, polymaleic acid and salts, polyaspartate, a polymer of (meth)acrylic acid and at least one monomer. The monomer is selected from the group consisting of

polyethyleneglycol monoallyl ether sulfate, l -allyloxy-2-hydroxypropylsulfonic acid, 2- acrylamido-2-methyl-propyl sulfonic acid and salts, sulphonated styrene, and vinyl phosphonic acid and salts.

[0012] Another embodiment discloses a method for recovering industrial process water comprising filtering the industrial process water through a membrane filtration unit, creating a retentate solution and a permeate solution, and then routing the retentate solution to a precipitation tank, wherein supernatant water and precipitated solids are formed.

[0013] In yet another embodiment, at least one alkali or hydroxide base is added to the precipitation tank to adjust the retentate solution to a pH ranging from about 9.0 to about 12.0. Alternatively, the pH may be adjusted to a range from about 10.0 to about 1 1 .5. [0014] Optionally, a coagulant or flocculent agent is added to the retentate solution in the precipitation tank. Another option is to seed the precipitation tank with a precipitation seed agent. A suitable precipitation seed agent comprises one or more members selected from the group consisting of calcium carbonate (CaC0 ), calcium sulfate (CaS0₄), magnesium silicate (MgSi0₃), magnesium hydroxide (Mg(OH)₂), and barium sulfate (BaS0₄).

[0015] In yet another embodiment, a method for recovering industrial process water is disclosed comprising pretreating industrial process water to reduce suspended solids to produce a pretreated solution. The pretreated solution is then injected with C0₂ to produce a conditioned solution. The conditioned solution is then filtered through a membrane filtration unit, creating a retentate solution and a permeate solution. The retentate solution is then routed to a precipitation tank, wherein supernatant water and precipitated solids are formed. Optionally, a portion of the supernatant water is recirculated by combining with the industrial process water before it is pretreated. The permeate solution may be recovered for use elsewhere. In another embodiment, the supernatant water is injected with C0₂ before combining with the industrial process water being treated. In yet another embodiment, the precipitated solids are removed from the precipitation tank. In yet another embodiment, cooling tower blowdown is recovered by feeding the permeate solution back into the cooling water system.

BRIEF DESCRIPTION OF THE DRAWING

[0016] FIG. 1 is a schematic diagram depicting an exemplary embodiment of a membrane filtration process for cooling tower blowdown treatment and water recovery.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0017] Although the exemplary embodiments disclose cooling tower blowdown treatments, these embodiments may be used to treat multiple types of industrial process waters, including but not limited to, cooling tower blowdown, commercial and residential HVAC systems, waters from oil refining, chemical processing, and power generating plants. As shown in the exemplary embodiment in FIG. 1 , the cooling tower blowdown (1) is first pretreated by a filtration unit (3) to produce a pretreated solution (5). The filtration unit may be any means suitable to effectively remove suspended solids, including but not limited to, multi-media filtration (MMF), microfiltration (MF), and ultrafiltration (UF). Other filters such as granular activated carbon filter, sand filter, fiber filters may also serve as pretreatment filters. The pH of the pretreated solution is reduced to 7.5 or lower by injecting C0₂ (7), producing a conditioned solution (9). Optionally, a membrane anti-scaling agent (1 1) can be added to prevent downstream membrane scaling. The conditioned solution flows through a membrane filtration unit (13), to produce a permeate stream (15) and a retentate stream (17). The membrane filtration unit (13) comprises reverse osmosis (RO) membranes or nanofiltration (NF) membranes, or both. The permeate stream (15) comprises purified water suitable for cooling tower makeup. The RO/NF retentate stream, or reject, ( 17) is routed to a precipitation tank (19) and treated to cause precipitation of solids. In the precipitation tank (19), the pH may be increased to a range between about 9.5 to about 12.0 by adding an alkali (21 ), for example, sodium hydroxide or lime. Optionally, a precipitation seed agent, such as CaC0₃ or CaS0₄ powders or slurry, may be added initially to act as crystallization nuclei to speed up precipitation within the precipitation clarifier (19). Another option is to add a coagulant or flocculent (23) to the precipitation tank (19) to facilitate the precipitation and liquid-solid separation. The supernatant water (25) may be re-circulated back by combining it with the blowdown (1 ) prior to the step of pretreating. The supernatant water (25) may also be treated by injecting C0₂ (27) to dissolve any remaining particles before combining it with the blowdown (1). A drain from the precipitation tank (19) serves to discharge the fluid, or sludge, (29) in the lower part of the precipitation tank (19) where the precipitated solids are accumulated.

[0018] In one embodiment, a method for recovering industrial process water is disclosed. The method comprises injecting C0₂ into industrial process water to produce a conditioned solution; and filtering the conditioned solution through a membrane filtration unit, producing a retentate solution and a permeate solution. The permeate solution may be recovered for use elsewhere.

[0019] In another embodiment, cooling water treatment chemicals that are easily removed by the methods described herein are chosen. Suitable anti-scalant chemicals for the cooling tower waters include, but are not limited to organic phosphonic acids and salts, and anionic polymers. The organic phosphonic acids and salts include, but are not limited to: aminotrimethylene phosphonic acid and salts; l-hydroxyethylidene- 1 , 1 - diphosphonic acid and salts; hexamethylene diamine tetra (methylene phosphonate); ethylenediamine tetra(methylene phosphonic acid and salts); bis (hexamethylene) triaminepentakis (methylene phosphonic acid and salts); diethylene triamine

pentamethylene phosphonic acid and salts; and 2-phosphono butane- 1 ,2,4 tricarboxylic acid and salts. The anionic polymers are selected from but not limited to:

poly(meth)acrylic acid and salts; polymaleic acid and salts; polyaspartate; a polymer of (meth)acrylic acid; and one or more monomers selected from the group consisting of polyethyleneglycol monoallyl ether sulfate, l -allyloxy-2-hydroxypropylsulfonic acid, 2- acrylamido-2-methyl-propyl sulfonic acid and salts, sulphonated styrene and vinyl phosphonic acid and salts.

[0020] Another embodiment discloses a method for recovering industrial process water comprising filtering the industrial process water through a membrane filtration unit, creating a retentate solution and a permeate solution, and then routing the retentate solution to a precipitation tank, wherein supernatant water and precipitated solids are formed. The precipitation tank (19) effectively removes fouling chemicals, including scaling and corrosion inhibitors and biocides, suspected of causing RO/NF membrane fouling. In the precipitation tank (19), the pH of the retentate stream (17) can be increased to between about 9.5 to about 12.0. The pH can be adjusted by adding an alkali or hydroxide base (21), for example, sodium hydroxide or lime.

[0021] When pH is increased to 9.5 and above, calcium can be removed in a precipitate form such as calcium carbonate and calcium sulfate. Magnesium can also be reduced by forming hydroxide precipitate. Silica or silicate salts can be removed by forming Si-Ca-Mg complex precipitates in the precipitation tank (19). Optionally, a precipitation seed agent may be added to speed-up precipitation. Suitable precipitation seed agents include, but are not limited to, calcium carbonate (CaC0₃), calcium sulfate (CaS0₄), magnesium silicate (MgSi0₃), magnesium hydroxide (Mg(OH)₂), and barium sulfate (BaS0₄). In addition to direct precipitation, co-precipitation can further help to remove inorganic ions such as barium, iron, manganese, and aluminum as well as organic compounds. Co-precipitation is a simultaneous precipitation of a normally soluble component with a macro-component from the same solution by the formation of mixed crystals, by adsorption, occlusion or mechanical entrapment. Accordingly, any cooling chemicals present in the retentate stream (17) may be co-precipitated in the precipitation tank (19).

[0022] Optionally, a coagulant or flocculant (23) may be added to speed up solid- liquid separation within the precipitation tank (19). Coagulation and flocculation are mechanisms that are used to chemically increase particle size to enhance precipitation. Coagulation is charge neutralization by a positively-charged coagulant. Both inorganic and polymer based coagulants can be used to build particle size by neutralizing the negative surface charges on particles via double layer compression and electrostatic attraction. Flocculation is a physical bridging mechanism that relies primarily on the size of the flocculant molecule more than its charge. There is an affinity between anionic- charged flocculants and inorganic solids in an alkaline solution.

[0023] In yet another embodiment, a method for recovering industrial process water is disclosed comprising pretreating industrial process water to reduce suspended solids to produce a pretreated solution. The pretreated solution is then injected with C0₂ to produce a conditioned solution. The conditioned solution is then filtered through a membrane filtration unit, creating a retentate solution and a permeate solution. The retentate solution is then routed to a precipitation tank, wherein supernatant water and precipitated solids are formed. Optionally, a portion of the supernatant water is recirculated by combining with the industrial process water before it is pretreated. The permeate solution may be recovered for use elsewhere. In another embodiment, the supernatant water is injected with C0₂ before combining with the industrial process water being treated. In yet another embodiment, the precipitated solids are removed from the precipitation tank. In yet another embodiment, cooling tower blowdown is recovered by feeding the permeate solution back into the cooling water system.

[0024] Methods for treating industrial process water with C0₂ sparging, or injection, are also disclosed. Injecting C0₂ serves multiple functions. It supplements bicarbonate in the conditioned solution (9) so there is sufficient carbonate to precipitate with calcium in the precipitation tank (19). In addition to supplementing bicarbonate in the conditioned solution (9), injecting C0₂ decreases scaling potential of the water being treated by lowering the pH. It therefore enhances the membrane tolerance to high hardness materials, such as Mg, Ca, and Fe. While acids can also be used to decrease the water scaling potential, C0₂ is generally not as corrosive to pipes and equipment, and is more cost effective and environmentally friendly than acids. Thus, the negative consequences of acid use can be reduced by using C0₂ in conjunction with, or instead of, an acid.

[0025] Selection of C0₂ injection points and pH control parameters can significantly influence cost effectiveness of the filtration process. In an open atmosphere system, it may not be economical to decrease pH to below 8.0 prior to RO/NF filtration (13), as a portion of injected C0₂ can escape to the atmosphere. However, if C0₂ is added in a closed system under pressure, the pressure will force the following equation towards the right, allowing the pH to drop to a desired level.

C0₂ + H₂0 <-> H₂C0₃ HC0₃ ^" + H⁺ (1)

[0026] Thus, C0₂ can be injected to closed piping between the filtration unit (3) and the RO/NF membrane filter (13) to decrease pH and simultaneously also supplement sufficient carbonate/bicarbonate for subsequent precipitation of calcium in the precipitation tank (19). Thus, in the retentate solution (17), bicarbonate will be dominant as shown in equation 2:

C0₂ + H₂0 <-» H₂C0₃ <→■ HC0₃ ^" + H⁺ (2) [0027] As described above, the retentate solution ( 17) is directed to the precipitation tank (19) for hardness and silica removal. It can be more efficient and desirable to convert as much bicarbonate to carbonate as possible, by way of heating or decreasing pressure, or both, prior to using an alkali to increase pH in the precipitation tank (19).

[0028] As shown in equation 3,

HC0₃ ^" + heat →· C0₃ + C0₂ + H₂0 (3) heat forces bicarbonate to produce carbonate and C0₂. Pressure of the retentate solution ( 17) can drop substantially as it flows from the RO/NF membrane filter (13) to the precipitation tank ( 19), and thus C0₂ can be evaporated or volatized. Conversion of bicarbonate to carbonate, by either heating or pressure drop, can reduce the requirement of dosing with alkali to increase pH for precipitation. The volatized C0₂ can also be collected and recycled for C0₂ injection as described above.

[0029] For the typical RO NF water purification process, there is no recirculation so the water recovery rate (Yp) is:

where Y_R is the reject ratio. Thus, if the reject ratio (YR) is 30%, the water recovery rate (YP) is 70%.

[0030] According to the exemplary embodiment in FIG. 1 , however, the water recovery rate (Y_P) can be increased significantly. In this embodiment, the supernatant from the precipitation tank (19) is re-circulated back to the filtration unit (3) and RO/NF (13) filtration. For this embodiment, ignoring the retentate of the filtration unit (3), the water recovery rate (Yp) is:

Y_P = 100% - Y_D (5) where YD is the drain ratio.

The drain ratio (Y_D) can be expresses as:

where R is the supernatant recirculation ratio and Y_R is the reject ratio. Thus, if the reject ratio (YR) is still 30% and the supernatant recirculation ratio (R) is 20%, then the water recovery rate (Yp) is 90%.

EXAMPLES

[0031] An industrial process water treatment program should be adjusted based on the water conditions and pH. Typically, a cooling water system is operated in a pH range from about 7.0 to about 9.0. In Example Sets 1 and 2, two typical cooling water treatment programs, at a pH of 8.3 and 8.9 respectively, were tested. The example sets show how the precipitation tank in FIG. 1 can be effectively used for removal of the membrane fouling agents including hardness, silica, and cooling chemicals. With effective removal of the membrane fouling components, the supernatant of the precipitation tank can be returned back for NF/RO filtration to further increase the water recovery from the cooling tower blowdown.

EXAMPLE SET 1 - TYPICAL COOLING WATER WITH A pH OF ABOUT 8.3

[0032] Example 1A. This example simulates a pretreated solution (5, as shown in FIG. 1) of typical cooling water with a pH of about 8.3. For Example 1 A, a sample of typical cooling tower blowdown (BD) was prepared and is shown in Table 1 . The cooling chemicals used in this example included 6.6 ppm terpolymer of acrylic acid/polyethyleneglycol monoallyl ether sulfate/1 -allyloxy-2-hydroxypropylsulfonic acid (terpolymer), and 7.6 ppm l -hydroxyethane- l , l ,-diphosphonic acid (HEDP) as anti- scalants. Additional chemicals included 190 ppm M-Alk as CaCO₃ 480 ppm calcium hardness as CaC0₃, 260 ppm magnesium hardness as CaC0₃, 740 ppm total hardness (H) ^•as CaC0₃, and 15 ppm silicate as Si0₂.

Table 1 : Typical alkaline cooling tower blowdown (BD) water chemistry

Cooling 190 480 260 740 15 510 690 409 6.6 7.6

BD

water

[0033] Example I B. This example simulates a retentate solution (17) of the filtration process shown in Fig. 1. Assuming the sample in Example 1A was purified using RO/NF filtration and a water recovery rate (Y_P) of 66.7%, the chemical

concentration in the retentate (rejected) solution is about 3 times the chemical

concentration before RO/NF filtration. Thus, for Example I B, a sample retentate stream was prepared as shown in Table 2. The sample comprised 19.8 ppm terpolymer of acrylic acid/polyethyleneglycol monoallyl ether sulfate/ l -allyloxy-2- hydroxypropylsulfonic acid (terpolymer), 22.8 ppm l -hydroxyethane-l , l ,-diphosphonic acid (HEDP), 570 ppm M-Alk as CaC0₃, 1440 ppm calcium hardness as CaC0₃, 260 ppm magnesium hardness as CaCO₃, 2220 ppm total hardness (H) as CaC0 , and 45 ppm silicate as Si0₂. The sample pH was adjusted to 6.62 with carbon dioxide sparging in a closed container.

Table 2: Sample retentate stream water chemistry

Si02 Chloride Sulfate Sodium Terpolymer HEDP ppm ppm ppm ppm ppm ppm

45 1530 2070 1226 19.8 22.8

[0034] Example 1 C. This example illustrates the precipitation tank ( 19) and resulting supernatant water (25) of Fig. 1. For Example 1 C, 3.7 ml 25% NaOH solution was added to 1 liter of the sample retentate solution ( 17) and mixed for 5 minutes. After 10 minutes precipitation and sedimentation, the supernatant water (25) of the sample was filtered with 0.22-micron filter paper. The filtrate was sampled for analysis and the results were listed in Table 3. The terpolymer dosage was tested by GE Water STP

Turbidity Test Kit and HEDP was characterized by ICP. As shown in Table 3, 90.1 % calcium hardness, 78.7% total hardness, 91.1 % silicate, 98.0% terpolymer , and 98.2% of the HEDP were removed.

[0035] Table 3 clearly shows that the potential membrane fouling factors of the sample retentate solution ( 17) including Ca²⁺, Mg²⁺, silicate, and cooling chemicals, can be effectively removed in the precipitation step. The supernatant water (25) can be recirculated to further increase the purified water recovery rate for cooling tower makeup.

Table 3: Filtrate water chemistry

EXAMPLE SET 2 - TYPICAL COOLING WATER WITH A pH OF ABOUT 8.9

[0036] Example 2A. This example simulates a pretreated solution (5, as shown in FIG. 1) of typical cooling water with a pH of about 8.9. Table 4 shows the water chemistry used for this example. The solution comprised 6.6 ppm terpolymer of acrylic acid/polyethyleneglycol monoallyl ether sulfate/1 -allyloxy-2-hydroxypropylsulfonic acid (terpolymer) and 7.6 ppm 1-hydroxyethane-l , 1 ,-diphosphonic acid (HEDP) for scaling control.

Table 4: Cooling water blow down chemistry

[0037] Example 2B. This example simulates a retentate solution ( 17) of the filtration process shown in Fig. 1 . Assuming the sample in Example 2A was purified using RO/NF filtration and a water recovery rate (Yp) of 66.7%, the chemical

concentration in the retentate (reject) solution is about 3 times the chemical concentration before RO/NF filtration. Thus, for Example 2B, a sample retentate stream was prepared as shown in Table 5. The solution contained 19.8 ppm terpolymer of acrylic

acid/polyethyleneglycol monoallyl ether sulfate/1 -allyloxy-2-hydroxypropylsulfonic acid, 22.8 ppm l -hydroxyethane-l , l ,-diphosphonic acid (HEDP), 1242 ppm calcium hardness as CaC0₃, 1746 ppm total hardness (H) as CaC0₃ and 932 ppm M-Alk as CaC0₃. The solution pH was adjusted to 6.60 with carbon dioxide sparging in a closed container.

Table 5 : Water chemistry of synthetic concentrated cooling blow down (BP) water

Si02 Chloride Sulfate Sodium Terpolymer HEDP ppm ppm ppm ppm Ppm ppm

45 1082 1350 975 19.9 22.8

[0038] Example 2C. This example illustrates the precipitation tank (19) and resulting supernatant water (25) of Fig. 1. For Example 2C, the solution was softened by adjusting pH using Ca(OH)₂ (Test No. 1 ) and Ca(OH)₂ plus NaOH solution (Test No. 2), respectively. The solution volume for each test was 1.0 liter. After 5 minutes mixing and 10 minutes sedimentation, the supernatant water was filtered with 0.22-micron filter paper for analysis. As shown in Table 6, about 61 % calcium hardness, 52.4%

magnesium hardness, 70% silicate, 99.5% terpolymer and 98.2% HEDP were removed when the solution pH was increased to 10.67 using calcium hydroxide alone. In another test using the same amount of Ca(OH)₂ but with addition of a small amount of NaOH to increase the solution pH to 10.95, the removal efficiency of the calcium hardness, magnesium hardness and silicate were further improved by 12.0%, 43.6% and 12.9%, respectively. Table 6: Water chemistry of filtrate

[0039] The above tests as described in Example Set 2 also clearly showed that the potential membrane fouling factors of the simulated RO concentrate including Ca²⁺, Mg²⁺, silicate and cooling chemicals can be very effectively removed in the clarification step and the supernatant can be returned back to further increase the water recovery rate for the water purification by NF/RO for the cooling tower blowdown reuse. By using Ca(OH)₂ alone or in combination with a small amount of NaOH to increase pH to a desired level, the cost associated with pH increase can be greatly reduced.

[0040] This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

[0041] What is claimed is:

Claims

1. A method for recovering industrial process water comprising:

(a) injecting C0₂ into said industrial process water to produce a conditioned solution; and

(b) filtering said conditioned solution through a membrane filtration unit, producing a retentate solution and a permeate solution.

2. The method of Claim 1 , wherein said industrial process water is treated with at least one anti-scalant.

3. The anti-scalant of Claim 2, wherein said anti-scalant is selected from the group consisting of organic phosphonic acid and salts and anionic polymers.

4. The organic phosphonic acids and salts of Claim 3, wherein said organic phosphonic acids and salts are selected from the group consisting of aminotrimethylene phosphonic acid and salts, 1-hydroxyethylidene-l , 1-diphosphonic acid and salts, hexamethylene diamine tetra (methylene phosphonate), ethylenediamine tetra(methylene phosphonic acid and salts), bis (hexamethylene) triaminepentakis (methylene phosphonic acid and salts), diethylene triamine pentamethylene phosphonic acid and salts, and 2- phosphono butane- 1 ,2,4-tricarboxylic acid and salts.

5. The anionic polymers of Claim 3, wherein said anionic polymers are selected from the group consisting of poly(meth)acrylic acid and salts, polymaleic acid and salts, polyaspartate, a polymer of (meth)acrylic acid, and at least one monomer.

6. The monomer of Claim 5, wherein said monomer is selected from the group consisting of polyethyleneglycol monoallyl ether sulfate, l -allyloxy-2- hydroxypropylsulfonic acid, 2-acrylamido-2-methyl-propyl sulfonic acid and salts, sulphonated styrene, and vinyl phosphonic acid and salts.

7. The method of Claim 1 , further comprising the step of pretreating said industrial process water to reduce suspended solids prior to step (a).

8. A method for recovering industrial process water comprising:

(c) filtering said industrial process water through a membrane filtration unit, creating a retentate solution and a permeate solution; and

(d) routing said retentate solution to a precipitation tank, wherein supernatant water and precipitated solids are formed.

9. The method of Claim 8, wherein at least one alkali or hydroxide base is added to said precipitation tank to adjust said retentate solution to a pH ranging from about 9.0 to about 12.0.

10. The method of Claim 8, wherein at least one alkali or hydroxide base is added to said precipitation tank to adjust said retentate solution to a pH ranging from about 10.0 to about 1 1.5.

1 1. The method of Claim 8, wherein said retentate solution further comprises cooling chemicals, and wherein said cooling chemicals are co-precipitated in said precipitation tank.

12. The method of Claim 8, wherein a coagulant agent is added to said retentate solution in said precipitation tank.

13. The method of Claim 8, wherein a flocculent agent is added to said retentate solution in said precipitation tank.

14. The method of Claim 8, further comprising the step of seeding said precipitation tank with a precipitation seed agent.

15. The method of Claim 14, wherein said precipitation seed agent comprises one or more members selected from the group consisting of calcium carbonate (CaC0₃), calcium sulfate (CaS0₄), magnesium silicate (MgSi0₃), magnesium hydroxide (Mg(OH)₂), and barium sulfate (BaS0₄).

16. The method of Claim 8, further comprising the step of removing said precipitated solids from said precipitation tank.

17. A method for recovering industrial process water comprising:

(e) pretreating said industrial process water to reduce suspended solids to produce a pretreated solution;

(f) injecting C0₂ into said pretreated solution to produce a conditioned solution;

(g) filtering said conditioned solution through a membrane filtration unit, producing a retentate solution and a permeate solution; and

(h) routing said retentate solution to a precipitation tank, wherein supernatant water and precipitated solids are formed.

18. The method of Claim 17, further comprising the step of increasing a bicarbonate concentration in said conditioned solution in step (f) by injecting C0₂ into said pretreated solution.

19. The method of Claim 17, further comprising the step of decreasing a pH of said conditioned solution in step (f) by injecting C0₂ into said pretreated solution.

20. The method of Claim 17, further comprising the step of recirculating at least a portion of said supernatant water by combining a portion of said supernatant water with said industrial process water prior to step (e).

21. The method of Claim 20, further comprising the step of increasing a bicarbonate solution in said portion of said supernatant water by injecting C0₂ into said portion prior to combining said portion with said industrial process water.

22. The method of Claim 17, further comprising the step of recovering said permeate solution.

23. The method of Claim 17, wherein said retentate solution further comprises cooling chemicals, and wherein said cooling chemicals are co-precipitated in said precipitation tank.

24. A method of increasing a bicarbonate concentration in industrial process water comprising injecting C0₂ into said industrial process water.

25. A method of decreasing a pH of industrial process water comprising injecting C0₂ into said industrial process water.

26. The method of Claim 25, wherein said pH is decreased to less than or equal to 7.0.