Patent Application
20160115061
The present invention relates to a water treatment system and method for, for example, cooling tower blowdown water or the like, a cooling facility, and a power generating facility.
In a cooling tower used at a plant facility or the like, heat exchange is performed between cooling water and high-temperature exhaust gas discharged from a boiler or the like. A portion of the cooling water becomes steam due to this heat exchange, so the ions or silica (SiO2) in the cooling water are concentrated. Accordingly, the cooling water discharged from the cooling tower (blowdown water) reaches a state with a high ion concentration or silica concentration.
Water containing large quantities of ions is released into the environment after being desalinated. Known examples of apparatuses for performing desalination treatment include a reverse osmosis membrane apparatus, a nanofiltration membrane apparatus, and an ion exchange membrane apparatus.
Of the ions contained in the water described above, monovalent positive ions such as Na+, K+, and NH4+ or negative ions such as Cl− and NO3− are ions with high solubility in water. On the other hand, divalent metal ions such as Ca2+, negative ions such as SO42− and CO32−, or silica are components constituting scale. Since salts or silica serving as components constituting scale have low solubility with respect to water, they are easily deposited as scale. In particular, Ca2+, SO42−, and carbonate ions (CO32− and HCO3−), and silica are contained in abundance in brine, industrial waste water, and blowdown water of cooling towers. When scale is generated inside the apparatus for performing the desalination treatment described above, the treatment capacity is diminished. Therefore, there is a demand to perform desalination treatment without generating scale.
The lime-soda method is known as a method for removing Ca2+. In the lime-soda method, sodium carbonate is added to water to be treated, and the Ca2+ in the water to be treated precipitates and settles as calcium carbonate and thereby removed from the water.
Patent Document 1 discloses a waste water treatment apparatus that uses the lime-soda method in which a chemical softening apparatus, an ion exchange apparatus, a reverse osmosis membrane apparatus, and the like are combined.
Patent Document 1: U.S. Pat. No. 7,815,804B
The lime-soda method involves a high treatment cost since it requires the addition of sodium carbonate for the purpose of treatment. With the lime-soda method, when 1 mol of Ca2+ is deposited as calcium carbonate, 2 mol of Na+ is generated. On the other hand, when SO42− is contained in water to be treated, it is not removed by the lime-soda method. That is, the lime-soda method results in an increase in the number of moles of ions contained in the water after treatment.
Even when Ca2+ is removed using an ion exchange membrane apparatus, 2 mol of Na+ is generated in order to treat 1 mol of Ca2+, and the number of moles of ions contained in the water after treatment increases.
In the system of Patent Document 1, water that has been treated by the lime-soda method and an ion exchange membrane apparatus is further treated to remove the ion content with a reverse osmosis membrane apparatus. Therefore, in the system of Patent Document 1, the molar concentration of ions increases, so the osmotic pressure in the reverse osmosis membrane apparatus becomes high, which leads to the problem that the treatment load becomes large. In addition, with the apparatus of Patent Document 1, SO42− is not removed, and SO42− remains in the treatment water, which makes it difficult to achieve a high water recovery ratio. Furthermore, the waste water treatment apparatus of Patent Document 1 also requires large quantities of chemicals when regenerating the ion exchange apparatus, and the high treatment cost is problematic.
In light of the problems described above, an object of the present invention is to provide a water treatment system and method for, for example, water to be treated that contains at least a salt and silica such as cooling tower blowdown water from a cooling tower used in a plant facility or the like, and a cooling facility and a power generating facility.
A first invention of the present invention for solving the above problems is a water treatment system comprising: a first scale inhibitor-supplying unit, which supplies a scale inhibitor to water to be treated that contains at least a salt and silica; a first pH-adjusting unit, which adjusts a pH of the water to be treated to which the scale inhibitor has been supplied using a pH-adjusting agent; a first desalinating apparatus, which is provided downstream of the first pH-adjusting unit and removes salts in the water to be treated and separates the water into first reclaimed water and first concentrated water; and a first crystallizing unit which, has a first crystallizing tank, which is provided downstream of the first desalinating apparatus and crystallizes calcium sulfate from the first concentrated water, and a first seed crystal-supplying unit which, supplies seed crystals of calcium sulfate to the first crystallizing tank.
A second invention is a water treatment system comprising: a first scale inhibitor-supplying unit, which supplies a scale inhibitor to water to be treated that contains at least a salt and silica; a first pH-adjusting unit, which adjusts a pH of the water to be treated to which the scale inhibitor has been supplied using a pH-adjusting agent; a first desalinating apparatus, which is provided downstream of the first pH-adjusting unit and removes salts in the water to be treated and separates the water into first reclaimed water and first concentrated water; a first crystallizing unit, which has a first crystallizing tank, which is provided downstream of the first desalinating apparatus and crystallizes calcium sulfate from the first concentrated water, and a first seed crystal-supplying unit, which supplies seed crystals of calcium sulfate to the first crystallizing tank; a first separating unit, which is provided downstream of the first crystallizing unit and separates calcium sulfate in the first concentrated water; a second scale inhibitor-supplying unit, which supplies a scale inhibitor to the first concentrated water from which calcium sulfate has been separated; a second pH-adjusting unit, which adjusts a pH of the first concentrated water to which the scale inhibitor has been supplied; and a second desalinating apparatus, which is provided downstream of the second pH-adjusting unit and removes salts in the first concentrated water and separates the water into second reclaimed water and second concentrated water.
A third invention is the water treatment system according to the second invention, further comprising: a second crystallizing unit, which has a second crystallizing tank, which is provided downstream of the second desalinating apparatus and crystallizes calcium sulfate from the second concentrated water, and has a second seed crystal-supplying unit, which supplies seed crystals of calcium sulfate to the second crystallizing tank.
A fourth invention is the water treatment system according to the second invention, further comprising: a second crystallizing unit, which has a second crystallizing tank, which is provided downstream of the second desalinating apparatus and crystallizes calcium sulfate from the second concentrated water, and a second seed crystal-supplying unit, which supplies seed crystals of calcium sulfate to the second crystallizing tank; a second separating unit, which is provided downstream of the second crystallizing unit and separates calcium sulfate in the second concentrated water; and a third desalinating apparatus, which removes salts in the second concentrated water and separates the water into third reclaimed water and third concentrated water.
A fifth invention is the water treatment system according to the first or second invention, wherein, when the pH is adjusted to not less than 10 by the first pH-adjusting unit or second pH-adjusting unit, calcium scale inhibitor which inhibits deposition of scale containing calcium is supplied from the first or second scale inhibitor-supplying unit.
A sixth invention is the water treatment system according to the first or second invention, wherein, when the pH is adjusted to not greater than 10 by the first pH-adjusting unit or second pH-adjusting unit, calcium scale inhibitor which inhibits deposition of scale containing calcium and silica scale inhibitor which inhibits deposition of silica are supplied from the scale inhibitor-supplying unit.
A seventh invention is the water treatment system according to the first or second invention, further comprising: one or both of a settling unit, which decreases a calcium carbonate concentration in the water to be treated; and a carbon dioxide gas separating unit, which separates carbon dioxide gas, provided upstream of the first or second scale inhibitor-supplying unit.
An eighth invention is the water treatment system according to the first or second invention, the reclaimed water being used as makeup water or recycled water of a plant facility.
A ninth invention is a cooling facility comprising the water treatment system described in any one of the first to eighth inventions.
A tenth invention is a power generating facility comprising the cooling facility described in the ninth invention.
An eleventh invention is a water treatment method comprising the steps of: a first scale inhibitor-supplying step, in which a scale inhibitor is supplied to water to be treated that contains at least a salt and silica; a first pH-adjusting step, in which a pH of blowdown water to which the scale inhibitor has been supplied is adjusted using a pH-adjusting agent; a first desalinating step, which is provided downstream of the first pH-adjusting step and in which salts in the blowdown water are removed and the water is separated into first reclaimed water and first concentrated water; a first crystallizing step, which is provided downstream of the first desalinating apparatus and in which calcium sulfate is crystallized from the first concentrated water, and a first seed crystal-supplying step, in which seed crystals of calcium sulfate are supplied in the first crystallizing step.
A twelfth invention is a water treatment method comprising the steps of: a first scale inhibitor-supplying step, in which a scale inhibitor is supplied to water to be treated that contains at least a salt and silica; a first pH-adjusting step, in which a pH of blowdown water to which the scale inhibitor has been supplied is adjusted using a pH-adjusting agent; a first desalinating step, which is provided downstream of the first pH-adjusting step and in which salts in the blowdown water are removed and the water is separated into first reclaimed water and first concentrated water; a first crystallizing step, which is provided downstream of the first desalinating apparatus and in which calcium sulfate is crystallized from the first concentrated water; a first seed crystal-supplying step, in which seed crystals of calcium sulfate are supplied in the first crystallizing step; a first separating step, which is provided downstream of the first crystallizing step, and in which calcium sulfate in the first concentrated water is separated; a second scale inhibitor-supplying step, in which a scale inhibitor is supplied to the first concentrated water from which calcium sulfate has been separated; a second pH-adjusting step, in which a pH of the first concentrated water to which the scale inhibitor has been supplied is adjusted; and a second desalinating step, which is provided downstream of the second pH-adjusting step and in which salts in the first concentrated water are removed and the water is separated into second reclaimed water and second concentrated water.
A thirteenth invention is the water treatment method according to the twelfth invention, further comprising the steps of: a second crystallizing step, which is provided downstream of the second desalinating step and in which calcium sulfate is crystallized from the second concentrated water; and a second seed crystal-supplying step, in which seed crystals of calcium sulfate are supplied to the second crystallizing tank.
A fourteenth invention is the water treatment method according to the twelfth invention, further comprising the steps of: a second crystallizing step, which is provided downstream of the second desalinating step and in which calcium sulfate is crystallized from the second concentrated water; a second seed crystal-supplying step, in which seed crystals of calcium sulfate are supplied to the second crystallizing tank; a second separating step, which is provided downstream of the second crystallizing step, calcium sulfate in the second concentrated water is separated; and a third desalinating step, in which salts in the second concentrated water are removed and the water is separated into third reclaimed water and third concentrated water.
A fifteenth invention is the water treatment method according to the eleventh or twelfth invention, wherein, when the pH is adjusted to not less than 10 by the first or second pH-adjusting step, calcium scale inhibitor which inhibits deposition of scale containing calcium is supplied in the scale inhibitor-supplying step.
A sixteenth invention is the water treatment method according to the eleventh or twelfth invention, wherein, when the pH is adjusted to not greater than 10 by the first or second pH-adjusting step, calcium scale inhibitor which inhibits deposition of scale containing calcium and silica scale inhibitor which inhibits deposition of silica are supplied in the scale inhibitor-supplying step.
A seventeenth invention is the water treatment method according to the eleventh or twelfth invention, further comprising: one or both of a settling step, in which a calcium carbonate concentration in the blowdown water is decreased, and a carbon dioxide gas separating step, in which carbon dioxide gas is separated, provided upstream of the first or second scale inhibitor-supplying step.
An eighteenth invention is the water treatment method according to the eleventh or twelfth invention, wherein the reclaimed water is used as makeup water or recycled water of a plant facility.
According to the present invention, water to be treated containing at least a salt and silica, such as cooling tower blowdown water from a cooling tower used in a plant facility or the like can be reclaimed and reused.
The following is a detailed description of preferred embodiments with reference to the attached drawings. Note that the invention is not limited by the embodiments, and when a plurality of embodiments are present, the invention is intended to include a configuration combining these embodiments.
As illustrated in
Here, in
Here, the present embodiment is described using cooling tower blowdown water generated in the cooling tower 11 (called “blowdown water” hereinafter) as the water to be treated containing at least a salt and silica. This cooling tower blowdown water 12 contains an abundance of Ca2+, SO42−, carbonate ions (CO32−, HCO3−), and silica, for example. As an example of the characteristics of the blowdown water, the water has a pH of 8, 20 mg/L of Na ions, 5 mg/L of K ions, 50 mg/L of Ca ions, 15 mg/L of Mg ions, 200 mg/L of HCO3 ions, 200 mg/L of Cl ions, 120 mg/L of SO4 ions, 5 mg/L of PO4 ions, and 35 mg/L of SiO2 ions. Of these, the concentrations of Ca ions, Mg ions, SO4 ions, and HCO3 ions are high, and scale (CaSO4, CaCO3, or the like) is produced by a reaction in the presence of these ions. In addition, the silica components present in the blowdown water also become adhered components of membrane adhesion depending on concentration rate.
Here, examples of plants that use a water cooling-type cooling tower include power generating facilities (such as an industrial power generating facility for selling power or in-plant power use; power generation consisting of thermal power generation, geothermal power generation, or the like), and plants having a power generating facility or cooling facility. In addition, examples of plants include general chemical plants, iron manufacturing plants, petroleum refining plants, plants for producing machinery, paper, cement, food items, and drugs, plants for mining minerals, oil, and gas, water treatment plants, incineration plants, and regional air conditioning facilities.
Furthermore, in addition to cooling tower blowdown water, examples of the water to be treated containing at least a salt and silica include acid mine drainage (AMD), oil and gas produced water (PW), flue gas desulfurization (FGD) waste water, for example, supply water for boiler plants using ground water, river water, or lake water, for example, as a water source, plant waste water recovery water of semiconductor or automobile factories, for example, and industrial park waste water.
This acid mine drainage (AMD) has a concentration of not greater than approximately 15 mg/L of SiO2 ions. Oil and gas produced water (PW) has a concentration from 1 to not greater than approximately 200 mg/L of SiO2 ions. Flue gas desulfurization (FGD) waste water has a concentration from 50 to not greater than 100 mg/L of SiO2 ions. Supply water for boiler plants using ground water, river water, or lake water, for example, as a water source has a concentration of not greater than 40 mg/L of SiO2 ions, and not greater than approximately 100 mg/L of total dissolved solids (TDS). Plant waste water recovery water of, for example, semiconductor or automobile factories, or industrial park waste water has not greater than approximately 25 mg/L of SiO2 ions and from 100 to not greater than approximately 300 mg/L of total dissolved solids (TDS).
In the embodiment illustrated in
Here, in a nanofiltration membrane (NF), an electrodialysis (ED), an electro dialysis reversal (EDR), an electro deionization (EDI), an ion exchanged resin apparatus (IEx), or an electrostatic desalinating apparatus (CDI), scale components (divalent ions, Ca2+, Mg2+, and the like), are selectively removed, and monovalent ions such as NaCl permeate. By suppressing the ion concentration of concentrated water, it is possible to improve the water recovery rate and conserve energy (for example, a reduction in pump power).
In addition, makeup water for cooling tower cooling water does not have to be purified water as long as the scale components (divalent ions, Ca2+, Mg2+) are removed, which yields the advantage that a nanofiltration membrane (NF) or the like can be used.
The first crystallizing tank 21A crystallizes the calcium sulfate 20, and removes it from the bottom and separates the calcium sulfate 20 using a dehydrating apparatus (not illustrated).
Also, as in the cooling tower blowdown water reclamation treatment system 10B illustrated in
In first scale inhibitor-supplying unit 14A, the scale inhibitor 13 is stored and is supplied under the control of the control unit 51A via the valve V1.
Here, the scale inhibitor 13 supplied to the blowdown water 12 has functions of inhibiting generation of crystal nuclei in the blowdown water 12, and also adsorbing to the surface of the crystal nuclei (seed crystals or small-diameter scale or the like that has deposited in excess of the saturation concentration) contained in the blowdown water 12, thereby inhibiting crystal growth.
In addition, the scale inhibitor 13 also has a function of dispersing particles in water such as deposited crystals (function of preventing deposition). The scale inhibitor used in the present embodiment is one that prevents deposition of scale containing calcium in the blowdown water 12. This will be called a “calcium scale inhibitor” hereinafter.
The calcium scale inhibitor has functions of inhibiting calcium sulfate or calcium carbonate crystal nucleus generation in the blowdown water and inhibiting crystal growth of calcium sulfate or calcium carbonate by adsorbing to the surface of crystal nuclei of calcium sulfate or calcium carbonate contained in the blowdown water (seed crystals or small-diameter scale or the like that has deposited in excess of the saturated concentration). Alternatively, there are also scale inhibitors having a function of dispersing particles in waste water such as deposited crystals (function of preventing deposition).
Here, examples of calcium scale inhibitors include phosphonic acid-based scale inhibitors, polycarboxylic acid-based scale inhibitors, and mixtures thereof. A specific example is FLOCON 260 (trade name, produced by BWA).
In addition, when Mg2+ is contained in the blowdown water 12, a scale inhibitor that prevents the deposition of scale containing magnesium (for example, magnesium hydroxide, magnesium carbonate, and magnesium sulfate) in the blowdown water can be used. This will be called a “magnesium scale inhibitor” hereafter.
Examples of magnesium scale inhibitors include polycarboxylic acid-based scale inhibitors and the like. A specific example is FLOCON 295N (trade name, produced by BWA).
In the present embodiment, the first pH-adjusting unit 16A, which introduces the pH-adjusting agent 15, is connected after the scale inhibitor 13 is supplied to the flow path upstream of the first desalinating apparatus 19A.
In the first pH-adjusting unit 16A, the pH-adjusting agent 15 is stored and is supplied under the control of a control unit 52A via the valve V2.
An acid (for example, sulfuric acid) or an alkaline agent (for example, calcium hydroxide or sodium hydroxide) is supplied as the pH-adjusting agent 15 from the first pH-adjusting unit 16A.
Here, the precipitation behaviors of calcium sulfate, silica, and calcium carbonate in the blowdown water 12 will be described in reference to
From
Thus, the first to third pH adjustments are performed as follows in consideration of the precipitation behaviors of calcium sulfate, silica, and calcium carbonate in the blowdown water 12.
1) First pH Adjustment (pH of not Less than 10)
In the first pH adjustment, the pH of the blowdown water 12 is measured by a pH gauge 55A upstream of the first desalinating apparatus 19A, and is controlled such that the pH value reaches a prescribed pH of not less than 10.
This is because silica dissolves at pH of not less than 10, as illustrated in
In the first pH adjustment, the quantity of scale inhibitor (calcium scale inhibitor) 13 that inhibits adhesion of calcium sulfate and calcium carbonate as substances that form scale on the reverse osmosis membrane 19a is supplied from the first scale inhibitor-supplying unit 14A.
2) Second pH Adjustment (pH of not Greater than 10)
In the second pH adjustment, the pH of the blowdown water 12 is measured by the pH gauge 55A upstream of the first desalinating apparatus 19A, and is controlled such that the pH value reaches a prescribed pH of not greater than 10.
This is because silica precipitates at pH of not greater than 10, as illustrated in
In the second pH adjustment, the quantity of scale inhibitor 13 that inhibits adhesion of calcium sulfate, calcium carbonate and silica as substances that form scale on the reverse osmosis membrane 19a is supplied from the first scale inhibitor-supplying unit 14A.
Here, as the silica scale inhibitor 13, two types of scale inhibitor are used: calcium scale inhibitor, and an inhibitor that prevents deposition of silica as scale in the water to be treated (called “silica scale inhibitor”). Examples of silica scale inhibitors include polycarboxylic acid-based scale inhibitors and mixtures thereof. A specific example is FLOCON 260 (trade name, produced by BWA).
3) Third pH Adjustment (pH of not Greater than 6.5)
In the third pH adjustment, the pH of the blowdown water 12 is measured by the pH gauge 55A upstream of the first desalinating apparatus 19A, and is controlled such that the pH value reaches a prescribed pH of not greater than 6.5.
This is because calcium carbonate dissolves at pH of not greater than 6.5, as illustrated in
In the third pH adjustment, the quantity of scale inhibitors (calcium scale inhibitor, silica scale inhibitor) 13 that inhibits adhesion of calcium sulfate and silica as substances that form scale on the reverse osmosis membrane 19a is supplied from the first scale inhibitor-supplying unit 14A.
Table 1 summarizes the first to third pH adjustments.
As shown in Table 1, when the pH is not less than 10, the scale inhibitor (calcium scale inhibitor) 13 is supplied to suppress calcium sulfate and calcium carbonate scale (∘ in table), and since silica dissolves, supply of scale inhibitor becomes unnecessary (× in table).
Also, when the pH is from 6.5 to 10, the scale inhibitors (calcium scale inhibitor, silica scale inhibitor) 13 are supplied to suppress calcium sulfate, calcium carbonate, and silica scale (∘ in table).
Furthermore, when the pH is not greater than 6.5, the scale inhibitors (calcium scale inhibitor, silica scale inhibitor) 13 are supplied to suppress calcium sulfate and silica scale (∘ in table), and since calcium carbonate dissolves, it is sufficient to prevent only calcium sulfate scale (× in table), and therefore the amount of calcium scale inhibitor supplied is smaller than the case of the second pH adjustment.
When the silica concentration in the first concentrated water 18A after concentration by the first desalinating apparatus 19A reaches a prescribed concentration or greater, there is a limit to the capacity of the silica scale inhibitor. Thus, when the silica concentration is not greater than the prescribed concentration (for example, 200 mg/L), the first, second, and third pH-adjusting steps are performed, and when the silica concentration is not less than the prescribed concentration (for example, 200 mg/L), it is preferred that the first pH-adjusting step (silica dissolution) be performed.
The first crystallizing unit 23A is constituted of the first crystallizing tank 21A and the first seed crystal-supplying unit 22A. The first seed crystal-supplying unit 22A is connected to the first crystallizing tank 21A. The first seed crystal-supplying unit 22A stores calcium sulfate seed crystals 20a as the seed crystals, and supplies the calcium sulfate seed crystals 20a as the seed crystals to crystallizing tank 21A by the opening and closing of the valve V3 under the control of the first controller 53A.
Furthermore, as illustrated in the cooling tower blowdown water reclamation treatment system 10B of
Next, the treatment steps of the cooling tower blowdown water reclamation treatment system 10A will be described in reference to
<pH-Adjusting Step>
The controller 52A of the first pH-adjusting unit 16A controls the pH of the blowdown water 12 at the inlet of the first desalinating apparatus 19A to a value at which silica is soluble in the water to be treated.
This treatment step will be described for the case where the “first pH adjustment” described above is applied. Specifically, the pH of the blowdown water 12 supplied to the first desalinating apparatus 19A is adjusted to not less than 10, preferably not less than 10.5, and more preferably not less than 11.
The pH gauge 55A measures the pH of the blowdown water 12 at the inlet of the first desalinating apparatus 19A. The controller 52A adjusts the degree of opening of the valve V2 and inputs alkali from the tank of the first pH-adjusting unit 16A into the blowdown water 12 such that the value measured by the pH gauge 55A reaches a prescribed pH control value.
In the first desalinating apparatus 19A, the pH-adjusted blowdown water 12 is treated. When the first desalinating apparatus 19A is a reverse osmosis membrane apparatus, the water that passes through the reverse osmosis membrane is recovered as reclaimed water 17A. The ions and scale inhibitor 13 contained in the blowdown water 12 cannot permeate the reverse osmosis membrane 19a. Therefore, the unpermeated side of the reverse osmosis membrane 19a becomes concentrated water 18A having a high ion concentration. When another type of desalinating apparatus such as, for example, an electrostatic desalinating apparatus is used, the blowdown water is similarly separated into treated water and concentrated water 18A having a high ion concentration (first concentrated water).
By means of the first desalinating step, silica is contained in the first concentrated water 18A in the dissolved state in the water to be treated, as illustrated in
When Mg2+ is contained in the blowdown water 12, the Mg2+ concentration contained in the first concentrated water 18A increases by means of the first desalinating step. However, generation of magnesium hydroxide scale is suppressed by magnesium scale inhibitor used as the scale inhibitor 13.
The first concentrated water 18A is fed toward the first crystallizing unit 23A.
The first concentrated water 18A discharged from the first desalinating apparatus 19A is stored in the first crystallizing tank 21A of the first crystallizing unit 23A. The first controller 53A of the first seed crystal-supplying unit 22A opens the valve V3, and adds calcium sulfate seed crystals 20a from the tank of the first seed crystal-supplying unit 22A to the first concentrated water 18A in the first crystallizing tank 21A.
Since the pH of the first concentrated water 18A in the first desalinating apparatus 19A is not less than 10, referring to
On the other hand, when the pH of the first concentrated water 18A is not less than 10, silica is present in the dissolved state in the first concentrated water 18A in the first crystallizing tank 21A. Even if the silica concentration in the first concentrated water 18A exceeds the saturation concentration, since no seed crystals of silica are present, it precipitates as small suspended matter such as colloidal particles, and does not readily settle.
According to
Furthermore, when an upstream settling unit or degassing unit is provided, as in an embodiment to be described later, the calcium carbonate concentration is reduced in advance. As a result, calcium carbonate does not readily crystallize with seed crystals of calcium sulfate 20 as nuclei in the first crystallizing tank 21A.
Furthermore, when calcium sulfate seed crystals 20a are present, calcium sulfate 20 crystallizes without dependence on pH, but the crystallization rate increases as pH decreases.
Here, the degree of calcium sulfate saturation index of the simulated water (25° C.) was taken as 460%. The added amount of scale inhibitor was taken as 2.1 mg/L. The pH conditions were taken as pH 6.5 (condition 1), pH 5.5 (condition 2), pH 4.0 (condition 3), and pH 3.0 (condition 4). The added amount of seed crystals was taken as 0 g/L.
When 2 hours and 6 hours had elapsed immediately after pH adjustment, the Ca concentration in the simulated water treated under each of the conditions was measured using an atomic absorption spectrometer (AA-7000, produced by Shimadzu Corp.), and the degree of saturation index was calculated. These results are shown in
According to
When the water to be treated contains carbonate ions, carbonate ions are removed from the water to be treated as CO2 under low pH conditions, as illustrated in Chemical Formula (1). Additionally, as can be understood from
[Formula 1]
CO2+H2O⇄H2CO3⇄HCO3−+H+⇄CO32−+2H+ (I)
From the results above, when the first crystallizing step is carried out under low pH conditions, since the content of calcium carbonate and silica is low, calcium sulfate of high purity crystallizes and is recovered from the bottom of the first crystallizing tank 21A.
Additionally, when the first crystallizing step is carried out at low pH, the acid-supplying unit 56 (refer to
By adjusting the pH to a prescribed value in the step of adding the acid 57 and by adding seed crystal calcium sulfate 20a in the crystallizing step as in the embodiment illustrated in
Here,
As shown in
From
Furthermore, using a hydrocyclone 31 which is a separating unit, calcium sulfate 20 having an average particle size of not less than 10 μm or preferably not less than 20 μm can be separated from the first concentrated water 18A. Some of the calcium sulfate 20 recovered by a dehydrating apparatus 32 adjacent to the hydrocyclone 31 which is a separating unit, pass through a seed crystal recirculating unit (not illustrated) and are stored in the first seed crystal-supplying unit 22A, and some of the recovered calcium sulfate 20 are supplied from the first seed crystal-supplying unit 22A to the first crystallizing tank 21A.
Here, in the first seed crystal-supplying unit 22A, acid treatment is performed on the stored calcium sulfate 20. When scale inhibitor 13 is adhered to the calcium sulfate 20 separated by the dehydrating apparatus 32, the function of the adhered scale inhibitor is reduced by acid treatment. The type of acid used here is not particularly limited, but sulfuric acid is optimal considering the reduction in power used by the second desalinating apparatus 19B.
The calcium sulfate crystallized in the first crystallizing tank 21A has a wide particle size distribution, but since calcium sulfate 20 of not less than 10 μm is separated and recovered from the first concentrated water 18A in the hydrocyclone 31, large calcium sulfate can be used as seed crystals. When large seed crystals are input, a large amount of large calcium sulfate can be crystallized. That is, it is possible to obtain high-quality calcium sulfate with a high recovery rate. Furthermore, large calcium sulfate is easy to separate in the hydrocyclone 31, and the hydrocyclone 31 can be reduced in size, leading to a reduction in power. Furthermore, large calcium sulfate is easy to dehydrate in the dehydrating apparatus 32, and the dehydrating apparatus 32 can be reduced in size, leading to a reduction in power.
On the other hand, a large amount of chemicals (acid and alkali) need to be supplied in order to change the pH in the water treatment process. The use of acids and alkalis leads to an increase in the ion quantity transported to the downstream side of the first crystallizing unit 23A, and causes an increase in the power used by the downstream desalinating apparatus (the second desalinating apparatus 19B in
The crystallization rate of calcium sulfate depends on the input volume of seed crystals.
Seed crystal added quantities: 0 g/L (condition 5), 3 g/L (condition 6), 6 g/L (condition 7).
When 2 hours had elapsed immediately after pH adjustment, the Ca concentration in the simulated water treated under each of the conditions was measured by the same method as in
From the results of
The first concentrated water 18A from which calcium sulfate 20 was separated is fed to the downstream second desalinating apparatus 19B. Water that passes through the downstream second desalinating apparatus 19B is recovered as reclaimed water 17B. Concentrated water 18B of the second desalinating apparatus 19A is discharged outside the system. When the second desalinating apparatus 19B is installed, after being treated by the first desalinating apparatus 19A, reclaimed water 18B can be recovered from the first concentrated water 18A from which calcium sulfate 20 was removed, and therefore the amount of reclaimed water 17 is the total of the first reclaimed water 17A and the second reclaimed water 17B, and the water recovery rate is improved. Furthermore, to prevent adhesion of scale, scale inhibitor 13 is supplied from a second scale inhibitor-supplying unit 14B, and pH adjustment at that time is controlled by a second pH-adjusting unit 16B. The control method is the same as that use for the first scale inhibitor-supplying unit 14A and the first pH-adjusting unit 16A.
In the cooling tower blowdown water reclamation treatment systems 10A and 10B of the present embodiment, ions are concentrated in the first desalinating apparatus 19A, but calcium sulfate 20 is removed in the first crystallizing unit 23A. For this reason, the first concentrated water 18A that flows into the downstream second desalinating apparatus 19B has a lower ion concentration than before treatment. For this reason, the osmotic pressure in the second desalinating apparatus 19B located downstream becomes lower, and the required power is reduced.
Furthermore, in order to remove carbonate ions in the cooling tower blowdown water 12, a degassing unit 61, which is a carbon dioxide gas separating unit that separates carbon dioxide gas, may be provided upstream of the first scale inhibitor-supplying unit 14A, as in the cooling tower blowdown water reclamation treatment system 10C illustrated in
In the cooling tower blowdown water reclamation treatment system 10C of
When the pH is not greater than 6.5, the carbonic acid is present primarily in the state of HCO3− and CO2 in the blowdown water 12. Blowdown water 12 that contains CO2 flows into the degassing unit 61. CO2 is removed from the blowdown water 12 in the degassing unit 61. The blowdown water 12 of which the carbonate ion concentration has been reduced by this degassing step is then fed to the first scale inhibitor-supplying unit 14A, which supplies scale inhibitor 13. Since the pH is not greater than 6.5 at this time, it is preferred that the pH adjustment described above be the third pH adjustment (pH not greater than 6.5).
In the present embodiment, the obtained reclaimed water 17 (17A, 17B) may be used as makeup water of the cooling tower 11.
In addition to makeup water, if used in a power generating facility, it may be used as cooling water makeup water for another cooling facility, desulfurizing apparatus makeup water, boiler makeup water, recycled water, and the like.
Next, a cooling tower blowdown water reclamation treatment system pertaining to Embodiment 2 will be described.
Also, as desalination treatment units, three-stage desalination treatment is performed with the first desalinating apparatus 19A, the second desalinating apparatus 19B, and a third desalinating apparatus 19C, in order to increase the produced quantity of reclaimed water 17 (17A, 17B, 17C).
Furthermore, similar to Embodiment 1, the first and second crystallizing units 23A and 23B have the first seed crystal-supplying unit 22A and first controller 53A, and a second seed crystal-supplying unit 22B and second controller 53B respectively. Additionally, on the upstream side of the second desalinating apparatus 19B are provided the second scale inhibitor-supplying unit 14B, which supplies the scale inhibitor 13, and its controller 51B, and a second controller 52B of the second pH-adjusting unit 16B, which supplies a pH-adjusting agent, and a second pH gauge 55B.
In the first settling unit 63A, Ca2+ and carbonate ions are crudely removed in advance as calcium carbonate from the water to be treated.
When the water to be treated contains metal ions other than Ca2+, metal ions that form hydroxides with low solubility in water are crudely removed in advance as metal hydroxides from the water to be treated in the first settling unit 63A.
Ca(OH)2 and anionic polymer coagulant (trade name Hishifloc H305, produced by Mitsubishi Heavy Industries Mechatronics Systems, Ltd.) are put in the water to be treated in the first settling unit 63A, and the pH in the first settling unit 63A is controlled to a value from 4 to 12, and preferably from 8.5 to 12.
As illustrated in
The solubility of metal hydroxides depends on pH. The solubility of metal ions in water increases as pH becomes more acidic. In the pH region mentioned above, the solubility of many metal hydroxides is low. In the pH region mentioned above, metal hydroxides having low solubility in water precipitate in the first settling unit 63A and settle on the bottom thereof.
The settled calcium carbonate and metal hydroxides are discharged from the bottom of the first settling unit 63A.
Because Mg2+ forms a salt that is hardly soluble in water, it is a component that readily deposits as scale. Mg(OH)2 precipitates at pH of not less than 10.
When treating water containing Mg2+ in the reclamation treatment system of the present embodiment, the pH of the water to be treated in the first settling unit 63A is adjusted to a pH at which magnesium compounds (primarily magnesium hydroxide) precipitate. Specifically, the pH of the blowdown water 12 is adjusted to not less than 10. By so doing, magnesium compounds precipitate from the blowdown water 12 and settle on the bottom of the first settling unit 63A, and are removed. As a result, Mg2+ in the blowdown water 12 is crudely removed, and the Mg2+ concentration decreases.
In the above case, the blowdown water 12 after being discharged from the first settling unit 63A is preferably adjusted to a pH at which the above-mentioned magnesium compounds are soluble. Specifically, when the settled pH is, for example, 10.5, the pH is reduced by approximately 0.1 to 0.5 and adjusted to not less than 10. By so doing, the magnesium compounds go into the dissolved state, and scale generation can be prevented in the downstream apparatuses and steps, especially the first desalinating apparatus 19A and the first desalinating step.
When multiple stages of the first settling unit 63A are provided, Mg2+ in the water to be treated can be reliably removed and the Mg2+ concentration in the water to be treated fed downstream can be reduced.
The supernatant in the first settling unit 63A, which is the water to be treated, is discharged from the settling tank. FeCl3 is added to the blowdown water 12, and solids such as calcium carbonate and metal hydroxides in the supernatant flocculate with Fe(OH)3.
The blowdown water 12 is fed to the first filtering apparatus 64A. The solids flocculated by Fe(OH)3 are removed by the first filtering apparatus 64A.
In the present embodiment, because the carbonate ions and calcium carbonate in the blowdown water 12 are removed, the supplied amount of scale inhibitor 13 which corresponds to the amount of removed carbonate ions and calcium carbonate can be proportionately reduced compared to Embodiment 1.
Furthermore, in cases where the Ca ion concentration in the blowdown water 12 is high, an ion exchange apparatus (not illustrated) may be provided upstream of the first pH-adjusting unit 16A and the first scale inhibitor-supplying unit 14A located the most upstream, and downstream of the first filtering apparatus 64A. The ion exchange apparatus is, for example, an ion exchange resin tower or an ion exchange membrane apparatus.
Furthermore, in the present embodiment, a settling step is further provided downstream of the first crystallizing unit 23A.
The first concentrated water 18A, which is the supernatant of the first crystallizing unit 23A, is fed to the second settling unit 63B. In the second settling unit 63B, Ca(OH)2 and anionic polymer coagulant (Hishifloc H305) are input in the first concentrated water 18A after the crystallizing step, and the pH in the second settling unit 63B is controlled to a value from 4 to 12, and preferably from 8.5 to 12. In the second settling unit 63B, calcium carbonate and metal hydroxides settle and are removed from the first concentrated water 18A. Settled calcium carbonate and metal hydroxides having low solubility in water are discharged from the bottom of the second settling unit 63B.
The first concentrated water 18A, which is the supernatant in the second settling unit 63B, is discharged from the tank. FeCl3 is added to the discharged first concentrated water 18A, and in the first concentrated water 18A, solids such as calcium carbonate and metal hydroxides in the water to be treated flocculate with Fe(OH)3.
The water to be treated is fed to the second filtering apparatus 64B. The solids flocculated by Fe(OH)3 are removed by the second filtering apparatus 64B.
Silica in the first concentrated water 18A, which is the supernatant of the first crystallizing unit 23A, may be removed from the first concentrated water 18A in the first settling step, or may be fed downstream without being removed.
Whether or not to remove silica in the first settling step is determined depending on the properties of the water to be treated and the first concentrated water 18A.
When silica is not removed, the first settling step is performed without recirculating the silica precipitate or supplying a silica precipitation aid in the second settling unit 63B. In this case, silica is separated from reclaimed water 17B and 17C in desalinating apparatuses (the second desalinating apparatus 19B and a third desalinating apparatus 19C) located downstream.
When removing silica, silica precipitate is recirculated and/or a silica precipitation aid is supplied from a supply unit (not illustrated) in the first concentrated water 18A in the second settling unit 63B.
The silica seed crystals are, for example, silica gel, and the silica precipitation aid is, for example, magnesium sulfate. When removing silica, the first concentrated water 18A in the second settling unit 63B is preferably adjusted to a pH from 8 to 10. When recirculation of silica precipitate is employed, silica precipitates using recirculation of deposited matter as nuclei. When MgSO4 is employed as a silica precipitation aid, magnesium silicate precipitates. The deposited silica or magnesium silicate settles on the bottom of the second settling unit 63B, and is discharged therefrom.
In cases where the blowdown water contains Mg2+, the Mg2+ and silica in the first concentrated water 18A react and precipitate in the first settling step. The step of removing silica and Mg2+ differs depending on the balance of the content of Mg2+ and the content of silica in the first concentrated water 18A in the second settling unit 63B.
When the Mg2+ concentration is low relative to the silica content in the first concentrated water 18A in the first settling step, Mg2+ is consumed in precipitation with silica. To remove excess silica not consumed in precipitation with Mg2+, magnesium sulfate is supplied as a silica precipitation aid. The supplied amount of silica precipitation aid is proportionate to the amount of excess silica consumed depending on the content of silica and the content of Mg2+ in the first settling step.
When the Mg2+ concentration is high relative to the silica content in the first concentrated water 18A in the first settling step, Mg2+ remains after precipitation of Mg2+ with silica. When the first concentrated water 18A is discharged from the second settling unit 63B while the remaining Mg2+ concentration is high, there is risk that scale containing Mg will precipitate in the desalinating apparatuses of subsequent stages (in
Then, the first concentrated water 18A in the first crystallizing tank 21A is adjusted to a value at which magnesium compounds (primarily magnesium hydroxide) can precipitate. By so doing, magnesium compounds settle in the first crystallizing tank 21A, and the Mg2+ concentration in the first crystallizing tank 21A is reduced. Additionally, after the first settling step, the first concentrated water 18A discharged from the second settling unit 63B is adjusted to a pH at which magnesium compounds are soluble. Specifically, the pH of the first concentrated water 18A is adjusted to not less than 10, preferably not less than 10.5, and more preferably not less than 11. By so doing, deposition of scale containing Mg in the desalinating apparatuses can be suppressed.
When treatment is carried out in multiple stages, the first concentrated water 18A that passed through the second filtering apparatus 64B of the second settling unit 63B flows into the water treatment unit of the next stage. In the water treatment unit of the next stage, the first scale inhibitor supplying step through the first settling step described above are carried out.
The crystallizing step is carried out in the same manner as in Embodiment 1.
At this time, in the first crystallizing step, the first controller 53A stores the pH range in which the scale inhibiting function of the calcium scale inhibitor is reduced. Specifically, the pH range in which the scale inhibiting function of the calcium scale inhibitor is reduced is not greater than 6.0, preferably not greater than 5.5, and more preferably not greater than 4.0.
The first controller 53A compares the measured value of the pH measuring unit and the pH range. When the measured value is within that pH range, the first controller 53A reduces the degree of opening of the valve V3 to reduce the supplied amount of calcium sulfate seed crystals 20a. When the measured value is higher than that pH range, the first controller 53A increases the degree of opening of the valve V3 to increase the supplied amount of calcium sulfate seed crystals.
Calcium sulfate precipitates if seed crystals are present, but when the calcium scale inhibitor functions, the crystallization rate decreases. For this reason, increasing the amount of seed crystals promotes crystallization. On the other hand, when the function of the calcium scale inhibitor has decreased, a sufficient crystallization rate is obtained even if there are few seed crystals.
When the supplied amount of seed crystals is adjusted according to pH in this manner, it is possible to reduce the used amount of seed crystals.
In the present embodiment, seed crystals may be intermittently supplied by periodically measuring pH during continuous operation. Alternatively, for example, the change in pH over time may be determined during trial operation of the system, and the supplied amount of seed crystals may be increased or decreased on the basis of that determined change over time.
This crystallizing step may be controlled in the same manner in the second crystallizing unit 23B as well.
The structure by which the supplied amount of seed crystals to the first crystallizing tank 21A is controlled will be described using
Control of the supplied amount of seed crystals according to the present embodiment is carried out by the following steps. An example in which the supplied amount of seed crystals is constantly controlled during continuous operation will be described below.
The first pH measuring unit 59A measures the pH of the first concentrated water 18A in the first crystallizing tank 21A. The measured pH value is transmitted to the controller 110.
The controller 110 stores the pH range in which the scale inhibiting function of the calcium scale inhibitor is reduced. The controller 110 compares the measured value of the first pH measuring unit 59A and the pH range, and adjusts the degrees of opening of the valve V8 and the valve V9.
In the present embodiment, a seed crystal concentration measuring unit (not illustrated), which measures the calcium sulfate seed crystal concentration in the first concentrated water 18A in the first crystallizing tank 21A, may also be installed in the first crystallizing tank 21A. The seed crystal concentration measuring unit measures the seed crystal concentration in the first crystallizing tank 21A. The measured concentration value is transmitted to the first controller 53A or the controller 110. The first controller 53A or the controller 110 stores the threshold value of seed crystal concentration, and when the seed crystal concentration is not greater than the threshold, it increases the supplied amount of seed crystals.
Furthermore, as a modified example of the present embodiment, a first concentration measuring unit (not illustrated) is installed upstream of the second settling unit 63B and downstream of the first crystallizing tank 21A. In cases where the hydrocyclone 31 of the first separating unit is provided, the first concentration measuring unit is preferably installed downstream of the hydrocyclone 31, but it may also be upstream of the hydrocyclone 31. The first concentration measuring unit is connected to the first controller 53A or the controller 110.
In the case of the second crystallizing unit 23B, a second concentration measuring unit having a similar configuration is installed instead of the first concentration measuring unit.
The first concentration measuring unit measures one or both of the calcium ion concentration and the sulfate ion concentration in the first concentrated water discharged from the first crystallizing tank 21A. The measured concentration value is transmitted to the first controller 53A or the controller 110.
The calcium ion concentration and sulfate ion concentration measured by the first concentration measuring unit depends on the crystallization rate in the first crystallizing tank 21A. With the same residence time, the crystallization rate increases as the calcium ion concentration and sulfate ion concentration decrease.
The first controller 53A and the controller 110 store the threshold values of one or both of calcium ion concentration and sulfate ion concentration.
When one or both of the calcium ion concentration and sulfate ion concentration measured by the first concentration measuring unit is not less than the threshold, the first controller 53A increases the degree of opening of the valve V3 to increase the supplied amount of seed crystals. When one or both of the calcium ion concentration and sulfate ion concentration measured by the first concentration measuring unit is less than the threshold, the first controller 53A decreases the degree of opening of the valve V3 to decrease the supplied amount of seed crystals.
When one or both of the calcium ion concentration and sulfate ion concentration measured by the first concentration measuring unit is not less than the threshold, the controller 110 increases the degrees of opening of the valve V8 and the valve V9 to increase the supplied amount of seed crystals. When one or both of the calcium ion concentration and sulfate ion concentration measured by the first concentration measuring unit is less than the threshold, the first controller 53A decreases the degrees of opening of the valve V8 and the valve V9 to decrease the supplied amount of seed crystals.
The supplied amount of seed crystals is controlled by the same steps as above for the second crystallizing unit 23B as well.
When the supplied amount of seed crystals is controlled depending on one or both of the calcium ion concentration and sulfate ion concentration after the crystallizing step in this manner, the used amount of seed crystals can be reduced.
Next, another embodiment of separation of calcium sulfate on the downstream side of the first crystallizing step will be described using
When three or more first classifiers are installed, they are designed such that the size of the calcium sulfate separated by each classifier decreases in order from the upstream side to the downstream side. The number of first classifiers installed in the direction of passage of the first concentrated water 18A and the particle sizes of the solids that can be separated by each of the classifiers are set as appropriate in consideration of the water recovery rate, calcium sulfate recovery rate, treatment costs, and the like.
In the reclamation treatment system 200 illustrated in
In the first classifier 31A located farthest upstream, calcium sulfate 20 of average particle size not less than 10 μm are classified and settle on the bottom of the first classifier 31A. The settled calcium sulfate 20 is discharged from the first classifier 31A and fed to the dehydrating apparatus 32. The supernatant of the first classifier 31A is fed to the second classifier 31B downstream. This supernatant contains primarily particles less than 10 μm in size (calcium sulfate, calcium carbonate, silica, and the like).
In the second classifier 31B located downstream, calcium sulfate 20 of average particle size not less than 5 μm are classified and settle on the bottom of the second classifier 31B. The supernatant of the first classifier 31B (first concentrated water 18A) is fed to the second settling unit 63B.
The calcium sulfate 20 settled in the second classifier 31B are discharged from the bottom of the second classifier 31B. The discharged calcium sulfate 20 is fed through a solid recirculating line 201 to the first crystallizing tank 21A, and is supplied into the first concentrated water 18A in the first crystallizing tank 21A.
The recirculated calcium sulfate 20 functions as seed crystals in the first crystallizing tank 21A, and crystals of the recirculated calcium sulfate grow by crystallization. Recirculated calcium sulfate that has grown to an average particle size of not less than 10 μm is fed together with the first concentrated water from the first crystallizing tank 21A to the first classifier 31A, and is separated from the first concentrated water 18A by the first classifier 31A, and transported to the dehydrating apparatus 32.
The supernatant of the second classifier 31B contains relatively small particles less than 5 μm in size, for example, having a particle size of approximately 2 to 3 μm. Particularly in the initial period of operation of the reclamation treatment system, calcium sulfate ends up being discharged from the first crystallizing tank 21A before growing to a sufficient size in the first crystallizing tank 21A, and the amount of calcium sulfate that flows into the second settling unit 63B is large. In such cases, the sediment in the second settling unit 63B contains a large quantity of calcium sulfate. Thus, in the present embodiment, a recirculating line 202 that connects the bottom of the second settling unit 63B and the first crystallizing tank 21A may be provided, and the solids containing calcium sulfate 20 that settled on the bottom of the second settling unit 63B can be recirculated to the first crystallizing tank 21A.
According to the present embodiment, as the amount of calcium sulfate recovered in the first separating unit increases, the water content of the recovered calcium sulfate decreases. Use of the water treatment steps and reclamation treatment system of the present embodiment leads to a reduction in the amount of relatively small calcium sulfate that flows out to the downstream side, and therefore, the water recovery rate can be increased and the amount of waste generated by water treatment can be reduced.
The second concentrated water 18B separated in the second desalinating apparatus 19B is treated in the downstream second crystallizing unit 23B in the same manner as in the first crystallizing unit 23A. Then, the second concentrated water 18B that has passed through the third settling unit 63C located downstream of the second crystallizing unit 23B is fed to the third desalinating apparatus 19C. The water that has passed through the third desalinating apparatus 19C is recovered as reclaimed water 17C. The third concentrated water 18C of the third desalinating apparatus 19C is discharged outside the system. When a third desalinating apparatus 19C is installed, reclaimed water 17C can be further recovered from the water that was treated by the second desalinating apparatus 19B, and therefore the water recovery rate of reclaimed water 17 is further improved.
An acid-adjusting unit 56, which is a second pH-adjusting unit that introduces acid 57, can be connected between the second desalinating apparatus 19B and the second crystallizing unit 23B. The acid may be, for example, hydrochloric acid, sulfuric acid, nitric acid, or the like. Sulfuric acid is particularly preferred because SO42− is removed as calcium sulfate in the crystallizing step and the quantity of ions that reach the downstream desalinating apparatus can be reduced. The pH is controlled to a low value (preferably not greater than pH 4) by a pH gauge (not illustrated). By so doing, the scale inhibitor 13 can be made ineffective.
Additionally, after the second crystallizing step by the second crystallizing unit 23B, the pH of the second concentrated water 18B may be adjusted such that the calcium scale inhibitor can function. Specifically, the pH is adjusted to not less than 4.0, preferably not less than 5.5, and more preferably not less than 6.0.
By so doing, the scale inhibitor can be made effective. This pH-adjusting step is carried out before the second desalinating step and after the first crystallizing step, or before the downstream third desalinating step and after the second crystallizing step.
In the water reclamation treatment system of the present embodiment, ions are concentrated in the first desalinating apparatus 19A, but calcium sulfate, calcium carbonate, silica, and the like are removed in the first crystallizing unit 23A and the second settling unit 63B. For this reason, the water that flows into the second desalinating apparatus 19B has a lower ion concentration than before treatment. For this reason, the osmotic pressure in the second desalinating apparatus 19B located downstream and in the third desalinating apparatus 19C located downstream becomes lower, and the required power is reduced.
Furthermore, as illustrated in
Examples of the zero liquid discharge apparatus 70 include a spray-drying apparatus that spray-dries the concentrated water with some exhaust gas, drying means that spray-dries it using all of the exhaust gas supplied to an exhaust gas flue, an evaporator or evaporation pond that dries it by evaporation, and the like.
In an evaporator, water is evaporated from the concentrated water, and the ions that had been contained in the concentrated water are precipitated as a solid and recovered as a solid. The water is recovered on the upstream side of the evaporator, and the amount of concentrated water is dramatically reduced, which makes it possible to reduce the size of the evaporator and reduce the energy required for evaporation.
An example of a spray-drying apparatus is illustrated in
Here, an example of the balance between the amount of exhaust gas 90 introduced into the spray-drying apparatus 91 and the liquid spray quantity of third concentrated water 18C is described.
When 100 kg/h of third concentrated water 18C per 1000 m3/h of introduced exhaust gas 90 is sprayed from the spray nozzle 92, the gas temperature drops by 200° C.
The moisture concentration in the exhaust gas 90 also increases by 10%. For example, when the moisture concentration before spraying of the introduced exhaust gas 90 is 9%, the moisture concentration after spraying of the exhaust gas that contributed to drying is 19%, increasing approximately 10%.
This 200° C. drop in gas temperature is roughly equivalent to the exhaust gas temperature after passing through an air pre-heater provided in the flue of a boiler.
However, since the amount of exhaust gas 90 bypassed to the spray-drying apparatus 91 is approximately 5% of all the exhaust gas, when the bypassed gas that contributed to drying is returned to the exhaust gas line, it will result in a moisture increase of approximately 10%/20=0.5%.
Furthermore, the temperature of the exhaust gas that passes through the exhaust gas line similarly drops by 200° C. because air is overheated in the air pre-heater and supplied to the boiler, and therefore, there is no temperature differential when it bypasses and returns. Specifically, when the gas temperature on the inlet side of the air pre-heater is 350° C., the gas temperature that dropped due to the gas passing through the air pre-heater and the temperature of the exhaust gas that passed through the branch line L11 and the gas supply line L12 and contributed to drying in the spray-drying apparatus 91 both similarly drop by 200° C., so as to result in roughly the same temperature.
According to the present embodiment, the third concentrated water 18C discharged from the third desalinating apparatus 19C is introduced into the spray-drying apparatus 91 via the spray nozzle 92, and the spray liquid is dried by the heat of the exhaust gas 90. As a result, the third concentrated water 19C does not require separate treatment by an industrial waste water treatment facility, and zero liquid discharge of the blowdown water 12 generated in the cooling tower 11 of a plant can be realized.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-142121 | Jul 2013 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2014/067957 | 7/4/2014 | WO | 00 |
