Tank for deaeration of water

Abstract: There is disclosed a deaeration tank which can sufficiently deaerate object water, is decreased in size, and has high treatment capability. The deaeration tank includes a tank body (11) which defines a deaeration chamber and receives object water, an air injection device (13) disposed within the deaeration chamber (21) for injecting air, a discharge passage (33) for discharging object water from the deaeration chamber (21), and a bubble-scavenging member (35) disposed in the discharge passage (33) for scavenging fine bubbles contained in object water which passes through the discharge passage (33). When object water is fed into the deaeration chamber (21), and air is injected into the deaeration chamber (21), thus-injected air ascends in object water in the form of coarse bubbles and is then released from the surface of the object water. During this ascent of coarse bubbles within the deaeration chamber (21), through contact with object water, coarse bubbles attract fine bubbles contained in object water, so that object water is deaerated. While thus-deaerated object water is passing through the discharge passage (33), fine bubbles, which move due to a turbulent flow in object water or in accordance with Brownian movement, are scavenged by the bubble-scavenging member (35).

Description: BACKGROUND OF THE INVENTION Field of the invention: The present invention relates to a deaeration tank. Description of the related art: Conventionally, in treating wastewater, i.e. object water of treatment (hereinafter merely referred to as object water), an organic coagulant is added to object water contained in a coagulating sedimentation tank so as to coagulate and settle suspended solids (SS) into sludge, which is then removed. However, when fine bubbles contained in object water adhere to the thus-formed sludge, the sludge does not settle but is suspended in object water. As a result, the suspended sludge flows out from the coagulating sedimentation tank into a subsequent treatment tank. Thus, in order to remove fine bubbles from object water, various pretreatments are performed before object water is subjected to coagulating sedimentation. Such pretreatments include a coarse bubble type deaeration method and a mechanical stirring method. FIG. 1 is a schematic sectional view showing a conventional deaeration tank which employs the coarse bubble type deaeration method. In FIG. 1, reference numeral 11 denotes a cylindrical or square tank body, and numeral 12 denotes a partition for dividing the tank body 11 into a deaeration section 21 and a discharge section 22. A communication opening 23 is formed between the lower end of the partition 12 and the bottom wall 11a of the tank body 11 to thereby allow communication between the deaeration section 21 and the discharge section 22. Also, a line L1 is connected to the deaeration section 21 at an upper position thereof so as to feed object water into the deaeration section 21, while a line L2 is connected to the discharge section 22 at an upper position thereof so as to discharge deaerated object water into an unillustrated coagulating sedimentation tank. An inorganic coagulant is added to the deaeration section 21, so that polarity of SS contained in object water is neutralized. A nozzle 13 for injecting air into the deaeration section 21 is disposed within the deaeration section 21 in the vicinity of the bottom wall 11a. A line L3 is connected to the nozzle 13 in order to feed air thereto. A plurality of injection ports 13a are formed in the nozzle 1 3. In the thus-structured deaeration tank, when object water is fed into the deaeration section 21 through the line L1, and air is fed to the nozzle 13 through the line L3, fed air is injected into the deaeration section 21 through the injection ports 13a of the nozzle 13. Thus-injected air ascends in object water in the form of coarse bubbles and is then released from the surface of object water. During this ascent of coarse bubbles within the deaeration section 21, through contact with object water, coarse bubbles attract fine bubbles contained in object water, so that object water is deaerated. Thus-deaerated object water descends within the deaeration section 21 and then enters the discharge section 22 through the communication opening 23. Then, deaerated object water ascends within the discharge section 22 and is discharged into the coagulating sedimentation tank through the line L2. However, in the above-described conventional deaeration tank, when the amount of air which has failed to become coarse bubbles is relatively large, some of the fine bubbles originally contained in object water remain intact without being attracted by coarse bubbles. As a result, object water is not deaerated sufficiently. Also, air which has failed to become coarse bubbles ascends in object water at a speed slower than that of object water which descends within the deaeration section 21. Accordingly, such air, together with fine bubbles contained in object water, descends within the deaeration section 21 following the descending flow of object water, then enters the discharge section 22 through the communication opening 23, and is finally discharged into the coagulating sedimentation tank through the line L2. To solve the problem, the distance between the bottom wall 11a and the nozzle 13 is made at least 500 mm longer than the distance between the bottom wall 11a and the lower end of the partition 12, or the feed rate of object water into the deaeration section 21 is reduced so as to reduce the descending speed of object water, thereby preventing air and fine bubbles from entering the discharge section 22 together with object water through the communication opening 23. However, when the distance between the bottom wall 11a and the nozzle 13 is made at least 500 mm longer than the distance between the bottom wall 11a and the lower end of the partition 12, the size of the deaeration tank increases accordingly. Also, when the feed rate of object water into the deaeration section 21 is reduced, the treatment capability of the deaeration tank decreases accordingly. US 5,207,875 A describes as seawater deaerator having, in principle, a somewhat similar structure. Seawater enters a flat cylindrical deareation chamber from below around the periphery of a disk-shaped baffle. Along the periphery of the chamber or the disk-shaped baffle a circular array of porous aeration stones is installed to introduce small air bubbles. From the upper wall of the chamber a number of vaporizing spouts open into a flash evaporator. In one embodiment a collar-shaped baffle is additionally arranged around the area of the vaporizing spouts to separate the rising bubbles from the water outflow. According to this document the bubbles introduced into the chamber are intentionally small bubbles and specifically seawater is selected as the medium to be treated since seawater, due to the particular relations of electric charges, surface tension and viscosity, would suppress a tendency of the small bubbles to agglomerate into larger bubbles. Thus, this deaerator is not comparable to that one of FIG. 1, where coarse bubbles are injected into object water, that is waste water, as defined above. The object of the present invention as claimed, accordingly, is to solve the above-mentioned problems in the conventional deaeration tank of FIG. 1, that is to provide a deaeration tank which can sufficiently deaerate object water, is decreased in size, and has high treatment capability. In that the deaeration tank as claimed comprises a bubble scavenging member in the discharge passage for scavenging fine bubbles still contained in the object water leaving the deaeration chamber, and in that the complete discharge passage is in a position higher than the air injection means the size of the deaeration tank can be reduced or, otherwise, the flow rate of the water can be increased. Gas bubble scavenging means comprising a plurality of parallel plates are principally known from US 3,488,926 A, but in this case the plates are arranged in parallel to the main direction of flow within a simple widening of a flow conduit for specifically oil pumped from a tanker. The plates are inclined sideways to allow the bubbles to ascend to a bubble collecting space directly above the plate array. There is no introduction of any additional bubbles for collecting the gas bubbles contained in the liquid to be treated, that is oil, as this is the case with the present invention. A structurally somewhat similar apparatus as that one of the present invention is also known from US 4,390,364 A, yet for removing fine particles from molten metal. In this case a tank is divided by partition walls very similar to the partition wall 12 of FIG. 1 of the present application, into three consecutive tank sections. The first section contains a packing of Interlock saddles or Raschig rings and a gas disperser therebelow. The second section may be empty except for the molten metal contained therein and an array of parallel plates extending into this section from its exit in an upwardly inclined manner. The inclined plates are to collect and further coalesce buoyant particles to form an agglomerated phase to rise to the surface in this section. Independent of that this apparatus does by no means form a deaeration tank and the introduced gas is by no means air, it distinguishes structurally from the deaeration tank of the present invention in that the gas disperser, normally, is arranged in a separate tank section outside that one comprising the inclined plates at its outlet and, at any rate, below a packing as mentioned above. In a specific embodiment of the present invention, the tank body is divided into a deaeration section and a discharge section by means of a partition wall, the deaeration section serving as the deaeration chamber. In this case, object water is fed into the deaeration section and deaerated object water is discharged from the discharge section. The discharge passage is a communication opening formed in the partition wall for connecting the deaeration section and the discharge section. In any case, fine bubbles which move due to a turbulent flow in the object water or in accordance with Brownian movement are scavenged by adhesion to the surface of each plate of the bubble-scavenging member. Since the velocity of the object water is substantially zero in the vicinity of the surface of each plate, fine bubbles adhering to the plate surface are not separated from the plate surface by flow of object water. Further, since the plates forming the bubble scavenging member are inclined downwards from the side of the deaeration section to the side of the discharge section, scavenged fine bubbles merge to become coarse bubbles. Thus-formed coarse bubbles separate from the plates by their own buoyancy, flow into the deaeration section, and then ascend within the deaeration section. On the other hand, suspended solids contained in object water together with fine bubbles coagulate into fine flocks as a result of addition of an inorganic coagulant. Because of a small difference in specific gravity between thus-formed fine flocks and object water, fine flocks are repelled by the plates upon impingement thereon. BRIEF DESCRIPTION OF THE DRAWINGS The structure and features of the deaeration tank according to the present invention will be readily appreciated as the same becomes better understood by referring to the drawings, in which: FIG. 1 is a schematic sectional view showing a conventional deaeration tank which employs a coarse bubble type deaeration method; FIG. 2 is a schematic sectional view showing a deaeration tank according to an embodiment of the present invention; FIG. 3 is a schematic plan view showing the deaeration tank according to the embodiment of the present invention; FIG. 4 is an enlarged view of a communication opening according to the embodiment of the present invention; and FIG. 5 is a sectional view showing a deaeration-tank/neutralizat ion-tank unit according to the embodiment of the present invention. DESCRIPTION OF PREFERRED EMBODIMENT An embodiment of the present invention will next be described in detail with reference to the drawings. In FIGS. 2 to 4, reference numeral 11 denotes a cylindrical tank body, and numeral 32 denotes a partition for dividing the tank body 11 into a deaeration section 21 and a discharge section 22. The deaeration section 21 defines a deaeration chamber for deaerating object water, while the discharge section 22 defines a discharge chamber for containing deaerated object water. A discharge passage, i.e. a communication opening 33 is formed in the partition 32 at a position higher than the center of the partition 32. The communication opening 33 establishes communication between the deaeration section 21 and the discharge section 22, and thus deaerated object water is discharged into the discharge section 22 through the communication opening 33. In place of the cylindrical tank body 11, a square tank body may be used. Line L1 is connected to the deaeration section 21 at an upper position thereof for the purpose of feeding object water into the deaeration section 21, while line L2 is connected to the discharge section 22 at an upper position thereof for the purpose of discharging deaerated object water from the discharge section 22 into an unillustrated coagulating sedimentation tank. An inorganic coagulant is added to the deaeration section 21 so as to neutralize polarity of SS contained in object water. A nozzle 13 serving as air injection means for injecting air into the deaeration section 21 is disposed within the deaeration section 21 in the vicinity of a bottom wall 11a. A line L3 is connected to the nozzle 13 in order to feed air thereto. A plurality of injection ports 13a are formed in the nozzle 13. In the thus-structured deaeration tank, when object water is fed into the deaeration section 21 through the line L1, and air is fed to the nozzle 13 through the line L3, fed air is injected into the deaeration section 21 through the injection ports 13a of the nozzle 13. Thus-injected air ascends in object water in the form of coarse bubbles and is then released from the surface of object water. During this ascent of coarse bubbles within the deaeration section 21, through contact with object water, coarse bubbles attract fine bubbles contained in object water, so that object water is deaerated. Thus-deaerated object water passes through the communication opening 33 and enters the discharge section 22. Then, deaerated object water ascends within the discharge section 22 and is discharged into the coagulating sedimentation tank through the line L2. In this course, air which has failed to become coarse bubbles after having been injected into object water through the nozzle 13 ascends in object water at a speed slower than that of object water which descends within the deaeration section 21. Accordingly, when such air, together with fine bubbles which have not been attracted by coarse bubbles, passes through the communication opening 33 following a flow of object water, the air enters the discharge section 22, and is finally discharged into the coagulating sedimentation tank through the line L2. To prevent this, a bubble-scavenging member 35 is disposed in the communication opening 33. The bubble-scavenging member 35 is composed of a plurality of parallel inclined plates 36 which are inclined downward from the side of the deaeration section 21 to the side of the discharge section 22. Also, a gap 37 for passing object water therethrough is defined between a lower end portion 36a of each inclined plate 36 and a portion 32a which extends diagonally upward from the lower edge of the communication opening 33 in the partition 32 into the interior of the discharge section 22. Further, an end plate 38 is disposed at each side of the communication opening 33 so as to prevent a short pass of object water between the deaeration section 21 and the discharge section 22. In this case, since the inclined plates 36 are arranged at narrow intervals with each other, object water which passes through the communication opening 33 slows down when passing between the inclined plates 36. At this time, fine bubbles, which move due to a turbulent flow in object water or in accordance with Brownian movement, are scavenged through adhesion to the surface of each inclined plate 36. Since the velocity of object water is substantially zero in the vicinity of the surface of each inclined plate 36, fine bubbles adhering to the plate surface are not separated from the plate surface by flow of object water. Thus-scavenged fine bubbles merge to become coarse bubbles. Thus-formed coarse bubbles separate from the inclined plates 36 by their own buoyancy, flow into the deaeration section 21, and then ascend within the deaeration section 21. As described above, fine bubbles contained in object water can be scavenged by means of the bubble-scavenging member 35, so that there is no need to increase the distance between the bottom wall 11a and the nozzle 13. Accordingly, the size of the deaeration tank can be reduced. Also, since the feed rate of object water into the deaeration section 21 can be increased, the treatment capability of the deaeration tank increases accordingly. On the other hand, suspended solids which are contained in object water together with fine bubbles coagulate into fine flocs as a result of addition of an inorganic coagulant. Because of a small difference in specific gravity between thus-formed fine flocs and object water, fine flocs are repelled by the inclined plates 36 upon impingement thereon. The inclination of the inclined plates 36 is determined so as to facilitate separation of formed coarse bubbles from the inclined plates 36 and to prevent fine flocs in object water from accumulating on the inclined plates 36. Next will be described a deaeration-tank/neutralization-tank unit in which the deaeration tank and a neutralization tank are combined in order to pretreat object water before it is subjected to coagulating sedimentation. FIG. 5 is a sectional view showing the deaeration-tank/neutralization-tank unit according to the embodiment of the present invention. In FIG. 5, reference numeral 11 denotes a tank body, numeral 13 denotes nozzles, numeral 13b denotes supports, numeral 21 denotes a deaeration section, numeral 22 denotes a discharge section, numeral 32 denotes a partition, numeral 33 denotes a communication opening, numeral 35 denotes a bubble-scavenging member, numeral 51 denotes an object water inlet to be connected with the line L1 (FIG. 2), numeral 52 denotes an object water outlet to be connected with the line L2, and numeral 53 denotes an air inlet to be connected with the line L3. A manhole 55 and a drain port 56 are disposed on a side wall 11b of the tank body 11 at a lower portion thereof. A neutralization tank 61 is disposed adjacent to the tank body 11. The neutralization tank 61 has an object water inlet 62 to be connected with the line L2 and an object water outlet 63 through which neutralized object water is discharged. In order to adjust the pH of object water to be in a predetermined range, an acid or alkali is added to the neutralization tank 61. A stirrer 65 is disposed within the neutralization tank 61 for the purpose of stirring object water. A motor 66 for actuating the stirrer 65 is disposed on the neutralization tank 61. Further, a manhole 68 and a drain port 69 are disposed on a side wall 61b of the neutralization tank 61 at a lower portion thereof. An inspection catwalk 70 is disposed on the tank body 11 and on the neutralization tank 61 so that an inspector can inspect the interior conditions of the tank body 11 and the neutralization tank 61 from above. The present invention is not limited to the above-described embodiment. Numerous modifications and variations of the present invention are possible in light of the spirit of the present invention, and they are not excluded from the scope of the present invention.

Claims: A deaeration tank, comprising: (a) a tank body (11) defining a deaeration chamber (21), (b) an inlet (L1) for introducing object water to be deaerated into said deaeration chamber (21), (c) air injection means (13) within said deaeration chamber (21) near the bottom thereof for injecting relatively coarse air bubbles into said object water in order to attract fine air bubbles contained in said object water, and (d) a discharge passage (33) for discharging object water from said deaeration chamber (21), characterized in (e) that the complete discharge passage (33) is in a position higher than said air injection means (13), (f) that a bubble-scavenging member (35) is disposed in said discharge passage (33) for scavenging fine bubbles still contained in the object water passing through said discharge passage, and (g) that said bubble-scavenging member (35) comprises a plurality of parallel plates (36) inclined downwardly from the side of said deaeration chamber (21) and adapted for said fine bubbles to adhere to the surface of said plates, agglomerate and then flow back into said deaeration chamber. The deaeration tank according to claim 1, wherein said tank body (11) is divided, by means of a partition (32), into said deaeration chamber (21) and a discharge section (22), said discharge passage (33) being provided in said partition. The deaeraton tank according to claim 2, wherein said discharge passage (33) is disposed at a position higher than the center of said partition (32).

Inventors: MISAWA KIHACHIRO, OKUMOTO YOSHIO, MISAWA, KIHACHIRO, OKUMOTO, YOSHIO
Applicants: SUMITOMO HEAVY INDUSTRIES, SUMITOMO HEAVY INDUSTRIES, LTD.
Application year: 1997
Main classification: B01D19
IPC codes: C02F1, B01D19