SG183043A1

SG183043A1 - Foam recovery device and foam recovery system

Info

Publication number: SG183043A1
Application number: SG2012052932A
Authority: SG
Inventors: Keisuke Sonoda; Seiji Furukawa; Shozo Nagao
Original assignee: Mitsubishi Heavy Ind Ltd
Priority date: 2007-07-24
Filing date: 2008-07-17
Publication date: 2012-08-30
Also published as: JP2009045614A; EG25363A; MY162983A; TW200925118A; JP5412042B2; SA08290459B1; TWI379808B

Abstract

Provided is a foam recovery device that can recover foam floating on the surface of desulfurized used seawater and drain only the foam-free used seawater into the surrounding sea area. The foam recovery device (20) is installed in a seawater oxidation treatment system (1) for draining used seawater discharged from a desulfurization tower of an exhaust gas desulfurizer using seawater as an absorbent and is configured to remove foam (4) floating on the surface of the used seawater by recovering the foam (4), wherein a foam recovery pit (40) is connected to an overflow dam (30) provided in a side face of the seawater oxidation treatment system (1), and a foam-collecting float (50) that is held floating so as to cross the seawater oxidation treatment system (1) separates the foam (4) floating on the surface (n) and a surface seawater flow from the main flow of the used seawater and leads the foam and the surface seawater flow to the foam recovery pit (40).FIGURE 1

Description

DESCRIPTION

FOAM RECOVERY DEVICE AND FOAM RECOVERY SYSTEM

[0001]

The present invention relates to treatment of effluent from an exhaust gas desulfurizer employed in an electric power plant, such as a coal-fired, crude-oil-fired, or heavy-oil- fired power plant, and particularly relates to a foam recovery device and a foam recovery system for removing foam from effluent from an exhaust gas desulfurizer performing desulfurization using a seawater method.

Background Art

[0002]

Conventicnally, in an electric power plant using coal, crude oil, or the like as fuel, sulfur oxides {30x}, such as sulfur dioxide (S0,), are removed from combustion exhaust gas (hereinafter called "boiler exhaust gas™) discharged from a boiler, and then the boiler exhaust gas is discharged into the atmosphere. Xnown examples of such desulfurization treatment with an exhaust gas desulfurizer include systems employing a limestone-plaster method, a spray dryer method, or a seawater method.

[0003]

An exhaust gas desulfurizer employing the seawater method (seawater desulfurizer) uses seawater as an absorbent. In this system, for example, seawater and boiler exhaust gas are supplied to the inside of a desulfurization tower (absorption tower) having a substantially cylindrical shape, such as a vertically disposed cylinder, to cause gas-liquid contact in a wet system, thereby removing sulfur oxides using the seawater as an absorbing sclution.

As shown in Fig. 23, for example, when the seawater (used seawater) used as an absorbent for desulfurization in the aforementioned desuifurization tower flows in a seawater oxidation treatment system (S0TS) 1 to be drained away, it is decarbonated (aerated) by aeration with aeration micro-air- bubbles 3 discharged from an aeration nozzle 2 disposed at the bottom of the seawater oxidation treatment system 1.

[0004]

When the pH is adjusted by the aforementioned decarbonation, a large amount of foam 4 is produced on the surface of the used seawater flowing in the seawater oxidation treatment system 1 due to interaction among the seration micro-air-bubbles 3, components {soot and dust, etc.} in the boiler exhaust gas introduced into the seawater in the desulfurization tower, and organic substances contained in the seawater. Not only does this foam 4 tend to remain but it also contains hazardous substances. Therefore, discharging the foam 4 from the seawater oxidation treatment system 1 together with the seawater directly into the surrounding sea area is undesirable from the viewpoints of scenery and environmental pollution.

The area of the seawater oxidation treatment system 1 for conducting aeration by generating aeration micro-air-bubbles 3 and decarbonating used seawater is called an aeration area 5.

[0005]

An oil recovery device for recovering oil flcating on the water surface is a known conventional technology similar or relating to elimination of foam on the water surface. This oil recovery device includes a floating portion that floats on the water surface and supports the oil recovery device, a suction portion for sucking oil, and an oil-collecting portion that collects ¢il from an oil-collecting aperture and leads the collected oil to the suction portion (for example, refer to Patent Document 1).

Furthermore, a device for recovering sludge or the like has aiso been proposed as a device that can easily recover paint sludge or the like floating in a recovery tank (for example, refer to Patent Document 2).

Patent Document 1: Japanese Unexamined Patent

Application, Publication No. 2004-351279 (refer to Fig. 1,

etc.)

Patent Document 2: Japanese Unexamined Patent Application

Publication, No. Hei 6-296911 (refer to Fig. 1, etc.)

Disclosure of Invention - [0006]

The above-described desulfurized used seawater flows in the seawater oxidation treatment system 1 and is drained into the surrounding sea area, and the foam 4 floating on the water surface causes scenery destruction and environmental pollution. Accordingly, in order tc solve these problems, a device for recovering the foam 4 on the water surface by appropriately separating and removing the foam 4 from the seawater is necessary. That is, there are demands for development of a foam recovery device that can recover the foam 4 floating on the surface of desulfurized used seawater by appropriately separating and removing the foam 4 from the desulfurized used seawater for draining only the used seawater, that is, not containing foam 4, into the surrounding sea area and also for development of a foam recovery system including such a feoam recovery device.

The present invention has been made under these circumstances, and an object of the present invention is to provide a foam recovery device that can collect foam floating on the surface of desulfurized used seawater and drain only the foam-free used seawater into the surrounding sea area, as well as a foam recovery system including such a foam recovery device. 0007]

The present invention employs the following sclutions for solving the aforementioned problems.

A foam recovery device according to a first aspect of the present invention is installed in a seawater oxidation treatment system for draining used seawater discharged from a desulfurization tower of an exhaust gas desulfurizer using seawater as an absorbent and configured to recover foam flcating on the surface of the used seawater by removing the foam, wherein a foam recovery pit is disposed so as to be connected via an overflow dam provided in a side face of the seawater oxidation treatment system, and a foam-collecting flcat that is held fleoating so as to cross the seawater oxidation treatment system is disposed to separate the foam floating on the surface and a surface seawater flow from the main flow of the used seawater and to lead the foam and the surface seawater flow to the foam recovery pit. [GO08]

In such a foam recovery device, the foam recovery pit is disposed so as to be connected via the overflow dam provided in a side face of the seawater oxidation treatment system, and the foam-collecting float that is held floating so as to cross the seawater oxidation treatment system is disposed to separate the foam floating on the surface and the surface seawater flow from the main flow of the used seawater and to lead the foam and the surface seawater flow to the foam recovery pit. Consequently, the installation position (height) of the feoam-collecting float varies with a buoyant force in accordance with the water level of the used seawater flowing in the seawater oxidation treatment system.

Therefore, the foam-collecting flcat is always held at approximately the same position with respect to the water surface and can thereby cover the upper portion of the used : seawater. As a result, the foam floating on the water surface and the surface seawater flow are separated from the main flow of the used seawater through the overflow dam that is provided in a side face of the seawater oxidation treatment system at a position lower than the heights of the side wall of the seawater oxidation treatment system and the foam-collecting float, thereby reliably recovering the foam and the surface seawater flow in the foam recovery pit.

[0009]

In the first aspect, it is preferable tc provide a return path that connects the foam recovery pit and the seawater oxidation treatment system and returns at least part of the collected seawater to the seawater oxidation treatment system by separating the collected seawater from the foam. With this, a suction and conveying device, such as a pump, which is needed for subsequent processing in the foam recovery pit can be reduced in size.

[0010]

In any one of the above-mentioned foam recovery devices, the overflow dam preferably has a mechanism for varying the dam height. By doing so, the height of the overfiow dam can be optimized according to, for example, the thickness of foam, resulting in an increase in the reliability of foam recover.

[0011]

In any one of the above-mentioned foam recovery devices, the side face in which the overflow dam is formed is preferably a slanted surface that intercepts the flow of used seawater flowing in the seawater oxidation treatment system.

By doing so, the intake of foam into the overflow dam can be smoothly performed.

[0012]

A feoam recovery device according to a second aspect of the present inventicn is installed in a seawater oxidation treatment system for draining used seawater discharged from a desulfurization tower of an exhaust gas desulfurizer using seawater as an absorbent and recovers foam floating on the surface of the used seawater by removing the foam, and the foam recovery device includes a foam recovery pit disposed near the seawater oxidation treatment system; a foam-holding member crossing the seawater oxidation treatment system so as "to block the path of seawater from under the water to a predetermined position above the water surface while leaving a bottom portion of the seawater oxidation treatment system; and a foam recovery portion for recovering the foam dammed by the foam-holding member from the water surface into the foam recovery pit.

[0013]

With such a foam recovery device, because it includes the foam recovery pit disposed next to the seawater oxidation treatment system, the foam-holding member crossing the seawater oxidation treatment system so as to block the path of seawater from under the water to a predetermined position above the water surface while leaving the bottom portion of the seawater oxidation treatment system, and the foam recovery portion for recovering the foam dammed by the foam-holding member from the water surface into the foam recovery pit, the foam-holding member can dam the flowing foam floating on the water surface, and the foam recovery portion can reliably recover the dammed foam into the foam recovery pit.

[0014]

In the second aspect, the foam recovery portion preferably includes a transfer portion that can reciprocate across the seawater oxidation treatment system and a scraper suspended from the transfer porticen. By deing so, the scraper that moves tcgether with the transfer portion scrapes foam floating and remaining on the water surface and transfers the foam, thereby recovering the foam in the foam recovery pit.

In this case, the foam can be recovered by separating the foam from the used seawater by providing a slanting wall face from a side wall of the seawater oxidation treatment system to the foam recovery pit.

[0015]

In the second aspect, the foam recovery portion is preferably a rotary scraper that rotates on an arc-shaped wall extending upward from a side wall of the seawater oxidation treatment system to the foam recovery pit. By doing so, the rotating scraper scrapes foam floating and remaining on the . water surface and transfers the foam, thereby recovering the foam in the foam recovery pit. In this case, since the arc- shaped wall is employed, rotation of the rotary scraper is not inhibited, and the foam can be recovered by separating it from the used seawater.

In this case, the rotary scraper is preferably rotationally driven by the hydraulic power of the used seawater flowing in the seawater oxidation treatment system.

By doing so, the rotary scraper can reduce energy consumption.

[0016]

In the second aspect, the foam recovery portion is preferably an ejector recovering fecam by sucking the foam from a suction port floating on the water surface into the foam recovery pit. By doing sco, the foam floating on the water surface can be recovered by separating it from the used seawater,

[0017]

In the second aspect, the foam recovery porticn is preferably a mesh belt conveyor having a squeezing roller above the foam recovery pit. By deing so, the foam floating on the water surface can be recovered by separating it from the used seawater.

[0018]

A foam recovery system according to a third aspect of the present invention employs a foam recovery device installed in a seawater oxidation treatment system for draining used seawater discharged from a desulfurization tower of an exhaust gas desulfurizer using seawater as an absorbent and recovering foam floating on the surface of the used seawater by separating and removing the foam from the used seawater, the foam recovery system including any one of the foam recovery devices described above, a foam treatment device for dehydrating and drying the foam recovered by the fcam recovery device, and a suction and conveying device for sucking the foam recovered in the foam reccvery pit and transferring the foam to the foam treatment device through a channel.

Such a foam recovery system includes any one of the foam recovery devices described above, the foam treatment device for dehydrating and drying the foam recovered by the foam recovery device, and the suction and conveying device for sucking the foam recovered in the foam recovery pit and transferring the foam to the foam treatment device through a channel; and the installation position (height) of a foam- collecting float of the foam recovery device varies with a buoyant force in accordance with the water level of the used seawater flowing in the seawater oxidation treatment system.

Therefore, the foam-collecting float is always held at approximately the same position on the water surface and can cover the upper portion of the used seawater. As a result, the foam flecating on the water surface and the surface seawater flow are separated from the main flow of the used seawater through the overflow dam that is provided in a side face of the seawater oxidation treatment system at a position lower than the heights of the side wall of the seawater oxidation treatment system and the foam-cecllecting float, thereby reliably recovering the foam in the foam recovery pit.

The foam thus recovered in the foam recovery pit is transferred to the foam treatment device with the suction and conveying device and is dehydrated and dried to separate a foam component from a seawater component.

According to the present invention described above, foam is recovered by appropriately separating and removing it from the surface .of the used seawater that is discharged from a desulfurization tower and then flows in a seawater treatment system to be drained. Therefore, only used seawater, free of foam, is drained into the surrounding sea area. Consequently, the problems of scenery destruction and environmental pollution due to foam floating on the water surface can be avoided.

Brief Description of Drawings

[0021] [FIG. 1] FIG. 1 illustrates an embodiment of a foam recovery device and a foam recovery system according to the present invention, showing a cross section of the foam recovery device viewed from the flow direction and the configuration of ground-based facilities. [FIG., 2] FIG. 2 is a plan view of a foam recovery device according to the present invention. [FIG. 3] FIG. 3 is a side view of a foam recovery device according to the present invention. [FIG. 4] FIG. 4 is a perspective view of a main portion of a first modification of a foam recovery device of the present invention. [FIG. 5] FIG. 5 is a plan view cf the first modification shown in FIG. 4.

FIG. 6] FIG. 6 is a plan view illustrating a second modification cf a foam recovery device of the present invention. [FIG. 7] FIG. 7 is a plan view illustrating a second embodiment of a foam recovery device according to the present invention. [FIG. 8] FIG. 8 is a perspective view illustrating a main portion of the foam recovery device shown in FIG. 7. [FIG. 9] FIG. 9 is a plan view illustrating a modification according to the second embodiment. [FIG. 10] FIG. 10 is a view illustrating a mechanism for varying dam height, when the overflow dam provided in a side wall of the seawater oxidation treatment system is viewed from the foam recovery pit side. [FIG. 11] FIG. 11 is a cross-sectional view illustrating a gate board shown in FIG. 10. [FIG. 12] FIG. 12 is a plan view of FIG. 10. [FIG. 13] FIG. 13 is a plan view illustrating a third embodiment of a foam recovery device according to the present invention. [FIG. 14] FIG. 14 is a perspective view illustrating an example of the configuration of a scraper shown in FIG. 13. [FIG. 15A] FIG. 15A is a plan view illustrating a first modification according te the third embodiment.

[FIG. 15B]) FIG. 15B is a cross-sectional view illustrating the first modification according to the third embodiment.

[FIG. 16A] FIG. 16A is a plan view illustrating a second modification according to the third embodiment.

[FIG. 16B] FIG. 16B is a cross-sectional view illustrating the second modification according to the third embodiment. [FIG. 17] FIG. 17 is a plan view illustrating a third modification according to the third embodiment.

[FIG. 181 FIG. 18 is a plan view illustrating a fourth modification according to the third embodiment.

[FIG. 19] FIG. 19 is a plan view illustrating a fifth modification according £0 the third embodiment.

[FIG. 20A] FIG. 20A is a side view illustrating a fourth embodiment of a foam recovery device according to the present invention.

[FIG. 20B] FIG. 20B is a plan view illustrating a fourth embodiment of a foam recovery device according to the present invention.

[FIG. 21A] FIG. 21A is a side view illustrating a fifth embodiment of a foam recovery device according to the present invention.

[FIG. 21B} FIG. 21B is a plan view illustrating the fifth embodiment of the foam recovery device according to the present invention. [FIG. 22] FIG. 22 is a side view illustrating a modification according to the fifth embodiment. [FIG. 23] FIG. 23 is a side view illustrating a conventional technology.

Explanation of Reference Signs:

[0022] 1: seawater oxidation treatment system lc: slanting face 4: foam 5, 5A to 5C: aeration area 10: foam recovery system 12: suction and conveying device 13: foam treatment device 20, 20A to 20D, 20A', 20D': foam recovery device oo 30: overflow dam 31: gate board 40: foam recovery pit 43: return path 50, 5CA to 50C: foam-ccllecting float 50D: foam-holding member (curtain wall) 51: slanting face 52: curved face 60: scraper 65: slanting wall face

66: arc-shaped wall 67: rotary scraper 80: suction port 81: fleat 84: ejector © 85: blower 90: squeezing roller 91: mesh belt

Best Mode for Carrying Out the Invention

[0023]

Embodiments of a foam recovery device and a foam recovery system according to the present invention will now be described with reference to the drawings. [First Embodiment]

A foam recovery system 10 shown in Figs. 1 to 3 includes a foam recovery device 20 that is installed, for example, in a seawater oxidation treatment system (SOTS) 1 for draining used seawater such as desulfurized seawater (seawater aerated by : passing through an aeration area 5) discharged from a desulfurization tower (not shown} of an exhaust gas desulfurizer using seawater as an absorbent and recovers foam 4 floating on the surface WL of used seawater by separating and removing the foam 4 from the used seawater. This foam recovery device 20 includes a foam recovery pit 40 connected to the seawater oxidation treatment system 1 through an overflow dam 30 provided in a side face of the seawater oxidation treatment system 1 and a foam-collecting float 50 that is held floating so as to cross the seawater oxidation treatment system 1. The foam-collecting float 50 is configured to separate the foam 4 floating on the surface WL and the surface seawater flow from the main flow of the used seawater and, as shown in the drawings by the arrow Fb, to lead the foam and the surface seawater flow to the foam recovery pit 40 through the overflow dam 30.

[0024]

The overflow dam 30 is a region formed by partially cutting out a side wall la of the seawater oxidation treatment system 1 at a position lower than the level of the water surface WL. Furthermore, the foam reccevery pit 40 is provided next to the overflow dam 30, namely, on the side wall la, i.e., the side face of the seawater oxidation treatment system 1 where the overflow dam 30 is provided, so as to be adjacent to the seawater oxidation treatment system 1.

Furthermore, the above-described overflow dam 30 preferably has a mechanism, described below, that varies the dam height for optimizing the height of the overflow dam 30 according to, for example, the foam thickness.

[0025]

The foam recovery pit 40 is a space connected to the seawater oxidation treatment system 1 through the overflow dam 30. The bottom face 41 of the foam recovery pit 40 is designed to be lower than the position of the overflow dam 30.

Since the circumference of the bottom face 41 is surrounded by a side wall 42, the foam recovery pit 40 can store the foam 4 and part of the used seawater separated from the main flow of the used seawater through the overflow dam 30. In this case, the part of the used seawater separated from the main flow of "the used seawater is the surface seawater flow led toward the overflow dam 30 by the foam-collecting float 50, described below. The capacity of the foam recovery pit 40 is determined in consideration of various conditions such as the performance of a suction and conveying device 12, described below, and the amount of used seawater to be treated.

[6026]

The foam recovery pit 40 is preferably provided with a return path 43 that connects the foam recovery pit 40 to the seawater oxidation treatment system 1. This return path 43 is, for example, a pipe that is connected to the bottom face 41 or a position near the bottom face 41 to an appropriate position of the seawater oxidation treatment system 1, and is provided for returning at least part of the surface seawater flow collected in the foam recovery pit 40 to the seawater oxidation treatment system 1 in order to reduce the treatment load in subsequent processing {such as treatment with the suction and conveying device 12) of the foam recovery pit 40, which will be described below. That is, in the foam recovery pit 40 described above, it is desirable that the recovered foam 4 be reliably separated from the surface seawater flow and the amount of used seawater to be treated in the subsequent processing be decreased by returning only the surface seawater flow to the seawater oxidation LrREInanR system 1. [C027]

Therefore, in order to avoid inflow of the foam 4 floating on the water surface into the return path 43, the foam recovery pit 40 is desirably attached with an appropriate foam separator therein. A specific example of the foam separator 1s a partition plate (not shown} attached to the vicinity of the return path 43 so as to surround an inlet opening 44. This partition plate has a height for blocking the upper flow of the flecating foam 4, and the lower portion of the partition plate is provided with a connection path for letting the seawater flow toward the bottom face 41.

Therefore, the foam 4 can be reliably separated from the seawater flowing out through the inlet opening 44.

[0028]

The foam-ccllecting float 50 is a float having a width dimension of approximately the same as the width W of the seawater oxidation treatment system 1: that is, it is held floating on the water surface WL so as to cross, i.e., to cover the upper portion of the seawater oxidation treatment system 1. The foam-collecting float 50 is installed such that, of the foam 4 and the used seawater flowing in the seawater oxidation treatment system 1, the foam 4 and the surface seawater flow are led to the foam recovery pit 40 via the overflow dam 30.

The foam-coliecting float 50 shown in the drawing is a float having an approximately trapezcidal shape in plan view.

The upstream side in the flow direction (arrow F in the drawing) of the used seawater is a slanting face 51 obliquely crossing the seawater oxidation treatment system 1. This slanting face 51 is inclined such that the side wall la provided with the overflow dam 30 is further downstream than the opposing side wall 1b.

[0029]

In addition, the foam-collecting float 50 floating on the water surface WL has a height (thickness) H consisting of an appropriate height hl of an above-water portion protruding above the water surface and an appropriate height h2 of an underwater portion submerging in the water. That is, the foam-collecting float 50 is configured so that the above-water portion with the height hl leads the flow of foam 4 floating on the water surface WL toward the foam recovery pit 40 and the underwater portion with the height hZ leads the surface seawater flow of used seawater toward the foam recovery pit 40. The height hl of the above-water portion described above may be determined depending on, for example, the condition of the foam 4 floating on the water surface. For example, the above-water portion may be approximately the same height as the upper ends of the side walls la and 1b.

Such a foam-colliecting fioat 50 is fixed in order not to be made to move from a predetermined position in the seawater oxidation treatment system 1 by the flow of water, while being able to move vertically with a buoyant force. That is, the foam-cellecting float 50 with the flotation structure can move in the vertical direction according to a change in the water level in the seawater oxidation treatment system 1, but is supported at a predetermined position so as not to move in the flow direction of the used seawater flowing in the seawater oxidation treatment system 1.

[0030]

The above-described foam-collecting float 50 is not limited to those having the slanting face 51 formed by a slanting side of a trapezecid (in plan view), as shown in Fig. 2, and can take various shapes.

In a first modification shown in Figs. 4 and 5, the slanting face 51 is formed by obliquely arranging a foam-— collecting float 50A having an approximate parallelogram shape in the seawater oxidation treatment system 1.

In a second modification shown in Fig. 6, instead of the linear slanting face 51, a curved face 52 formed by a foam- collecting float 50B may be used to lead foam 4 and a surface seawater flow into the foam recovery pit 40.

[0031]

The foam-collecting float 50 may be a float having, for example, a hollow structure conforming tc the size and shape of the seawater oxidation treatment system 1 or may be a commercially available oil fence that is advantagecus in terms of cost reduction. The oil fence desirably includes a slider that can respond to a change in the sea level, that is, a change in the water level.

[0032] :

The foam recovery system 10 includes a transfer path made of a piping 11 having one end arranged in the foam recovery pit 40. The piping 11 transfers the foam 4 recovered in the foam recovery pit £0 having the structure described above for treatment. The other end of the piping 11 forming the transfer path is connected to the suction and conveying device 12. Furthermore, a foam treatment device 13 is disposed at a discharging side of the suction and conveying device 12.

[0033]

The above-described suction and conveying device 12 is, for example, a pump such as an ejector pump or a vacuum pump.

The foam treatment device 13 is, for example, a centrifuge for dehydrating the recovered foam 4 and separating it into a foam component and seawater. The separated seawater is drained into the surrounding sea area, and the foam component is dried into a solid. This solid is reused in the facilities or buried underground.

That is, the foam recovery system 10 includes, in addition to the foam-collecting float 50, disposed in the seawater treatment system 1, having a flotation structure (water-base facilities), ground-based facilities including the suction and conveying device 12 for sucking the recovered foam 4 recovered from the foam recovery pit 40 and conveying the foam 4 to the foam treatment device 13 and the foam treatment device 13 for dehydrating and drying the foam 4 recovered in the foam recovery pit £0.

[0034]

Next, the functions of the foam recovery system 10 having the configuration described above will be described together with a treatment process for recovering the foam.

Desulfurized used seawater drained from a desulfurization tower flows in the seawater oxidation treatment system 1 in the direction shown by the arrow F. The foam 4 floats on the surface of the used seawater flowing in the seawater treatment system 1. When the foam 4 reaches the foam-collecting float 50, the fcam 4 and the surface seawater flow are separated from the flow of the used seawater by the slanting face 51.

Since the foam-collecting float 50 has the flotation structure, its positional relation with the surface of the used seawater is maintained approximately constant, even if the water level changes.

[0035]

As a result, the foam 4 on the water surface and the surface seawater flow flowing in the upper portion of the used seawater are separated from the main flow of the used seawater by being guided on the slanting face 51 and fall into the foam recovery pit 40 to be recovered. On the other hand, the main flow of the used seawater, other than the foam 4 and the surface seawater flow flowing in the upper portion of the used seawater, passes below the slanting face 51.

The foam 4 recovered in the foam recovery pit 40 is sucked by operating the suction and conveying device 12 and is conveyed to the foam treatment device 13 through the piping 11.

[0036]

The foam 4 thus conveyed to the foam treatment device 13 is separated into seawater and a foam component as required.

The separated seawater, free of foam, is drained into the surrounding sea area, and the separated foam component is dried into a solid and reused in the facilities or buried underground at an appropriate site.

Therefore, the foam 4 can be removed by appropriately separating and recovering the foam 4 from the surface of the used seawater drained from a desulfurization tower and flowing in the seawater treatment system 1 for draining the used seawater. Accordingly, only the used seawater, that is, not containing the foam 4, can be drained into the surrounding sea area, and the problems of scenery destruction and environmental pollution caused by fcam 4 floating on the water surface can be avoided.

[0037]

The above-described foam-collecting flecat 50, the foam recovery pit 40, and the foam recovery system 10 may be provided for each desulfurization tower that drains used seawater or may be provided for a single seawater oxidation treatment system 1 that receives used seawater drained from a plurality of desulfurization towers.

[0038] [Second embodiment]

A second embodiment of the foam recovery device of the present invention will now be described with reference to the . drawings. The same portions as those in the above-described embodiment are designated with the same reference numerals, and detailed descriptions thereof are omitted.

A foam recovery device 20A shown in Figs. 7 and 8 includes a plurality of columns of aeration areas 5 aligned at an upstream side. In the configuration shown in the drawings,

three columns of aeration areas 5A, 5B, and LC are aligned parallel to each other. In this case, for example, by maintaining one of the three columns in turn, continuous operation is possible by using the other two columns. The number of the columns of aeration areas 5 is not limited to three as described above.

[0039]

In this embodiment, an inexpensive oil fence 50C is empioyed as a foam-collecting float. This oil fence 530C desirably includes a slider (not shown) that can respond to a change in sea level.

In this embodiment, a dehydration tank 45 and a condensation tank 46 are connected at the downstream side of the foam recovery pit 40. The foam that is guided by the oil fence 50C and recovered in the foam recovery pit 40 together with used seawater through the overflow dam 30 can be drained into the dehydration tank 45 from the foam recovery pit 40, for example, by operating a float pump (not shown) disposed at the water surface in the foam recovery pit 40. In the dehydration tank 45, the foam is separated from the used seawater and is sent to the condensation tank 46. The used seawater flowing into the foam recovery pit 40 returns to the seawater oxidation treatment system 1 Through a return path 43 disposed near the bottom thereof. : [0C40]

Furthermore, in this embodiment, an overflow dam 30 is provided in a slanting face lc formed by narrowing down the cross-sectional area of the channel in the seawater oxidation treatment system 1. Accordingly, the overflow dam 30 is provided in the slanting face lc which intersects the flow direction. Therefore, in cooperation with a curved face formed by the oil fence 50C, a flow for recovering the foam in the foam recovery pit 40 is smoother compared to the case where the overflow dam 30 is provided in a side wall la parallel to the flow direction.

[0041]

In the embodiment shown in Figs. 7 and 8, the overflow dam 30 is provided in a part of the slanting face lc.

However, for example, in a foam recovery device 20AT of a modification shown in Fig. 9, the overflow dam 30 is provided over the entire slanting face lc. With the overflow dam 30 having such a configuration, the recovery can be conducted more smoothly and mere efficiently.

In this modification, the return path 43 is nct provided, but a return path 43 may be provided if necessary.

[0042] ~ The above-described overflow dam 30 preferably includes, for example, as shown in Figs. 10 to 12, a mechanism for varying the dam height for adjusting the height of the dam according to, for example, the thickness of foam and a change in the water level. Fig. 10 is a drawing of the overflow dam disposed in a side wall la of the seawater oxidation treatment system 1 viewed from the foam recovery pit 40 side.

In the configuration shown in the drawing, the overflow dam 30 is provided with a gate board 31. The gate board 31 is, as shown in a plan view of Fig. 12, held with guides 32 at both ends s¢ as to be vertically slidable. The upper end of the gate board 31 is attached with floats 34, with rods 33 that can vary the height (length).

[0043]

The rods 33 in this case are, for example, bolts that are formed in the gate board 31 and that threadedly engage with female screws. The float height can be controlled by changing the inserted amount (screwed length). That 1s, the distance from the upper end of the gate board 31 defining the height of the overflow dam 30 to the floats 34 floating on the water surface can be controlled. The members indicated by reference numeral 35 in the drawings are sealing packing attached near both sides and z lower end of the gate board 31. oo The mechanism for varying the height of the dam is not limited to the configuration example described above. For example, the gate board 31 may be mechanically moved in the vertical direction with a driving source such as an electric motor. :

[Third embodiment]

A third embodiment of the foam recovery device of the present invention will now be described with reference to the drawings. The same portions as those in the above-described : embodiments are designated with the same reference numerals, and detailed descriptions thereof are omitted.

A foam recovery device 20B shown in Figs. 13 and 14 is installed in a seawater oxidation treatment system (SOTS) 1 for draining used seawater discharged from a desulfurization tower of an exhaust gas desulfurizer using seawater as an absorbent and separates foam floating on the surface of the used seawater for recovering the foam. The foam recovery device 20B includes a foam recovery pit 40 disposed near the seawater oxidation treatment system 1, a foam-holding member 50D, and a scraper 60 serving as a foam recovery portion.

[0045]

The foam-holding member 50D is disposed across the seawater oxidation treatment system 1 and blocks the path of used seawater from under the water to a predetermined position above the water surface while leaving a bottom portion of the seawater oxidation treatment system 1. The foam-holding member 50D is preferably, for example, a curtain wall, a foam- collecting float, or an oil fence. That is, the fodm=holding member 50D dams foam floating on the surface of the used seawater flowing in the seawater oxidation treatment system 1 and holds the feoam, while allowing the used seawater to flow in the bottom portion of the seawater oxidation treatment system 1.

The foam dammed by the feoam-hclding member 50D remains on the water surface floating at the upstream side of the foam- holding member 50D. The scraper 60 serves as a foam recovery portion for collecting this foam into the foam recovery pit 40. In the example shown in the drawings, though a device and other components for treating the foam collected in the foam recovery pit 40 are not shown in the drawings, for example, the configuration described in the above-described embodiments may be optionally employed.

[0046]

An example of the configuration of the scraper 60 will now be described with reference to Figs. 13 to 15.

The scraper 60 shown in the drawings includes a transfer portion 61 that is reciprocatable across on the seawater oxidation treatment system 1 and a scraper 62 that is suspended from the transfer portion 61 so as to be vertically movable.

The transfer portion 61 is a device that is driven by, for example, an electric motor and travels on a pair of rails 63 disposed across the upper portion of the seawater oxidation freatment system 1. In the configuration of the example shown in the drawings, the foam-holding member 50D is a curtain wall

53. One of the rails 63 is laid on the upper face of the curtain wall 53, and the other rail 63 is laid on a rib 64 crossing the seawater oxidation treatment system 1. However, the rails 63 are not particularly limited: for example, both rails 63 may be laid on a specially designed frame.

[0047]

In the thus configured scraper 60, the transfer portion 61 travels on the rails 63 and reciprocates for scraping the foam floating and remaining on the water surface with the scraper 62 and transferring the foam to the foam recovery pit 40. That is, when the transfer portion 61 travels toward the foam recovery pit 40, the lower end cof the scraper 62 is lowered to a position underwater. Consequently, the foam floating on the water surface can be reliably transferred to the foam recovery pit 40. When the transfer portion 61 travels toward the opposite side wall 1b from the foam recovery pit 40, the lower end is lifted to a sufficient height from the water surface so that the scraper 62 is not in contact with the foam.

[0048]

A first modification of the above-described scraper 60 : will now be described with reference to Figs. 15A and 15B. In this first modification, a scraper that moves together with the transfer portion 61 transfers foam while scraping it. In a portion for recovering the foam in the foam recovery pit 40,

a slanting wall face 65 has a height that gradually increases from the upper end of the overflow dam 30 disposed in the side wall la of the seawater oxidation treatment system 1 toward the foam recovery pit 40.

With the slanting wall face 65 having a height increasing from the side wall la of the seawater oxidation treatment system 1 toward the foam recovery pit 40, the lower end of the scraper 62 is lifted by the slanting wall face 65 to be inclined (refer to reference numeral 62a in the drawing), according to the movement of the transfer portion 61 toward the foam recovery pit 40, that is, in the rightward direction in the drawing of Fig. 15B (refer to reference numerals 61 — 6la — ¢lb in the drawing). Consequently, when the scraper passes the slanting wall face 65, the foam is held by the scraper 62, and the used seawater freely falls due to gravity.

Therefore, the foam separated from the used seawater can be recovered, resulting in a reduction in load in subsequent processing.

[0049]

Then, the transfer portion 61 moves over the slanting wall face 65 to a position above the foam recovery pit 40, and the foam transferred by the scraper 62b with an increased slanting angle falls and is recovered in the pit. This scraper 62b 1s released from the slanting state and hangs downward (refer to reference numeral 62b' in the drawing) when its lower end goes over the slanting wall face 65. Then, the transfer portion 61 moves toward the side wall 1b, with the scraper 62 lifted.

The shape of the slanting wall face 65 is designed such that the highest portion; namely, the foam recovery pit 40 side, is higher than the maximum water level (for example, the water level at high tide) of the used seawater flowing in the seawater oxidation treatment system 1. :

[0050]

Such a foam recovery device includes the foam recovery pit disposed near the seawater oxidation treatment system, the focam-holding member crossing the seawater oxidation treatment system so as to block the path of seawater from under the water to a predetermined position above the water surface while leaving a bottom portion of the seawater oxidation .. treatment system, and a foam recovery portion for recovering the foam dammed by the foam-holding member from the water surface in the foam recovery pit. Therefore, the flowing foam that floats on the water surface can be dammed by the foam- holding member, and the dammed foam can be reliably recovered in the fcam recovery pit by the foam recovery portion.

[0051]

A second modification of the above-described scraper 60 will now be described with reference to Figs. 186A and 16B. In this second modification, a rotary scraper 67 that rotates on an arc-shaped wall 66 extending upward from a side wall la of the seawater oxidation treatment system 1 toward the foam recovery pit 4C is employed.

The rotary scraper 67 includes a plurality of arms 70 radiating out from a rctary shaft 69 that is connected to a driving device 68 including, for example, an electric motor and a reduction gear. The top end of each arm 70 1s attached with a scraper 71.

[0052]

The arc-shaped wall 66 in this case is basically equivalent to the above-described slanting wall face 65, but has a shape that can maintain a predetermined positional relation with the scrapers 71 that can be rotationally moved along the wall face, without disturbing the rotation of the rotary scraper 67. The scrapers 71 in this case are preferably provided with, for example, brushes at the top ends.

Therefore, the foam held by the curtain wall 53 flows toward the arc-shaped wall 66 by driving the rotary scraper 67. The rotating scrapers 71 sequentially transfer used seawater together with the foam toward the foam recovery pit 40. The foam is separated from the used seawater at the arc- shaped wall 66 and then falls in the foam recovery pit 40 to be recovered. On the other hand, the used seawater separated from the foam flows down along the arc-shaped wall 66 toward the seawater oxidation treatment system 1 to be returned thereto.

[0053]

In such a configuration, fecam floating and remaining on the water surface is scraped by the rotating scrapers 71 and can be transferred to the foam recovery pit 40 to be recovered. In this case, since the arc-shaped wall 66 is employed, the rotation of the rotary scraper 67 is not disturbed, and the foam can be separated from used seawater and recovered.

In this embodiment and moedifications, the foam-holding member 50D and the curtain wall 53 are arranged so as to be orthogonal to the seawater oxidation treatment system 1.

However, for example, as a third modification shown in Fig. 17, an inclined curtain wall 53' for leading foam to the overflow dam 30 may be employed.

In this embodiment and modifications, the foam-holding member 50D and the curtain wall 53 are arranged so as to be orthogonal to the seawater oxidation treatment system 1.

However, for example, as a fourth modification shown in Fig. 18, an oil fence 50C may be employed.

[0054]

The rotary scraper 67 of the above-mentioned second modification may be rotationally driven by the hydraulic power of used seawater flowing in the seawater cxidation treatment system 1, for example, as in a fifth modification shown in

Fig. 19, instead of a driving source such as an electric motor. That is, as the rotary scraper 67' shown in the drawing, a hydraulic turbine 72 may be installed in the oo seawater oxidation treatment system 1 and rotated by the flow of used seawater to give a driving force, resulting in a reduction in energy consumption.

Reference numeral 73 in the drawing denotes a gear box for reducing the rotational velocity of the hydraulic turbine 72 and transmitting the rotary power to the rotary scraper 67".

[0055] [Fourth embodiment]

A fourth embodiment of the foam recovery device of the present invention will now be described with reference to the drawings. The same portions as those in the above-described embodiments are deslgnated with the same reference numerals, and detailed descriptions thereof are omitted.

A foam recovery device 20C shown in Figs. 20A and 20B is an ejector recovering foam by sucking the foam from a suction port 80 floating on the water surface into the foam recovery pit 40.

[0056]

The suction port 8C floats by means of a buoyant force applied to floats 81 in the state that a suction opening 80a opens downward, while maintaining a predetermined distance from the water surface. In the configuration example shown in the drawings, arms 82 radiating out from the suction port 80 in four directions are bent downward, and the top ends of the arms 82 are provided with the floats 81. Accordingly, a gap from the water surface to the suction port 80 is formed by the bent portions of the arms 82, and the suction port 80 can float stably on the water surface.

A pipe 83, such as a piping or a hose, is connected to the above-described suction port 80, and an ejector 84 disposed in the foam recovery pit 40 is connected to the pipe 83.

[0057]

The ejector 84 is a device for sucking foam by sending alr to an ejector tube 86 from a blowing device 85, such as a compressor or a blower, to generate a negative pressure at a pipe outlet 83a opening in the ejector tube 86. In the configuration shown in the drawings, the outlet 86a of the ejector tube 86 opens downward inside the foam recovery pit 40, and the pipe 83 is concentrically arranged in the ejector tube 86 at the portion extending downward.

Therefore, air sent from the blowing device 85 blows in the ejector tube 86 at high speed, thereby generating a negative pressure in the pipe outlet 83a and in the pipe 83.

Consequently, foam below the suction port 80 and at the vicinity thereof is sucked and recovered into the foam recovery pit 40 through the pipe 83. As a result, the foam 4 floating on the water surface is separated from the used seawater and can be recovered in the foam recovery pit 40.

In this embodiment, though it is not shown in the drawings, a sensor detecting the height of foam on the seawater surface is installed, and the blowing device 85 may be driven according to the foam accumulation status. By doing so, a reduction in energy consumption can be achieved.

[0058] [Fifth embodiment]

A fifth embodiment of the foam recovery device of the present invention will now be described with reference to the drawings. The same portions as those in the above-described embodiments are designated with the same reference numerals, and detailed descriptions thereof are omitted.

A foam recovery device 20D shown in Figs. 21A and 21B is a conveying device having a mesh belt 91 provided with a squeezing roller 90 above the foam recovery pit 40. This foam recovery device 20D recovers the foam dammed on the water surface which is dammed by, for example, the foam-collecting float 50 or the oil fence 50C of the above-described embodiments.

[0059]

This mesh belt 91 is a fine-meshed net belt allowing used seawater to pass through. The conveying device rotates thismesh belt 91 clockwise and includes a first roller 92 positioned approximately on the water surface, a second reller 93 located roughly above the side wall la constituting the seawater oxidation treatment system 1, a third roller 94 located above the foam recovery pit 40, a guide roller 95 located under the second roller 92, and a driving mechanism (not shown). In this case, the height positions of the first roller 92, the second roller 93, and the third roller 94 are determined such that the belt conveying from the first roller 92 to the second roller 93 is an upward belt, and the belt conveying from the second roller 93 to the third roller 94 is a downward belt. The member indicated by reference numeral 26 in the drawing is a seawater guide. Each roller is opticnally provided with an auxiliary roller.

[0060]

When the conveying device with the above-menticned configuration is driven, since the first roller 92 is positioned approximately on the water surface, the mesh belt 91 passing through this first roller 92 and running upward collects and transfers the foam floating on the water surface.

On this occasion, used seawater, as well as foam, adheres to the mesh belt 21, but this used seawater passes through the mesh belt 91 and falls into the seawater oxidation treatment system 1 while being conveyed toward the second roller 93.

During the downward running of the belt from the second roller 93 to the third roller 94, relatively large foam adhering to the mesh belt 91 freely falls into the foam recovery pit 40 for recovery. Relatively small foam that cannot freely fall is removed from the mesh belt 91 when it passes through the squeezing roller 90, and the foam falls into the foam recovery pit 40 for recovery.

[0061]

In addition, since the seawater guide 96 inclined such that the seawater oxidation treatment system 1 side is lower than the foam recovery pit 40 side is disposed above the side wall la, the used seawater that falls from the mesh belt 91 passing through above the seawater guide 96 returns reliably to the seawater oxidation treatment system 1, without falling in the foam recovery pit 40.

The foam recovery device 20D having the above-mentioned configuration can also recover the foam 4 floating on the water surface by separating it from the used seawater.

Furthermore, this foam recovery device Z0D does not need the : overflow dam 30.

[0062] :

In the conveyer device described above, for example, as shown in Fig. 22, in a possible modification, the third roller 24 for letting the mesh belt 91 run downward is omitted. The transfer path is not particularly limited, and various a1 modifications are possible.

[0063]

As described above, in the foam recovery device cf the present invention, the foam 4 can be removed by appropriately separating and recovering it from the surface of the used seawater drained from a desulfurization tower and flowing in the seawater oxidation treatment system 1 for draining the used seawater away. Accordingly, only the used seawater, that is, not containing the foam 4, can be drained into the surrounding sea area. As a result, the problems of scenery destruction and environmental pollution caused by foam 4 floating on the water surface can be solved. Furthermore, the foam 4 collected by the foam-collecting device described in each embodiment can be transferred to the foam treatment device 13 and then dehydrated and dried to be separated into a foam component and a seawater component, as described in the first embodiment.

The present invention is not limited to the aforementioned embodiments and can be variously modified within the scope of the present invention.

Claims

1. A foam recovery device installed in a seawater oxidation treatment system for draining used seawater discharged from a desulfurization tower of an exhaust gas desulfurizer using seawater as an absorbent and configured to recover foam floating on the surface of the used seawater by removing the foam, wherein a foam recovery pit is disposed so as to be connected via an overflow dam formed in a side face of the seawater oxidation treatment system, and a feoam-collecting float that is held floating so as to cross the seawater oxidation treatment system is disposed to separate the foam flcating on the surface and a surface seawater flow from the main flow of the used seawater and to lead the foam and the surface seawater flow to the foam recovery pit.

2. The foam recovery device according to Claim 1, comprising a return path that connects the foam recovery pit and the seawater oxidation treatment system and returns at least part of the collected seawater to the seawater oxidation treatment system by separating the collected seawater from the foam.

3. The foam recovery device according to Claim 1 or 2, wherein the overflow dam includes a mechanism for varying the dam height.

4. The foam recovery device according to any one of Claims 1 to 3, wherein the side face in which the overflow dam is formed is a slanted surface that intercepts the flow of used seawater flowing in the seawater oxidation treatment system.

5. A foam recovery device installed in a seawater oxidation treatment system for draining used seawater discharged from a desulfurization tower of an exhaust gas desulfurizer using seawater as an absorbent and recovering foam floating on the surface of the used seawater by removing the foam, the foam recovery device comprising: a foam recovery pit disposed near the seawater oxidation treatment system; a foam-holding member crossing the seawater oxidation treatment system sc as to block the path of seawater from under the water to a. predetermined position above the water surface while leaving a bottom portion of the seawater oxidation treatment system; and a foam recovery portion for recovering the foam dammed by the foam-holding member from the water surface into the foam recovery pit.

6. The foam recovery device according to Claim 5, wherein the foam recovery portion includes a transfer portion that can reciprocate across the seawater oxidation treatment system and a scraper suspended from the transfer portion so as to be vertically movable.

7. The foam recovery device according to Claim 6, wherein the foam recovery portion includes a slanting wall face having a height increasing from the side wall of the seawater oxidation treatment system toward the foam recovery pit.

8. The foam recovery device according to Claim 5, wherein the foam recovery portion is a rotary scraper that rotates on an arc-shaped wall extending upward from a side wall of the seawater oxidation treatment system to the foam recovery pit.

9. The foam recovery device according to Claim 8, wherein the rotary scraper is rotationally driven by the hydraulic power of the used seawater flowing in the seawater oxidation treatment system.

10. The foam recovery device according to Claim 5, wherein the foam recovery portion is an ejector recovering foam by sucking the foam from a suction port floating on the water surface into the foam recovery pit.

11. The foam recovery device according to Claim 5, wherein the foam recovery portion is a mesh belt conveyor having a squeezing roller above the foam recovery pit.

12. A foam recovery system employing a foam recovery device installed in a seawater oxidation treatment system for draining used seawater discharged from a desulfurization tower of an exhaust gas desulfurizer using seawater as an absorbent and configured to recover foam floating on the surface of the used seawater by separating and removing the foam from the used seawater, the foam recovery system comprising:

a foam recovery device according to any one of Claims 1 to 11;

a foam treatment device for dehydrating and drying the foam recovered by the foam recovery device; and a suction and conveying device for sucking the foam recovered in the foam recovery pit and transferring the foam to the foam treatment device through a channel.