Exhaust gas treating tower

Provided is an exhaust gas treating tower in which exhaust gas flow velocity is increased more than a prior art case so that exhaust gas treating efficiency can be enhanced or the exhaust gas treating tower can be made compact if equivalent performance is to be maintained. Also, an exhaust gas treating tower ensuring a liquid recovery is provided. In an exhaust gas treating tower 10A, liquid columns C are generated and also a liquid drop generating member 20 is provided to thereby generate liquid drops M therearound to be floated. Also, liquid is spouted from spray nozzles to thereby generate liquid films F in area different from the liquid columns C. In an exhaust gas treating tower 110, a liquid drop eliminator 120 is provided upstream of a mist eliminator 118. Interval P1 of collecting plates 121 of the liquid drop eliminator 120 is made larger than interval P2 of collecting plates 119 of the mist eliminator 118. Thereby, liquid drops having larger particle diameter contained in the exhaust gas are collected by the liquid drop eliminator 120.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an exhaust gas treating tower that is provided in various kinds of plants, boilers or the like.

2. Description of the Prior Art

In order to remove sulfur oxides (SO2) contained in the exhaust gas of various kinds of plants, boilers or the like, an exhaust gas treating tower of gas-liquid contact type is often used.

In the exhaust gas treating tower of this type, what is called a liquid column type is known in which absorbing liquid of the sulfur oxides is upwardly spouted in a column shape, as is known by the Japanese laid-open utility model laid-open application 1984-53828 (FIG. 1), for example. As shown inFIGS. 31 and 32here, in such an exhaust gas treating tower1of liquid column type, the exhaust gas is introduced from an inlet port2formed in a lower side portion of the exhaust gas treating tower1. While this exhaust gas is flowing up toward an outlet port3formed in an upper portion of the tower, it makes contact with liquid columns C spouted in the column shape and thereby the sulfur oxides contained in the exhaust gas is removed.

In the exhaust gas treating tower of liquid column type so constructed, fine liquid drops (generally called a mist) are contained in the exhaust gas that has made contact with the liquid columns C to be discharged from the outlet port3and in order to recover the mist, there is provided an eliminator5(FIG. 31) or a mist eliminator6(FIG. 32) at the outlet port3.

In the above-mentioned exhaust gas treating tower1of liquid column type, in order to enhance the exhaust gas treating efficiency (treating quantity per unit time), it is necessary to make a large size plant or to increase the exhaust gas flow velocity. However, needless to mention, to make a large size plant is usually not preferable. Thus, to make the exhaust gas flow velocity higher than the present situation is considered. But in the conventional exhaust gas treating tower1, as shown inFIG. 9, if the gas flow velocity is increased beyond a certain level, while the sulfur oxides cannot be sufficiently removed by the liquid columns C, the exhaust gas passes through the tower to be blown off outside as it is. Thus, there is a problem that the exhaust gas treating efficiency is hardly enhanced.

Also, in the example shown inFIG. 32, there will be caused a problem that while the liquid drops in the exhaust gas cannot be sufficiently recovered by the mist eliminator6, the liquid drops together with the exhaust gas pass through the mist eliminator6to be discharged outside.

Here, as the exhaust gas flowing upward from below makes gas-liquid contact with the liquid columns C, the liquid drops generated in the vicinity of the liquid columns C receive an upward resisting force by the exhaust gas flow. According to the balance between the gravity force corresponding to the weight (diameter) of the liquid drops and the resisting force of the upwardly flowing exhaust gas (air resisting force), the liquid drops having a weight (diameter) beyond a certain level are entrained with the exhaust gas flow to move up toward the mist eliminator6in the exhaust gas treating tower1.

At this time, if the flow velocity of the exhaust gas becomes higher, the upper limit of the diameter of the liquid drops moving up in the exhaust gas treating tower1becomes correspondingly larger and the quantity of the upwardly moving liquid drops also increases as a whole. Thus, the quantity of the liquid drops that must be collected in the mist eliminator6increases and the quantity of the liquid sticking to surfaces of collecting plates6aof the mist eliminator6also increases.

On the other hand, while the flow velocity of the exhaust gas is high, the liquid sticking to the surfaces of the collecting plates6ais again scattered by the exhaust gas, resulting in that the liquid passes through the mist eliminator6.

When the exhaust gas treating tower1is to be designed, a flow velocity of the exhaust gas at a steady operation time is set and, based on the so set exhaust gas flow velocity, the diameter of the liquid drops that move up in the exhaust gas treating tower1together with the exhaust gas is obtained and the mist eliminator6is designed so that the liquid drops of the so obtained diameter can be securely collected.

Nevertheless, in the exhaust gas treating tower1, the exhaust gas flow is not always uniform but due to various causes, the flow often becomes unsteady and the flow velocity becomes also different according to the place. For this reason, actually, there often exists such an area where the exhaust gas flows at a velocity higher than the designed flow velocity of the steady operation time. In this area, the liquid drops of a diameter larger than a presumed diameter at the time of design move up toward the mist eliminator6together with the exhaust gas and this likewise results in that the liquid is not sufficiently collected by the mist eliminator6but passes therethough.

SUMMARY OF THE INVENTION

In view of the above-mentioned technical problems in the prior art, it is an object of the present invention to provide an exhaust gas treating tower by which the exhaust gas treating efficiency is enhanced by increasing the exhaust gas flow velocity more than the prior art case.

Also, it is an object of the present invention to provide an exhaust gas treating tower by which liquid can be securely recovered.

With the above objects in mind, the inventors here have carried out extensive studies and obtained the following observations.

That is, in the exhaust gas treating tower1, there are provided a plurality of nozzles4that spout the liquid to form the liquid columns C and the liquid spouted in the column shape from the respective nozzles4spreads sideward at the top position of the column shape and then flows down. Thus, between the liquid columns C spouted from the plurality of nozzles4, there are generated a rich area and a lean area of the liquid in the same one plane. As the exhaust gas flowing upward from below makes contact with the liquid columns C and the liquid drops in the surroundings of the liquid columns C so that the sulfur oxides are removed, the exhaust gas receives a resisting force by making contact with the liquid columns C and the liquid drops. If the flow velocity of the exhaust gas is increased, the resisting force given by the liquid columns C and the liquid drops becomes insufficient at the lean area of the liquid generated between the mutually adjacent nozzles4,4and this is presumed as the reason why such a phenomenon is caused that the exhaust gas is blown off outside as it is and the sulfur oxides cannot be sufficiently removed.

Thus, in the present invention, an exhaust gas treating tower comprising a tower body in which exhaust gas introduced from below is discharged outside from above is characterized in that the exhaust gas treating tower comprises a first substance removing portion that generates liquid columns in the tower body by spouting liquid upward from below in a column shape so that, by the exhaust gas making contact with the liquid columns, a substance contained in the exhaust gas is removed and a second substance removing portion that is provided in an area different from the liquid columns generated in the first substance removing portion so that, by the exhaust gas making contact with the liquid, the substance contained in the exhaust gas is removed.

In the exhaust gas treating tower constructed as mentioned above, the exhaust gas introduced from below of the tower body makes contact with the liquid columns in the first substance removing portion so that the substance contained in the exhaust gas is removed and further makes contact with the liquid in the second substance removing portion, that is provided in the area different from the liquid columns generated in the first substance removing portion, so that the substance contained in the exhaust gas is further removed.

It will be most preferable if the exhaust gas treating tower is constructed such that an inlet port of the exhaust gas is provided in a side wall of the tower body below both of the first and second substance removing portions.

While the second substance removing portion is provided in the area different from the liquid columns generated in the first substance removing portion, the second substance removing portion concretely can be provided either above or below, or both above and below, the liquid columns in the tower body.

Also, a nozzle that forms a liquid film by spouting the liquid in an umbrella shape may be provided as the second substance removing portion. This nozzle is preferably provided in a plural number and is preferably arranged such that the liquid films generated by the nozzles lap on the liquid films generated by adjacent ones of the nozzles so that no gap is formed therebetween.

Also, the liquid to be spouted from the nozzles may be pressurized by a pump.

These nozzles are preferably provided in a piping that supplies the liquid for generating the liquid columns in the first substance removing portion. Thereby, the piping can be commonly used both for the first and second substance removing portions and reduction of the opening rate in the tower body can be suppressed to the minimum.

A collision member with which the liquid falling down from the liquid columns generated in the first substance removing portion or the liquid films generated by the nozzles collides so that liquid drops are generated may be provided as the second substance removing portion. The collision member can generate the liquid drops, when the liquid falling down from the liquid films generated by the nozzles collides with the collision member. That is, in this case, the second substance removing portion comprises both of the nozzles and the collision member. Also, the liquid drops can be generated, when the liquid falling down from the liquid columns generated in the first substance removing portion collides with the collision member. That is, in this case, the second substance removing portion comprises only the collision member.

Also, the collision member may comprise a wall surface extending in an upward and downward direction of the tower body so that the liquid drops generated by the collision member are retained in the vicinity of the wall surface by friction force with the wall surface.

The exhaust gas treating tower mentioned above may also be characterized in comprising a tower body in which exhaust gas introduced from below is discharged outside from above, a liquid column generating portion that generates liquid columns in the tower body by spouting liquid upward from below in a column shape so that, by the exhaust gas making contact with the liquid columns, a substance contained in the exhaust gas is removed and a liquid column/liquid film generating portion that generates liquid columns and/or liquid films in an area different from the liquid columns so that, by the exhaust gas making contact with the liquid, the substance contained in the exhaust gas is removed.

Also, in the present invention, an exhaust gas treating tower comprising a tower body in which exhaust gas introduced from below is discharged outside from above is characterized in that the exhaust gas treating tower comprises: a liquid supply portion that supplies liquid into the tower body so that, by the exhaust gas making contact with the liquid, a substance contained in the exhaust gas is removed, a first liquid drop collecting portion provided on a downstream side of the liquid supply portion in a flow direction of the exhaust gas so as to collect the liquid drops contained in the exhaust gas that has made contact with the liquid, and a second liquid drop collecting portion provided on the downstream side of the liquid supply portion in the flow direction of the exhaust gas and on an upstream side of the first liquid drop collecting portion so as to collect the liquid drops larger than the liquid drops to be collected by the first liquid drop collecting portion out of the liquid drops contained in the exhaust gas.

The present exhaust gas treating tower may be constructed in any of types but, most preferably, may be constructed, for example, in what is called the liquid column type in which the liquid supply portion generates the liquid columns by spouting the liquid upward from below in a column shape so that, by the exhaust gas making contact with the liquid columns, a substance contained in the exhaust gas is removed.

By providing the second liquid drop collecting portion on the upstream side of the first liquid drop collecting portion, in the upstream second liquid drop collecting portion, the liquid drops larger than the liquid drops to be collected by the first liquid drop collecting portion are collected. Thereby, in the downstream first liquid drop collecting portion, only the liquid drops smaller than the liquid drops collected by the second liquid drop collecting portion are collected.

A concrete construction may be made such that the first liquid drop collecting portion comprises a plurality of first collecting plates arranged inclinedly relative to the flow direction of the exhaust gas with a predetermined pitch being maintained between each of the first collecting plates and the second liquid drop collecting portion comprises a plurality of second collecting plates arranged inclinedly relative to the flow direction of the exhaust gas with a predetermined pitch, larger than the pitch of the first collecting plates, being maintained between each of the second collecting plates.

Here, the pitch of the second collecting plates may be set based on a flow velocity of the exhaust gas at a usual operation time in the tower body. For example, at the usual operation time in the tower body, supposing that the flow velocity of the exhaust gas is 5 m/s, it is preferable that the inclination angle α of the second collecting plates is 28° and the pitch thereof is 100 to 150 mm. In this case, in the second collecting plates, the liquid drops having the particle diameter of approximately 3 mm or more can be collected. Also, in this case, it is preferable that the pitch of the first collecting plates is set to 40 to 60 mm.

The pitch of the second collecting plates may also be set based on a maximum flow velocity of the exhaust gas in the tower body. Thereby, even if the flow of the exhaust gas in the tower body is in an unsteady state, the liquid drops can be sufficiently collected.

According to the present invention, the gas-liquid contact efficiency is enhanced and the exhaust gas treating efficiency can be enhanced. Thus, by increasing the flow velocity of the exhaust gas more than in the prior art case, the performance of the exhaust gas treating tower can be enhanced. Or if the equivalent performance is to be maintained, the exhaust gas treating tower can be made compact to that extent.

Also, according to the present invention, by providing the liquid drop eliminator, the flow velocity of the exhaust gas can be increased or even if there is caused an area where the exhaust gas flow velocity becomes higher than presumed, the liquid can be securely recovered.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Herebelow, the present invention will be described more concretely based on embodiments according to the present invention with reference to the appended drawings.

First Embodiment

FIG. 1is an explanatory cross sectional view of a construction of an exhaust gas treating tower10A of a first embodiment. As shown inFIG. 1, the exhaust gas treating tower10A comprises a tower body11formed, for example, in a duct shape having a rectangular cross sectional shape and has its bottom portion closed by a bottom plate12and its upper portion formed with an opening portion13. Also, in a lower side wall of the tower body11, an inlet port14opens through which exhaust gas is introduced into the tower body11.

There is provided in the tower body11a piping16comprising a plurality of nozzles15. The piping16is supplied with liquid, stored in the bottom portion of the tower body11, pumped up by a pump17. This liquid is spouted upward from the nozzles15to form liquid columns C of a column shape. The plurality of nozzles15are arranged with an appropriately set interval between them so that no gap is generated between the liquid columns C spouted from the mutually adjacent nozzles15.

In the present embodiment, there is provided a liquid drop generating member20at a position below the nozzles15and above the inlet port14in the tower body11.

As shown inFIGS. 2 and 3, the liquid drop generating member20, often called a grid etc., is formed in a grid shape as a whole in which longitudinal plate portions (collision members)21and lateral plate portions (collision members)22are assembled together so as to orthogonally cross each other with predetermined intervals between them. The longitudinal plate portions21and the lateral plate portions22have their respective upper surfaces21a,22aformed in a flat shape having a predetermined width. Also, the longitudinal plate portions21and the lateral plate portions22, respectively, have a predetermined height, so that, in the portions surrounded by the mutually adjacent longitudinal plate portions21,21and lateral plate portions22,22, spaces S are formed.

In the exhaust gas treating tower10A constructed as mentioned above, the liquid spouted upward from the nozzles15forms the liquid columns C and falls down. The liquid so falling down collides with the upper surfaces21a,22aof the liquid drop generating member20to become fine liquid drops M.

While the liquid drops M so generated usually fall down as they are in a floating state, in the present embodiment, there are formed the spaces S in the liquid drop generating member20. Hence, by friction force with the wall surfaces of the longitudinal plate portions21and the lateral plate portions22, the liquid drops M are retained in the floating state longer than usual in the spaces S. It is to be noted, as easily understood, that this phenomenon is the same as that a fluid flow velocity becomes smaller by friction with a wall surface as the fluid approaches nearer to the vicinity of the wall surface along the flow.

Then, the liquid drops M further fall down in the exhaust gas treating tower10A to be stored in the bottom portion.

On the other hand, the exhaust gas introduced substantially horizontally from the inlet port14turns in the exhaust gas treating tower10A to flow upward. Then, the exhaust gas makes contact with the liquid columns C spouted upward from the nozzles15, as a first substance removing portion, so that sulfur oxides in the exhaust gas are absorbed into the liquid and the exhaust gas is discharged outside from the opening portion of the upper position. Also, in the liquid drop generating member20as a second substance removing portion, the fine liquid drops M are generated by the liquid colliding with the upper surfaces21a,22ato be retained in the floating state in the spaces S and the exhaust gas makes contact with the liquid drops M so that the sulfur oxides in the exhaust gas are further absorbed into the liquid drops M.

It is to be noted that, as shown inFIG. 1, there is provided an eliminator18at an upper position of the exhaust gas treating tower10A and the fine liquid drops M remaining in the exhaust gas are removed to be recovered by the eliminator18.

As mentioned above, by the exhaust gas treating tower10A being provided with the liquid drop generating member20, not only the liquid columns C are formed but also the liquid drops M of the floating state can be generated in the vicinity of the liquid drop generating member20. Thereby, the liquid drops M are caused to exist in the area of the exhaust gas treating tower10A where there has been no gas absorbing liquid in the prior art case and this results in enhancing the removing performance of the sulfur oxides.

Also, as the exhaust gas receives resisting force by making contact with the liquid columns C and the liquid drops M, as compared with the case of only the liquid columns C in the prior art, the resisting force can be increased as a whole by the existence of the liquid drops M and thereby the gas-liquid contact efficiency can be enhanced. Thus, even if the flow velocity of the exhaust gas is increased more than the conventional case, the boundary flow velocity by which the exhaust gas is blown off as it is can be enhanced and the sulfur removing performance of the exhaust gas treating tower10A can be remarkably enhanced. Also, if the same or equivalent performance is to be obtained, the exhaust gas treating tower10A can be made smaller than the conventional case to the extent that the flow rate of the exhaust gas is increased.

In the present embodiment, while the liquid drop generating member20is arranged below the nozzles15, as shown inFIG. 4, such a construction can be employed as to arrange the liquid drop generating member20above the liquid columns C generated by the nozzles15. Also, it is a matter of course that the liquid drop generating members20can be arranged both above and below the nozzles15.

In case the liquid drop generating member20is arranged above the liquid columns C, the liquid drops M generated at the liquid columns C and entrained with the exhaust gas flowing upward are retained in the spaces S of the liquid drop generating member20. Hence, the sulfur oxides removing effect of the exhaust gas and the resisting force giving effect against the flow of the exhaust gas can be obtained.

Second Embodiment

Next, an example in which an exhaust gas treating tower10B is additionally provided with spray nozzles30will be described. It is to be noted that, as the basic construction of the exhaust gas treating tower10B is the same as the above-mentioned first embodiment, designation by the same reference numerals is employed and description thereof will be omitted.

As shown inFIG. 5, the exhaust gas treating tower10B comprises a piping31provided with the plurality of spray nozzles30at a position below the nozzles15and above the inlet port14in the tower body11.

A pressure elevating pump33is connected to the piping31so that pressure of the liquid pumped up by the pump17from the bottom portion of the tower body11is further elevated. It is to be noted that, without providing the pump17and the pressure elevating pump33in two stages, such a construction can be employed as to pump the liquid up from the bottom portion of the tower body11only by the pressure elevating pump33. In this case, the pressure elevating pump33preferably elevates the pressure of the liquid higher than the pressure of the pump17. Also, such a construction as to have no pressure elevating pump33but to have only the pump17is possible.

The liquid of which pressure has been elevated by the pressure elevating pump33is spouted from each of the spray nozzles30in an umbrella shape (conical shape) having its entire outer circumferential periphery formed by a continuous liquid film F. The plurality of spray nozzles30are arranged so that the liquid films F spouted in the umbrella shape from the mutually adjacent spray nozzles30lap one on another and no gap between the liquid films F is formed in the tower body11.

In the exhaust gas treating tower10B constructed as mentioned above, the exhaust gas introduced substantially horizontally from the inlet port14turns in the exhaust gas treating tower10B to flow upward. Then, the exhaust gas makes contact with the liquid columns C spouted upward from the nozzles15, as the first substance removing portion, so that the sulfur oxides in the exhaust gas is absorbed into the liquid and the exhaust gas is discharged from the opening portion13of the upper position. Also, the exhaust gas makes contact with the liquid films F spouted in the umbrella shape from the spray nozzles30, as the second substance removing portion, and thereby also the sulfur oxides in the exhaust gas can be absorbed.

As mentioned above, by the exhaust gas treating tower10B being provided with the spray nozzles30, the liquid films F are caused to exist in the area, different from the liquid columns C, of the exhaust gas treating tower10B where there has been no gas absorbing liquid in the prior art case and this results in enhancing the removing performance of the sulfur oxides.

At this time, the spray nozzles30are arranged so that the liquid films F spouted in the umbrella shape from the mutually adjacent spray nozzles30lap one on another and no gap between the liquid films F is formed in the tower body11. Thereby, the liquid is caused to exist even in the portion where the existence of the liquid by forming the liquid columns C is lean. Also, the removing performance of the sulfur oxides in the exhaust gas treating tower10B can be made uniform and also an effect to rectify the flow of the gas can be obtained.

Also, as the exhaust gas receives resisting force by making contact with the liquid columns C and the liquid films F, as compared with the case of only the liquid columns C in the prior art, the resisting force can be increased as a whole by the existence of the liquid films F and thereby the gas-liquid contact efficiency can be enhanced. Thus, even if the flow velocity of the exhaust gas is increased more than the conventional case, the boundary flow velocity by which the exhaust gas is blown off as it is can be enhanced and the sulfur removing performance of the exhaust gas treating tower10B can be remarkably enhanced. Also, if the same or equivalent performance is to be obtained, the exhaust gas treating tower10B can be made smaller than the conventional case to the extent that the flow rate of the exhaust gas is increased.

By the way, in the present embodiment, in addition to the liquid columns C, the liquid films F are formed by the spray nozzles30that spout the liquid of which pressure has been elevated by the pressure elevating pump33. While such a construction is considered as to use no liquid column C but to provide the spray nozzles30in plural stages so that the removal of the sulfur oxides is done only by the liquid films F of the plural stages, in this case, pressure of all the liquid to be spouted must be elevated by the pressure elevating pump33. On the contrary, in the present embodiment described above, by spouting the liquid films F from the spray nozzles30, pressure of only the liquid to be supplied to the spray nozzles30can be elevated by the pressure elevating pump33.

In the present embodiment, while the spray nozzles30are arranged below the nozzles15, as shown inFIG. 6, such a construction can be employed as to arrange the spray nozzles30above the liquid columns C generated by the nozzles15. Also, it is a matter of course that the spray nozzles30can be arranged both above and below the nozzles15.

Third Embodiment

Next, an example in which an exhaust gas treating tower10C is additionally provided with a combination of the liquid drop generating member20and the spray nozzles30will be described. It is to be noted that, as the basic construction of the exhaust gas treating tower10C is the same as the above-mentioned first and second embodiments, designation by the same reference numerals is employed and description thereof will be omitted.

As shown inFIG. 7, the exhaust gas treating tower10C comprises the piping31provided with the plurality of spray nozzles30at a position below the nozzles15and above the inlet port14in the tower body11. Further, the exhaust gas treating tower10C comprises the liquid drop generating member20at a position below the spray nozzles30and above the inlet port14.

In the exhaust gas treating tower10C constructed as mentioned above, the liquid spouted upward from the nozzles15forms the liquid columns C and falls down. The liquid so falling down collides with the upper surfaces21a,22aof the liquid drop generating member20to become the fine liquid drops M.

Also, the liquid of which pressure has been elevated by the pressure elevating pump33is spouted from each of the spray nozzles30in the umbrella shape (conical shape) to form the liquid film F. The liquid that has formed the liquid films F further falls down and collides with the upper surfaces21a,22aof the liquid drop generating member20to become the fine liquid drops M.

The liquid drops M so generated are retained in the floating state in the plurality of spaces S formed in the liquid drop generating member20.

Then, the liquid drops M further fall down in the exhaust gas treating tower10C to be stored in the bottom portion.

In the above-mentioned exhaust gas treating tower10C, the exhaust gas introduced substantially horizontally from the inlet port14turns in the exhaust gas treating tower C to flow upward. Then, the exhaust gas makes contact with the fine liquid drops M retained in the floating state in the spaces S of the liquid drop generating member20as the second substance removing portion and also makes contact with the liquid films F spouted in the umbrella shape from the spray nozzles30likewise as the second substance removing portion as well as with the liquid columns C spouted upward from the nozzles15as the first substance removing portion. Thereby, the sulfur oxides in the exhaust gas are absorbed into the liquid and then the exhaust gas is discharged outside from the opening portion13of the upper position.

As mentioned above, by the exhaust gas treating tower10C being provided with the liquid drop generating member20and the spray nozzles30, the liquid drops M and the liquid films F are caused to exist in the area of the exhaust gas treating tower10C where there has been no gas absorbing liquid in the prior art case and this results in enhancing the removing performance of the sulfur oxides.

Also, as the exhaust gas receives resisting force by making contact with the liquid columns C, the liquid films F and the liquid drops M, as compared with the case of only the liquid columns C in the prior art, the resisting force can be increased as a whole by the existence of the liquid films F and the liquid drops M and thereby the gas-liquid contact efficiency can be enhanced. Thus, even if the flow velocity of the exhaust gas is increased more than the conventional case, the boundary flow velocity by which the exhaust gas is blown off as it is can be enhanced and the sulfur removing performance of the exhaust gas treating tower10C can be remarkably enhanced. Also, if the same or equivalent performance is to be obtained, the exhaust gas treating tower10C can be made smaller than the conventional case to the extent that the flow rate of the exhaust gas is increased.

By the way, in the present embodiment comprising both of the liquid drop generating member20and the spray nozzles30, as compared with the first embodiment comprising only the liquid drop generating member20and the second embodiment comprising only the spray nozzles30, the liquid of the liquid films F formed by the spray nozzles30collides with the upper surfaces21a,22aof the liquid drop generating member20to become the liquid drops M. Hence, the quantity of generation of the liquid drops M becomes more than that of a case of simple combination. Therefore, the above-mentioned effect of the exhaust gas treating tower10C of the present embodiment becomes further remarkable.

In the present embodiment, while the liquid drop generating member20and the spray nozzles30are arranged below the nozzles15, as shown inFIG. 8, such a construction can be employed as to also arrange the same ones above the liquid columns C formed by the nozzles15. Also, it is a matter of course that none of the liquid drop generating member20and the spray nozzles30is arranged below the nozzles15but they can be arranged only above the liquid columns C.

Here, various tests to evaluate the performance of the exhaust gas treating towers10A,10B and10C of the first to the third embodiments have been carried out and the results are shown below:

The exhaust gas treating tower10A of the first embodiment shown inFIG. 1, the exhaust gas treating tower10B of the second embodiment shown inFIG. 5and the exhaust gas treating tower10C of the third embodiment shown inFIG. 7as well as the prior art exhaust gas treating tower1, for comparison purpose, shown inFIG. 31are used for the tests. Where the SO2density at the tower inlet (inlet port14) is 2700 ppm D and the liquid for the sulfur removal is of NH3concentration of 270 m mol/l and calcium carbonate concentration of 115 m mol/l, the relation between the gas velocity and the SO2density at the outlet (opening portion13) of the exhaust gas treating tower10is investigated. At this time, in the prior art exhaust gas treating tower1and the exhaust gas treating tower10A of the first embodiment comprising only the liquid drop generating member20, the circulation flow rate of the liquid is 304 m3/(m2×h). In the exhaust gas treating tower10B of the second embodiment comprising only the spray nozzles30and the exhaust gas treating tower10C of the third embodiment comprising both of the liquid drop generating member20and the spray nozzles30, the circulation flow rate of the liquid for generating the liquid columns C is 274 m3/(m2×h) and the flow rate of the liquid supplied into the spray nozzles30is 59 m3/(m2×h).

As the result thereof, as shown inFIG. 9, as compared with the prior art exhaust gas treating tower1, in the exhaust gas treating towers10A,10B and10C, the flow velocity of the gas at which the SO2density at the outlet becomes high (this is called a boundary flow velocity) is greatly enhanced. Especially, in the exhaust gas treating tower10C of the third embodiment comprising both of the liquid drop generating member20and the spray nozzles30, as compared with the exhaust gas treating tower10A of the first embodiment comprising only the liquid drop generating member20and the exhaust gas treating tower10B of the second embodiment comprising only the spray nozzles30, the boundary flow velocity is high.

Also, the relation between a flow rate of a downflow liquid per unit cross sectional area (this is called a unit flow rate) of the liquid column C and the gas flow velocity (boundary flow velocity) is investigated.

As the result thereof, as shown inFIG. 10, it is understood that, if the unit flow rate of the liquid is of the same conditions, as compared with the prior art exhaust gas treating tower1, in the exhaust gas treating towers10A,10B and10C, the boundary flow velocity is greatly enhanced.

Further, the relation between the unit flow rate of the liquid column C and the sulfur removing rate is investigated.

As the result thereof, as shown inFIG. 11, if the unit flow rate of the liquid is of the same conditions, as compared with the prior art exhaust gas treating tower1, in the exhaust gas treating towers10A,10B and10C, the sulfur removing rate is greatly enhanced. That is, if the flow rate is the same, the absorbing capacity coefficient is enhanced by 10% (in the case of the exhaust gas treating tower10B) to 30% (in the case of the exhaust gas treating towers10A and10C). Thus, it is understood that, as compared with the prior art exhaust gas treating tower1, the sulfur removing performance is enhanced by 1.1 to 1.3 times.

Fourth Embodiment

Next, an example in which, like in the above-mentioned second embodiment, an exhaust gas treating tower10D is additionally provided with spray nozzles30will be described. It is to be noted that, as the basic construction of the exhaust gas treating tower10D is the same as the above-mentioned first embodiment, designation by the same reference numerals is employed and description thereof will be omitted.

As shown inFIG. 12, the exhaust gas treating tower10D comprises the plurality of spray nozzles30at a position below the nozzles15and above the inlet port14in the tower body11.

Here, as the difference in the construction from the exhaust gas treating tower10B of the above-mentioned second embodiment in which the spray nozzles30are provided in the piping31that is separate from the piping16in which the nozzles15are provided, in the exhaust gas treating tower10D of the present embodiment, the spray nozzles30are provided in the piping16in which the nozzles15are provided.

InFIGS. 13 to 15, examples of detailed structures by which the spray nozzles30are fitted to the piping16are shown, wherein each ofFIGS. 13 to 15comprises (a) as a front view and (b) as a cross sectional view at the position of arrows of (a).

In the exhaust gas treating tower10D-1ofFIG. 13, the piping16is provided with flange members40, projecting upward, to which the nozzles15are fitted. Also, the piping16is provided with flange members41projecting substantially horizontally. The flange members41are fitted with the spray nozzles30that downwardly spout the liquid in the umbrella shape so as to form the liquid films F. Here, each of the flange members41can be appropriately arranged so that, for example, one flange member41corresponds to two or three nozzles15.

In case the spray nozzles30are provided to be added to an existing exhaust gas treating tower so that the exhaust gas treating tower10D-1is realized, the flange members41are fitted to the piping16and the spray nozzles30are fitted to the flange members41.

In the exhaust gas treating tower10D-2ofFIG. 14, the piping16is provided with the flange members40, projecting upward, to which the nozzles15are fitted and also is provided with flange members42likewise projecting upward. The flange members42are fitted with extension pipes43that have their distal end portions fitted with the spray nozzles30. The extension pipes43are formed in a bent shape and arranged so as to maintain an attitude and position of the spray nozzles30such that the liquid is spouted downward from the spray nozzles30and yet the spouted liquid does not interfere with the piping16. Here, each of the flange members42can be arranged, for example, at a mid position between the mutually adjacent two nozzles15of a pair so that one flange member42corresponds to two nozzles15.

In case the spray nozzles30are provided to be added to an existing exhaust gas treating tower so that the exhaust gas treating tower10D-2is realized, the flange members42are fitted to the piping16and the extension pipes43and the spray nozzles30are fitted to the flange members42.

In the exhaust gas treating tower10D-3ofFIG. 15, the piping16is provided with the flange members40, projecting upward, to which the nozzles15are fitted and the flange members40are provided with the spray nozzles30via take-off pipes45.

Each of the take-off pipes45has an equivalent inner diameter to the flange member40and comprises a main body portion45ahaving its upper and lower ends fitted with flanges so as to be interposed between the flange member40and the nozzle15and a bifurcating portion45bthat bifurcates sideward from the main body portion45aand has its distal end fitted with the spray nozzle30. The bifurcating portion45bis formed in a bent shape and arranged so as to maintain an attitude and position of the spray nozzle30such that the liquid is spouted downward from the spray nozzle30and yet the spouted liquid does not interfere with the piping16. Here, the take-off pipe45can be arranged so that, for example, one take-off pipe45corresponds to two nozzles15.

In case the spray nozzles30are provided to be added to an existing exhaust gas treating tower so that the exhaust gas treating tower10D-3is realized, the existing nozzles15are detached from the flange members40and then the take-off pipes45are attached and the nozzles15are again fitted to these take-off pipes45and the spray nozzles30are fitted to the distal end portions of the take-off pipes45.

In the constructions shown inFIGS. 12 to 15, the liquid of which pressure is elevated by the pump17passes through the piping16and is spouted from the nozzles15and the spray nozzles30to thereby form the liquid columns C and the liquid films F. Thus, like in the exhaust gas treating tower10B of the above-mentioned second embodiment, by the exhaust gas treating towers10D (10D-1,10D-2,10D-3) being provided with the spray nozzles30, enhancement of the removing performance of the sulfur oxides, enhancement of the sulfur removing performance, etc. become possible.

In the exhaust gas treating towers10A,10B and10C of the first to the third embodiments, there are provided the liquid drop generating member20and/or the piping31to which the spray nozzles30are fitted and, to this extent, the opening rate of the gas path in the exhaust gas treating towers10A,10B and10C is reduced and the pressure loss of the gas is increased.

Contrary to this, in the exhaust gas treating tower10D of the present embodiment, the spray nozzles30are provided in the piping16in which the nozzles15for generating the liquid columns C are provided. Hence, the reduction of the opening rate is suppressed and the pressure loss can be made smaller.

Here, various tests have been done for comparison between the exhaust gas treating towers10D (10D-1,10D-2,10D-3) of the present embodiment and the exhaust gas treating tower10B of the second embodiment shown inFIG. 5and the results are shown below:

In the exhaust gas treating tower10B as well as in the exhaust gas treating towers10D-1,10D-2and10D-3, respectively, the temperature in the tower is 30° C., the flow velocity of the gas is 2.5 to 4.5 m/s, the SO2density at the tower inlet (inlet port14) is 500 ppm D, the liquid for the sulfur removal is of calcium carbonate concentration of 160 m mol/l, the height of spouting of the liquid columns C from the nozzles15is 1 to 5 m and the circulation flow rate of the liquid is 150 to 600 m3/(m2×h).

In the above-mentioned state, the relation between the unit circulation flow rate and the sulfur removing rate and the relation of the pressure loss to the flow velocity of the gas are investigated.

FIGS. 16 and 17show the results of the tests.

As shown inFIG. 16, between the exhaust gas treating towers10D-1,10D-2and10D-3of the present embodiment and the exhaust gas treating tower10B of the second embodiment shown inFIG. 5, it is understood that approximately the same sulfur removing performance is obtained. Also, as shown inFIG. 17, between the exhaust gas treating towers10D-1,10D-2and10D-3of the present embodiment and the exhaust gas treating tower10B of the second embodiment shown inFIG. 5, it is understood that the pressure loss is more largely reduced in the exhaust gas treating towers10D-1,10D-2and10D-3of the present embodiment. That is, in the exhaust gas treating towers10D-1,10D-2and10D-3of the present embodiment, as compared with the exhaust gas treating tower10B of the second embodiment, while the sulfur removing rate is maintained, the pressure loss can be largely reduced.

By the way, at the portions on which the liquid does not directly hit in the exhaust gas treating tower, scales are liable to stick due to the SO2component in the liquid. For example, in the exhaust gas treating towers10A,10B and10C of the first to the third embodiments, there are provided the liquid drop generating member20and/or the piping31to which the spray nozzles30are fitted. Hence, as compared with the exhaust gas treating tower10D (10D-1,10D-2,10D-3), the surface area of the portions on which the liquid does not directly hit is large and the scales easily stick there. If the sticking scales drop, there is a possibility that the below positioned nozzles, pipings or the like may be damaged. In the exhaust gas treating towers10D (10D-1,10D-2,10D-3) of the present embodiment, the spray nozzles30are provided in the piping16and thereby the portions to which the scales may stick can be made minimum and occurrence of the damage can also be suppressed.

Also, in case the spray nozzles30are provided to be added to an existing exhaust gas treating tower so that the exhaust gas treating towers10D-1,10D-2and10D-3are realized, the flange members41, the extension pipes43and the take-off pipes45are fitted to the existing piping16and then the nozzles15can be fitted to them. Also, the spray nozzles30can be fitted to the distal end portions of the take-off pipes45. As compared with the exhaust gas treating towers10A,10B and10C in which the liquid drop generating member20and/or the piping31must be provided and a large scale of installation work is required therefor, an exhaust gas treating tower having less number of parts and less manufacturing cost can be realized with an easy work of installation.

Especially, in case of the exhaust gas treating tower10D-3shown inFIG. 15, only by fitting the take-off pipes45to the existing flange members40to which the nozzles15are fitted, the exhaust gas treating tower10D-3can be realized. Thus, as compared with the exhaust gas treating towers10D-1and10D-2in which welding or the like is required for fitting the flange members41and the extension pipes43, the same effect as mentioned above can be obtained with easy work and less cost.

Also, in the exhaust gas treating tower10D-2shown inFIG. 14, it is likewise possible to fit the extension pipes43and the spray nozzles30to the existing flange members40to which the nozzles15are fitted, but this will not be preferable, because, in that case, the number of the nozzles15for forming the liquid columns C will be reduced.

It is to be noted that, in the present fourth embodiment mentioned above, while the example has been described in which the place and number of installations of the flange members41and the extension pipes43of the exhaust gas treating towers10D-1and10D-2are decided by the relation with the installation positions of the nozzles15, the invention is not limited thereto. Especially, in case an existing exhaust gas treating tower is not modified but the exhaust gas treating towers10D-1and10D-2are newly installed, the flange members41and the extension pipes43may be provided at such positions and in such number that the arrangement of the spray nozzles30can be optimized.

By the way, in the exhaust gas treating towers10A,10B,10C and10D of the first to the fourth embodiments (hereinafter these exhaust gas treating towers are simply referred to as the exhaust gas treating tower10, unless a discrimination is specifically needed.), it is effective if constructions mentioned below are combined therewith:

As shown inFIG. 18, in the portion of the inlet port14of the exhaust gas treating tower10, between a perpendicular inner wall surface10aof the exhaust gas treating tower10and an upper inner surface14aof the inlet port14, an inclined surface portion48having an inclination of a predetermined angle is formed. By this inclined surface portion48, the cross sectional area of the inlet port14is gradually enlarged toward upward as it approaches nearer to the perpendicular inner wall surface10aof the exhaust gas treating tower10.

By forming such inclined surface portion48, at the portion where the flow of the exhaust gas introduced from the inlet port14turns upward, the flow velocity on the inner wall surface side can be increased and thereby a bias flow in the tower body11of the exhaust gas treating tower10can be suppressed.

By combining the inclined surface portion48with each of the above-mentioned embodiments, the flow of the exhaust gas can be made uniform and the above-mentioned effects can be made more remarkable.

InFIG. 19, in front of the inlet port14in the tower body11of the exhaust gas treating tower10, a plurality of rectifying plates50are provided along the direction approximately orthogonal to the flow direction of the exhaust gas supplied from the inlet port14. The rectifying plates50are arranged such that the rectifying plates50that exist nearer to the inlet port14are provided at higher positions so that their heights are different from each other. Also, a flap51is provided projecting inclinedly from the crossing portion of the upper inner surface portion14aof the inlet port14and the perpendicular inner wall surface portion10a.

By the rectifying plates50and the flap51constructed as mentioned above, at the portion where the exhaust gas introduced from the inlet port14turns upward, the exhaust gas is led to the rectifying plates50by the flap51and hit on each of the rectifying plates50to thereby be turned upward. If there are no such rectifying plates50, the higher is the flow velocity of the exhaust gas, the more proceeds the exhaust gas straight toward the perpendicular inner wall surface10bin front of the inlet port14and the more becomes the component that hits on the perpendicular inner wall surface10bto thereby be directed upward. On the contrary, by the flow of the exhaust gas hitting on each of the rectifying plates50to thereby be turned, as mentioned above, the bias flow in the tower body11of the exhaust gas treating tower10can be suppressed. By combining such rectifying plates50with each of the mentioned embodiments, the flow of the exhaust gas can also be made uniform and the above-mentioned effects can be made further remarkable.

Here, various tests for verifying the effect of providing the above-mentioned inclined surface portion48and the rectifying plates50have been carried out and the results thereof are shown below:

In the exhaust gas treating tower10provided with the inclined surface portion48as shown inFIG. 18and the exhaust gas treating tower10provided with the rectifying plates50shown inFIG. 19as well as in the prior art exhaust gas treating tower1shown inFIG. 31, the tests have been done on the same conditions as mentioned above and the relation between the unit flow rate of the liquid and the sulfur removing rate [seeFIG. 20(a)] and the relation between the gas flow velocity and the sulfur removing rate [seeFIG. 20(b)] are investigated.

As the results thereof, as shown inFIGS. 20(a) and20(b), if the unit flow rate of the liquid and the gas flow velocity are of the same conditions, as compared with the prior art exhaust gas treating tower1, it is understood that the sulfur removing rate is enhanced in the exhaust gas treating towers10provided with the inclined surface portion48or the rectifying plates50.

Thus, by providing the inclined surface portion48or the rectifying plates50, the performance of the exhaust gas treating towers10A,10B,10C and10D can be enhanced.

Fifth Embodiment

FIG. 21is an explanatory view of an exhaust gas treating tower100of a fifth embodiment.

As shown inFIG. 21, the exhaust gas treating tower100comprises a tower body111formed in a duct shape having, for example, a rectangular cross sectional shape and has its bottom portion closed by a bottom plate112and its upper portion formed with an opening portion113. Also, in a lower side surface of the tower body111, an inlet port114opens through which the exhaust gas is introduced into the tower body111.

There is provided in the tower body111a piping116comprising a plurality of nozzles115. The piping116is supplied with the liquid, stored in the bottom portion of the tower body111, pumped up by a pump117. This liquid is spouted upward from the nozzles15as a liquid supply portion to form the liquid columns C in the tower body111. The plurality of nozzles115are arranged with an appropriately set interval between them so that no gap is generated between the liquid columns C spouted from the mutually adjacent nozzles115.

In the exhaust gas treating tower100constructed as mentioned above, the exhaust gas introduced substantially horizontally from the inlet port114turns in the exhaust gas treating tower100to flow upward. Then, the exhaust gas makes contact with the liquid columns C spouted upward from the nozzles115so that the sulfur oxides in the exhaust gas are absorbed into the liquid and then the exhaust gas is discharged from the opening portion113of the upper position.

In the present embodiment, the exhaust gas treating tower100is also provided with a mist eliminator (a first liquid drop collecting portion)118and a liquid drop eliminator (a second liquid drop collecting portion)120both at the opening portion113as an exhaust gas discharge port.

The mist eliminator118is such one as is used in the prior art exhaust gas treating tower1and comprises a plurality of collecting plates (a first collecting plate)119for removing fine liquid drops (herein often called a mist) contained in the exhaust gas that has passed through the liquid columns C. These collecting plates119are arranged with a predetermined interval between them and each of the collecting plates119is provided inclinedly with a predetermined angle relative to the flow direction of the exhaust gas. Here, the collecting plates119may be formed in various shapes if they have a surface inclined with a predetermined angle relative to the flow direction of the exhaust gas, such as a zigzag cross sectional shape having a plurality of bent portions119a, a cross sectional shape like an inequality mark having one bent portion only, a simply inclined flat plate shape having no bent portion or the like.

On the other hand, the liquid drop eliminator120is provided below the mist eliminator118, that is, on the upstream side of the mist eliminator118in the flow direction of the exhaust gas. While the liquid drop eliminator120comprises a plurality of collecting plates (a second collecting plate)121like the mist eliminator118, this liquid drop eliminator120is for collecting the liquid drops having a particle diameter larger than the particle diameter of the mist to be collected by the mist eliminator118and the interval between each of the collecting plates121is set larger than the interval of the collecting plates119of the mist eliminator118.

As shown inFIG. 22(a) being a plan view andFIG. 22(b) being a cross sectional elevation both of the liquid drop eliminator120, the liquid drop eliminator120comprises bar-like or pipe-like connecting members122,123arranged at upper and lower positions and a predetermined number of the collecting plates121are fitted to the connecting members122,123with a predetermined interval (pitch) P1being maintained between each of the collecting plates121. Portions121a,121bof each of the collecting plates121to be fixed to the connecting members122,123are arranged substantially in parallel with the axial direction of the tower body111(the flow direction of the exhaust gas) and an inclined portion121C is formed being inclined with an angle α relative to the axial direction of the tower body111between the portions121aand121b.

Here, in the exhaust gas treating tower100of the present embodiment, for example, in order for the liquid drop eliminator120to collect the liquid drops having the particle diameter of 3 mm or more and for the mist eliminator to collect the liquid drops (mist) having the particle diameter of less than 3 mm, it is preferable to set the interval (pitch) P1of the collecting plates121of the liquid drop eliminator120to 100 to 150 mm and an interval (pitch) P2(FIG. 21) of the collecting plates119of the mist eliminator118to 40 to 60 mm.

Such interval P1of the collecting plates121of the liquid drop eliminator120can be obtained as follows, as published by a reference document: “Bubbles Liquid props Dispersion Engineering” by Hioki-Toshimi, Maki Shoten Publishing Co., Oct. 30, 1982.

The principle to collect the liquid drops (including the mist) in the liquid drop eliminator120makes use of an inertia force of the liquid drops. That is, by changing the flow direction of the exhaust gas that flows in one direction by the collecting plates121, the liquid drops, having a specific gravity larger than the exhaust gas, are caused to make a movement different from the exhaust gas to thereby stick to the collecting plates121.

More in detail, where the exhaust gas flows between the collecting plates121,121arranged with equal intervals and the flow direction of the exhaust gas is thereby changed, supposing that the liquid drops in the exhaust gas are moving with a locus having a radius of curvature r, these liquid drops receive a centrifugal force (inertia force) and a resistance due to viscosity of the exhaust gas. In this state, the equation of motion in the radial direction of the liquid drops is approximately as follows:

In the Equation 1, m is a mass of the liquid drop, u is a streamline directional velocity of the exhaust gas, ν is a radial directional moving velocity of the liquid drop and μ is a viscosity of the exhaust gas.

In the Equation 1, if the liquid drop is a fine liquid drop, as the term of acceleration can be neglected, the radial directional moving velocity ν of the mist is as follows:

In the Equation 2, ρLis a density of the liquid drop.

Next, where t is a time for the exhaust gas to be refracted by the angle α, a distance ΔS for the liquid drop to move in the radial direction during the time t is as follows:

Hence, the collecting efficiency η for the liquid drop to collide with the collecting plate121to be collected is as follows:

In the Equation 4, S is a flow path width at the refracting portion of the collecting plate121.

In the minimum liquid drop diameter dminin the case where the liquid drop is collected by 100% (herein this is referred to as a collecting boundary liquid drop diameter), η equals one (η=1) and hence dminis as follows:

The viscosity μ of the exhaust gas and the density ρLof the liquid drop are decided by the kinds of the exhaust gas to be treated and the liquid to be used in the exhaust gas treating tower100. Hence, by deciding one or more of the stream line directional velocity u of the exhaust gas, the operation condition of the exhaust gas treating tower100, the collecting boundary liquid drop diameter dminof the liquid drop to be collected by the liquid drop eliminator120, the angle α by which the flow direction of the exhaust gas is to be changed and the flow path width of the refracting portion of the collecting plate121, the remaining parameters can be decided.

FIG. 23shows the relation between the flow velocity of the exhaust gas and the collecting boundary liquid drop diameter dminthat has been obtained by the theory as mentioned above.FIG. 24(a) is a cross sectional view of the liquid drop eliminator120ofFIG. 22that is schematized for investigating the relation shown inFIG. 23.

InFIG. 24(a), where the angle α by which the flow direction of the exhaust gas is to be changed (that is, the inclination angle α of the collecting plates121) is set to 28° and the interval P1of the collecting plates121is set to 25, 50, 75, 100, 125, 150, 175 and 200 mm, respectively, the collecting boundary liquid drop diameters dmincorresponding to the flow velocity u of the exhaust gas of 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0 and 11.0 m/s, respectively, are obtained.

It is to be noted that the temperature of the exhaust gas is 30° C., the viscosity μ of the exhaust gas is 1.83×10−5kg/m/s, lime water is used as the liquid and the density ρLof the liquid (liquid drop) is 1150 kg/m3.

Also,FIG. 25shows the relation between the flow velocity of the exhaust gas and the collecting boundary liquid drop diameter dminin the case where the same conditions as mentioned above are applied and water is used as the liquid. Here, the density ρLof the liquid (liquid drop) is 998 kg/m3.

As understood fromFIGS. 23 and 25, if the particle diameter (the collecting boundary liquid drop diameter dmin) of the liquid drops that are wanted to be collected and the flow velocity u of the exhaust gas in the exhaust gas treating tower100are set, an optimal interval P1of the collecting plates121can be selected.

As a matter of course, even in the case where the inclination angle α of the collecting plates121is changed, the same relation can be obtained and thereby an optimal interval P1of the collecting plates121can be selected.

Also, as shown inFIG. 24(b), in the case where each of the collecting plates121is formed in a cross sectional shape of an inequality mark shape having one bent portion121donly, the relation between the collecting boundary liquid drop diameter dminand the flow velocity of the exhaust gas in the exhaust gas treating tower100can be likewise obtained and based on this, an optimal interval P1of the collecting plates121can be selected.

FIG. 26shows the relation in the case where lime water is used as the liquid andFIG. 27shows the relation in the case where water is used as the liquid both in the collecting plates121having the cross sectional shape of the inequality mark shape. Here, the inclination angle α of the collecting plates121is set to 45°, that is, each of the collecting plates121is constructed to be bent by the angle of 90° around a bent portion121d[FIG. 24(b)].

Even in the case where the collecting plates121are formed in the inequality mark shape, the particle diameter (the collecting boundary liquid drop diameter dmin) of the liquid drops that are wanted to be collected and the flow velocity of the exhaust gas in the exhaust gas treating tower100are set based on the relation shown inFIGS. 26 and 27and thereby an optimal interval P1of the collecting plates121can be selected.

In the present embodiment, the liquid drop eliminator120shown inFIG. 22, that is, the construction (shape) having the relation shown inFIGS. 23 and 25is employed in which the interval P1of the collecting plates121is set to 200 mm and the inclination angle α of the collecting plates121is set to 28°. On the other hand, the mist eliminator118, that is, the construction (shape) having the relation shown inFIGS. 26 and 27is employed, in which the interval of the collecting plates119is set to 20 mm and the inclination angle α of the collecting plates119having three bent portions119a(FIG. 21) is set to 45°.

The flow velocity u of the exhaust gas is 5 m/s, the temperature of the exhaust gas is 30° C. and the viscosity μ of the exhaust gas is 1.83×10−5kg/m/s. In this state, with respect to the liquid drop eliminator120and the mist eliminator118in the case where lime water and water, respectively, are used as the liquid, the relation between the liquid drop diameter and the collecting efficiency is obtained (As to the mist eliminator118, the above-mentioned liquid drop collecting theory of the liquid drop eliminator120is applied as it is).

FIG. 28shows the relation between the liquid drop diameter and the collecting efficiency, obtained as the result of the above tests. As shown inFIG. 28, in any of the case where lime water or water is used as the liquid, in the mist eliminator118, the collecting efficiency η=1.0 is attained at the liquid drop diameter of approximately 3.00×10−5m (30 μm). If no liquid drop eliminator120is provided but only the mist eliminator118is provided, the mist eliminator118will collect all the liquid drops having the liquid drop diameter larger than this.

On the contrary to this, in the liquid drop eliminator120, in any of the case where lime water or water is used as the liquid, the collecting efficiency η=1.0 is attained at the liquid drop diameter of approximately 1.40×10−4to 1.50×10−4(140 to 150 μm).

Thus, by providing the liquid drop eliminator120on the upstream side of the mist eliminator118, the liquid drops having the liquid drop diameter of approximately 1.40×10−4to 1.50×10−4(140 to 150 μm) or more can be collected by the liquid drop eliminator120and the fine liquid drops having the liquid drop diameter of less than approximately 1.40×10−4to 1.50×10−4(140 to 150 μm) can be collected by the downstream mist eliminator118.

As mentioned above, in the exhaust gas treating tower100, the liquid drop eliminator120is arranged on the upstream side of the mist eliminator118and moreover the liquid drop eliminator120comprises the collecting plates121in which the interval P1between each of the collecting plates121is larger than the interval P2between each of the collecting plates119of the mist eliminator118. By employing such construction, the liquid drops having the larger liquid drop diameter included in the exhaust gas can be collected by the liquid drop eliminator120.

Thereby, in the mist eliminator118, the flow velocity of the exhaust gas can be increased more than in the prior art case. Also, even if the liquid drops having the liquid drop diameter larger than the prior art case move up toward the mist eliminator118, these liquid drops can be collected by the upstream liquid drop eliminator120. Thereby, the load of the mist eliminator118can be alleviated and such a case that the mist cannot be sufficiently collected by the mist eliminator118but the liquid passes through the mist eliminator118as it is can be avoided.

Also, even if there exists an area where the flow velocity becomes locally higher as compared with the flow velocity of the exhaust gas as designed for the exhaust gas treating tower100and the liquid drops having the liquid drop diameter larger than presumed at the designing time move up with the exhaust gas, such liquid drops can be collected by the liquid drop eliminator120and in this case also, the liquid can be prevented from passing through the mist eliminator as it is.

Thus, by providing the liquid drop eliminator120, the liquid can be securely recovered.

Here, tests have been carried out for confirming the effect of the liquid drop eliminator120of the present embodiment.

Test object: Two stages of eliminators, that is, the liquid drop eliminator120on the upstream side and the mist eliminator118on the downstream side, are provided. The liquid drop eliminator120is of the shape shown inFIG. 22in which the interval P1of the collecting plates121is 100 mm and the inclination angle α of the collecting plates121is 28°. On the other hand, the mist eliminator118is of the shape shown inFIG. 21in which the interval P2of the collecting plates119is 40 mm and the inclination angle α of the collecting plates119having three bent portions119ais 45°.

Comparison Object: Two stages of the mist eliminator118having the same shape as the test object are provided. The interval P2of the collecting plates119is 40 mm and the inclination angle α of the collecting plates119having the three bent portions119ais 45°.

Liquid: Lime water

The mist density and pressure are measured on the upstream side (inlet side) and on the downstream side (outlet side) of the liquid drop eliminator120and the mist eliminator118(in the case of the Test Object) and the mist eliminators118(in the case of the Comparison Object).

FIG. 29shows the relation between the inlet side mist density and the outlet side mist density as the result of the tests.

As shown inFIG. 29, in contrast to the Comparison Object having no liquid drop eliminator120, in the Test Object having the liquid drop eliminator120, even if the inlet side mist density is increased, there is no large increase of the outlet side mist density as in the Comparison Object and it is understood that discharge of the liquid outside the exhaust gas treating tower100is suppressed by the liquid drop eliminator120.

Also,FIG. 30shows comparison of the pressure loss between the Test Object and the Comparison Object and it is understood that, regardless of the inlet side mist density, the pressure loss can be suppressed by providing the liquid drop eliminator120having the larger pitch (the interval P1).

It is to be noted that, in the present embodiment, while the interval P1of the liquid drop eliminator120is set corresponding to the flow velocity u of the exhaust gas, the flow velocity of the exhaust gas to be used therefor may be the flow velocity of the exhaust gas of the usual operation time in the tower body111or may be set based on the maximum flow velocity of the exhaust gas in the tower body111. Thereby, even if the flow of the exhaust gas in the tower body111is unsteady, the liquid drops can be sufficiently collected.

Other than mentioned above, to the extent that no deviation is caused from the main object of the present invention, it is possible that the constructions of the above-described embodiments are appropriately combined or modifications thereof are added.