| Title of Invention | SEA WATER FLUE GAS DESULFURIZATION SYSTEM |
|---|---|
| Abstract | ABSTRACT A seawater flue gas desulfurization system is capable of oxidizing wastewater with high efficiency in a short time while preventing an extreme decrease in the concentrations of sulfurous-acid-based materials in the wastewater discharged from a seawater flue gas desulfurization device and a decrease in the pH of the wastewater due to the oxidation treatment. The seawater flue gas desulfurization system has a desulfurization absoration tower 17 that uses seawater as an absorbing solution and a wastewater oxidation tank 20 that oxidizes sulfurous-acid-based materials contained in the wastewater discharged from the desulfurization absorption tower. In the wastewater oxidation tank 20, air is introduced stepwise into the wastewater containing the sulfurous-acid-based materials through at least two stages of air intake nozzles 33, thereby oxidizing the sulfurous-acid-based materials in the wastewater, and seawater is introduced stepwise into the wastewater through at least two stages of seawater injecting ports 26 in time with the stepwise progression of oxidation, thereby diluting the wastewater. |
| Full Text | DESCRIPTION SEAWATER FLUE GAS DESULFURIZATION SYSTEM Technical Field [0001] The present invention relates to a seawater flue gas desulrurization system. Background Art [0002] As an example, power stations may be equipped with flue gas desulfurization devices to absorb and remove sulfur dioxide (S02) from exhaust gas discharged from a coal-fired boiler. Many flue gas desulrurization devices are based on the limestone-gypsum method using calcium carbonate (CaC03) as an absorbent. However, in power stations located near the sea, flue gas desulrurization devices based on the seawater method using seawater as an absorbing solution, which costs less than limestone-gypsum ones, are also used. [0003] Seawater flue gas desulfurization devices remove S02 from exhaust gas by absorption by seawater, and therefore, the seawater used for desulfurization contains high concentrations of sulfurous-acid-based materials including sulfite ion (S032~) , bisulfite ion (HS03") and sulfurous acid (H:S02) . Thus., typicallv, before discharging seawacer L.hai was used for desulfurization into the sea, HSOr and SO/" are oxidized into chemically harmless sulfate ions (HS04~ and S0-_2~) . For example, in "Air Pollution Control Regulatory & Technology Development" by Alain Bill, Alstom, November 17, 2003, p. 35, there is described a technique in which fresh seawater is added co waste-water containing 3022' discharged from a seawater flue gas desulfurization absorption tower, and the mixture of the wastewater and the seawater is subjected to an aeration treatment in an oxidation tank to oxidize S032" to S042~ and to adjust the pH to 5.5 to 6.0 before discharge into the sea. [0004] On the other hand, with regard to the limestone-gypsum flue gas desulfurization device, in Japanese Patent Application Publication No. 2002-210326, there is described a water stream oxidizing apparatus that oxidizes S032" in an alkali absorbing solution into S042~ by mixing part of the alkali absorbing solution, which is removed from a reservoir in a flue gas desulfurization absorption tower, with minute bubbles of air, which is introduced through an air intake pipe attached to the pipe for feeding the alkali absorbing solution at a point downstream of an orifice, when injecting the part of the alkali absorbing solution back into the remaining alkali absorbing solution in the reservoir. Nor.-Patent Document 1: "Air Pollution Ccncrol Regulatory £.- Techr.clcgy Developirien-11 i;y Alain Bill, Alstcm, November 17, 20 0 3, p. 35 Patent Document 1: Japanese Patent Application Laid-open No. 2002-21C326 Disclosure of the Invention [0005] According to the method described in the non-patent Document 1, the wastewater discharged from the flue gas desulfurization absorption tower is mixed and diluted with fresh seawater to prevent dissipation of S02 and increase in pH, and then the mixture is subjected to an aeration treatment in the oxidation tank to oxidize S032" into harmless S04'", increase the pH by decarboxylation, and recover the dissolved oxygen. However, as the oxidation of S032" in the oxidation tank proceeds, the S042" concentration increases, and therefore, the pH in the oxidation tank decreases. If the pH becomes lower than 6, the rate of oxidation rapidly decreases, and the aeration treatment therefore takes longer. The aeration treatment involves a large amount of air blown using a blower, which requires large amounts of power, which is expensive. Thus, there is a problem in that the operation cost significantly increases as the duration of the aeration treatment increases. In addition, if the pH is lower than 6, the equilibrium partial pressure of suij_urcus acid in Lhe seawater is high, and the risk of dissipation of S32 is also high. Even if nhe wastewater from the flue gas desulfurization absorption cower is diluted with a larger amount of seawater in order to maintain a high pK, the problem described above is not solved, because the concentration of £032" to be oxidized significantly decreases, and therefore the rate of oxidation also significantly decreases, and the aeration treatment therefore takes longer. [0006] Thus, in view of the circumstances described above, an object of the present invention is to provide a seawater flue gas desulfurization system capable of oxidizing wastewater with high efficiency in a short time while preventing an extreme decrease of the concentrations of sulfurous-acid-based materials in the wastewater discharged from a seawater flue gas desulfurization device and a decrease of the pH of the wastewater due to the oxidation treatment. [0007] In order to attain the object, according to the present invention, there is provided a seawater flue gas desulfurization system comprising: a seawater flue gas desulfurization device that uses seawater as an absorbing solution, and a wastewater oxidation device that oxidizes a sulfurous-acid-based material contained in wastewater discharged from the seawater flue gas desulfurization device, in which the wastewater oxidation device oxidizes the sulfurous-acid-based material in r.he wastewater bv introducing air into the wascewater containina the sulfurous-acid-based material in at least two stages and dilutes the wastewater by introducing seawater into the wastewater in at least two stages in time with the stepwise progression of oxidation. [0008] In this arrangement, the wastewater is diluted stepwise in time with the stepwise progression of oxidation. Therefore, even if the pH of the wastewater decreases because of the oxidation, the wastewater is diluted with seawater additionally supplied thereto, and the pH immediately increases, so that a predetermined pH can be maintained. In addition, since the wastewater is diluted stepwise in time with the stepwise progression of oxidation, the concentration of the sulfurous-acid-based material in the wastewater does not extremely decrease, although it does decrease gradually. Thus, an abrupt decrease of the rate of oxidation can be prevented, so that the oxidation of the wastewater can be carried out with high efficiency in a short time. [0009] The seawater flue gas desulfurization system according to the present invention preferably further comprises heating means that heats the seawater taken from the sea and feeds the heated seawater to the wastewater oxidation device as the seawater used for dilution. Ir. this arrangement, since -he v.-astewa:er is diluted with the heated seawater, oxidation and dissipation of carbonic acid can be accelerated. [0010] In the seawater flue gas desulfurization system described above, the wastewater oxidation device preferably has plural measuring means for measuring the pH of or the concentration of the sulfurous-acid-based material in the wastewater in the wastewater oxidation device, which are arranged in stages corresponding to the stages of the dilution of the wastewater, and controlling means for adjusting the flow rate of the seawater introduced for dilution in at least two stages based on the values of the pH or the concentration of the sulfurous-acid-based material measured by the measuring means. In this arrangement, since the rate of dilution with seawater can be controlled, an extreme decrease m the concentration of the sulfurous-acid-based material in the wastewater and a decrease in the pH of the wastewater can be reliably prevented. [0011] In the seawater flue gas desulfurization system described above, the wastewater oxidation device is preferably configured so that the superficial velocity of the air introduced for oxidation differs between the at least two stages of introduction of the air for oxidation. In this arrangement, the superficial velocity can be higher in earlier stages at which "he concentration of the sulfurous-acid-based material is higher and can be lower in later stages at which the concentration of the sulfurous-acid-based material is lower and the concentration of dissolved oxygen is higher. Thus, installation and use of an unnecessary aerator can be avoided. [0012] In the seawater flue gas desulfurization system described above, preferably, the wastewater oxidation device has means for introducing a mixed flow of the seawater for dilution and the air for oxidation into the wastewater, so that introduction of the air and introduction of the seawater are carried out simultaneously in each of the stages. In this arrangement, since the seawater containing bubbles of air for oxidation is introduced into the wastewater, the wastewater can be brought into contact with air with a larger contact area, so that the oxygen utilization can be improved. If an arrangement in which the pipe for the seawater used for dilution is provided with an orifice and an intake pipe for air used for oxidation disposed downstream from the orifice is used as the introducing means described above, smaller air bubbles can be produced, so that the oxygen utilization can be further improved. [ 0 013 } -reneraoly, plural means for introducing the mixed flow of the seawater for dilution and the air for oxidation are provided in each stag-e and are arranged in a staggered configuration so that the introduced mixed flows do not overlap each other. In this arrangement, the oxygen utilization can be prevented from decreasing due to combination of air bubbles due to overlap between introduced mixed flows, and the mixed flows can be introduced uniformly over the wastewater oxidizing device. [0014] A.s described above, according to the present invention, there is provided a seawater flue gas desulfurization system capable of oxidizing wastewater with high efficiency in a short time while preventing extreme decreases in the concentrations of sulfurous-acid-based materials in the wastewater discharged from a seawater flue gas desulfurization device and decreases in the pH of the wastewater due to the oxidation treatment. Brief Description of the Drawings [0015] Figure 1 is a schematic diagram showing an embodiment of a seawater flue gas desulfurization system according to the present invention; Figure 2 is a schematic diagram showing another embodiment of a seawater flue gas desulfurization svsuern according to the oresent invention; Figure 3 is a schematic diagram showing another embodiment of a seawater flue gas desulfurization system according to the present invention,- Figure 4 is a schematic diagram showing another embodiment of a seawater flue gas desulfurization system according to the present invention; Figure 5 is a diagram showing an arrangement of water stream oxidizing devices used in the embodiment shown in Figure 4; Figure 6 is a cross-sectional view of the water stream oxidizing device used in the embodiment shown in Figure 4; and Figure 7 includes graphs showing variations of the residual rate of sulfurous acid and the saturation factor of dissolved oxygen in a wastewater oxidation tank. Best Mode for Carrying Out the Invention [0016] In the following, a seawater flue gas desulfurization system according to an embodiment of the present invention will be described with reference to the drawings. Figure 1 is a schematic diagram showing a seawater flue gas desulfurization system according to an embodiment of the present invention. [0017] As shewn in Figure 1, a seawater flue gas desulrunzation system according to this embodiment mainly comprises a coal-fired or oil-fired boiler 10, a seawater desulfurization absorption- tower 17 for removing SOi from the exhaust gas discharged from the boiler by absorption by seawater, and a wastewater oxidation tank 20 for oxidizing the seawater having absorbed S02 discharged from the seawater desulfurization absorption tower with air blown thereto. [0018] The boiler 10 is provided with a steam turbine 11 that is driven by steam produced by the boiler, an electric generator 12 that is driven by the steam turbine to generate electric power, and a steam condenser 13 that cools the steam used for driving the steam turbine by the process of heat exchange with seawater taken from the sea 1 to condense the steam into water. Furthermore, between the boiler 10 and the seawater desulfurization absorption tower 17, there are provided an electric dust collector 14 for separating and collecting dust from the exhaust gas of the boiler, and a blower 15 for feeding the exhaust gas of the boiler to the seawater desulfurization absorption tower 17. [0019] Between the steam condenser 13 and the seawater desulfurization absorption tower 17, there are provided a desulfurizir.g seawater pipe IS and a pump 16 for feeding part or 3he seawater used for cooling steam in the steam condenser 13 to the seawater desulfurization absorption tower 17. Furthermore, in the seawater desulfurization absorption tower 17, there are provided plural spray nozzles for bringing the seawater from the steam condenser, which serves as an absorbing solution, into gas-liquid contact with the exhaust gas of the boiler. At the exhaust gas outlet of the seawater desulfurization absorption tower 17, there is provided a chimney 18 for discharging the desulfurized gas to the atmosphere. Between the seawater desulfurization absorption tower 17 and the wastewater oxidation tank 20, there is provided a wastewater conduit 21 for feeding the seawater having absorbed S02 discharged from the seawater desulfurization absorption tower 17 (hereinafter referred to simply as "wastewater") to one end of the wastewater oxidation tank 20. [0020] The wastewater oxidation tank 20 is designed to flow the wastewater containing S02 from the one end to the other end thereof. At the other end of the wastewater oxidation tank 20, there is provided an outlet pipe 23 for discharging the oxidized wastewater to the sea 1. The size of the wastewater oxidation tank 2 0 depends on the amount of desulfurization, the amount of wastewater of the steam condenser, the alkalinity of the seawater, and the arrangement and piping planning of each plane. j'or example, zhe 'vastev.-axer oxidarion eank 2C can have a width of 10 m, a depth of 3 m, and a length of 300 in. The flow speed of the wastewater flowing through the wastewater oxidation tank 20 ranges from 10 to ISO meters per minute, for example. [0021] The wastewater oxidation tank 20 is provided with a diluting seawater pipe 25 for supplying part of the seawater used for cooling steam in the steam condenser 13 to the wastewater oxidation tank 2 0. The diluting seawater pipe 25 has plural stages of seawater injecting ports 26a to 26n, which are arranged along the direction of the flow of the wastewater so that seawater can be introduced into the wastewater stepwise. The number n of stages of the seawater injecting ports 26 is preferably 2 to 50. The outlet of the diluting seawater pipe 25 is connected to the outlet pipe 23. [0022] At the bottom of the interior of the wastewater oxidation tank 20, an air pipe 32 extends from the side of the inlet for the wastewater to the side of the outlet. Furthermore, the air pipe 32 has plural stages of air blowing nozzles 33a to 33n, which are arranged along the direction of the flow of the wastewater so that air can be blown to the wastewater stepwise. The number n of the stages of the air blowing nozzles 33 and the interval between the air blowing nozzles 33 are determined takina into account the sulfurcus acid ion concentration, the dissolved oxygen concentration, the flow speed, the seawater properties, and the wastewater quality standards to be met at the cutlet to the sea of each plant. The air pipe 3 2 is provided with an oxidizing air blower 31 for feeding atmospheric air to the air blowing nozzles 3 3. [0023] In this arrangement:, first, the boiler 10 makes water supplied from the steam condenser 13 evaporate into steam, the steam turbine 11 is driven by the steam to make the electric generator 12 generate electric power. The steam used in the steam turbine is cooled and condensed into water by the process of heat exchange in the steam condenser 13, and the water is supplied back to the boiler 10. The exhaust gas of the boiler 10 is introduced into the seawater desulfurization absorption tower 17 after the electric dust collector 14 removes dust from the exhaust gas. Part of the seawater heated by steam in the steam condenser 13 is supplied to the seawater desulfurization absorption tower 17 through the desulfurizing seawater pipe 19. In the seawater desulfurization absorption tower 17, the heated seawater, which serves as an absorbing solution, is sprayed into the exhaust gas of the boiler, and S02 in the exhaust gas is absorbed into the seawater so as to be converted into sulfurous-acid-based materials including sulfurous acid !H:£CK) , bisulfite ion (HSCV), and sulfite ion (SG-J~) . The exhaust gas free of SO, is discharged to "he atmosphere through the chimney 18. The seawater having absorbed S02 is discharged from the seawater desulfurization absorption tower 17 and is introduced into the wastewater oxidation tank 20 through the wastewater conduir 21. [0024] At the wastewater inlet of uhe wastewater oxidation tank 20, in addition to the seawater having absorbed S02, that is, the wastewater containing SO-,2', a large amount of seawater heated in the steam condenser 13 is introduced through the first seawater injecting port 26a to dilute the wastewater. The wastewater discharged from the seawater desulfurization absorption tower 17 typically has a low pH. Thus, the pH of the wastewater is raised by the dilution to a value at which oxidation quickly proceeds by aeration (6 or higher, for example). The wastewater discharged from the seawater desulfurization absorption tower 17 typically has a high S032" concentration. Thus, the S032" concentration of the wastewater is lowered by the dilution to a value at which S02 is not dissipated into the gas phase (1.2 mmol/L or less, for example) . However, if the S032" concentration is excessively reduced by the dilution, the rate of the oxidation of SOa2" by aeration decreases, and the oxidation efficiency decreases. Therefore, the S032' concentration of the wastewater is maintained at a value at which nigh oxidation efficiency is ensured (c.5 T^mol/L or higher, for example). [0025] Then, air is blown through the first air blowing nozzle 33a into the wastewater flowing in the wastewater oxidation tank 2 0 to carry ouc an aeration treatment. By chis treatment, 5032~ in the wastewater is oxidized to S04~', which is chemically harmless. Since SO42" is produced, the pH of "he wastewater is lowered. Thus, seawater is introduced through the second seawater injecting port 26b to dilute the wastewater again. 3y this dilution, the pH of the wastewater is raised and maintained at a value at which the oxidation quickly proceeds by aeration described above. As described above, if the S032" concentration is excessively lowered by the dilution, the race of the oxidation decreases. Therefore, the degree of dilution is minimized within a range in which an adequate pH can be achieved. [0026] Then, air is blown through the second air blowing nozzle 33b into the wastewater flowing in the wastewater oxidation tank 20 to carry out an aeration treatment again. By this treatment, S032" in the wastewater is oxidized to S042", which is chemically harmless, and the pH of the wastewater is lowered again. Thus, seawater is introduced through the third seawater injecting port 26c -o dilute the wa stewster again so that high oxidation efficiency is maintained while maintaining a predetermined pH value. Then, air is blown through the third air blowing nozzle 3 3c into the wastewater to cause oxidation of S0;-'. Similarly, introduction of seawater through the fourth to the n-th seawater injecting ports 26d to 26n and air blown through the fourth to the n-th air blowing nozzles 33d to 33n are alternately carried out. The amount of seawater introduced is preferably reduced stepwise. [0027] At the outlet for the wastewater of the wastewater oxidation tank 20, the wastewater whose S032' concentration has been reduced to or below a discharge standard is discharged to the sea 1 through the outlet pipe 23. At the same time, the remaining seawater, which has not been injected into the wastewater through the seawater injecting ports 26, is introduced into the wastewater in the outlet pipe 23 through the end outlet of the diluting seawater pipe 25 and is discharged to the sea 1. Thus, the pH of the wastewater can be improved. [0028] As described above, since plural seawater injecting ports 26a to 26n and plural stages of air blowing nozzles 33a to 33n are arranged along the direction of the flow of the wastewater in the wastewater oxidation tank 20, the wastewater can be diluted in time with the progression of the oxidation of SGV" in the wastewater. Therefore, an extreme decrease of the S0;2" concent rat ion of the wastewater or a decrease of the rate of oxidation due to a decrease of the pH of the wastewater due to the oxidation treatment can be prevented, and therefore, the wastewater can be oxidized with high efficiency. [0023] The present invention is not limited to the embodiment described above, and various modifications are possible. For example, as shown in Figure 2, plural measuring instruments 35a to 35n may be provided along the direction of the flow of the wastewater in the wastewater oxidation tank 20. Furthermore, the seawater injecting ports 26a to 26n may be provided with valves 27a to 27n for adjusting the amount of seawater to be supplied, respectively. Furthermore, there may be provided a control device 37 that communicates with the measuring instruments 3 5a to 3 5n and the valves 27a to 27n to control the flow rate of the seawater introduced through the seawater injecting ports 26a to 26n by opening or closing the valves 27a to 27n based on the measurements obtained by the measuring instruments 35a to 35n. The measuring instruments 35a to 35n are preferably capable of measuring not only the pH and the oxidation-reduction potential (ORP) of the wastewater, but also the dissolved oxygen (DO) . [0030] In the arrangement described above, for example, when the pl-j of the wastewater measured by che fearth measuring instrument 3 5d becomes lower than a predetermined value, the valve 27b on the second seawater injecting port 26b, which is located upstream of the fourth measuring instrument 35d, is opened to increase the amount of seawater uo be supplied. When the ORP of the ■wastewater measured by the second measuring instrument 35b becomes higher than a predetermined value, and the SCh2" concentration significantly decreases, the valve 2 7a at the first seawater inj ecting port 2 6a, which is located upstream of the second measuring instrument 35b, is closed so as to reduce the amount of seawater to be supplied. [0031] As described above, since the plurality of stages of measuring instruments 35a to 35n are arranged along the direction of the flow of the wastewater, and the plural stages of seawater injecting ports 26a to 26n are provided with the valves 27a to 27n, respectively, the rate of dilution of the wastewater with seawater can be adjusted according to the pH or the S032" concentration of the wastewater flowing in the wastewater oxidation tank 20. Therefore, an extreme decrease of the S032" concentration of the wastewater, or a decrease of the rate of oxidation due to a decrease of the pH of the was LewaLer c&n he reliably prevanned, and high oxidation efficiency can be reliably maintained. [0032] Alternatively, as shown in Figure 3, plural stages of air plowing nozzles 33a to 33n in the wastewater oxidation tank 20 may be arranged at different intervals. In the upstream part of the wastewater oxidation tank 20, the S03^" concentration is high, the rate of oxidation is high, and therefore, the dissolved oxygen concentration tends to easily decrease, so that the superficial velocity" (the amount of airflow per cross section of the wastewater oxidation tank 20) of the oxidizing air lias to be high. However, in the downstream part of the wastewater oxidation tank 20, the S03"' concentration is low, and the rate of oxidation is reduced, so that the superficial velocity of the oxidizing air can be low. [0033] Therefore, as shown in Figure 3, it is preferable that the air blowing nozzles 33a and 33b located in the upstream part of the wastewater oxidation tank 20 be disposed at a narrower interval, and the air blowing nozzles 33m and 33n located in the downstream part be disposed at a wider interval. If the air blowing nozzles 33 are arranged so that the superficial velocity of the oxidizing air differs between the upstream part and the downstream part of the wastewater oxidation tank 20 in this vjay, ins '-aI lac ion and use of an unnecessary aerator can be avoided. [0034] Alternatively, as shewn in Figure 4, plural stages of water stream oxidizing devices 4 0a to 4On, which are means for mixing the oxidizing air with the diluting seawater and ejecting the mixture in the direction of the flow of the wastewater, may be provided in the wastewater oxidation tank 2 0. As shown in Figure 5, the water stream oxidizing devices 40 are preferably disposed in a staggered arrangement in the wastewater oxidation tank 20. Figure S shows a structure of the water stream oxidizing device 40. [0035] As shown in Figure 6, the water stream oxidizing device 40 mainly comprises a seawater supply pipe 41 for receiving the diluting seawater, an air intake pipe 43 for taking in atmospheric air, an injection nozzle 42 for injecting a multiphase flow of seawater and air into the wastewater, and a throttle (orifice) 44. Each seawater supply pipe 41 is connected to the associated seawater injecting port at one end thereof (not shown) and is connected to one end of the injection nozzle 42 with the throttle 44 interposed therebetween. The throttle 44 is composed of a flange 4 5 on the side of the seawater supply pipe, a flange 46 on the side of the injection nozzle, and a throttle plate 47 disposed between the flanges. The throttle plate 4? has a throttle hole 48 having a diameter smaller than the inner diameter of the inj action nozzle 4 2. [0036] The air intake pipe 43 is connected to the side wail of the injection nozzle 42 at a point downstream from the throttle 44. The injection nozzle 42 and the air intake pipe 4 3 communicate with each other via an opening 4 9. The other end of the air intake pipe 43 opens to the atmosphere at a position higher than the surface of the wastewater flowing in the wastewater oxidation tank. The injection nozzle 42 is inclined with the injection port being lower than the end on the side of the throttle 44. For example, the injection nozzle 42 is inclined 7 to 15 degrees with respect to the horizontal plane. The water stream oxidizing device 40 may be made of stainless steel (SUS), as well as fiber reinforced plastic (FRP) and polyvinyl chloride fPVC), which are light and have high strength, for example. [0037] In the arrangement described above, when the diluting seawater is fed to the seawater supply pipe 41, the seawater rushes against the throttle plate 47 of the throttle 44 and passes through the throttle hole 48 to flow into the injection nozzle 42. At this time, the seawater produces a negative pressure in the region downstream from the throttle 44, and therefore, atmospheric air flowing through the air intake pipe 4 3 rushes into the seawa^sr through the opening 49 formed near the throttle 44. Thus, a multiphase flow of seawater and air, which is a flow of seawater containing minute air bubbles, is produced. The multiphase flow is injected obliquely downward from the injection port of the injection nozzle 42 and then flows upward while widely dispersing in the wastewater after flowing near the bottom surface of the wastewater oxidation tank 20, as shown in Figures 4 and 5. [0038] Since the water stream oxidizing devices 4 0 that inject the gas-liquid multiphase flow of the diluting seawater containing minute bubbles of oxidizing air are provided in the wastewater oxidation tank 20 as described above, the air comes into contact with the wastewater at a larger contact surface, and therefore, the oxygen utilization is significantly improved. Furthermore, since the oxidizing air can be taken in through the air intake pipe 43, the oxidizing air blower 31 shown in Figure 1 can be omitted. Furthermore, as shown in Figure 5, since the water stream oxidizing devices 40 are disposed in a staggered arrangement so that the gas-liquid multiphase flows 51 injected from the water stream oxidizing devices 40 do not overlap, a decrease of the oxygen utilization due to combination of minute air bubbles is prevented, and the air bubbles can be uniformly distributed in the wastewater oxidation tank 2 0 . [0035J In the above description, the wastewater is caused to flow through one wastewater oxidation tank, and seawater and air are introduced stepwise into the wastewater in the wastewater oxidation tank. However, the wastewater can also be caused to flew through plural tanks arranged in series, and seawater and air can be introduced stepwise into the wastewater in each of the tanks. Such an arrangement provides the same advantages as those in the case in which the wastewater is caused to flow through one wastewater oxidation tank. Example [0040] In the wastewater oxidation tank having a length of 140 m, the sulfurous acid/sulfuric acid concentration of the wastewater at the inlet of the wastewater oxidation tank is set at 1.00 mmol/L by seawater dilution, and the sulfurous acid/sulfuric acid concentration of the wastewater at distances of 20 m, 40 m and 60 m from the inlet are set at 0.90 mmol/L, 0.82 mmol/L and 0.75 mmol/L, respectively, by seawater addition. The superficial velocity of the oxidizing air is maintained at 1.0 cm/sec. The residual rate of sulfurous acid and the saturation factor of dissolved oxygen in the "wastewater oxidation tank in this case are shown in Table 1 and Figure 7. [0041] For reference, the results of Reference Examples 1 to 3, in which the wastewater is diluted with seawater only at the inlet of the wastewater oxidation tank so that the sulfurous acid/sulfuric acid concentration of the wastewater at the inlet is 0.75 mmol/L, 1.00 mmol/L and 1.30 mmol/L, respectively, are also shown in Table 1 and Figure 7. Furthermore, the result of Reference Example 4, in which the superficial velocity in a rear part of the oxidation tank extending from a distance of 80 m to a distance of 140 m from the inlet is reduced to 0.5 cm/sec, is also shown in Table 1. [0042] As shown in Table 1 and Figure 7, compared with Reference Example 1, in this example, the sulfurous acid concentration increased, and the oxidation rate improved because of the decrease in dilution rate. In addition, in this example, the decrease in oxidation rate due to a decrease in pH is reduced compared with Reference Example 2, and thus, the residual rate of sulfurous acid in the rear part of the wastewater oxidation tank extending from a distance of 50 m from the inlet is minimized. In Reference Example 4, in which the superficial velocity in the rear part of the wastewater oxidation tank extending from a distance of 80 -L from the inlet is 0.5 m/sec, che residual rate of sulfurcus acid and the saturation factor of dissolved oxygen do not vary significantly compared with Reference Example 2, and therefore, the cost of installation and cower of the blower can be saved. CLAIMS 1. A seawater flue gas desulfurization system comprising: a seawater flue gas desulfurization device chat uses seawater as an absorbing solution,- and a wastewater oxidation device that oxidizes a sulfurous-acid-based material contained in wastewater discharged from the seawater flue gas desulfurization device, wherein the wastewater oxidation device oxidizes the sulfurous-acid-based material in the wastewater by introducing air into the wastewater containing the sulfurous-acid-based material in at least two stages and dilutes the wastewater by introducing seawater into the wastewater in at least two stages in time with the stepwise progression of oxidation. 2. The seawater flue gas desulfurization system according to claim 1, further comprising: heating means that heats the seawater taken from the sea and feeds the heated seawater to the wastewater oxidation device as the seawater used for dilution. 3. The seawater flue gas desulfurization system according to claim 1 or 2, wherein the wastewater oxidation device has plural measuring means for measuring the pK of, or uhe concentration of, the sulfurcus-acid-based material in the wastewater in the wastewater oxidation device, which are arranged in stages corresponding to the stages of the dilution of the wastewater, and controlling means for adjustinc the flow rate of the seawater introduced for dilution in at least two stages based on the values of the pH or the concentration of the sulfurous-acid-based material measured by the measuring means. 4. The seawater flue gas desulfurization system according to any of" claims 1 to 3, wherein the wastewater oxidation device is configured so that the superficial velocity of the air introduced for oxidation differs between the at least two stages of introduction of the air for oxidation. 5. The seawater flue gas desulfurization system according to any of claims 1 to 4, wherein the wastewater oxidation device has means for introducing a mixed flow of the seawater for dilution and the air for oxidation into the wastewater, so that introduction of the air and introduction of the seawater are carried out simultaneously in each of the stages. 6. The seawater flue gas desulfurization system according to claim 5, wherein plural means for introducing the ~iixsd flew of the seawater for dilution and nhe air for oxidation are provided in ea.cn s;agg and arranged in a staggered configuraticn so that the introduced mixed flows do not overlap each other. |
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| Patent Number | 269873 | |||||||||||||||||||||
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| Indian Patent Application Number | 2414/CHENP/2009 | |||||||||||||||||||||
| PG Journal Number | 47/2015 | |||||||||||||||||||||
| Publication Date | 20-Nov-2015 | |||||||||||||||||||||
| Grant Date | 13-Nov-2015 | |||||||||||||||||||||
| Date of Filing | 29-Apr-2009 | |||||||||||||||||||||
| Name of Patentee | MITSUBISHI HEAVY INDUSTRIES, LTD. | |||||||||||||||||||||
| Applicant Address | 16-5, KONAN 2-CHOME, MINATO-KU, TOKYO 108-8215 | |||||||||||||||||||||
Inventors:
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| PCT International Classification Number | B01D 53/50 | |||||||||||||||||||||
| PCT International Application Number | PCT/JP08/51341 | |||||||||||||||||||||
| PCT International Filing date | 2008-01-30 | |||||||||||||||||||||
PCT Conventions:
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