DESCRIPTION SEAWATER FLUE-GAS DESULFURIZATION SYSTEM AND POWER
GENERATING SYSTEM Field

[0001] The present invention relates to a seawater flue-gas desulfurization system that desulfurizes sulfur oxides in flue gas discharged from coal-fired, crude oil-fired, and heavy oil-fired industrial combustion facilities, using seawater, and a power generating system. Background

[0002] In a power plant using coal or crude oil as fuel, combustion flue gas (hereinafter, referred to as "flue gas") discharged from a boiler by burning fossil fuel such as coal includes a sulfur content such as sulfur oxides (SOx)- For this reason, the flue gas is desulfurized, and is discharged to the air after removing SOx such as sulfur dioxides (S02) included in the flue gas. As such a desulfurization processing method, there are a limestone gypsum method, a spray drier method, a seawater method, and the like.

[0003] Since the power plant or the like needs a large amount of cooling water, there are many cases where it is constructed at a location adjacent to the sea. For this reason, from the viewpoint of suppressing an operating cost necessary for the desulfurization process, a seawater flue-gas desulfurization device using seawater desulfurization of performing desulfurization using the seawater as an absorbent absorbing the sulfur oxides in the flue gas is proposed.

[0004] The seawater flue-gas desulfurization device supplies the seawater and the boiler flue gas into a desulfurizer (an absorber) vertically positioning a cylindrical shape such as a substantially cylinder or a rectangular shape to come in gas-liquid contact using the seawater as the absorbent, thereby removing SOx. The seawater (sulfur-content absorbing seawater) used as an absorbent material in the desulfurizer after desulfurization flows in, for example, an upside-opened long water channel (Seawater Oxidation Treatment System; SOTS) , is mixed with the seawater, diluted, and discharged. The sulfur-content absorbing seawater is decarboxylated (gas-exploded) by microscopic bubbles effluent from an aeration device provided on the bottom of a part of the water channel (for example, see Patent Literatures 1 to 3).

[0005] In the seawater flue-gas desulfurization device, when the desulfurization is performed using the seawater, a desulfurization rate of the flue gas acquired from a ratio of the flue gas supplied into the desulfurizer and the flue gas discharged to the outside of the desulfurizer is adjusted to be a predetermined value (for example, about 90%) .

Citation List Patent Literature

[0006] Patent Literature 1: Japanese Laid-open Patent Publication No. 2006-055779

Patent Literature 2: Japanese Laid-open Patent Publication No. 2009-028570

Patent Literature 3: Japanese Laid-open Patent Publication No. 2009-028572 Summary

Technical Problem

[0007] When the desulfurization is performed using the seawater, the desulfurization rate of the flue gas may be higher than a predetermined value (for example, about 90%) according to seawater properties such as seawater alkalinity, seawater temperature, seawater pH, and sulfate ion (S042-) concentration included in the desulfurized seawater.

[0008] When the seawater is supplied into the desulfurizer, adjustment of the supply amount of seawater is controlled by changing the number of driven pumps, and thus it is difficult to perform fine adjustment of the supply amount of seawater supplied into the desulfurizer. For this reason, there is a problem that it is difficult to perform the fine adjustment of the desulfurization rate of the flue gas, when the desulfurization rate of the flue gas is higher than the predetermined value.

[0009] The invention has been made in view of the problem, and an object thereof is to provide a seawater flue-gas desulfurization system and a power generating system, capable of easily performing adjustment of a desulfurization rate of flue gas. Solution to Problem

[0010] According to a first aspect of the present invention in order to solve the problems, there is provided a seawater flue-gas desulfurization system including: a flue-gas desulfurization absorber that allows flue gas and seawater to come in gas-liquid contact to wash the flue gas; a dilution mixing basin that is provided on a downstream side of the flue-gas desulfurization absorber, and dilutes and mixes sulfur-content absorbing seawater including a sulfur content with dilution seawater; a seawater supply line that supplies the seawater to the flue-gas desulfurization absorber; a surplus seawater branch pipe that is branched from the seawater supply line in any one or both of the inside and the outside of the flue-gas desulfurization absorber, and supplies a part of the seawater to any one or both of a tower bottom portion of the flue-gas desulfurization absorber and the dilution mixing basin; and a control valve that is provided on the surplus seawater branch pipe and controls a surplus seawater branch amount.

[0011] According to a second aspect of the present invention, there is provided the seawater flue-gas desulfurization system according to the first aspect, wherein the branch portion of the surplus seawater branch pipe is provided on a downstream of a seawater feeding pump provided on the seawater supply line.

[0012] According to a third aspect of the present invention, there is provided the seawater flue-gas desulfurization system according to the first or second aspect, wherein a spray amount of the seawater from the spray nozzle of spraying the seawater into the flue-gas desulfurization absorber is calculated on the basis of a desulfurization rate obtained by calculating a desulfurization rate in the flue-gas desulfurization absorber, and an opening degree of the control valve provided on the surplus seawater branch pipe is adjusted to control the spray amount of the seawater.

[0013] According to a fourth aspect of the present invention, there is provided the seawater flue-gas desulfurization system according to any one of the first to third aspects, wherein the flue-gas desulfurization absorber, the dilution mixing basin, and the oxidation basin are configured in the same basin.

[0014] According to a fourth aspect of the present invention, there is provided a power generating system including at least one of: a boiler; a steam turbine that uses flue gas discharged from the boiler as a heat source for generating steam, and drives a power generator using the generated stream; the seawater flue-gas desulfurization system according to any one of the first to fourth aspects; a condenser that recovers water condensed by the steam turbine and circulate the water; a flue-gas denitration device that denitrates the flue gas discharged from the boiler; a precipitation device that removes soot dust in the flue gas; a heat exchanger that includes a heat recovery unit performing heat exchange between the flue gas and a heat medium circulating in the heat exchanger, and a reheater performing heat exchange between purged gas discharged from the flue gas desulfurization absorber washing the flue gas by gas-liquid contact between the flue gas and the seawater, and the heat medium, to reheat the purged gas; and a stack that discharges the purged gas desulfurized by the seawater flue-gas desulfurization system to the outside. Advantageous Effects of Invention

[0015] According to the invention, it is possible to easily perform the adjustment of the desulfurization rate of the flue gas. Brief Description of Drawings

[0016] FIG. 1 is a schematic diagram illustrating a configuration of a seawater flue-gas desulfurization system according to a first embodiment of the invention.

FIG. 2 is a diagram illustrating an example of a driving method of adjusting a desulfurization rate of flue gas.

FIG. 3 is a schematic diagram illustrating a configuration of a power generating system according to a second embodiment of the invention. Description of Embodiments

[0017] Hereinafter, the invention will be described in detail with reference to the drawings. In addition, the invention is not limited to the following embodiments. In addition, constituent elements in the following embodiments include what is easily conceivable by a person skilled in the art, what is substantially the same, and what is in a so-called equivalent scope. In addition, the constituent elements described in the following embodiments may be appropriately combined. First Embodiment

[0018] A seawater flue-gas desulfurization system according to a first embodiment of the invention will be described with reference to the drawings. FIG. 1 is a schematic diagram illustrating a configuration of the flue-gas desulfurization system. As illustrated in FIG. 1, a seawater flue-gas desulfurization system 10 according to the embodiment includes a flue-gas desulfurization absorber 11, a dilution mixing basin 12, and an oxidation basin 13.

[0019] Seawater 21 is pumped from sea 22 up to a seawater supply line Lll by a pump 23, partial seawater 21a is supplied to the flue-gas desulfurization absorber 11 through the seawater supply line L12 by a pump 24, and the other seawater 21b is supplied to the dilution mixing basin 12 through the dilution seawater supply line L13. As the seawater 21, the seawater directly pumped up from the sea 22 by the pump 23 is used, but the invention is not limited thereto, and drainage of the seawater 21 discharged from a condenser (not illustrated) may be used.

[0020] The flue-gas desulfurization absorber 11 is a tower that purifies a flue gas 25 by gas-liquid contact between the flue gas 25 and the seawater 21a. In the flue-gas desulfurization absorber 11, the seawater 21a is sprayed upward from a spray nozzle 2 6 in a liquid columnar shape, and the flue gas 25 comes in gas-liquid contact with the seawater 21a supplied through the seawater supply line L12 to perform desulfurization the sulfur content in the flue gas 25. In the embodiment, the spray nozzle 26 is a spray nozzle that allows the seawater to be sprayed upward in the liquid columnar shape, but the invention is not limited thereto, and the seawater may be sprayed downward in a shower shape.

[0021] That is, in the flue-gas desulfurization absorber 11, the flue gas 25 comes in gas-liquid contact with the seawater 21a, a reaction illustrated in the following formula (I) is caused, the sulfur content such as SOx contained in a form of SO2 in the flue gas 2 5 is absorbed to the seawater 21a, and the sulfur content in the flue gas 25 is removed using the seawater 21a.
S02(G) + H20 -» H2S03(L) -> HSO3" + H+ (I)

[0022] H2SO3 generated by the gas-liquid contact between the seawater 21a and the flue gas 25 is dissociated by the seawater desulfurization, pH for releasing hydrogen ions (H+) in the seawater 21a is lowered, and a large amount of sulfur contents are absorbed into a sulfur-content absorbing seawater 27. For this reason, the sulfur-content absorbing seawater 27 includes the sulfur content with high concentration. In this case, pH of the sulfur-content absorbing seawater 27 is, for example, about 3 to 6. The sulfur-content absorbing seawater 27 absorbing the sulfur content in the flue-gas desulfurization absorber 11 is stored in the tower bottom portion of the flue-gas desulfurization absorber 11. The sulfur-content absorbing seawater 27 stored in the tower bottom portion of the flue-gas desulfurization absorber 11 is fed to the dilution mixing basin 12 through the sulfur-content absorbing seawater discharge line L14. The sulfur-content absorbing seawater 27 is mixed with the seawater 21b supplied to the dilution mixing basin 12 in the dilution mixing basin 12 to be diluted.

[0023] In addition, a purged gas 29 desulfurized in the flue-gas desulfurization absorber 11 is discharged to the air through the purged gas discharge passage L15.

[0024] In addition, the seawater supply line L12 is provided with the surplus seawater branch pipe L21 or L22 or both thereof. The surplus seawater branch pipe L21 is connected to the seawater supply line L12 at a branch portion 28A between the pump 24 of the seawater supply line L12 and the flue-gas desulfurization absorber 11. In addition, the surplus seawater branch pipe L22 is connected to a branch portion 2 8B of the seawater supply line L12 in the flue-gas desulfurization absorber 11. A surplus seawater 21c extracted from the surplus seawater branch pipes L21 and L22 is fed to the dilution mixing basin 12. The surplus seawater branch pipes L21 and L22 are provided with control valves VI1 and V12, and adjust the amount of the surplus seawater 21c extracted from the surplus seawater branch pipes L21 and L22.

[0025] By extracting a part of the seawater 21a as the surplus seawater 21c from the seawater supply line L12 by the surplus seawater branch pipes L21 and L22, it is possible to easily adjust the amount of seawater 21a supplied to the flue-gas desulfurization absorber 11, and thus it is possible to easily adjust the desulfurization rate of the flue gas 25 in the flue-gas desulfurization absorber 11. In addition, since the ejection pressure of the pump 24 is suppressed, it is possible to reduce the power for supplying the seawater 21a to the flue-gas desulfurization absorber 11. Moreover, since the surplus seawater 21c extracted to the surplus seawater branch pipes L21 and L22 is supplied to the dilution mixing basin 12, the sulfur-content absorbing seawater 27 is mixed, so that it is possible to reduce the concentration of S02 in the sulfur-content absorbing seawater 27. Thus, it is possible to prevent S02 included in the sulfur-content absorbing seawater 27 in the dilution mixing basin 12 from being re-scattered to the air.

[0026] The desulfurization rate of the flue gas 25 is adjusted according to the amount of the surplus seawater 21c extracted to the surplus seawater branch pipes L21 and L22 on the basis of a ratio (outlet SO2 concentration/inlet SO2 concentration) of inlet S02 concentration and outlet S02 concentration in the flue gas 25 supplied to the flue-gas desulfurization absorber 11 or seawater properties of the sulfur-content absorbing seawater 27.

[0027] In the embodiment, the seawater properties mean alkalinity of the sulfur-content absorbing seawater 27, seawater temperature, pH, S04 concentration, and the like. The alkalinity is the content of a component consuming acid such as carbonic acid (H2CO3) , carbonate ions (C032-) , bicarbonate ions (HCO3") , OH-, salt (silicic acid, phosphoric acid, and boric acid) of organic acid or weak acid. When the desulfurization rate of the flue gas 25 is adjusted according to the amount of the surplus seawater 21c extracted to the surplus seawater branch pipes L21 and L22 on the basis of the seawater properties of the sulfur-content absorbing seawater 27, it is adjusted on the basis of at least one or more of the alkalinity, the seawater temperature, the pH, and the SO4 concentration of the sulfur-content absorbing seawater 27. Preferably, it is adjusted on the basis of the alkalinity (HC03~) as the seawater properties among them.

[0028] The flue-gas desulfurization absorber 11 is provided with an S02 concentration meter for measuring the inlet S02 concentration and the outlet S02 concentration of the flue gas 25, at the inlet and the outlet of the flue gas 25. In addition, the flue-gas desulfurization absorber 11 is provided with a thermometer, a pH measuring instrument, and an S04 concentration meter to measure the seawater temperature, the pH, and the S04 concentration of the sulfur-content absorbing seawater 27.

[0029] FIG. 2 is a diagram illustrating an example of a driving method of adjusting the desulfurization rate of the flue gas 25. As illustrated in FIG. 2, the desulfurization rate of the flue gas 25 in the flue-gas desulfurization absorber 11 and the seawater properties of the sulfur-content absorbing seawater 27 are acquired (Step Sll). It is determined whether or not the desulfurization rate of the flue gas 25 is equal to or more than a predetermined threshold value (for example, a setting value + a) (Step S12). Herein, in the embodiment, the predetermined threshold value of the desulfurization rate means, for example, a value of a sum of a predetermined setting value (for example, the desulfurization rate is 90%) generally necessary for desulfurization and an extra a (for example, the desulfurization rate is several %), in the flue-gas desulfurization absorber 11.

[0030] When the desulfurization rate of the flue gas 25 is equal to or more than the predetermined threshold value (for example, the setting value + a), the spray amount necessary for spraying the seawater 21a is calculated from the seawater properties of the sulfur-content absorbing seawater 27 and the desulfurization rate of the flue gas 25 (Step S13). Opening degrees of the control valves Vll and V12 are adjusted on the basis of the spray amount necessary for spraying the seawater 21a (Step S14). Opening and closing degrees of the control valves Vll and V12 are adjusted on the basis of the calculated opening degrees of the control valves Vll and V12 (Step S15).

[0031] By adjusting the opening and closing degrees of the control valves Vll and V12 on the basis of the calculated opening degrees of the control valves Vll and V12, it is possible to adjust the amount of the seawater 21a supplied to the flue-gas desulfurization absorber 11, and thus it is possible to easily adjust the spray amount of the seawater 21a sprayed from the spray nozzle 26. Accordingly, as described above, in the flue-gas desulfurization absorber 11, it is possible to easily adjust the desulfurization rate of the flue gas 25.

[0032] In addition, in the embodiment, the surplus seawater branch pipes L21 and L22 are connected to the dilution mixing basin 12, and the surplus seawater 21c extracted from the surplus seawater branch pipes L21 and L22 is fed to the dilution mixing basin 12. However, the destination of the extracted surplus seawater 21c is not limited to the dilution mixing basin 12. The extracted surplus seawater 21c may be fed to the tower bottom portion of the flue-gas desulfurization absorber 11, or may be directly fed to the oxidation basin 13. In addition, the extracted surplus seawater 21c may be fed to both of the dilution mixing basin 12 and the tower bottom portion of the flue-gas desulfurization absorber 11, or may be fed to both of the oxidation basin 13 and the tower bottom portion of the flue-gas desulfurization absorber 11. In addition, the extracted surplus seawater 21c may be fed to the dilution mixing basin 12, the oxidation basin 13, and the tower bottom portion of the flue-gas desulfurization absorber 11.

[0033] The dilution mixing basin 12 is a basin that is provided on the downstream side of the flue-gas desulfurization absorber 11, and dilutes and mixes the sulfur-content absorbing seawater 27 including the sulfur content with the dilution seawater 21b. In the dilution mixing basin 12, the sulfur content in the flue gas 25 comes in contact with the seawater 21a in the flue-gas desulfurization absorber 11 to generate the sulfur content by seawater desulfurization, and the sulfur-content absorbing seawater 27 including the generated sulfur content is mixed and diluted with the seawater 21b. By mixing and diluting the sulfur-content absorbing seawater 27 with the seawater 21b, the pH of the sulfur-content absorbing dilution seawater 31 in the dilution mixing basin is raised, so that it is possible to prevent S02 gas from being re-dissipated. In addition, leaking of the S02 dissipated in the dilution mixing basin 12 to the outside is prevented, so that it is possible to prevent irritating odor from exhibiting.

[0034] The sulfur-content absorbing dilution seawater 31 is fed to the oxidation basin 13 provided on the downstream side of the dilution mixing basin 12. The oxidation basin is a basin that is provided on the downstream side of the dilution mixing basin 12 and has an aerator (the aeration device) 32 performing a water quality recovering process of the sulfur-content absorbing dilution seawater 31.

[0035] The aerator 32 includes an oxidizing air blower 34 that supplies air 33, and an aeration tube 35 that feeds the air 33, and an oxidation air nozzle 36 that supplies the air 33 to the sulfur-content absorbing dilution seawater 31 in the oxidation basin 13. The outer air 33 is fed from the oxidation air nozzle 36 into the oxidation basin 13 through the aeration tube 35 by the oxidizing air blower 34, to cause dissolution of oxygen represented in the following formula (II). The sulfur content in the sulfur-content absorbing dilution seawater 31 in the oxidation basin 13 comes in contact with the air 33, to cause an oxidation reaction of bisulfite ions (HS03~) , and a decarboxylation reaction of bicarbonate ions (HC03~) represented in the following formulas (III) to (V), and the water quality of the sulfur-content absorbing dilution seawater 31 is recovered to be water quality recovery seawater 37.
02(G) -» 02(L) (II)
HS03" + 1/202 -> SO42" + H+ (III)
HCO3" + H+ -> C02(G) + H20 (IV)
CO32" + 2H+ -> C02(G) + H20 (V)

[0036] Accordingly, it is possible to raise the pH of the sulfur-content absorbing dilution seawater 31 and to reduce COD, and it is possible to discharge the water quality recovery seawater 37 in which the pH, the dissolved oxygen concentration, and the COD are in the seawater dischargeable level. In addition, even when gas is generated when the water quality recovery of the sulfur-content absorbing dilution seawater 31 in the oxidation basin 13 is performed, it is possible to diffuse the generated gas in the oxidation basin 13 by making S02 environmental standard concentration to be satisfied. The water quality recovery seawater 37 is discharged to the sea 22 through the seawater discharge line L31.

[0037] As described above, the seawater flue-gas desulfurization system 10 according to the embodiment adjusts the amount of the surplus seawater 21c extracted to the surplus seawater branch pipes L21 and L22 on the basis of the ratio of the inlet S02 concentration to the outlet S02 concentration of the flue gas 25 supplied to the flue-gas desulfurization absorber 11 and the alkalinity of the sulfur-content absorbing seawater 27, to adjust the spray amount of the seawater 21a sprayed from the spray nozzle 2 6, and it is possible to easily adjust the desulfurization rate of the flue gas 25. In addition, it is possible to reduce the power for supplying the seawater 21a to the flue-gas desulfurization absorber 11. In addition, the surplus seawater 21c is mixed with the sulfur-content absorbing seawater 27 in the dilution mixing basin 12, and it is possible to decreases the SO2 concentration in the sulfur-content absorbing seawater 27. For this reason, when the sulfur-content absorbing seawater 27 flowing in the outdoor open type oxidation basin 13 is subjected to an oxidation process to perform water quality recovery, SO2 absorbed in the flue-gas desulfurization absorber 11 is dissipated in the dilution mixing basin 12, S02 gas is prevented from leaking to the outside, and it is possible to prevent irritating odor from exhibiting.

[0038] Therefore, according to the seawater flue-gas desulfurization system 10 according to the embodiment, the seawater flue-gas desulfurization device with high stability and reliability can be provided while keeping the stabilized desulfurization rate of the flue gas 25.

[0039] In addition, in the embodiment, the seawater flue-gas desulfurization system that performs the process of the seawater 21a used in the seawater desulfurization in the flue-gas desulfurization absorber 11 has been described, but the invention is not limited thereto. The seawater flue-gas desulfurization device may be applied to, for example, the seawater flue-gas desulfurization device that performs the seawater desulfurization of the sulfur oxides included in the flue gas discharged from factories, large-scale and middle-scale coal-fired plants, large-scale boilers for electric power industry or boilers for general industry, ironworks, and refineries.

[0040] In addition, in the embodiment, the flue-gas desulfurization absorber 11, the dilution mixing basin 12, and the oxidation basin 13 are independent as different basins, and the flue-gas desulfurization absorber 11, the dilution mixing basin 12, and the oxidation basin 13 are connected. However, the embodiment is not limited thereto, the flue-gas desulfurization absorber 11, the dilution mixing basin 12, and the oxidation basin 13 may be configured integrally as one basin, and the dilution mixing basin 12 and the oxidation basin 13 may be configured integrally as one basin. Second Embodiment

[0041] A power generating system according to a second embodiment of the invention will be described with reference to the drawings. As a seawater flue-gas desulfurization system applied to the power generating system according to the embodiment, the seawater flue-gas desulfurization system according to the first embodiment is used. In addition, the same reference numerals and signs are given to the same members as the first embodiment, and the description thereof is not repeated.

[0042] FIG. 3 is a schematic diagram illustrating a configuration of the power generating system according to the second embodiment of the invention. As illustrated in FIG. 3, a power generating system 40 according to the embodiment includes a boiler 41, a steam turbine 42, a condenser 43, a flue-gas denitration device 44, a precipitation device 45, and a seawater flue-gas desulfurization system 10. In the embodiment, as described above, the sulfur-content absorbing seawater 27 means used seawater absorbing the sulfur content such as S02 in the seawater flue-gas desulfurization system 10.

[0043] The boiler 41 ejects and burns fuel 46 supplied from an oil basin or a coal mill with air 48 preheated by the air heater (AH) 47, from a burner (not illustrated). The air 48 supplied from the outside is fed to the air heater 47 by a pressure fan 49, and is preheated. The fuel 4 6 and the air 4 8 preheated by the air heater 47 are supplied to the burner, and the fuel 4 6 is burned in the boiler 41. Accordingly, steam 50 for driving the steam turbine 42 is generated.

[0044] A flue gas 51 generated by combustion in the boiler 41 is fed to the flue-gas denitration device 44. In addition, the flue gas 51 performs heat exchange with water 52 discharged from the condenser 43, and is used as a heat source for generating the steam 50. The steam turbine 42 drives a power generator 53 using the steam 50. The condenser 43 recovers the water 52 condensed in the steam turbine 42, returns it to the boiler 41 again, and circulates it.

[0045] The flue gas 51 discharged from the boiler 41 is denitrated in the flue-gas denitration device 44, is subjected to heat exchange with the air 48 in the air heater 47, and then is fed to the precipitation device 45, and soot dust in the flue gas 51 is removed. The flue gas 51 of which dust is removed by the precipitation device 45 is supplied into the seawater flue-gas desulfurization system 10 by a drawing-in fan 55. In this case, the flue gas 51 is subjected to heat exchange with the purged gas 29 desulfurized and discharged by the seawater flue-gas desulfurization system 10, in a heat exchanger 56, and then is supplied into the seawater flue-gas desulfurization system 10. In addition, the flue gas 51 may be directly supplied to the seawater flue-gas desulfurization system 10 without the heat exchange with the purged gas 29 in the heat exchanger 56.

[0046] In addition, the heat exchanger 56 includes a heat recovery device, and a reheater, and a heat medium circulates between the heat recovery device and the reheater. The heat recovery device is provided between the air heater 47 and the precipitation device 45, and performs heat exchange between the flue gas 51 discharged from the boiler 41 and the heat medium. The reheater is provided on the downstream side of the flue-gas desulfurization absorber 11, performs heat exchange between a purged gas 57 discharged from the flue-gas desulfurization absorber 11 and the heat medium, and reheats the purged gas 29.

[0047] The seawater flue-gas desulfurization system 10 is the seawater flue-gas desulfurization device according to the first embodiment. That is, the seawater flue-gas desulfurization system 10 includes the flue-gas desulfurization absorber 11, the dilution mixing basin 12, the oxidation basin 13, and the surplus seawater branch pipes L21 and L22.

[0048] In the seawater flue-gas desulfurization system 10, as described above, the sulfur content contained in the flue gas 51 is subjected to seawater desulfurization using the seawater 21 pumped up from the sea 22. In addition, the seawater 21 is pumped up from the sea 22 by the pump 23, and is subjected to the heat exchange in the condenser 43, and then the partial seawater 21a is fed to the seawater flue-gas desulfurization system 10 through the seawater supply line L12 by the pump 24. In addition, the other seawater 21b is fed to the upstream side of the dilution mixing basin 12 through the seawater supply line L13. In the seawater flue-gas desulfurization system 10, the flue gas 51 and the seawater 21a are allowed to come in gas-liquid contact, to absorb the sulfur content in the flue gas 51 to the seawater 21a. The sulfur-content absorbing seawater 27 absorbing the sulfur content is fed from the flue-gas desulfurization absorber 11 to the upstream side of the dilution mixing basin 12, is mixed with the seawater 21b, and is diluted.

[0049] In addition, the flue gas 51 purged in the seawater flue-gas desulfurization system 10 becomes the purged gas 29, which is discharged from a stack 57 to the outside through the purged gas discharge passage L15.

[0050] In the embodiment, in the seawater flue-gas desulfurization system 10, the seawater supply line L12 is provided with surplus seawater branch pipes L21 and L22. The surplus seawater branch pipe L21 is connected to the seawater supply line L12 between the pump 24 of the seawater supply line L12 and the flue-gas desulfurization absorber 11. In addition, the surplus seawater branch pipe L22 is connected to the seawater supply line L12 in the flue-gas desulfurization absorber 11. The surplus seawater 21c extracted from the surplus seawater branch pipes L21 and L22 is fed to the dilution mixing basin 12. By extracting a part of the seawater 21a as the surplus seawater 21c from the seawater supply line L12 by the surplus seawater branch pipes L21 and L22, the amount of the seawater 21a supplied to the flue-gas desulfurization absorber 11 is adjusted, to adjust the desulfurization rate of the flue gas 51 in the flue-gas desulfurization absorber 11. As described above, the desulfurization rate of the flue gas 25 is adjusted by the amount of the surplus seawater 21c extracted from the surplus seawater branch pipes L21 and L22 on the basis of the ratio (outlet S02 concentration/inlet S02 concentration) of the inlet S02 concentration and the outlet SO2 concentration in the flue gas 51 supplied to the flue-gas desulfurization absorber 11 or the alkalinity of the sulfur-content absorbing seawater 27. Accordingly, it is possible to easily adjust the amount of extracting a part of the seawater 21a from the seawater supply line L12 by the surplus seawater branch pipes L21 and L22, and thus it is possible to easily adjust the amount of the seawater 21a supplied to the flue-gas desulfurization absorber 11. For this reason, it is possible to easily adjust the desulfurization rate of the flue gas 51 in the flue-gas desulfurization absorber 11. In addition, since the ejection pressure of the pump 24 is suppressed, it is possible to reduce the power for supplying the seawater 21a to the flue-gas desulfurization absorber 11.

[0051] In addition, the seawater 21 pumped up from the sea 22 is subjected to heat exchange in the condenser 43, then is fed to the seawater flue-gas desulfurization system 10, and is used in the seawater desulfurization. However, the seawater 21 pumped up from the sea 22 may be directly fed to the seawater flue-gas desulfurization system 10 without the heat exchange in the condenser 43, to' be used in the desulfurization.

[0052] The sulfur-content absorbing seawater 27 is mixed with the seawater 21b in the dilution mixing basin 12, the diluted sulfur-content absorbing dilution seawater 31 is fed to the oxidation basin 13, to recover the water quality of the sulfur-content absorbing dilution seawater 31 in the oxidation basin 13, thereby being the water quality recovery seawater 37. The water quality recovery seawater 37 obtained by the oxidation basin 13 is discharged-_from the oxidation basin 13 to the sea 22 through the seawater discharge line L32, in which the pH, the dissolved oxygen level, and the COD are in the seawater dischargeable level.

[0053] In addition, a part of the seawater 21 may be supplied from the seawater supply line Lll to the downstream side of the water quality recovery seawater 37 in the oxidation basin 13 through the dilution seawater supply line L13. Accordingly, it is possible to further dilute the water quality recovery seawater 37. Accordingly, the pH of the water quality recovery seawater 37 is raised, the pH of the seawater drainage is raised to the vicinity of the seawater, to satisfy the drainage standard (pH 6.0 or higher) of the pH of the seawater drainage and to reduce the COD, and thus it is possible to perform the discharge in which the pH and the COD of the water quality recovery seawater 37 are in the seawater dischargeable level.

[0054] As described above, according to the power generating system 40 according to the embodiment, it is possible to easily adjust the desulfurization rate of the flue gas 51 in the flue-gas desulfurization absorber 11 and to decrease the power for supplying the seawater 21a to the flue-gas desulfurization absorber 11, to suppress a running cost. In addition, the surplus seawater 21c extracted in the surplus seawater branch pipes L21 and L22 is supplied to the dilution mixing basin 12, it is possible to decrease the S02 concentration in the sulfur-content absorbing seawater 27, and thus it is possible to prevent the S02 included in the sulfur-content absorbing seawater 27 in the dilution mixing basin 12 from being re-scattered to the air. Accordingly, it is possible to provide the power generating system with high stability and high reliability while the flue gas 51 keeps the stable desulfurization rate.

[0055] In addition, a seawater flue-gas desulfurization device 10 according to the embodiment may be used to remove the sulfur content in the sulfur content absorption solution generated by performing the seawater desulfurization of the sulfur oxides included in the flue gas discharged from factories for various industries, large-scale and middle-scale coal-fired plants, large-scale boilers for electric power industry or boilers for general industry.

Reference Signs List

[0056] 10 SEAWATER FLUE-GAS DESULFURIZATION SYSTEM
11 FLUE-GAS DESULFURIZATION ABSORBER
12 DILUTION MIXING BASIN
13 OXIDATION BASIN 21, 21a, 21b SEAWATER 21c SURPLUS SEAWATER 22 SEA
23, 24 PUMP
25, 51 FLUE GAS
26 SPRAY NOZZLE
27 SULFUR-CONTENT ABSORBING SEAWATER 28A, 28B BRANCH PORTION 29 PURGED GAS
31 SULFUR-CONTENT ABSORBING DILUTION SEAWATER
32 AERATOR (AERATION DEVICE)
33 AIR
34 OXIDIZING AIR BLOWER
35 AERATION TUBE
3 6 OXIDATION AIR NOZZLE
37 WATER QUALITY RECOVERY SEAWATER
4 0 POWER GENERATING SYSTEM
41 BOILER
42 STEAM TURBINE
43 CONDENSER
44 FLUE-GAS DENITRATION DEVICE
45 PRECIPITATION DEVICE 4 6 FUEL
47 AIR HEATER (AH)
48 AIR
49 PRESSURE FAN
50 STEAM
52 WATER
53 POWER GENERATOR
55 DRAWING-IN FAN
56 HEAT EXCHANGER
57 STACK
Lll, L12 SEAWATER SUPPLY LINE
L13 DILUTION SEAWATER SUPPLY LINE
L14 SULFUR-CONTENT ABSORBING SEAWATER DISCHARGE LINE
L15 PURGED GAS DISCHARGE PASSAGE
L21, L22 SURPLUS SEAWATER BRANCH PIPE
L31, L32 SEAWATER DISCHARGE LINE

CLAIMS

1. A seawater flue-gas desulfurization system comprising:

a flue-gas desulfurization absorber that allows flue gas and seawater to come in gas-liquid contact to wash the flue gas;

a dilution mixing basin that is provided on a downstream side of the flue-gas desulfurization absorber, and dilutes and mixes sulfur-content absorbing seawater including a sulfur content with dilution seawater;

a seawater supply line that supplies the seawater to the flue-gas desulfurization absorber;

a surplus seawater branch pipe that is branched from the seawater supply line in any one or both of the inside and the outside of the flue-gas desulfurization absorber, and supplies a part of the seawater to any one or both of a tower bottom portion of the flue-gas desulfurization absorber and the dilution mixing basin; and

a control valve that is provided on the surplus seawater branch pipe and controls a surplus seawater branch amount.

2. The seawater flue-gas desulfurization system according to claim 1, wherein the branch portion of the surplus seawater branch pipe is provided on a downstream of a seawater feeding pump provided on the seawater supply line.

3. The seawater flue-gas desulfurization system according to claim 1 or 2, wherein a spray amount of the seawater from the spray nozzle of spraying the seawater into the flue-gas desulfurization absorber is calculated on the basis of a desulfurization rate obtained by calculating a desulfurization rate in the flue-gas desulfurization absorber, and an opening degree of the control valve provided on the surplus seawater branch pipe is adjusted to control the spray amount of the seawater.

4. The seawater flue-gas desulfurization system according to any one of claims 1 to 3, wherein the flue-gas desulfurization absorber, the dilution mixing basin, and the oxidation basin are configured in the same basin.

5. A power generating system comprising at least one of:
a boiler;

a steam turbine that uses flue gas discharged from the boiler as a heat source for generating steam, and drives a power generator using the generated stream;

the seawater flue-gas desulfurization system according to any one of claims 1 to 4;

a condenser that recovers water condensed by the steam turbine and circulate the water;

a flue-gas denitration device that denitrates the flue gas discharged from the boiler;

a precipitation device that removes soot dust in the flue gas;

a heat exchanger that includes a heat recovery unit performing heat exchange between the flue gas and a heat medium circulating in the heat exchanger, and a reheater performing heat exchange between purged gas discharged from the flue gas desulfurization absorber washing the flue gas by gas-liquid contact between the flue gas and the seawater, and the heat medium, to reheat the purged gas; and

a stack that discharges the purged gas desulfurized by the seawater flue-gas desulfurization system to the outside.