WO2008038348A1

WO2008038348A1 - Treating apparatus for exhaust gas containing sulfuric acid mist and treating method therefor

Info

Publication number: WO2008038348A1
Application number: PCT/JP2006/319159
Authority: WO
Inventors: Mitsuaki Yanagida; Toshiaki Misaka; Masaki Hayatsu
Original assignee: Hitachi Plant Technologies, Ltd.
Priority date: 2006-09-27
Filing date: 2006-09-27
Publication date: 2008-04-03

Abstract

A treating apparatus, and treating method, for exhaust gas containing sulfuric acid mist that excel in the elimination performance even for submicron-order sulfuric acid mist. There is provided an apparatus comprising saturating means (26) for saturating through feeding of water in the form of steam, etc. into exhaust gas (19) containing sulfuric acid mist; venturi duct (28) for mist generation through adiabatic expansion of the exhaust gas (19) having passed through the saturating means (26); ion generating means (30) for generating of ions in the vicinity of throat portion (48) of the venturi duct (28); and wet electric dust collector (32)disposed downstream of the venturi duct (28). Control unit (46) controls the amount of water required for saturating of the exhaust gas (19).

Description

Specification

Apparatus and method for treating exhaust gas containing sulfuric acid mist

Technical field

TECHNICAL FIELD [0001] The present invention relates to an apparatus and method for treating exhaust gas containing sulfuric acid mist, and particularly suitable for exhaust gas containing sulfuric acid mist discharged from boilers using fossil fuels such as coal and heavy oil. And a processing method.

Background art

[0002] Boilers using fossil fuels such as coal and heavy oil are widely used in thermal power plants and the like, and combustion exhaust gas discharged from this type of boiler power contains sulfur oxides. Therefore, for this type of exhaust gas from boiler boilers, etc., after removing dust by a dry electrostatic precipitator, sulfur oxide is removed by a wet desulfurizer and exhaust gas is removed by a wet electrostatic precipitator at the final stage. It is generally performed to remove dust and mist remaining on the surface. The exhaust gas that has passed through the wet desulfurization system contains sulfuric acid mist with a particle size of S micron order or submicron order, and these sulfuric acid mists are removed by a subsequent wet electrostatic precipitator.

[0003] However, the wet electrostatic precipitator is greatly affected by the particle size of the mist to be collected, and the collection performance is relatively good for micron-order mist. Power to show performance For sub-micron mist with a particle size of less than 1 μm, there is a problem in that the collection performance drops sharply. For this reason, if the sub-micron sulfuric acid mist is contained in the exhaust gas that has passed through the wet desulfurization system, the strong sulfuric acid mist that cannot be removed by the wet electrostatic precipitator will be released to the atmosphere. And bring about air pollution. In addition, in order to prevent such air pollution, the capacity of the wet electrostatic precipitator must be increased, resulting in an increase in cost.

[0004] As a measure for solving such problems, Patent Document 1 discloses that a liquid such as water is sprayed on the exhaust gas introduced into the wet desulfurization apparatus, and the temperature of the exhaust gas is set to 120 ° C to 150 ° C. The method of cooling down to is disclosed. According to this method, the average particle diameter of sulfuric acid mist in the exhaust gas introduced into the wet desulfurization apparatus can be made relatively large. Therefore, wet desulfurization The average particle diameter of the sulfuric acid mist in the exhaust gas that has passed through the apparatus also becomes relatively large, and the collecting performance of sulfuric acid mist in the subsequent wet electrostatic precipitator can be enhanced.

[0005] In addition, Patent Document 2 and Patent Document 3 disclose methods for removing particles and mist of submicron order in a gas. In this method, an ion generating electrode is provided at the throat part of the bench lily, and ionized particles and mist are trapped in the ejected water droplets.

Patent Document 1: Japanese Patent Laid-Open No. 2002-45643

Patent Document 2: US Patent No. 4093430

Patent Document 3: US Patent No. 4541844

Disclosure of the invention

Problems to be solved by the invention

However, although the method disclosed in Patent Document 1 has a certain effect, submicron-order sulfuric acid mist still remains in the exhaust gas that has passed through the wet desulfurization apparatus. Therefore, improvement of technology has been desired. In addition, the methods disclosed in Patent Document 2 and Patent Document 3 have room for improvement in which formation of fine water droplets for capturing ionized particles and mists is difficult.

[0007] An object of the present invention is to provide an apparatus and method for treating an exhaust gas containing sulfuric acid mist that improves the problems of the prior art and has excellent removal performance for sulfuric acid mist of submicron order in the exhaust gas. It is to provide.

Means for solving the problem

[0008] In order to achieve the above object, an apparatus for treating exhaust gas containing sulfuric acid mist according to the present invention includes a saturation means for supplying water to the exhaust gas containing sulfuric acid mist for saturation, and the saturation means. Fog generating means for passing the exhaust gas through the throat part and generating mist by adiabatic expansion, an ion generating means for generating ions with respect to the exhaust gas in the vicinity of the throat part of the mist generating means, and a stage subsequent to the fog generating means It is characterized by having a wet type electrostatic precipitator installed.

In the present invention, “saturation” means that the degree of saturation of moisture in exhaust gas is 90% or more, and includes a supersaturated state. As the saturation means, means for supplying water vapor to the exhaust gas or water spray means for supplying mist-like water is used. [0010] As the mist generating means according to the present invention, a bench lily duct is preferably used. However, a duct having a throttle valve or a restriction orifice can be used instead of the bench duct. Further, the saturation means according to the present invention may include a control means that takes in information on the flow rate, temperature, and saturation of the exhaust gas and controls the amount of water supplied to the exhaust gas in accordance with the information. Hope.

[0011] In the method for treating exhaust gas containing sulfuric acid mist according to the present invention, after supplying water to the exhaust gas containing sulfuric acid mist and saturating the exhaust gas, the exhaust gas is passed through the throat portion to generate mist by adiabatic expansion. And generating ions with respect to the exhaust gas, and then guiding the exhaust gas to a wet-type electric dust collector. In this case, it is desirable that the flow velocity of the exhaust gas at the throat portion is 20 to 50 mZ seconds.

[0012] In addition, according to the method for treating an exhaust gas containing sulfuric acid mist according to the present invention, the amount of water supplied to the exhaust gas is controlled so that the exhaust gas is saturated in a steady state, and the method is intermittently performed. The amount of moisture supplied to the exhaust gas is controlled to be several times to several tens of times that in a steady state when cleaning the dust collecting electrode of the wet type electrostatic precipitator.

The invention's effect

[0013] When the exhaust gas saturated by the saturation means passes through the throat portion of the mist generation means, the dust and mist in the exhaust gas are charged by the ions generated by the ion generation means. Submicron-order sulfuric acid mist is also charged and ionized. The exhaust gas expands rapidly immediately after passing through the throat part of the fog generating means. The steam in the exhaust gas saturated by the adiabatic expansion action at this time condenses, generating fog. This mist has a particle size of several microns and is finer than a mist of several tens of microns generated by mechanical means such as a water spray nozzle. Such fine mist fills countlessly on the rear side of the mist generating means.

[0014] The dust and mist that have been ionized are repeatedly collided with these countless fine mists, and then coalesce and agglomerate. As a result, the formation of micron-order mist particles with fog as the nucleus proceeds. Most of the submicron-order sulfuric acid mist coalesces and agglomerates with mist, and at the stage where the exhaust gas flows into the wet electrostatic precipitator, the number of submicron-order sulfuric acid mist in the exhaust gas is significantly reduced. For this reason, the wet electrostatic precipitator It is easy to collect mist particles having a relatively large particle size of Lon order, and the removal rate of sulfuric acid mist coalesced and aggregated with the mist particles is improved.

[0015] In addition, submicron-order sulfuric acid mist remaining in the exhaust gas and flowing into the wet electrostatic precipitator without charging with the mist is also charged. For this reason, in the electric field in the wet electrostatic precipitator, the submicron-order sulfuric acid mist is easily attracted to the large mist particles by the Coulomb force generated between the large mist particles. It is easily collected by the dust collector electrode of the wet type electrostatic precipitator accompanying the mist particles. Therefore, according to the present invention, it exhibits excellent removal performance against submicron sulfuric acid mist in the exhaust gas.

[0016] In the present invention, moisture such as water vapor supplied to the exhaust gas by the saturating means is finally collected at the dust collection electrode of the wet electrostatic precipitator. As a result, these moistures serve as washing water, and have the secondary effect of reducing the washing load on the dust collecting electrode.

[0017] In addition, the amount of water supplied to the exhaust gas is controlled so that the moisture of the exhaust gas is saturated in a steady state, and at the time of cleaning the dust collection electrode of the wet electrostatic precipitator that is intermittently performed, If the amount of water to be supplied is controlled to be several times to several tens of times that at the normal time, it is possible to cover most of the washing load at the time of washing with water supplied by the saturation means. Brief Description of Drawings

FIG. 1 is an explanatory view showing an embodiment of a processing apparatus and a processing method according to the present invention.

FIG. 2 is a system diagram illustrating a boiler exhaust gas treatment facility in which a treatment apparatus according to the present invention is incorporated.

FIG. 3 is an explanatory view showing a modification of the saturation means according to the present invention.

Explanation of symbols

[0019] 10 …… Boiler, 11, 13, 15, 17, 19, 21, 23 …… Exhaust gas, 12 …… Denitration equipment, 14 ··· Heat exchange, 16 …… Dry-type electrostatic precipitator, 18 …… Wet desulfurization equipment, 20 …… Processing equipment according to the present invention, 22 …… Warming device, 24 …… Chimney, 26 …… Saturation means, 28 …… Bench lily duct, 30 …… Ion generation means, 32 …… wet electrostatic precipitator, 34 …… duct, 3 6 …… (tapered) duct, 38 …… steam generator, 40 …… nozzle, 42 …… steam piping, 44 …… Flow control valve, 46 …… Control, 48 …… Throat section, 50 …… Discharge electrode, 52 ……… DC high-voltage power supply, 54 …… diffuser, 56, 58 …… duct.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is an explanatory diagram showing an embodiment of a processing apparatus and a processing method according to the present invention, and the processing apparatus is incorporated, for example, on the rear stage side of the boiler exhaust gas treatment facility shown in FIG. Exhaust gas 11 from boilers 10 using fossil fuels such as coal and heavy oil contains dust, nitrogen oxides, and sulfur oxides. The exhaust gas 11 is first guided to a denitration device 12 to remove nitrogen oxides. Next, the temperature of the exhaust gas 13 that has passed through the denitration device 12 is lowered to around 160 ° C. by the heat exchanger 14. Next, the exhaust gas 15 that has passed through the heat exchanger 14 is introduced to a dry electrostatic precipitator 16 to remove dust. Next, the exhaust gas 17 passed through the dry electrostatic precipitator 16 is guided to the wet desulfurizer 18 to remove sulfur oxides. Next, the exhaust gas 19 that has passed through the wet desulfurization apparatus 18 is guided to the treatment apparatus 20 according to the present invention, and dust and mist remaining in the exhaust gas 19 are removed. The exhaust gas 21 that has passed through the treatment device 20 is preheated in a warmer 22 for preventing white smoke, and the heated exhaust gas 23 is discharged into a chimney 24 force atmosphere.

As shown in FIG. 1, the processing apparatus 20 according to the present invention is mainly composed of a saturation means 26, a bench duct 28 that is a mist generation means, an ion generation means 30, and a wet electrostatic precipitator 32. Is done. Exhaust gas 19 that has passed through the wet desulfurization device 18 flows into the saturation means 26 from the duct 34. The saturation means 26 has a tapered duct 36, and steam generated by the steam generator 38 is blown into the duct 36 from the nozzle 40. The amount of water vapor blown from the steam generator 38 into the duct 36 is adjusted by controlling the opening degree of the flow control valve 44 disposed in the steam pipe 42 by the controller 46. The saturating means 26 may be configured to spray mist-like water from a water sprayer instead of water vapor. In this case as well, the amount of water sprayed on the duct 36 is adjusted by the control means.

A bench lily duct 28 is connected to the rear end of the duct 36. The bench lily duct 28 has a throat portion 48 with a narrowed inner diameter. The inner diameter of the throat portion 48 is designed so that the flow rate of the exhaust gas 19 passing through is 20 to 50 mZ seconds. In the vicinity of the throat portion 48, a discharge electrode 50, which is a constituent member of the ion generating means 30, is disposed. The ion generation unit 30 includes a DC high-voltage power supply 52, and the DC high-voltage power supply 52 maintains a high voltage (several tens of kV). Current is discharged from the held discharge electrode 50, and negative ions are generated for the exhaust gas passing through the discharge action.

The rear portion of the bench lily duct 28 is a diffuser 54 having a divergent shape, and the rear end of the diffuser 54 is connected to the inlet of the wet electrostatic precipitator 32 via the duct 56. The exhaust gas 21 that has passed through the wet electrostatic precipitator 32 is sent to the heater 22 through the duct 58.

[0024] Hereinafter, the operation of the processing apparatus 20 according to the present invention will be described. Dust and mist remain in the exhaust gas 19 after passing through the wet desulfurization device 18, and the mist contains a considerable amount of sulfuric acid mist having a particle size of micron order or submicron order. The saturating means 26 supplies water vapor to the exhaust gas 19 passing through the duct 36 to saturate the exhaust gas 19. The controller 46 takes in information on the flow rate, temperature, and saturation of the exhaust gas 19 and calculates the amount of water vapor supplied to the exhaust gas 19 based on the information. Based on the calculation result, the opening degree of the flow rate control valve 44 is controlled to adjust the amount of water vapor supplied into the duct 36. As a result, the water vapor blown from the nozzle 40 is mixed with the exhaust gas 19 in the duct 36, and the exhaust gas 19 is saturated to a saturation degree of 90% and is sent to the bench lily duct 28.

[0025] In order to uniformly saturate the exhaust gas 19, it is necessary to sufficiently mix and diffuse the steam with respect to the exhaust gas 19, and the exhaust gas 19 reaches the venturi dart 28 even at the position where the steam is blown. The shape and volume of the dirt 36 are designed so that the retention time of the exhaust gas 19 until it is 0.5 seconds or longer.

[0026] When spraying water instead of water vapor, the amount of water supplied into the duct 36 is adjusted in the same way. In the case of water spraying, it is necessary to saturate the exhaust gas 19 by evaporating the sprayed water, and in order to promote evaporation, the spray nozzle should be selected so that the mist particle size is 30 m or less. is important. In the case of water spraying, it takes more time for the sprayed water to sufficiently mix with the exhaust gas and evaporate, compared to steam blowing, so that the exhaust gas 19 also reaches the bench lily duct 28 at the water spray position. The shape and volume of the duct 36 are designed so that the retention time of the exhaust gas 19 is 1 second or longer.

[0027] In the water spray, the sensible heat of the exhaust gas 19 becomes a source of energy for promoting evaporation, and the temperature of the exhaust gas 19 rapidly decreases due to the heat of vaporization during evaporation. Therefore, if the exhaust gas 19 is hot due to various circumstances and you want to lower this temperature, water spray is available. It is effective. Conversely, when the temperature of the exhaust gas 19 is relatively low and vaporization cannot be promoted, it is advantageous to blow in water vapor.

[0028] The exhaust gas 19 saturated by the saturating means 26 is contracted by the throat portion 48 of the bench lily duct 28 and passes through the throat portion 48 at a high speed of 20 to 50 mZ seconds as described above. At this time, dust or mist in the exhaust gas 19 is charged by negative ions generated by the discharge from the discharge electrode 50. Submicron-order sulfuric acid mist is also charged and ionized. Since the discharge electrode 50 is disposed in the vicinity of the throat portion 48, it is possible to efficiently form a spatial electric field with respect to the exhaust gas 19 that has contracted. Further, as described above, since the exhaust gas 19 passes through the throat portion 48 at a high speed, generation of sparks due to discharge from the discharge electrode 50 is suppressed. For this reason, the applied voltage at the discharge electrode 50 can be increased to increase the charging efficiency against dust and mist.

[0029] Immediately after passing through the throat portion 48, the exhaust gas 19 rapidly expands in the diffuser 54. At this time, the adiabatic expansion action condenses the vapor in the exhaust gas 19 that is close to saturation, generating mist. This mist is finer than a mist generated by mechanical means such as a water spray nozzle, and such a fine mist fills the diffuser 54 innumerably.

[0030] The ionized dust or mist repeats and collides with these countless fine mists, and coalesces and aggregates with the mists. As a result, in the diffuser 54 and the duct 56, formation of mist particles having a particle size on the order of microns centered on fog is progressed. Most of the sub-micron-order sulfuric acid mist coalesces and aggregates with fog, and at the stage where the exhaust gas 19 flows into the wet electrostatic precipitator 32, the number of sub-micron-order sulfuric acid mist in the exhaust gas 19 is significantly reduced. . For this reason, the wet electrostatic precipitator 32 facilitates the collection of mist particles having a comparatively large particle size on the order of microns, and the removal rate of sulfuric acid mist coalesced and aggregated with the mist particles is also improved.

[0031] Further, the submicron sulfuric acid mist remaining in the exhaust gas 19 without flowing into the mist and flowing into the wet electrostatic precipitator 32 is also charged by the discharge from the discharge electrode 50. For this reason, in the electric field inside the wet electrostatic precipitator 32, the submicron-order sulfuric acid mist is easily attracted to the large mist particles by the Coulomb force generated between the large mist particles. Wet electrostatic dust collection accompanied by large diameter mist particles Easily collected on 32 dust collectors.

Therefore, according to the processing apparatus 20 according to the present embodiment, excellent removal performance is exhibited with respect to the sulfuric acid mist of the submicron order in the exhaust gas. According to the results of the study by the present inventor, although there is a large difference depending on the processing conditions, the sulfuric acid mist concentration at the outlet of the wet electrostatic precipitator 32 is a fraction or tens of minutes compared to the conventional method described in the background section. It can be reduced to one.

[0033] Normally, in the wet electrostatic precipitator 32, washing water is sprayed continuously or intermittently on the dust collecting electrode to wash away dust and mist trapped on the dust collecting electrode. In the processing apparatus 20 according to the present embodiment, moisture such as water vapor supplied to the exhaust gas 19 by the saturating means 26 is finally collected at the dust collection electrode of the wet electrostatic precipitator 32. As a result, these moistures serve as washing water, and the washing load is reduced. That is, the treatment apparatus 20 according to the present embodiment reduces the cleaning load necessary for cleaning the dust collection electrode of the wet electrostatic precipitator 32 in addition to the main effect of improving the removal performance of sulfuric acid mist in the exhaust gas. The secondary effect is as follows. In addition, since the concentration of sulfuric acid mist is reduced by the supplied water before being collected by the dust collecting electrode, there is an effect of suppressing corrosion of the dust collecting electrode.

[0034] There is a method for more actively utilizing such a secondary effect on cleaning.

That is, the controller 46 controls the amount of water supplied from the saturation means 26 so that the moisture of the exhaust gas 19 is saturated at the steady state, and at the time of cleaning the dust collection electrode of the wet electrostatic precipitator 32 that is performed intermittently. The amount of water supplied from the saturating means 26 is controlled to be several times to several tens of times that in the steady state. By providing the saturating means 26 with such a function, it is possible to cover most of the cleaning load of the full-scale cleaning performed intermittently with the water supplied from the saturating means 26.

In the embodiment, the case where the tapered duct 36 is used as the moisture supply container for the exhaust gas 19 in the saturation means 26 has been described. However, the present invention is not limited to this, and as shown in FIG. 3, a container 60 having a sufficiently large channel cross-sectional area with respect to the inflow duct 34 of the exhaust gas 19 is used. Steam or the like may be blown into the exhaust gas 19 that has flowed in from the nozzle 40. Moreover, in the said embodiment, the case where the bench lily single duct 28 was used as fog generation means was shown. However, the present invention is not limited to this. A duct having a throttle valve having a groove portion and a restriction orifice can be used instead.

The treatment apparatus and treatment method for exhaust gas containing sulfuric acid mist according to the present invention is a relatively high-temperature boiler in which the upstream equipment from the denitration device 12 to the wet desulfurization device 18 is omitted in the boiler exhaust gas treatment facility shown in FIG. It can also be applied when exhaust gas is treated directly. Moreover, the treatment apparatus and treatment method for exhaust gas containing sulfuric acid mist according to the present invention are not limited to boiler exhaust gas, and can be applied to exhaust gas containing sulfuric acid mist discharged from various furnaces.

Claims

The scope of the claims

[1] Saturation means for supplying moisture to exhaust gas containing sulfuric acid mist to saturate, fog generation means for passing the exhaust gas that has passed through the saturation means through the throat portion and generating mist by adiabatic expansion, and the mist generation Including a sulfuric acid mist characterized by comprising an ion generating means for generating ions with respect to the exhaust gas in the vicinity of the throat portion of the means, and a wet electrostatic precipitator disposed after the fog generating means. Exhaust gas treatment equipment.

[2] The treatment of exhaust gas containing sulfuric acid mist according to claim 1, wherein the saturation means is means for supplying water vapor to the exhaust gas or water spray means for supplying mist-like water. apparatus.

[3] The apparatus for treating an exhaust gas containing sulfuric acid mist according to claim 1 or 2, wherein the mist generating means is a bench lily duct.

4. The apparatus for treating exhaust gas containing sulfuric acid mist according to claim 1 or 2, wherein the mist generating means is a duct having a throttle valve or a restriction orifice.

[5] The saturation unit includes a control unit that takes in information on the flow rate, temperature, and saturation of the exhaust gas, and controls the amount of moisture supplied to the exhaust gas according to the information. An apparatus for treating exhaust gas containing the sulfuric acid mist according to any one of claims 1 to 4.

[6] After supplying moisture to the exhaust gas containing sulfuric acid mist and saturating the exhaust gas, the exhaust gas is passed through the throat portion to generate mist by adiabatic expansion, and ions are generated with respect to the exhaust gas. A method for treating exhaust gas containing sulfuric acid mist, wherein the exhaust gas is guided to a wet electrostatic precipitator.

7. The method for treating exhaust gas containing sulfuric acid mist according to claim 6, wherein the flow rate of the exhaust gas at the throat portion is 20 to 50 mZ seconds.

[8] The amount of water supplied to the exhaust gas is controlled so that the exhaust gas is saturated at steady state, and when the dust collecting electrode of the wet electrostatic precipitator is intermittently performed, several times from the steady state 7. The method for treating an exhaust gas containing sulfuric acid mist according to claim 6, wherein the amount of water supplied to the exhaust gas is controlled to be several tens of times.