JP3923681B2 - Exhaust gas dedusting apparatus and method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a dust removing apparatus and a dust removing method suitable for removing fine particles having a particle size in submicron units from combustion exhaust gas discharged from a wet limestone-gypsum desulfurization apparatus installed in a thermal power plant or the like. It is.
[0002]
[Prior art]
The combustion gas discharged from the boiler of a coal-fired power plant contains about 20 g / m ³ N fine particles. Most of the fine particles are coal ash mainly composed of silica and alumina having a particle diameter of 0.1 to 20 μm. An electrostatic precipitator is generally installed for the purpose of removing such fine particles, and this electrostatic precipitator is a high-performance one that reduces the fine particles in the combustion exhaust gas to 100 to 200 mg / m ³ N. Then, the combustion exhaust gas in which the fine particles contained in the electrostatic precipitator are reduced to a predetermined amount is introduced into a wet limestone-gypsum desulfurization apparatus, where it comes into contact with an absorbent containing an alkaline agent such as limestone. In this case, part of the fine particles contained in the combustion exhaust gas is also removed by the absorbing liquid. The fine particle concentration can be adjusted to 30 to 50 mg / m ³ N at the outlet of the wet limestone-gypsum desulfurization apparatus.
[0003]
Recently, there is a high demand for lower dust in the smoke exhaust port gas of the boiler exhaust gas after the purification treatment, and it is necessary to develop a technology for further reducing the fine particle concentration in the smoke exhaust port gas. It has been regarded as a problem that when the concentration of fine particles in the smoke outlet gas becomes high, it causes visual pollution such as purple smoke. The cause of this visual pollution is assumed to be that sulfuric acid mist and the like are scattered from the desulfurization apparatus in addition to the fine particles.
[0004]
In order to eliminate such visual pollution, a dedusting system is known in which the concentration of fine particles can be reduced to 10 mg / m ³ N or less by introducing an outlet gas of a wet limestone-gypsum desulfurization apparatus into a wet electrostatic precipitator. It has been. In general, since a dry electrostatic precipitator is installed upstream of the wet limestone-gypsum desulfurization apparatus, the particle size of the wet electric precipitator not collected by the dry electrostatic precipitator or the wet limestone-gypsum desulfurization apparatus is 1 μm or less. Therefore, it is necessary to collect fine particles having a particle size of a submicron unit, and a higher performance than a dry electrostatic precipitator is required. For this reason, the apparatus configuration of the wet electrostatic precipitator is inevitably increased in capacity, and when such a wet electrostatic precipitator is used to construct an integrated flue gas treatment system for a thermal power plant, the system becomes large-scale. .
[0005]
As a method for preventing a large-scale smoke treatment system from being installed, the equipment cost is lower than that of a wet type electrostatic precipitator, and a system that achieves low dust generation by a simple method is used as an exhaust gas in the desulfurizer outlet gas shown in FIG. There is a method in which cooling water having a lower temperature is sprayed to remove fine particles in the cooled exhaust gas (JP-A-8-215535, etc.).
[0006]
The configuration of the apparatus shown in FIG. 3 will be described below. Most of the exhaust gas 10 is collected by the dry electrostatic precipitator 11 and introduced into the absorption tower 12 of the desulfurization apparatus. In the absorption tower 12, the absorption liquid 20 is pressurized by the absorption tower circulation pump 21 and sprayed from the spray section 23 through the absorption liquid circulation pipe 22. The dust that has not been removed by the dry electrostatic precipitator 11 is further removed by inertial collision with the absorbing liquid sprayed in the absorption tower 12, but the dust having a small particle size in submicron units is not removed but the absorption tower 12. Discharged from.
[0007]
On the other hand, in the gas flow path at the outlet of the desulfurization apparatus, the cooling water in the cooling water tank 30 is pressurized by the cooling water pump 32 and sprayed by the cooling unit 33. In the cooling unit 33, moisture condenses and enlarges in the core of the dust, so that the particle size becomes larger and the dust collection efficiency by the spray cooling water due to the inertia force is increased. Moreover, a cooling effect is accelerated | stimulated by installing the spray stage of the cooling part 33 in multiple stages with respect to a gas flow, and dust collection efficiency is improved. The dust in the cooling water mist collected by the cooling unit 33 is collected by the mist eliminator 40 together with the cooling water.
[0008]
The dust and cooling water collected by the mist eliminator 40 are returned to the cooling water tank 30 through the drain pipe 41. The cooling water tank 30 is provided with a cooling source 31 to prevent the temperature of the cooling water from rising. An overflow pipe 34 for returning water from the cooling water tank 30 to the absorption tower 12 is provided in order to collect the condensed water.
[0009]
The exhaust gas at the outlet of the desulfurizer contains soot that is saturated with water and has not been removed by the desulfurizer. The system shown in FIG. 3 makes this exhaust gas contact cooling water at a temperature lower than that, condenses the moisture in the exhaust gas with dust as a core, creates an enlarged mist, and supplies the mist and the supplied cooling water. By removing with a mist removing device (mist eliminator) 40, the dust concentration at the outlet of the chimney 13 can be made lower than the dust concentration in the exhaust gas at the outlet of the desulfurization device.
[0010]
[Problems to be solved by the invention]
In the above prior art, cooling water is sprayed into the exhaust gas at the outlet of the desulfurization apparatus. On the other hand, the absorption liquid sprayed in the absorption tower 12 of the desulfurization apparatus is accompanied by the gas and partly scatters as mist. The mist scattered from the desulfurizer has a concentration of 30 to 50 g / m ³ N, and the mist contains 10 to 20% of a solid matter of a desulfurizing agent. Accordingly, the solid matter scattered from the desulfurization apparatus contains ^{3 to} 10 g / m ³ N as a concentration.
[0011]
Most of the mist scattered from the desulfurizer and the solids contained in the mist are collected by the cooling water sprayed at the outlet of the desulfurizer, but since the cooling water is circulated, the solid concentration in the cooling water increases. It will be. After being sprayed into the gas, the recovered cooling water contains the water condensed by supercooling and the water in the mist that scatters from the desulfurization unit. In order to recover these waters as make-up water for the desulfurization unit The solids concentration in the cooling water eventually becomes balanced and constant, but the concentration increases to 10-20%. When the solid substance concentration in the cooling water increases, the cooling water is entrained by the gas, so that the solid matter contained in the cooling water also re-scatters, and the dust concentration in the gas at the exit of the chimney 13 increases.
[0012]
An object of the present invention is to solve the above-described problems of the prior art. By preventing the solid concentration in the cooling water sprayed at the outlet of the desulfurization apparatus from increasing, the solids in the spray cooling water are regenerated. It is to prevent the dust concentration in the gas at the smoke outlet from increasing.
[0013]
[Means for Solving the Problems]
In the present invention, two stages of mist eliminators are installed in the gas flow path at the outlet of the desulfurization apparatus, and cooling water is sprayed between the mist eliminator at the front stage and the mist eliminator at the rear stage.
[0014]
[Means for Solving the Problems]
The above-described problem of the present invention is solved by the following configuration.
That is, the invention according to claim 1 is provided in a gas flow path in which an absorption tower for contacting and removing the sulfur oxide in the exhaust gas by bringing the combustion exhaust gas into contact with an alkaline absorption liquid is discharged from the absorption tower. that in the opposite direction against the gas flow direction after the desulfurization, the droplet spray unit for spraying liquid droplets that are cooled to a temperature lower than the gas to the gas, for supplying cooling water to said liquid droplet spraying means A cooling water system, a mist eliminator provided in each of a gas flow path on the upstream side and the downstream side of the droplet spraying means, a flow path for returning mist collected by the upstream mist eliminator to an absorption tower, and the downstream mist An exhaust gas dedusting apparatus including a flow path for returning the mist collected by the eliminator to the cooling water system in order to use the cooling source to form cooling water having a temperature lower than that of the gas .
The invention according to claim 2 is a liquid cyclone provided in a flow path for returning the mist collected by the latter-stage mist eliminator to the cooling water system, and a flow path for returning the slurry diluted with the liquid cyclone to the cooling water system. 2. The exhaust gas dedusting apparatus according to claim 1, further comprising a flow path for returning the slurry concentrated in the liquid cyclone to the absorption tower.
[0015]
In the invention according to claim 3, the combustion exhaust gas is brought into contact with the alkaline absorbing liquid in the absorption tower to absorb and remove sulfur oxides in the exhaust gas, and then the reverse direction from the cooling water system with respect to the gas flow direction after desulfurization. In addition, droplets cooled to a temperature lower than the gas are sprayed on the gas, mist is removed from the exhaust gas on the front side and the rear side of the droplet spraying position, and the exhaust gas on the front side of the droplet spraying position is removed. The mist collected from the mist is returned to the absorption tower, and the mist collected from the exhaust gas at the rear stage of the droplet spraying position is returned to the cooling water system so as to be cooled to a temperature lower than the gas. An exhaust gas desulfurization dedusting method characterized by the above.
According to a fourth aspect of the present invention, after once collecting the mist collected from the exhaust gas on the downstream side of the droplet spraying position, a concentrated slurry and a diluted slurry are obtained, and the diluted slurry is removed from the cooling water. The exhaust gas dedusting method according to claim 3, wherein the exhaust gas is returned to the system and the concentrated slurry is returned to the absorption tower.
[0016]
[Action]
When configured as described above, the mist containing the solid matter scattered from the desulfurization device inertially collides with the mist eliminator provided at the desulfurization device outlet together with the desulfurized exhaust gas, and most of the mist and solid matter are removed. Is done. The mist and solid matter removed by the former stage mist eliminator are extracted from the former stage mist eliminator as drain and collected in the desulfurization apparatus. Here, the solid in the outlet gas of the former mist eliminator is soot having a particle size of submicron units that has passed through the former mist eliminator.
[0017]
This dust is cooled by the cooling water sprayed from the droplet spraying means, is enlarged when moisture condenses in the core of the dust, and is collected in the spray cooling water by inertial collision with the fine droplets of the cooling water. The The cooling water mist collected up to soot having a particle size in the submicron unit is further removed by a downstream mist eliminator on the downstream side. The mist containing the cooling water and the solid matter collected by the post-stage mist eliminator is extracted from the post-stage mist eliminator and returned to the cooling water system. That is, the cooling water is circulated and used by the droplet spraying means.
[0018]
The solid matter in the mist removed by the post-stage mist eliminator is soot having a particle size of almost submicron units, and the condensed water collected together with the cooling water and the water in the mist are returned to the desulfurization unit. The solid concentration can be 0.1% or less. Thereby, even if the cooling water once collected by the latter stage mist eliminator is re-sprayed as mist from the droplet spraying means, it is discharged into the atmosphere because the solid matter concentration in the mist is 0.1% or less. The dust concentration hardly increases.
[0019]
In addition, if a liquid cyclone is provided in the flow path for returning the mist collected by the post-stage mist eliminator to the cooling water system, and the slurry diluted with the liquid cyclone is returned to the cooling water system, the solids concentration in the cooling water is further reduced. It is possible to prevent an increase in the concentration of dust released into the atmosphere even if it is re-scattered into the gas. [0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments.
FIG. 1 is a schematic view of an exhaust gas treatment apparatus according to a specific example of the present invention.
[0021]
Most of the exhaust gas 10 is collected by a dry electrostatic precipitator 11 and introduced into an absorption tower 12 of a desulfurization apparatus. The absorption liquid 20 stored in the lower part of the absorption tower 12 is pressurized by the absorption tower circulation pump 21 and sprayed from the spray section 23 through the absorption liquid circulation pipe 22. The dust that has not been removed by the dry electrostatic precipitator 11 is further removed by inertial collision with the absorbing liquid sprayed in the absorption tower 12, but the dust having a small particle size in submicron units is not removed but the absorption tower 12. Discharged from.
[0022]
On the other hand, at the outlet of the desulfurization apparatus, the cooling water in the cooling water tank 30 is pressurized by the cooling water pump 32 and sprayed by the cooling unit 33. In the cooling unit 33, the moisture is condensed and enlarged in the dust core, so that the particle size is increased and the collection efficiency by the inertial force is increased. Moreover, a cooling effect is accelerated | stimulated by installing the spray stage of the cooling part 33 in multiple stages with respect to a gas flow, and dust collection efficiency is improved. The dust in the mist collected by the cooling unit 33 is collected together with the cooling water by the mist eliminator 40b. The dust and cooling water collected by the mist eliminator 40b are returned to the cooling water tank 30 through the drain pipe 41b. An overflow pipe 34 for returning water from the cooling water tank 30 to the absorption tower 12 is provided in order to collect the condensed water.
[0023]
The above configuration is the same as the prior art shown in FIG. 3, but in the configuration of the present invention shown in FIG. 1, a front mist eliminator 40a and a rear mist eliminator 40b are provided before and after the cooling section 33 at the outlet of the absorption tower 12. It is characterized by being. The upstream mist eliminator 40 a is provided with an absorption tower return pipe 41 a for returning the collected mist and solid matter from the collected absorption tower 12 to the absorption tower 12.
[0024]
With this configuration, most of the mist scattered from the absorption tower 12 and the solids contained in the mist are collected by the upstream mist eliminator 40a and returned to the absorption tower 12 by the absorption tower return pipe 41a. Mist concentration in the gas which has not been removed by the pre-stage mist eliminator 40a is 100~200mg / ^{m 3} N, solids concentration in the mist is 20~40mg / ^{m 3} N. Further, soot having a particle size of a submicron unit that has passed through the absorption tower 12 and the former stage mist eliminator 40a is also included in the solid matter.
[0025]
In the cooling unit 33, the desulfurizer outlet gas is rapidly cooled by contact with the sprayed cooling water, and the water vapor in the gas forms a supercooled state. In the process of flying through the cooling unit 33, the water vapor in the supercooled state easily condenses using dust as a condensation nucleus, and the dust itself is enlarged. The condensed series of particles is collected by being guided to a downstream mist eliminator 40b installed in a gas flow path on the downstream side of the cooling unit 33. The spraying stage of the cooling unit 33 is multi-staged and cooled and condensed. In the spray stage on the front stage side, the dust removal effect can be further increased by causing the particles enlarged due to supercooling to collide with the cooling water droplets in inertia in the spray stage on the rear stage side.
[0026]
The cooling water used in the cooling unit 33 is collected by the post-stage mist eliminator 40b, and the water returned to the cooling water tank 30 through the drain pipe 41b is used. Cooling water is exchanged in the cooling water tank 30 by a cooling source 31 and cooled. The gas from which the dust and a part of the moisture are collected is introduced into a gas / gas heat exchanger (not shown) and heated, and then discharged from the chimney 13.
[0027]
With the configuration of FIG. 1, the solid concentration in the cooling water used in the cooling unit 33 that has conventionally been 10 to 20% can be reduced to 0.1% or less. Therefore, even if the cooling water containing solid matter is entrained in the gas and scattered as a mist to the downstream side of the cooling unit 33, even if a part of the cooling water is discharged from the chimney 13 without being collected by the rear-stage mist eliminator 40 b, the chimney 13 The dust concentration at the outlet does not increase.
[0028]
FIG. 2 is a schematic view of an exhaust gas treatment apparatus according to another embodiment of the present invention. In FIG. 2, reference numerals 10 to 13, reference numerals 20 to 23, reference numerals 30 to 34, and reference numerals 40a to 41b are the same as those in FIG.
[0029]
The feature of the configuration shown in FIG. 2 is that a hydrocyclone 42 is provided on the drain pipe 41b of the post-stage mist eliminator 40b. The mist collected by the post-stage mist eliminator 40b is introduced into the hydrocyclone 42, where the solid matter in the recovered mist is concentrated by utilizing centrifugal force. The slurry in which the solid matter is concentrated is returned to the absorption tower 12 via the concentrated slurry pipe 44.
[0030]
On the other hand, the supernatant diluted with the liquid cyclone 42 is returned to the cooling water tank 30 through the dilution slurry pipe 43. In the present embodiment, since the solid matter in the mist collected by the rear mist eliminator 40b is diluted by the liquid cyclone 42 before being returned to the cooling water tank 30, the solid matter concentration in the circulating cooling water is further increased. It can be reduced, and an increase in the dust concentration at the exit of the chimney 13 due to re-scattering can be prevented.
[0031]
【The invention's effect】
According to the present invention, by providing the mist eliminator on the upstream side and the downstream side of the droplet spraying means, most of the solid matter in the mist scattered from the absorption tower can be collected and removed by the upstream mist eliminator. Therefore, the solid concentration in the cooling water does not increase, and the dust concentration at the smoke outlet does not increase due to the re-scattering of the solid into the gas.
[0032]
Further, the mist eliminator usually cleans the inertial collision surface of the mist by spraying water in order to prevent adhesion of solid matter. In the present invention, if the cooling water is sprayed in the vicinity of the downstream side of the upstream mist eliminator, it can also serve as cleaning water, so that there is an effect of reducing the amount of cleaning water, that is, reducing utility.
[Brief description of the drawings]
FIG. 1 is a schematic view of an absorption tower showing an embodiment of the present invention.
FIG. 2 is a schematic view of an absorption tower showing an embodiment of the present invention.
FIG. 3 is a schematic view of an absorption tower showing an example of the prior art.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Exhaust gas 11 Dry type electrostatic precipitator 12 Absorption tower 13 Chimney 20 Absorption liquid 21 Absorption tower circulation pump 22 Absorption liquid circulation piping 23 Spray part 30 Cooling water tank 31 Cooling source 32 Cooling water pump 33 Cooling part 34 Overflow piping 40 Mist eliminator 40a Previous stage mist Eliminator 40b Rear mist eliminator 41a Absorption tower return piping 41, 41b Drain piping 42 Hydrocyclone 43 Diluted slurry piping 44 Concentrated slurry piping

Claims (4)

Provided in the gas flow path absorption tower combustion exhaust gas is brought into contact with the alkaline absorbent solution to remove absorbed sulfur oxides in the exhaust gas is arranged, for the gas flow direction after the desulfurization discharged from the absorption tower Conversely , droplet spraying means for spraying droplets cooled to a temperature lower than the gas onto the gas;
A cooling water system for supplying cooling water to the droplet spraying means;
Mist eliminators respectively provided in the gas flow paths on the front and rear sides of the droplet spraying means;
A flow path for returning the mist collected by the preceding mist eliminator to the absorption tower;
An exhaust gas dedusting apparatus comprising a flow path for returning the mist collected by the latter-stage mist eliminator to the cooling water system in order to make the cooling water at a temperature lower than the gas using a cooling source. .   A liquid cyclone provided in a flow path for returning the mist collected by the latter-stage mist eliminator to the cooling water system, a flow path for returning slurry diluted with the liquid cyclone to the cooling water system, and concentrated in the liquid cyclone. The exhaust gas dedusting apparatus according to claim 1, further comprising a flow path for returning the slurry to the absorption tower. After the combustion exhaust gas is brought into contact with an alkaline absorbing liquid in the absorption tower to absorb and remove sulfur oxides in the exhaust gas,
In the opposite direction from the cooling water system for the flow direction of the gas after desulfurization, the droplets are cooled to a temperature lower than the gas sprayed to gases,
Remove the mist from the exhaust gas on the front side and the rear side of the droplet spraying position,
The mist collected from the exhaust gas on the front side of the droplet spraying position is returned to the absorption tower,
An exhaust gas desulfurization dedusting treatment method , wherein the mist collected from the exhaust gas at the downstream side of the droplet spraying position is returned to the cooling water system in order to make the cooling water cooled to a temperature lower than the gas.   After once collecting the mist collected from the exhaust gas on the downstream side of the droplet spraying position, a concentrated slurry and a diluted slurry are obtained, and the diluted slurry is returned to the cooling water system, where the concentrated slurry is recovered. The exhaust gas dedusting method according to claim 3, wherein the exhaust gas is returned to the absorption tower.

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