JP2018030091A - Particle removal device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a particle removal device capable of removing efficiently condensable particles generated from a material contained in exhaust gas.SOLUTION: A particle removal device 1 includes the first cooling part 3 for spraying droplets to gas containing SO, and cooling the gas to a temperature near a sulfuric acid dew point and higher than the sulfuric acid dew point, the second cooling part 4 for spraying droplets to the gas having passed through the first cooling part 3, and cooling the gas to a temperature near a water dew point and higher than the water dew point, and an electric field formation part 5 for forming an electric field to a space where the gas having passed through the second cooling part 4 is circulated.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a particle removing device, and more particularly to a particle removing device that removes condensable particles such as sulfuric acid mist generated from substances contained in exhaust gas from a boiler.

The exhaust gas discharged from the oil boiler includes, for example, SO ₂ gas and SO ₃ gas. In a wet desulfurization apparatus installed in an exhaust gas treatment facility, a desulfurization reaction is caused in an absorption tower by absorption with an absorbing liquid with respect to sulfur components such as SO ₂ gas and SO ₃ gas contained in exhaust gas. Therefore, in the absorption tower, the exhaust gas is cooled to the water saturation temperature in the cooling section upstream of the inlet section of the absorption tower. As a method for cooling the exhaust gas, it is common to spray water in the exhaust gas.

In the wet desulfurization apparatus, SO ₂ gas is easily collected by gas absorption treatment. On the other hand, the SO ₃ gas becomes mist during the process of cooling the exhaust gas and becomes condensable particles. For this reason, in the wet desulfurization apparatus, the efficiency of collecting misted SO ₃ (sulfuric acid mist) is poor, and the sulfuric acid mist comes out as purple smoke from the chimney.

JP 10-174899 A (Patent No. 3572164) Japanese Patent Laying-Open No. 2005-349272 (Japanese Patent No. 4326403)

When the exhaust gas is cooled, the SO ₃ gas contained in the exhaust gas changes from gas to mist when the acid dew point is equal to or higher than the water dew point. For this reason, when a large amount of exhaust gas is cooled in a short time, a large amount of fine sulfuric acid mist of the submicron class (misted SO ₃ ) is generated. As a result, even if a large amount of absorbing liquid is dropped in the cooling tower body or the absorption tower on the downstream side of the cooling tower, these mists are collected only by physical collision with the liquid droplets, Is not expensive.

  In order to prevent harmful effects due to the generation of a large amount of sulfuric acid mist, thermal power plants that use high sulfur fuels (for example, heavy oil and petroleum coke) in the exhaust gas upstream of the electric dust collector (EP) In some cases, ammonia is injected. In this case, solid ammonium sulfate (ammonium sulfate) is produced by the ammonia injection, and ammonium sulfate is collected together with dust in the subsequent electric dust collector. However, since ammonia is used, the operating cost is high, and it is also necessary to treat the reaction product and treat surplus ammonia absorbed in the waste water of the downstream desulfurization apparatus. In some cases, a wet electrostatic precipitator is installed on the downstream side of the wet desulfurization apparatus, and high-concentration sulfuric acid mist is collected by the desulfurized wet electrostatic precipitator. In this case, since a high-concentration sulfuric acid mist is processed, the wet electrostatic precipitator must be enlarged, and there is a problem that the construction cost is high.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a particle removal apparatus capable of efficiently removing condensable particles generated from substances contained in exhaust gas. And

In order to solve the above problems, the particle removing apparatus of the present invention employs the following means.
That is, the particle removing apparatus according to the present invention sprays droplets on a gas containing a target substance, and cools the gas to a predetermined temperature near the acid dew point of the target substance and above the acid dew point. A cooling unit, a second cooling unit that sprays droplets on the gas that has passed through the first cooling unit, and cools the gas to a temperature near the water dew point and above the water dew point; and the second An electric field forming unit that forms an electric field in a space in which the gas that has passed through the cooling unit flows.

According to this configuration, in the first cooling unit, droplets are sprayed on the gas containing the target substance (for example, SO ₃ ), and the gas is in the vicinity of the acid dew point of the target substance and the acid dew point (SO ₃ of SO ₃ ). In this case, it is cooled to a temperature equal to or higher than the sulfuric acid dew point (eg, acid dew point + 5 ° C to + 20 ° C). Thereby, a part of the liquid evaporates while taking up the target substance, and a mist having a relatively coarse particle diameter (in the case of SO ₃ , sulfuric acid mist) is generated. Then, in the second cooling unit, droplets are sprayed on the gas that has passed through the first cooling unit, and the gas is cooled to a temperature near the water dew point and above the water dew point. As a result, fine condensable particles are generated from the target substance that has not been taken into the droplet sprayed by the first cooling unit. The fine condensable particles are, for example, 0.1 μm or more and 1.0 μm or less. Fine condensable particles are generated in the immediate vicinity of the droplet sprayed by the second cooling unit. Then, an electric field is formed in the space in which the gas flows by the electric field forming unit, and the gas flows in the formed electric field, so that the droplets and the fine condensable particles are dielectrically polarized with each other, and the condensability Fine particles are attracted to the droplets. By maintaining the temperature at a predetermined temperature higher than the acid dew point in the first cooling unit, a mist having a relatively coarse particle diameter is generated, and when the gas is cooled to the vicinity of the water dew point in the second cooling unit, the number of condensable particles Can be prevented, and the sulfuric acid mist can be prevented from being miniaturized. Mist having a relatively coarse particle diameter is easy to be collected by a desulfurization apparatus installed on the downstream side because the particle diameter is large.

  In the above invention, the liquid droplets passing through the electric field formed by the electric field forming unit are supplied to an absorption tower of a wet desulfurization apparatus, and water stored in the absorption tower is used as the first cooling unit or the first It is supplied to 2 cooling units, and may be reused as water supplied to the gas by the first cooling unit or the second cooling unit.

  According to this configuration, the water used in the first cooling section of the particle removal apparatus circulates between the particle removal apparatus and the absorption tower of the wet desulfurization apparatus, and the amount of water that needs to be newly supplied is reduced. Can be reduced.

  In the above invention, the electric field forming unit may include two electrodes facing each other and form an electric field between the two electrodes.

  According to this configuration, when a voltage is applied to one electrode, an electric field is formed. When droplets are sprayed from the second cooling unit, the droplets are positively and negatively polarized by the formed electric field. The fine condensable particles generated in the immediate vicinity of the droplet are themselves dielectrically polarized, and the condensable particle has a charge opposite to the polarity of the droplet. It is attracted and attached.

  In the above invention, the electric field forming unit includes a ground electrode and a discharge electrode having a barb portion provided to face the ground electrode, and an AC voltage is applied to the discharge electrode, and the second cooling unit The droplets sprayed from may be charged alternately with a positive charge and a negative charge with a time difference.

  According to this configuration, a group of sprayed droplets is alternately charged to positive and negative charges with a time difference, respectively, so that a droplet group having a positive charge and a droplet group having a negative charge are charged. An electric field is formed between the two.

  In the above invention, the electric field forming unit may have a configuration capable of charging a droplet sprayed from a nozzle included in the second cooling unit to a positive charge and a negative charge.

  According to this configuration, since the sprayed droplets can be charged to positive and negative charges, a group of positively charged droplets and negative charges can be provided without providing an external electrode. An electric field is formed between droplet groups having

In the above invention, the electric field forming section may be installed in a plurality of stages along the gas flow direction.
According to this configuration, the collection efficiency can be further increased as compared with the case where only one electric field forming unit is installed.

  According to the present invention, condensable particles generated from a substance contained in exhaust gas can be efficiently removed.

It is a schematic block diagram which shows the absorption tower of the particle removal apparatus and wet desulfurization apparatus which concern on one Embodiment of this invention. It is a schematic block diagram which shows the 1st Example of the electric field formation part of the particle removal apparatus which concerns on one Embodiment of this invention. It is a schematic block diagram which shows the 2nd Example of the electric field formation part of the particle removal apparatus which concerns on one Embodiment of this invention. It is a schematic block diagram which shows the 3rd Example of the electric field formation part of the particle removal apparatus which concerns on one Embodiment of this invention. It is a schematic block diagram which shows the 4th Example of the electric field formation part of the particle removal apparatus which concerns on one Embodiment of this invention. It is a schematic diagram which shows the droplet and condensable particle | grains in an electric field.

  As shown in FIG. 1, the particle removal apparatus 1 according to an embodiment of the present invention is installed on the upstream side of the gas flow of the absorption tower 40 of the wet desulfurization apparatus, and cools the exhaust gas, for example, lowers the exhaust gas to the water dew point. In the process, the condensable particles (such as sulfuric acid mist) which are fine mists are attached to the sprayed droplets. The droplets to which the sulfuric acid mist adheres are collected by a collecting part such as an absorption tower 40, a mist eliminator or an electric dust collector of a wet desulfurization apparatus provided on the downstream side, and the sulfuric acid mist is removed from the exhaust gas. . In the example shown in FIG. 1, a mist eliminator 41 as a collection unit is installed at the upper part of the absorption tower 40.

The exhaust gas is a gas generated when fuel (for example, heavy oil or petroleum coke) is burned. The gas to be removed includes, for example, a sulfur content (SO ₃ or the like). In the following, the condensable particles are sulfuric acid mist in which SO ₃ is mist, and a case where sulfuric acid mist is collected will be described, but the present invention is not limited to this example. Examples of the condensable particles include mist-like HF, HCl, HBr and the like other than sulfuric acid mist.

  As shown in FIG. 1, the particle removing apparatus 1 includes a first cooling unit 3, a second cooling unit 4, an electric field forming unit 5, and the like. The first cooling unit 3, the second cooling unit 4, and the electric field forming unit 5 are accommodated in the casing 10 of the particle removing device 1. The casing 10 is provided separately from the absorption tower 40 and is installed in the inlet duct of the absorption tower 40.

The 1st cooling part 3 is a nozzle, for example, and is comprised so that flow volume distribution may become uniform in the width direction. The first cooling unit 3 is supplied with exhaust gas containing SO ₃ gas that becomes condensable particles (sulfuric acid mist), sprays droplets on the exhaust gas, and the exhaust gas is in the vicinity of the sulfuric acid dew point and above the sulfuric acid dew point. Cool to temperature (eg, sulfuric acid dew point + 5 ° C to + 20 ° C). As a result, the droplets evaporate only a portion of the water while taking in the SO ₃ gas, and sulfuric acid mist having a relatively coarse particle diameter is generated. Since the sulfuric acid mist having a relatively coarse particle diameter has a large particle diameter, it is easily collected by a desulfurization apparatus installed on the downstream side. In addition, by maintaining the first cooling unit 3 at a predetermined temperature equal to or higher than the sulfuric acid dew point, sulfuric acid mist having a relatively coarse particle diameter is generated, and the number of sulfuric acid mists generated in the cooling process by the second cooling unit 4 in the subsequent stage. Can be suppressed, or the sulfuric acid mist can be prevented from being miniaturized. The exhaust gas that has passed through the first cooling unit 3 is supplied to the second cooling unit 4.

The 2nd cooling part 4 is a nozzle, for example, and is comprised so that flow volume distribution may become uniform in the width direction. The second cooling unit 4 sprays droplets on the exhaust gas that has passed through the first cooling unit 3, and cools the exhaust gas to a temperature near the water dew point and above the water dew point. At this time, as shown in FIG. 6, since the region A below the acid dew point is formed in the immediate vicinity of the droplet 51, the SO ₃ gas that has not been taken into the droplet by the first cooling unit 3 is Separately from the sulfuric acid mist generated by the cooling unit 3, it is generated as fine condensable particles (sulfuric acid mist) 52. That is, sulfuric acid mist is generated in the immediate vicinity of the droplet.

  The electric field forming unit 5 forms an electric field in the space in which the exhaust gas that has passed through the second cooling unit 4 flows. An electric field is formed in the space where the exhaust gas circulates by the electric field forming unit 5, and the exhaust gas circulates in the formed electric field, whereby the droplet 51 sprayed by the second cooling unit 4 as shown in FIG. 6. Then, the sulfuric acid mist 52 generated around the dielectric is polarized and the sulfuric acid mist 52 is attracted to the droplet 51.

Next, operation | movement of the particle removal apparatus 1 which concerns on this embodiment is demonstrated.
First, the exhaust gas supplied to the particle removing device 1 is introduced into the first cooling unit 3. In the first cooling section 3, exhaust gas containing SO ₃ is supplied and cooled to a predetermined temperature above the sulfuric acid dew point in the vicinity of the sulfuric acid dew point (for example, sulfuric acid dew point + 5 ° C. to + 20 ° C. or less). Coarse sulfuric acid mist is produced. Next, in the second cooling unit 4, droplets are sprayed on the gas that has passed through the first cooling unit 3. At this time, the exhaust gas is cooled to a temperature not lower than the water dew point near the water dew point. As a result, sulfuric acid mist is generated in the vicinity of the droplet.

  Then, an electric field is formed in the space in which the gas flows by the electric field forming unit 5, and the gas flows in the formed electric field, so that the liquid droplets are dielectrically polarized, and the generated sulfuric acid mist is also dielectric. Polarize. As shown in FIG. 6, the fine sulfuric acid mist 52 generated in the very vicinity of the droplet 51 has a charge opposite to the polarity of the droplet 51, so that the sulfuric acid mist 52 is liquid. It is attracted to the droplet 51.

The droplets that have passed through the electric field formed by the electric field forming unit 5 are attached with sulfuric acid mist, and are collected by, for example, an absorption tower 40 of a wet desulfurization apparatus, a mist eliminator 41, or a wet electric dust collector. Compared with the case of trying to collect the fine sulfuric acid mist itself, the droplets with the sulfuric acid mist attached are easily collected by the portion. As a result, sulfuric acid mist generated from SO ₃ contained in the exhaust gas can be efficiently removed.

  When the particle removal apparatus 1 is used in combination with a wet desulfurization apparatus, as shown in FIG. 1, the droplets that have passed through the electric field formed by the electric field forming unit 5 are supplied to the absorption tower 40 of the wet desulfurization apparatus. The And the water stored in the absorption tower 40 is supplied to the 1st cooling part 3 via the circulation path 42, and is reused as the droplet which the 1st cooling part 3 supplies with respect to waste gas. A circulating water pump 43 is provided in the circulation path 42.

  Thereby, the water used in the 1st cooling part of a particle removal apparatus circulates between the particle removal apparatus 1 and the absorption tower 40 of a wet desulfurization apparatus, and reduces the quantity of the water which needs to be newly supplied. it can.

As described above, according to the present embodiment, spraying is once suppressed so that the first cooling unit 3 is cooled to a predetermined temperature equal to or higher than the sulfuric acid dew point in the vicinity of the sulfuric acid dew point (for example, sulfuric acid dew point + 5 ° C to + 20 ° C). Thus, a sulfuric acid mist having a relatively coarse particle diameter is generated, and an increase in the number of sulfuric acid mists in the subsequent cooling process by the second cooling unit 4 can be suppressed, or miniaturization of the sulfuric acid mist can be suppressed.
The inventors of the present invention cooled the first cooling unit 3 to a predetermined temperature equal to or higher than the sulfuric acid dew point in the vicinity of the sulfuric acid dew point (for example, sulfuric acid dew point + 5 ° C. to + 20 ° C. or less). In the combination, it was confirmed that the collection efficiency was increased. On the other hand, it has been confirmed that the collection efficiency is lowered when cooling is performed only to a temperature higher than a predetermined temperature above the sulfuric acid dew point, or when cooling is performed to a temperature lower than the sulfuric acid dew point. This is because when the liquid is cooled only to a temperature higher than the predetermined temperature above the sulfuric acid dew point, the SO ₃ gas is not sufficiently taken into the droplets, and a large number of SO ₃ gases are rapidly turned into fine sulfuric acid mist during the subsequent cooling process. It is guessed. In addition, when cooled to a temperature lower than the sulfuric acid dew point, sulfuric acid mist with a relatively coarse particle size was not generated, and the number of sulfuric acid mists increased or the sulfuric acid mist became finer. It is presumed that they were not collected in
As mentioned above, according to this embodiment, the sulfuric acid mist produced | generated by the sulfur content contained in waste gas can be removed efficiently.

  In addition, although embodiment mentioned above demonstrated the case where the 2nd stage spray of the 1st cooling part 3 and the 2nd cooling part 4 was performed, this invention includes the case where the multistage spray of 3 or more stages is performed.

<Electric field forming part>
Next, with reference to FIGS. 2 to 5, the electric field forming unit 5 applied in the particle removing apparatus 1 according to the present embodiment will be described.

<Electric field forming portion (first embodiment)>
For example, as in the example illustrated in FIG. 2, the electric field forming unit 5 includes opposed electrodes and forms an electric field between the opposed electrodes.

  As shown in FIG. 2, the electric field forming unit 5 includes a mesh-shaped electrode 11 having a large aperture ratio that does not hinder the flow of two exhaust gases arranged in parallel, and the flow of the exhaust gas similarly disposed between these electrodes 11. The mesh-shaped electrode 12 having a large aperture ratio that does not hinder the flow rate is provided so as to be orthogonal to the flow direction of the exhaust gas. A voltage is applied to the electrode 12 by a high voltage generator.

  When a voltage is applied to the electrode 12, an electric field is formed in the gas flow direction. Here, when the droplet is sprayed from the second cooling unit 4 from the upper side to the lower side, that is, in the same direction as the gas flow direction, the droplet is dielectrically polarized positively and negatively by the formed electric field.

  The sulfuric acid mist generated in the vicinity of the droplets contained in the exhaust gas is dielectrically polarized like the droplets. In the fine sulfuric acid mist generated in the vicinity of the droplet, the charge closer to the droplet has a polarity opposite to that of the droplet. A portion of the sulfuric acid mist having a negative charge is attracted to the positive electrode side of the droplet, and the sulfuric acid mist is attracted to and attached to the droplet. A portion having a charge on the positive electrode side in the sulfuric acid mist is attracted to the negative electrode side of the droplet, and the sulfuric acid mist is attracted to and attached to the droplet. And the droplet which capture | acquired sulfuric acid mist is easily collected by collection parts, such as the absorption tower 40 of a wet desulfurization apparatus, the mist eliminator 41, and an electric dust collector.

<Electric field forming portion (second embodiment)>
Moreover, the electric field formation part 5 may form the electric field which generates a corona discharge, as shown in FIG.
In this case, the electric field forming unit 5 includes a mesh-shaped ground electrode 21 having a large aperture ratio that does not inhibit the flow of exhaust gas, and a discharge electrode 22 having a barb portion 23 provided to face the ground electrode 21 in the flow direction of exhaust gas. And so as to be orthogonal. A voltage is applied to the discharge electrode 22 by an AC high voltage generator.

  Due to the discharge by the discharge electrode 22, an alternating voltage is used to form a droplet group in which positive and negative are alternately charged with a temporal phase difference. That is, a group of droplets having a positive charge is repeated by applying a positive charge to the droplet, then applying a negative charge to the droplet, and then applying a positive charge. And droplet groups having negative charges are alternately formed. An electric field is formed between the droplet group having a positive charge and the droplet group having a negative charge. The fine droplets in the electric field are dielectrically polarized positively and negatively by the formed electric field.

  The sulfuric acid mist generated in the very vicinity of the droplets contained in the exhaust gas is dielectrically polarized in the same manner as the droplets, and the sulfuric acid mist is attracted to and attached to the droplets as in the first embodiment. And the droplet which caught sulfuric acid mist is easily collected by collection parts, such as mist eliminator 41 and an electric dust collector.

<Electric field forming portion (third embodiment)>
Furthermore, as shown in FIGS. 4 and 5, the electric field forming unit 5 may form an electric field by sprayed droplets by a charging nozzle method combined with the second cooling unit 4.

As shown in FIG. 4, the second cooling unit 4 has charging nozzles 31a and 31b.
The charging nozzle 31a has a configuration in which the droplets to be sprayed can be charged so that the droplets to be sprayed are positive and the droplet to be sprayed is negative. For example, the electric field forming unit 5 includes a voltage applying unit 32a that applies a negative DC voltage to the charging nozzle 31a and a voltage applying unit 32b that applies a static DC voltage to the charging nozzle 31b.

  As a result, the group of sprayed droplets is charged with positive and negative charges, respectively, and an electric field is generated between these groups in a direction perpendicular to the gas flow without providing an external electrode. It is formed.

  The generated sulfuric acid mist is guided into an electric field formed by a group of positively charged droplets and a group of negatively charged droplets. The sulfuric acid mist is effectively trapped in the droplets by electrostatic force in the vicinity of the polarized droplets. Thereafter, the droplets capturing the sulfuric acid mist are easily collected by a collection unit such as a mist eliminator 41 or an electric dust collector.

<Electric field forming portion (fourth embodiment)>
The second cooling unit 4 includes charging nozzles 33a and 33b as shown in FIG.
The electric field forming unit 5 includes a voltage applying unit 34 that supplies an alternating voltage to the charging nozzles 33a and 33b, and the voltage applying unit 34 applies an alternating electric field to the charging nozzles 33a and 33b.

  In the case of having this configuration, the polarity of the electric charge held by the droplet varies with time. For this reason, groups of droplets having positive and negative charges in the upper and lower gas flow directions are alternately formed, and an electric field is formed in the gas flow direction.

  The generated sulfuric acid mist is guided into an electric field formed by a group of positively charged droplets and a group of negatively charged droplets. The sulfuric acid mist is effectively trapped in the droplets by electrostatic force in the vicinity of the polarized droplets. Thereafter, the droplets capturing the sulfuric acid mist are easily collected by a collection unit such as a mist eliminator 41 or an electric dust collector.

  In addition, although the structure of the electric field formation part 5 mentioned above demonstrated 1 step | paragraph, this invention is not limited to this example, You may arrange | position with two or more steps | paragraphs. Thereby, the collection efficiency of sulfuric acid mist can further be improved.

1: Particle removal device 3: 1st cooling part 4: 2nd cooling part 5: Electric field forming part 10: Casing 11: Electrode 12: Electrode 21: Earth electrode 22: Discharge electrode 23: Spear part 31a: Charging nozzle 31b: Charging Nozzle 32a: Voltage application unit 32b: Voltage application unit 33a: Charging nozzle 33b: Charging nozzle 40: Absorption tower 41: Mist eliminator 42: Circulation path 43: Circulating water pump

Claims (6)

A first cooling unit that sprays droplets on a gas containing a target substance, and cools the gas to a predetermined temperature near the acid dew point of the target substance and above the acid dew point;
A second cooling unit that sprays droplets on the gas that has passed through the first cooling unit, and cools the gas to a temperature near the water dew point and above the water dew point;
An electric field forming unit that forms an electric field in a space in which the gas that has passed through the second cooling unit flows;
A particle removal apparatus comprising: The droplets that have passed through the electric field formed by the electric field forming unit are supplied to an absorption tower of a wet desulfurization apparatus,
Water stored in the absorption tower is supplied to the first cooling unit or the second cooling unit, and is reused as water supplied to the gas by the first cooling unit or the second cooling unit. The particle removing apparatus according to claim 1.   The particle removal apparatus according to claim 1, wherein the electric field forming unit includes two electrodes facing each other, and forms an electric field between the two electrodes.   The electric field forming unit includes a ground electrode and a discharge electrode having a barb portion provided to face the ground electrode, and an AC voltage is applied to the discharge electrode and sprayed from the second cooling unit. The particle removing apparatus according to claim 1, wherein the droplet is alternately charged with a positive charge and a negative charge at a time difference.   The particle removal apparatus according to claim 1, wherein the electric field forming unit has a configuration capable of charging a droplet sprayed from a nozzle included in the second cooling unit to a positive charge and a negative charge.   The particle removing apparatus according to claim 3, wherein the electric field forming unit is installed in a plurality of stages along the gas flow direction.

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