JPH0957054A - Dust-charging wet desulfurizer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently remove the soot and dust in a waste gas and to prevent the generation of visible smoke by effectively utilizing a mist eliminator at the waste gas outlet of the absorption tower of the wet desulfurizer. SOLUTION: A demister 8 set close to the waste gas outlet of a desulfurizer is allowed to act also an electrostatic precipitator. A charging region consisting of a discharge-electrode wire 15 and a grounded electrode plate 19 is provided in a duct 28 between the outlet 27 for the waste gas treated in a desulfurizing and absorbing tower and the demister 8. A gap is furnished between the charging region and demister 8, and a mist collecting plate 22 and a cleaning spray 11 are set in the gap. The mist collecting plate 22 is connected to the grounded electrode plate 19 through a conductor or it is not connected to the grounded plate 19 through the conductor and the parallel mist collecting plates 22 are positively and negatively charged by turns. Further, a part or the whole of the cleaning soln. is periodically supplied to the absorption tower of the wet desulfurizer as makeup water.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dust collecting method for electrically removing dust discharged from a boiler, a heating furnace or the like electrically in a wet desulfurization apparatus including a mist eliminator, more specifically, using corona discharge.

[0002]

Exhaust gas from coal-fired boilers, heating furnaces, etc. contains a large amount of soot and dust, which is removed by various dedusting devices before being released into the atmosphere. An electric dust collector that uses corona discharge is an example of a powerful dust removing device. This device has a discharge electrode and a dust collecting electrode in the gas flow path, charges the discharge electrode with a negative DC high voltage, and grounds the dust collecting electrode to generate corona discharge between the two electrodes. The dust particles in the exhaust gas passing between the electrodes are charged, and the dust particles are separated from the exhaust gas by the Coulomb force, which is extremely effective in removing the dust particles.

The electrostatic precipitator is classified into a dry type and a wet type according to a method of removing soot dust adhering to the dust collecting electrode. In a dry electrostatic precipitator, soot particles (dust) adhering to the surface of the dust collecting electrode are hammered to the dust collecting electrode, and are sifted to the lower hopper. On the other hand, a wet electrostatic precipitator is one in which the surface of the dust collecting electrode is washed with a large amount of running water to wash away the dust particles adhering to the dust collecting electrode.

In recent years, regulations on the amount of discharged dust tend to be tightened from the standpoint of environmental protection. In addition, due to submicron particles (particle size 0.1-1.0 μm) that cannot be collected by the current wet electrostatic precipitator, visible smoke is generated due to light disturbance after emission of exhaust gas into the atmosphere. To do is a problem. For this reason, it was necessary to improve the dust removal capability of the flue gas. However, there is a limit to improving the performance of the dust removing device, and it is considered to improve the dust removing efficiency of the exhaust gas treatment system as a whole. For example, as a dust removal efficiency improvement system, a dry electrostatic precipitator was installed on the upstream side of the gas flow, and after removing dust, a wet electrostatic precipitator and a bag filter were installed when the gas temperature passed through the desulfurization equipment. It is generally considered that a second dust removal is performed to reduce the amount of dust emitted into the atmosphere.

As shown in the conventional purification process flow of the coal-fired boiler exhaust gas shown in FIG. 7, the exhaust gas containing the soot dust exhausted from the boiler 1 first passes through the dry type electrostatic precipitator 2.
After removing a certain amount of soot and dust, the heat is absorbed by the heat exchanger 3 and then guided to the wet desulfurization device 4. This desulfurization equipment 4
Has an inlet gas temperature of about 130 ° C., but the contact with the spray droplets in the desulfurization device absorption tower lowers the desulfurization device outlet gas temperature to 55 ° C. Therefore, the desulfurization device 4
The exhaust gas at the outlet of the above contains saturated steam having a temperature of 55 ° C. In the wet desulfurization apparatus absorption tower, the desulfurization absorption liquid is sprayed countercurrently to the exhaust gas to absorb and remove sulfur dioxide gas into the absorption liquid. Next, the exhaust gas is sent to the wet electrostatic precipitator 6 arranged downstream of the desulfurization device, the dust in the exhaust gas is further removed, and the treated exhaust gas is heated by the heat exchanger 3 to 10
After being reheated to 0 ° C. to prevent white smoke due to steam, it is exhausted from the chimney 7.

A method of installing such a dry type electrostatic precipitator 2 on the upstream side of the gas flow and installing a wet type electrostatic precipitator 6 in the downstream of the desulfurization device 4 can be found in Japanese Patent Publication No. 06-138926.

[0007]

By the way, inside the absorption tower of the wet desulfurization apparatus, the exhaust gas and the absorption liquid are brought into contact with each other in a countercurrent to remove the sulfur oxide (SO ₂ ) from the exhaust gas.
At that time, since fine absorbing liquid droplets (absorbing liquid mist) are entrained in the gas flow, it is common to remove this absorbing liquid mist by installing a mist eliminator near the exhaust gas outlet of the absorption tower of the wet desulfurization device. Is. Normally, the exhaust gas is supplied from the inlet at the lower part of the absorption tower of the desulfurization device and discharged from the outlet at the upper part of the absorption tower of the desulfurization device, so that the mist eliminator is installed near the upper part of the absorption tower. Even when a wet electrostatic precipitator is installed, it is necessary to install a mist eliminator for collecting mist, so it was necessary to pipe a duct from the mist eliminator treatment exhaust gas outlet to the wet electrostatic precipitator installed on the ground.

Therefore, when a wet electrostatic precipitator is to be additionally installed in an existing exhaust gas treatment plant, it is necessary to newly install a complicated duct pipe. Further, the wet electrostatic precipitator main body needs to be installed on the ground in consideration of its weight, and it may not be possible to install it due to lack of ground space in the existing plant.

Therefore, there is a demand for development of a flue gas dedusting system which utilizes the limited space of an existing plant and is capable of highly efficient dust removal at a relatively low cost.

An object of the present invention is to effectively utilize the exhaust gas duct portion where the mist eliminator at the exhaust gas outlet of the absorption tower of the wet desulfurization device is arranged to efficiently remove the soot dust in the exhaust gas and to make visible smoke. To prevent the occurrence of.

[0011]

The above object of the present invention is achieved by the following constitution. That is, in a wet desulfurization absorption tower having a mist eliminator at the end of the exhaust gas duct of the treated exhaust gas outlet, in the wet desulfurization absorption tower exhaust gas duct of the exhaust gas outlet of the wet desulfurization absorber, a charging region including a discharge electrode and a ground electrode on the upstream side of the mist eliminator. A dust-charged wet desulfurization system in which the mist collecting plate provided in the mist eliminator is electrically insulated from the joint portion of the exhaust gas duct, and the mist collecting plate and the charge area ground electrode are connected by a conductor. Apparatus, or in a wet desulfurization absorption tower having a mist eliminator at the end of the exhaust gas duct of the treated exhaust gas outlet,
The wet desulfurization absorption tower exhaust gas outlet is provided with a charging area including a discharge electrode and a ground electrode on the upstream side of the mist eliminator in the exhaust gas duct, and every other one of a number of parallel mist collecting plates provided in the mist eliminator. Is a dust-charged wet desulfurization device for applying a positive charge to the mist collecting plate, or sandwiching the mist collecting plate or applying a negative charge to the mist collecting plate adjacent to the mist collecting plate.

In the above dust-charged wet desulfurization apparatus, by expanding the cross-sectional area of the exhaust gas duct of the mist eliminator portion where the mist collecting plate is provided from the cross-sectional area of the exhaust gas duct in the charging area including the discharge electrode and the ground electrode, A structure in which the exhaust gas flow velocity in the mist eliminator portion is reduced as compared with the exhaust gas flow velocity in the charging region, and a conductive portion of a component including an exhaust gas duct as a conductor between ground electrodes or in a joint conductor having the same sign as the ground electrode. It is also possible to use a configuration that uses.

The present invention is characterized in that a dry type electrostatic precipitator is provided upstream of the combustion exhaust gas flue and a desulfurization plant is provided downstream thereof, and the function of the electrostatic precipitator is added to the mist eliminator installed near the desulfurization plant exhaust gas outlet. It is what

A charging zone composed of a discharge electrode and a ground electrode is provided on the upstream side of the mist eliminator in the exhaust gas duct at the exhaust gas outlet of the desulfurization absorption tower process. For example, the discharge electrode wire and the ground electrode plate are arranged so as to extend vertically in order to prevent the accumulation and accumulation of mist and dust in the exhaust gas duct that extends horizontally from the desulfurization absorption tower treatment exhaust gas outlet, and each becomes a casing duct. Are electrically insulated by connecting with an insulator.

It is preferable that a gap is provided between the charging area and the mist eliminator, and a mist collecting plate cleaning spray is installed in this gap. The supply of this cleaning spray is
Make-up water for the wet desulfurization absorbent is used. Since the amount of make-up water is small, in order to supply the whole area of the front surface of the mist collecting plates that are connected at the same time, the spray spray area is sequentially changed to supply the make-up water.

The mist collecting plate of the mist eliminator is made of a corrugated metal plate as viewed from above, and is made up of several tens of cm intervals. The mist collecting plate and the casing duct are
The mist collecting plate is electrically insulated by being connected with an insulator, and each mist collecting plate is connected to the above-mentioned ground electrode plate by a conductor. Alternatively, the mist collecting plate is not coupled to the ground electrode plate by a conductor, but positive and negative charges are alternately applied to the mist collecting plates that are continuous.

The soot dust and mist collected by the mist collecting plate are sent to the cleaning liquid reservoir provided on the downstream side of the collecting plate, and a part of the cleaning liquid in the cleaning liquid reservoir is sent to the mist collecting plate cleaning spray. In addition, a part or all of this cleaning liquid is periodically sent to the wet desulfurization absorption tower as make-up water.

According to the present invention, the wet desulfurization absorbing liquid mist collides with the surface of the mist collecting plate, and the water content of the mist itself causes
The surface of the mist collecting plate is always in a wet state and flows over the plate from the upper side to the lower side. Therefore, it becomes possible to prevent the soot dust charged in the charging area from accumulating on the mist collecting plate or re-scattering even if it is collected by inertial collision or Coulomb force on the mist collecting plate. Further, since a small amount of cleaning liquid or industrial water containing relatively few impurities is sprayed onto the gas flow upstream portion of the mist collecting plate, it is possible to prevent slag from accumulating and accumulating the alkali component in the mist.

These collected mists and collected soot dusts are sent to the cleaning liquid reservoir and then sent as make-up water to the wet desulfurization absorption tower, and the soot dusts are treated at the same time as the waste liquid of the desulfurization device, so that a unique fixing treatment is required There is no need to do it.

Further, by providing a gap between the charging area and the mist collecting plate, the flying soot dust charged through the charging area is also charged to the uncharged absorbing solution mist or cleaning solution mist. This will give time for the particles to adhere, and form combined particles of mist and dust that are larger in diameter than the dust particles alone. These bound particles fly between the coalesced mist collecting plates, but because of their large diameter and heavy weight, their entrainment in the gas flow is suppressed, and they are efficiently attached and collected on the surface of the mist collecting plate mainly due to inertial collision. Will be done.

Further, the charged soot and dust which have not been combined with these mists are also adhered and removed to the mist collecting plate by the Coulomb force. In order to strengthen this Coulomb force, it is effective to apply positive and negative charges alternately to the mist collecting plates that are in parallel.
By doing so, an electric field from the negative direction to the positive direction is formed between the mist collecting plates, and the negatively charged soot dust is reliably collected so as to be pressed against the mist collecting plate of the positive electrode.

As another function, the scattered mist from the wet desulfurization absorption tower is charged with electric charges in the charging region,
The Coulomb force makes it easier for the mist collecting plate to adhere to the mist collecting plate, so that the mist collecting area can be made more compact.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to the drawings. Example 1 FIG. 4 shows a system diagram of a flue gas treatment apparatus of a coal-fired boiler plant adapted to the present invention. Exhaust gas containing soot dust exhausted from the boiler 1 first passes through the dry electrostatic precipitator 2 to remove a certain amount of soot, and then is absorbed by the heat exchanger 3 and then guided to the wet desulfurization device 4. Although the inlet gas temperature of the desulfurizer 4 is about 130 ° C., the desulfurizer outlet gas temperature is lowered to 55 ° C. by coming into contact with the spray droplets in the desulfurizer absorber tower. Therefore, the exhaust gas at the outlet of the desulfurization device 4 contains saturated steam having a temperature of 55 ° C. In the absorption tower of the wet desulfurization device, the desulfurization absorption liquid is absorbed and removed by the countercurrent spraying of the desulfurization absorption liquid with respect to the exhaust gas. Mist) is entrained in the exhaust gas flow. The diameter of the absorbing liquid mist entrained in the exhaust gas flow is several μm
Is up to several thousand μm, which is larger than the diameter of dust (0.1 to 10 μm).

The exhaust gas containing the mist and dust is effectively charged in the charging region consisting of the discharge electrode wire 15 and the ground electrode plate 19 of the mist eliminator 8 provided in the duct immediately after the outlet of the absorption tower, and the mist eliminator 8 is discharged. The mist collecting plate 22 is attached and removed by inertial collision. The treated exhaust gas from which dust has been removed is reheated to 100 ° C. by the heat exchanger 3 to prevent white smoke due to steam, and then exhausted from the chimney 7.

FIG. 3 is a sectional view of the mist eliminator 8 portion of FIG. 1 from above, and FIGS. 1 and 2 show the wet desulfurization absorber 4 having the mist eliminator 8 from the absorption tower exhaust gas outlet 27 to the mist eliminator 8. A detailed view of an apparatus in which a charging area composed of a discharge electrode wire 15 and a ground electrode plate 19 is provided between the two is shown.

The casing is formed so that a plurality of ground electrode plates 19 made of metal plates are arranged in the downstream region from the exhaust gas outlet 27 of the wet desulfurization absorber 4 in parallel with each other at equal intervals in the direction perpendicular to the gas flow. It is supported by the duct 28 via the support insulator 21. The arrangement of the ground electrode plates 19 does not need to be perpendicular to the gas flow and does not need to be equidistant from each other when the gas flow velocity is large and the accumulation of mist or dust does not occur.

Discharge electrode wires 15 are stretched at the centers between the ground electrode plates 19 arranged in parallel with each other. The discharge electrode wires 15 that are close to each other with the ground electrode plate 19 interposed therebetween are conductor-coupled to each other, and are attached to the casing duct 28 by the support insulator 17. For this reason, all the sections in the exhaust gas flow direction form electrically conductive sections. A plurality of similar sections of the discharge electric wire 15 and the ground electrode plate 19 are gathered to form a charging area.

On the other hand, the mist collecting plate 22 of the mist eliminator 8 and the casing duct 28 are connected by an insulator 23 and are electrically insulated. As shown in FIG. 2, the mist collecting plates 22 are connected by a conductor. The mist collecting plate 22 and the ground electrode plate 19 are connected by a connecting conductor 20, and a ground wire 25 is connected to one end thereof. Further, the ground wire 25 is connected to the casing duct 28 through a tubular insulator 24 for electrically insulating the casing duct 28.
It is grounded to the surface of the earth by a grounding wire 25 penetrating through

A negative charge is applied to the discharge electrode wire 15 from the high voltage power source 18, and a positive charge is applied to the ground electrode plate 19. Therefore, each mist collecting plate 22 coupled by the ground electrode plate 19 and the coupling conductor 20 is also positively charged. The discharge electrode wire 15 and the ground electrode plate 1
A high voltage of 8 kV / cm is applied between 9 and 9 to form a corona electric field. The flow velocity of gas passing through the charged region where the corona electric field is formed is about 5 m / s. Therefore, in order to realize an ideal contact time of 0.036 seconds or more in the charging area, it is desirable that the length of the effective charging area is 18 cm or more.

The exhaust gas introduced from the exhaust gas inlet 26 of the wet desulfurization apparatus 4 is absorbed by the absorbent spray nozzle 10 provided at the bottom of the absorption tower through the absorbent spray pipe 14.
Is desulfurized by the absorbing liquid sprayed in. After the desulfurization treatment, the soot dust and the absorbing liquid mist in the exhaust gas pass through the charged area composed of the discharge electrode wire 15 and the ground electrode plate 19,
Negative ions attach to the surface and are thus negatively charged, repel each other and continue flying while spreading to the surroundings, but some of them collide the cleaning water supplied from the pipe 12 from the mist collecting plate cleaning spray 11 to the mist. Or, they are attracted by the Coulomb force and combine with each other to form a combined product of dust and mist. The soot and mist combination is collected by inertial collision with the surface of the mist collecting plate 22,
Since a water film flow is formed on the surface of the mist collecting plate 22 due to the water content of the mist or the washing water, it flows down on the mist collecting plate 22 without re-scattering, and falls below the collecting plate 22. It is sent to the cleaning liquid reservoir 9 provided. The charged dust that has not been combined with these mists also adheres to the mist collecting plate 22 due to the Coulomb force and flows down to the cleaning liquid reservoir 9 as in the former case.

A part of the cleaning liquid in the cleaning liquid reservoir 9 is sent to the mist collecting plate cleaning spray 11 via the pipe 12, and a part or the whole amount of this cleaning liquid is periodically supplied to the wet desulfurization absorber 4 by the water pipe 13. Will be sent as makeup water.

Example 2 The example shown in FIG. 5 comprises the same components as the mist eliminator shown in FIGS. 1 and 2, except that the discharge electrode wire 15 provided inside a casing duct (not shown) This is a method of applying a high voltage to the mist collecting plate 22 independently of applying a voltage between the ground electrode plates 19.

As a result, the Coulomb force at the mist collecting plate 22 can be increased. In the example shown in FIG. 5, positive and negative charges are alternately applied to the mist collecting plates 22 that are continuous. The applied voltage is about 8 kV / cm as in the charging section, but an electrostatic field is formed between these mist collecting plates 22. By doing so, an electric field from the negative direction to the positive direction is formed between the mist collecting plates 22, and the negatively charged soot dust is reliably collected so as to be pressed against the mist collecting plate 22 of the positive electrode.

Embodiment 3 In this embodiment, in order to reduce the accumulation of absorbing liquid mist and charged dust on the charge area electrode, a mist collecting plate is provided in the casing duct 28 of the mist eliminator as shown in FIG. 22 is provided, and the charging area provided with the discharge electrode wire 15 and the ground electrode plate 19 is provided in the upstream duct 27 that is narrower than the cross-sectional area of the casing duct 28.

Exhaust gas passing through the duct 27 having a relatively narrow cross-sectional area increases its passage speed, so that the electrodes 15, 19 are
It is possible to effectively blow off the absorbing solution mist and charged soot dust adhering to the surface.

As a conductor between the ground electrodes 19 used in the first to third embodiments, or instead of the joint conductor 20 having the same sign as the ground electrode, a constituent conductive portion including the bodies of the ducts 27 and 28 is used. But it doesn't matter.

[0037]

EFFECTS OF THE INVENTION By using the present invention, the soot dust in the exhaust gas charged by corona discharge can be efficiently removed at the outlet of the desulfurization plant, the amount of soot emitted to the atmosphere is reduced, and the visible smoke is prevented. Is possible. At the same time, the existing desulfurization plant is only slightly improved so that the cost does not increase.

Further, since the mist collecting plate, which is the dust collecting electrode, is always washed with mist or desulfurization device make-up water, re-scattering of dust adhering on the dust collecting electrode (mist collecting plate) can be prevented. Moreover, it is not necessary to newly install a washing facility. In addition, since the dust is collected by the mist collecting plate cleaning liquid and then supplied as desulfurization make-up water, it is not necessary to install a special soot and dust fixing facility. Therefore, it is possible to effectively use the existing space.

[Brief description of drawings]

FIG. 1 shows an absorption tower portion of a dust-charged wet desulfurization apparatus according to an embodiment of the present invention.

FIG. 2 is a perspective view of a mist eliminator portion of a dust-charged wet desulfurization apparatus according to an embodiment of the present invention.

FIG. 3 is a configuration diagram of a mist eliminator portion of a dust-charged wet desulfurization apparatus according to an embodiment of the present invention.

FIG. 4 shows a flow chart of a boiler exhaust gas purification treatment apparatus to which the dust-charged wet desulfurization apparatus of one embodiment of the present invention is applied.

FIG. 5 is a perspective view of a mist eliminator portion (a casing duct and the like are omitted) of the dust-charged wet desulfurization apparatus according to an embodiment of the present invention.

FIG. 6 is a schematic horizontal cross-sectional view of a mist eliminator portion of a dust-charged wet desulfurization apparatus according to an embodiment of the present invention.

FIG. 7 shows a flow of a conventional exhaust gas purification processing apparatus for a coal-fired boiler.

[Explanation of symbols]

1 Boiler 2 Dry Electrostatic Precipitator 3 Heat Exchanger 4 Wet Desulfurization Device 6 Wet Electrostatic Precipitator 7 Chimney 8 Mist Eliminator 9 Cleaning Water Reservoir 10 Absorption Liquid Spray 11 Cleaning Water Spray 12 Cleaning Water Spray Piping 13 Water Pipe 14 Absorption Liquid Spray Nozzle 15 Discharge Electrode Wire 16 Discharge Electrode Distribution Line 17 Wire Support Insulator 18 High Voltage Generator 19 Ground Electrode Plate 20 Coupling Conductor 21 Ground Electrode Plate Support Insulator 22 Mist Collection Plate 23 Mist Collection Plate Support Insulator 24 Tubular Insulator 25 Ground Wire 26 Desulfurization Absorption Tower Exhaust Gas Inlet 27 Desulfurization absorption tower exhaust gas outlet 28 Casing duct

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Noriaki Taniguchi 6-9 Takaracho, Kure City, Hiroshima Prefecture Babcock Hitachi Kure Factory

Claims (4)

[Claims] 1. A wet desulfurization absorber having a mist eliminator at the end of an exhaust gas duct of a treated exhaust gas outlet, including a discharge electrode and a ground electrode upstream of the mist eliminator in the exhaust gas duct of the exhaust gas outlet of the wet desulfurization absorber. Having a charged area and electrically insulating a joint portion between the mist collecting plate provided in the mist eliminator and the exhaust gas duct, and connecting the mist collecting plate and the charged area ground electrode with a conductor. A dust-charged wet desulfurization device characterized by: 2. A wet desulfurization absorber having a mist eliminator at the end of the exhaust gas duct of the treated exhaust gas outlet, including a discharge electrode and a ground electrode upstream of the mist eliminator in the exhaust gas duct of the exhaust gas outlet of the wet desulfurization absorber. A positive charge is applied to every other multiple mist collecting plates that are provided in the mist eliminator and have a charging area, and are sandwiched between the mist collecting plates or adjacent to the mist collecting plate. A dust-charged wet desulfurization device, characterized in that a negative charge is applied to the mist collecting plate. 3. Exhaust gas in the charged area by widening the cross-sectional area of the exhaust gas duct in the mist eliminator portion where the mist collecting plate is provided compared to the cross-sectional area of the exhaust gas duct in the charged area including the discharge electrode and the ground electrode. The dust-charged wet desulfurization apparatus according to claim 1 or 2, wherein the exhaust gas flow rate in the mist eliminator section is reduced more than the flow rate. 4. The dust according to claim 1, wherein a constituent conductive portion including an exhaust gas duct is used as a conductor between ground electrodes or as a joint conductor having the same sign as the ground electrode. Charged wet desulfurization equipment.