WO2006080636A1

WO2006080636A1 - Hybrid-type method and apparatus for treating exhaust gas

Info

Publication number: WO2006080636A1
Application number: PCT/KR2005/003167
Authority: WO
Inventors: In Seob Lee
Original assignee: In Seob Lee
Priority date: 2004-11-17
Filing date: 2005-09-23
Publication date: 2006-08-03
Also published as: KR100613303B1; KR20060054910A

Abstract

The present invention relates to a method and apparatus for treating exhaust gas exhausted from thermal installations such as a municipal solid waste incinerator and a furnace, or from air pollutant emitting facilities that emit both dust and gas. A hybrid-type method for treating exhaust gas according to the present invention comprises a release agent adhesion step of forming a release agent layer by evacuating air from the interior of a bag filter to the outside, and supplying release agent composition powder comprising porous expansion ceramic, a binder and a thickener into the bag filter so that the release agent composition powder can adhere to a surface of a bag of the bag filter; a chemical adhesion step of forming a chemical layer by evacuating the air from the interior of the bag filter to the outside, and supplying chemical powder into the bag filter so that the chemical powder can adhere to a surface of the release agent layer; a wet treatment step of spraying an alkaline material to the exhaust gas exhausted from an incinerator to neutralize the exhaust gas, and passing the exhaust gas through a mist eliminator to remove dust and moisture from the exhaust gas; and a dry treatment step of removing residual hazardous substances by passing the wet treated exhaust gas through the bag filter having the bag with the release agent layer and the chemical layer sequentially adhering thereto in the release agent adhesion step and the chemical adhesion step.

Description

HYBRID-TYPE METHOD AND APPARATUS FOR TREATING EXHAUST GAS

Technical Field The present invention relates to a method and apparatus for treating exhaust gas exhausted from thermal installations such as a municipal solid waste incinerator and a furnace, or from air pollutant emitting facilities that emit both dust and gas. More particularly, the present invention relates to a method and apparatus for treating exhaust gas, wherein dust is removed by primarily spraying an alkaline solution to acid exhaust gas to neutralize the exhaust gas and residual hazardous substances of the exhaust gas are treated by secondly passing the exhaust gas through a bag filter with a release agent layer and a chemical layer adhering thereto.

Background Art Exhaust gas generated from an incinerator for incinerating municipal solid wastes or industrial wastes contains hazardous substances such as dust, acid gases (HCl, SOx, NOx, HF, etc.), heavy metals (Hg, Cd, Pb, As, Zn, etc.), and dioxin. A variety of conventional methods for treating such exhaust gas containing the aforementioned hazardous substances have been known. Fig. 6 shows a block diagram of an apparatus for treating exhaust gas, wherein exhaust gas exhausted from an incinerator 10 is cooled in a waste heat recovery boiler or a wet cooling tower 12 employing spraying, dust contained in the exhaust gas is primarily collected by a dry electrostatic precipitator (EP) 14, and the exhaust gas is neutralized by a wet scrubber 16 and then emitted through a chimney 20 via a heat exchanger 18. However, the exhaust gas treatment apparatus shown in Fig. 6 has a problem in that dioxin is generated again if the temperature of the exhaust gas in the dry electrostatic precipitator 14 is 25O⁰C or higher.

Furthermore, Fig. 7 shows a schematic diagram of an apparatus for treating exhaust gas, wherein exhaust gas exhausted from an incinerator 10 is first cooled in a waste heat recovery boiler or a wet cooling tower 12, a lime slurry is supplied from a slurry spray tower 13 to remove dust from the exhaust gas and neutralize the exhaust gas, and the exhaust gas is passed through a bag of a bag filter 21 to which lime powder is supplied. However, the apparatus has problems in that mercury or dioxin is incompletely removed, and maintenance and repair of the apparatus are inconvenient and need high costs since the bag filter should be frequently exchanged specifically due to solidification of the lime in the bag filter.

Furthermore, Fig. 8 shows a schematic diagram of an apparatus for treating exhaust gas, wherein exhaust gas exhausted from an incinerator 10 is first cooled in a waste heat recovery boiler or a wet cooling tower 12 and then treated by a dust removal tower 13 to which a lime slurry is supplied, dust removal and neutralization treatment are applied to the exhaust gas by a gas absorption tower 15 to which sodium hydroxide is supplied, and the exhaust gas is then passed through a wet electrostatic precipitator. However, the apparatus has a problem in that effects of removal of dust or dioxin are lower as compared with a method using a bag filter. The conventional exhaust gas treatment methods described above comprise performing wet neutralization treatment of exhaust gas, removing moisture from the exhaust gas in a heat exchanger, and exhausting the exhaust gas; or supplying a lime slurry to the exhaust gas to perform semi-dry neutralization treatment of the exhaust gas, passing the neutralized exhaust gas through a bag filter, and exhausting the treated exhaust gas. That is, the conventional exhaust gas treatment methods do not teach or suggest a method and apparatus for treating exhaust gas by wet-scrubbing acid exhaust gas and subsequently passing the exhaust gas directly through a bag filter.

This is because there is a problem in that a bag filter should be frequently exchanged since the life of a bag of the bag filter is shortened if moisture is introduced into the bag filter, although the use of the bag filter is most efficient to remove a large amount of dust contained in exhaust gas exhausted during incineration or combustion. Therefore, in order to prevent a large amount of moisture from being introduced into a bag filter or prevent the introduced moisture from being condensed, a conventional exhaust gas treatment apparatus using a bag filter should have an additional heater installed to additionally remove moisture and to maintain the temperature of exhaust gas flowing into the bag filter at 100⁰C or higher in a case where a semi-dry or wet scrubber is used in front of the bag filter. Since this increases installation and maintenance costs of the facilities and imparts a burden on the facilities in view of installation and maintenance thereof, the conventional exhaust gas treatment apparatus has not been frequently employed. The inventors of the present invention filed a patent application with the Korean

Intellectual Property Office, which discloses an exhaust gas treatment apparatus capable of primarily wet-scrubbing exhaust gas and secondly passing the exhaust gas through a bag filter to dry-scrub the exhaust gas (hereinafter, a method and apparatus for treating exhaust gas by using this method is referred to as 'hybrid-type method and apparatus for treating exhaust gas'). An exhaust gas treatment apparatus invented by the inventors of the present invention is disclosed in Korean Laid-Open Patent Publication No. 2004-0086039 (entitled 'Dry-type air purification apparatus with wet-type mist eliminator attached thereto' and published on October 8, 2004). Fig. 9 is a schematic diagram of an exhaust gas treatment apparatus invented and filed by the inventors of the present invention. The apparatus primarily wet-scrubs exhaust gas by spraying sodium hydroxide to the exhaust gas and passing the exhaust gas through a mist eliminator 260, and secondly scrubs the exhaust gas by passing the exhaust gas through a bag 340 of a bag filter to which release agent powder and lime powder sequentially adhere, so that residual hazardous components can be removed from the exhaust gas. All technical contents of the exhaust gas treatment apparatus disclosed in the aforementioned patent application are incorporated herein as a part of the present invention.

However, the hybrid-type apparatus for treating exhaust gas has a problem in that a dedusting operation should be frequently performed on the bag since excessive moisture is contained in exhaust gas passing through a wet scrubbing unit 200 and thus a lime layer adhering to an outer side of a release agent layer of the bag 340 of the bag filter is rapidly solidified (plasterized) to cause a pressure loss in the bag. Further, the hybrid-type apparatus for treating exhaust gas has a problem in that a release agent and lime powder supplied to the bag filter 300 does not uniformly adhere to the surface of the bag 340 so that the exhaust gas is exhausted in a state where dust or hazardous substances contained in the exhaust gas are not removed therefrom, or a release agent and lime powder newly supplied for adhesion to the bag after a dedusting operation are discharged to the outside of a housing of the bag filter.

Disclosure of Invention Technical Problem

The present invention is conceived to solve the problems in the foregoing hybrid- type apparatus for treating exhaust gas. An object of the present invention is to provide a hybrid-type method and apparatus for treating exhaust gas, which can more effectively remove hazardous components of exhaust gas. Particularly, an object of the prevent invention is to provide a hybrid-type method and apparatus for treating exhaust gas, wherein acid exhaust gas is neutralized and dust is removed from the exhaust gas by primarily wet-scrubbing the exhaust gas through spraying of an alkaline chemical such as sodium hydroxide to the exhaust gas and effectively removing moisture from the wet- scrubbed exhaust gas so that the treated exhaust gas can be supplied to a bag filter. Furthermore, an object of the present invention is to provide a method and apparatus for treating exhaust gas, wherein all the amounts of a release agent and chemical powder for secondary dry-scrubbing of exhaust gas, which are supplied to a bag filter, can uniformly adhere to a bag of the bag filter without waste thereof.

Technical Solution

A hybrid-type method for treating exhaust gas according to an aspect of the present invention is a hybrid-type method for treating exhaust gas containing acid gas and dust exhausted from air pollutant emitting facilities. The method comprises a release agent adhesion step of forming a release agent layer by evacuating air from the interior of a bag filter to the outside, and supplying release agent composition powder comprising porous expansion ceramic into the bag filter so that the release agent composition powder can adhere to a surface of a bag of the bag filter; a chemical adhesion step of forming a chemical layer by evacuating the air from the interior of the bag filter to the outside, and supplying chemical powder into the bag filter so that the chemical powder can adhere to a surface of the release agent layer; a wet treatment step of spraying an alkaline material to the exhaust gas exhausted from the facilities to neutralize the exhaust gas, and passing the exhaust gas through a mist eliminator to remove dust and moisture from the exhaust gas; and a dry treatment step of removing residual hazardous substances by passing the wet treated exhaust gas through the bag filter having the bag with the release agent layer and the chemical layer sequentially adhering thereto in the release agent adhesion step and the chemical adhesion step.

It is preferred that each of the release agent adhesion step and the chemical adhesion step further comprise an external air supply step of intermittently supplying external air into the bag filter from a lower portion of the bag filter during the supply of each of the release agent powder and the chemical powder to the bag filter, so that the supplied powder can adhere with a uniform thickness to the surface of the bag. Furthermore, it is preferred that a rotary valve comprising a plurality of blades disposed at a predetermined interval along the circumference of the rotary valve be installed at the lower portion of the bag filter, and the external air supply step be performed by rotating the rotary valve at a predetermined speed.

Preferably, the dry treatment step further comprises a dedusting step of removing the release agent powder and chemical powder adhering to the surface of the bag by supplying high-pressure air into the bag of the bag filter if a difference in pressure between the release agent layer and the chemical layer of the bag filter is a predetermined value or higher, so that the bag of the bag filter can be continuously used without exchange thereof.

hi the hybrid-type method for treating exhaust gas according to the present invention, the wet treatment step primarily scrubs acid exhaust gas by spraying the alkaline chemical to the exhaust gas to neutralize the exhaust gas and removing a product generated through reaction with the alkaline chemical, moisture, and hazardous gas dissolved in moisture, which are included in the exhaust gas, by a mist eliminator, and the dry treatment step secondarily scrubs fine dust, dioxin, acid gas, water-insoluble gas, odor, and the like by passing the exhaust gas through the release agent layer and the chemical layer. Particularly, the chemical layer can be formed to have a larger thickness by adhering the release agent composition powder comprising porous expansion ceramic, a binder and a thickener to the surface of the bag and subsequently adhering the chemical layer such as lime to the surface of the release agent layer. If plasterization occurs due to adsorption of dust or moisture by the chemical layer, high-pressure air is supplied into the bag and the plasterized layer is easily separated from the bag due to the release agent powder, so that the bag filter can be semi-permanently used. Although the release agent can comprise only porous expansion ceramic, it is desirable to enhance an adhesion force by mixing a binder and a thickener with the porous expansion ceramic at a proper ratio. Preferably, the release agent composition comprises 90 to 99.5 wt% of porous expansion ceramic, 0.5 to 9 wt% of binder, and 0 to 1 wt% of thickener, thereby ensuring good adhesion to and easy dedusting from the surface of the bag of the bag filter, and increasing the thickness of the chemical layer such as lime powder. The porous expansion ceramic may be prepared by calcining at least one rock component selected from the group consisting of obsidian, perlite, pitchstone, vermiculite, pumice and shale at a temperature range of 900 to 1,600⁰C.

According to the present invention, a wet scrubber can be installed in front of a conventional bag filter by adding the step of adhering the release agent to the bag. Upon installation of a wet scrubber in front of the bag filter in the prior art, excessive moisture is introduced into the rear bag filter to rapidly shorten the life of the bag, resulting in frequent exchange of the bag. Since this causes inconvenience in work and increased maintenance costs, the configuration has not been widely used in spite of its superior scrubbing performance. Therefore, a semi-dry/bag filter method having a reaction rate and efficiency lower than those of a wet/bag filter method has been used as an exhaust gas scrubbing method. Furthermore, although a conventional method for removing acid gas, dioxin and the like by forming a chemical layer of lime or the like on a bag of a bag filter has been known, the method could not be used since it was difficult to thickly form the chemical layer, and particularly, the chemical layer of lime or the like was plasterized, which leads to exchange of the filter. Therefore, studies on use of a membrane filter or a ceramic filter in an exhaust gas treatment apparatus have been chiefly made.

However, according to the present invention, a release agent layer is first formed by adhering release agent powder containing the foregoing components to a bag of a general bag filter, and a chemical layer reacting with exhaust gas is formed by secondly adhering a chemical such as lime powder to the release agent layer. Particularly, since plasterization of the release agent layer is not proceeded even though the release agent layer reacts with moisture or exhaust gas, the release agent layer and the chemical layer can be easily separated from the bag by applying pulsed air pressure thereto. Thus, the bag filter can be used semi-permanently.

Brief Description of Drawings

Fig. 1 is a schematic diagram of a hybrid-type apparatus for treating exhaust gas according to the present invention. Fig. 2 is a detailed view illustrating a chemical spray means and a bag filter of Fig.

1.

Fig. 3 is a perspective view of a mist eliminator installed in a wet scrubbing means. Fig. 4 shows various arrangement states of chemical spray nozzles and mist eliminators of the wet scrubbing means. Fig. 5 is a detail view of a bag filter of a dry scrubbing means.

Figs. 6 to Fig. 8 are schematic diagrams of conventional apparatuses for treating exhaust gas.

Fig. 9 is a schematic view of a conventional hybrid-type apparatus for treating exhaust gas. <Brief Explanation of Reference Numerals in the Drawings)

100: Incinerator 110: Waste heat recovery boiler

120: Wet scrubbing barrel 140: Powder supply means

150: Bag filter 160: Blower

200: Chemical spray means 300: Wet scrubbing means 400: Dry scrubbing means Best Mode for Carrying Out the Invention

Hereinafter, principles of scrubbing exhaust gas in a wet treatment process and a dry treatment process will be described.

In a wet treatment process, acid exhaust gas is neutralized by spraying an alkaline chemical to the exhaust gas such that the alkaline chemical comes into contact with the exhaust gas, and moisture and dust are primarily removed from the exhaust gas by passing the exhaust gas through a mist eliminator. Although a calcium based (Ca(OH)₂, CaO and CaCO₃) solution and a sodium based (NaHCO₃, NaOH and Na₂CO₃) solution can be used as the alkaline chemical, the sodium based solution is preferably used since upon use of the calcium based solution, a reaction product has low solubility as compared with the sodium based solution, resulting in formation of a great deal of scale in a reactor due to precipitation.

If sodium hydroxide is used as a chemical in the wet treatment process, acid exhaust gas is neutralized according to the following reaction equations 1 to 4. Although sulfur dioxide or hydrogen chloride easily dissolved in water or an alkaline solution is easily removed in the wet treatment process, NO, dioxin and other hazardous gases that are not easily dissolved in water or an alkaline solution are hardly removed in the wet treatment process but exhausted and then removed in a dry treatment process to be described later. Dust is removed by inertial impaction with droplets of a sodium hydroxide solution sprayed from nozzles in the wet treatment process or interception by particles of the droplets, and fine particles are removed while passing through a mist eliminator by colliding with the droplets due to diffusion resulting from Brownian movement, and other gravity, electric force, and the like.

[Reaction Equation 1] SO₂ + 2NaOH → Na₂SO₃ + H₂O

[Reaction Equation 2] SO₂ + NaOH → NaHSO₃ [Reaction Equation 3] HCl + 2NaOH => NaCl + H₂O [Reaction Equation 4] NO + 2NaOH + 1/2O₂ => Na₂(NO₃)₂

Hazardous substances remaining in the exhaust gas are removed in the dry treatment process while passing through a chemical layer and a release agent layer attached to the surface of a bag of a bag filter. Lime powder, activated carbon powder, zeolite powder, diatomite powder or a mixture thereof obtained by mixing them at a proper mixing ratio can be used for the chemical layer according to the type and concentration of the exhaust gas. It is preferred that lime be used to scrub acid exhaust gas. The release agent layer formed of powder of a composition comprising porous expansion ceramic, a binder and a thickener is not solidified or plasterized on the surface of the bag even though the exhaust gas containing a large amount of moisture passes through the release agent layer. Therefore, even though the lime layer (chemical layer) for removing the hazardous components remaining in the exhaust gas is plasterized, application of pulsed air under high pressure within the bag allows the lime layer to be easily separated along with an outer lime layer of the bag. Accordingly, hazardous exhaust gas containing a large amount of moisture or sticky particulate matters can be filtered to collect dust from the exhaust gas, thereby scrubbing the exhaust gas.

If a chemical layer formed of lime powder is used in the dry treatment process, acid exhaust gas is removed through neutralization according to the following reaction equations 5 to 9. [Reaction Equation 5]

Ca(OH)₂ + SO₂ => CaSO₃ + H₂O

[Reaction Equation 6]

CaSO₃ + 1/2O₂ => CaSO₄

[Reaction Equation 7] 2Ca(OH)₂ + 4NO + 3O₂ → 2Ca(NO₃)₂ + 2H₂O

[Reaction Equation 8]

Ca(OH)₂ + 2HCl => CaCl₂ + 2H₂O

[Reaction Equation 9]

Ca(OH)₂ + 2HF → CaF₂ + 2H₂O Furthermore, certain hazardous air pollutants (HAPs) such as dioxin and heavy metals are collected and removed while passing through the lime layer, the release agent layer and the bag of the bag filter by means of inertial impaction, direct interception or diffusion in a state that some of the HAPs are adsorbed by the lime layer, and some of them are adsorbed by dust. In addition, some of the HAPs that are not removed through a reaction with the lime layer may be adsorbed and removed by activated carbon injected in front of the bag filter. Furthermore, if NaClO₂ as an additive is injected in front of the bag filter to improve the efficiency of removal of NO, scrubbing treatment is performed according to the following reaction equations 10 and 11. Similarly to the wet treatment process, dioxin, fine dust, gas and malodor are removed by inertial impaction and interception while passing through the lime layer, the release agent layer and the bag, and fine particles are removed by diffusion due to Brownian movement, and other gravity, electric force and the like.

[Reaction Equation 10]

4NO + NaClO₂ + 2Ca(OH)₂ => 2Ca(NO₂)₂ + NaCl + 2H₂O [Reaction Equation 11 ]

2SO₂ + NaClO₂ + 2Ca(OH)₂ → 2CaSO₄ + NaCl + 2H₂O

A hybrid-type apparatus for treating exhaust gas according to another aspect of the present invention is an apparatus for treating exhaust gas containing acid gas and dust exhausted from air pollutant emitting facilities, and comprises a wet scrubbing means including a wet scrubbing barrel having an inlet through which exhaust gas is introduced, an outlet through which treated exhaust gas flows out, and a drain hole formed at a position in a side surface thereof spaced apart by a certain distance upwardly from the bottom thereof, an alkaline chemical spray means for spraying an alkaline material to an inlet side within the wet scrubbing barrel, and a mist eliminator disposed within the wet scrubbing barrel to divide the interior of the wet scrubbing barrel into an inlet-side space and an outlet-side space and having the bottom thereof positioned below the drain hole; a dry scrubbing means including a duct having one end connected to the wet scrubbing barrel, a bag filter connected to the other end of the duct, and a powder supply means connected to the duct to supply release agent powder and chemical powder to the bag filter through the duct; and a blower connected to the bag filter to blow out the exhaust gas through a chimney. Here, the powder supply means supplies the release agent powder to the duct during operation of the blower to cause the release agent powder to adhere to a surface of a bag of the bag filter so as to form a release agent layer with a predetermined thickness and subsequently supplies the chemical powder to cause the chemical powder to adhere to a surface of the release agent layer so as to form a chemical layer with a predetermined thickness, and the alkaline chemical spray means sprays the alkaline material into the wet scrubbing barrel. Accordingly, the exhaust gas exhausted from the air pollutant emitting facilities is exhausted after being primarily scrubbed in the wet scrubbing means and then secondly scrubbed in the dry scrubbing means. Furthermore, in a hybrid-type apparatus for treating exhaust gas according to the present invention, the bag filter includes a baffle installed between an inlet connected to the duct and the bag, and a rotary valve installed at a lower portion of the bag filter, the rotary valve includes a plurality of blades arranged at a predetermined interval along the circumference of the rotary valve, and the rotary valve is rotated at a predetermined speed to intermittently supply external air from the lower portion of the bag filter when the chemical spray means supplies the release agent powder and the chemical powder to the bag filter, so that the release agent powder and the chemical powder can uniformly adhere to the surface of the bag.

Lime powder, activated carbon powder, zeolite powder, diatomite powder or a mixture thereof obtained by mixing them at a proper mixing ratio can be used as the chemical powder according to the type and concentration of the exhaust gas.

Hereinafter, preferred embodiments of the hybrid-type apparatus for treating exhaust gas according to the present invention will be described with reference to the accompanying drawings. Fig. 1 is a schematic diagram of the hybrid-type apparatus for treating exhaust gas according to the present invention. As shown in Fig. 1, the apparatus for treating exhaust gas according to this embodiment comprises a wet scrubbing means 300 for primarily wet- scrubbing introduced acid exhaust gas by spraying a sodium hydroxide solution to the exhaust gas; a dry scrubbing means 400 for secondly dry-scrubbing the exhaust gas by passing the exhaust gas through a bag filter having a bag with a chemical layer applied thereto; and a blower 160 for exhausting the exhaust gas through a chimney. The blower 160 sucks the exhaust gas so that the exhaust gas can pass through the wet scrubbing means 300 and the dry scrubbing means 400, and then causes the exhaust gas to be exhausted through the chimney 170. Exhaust gas exhausted from an incinerator 100 is cooled in a waste heat recovery boiler 110 and then introduced into the wet scrubbing means 300. The wet scrubbing means 300 comprises a wet scrubbing barrel 120, an alkaline chemical spray means 200 for spraying a sodium hydroxide solution into the wet scrubbing barrel 120, and mist eliminators 125 installed in the wet scrubbing barrel 120 to remove dust and moisture of exhaust gas to which the sodium hydroxide solution has been sprayed. Although two mist eliminators 125 are installed in this embodiment, the number of the mist eliminators is not limited thereto. The mist eliminators can be arranged in various configurations as shown in Fig. 4.

Furthermore, the exhaust gas primarily scrubbed in the wet scrubbing means 300 is introduced into the dry scrubbing means 400. The dry scrubbing means 400 comprises a bag filter 150, a duct of which one end is connected to the bag filter 150 and the other end is connected to the wet scrubbing barrel 120, and a powder supply means 140 connected to the duct to supply release agent powder and lime powder to a bag of the bag filter 150. Fig. 2 is a detailed view illustrating the chemical spray means and the bag filter of

Fig. 1, and Fig. 3 is a perspective view of the mist eliminator installed in the wet scrubbing means.

Referring to Fig. 2, the wet scrubbing barrel 120 is provided with an inlet 12Od through which the exhaust gas is introduced and an outlet 12Oe through which the treated exhaust gas flows out. A drain hole 120a is formed at a position in a side surface of the wet scrubbing barrel 120 spaced apart by a certain distance upwardly from the bottom of the wet scrubbing barrel. Furthermore, the alkaline chemical spray means 200 comprises spray nozzles 121 installed on an inlet side within the wet scrubbing barrel 120, a reservoir 190 for storing a sodium hydroxide solution, and a pump 180 and pipes 122 and 181 for supplying the sodium hydroxide solution of the reservoir to the nozzles. In addition, the reservoir 190 is connected through pipes 211 and 212 to a chemical tank 210 with sodium hydroxide stored therein, and the sodium hydroxide is supplied into the reservoir by a chemical pump 220. Although not shown in Fig. 2, the chemical pump is controlled by a controller so that a pH level in the reservoir can be maintained consistently by controlling the quantity of sodium hydroxide supplied to the reservoir, according to a pH value measured by a pH sensor installed at the reservoir 190. Furthermore, a concentrating tank 192 and a dehydrator 194 for treating sludge are connected to the reservoir 190 through pipes 191 and 193, and a pipe 195 is installed to recirculate a clean solution, which is obtained in the dehydrator by removing collected dust and sludge such as a product generated through reaction with sodium hydroxide, into the reservoir 190. In addition, a drainpipe 128 for cleaning sludge and the like at the bottom of the wet scrubbing barrel 120 is connected to the reservoir 190. Reference numeral 128a is a valve for opening and closing the drainpipe.

Particularly, the mist eliminators 125 are disposed within the wet scrubbing barrel 120 to divide the interior of the wet scrubbing barrel 120 into an inlet-side space 126 and an outlet-side space 127. Furthermore, the bottoms of the mist eliminators 125 are mounted on an installation stand 120b placed below the drain hole 120a, and side surfaces of the mist eliminators except the bottoms thereof are closely attached to an inner surface of the wet scrubbing barrel 120. Therefore, collected dust separated from the exhaust gas passing through the mist eliminators 125, a product generated through reaction with sodium hydroxide, and the sprayed solution flow into and are collected in a lower portion of the wet scrubbing barrel 120, and then are drained to the reservoir 190 through the drain hole 120a.

Since the bottoms of the mist eliminators 125 are positioned below the drain hole 120a, water is always filled in a space between the bottoms of the mist eliminators 125 and the bottom of the wet scrubbing barrel 120 so that the exhaust gas cannot pass through the space. Therefore, the exhaust gas is introduced into the dry scrubbing means 400 in a state where moisture is always removed from the exhaust gas through the mist eliminators 125. Referring to Fig. 3, the mist eliminator 125 comprises an upper plate 125a with handles installed thereon, a frame 125d for receiving a plurality of blades 125b, a lower plate 125c, and the plurality of blades 125b installed at the upper plate 125a and the lower plate 125c. Each of the blades 125b comprises a first impact part 125b-l, a second impact part 125b-2 bent at a certain angle with respect to and extending from the first impact part 125b-l, and a third impact part 125b-3 bent in a direction opposite to the bent direction of the second impact part 125b-2 and extending therefrom. As shown in Fig. 3, projections 125b-4 are formed at connection portions of the respective impact parts to reduce the width of a flow, thereby increasing a flow velocity. Furthermore, installation grooves 125c-l for use in installing the blades 125b are formed on the upper plate 125a and the lower plate 125c, and ends of the first and third impact parts are rounded to be inserted into and mounted in the installation grooves 125c-l . Although the mist eliminator 125 in this embodiment comprises the upper plate 125a, a mist eliminator without an upper plate may also be used so that the mist eliminator can be easily attached to or detached from the wet scrubbing barrel 120, if necessary. Fig. 4 shows various arrangement states of the chemical spray nozzles and the mist eliminators of the wet scrubbing means. Spray nozzles 121 may be installed (contrary to those shown in Fig. 2) to face in a downstream direction of the flow of exhaust gas (a direction designated by arrows) as shown in Fig. 4a, pairs of spray nozzles 121 may be installed such that spray directions thereof are opposite to each other as shown in Fig. 4b, or spray nozzles 121 may be installed between the plurality of mist eliminators 125 as shown in Fig. 4c.

Referring to Figs. 2 and 5, a duct 154 of the dry scrubbing means 400 has one end connected to the outlet of the wet scrubbing barrel 120, and the other end connected to an inlet of the bag filter 150. Furthermore, the powder supply means 140 comprises a release agent hopper 130 for supplying a release agent, and a lime hopper 132 for supplying lime. The respective hoppers are installed such that they are connected to the duct 154 to supply powder independently. Although not shown in the figures, it is preferred that a screw conveyor for crushing and transferring powder be installed in a duct 133. As shown in Fig. 5, the bag filter 150 comprises a housing 158, a plurality of bags 152 installed in the housing, and a baffle 151 installed between the bags 152 and an inlet 158a of the housing. A release agent layer 156 and a lime layer 157 formed of the powder supplied from the powder supply means 140 adhere to each of the bags 152. It is preferred that the release agent powder be neutral, have a low specific gravity of 0.13 ton/m³ and a porosity of 70% or more, and be hardly plasterized even though moisture is absorbed into the release agent powder, and components thereof comprise silica (SiO₂) as a drying/damp-proofϊng agent, alumina (Al₂O₃) as an adsorbing/dehydrating agent, potassium oxide (K₂O) as a catalyst reacting with water, sodium oxide (Na₂O) as a reducer/catalyst, calcium oxide (CaO) as a moisture capturing/drying agent, and iron oxide (Fe₂O₃) as a moisture adsorbent. The release agent comprising the aforementioned components preferably has the following composition: 69 to 79.5 wt% of silica, 10.9 to 17 wt% of alumina, 0.5 to 6.4 wt% of potassium oxide, 1.5 to 5.5 wt% of sodium oxide, 0.1 to 3.0 wt% of calcium oxide and 0.1 to 2.0 wt% of iron oxide. Further, the lime layer 157 is formed of a mixture of lime and at least one selected from activated carbon, silica gel, starch, bentonite, alumina, diatomite, zeolite, perlite, and ceramic according to air pollutants. Furthermore, since particles of the release agent powder are larger than those of lime powder as shown in Fig. 5, pores of the release agent layer 156 are larger than those of the lime layer 157. An outlet 158b formed at an upper portion of the housing 158 is connected to the blower 160 through a duct 161. In addition, a discharge port 158c is formed at a lower portion of the housing 158 to drain the release agent and lime removed by high-pressure air of a compressor (not shown), and a rotary valve 153 is installed at the discharge port 158c. The rotary valve 153 comprises a plurality of blades 153a formed at a predetermined interval along the circumference of the rotary valve 153, and discharges the release agent and lime removed in the bag filter to the outside by rotation of the plurality of blades 153a. The rotary valve 153 and the baffle 151 enable uniform formation of the release agent layer 156 and the lime layer 157 when the blower 160 sucks air from the interior of the housing 158 to form a vacuum state therein and the release agent and the lime powder are simultaneously supplied through the duct 154 to form the release agent layer 156 and the lime layer 157 in the bag 152. That is, when the release agent powder or the lime powder is supplied into the housing, the rotation of the rotary valve 153 at a constant speed allows the powder supplied to the lower portion of the housing due to the baffle 151 to be entrained by and raised along with external air intermittently supplied through a clearance C by means of the rotation of the rotary valve 153, so that the release agent powder or the lime powder can uniformly adhere to the plurality of bags 152. Reference numeral 153b designates a reinforcement plate for adjusting a gap between the housing and the blade and preventing wear of the blade 153a.

Next, the operation of the hybrid-type apparatus for treating exhaust gas will be described with reference to Figs. 2 and 5.

First, the blower 160 connected to the bag filter is operated to blow out exhaust gas through the chimney so that vacuum can be formed in the housing 158 of the bag filter 150 to be lower than the atmospheric pressure. Next, a predetermined amount of release agent powder is supplied to the duct 154 from the release agent hopper 130a so that the release agent layer 156 can be formed on the surface of the bag 152. Then, a predetermined amount of lime powder is supplied to the duct 154 from the lime hopper 132a so that the lime layer 156 can be formed on the surface of the release agent layer 156 formed on the bag 152. At this time, the rotary valve 153 is simultaneously operated such that external air is intermittently supplied through a gap between the discharge port 158c and the blades 153a, thereby enabling the powder to uniformly adhere to the surface of the bag 152. In addition, there is an advantage in that the rotation of the rotary valve 153 supplies the external air so that the supplied powder can fly upward, thereby causing all the supplied powder to adhere to the bag 152 of the bag filter 150. After the release agent and lime adhesion process is completed, the rotation of the rotary valve 153 is stopped.

Subsequently, the pump 180 of the alkaline chemical spray means 200 is operated and the nozzles 121 spray the sodium hydroxide solution stored in the reservoir 190 so that acid exhaust gas supplied from the incinerator can be neutralized. While the exhaust gas passes through the mist eliminators 125 disposed within the wet scrubbing barrel 120, most of moisture is collected at the bottom of the wet scrubbing barrel 120 and then drained to the reservoir 190 through the pipe 126 connected to the drain hole 120a formed in the side surface of the wet scrubbing barrel 120. Therefore, since the space between the bottom of the wet scrubbing barrel 120 and the bottoms of the mist eliminators 125 is sealed by water, the exhaust gas is exhausted only through spaces among the blades 125b of the mist eliminators 125, so that inflow of exhaust gas containing excessive moisture into the dry scrubbing means 400 can be prevented. Next, while the exhaust gas supplied to the bag filter 150 of the dry scrubbing means 400 passes through the lime layer 157, acid gas is neutralized and dust or other impurities are removed by being adsorbed or trapped in inner pores of the lime layer 157.

If pressure loss in the bag 152 increases due to clogging of the pores of the release agent layer and the lime layer as the bag filter 150 is continuously used for exhaust gas treatment, high-pressure air is supplied into the bag 152 to separate the release agent layer and the lime layer from the bag. Since the release agent layer is not plasterized even though it absorbs moisture, the release agent layer is easily separated from the bag when the high-pressure air is applied in a pulse manner to the bag for the separation of the release agent layer. Therefore, the lime layer adhering to the release agent layer is also easily separated from the bag. Accordingly, when the release agent layer and the lime layer are separated from the bag and a fresh release agent and lime are then caused to adhere to the bag as described above, the bag of the bag filter can be used semipermanently. Since technical contents of a dedusting means for removing dust adhering to the bag 152 of the bag filter 150 are known in the art, detailed descriptions thereof will be omitted. With the aforementioned process, the hybrid-type apparatus for treating exhaust gas according to the present invention primarily scrubs exhaust gas, which has been exhausted from the incinerator, in the wet scrubbing means and secondly scrubs the exhaust gas in the dry scrubbing means to remove hazardous substances from the exhaust gas so that only clean air is exhausted to the atmosphere.

Industrial Applicability

According to the present invention, there is provided a hybrid-type method and apparatus for treating exhaust gas, wherein acid exhaust gas is neutralized and dust is removed from the exhaust gas by primarily wet-scrubbing the exhaust gas through spraying of an alkaline chemical such as sodium hydroxide to the exhaust gas and effectively removing moisture from the wet-scrubbed exhaust gas so that the treated exhaust gas can be supplied to a bag filter. Particularly, according to the present invention, the bag of the bag filter has the release agent, which is not to be plasterized, adhering to the surface of the bag and the chemical powder such as lime adhering to the release agent, so that exhaust gas primarily wet-scrubbed can be supplied directly to the bag filter and then subjected to secondary scrubbing therein, thereby effectively scrubbing the exhaust gas and reducing manufacturing and maintenance costs of facilities.

Furthermore, the present invention provides a method and apparatus capable of effectively and uniformly adhering release agent powder and chemical powder to the bag of the bag filter to increase effects of dry scrubbing treatment. Since the release agent that is not to be plasterized is used, the bag of the bag filter can be used semi-permanently.

It should be understood that the technical spirit of the present invention is not limited to the embodiments of the present invention described above and illustrated in the drawings. The scope of the present invention should be defined only by the appended claims. It is apparent to those skilled in the art that various modifications and changes can be made thereto within the technical spirit of the invention. Therefore, the modifications and changes will fall within the scope of the present invention so long as they are apparent to those skilled in the art.

Claims

1. A hybrid-type method for treating exhaust gas containing acid gas and dust exhausted from air pollutant emitting facilities, the method comprising: a release agent adhesion step of forming a release agent layer by evacuating air from the interior of a bag filter to the outside, and supplying release agent composition powder comprising porous expansion ceramic into the bag filter so that the release agent composition powder can adhere to a surface of a bag of the bag filter; a chemical adhesion step of forming a chemical layer by evacuating the air from the interior of the bag filter to the outside, and supplying chemical powder into the bag filter so that the chemical powder can adhere to a surface of the release agent layer; a wet treatment step of spraying an alkaline material to the exhaust gas exhausted from the air pollutant emitting facilities to neutralize the exhaust gas, and passing the exhaust gas through a mist eliminator to remove dust and moisture from the exhaust gas; and a dry treatment step of removing residual hazardous substances by passing the wet treated exhaust gas through the bag filter having the bag with the release agent layer and the chemical layer sequentially adhering thereto in the release agent adhesion step and the chemical adhesion step.

2. The method according to Claim 1, wherein the release agent composition powder further comprises a binder and a thickener.

3. The method according to Claim 1 or 2, wherein each of the release agent adhesion step and the chemical adhesion step further comprises an external air supply step of intermittently supplying external air into the bag filter from a lower portion of the bag filter during the supply of each of the release agent powder and the chemical powder to the bag filter.

4. The method according to Claim 3, wherein the dry treatment step further comprises a dedusting step of removing the release agent powder and chemical powder adhering to the surface of the bag by supplying high-pressure air into the bag of the bag filter if a difference in pressure between the release agent layer and the chemical layer of the bag filter is a predetermined value or higher.

5. The method according to Claim 4, wherein the bag filter comprises a rotary valve installed at the lower portion of the bag filter, the rotary valve comprises a plurality of blades disposed at a predetermined interval along the circumference of the rotary valve, and the external air supply step is performed by rotating the rotary valve at a predetermined speed.

6. The method according to Claim 4 or 5, wherein the release agent composition comprises 90 to 99.5 wt% of porous expansion ceramic, 0.5 to 9 wt% of binder, and 0 to 1 wt% of thickener.

7. The method according to Claim 6, wherein the porous expansion ceramic is prepared by calcining at least one rock component selected from the group consisting of obsidian, perlite, pitchstone, vermiculite, pumice and shale at a temperature range of 900 to 1,600⁰C.

8. A hybrid-type apparatus for treating exhaust gas containing acid gas and dust exhausted from air pollutant emitting facilities, the apparatus comprising: a wet scrubbing means including a wet scrubbing barrel having an inlet through which exhaust gas is introduced, an outlet through which treated exhaust gas flows out, and a drain hole formed at a position in a side surface thereof spaced apart by a certain distance upwardly from the bottom thereof, an alkaline chemical spray means for spraying an alkaline material to an inlet side within the wet scrubbing barrel, and a mist eliminator disposed within the wet scrubbing barrel to divide the interior of the wet scrubbing barrel into an inlet-side space and an outlet-side space and having the bottom thereof positioned below the drain hole; a dry scrubbing means including a duct having one end connected to the wet scrubbing barrel, a bag filter connected to the other end of the duct, and a powder supply means connected to the duct to supply release agent powder and chemical powder to the bag filter through the duct; and a blower connected to the bag filter to blow out the exhaust gas through a chimney, wherein the powder supply means supplies the release agent powder to the duct during operation of the blower to cause the release agent powder to adhere to a surface of a bag of the bag filter so as to form a release agent layer with a predetermined thickness and subsequently supplies the chemical powder to cause the chemical powder to adhere to a surface of the release agent layer so as to form a chemical layer with a predetermined thickness, and the alkaline chemical spray means sprays the alkaline material into the wet scrubbing barrel, whereby the exhaust gas exhausted from the air pollutant emitting facilities is exhausted after being primarily scrubbed in the wet scrubbing means and then secondly scrubbed in the dry scrubbing means.

9. The apparatus according to Claim 8, wherein the bag filter includes a baffle installed between an inlet connected to the duct and the bag, and a rotary valve installed at a lower portion of the bag filter, the rotary valve includes a plurality of blades arranged at a predetermined interval along the circumference of the rotary valve, and the rotary valve is rotated at a predetermined speed to intermittently supply external air from the lower portion of the bag filter when the chemical spray means supplies the release agent powder and the chemical powder to the bag filter, so that the release agent powder and the chemical powder can uniformly adhere to the surface of the bag.

10. The apparatus according to Claim 8 or 9, wherein the chemical powder is lime powder.

11. The apparatus according to Claim 8 or 9, wherein the chemical powder is a mixture of at least one selected from activated carbon, silica gel, starch, bentonite, alumina, diatomite, zeolite, perlite, and ceramic.