JP2000015058A - Treatment apparatus and method for incinerator exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a treatment apparatus and method for incinerator exhaust gas capable of treating dioxins adhering on dust and the like. SOLUTION: In an incinerator exhaust gas treatment apparatus of an incinerator provided with a heat recovery system 2 for recovering heat from an exhaust gas discharged from an incinerator 1, a dust collector 3 for removing dust from the exhaust gas which has passed through the heat recovery system 2, an adsorption reactor 4 packed with a granular carbonaceous adsorbent for allowing the dust-removed exhaust gas to pass through and a regenerator 5 for executing regeneration treatment by heating the carbonaceous adsorbent extracted from the adsorption reactor 4, an oxidizing agent supply device 8 for adding ozone or hydrogen peroxide to the exhaust gas within the heat recovery system 2 and an alkali agent supply device 9 for adding an alkali agent to the exhaust gas before the dust collector 3 are provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and an apparatus for treating exhaust gas from an incinerator, and more particularly to a method and an apparatus suitable for reducing dioxin.

[0002]

2. Description of the Related Art Since exhaust gases from incinerators, particularly municipal waste incinerators, contain harmful substances such as dust, sulfur oxides and nitrogen oxides, various removal techniques have been developed. Regarding dioxins which are particularly toxic among the harmful substances contained therein, it cannot be said that a treatment technology has yet been established.

[0003] There are roughly two types of dioxin treatment techniques: a technique for suppressing the generation of dioxins and a technique for removing the generated dioxins.

[0004]

The former is intended to suppress the generation of dioxins by complete combustion at a high temperature of 850 ° C. or higher.
Since dioxins are synthesized in a temperature range of 400 ° C., it is difficult to completely suppress the generation.

On the other hand, as the latter, there is a technique of oxidatively decomposing dioxins with oxygen contained in exhaust gas using a metal oxide catalyst or a technique of adsorbing with activated carbon. However, these methods are suitable for treating gaseous dioxins, but cannot treat dioxins adhering to dust and the like, and there has been a problem in treating dust containing dioxins.

Therefore, the present invention has been made in view of the above problems,
An object of the present invention is to provide an incinerator exhaust gas treatment apparatus and method capable of treating dioxins attached to dust and the like.

[0007]

In order to solve the above-mentioned problems, an exhaust gas treatment apparatus for an incinerator according to the present invention comprises a heat recovery system for recovering heat from exhaust gas and removing dust from exhaust gas passing through the heat recovery system. A dust collector, and an adsorption reactor filled with granular carbonaceous adsorbent and passing exhaust gas after dust removal,
A regenerator that regenerates the carbonaceous adsorbent by heating the carbonaceous adsorbent taken out of the adsorption reactor. An oxidizing agent supply device for adding hydrogen peroxide and / or ozone as an oxidizing agent to the exhaust gas, an alkali agent supplying device for adding an alkaline agent to the exhaust gas flow in front of the dust collector, and A desorption gas supply system for returning the desorption gas generated in the regenerator to the exhaust gas flow.

On the other hand, the method for treating exhaust gas of an incinerator according to the present invention comprises a heat recovery step of recovering heat from exhaust gas, a dust collection step of collecting and removing dust from the exhaust gas after heat recovery, An adsorption step of adsorbing harmful gases by passing the exhaust gas after dust removal through the granular carbonaceous adsorbent filled in, and a regeneration step of taking out the carbonaceous adsorbent from the adsorption reactor and heating it to perform a regeneration treatment. And an oxidizing agent adding step of adding hydrogen peroxide and / or ozone to the exhaust gas during the heat recovery step or before the entrance of the dust collector, and the exhaust gas before the dust collecting step. Adding an alkaline agent and a desorbed gas obtained in the regeneration step.

[0009] By adding hydrogen peroxide or ozone as an oxidizing agent to the exhaust gas, dioxins and precursors (eg, chlorobenzene,
Chlorophenol) is oxidatively decomposed. In particular, dioxins and precursors attached to dust are also effectively oxidatively decomposed. As a result, the concentration of dioxins contained in the dust removed by the dust collector decreases. By adding an alkaline agent to the exhaust gas after the temperature is lowered, HCl originally present in the exhaust gas and HCl generated by the oxidative decomposition reaction react with the alkaline agent to form dust. In addition, sulfur oxides in the exhaust gas also react to produce sulfites and sulfates, which become dust,
Removed by dust collector. Examples of the alkaline agent include calcium and magnesium hydroxides, oxides, carbonates, and minerals and dusts containing these compounds such as limestone and dolomite.

The exhaust gas from which dust has been removed is sent to an adsorption reactor, and dioxins remaining in the exhaust gas are adsorbed and removed by a carbonaceous adsorbent. On the other hand, the oxidant remaining in the exhaust gas is reduced to oxygen or water by the carbonaceous adsorbent. Therefore, the oxidizing agent and dioxins do not remain in the exhaust gas. Furthermore, it is possible to reliably perform oxidative decomposition of dioxins by adding a large amount of an oxidizing agent. Activated carbon, activated coke, activated char, and the like can be used as the carbonaceous adsorbent.

The desorbed gas generated during regeneration of the adsorbent includes:
Although it contains SO ₂ and HCl which is a decomposition product, it can be recovered by reacting it with the above-mentioned alkali agent by returning it to the front of the dust collector.

Here, it is preferable that the oxidizing agent is added to the exhaust gas in a temperature range of 300 ° C. or lower.

Dioxins are known to be produced from precursors at 200 to 400 ° C. using heavy metals as catalysts. In addition, hydrogen peroxide and ozone serving as oxidizing agents are 300 ° C.
At very high temperatures, there is a possibility of thermal decomposition, so it is effective to add an oxidizing agent in a temperature range of 300 ° C. or less.

After dust collection, ammonia may be added to the exhaust gas before adsorption. With the added ammonia, nitrogen oxides in the exhaust gas are reduced to nitrogen by a reduction reaction using a carbonaceous adsorbent as a catalyst and denitrated.

[0015]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an overall flow diagram of an incineration system for municipal waste including an exhaust gas treatment device for an incinerator according to the present invention.

This system includes an incinerator 1 for almost completely burning municipal waste at high temperature, a heat recovery system 2 for recovering heat from exhaust gas, and a temperature controller 1 for further cooling the exhaust gas after heat recovery.
1 (for example, a cooling tower), a dust collector 3 (for example, a bag filter) for removing dust from exhaust gas after cooling, and a carbonaceous adsorbent (for example, for adsorbing and removing harmful gases and the like from exhaust gas after dust removal). , Activated carbon) filled adsorption reactor 4
A regenerator 5 for heating and regenerating the carbonaceous adsorbent in the adsorption reactor 4, a separator 6 (for example, a vibrating screen) for removing unnecessary components from the regenerated carbonaceous adsorbent, and a chimney 7 for discharging exhaust gas. And Then, the incinerator 1 and the heat recovery system 2, the heat recovery system 2 and the temperature controller 11, the temperature controller 11 and the dust collector 3,
The dust collector 3 and the adsorption reactor 4, and the adsorption reactor 4 and the chimney 7 are lines L 1, L 3, L 4, L 5, L which are gas pipes, respectively.
6. On the other hand, the bottom of the adsorption reactor 4 and the top of the regenerator 5 are connected by a line L7, and the bottom of the regenerator 5 and the separator 6 are connected by a line L8, and the outlet of the carbonaceous adsorbent of the separator 6 and the adsorption reactor 4 are connected. Is the top of the line L9
Connected by A conveyor or the like is used for the line L9.

The heat recovery system 2 includes a boiler 21 that generates hot water or steam using the high heat of the exhaust gas, and an economizer 22 that preheats water supplied to the boiler 21 by the exhaust gas passing through the boiler 21. An oxidant supply device 8 for adding hydrogen peroxide H ₂ O ₂ or ozone O ₃ to exhaust gas is connected to a line L2 connecting the boiler 21 and the economizer 22 by a line L11.

A line L4 connecting the temperature controller 11 and the dust collector 3 is connected to a line L10 for leading desorbed gas generated in the regenerator 5, and a downstream side of the line L10 Is added to the exhaust gas by a line L12. An ammonia supply device 10 for adding ammonia to exhaust gas is connected to a line L5 connecting the dust collector 3 and the adsorption reactor by a line L13.

Next, the operation of this system, that is, the method for treating exhaust gas from an incinerator according to the present invention will be described.

The municipal solid waste put into the incinerator 1 is about 800
It is incinerated at a high temperature of ９950 ° C. and almost completely burned. The high-temperature exhaust gas from the incinerator 1 is sent to the boiler 21 via the line L2, and heat is recovered by changing the water supplied by the exhaust heat into hot water or steam. By this heat recovery, 2
The exhaust gas whose temperature has dropped to about 50 ° C. is sent to the economizer 22 through the line L2. At this time, the oxidant H ₂ O ₂ or O ₂ supplied from the oxidant supply device 8 through the line L11 is supplied. ₃ is added to the exhaust gas. In the economizer 22, the boiler 2
Further heat recovery is achieved by preheating the feed water to 1.
As a result, the exhaust gas temperature at the exit of the economizer 22 is 2
It drops to around 00 ° C. This exhaust gas is sent to the temperature controller 11 through the line L3, and further cooled to 120 to 180 ° C.

An oxidizing agent added in front of the economizer 22 oxidizes and decomposes dioxins and their precursors to produce HCl and the like. H ₂ O ₂ or O ₃ used as an oxidizing agent thermally decomposes at 400 ° C. or higher,
At 0 ° C or lower, the oxidative decomposition reaction is suppressed, but the boiler 2
Since the exhaust gas temperature between the outlet 1 and the temperature controller 11 is 200 ° C. to 250 ° C. as described above, the oxidative decomposition reaction is effectively performed, and dioxins and their precursors can be removed. Further, in these temperature ranges, the generation reaction of dioxins tends to occur, but the precursor itself is also removed by the oxidative decomposition reaction, so that the generation itself of dioxins can be suppressed.

The exhaust gas discharged from the temperature controller 11 is mixed with a desorbed gas from a regenerator 5 to be described later via a line L10, and then an alkali agent such as calcium hydroxide Ca is supplied from an alkali agent supply device 9. (OH) ₂ is added. HCl and SOx, NOx contained in the exhaust gas react with the alkaline agent to produce a calcium salt,
Floating in the exhaust gas stream as dust. These dusts including incineration ash and the like are captured and removed by the dust collector 7.
The above-mentioned oxidative decomposition reaction proceeds between dioxins and their precursors attached to dust such as incineration ash and the oxidizing agent, so that the amount of dioxins and their precursors attached to dust is also effectively reduced Can be done.

Ammonia is added to the exhaust gas discharged from the dust collector 2 from the ammonia supply device 10 via the line L13, and sent to the adsorption reactor 4 via the line L5.

In the adsorption reactor 4, the carbonaceous adsorbent acts as a catalyst, and the denitration reaction by the added ammonia and the nitrogen oxide NOx in the exhaust gas proceeds to be decomposed into N ₂ gas. The oxidizing agent is also decomposed into steam and oxygen by a reduction reaction. Further, SOx and the like in the exhaust gas are adsorbed and removed. As a result, the exhaust gas from which the harmful gas has been removed is discharged from the chimney 7 to the atmosphere via the line L6.

The performance of the carbonaceous adsorbent deteriorates due to the adsorption of SOx and the like in the exhaust gas. The carbonaceous adsorbent whose performance has been reduced and inactivated is taken out from the bottom of the adsorption reactor 4 and sent to the regenerator 5 through the line L7, where 300 to 600
After being heated and regenerated in an inert gas atmosphere at ℃, and cooled, it is sent to the separator 6 by a line L8. Most of the desorbed gas separated from the carbonaceous adsorbent in the regenerator 5 is S
It consists of O ₂ , which includes adsorbed HCl and the like. This gas is sent upstream of the dust collector 3 by the line L10 as described above. SO in the desorbed gas sent
As described above, ₂ and HCl become dust due to the alkali chemical added afterwards, and are collected by the dust collector 3.

In the separator 6, after the powdered adsorbent and dust are removed from the regenerated carbonaceous adsorbent, the carbonaceous adsorbent is returned to the adsorption reactor 4 via the line L9.

When an oxidizing agent is added to exhaust gas to oxidize and decompose dioxins and their precursors, in order to achieve the currently required regulation value of 0.1 to 1.0 ng TEQ / m ³ N. Requires a large amount of oxidizing agent to be introduced. In this case, however, an unreacted oxidizing agent harmful to the human body will remain in the exhaust gas in a large amount and must be removed. In this embodiment, the remaining oxidizing agent has an advantage that almost no oxidizing agent remains in the exhaust gas discharged from the chimney 7 because the oxidizing agent itself is decomposed by a reduction reaction in the adsorption reactor 4.

In the above description, the embodiment using the heat recovery system including the boiler, the economizer, and the temperature controller has been described. However, the configuration of the heat recovery system is not limited to this, and only the boiler or the air preheating is used. It may be a simple configuration such as only a heater or a temperature controller, or a configuration in which a plurality of boilers are combined. In any case, the oxidizing agent is preferably supplied to a region where the temperature of the exhaust gas is 300 ° C. or lower. For example, when the same heat recovery system 2 as the embodiment shown in FIG. 1 is used, the line L11 from the oxidant supply device 8 is connected to the line L3 connecting the economizer 22 and the temperature controller 11. Well,
Alternatively, it may be directly connected to any one of the boiler 21, the economizer 22, and the temperature controller 11. Of course, when connecting inside the boiler 21, it goes without saying that it is necessary to add an oxidizing agent in the downstream region where the exhaust gas temperature drops below 300 ° C.

As the dust collector, various dust collectors such as an electric dust collector can be used in addition to the bag filter type.

Although an example in which calcium hydroxide is used as the alkali agent has been described, calcium, magnesium oxides, hydroxides, and carbonates may be used, and minerals such as limestone and dolomite or dust containing these may be used. May be used.

The carbonaceous adsorbent used in the adsorption reactor 4 is activated carbon obtained by adding a binder to a carbon-containing substance such as coal, molding and then heat-treating or activating with steam, air, or the like.
In addition to activated coke and activated charcoal, those in which a compound such as vanadium, iron, or copper is supported can be used.

As the adsorption reactor 4, it is preferable to use a moving bed type adsorption reactor, and a cross-flow type or countercurrent type adsorption reactor can be used. The use of such a moving bed type adsorption reactor facilitates the regeneration of the carbonaceous adsorbent. In the present embodiment, the sulfur oxides and the like in the desorbed gas are treated by mixing the desorbed gas with the exhaust gas before the addition of the alkali agent. You may.

The ammonia may be added to the exhaust gas at any position from the incinerator 1 to the adsorption reactor 4 instead of to the exhaust gas after passing through the dust collector.

[0034]

EXAMPLES The present inventors conducted a comparative experiment to confirm the effect of reducing the concentration of dioxin in exhaust gas by using the apparatus and method for treating exhaust gas in an incinerator according to the present invention. Hereinafter, the experimental results will be described.

EXAMPLES 1 AND 2 AND COMPARATIVE EXAMPLE The exhaust gas from a refuse incinerator was taken out at 100 m ³ N / h, cooled to about 250 ° C., and a predetermined amount of an oxidizing agent shown in Table 1 was added. The mixture was supplied to the held temperature controller, and Ca (OH) ₂ was added to the exhaust gas discharged from the temperature controller at a ratio of 1.5 g / m ³ N, and then introduced into a bag filter kept at about 160 ° C. The exhaust gas which has passed through the bag filter by the addition of NH ₃ at a rate of 120 ppm, granular activated carbon was processed by passing through the 170 liters (100 kg) packed moving bed adsorption reactor. The residence time of the activated carbon in the reactor and 1000h, the inactivated charcoal is withdrawn continuously 0.1 kg / h from the adsorption reactor bottom and fed into the regenerator, approximately under N ₂ gas atmosphere at 450
A regeneration treatment was performed at 1 ° C. for 1 hour, and the generated desorbed gas was returned to the front of the bag filter.

[0036]

[Table 1]

In each case, the concentration of dioxins and oxidizer in the exhaust gas at the inlet and outlet of the adsorption reactor, the concentration of dioxin in dust captured by the bag filter, and the type of dioxins and precursor in the desorbed gas. Table 2 shows the results of comparing the concentrations of a certain hexachlorobenzene and pentachlorophenol.

[0038]

[Table 2]

Embodiments 1 and 2 which are processing methods according to the present invention
It was confirmed that each of them could reduce the dioxin concentration in the exhaust gas and the dust as compared with the comparative example. Further, it was confirmed that the oxidizing agent could be removed by the adsorption reactor, and the concentration in the exhaust gas could be reduced. The concentrations of dioxins and precursors in the desorbed gas also did not increase during operation, and it was confirmed that dioxins could be decomposed by circulating the desorbed gas.

[0040]

As described above, according to the present invention,
By adding an oxidizing agent to the exhaust gas to oxidize and decompose dioxins, the concentration of dioxins adhering to the gas and to the dust can be reduced. further,
Since the oxidant is reduced and decomposed by the carbonaceous adsorbent in the adsorption reactor, no extra oxidant is released into the atmosphere.

[Brief description of the drawings]

FIG. 1 is an overall flow chart of an incineration system including an exhaust gas treatment device of an incinerator according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Incinerator, 2 ... Heat recovery system, 3 ... Dust collector, 4 ... Adsorption reactor, 5 ... Regenerator, 6 ... Separator, 7 ... Chimney, 8 ... Oxidant supply device, 9 ... Alkaline chemical supply device Reference numeral 10: ammonia supply device, 11: temperature controller, 21: boiler, 22: economizer, L1 to L13: line.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B01D 53/56 B01D 53/34 129Z 53/68 134A (72) Inventor Kohei Goto Yuyogaoka, Hiratsuka-shi, Kanagawa No. 63-30 Sumitomo Heavy Industries Machinery Co., Ltd. Hiratsuka Plant F-term (reference) 4D002 AA02 AA12 AA19 AA21 AC04 BA03 BA04 BA05 BA06 BA12 BA13 BA14 CA01 CA07 CA11 CA13 DA05 DA06 DA07 DA11 DA12 DA16 DA21 DA22 DA23 DA41 DA51 DA52 EA02 EA08 GA01 GA02 GB02 GB03 GB06 GB08 HA10 4D012 CA12 CA13 CA15 CA16 CB11 CD03 CE01 CE02 CF02 CF04 CF05 CF06 CH01 CK01 4D020 AA05 AA06 AA10 BA01 BA02 BA08 BA09 BA16 BB01 BB03 BB10 CA07 CA08 CD02 CD03 DA02 DB01 DB02 DB03 DB11

Claims (6)

[Claims] 1. A heat recovery system for recovering heat from exhaust gas of an incinerator, a dust collector for removing dust from the exhaust gas passing through the heat recovery system, and a granular carbonaceous adsorbent filled with the exhaust gas. An exhaust gas treatment device for an incinerator, comprising: an adsorption reactor that allows the exhaust gas to pass therethrough; and a regenerator that performs a regeneration process by heating the carbonaceous adsorbent taken out of the adsorption reactor. An oxidant supply device for adding hydrogen peroxide and / or ozone as an oxidant to the exhaust gas inside the system or before the dust collector inlet; and an alkali for adding an alkali chemical to the exhaust gas stream before the dust collector inlet. An exhaust gas treatment device comprising: a chemical supply device; and a desorption gas supply system that returns desorption gas generated in the regenerator to an exhaust gas flow in front of the dust collector. 2. The oxidant supply device according to claim 1, wherein the exhaust gas temperature is 3
The exhaust gas treatment apparatus according to claim 1, wherein the oxidizing agent is added to the exhaust gas in a temperature range of 00C or lower. 3. The exhaust gas treatment device according to claim 1, further comprising an ammonia supply device for adding ammonia to the exhaust gas between the dust collector and the adsorption reactor. 4. A heat recovery step for recovering heat from the exhaust gas of an incinerator, a dust collection step for collecting and removing dust from the exhaust gas after the heat recovery, and a granular carbonaceous material filled in the adsorption reactor. An incineration process comprising: an adsorption step of adsorbing harmful gas by passing exhaust gas after dust removal through an adsorbent; and a regeneration step of performing a regeneration treatment by heating the carbonaceous adsorbent taken out of the adsorption reactor. In the method for treating exhaust gas in a furnace, an oxidizing agent adding step of adding hydrogen peroxide and / or ozone to the exhaust gas during the heat recovery step or before the entrance of the dust collector; An exhaust gas treatment method, comprising: adding a desorbed gas obtained in the regeneration step. 5. The exhaust gas treatment method according to claim 4, wherein the oxidizing agent adding step is performed in the temperature range of 300 ° C. or lower during or after the heat recovery step. 6. The exhaust gas treatment method according to claim 4, further comprising a step of adding ammonia to exhaust gas between the dust collection step and the adsorption step.