JPH0788329A - Treatment of waste gas containing organohalogen compound - Google Patents

Abstract

PURPOSE:To decompose and remove the poisonous org. halogen compds. such as dioxine in a waste gas generated from the incineration of various wastes while suppressing the resynthesis of the compds. CONSTITUTION:A waste gas contg. org. halogen compds. discharged from combustion equipment 1 is passed through a catalyst bed to decompose and remove the compds. The catalyst bed is set as the heat accumulator of a regenerative heat exchanger 3. An NOx removing catalyst is preferably used as the catalyst of the bed, air is used as the cooling medium of the heat exchanger, and the heated air is preferably used as the combustion air of the equipment 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating an exhaust gas containing an organic halogen compound, and in particular, using a toxic organic halogen compound such as polychlorinated dibenzodioxin or polychlorinated dibenzofuran contained in an incinerator exhaust gas using a catalyst. The present invention relates to a method for treating exhaust gas, which is decomposed and removed by means of.

[0002]

2. Description of the Related Art Research on removal technology for trace amounts of toxic organic chlorine compounds such as dioxins, PCBs and chlorophenols contained in exhaust gas generated from incineration facilities for treating industrial waste and municipal waste. Has a short history,
Although it is being put to practical use as an individual technology, it has not been established as a total system including economic efficiency.

Of these, the substance called dioxin is a compound called polychlorinated dibenzodioxin,
Depending on the number of chlorine, there are dichlorides, tetrachlorides, pentachlorides, hexachlorides, etc. There are more than 70 isomers, and dibenzodioxin tetrachloride (T ₄ CDD) is known to be the strongest toxic substance. ing. Dioxin is a very stable substance that does not dissolve in water and its toxicity does not disappear semipermanently, so it is considered to be an important chemical substance for environmental pollution in combination with its strong toxicity. In general, as a technique for decomposing and removing toxic organic chlorine compounds including dioxins, a so-called direct combustion type treatment method in which high temperature combustion is performed, an adsorption method with activated carbon, a cleaning method with a chemical agent, a decomposition method with a catalyst and the like are known.

Of these, the direct combustion type treatment method is one in which complete oxidative decomposition of the toxic organochlorine compound is carried out by a combustion process, and it is necessary to maintain a high temperature of 1000 ° C. or higher when carrying out the method. However, the combustion temperature in the incinerator is 800-
Since the temperature is 950 ° C., it is necessary to further raise the temperature in the furnace or provide a reburning section in order to oxidatively decompose the organic chlorine compound. However, in order to raise the temperature in the furnace, there is a problem that the furnace must be completely remodeled, and if the temperature is 950 ° C. or higher, the ash content of the incinerator is melted and the furnace wall is damaged or adheres to the furnace wall.

Further, in the case of the method of providing the re-combustion section, there is a drawback that the total amount of exhaust gas and the running cost due to the fuel for re-combustion increase significantly. Moreover, since the concentration of the substance to be treated in the exhaust gas is low, the treatment efficiency is inevitably low. On the other hand, the adsorption method requires regeneration of waste activated carbon, and the washing method requires secondary treatment of waste liquid. Further, these secondary treatment means are very troublesome, and thus cannot be said to be a practical decomposition and removal technique.

It has been discovered that the catalytic decomposition method, which is expected to be most practical, decomposes dioxin and the like in a certain temperature range (200 to 500 ° C.). However, the current method has the following restrictions on use. Since the catalyst has no cleaning function, the opening size of the through hole (exhaust gas passage) of the catalyst has to be increased, so that the surface area per unit volume of the catalyst becomes small and the catalyst has a large capacity.

If the opening size of the through holes of the catalyst is made small and the surface area per unit volume of the catalyst is made large, the capacity of the catalyst can be made small, but since there is no cleaning function,
In this case, it must be installed after removing dust with a bag filter. On the other hand, the active temperature range of the catalyst (250
℃ -450 ℃ is the heat resistant temperature of bag filter (200 ℃)
Since the temperature is higher than ˜250 ° C.), there is a practical limitation that the exhaust gas after passing through the bag filter must be reheated.

Since the current catalyst does not have a function of reducing the temperature of exhaust gas, if it is installed in the exhaust gas at 300 ° C., for example, even if dioxin and the like can be decomposed at this portion, dust collection by a bag filter or the like after that is possible. The process of lowering the exhaust gas temperature to the heat resistant temperature of the furnace, that is, a economizer and an air preheater are installed to increase the heat utilization efficiency such as the boiler efficiency.
In this part, it was revealed that the fly ash and the metal, which is the heat transfer surface for cooling, are involved to re-synthesize dioxins. The only method currently proposed for suppressing this re-synthesis is rapid water spray temperature reduction, but this method has a problem in terms of energy recovery efficiency.

[0009]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, decomposes and removes while suppressing the resynthesis of toxic organic chlorine compounds such as dioxins generated from the incineration of various wastes, An object of the present invention is to provide an exhaust gas treatment method capable of reducing the temperature in the catalyst to a temperature below the re-synthesis temperature range of dioxins and the like.

[0010]

In order to solve the above-mentioned problems, the present invention provides a method for treating exhaust gas which decomposes and removes exhaust gas containing an organic halogen compound discharged from a combustion device through a catalyst layer, wherein the catalyst layer is It is supposed to be installed as a heat storage body of a heat storage type heat exchanger.

As described above, in the present invention, toxic organohalogen compounds such as polychlorinated dibenzodioxin and polychlorinated dibenzofuran contained in incinerator exhaust gas are
In the method of removing by using a catalyst, the catalyst layer supporting the catalyst is used as a heat storage body of a heat storage heat exchanger to suppress re-synthesis of toxic organochlorine compounds while decomposing and removing them in the process of reducing the temperature of exhaust gas. In the above, the catalyst of the catalyst layer is a nitrogen oxide removal (Denox) catalyst or a modified De
By using the nox catalyst, it is possible not only to suppress the resynthesis of the organic chlorine compound but also to decompose and remove it, and also to have a denitration function.

Further, in the above, the heat storage type heat exchanger is
Air is used as a cooling medium, and the heated air can be used as combustion air for a combustion device, particularly as secondary combustion air, and the flow of exhaust gas and the air passing through the heat exchanger as a countercurrent flow. By reliably backwashing with air per cycle, it is possible to prevent ash from adhering to the catalyst and blocking by ash. The heat storage body which is the catalyst layer is preferably a honeycomb structure having a through hole with an equivalent diameter of 2 mm or more and an opening ratio of 50% or more. And in the said heat storage type heat exchanger, exhaust gas temperature is 300-450 degreeC at an inlet.
Can be cooled to 150-250 ° C at the outlet.

[0013]

The present invention uses a catalyst to remove toxic organic chlorine compounds such as polychlorinated dibenzodioxins and polychlorinated dibenzofurans contained in exhaust gas from incinerators for treating industrial wastes and municipal wastes. The catalyst layer using the catalyst is used as a heat storage body of a heat storage heat exchanger to decompose and remove the toxic organochlorine compound while suppressing the resynthesis of the toxic organochlorine compound in the process of reducing the temperature of the exhaust gas.

The reaction temperature for resynthesizing and decomposing dioxin and the like is an extremely important factor, and this temperature region is largely characterized in that resynthesis and decomposition are almost the same. Both are 250 to 450 ° C., preferably 250 to 4
This is a temperature range of 00 ° C. If the temperature is lower than 200 ° C, not only the removal efficiency is low, but also the poisoning of the catalyst by HCl or SOx in the exhaust gas becomes large and the deterioration is significantly accelerated. On the other hand, if the reaction temperature is too high, the catalyst may be deteriorated and it becomes difficult to use it for a long time.

The catalyst applied to the present invention is not particularly limited, but an acid resistant catalyst that is not easily affected by the sulfur compounds and halogen compounds contained in the processing gas is preferable. Denox catalyst or modified D
Exhaust gas temperature of 200-500 ° C. under oxidative conditions (6-12% O ₂ content or higher)
Preferably, by disposing in a temperature range of 250 to 400 ° C. to decompose organic chlorine compounds such as dioxins and nitrogen oxides, PCT / EP90 / 01685,
These catalysts are known and described in JP-A-3-8415 and JP-A-3-122221, and these catalysts can be used in the present invention.

On the other hand, when dioxin and the like are resynthesized in the exhaust gas cooling section at 250 to 450 ° C., for example, VGB
Kraftwork Technique (VGB Kraft werk tecknik
) Volume 69, August 8, 1989, S795-802 or VDI Berichte NR, 895, 1
991, S193-210.
FIG. 2 shows a process chart of an exhaust gas treatment method using a known catalyst. In this method, dioxins and the like are resynthesized in a economizer or an air preheater at a subsequent stage.
Since the catalyst does not have a washing function and the catalyst is opened for a long time, the opening of the catalyst is blocked by fly ash, which poses a problem that the opening size is restricted.

When it is actually used in a practical machine, as shown in FIG. 3, it is installed after dust ash is removed by a dust collector such as a bag filter, but the exhaust gas after passing through the dust collector is removed. Since the catalyst has to be reheated to a certain temperature range, the energy is wasted. FIG. 1 shows an example in which a heat storage type heat exchanger with a catalytic function according to the present invention, for example, a Jungstrom type air preheater or the like, in which a heat storage body that continuously exchanges heat by contact with exhaust gas is changed and circulated, is installed in an actual apparatus. It is a process drawing.

By installing a Denox catalyst or a modified Denox catalyst, for example, as a heat storage material of a Jungstrom type air preheater in a temperature range for regenerating dioxin in exhaust gas, the catalyst suppresses resynthesis of dioxin and the like at the same time. While decomposing, the exhaust gas temperature can be rapidly reduced to a temperature at which it can be passed through a dust collector such as a bag filter in the subsequent stage. Moreover, since the catalyst is also a Denox catalyst, the nitrogen oxide itself is decomposed.

As described above, the heat storage heat exchanger has a composite function capable of simultaneously performing the four functions. 1 to
The exhaust gas temperature shown in 3 is a general temperature, and the temperature is not limited. Further, in the above description, a toxic organochlorine compound such as dioxin has been described, but the present invention is not limited to dioxin and the like, and an organohalogen compound containing halogen such as bromine, iodine and fluorine may be similarly treated. You can

[0020]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto. Example 1 FIG. 4 is a process diagram of the apparatus used in this example. In FIG. 4, an air preheater and a water atomizing gas cooling tower are installed in the re-synthesis temperature region of dioxins and the like so that the experiment can be performed under the same conditions as the process diagram in which the heat storage heat exchanger with a catalytic function of the present invention is installed. In the process chart of the case, the ducts were replaced and three types of experiments were conducted to examine the difference in effect.

The object of combustion is plastic waste, and the conditions are such that the exhaust gas temperature at the waste heat boiler outlet is reduced to 350 ° C. and the exhaust gas temperature at the bag filter inlet is reduced to 200 ° C. As a catalyst layer as a heat storage body of the heat storage heat exchanger, a commercially available titanium oxide-based catalyst was used in a honeycomb molded body having an opening of 4.0 mm. The space velocity (SV value) of this catalyst layer is about 10
It was set to 000 hr ^-1 . Analytical values such as dioxin,
Toxic equivalent equivalent concentration of 2, 3, 7, 8-TCDD (EPA
Method ... displayed by TEQ). The results of the experiment are shown in Table 1.

[0022]

[Table 1]

As a result of the experiment, the toxicity equivalent conversion concentration (TEQ) of dioxin and the like increased by 4.6 times in air preheating, and it was clearly recognized that dioxin and the like were resynthesized. In the gas cooling tower, resynthesis of dioxins and the like was suppressed, and a slight reduction effect was observed. The heat storage type heat exchanger using a catalyst shows a high resolution of 95%, which is about 1 in comparison with the air preheater that causes re-synthesis.
A difference of the order of 1/00 was found.

As a matter of course, the effect of reducing nitrogen oxides was observed only in the heat storage heat exchanger using the catalyst, and the denitration rate was about 65%. In this embodiment, a Jungstrom type heat storage type heat exchanger was used, but as the heat storage type heat exchanger, an axial flow type or a radial flow type rotary heat storage type, or a heat storage chamber type is used. The same thing can be used.

[0025]

The present invention is configured as described above,
It succeeded in effectively removing the toxic organohalogen compound contained in the exhaust gas from the incinerator while reducing the temperature (heat recovery) using a catalyst in the resynthesis temperature range. That is, the toxic organohalogen compound is decomposed, and the temperature is reduced (heat recovery) while passing through the catalyst in its resynthesis temperature range.
However, the re-synthesis is suppressed, and the nitrogen oxides can be decomposed.

A heat storage type heat exchanger having a composite function capable of simultaneously performing the above four functions. INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide an innovative technology which is the most economical and has a great effect and which does not cause energy loss.

[Brief description of drawings]

FIG. 1 is a process diagram of an exhaust gas treating apparatus using a heat storage heat exchanger with a catalytic function of the present invention.

FIG. 2 is a process diagram showing an example of an exhaust gas treating apparatus using a known catalyst.

FIG. 3 is a process diagram showing another example of an exhaust gas treating apparatus using a known catalyst.

FIG. 4 is a process diagram showing the experimental apparatus used in Example 1.

[Explanation of symbols]

1: incinerator, 2: waste heat boiler, 3: heat storage heat exchanger with catalytic function, 4: dust collector, 5: stack, 6: catalyst, 7: economizer or air preheater, 8: water spray Gas cooling tower, 9: Air

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuyoshi Kaneko 11-11 Haneda Asahi-cho, Ota-ku, Tokyo Inside EBARA CORPORATION

Claims (6)

[Claims] 1. A method of treating exhaust gas, which decomposes and removes exhaust gas containing an organic halogen compound discharged from a combustion apparatus through a catalyst layer, wherein the catalyst layer is installed as a heat storage body of a heat storage heat exchanger. Exhaust gas treatment method. 2. The exhaust gas treatment method according to claim 1, wherein the catalyst of the catalyst layer is a nitrogen oxide removal catalyst. 3. The exhaust gas treatment method according to claim 1, wherein the regenerative heat exchanger uses air as a cooling-side medium and uses the heated air as combustion air for a combustion device. . 4. The heat storage body, which is the catalyst layer, is a honeycomb structure having through holes having an equivalent diameter of 2 mm or more and an opening ratio of 50% or more.
Exhaust gas treatment method described. 5. The exhaust gas treatment method according to claim 3, wherein in the heat storage heat exchanger, the exhaust gas passing through the heat storage body and the air of the cooling medium flow in countercurrent. 6. The exhaust gas according to claim 1, wherein the heat storage heat exchanger reduces the exhaust gas temperature from 300 ° C. to 450 ° C. to 150 ° C. to 250 ° C. Processing method.