JPH10216464A - Spraying method of powdery reaction agent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method enabling to appropriately spray a powdery reaction agent for an exhaust gas treatment. SOLUTION: This device is constituted to spray a powdery alkali absorber as the powdery reaction agent and a powdery adsorbent into exhaust gas in order to remove harmful substance in the exhaust gas discharged in company with combustion and heat. In this case, a mixture of active carbon and an auxiliary is used as the powdery adsorbent. The powdery alkali absorber, e.g. slaked lime is fed from a slacked lime feed device 6, and the powdery adsorbent is mixed the active carbon with the auxiliary by a mixture feed device 7 to be fed to a flue 5 respectively from the mixture feed device 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a municipal solid waste incineration plant,
Detoxification of flue gas containing harmful substances discharged from combustible waste treatment facilities and other combustion equipment in general in combustion processes and toxic substances discharged in heating processes in metal smelting factories etc. It relates to a processing method. More specifically, the present invention relates to a method of spraying a powder reactant when removing harmful substances using a powder reactant such as an alkali absorbent or an adsorbent.

[0002]

2. Description of the Related Art Several methods have been disclosed as methods for treating combustion exhaust gas containing harmful substances such as dust, acid gas, mercury, and dioxins discharged from incinerators and the like.

[0003] For example, the method disclosed in Japanese Patent Application Laid-Open No. Hei 5-31323 discloses a method in which an adsorbent such as activated carbon and a basic absorbent such as slaked lime are supplied by separate supply means without mixing powdered activated carbon with slaked lime. It is to be blown into the flue at the entrance. The activated carbon adsorbs heavy metals such as mercury in exhaust gas and also adsorbs harmful organic chlorine compounds such as dioxin. The activated carbon to which these harmful substances are adsorbed is collected by a dust collector such as a bag filter provided downstream, and is removed from the exhaust gas. Also, in general,
The combustion exhaust gas contains an acidic component such as hydrogen chloride, and the acidic component is removed by the basic absorbent sprayed into the exhaust gas.

Japanese Patent Application Laid-Open No. 7-204432 discloses that slaked lime and activated carbon are mixed and stored in the same silo, and a mixture of slaked lime and activated carbon is blown into a flue by one supply means.

[0005]

However, in the former method (Japanese Unexamined Patent Publication No. Hei 5-31323), slaked lime and activated carbon are supplied to the flue by separate supply means. Does not mix slaked lime and powdered activated carbon sufficiently. Therefore, activated carbon does not disperse sufficiently uniformly on the filter cloth surface during the filtration and dust collection process of a bag filter, etc.
The effect of activated carbon to adsorb and remove mercury and dioxins tends to decrease.

[0006] In general, carbon-based powders such as activated carbon are flammable, and when there is a large amount of flammable volatile components, there is a risk of ignition or dust explosion due to the influence of static electricity or the like. In the case of high-quality activated carbon with sufficient activation and devolatilization,
Although the possibility of dust explosion is extremely small, the possibility of ignition or dust explosion is not completely negligible depending on the presence of ignition sources and operating conditions.

In consideration of this point, since activated carbon is not preliminarily mixed with slaked lime or the like and is sprayed with activated carbon alone,
This is not enough in that the risk of ignition and dust explosion in the activated carbon silo and in the spraying process has not been sufficiently reduced.

In the latter method (Japanese Patent Laid-Open No. 7-204432), slaked lime and powdered activated carbon are mixed in advance in a silo or before a silo is charged, so that the two can be effectively mixed. Since the spraying is performed by the means, the blowing amount of the powdered activated carbon and the slaked lime cannot be adjusted alone. That is, when the slaked lime supply amount for removing the acid gas is increased, the activated carbon blowing amount is increased at the same time, and when the activated carbon is consumed more than necessary or the activated carbon blowing amount is increased, the slaked lime supply amount is increased. However, there is a problem that slaked lime is consumed wastefully.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve these problems and has the following features.

First, the present invention provides a method for spraying a powder alkaline absorbent and a powder adsorbent as a powder reactant into an exhaust gas in order to remove harmful substances in the exhaust gas discharged due to combustion or heating. It is characterized in that a mixture of activated carbon and auxiliaries is used as a powder adsorbent.

In the method of the present invention, preferably,
As the powdered alkaline absorbent, at least one of slaked lime, calcium carbonate, quicklime, and dolomite is used.

Further, as an auxiliary agent, at least one of an alkaline agent such as slaked lime, a stripping agent such as diatomaceous earth and dolomite powder, and a powdery catalyst is used.

As the powder reactants, two powder adsorbents composed of a mixture of powdered alkaline absorbent and activated carbon and an auxiliary are used, so that the possibility of ignition or dust explosion by activated carbon alone can be avoided by mixing with the auxiliary. The advantage that can be achieved, the advantage that the spray amount can be adjusted according to the required amount of slaked lime and activated carbon, and the fact that activated carbon and auxiliary agent are sufficiently mixed in advance, the uniform dispersion of activated carbon on the bag filter filter cloth surface in the dust collector The contact efficiency is improved, and the advantage that mercury and dioxins can be efficiently adsorbed and removed in the process of filtration and dust collection is simultaneously obtained. In other words, there is no danger of dust explosion and high mercury and dioxin removal effects can be achieved.
It is possible to suppress wasteful consumption of slaked lime and activated carbon.

By using the auxiliary agent to form a mixture with activated carbon, the activated carbon is diluted, and the risk of ignition and dust explosion due to the activated carbon can be reduced. When a powdered alkaline absorbent such as slaked lime is used as an auxiliary agent, the exhaust gas can be more effectively purified because the alkaline agent neutralizes acidic components in the exhaust gas. When a release agent such as diatomaceous earth is used as the auxiliary agent, an increase in pressure loss of dust deposited on the surface of the bag filter filter cloth at the subsequent stage can be prevented. When a powdery catalyst is used as an auxiliary agent, the effect of removing dioxins and the like in exhaust gas is further increased in addition to the effect of activated carbon. By using a plurality of these auxiliaries, the effects described herein can be obtained synergistically.

The mixture of the activated carbon and the auxiliaries is preferably preliminarily mixed so that the weight ratio of the activated carbon is 20 to 80%.

Since the weight ratio of activated carbon in the mixture of activated carbon and slaked lime is set to 20 to 80%, the risk of ignition or dust explosion due to activated carbon alone can be avoided, and the required amount of spraying of activated carbon and slaked lime can be stabilized. It is possible to do it.

If the weight ratio of the activated carbon in the mixture is set to 20% or less, in order to achieve a predetermined spray amount of the activated carbon, the spray amount of the whole mixture is increased, and an auxiliary such as excess slaked lime is sprayed. However, it is not preferable because the auxiliary agent is excessively consumed. When it is 80% or more, the effect of avoiding the danger of ignition and dust explosion due to the activated carbon being diluted by mixing with slaked lime is diminished, and the ignition and dust explosion caused by volatiles and static electricity contained in the activated carbon are reduced. It is not preferable because the risk increases.

As the activated carbon, coconut shell, peat,
There are charcoal type, etc., but all can be used.

[0019]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows an embodiment in which the method for spraying slaked lime and an adsorbent according to the present invention is applied to a refuse incineration plant.

In FIG. 1, reference numeral 1 denotes a boiler, 2 denotes a cooling tower, 3 denotes a filtration type dust collector such as a bag filter, and
Are chimneys, which are sequentially connected by a chimney 5.

The present invention has a slaked lime supply device 6 for supplying slaked lime as a powder alkaline absorbent, and a mixture supply device 7 for feeding a mixture of activated carbon and an auxiliary as a powder adsorbent. The slaked lime supply device 6 and the mixture supply device 7 are provided with a transport tube 8 as a separate transport path,
9 connects to the flue 5 between the cooling tower 2 and the dust collector 3.

In the apparatus according to the present invention, the combustion exhaust gas discharged from the incinerator (not shown) is introduced into the boiler 1 and is cooled to 250 to 400 ° C. by heat recovery. Subsequently, the exhaust gas is reduced by the cooling tower 2 to 120 to
The temperature is lowered to 250 ° C. and introduced into the bag filter 3.
On the other hand, slaked lime and a mixture of activated carbon and an auxiliary supplied from the slaked lime supply device 6 and the mixture supply device 7, respectively, are sprayed into the flue 5 at the entrance of the bag filter 3 through the conveying tubes 8, 9, and 3 is introduced.

Exhaust gas containing harmful substances, slaked lime, and a mixture of activated carbon and auxiliaries introduced into the bag filter 3 are collected during the filtration and collection of the flue 5 at the entrance of the bag filter 3 and the filter cloth surface of the bag filter 3. The mercury and dioxins contained in the exhaust gas are removed by sufficient contact and the adsorption action of the activated carbon. At the same time, dust contained in the exhaust gas is removed in the filtration and dust collection process, and HCl and SOx are removed by slaked lime.
Since such acidic gases are removed, the exhaust gas is sufficiently cleaned by the bag filter 3. The clean exhaust gas after leaving the bag filter 3 is discharged from the chimney 4 to the atmosphere.

Each part of the apparatus of this embodiment as described above will be described in more detail.

The temperature at which the exhaust gas is treated by the bag filter 3 is preferably as low as 200 ° C. or less in order to increase the efficiency of removing acidic gas and the effect of adsorbing mercury and dioxins. However, if the temperature is set to 150 ° C. or lower, the acid dew point of the acid gas approaches, so that the corrosion of the device occurs, which is not preferable. Therefore, it is preferable to lower the temperature within a range in which the corrosion of the device does not occur.

As long as the exhaust gas temperature suitable for the bag filter 3 can be achieved in the cooling tower 2, other heat recovery means may be used or may be omitted.

The spraying position of the mixture of slaked lime or activated carbon and the auxiliary agent, that is, the connecting position of the conveying tubes 8 and 9 is determined by the position where the powder sprayed on the filter cloth is deposited when filtering and collecting with a bag filter. Alternatively, it may be the flue 5 at the entrance of the bag filter 3, the bag filter 3 directly without passing through the flue 5, or the flue 5 at the entrance of the cooling tower 2. However, when connecting to the flue 5 at the inlet of the cooling tower 2, it is relatively preferable because the powder mixture of slaked lime and the adsorbent may partially drop and lose due to inertia in the cooling tower 2. In order to reduce the loss of the mixture before reaching the bag filter 3, it is preferable to connect the mixture directly to the flue 5 immediately before the bag filter 3 or to the upper part of the bag filter 3.

The slaked lime supply device 6 and the activated carbon / auxiliary mixture supply device 7 generate a silo for storing the powder, a table feeder for quantitatively cutting the powder, etc., and air for conveying air. It is equipped with a blower or an air compressor, a transport tube for transporting the powder by air, and the like, but any type can be used as long as the powder such as slaked lime meets the requirement of being easily sprayed into the exhaust gas.

The setting of the spray amount by the slaked lime supply device 6 is as follows.
The method may be set according to the acid gas concentration before the treatment, or a method of detecting the acid gas concentration of the exhaust gas after the treatment and appropriately setting the concentration to be equal to or lower than a predetermined concentration. The control method does not matter.

The setting of the spray amount by the mixture supply device 7 of the activated carbon and the auxiliary agent is set in accordance with the concentration before the treatment estimated from the waste, etc., or the mercury concentration, dioxin concentration or the like in the exhaust gas after the treatment. By detecting the concentration of the indicator substance instead of these, a method of appropriately setting the concentration to be equal to or lower than a predetermined concentration may be mentioned, but the setting method and the exhaust gas concentration control method are not particularly limited. The spraying amount of activated carbon depends on the concentration of harmful substances and the degree of detoxification, and thus cannot be particularly limited.
It is desirable to spray at a rate of 1.0 g / Nm ³ . At this time, the weight concentration of the activated carbon in the dust collected by the bag filter 3 including dust and slaked lime is about 0.2 to 20.
%.

Since the slaked lime supplied by the slaked lime supply device 6 neutralizes and removes the acidic components in the exhaust gas, other powdered alkaline agents such as calcium carbonate may be used.

The activated carbon to be supplied by the activated carbon / auxiliary mixture supply device 7 is not limited to activated carbon, and a carbon-based porous powder having a specific surface area of at least 100 m ² / g may be used instead. Adsorption performance of dioxins can be obtained. However, in consideration of safety such as avoiding dust explosion during storage of silos, the carbon-based powder is manufactured including a process of sufficiently volatilizing volatile components, and preferably has a sufficiently high ignition point.

As an auxiliary agent to be mixed with the activated carbon, an alkali agent such as slaked lime, a stripping agent such as diatomaceous earth, and a powdery catalyst are used. It is preferable that the mixing ratio of the activated carbon is 20 to 80%. When the weight ratio of the activated carbon is set to 20% or less, it is not preferable because an auxiliary agent such as slaked lime is sprayed at the same time when the required spray amount of the activated carbon is achieved, and the auxiliary agent is excessively consumed. When it is 80% or more, the effect of avoiding the danger of ignition and dust explosion due to the activated carbon being diluted by mixing with slaked lime is diminished, and the ignition and dust explosion caused by volatiles and static electricity contained in the activated carbon are reduced. It is not preferable because the risk increases.

When a powdered alkaline absorbent such as slaked lime is used as the mixing aid, the alkaline agent neutralizes acidic components in the exhaust gas, so that the exhaust gas can be more effectively purified. When a release agent such as diatomaceous earth is used as an auxiliary agent, an increase in pressure loss of dust deposited on the surface of the filter cloth of the bag filter 3 at the subsequent stage can be prevented. When a powdery catalyst is used as an auxiliary agent, the effect of removing dioxins and the like in exhaust gas is further increased in addition to the effect of activated carbon. By using a plurality of these auxiliaries, the effects described herein can be obtained synergistically. In practice, it is better to select the auxiliary agent and determine the mixing ratio in consideration of these effects. For example, during normal operation, slaked lime is 60% and activated carbon is 40%. In order to further remove dioxin at a higher level, there is a method of mixing a catalyst.

As a method of mixing the activated carbon and the auxiliary, a mixing ratio is determined in advance, and the powder is stirred and mixed in a lorry tank when the powder is charged by a lorry vehicle or the like, and then the powder is charged into a powder silo. However, any method may be used as long as a plurality of powders can be sufficiently mixed.

More specifically, the harmful substances removed by the present invention are not limited to the four types described above, and heavy metals such as lead and cadmium are simultaneously absorbed and removed in addition to mercury. Further, in addition to dioxins, it is possible to remove aromatic organochlorine compounds such as chlorobenzene and chlorophenol, which are precursors of dioxins, and other organic chlorine compounds related to generation and resynthesis of dioxins.

Here, the term "dioxins" is a general term for polydibenzoparadioxin and polydibenzofuran, and is a guideline for cleaning plants designated by the Ministry of Health and Welfare based on its toxicity conversion value.

[0039]

【Example】

<Example 1> An example showing the effect of the present invention obtained by employing the method of spraying slaked lime and an adsorbent according to the present invention in a refuse incineration plant will be described.

Table 1 shows a comparison between the embodiment in which the present invention is implemented and a comparative example using the conventional method, in which the effects of removing harmful substances are compared.

Example 1 shows the results of the operation performed with the apparatus arrangement shown in FIG. 1. The operating conditions of the exhaust gas treatment facility were as follows: the exhaust gas temperature at the boiler outlet was 250 ° C .; 40,000
Nm ³ / h, slaked lime was used as an auxiliary, and the mixing ratio of activated carbon was 40%.

In Comparative Example 1, as shown in FIG. 2, the supply of slaked lime was the same as that of the Example, but the activated carbon was supplied through the transfer tube 11 by the activated carbon supply device 10 without being mixed with the auxiliary agent. Is shown alone, and the operating conditions of the exhaust gas treatment facility were the same as in Example 1.

The results in Table 1 show that the acid gas typified by dust and HCl could be removed at a high level in both Example 1 and Comparative Example 1 by the bag filter. On the other hand, with respect to mercury and dioxins, it is shown that Example 1 in which the present invention was carried out achieved a higher level of removal than Comparative Example 1. That is, by performing the powder reactant spraying method of the present invention, the activated carbon and slaked lime mixture is well mixed in advance, so that the activated carbon is uniformly dispersed on the surface of the bag filter cloth, and the filtration dust collection process Shows that high levels of adsorption and removal of mercury and dioxins by activated carbon can be achieved.

[0044]

Table 1 Comparison between Example 1 and Comparative Example 1 Note: Concentration of exhaust gas at boiler outlet before treatment Concentration of exhaust gas at bag filter outlet after treatment Dioxin concentration is equivalent to toxic equivalent

Further, the concentration of dioxins at the outlet of the bag filter (concentration after treatment) was examined by changing the spray amount of the powdered activated carbon.

FIG. 3 is a diagram comparing Example 1 and Comparative Example 1 with respect to the dioxin concentration at the outlet of the bag filter by changing the amount of powdered activated carbon sprayed.

The results in FIG. 3 show that the concentration of dioxins at the outlet of the bag filter decreases as the spray amount of the powdered activated carbon increases. Compared with Comparative Example 1 without carrying out the present invention, since the first embodiment to which the present invention can lower the dioxin concentration was shown to have high adsorption removal performance, in particular, and 0.1 g / Nm ³ or less When the spray amount is small, it indicates that Example 1 of the present invention is excellent. The same effect of removing mercury was confirmed.

<Example 2> Next, a trial calculation was made on the consumption of slaked lime and the adsorbent, and a comparison with the conventional method was made.

Table 2 is a table comparing the consumption of the slaked lime and the adsorbent between Example 2 according to the present invention and Comparative Examples 2 and 3 according to the conventional method.

The second embodiment according to the present invention is the same as the first embodiment, and the second comparative example is the same as the first comparative example. Comparative Example 3 is a comparative example in which a mixed powder in which slaked lime and an adsorbent are preliminarily mixed is sprayed by one supply device, and the mixing ratio of activated carbon is 5% by weight.

For comparison, the operating conditions of the exhaust gas treatment facility were the same as those described in Example 1, and the amounts of slaked lime and the adsorbent were constant when the HCl concentration and mercury concentration at the bag filter outlet were constant. Alternatively, each was controlled for 48 hours so as to be a fixed value or less. All adsorbents used powdered activated carbon.

From the results shown in Table 2, Comparative Example 2 shows the results when the activated carbon was sprayed separately without mixing with the auxiliaries. The consumption of slaked lime for removing the acid gas was determined in the Example of the present invention. Same as 2, but due to poor mixing of activated carbon, it was necessary to increase the sprayed amount of activated carbon. Comparative Example 3 is a result of spraying a mixed powder in which activated carbon is previously mixed from one supply device. In order to control the concentration at a predetermined outlet, the blowing amount of activated carbon or slaked lime increases, and activated carbon and The slaked lime was wasted. That is, when the present invention achieves the predetermined removal performance, it is possible to reduce the amount of consumption. In total cost, Example 2 of the present invention is about 17% of Comparative Example 2, and Comparative Example 3 is about 17%. Thus, a cost reduction of about 29% can be obtained.

[0053]

[Table 2] Comparison of consumption of slaked lime and activated carbon Note: The values in the second half of the table are relative values when the example is set to 1. Total cost is the value when the unit price of the adsorbent is 10 times that of slaked lime. The actual concentration is one hour obtained at the bag filter outlet. Average measurement

[0054]

According to the present invention, a powder alkaline absorbent such as slaked lime and a powder adsorbent are used as a powder reactant, and a mixture of activated carbon and an auxiliary is used as the powder adsorbent. The advantage that the possibility of explosion can be avoided by mixing with the auxiliary, the advantage that the spray amount can be adjusted according to the required amount of slaked lime and activated carbon, and the fact that activated carbon and the auxiliary are sufficiently mixed in advance, The uniform dispersion of the activated carbon on the bag filter surface improves the contact efficiency, and at the same time provides the advantage of efficiently adsorbing and removing mercury and dioxins in the process of filtering and collecting dust. That is, there is no danger of dust explosion, a high effect of removing mercury and dioxins can be achieved, and wasteful consumption of slaked lime and activated carbon can be suppressed.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an embodiment in which the present invention is employed in a refuse incineration facility.

FIG. 2 is a diagram showing an example of a conventional method for spraying an adsorbent and slaked lime for comparison with the present invention.

FIG. 3 is a graph showing a relationship between a spray amount of powdered activated carbon and a concentration of dioxins, and comparing an example of the present invention with a comparative example.

[Explanation of symbols]

 Reference Signs List 3 dust collector (bag filter) 5 flue 6 slaked lime supply device 7 mixture supply device 8 transport path (transport tube) 9 transport path (transport tube)

Continued on the front page (72) Inventor Masaru Ayukawa 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd.

Claims (4)

[Claims] 1. A method of spraying a powder alkaline absorbent and a powder adsorbent into a flue gas as a powder reactant in order to remove harmful substances in the flue gas discharged by combustion or heating. A method for spraying a powdered reactant, comprising using a mixture of activated carbon and an auxiliary agent, and separately providing a means for supplying the mixture and a means for supplying a powdered alkaline absorbent. 2. As a powder alkaline absorbent, slaked lime,
The method according to claim 1, wherein at least one of calcium carbonate, quicklime and dolomite is used. 3. The method according to claim 1, wherein at least one of an alkaline agent such as slaked lime, a stripping agent such as diatomaceous earth and dolomite powder, and a powdery catalyst is used as the auxiliary agent. . 4. The powdered reactant according to claim 1, wherein the mixture of the activated carbon and the auxiliary agent is preliminarily mixed so that the weight ratio of the activated carbon is 20 to 80%. Spray method.