JP2020151657A - Exhaust gas treatment device and exhaust gas treatment method - Google Patents

Abstract

To reduce the size of a dust collection ash circulation facility and suppress an increase in pressure loss of a bag filer.SOLUTION: When supplying an alkali agent to exhaust gas on the upstream side of an inlet of a bag filter 10 that collects soot dust in the exhaust gas, distributing collected ash dust collected in the bag filter 10 into a circulated ash dust and a waste, and supplying the circulated ash dust to the exhaust gas on the upstream side of the inlet of the bag filter 10, exhaust gas treatment for removing acidic gas in exhaust gas controls distribution of the circulated ash dust and the waste according to chlorine concentration or sulfur concentration of the collected ash dust collected in the bag filter 10.SELECTED DRAWING: Figure 1

Description

The present invention relates to an exhaust gas treatment apparatus and an exhaust gas treatment method, and in particular, an exhaust gas treatment apparatus and an exhaust gas that removes an acidic gas component in an exhaust gas discharged from a waste heat treatment furnace such as a waste incinerator or a melting furnace. Regarding the processing method.

A bug filter that is a dust collector that collects and removes soot dust in order to remove acid gas from exhaust gas containing soot and acid gas (hydrogen chloride gas HCl, sulfite gas SO _2, etc.) discharged from waste incinerators. An alkaline chemical such as slaked lime (also called an alkaline agent) is supplied to the exhaust gas flowing in the exhaust gas duct in front of the gas, and the alkaline agent is adhered and held on the filter cloth of the bag filter, and in the exhaust gas duct and on the filter cloth. The acidic gas and the alkaline agent are brought into contact with each other to generate a reaction product of the acidic gas and the alkaline agent by a neutralization reaction, and this reaction product is collected with a filter cloth together with soot and dust with a bag filter to obtain the acidic gas from the exhaust gas. Is being removed.

Collected soot (called dust collecting ash), reaction products of alkaline agent and acid gas, and unreacted alkaline agent (collectively referred to as dust collecting ash, etc.) adhere to the surface of the filter cloth of the bag filter. are doing.

These dust-collecting ash and the like adhering to the surface of the filter cloth are peeled off from the surface by the pulse jet airflow jetted from the inner surface to the outer surface of the tubular filter cloth material by the pulse jet injection device for backwashing, and fall. Once deposited at the bottom of the bag filter, it is discharged to the outside as appropriate. The injection by the pulse jet injection device is performed, for example, at predetermined time intervals.

The amount of alkaline agent supplied is greater than or equal to the chemically required amount assumed from the neutralization reaction with acid gas (for example, equivalent ratio of about 1.5) (equivalent ratio: weight of alkaline agent actually supplied (or). The number of moles) / the weight (or number of moles) of the alkaline agent required for the reaction with HCl and SO ₂ ) is supplied to sufficiently remove the acid gas component, and the component in the exhaust gas when discharged to the outside. The regulation value is satisfied.

When the alkaline agent is supplied at such a high equivalent ratio, an unreacted alkaline agent that does not contribute to the reaction with the acid gas is generated, and when the dust collecting ash is discharged, it is discharged from the bag filter without reacting. Will be done.

Therefore, the dust-collected ash collected and collected by the bag filter is circulated and supplied into the exhaust gas on the inlet side of the bag filter (referred to as dust-collected ash circulation), so that the unreacted dust-collected ash contained in the dust-collected ash and the like is unreacted. Patent Document 1 discloses that the alkaline agent is effectively used, the amount of the newly supplied alkaline agent is reduced, and the operating cost is reduced.

Further, as a control method in this dust collection ash circulation, in Patent Document 2, the circulation rate, which is the ratio of the circulation dust collection ash amount to the dust collection ash amount collected by the bug filter, is controlled to be increased or decreased in a stepwise manner. The amount of newly blown neutralizing agent (alkaline agent) is changed according to the HCl concentration at the outlet of the bag filter.

Further, in Patent Document 3, the amount of the newly blown desalting agent (alkaline agent) is kept constant in principle, and the circulation rate of the dust collecting ash is increased (several times to ten times) according to the HCl concentration at the inlet or outlet of the bag filter. I'm changing.

Japanese Unexamined Patent Publication No. 2014-24502 Japanese Patent No. 5955622 Japanese Patent No. 6199329

Depending on the acid gas concentration in the exhaust gas at the inlet and outlet of the bag filter, the ratio of the amount of newly blown alkaline agent to the amount of circulating dust collected ash, etc., the unreacted alkaline agent in the dust collected ash collected by the bag filter The amount changes.

However, conventionally, since the dust collecting ash is circulated without paying attention to the amount of the unreacted alkaline agent in the dust collecting ash used for the dust collecting ash circulation, when the unreacted alkaline agent is small, a large amount of the dust collecting ash is circulated. Need to be done. In addition, the equipment for circulating dust ash becomes large.

Further, since the amount of circulating dust collected ash flowing into the bag filter is large, the amount of dust collected ash adhering to the filter cloth is also large, and the pressure loss of the bag filter is also large.

The present invention has been made to solve the above-mentioned conventional problems, and aims to reduce the circulation amount of circulating dust collecting ash, downsize the dust collecting ash circulation equipment, and suppress an increase in pressure loss of a bag filter. Is the subject.

Alkali agents for neutralizing acid gas, such as slaked lime, react with acid gas by the reaction of the following formula to remove acid gas from exhaust gas. Therefore, calcium chloride CaCl ₂ , which is a reaction product, and calcium sulfite are used in the dust collection ash. Calcium CaSO ₃ and calcium sulfate CaSO ₄ are included. Therefore, unreacted slaked lime tends to be small in the dust-collected ash containing a large amount of reaction products and having a high chlorine concentration and sulfur concentration.
Ca (OH) ₂ + 2HCl → CaCl ₂ + 2H ₂ O… (1)
Ca (OH) ₂ + SO ₂ → CaSO ₃ + H ₂ O… (2)
CaSO ₃ + 0.5O ₂ → CaSO ₄ … (3)

Therefore, by collecting and circulating low chlorine concentration dust collecting ash containing a large amount of unreacted slaked lime, the amount of circulating dust collecting ash is set to an appropriate amount and reduced compared to the past, and the dust collecting ash circulation equipment is downsized and bugs. It is possible to suppress an increase in the pressure loss of the filter.

The present invention has been made by paying attention to such a point. In an exhaust gas treatment device for removing acidic gas in exhaust gas, a bug filter that collects soot and dust in exhaust gas and an upstream side from the inlet of the bug filter. The alkaline agent supply means for supplying the alkaline agent to the exhaust gas and at least a part of the dust collecting ash collected by the bag filter are supplied to the exhaust gas upstream from the inlet of the bag filter as circulating dust collecting ash. Measure the chlorine concentration of the ash circulation supply means, the dust collection ash distribution means for distributing the dust collection ash collected by the bag filter into the circulation dust collection ash and the waste, and the dust collection ash collected by the bag filter. Distributing the circulating dust collecting ash and the waste by the chlorine concentration measuring means or the sulfur concentration measuring means for measuring the sulfur concentration and the dust collecting ash distributing means according to the measured chlorine concentration or sulfur concentration of the dust collecting ash. The problem is solved by an exhaust gas treatment device including a dust collecting ash distribution control means for controlling.

The present invention also provides an exhaust gas treatment method for removing acidic gas in an exhaust gas, in which an alkaline agent is supplied to the exhaust gas on the upstream side of the inlet of the bag filter that collects soot and dust in the exhaust gas, and is collected by the bag filter. When the collected dust collected ash is distributed to the circulating dust collected ash and the waste, and the circulating dust collected ash is supplied to the exhaust gas on the upstream side from the inlet of the bag filter, the chlorine concentration of the collected dust collected ash by the bag filter is used. Alternatively, the problem is similarly solved by controlling the distribution of the circulating dust collector ash and the waste gas according to the sulfur concentration.

Here, at least one of the supply amount of the alkaline agent and the supply amount of the circulating dust collecting ash is controlled based on at least one of the acid gas concentrations in the exhaust gas on the inlet side and the outlet side of the bug filter. Can be done.

In addition, when a dust collection ash storage tank for supplying circulating dust collection ash is provided, the chlorine concentration of the dust collection ash is set when the dust collection ash is distributed between the circulation dust collection ash and the waste. When it is below the value, or when the sulfur concentration of the dust collection ash is below the set sulfur concentration standard value, all the dust collection ash is distributed as the circulation dust collection ash, and the circulation collection in the dust collection ash storage tank. The chlorine concentration reference value or sulfur concentration reference value of the dust collection ash can be adjusted according to the amount of dust ash.

According to the present invention, the circulating dust collection ash and waste of the dust collection ash collected according to the amount of the unreacted alkaline agent contained in the dust collection ash by measuring the chlorine concentration or the sulfur concentration of the dust collection ash. Since the distribution with and is controlled, the circulation amount of the circulating dust collecting ash can be reduced, the dust collecting ash circulation equipment can be miniaturized, and the increase in the pressure loss of the bag filter can be suppressed.

Block diagram showing the configuration of the embodiment of the present invention Similarly, a flow chart showing the processing procedure of dust collection ash distribution control.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the contents described in the following embodiments and examples. Further, the constituent requirements in the embodiments and examples described below include those that can be easily assumed by those skilled in the art, those that are substantially the same, that is, those in a so-called equal range. Further, the components disclosed in the embodiments and examples described below may be appropriately combined or appropriately selected and used.

In the following description of the embodiment, soot dust (dust collecting ash) collected and discharged by a bag filter described later, an unreacted alkaline agent, and a reaction product of an acid gas and an alkaline agent are collectively referred to as dust collecting ash. ..

As shown in FIG. 1, the present embodiment is an exhaust gas treatment device for removing acidic gas in exhaust gas, for collecting soot dust in exhaust gas sent from a waste incinerator or the like (not shown) by an exhaust gas duct 8. The bag filter 10, the decalcification supply device 20 which is an alkali agent supply means for supplying an alkaline agent, for example, slaked lime to the exhaust gas on the upstream side from the inlet of the bag filter 10, and the dust collecting ash hopper below the bag filter 10. (Not shown) The dust collection ash distribution device 32 that distributes the dust collection ash discharged from the lower part for disposal or circulation, and the dust collection ash distributed by the dust collection ash distribution device 32 are sent to the waste ash treatment system. For example, the waste dust collection ash transport device 34 composed of a screw conveyor and the dust collection ash distributed by the dust collection ash distribution device 32 are collected and circulated and supplied in the right direction of the figure for disposal. For this purpose, for example, a circulating dust collecting ash transporting device 36 composed of a screw conveyor and a circulating dust collecting ash transporting device 36 for transporting to the left in the figure and a dust collecting ash circulated and supplied by the circulating dust collecting ash transporting device 36 are temporarily stored. For example, a dust collecting ash storage tank 38 composed of a silo and a circulating dust collecting tank 8 for supplying the dust collecting ash stored in the dust collecting ash storage tank 38 to the exhaust gas duct 8 on the upstream side from the inlet of the bag filter 10. An ash supply device 40, a chlorine concentration meter 50 for measuring the chlorine concentration of the dust collected ash discharged from the bag filter 10, a level meter 52 for measuring the layer height level of the dust collected ash in the dust collecting ash storage tank 38, and a level meter 52. In the dust collection ash distribution control device 54 that controls the dust collection ash distribution device 32 according to the chlorine concentration measurement value of the chlorine concentration meter 50 and the level measurement value of the level meter 52, and in the exhaust gas on the outlet side of the bug filter 10. The acid gas concentration meter 60 for measuring the concentration of the acidic gas (for example, HCl or SO ₂ ), the acid gas concentration meter 62 for measuring the acid gas concentration in the exhaust gas on the inlet side of the bag filter 10, and the acid gas concentration meter. At least one of the acid gas concentration measurement values of 60 and 62 controls at least one of the amount of slaked lime supplied by the smelting lime supply device 20 and the amount of circulating dust collecting ash supplied by the circulating dust collecting ash supply device 40. It is equipped with a slaked lime / circulating dust collection ash supply amount control device 64.

As the slaked lime supply device 20, for example, a cutting device capable of controlling the cutting amount such as a hopper and a table feeder for accommodating slaked lime can be used.

The dust collecting ash distribution device 32 uses, for example, a screw conveyor to switch the direction of sending the dust collecting ash toward the two transport devices on the left and right in the figure, and circulates the dust collected ash by the circulating dust collecting ash transport device 36. The amount to be supplied (left side in the figure) and the amount to be sent to the waste ash treatment system by the waste dust collecting ash transport device 34 and discarded (right side in the figure) are distributed. Alternatively, the waste dust collection ash transfer device 34 and the circulation dust collection ash transfer device 36 can be integrated by using, for example, a long conveyor, and the transfer direction of the conveyor can be switched to switch the supply destination of the dust collection ash. is there.

In the dust collecting ash storage tank 38 provided on the outlet side of the circulating dust collecting ash transport device 36, a level meter for measuring the layer height of the dust collecting ash stored as the amount of circulating dust collecting ash in the dust collecting ash storage tank 38. 52 is provided. The level meter 52 measures, for example, the layer height level by the presence or absence of rotation of a large number of propellers provided in the horizontal direction at each predetermined height, measures the weight of the dust collecting ash storage tank 38 with a load cell, microwaves, and the like. It is possible to use a device that projects infrared rays from above and measures the layer height level by the reflection. By controlling the circulation amount by the output of the level meter 52, the level of the dust collection ash in the dust collection ash storage tank 38 is maintained within a certain range, regardless of the operating state of the circulation dust collection ash transfer device 36. The dust collecting ash can be supplied to the circulating dust collecting ash supply device 40.

As the circulating dust collecting ash supply device 40, a cutting device such as a table feeder that can control the cutting amount can be used. The position of the circulating dust collecting ash supply device 40 in the exhaust gas duct 8 may be the downstream side or the upstream side of the slaked lime supply device 20 illustrated in the figure.

The circulating dust collecting ash transport device 36, the dust collecting ash storage tank 38, and the circulating dust collecting ash supply device 40 constitute the dust collecting ash circulation supply means.

As the chlorine concentration meter 50, for example, a fluorescent X-ray spectroscopic analyzer or the like that can measure the chlorine concentration in the dust collecting ash semi-continuously is used. In addition, a substance that directly or indirectly measures the concentration of calcium chloride CaCl ₂ which is a reaction product can also be used for control. As for the unreacted slaked lime Ca (OH) ₂ concentration may also be used to indirectly controlling the pH meter to measure, for example, unreacted slaked lime Ca (OH) ₂ concentration.

The exhaust gas treatment device of the embodiment is discharged from a waste incinerator (not shown) or the like, and removes acid gas from combustion exhaust gas containing soot and acid gas (HCl, SO ₂ ).

Specifically, an acid agent (slaked lime in the embodiment) made of, for example, slaked lime or baking soda is supplied to the exhaust gas flowing in the exhaust gas duct 8 in front of the bag filter 10 that collects soot and dust, and the alkaline agent is used in the bag filter 10. It is adhered and held on a tubular filter cloth (not shown), and the acid gas and the alkaline agent are brought into contact with each other in the exhaust gas duct 8 and the filter cloth, and a reaction product of the acid gas is generated by a neutralization reaction, which is filtered. Collect with a cloth to remove acid gas.

Then, most of the reaction products with soot, slaked lime, and acid gas contained in the exhaust gas flowing into the bag filter 10 (collectively referred to as dust collecting ash) adhere to the filter cloth.

Further, the filter cloth is periodically backwashed and collected by, for example, a pulse jet air stream periodically ejected from the inside of the filter cloth by a pulse jet injection device (not shown) arranged above the bag filter 10. The dust ash is peeled off from the surface of the filter cloth, falls, accumulates on the dust collecting ash hopper under the bag filter 10, and is appropriately discharged by a dust collecting ash cutting device (not shown).

In the present embodiment, the circulating dust collecting ash supply device 40 blows the dust collected ash collected by the bag filter 10 into the exhaust gas on the upstream side from the inlet of the bag filter 10 to perform unreacted dust collecting ash circulation. Effective use of slaked lime can reduce the amount of newly supplied slaked lime.

Hereinafter, a specific processing procedure for dust collection ash distribution control in the present embodiment will be described with reference to FIG.

First, before starting the treatment, it is determined whether the dust collecting ash discharged from the bag filter 10 is distributed as circulating dust collecting ash to the dust collecting ash storage tank 38 or distributed as waste. Set the standard value of the chlorine concentration of the dust collecting ash as the standard. If the measured value of the chlorine concentration of the dust collection ash is less than the standard value, the calcium chloride concentration, which is a reaction product in the dust collection ash, is low and a large amount of unreacted slaked ash is contained, so the dust collection ash is used as the circulating dust collection ash. When the measured value of the chlorine concentration of the dust-collected ash is higher than the reference value, the calcium chloride concentration of the dust-collected ash is high and the amount of unreacted slaked ash is small, so that the dust-collected ash is distributed as waste.

In step 100, the acidic gas is removed by supplying only the slaked lime into the exhaust gas duct 8, and the acidic gas concentration in the exhaust gas on the outlet side measured by the acidic gas concentration meter 60 on the outlet side of the bag filter 10. In step 110, the entire amount of dust collected ash is sent to the dust collecting ash storage tank 38 side so as to be used as circulating dust collecting ash, and the dust collecting ash is sufficiently sent to the dust collecting ash storage tank 38 (for example, dust collecting ash). (Up to 50% high level of ash layer).

When the layer height level of the dust-collecting ash in the dust-collecting ash storage tank 38 measured by the level meter 52 in step 120 is, for example, 50% or more, and it is determined in step 130 that the dust-collected ash is sufficiently accumulated, step 140 Proceed to, the circulating dust collecting ash supply device 40 supplies the circulating dust collecting ash of the dust collecting ash storage tank 38 to the exhaust gas duct 8, that is, the circulating dust collecting ash is supplied, and the dust collecting ash cut out from the bag filter 10 is supplied. Distributing, that is, distributing dust-collected ash, is started. At this time, at least one of the slaked lime supply amount or the circulating dust collection ash supply amount is based on the acid gas concentration measurement value in at least one exhaust gas of the bag filter 10 inlet or outlet by the slaked lime / circulating dust collecting ash supply amount control device 64. Is adjusted so that the acid gas concentration in the exhaust gas at the outlet side of the bag filter measured by the acid gas concentration meter 60 is controlled to be equal to or less than the regulation value.

In step 150, the chlorine concentration in the dust collected ash is measured by the chlorine concentration meter 50, and in step 160, it is determined whether or not the chlorine concentration in the dust collected ash is equal to or less than the reference value (for example, 25% by weight). When it is below the standard value, it is judged that the calcium chloride CaCl ₂ content of the reaction product in the dust collection ash is low and the content of unreacted slaked lime is high, and the step is to use the dust collection ash as the circulating dust collection ash. At 170, it is sent to the dust collecting ash storage tank 38 side and supplied as circulating dust collecting ash.

On the other hand, when the chlorine concentration in the dust-collected ash is higher than the reference value in step 160, it is determined that the calcium chloride CaCl ₂ content is high and the unreacted slaked lime content is low, and the process proceeds to step 180 to collect the dust-collected ash. Discard. When proceeding to step 180, a timer control may be added so as to proceed to step 180 after a certain period of time in consideration of the time required for transportation from the chlorine concentration meter 50 to the dust collector ash distribution device 32. In this way, the dust collected ash is distributed to the circulating dust collected ash and the waste based on the chlorine concentration of the dust collected ash.

After completion of step 170 or 180, the process returns to step 150 and the control is repeated so as to distribute the dust-collected ash based on the chlorine concentration in the dust-collected ash.

The chlorine concentration reference value used as a reference when determining whether to circulate and dispose of the dust-collected ash in step 160 is, for example, a high-level measured value of the dust-collected ash layer of the level meter 52 of the dust-collecting ash storage tank 38. Can be changed as shown in Table 1 below.

That is, when the high level of the dust collecting ash layer of the dust collecting ash storage tank 38 is 20% or less, all the dust collecting ash is sent to the dust collecting ash storage tank 38 to increase the storage amount of the circulating dust collecting ash.

When the high level of the dust collecting ash layer is between 20 and 40%, the standard value is set to, for example, 27% by weight, which is higher than the standard standard value of 25% by weight, and the dust collecting ash is circulated. Increase the proportion of dust ash. As a result, the amount of circulating dust collected ash stored in the dust collecting ash storage tank 38 can be increased, and an appropriate amount can be stored.

When the high level of the dust collecting ash layer is between 40 and 60%, the standard value of 25% by weight is used as the reference value.

On the other hand, when the high level of the dust collecting ash layer is between 60 and 80%, the standard value is set to, for example, 23% by weight, which is lower than the standard standard value of 25% by weight, and the dust collecting ash is circulated. Reduce the proportion of dust collected ash. As a result, the amount of circulating dust collected ash stored in the dust collecting ash storage tank 38 does not become excessive, and an appropriate amount can be stored.

When the high level of the dust collecting ash layer is 80% or more, it is not necessary to further store the circulating dust collecting ash, and all of them are discarded.

As a result, the amount of dust collected ash stored in the dust collecting ash storage tank 38 can be controlled to prevent it from becoming excessive or too small, and an appropriate amount can be stored.

The dust collecting ash storage tank does not have to be provided.

Further, in the above-described embodiment, slaked lime was used as the alkaline agent as the neutralizing agent, but the type of the neutralizing agent is not limited to this, and may be, for example, baking soda or dolomite.

Furthermore, when controlling by measuring the sulfur concentration with a sulfur concentration meter instead of measuring the chlorine concentration with a chlorine concentration meter, the sulfur concentration meter is equipped with a fluorescent X-ray spectroscopic analyzer or the like to semi-continuously measure the sulfur concentration in the dust collecting ash. Use the one that can be measured. The distribution is judged based on the sulfur concentration standard value instead of the chlorine concentration standard value.

8 ... Exhaust gas duct 10 ... Bug filter 20 ... Elimination lime supply device 32 ... Dust collection ash distribution device 34 ... Waste dust collection ash transfer device 36 ... Circulating dust collection ash transfer device 38 ... Dust collection ash storage tank 40 ... Circulation dust collection ash supply device 50 ... Chlorine concentration meter 52 ... Level meter 54 ... Dust collection ash distribution control device 60, 62 ... Acid gas concentration meter 64 ... Smelting lime / circulating dust collection ash supply amount control device

Claims (6)

In an exhaust gas treatment device that removes acid gas in exhaust gas
A bug filter that collects soot and dust in the exhaust gas,
An alkaline agent supply means for supplying an alkaline agent to the exhaust gas on the upstream side of the inlet of the bug filter,
A dust collecting ash circulation supply means for supplying at least a part of the dust collecting ash collected by the bug filter to the exhaust gas on the upstream side of the inlet of the bug filter as circulating dust collecting ash.
A dust collecting ash distribution means for distributing the dust collected ash collected by the bug filter into the circulating dust collecting ash and the waste.
A chlorine concentration measuring means for measuring the chlorine concentration of the dust collected ash collected by the bag filter or a sulfur concentration measuring means for measuring the sulfur concentration.
A dust collection ash distribution control means that controls the distribution of the circulating dust collection ash and the waste by the dust collection ash distribution means according to the measured chlorine concentration or sulfur concentration of the dust collection ash.
An exhaust gas treatment device characterized by being equipped with. An alkaline agent / circulation that controls at least one of the supply amount of the alkaline agent and the supply amount of the circulating dust collecting ash based on at least one of the acid gas concentrations in the exhaust gas on the inlet side and the outlet side of the bag filter. The exhaust gas treatment apparatus according to claim 1, further comprising a dust collecting ash supply amount control means. When the dust collecting ash circulation supply means has a dust collecting ash storage tank and the dust collecting ash distribution controlling means controls distribution to the circulating dust collecting ash and waste, the chlorine concentration of the dust collecting ash is set. When it is below the chlorine concentration standard value, or when the sulfur concentration of the dust collection ash is below the set sulfur concentration standard value, all the dust collection ash will be distributed as circulating dust collection ash and inside the dust collection ash storage tank. The exhaust gas treatment apparatus according to claim 1 or 2, wherein the chlorine concentration reference value or the sulfur concentration reference value of the dust collecting ash is adjusted according to the amount of the circulating dust collecting ash. In an exhaust gas treatment method that removes acid gas in exhaust gas,
While supplying an alkaline agent to the exhaust gas on the upstream side from the inlet of the bug filter that collects soot and dust in the exhaust gas,
When the dust-collected ash collected by the bug filter is distributed to the circulating dust-collected ash and the waste, and the circulating dust-collected ash is supplied to the exhaust gas on the upstream side from the inlet of the bug filter.
An exhaust gas treatment method characterized by controlling the distribution of circulating dust collected ash and waste according to the chlorine concentration or sulfur concentration of the dust collected ash collected by the bag filter. It is characterized in that at least one of the supply amount of the alkaline agent and the supply amount of the circulating dust collecting ash is controlled based on at least one of the acid gas concentrations in the exhaust gas on the inlet side and the outlet side of the bug filter. The exhaust gas treatment method according to claim 4. If you have a dust collecting ash storage tank for supplying circulating dust collecting ash, the chlorine concentration of the dust collecting ash is less than or equal to the set chlorine concentration standard value when distributing the dust collecting ash to the circulating dust collecting ash and the waste. When, or when the sulfur concentration of the dust collecting ash is less than the set sulfur concentration standard value, all the dust collecting ash is distributed as the circulating dust collecting ash, and the circulating dust collecting ash in the dust collecting ash storage tank is used. The exhaust gas treatment method according to claim 4 or 5, wherein the chlorine concentration reference value or the sulfur concentration reference value of the dust-collected ash is adjusted according to the amount.

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