JP2013142501A - Exhaust gas treatment device and exhaust gas treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas treatment device and an exhaust gas treatment method that can remove mercury from exhaust gas while preventing mercury from being mixed into recovery ash which is recovered by a dry dust collector.SOLUTION: The exhaust gas treatment device has the dry dust collector 5 on a smoke path 2 of exhaust gas exhausted from a boiler 1 in which fuel is burned, wherein a catalyst for SOoxidation which is arranged on the smoke path 2 of the upstream side of the dry dust collector 5 and oxidizes a part of SOin the exhaust gas flowing through the smoke path 2 into SOand a flow rate adjusting means which adjusts the flow rate of the exhaust gas in contact with the catalyst for SOoxidation are provided.

Description

  The present invention relates to an exhaust gas treatment apparatus and an exhaust gas treatment method.

  For example, Patent Document 1 discloses a technique for treating exhaust gas discharged from a boiler that uses fossil fuel to burn using air. According to this, the exhaust gas discharged from the boiler is introduced into the denitration device to remove nitrogen oxides in the exhaust gas, and then introduced into the dry dust collector to remove the dust in the exhaust gas. The exhaust gas from which the dust is removed is introduced into a wet desulfurization apparatus to remove sulfur oxides in the exhaust gas.

  On the other hand, the exhaust gas generated by burning fossil fuel contains harmful substances such as mercury in addition to nitrogen oxides and sulfur oxides. In this regard, Patent Document 1 utilizes the property that heavy metals such as mercury in the exhaust gas easily adhere to the surface of the ash particles discharged from the boiler when the exhaust gas temperature decreases, and actively attaches mercury to the ash particles. Thus, a technique is disclosed in which mercury is removed together with ash particles with a dry dust collector, and then mercury remaining in the exhaust gas that has passed through the dry dust collector is absorbed by an absorption liquid of a wet desulfurization apparatus.

By the way, in Patent Document 2, when fossil fuel containing a relatively large amount of sulfur is burned in a boiler, the concentration of SO _{3 in} the exhaust gas becomes high, and such exhaust gas has a poor removal rate of heavy metals such as mercury. It has been pointed out. This is because when SO ₃ and mercury coexist in the exhaust gas, SO ₃ adheres first to the ash particles in the exhaust gas, and this attached SO ₃ acts so as to inhibit the adhesion of mercury to the ash particles. It is thought to do.

On the other hand, Patent Document 2 discloses a technique for improving the mercury removal rate by adding an SO ₃ remover to the exhaust gas upstream of the dry dust collector and reducing the SO ₃ concentration in the exhaust gas. Yes.

International Publication WO2004 / 023040 International Publication No. WO2008 / 078722

  However, when removing the ash particles to which mercury is attached as in Patent Documents 1 and 2 with a dry dust collector, the recovered ash collected with the dry dust collector contains mercury. Landfill processing cannot be performed, and processing to remove mercury from the collected ash is required. Further, in the wet desulfurization apparatus, the absorbent (for example, calcium sulfite) is oxidized and gypsum is by-produced. However, since this gypsum also contains mercury, the gypsum cannot be reused as it is.

  An object of the present invention is to suppress mercury from being mixed into the collected ash collected by the dry dust collector.

FIG. 3 shows the relationship between the mercury removal rate in the dry dust collector and the SO ₃ concentration of the exhaust gas introduced into the dry dust collector when mercury is attached to the ash particles and removed by the dry dust collector. As shown in the figure, the mercury removal rate decreases as the SO ₃ concentration of the exhaust gas increases, and when the SO ₃ concentration reaches about 20 ppm or more, the mercury removal rate becomes zero. This indicates that SO ₃ adhering to the ash particles prior to mercury inhibits the adhesion of mercury to the ash particles. Therefore, if the SO ₃ concentration of the exhaust gas flowing upstream of the dry dust collector is maintained at a predetermined value, for example, 20 ppm or more, and the SO ₃ is actively attached to the ash particles, the adhesion of mercury to the ash particles is suppressed. This makes it possible to prevent mercury from being mixed into the collected ash of the dry dust collector.

Specifically, in order to solve the above problems, an exhaust gas treatment apparatus of the present invention is an exhaust gas treatment apparatus provided with a dry dust collector in a flue of exhaust gas discharged from a boiler that burns fuel, on the upstream side of the dry dust collector. An SO ₂ oxidation catalyst that is disposed in the flue and oxidizes part of SO _{2 in} the exhaust gas flowing through the flue to SO ₃ , and a flow rate adjusting means that adjusts the flow rate of the exhaust gas in contact with the SO ₂ oxidation catalyst It is characterized by providing.

Thus, by providing the SO ₂ oxidation catalyst in the flue upstream of the dry dust collector, the SO ₃ concentration of the exhaust gas flowing into the dry dust collector can be increased. Here, since the SO ₂ concentration of the exhaust gas varies depending on the properties of the fuel, etc., the flow rate adjusting means adjusts the flow rate of the exhaust gas in contact with the SO ₂ oxidation catalyst, and maintains the SO ₃ concentration of the exhaust gas at or above the set concentration. As a result, it is possible to continuously prevent mercury from adhering to the ash particles. As a result, since it is possible to prevent mercury from being mixed into the collected ash collected by the dry dust collector, not only the reuse of the collected ash is facilitated, but also the processing when landfilling the collected ash becomes unnecessary.

Here, the SO ₂ oxidation catalyst includes, for example, a noble metal component, and when exhaust gas at 350 ° C. or higher passes through a catalyst layer on which the catalyst is supported, 80% or more of SO _{2 in} the exhaust gas. It has a function to oxidize to SO ₃ .

In this case, the mercury oxidizer is provided in a flue upstream of the dry dust collector and contains a mercury oxidation device that contains a mercury oxidation catalyst that oxidizes mercury in the exhaust gas flowing through the flue to divalent mercury. It is assumed that an SO ₂ oxidation catalyst is provided in the exhaust gas flow path.

In other words, the mercury contained in the exhaust gas discharged from the boiler is in the form of metallic mercury, but by oxidizing this metallic mercury with a mercury oxidation catalyst, the vapor pressure is lower than that of metallic mercury and it is water-soluble. It can be converted to high divalent mercury oxide. Thereby, the removal of mercury contained in the exhaust gas is left to the downstream side of the dry dust collector, and can be easily removed from the exhaust gas, for example, by contacting with a known absorbent. Divalent mercury is more likely to adhere to ash particles in the exhaust gas than metal mercury, but by adjusting the SO ₃ concentration of the exhaust gas flowing upstream of the dry dust collector to an appropriate concentration, Can prevent the adhesion of mercury. Further, the SO ₂ oxidation catalyst can be provided in the exhaust gas flow path in the mercury oxidation apparatus, so that the configuration of the apparatus can be easily and compactly accommodated.

Here, the mercury oxidation catalyst is composed of, for example, titanium, and when exhaust gas of 350 ° C. or more and 400 ° C. or less flows through the catalyst layer on which the catalyst is supported, 90% of the metallic mercury in the exhaust gas. It has a function of suppressing oxidation of SO ₂ to 1% or less while oxidizing at least% to divalent mercury.

The catalyst for SO ₂ oxidation is housed in a frame that is open at both ends to form a catalyst unit, and a gate valve that opens and closes the inlet portion is provided at the inlet portion into which the exhaust gas of the catalyst unit flows to adjust the flow rate. The means has a mechanism for adjusting the opening amount of the inlet portion by sliding the valve body of the gate valve.

Alternatively, the SO ₂ oxidation catalyst is provided in the middle of a bypass pipe that bypasses the mercury oxidation catalyst by branching the exhaust gas flow channel upstream of the mercury oxidation catalyst. A flow path adjustment valve that adjusts the flow rate of the exhaust gas flowing through the pipe line may be formed.

Further, instead of these, the SO ₂ oxidation catalyst is accommodated in a frame that is open at both ends to form a catalyst unit, and this catalyst unit has at least one exhaust gas flow upstream or downstream of the mercury oxidation catalyst. The angle of the axis of the frame body is variably supported with respect to the flow direction of the exhaust gas flowing through the exhaust gas flow path, and the flow rate adjusting means adjusts the angle of the axis of the frame body with respect to the flow direction of the exhaust gas. It is good also as what has a mechanism to do.

By configuring the flow rate adjusting means as a gate valve, a flow rate adjusting valve, or an angle adjusting mechanism in this way, the flow rate of the exhaust gas flowing through the catalyst unit can be adjusted with a simple configuration, and the SO ₃ concentration of the exhaust gas can be adjusted. become.

Here, it is assumed that the operation of the flow rate adjusting means is controlled by the control means, and this control apparatus includes the SO ₂ concentration of the exhaust gas flowing through the flue between the boiler and the mercury oxidation apparatus, the mercury oxidation apparatus, and the dry dust collector. The SO ₃ concentration of the exhaust gas introduced into the dry dust collector is determined based on the difference between the SO ₂ concentration of the exhaust gas flowing through the flue between and the operation of the flow rate adjusting means based on the determined SO ₃ concentration. Shall.

That is, the mercury oxidation catalyst also promotes the reaction of converting SO ₂ in the exhaust gas to SO ₃ , and therefore, by obtaining the SO ₂ concentration of the exhaust gas flowing upstream and downstream of the mercury oxidation apparatus, mercury oxidation The SO ₃ concentration of the exhaust gas after passing through the apparatus can be determined. Then, by controlling the flow rate adjusting means based on the SO ₃ concentration determined in this way, regardless of such changes in the exhaust gas property, it is possible to stabilize the SO ₃ concentration.

  Also, a wet desulfurization device that is disposed in the flue downstream of the dry dust collector to remove sulfur oxides in the exhaust gas, and a soot dust in the exhaust gas that is disposed in the flue between the dry dust collector and the wet desulfurization device. And a wet dust removing device for removing water.

  That is, since mercury in the exhaust gas is oxidized to water-soluble divalent mercury, when this oxidized mercury is introduced into the wet desulfurization apparatus, the mercury together with the sulfur oxide in the exhaust gas is removed from the wet desulfurization apparatus. Mercury is mixed in the product, for example, gypsum, which is absorbed in the absorption liquid and is generated by absorption of sulfur oxides in the absorption liquid, making it difficult to reuse the gypsum. Therefore, as in the present invention, by placing the wet dust remover in the flue between the dry dust collector and the wet desulfurizer, mercury in the exhaust gas is absorbed by the dust removing liquid sprayed in the wet dust remover. Therefore, mercury can be prevented from flowing into the wet desulfurization apparatus, and mercury can be prevented from being mixed into the gypsum recovered by the wet desulfurization apparatus. This facilitates reuse of gypsum. In addition, since the amount of mercury contained in the exhaust gas is extremely small and can be removed with a small amount of liquid, the waste liquid after use can be treated with simple equipment compared to equipment for treating soot dust. .

The present invention may be made by providing a reducing agent addition device for adding a reducing agent to reduce the SO ₃ in the exhaust gas to SO ₂ in exhaust gas flowing through the flue between the dry dust collector and a wet desulfurization system.

That is, SO ₃ in the exhaust gas is less likely to be absorbed by the absorption liquid of the wet desulfurization apparatus than SO _2, and therefore, if the SO ₃ concentration in the exhaust gas becomes high, SO ₃ may not be completely removed by the wet desulfurization apparatus. Therefore, sulfur oxidation is performed by adding a reducing agent that reduces SO ₃ to SO ₂ in the exhaust gas flowing in the flue upstream of the wet desulfurization apparatus, and converting SO ₃ into SO ₂ that can be easily removed by the wet desulfurization apparatus. The removal rate of things can be increased.

Alternatively, a wet dust collector that removes SO ₃ in the exhaust gas flowing through the flue may be provided in the flue downstream of the wet desulfurization apparatus. According to this, SO ₃ in the exhaust gas that has passed through the wet desulfurization apparatus can be removed.

In order to solve the above problems, an exhaust gas treatment method of the present invention is an exhaust gas treatment method for removing dust by introducing exhaust gas discharged from a boiler that burns fuel to a dry dust collector, and the exhaust gas flowing upstream of the dry dust collector Part of the SO ₂ therein is oxidized to SO ₃ , and the SO ₃ concentration in the exhaust gas is adjusted to 20 ppm or more.

That is, as shown in FIG. 3, SO ₃ concentration SO ₃ concentration of mercury removal rate becomes zero exhaust gas introduced into the dry dust collector, that is, by adjusting the above 20 ppm, dry dust collector that does not contain mercury Recovered ash can be obtained. If the SO ₃ concentration in the exhaust gas increases, the acid dew point increases and there is a risk of acid corrosion of the equipment material in the exhaust gas flow path. Therefore, the SO ₃ concentration of the exhaust gas introduced into the dry dust collector is It is good to set it as the range of 20 ppm or more and 30 ppm or less, preferably 25 ppm or more and 30 ppm or less.

In the exhaust gas treatment method of the present invention, exhaust gas discharged from a boiler that burns fuel is brought into contact with a mercury oxidation catalyst to oxidize mercury in the exhaust gas to divalent mercury, and then the exhaust gas is put into a dry dust collector. An exhaust gas treatment method for introducing and removing dust, and removing exhaust gas removed by a dry dust collector to a wet desulfurization device, and desulfurizing the exhaust gas, wherein a part of SO _{2 in} the exhaust gas flowing upstream of the dry dust collector is oxidized to SO _3. Then, the SO ₃ concentration in the exhaust gas is adjusted to 20 ppm or more, and the dust removal liquid is sprayed on the exhaust gas before passing through the dry dust collector and being introduced into the wet desulfurization apparatus.

  According to the present invention, it is possible to prevent mercury from being mixed into the collected ash collected by the dust collector.

1 is a system diagram of a first embodiment of an exhaust gas treatment apparatus to which the present invention is applied. It is a block diagram of the hydrogen oxidation apparatus in 1st Embodiment of the waste gas processing apparatus formed by applying this invention. Is a diagram showing a relationship between SO ₃ concentration of the exhaust gas to be introduced into the dry dust collector (ppm) removal rate of mercury in the dry dust collector and (%). The relationship between the combustible S content (%) of coal and the amount of circulating exhaust gas required for the oxidation of SO _{2 in} the exhaust gas in order to obtain SO ₃ necessary to prevent mercury adsorption on the ash particles was shown. In the figure, the dotted line and the solid line represent the SO ₃ concentration of the exhaust gas introduced into the dry dust collector. It is a block diagram of the hydrogen oxidation apparatus in 2nd Embodiment of the waste gas processing apparatus formed by applying this invention. It is a block diagram of the hydrogen oxidation apparatus in 3rd Embodiment of the exhaust gas processing apparatus formed by applying this invention.

(First embodiment)
Hereinafter, a first embodiment of an exhaust gas treatment apparatus to which the present invention is applied will be described in detail with reference to the drawings. In the present embodiment, an example in which pulverized coal obtained by pulverizing coal is used as the fuel to be supplied to the boiler is not limited to this example, and other fossil fuels can be used.

In the present embodiment, the SO ₂ oxidation catalyst includes, for example, a noble metal component, and when exhaust gas at 350 ° C. or higher passes through a catalyst layer on which the catalyst is supported, 80 of SO _{2 in} the exhaust gas. % or more was assumed to have a function of oxidizing the S0 _2, and is a mercury oxidation catalyst, for example, is configured to include a titanium, a catalyst layer in which the catalyst is supported 350 ° C. or higher 400 ° C. or less of the exhaust gas flowing In this case, it has a function of suppressing oxidation of SO ₂ to 1% or less while oxidizing 90% or more of metallic mercury in the exhaust gas to divalent mercury, but is not limited thereto.

  As shown in FIG. 1, a flue 2 through which exhaust gas flows is connected to an exhaust gas outlet of the boiler 1. In the middle of the flue 2, a mercury oxidizer 3, an air preheater 4, a dry dust collector 5, a wet dust remover 6, and a wet desulfurizer 7 are provided in this order, and smoke downstream of the wet desulfurizer 7. The road 2 is connected to the chimney 8.

  In the boiler 1, a burner (not shown) is attached to a furnace, and a fuel flow path to which fuel pulverized coal is supplied and a combustion gas flow path to which combustion air is supplied are connected to the burner.

  As shown in FIG. 2, the mercury oxidation apparatus 3 is provided with a plurality of stages (two stages in FIG. 2) of catalyst packed layers 10 at predetermined intervals in the flow direction of the exhaust gas in the container 9. Each catalyst packed layer 10 is formed by, for example, laminating a plate-like or honeycomb-like catalyst element carrying a catalyst in a frame to form a parallel flow type catalyst unit 11, and this catalyst unit 11 is defined as an exhaust gas flow direction. They are arranged side by side in the intersecting direction.

Most of the catalyst unit 11 is constituted by a catalyst element carrying a mercury oxidation catalyst. For example, a corner of the lower catalyst packed bed 10 is constituted by a catalyst element carrying an SO ₂ oxidation catalyst. The catalyst unit 11a is provided. The catalyst unit 11a is provided with a gate valve 12 serving as a flow rate adjusting means for adjusting the flow rate of the exhaust gas at an inlet portion into which the exhaust gas flows. The gate valve 12 slides in a direction crossing the flow direction of the exhaust gas through the wall of the container 9 from the outside of the container 9, and opens and closes the inlet portion of the catalyst unit 11a. Yes. The valve body 13 is driven by a drive device (not shown), and the operation of the drive device is controlled by a signal output from the control device 14 (FIG. 1).

Next, the SO ₃ concentration control device 15 that controls the operation of the gate valve 12 will be described. The SO ₃ concentration control device 15 includes a control device 14, an SO ₂ concentration meter 16, a continuous mercury monitor 17, and the like. The SO ₂ concentration meter 16 and the continuous mercury monitor 17 are each electrically connected to the control device 14. A first sampling pipe 18 is connected to the flue 2 connecting the boiler 1 and the mercury oxidizer 3, and a second sampling pipe 19 is connected to the flue 2 connecting the air preheater 4 and the dry dust collector 5. It is connected. The first sampling pipe 18 and the second sampling pipe 19 are respectively connected to the SO ₂ concentration meter 16, and the exhaust gas extracted from the flue 2 is introduced into the SO ₂ concentration meter 16 through each sampling pipe, and the SO ₂ concentration Is to be measured. SO ₂ concentration of the exhaust gas measured by the SO ₂ concentration meter 16 is converted into an electric signal by SO ₂ concentration meter 16 is output, and is input to the control device 14.

  A third sampling pipe 20 is connected to the flue 2 connecting the dry dust collector 5 and the wet dust remover 6. The third sampling pipe 20 is connected to the continuous mercury monitor 17, and the exhaust gas extracted from the flue 2 is introduced into the continuous mercury monitor 17 via the third sampling pipe 20, and the mercury concentration of the exhaust gas is continuously measured. Being monitored. The mercury concentration of the exhaust gas measured by the continuous mercury monitor 17 is converted into an electrical signal by the continuous mercury monitor 17 and output, and is input to the control device 14.

The control device 14 receives signals output from the SO ₂ concentration meter 16 and the continuous mercury monitor 17 respectively, and controls the operation of the valve body 13 of the gate valve 12 based on these input signals.

On the other hand, a reducing agent for reducing SO ₃ in the exhaust gas to SO ₂ is added to the flue 2 connecting the dry dust collector 5 and the wet dust removing device 6 by the reducing agent adding device 21.

  Next, the operation of the exhaust gas processing apparatus configured as described above will be described. In the following description, the catalyst unit 11a of the mercury oxidizer 3 is assumed to have the gate valve 12 opened at a predetermined opening degree.

The boiler 1 is supplied with combustion air and pulverized coal to burn the pulverized coal. The exhaust gas discharged from the boiler 1 flows through the flue 2, is guided to the mercury oxidation device 3, and flows into the catalyst unit 11. Mercury in the exhaust gas flowing through the catalyst unit 11 comes into contact with the mercury oxidation catalyst and is oxidized from metallic mercury to divalent mercury. On the other hand, in the exhaust gas that has flowed into the catalyst unit 11a through the opened gate valve 12, SO _{2 in} the exhaust gas comes into contact with the SO ₂ oxidation catalyst, and a part of SO ₂ is oxidized to SO ₃ . As a result, the SO ₃ concentration of the exhaust gas that has passed through the mercury oxidizer 3 is increased to a predetermined concentration (for example, 20 ppm or more). The temperature of the exhaust gas flowing through the mercury oxidizer 3 is, for example, 380 ° C., which is a suitable temperature for the mercury oxidation catalyst and the SO ₂ oxidation catalyst to exhibit their catalytic functions.

The exhaust gas that has passed through the mercury oxidizer 3 and led to the air preheater 4 is heat-exchanged with the combustion air supplied to the boiler 1 and cooled to a predetermined temperature. The exhaust gas that has passed through the air preheater 4 is guided to the dry dust collector 5, and most of the dust (ash particles) in the exhaust gas is collected. Here, since the divalent mercury in the exhaust gas is prevented from adhering to the ash particles by SO ₃ adhering to the ash particles in the exhaust gas first, the dry dust collector does not adhere to the ash particles. Go through 5 as it is.

Exhaust gas that has passed through the dry dust collector 5, in the course of flowing through the flue 2, by reducing agent SO ₃ is a basic substance, including sodium component is sprayed by the reducing agent addition device 21, SO ₃ in the exhaust gas Is reduced to SO ₂ .

  Subsequently, the exhaust gas guided to the wet dust remover 6 comes into contact with the dust removing spray liquid sprayed from the nozzle. Here, since the mercury in the exhaust gas introduced into the wet dust removing device 6 is oxidized into highly water-soluble divalent mercury, the mercury in contact with the spray liquid is absorbed by the spray liquid and easily removed from the exhaust gas. Is done. Moreover, the dust remaining in the exhaust gas is also removed from the exhaust gas by contacting the spray liquid. The drainage liquid in which mercury or dust is absorbed in this way is collected at the bottom of the container of the wet dust removal device 6, and then drained out of the container from the drain port, for example, a drainage treatment apparatus (not shown), etc. This separates and removes mercury and dust from the liquid.

The exhaust gas from which mercury has been removed by the wet dust removing device 6 is guided to the wet desulfurization device 7 and comes into contact with the absorbing liquid sprayed from the nozzle, so that sulfur oxide (mainly SO ₂ ) in the exhaust gas is absorbed by the absorbing liquid. And removed from the exhaust gas. The exhaust gas from which the sulfur oxide has been removed by the wet dust remover 6 is released from the chimney 8 into the atmosphere.

Next, the operation of the SO ₃ concentration control device 15 which is a characteristic configuration of the present embodiment will be described. Exhaust gas flowing through the flue 2 upstream of the mercury oxidizer 3 is extracted by the first sampling pipe 18, while exhaust gas flowing through the flue 2 downstream of the mercury oxidizer 3 is extracted by the second sampling pipe 19. , the exhaust gas withdrawn by the sampling pipes, respectively SO ₂ concentration in the SO ₂ concentration meter 16 is measured.

SO ₂ concentration SO ₂ concentration measured by the meter 16 is inputted to the control unit 14 is converted into an electric signal, respectively, through the difference between the SO ₂ concentration, i.e., the exhaust gas is mercury oxidation device 3 leaving the boiler 1 wherein Thus, the SO ₃ oxidation rate at which SO ₂ in the exhaust gas is oxidized to SO ₃ before reaching the dry dust collector 5 is determined. Controller 14 thus determined SO ₃ oxidation rate, desirably, the oxidation rate of the SO _3, the pulverized coal fuel properties and SO ₃ concentration of the exhaust gas in a boiler 1 outlet based on such combustion state of the boiler 1 Based on the predicted value, the SO ₃ concentration of the exhaust gas flowing into the dry dust collector 5 is determined, and the relationship between the SO ₃ concentration of the exhaust gas introduced into the dry dust collector 5 of FIG. 3 and the mercury removal rate in the dry dust collector 5 is determined. The operation of the gate valve 12 of the mercury oxidizer 3 is controlled so as to maintain the SO ₃ concentration at which the mercury removal rate in the dry dust collector 5 becomes zero.

More specifically, the control device 14, for example, the relationship in FIG. 3, the prediction error of the SO ₃ concentration in the exhaust gas at the outlet of the boiler 1, and SO ₂ in the exhaust gas before and after the mercury oxidation device ₃ are oxidized to SO _3. measurement error of the oxidation rate of SO _3, and, in consideration of the response delay in SO ₂ in the exhaust gas is converted to be oxidized SO _3, is SO ₃ concentration of the exhaust gas flowing into the dry dust collector 5, for example, 25ppm The operation of the gate valve 12 is controlled so as to be maintained as described above. Here, if the SO ₃ concentration in the exhaust gas becomes too high, the acid dew point rises, and there is a possibility that the problem of acid corrosion of the equipment material may occur in the exhaust gas passage. For example, if the SO ₃ concentration exceeds 50 ppm, a large amount of SO ₃ removal agent (such as a reducing agent) is required, and excess SO ₃ may slip to the subsequent stage. Therefore, the SO ₃ concentration is controlled to 50 ppm or less, preferably 25 ppm or more and 30 ppm or less.

When the opening degree of the valve body 13 of the gate valve 12 increases, the mercury oxidation apparatus 3 increases the flow rate of the exhaust gas flowing into the catalyst unit 11a and increases the SO ₃ concentration of the exhaust gas. When the opening is reduced, the flow rate of the exhaust gas flowing into the catalyst unit 11a is reduced, and the SO ₃ concentration of the exhaust gas is reduced. Therefore, for example, when the SO ₃ concentration of the exhaust gas flowing into the dry dust collector 5 decreases and approaches 25 ppm, the opening of the valve body 13 is controlled to increase, and the SO ₃ concentration of the exhaust gas increases to 30 ppm. When the angle approaches, the control is performed so that the opening degree of the valve body 13 is reduced.

  In addition, it is also possible to control the mercury concentration of the exhaust gas flowing downstream of the dry dust collector 5 from the measured value of the continuous mercury monitor 17 and reflect the result in the operation of the gate valve 12.

Unlike the prior art in which SO ₃ in the exhaust gas flowing upstream of the dry dust collector 5 is actively reduced to promote mercury adsorption on the ash particles, this embodiment removes mercury from the exhaust dust collector 5. By leaving to the downstream side and adjusting and maintaining the SO ₃ concentration of the exhaust gas flowing into the dry dust collector 5 within a concentration range in which the mercury removal rate in the dry dust collector 5 is zero, mercury is prevented from adhering to the ash particles. Yes. Furthermore, even if the SO ₂ concentration of the exhaust gas varies depending on the properties of the fuel, the variation of the SO ₃ concentration of the exhaust gas flowing into the dry dust collector 5 is suppressed by adjusting the flow rate of the exhaust gas that passes through the catalyst unit 11a. Can do. As a result, it is possible to prevent mercury from being mixed into the dust collected by the dry dust collector 5, and as a result, not only can the dust be reused, but also processing of the dust when landfilling can be omitted. .

Further, according to the present embodiment, the wet dust removing device 6 is installed on the upstream side of the wet desulfurization device 7, and mercury in the exhaust gas is removed by the wet dust removing device 6. Thereby, it is possible to prevent mercury from flowing into the wet desulfurization apparatus 7 and to prevent mixing of gypsum into the gypsum which is a by-product, so that the gypsum can be reused as it is. Furthermore, according to the present embodiment, exhaust gas discharged from the chimney 8 into the atmosphere is removed with high removal rates of soot, SO ₂ , SO ₃ , and mercury, so a high-performance exhaust gas purification device is constructed. can do.

Fig. 4 assumes that a part of the exhaust gas is returned to the boiler 1 and circulated to prevent combustible S content (%) of coal as fuel and mercury adhesion to ash particles in the exhaust gas. to obtain a SO ₃ required a diagram illustrating a relationship between the circulation exhaust gas quantity necessary for the oxidation of SO ₂ in the flue gas, solid line dotted and 30ppm of 20ppm is exhaust gas both of which are introduced into the dry dust collector 5 Represents the SO ₃ concentration. The S component in the exhaust gas burns to become SO ₂ , and about 2% of a part thereof is oxidized to SO ₃ . For example, when combustible coal having an S concentration of 0.5% is combusted, the exhaust gas contains about 400 ppm of SO ₂ , of which about ₃ ppm of SO ₃ is generated. In this case, a certain amount of mercury in the exhaust gas adheres to the dust and is collected by the dry dust collector 5. In contrast, in order to adjust the SO ₃ concentration in 20-30Ppm, is circulated by extracting part of exhaust gas, when the oxidation of SO ₂ to SO ₃ by the SO ₂ oxidation catalyst, an enormous amount of exhaust gas (e.g., total The exhaust gas amount (3.1% to 5.7%) must be circulated, and the combustion temperature of the boiler 1 must be raised.

In this regard, as in the present embodiment, when a SO ₂ oxidation catalyst is provided to oxidize a part of SO ₂ to SO ₃ , the power of the fan required for exhaust gas circulation and the energy for raising the temperature are increased. Since it becomes unnecessary, the energy efficiency of the entire system can be improved.

(Second Embodiment)
Next, a second embodiment of the exhaust gas treatment apparatus to which the present invention is applied will be described in detail with reference to FIG. In the present embodiment, differences from the first embodiment will be described, and the same components as those in the first embodiment will be denoted by the same reference numerals and description thereof will be omitted.

As shown in FIG. 5, the mercury oxidation apparatus 23 of the present embodiment bypasses the catalyst packed bed 10 by a bypass line 24 instead of the gate valve 12 that opens and closes the inlet portion of the catalyst unit 11 a of FIG. 2, The catalyst unit 11 a filled with the catalyst for SO ₂ oxidation and the flow rate adjusting valve 25 that is a flow rate adjusting means for adjusting the flow rate of the exhaust gas flowing through the bypass line 24 are provided in the middle of the bypass line 24. The configuration is different from that of the first embodiment.

One end of the bypass line 24 is connected to the exhaust gas flow path upstream of the catalyst packed bed 10 in the container 9, and the other end is connected to the flue 2 connected to the outlet of the container 9. The catalyst unit 11a is configured, for example, as a parallel flow type by laminating catalyst elements carrying a plate-like or honeycomb-like SO ₂ oxidation catalyst in a frame. The catalyst unit 11 a has an inlet portion and an outlet portion that are hermetically connected to the bypass conduit 24, respectively, and forms part of the bypass conduit 24. The bypass conduit 24 upstream of the catalyst unit 11 a is provided with a flow rate adjustment valve 25, and the opening degree of the flow rate adjustment valve 25 is controlled by a command output from the control device 14.

According to the present embodiment, by controlling the opening degree of the flow rate adjustment valve 25 by the control device 14, the exhaust gas flow rate flowing through the catalyst unit 11a, that is, the exhaust gas flow rate contacting with the SO ₂ oxidation catalyst can be adjusted. . Thus, it maintained at the set concentration range SO ₃ concentration in flue gas having passed through the mercury oxidation device 3, that the mercury from adhering can continuously prevent the ash particles. As a result, as in the first embodiment, it is possible to prevent mercury from being mixed into the dust collected by the dry dust collector 5, not only facilitating the reuse of the dust, but also the disposal of the dust when landfilling. Is no longer necessary. Therefore, even if the mercury oxidation apparatus 23 of the present embodiment is replaced with the mercury oxidation apparatus 3 of the first embodiment, the same effect as that of the first embodiment can be obtained.

(Third embodiment)
Next, a third embodiment of the exhaust gas treatment apparatus to which the present invention is applied will be described in detail with reference to FIG. In the present embodiment, differences from the first embodiment will be described, and the same components as those in the first embodiment will be denoted by the same reference numerals and description thereof will be omitted.

  The mercury oxidation apparatus 27 of the present embodiment replaces the gate valve 12 that opens and closes the inlet portion of the catalyst unit 11a in FIG. 2 and the flow rate adjustment valve 25 provided in the bypass line 24 in FIG. The catalyst unit 11a is disposed in the inner space, that is, in the space downstream of the catalyst packed bed 10, and the angle of the axial center of the frame of the catalyst unit 11a with respect to the flow direction of the exhaust gas flowing through the exhaust gas flow path as a flow rate adjusting means. Is variably supported so that the flow rate of the exhaust gas flowing into the catalyst unit 11a can be adjusted.

  The catalyst unit 11a has, for example, a rod-like shape in which one end side is pivotally supported on the inner wall or the like of the container 9 while both ends of the frame open, and the other end side extends through the wall of the container 9 into the container 9. Alternatively, a plate-like angle adjusting member 28 is connected, and the other end side rotates in the circumferential direction around an axis that supports the one end side in conjunction with the movement of the angle adjusting member 28. In addition, although the catalyst unit 11a of this embodiment is provided in the downstream of the catalyst packed bed 10, it should just be provided in at least one of the upstream of the catalyst packed bed 10, or the downstream. The angle adjusting member 28 is slidably supported in the longitudinal direction (arrows in FIG. 6) by a driving device (not shown), and the operation of the angle adjusting member 28 is controlled by a command output from the control device 14. It is like that.

According to the present embodiment, since the control device 14 controls the slide amount of the angle adjusting member 28, the projected area of the inlet portion of the catalyst unit 11a projected onto the surface orthogonal to the flow direction of the exhaust gas is adjusted. It is possible to adjust the flow rate of exhaust gas flowing into the catalyst unit 11a, that is, the flow rate of exhaust gas in contact with the SO ₂ oxidation catalyst. Accordingly, since the SO ₃ concentration in flue gas having passed through the mercury oxidation device 3 is maintained at the set concentration range, it is possible to prevent the mercury from adhering to the ash particles continuously. As a result, as in the first embodiment, mercury can be prevented from being mixed into the dust collected by the dry dust collector 5, so that not only the dust can be easily reused, but also the dust generated during landfilling can be reduced. No processing is required. Therefore, even if the mercury oxidation apparatus 23 of the present embodiment is replaced with the mercury oxidation apparatus 3 of the first embodiment, the same effect as that of the first embodiment can be obtained.

  As mentioned above, although embodiment of this invention has been explained in full detail with drawing, the said embodiment is only an illustration of this invention and this invention is not limited only to the structure of the said embodiment. Needless to say, changes in design and the like within the scope of the present invention are included in the present invention.

For example, in the above embodiment, SO ₃ concentration controller 15 determines based on the SO ₃ concentration in exhaust gas flowing into the dry dust collector 5 to the predicted value of the SO ₃ concentration of oxidation rate and boiler 1 outlet of the SO ₃ However, an actual measurement value of the SO ₃ concentration of the exhaust gas flowing into the dry dust collector 5 may be used.

Further, in the above embodiment, as shown in FIG. 1, the reducing agent addition device 21 is arranged so that the SO ₃ reducing agent is added to the exhaust gas flowing through the flue 2 upstream of the wet desulfurization device 7. However, instead of the reducing agent addition device 21, a wet dust collector is disposed in the flue 2 between the wet desulfurization device 7 and the chimney 8, and SO _{3 in} the exhaust gas that has not been absorbed by the wet desulfurization device 7. May be removed with a wet dust collector.

In this embodiment, the method of reducing SO ₃ to SO ₂ has been described as a method of removing SO ₃ in the exhaust gas, but instead, a method of neutralizing and removing SO ₃ is employed. It is also possible. In either case, it is desirable to add a reducing agent or a neutralizing agent to the flue 2 on the upstream side of the wet dust remover 6 in order to remove the product produced by the reaction.

1 Boiler 2 flue 3,23,27 mercury oxidation device 5 dry dust collector 7 wet desulfurization system 11,11a catalyst unit 12 a gate valve 13 valve 14 control device 15 SO ₃ concentration controller 21 reducing agent adding device 24 bypass line 25 Flow adjustment valve 28 Angle adjustment member

Claims (11)

An exhaust gas treatment apparatus including a dry dust collector in an exhaust gas flue discharged from a boiler that burns fuel,
An SO ₂ oxidation catalyst that is disposed in the flue upstream of the dry dust collector and oxidizes a part of SO _{2 in} the exhaust gas flowing through the flue to SO ₃ , and contacts the SO ₂ oxidation catalyst An exhaust gas treatment device comprising a flow rate adjusting means for adjusting the flow rate of the exhaust gas. A mercury oxidation apparatus that is provided in the flue upstream of the dry dust collector and contains a mercury oxidation catalyst that oxidizes mercury in the exhaust gas flowing through the flue to divalent mercury;
The exhaust gas treatment apparatus according to claim 1, wherein the SO ₂ oxidation catalyst is provided in an exhaust gas flow path of the mercury oxidation apparatus. The SO ₂ oxidation catalyst is accommodated in a frame that is open at both ends to form a catalyst unit, and an inlet portion of the catalyst unit into which the exhaust gas flows is provided with a gate valve that opens and closes the inlet portion,
The exhaust gas treatment apparatus according to claim 2, wherein the flow rate adjusting means includes a mechanism that adjusts an opening amount of the inlet portion by sliding a valve body of the gate valve. The SO ₂ oxidation catalyst is provided in the middle of a bypass line that branches the exhaust gas passage upstream of the mercury oxidation catalyst and bypasses the mercury oxidation catalyst,
The exhaust gas treatment apparatus according to claim 2, wherein the flow rate adjusting means is a flow path adjusting valve that adjusts a flow rate of the exhaust gas flowing through the bypass pipe. The SO ₂ oxidation catalyst is accommodated in a frame that is open at both ends to form a catalyst unit, and the catalyst unit is provided in at least one exhaust gas flow path upstream or downstream of the mercury oxidation catalyst. The angle of the axis of the frame body is variably supported with respect to the flow direction of the exhaust gas flowing through the exhaust gas flow path,
The exhaust gas treatment apparatus according to claim 2, wherein the flow rate adjusting means includes a mechanism for adjusting the angle. Control means for controlling the operation of the flow rate adjusting means is provided,
The control device includes SO ₂ concentration of the exhaust gas flowing through the flue between the boiler and the mercury oxidizer, and SO _{2 of the} exhaust gas flowing through the flue between the mercury oxidizer and the dry dust collector. 6. The SO ₃ concentration of the exhaust gas introduced into the dry dust collector is determined based on a difference from the _two concentrations, and the operation of the flow rate adjusting means is controlled based on the determined SO ₃ concentration. The exhaust gas treatment apparatus according to any one of the above.   A wet desulfurization device that is disposed in the flue downstream of the dry dust collector to remove sulfur oxides in the exhaust gas, and is disposed in the flue between the dry dust collector and the wet desulfurization device. The exhaust gas treatment device according to any one of claims 2 to 6, further comprising a wet dust removal device that removes soot and dust in the exhaust gas. 8. A reducing agent addition device for adding a reducing agent for reducing SO ₃ in the exhaust gas to SO ₂ in the exhaust gas flowing through the flue between the dry dust collector and the wet desulfurization device. The exhaust gas treatment apparatus according to any one of the above. The exhaust gas treatment apparatus according to any one of claims 2 to 7, wherein a wet dust collector that removes SO ₃ in the exhaust gas flowing through the flue is provided in the flue downstream of the wet desulfurization apparatus. An exhaust gas treatment method for removing dust by introducing exhaust gas discharged from a boiler that burns fuel to a dry dust collector,
A method for treating exhaust gas, comprising oxidizing part of SO _{2 in} the exhaust gas flowing upstream of the dry dust collector to SO ₃ and adjusting the concentration of SO ₃ in the exhaust gas to 20 ppm or more. After contacting exhaust gas discharged from a boiler that burns fuel with a mercury oxidation catalyst to oxidize mercury in the exhaust gas to divalent mercury, the exhaust gas is guided to a dry dust collector to remove dust, and the dry dust collector An exhaust gas treatment method in which the exhaust gas that has been dust-removed is guided to a wet desulfurization apparatus and subjected to desulfurization treatment,
The portion of the SO ₂ in the flue gas flowing through the upstream side of the dry dust collector to be oxidized to SO ₃ by adjusting the SO ₃ concentration in the exhaust gas than 20 ppm,
An exhaust gas treatment method, wherein a dust removal liquid is sprayed on the exhaust gas before passing through the dry dust collector and introduced into the wet desulfurization apparatus.

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