WO2020161874A1

WO2020161874A1 - Combustion system

Info

Publication number: WO2020161874A1
Application number: PCT/JP2019/004518
Authority: WO
Inventors: 英嗣清永; 吉田　和広; 啓一郎盛田; 徹村山; 春田　正毅; 雄介猪股
Original assignee: 中国電力株式会社; 公立大学法人首都大学東京
Priority date: 2019-02-07
Filing date: 2019-02-07
Publication date: 2020-08-13
Also published as: JPWO2020161874A1

Abstract

Provided is a combustion system that is capable of removing nitrogen oxides exceeding a regulation value while keeping the amount of ammonia slip level at or below a prescribed value, even when a denitration catalyst used in a denitration apparatus degrades. A combustion system 1 comprises: a first denitration apparatus 30 for removing nitrogen oxides from exhaust gas expelled from a boiler 10; and a second denitration apparatus 70, positioned downstream of an air preheater 40, for removing nitrogen oxides from exhaust gas expelled from the air preheater 40. The first denitration apparatus 30 controls ammonia dosage on the basis of the amount of ammonia slip. The second denitration apparatus 70 controls ammonia dosage on the basis of outlet nitrogen oxide concentration.

Description

Combustion system

The present invention relates to a combustion system.

At coal-fired power plants, nitrogen oxides are generated as coal burns, but due to regulations such as the Air Pollution Control Law, their emissions are restricted to below a certain level. Therefore, a denitration device is installed in the power plant to reduce and decompose nitrogen oxides. This denitration device is filled with a denitration catalyst, and by coexisting ammonia (gas), a reduction reaction is expressed at high temperature.

Since this denitration catalyst efficiently performs a selective catalytic reduction reaction in a high temperature atmosphere of 300°C to 400°C, it is necessary to denitrate the exhaust gas containing a large amount of soot dust immediately after burning in the boiler. .. Therefore, when used for a long period of time, coal ash is deposited on the catalyst surface over time and covers the entire surface of the catalyst, which reduces the activity of the denitration catalyst.

When the NOx removal catalyst deteriorates, it is necessary to increase the amount of ammonia input required for the NOx removal reaction. When the amount of ammonia input increases, it reacts with the sulfur content derived from coal to produce ammonium sulfate. This ammonia sulfate blocks the heat exchanger in the latter stage of the denitration device, and cannot exhaust the exhaust gas for heat exchange in the heat exchanger, so the power plant may have to be stopped.

In this regard, Patent Document 1 monitors the temperature of the catalyst layer to automatically set the amount of unreacted leaked ammonia into the process gas to a predetermined value or less, and automatically detects the amount of ammonia when the temperature of the catalyst layer is low. Disclosed is a method of controlling the injection amount of ammonia in a dry flue gas denitration device, which controls the injection and activates the denitration device so that the amount of leaked ammonia does not exceed a predetermined value.

JP-A-60-71027

However, the method disclosed in Patent Document 1 merely aims to prevent the amount of leaked ammonia from exceeding a predetermined value, and did not deal with the reduction of the denitration rate due to the deterioration of the denitration catalyst.

The present invention provides a combustion system capable of removing nitrogen oxides exceeding a regulation value while suppressing the amount of leaked ammonia to a predetermined value or less even when the denitration catalyst used in a denitration device is deteriorated. To aim.

The present invention is a combustion system, wherein a boiler that burns fuel, an exhaust passage through which exhaust gas generated by combustion of the fuel in the boiler flows, and an exhaust passage that are arranged in the exhaust passage A first denitration device that removes nitrogen oxides from the exhaust gas discharged from the boiler, and heat exchange between the exhaust gas and the combustion air in the exhaust passage and at a subsequent stage of the first denitration device. An air preheater that supplies combustion air after heat exchange to the boiler and discharges exhaust gas after heat exchange; A second denitration device that removes nitrogen oxides from the exhaust gas discharged from the air preheater, wherein the first denitration device includes a first ammonia injection part that injects ammonia into the exhaust gas; An ammonia amount detection unit that detects the amount of leaked ammonia at the outlet of the first denitration device, and controls the amount of ammonia injected by the first ammonia injection unit based on the amount of leaked ammonia detected by the ammonia amount detection unit. The second denitration device includes a first ammonia injection control unit, and a second ammonia injection unit that injects ammonia into the exhaust gas and a nitrogen oxide concentration at an outlet of the second denitration device. A nitrogen oxide concentration detector for detecting, and a second ammonia injection controller for controlling the amount of ammonia injected by the second ammonia injector based on the nitrogen oxide concentration detected by the nitrogen oxide concentration detector. And a combustion system.

In addition, it is preferable that the second denitration device has a denitration catalyst that contains vanadium pentoxide in an amount of 43 wt% or more, has a BET specific surface area of 30 m ² /g or more, and is used for denitration at 200° C. or less.

Further, it is preferable that the first ammonia injection control unit controls the ammonia injection amount so that the leak ammonia amount detected by the ammonia amount detection unit is 5 ppm or less.

Further, it is preferable that a chimney that emits exhaust gas into the atmosphere is installed at the end of the exhaust passage, and the second denitration device is installed in the chimney.

According to the present invention, even if the NOx removal catalyst used in the NOx removal device is deteriorated, it is possible to remove nitrogen oxides exceeding the regulation value while suppressing the amount of leaked ammonia to a predetermined value or less.

1 is an overall configuration diagram of a combustion system according to a first embodiment of the present invention. It is a figure which shows the internal structure of the 1st denitration apparatus contained in the combustion system which concerns on 1st Embodiment of this invention. It is a figure which shows the structure of the denitration catalyst used by the 1st denitration apparatus contained in the combustion system which concerns on 1st Embodiment of this invention. It is a functional block diagram of the 1st denitration device contained in the combustion system concerning a 1st embodiment of the present invention. It is a graph which shows the property of the denitration catalyst used by the 2nd denitration device contained in the combustion system concerning a 1st embodiment of the present invention. It is a graph which shows the property of the denitration catalyst used by the 2nd denitration device contained in the combustion system concerning a 1st embodiment of the present invention. It is a graph which shows the property of the denitration catalyst used by the 2nd denitration device contained in the combustion system concerning a 1st embodiment of the present invention. It is a graph which shows the property of the denitration catalyst used by the 2nd denitration device contained in the combustion system concerning a 1st embodiment of the present invention. FIG. 3 is a functional block diagram of a second denitration device included in the combustion system according to the first embodiment of the present invention. It is a whole block diagram of the combustion system which concerns on 2nd Embodiment of this invention. It is a figure which shows the internal structure of the chimney as a 2nd denitration apparatus contained in the combustion system which concerns on 2nd Embodiment of this invention. It is a figure which shows the internal structure of the chimney as a 2nd denitration apparatus contained in the combustion system which concerns on 2nd Embodiment of this invention. It is a figure which shows the internal structure of the chimney as a 2nd denitration apparatus contained in the combustion system which concerns on 2nd Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[1. First Embodiment]
[1.1 Overall configuration]
FIG. 1 is an overall configuration diagram of a combustion system 1 according to the first embodiment of the present invention. As shown in FIG. 1, the combustion system 1 includes a boiler 10 as a combustion device, a pulverized coal machine 20, an exhaust passage L1, a first denitration device 30, an air preheater 40, and a heat recovery device. The gas heater 50, the dust collector 60, the second denitration device 70, the induced draft fan 80, the desulfurization device 90, the gas heater 100 as a heater, and the chimney 110 are provided.

The boiler 10 burns pulverized coal as fuel together with air. In the boiler 10, combustion of pulverized coal produces exhaust gas. In addition, combustion of pulverized coal produces coal ash such as clinker ash and fly ash. The clinker ash generated in the boiler 10 is discharged to the clinker hopper 11 arranged below the boiler 10 and then conveyed to a coal ash recovery silo (not shown).

The boiler 10 is formed in a substantially inverted U shape as a whole. The exhaust gas generated in the boiler 10 moves in an inverted U shape along the shape of the boiler 10. The temperature of the exhaust gas in the vicinity of the exhaust gas outlet of the boiler 10 is, for example, 300 to 400°C.

The pulverized coal machine 20 pulverizes coal supplied from a coal bunker (not shown) into a fine particle size to form pulverized coal. The pulverized coal machine 20 mixes pulverized coal and air to preheat and dry the pulverized coal. The pulverized coal formed in the pulverized coal machine 20 is supplied to the boiler 10 by blowing air.

The exhaust passage L1 is connected to the boiler 10 on the upstream side. The exhaust passage L1 is a passage through which exhaust gas generated in the boiler 10 flows.

The first denitration device 30 is arranged downstream of the boiler 10 in the exhaust path L1. The exhaust gas generated from the boiler 10 is supplied to the first denitration device 30. The first denitration device 30 removes nitrogen oxides from the exhaust gas with a denitration catalyst. The configuration of the first denitration device 30 will be described in detail later. The temperature of the exhaust gas in the first denitration device 30 is, for example, 300 to 400°C.

In the first denitration device 30, nitrogen oxides are removed from the exhaust gas by the selective catalytic reduction method. According to the selective catalytic reduction method, nitrogen oxides can be efficiently removed from exhaust gas by producing nitrogen and water from nitrogen oxides with a reducing agent and a denitration catalyst. The reducing agent used in the selective catalytic reduction method contains ammonia. When ammonia is used as the reducing agent, ammonia in any state of ammonia gas, liquid ammonia and aqueous ammonia solution may be used.

More specifically, the first denitration device 30 injects ammonia gas into the introduced exhaust gas, and then mixes the mixed gas with a honeycomb molded body having a denitration catalyst fixed thereon or an alumina carrying the denitration catalyst. It can be configured to contact fibers such as fibers. An example of the configuration of the first denitration device 30 will be described later.

The air preheater 40 is arranged in the exhaust path L1. The air preheater 40 performs heat exchange between the exhaust gas and the combustion air sent from a forced draft fan (not shown), and recovers heat from the exhaust gas. The air for combustion is heated in the air preheater 40 and then supplied to the boiler 10.

The gas heater 50 is arranged downstream of the air preheater 40 in the exhaust path L1. The gas heater 50 is supplied with the exhaust gas whose heat is recovered in the air preheater 40. The gas heater 50 further recovers heat from the exhaust gas.

The dust collector 60 is arranged downstream of the gas heater 50 in the exhaust path L1. The dust collector 60 is supplied with the exhaust gas heat-recovered by the gas heater 50. The dust collector 60 is a device that collects soot dust such as coal ash (fly ash) in the exhaust gas by applying a voltage to the electrodes. The fly ash collected by the dust collector 60 is conveyed to a coal ash recovery silo (not shown). The temperature of the exhaust gas in the dust collector 60 is, for example, 80 to 120°C.

The second denitration device 70 is arranged downstream of the dust collector 60 in the exhaust passage L1. The second denitration device 70 is supplied with the exhaust gas after the soot dust is collected by the dust collector 60. The second denitration device 70 removes nitrogen oxides from the exhaust gas with a denitration catalyst. The configuration of the second denitration device 70 and the denitration catalyst used in the second denitration device 70 will be described in detail later. The temperature of the exhaust gas in the second denitration device 70 is, for example, 130 to 200°C.

The second denitration device 70, like the first denitration device 30, removes nitrogen oxides from the exhaust gas by the selective catalytic reduction method. In particular, the second denitration device 70 suppresses the emission amount of nitrogen oxides in the entire combustion system 1 to be equal to or less than the regulated value. Therefore, in the first denitration device 30, the deterioration of the denitration catalyst progresses and the decomposition is completed. The nitrogen oxides that were not present are removed.
Further, similar to the first denitration device 30, the reducing agent used in the second denitration device contains ammonia. When ammonia is used as the reducing agent, any of ammonia gas, liquid ammonia, and aqueous ammonia solution may be used.

The induction fan 80 is arranged on the exhaust path L1 downstream of the second denitration device 70. The induced draft fan 80 takes in the exhaust gas from which the nitrogen oxides are removed in the second denitration device 70 from the primary side and sends it to the secondary side.

The desulfurization device 90 is arranged in the exhaust passage L1 downstream of the induced draft fan 80. The exhaust gas sent from the induced draft fan 80 is supplied to the desulfurization device 90. The desulfurization device 90 removes sulfur oxides from the exhaust gas. Specifically, the desulfurization apparatus 90 sprays a mixed liquid (limestone slurry) of limestone and water onto the exhaust gas to absorb the sulfur oxide contained in the exhaust gas into the mixed liquid and remove the sulfur oxide from the exhaust gas. The temperature of the exhaust gas in the desulfurizer 90 is, for example, 50 to 120°C.

The gas heater 100 is arranged downstream of the desulfurization device 90 in the exhaust path L1. Exhaust gas from which sulfur oxides have been removed in the desulfurization device 90 is supplied to the gas heater 100. The gas heater 100 heats exhaust gas. The gas heater 50 and the gas heater 100 are composed of an exhaust gas flowing between the air preheater 40 and the dust collector 60 and an exhaust gas flowing between the second denitration device 70 and the desulfurization device 90 in the exhaust passage L1. You may comprise as a gas gas heater which heat-exchanges between them.

The chimney 110 is connected to the downstream side of the exhaust path L1. The exhaust gas heated by the gas heater 100 is introduced into the chimney 110. Since the exhaust gas introduced into the chimney 110 is heated by the gas heater 100, it is effectively discharged from the upper part of the chimney 110 by the chimney effect. Further, by heating the exhaust gas in the gas heater 100, it is possible to prevent the vapor from condensing and producing white smoke above the chimney 110. The temperature of the exhaust gas near the exit of the chimney 110 is 110° C., for example.

[1.2 First denitration device]
FIG. 2 is a configuration diagram of the first denitration device 30. As shown in FIG. 2, the first denitration device 30 includes a denitration reactor 31, a plurality of stages of denitration catalyst layers 32, 32, 32 arranged inside the denitration reactor 31, and a denitration catalyst layer 32. A rectifying layer 33 arranged on the upstream side, a rectifying plate 34 arranged near the inlet of the denitration reactor 31, and an ammonia injection part 35 arranged on the upstream side of the denitration reactor 31 are provided.

The denitration reactor 31 serves as a place for the denitration reaction in the denitration device 30.
The denitration catalyst layers 32 are arranged inside the denitration reactor 31 in a plurality of stages (three stages in the present embodiment) along the flow path of the exhaust gas at predetermined intervals.

FIG. 3 is a configuration diagram of the denitration catalyst layer 32.
As shown in FIG. 3, the denitration catalyst layer 32 includes, for example, a plurality of honeycomb catalysts 322 as denitration catalysts. More specifically, the denitration catalyst layer 32 includes a plurality of casings 321, a plurality of honeycomb catalysts 322 housed in the plurality of casings 321, and a seal member 323.

The casing 321 is composed of a rectangular tubular metal member with one end and the other end open. The casing 321 is arranged such that the opened one end and the other end face the exhaust gas flow path in the denitration reactor 31, that is, the exhaust gas flows through the inside of the casing 321. Further, the plurality of casings 321 are connected and arranged so as to be in contact with each other so as to close the exhaust gas flow path in the denitration reactor 31.

The honeycomb catalyst 322 is formed in a long shape (rectangular solid shape) in which a plurality of exhaust gas circulation holes 324 extending in the longitudinal direction are formed. The plurality of honeycomb catalysts 322 are arranged so that the exhaust gas flow holes 324 extend along the exhaust gas flow path. In the present embodiment, the plurality of honeycomb catalysts 322 are arranged inside the denitration reactor 31 while being housed in the casing 321.

The seal member 323 is arranged between the honeycomb catalysts 322 that are arranged adjacent to each other in the lateral direction, and prevents the exhaust gas from flowing into the gap between the honeycomb catalysts 322 that are arranged adjacent to each other. In the present embodiment, the seal member 323 is made of a sheet-like member having conductivity, and is provided at a predetermined length portion (for example, 150 mm from the end) on one end side and the other end side in the longitudinal direction of the honeycomb catalyst 322. It is wrapped around.

As the sealing member 323, it is possible to use ceramic paper which is configured by mixing conductive fibers or a conductive filler with an inorganic fiber and a binder containing alumina or silica as a main component.

In the above-mentioned denitration catalyst layer 32, as the honeycomb catalyst 322, for example, one having a rectangular parallelepiped shape of 150 mm×150 mm×860 mm and 400 (20×20) exhaust gas circulation holes having an opening of 6 mm×6 mm is used. Further, as the casing 321, a casing capable of accommodating 72 honeycomb catalysts 322 (6 vertical×12 horizontal) is used. Then, 120 to 150 of these casings 321 are used for one layer of the denitration catalyst layer 32. That is, 9000 to 10000 honeycomb catalysts 322 are installed in the single denitration catalyst layer 32.

In FIG. 2, the rectifying layer 33 is arranged on the upstream side of the denitration catalyst layer 32. The rectification layer 33 is composed of a metal member or the like having a plurality of openings formed in a lattice shape, and partitions the exhaust gas flow path in the denitration reactor 31. The rectification layer 33 rectifies the exhaust gas that flows through the exhaust passage L1 and is introduced into the denitration reactor 31, and evenly guides it to the denitration catalyst layer 32.

The rectifying plate 34 is arranged upstream of the rectifying layer 33 near the inlet of the denitration reactor 31. More specifically, the rectifying plate 34 is arranged at the bent portion of the denitration reactor 31 or the inner wall of the exhaust passage L1 and projects from the inner wall to the inner surface side. The current plate 34 regulates the flow of the exhaust gas in the bent portion of the exhaust passage L1 or the denitration reactor 31.

By rectifying the exhaust gas by the rectifying layer 33 and the rectifying plate 34, the uneven flow introduced to the denitration catalyst layer 32 is reduced, and clogging and abrasion of the denitration catalyst layer 32 due to dust are prevented.

The ammonia injection unit 35 is arranged on the upstream side of the denitration reactor 31 and injects ammonia into the exhaust passage L1.

According to the first denitration device 30 having the above configuration, first, in the ammonia injecting section 35, ammonia is injected into the high temperature exhaust gas (300° C. to 400° C.) flowing through the exhaust passage L1. The exhaust gas into which the ammonia has been injected is rectified by the rectifying plate 34 and the rectifying layer 33 and introduced into the denitration catalyst layer 32.

In the denitration catalyst layer 32, when the exhaust gas containing ammonia passes through the exhaust gas circulation holes of the honeycomb catalyst, the nitrogen oxides and ammonia react with each other according to the following chemical reaction formula, and decomposed into harmless nitrogen and steam. ..
4NO+4NH ₃ +O ₂ →4N ₂ +6H ₂ O
NO+NO ₂ +2NH ₃ →2N ₂ +3H ₂ O

The above method is called the selective catalytic reduction method. In the above reaction, when the amount of NH ₃ added to the amount of NOx is large, the denitration rate is also improved, but unreacted NH ₃ (hereinafter referred to as leak NH ₃ ) is increased. If the leak NH ₃ is large, it reacts with SO ₃ in the exhaust gas to generate acidic ammonium sulfate (NH ₄ HSO ₄ ), and this acidic ammonium sulfate promotes the adhesion of dust contained in the exhaust gas, and the air preheater installed in the latter stage. The element etc. will be clogged. Therefore so that the leakage NH ₃ equal to or less than a predetermined value, the management of the injection amount of NH ₃ is performed. In the present embodiment, as an example, the injection amount of NH ₃ is controlled so that the leak NH ₃ is 5 ppm or less.

FIG. 4 is a functional block diagram of the first denitration device 30. The first denitration device 30 includes an ammonia injection unit 351, an ammonia amount detection unit 352, and an ammonia injection control unit 353 as functional blocks.

The ammonia injection unit 351 injects ammonia into the exhaust gas discharged from the boiler 10. Further, the ammonia injection unit 351 corresponds to the ammonia injection unit 35 in FIG.
The ammonia amount detection unit 352 detects the amount of leak NH _{3 at} the outlet of the first denitration device 30.
The ammonia injection control unit 353 controls the ammonia injection amount by the ammonia injection unit 351 based on the leak NH ₃ amount detected by the ammonia amount detection unit 352.

Since the first denitration device 30 has the above-described configuration, it is possible to control the injection amount of NH ₃ so that the leak NH ₃ becomes a certain value or less.

[1.3 Second denitration device]
Although not shown, the second denitration device 70 has a plurality of stages of denitration catalyst layers containing a plurality of honeycomb catalysts as denitration catalysts as its internal configuration, as in the first denitration device 50.

As this denitration catalyst, a denitration catalyst having vanadium pentoxide in an amount of 43 wt% or more, a BET specific surface area of 30 m ² /g or more, and used for denitration at 200° C. or lower is used.
The applicant applied for PCT/JP2016/0776870 on September 12, 2016 as an international application for this denitration catalyst, and after being transferred to Japan, was granted a patent decision as Patent 6093101 on February 17, 2017. .. The outline of this denitration catalyst will be described below.

5 to 8 are obtained by quoting the graphs disclosed in the above-mentioned Japanese Patent No. 6093101 and changing the names of the plotted points in each graph.
In the graphs of FIGS. 5 to 8, the vanadium catalysts of Examples 1 to 3 and Comparative Examples 1 to 5 were prepared by the following method.

[Examples 1 to 3 and Comparative Examples 1 to 2]
Ammonium vanadate was dissolved in the oxalic acid solution (vanadium:oxalic acid molar ratio=1:2-1:4). After all the components were completely melted, the water content in the solution was evaporated on a hot stirrer and dried in a dryer at 120° C. overnight. Then, the dried powder was calcined in air at 300° C. for 4 hours.
The sample names are respectively “V ₂ O ₅ _SG — 1:1” (Comparative Example 1), “V ₂ O ₅ _SG — 1:2” (Example 1), and “V ₂ O ₅ _SG — 1:3” (Example). _{_{2), "V 2 O 5}} _SG_1: 4" ( example _{_{3), "V 2 O 5}} _SG_1: 5" was (Comparative example 2).

[Comparative Example 3]
Vanadium pentoxide (V ₂ O ₅ ) obtained by thermally decomposing ammonium vanadate (NH ₄ VO ₃ ) in air at 300° C. for 4 hours was used as a denitration catalyst of Comparative Example 3. The sample name of the denitration catalyst of Comparative Example 3 was “V ₂ O _{5 —} 300”.

[Comparative Example 4]
Vanadium pentoxide obtained by thermally decomposing ammonium vanadate in air at 400° C. for 4 hours was used as a denitration catalyst of Comparative Example 4. The sample name of the denitration catalyst of Comparative Example 4 was “V ₂ O _{5 —} 400”.

[Comparative Example 5]
Vanadium pentoxide obtained by thermally decomposing ammonium vanadate in air at 500° C. for 4 hours was used as a denitration catalyst of Comparative Example 5. The sample name of the denitration catalyst of Comparative Example 5 was “V ₂ O _{5 —} 500”.

FIG. 5 shows the NH ₃ —SCR activity of the V ₂ O ₅ —SG catalyst. FIG. 5(a) shows the NO conversion rate at each reaction temperature in the NH ₃ —SCR reaction using each catalyst. Further, FIG. 5( b) shows the relationship between the vanadium:oxalic acid ratio and the NO conversion rate at a reaction temperature of 120° C. In Example 2 (V ₂ O ₅ _SG_1:3), which is a catalyst having a vanadium:oxalic acid ratio of 1:3, the NO conversion was the highest, and when oxalic acid was added further, the NO conversion decreased. .. Example 3 (V ₂ O ₅ _SG_1:4) had a lower NO conversion rate than Example 1 (V ₂ O ₅ _SG_1:2), despite having a larger specific surface area.

In FIG. 6, each of V ₂ O ₅ _SG of Examples 1 to 3 and Comparative Example 1, and the above Comparative Example 3 (V ₂ O ₅ _300), Comparative Example 4 (V ₂ O ₅ _400), and Comparative Example 5 are shown. The relationship between the BET specific surface area and the NO conversion rate in (V ₂ O _{5 —} 500) is shown. The plots indicated by square points show the relationship between the BET specific surface area after the selective catalytic reduction reaction and the NO conversion rate in Example 2 (V ₂ O ₅ _SG_1:3). Again, the NO conversion was shown to be highest in Example 2 (V ₂ O ₅ _SG_1:3), which is a catalyst with a vanadium:oxalic acid ratio of 1:3.

The amount of acid sites on the catalyst surface can be estimated by NH ₃ -TPD (TPD: thermal desorption program). Therefore, using Bellcat manufactured by Microtrac Bell, in a device, Comparative Example 3 (V ₂ O ₅ _300), Comparative Example 4 (V ₂ O ₅ _400), Comparative Example 5 (V ₂ O ₅ _500), 0.1 g of each catalyst of Example 1 (V ₂ O ₅ _SG_1:2) and Example 2 (V ₂ O ₅ _SG_1:3) was pretreated for 1 hour at 300° C. under He (50 ml/min) flow. .. Then, the temperature was lowered to 100° C., and 5% ammonia/He (50 ml/min) was passed for 30 minutes to adsorb ammonia. The flowing gas was switched to He (50 ml/min), the temperature was stabilized for 30 minutes, the temperature was raised at 10° C./min, and ammonia having a mass number of 16 was monitored by a mass spectrometer.

Comparative Example 3 (V ₂ O ₅ _300), Comparative Example 4 (V ₂ O ₅ _400), Comparative Example 5 (V ₂ O ₅ _500), Example 1 (V ₂ O ₅ _SG_1:2), Example 2 ( Table 1 shows the measurement results of the amount of NH ₃ desorption when each of V ₂ O ₅ —SG — 1:3) was used.
When the values of these NH ₃ desorption amount and the BET specific surface area of each catalyst are plotted, the graph of FIG. 7 is obtained. As can be seen from the graph of FIG. 7, it was shown that the amount of NH ₃ desorbed increases substantially in proportion to the BET specific surface area of V ₂ O ₅ . Moreover, when the correspondence between the NH ₃ desorption amount of each catalyst and the NO conversion rate was plotted, the graph of FIG. 8 was obtained. That is, it was shown that the NO conversion rate increases as the amount of NH ₃ desorbed=the amount of acid sites on the catalyst surface increases.

As described above, in the selective catalytic reduction reaction using ammonia as a reducing agent, the denitration catalyst containing vanadium oxide in an amount of 43 wt% or more in terms of vanadium pentoxide and having a specific surface area of 30 m ² /g or more is 200 High denitration efficiency at low temperature below ℃. On the other hand, no SO ₂ oxidation is observed.

In the second denitration apparatus 70, vanadium oxide is present at 43 wt% or more in terms of vanadium pentoxide, and a denitration catalyst having a specific surface area of 30 m ² /g or more is used. Even if it exists, it can exert a high denitration effect. Therefore, the second denitration device 70 suppresses the emission amount of nitrogen oxides in the entire combustion system 1 to be equal to or less than the regulation value, and therefore the first denitration device 30 is decomposed due to deterioration of the denitration catalyst. It becomes possible to remove nitrogen oxides that could not be cut off.

FIG. 9 is a functional block diagram of the second denitration device 70. The second denitration device 70 includes an ammonia injection unit 751, a nitrogen oxide concentration detection unit 752, and an ammonia injection control unit 753 as functional blocks.

The ammonia injection unit 751 injects ammonia into the exhaust gas after the soot dust is collected in the dust collector 60.
The nitrogen oxide concentration detector 752 detects the nitrogen oxide concentration at the outlet of the second denitration device 70.
The ammonia injection control unit 753 controls the amount of ammonia injection by the ammonia injection unit 751 based on the nitrogen oxide concentration detected by the nitrogen oxide concentration detection unit 752.

The second denitration device 70 having the above-mentioned configuration makes it possible to control the injection amount of NH ₃ so that the emission amount of nitrogen oxides in the entire combustion system 1 becomes equal to or less than the regulation value.

[1.4 Effects of First Embodiment]
As described above, the combustion system 1 according to the first embodiment configured as described above is disposed in the exhaust passage L1 through which the exhaust gas generated from the boiler 10 that burns the fuel flows, and the exhaust passage L1. The first denitration device 30 for removing nitrogen oxides from the exhaust gas discharged from the boiler 10 by the catalyst, and the second denitration catalyst from the air preheater 40 at the latter stage of the air preheater 40 arranged in the exhaust passage L1. The second denitration device 70 is provided with a second denitration device 70 that removes nitrogen oxides from the exhaust gas that is discharged. The first denitration device 30 controls the ammonia injection amount based on the leak NH ₃ amount, and the second denitration device 70 The amount of ammonia injection is controlled based on the nitrogen oxide concentration at the outlet of the denitration device.

As a result, even if the denitration catalyst used in the first denitration device 30 is deteriorated, the amount of leak NH ₃ leaked in the first denitration device 30 is suppressed to a predetermined value or less, and the nitrogen oxide exceeding the regulation value is exceeded. Can be removed. Further, it becomes possible to suppress the clogging of the air preheater 40 due to ammonium sulfate.

In addition, the second denitration device 70 uses vanadium pentoxide in an amount of 43 wt% or more, has a BET specific surface area of 30 m ² /g or more, and uses a denitration catalyst used for denitration at 200° C. or lower.

As a result, by using the denitration catalyst capable of low-temperature denitration in the second denitration device 70, the nitrogen oxides that could not be completely removed in the first denitration device 30 in order to suppress the amount of leak NH ₃ were removed. It is possible to remove the denitrification device 30 at a later stage.

[2. Second Embodiment]
[2.1 Overall configuration]
FIG. 10 is an overall configuration diagram of a combustion system 1A according to the second embodiment of the present invention. In addition, in order to make the description easy to understand, the difference between the combustion system 1A according to the second embodiment and the combustion system 1 according to the first embodiment will be mainly described below.

Unlike the combustion system 1, the combustion system 1A does not include the second denitration device 70 as shown in FIG. Instead, in the combustion system 1A, the chimney 110A has a function as a second denitration device.

The chimney 110A has therein a denitration device that uses the same denitration catalyst as that used in the second denitration device 70 in the first embodiment. 11A to 11C show the internal structure of the chimney 110A.

[2.2 Chimney]
For example, as shown in FIG. 11A, the chimney 110A may be provided with a spiral groove 111 on the inner wall of the chimney 110A, and the low temperature denitration catalyst containing vanadium may be applied to the groove 111. Alternatively, as shown in FIG. 11B, a stepwise fin 112 may be provided on the inner wall of the chimney 110A, and the low temperature denitration catalyst may be applied to the fin 112.
More specifically, the low-temperature denitration catalyst is applied to the refractory bricks forming the spiral groove 111 and the stepped fin 112, and then fired to form the inner wall of the chimney 110A as the second denitration device. Is possible.

In a chimney provided in a normal combustion system, the degree of deterioration of refractory bricks due to corrosion increases as the years of use elapse, but the degree of deterioration can be reduced by applying a low-temperature denitration catalyst containing vanadium. It will be possible.

Alternatively, as shown in FIG. 11C, a denitration catalyst layer 113 having a honeycomb catalyst may be installed inside the chimney 110A, similarly to the second denitration device 70 included in the combustion system 1 of the first embodiment. Good. The denitration catalyst layer 113 may be installed in one stage or in multiple stages.

Since the height of the chimney of a power plant is generally around 200 m, it is preferable to apply the denitration catalyst or install the denitration catalyst at a position as low as possible for maintenance.
When applying the denitration catalyst to the spiral groove 111 and the stepped fin 112, it is possible to apply from the lowermost part to the uppermost part of the chimney, but since the cost increases as the amount of catalyst increases, from the lowermost part, It is advisable to apply the resin to a height such that the required amount of catalyst associated with the amount of exhaust gas can be secured. In addition, when the denitration catalyst layer 113 is additionally stacked, the denitration catalyst layer 113 having a honeycomb catalyst coated with the denitration catalyst may be installed at a height of 2 m to 25 m in the stack. This assumes that the honeycomb catalyst is about 1 m at the longest and the gap between the denitration catalyst layers 113 is about 3 m at the highest, and it is assumed that five denitration catalyst layers are installed.

[2.3 Effect of Second Embodiment]
As described above, the combustion system 1A according to the second embodiment configured as described above can achieve the same effect as the combustion system 1 according to the first embodiment.

Further, in the combustion system 1A, by using the chimney as the second denitration device, the space of the second denitration device 70 in the combustion system 1 becomes unnecessary, and the low temperature denitration catalyst containing vanadium is applied to the inner wall of the chimney. This makes it possible to suppress corrosion.

1 1A Combustion system 10 Boiler 20 Pulverized coal machine 30 70 Denitrification device 40 Air preheater 50 Gas heater 60 Dust collector 80 Induction fan 90 Desulfurization device 100 Gas heater 351 751 Ammonia injection part 352 Ammonia amount detection part 353 753 Ammonia injection control part 752 Nitrogen oxide concentration detector

Claims

A boiler that burns fuel,
An exhaust passage through which exhaust gas generated by burning the fuel in the boiler flows,
A first denitration device that is disposed in the exhaust passage and that removes nitrogen oxides from the exhaust gas discharged from the boiler by the first denitration catalyst;
In the latter stage of the first denitration device arranged in the exhaust passage, heat is exchanged between the exhaust gas and the combustion air, the combustion air after heat exchange is supplied to the boiler, and the exhaust gas after heat exchange is discharged. Air preheater to discharge,
A second denitration device that is disposed in the exhaust path and is provided at a subsequent stage of the air preheater to remove nitrogen oxides from the exhaust gas discharged from the air preheater by the second denitration catalyst;
The first denitration device is
A first ammonia injection part for injecting ammonia into the exhaust gas;
An ammonia amount detector that detects the amount of leaked ammonia at the outlet of the first denitration device;
A first ammonia injection control unit that controls the ammonia injection amount by the first ammonia injection unit based on the amount of leaked ammonia detected by the ammonia amount detection unit,
The second denitration device is
A second ammonia injection part for injecting ammonia into the exhaust gas;
A nitrogen oxide concentration detector for detecting the nitrogen oxide concentration at the outlet of the second denitration device;
A combustion system comprising: a second ammonia injection control unit that controls an ammonia injection amount by the second ammonia injection unit based on the nitrogen oxide concentration detected by the nitrogen oxide concentration detection unit.
The said 2nd denitration apparatus uses vanadium pentoxide 43 wt% or more, BET specific surface area is 30 m 2 /g or more, and uses a denitration catalyst used for denitration at 200° C. or less. Combustion system.
The combustion system according to claim 1 or 2, wherein the first ammonia injection control unit controls the ammonia injection amount so that the amount of leaked ammonia detected by the ammonia amount detection unit is 5 ppm or less.
At the end of the exhaust passage, a chimney that emits exhaust gas into the atmosphere is installed,
The combustion system according to any one of claims 1 to 3, wherein the second denitration device is installed in the chimney.