JPH07136464A - Apparatus and method for treating nitrogen oxide in exhaust gas - Google Patents

Abstract

PURPOSE:To provide an apparatus and method for converting efficiently NOx in exhaust gas, the temperature of which ranges from room temperature to a high temperature, into harmless compounds. CONSTITUTION:An adsorption column 5 filled with an adsorbent for NOx is installed in front of a reaction column filled with a denitration catalyst 14. When the temperature of exhaust gas is low, the gas is fed to the adsorption column 5; when the temperature is high, the gas is fed directly to the reaction column from a bypass 8 without passing through the adsorption column 5. For low temperature exhaust gas with its NOx concentration being a defined value or below, a part or all of the exhaust gas which passed through the adsorption column 5 can bypass the reaction column. The addition of a reductant for NOx is controlled on the basis of the measured value of a concentration sensor for NOx in the exhaust gas between the adsorption column 5 and the reaction column. A NOx concentration sensor 9 and a means for measuring the rate of change of NOx concentration by time are installed downstream from the reaction column, and the addition of the reductant can also be controlled based on the measured values.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and method for treating, removing and detoxifying exhaust gas containing nitrogen oxides.

[0002]

2. Description of the Related Art At present, nitrogen oxides (N) contained in various exhaust gases including exhaust gas emitted from thermal power plants
Ox) can be removed by contacting it with a catalyst in the presence of a reducing agent such as ammonia to convert it into nitrogen, by adsorbing it with an adsorbent, and irradiating it with an electron beam in the presence of ammonia to convert it to ammonium nitrate. It is known how to do it. Among them, the ammonia catalytic reduction method is widely used mainly for the treatment of exhaust gas from large-scale thermal power plants, and a method using a titanium oxide-based catalyst as disclosed in JP-A-52-22839 is typical. .

[0003]

However, in the conventional ammonia catalytic reduction method, the efficient operating temperature of the catalyst is usually 300.
Since the temperature is not lower than 0 ° C and the temperature of not lower than 250 ° C is required even in the case of a low temperature active catalyst, there is a drawback that the removal efficiency is not sufficient when the exhaust gas temperature is low. Further, normally, even if the exhaust gas temperature is 300 ° C. or higher, the NOx removal rate will be low if the exhaust gas temperature or the temperature of the catalyst layer has not risen sufficiently at startup, such as in a gas turbine. There was a flaw. As one of the solutions to this drawback, as disclosed in JP-A-58-124107, when the NOx concentration in the exhaust gas may exceed the regulation value before the catalyst reaches the operating temperature, the inside of the combustion chamber There is a method of reducing the NOx emission by changing the combustion state by injecting steam or water into. However, injecting a large amount of water will reduce the thermal efficiency of the combustor, so this method will reduce NO.
It is not realistic to significantly reduce x emissions.

On the other hand, it is known that a method using an adsorbent is effective as a method for removing NOx at a low temperature. However, with this method, although removal of NOx at a low temperature is relatively easy, there is a problem that the adsorption capacity is lowered and the NOx removal efficiency is lowered when the exhaust gas temperature is high. Furthermore, after reaching the saturated adsorption, it is necessary to replace or regenerate the adsorbent, which is economically problematic in treating exhaust gas containing a large amount of NOx. Further, when trying to regenerate the adsorbent, it is necessary to detoxify the NOx released during regeneration. An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to provide an apparatus and method for efficiently detoxifying NOx in exhaust gas from a room temperature region to a high temperature region of 500 ° C. or higher. In particular, an object of the present invention is to provide an apparatus and method capable of covering a temperature range in which the conventional ammonia reduction method does not show sufficient efficiency when the exhaust gas temperature is low at the time of starting a gas turbine, a boiler or the like. .

[0005]

The above objects of the present invention can be achieved by the following constitutions. That is, in a method of converting nitrogen oxides in exhaust gas in the presence of a catalyst with a reducing agent to render them harmless, a reaction tower filled with a catalyst for reducing nitrogen oxides and a reducing agent for the reducing agent added to the reaction tower Addition means, a treatment device for nitrogen oxides in the exhaust gas, which installs an adsorption tower filled with a nitrogen oxide adsorbent in the exhaust gas passage in the preceding stage of the reaction tower,
Alternatively, a method for treating nitrogen oxides in exhaust gas, in which the nitrogen oxides are mainly adsorbed and removed by an adsorbent in a region where the exhaust gas temperature is low, and the nitrogen oxides are reduced and removed by a reduction catalyst for the nitrogen oxides in a region where the exhaust gas temperature is high. Is.

The feature of the present invention resides in that an adsorption tower filled with a NOx adsorbent is installed in front of a reaction tower filled with a NOx reduction catalyst (denitration catalyst). Furthermore, the present invention allows a part or all of the exhaust gas to bypass the adsorption tower and directly
A configuration may be used in which a bypass line is installed to flow into a reaction tower filled with a NOx reduction catalyst. Furthermore, the present invention may have a configuration in which a bypass line is installed for bypassing a part or all of the exhaust gas after passing through the adsorption tower to the reaction tower.
In addition, the present invention uses NO in the exhaust gas passage between the adsorption tower and the reaction tower.
An x concentration measuring means may be provided, and a reducing agent adding means may be provided for controlling the amount of the reducing agent added to the reaction tower based on the measured value of the NOx concentration measuring means. Further, as a control method different from this, the present invention is provided with measuring means for the NOx concentration in the exhaust gas and the time change rate of the NOx concentration respectively in the exhaust gas passage downstream of the reaction tower, and the measurement values of both the measuring means are used as a reference. As a configuration, a reducing agent addition means for controlling the addition amount of the reducing agent to the reaction tower may be provided.

In the present invention, NOx in the exhaust gas is removed by the action of the adsorbent and / or the denitration catalyst depending on its temperature range. Therefore, when a part or all of NOx in the exhaust gas is removed by the adsorption tower, it is not always necessary to add a reducing agent before the reaction tower. When NOx is released into the exhaust gas, the NOx concentration may be higher than the original exhaust gas. In this case, it is necessary to increase the amount of the reducing agent added in front of the reaction tower in proportion thereto. Therefore, the amount of reducing agent added is controlled by the adsorption tower (adsorbent) and the reaction tower (reduction catalyst).
During this period, that is, immediately before the NOx removal catalyst, the NOx concentration is measured,
It is desirable to add a reducing agent corresponding to the amount.

Further, as a control method different from this, a means for measuring the NOx concentration in the exhaust gas and the time change rate of the NOx concentration is provided in the downstream of the reaction tower (reduction catalyst), and the denitration catalyst inlet is based on these values. It is also possible to predict the change in the NOx concentration over time and control the addition amount of the reducing agent necessary for reducing and purifying NOx based on the result. In this case, it is desirable to refer to the reaction characteristic data of the denitration catalyst evaluated under various reaction conditions in combination with information such as the temperature of the inlet or the inside of the denitration catalyst, the flow rate of the exhaust gas, and the amount of the reducing agent added.

The adsorption tower used in the present invention may be a fixed bed adsorption tower filled with a granular or honeycomb adsorbent, a fluidized bed adsorption tower using a granular or powdery adsorbent, and the like. The form of the tower is not limited. It is also possible to provide a plurality of adsorption towers and use them by switching them depending on the exhaust gas conditions, or to add a device for exchanging the NOx adsorbent in the adsorption tower with a new one during the operation of the plant. The form of the reaction tower used in the present invention is not particularly limited. It is possible to use a reactor in which an ordinary granular, honeycomb-shaped, or plate-shaped denitration catalyst is installed.

In the present invention, the types of the NOx adsorbent and the denitration catalyst are not particularly limited. As an example, as the adsorbent, various zeolites, clay minerals, oxides such as alumina, silica and titania, iron compounds,
Perovskite compounds, other metals and noble metals can be used. Further, a substance that not only adsorbs but also reacts with NOx to form and immobilize a compound such as metal nitrate under the condition that the reaction tower is operating.
Can be used as long as it can release the adsorbent and recover the adsorption ability. The shape of the adsorbent may be granular, plate-shaped, honeycomb-shaped or the like, and is not particularly limited. It is also possible to use a powdery adsorbent in a fluidized bed adsorption tower. On the other hand, as the denitration catalyst, various metal oxides such as V, Mo, W, and Fe or noble metals are supported on titania, various zeolites and various metals or noble metals are supported on zeolite, and perovskite is also used. Complex oxides can also be used. In the method of the present invention, as the NOx reducing agent, ammonia, urea, carbon monoxide, various hydrocarbons and the like can be used and are not particularly limited.

[0011]

According to the method of the present invention, when the exhaust gas temperature is lower than 250 ° C., NOx is adsorbed and removed by the action of the NOx adsorbent installed in the preceding stage of the reaction tower filled with the denitration catalyst.
Further, when the exhaust gas temperature is 250 ° C. or higher, the NOx removal activity by the denitration catalyst in the latter stage is in a sufficiently high temperature range, so that high denitration efficiency can be obtained as a whole even if the capacity of the adsorbent decreases. Furthermore, in a power generation system that repeatedly starts and stops like a gas turbine, when the exhaust gas temperature is low, NOx is adsorbed and removed by the adsorbent in the previous stage, and the adsorbent is regenerated with the rise in exhaust gas temperature, that is, the adsorbed NOx is released. Is done automatically. Therefore, it is not necessary to provide a special adsorbent regeneration means. Further, when NOx is released from the adsorbent, since the NOx removal catalyst in the latter stage is in a temperature range where it has sufficient activity, NOx and added reducing agents such as ammonia, urea, carbon monoxide, various hydrocarbons, etc. The reaction of 1) sufficiently progresses, and as a result, NOx in the exhaust gas is converted into nitrogen and rendered harmless.

Here, when the temperature of the exhaust gas is high, after regeneration of the adsorbent, the exhaust gas is bypassed through the adsorption tower (adsorbent) to bypass the adsorption tower, and after adding the reducing agent, flow directly into the reaction tower. Is also possible. For that purpose, it is necessary to install a line in which part or all of the exhaust gas bypasses the adsorption tower (adsorbent) and directly flows into the reaction tower filled with the nitrogen oxide reduction catalyst. This can prevent pressure loss in the adsorption tower (adsorbent). On the other hand, when the exhaust gas temperature is low, it is possible to bypass the gas reaction tower downstream of the adsorption tower (adsorbent) in the same manner. This can prevent pressure loss in the reaction tower.

As a system to which the present invention is applied, it is preferable that the exhaust gas temperature fluctuates by at least 100 ° C. or more. However, the temperature fluctuation referred to here includes not only the case where the temperature fluctuates periodically but also the case where the low-temperature exhaust gas is temporarily discharged such as when the gas turbine is started. If the exhaust gas temperature is always 300 ° C or higher, N
Ox can be removed by a conventional ammonia reduction method or the like. On the other hand, when the exhaust gas temperature is constantly low at 200 ° C. or lower, it can be dealt with by an adsorption method or the like. The present invention is a system that adopts the advantages of both the ammonia reduction method and the adsorption method and compensates for the drawbacks. In particular, the ammonia reduction method has a feature of the present invention in that it can cope with a low temperature range where the NOx removal rate is low. .

[0014]

EXAMPLES Examples of the present invention will be described in detail below. Example 1 FIG. 1 shows an example of a system in which the method of the present invention is applied to purify NOx in combustion exhaust gas from a boiler. The boiler 3 burns by supplying air 1 and fuel 2. The exhaust gas passes through the adsorption tower 5 and / or the bypass line 8 and passes through the reaction tower filled with the denitration catalyst 14 by reduction in the presence of ammonia, and is discharged as the purified gas 15.
When the temperature detected by the temperature sensor 10 of the denitration catalyst 14 is equal to or higher than the operation lower limit temperature of the denitration catalyst 14, the valve 12 is operated by a command from the control device 11 based on the value of the NOx concentration sensor 9 provided in the exhaust gas duct. After opening, the optimum amount of ammonia for reducing NOx in the exhaust gas is injected from the ammonia tank 13 to the upstream side of the denitration catalyst 14.

When the temperature detected by the temperature sensor 10 is lower than the operating lower limit temperature of the denitration catalyst 14, the valve 12 is closed and the supply of ammonia from the ammonia tank 13 to the denitration catalyst 14 is stopped. When the NOx value is measured by the NOx concentration sensor 9 and there is a possibility that the NOx value exceeds the emission control value, the valves 4 and 6 of the exhaust gas ducts before and after the adsorption tower 5 and the valve 7 of the bypass line 8 are instructed by the control device 11. The NOx in the exhaust gas is adsorbed by the adsorbent in the adsorption tower 5 so that a part or the whole of the exhaust gas passes through the adsorption tower 5, and the exhausted NOx concentration becomes equal to or lower than the regulation value.
NOx adsorbed by the adsorbent in the adsorption 5 is desorbed by passing a part or all of the exhaust gas through the adsorption tower 5 while the denitration catalyst 14 is operating. NOx released
Is reduced and purified together with NOx in the combustion exhaust gas by the denitration catalyst 14.

FIG. 2 shows an operating method at the time of startup of the plant to which the nitrogen oxide treatment system of FIG. 1 is applied. When the combustion of the boiler 3 is started in a state where the exhaust gas does not flow to the adsorption tower 5 and the ammonia from the ammonia tank 13 is not added to the exhaust gas, the NOx concentration discharged from the plant is as shown by C ₁ in FIG. And the emission control value C ₀ is exceeded. However, when the NOx concentration rises to near the emission control value C ₀ , the valves 4 and 6 are gradually opened, and the valve 7 is gradually throttled to allow the exhaust gas to flow through the adsorption tower 5, whereby the NOx concentration in the exhaust gas is reduced. It is reduced to below the regulation value like C ₂ . After that, when the adsorption tower 5 reaches the NOx desorption temperature T ₁ as the exhaust gas temperature rises, the NOx concentration in the exhaust gas rises like C ₃ . But no
Before reaching the x desorption temperature T ₁ , the injection of ammonia is started when the temperature of the denitration catalyst 14 reaches the operation lower limit temperature T ₀ , and the optimum amount of ammonia is added with the NOx concentration sensor 9 as a reference. Therefore, N in the exhaust gas like C ₄
The Ox concentration is reduced to the regulation value C ₀ or less. When NOx desorption from the adsorption tower 5 is completed, the valves 4 and 6 are closed and the valve 7 is opened to start the steady operation.

Example 2 This example corresponds to the system shown in FIG. 1 provided with a plurality of adsorption towers. A conceptual diagram of the system is shown in FIG. An adsorption tower 17 is installed in the exhaust gas duct in parallel with the adsorption tower 5. When the operation of the boiler 3 is stopped while NOx is adsorbed on a part of the adsorbent of the adsorption tower 5, and when the adsorption tower 5 cannot adsorb NOx sufficiently when the operation is restarted, exhaust gas ducts before and after the adsorption tower 17 are provided. The exhaust NOx concentration can be made equal to or less than the regulated value by opening the valves 16 and 18 in the above and passing a part or all of the exhaust gas through the adsorption tower 17 to adsorb NOx on the adsorbent in the adsorption tower 17.

Embodiment 3 A conceptual diagram of this embodiment is shown in FIG. In this embodiment, a flow path switching valve 19 is provided in the exhaust gas duct upstream of the denitration catalyst 14 of the system shown in FIG. 1, and a bypass line 20 in which a part or all of the exhaust gas bypasses the denitration catalyst 14 is provided. It is a corresponding system. Temperature sensor 10
When the temperature of the exhaust gas detected in 1 is lower than the lower limit operating temperature of the denitration catalyst 14 and the value of the NOx concentration sensor 9 is lower than the NOx emission regulation value, the valve 19 is operated by a command from the control device 11 A part or all of the gas can be passed through the bypass line 20 to reduce the pressure loss of the exhaust gas flow. If the value of the NOx concentration sensor 9 is equal to or higher than the NOx emission regulation value, the exhaust gas is passed through the denitration catalyst 14. Other operations are the same as in Example 1.

Example 4 An example of a system in which the method for treating nitrogen oxides according to the present invention is applied to purify NOx in combustion exhaust gas of a gas turbine is shown in FIG.
Shown in. The combustion exhaust gas from the gas turbine 21 passes through the heat exchanger 22 and is then NO in the adsorbent 23 and the denitration catalyst 24.
x is purified and is discharged as purified gas 15 from the chimney 26 through the heat exchanger 25. NOx concentration in exhaust gas is NO
The x concentration sensor 9 and the temperature sensor 10 measure the inlet temperature of the denitration catalyst 24. The temperature of the sensor 10 is the denitration catalyst 2
4 exceeds the lower limit operating temperature, the measured value of the sensor 9 is used as a reference, and the valve 1 is instructed by the controller 11
2 is operated and NO in the exhaust gas from the ammonia tank 13
Inject the optimum amount of ammonia for the reduction of x.

Embodiment 5 An embodiment of a system in which the nitrogen oxide treatment method of the present invention is applied to purify NOx in combustion exhaust gas of a gas turbine is shown in FIG.
Shown in. The system shown in FIG. 6 uses a reactor 27 in which the adsorbent 23 and the denitration catalyst 24 of FIG. 5 are integrated, and ammonia is injected into the exhaust gas duct upstream of the reactor 27. After passing through the heat exchanger 22, the combustion exhaust gas from the gas turbine 21 is purified of NOx by a reactor 27 in which an adsorbent 23 and a denitration catalyst 24 are integrated, and passes through a heat exchanger 25 to produce a purified gas 15 from a chimney 26. Is discharged. NOx concentration sensor 9 for measuring NOx concentration in exhaust gas
In addition, the temperature sensor 10 measures the inlet temperature of the denitration catalyst.

When the temperature of the sensor 10 exceeds the operating lower limit temperature of the denitration catalyst 24, the control device 11 causes the sensor 9 to operate.
Based on the NOx concentration obtained from the above, the time change rate of the NOx concentration is calculated. Based on these values, the temperature obtained from the sensor 10, and the ammonia injection amount obtained from the opening degree of the valve 12, the denitration catalyst 24 stored in the controller 11 in advance is stored.
The transition of the NOx concentration at the inlet of the denitration catalyst 24 is predicted using the reaction characteristic data of 1., the valve 12 is operated based on the result, and the optimum amount of ammonia for reducing NOx in the exhaust gas is injected from the ammonia tank 13. . When the temperature of the sensor 10 is equal to or lower than the operation lower limit temperature of the denitration catalyst 24, the valve 12 is closed and the supply of ammonia is stopped.

[0022]

According to the present invention, it is possible to efficiently remove nitrogen oxides in exhaust gas over a wide temperature range. In particular, it is very effective for removing nitrogen oxides in exhaust gas in a system in which the exhaust gas temperature changes from a low temperature region to a high temperature region.

[Brief description of drawings]

FIG. 1 is a diagram showing a flow of a flue gas denitration system according to an embodiment of the present invention.

FIG. 2 is a diagram showing one of plant operating methods to which the nitrogen oxide treatment system of the present invention is applied.

FIG. 3 is a diagram showing a flow of a flue gas denitration system according to an embodiment of the present invention.

FIG. 4 is a diagram showing a flow of a flue gas denitration system according to an embodiment of the present invention.

FIG. 5 is a diagram showing a flow of a flue gas denitration system according to an embodiment of the present invention.

FIG. 6 is a diagram showing a flow of a flue gas denitration system according to an embodiment of the present invention.

[Explanation of symbols]

1 ... Air, 2 ... Fuel, 3 ... Boiler, 4 ... Valve, 5 ... Adsorption tower, 6 ... Valve, 7 ... Valve, 8 ... Bypass line,
9 ... NOx concentration sensor, 10 ... Temperature sensor, 11 ... Control device, 12 ... Valve, 13 ... Ammonia tank, 14 ...
DeNOx catalyst, 15 ... Purified gas, 16 ... Valve, 17 ... Adsorption tower, 18 ... Valve, 19 ... Flow path switching valve, 20 ...
Bypass line, 21 ... Gas turbine, 22 ... Heat exchanger, 23 ... Adsorbent, 24 ... Denitration catalyst, 25 ... Heat exchanger,
26 ... Chimney, 27 ... Reactor

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B01D 53/56 53/74 53/81 53/86 ZAB B01D 53/34 129 E 129 A 53/36 ZAB (72) Inventor Hiroshi Miyadera 1-1-1, Omika-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi Research Laboratory

Claims (10)

[Claims] 1. Nitrogen oxide in exhaust gas in the presence of a catalyst,
In the method of converting and detoxifying with a reducing agent, a reaction tower filled with a catalyst for reducing nitrogen oxides, a reducing agent adding means of the reducing agent added to the reaction tower, and nitrogen in the exhaust gas passage in the preceding stage of the reaction tower. An apparatus for treating nitrogen oxides in exhaust gas, comprising an adsorption tower filled with an adsorbent for oxides. 2. The apparatus for treating nitrogen oxides in exhaust gas according to claim 1, wherein a part or all of the exhaust gas bypasses the adsorption tower and a bypass line for directly flowing into the reaction tower is installed. 3. The apparatus for treating nitrogen oxides in exhaust gas according to claim 1, wherein a bypass line is provided for bypassing a part or all of the gas that has passed through the adsorption tower to the reaction tower. 4. NO in the exhaust gas passage between the adsorption tower and the reaction tower
4. An x-concentration measuring means is provided, and a reducing agent adding means for controlling the addition amount of the reducing agent to the reaction tower is provided based on the measured value of the NOx concentration measuring means.
5. A treatment device for nitrogen oxides in exhaust gas according to any one of 1. 5. A reducing agent for the reaction tower based on the measured values of the NOx concentration in the exhaust gas and the time change rate of the NOx concentration provided in the exhaust gas passage downstream of the reaction tower, respectively. The apparatus for treating nitrogen oxides in exhaust gas according to any one of claims 1 to 4, further comprising a reducing agent addition means for controlling the addition amount of 6. Exhaust gas characterized by mainly adsorbing and removing nitrogen oxides by an adsorbent in a region where exhaust gas temperature is low, and reducing and removing nitrogen oxides by a reduction catalyst for nitrogen oxides in a region where exhaust gas temperature is high. Method for treatment of nitrogen oxides in water. 7. A catalyst for reducing nitrogen oxides directly in a region where the exhaust gas temperature is low, where the exhaust gas is mainly treated with an adsorbent, and in a region where the exhaust gas temperature is high, a part or all of the exhaust gas is not treated with the adsorbent. The method for treating nitrogen oxides in exhaust gas according to claim 6, wherein the nitrogen oxides are reduced and removed by means of. 8. The exhaust gas according to claim 6, wherein a part or all of the gas treated with the adsorbent is discharged to the outside of the system without being subjected to the reduction treatment of the nitrogen oxides by the nitrogen oxide reduction catalyst. Method for treatment of nitrogen oxides in water. 9. The additive amount of the nitrogen oxide reducing agent is controlled based on the NOx concentration in the exhaust gas after the adsorption treatment and before the nitrogen oxide reduction treatment by the reduction catalyst. 9. The method for treating nitrogen oxides in exhaust gas according to any one of 8 to 8. 10. The addition amount of the reducing agent for nitrogen oxide treatment is controlled on the basis of the NOx concentration in the exhaust gas after the reduction treatment of nitrogen oxides by the reduction treatment and the time change rate of the NOx concentration. The method for treating nitrogen oxides in exhaust gas according to any one of claims 6 to 9.