JP3347762B2 - Method and apparatus for removing nitrous oxide from exhaust gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION This invention related to nitrous oxide (N ₂ O) removal method contained in the exhaust gas during the time of load change, particularly
Re-use the nitrous oxide removal catalyst during the removal of nitrous oxide in exhaust gas.
Related to how to live.

[0002]

2. Description of the Related Art In recent years, environmental problems such as global warming caused by artificially emitted carbon dioxide (CO ₂ ) and other greenhouse substances and destruction of the ozone layer due to chlorofluorocarbons have been highlighted. In the case of a fluidized-bed boiler, nitrous oxide (N ₂ O), which contributes to both destruction of the ozone layer, is 1/3 to 1/3 of the amount of nitrogen monoxide (NO) and nitrogen dioxide (NO ₂ ) contained in exhaust gas. There is a report that it reaches 1/5 volume.

[0003] Currently, the titanium oxide-based catalysts has become the mainstream of the stationary source denitration catalyst, almost no ammonia reduction activity of N ₂ O, N ₂ O in the exhaust gas is directly released into the atmosphere At present, the development of a highly active N ₂ O removal catalyst is being promoted.

[0004]

Since the N ₂ O removal catalyst under development is a catalyst that thermally decomposes N ₂ O, the removal activity greatly varies depending on a change in gas temperature. For example, when starting or stopping a fluidized bed boiler or when changing a low load,
The N ₂ O concentration in the fluidized-bed boiler exhaust gas tends to increase, but at this time, when the gas temperature is low, the N ₂ O exhaust gas is not removed and is directly released into the atmosphere. .

Further, in order to utilize the thermal decomposition reaction of the N ₂ O removal catalyst, a high N
_{Although a 2} O removal rate can be obtained, the oxidation rate of sulfur dioxide (SO ₂ ) also becomes higher than the N ₂ O removal rate with the reaction temperature. Therefore, the N ₂ O removal catalyst layer must always be installed in a high temperature range. Can not.

Further, the above-mentioned N ₂ O removal catalyst is a catalyst which is liable to be deteriorated as compared with currently used catalysts for NO and NO _2, for example, a titanium oxide catalyst. An object of the present invention, N ₂ O removal during N ₂ O removal process operation of the exhaust gas
Emissions from combustion equipment such as boilers, including catalyst regeneration methods
It is an object of the present invention to provide a method for removing N ₂ O in a gas .

[0007]

The above object of the present invention is achieved by the following constitution. That is, the nitrous oxide-removing catalyst layer for removing nitrous oxide in exhaust gas discharged from the combustion device, relatively fed together from a combustion device and the exhaust gas ratio較低temperature to the operating conditions of the combustion apparatus A high-temperature, high-temperature gas is introduced with its mixing ratio adjusted , and nitrous oxide is added.
When the activity of the element removal catalyst decreases, the relatively high temperature
To regenerate the activity of the nitrous oxide removal catalyst
That is a nitrous oxide removal method in the exhaust gas.

[0008] Here, the operating conditions of the combustion device is detected on the basis of nitrous least one measurement of nitric oxide concentration and the exhaust gas temperature in the exhaust gas, when the measured value is within the setting range relatively low temperature Introducing the exhaust gas, when the nitrous oxide concentration in the exhaust gas tends to increase or when the exhaust gas temperature tends to decrease, the rate of increase in the nitrous oxide concentration in the exhaust gas or the decrease in the exhaust gas temperature One of the methods is to mix a relatively high-temperature gas discharged from a combustion device with the exhaust gas and introduce the mixed gas into the nitrous oxide removal catalyst layer so as to obtain an optimum temperature condition for nitrous oxide removal according to the rate. Is the way.

A mixed gas of the exhaust gas and the high-temperature gas is introduced into the nitrous oxide removal catalyst layer at a predetermined mixing ratio of the exhaust gas and the high-temperature gas according to a program preset according to the operating conditions of the combustion apparatus. A method can also be adopted.

[0010]

The exhaust gas usually introduced into the nitrous oxide removal catalyst layer is, for example, a temperature of 300 to 55 in a fluidized bed boiler.
The exhaust gas is about 0 ° C., and the high-temperature gas is, for example, a gas in a temperature range of 600 to 900 ° C. in a fluidized-bed boiler. The optimum temperature is selected according to the component of the N ₂ O removal catalyst. Adjust the exhaust gas temperature to the optimum temperature or adjust the ratio of exhaust gas to high temperature gas to obtain N ₂ O
It is desirable to introduce it into the removal catalyst layer.

The combustion apparatus of the present invention is a fluidized-bed boiler, an engine of a car, a waste incinerator of a hospital, and the like. The N ₂ O removal catalyst used in the present invention is as shown in Table 1, and an appropriate use temperature differs depending on the catalyst component.

(Table 1) Carrier Operating temperature (300 to 550 ° C.) Operating temperature (500 to 750 ° C.) Al ₂ O ₃ , ZrO ₂ , Rh, Pt, Ir, Co, Fe, SiO ₂ Pd, Ru Ni, Cu silicalite, Rh, Pd, Ru, mordenite Ir, Fe, Cu perovskite _{La 1.5 Sr 0.5 CuO 4 La 0.8} Sr 0.2 CoO 3

[0014]

The optimum temperature for use differs depending on the components of the N ₂ O removal catalyst as shown in Table 1. However, since the temperature of the exhaust gas changes depending on the operating conditions of a combustion device such as a boiler, which is an exhaust gas generating source, it is necessary to adjust the ambient temperature of the N ₂ O removal catalyst. That is, when the boiler is started, stopped,
Alternatively, by introducing a high-temperature gas into the N ₂ O catalyst layer at a low load, the N ₂ O concentration at the outlet of the catalyst layer does not suddenly change and a large amount of N ₂ O gas is not released into the atmosphere. . When the activity of the N ₂ O removal catalyst decreases,
By introducing only a relatively high-temperature hot gas, the N ₂ O removal catalyst
Activity can be regenerated.

[0015]

Embodiments of the present invention will be described below. In removing N ₂ O from the exhaust gas from the combustion apparatus according to the present invention, an experiment was conducted as a preliminary experiment to confirm the change in activity of the N ₂ O removal catalyst with respect to the gas temperature. The N ₂ O removal catalyst used is as follows. Experimental Example 1 FIG. 2 shows the change in the activity of the N ₂ O removal catalyst with respect to the gas temperature. 200 ppm of NO as gas, 150 N ₂ O
It is a result measured using a synthetic simulation gas of ppm, O ₂ 3%, H ₂ O 10%, and SO ₂ 100 ppm. As shown in FIG. 2, when the gas temperature is easily affected by a change in the temperature and the gas temperature decreases, the activity suddenly deteriorates.

FIG. 1 is an overall system diagram in which an embodiment of the present invention is applied to purification of exhaust gas containing a large amount of N ₂ O gas from a fluidized bed boiler 1. The fluidized-bed boiler 1 has a split economizer 2,
3. The superheater 4 is arranged, and the superheated steam is supplied to the turbine 5. Exhaust gas from the fluidized-bed boiler 1 is guided via a duct 6 to a catalyst layer 7 filled with the N ₂ O removal catalyst. Here after heat exchange N ₂ O is the heat of exhaust gas that is removed at one economizer 3, NO, is introduced into the NO ₂ removing device 9, NH ₃ from NH ₃ injection line 10 and the NO, NO
_The exhaust gas is purified by the reaction with the NO removal catalyst and the NO ₂ catalyst in the ₂ removal device 9. Incidentally, NO, titanium the de-NO of NO ₂ removal device 9, NO ₂ catalyst which is commonly conventionally,
An oxide such as tungsten, molybdenum, or vanadium or an oxide such as manganese, cobalt, or chromium is used.

At this time, about 300
Exhaust gas of ５550 ° C. is discharged from the duct 6,
The high-temperature gas of 00 to 900 ° C. is discharged from a high-temperature duct 11 provided near the superheater 4 and can be supplied to the N ₂ O removal catalyst layer 7. The exhaust gas duct 6 and the high-temperature duct 11 are provided with dampers 12 and 13, respectively. In addition, a bypass line 15 for the exhaust gas bypassing the economizer 3 and a damper 16 in the bypass line 15 are provided to remove N ₂ O by the exhaust gas. The temperature of the exhaust gas introduced into the catalyst layer 7 and the economizer 3 is controlled.

In the fluidized-bed boiler 1 of this embodiment, the N ₂ O removal catalyst layer 7 is usually arranged in a temperature range of about 300 to 550 ° C. when only the damper 12 is opened. As shown in Experimental Example 1, N ₂ O removal catalyst is susceptible to changes in temperature, the gas temperature decreases its activity becomes suddenly deteriorated, the concentration of N ₂ O N ₂ O removal catalyst layer outlet Get higher.

However, even if the N ₂ O concentration in the exhaust gas increases or the exhaust gas temperature decreases due to fluctuations in the operation of the fluidized bed boiler 1, FIG. 3 is set in advance according to the operating conditions of the fluidized bed boiler 1. According to the time chart shown in FIG. 5, the opening of the dampers 12, 13 is adjusted by the output of the damper opening adjusting device 17, and the high-temperature exhaust gas is introduced into the N ₂ O removal catalyst layer 7 to remove the N ₂ O gas. And a large amount of N ₂ O gas is not released to the atmosphere. At this time, the thermometers 1 respectively provided in the exhaust gas duct 6 and the high-temperature duct 11
9, 20 and the dampers 12, 13 are connected to the damper opening adjusting device 17
By cooperating with each other, the N ₂ O removal reaction in the N ₂ O removal catalyst layer 7 can be more accurately set to the optimum condition.

Furthermore, it is also closing adjustment of the damper 12, 13 by the command of the damper opening adjustment device 17 while measuring the N ₂ O concentration by the fluidized bed boiler 1 N ₂ O concentration measuring device 21 at the outlet of the exhaust gas.

When a high-temperature gas flows from the high-temperature duct 11,
By opening and closing the dampers 12, 13, the amount of gas in the economizer bypass line 15 is made smaller than usual and the amount of gas to the economizer 3 is increased, so that the economizer 3 can lower the temperature to a low temperature.

Although the N ₂ O removal catalyst used in the above embodiment of the present invention deteriorates, a method for reactivating the deteriorated N ₂ O removal catalyst has not been established yet at present. However, the present inventors have succeeded in reactivating the time-degraded N ₂ O removal catalyst by the following simple method.

The method comprises introducing a relatively low temperature exhaust gas which normally suppresses the oxidation of sulfur dioxide into a nitrous oxide removal catalyst layer for removing nitrous oxide in the exhaust gas discharged from the combustion device, This is a method for regenerating a nitrous oxide removing catalyst in which a high-temperature gas supplied from a combustion device is introduced when the activity of the nitrous oxide removing catalyst in the nitric oxide removing catalyst layer decreases.

The N ₂ O removal catalyst is considered to be deteriorated due to adsorption of oxygen, water, SO _2, etc., and the exhaust gas (fluidized bed boiler) has a higher temperature than the temperature normally used (300 to 550 ° C. in a fluidized bed boiler). It has been found that it is possible to provide a bypass line to introduce N ₂ O from the combustion device to the N ₂ O removal catalyst layer from the combustion device and to reactivate the N ₂ O removal catalyst layer by temporarily exposing it to a high-temperature gas.

An experiment for confirming the conditions for regenerating the N ₂ O removing catalyst with reduced activity was carried out as follows. That is, after flowing a simulated gas at 600 ° C. for 1 hour through the N ₂ O removal catalyst having deteriorated performance, NO 200 ppm, N ₂ O 150 ppm,
The N ₂ O removal rate was determined under the gas conditions of O ₂ 3%, H ₂ O 10%, and SO ₂ 100 ppm. It should be noted that the performance of N ₂ O
The removal rate of the removal catalyst was determined under the same gas conditions. FIG. 4 shows the results.

[0026] Thus, in the apparatus of FIG. 1, N ₂ O
When the performance of the removal catalyst decreases, the damper 13
The opening can be reactivated catalyst by than the gas temperature which normally use exposing the N ₂ O removal catalyst layer 7 in the hot exhaust gas (600 to 900 ° C.). Thus, by exposing the lowered N ₂ O removal catalyst to a high-temperature gas, the performance can be improved, and the catalyst can be used for a long time.

[0027]

According to the present invention, even if the N ₂ O concentration at the outlet of the N ₂ O removal catalyst may suddenly increase due to a change in operating conditions such as a change in the load of the combustion device, the high-temperature gas may be supplied in advance to the N ₂ O removal catalyst. _By introducing into the ₂ O removal catalyst layer, N ₂
O gas can be decomposed and removed. Further deteriorated N ₂ O removal contact
As a medium, only a relatively high-temperature gas is introduced to remove N ₂ O.
The activity of the medium can be easily regenerated and the same N ₂ O
The removal catalyst can be used for a long time.

[Brief description of the drawings]

FIG. 1 is an overall system diagram of one embodiment of the present invention.

FIG. 2 is a graph showing the performance of an N ₂ O removal catalyst according to one embodiment of the present invention.

FIG. 3 is a time chart of the exhaust gas temperature and the N ₂ O concentration according to the operating conditions of the fluidized-bed boiler of one embodiment of the present invention, and a time chart of the opening degrees of the exhaust gas duct and the high-temperature duct.

FIG. 4. Degraded N ₂ O removal catalyst and reactivated N ₂
It is a figure which shows the performance of an O removal catalyst.

[Explanation of symbols]

1: fluidized bed boiler, 2: 3, economizer, 4: superheater, 5:
Turbine, 6 ... exhaust gas duct, 7 ... N ₂ O removal catalyst layer,
9: NO and NO ₂ removal device, 11: high temperature duct, 12:
Exhaust gas duct damper, 13 High temperature gas duct damper, 1
7 ... damper opening adjustment device, 19, 20 ... thermometer, 21 ...
N ₂ O concentration measurement device

Claims (3)

(57) [Claims] To 1. A nitrous oxide-removing catalyst layer for removing nitrous oxide in exhaust gas discharged from the combustion device, supplied together from the exhaust gas combustion device for relatively low temperature operating conditions of the combustion apparatus The relatively high-temperature high-temperature gas is introduced by adjusting the mixing ratio, and the activity of the nitrous oxide removal catalyst is reduced.
When the temperature drops, only the relatively high-temperature hot gas is introduced.
A method for removing nitrous oxide in exhaust gas, comprising regenerating the activity of a nitrous oxide removing catalyst . 2. An operating condition of the combustion device is detected based on a measured value of at least one of a concentration of nitrous oxide in an exhaust gas and an exhaust gas temperature, and when the measured value is within a set range.
Introduces the exhaust gas of low temperature relatively, nitrous if when nitric oxide concentration tends to increase or the exhaust gas temperature tends to decrease the rate of increase in nitrous oxide concentration in the exhaust gas in the exhaust gas Alternatively, a relatively high-temperature gas discharged from the combustion device is mixed with the exhaust gas and introduced into the nitrous oxide removal catalyst layer so that the optimal temperature condition for nitrous oxide removal is obtained according to the rate of decrease in the exhaust gas temperature. 2. The method for removing nitrous oxide in exhaust gas according to claim 1, wherein: 3. A mixed gas of exhaust gas and high-temperature gas is introduced into the nitrous oxide removal catalyst layer at a preset mixing ratio of exhaust gas and high-temperature gas according to a program preset according to operating conditions of the combustion device. 2. The method according to claim 1, wherein
The method for removing nitrous oxide in exhaust gas as described in the above.