JPH0739724A - Apparatus for feeding ammonia in high temperature exhaust gas denitrification equipment - Google Patents

Abstract

PURPOSE:To perform denitrification with high efficiency by suppressing conversion reaction of NH3 into NOX in an ammonia feeding pipe of a high temp. exhaust gas denitrification equipment and feeding a required appropriate amt. of NH3 into a denitrification apparatus. CONSTITUTION:In an ammonia feeding apparatus of a high temp. exhaust gas denitrification equipment wherein denitrification of nitrogen oxides in a high temp. exhaust gas 1 is performed by feeding ammonia therein in the presence of a denitrification catalyst 2 and performing reduction thereof into harmless nitrogen, conversion reaction of fed NH3 into NOX is suppressed by insulating thermally at least a part or the whole of the apex parts of the ammonia feeding pipe 4 and a nozzle 6 provided in a duct of the high temp. exhaust gas or holding the inner wall temp. of the ammonia feeding pipe and the nozzle at 400 deg.C or lower by providing a cooling means.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an exhaust gas denitration equipment,
Particularly, the present invention relates to an ammonia injecting device for high temperature exhaust gas denitration equipment suitable for denitrifying nitrogen oxides in high temperature exhaust gas.

[0002]

2. Description of the Related Art As a method for reducing nitrogen oxides (NOx) contained in exhaust gas from gas turbines, boilers, etc., ammonia is injected in the presence of a denitration catalyst to remove NO in exhaust gas.
The so-called selective catalytic reduction (SCR) method of reducing NOx by reducing x and ammonia (NH ₃ ) gas into harmless nitrogen by catalytic reaction is widely adopted in denitration plants in Japan and overseas. In recent years, there is a tendency that a gas turbine is installed independently as a measure against peak power, and a denitration device is directly installed to remove NOx in exhaust gas from a gas turbine outlet as a measure for exhaust gas. In the conventional general denitration device, the temperature of the treated exhaust gas is 250 ° C to 4 ° C.
Compared to a relatively low temperature of 50 ° C, in the case of an exhaust gas denitration device for a gas turbine, the temperature of the outlet exhaust gas is 450 ° C.
There was a problem that the temperature was as high as ˜650 ° C. In Figure 6,
As a typical example of the high temperature exhaust gas denitration device, the configuration of a gas turbine exhaust gas denitration device for a simple cycle is shown. In the figure, the exhaust gas 1 of the gas turbine is 450 to 650.
The exhaust gas has a high temperature of about 0 ° C., an ammonia injection pipe 4 is installed in a casing (duct) 2 of the exhaust gas 1, and a mixed gas 8 of ammonia and air supplied from the inside of the ammonia injection pipe 4 is injected with ammonia. It is ejected from the nozzle 6 into the duct 2. After NOx contained in the exhaust gas 1 is mixed with ammonia, it is so-called catalytically decomposed in the NOx removal catalyst bed 3 to become harmless nitrogen, and is discharged to the outside of the system as a clean gas. Here, as the ammonia injection pipe 4, a stainless steel pipe or the like having sufficient heat resistance even in high-temperature exhaust gas is generally used, and conventionally, an ammonia injection pipe for exhaust gas of medium temperature is used. As in No. 4, it was installed in the exhaust gas duct 2 as a bare tube. As a conventional technique, for example, Japanese Patent Application Laid-Open Nos. 55-69395 and 55-69392, which are the prior applications of the present applicant, can be cited. This is ammonia injection inserted into a high temperature combustion gas passage. In order to reduce the heat absorption amount of the pipe and to insulate and protect the injection pipe from high temperature exhaust gas to prevent burnout, a block of fireproof and heat insulating material is provided on the outer peripheral portion of the ammonia injection pipe.

[0003]

In the denitration apparatus of high-temperature exhaust gas [0005] by catalytic cracking action of the catalyst and its catalytic support member, implanted NH ₃ (ammonia) is a reaction occurs which is converted to decompose NOx, NH ₃ It has been previously pointed out that the NOx removal reaction efficiency decreases due to a decrease in concentration and an increase in NOx at the entrance of the NOx removal device. As a countermeasure, for example by coating aluminum and for NOx conversion prevention of NH _3, although such a method of preventing NOx conversion by catalytic decomposition of NH ₃ has been proposed, in NH ₃ at the ammonia injection pipe is conventional It has been considered that NOx conversion due to catalytic decomposition is unlikely to occur. This is because the temperature of the mixed gas of NH ₃ and air introduced into the ammonia injection pipe is as low as about 30 to 50 ° C., so that the temperature of the inner wall of the ammonia injection pipe is NH _{3 as} shown in FIG.
It was thought that the NOx conversion starting temperature of 500 ° C. would not be reached. However, when the duct diameter of the exhaust gas increases, the conditions for the reaction of NOx conversion of NH ₃ to occur at the tip of the ammonia injection pipe are set, and the ammonia injection pipe of the ammonia injection pipe is not expected even in the low temperature region. It was found that NH ₃ was decomposed by the inner wall and a NOx conversion reaction occurred. This phenomenon not only reduces the amount of NH ₃ required for the reaction to be supplied to the denitration device and lowers the denitration efficiency, but also increases the amount of NOx at the inlet of the denitration device due to NOx conversion due to the decomposition of NH ₃ , resulting in denitration. The double adverse effect of increasing the catalyst filling amount due to the increase in load occurs, and there is a problem in that the performance and efficiency of the exhaust gas denitration device are significantly reduced.

An object of the present invention is to solve the above-mentioned problems in the prior art, that is, N by decomposition of NH _{3 on} the inner wall of the ammonia injection pipe of the denitration equipment for high temperature exhaust gas.
It is an object of the present invention to provide an ammonia injecting device in a high temperature exhaust gas denitration equipment that suppresses Ox conversion and supplies a necessary and appropriate amount of NH ₃ to the denitration device to perform denitration with high performance and efficiency.

[0005]

In order to achieve the above object of the present invention, at least a part of the outer peripheral portion of the ammonia injection pipe and nozzle used in the denitration equipment for high temperature exhaust gas is provided with heat insulating means, or, for example, A cooling means such as a double-pipe heat exchange method using water or air is provided so that the inner wall temperature of the ammonia injection pipe and the nozzle portion is 400 ° C. or lower, and NOx is generated by decomposition of ammonia.
It suppresses the conversion reaction. INDUSTRIAL APPLICABILITY The present invention relates to a nitrogen oxide (NOx) contained in a high-temperature exhaust gas, an ammonia injecting device in a high-temperature exhaust gas denitration facility for injecting ammonia in the presence of a denitration catalyst to reduce harmless nitrogen by a catalytic reaction. At least part of the outer circumference of the nozzle and the ammonia injection pipe provided in the exhaust gas duct, or by providing a cooling means by heat exchange with water or air, for example, the ammonia injection pipe and the inner wall of the nozzle Is an ammonia injecting device for a high temperature exhaust gas denitration facility configured to maintain the temperature of 400 ° C. or lower and suppress NOx conversion due to decomposition of NH ₃ .

[0006]

The heat insulating construction or cooling means applied to the ammonia injection pipe and the nozzle portion has the effect of suppressing the temperature of the inner wall portion of the ammonia injection pipe and the nozzle from rising more than necessary, and The temperature of the inner wall of the nozzle can be maintained at 400 ° C. or lower to suppress the NOx conversion reaction due to the decomposition of ammonia on the inner wall portion. As a result, there is no decrease in the amount of ammonia introduced into the denitration catalyst bed, so that the denitration reaction can be efficiently continued. In addition, since there is no increase in the NOx concentration at the denitration catalyst bed inlet that occurs due to NOx conversion due to the decomposition of ammonia, it is not necessary to increase the catalyst filling amount excessively, and an exhaust gas denitration facility with low equipment costs and maintenance costs is realized. be able to.

[0007]

Embodiments of the present invention will be described below in more detail with reference to the drawings. FIG. 1 is a schematic diagram showing the configuration of an ammonia injecting apparatus for high temperature exhaust gas denitration equipment according to the present invention, and FIG. 2 is a sectional view taken along line AA of FIG. In the figure, ammonia (NH ₃ ) gas is a mixed gas 8 of ammonia and air diluted with air to about 5% to prevent explosion,
It is introduced into the ammonia injection pipe 4 in a state close to the atmospheric temperature of about 30 to 50 ° C. A heat insulating material 5 is provided on the outer circumference of the ammonia injection pipe 4. As shown in FIG. 2, it is preferable that the heat insulating material 5 covers the tip of the ammonia injection nozzle 6 in order to improve the heat insulating effect. However, the temperature of the ammonia injection pipe 4 and the inner wall of the ammonia injection nozzle 6 is As long as the temperature can be maintained at 400 ° C. or lower, the heat insulating material 5 may be partially heat-insulated. A rock wool material, a glass wool material, or the like is generally used as the heat insulating material 5. However, in order to reduce the pressure loss of the exhaust gas, a heat insulating effect is obtained so that the area of the exhaust gas duct blocked by the group of the ammonia injection pipes 4 does not become large. Insulation 5 as high as possible
It is preferable to use a heat insulating material that can reduce the thickness of the. NO due to ammonia decomposition in high temperature exhaust gas
The x conversion is highly temperature dependent. FIG. 3 shows the NOx conversion rate of ammonia at each temperature.
Shows the NOx conversion rate of NH ₃ in the exhaust gas duct, curve B is NH ₃ injection tube (in particular, NH ₃ and far distal portion of a mixed gas supply opening of the air) NO of NH ₃ in
x conversion is shown. It is considered that the curve B is shifted to a lower temperature side than the curve A because the tip portion of the NH ₃ injection pipe 4 is a condition advantageous for NOx conversion of NH ₃ shown below. To be (1) Since the flow rate of the mixed gas 8 of NH ₃ and air is small, the flow rate of the gas at the tip of the NH ₃ injection pipe 4 is low, and therefore the residence time is long. (2) The NH ₃ concentration in the exhaust gas is on the order of several tens of ppm, whereas the NH ₃ concentration in the mixed gas 8 of NH ₃ and air is about 5%, which is about 1000 times higher. Therefore, NH ₃ in order to suppress the conversion to NOx at the injection tract, the inner wall temperature of the NH ₃ injection tube 4 it can be seen that it is necessary to maintain the 400 ° C. or less. FIG. 4 shows the effect when the NH ₃ injection apparatus of the present invention is applied to the denitration equipment for high-temperature exhaust gas at 600 ° C. in comparison with the conventional example. N when the heat insulating material 5 is not applied to the ammonia injection pipe (outer diameter 60 mm) 4 installed in the exhaust gas duct 2 having a width of 10 m
H ₃ injection pipe inner wall temperature (curve C) and NH ₃ injection pipe inner wall temperature (curve D) when the heat insulating material 5 having a thickness of 30 mm is applied
Indicates. In the curve C, which is a conventional example, the ammonia injection pipe 4
Approximately half of the total temperature rises above 400 ° C, and NH ₃ NOx
The conversion is expected to occur above 400 ° C. However, in the curve D of the present invention, it can be seen that the temperature of the inner wall of the ammonia injection pipe 4 is kept at 400 ° C. or less, and thus it is extremely effective in preventing NOx conversion of NH ₃ . FIG. 5 shows another embodiment of the present invention. When the exhaust gas temperature becomes relatively low at about 550 ° C., there is no need to install the heat insulating material 5 over the entire ammonia injection pipe 4 as shown in FIG. It is sufficient if the temperature of the inner wall of the nozzle tip portion of the injection pipe 4 can be maintained at 400 ° C. or lower. In the above embodiments, a heat insulating material is applied to a part or all of the outer peripheral portion of the ammonia injection pipe and the nozzle so that the temperature of the ammonia injection pipe and the inner wall portion of the nozzle is 4%.
Although the example in which the temperature is kept at 00 ° C. or lower has been described, the ammonia injection pipe and the nozzle may be a double pipe system, and means for cooling part or all of the ammonia injection pipe and the nozzle through cold water or cold air may be provided.

[0008]

As described in detail above, according to the ammonia injecting apparatus for the high temperature exhaust gas denitration equipment of the present invention, the temperature of the inner wall of the ammonia injecting pipe and the nozzle is all 4
Since it is possible to maintain the temperature below 00 ° C., it is possible to effectively prevent the NOx conversion reaction of the injected NH ₃ , and it is always possible to keep the proper amount of N required for the denitration catalyst bed.
Since H ₃ can be supplied, it is not necessary to prevent the performance of the denitration catalyst from deteriorating due to insufficient supply of NH ₃ and to fill an excessive amount of denitration catalyst. Further, since wasteful consumption of NH ₃ is eliminated, running cost can be reduced, and a high-temperature exhaust gas denitration equipment with low cost and high reliability can be realized.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an arrangement configuration of an ammonia injection pipe of a high temperature exhaust gas denitration device shown in an example of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 shows NH ₃ in the high temperature exhaust gas duct (A) and the ammonia injection pipe (B) shown in the embodiment of the present invention.
Is a graph showing the relationship between the NOx conversion rate and the inner wall temperature.

FIG. 4 is a graph showing the temperature distribution on the inner wall of the NH ₃ injection pipe in the case where the heat insulating material is not applied to the ammonia injection pipe shown in the embodiment of the present invention (C) and the case where the heat insulating material is applied (D).

FIG. 5 is a schematic diagram showing an arrangement configuration of an ammonia injection pipe of a high temperature exhaust gas denitration device which is another embodiment of the present invention.

FIG. 6 is a schematic diagram showing an arrangement configuration of an ammonia injection pipe of a conventional denitration device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Exhaust gas 2 ... Casing (duct) 3 ... DeNOx catalyst bed 4 ... Ammonia injection pipe 5 ... Heat insulating material 6 ... Ammonia injection nozzle 7 ... Catalyst support member 8 ... Mixed gas of ammonia and air A ... NH ₃ in high temperature exhaust gas duct NH ₃ injection in the case of construction of NOx conversion B ... NH ₃ injection pipe temperature D ... insulation NH ₃ injection tube wall when not applying a NOx conversion rate C ... insulation NH ₃ in (tip) in Inner wall temperature

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location B01D 53/36 ZAB

Claims (1)

[Claims] 1. A nitrogen oxide contained in high temperature exhaust gas,
In an ammonia injection device for exhaust gas denitration equipment that injects ammonia in the presence of a denitration catalyst and catalytically reduces it to harmless nitrogen, at least part of the outer circumference of the nozzle and the ammonia injection pipe provided in the duct for high-temperature exhaust gas is provided with heat insulating means. Alternatively, a means for maintaining the temperature of the ammonia injection pipe and the inner wall of the pipe leading to the nozzle tip portion at a temperature of 400 ° C. or lower that can suppress the reaction of decomposing ammonia and converting into nitrogen oxides is provided. Ammonia injection device for high temperature exhaust gas denitration equipment.