JP3361994B2 - Ammonia analyzer - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an NH ₃ analyzer for continuously measuring the concentration of ammonia (NH ₃ ) contained in exhaust gas. Such an NH ₃ analyzer is
For example, it is installed at the outlet of a flue gas denitration device for treating low-temperature exhaust gas after the air preheater of an oil-fired boiler or a dust collector with NH ₃ injection, and is used to measure the NH ₃ concentration in the exhaust gas after exhaust gas treatment. To be done.

[0002]

2. Description of the Related Art FIG. 1 shows a schematic configuration diagram of an example of a conventional NH ₃ analyzer. Explaining the measurement principle, there are two types of NH ₃ analyzers for flue gas exhaust gas using a catalyst, an oxidation type and a reduction type, each of which is a sampling probe line consisting of NH ₃ system and NO _x system sampling probe lines. Part 5
1, an analysis unit 52 having an analyzer for measuring the NO concentration of each system, and a calculation unit 53 for calculating the NH ₃ concentration from the NO concentrations obtained from the two analyzers. A catalyst C is provided on one side (NH ₃ system) of the sampling probe line, an ammonia oxidation catalyst is used for the oxidation type, and an ammonia reduction catalyst is used for the reduction type.

The principle of measurement of the oxidized form is to oxidize NH _{3 of} NH ₃ type to equimolar NO by the function of an oxidation catalyst and detect the concentration of this NO to measure the NH ₃ concentration. Since NO _x is also generally present in the flue gas, the NO ₂ in the exhaust gas is reduced to NO by the NO ₂ —NO converter upstream of the detector. In the NO _X system flow path, NO _X
Only the concentration is detected, and NH ₃ and NO _x are detected in the NH ₃ system flow path.
Since the total concentration of is detected, the difference between the detection values of the detectors of these two flow paths becomes the NH ₃ concentration. The measurement principle of the reduced form, the equimolar of the NO _X and NH ₃ in the NH ₃ system by the action of the reduction catalyst
The NH ₃ concentration is measured by carrying out the reaction with, and detecting the NO _X concentration that is deficient in the reaction.
In this case, the NH _3-side passage is detected amount corresponding reduced concentration of NO _X NH ₃ concentration, the difference between the detected value of both flow paths is NH ₃
It becomes the concentration.

In a conventional NH ₃ analyzer, two sampling pipes divided into an NH ₃ system and a NO _x system are inserted in a flue pipe, and a sample gas is supplied from the tip of the sampling pipe by a pump provided in the analysis unit. I'm sucking. The sampling pipe is about 2 to prevent the condensation of water in the exhaust gas.
It is heated above 00 ° C. Since the dust contained in the exhaust gas may reach the NH ₃ detection section together with the exhaust gas, in order to prevent this, a dust removal filter is installed in advance in the sampling probe flow path after the suction port of the sampling pipe. The catalyst C is provided in the sampling pipe located in the flue pipe.

[0005]

[0007] Figure 2, NH ₃ analyzer sampling probe after long-term operation of the boilers by installing a NH ₃ analyzer at the outlet of the NH ₃ injection with dust collecting apparatus for heavy oil fired boiler It is a partial cross-sectional side view of the sampling pipe of FIG. A heater 6 is provided around the metal sampling pipe 62.
6 is provided, and the temperature thereof is set to 400 ° C., for example, but the tip of the sampling pipe 62 has the exhaust gas temperature.
Under the influence of (normally about 140 to 150 ° C.), the temperature of the sampling pipe 62 gradually decreases toward the tip. The temperature at the tip of the sampling pipe 62 is approximately 140 ° C. to 150 ° C., which is the exhaust gas temperature.

Dust 68 such as ammonium hydrogensulfate adheres to the tip of the sampling pipe 62. It is known that when the dust 68 adheres, the indicated value of the NH ₃ analyzer shows an abnormal value. The mechanism is shown below. The cause of the dust 68 adhering to the tip of the sampling pipe 62 is that the ammonium sulfate solid fine particles contained in the flue gas become acidic ammonium hydrogen sulfate (liquid) at about 160 ° C. to 250 ° C. This is because. This can be represented by a chemical formula as shown in the following formula (1). (NH ₄ ) ₂ SO ₄ (solid) → NH ₄ HSO ₄ (liquid) + NH ₃ (gas) (1)

Flue gas temperature rises (boiler load rises)
Or the NH ₃ concentration decreases, part of the ammonium hydrogensulfate deposited and deposited decomposes and NH
_Because it releases ₃ , the analyzer reading will increase. This can be represented by a chemical formula as shown in the following formula (2). NH ₄ HSO ₄ (liquid) → NH ₃ (gas) + SO ₃ (gas) + H ₂
O (gas) (2)

On the contrary, when the flue gas temperature decreases (boiler load decreases) or the NH ₃ concentration increases,
Part of the ammonium bisulfate deposited and deposited is NH ₃
Since the gas is absorbed and converted to ammonium sulfate, the indicated value of the analyzer decreases. This can be represented by a chemical formula as shown in formula (3) below. NH ₄ HSO ₄ (liquid) + NH ₃ (gas) → (NH ₄ ) ₂ SO ₄ (solid) (3)

It is known that the equilibrium relationship between ammonium sulfate and ammonium hydrogensulfate changes depending on the temperature and the NH ₃ partial pressure, as shown in FIG. 3 showing the values measured by the flow method. In the region where the gas temperature is about 250 ° C or higher, the fine particles of ammonium sulfate in the flue gas are (1) and (2).
According to the formula, it decomposes and releases NH ₃ gas. For example NH ₃
10 mg / m in the dust from the outlet of the dust collector with injection
It can theoretically be said that the presence of a ³ N ammonium sulphate component increases the analyzer reading by about 3 ppm in the case of an NH ₃ analyzer without a filter. In addition, even when a filter is provided, the inventors have experienced in an actual machine that ammonium sulfate adhering to the filter adsorbs and desorbs NH ₃ depending on the temperature and the NH ₃ concentration, causing an abnormality in the indicated value of the analyzer.

In principle, the NO ₃ reduction type NH ₃ analyzer is applied when the NO concentration in the gas is higher than the NH ₃ concentration. However, when the boiler is started, the NH ₃ concentration is temporarily higher than the NO concentration. There are times when In such a case, it was found that NH ₃ was absorbed by the reducing catalyst and the subsequent NH ₃ indicated value was increased. Therefore, the catalyst temperature and NH
_When the relationship between the _three adsorption amounts was investigated, it was confirmed that a larger amount of adsorption of NH ₃ occurred when the heater temperature (catalyst temperature) was lower, as shown in FIG. If the catalyst is provided in the sampling pipe, the temperature of the catalyst may change under the influence of the change in exhaust gas temperature.

As described above, in the conventional NH ₃ analyzer, the measurement accuracy of the NH ₃ concentration in the flue tube is poor, and the responsiveness is extremely deteriorated particularly when the NH ₃ concentration changes due to the change of the exhaust gas temperature. There was a problem of doing. Therefore, the present invention is
It is intended to improve the measurement accuracy of an NH ₃ analyzer used for measuring the NH ₃ concentration in flue gas.

[0012]

One aspect of the ammonia analyzer of the present invention is a sampling probe that inserts a sampling pipe into a flue pipe to guide exhaust gas to the outside of the flue pipe, and a ammonia concentration in the exhaust gas directly or directly. An ammonia detection unit for measuring via a catalyst, and a temperature control unit for maintaining the exhaust gas passage from the exhaust gas inlet of the sampling pipe to the ammonia detection unit within a range of 250 ° C to 400 ° C. Be prepared.

The decomposition temperature of ammonium sulphate was investigated in order to prevent the deposition of ammonium hydrogen sulphate in the exhaust gas channel, especially in the exhaust gas inlet. 5A and 5B are diagrams showing a decomposition visual test of ammonium sulfate, where FIG. 5A is a schematic diagram of an apparatus, FIG. 5B is a schematic diagram showing a change in the state of a sample, and FIG. 5C is a diagram showing test results. The vertical axis of (C) represents temperature, and the horizontal axis represents elapsed time. As the measuring method, about 5 mg of powdery ammonium sulfate was placed on the heating part made of metal, and the state change of the sample was observed while monitoring the temperature of the heating part. Ambient temperature was 20 ° C. At 250 ° C or lower, ammonium hydrogensulfate was not decomposed and remained attached and deposited, but at 250 ° C or higher, ammonium hydrogensulfate was decomposed. The decomposition rate gradually increases from 250 ℃,
It was confirmed that ammonium hydrogen sulfate was immediately decomposed at about 300 ° C or higher.

From this result, it is possible to prevent the deposition of ammonium hydrogensulfate at a temperature of 250 ° C. or higher. Also, at temperatures above 400 ° C, NH ₃ oxidizes and NO
It was found in the process of the probe improvement test by the inventors that the NH ₃ reading value was lowered. Therefore, if the temperature of the exhaust gas flow path from the exhaust gas inlet of the sampling pipe to the ammonia detecting portion is kept within the range of 250 ° C to 400 ° C, the NH ₃ concentration can be accurately measured.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Another aspect of the ammonia analyzer of the present invention is to insert a sampling pipe into the flue pipe to guide the exhaust gas to the outside of the flue pipe, and to measure the ammonia concentration in the exhaust gas directly or with a catalyst. Ammonia detection section for measuring via an exhaust gas is provided, and a filter for dust removal is provided at the exhaust gas inlet of the sampling pipe so as to be exposed to the exhaust gas flow in the flue pipe.

N produced by decomposition of ammonium sulfate
When the concentration of ammonium sulfate particles in the exhaust gas is so high that the H ₃ concentration cannot be ignored, it is necessary to remove the ammonium sulfate particles by a filter. If the filter is installed at the tip of the sampling pipe and the entire filter is exposed to the exhaust gas flow in the flue pipe, the adsorption and desorption of NH ₃ in the dust adhering to the filter will be saturated in a short time, and the response of the ammonia detection unit will be reached. It was confirmed that the effect on speed was almost negligible. This is because the amount of exhaust gas that comes into contact with the filter in a certain period of time is several hundred times to several thousand times that in the case where the filter is provided inside the probe.

The filter is preferably a cloth bag filter. The bag filter is fluttered by the exhaust gas flow of the flue pipe, and the attached dust can be shaken off to reduce the attachment of dust. It is preferable that a sheath heater is provided in a coil shape on the sampling pipe, and the thickness of the tip end portion (exhaust gas intake side) of the sampling pipe is increased. As a result, it is possible to increase the heat capacity of the tip portion and make it easy to maintain the sampling pipe at a predetermined temperature from the exhaust gas inlet to the ammonia detector. It is preferable that the heaters at the tip of the sampling pipe have a high density. As a result, it is possible to maintain the tip portion of the sampling pipe whose temperature is likely to drop under the influence of the exhaust gas temperature at a predetermined temperature.

Another aspect of the ammonia analyzer of the present invention is that
It has a sampling probe that inserts a sampling pipe into the flue pipe and guides the exhaust gas to the outside of the flue pipe, and a flow path that is divided into two systems, an ammonia system and a nitrogen oxide system. It has an ammonia reduction catalyst and measures the concentration of nitric oxide in each channel,
An ammonia detecting unit for obtaining an ammonia concentration from the difference in concentration is provided, and a heating box installed outside the flue pipe for holding the ammonia oxidation catalyst or the ammonia reduction catalyst at a constant temperature is provided.

Adsorption of NH _{3 on} the ammonia oxidation catalyst or ammonia reduction catalyst increases when the catalyst temperature decreases, and the amount of adsorbed NH ₃ changes when the catalyst temperature changes. By installing the catalyst in a heating box that does not receive the heat and maintaining it at a constant temperature,
It is possible to suppress an error in the indicated value of the analyzer due to the amount of H ₃ adsorbed.

In that case, the exhaust gas flow path from the exhaust gas inlet of the sampling pipe to the ammonia conversion catalyst is set to 250.
It is preferable to include a temperature control unit for keeping the temperature within the range of ℃ to 400 ℃. Further, it is preferable that the exhaust gas inlet of the sampling pipe is provided with a filter for dust removal so as to be exposed to the exhaust gas flow in the flue pipe.

[0021]

6 to 8 show a sampling probe of an embodiment of a sampling probe of an ammonia analyzer (reduction type) for exhaust gas from a flue pipe according to the present invention. FIG. 6 is a front sectional view and FIG. Sectional drawing in the AA line position in FIG.
FIG. 8 is an enlarged cross-sectional view taken along line ◯ in FIG. Note that FIG. 6 shows a sectional view taken along the line BB in FIG. 7. Figure 9
Represents a conceptual diagram of the embodiment.

A sampling pipe 1 to be inserted into a flue pipe for collecting exhaust gas is provided, and one end of the sampling pipe 1 serves as an exhaust gas inlet 1a. Sampling pipe 1
The outer metal cover 6 and the inner metal tube 2 are welded and integrated. The thickness of the tube 2 is formed thick at the tip. The sampling pipe 1 is
A heater 3 is wound around the tube 2 in a coil shape, and the outside of the heater 3 is covered with a heat insulating material 4. The heater 3 is wound so as to have a high density on the tip side of the tube 2. The heater 3 is controlled by the temperature control unit 31, and the temperature in the vicinity of the gas intake port 1a of the sampling pipe 1 is, for example, 3
The temperature is kept at 00 ° C. and is controlled so that it does not exceed 400 ° C. at any place of the sampling pipe 1.

The exhaust gas inlet 1a is provided with a filter support 5 and, for example, 3 μm so as to cover the filter support 5.
A bag filter 7 for removing m-mesh dust is provided. The bag filter 7 is exposed to the exhaust gas flow in the flue pipe. A backwashing air mechanism (not shown) that removes dust adhering to the bag filter 7 by flowing air in the sampling pipe 1 in the reverse direction is provided, and the backwashing of the bag filter 7 is performed regularly or as needed. Is performed.

The base end side of the sampling pipe 1 is inserted inside the heating box 9, and inside the heating box 9, N
It is branched into two systems of an O _x flow path 11 and an NH ₃ flow path 13 and guided to the outside of the heating box 9. The NH ₃ flow path 13 is guided to the outside of the heating box 9 through the NH ₃ reduction electric furnace unit 15 inside the heating box 9. The NH ₃ flow path 13 between the sampling probe 1 and the NH ₃ reduction electric furnace unit 15 is covered with a heat insulating material 17, and the heat insulating material 1
The furnace inlet heater 19 provided inside the
It is kept at 00 ° C. The furnace inlet heater 19 is controlled by the temperature controller 31.

In the NH ₃ flow path 13, inside the NH ₃ reduction electric furnace unit 15, NH ₃ and NO are reacted to generate nitrogen (N ₂ ).
And a catalytic reaction tube filled with an NH ₃ reduction catalyst 21 for converting into water (H ₂ O). The NH ₃ reduction catalyst is heated to about 400 ° C. by the NH ₃ reduction electric furnace unit 15 and kept at a constant temperature. A space heater 23 is provided inside the heating box 9 to keep the temperature inside the heating box 9 at 150 ° C., for example. The space heater 23 is also controlled by the temperature controller 31. The NO _x flow path 11 and the NH ₃ flow path 13 led to the outside of the heating box 9 are
NO _x system NO detector 25 and NH ₃ system NO detector 2 respectively
Connected to 7. The NO detectors 25 and 27 are of chemiluminescence type, for example. The flow paths downstream of the NO detectors 25 and 27 are led to the exhaust port via a pump 29 that sucks the exhaust gas.

The measurement principle of the NH ₃ analyzer (reduced type) to which the device of the present invention is applied is that the sample collected from the flue tube (NO-
NH ₃₎ concentration divided into two systems of the NO _X system NH ₃ system and the NO concentration is measured to be measured, is detected by NO detector 25 and 27 provided downstream of each system, the two output signals The NH ₃ concentration is measured by calculating the difference between

The flow of exhaust gas will be described with reference to FIGS. 6 to 9. The pump 29 is operated and the exhaust gas in the flue pipe is taken into the sampling pipe 1 from the exhaust gas inlet 1a via the bag filter 7. The dust in the exhaust gas is removed by the bag filter 7. The bag filter 7 flaps because it is exposed to the exhaust gas flow in the flue pipe, and the dust adhering to the bag filter 7 is wiped off so that it is difficult to adhere. The inside of the sampling pipe 1 is 300 by the heater 3.
Since the temperature is maintained at 0 ° C., it is possible to prevent ammonium hydrogensulfate from being deposited and deposited due to some dust contained in the exhaust gas that has passed through the bag filter 7.

The collected exhaust gas is sent to the heating box 9 via the sampling pipe 1 and is branched into two systems of a NO _x flow path 11 and an NH ₃ flow path 13. NH ₃ flow passage 13 NH ₃ in samples sent to the the action of NH ₃ reduction catalysts 21 provided in the NH ₃ reducing electric furnace unit 15, by the following equation, to react with equimolar NO. NO + NH ₃ + (1/4) O ₂ → N ₂ + (3/2) H ₂
O

[0029] NH NH ₃ than conversion catalyst downstream of the _third flow path 13
The NO concentration of the exhaust gas is obtained by subtracting NO that has reacted with NH ₃ from NO originally contained in the exhaust gas. Since NO _x is generally present in the exhaust gas in addition to NH ₃ , NO ₂ in the exhaust gas is converted to NO ₂ upstream of the detector.
-Reduced to NO by NO converter and N by NO detector
When the O concentration is detected, the NO ₃ concentration reduced by the NH ₃ concentration is detected in the NH ₃ flow channel 13, so that both flow channels 1
The difference between the NO detection values of 1 and 13 is the NH ₃ concentration.

Although the NH ₃ reduction catalyst was used in the examples, it can be applied to an oxidized NH ₃ analyzer by filling with an NH ₃ oxidation catalyst instead. The measurement principle of the oxidized NH ₃ analyzer is to equivalently detect the NH ₃ concentration by bringing NO and NH ₃ contained in the exhaust gas into contact with a catalyst and detecting the concentration of NO produced by the reaction. The reaction formula is as follows. 4NH ₃ + 5O ₂ → 4NO + 6H ₂ O

[0031] NH NH ₃ than the oxidation catalyst downstream of the _third flow path 13
In the exhaust gas of NO, NO that was originally generated by the oxidation of NH ₃ was added to NO that was originally included. NO ₂ to NO ₂
-Reduced to NO by NO converter, NO _X flow path 11
NO is detected by the NO detectors provided downstream of the NH ₃ flow path 13 and the NH ₃ flow path 13, respectively, and the difference between the detection values of the two flow paths becomes the NH ₃ concentration.

When the exhaust gas in the flue pipe contains a small amount of dust, the exhaust gas may be collected by removing the bag filter 7. Although the present invention is applied to an NH ₃ analyzer using a catalyst in the examples, the present invention is not limited to this,
It can also be applied to an NH ₃ analyzer which does not use a catalyst. In such a case, NH ₃ from the sampling pipe
It is preferable to maintain the temperature of the exhaust gas flow path to the detector at a constant temperature within the range of 250 ° C to 400 ° C.

Although a chemiluminescence type detector is used in the embodiment, the present invention is not limited to this, and other detectors such as a wavelength modulation type ultraviolet type and a second derivative absorption spectroscopy type may be used. It can also be applied to a conventional NH ₃ analyzer. Although the bag filter is used in the embodiment, the present invention is not limited to this, and another filter such as a metal filter may be used. An NH ₃ analyzer equipped with such a sampling probe is an NH injected for performing denitration treatment and dust collection treatment of exhaust gas from an oil-fired boiler, for example.
It can be used to control the ₃ concentration and control the NH ₃ dose.

[0034]

According to the present invention, the exhaust gas flow path from the exhaust gas inlet of the sampling pipe to the ammonia detecting section is set to 25
Keeping in the range of 0 ℃ to 400 ℃, to suppress the adhesion of ammonium hydrogen sulfate, NH ₃ to ammonium hydrogen sulfate
Since it is designed to suppress the adsorption / desorption of NH _{3 and} the oxidation of NH ₃ ,
The NH ₃ concentration can be measured accurately.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a conventional NH ₃ analyzer.

[2] partially sectional side representing the NH ₃ analyzer sampling probe of the sampling pipe after the outlet of the NH ₃ injection with dust collecting apparatus for heavy oil fired boiler by installing a NH ₃ analyzer and long-term operation of the boiler It is a figure.

FIG. 3 is a diagram showing an equilibrium relationship between ammonium sulfate and ammonium hydrogen sulfate.

FIG. 4 is a diagram showing an NH ₃ adsorption amount ratio to a catalyst with respect to a heater temperature.

5A and 5B are diagrams showing a decomposition visual test of ammonium sulfate, where FIG. 5A is a schematic diagram of an apparatus, FIG. 5B is a schematic diagram showing a state change of a sample, and FIG. 5C is a diagram showing test results.

FIG. 6 is a front sectional view showing a sampling probe according to an embodiment.

7 is a cross-sectional view taken along the line AA in FIG.

FIG. 8 is an enlarged cross-sectional view taken along the circle mark in FIG.

FIG. 9 is a block diagram showing a conceptual diagram of the embodiment.

[Explanation of symbols]

1 Sampling Pipe 2 Metal Tube 3 Heater 4, 17 Heat Insulation Material 5 Filter Support 7 Bag Filter 9 Heating Box 11 NO _X Flow Path 13 NH ₃ Flow Path 15 NH ₃ Reduction Electric Furnace Unit 19 Furnace Inlet Heater 21 NH ₃ Reduction Catalyst 23 heater 25 NO _X system NO detector 27 NH ₃ system NO detector 29 pump 31 temperature control unit

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoshi Yada 5-34-6 Shiba, Minato-ku, Tokyo Mitsubishi Heavy Industries Environmental Engineering Co., Ltd. (72) Inventor Yasuhiro Ishii 5-34-6 Shiba, Minato-ku, Tokyo Mitsubishi Heavy Industries Environmental Engineering Co., Ltd. (72) Inventor Hiroaki Obata 534-6 Shiba, Minato-ku, Tokyo Mitsubishi Heavy Industries Environmental Engineering Co., Ltd. (56) Reference JP-A-59-192936 (JP, A) JP Japanese Unexamined Patent Publication No. 8-114584 (JP, A) Japanese Unexamined Patent Publication No. 10-332668 (JP, A) Japanese Unexamined Patent Publication No. 7-333144 (JP, A) Japanese Unexamined Patent Publication No. 2-162230 (JP, A) Actual Development Sho 57-19446 (JP , U) Actually developed 60-29266 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01N 1/00 101 G01N 1/22 G01N 31/00 JISST file (JOIS)

Claims (5)

(57) [Claims] 1. A sampling probe for inserting a sampling pipe into the flue pipe to guide the exhaust gas to the outside of the flue pipe, and an ammonia detection unit for measuring the ammonia concentration in the exhaust gas directly or via a catalyst. The ammonia analyzer includes a temperature control unit for maintaining the exhaust gas flow path from the exhaust gas inlet of the sampling pipe to the ammonia detection unit within a range of 250 ° C to 400 ° C, and the sampling pipe has a heater density at a tip portion. The ammonia analyzer is characterized in that a heater is provided so as to be large, and the tip end portion of the sampling pipe has a large wall thickness and a large heat capacity. 2. The ammonia analyzer according to claim 1, wherein a filter for removing dust is provided at an exhaust gas inlet of the sampling pipe so as to be exposed to an exhaust gas flow in a flue pipe. 3. The ammonia detecting section has a flow path divided into two systems, an ammonia system and a nitrogen oxide system, and the ammonia system flow path has an ammonia oxidation catalyst or an ammonia reduction catalyst, and The ammonia analyzer according to claim 1 or 2, which is an ammonia detection unit that measures the nitric oxide concentration and obtains the ammonia concentration from the difference in concentration. 4. The ammonia analyzer according to claim 1, wherein the heater is a sheath heater. 5. The ammonia analyzer according to claim 2, 3 or 4, wherein the filter is a bag filter.