JP3174671B2 - Nitrogen oxide purifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to nitrogen oxides (NO _x ).
The present invention relates to a purifying device. More particularly, the purpose of particularly removing NO _x in the exhaust gases emitted from automobiles, introducing air into the automobile road tunnels started crossing an exhaust gas purification, in particular sealed high degree of parking, or in the building near the intersection The present invention relates to a purifying device used for purifying water and the like.

[0002]

In recent years, NO _x, which is emitted from automobiles from can lead to the destruction of local environmental degradation and the global environment, the development of technology or to purify Dari prevent their occurrence has been promoted. However, especially in the car society evolves, from becoming large air volume at low concentration will immediately mixed with the atmosphere after the occurrence for NO _x generated from the car, the purification has been difficult. However, in motorway tunnels, for stagnant exhaust gas to a certain enclosed space toxic gas concentrations including NO _x from outside the tunnel rises. In such a tunnel, ventilation is performed so that the concentration of the harmful gas inside does not exceed the reference value, but NO _x is emitted from the exhaust port by several tens times or more of the normal atmosphere. Although automobile tunnels using underground urban recently has been planned, a bad place exhaust location or original environment of the tunnel air is concern deteriorated further environmental purification device of the NO _x is sought I have. Heretofore, this type of purification apparatus has generally been a denitration apparatus as disclosed in Japanese Patent Application Laid-Open No. 1-224031. Hereinafter, the configuration will be described with reference to FIG. As shown in FIG. 5, NO contained in tunnel exhaust gas 101 drawn in by fan 104
Of nitrogen monoxide (NO) and nitrogen dioxide (NO ₂ ), which are the main components of _x , NO is oxidized by the oxidizing unit 102 to NO ₂ . And NO ₂ obtained by this oxidation, both originally both present are a NO ₂ NO ₂ absorbent filter 1
03 is absorbed.

[0003]

When purifying exhaust gas from an actual automobile tunnel by using the denitration apparatus shown in the conventional example, NO is present in the exhaust gas at a concentration several times or more higher than NO _2. Therefore, how to convert this NO to NO ₂ stably at a high rate, and
The most important point is not to produce excess oxidizing substances such as organic acids and ozone except for oxidizing to O ₂ .
The NO concentration in an automobile tunnel has a very large fluctuation range because air flows through the tunnel at a high speed and the exhaust gas from the automobile is exhausted from the tunnel without being sufficiently diffused. Is also early. The device for the oxidation of NO consists of arranging the electrode plates directly in the flow of the exhaust gas and applying a high voltage to the N gas in the gas.
There are a method of oxidizing O and a method of oxidizing NO by introducing ozone into a gas using a pipe or a nozzle and mixing the gas with the gas. In any of the oxidation methods, the oxidation ability is adjusted by the voltage or current value. However, there is a time delay from when an instruction is issued by the oxidation ability control device to when the oxidation ability in the actual oxidation space reaches the designated value. In particular, in the method of introducing ozone, it takes time for the required amount of ozone to reach the oxidation space from the ozone generator. on the other hand,
Even when measuring the NO concentration in the gas, the time required for the gas to be measured to reach the measuring instrument and the time for analysis by the measuring instrument are required. Although a reasonable amount of data can be obtained without considering these time differences in a laboratory-level model, in actual tunnel-scale denitration, the fluctuation range of the purification rate is large, and a large amount of unreacted ozone is generated. become. In addition to these phenomena, when the fluctuation is abrupt, even if the oxidation capacity is adjusted accordingly,
There is a phenomenon that the actual NO oxidation rate cannot be maintained at a high rate. This depends on the size of the oxidation space and the environmental conditions at that time. To maintain the oxidation rate of NO at a high rate, there is a method of setting the oxidation capacity according to the maximum fluctuation of the NO concentration. However, this method not only generates a large amount of unreacted ozone but also requires a large amount of energy required for the oxidation. It becomes something.

Accordingly, a first object of the present invention is to provide a nitrogen oxide purifying apparatus having a high purifying efficiency for controlling an oxidizing ability in accordance with a change in NO concentration. Second embodiment of the present invention
An object of the present invention is to provide a nitrogen oxide purifying apparatus which can cope with a rapid change in NO concentration.

[0005]

A first technical means of the present invention for achieving the first object is a device for driving a gas to be purified which enters the device, and a device for discharging NO by discharging or ozone. an oxidation unit for oxidizing the _2, an absorption unit with an absorbent that absorbs NO ₂ in the downstream of the oxidation unit, continuously measured to the measuring apparatus the concentration of NO in the cleaning gas introduced into the device And an oxidizing ability control device that continuously controls the oxidizing ability of the oxidizing part in accordance with the measured value by feeding back the measured value, and before the gas at the time when the NO concentration is measured reaches the oxidizing part. Another object of the present invention is to regulate the positional relationship between the concentration measuring section and the oxidizing section so that the oxidizing ability of the oxidizing section matches the gas composition.

More specifically, it takes a long time for the NO concentration to be sucked, measured, and output by the NO concentration meter.
This time is defined as A. Next, it takes time to read the output data by the oxidizing capability control device and to give a numerical value of a voltage or current value for controlling the capability of the oxidizing device. This time is B. Finally, it takes time for the oxidizing device to convert to a predetermined capability based on information from the oxidizing capability control device and to cover the oxidizing portion in the exhaust gas flow path and the oxidizing capability. This time is C. In other words, it takes A + B + C to measure the concentration of NO to be oxidized and then adjust the oxidizing part to its oxidizing ability. At least when the NO concentration in the gas is measured, the gas reaches the oxidizing part. Must be before A + B + C time.

[0007] A second means for achieving the second object is NO.
Regarding the concentration fluctuation, the larger the instantaneous fluctuation in both the concentration increase and the concentration decrease, the oxidizing ability is controlled so that the oxidizing ability becomes richer with respect to the NO concentration, and the NO ₂ absorption section is downstream. A device capable of purifying ozone will be installed in the country.

[0008]

According to the first technical means, the oxidizing capacity of the oxidizing unit space can be adjusted according to the time when the gas whose NO concentration has been measured reaches the oxidizing unit space of the denitration apparatus. No NO is left or excessive oxidizing substances are produced. On the other hand, according to the second technical means, NO can be oxidized stably at a high rate even when the NO concentration fluctuates greatly, and harmful ozone emission can be prevented.

[0009]

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited to only these examples. Embodiment 1 FIG. 1 shows an embodiment of the purification device of the present invention. Reference numeral 21 denotes a purifying device main body, and a fan 23, an absorbing portion 24 provided with a layer of a dry absorbent for absorbing NO ₂ , and ozone from an ozone generating device 25 are provided in a passage 22 of the gas to be purified communicating with the inside 20 of the tunnel. Ozone supply device 26 for uniformly supplying to the oxidation space
And a measuring unit 30 facing the sampling line 29 of the NO concentration measuring device 28. Numeral 31 indicates the flow of the exhaust gas. The point at which the NO concentration in the exhaust gas is measured is point P of the measuring unit 30, where the gas is continuously sent to the NO concentration measuring device 28 via the sampling line 29. The continuous measured values obtained here are sent to the oxidation capacity control device 33 via the output line 32, where the adjustment value of the oxidation capacity is determined, and the instruction is sent to the ozone generator 25 through the instruction line. The ozone generator adjusts the output according to the instruction and sends it to the ozone supply device 26.

As described above, an apparatus capable of treating exhaust gas of 10,000 m ³ / h is constituted. In addition, about 500 liters of porous alumina having a particle size of about 10 mm is used as an absorbent for absorbing NO ₂ . The time from the measurement of NO concentration to the supply of ozone is the shortest. 1) The time from exhaust gas sampling to the output of NO concentration: 25 seconds 2) Calculated by the oxidation capacity control device and instructed to the ozone generator 3) Time required for the ozone generator to send out ozone with the output as instructed and the oxidizing space to be filled with the amount of ozone: about 20 seconds. The total time of more than about 46 seconds was about 46 seconds. . Since the actual exhaust gas chose point of approximately 60 seconds to reach from the sampling point to the point Q of oxidizing unit space as a point P, a supply command of ozone Okurashi about 1 4 seconds in actual control.

FIG. 2 shows an evaluation result of the NO _x purification performance by this control. Here, (a) shows one period in which the NO concentration is relatively stable, and (b) shows the evaluation result in one period in which the fluctuation of the NO concentration is relatively large. As is clear from FIG. 2, when the concentration of NO is relatively stable, almost 90%
The degree of the NO _x purification rate is obtained, more than 80% of the purification rate is obtained even when a relatively large variation. Ozone concentration, NO
The concentration is the concentration in the oxidation space, the NO concentration was the data immediately before mixing with ozone, and the ozone was determined by calculation by measuring the concentration and amount immediately before being injected into the oxidation space.

[Comparative Example] As a comparative example, a sampling line 9 for measuring the concentration of NO is provided at a position shown by a dotted line in FIG. The NO measuring device 8 and the oxidizing ability control device 3 have the same specifications as those used in the first embodiment, and are used in common with the embodiment after the ozone generator. It took about 15 seconds for the exhaust gas to reach from the sampling point R of this comparative example to the oxidation space Q point. Each measuring device, control device, and ozone generating device were evaluated by giving instructions as quickly as possible, and the results were as shown in FIG. As is clear from FIG. 3, a difference between the ozone concentration and the NO concentration is seen,
Even when the NO concentration is relatively stable (a), the NO _x purification rate falls below 80%, and when the NO concentration fluctuation is large (b)
As a result, the NO _x purification rate was reduced to about 50%.

Embodiment 2 FIG. 4 shows a second embodiment of the present invention.
Shows the evaluation results obtained by This is NO concentration fluctuation
High NO even when is large_xTo maintain the purification rate
This is an example. To determine the oxidizing capacity at a certain point,
In the control circuit, the NO concentration at the time of
It is what you put. In practice, when there is a concentration fluctuation,
The slope of the curve at the point of
This is to give an instruction to increase the salary. In FIG.
The time line of the horizontal axis is 1 second / 1 cm,
Write on the graph where the NO concentration on the axis is 1 ppm / 1 cm.
To supply extra ozone for the sine value.
gave. For example, when the NO concentration at a certain point is 2 ppm,
The concentration at the point of 2 tends to increase by 2 ppm in 10 seconds.
The amount increased by 2/10 of 2 ppm (total
2.4 ppm) of ozone. NO concentration drops
Also adjust in the increasing direction when there is a tendency. However, this control
Since the oxidizing ability changes under rich conditions in total,
There is a risk that unreacted ozone will be discharged as it is.
Including activated carbon, Mn oxide, Cu oxide and Fe oxide
Install an ozone purification filter after the absorbent, or
It is necessary to mix these substances into the agent itself. This embodiment
In the absorption of alkali containing active carbon as a main component
The evaluation was performed using the agent. For the above control and absorbent
FIG. 4 shows the result. (A) NO concentration is relatively stable
(B) shows the results during the period of large fluctuation
You. At this time, no ozone was emitted. NO concentration
NO even when the fluctuation is large x Purification rate is high and stable
I have.

[0014]

As described above, according to the present invention, the oxidizing capacity of the oxidizing space can be adjusted according to the time when the gas whose NO concentration is measured reaches the oxidizing space of the denitration apparatus. Does not remain or excess oxidizing substances are produced. Further, even when the NO concentration fluctuates greatly, NO can be oxidized stably at a high rate, and harmful ozone emission can be prevented.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a configuration of a nitrogen oxide purifying apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram showing performance of the apparatus.

FIG. 3 is a diagram showing the performance of a device of a comparative example.

FIG. 4 is a diagram showing characteristics of the device according to the second embodiment of the present invention.

FIG. 5 is a schematic diagram showing a configuration of a conventional denitration apparatus.

[Explanation of symbols]

 Reference Signs List 20 Inside of tunnel 21 Purifier body 22 Exhaust gas passage 23 Fan 24 Dry absorbent layer 25 Ozone generator 26 Ozone supply device 27 Oxidation unit 28 NO concentration measurement device 29 Gas sampling line 30 Measurement unit 31 Exhaust gas flow 32 Output of measurement device Line 33 Oxidation capacity controller 34 Instruction line to ozone generator

Continuation of the front page (56) References JP-A-5-64721 (JP, A) JP-A-1-224031 (JP, A) JP-A-60-190217 (JP, A) JP-A-1-296000 (JP, A) , A) Hikaru 2-124556 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) B01D 53/34-53/90

Claims (2)

(57) [Claims] And 1. A driving an exhaust gas discharged from automobiles apparatus, an oxidation unit for oxidizing nitrogen monoxide to nitrogen dioxide due to discharge or ozone, in the downstream of the oxidation unit, absorbent for absorbing the nitrogen dioxide Absorber with agent and front
A measuring device for measuring the concentration of nitrogen monoxide of the exhaust gas to be introduced into the serial oxidizing unit, based on an output of the measuring device
Wherein controlling the oxidative capacity of the oxidation unit comprises an oxidation capacity control device, wherein the concentration measuring unit of the measuring device and the oxidation unit, the oxidation unit before said exhaust gas concentration measurement unit reaches the oxidation section Are in a positional relationship such that they can reach an oxidizing ability according to a command of the oxidizing ability control device. 2. An ozone purifying unit for purifying ozone downstream of the absorbing unit, wherein the oxidizing capability control device controls the oxidizing capability of the oxidizing unit so that the oxidizing capability is rich with respect to the measured concentration. The nitrogen oxide purifying apparatus according to claim 1, wherein the apparatus is controlled.