JPH0226616A - Device for purifying ventilation gas for road tunnel - Google Patents

Abstract

PURPOSE:To effect denitrification efficiently by circulating regeneration gases containing NH3 through a NOX adsorbent regeneration zone, withdrawing a part thereof to vent it to atmosphere through a denitrification reactor, while ventilation gases containing NOX are dehumidified before the NOX is absorbed. CONSTITUTION:After ventilation gases containing NOX are sent to a dehumidifying device 1 to be dehumidified, they are led to a NOX adsorption device 2, where the NOX is adsorbed and removed to make the gases harmless. Using the ventilation gases thus made harmless, the dehumidifying agents of the dehumidifying device 1 are regenerated. On the other hand, NOX adsorbents are regenerated by the use of gases for regeneration into which NH3 has been injected from a NH3 supply device 3, wherein said gases are used by circulating them by means of a blower 4, while a part thereof is withdrawn through a withdraw line to be vented to atmosphere after being passed through a denitrification reactor 5.

Description

[Detailed Description of the Invention] Industrial Application Fields Various road tunnels, such as mountain tunnels, undersea tunnels, underground roads, roads with shelters, etc., are long and have a large volume of automobile traffic, and are used to protect the health of passersby and improve visibility. It is necessary to provide a considerable amount of ventilation to improve the In addition, even if the tunnel is relatively short, in urban areas or its suburbs, carbon monoxide (C
O) As a method to prevent air pollution caused by nitrogen oxides (NOx), etc., the air inside the tunnel is sucked and exhausted (diffusion).
A method is being adopted to do so.

However, simply dispersing ventilation gas directly into the surrounding area will not help improve the local environment, and it may lead to the expansion of highly contaminated areas, especially in urban areas or their suburbs where pollution from automobile exhaust gas is spread over a flat area. It could become. Tunnels and shelters are used to prevent pollution from existing roads.
The above-mentioned circumstances are exactly the same in the case of installation, etc.

The present invention relates to a purification device that efficiently removes low-grade nitrogen oxides contained in ventilation gas from various road tunnels and renders them harmless.

BACKGROUND OF THE INVENTION In general, adsorption apparatus types can be broadly classified into fixed type and moving bed type.

In the fixed bed method, multiple adsorption devices are installed in parallel, the adsorbent adsorbs a predetermined amount of the target substance, and when the concentration of the target substance at the outlet of the adsorption device reaches the limit, the device is switched and the adsorbent is desorbed. Perform playback.

When handling a large amount of gas, the adsorbent filling amount is kept low due to gas flow resistance, which increases the frequency of equipment switching. Therefore, depending on the time required for desorption and regeneration, the number of adsorption devices installed in parallel increases, and the scale of the entire facility becomes extremely large.

On the other hand, in the moving bed method, the adsorbent is generally brought into countercurrent contact with the gas, and the adsorbents that have adsorbed a large amount of the target substance are sequentially extracted and desorbed and regenerated, while new or desorbed and regenerated adsorbents are sequentially filled. .

Therefore, the adsorption device can be operated continuously and there is no need to change the device, so the scale of the equipment can be smaller compared to the fixed bed method.

As a conventional method, the moving bed method proposed by the Institute of Industrial Development as a system for removing NOx from combustion exhaust gas is used.
An example of an Ox adsorption device (Research on the development of a new denitrification system using a special adsorption oxidation catalyst, Institute of Industrial Development, May 1978) is shown in Figure 4.

Note that this proposed device is intended for combustion exhaust gas with a NOx concentration of 100 pp- or more.
Since the target is completely different from the treatment of road tunnel ventilation gas of about ppm level, it cannot be applied as is, but basically this system can be used as a reference.

The above NOx removal system will be explained below based on FIG. 4.

The dehumidifying section at the top of the dehumidifying tower is filled with silica gel as a dehumidifying agent, and the water in the exhaust gas (NOx + air + H20) introduced from line (41) is adsorbed by it. The desiccant that has absorbed moisture moves downward under its own weight and enters the regeneration section.

In the regeneration section, the desiccant is brought into contact with the regeneration drying gas (using the outlet gas of the adsorption section) introduced through the line (43), and the adsorbed moisture is desorbed from the desiccant. The dehumidifying agent is thus regenerated, blown up together with the drying gas, and circulated again to the upper part of the dehumidifying tower.

In this way, the desiccant silica gel repeats adsorption, desorption, and regeneration, and circulates within the system. The exhaust gas introduced from the line (41) is dehumidified and dehumidified and goes to the adsorption section at the top of the adsorption tower.

The dry gas for regeneration from the line (43) obtains moisture in the regeneration section of the dehumidification tower and is released into the atmosphere as purified gas (air + H20).

On the other hand, the adsorption section at the top of the adsorption tower is filled with NOx adsorbent,
NOx in the dry exhaust gas (air + NOx) from the dehumidification tower is adsorbed by this. The adsorbent that has adsorbed NOx moves downward under its own weight and enters the desorption/regeneration section. In the detachment/regeneration department,
The adsorbent is heated to 400°C by a heater (46),
NOx that comes into contact with and is adsorbed by the dry expelled gas described below
is regenerated by desorption, blown up together with dry air, and circulated again to the upper part of the adsorption tower.

The dry expelled gas introduced from the line (44) uses a part of the outlet gas of the adsorption section, and NOx is desorbed from the adsorbent in the desorption/regeneration section, and NOx is desorbed from the line (45). It is taken out of the system as a released gas. Line (42)
Dry exhaust gas (NOx + air) introduced from the line (43
) is introduced into the regeneration section of the dehumidification tower as dry gas for regenerating the desiccant agent, and the remainder is used as dry expelled gas for desorption and desorption of the adsorption tower.
Introduced to the reproduction department.

The desorption gas taken out of the system from the line (45) includes:
Since the gas contains NOx desorbed from the adsorbent, it has been proposed to remove NOx by a method of absorbing the NOx in the desorbed gas into an alkaline aqueous solution or the like (wet absorption method). However, in this wet absorption method, NOx is accumulated in the absorption liquid as nitrates and nitrites, so management of the absorption liquid, post-treatment (waste liquid treatment), etc. are required, which complicates the process and increases processing costs.

The present applicants have already proposed a method for regenerating the adsorbent that has adsorbed NOx by treating it with air containing NH3 as a method for making this desorbed gas harmless and releasing it into the atmosphere. 313777). This method uses a selective reduction reaction (denitrification reaction) of NOx using NH3 to remove NOx.
N adsorbed on the adsorbent.

The adsorbent is regenerated by desorbing X into harmless N2 and N20. In addition, in order to desorb and regenerate the adsorbent that has adsorbed NOx only by increasing the temperature, it is necessary to
The adsorbent must be heated to ℃, but if zeolite supporting a copper salt that has a denitrification catalytic function is used as the NOx adsorbent, the adsorbent can be heated to air containing NH3 (regeneration gas).
This can be regenerated by bringing it into contact with the liquid at a low temperature of 100 to 300°C (Japanese Patent Application No. 133446/1989).
(see issue).

Problems to be Solved by the Invention By the way, as mentioned above, in the method of injecting NH3 into the regeneration gas used for regenerating the NOx adsorbent, N
There is a possibility that unreacted NOx that did not react with NH3 and excess NH3 are included in the NOx desorbed from the Ox adsorbent. In order to prevent excess NH3 from being contained in the desorption gas, it is necessary to accurately control the amount of NH3 injected into the regeneration gas. Conversely, if the amount of NH3 injected is insufficient,
Since the regeneration of the NOx adsorbent becomes insufficient, NOx
The operation of the adsorbent desorption/regeneration section becomes extremely difficult.

In addition, in order to completely regenerate the NOx adsorbent, if the amount of NH3 injected into the regeneration gas is too large, the desorption gas will contain an excess of NH3, so this gas may be further It is necessary to introduce it into a denitrification reactor and make it harmless by a denitrification reaction between NOx and NH3 or an oxidative decomposition reaction of NH3.

However, when the regeneration gas is not recycled, the amount of gas to be processed is larger than when the regeneration gas is recycled and a portion is extracted, and the scale of the denitrification reactor is likely to increase.

In the moving bed type dehumidification/NOx adsorption equipment used in the NoxllA deposition system of the Industrial Development Institute mentioned above, when handling a large amount of gas, the flow path must be cut off to lower the gas flow resistance. It is necessary to increase the area. on the other hand,
In order to increase adsorption efficiency, it is necessary to extract and fill adsorbent particles uniformly in the cross-sectional direction of the channel, but this is extremely difficult. In addition, gravity is used to move the adsorbent,
In the method of blowing dry air from the bottom of the adsorption tower to the top, problems arise such as wear, cracking, and powdering of the adsorbent itself. Furthermore, wear on the inner surface of the tower and lift vibe is a problem, and
The structure of the tower is complicated and the operation of the equipment is not easy.

Means for Solving the Problems The road tunnel ventilation gas purification device according to the present invention has NO.
Road tunnel ventilation gas purification equipped with an adsorption dehumidifier that dehumidifies x-containing ventilation gas and regenerates a dehumidifier using the purified ventilation gas, and a NOx adsorption device that denitrates the dehumidified ventilation gas In the equipment, there is a gas circulation line that circulates most of the regeneration gas containing NH3 through the regeneration zone of the NOx adsorbent, and a part of the regeneration gas is extracted from the same circulation line and passed through the denitrification reactor, and then released into the atmosphere. It is characterized by being provided with a gas extraction line for releasing gas to.

As the adsorption type dehumidification device and the NOx adsorption device, it is preferable to use a rotary adsorption device in which the dehumidifier and the NOx adsorbent are moved in a direction perpendicular to the gas flow. This device allows continuous extraction, regeneration, and filling of the desiccant and NOx adsorbent.

As a desiccant agent, preferably honeycomb structured silica gel is used.

As the NOx adsorbent, it is preferable to use a honeycomb structure.
Use zeolite with copper salt supported on it.

EXAMPLE An example of a purification apparatus to which the present invention is applied will be explained with reference to the overall flowchart of FIG.

The ventilation gas containing NOx is led to a dehumidifier (1), and moisture in the ventilation gas is adsorbed and removed by a dehumidifier to obtain dry ventilation gas. This gas is then passed through a NOx adsorption device (2
) to adsorb and remove NOx, making it harmless.

Dehumidifier (1) uses this harmless and dry ventilation gas.
Regenerate the dehumidifier. On the other hand, the NOx adsorption device (2)
The adsorbent that has adsorbed Ox is regenerated with a regeneration gas containing NH3.

The greatest feature of the present invention is that NH3
Most of the regeneration gas into which NH3 is injected from the supply device (3) is circulated and used by the blower (4) provided in the gas circulation line, and a part of the regeneration gas is extracted as purge gas through the gas extraction line. This purge gas is passed through a denitrification reactor (5) and then released into the atmosphere.

When regenerating a NOx adsorbent with a gas containing NH, in order to efficiently react the adsorbed NOx and NH3 in the adsorbent,
It is preferable to heat the adsorbent and the recycling gas for regeneration to an appropriate temperature (100 to 300°C) using a heater (8) before regeneration. Further, it is preferable to recycle the regeneration gas from the viewpoint of energy saving. Furthermore, by circulating the regeneration gas containing excess NH, adsorbed NOx in the adsorbent can be more completely reduced and removed, and more complete regeneration of the adsorbent can be achieved.

When regenerating NOx adsorbents using conventional methods, low-efficiency NH3
must be accurately mixed and dispersed in the regeneration gas, and the amount must correspond to the amount of NOx adsorbed in the adsorbent, that is, an amount necessary and sufficient for reduction and removal. This amount cannot be controlled unless the amount of NOx adsorbed in the adsorbent is accurately measured, but as a practical matter it is impossible to continuously measure NOx in the solid adsorbent. In reality, regeneration of the NOx adsorbent by conventional methods is highly likely to result in either leakage of excess NH3 or incomplete regeneration of the adsorbent due to insufficient amount of injected N·H3.

In contrast, the device according to the invention allows an excess of NH3 to be present in the regeneration zone of the NOx adsorbent, so that by supplying a sufficient amount of NH to the same regeneration zone,
This is a truly practical and economical device that enables complete regeneration of the NOx adsorbent and does not require precise control of NH3 injection.

A part of the circulating gas for regeneration is extracted as purge gas, but excess NH contained in this purge gas or NOx released unreacted from the adsorbent is removed by a gas generator installed downstream of the heater (7). It is rendered harmless by the denitration reactor (5).

Since the amount of purge gas treated in the denitrification reactor (5) is very small, the denitrification reactor (5) may be small-sized, and the purge gas can be effectively and inexpensively rendered harmless.

Note that circulating the regeneration gas and extracting a portion of it as purge gas is also necessary in order to employ a rotary adsorption device, as will be described later.

By the way, in the flow sheet of FIG. 1, if the regeneration circulation gas leaks into the ventilation gas after NOx adsorption and removal, the purification rate of the equipment will decrease. When aiming at a purification rate of 60% or more, leakage of the regeneration circulation gas to the purification ventilation gas becomes a major problem.

The NOx adsorption device (2) is a rotary adsorption device.

In this device, there is a sliding part between the NOx adsorbent block (adsorbent rotor) and the ventilation gas or regeneration gas nozzle, and it is difficult to completely seal this part. Therefore, in order to prevent the purification rate from decreasing due to the gas leak, the operating pressure of the regeneration section (cooling, regeneration, preheating) needs to be lower than that of the NOx adsorption section. In this case, gas leaks from the NOx adsorption section to the regeneration section. The gas equivalent to this leak is
It is necessary to extract it from the regeneration gas circulation line. In addition, the NOx adsorbent is N.

At the same time as X, a small amount of moisture is adsorbed, which is desorbed in the regeneration section and accumulated in the regeneration circulating gas.

In order to suppress the moisture content in the recycling gas for regeneration to a predetermined concentration, it is necessary to supply a predetermined amount of dry air to the gas circulation line and to extract the circulating gas containing moisture from the line.

That is, in the device according to the present invention, consideration is given to using the leak gas from the sliding portion of the rotary NOx adsorption device (2) as the main source of supply of dry air to the regeneration circulating gas.

Next, a purification device using a rotary adsorption device as an adsorption device for dehumidification and denitrification will be described.

The adsorption device adopted in the method proposed by the Industrial Development Research Institute uses a moving bed method, as described above based on Figure 4, to move the dehumidifier and NOx adsorbent from the upper part of the tower to the lower part. The dehumidifier and NOx are transferred under their own weight and brought into countercurrent contact with the gas for adsorption, desorption, and regeneration.
The adsorbent is blown up together with dry air and circulated to the top of the tower. In this device, in addition to abrasion and powdering of the dehumidifier and NOx adsorbent, abrasion of the inner surface of the tower and lift vibe is a problem. Wear and pulverization of the dehumidifier and NOx adsorbent not only shorten their service life (usable period) and increase the amount of renewal thereof, but also increase gas flow resistance (pressure drop) within the moving bed. Additionally, expensive wear-resistant materials must be used for the inner surface of the tower and soft vibrator. Furthermore, considering that the structure of the tower is complicated and the operation of the device is not easy, this device cannot be used as a practical device.

In contrast, in this embodiment, a rotary adsorption device is used that can continuously extract, regenerate, and fill the dehumidifier and NOx adsorbent by moving them in a direction perpendicular to the gas flow. ing. This device attempts to achieve the same performance as the conventional device described above using a simpler method, and is a truly practical device because of its low gas flow resistance and simple structure.

First, an example of a rotary dehumidifier will be described with reference to FIG. 2. Dehumidification device (1) used in the purification device of the present invention
The system dehumidifies the ventilation gas to be purified, and regenerates the dehumidifier using the denitrified dry gas. That is, the desiccant is regenerated using the drying gas for regeneration which is approximately the same amount as the ventilation gas to be purified. For this purpose, plate-shaped adsorbents using silica gel as a desiccant agent (moisture adsorbent) are layered with appropriate spacers interposed, flat plates and corrugated plate adsorbents are stacked alternately, or an integrated honeycomb structure is used for dehumidification. Using a wet rotor, create a gas flow path that divides the inside of the rotor into two. Ventilation gas to be purified is then flowed through one of these, dry gas for regeneration is flowed through the other, and the rotor is rotated.

This allows continuous dehumidification treatment.

Next, an example of a rotary NOx adsorption device will be described with reference to FIG. The NOx adsorption device (2) used in the purification device of the present invention adsorbs and removes NOx in dehumidified ventilation gas, obtains harmless dry ventilation gas, and at the same time
The NOx adsorbent is regenerated using a regeneration circulating gas containing the following. To this end, we have stacked plate-like adsorbents made of zeolite with copper salts supported on them with appropriate spacers in between, alternately stacked flat and corrugated adsorbents, and integrated honeycomb structures to remove NOx. Using a rotor, create a gas flow path that divides the inside of the rotor into four. Then, the ventilation gas to be purified after dehumidification is passed through the adsorption zone, and the NH3
The regeneration circulating gas containing the gas is passed through the cooling zone, regeneration zone, and preheating zone in this order, and the rotor is rotated. This allows continuous adsorption and removal of NOx.

Effects of the Invention According to the ventilation gas purification device of the present invention, there is a gas circulation line that circulates most of the regeneration gas containing NH3 through the NOx adsorbent regeneration zone, and a gas circulation line that circulates a part of the regeneration gas from the same circulation line. A gas extraction line is installed to extract the gas, pass it through the denitrification reactor, and then release it to the atmosphere.
Excess NH3 can be present in the regeneration zone of the NOx adsorbent, resulting in a sufficient amount of N to the regeneration zone.
The supply of H3 allows complete regeneration of the NOx adsorbent and also does not require precise control of NH3 injection.

[Brief explanation of the drawing]

Figure 1 is a flow sheet showing an embodiment of the present invention, Figure 2 is a perspective view of a rotary dehumidifier, Figure 3 is a perspective view of a rotary NOx adsorption device, and Figure 4 is a conventional NOx removal system. This is a flow sheet showing the law. that's all

Claims (1)

[Claims] Road tunnel ventilation gas purification comprising an adsorption dehumidifier that dehumidifies NOx-containing ventilation gas and regenerates a dehumidifier using the purified ventilation gas, and a NOx adsorption device that denitrates the dehumidified ventilation gas. In the equipment, there is a gas circulation line that circulates most of the regeneration gas containing NH_3 through the regeneration zone of the NOx adsorbent, and a part of the regeneration gas is extracted from the same circulation line, passed through the denitrification reactor, and then released into the atmosphere. A device characterized in that it is provided with a gas extraction line for releasing gas to.