JPH0616814B2 - Ventilation gas purification method in road tunnel - Google Patents

Description

TECHNICAL FIELD The present invention relates to a mountain tunnel for roads, an underground road, a road with a shelter, etc. (in this specification, these are collectively referred to as “road tunnel”) The present invention relates to a method for purifying ventilation gas, in which contaminated air is ventilated and the ventilation gas is subjected to purification treatment such as nitrogen oxide (NOx) removal.

BACKGROUND OF THE INVENTION In a long-distance road-traffic tunnel,
It is necessary to ventilate the contaminated air inside in order to protect the health of drivers and pedestrians and improve the permeability of soot in the tunnel. In addition, even in a relatively short distance road tunnel, for the one in the urban area or its suburbs, the contaminated air in the tunnel is ventilated in order to cope with the air pollution due to carbon monoxide gas and NOx concentrated in the entrance and exit. There is a need to.

However, if ventilation gas is diffused around the tunnel as it is, it is not only against the improvement of the local environment, but also the pollution level is high especially in the urban area where the exhaust gas pollution is spreading in the plane or its suburbs. It could lead to further expansion of the contaminated area. The above-mentioned situation is exactly the same even when a road is tunneled or a shelter is installed as a measure against pollution of an existing road.

Therefore, there is a demand for a method capable of efficiently removing NOx from ventilation gas emitted from a road tunnel.

2. Description of the Related Art As a method of purifying ventilation gas in a road tunnel, the present applicant dry-processes the ventilation gas discharged from the road tunnel with a zeolite-based adsorbent to mainly adsorb and remove NOx,
We proposed a method of regenerating an NOx-adsorbed adsorbent by treating it with NH ₃ -containing high-temperature air, and filed a patent application separately from this case.

Problems to be Solved by the Invention By the way, in general, the NOx adsorption capacity of a zeolite-based adsorbent is clear from the graph of FIG. 2 which will be described later and shows the relationship between the NOx adsorption capacity of a copper-containing zeolite-based adsorbent and moisture. As such, it is significantly inhibited by coexisting moisture. Therefore, if moisture coexists, a large amount of zeolite adsorbent, which is a relatively expensive substance, must be used. Further, the zeolite-based adsorbent irreversibly absorbs coexistence of moisture, so the adsorbed moisture must be desorbed by heating in the regeneration process of the adsorbent, which consumes a large amount of energy. Will be needed.

Therefore, the following items are required for the purification of ventilation gas using the zeolite-based adsorbent.

(1) Remove moisture from ventilation gas in advance to prevent the NOx adsorption capacity of the zeolite adsorbent from being inhibited by moisture.

(2) Minimize the energy consumption required to remove moisture from ventilation gas.

In view of the above situation, an object of the present invention is to provide a practical ventilation gas purification method capable of efficiently removing NOx from ventilation gas emitted from a road tunnel at low energy cost.

Means for Solving the Problems The method for purifying ventilation gas according to the present invention is a method of dry-treating ventilation gas having a NOx concentration of 5 ppm or less discharged from a road tunnel with a zeolite adsorbent to remove NOx by adsorption. In the hygroscopic process before the adsorption process, the moving block row holding the silica gel dehumidifying agent is intermittently moved countercurrently to the hygroscopic zone through which the ventilation gas flows, to absorb the ventilation gas, and then the outlet of the hygroscopic zone. Preheat the flow of dry treated ventilation gas after removing NOx to the blocks that have reached the end sequentially.
It is sent to the cooling zone and intermittently moved in the countercurrent direction from its inlet end to be dried by aeration, and the moving block is extracted from the middle part of the preheating / cooling zone and sent to the heating zone where the dehumidifying agent is heated. After drying, insert the regeneration block back into the pre-heating / cooling zone at the original position of the block row,
It is characterized by returning from the exit end of the preheating / cooling zone to the entrance end of the moisture absorption zone.

In a preferred embodiment of this invention, in the moisture absorption step,
Silica gel-based dehumidifiers can be used not only for moisture in ventilation gas,
It also adsorbs and removes various coexisting hydrocarbon vapors, oil mists, and soot and dust. Moisture absorption by the dehumidifying agent and regeneration of the absorbed dehumidifying agent are preferably carried out by a moving bed type moisture absorbing section, preheating / cooling section and heating section. However,
A method may be used in which the fixed bed is filled with the dehumidifying agent and the ventilation gas to be absorbed and the dried treated ventilation gas for regeneration are alternately passed through the fixed bed of the dehumidifying agent.

Most of the moisture adsorbed on the dehumidifying agent is desorbed and removed from the dehumidifying agent by aeration drying with a treatment ventilation gas, and the rest is desorbed and removed by heat drying.

In the NOx adsorption step, a zeolite-based adsorbent containing a metal oxide such as copper or vanadium is preferably used as the adsorbent.

In the NOx adsorbent regeneration step, NOx is selectively reduced to nitrogen gas by NH ₃ as a reducing agent and desorbed from the adsorbent. As a result, the adsorbent is regenerated. Regeneration of the adsorbent is carried out at a temperature of 100 ° C or higher, preferably 150 ° C or higher.

The adsorption of NOx and the regeneration of the adsorbent are preferably carried out by a moving bed type adsorption section, preheating / cooling section and regeneration section. However, a method may be used in which the fixed bed is filled with the adsorbent and the ventilation gas to be purified and the NH ₃ -containing high-temperature air for regeneration are alternately passed through the fixed bed.

EXAMPLES Next, examples of the present invention will be specifically described.

Example In FIG. 1, a ventilation blower is installed from a road tunnel (1).
The ventilation gas discharged by (2) is guided to the moisture absorption section (4) of the moisture absorption facility (3). The moisture absorption equipment (3) preheats the moisture absorption part (4) that adsorbs the moisture in the ventilation gas with the dehumidifying agent and the absorbed dehumidifying agent with dry ventilation gas, and cools the regenerated dehumidifying agent after heating. It is composed of a preheating / cooling unit (5) and a heating unit (6) for regenerating the dehumidifying agent coming from the preheating / cooling unit (5) by heating and drying. Moisture absorber (4), preheating / cooling unit (5) and heating unit
Each of (6) is a moving bed type, and a plurality of moving blocks (7) holding a silica gel dehumidifying agent are arranged in a line inside the moisture absorbing section (4) and the preheating / cooling section (5). There is. The moving block (7) is intermittently moved in the moisture absorption section (4) in the countercurrent direction to the ventilation gas flow, and the one reaching the outlet end of the moisture absorption section (4) is the preheating / cooling section (5). And is discontinuously moved in the interior from the inlet end toward the outlet end. Then, the moving block (7) is taken out at an intermediate portion of the preheating / cooling section (5) and sent to the heating section (6). After the dehumidifying agent is regenerated, the moving block (7) is inserted again into the original position of the block row of the preheating / cooling unit (5), and the moving end (5) is moved from the outlet end of the preheating / cooling unit (5) to the inlet end of the moisture absorption unit (4). Returned to.

In the preheating / cooling section (5), the NOx adsorbing section of the NOx removal facility (8) described later is provided in the countercurrent direction to the moving direction of the block
The dried treated ventilation gas from (9) is circulated. As a result, this dried treated ventilation gas is used for cooling the dehumidifying agent regenerated by heating on the outlet end side of the preheating / cooling section (5) and for preheating the absorbed unregenerated dehumidifying agent on the inlet end side. Used respectively. Also, the heating section (6) has a N
From the adsorbent regeneration part (11) of the Ox removal equipment (8) to the blower (12)
The hot air that has been sent through and heated by the heater (13) is circulated.

In the moisture absorption section (4), the ventilation gas moisture is
The dried silica gel dehumidifying agent held in (7) adsorbs the ventilation gas adsorbed up to a dew point of -16 ° C and dried in this way from the moisture absorption section (4) to the NOx adsorption section (8) of the NOx removal facility (8). 9) sent to. Next, the moving block (7) holding the absorbed dehumidifying agent is moved from the moisture absorbing section (4) to the preheating / cooling section (5), and the dehumidifying agent on the inlet end side of the moving block (this is It is preheated by a NOx removing section (9) described later to dehumidify the moisture to a dew point of −22 ° C., and is dried to some extent. The transfer block (7) is then sent from the middle part of the preheating / cooling section (5) to the heating section (6), where the dehumidifying agent is heated to a temperature of 150 ° C by hot air to be completely dried and regenerated. To be The moving block (7) holding the regenerated dehumidifying agent is inserted into the original position of the block row of the preheating / cooling section (5), cooled by the drying treatment ventilation gas at the outlet end side, and then the moisture absorption section (4). Returned to the entrance end of. The heat quantity of the process ventilation gas required for drying the dehumidifying agent is sufficiently supplemented by the heat of adsorption of the moisture in the moisture absorbing section (4) and the NOx adsorbing section (9) and by cooling the dehumidifying agent after heating.

NOx removal equipment (8) installed on the downstream side of the moisture absorption equipment (3)
Is a NOx adsorber (9) that adsorbs NOx in ventilation gas with an adsorbent, and a preheater / cooler (10) that preheats the unregenerated adsorbent in the NOx adsorbed state and cools the adsorbent after regeneration. It mainly comprises an adsorbent regeneration section (11) for NOx desorption treatment of the adsorbent coming from the preheating / cooling section (10). The NOx adsorbing section (9), the preheating / cooling section (10) and the adsorbent regeneration section (11) are all of a moving bed type, and the plurality of moving blocks (14) holding the NOx adsorbent are the NOx adsorbing section. (9) → preheating / cooling section (10) → adsorbent regeneration section (11) → preheating / cooling section (10) → NO
The x adsorption portion (9) is moved alternately in the order, and these portions (9), (10) and (11) are stopped for a certain period of time.

As the adsorbent, a zeolite adsorbent containing a metal oxide such as copper or vanadium is used. Part of the treated ventilation gas from which NOx has been removed by the dry treatment in the NOx adsorbing section (9) is sent to the preheating / cooling section (5) of the moisture absorption equipment (3) as described above. The rest of the gas is the NOx adsorption part.
It is sent from (9) through the switching valve (15) to the preheating / cooling section (10) and is circulated in the vertical direction. As a result, this treated ventilation gas is used for preheating the unregenerated adsorbent that moves from the NOx adsorption part (9) to the adsorbent regeneration part (11) and for cooling the regenerated adsorbent that moves in the opposite direction after heating. Used respectively.

In the adsorbent regeneration unit (11), the unregenerated adsorbent of the moving block (14) coming from the preheating / cooling unit (10) is contact-treated with high-temperature air containing NH ₃ . This air is preheated / cooled (10)
It is the process ventilation gas that is discharged from the exhaust gas, is sent to the adsorbent regeneration section (11) by the circulation blower (16), and is 100 ℃ by the heater (17).
It is heated above. NH ₃ is added to the heated air from the cylinder (18). As a result, NOx is NH ₃ as a reducing agent.
Is reduced to nitrogen gas and desorbed from the adsorbent to regenerate the adsorbent.

The air that has passed through the adsorbent regeneration unit (11) is circulated blower (16).
Is circulated and reused, and the process ventilation gas is replenished from the preheating / cooling unit (11) as necessary. Also, a part of this air is extracted from the circulation line, and as described above, the moisture absorption facility (3)
It is sent to the heating part (6) of the as hot air for regenerating the dehumidifying agent.

Zeolite NOx Adsorption Capacity The relationship between the NOx adsorption capacity and moisture content of the zeolite adsorbent containing copper oxide is shown in FIG. From the figure, NO of zeolite
It can be seen that the x adsorption capacity is significantly inhibited by moisture.

Dehumidifying Properties of Adsorbents The relationship between the relevant temperature and the equilibrium adsorption amount of water is shown in FIG. 3 for zeolite and silica gel. As is clear from the figure, zeolite shows almost constant moisture absorption at any relevant temperature, whereas silica gel has a relative moisture absorption of 0.
A moisture absorption amount of approximately 60% is almost proportional to humidity. This shows that zeolite adsorbs moisture irreversibly, while silica gel adsorbs moisture reversibly. Generally, in the case of irreversible adsorption of moisture, heating is required to desorb water from the dehumidifying agent and dry it, but in the case of reversible adsorption, heating is not absolutely necessary. The agent can be dried with dry air. However, if the moisture content adsorbed on silica gel becomes 0.01 kg (water content) / kg (silica gel) or less, the drying speed becomes very slow and heating becomes impractical unless heating is performed. Therefore, in the process of the present invention, silica gel drying with dry air is limited to an area having an adsorbed moisture content of 0.01 kg (moisture) / kg (silica gel) or more, and the remaining moisture is desorbed and removed by heating.

Test 1 (Silica gel moisture absorption test) Referring to FIGS. 4 and 5, a pair of upper and lower 5-mesh stainless steel wire nets are provided on the upper and lower surfaces of the pair of left and right stainless steel side plates (51, 52). Weld each side of (53) (54), and the thickness is 1.8mm between the upper and lower wire nets (53) (54).
The dehumidifying agent (55) consisting of the plate-like silica gel of was inserted. Thus, a plurality of silica gel dehumidifying agent test pieces (56) were manufactured.

Separately from this, as shown in FIG. 5, a 10 m long polyvinyl chloride rectangular duct (59) having guide grooves (57) and (58) on both inner sides was prepared.

Insert the side plates (51) (52) of the sufficiently dried test piece (56) into the guide grooves (57) (58) of the rectangular duct (59), respectively.
Ducts of multiple test pieces (56), one by one every 5 minutes
It was pushed into the inlet end of (59), moved in the pushing direction at a speed of 1.2 m / h, and pulled out from the outlet end one by one every 5 minutes. Also, in the countercurrent direction to the insertion direction,
Air containing 2% moisture was pumped at 36 / min.

After operating for 16 hours, air sampling for moisture analysis is performed from the sampling unit provided in the duct (59) at intervals of 1 m, moisture is measured for each sampling air, and the duct is used.
The concentration distribution of moisture in (59) was investigated. Also, after the air circulation and the insertion of the test piece were completed, the duct (59) was opened, the water content in the test piece at each sampling position in the duct (59) was analyzed, and the equilibrium partial pressure of silica gel was calculated from this. . The results thus obtained are shown in FIG. From the figure, it can be seen that the plate-like silica gel has a sufficient moisture absorption capacity under the above conditions.

Test 2 (moisture absorption test of silica gel) Using a rectangular duct having the same structure as the duct used in Test 1,
As the test piece to be pushed into the duct, the test piece used in Test 1 was treated with air having a moisture content of 1.6% to adsorb the moisture to a saturated state, and the air fed into the duct had a dew point of − The operation was performed under the same conditions as in Test 1 except that dry air of 22 ° C. was used. Then, the concentration distribution of moisture in the duct and the equilibrium partial pressure of silica gel were obtained. The results are shown in FIG. From the figure, it can be seen that about 90% of the moisture contained in the test piece pushed into the duct is adsorbed and removed by the dry air.

EFFECTS OF THE INVENTION According to the method for purifying ventilation gas of the present invention, the ventilation gas discharged from the road tunnel is dry-processed with a zeolite-based adsorbent to obtain N 2.
When the Ox is adsorbed and removed, the ventilation gas is preliminarily adsorbed with a silica gel-based dehumidifying agent before the NOx adsorption treatment.
The NOx adsorption capacity of the zeolitic adsorbent can be significantly improved compared to the case where the moisture absorption treatment is not performed before the Ox adsorption treatment (If the moisture content in the ventilation guy is 0.1%, the NOx adsorption amount Improves about 15 times). Therefore, the amount of the expensive zeolite-based adsorbent used can be significantly reduced (actually to 1/5 or less), and the NOx removal equipment can be downsized.

To regenerate the absorbed dehumidifying agent, before heating and drying,
Since the dehumidifying agent is dried by aeration with the dried treatment ventilation gas after removing NOx, the heat quantity required for heating and drying the dehumidifying agent is
It can be significantly (actually 1/4) reduced as compared with the case where the moisture absorption treatment is not performed before the adsorption treatment.

Therefore, according to the method of the present invention, it is possible to reliably prevent the expensive zeolite-based adsorbent from deteriorating the NOx adsorption performance, and to efficiently purify the ventilation gas at a low energy cost.

Since a silica gel-based dehumidifying agent is used,
Silica gel not only adsorbs and removes the moisture in the ventilation gas, but also adsorbs and removes various coexisting hydrocarbon vapors, oil mist, and soot. Therefore, since these coexisting substances do not accumulate in the NOx removal equipment on the downstream side, it is not necessary to heat the NOx adsorbent at a temperature as high as 250 ° C. or higher to remove the accumulated substances, and an expensive zeolite adsorbent is used. It is possible to avoid the performance deterioration due to the sintering of.

Further, in the hygroscopic step before the NOx adsorption treatment, the moving block row holding the silica gel dehumidifying agent is intermittently moved in the countercurrent direction to the hygroscopic zone in which the ventilation gas flows,
The moisture of the ventilation gas can be adsorbed up to the dew point by the dry silica gel-based dehumidifying agent held in the moving block row. Thus, the hygroscopic treatment of the ventilation gas can be effectively performed.

The blocks reaching the outlet end of the moisture absorption zone are sequentially sent to the preheating / cooling zone in which the dried process ventilation gas after NOx removal is made to flow and are also intermittently moved in the countercurrent direction from the inlet end, so dry process ventilation The gas can be used for cooling the dehumidifying agent regenerated by heating at the outlet end side of the preheating / cooling zone, and for preheating the absorbed unregenerated dehumidifying agent at the inlet end side. Thus, the dehumidifying agent can be effectively dried by aeration.

Furthermore, the moving block is extracted from the middle part of the preheating / cooling zone and sent to the heating zone, where the dehumidifying agent is heated, so the dehumidifying agent can be heated by hot air and completely dried, and can be reused. You can

The heat quantity of the processing ventilation gas required for drying the dehumidifying agent is sufficiently supplemented by the heat of adsorption of moisture in the moisture absorption zone and the NOx adsorption zone and by cooling the dehumidifying agent after heating.

[Brief description of drawings]

FIG. 1 is a flow sheet showing an embodiment of the present invention, FIG. 2 is a graph showing the relationship between water concentration and NOx equilibrium adsorption amount, FIG. 3 is a graph showing the relationship between relational temperature and equilibrium adsorption amount, and FIG.
The figure is a perspective view of the test piece, FIG. 5 is a perspective view of a rectangular duct containing the test piece, and FIGS. 6 and 7 are graphs showing the relationship between the floor length and the water partial pressure. (1) …… Reverse path tunnel, (3) …… Moisture absorption equipment, (4) …… Moisture absorption part, (5) …… Preheating / cooling part, (6) …… Heating part, (7)…
… Movement block, (8) …… NOx removal equipment, (9) …… N
Ox adsorber, (10) ... preheating / cooling unit, (11) ... adsorbent regeneration unit, (14) ... moving block.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigenori Onizuka 1-6-14 Edobori, Nishi-ku, Osaka City, Osaka Prefecture Hitachi Shipbuilding Co., Ltd. (56) References JP-A-47-14071 (JP, A) JP-A-SHO 49-44969 (JP, A) JP-A-50-10282 (JP, A) JP-A-53-28944 (JP, A) JP-B-53-17114 (JP, B2)

Claims (2)

[Claims] 1. The concentration of NOx emitted from a road tunnel is 5 ppm.
The following ventilation gases are dry treated with a zeolite-based adsorbent to produce N
In adsorbing and removing Ox, in the hygroscopic process before the NOx adsorbing process, the moving block row holding the silica gel dehumidifying agent is intermittently moved in the countercurrent direction to the hygroscopic zone through which the ventilation gas flows and the ventilation gas is discharged. Preheats the blocks that reach the outlet end of the moisture absorption zone by sequentially adsorbing dry treated ventilation gas after removing NOx.
It is sent to the cooling zone and intermittently moved in the countercurrent direction from its inlet end to be dried by aeration, and the moving block is extracted from the middle part of the preheating / cooling zone and sent to the heating zone where the dehumidifying agent is heated. After drying, insert the regeneration block back into the pre-heating / cooling zone at the original position of the block row,
A method for purifying ventilation gas in a road tunnel, which comprises returning from the exit end of the preheating / cooling zone to the entrance end of the moisture absorption zone. 2. In the description of claim 1, N
A method of treating an adsorbent that has adsorbed Ox with high-temperature air containing NH ₃ to regenerate it.