JPH07204458A - Wet exhaust gas desulfurizing method and apparatus - Google Patents

Abstract

PURPOSE:To enhance desulfurization capacity and dust extraction capacity in the absorbing tower of a wet exhaust desulfurizer having a vertical absorbing tower. CONSTITUTION:In a wet exhaust gas desulfurizer equipped with a vertical absorbing tower 2 having an exhaust gas inlet 1a and a treated exhaust gas outlet 5a and permitting exhaust gas to pass from below to above and two or more stages of spray headers 3, 17, 18, 19 having a large number of spray nozzles 4 and arranged in the absorbing tower and absorbing sulfur dioxide in exhaust gas by the liquid droplets of the absorbing soln. sprayed from the spray nozzles, upward nozzles are provided to the lower stage spray header 3 and downward nozzles are provided to the second stage spray header 17 to form an area high in the density of sprayed liquid droplets. By this constitution, desulfurization capacity and dust extraction capacity can be enhanced without increasing flow resistance and the use amt. of the absorbing soln. and the apparatus can be made compact.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wet exhaust gas desulfurization method and apparatus, and more particularly to a highly efficient wet exhaust gas desulfurization method and apparatus suitable for reducing sulfur oxides and dust in exhaust gas.

[0002]

2. Description of the Related Art In order to prevent air pollution, a wet limestone-gypsum desulfurization device has been widely put into practical use as a device for removing sulfur oxides in exhaust gas. A conventional technique of this wet limestone-gypsum desulfurization device is shown in FIG. Exhaust gas 1 containing sulfur oxides and soot dust generated from a thermal power plant or the like is guided to an absorption tower 2 of an exhaust gas desulfurization device. In the absorption tower 2, at least two or more spray headers (3, 17, 18, 19) equipped with a large number of spray nozzles are installed, and an absorption liquid sprayed as fine liquid droplets from the spray nozzle 4 mounted downward is used. By contacting the exhaust gas 1, the sulfur oxides in the exhaust gas are chemically absorbed on the surface of the absorbing droplet, and the soot dust is physically removed by collision with the droplet. The minute droplets accompanying the exhaust gas flow are removed by the mist eliminator 5 installed at the upper part of the uppermost spray header 19, and the purified exhaust gas 6 is installed on the downstream side of the absorption tower if necessary and reheated. It is heated by the equipment and discharged from the chimney. Most of the droplets sprayed from the nozzle 4 absorb the sulfur oxide and then fall into the absorption tower circulation tank 7 provided at the lower part of the absorption tower.

Sulfur oxide (SO ₂ ) absorbed in the absorption liquid
Reacts with limestone (CaCO ₃ ) contained in the absorption liquid, and is further oxidized by the air 8 supplied to the absorption tower circulation tank 7 to become gypsum (CaSO ₄ .2H ₂ O). This series of reactions is represented by the following formula.

[0004]

[Chemical formula 1] SO ₂ + 2H ₂ O + CaCO ₃ + 1 / 2O ₂ → C
aSO ₄ .2H ₂ O + CO ₂ The removed soot and dust fall into the absorption tower circulation tank 7 together with the absorption liquid. On the other hand, the limestone 9 which is the absorbent is stored as limestone slurry in the limestone supply facility 10 and is supplied to the absorption tower circulation tank 7 by the limestone slurry pump 11. Further, in order to recover the gypsum produced in the absorption tower, a part of the absorption liquid in the absorption tower circulation tank 7 is withdrawn by the pump 12
Then, the liquid is sent to the gypsum dewatering facility 13, and the gypsum and soot and dust contained in the absorbing liquid are collected as a solid substance 14. A part of the dehydrated liquid of gypsum and dust is discharged to the outside of the system through the drain line 15 in order to prevent impurities from concentrating in the system, and the remaining liquid is used as makeup water for limestone slurry production in the limestone supply facility 10. The rest is sent to the absorption tower through the dehydration liquid return line 16.

In the absorption tower, the absorption liquid in the tank 7 is sent to the spray header by the circulation pump 23 and is sprayed from the spray nozzle 4 described above. The amount of the absorption liquid circulated and sprayed is the amount of the exhaust gas and the sulfur oxidation in the exhaust gas. It is determined by the product concentration and the required desulfurization rate. On the other hand, since the flow rate per one stage of the spray header is determined by the capacity of the spray nozzle used and the spray nozzle mounting interval, it is usually necessary to make the spray header 3 to 6 stages. That is, the absorbing liquid is divided and sprayed into the spray headers 3, 17, 18, and 19 in the absorption tower. Here, the sprayed state of the absorbing liquid sprayed from the spray nozzle 4 is shown in FIG. The absorbing liquid is sprayed in a conical ring generally called a hollow cone, and the spray angle is about 80 to 120 °. Immediately after being sprayed from the spray nozzle 4, the absorbing liquid 20 sprayed from the spray nozzle 4 has a high density of absorbing droplets.
The droplet density decreases as the flight distance increases after being sprayed from. Therefore, the efficiency of removing sulfur oxides and soot from the exhaust gas becomes large in the portion where the droplet density is high immediately after being sprayed from the spray nozzle 4. Therefore, in order to improve the removal efficiency of sulfur oxides and dust, it is desirable to increase the droplet density of the absorbing liquid in the absorption tower, but in the above-mentioned conventional technology, the absorbing liquid is divided and sprayed into each spray header. Therefore, the droplet density of the absorbing liquid sprayed from each spray header was almost the same in all spray header parts.

Further, by increasing the flow velocity of the exhaust gas in the absorption tower, the diffusion and absorption rate of the sulfur oxides into the absorption liquid can be increased, and the collision speed of the soot and dust with the absorption liquid also increases, so that the removal efficiency can be improved. Further, since the required absorption tower cross-sectional area is reduced, the absorption tower diameter can be made smaller and the equipment cost can be reduced. However, the mist eliminator 5 installed in the upper part of the absorption tower has a limit flow velocity of about 3 m / s. However, if it is more than that, the mist collected by the mist eliminator 5 is scattered again, so that the gas flow velocity in the absorption tower needs to be equal to or lower than the limit flow velocity of the mist eliminator 5. An outline of the structure of a conventional mist eliminator provided in the last flow section in the absorption tower is shown in the upper right part of FIG. It is formed by arranging a number of corrugated plates bent in a dogleg shape at a predetermined interval in the vertical direction (horizontal type), and the mist in the processing gas adheres to the corrugated plates due to inertia while passing between corrugated plates. However, if the gas flow velocity is too high (the limit flow velocity is 3 m / s), the liquid droplets will not fall down but will be hit by the gas and the droplets will fly upward.

FIG. 5 is an explanatory view showing another conventional technique.
In FIG. 5, the spray headers 3, 17,
18 and 19 are provided, and the spray liquid is sprayed from the spray nozzle 4 provided in each spray header in a downward direction which is a countercurrent to the exhaust gas flow direction. A perforated plate 21 is provided below the spray header 3 at the uppermost stream stage (the lowermost stage in the figure). The purpose of this perforated plate is to rectify the exhaust gas that has flowed into the absorption tower 2 from the exhaust gas inlet provided on the side wall of the tower so that the exhaust gas flows as uniformly as possible in the horizontal cross section of the absorption tower.

When the absorbing droplets sprayed from the spray nozzle 4 fall into contact with the porous plate 21 and drop through the porous plate into the absorption tower circulation tank at the lower part of the tower, gypsum in the absorbing liquid is deposited on the porous plate. There is a tendency to block the aperture of the perforated plate,
This tendency is particularly remarkable on the lower surface of the porous plate. Therefore, in order to prevent this, the spray header 22 having the upward spray nozzle 4'is provided at the lower part of the perforated plate.

From the nozzles provided in the spray headers 3 and 22, the absorbing liquid is sprayed in the opposite direction.
Since it was divided into 1, it was not possible to increase the spray droplet density in the absorption tower.

[0010]

The above-mentioned prior art does not consider increasing the droplet density of the absorbing liquid in the absorption tower to increase the removal efficiency of sulfur oxides and dust, and the When the amount of sulfur oxides or the amount of soot and dust is large, it is necessary to increase the amount of circulating spray of the absorbing liquid in the absorption tower, so that the number of stages of the spray header is increased, which causes a problem of increase in equipment cost and operation cost. Further, since the gas flow velocity in the absorption tower cannot be increased due to the restriction of the limit flow speed of the mist eliminator, there is a problem that the absorption tower diameter increases and the equipment cost increases as the amount of treated gas increases.

An object of the present invention is to form a region in the absorption tower in which the density of droplets of the absorbing liquid is high, so that sulfur oxides and soot and dust can be removed with high efficiency and the gas flow velocity in the absorption tower can be increased. An object of the present invention is to provide an economical exhaust gas desulfurization apparatus and a desulfurization method capable of reducing the absorption tower diameter.

[0012]

In order to achieve the above object, the invention claimed in the present application is as follows. (1) A solid absorption tower having an exhaust gas inlet and a treated exhaust gas outlet for passing exhaust gas from below to above, and a plurality of stages of spray headers having a large number of spray nozzles and arranged in the absorption tower, In the wet exhaust gas desulfurization apparatus for absorbing and removing the sulfur oxide therein by the spray absorption droplets from the spray nozzle, an upward spray nozzle is provided in the lowermost spray header of the spray header in the absorption tower, and a second subsequent spray nozzle. A wet exhaust gas desulfurization device characterized in that a downward spray nozzle is provided in the spray header.

(2) In the invention of (1) above, the wet exhaust gas desulfurization apparatus is characterized in that a downward spray nozzle is provided in the spray header provided in a downstream region above the second stage spray header in the absorption tower. . (3) A solid absorption tower having an exhaust gas inlet and a treated exhaust gas outlet for passing exhaust gas from below to above, and a plurality of stages of spray headers having a large number of spray nozzles and arranged in the absorption tower, In a wet exhaust gas desulfurization device that absorbs and removes sulfur oxides in the spray absorption droplets from the spray nozzle, a combination of a spray header provided with an upward spray nozzle and a spray header provided with a downward spray nozzle in the next stage above it is used. A wet exhaust gas desulfurization apparatus comprising a spray header at the lowermost stage and a next stage, and one or more spray headers provided at an upper stage downstream of the spray header.

(4) In the invention of (1), (2) or (3), the combination of the spray header having the upward spray nozzle and the spray header having the downward spray nozzle of the next stage is combined with the upper spray nozzle. The present invention relates to a wet exhaust gas desulfurization device, which is configured such that its horizontal mounting positions face each other at substantially the same center. (5) The exhaust gas is passed from the lower part to the upper part in the rigid absorption tower, and the absorbing liquid is sprayed from a spray nozzle provided in a plurality of stages of spray headers arranged in the absorption tower to absorb and remove sulfur oxides in the exhaust gas. In the wet exhaust gas desulfurization method, the exhaust gas velocity in the absorption tower is set to more than 3 m / s and 7 m / s or less, the spray nozzle of the lowermost spray header is upwardly injected, and the spray nozzle of the next upper spray header is downwardly injected, and A spray header is also installed above them to enable injection from the spray nozzle, the mist in the exhaust gas is removed by the vertical corrugated sheet mist eliminator installed in the exhaust gas duct downstream of the absorption tower outlet, and the sulfur oxidation of the exhaust gas in the absorption tower is performed. The feature is that when the material throughput (load) decreases, the injection of absorbing liquid is stopped from the upper spray header according to the load. Wet flue gas desulfurization how to.

[0015]

In the absorption tower, the first upward spray nozzle and the second downward spray nozzle from the bottom form a region in which the droplet density of the absorbing liquid is high, and by omitting the mist eliminator in the absorption tower, Since the contact efficiency between the exhaust gas and the absorbing liquid can be increased by increasing the gas flow velocity inside,
The efficiency of removing sulfur oxides and soot in the exhaust gas can be increased.

Further, by making the nozzle center of the upward nozzle of the spray header of the first stage from the bottom and the nozzle center of the downward nozzle of the spray header of the second stage from the bottom face substantially on the same line, a further liquid is introduced at the inlet of the absorption tower. Areas with high drop density can be formed. Further, as shown in FIG. 1, when the exhaust gas flows from the inlet provided in the side wall of the rigid absorption tower and the flow direction is deflected upward, the gas flow tends to be biased to the side wall opposite to the inlet. In this case, since a region having a high droplet density is formed in the lowermost stage, there is an effect of correcting this drift.

[0017]

FIG. 1 shows an embodiment of the present invention. The exhaust gas 1 containing sulfur oxides and dust is introduced into the absorption tower 2 of the exhaust gas desulfurization apparatus via the absorption tower exhaust gas inlet 1a. In the absorption tower, the spray nozzle 4 is attached upward to the first stage (lowermost stage) spray header 3, and the spray nozzle 4 is attached downward to the second stage spray header 17. Exhaust gas introduced into the absorption tower is a region of high droplet density sprayed from the spray nozzle 4 attached to the first stage spray header 3 and the second stage spray header 17, where sulfur oxides and soot dust are efficiently removed, Furthermore, the spray header 1 in the third and fourth stages
Residual sulfur oxides and dust are removed by the absorbing liquid sprayed from the spray nozzle 4 attached to Nos. 8 and 19. The spray headers after the third stage may be installed in the required number of stages according to the amount of sulfur oxides in the exhaust gas. Since the exhaust gas that has passed through the spray portion and is purified contains fine droplets (mist), the mist is removed by the mist eliminator 5 installed in the absorption tower outlet duct 5a.

An outline of the mist eliminator 5 provided in the horizontal absorption tower outlet duct 5a is shown in the upper right portion of FIG. The corrugated plate is installed vertically as a vertical shape, and the collected mist becomes droplets that travel along the corrugated plate and quickly flow downward to be collected by a hopper provided at the bottom. Therefore, since the amount of liquid accumulated in the corrugated plate (folded plate) is small, the liquid film is not easily torn, and the desulfurization rate can be improved by increasing the gas flow rate to about 7 m / s, which exceeds the conventional 3 m / s.

The sulfur oxide absorbed in the absorbing solution reacts with limestone in the absorbing solution and oxygen in the air 8 supplied to the absorption tower circulation tank 7 to produce gypsum. In order to collect the gypsum and soot in the absorbing liquid, a part of the absorbing liquid is extracted and sent to the gypsum collecting facility 13 by the pump 12, the gypsum and soot in the absorbing liquid are collected as solid matter 14, and the dehydrated liquid is the system. In order to prevent impurities from concentrating inside, a part is discharged out of the system through the drain line 15, and the remaining dehydrated liquid is returned to the absorption tower via the line 16 or sent to the limestone supply facility 10 as make-up water. To be done.

Absorbed liquid droplets that have absorbed sulfur oxides and have collected soot in the absorption tower fall into the absorption tower circulation tank 7 provided in the lower part of the absorption tower. The gas-liquid contact in the spray type absorption tower is
It is the contact between the droplets of the absorbing liquid sprayed from the spray nozzle and the exhaust gas.For the absorption of sulfur oxides, if the limestone concentration in the absorbing liquid, the amount of the absorbing liquid sprayed, and the exhaust gas flow rate in the absorption tower are constant, absorption The gas-liquid contact area in the tower has an effect. Therefore, in the prior art, the spray nozzle was arranged so that the droplet density in the absorption tower was uniform, but by forming a region where the droplet density is high in the absorption tower with the same gas-liquid contact area, the exhaust gas and absorption Contact with the liquid becomes severe. Further, when the flow rate of the exhaust gas in the absorption tower is increased, the contact between the exhaust gas and the absorbing liquid becomes more vigorous, and the mass transfer rate of the sulfur oxide from the exhaust gas into the absorbing liquid increases. Even if the gas-liquid contact area is the same as the conventional one, a region having a high droplet density is formed, and the exhaust gas flow rate in the absorption tower is increased, whereby the absorption efficiency of sulfur oxides can be increased.

The removal of soot is a physical collision between the droplets of the absorbing liquid sprayed from the spray nozzle and the soot. The higher the droplet density and the higher the gas flow velocity in the absorption tower, the higher the probability of collision between the droplets and soot. Therefore, by forming a region having a high droplet density in the absorption tower, a higher dust removal efficiency than that of the conventional one can be obtained. In addition, when the load of the boiler that discharges exhaust gas decreases at night, that is, when the amount of treated gas in the absorption tower decreases, in order to reduce operating costs, the topmost (last) spray header in the absorption tower spray section is reduced. The spray of the absorbing liquid is stopped in order from the above according to the load. Therefore, at the minimum load, the absorbing liquid is sprayed only from the spray header of the first stage at the lowermost stage and the second stage above it. Also in this case, a region having a high density of absorbed liquid droplets can be formed.

In order to confirm the effect of the present invention, a test was conducted using a pilot plant having a treatment gas amount of 10,000 m ³ N / h. The results are shown below. 1. Test conditions Absorption tower inlet exhaust gas amount: 10,000 m ³ N / h Absorption tower inlet sulfur oxide concentration: 2000 ppm Absorption tower inlet soot dust concentration: 100 mg / m ³ N Absorbing liquid spray amount: 200 m ³ / h Number of spray header stages: 4 stages Spray nozzle Installation direction and exhaust gas flow velocity in absorption tower Conventional technology: All four stages installed downward, exhaust gas flow velocity 2.5m
/ S Invention I: 1st stage (lowermost stage) upward mounting 2 to 4th stage downward, exhaust gas flow rate 2.5m / s Invention II: 1st stage upwards 2 to 4th stage downward mounting, exhaust gas flow velocity 4m / s 2. Test results

[0023]

[Table 1] Another embodiment of the present invention is shown in FIG. In this embodiment, the absorption tower 2
In, the spray nozzle 4 is attached upward to the first stage (lowermost stage) spray header 3 and the downward spray nozzle 4 is attached to the second stage spray header 17 to form a region in which the droplet density of the absorbing liquid sprayed from the spray nozzle 4 is high. 3 more
By mounting the spray nozzle 4 upward on the stage spray header 18, a region where the droplet density of the absorbing liquid is high is formed between the spray nozzle 4 and the downward spray nozzle 4 mounted on the fourth stage spray header 19.

The effect of this embodiment is that the efficiency of removing sulfur oxides and dust can be improved by increasing the area where the droplet density of the absorbing liquid formed in the absorption tower is high. In the present embodiment, the number of combinations of the upward spray header and the downward spray header and the mounting location are not particularly limited, and the effect is obtained in many cases. In the embodiment of FIG. 1 and FIG. 2, by making the nozzle center positions of the upward nozzle and the downward nozzle substantially coincide with each other and forming the conical annular spray region formed by the nozzle all over the absorption tower cross section,
In particular, it is possible to form an absorption tower having a high spray droplet density and a high absorption performance.

[0025]

According to the present invention, the efficiency of removing sulfur oxides and dust can be significantly improved as compared with the prior art. This has the effect of being able to reduce the amount of sprayed absorption liquid and reduce the power of the absorption liquid circulation pump. Further, since the absorption tower diameter can be reduced, there is an effect that the absorption tower installation area and equipment cost can be reduced. In addition, since the pressure loss of the absorption tower can be reduced, the power of the ventilation fan of the exhaust gas desulfurization device can be reduced.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an embodiment of the present invention.

FIG. 2 is an explanatory view of another embodiment of the present invention.

FIG. 3 is an explanatory diagram of a conventional technique.

FIG. 4 is an explanatory view of spray droplets from a spray nozzle.

FIG. 5 is an explanatory diagram of another conventional technique.

[Explanation of symbols]

1 ... Exhaust gas, 1a ... Absorption tower exhaust gas inlet, 2 ... Absorption tower, 3
... Lowest stage spray header, 4 ... Spray nozzle, 5 ... Mist eliminator, 5a ... Absorption tower outlet duct, 6 ... Purified gas, 7 ... Absorption tower circulation tank, 8 ... Air, 12 ... Absorption solution extraction pump, 17 ... Second stage spray header , 18 ... 3rd stage spray header, 19 ... 4th stage spray header, 23 ... Circulation pump.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location B01D 53/34 125 Q (72) Inventor Takanori Nakamoto 6-9 Takaracho, Kure City, Hiroshima Prefecture Babcock Hitachi Kure Factory Co., Ltd. (72) Inventor Hiroyuki Kaku 3-36 Takaracho, Kure City, Hiroshima Prefecture Babcock Hitachi Kure Research Institute Co., Ltd.

Claims (5)

[Claims] 1. A rigid absorption tower having an exhaust gas inlet and a treated exhaust gas outlet for passing exhaust gas from below to above, and a plurality of stages of spray headers having a plurality of spray nozzles and arranged in the absorption tower. In a wet exhaust gas desulfurization apparatus that absorbs and removes sulfur oxides in exhaust gas by spraying and absorbing droplets from the spray nozzle, an upward spray nozzle is provided in the lowermost spray header of the spray header in the absorption tower, followed by the next two stages. A wet exhaust gas desulfurization device characterized in that a downward spray nozzle is provided in the eye spray header. 2. The wet exhaust gas desulfurization device according to claim 1, wherein a downward spray nozzle is provided in a spray header provided in a downstream region above the second stage spray header in the absorption tower. 3. A solid absorption tower having an exhaust gas inlet and a treated exhaust gas outlet for passing exhaust gas from below to above, and a plurality of stages of spray headers having a plurality of spray nozzles and arranged in the absorption tower. In a wet exhaust gas desulfurization apparatus that absorbs and removes sulfur oxides in exhaust gas by spraying and absorbing droplets from the spray nozzle, a set in which a spray header provided with an upward spray nozzle and a spray header provided with a downward spray nozzle in the next stage above it are arranged. A wet exhaust gas desulfurization device characterized in that the combination is composed of a spray header at the lowermost stage and a next stage, and at least one is also provided at the upper stage in the downstream region. 4. A combination of a spray header having an upward spray nozzle attached thereto and a spray header having a downward spray nozzle attached to the next stage thereof according to claim 1, 2 or 3, wherein the horizontal installation positions of the upper and lower spray nozzles are substantially the same center. Wet exhaust gas desulfurization device characterized by having a structure facing each other. 5. Absorbing the sulfur oxides in the exhaust gas by passing the exhaust gas from the lower side to the upper side in the rigid absorption tower and spraying the absorbing liquid from a spray nozzle provided in a plurality of stages of spray headers arranged in the absorption tower. In the wet exhaust gas desulfurization method of removing, the exhaust gas velocity in the absorption tower is set to more than 3 m / s and 7 m / s or less, and the spray nozzle of the lowermost spray header is directed upward and the spray nozzle of the next upper spray header is directed downward. , And a spray header is provided above them so that they can be sprayed from the spray nozzle.
When the mist in the exhaust gas is removed by the vertical corrugated sheet mist eliminator installed in the exhaust gas duct downstream of the absorption tower outlet, and when the amount of sulfur oxides treated in the exhaust gas in the absorption tower decreases, the load is transferred from the upper spray header. A wet flue gas desulfurization method characterized in that the injection of the absorbing liquid is stopped accordingly.