JPH0761408B2 - Exhaust gas treatment method and apparatus thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to dusts and fine mist discharged from metal melting, metal pickling or chemical reaction processes, semiconductors, optical fibers, new ceramics, solar cell manufacturing processes, etc. ,
The present invention relates to a method and an apparatus for treating an exhaust gas containing liquid fumes, combustion smoke and the like (in the present specification, these may be collectively referred to simply as dust).

(Prior Art) Conventionally, there are various methods for treating exhaust gas containing dust, fine mist, liquid fumes, or combustion smoke based on the characteristics of the dust, etc., but collecting fine dust of 10 μm or less As an effective means often used in the above, a device such as a venturi scrubber, an electrostatic precipitator or a bag filter is known.

(Problems to be Solved by the Invention) However, the above-mentioned means has the following problems.

First, the Venturi scrubber is a method of injecting liquid into a high-speed gas flow region called the throat to generate fine droplets and inertially colliding and collecting dust in exhaust gas. The pressure loss in the throat is very high at 50-1500mmAq,
It has the disadvantage of requiring a high-pressure loss blower and high operating costs. Further, the electrostatic precipitator is a method of causing a corona discharge between the electrodes with a direct current high-voltage current, flowing an exhaust gas containing dust there to charge the dust with a negative charge, and adhering it to the anode and collecting it, for example, 100 m ³ / The dust collecting electrode requires a large installation space of about 70 m ² to process the dust-containing exhaust gas of min. In addition, not only the equipment cost is very high such as handling a high voltage and a rectifier, but also dust collecting. Since there is a limit to the electric resistance value at the time of use, there are drawbacks that use conditions and operation conditions are complicated and maintenance is complicated. Further, the tap filter is a filter cloth such as woven cloth or felt, which collects dust in the gas by filtration, but the filtration speed is 0.01 to 0.03 m / s and can be operated only in a slow region. For example, in order to process 100 m ³ / min dust-containing exhaust gas, a filter area of about 60 to 170 m ² is required, which not only makes the device large and increases the equipment cost but also
The pressure loss increases as it is collected, and maintenance problems such as clogging of the filter cloth are likely to occur.Particularly, the collection of dust that has a hygroscopic property such as SiO ₂ (silica) and solder fume and gels There is a drawback that the cloth is completely clogged and the gas flow part is blocked to make it impossible to process.

As described above, the collection of fine dust is not preferable in the conventional technology in terms of equipment cost, pressure loss, and installation space, and usage conditions, operating conditions, maintenance are complicated, and a practical exhaust gas treatment method. But it didn't.

(Means for Solving Problems) The present invention has been invented in view of the above problems, and is not only advantageous in terms of equipment cost, pressure loss, and installation space, but also in use conditions. The present invention aims to provide an exhaust gas treatment method and its device, which are easy and easy to operate and maintain.

The configuration of the present invention will be described below.

That is, in the present invention, in the wet exhaust gas treatment method, the exhaust gas is brought into gas-liquid contact with a liquid having a temperature higher than that of the exhaust gas to make water vapor in the exhaust gas into a saturated state, and then brought into gas-liquid contact with a liquid having a temperature lower than that of the exhaust gas in the exhaust gas. The exhaust gas treatment method is characterized by collecting dust and the like in the exhaust gas by a conventional method after supersaturating the water vapor of The first wet scrubber is provided with a heating source capable of heating the circulating liquid circulating therein, and the second wet scrubber is provided with a cooling source capable of cooling the circulating liquid circulating therein. The exhaust gas treatment device is defined as the second aspect of the present invention, and in the exhaust gas treatment device, a circulating liquid circulating in a wet scrubber in which exhaust gas is brought into gas-liquid contact can be heated. The exhaust gas treatment device characterized by a circulating fluid to circulate the inner rotating body scrubber annexed a cooling source capable of cooling as well as attaching a source is to the structure Summary of the third invention. The liquid used for the above gas-liquid contact is water or water containing a small amount of a chemical for the purpose of neutralization, absorption, deodorization and the like.

Here, the above-mentioned wet scrubber used in the present invention means, for example, a packed tower filled with various kinds of packing, a perforated plate tower by a downcomer method or a leak shelf method, a spray tower, and a spray tower with a net. Cage,
Either one of them or a combination of a plurality of them may be selected. The spray tower with a net means a countercurrent or a parallel flow in which one or more nets arranged so as to be orthogonal to the gas flow direction and a spray nozzle capable of uniformly spraying a liquid on the net are arranged. This means a flow-type wet cleaning device, in which water or chemicals sprayed from a spray nozzle forms a thin film on the net, but this thin film instantaneously spreads and flows, so that formation and destruction are repeated continuously. , A washing effect is provided, and a new thin film of water or a chemical solution is always formed on the net, and at the same time dust adheres to this thin film, and the thin film is always washed off, so that a dust layer is formed on the net. Exhaust gas does not accumulate and always flows through the mesh of the net, and the mesh is not blocked. The shape of the net mesh does not matter,
The mesh size is 3 mesh or more, and particularly 4 mesh or more is effective. However, if it is too fine, dust easily accumulates and grows to block the mesh, so 20 mesh or less is desirable. The net may be made of metal or resin, and when a plurality of nets are provided, they may be stacked or held at an arbitrary interval.

By the way, the wet scrubber that can be most effectively used in the present invention is such that if the packed tower is operated for a long period of time, the packing is easily clogged and clogged, and
Since the pressure loss per tower is 100 mmAq or more, a high pressure loss blower is required in consideration of the exhaust gas suction duct pressure loss, and further, since the spray tower is considerably lower than the gas-liquid contact effect of the packed tower, the perforated plate tower, etc., While there are disadvantages such as slow gas superficial velocity and spray liquid velocity of 1200 L / min ・ m ² or more, the scrubber with a net has high gas-liquid contact efficiency and can be blocked by clogging. A scrubber with a net is the most desirable because it has a small pressure loss per tower and there are no maintenance problems. The rotary scrubber was first disclosed by the applicant in Japanese Patent Application No. 61-54331, but in short, the exhaust gas was brought into contact with the liquid sprayed from the cleaning nozzle before the suction port, and the gas liquid That can be discharged as clean gas from the discharge port by letting it flow in a mixed jet state, sucking it into a centrifugal rotating impeller equipped in the spiral tower, mixing and mixing gas and liquid, absorbing and coagulating and separating harmful components in exhaust gas. A device in which a member having a large number of fine holes is arranged in the suction port of the above method, or a device in which a fin-shaped projection for disturbing a flow that causes a vortex is arranged on the inner wall of the spiral cylinder is effective. Is.

Next, there is a means for humidifying the circulating liquid circulating in the wet scrubber at high temperature. Examples of means for heating include:
It does not matter whether the waste heat of the factory is directly used, the heat of the boiler is directly used, the heat exchanger is used, the electric heater is used, or the like. The humidifying means includes (a) a normal spray nozzle and (b) one. It is preferable to use a fluid nozzle, (c) dimer nozzle, or the like. When the heating / humidifying temperature is 50 ° C. or less, the absolute humidity for supersaturation is insufficient, and the effect is reduced. It is desirable to set the temperature above ℃. Further, although it is means for cooling and humidifying the circulating liquid circulating in the wet scrubber, as means for rapidly cooling,
For example, an air cooling tower or a refrigerator may be used, and as humidifying means, (a) a normal spray nozzle, (b) a one-fluid nozzle, or (c) a dimer nozzle may be used. Well, if the cooling / humidifying temperature is 0 ° C or lower, normal industrial operation becomes difficult, and if it is 40 ° C or higher, the amount of evaporated water increases, and the condensed mist scatters at the outlet after treatment, causing a new problem. 40 ~ obtained
0 ° C is optimal.

(Operation) According to the application of the method and the device of the present invention, the exhaust gas containing dust or the like is heated and humidified by gas-liquid contact with the high temperature circulating liquid to make the water vapor saturated, and the exhaust gas containing the low temperature circulating liquid in the next step becomes It is cooled by gas-liquid contact and the water vapor becomes supersaturated.
In a supersaturated atmosphere, vapor will condense on the surface of a cold substance, but the dust contained in the exhaust gas will be heated once under high humidity and then rapidly cooled, so that water will condense on the particle surface. As a result, the particle size becomes large and it becomes easy to collect the particles.

(Effects of the Invention) According to the present invention configured as described above, since it is possible to increase the particle size by aggregating water on the particle surface of dust or the like in the exhaust gas, it is extremely easy to collect the fine particles. It is not necessary to use a corresponding device which is expensive and whose usage conditions are complicated, it can be carried out by slightly modifying the existing equipment, and can be easily used only by controlling the pressure loss and temperature of the device. In addition, if the rotary scrubber is attached after the second wet scrubber, it can be collected regardless of the amount of water condensed on the particle surface, and the removal performance can be greatly improved.

Also, the same effect can be obtained by using a rotating body scrubber as the second wet scrubber.

(Example) FIGS. 1 to 3 are views for explaining an apparatus for carrying out the method of the present invention (first invention), and FIG. 1 shows the first tower and the second tower. 3 shows a case where a spray tower is used, FIG. 2 shows a case where both the first tower and the second tower are spray towers with a net, and a rotary scrubber is attached after the second tower, and FIG. Shows the case where a rotating scrubber is used as an alternative to the second tower.

Here, the case where the method of the present invention is carried out by the apparatus illustrated in FIG. 1 will be described.

In the drawings, reference numeral 1 is a spray tower of the first tower (or a spray tower with a net), and has a heating source 2 for previously heating the circulating liquid fed into the tower. Further, 3 is a spray tower of the second tower (or a spray tower with a net), and has a cooling source 4 for previously cooling the circulating liquid fed into the tower. 5 is a mist catcher and 6 is a fan. In addition, 7 and 8 are circulating fluid tanks, and 9 and 10 are pumps. Briefly explaining the treatment of exhaust gas in such an apparatus, first, the exhaust gas A is introduced into the first tower 1, and the high-temperature circulating liquid is spray-sprayed from the circulating liquid tank 7 by the pump 9 in the first tower 1 to form gas-liquid. They are touched and saturated. Further, the low-temperature circulating liquid introduced into the second tower 3 via the trap 11 and cooled by the pump 10 from the circulating liquid tank 8 is spray-sprayed and brought into gas-liquid contact to become a supersaturated state. In this way, the fine dust and particles of liquid fume contained in the exhaust gas are heated once under high humidity and then rapidly cooled, so that water is aggregated on the surface of the particles, and the particle size becomes large and is easily trapped. It will be easier to gather. Thereafter, fine dust and liquid fumes in the exhaust gas having a large particle size are collected by a conventional means such as the mist catcher 5, and are discharged into the atmosphere as purified gas B by the fan 6.

2 and 3 are basically the same as those in FIG. 1 except that a spray tower with a net is used instead of the spray tower, and the spray tower shown in FIG. In some cases, the removal performance is further improved because what is to be collected by the mist catcher in FIG. 1 is collected again by the rotating scrubber. Further, the one shown in FIG. 3 uses a rotating scrubber as an alternative to the second wet scrubber to simultaneously perform cooling and humidification and collection processing, but it is removed as compared with a spray tower or a spray tower with a net alone. In terms of performance, it has been upgraded.

(Experiment) Example 1 A scrubber system with a net was adopted for both the first tower and the second tower, and the exhaust gas was treated under the following conditions.

Conditions: 3 stages of spray with a net Gas velocity: 3024Kg / m ² · hr Liquid velocity: 18000Kg / m ² · hr (per 1 stage) Circulating liquid temperature: 1st tower 67 ° C: 2nd tower 32 ° C Dust type: Ammonium chloride Removal performance: Inlet concentration 200 mg / m ³ : Outlet concentration 18 mg / m ³ Removal rate: 91% Example 2 The first tower and the second tower were sprayed with a net, followed by a rotary scrubber under the following conditions. Originally, the exhaust gas was treated.

Conditions: The conditions for spraying with a net are the same as in Example 1.

The rotating body scrubber conditions were such that the suction stage front stage liquid velocity was 1530 Kg / m ² · hr.

Dust type: Ammonium chloride Removal performance: Inlet concentration 200 mg / m ³ : Outlet concentration 3.8 mg / m ³ Removal rate: 98% Example 3 Both the first tower and the second tower adopt the spray tower system,
The exhaust gas was treated under the following conditions.

Conditions: 4 stages of spraying Gas velocity: 2160Kg / m ² · hr Liquid velocity: 72000Kg / m ² · hr (per 1 stage) Circulating liquid velocity: 1st tower 65 ° C: 2nd tower 32 ° C Dust type: Ammonium chloride removal Performance: Inlet concentration 130 mg / m ³ : Outlet concentration 13 mg / m ³ Removal rate: 90% Example 4 Both the first tower and the second tower adopt the spray tower system,
The exhaust gas was treated under the following conditions.

Conditions: 4 stages of spray Gas velocity: Same as in Experiment 3 Liquid velocity: Same as in Experiment 3 Circulating liquid velocity: 1st tower 60 ℃ 2nd tower 26.5 ℃ Dust type: Dry grass burning smoke Removal performance: Inlet concentration 3700CPM: Outlet concentration 56 CPM removal rate: 98% (Note) CPM: Count of scattered light by light scattering type dust meter measurement.

[Brief description of drawings]

1 to 3 are views for explaining an apparatus for carrying out the method of the present invention (first invention), and FIG. 1 shows both the first tower and the second tower as a spray tower. FIG. 2 shows a case where a spray tower with a net is adopted as the first tower and the second tower, and a rotary scrubber is attached after the second tower, and FIG. The case where a rotating scrubber is used as an alternative to the tower is shown. 1, 3 ... Spray tower (or netted spray tower), 2 ... Heating source, 4 ... Cooling source, 5 ... Mist catcher, 6 ... Fan, 7.8 ... Circulating fluid tank, 9/10 ... Pump, 11 ... Trap , 12 ... Rotating body scrubber, A ... Exhaust gas, B ... Cleaning gas.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasushi Abe 4-1-131, Mizudo-cho, Amagasaki City, Hyogo Prefecture Seiko Kakoki Co., Ltd. (56) Reference JP-A-48-25971 (JP, A)

Claims (3)

[Claims] 1. A wet exhaust gas treatment method,
After the water vapor in the exhaust gas is saturated by gas-liquid contact with the liquid at a temperature higher than that of the exhaust gas, the water vapor in the exhaust gas is made into a supersaturated state by gas-liquid contact with the liquid at a temperature lower than that of the exhaust gas. A method for treating exhaust gas, which comprises collecting such substances. 2. In a wet type exhaust gas treatment apparatus, a heating source capable of heating a circulating liquid circulating therein is attached to a first wet scrubber with which exhaust gas is brought into gas-liquid contact, and a second wet scrubber is attached to the inside thereof. An exhaust gas treatment device, characterized in that a cooling source capable of cooling the circulating liquid is attached. 3. In a wet type exhaust gas treatment apparatus, a heating source capable of heating a circulating liquid circulating therein is attached to a wet scrubber to which exhaust gas is brought into gas-liquid contact, and a circulating liquid circulating inside the rotating scrubber is provided. An exhaust gas treatment device, which is provided with a cooling source capable of cooling.