JPH11104442A - Method and apparatus for removing acidic gas in exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve acidic gas absorption efficiency and absorbent utilization by a method wherein an absorbent is homogeneously dispersed in exhaust gas and retention time of the absorbent in a reactor is lengthened. SOLUTION: A method for removing acidic gas in exhaust gas is constituted in such a way that a slurry of an absorbent is injected in a vertical reactor 1 in which the exhaust gas flows upward and while the slurry of the absorbent is dried by heat of the exhaust gas, acidic gas included in the exhaust gas is absorbed in the absorbent and dried solid substance included in the exhaust gas exhausted from the reactor 1 is separated and a part of the separated solid substance is recirculated into the reactor 1. In this case, the slurry of the absorbent is injected downward into the reactor 1 to brought it into countercurrent contact with the stream of the exhaust gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing acidic gases such as sulfur oxides and hydrogen chloride contained in exhaust gas discharged from a coal-fired boiler, a refuse-burning furnace, etc., and releasing the gas into the atmosphere. The present invention relates to a method and an apparatus for detoxifying exhaust gas.

[0002]

2. Description of the Related Art As means for removing sulfur oxides and the like in this kind of exhaust gas,
For example, as shown in Japanese Patent Publication No. 6-63209, an absorbent slurry such as slaked lime slurry is injected into a vertical reactor in which the exhaust gas flows upward, and the absorbent slurry is dried by the heat of the exhaust gas. While absorbing the acidic gas such as sulfur oxides contained in the exhaust gas into the absorbent, the dried reaction products, unreacted slaked lime and other solids contained in the exhaust gas discharged from the reactor are separated and separated. A so-called semi-dry deflow process, consisting of recirculating a portion of the solids that have been recycled to the reactor, has been known in the art.

There is a need for this semi-dry deflow process to further improve acid gas absorption efficiency and absorbent utilization. In order to increase the absorption efficiency of the acidic gas and the utilization rate of the absorbent, it is necessary to lengthen the residence time of the absorbent in the reactor and to sufficiently react the absorbent with the acidic gas. It is also important to uniformly disperse the absorbent in the exhaust gas flowing in the reactor.

[0004] However, in the case of the conventional semi-dry deflow process, the absorbent slurry is injected by an injection nozzle arranged upward at the lower end of the reactor so as to flow in parallel with the exhaust gas flow. However, it was difficult to uniformly disperse the absorbent. Also, the exhaust gas flow near the axis of the reactor is vertically upward,
In particular, the residence time of the absorbent in this part was short.

[0005] An object of the present invention is to solve the above-mentioned problems, to disperse the absorbent homogeneously in the exhaust gas, to lengthen the residence time of the absorbent in the reactor, to improve the acid gas absorption efficiency and the absorbent. The purpose is to improve utilization.

[0006]

According to the method for removing acid gas in exhaust gas according to the present invention, an absorbent slurry is injected into a vertical reactor in which the exhaust gas flows upward, and the absorbent slurry is dried by heat of the exhaust gas. The acidic gas contained in the exhaust gas is absorbed by the absorbent while the dried reaction product, unreacted absorbent and other solid substances contained in the exhaust gas discharged from the reactor are separated, and the separated solid substance is separated. A method for removing acid gas in exhaust gas, comprising recirculating a part of the exhaust gas to a reactor, characterized in that an absorbent slurry is jetted downward into the reactor and brought into contact with the exhaust gas stream and countercurrent. It is.

Further, the apparatus for removing acidic gas from exhaust gas according to the present invention comprises a vertical reactor having an exhaust gas inlet at a lower end and an exhaust gas outlet at an upper end, means for injecting an absorbent slurry into the reactor, A device for removing acid gas from exhaust gas, comprising: a separation device for separating dried solids contained in exhaust gas discharged from the reactor, and a recirculation path for recirculating a part of the separated solids to the reactor. Wherein the injection nozzle of the absorbent slurry injection means is arranged downward in the reactor.

The term "downward" includes obliquely downward as well as vertically downward.

According to the present invention, since the adsorbent slurry stream is brought into countercurrent contact with the exhaust gas stream, a violent turbulent state in which the exhaust gas, the absorbent, and the solid matter are mixed near the merge is formed. Therefore, contact between the exhaust gas and the absorbent is performed vigorously in the reactor, and the absorbent and solids are homogeneously dispersed in the exhaust gas. In addition, since the absorbent slurry floats in the reactor after coming into contact with the exhaust gas flow and the countercurrent, the residence time of the absorbent in the reactor near the axis of the reactor is longer than that in the related art. As a result, the residence time of the absorbent as a whole in the reactor becomes longer.

[0010] The shape of the reactor is usually cylindrical,
It may be a rectangular tube having a polygonal cross section. Further, the lower end of the reactor may be formed in a tapered shape that becomes thinner downward.

The absorbent can be selected, for example, from calcium oxides and hydroxides, magnesium oxides and hydroxides, and alkali metal oxides, hydroxides and carbonates.

The adsorbent slurry injection means includes a pressure pump, a blower for supplying injection air, and the like, in addition to the injection nozzle. The injection nozzle is preferably arranged at an intermediate height in the reactor. Further, the injection nozzle may be disposed substantially vertically downward near the axis of the reactor, or may be disposed obliquely downward on the inner surface of the peripheral wall of the reactor.

The exhaust gas discharged from the reactor contains a solid product such as a reaction product generated by a chemical reaction between the sulfur oxide and the like and the absorbent, an unreacted absorbent and ash. These solids are dried by the heat of the exhaust gas and are suspended in the exhaust gas. As a separation device for separating these solids from the exhaust gas, a cyclone is suitably used.

The exhaust gas is then sent to a dust collector, such as an electric dust collector or a bag filter, where the dust and ash particles are removed and purified, and then discharged into the atmosphere from a chimney.

A part of the solid matter separated from the exhaust gas by a cyclone or the like is recycled to the reactor, and the amount of the recycle is 50 times the supply amount of the fresh absorbent to the reactor.
~ 100 times. The remainder of the solids is taken out of the system as a by-product.

The recirculation path for recirculating a portion of the solids to the reactor is formed by a feeder such as a conduit, a screw feeder, or a combination thereof. Also,
A solids tank may be provided between the cyclone and the solids recirculation path. The recycled solids are preferably fed near or slightly below the junction of the exhaust gas stream and the absorbent slurry stream in the reactor.

As a result of a part of the solids being recycled to the reactor, the solids and the absorbent suspended in the reactor are mixed by the exhaust gas stream and are homogeneously dispersed in the exhaust gas. The solid concentration in the reactor is preferably 500 to 10
It is maintained at 00 g / Nm ³ .

In the process of the present invention, the exhaust gas stream is preferably brought into contact with cooling water before contacting with the absorbent slurry, for example cooled to about 70-250 ° C. Similarly, in the apparatus of the present invention, preferably, a cooling water injection means for cooling the exhaust gas is provided below the vicinity of the junction of the exhaust gas flow and the absorbent slurry flow in the reactor. The cooling water is usually injected upward in the axial direction of the reactor. Acid gas absorption efficiency increases as the operating temperature in the reactor decreases. The absorption reaction between the acidic gas and the absorbent is
It is mainly carried out on the surface of a solid material floating in the reactor, and is more likely to occur when the solid material is in a wet state in which the surface of the solid material is covered with a film of water. Therefore, if the exhaust gas stream is cooled by contacting it with cooling water before the exhaust gas stream is brought into contact with the absorbent slurry as described above, the acid gas absorption efficiency can be improved by pre-wetting the surface of the solid matter dispersed in the exhaust gas. Can be further improved.

[0019]

Next, preferred embodiments of the present invention will be described with reference to the drawings.

A. First Embodiment This embodiment is shown in FIG. In FIG. 1, an apparatus for removing acidic gas from exhaust gas according to the present invention comprises a vertical reactor (1) having an exhaust gas inlet (2) at a lower end and an exhaust gas outlet (3) at an upper end, and a reactor (1). An injection device (4) for injecting the absorbent slurry, and a cyclone (5) for separating dried solids contained in exhaust gas discharged from the reactor (1);
Part of the solid separated by the cyclone (5) is transferred to the reactor (1).
And a recirculation path (6) for recirculation.

The lower end portion (11) of the reactor (1) has a circular cross section and is formed in a tapered shape that becomes thinner downward, and the remaining portion (12) is formed in a cylindrical shape. .

The absorbent slurry comprises an aqueous slurry of slaked lime. The slurry is prepared by digesting quicklime with water in a digester (44).

The absorbent slurry injection device (4) includes a pressure pump (41) for pressurizing the absorbent slurry, and an injection nozzle (42).
And an injection air supply blower (43). The absorbent slurry injection nozzle (42) is disposed obliquely downward at the center of the height of the peripheral wall of the cylindrical portion (12) of the reactor (1).

Further, a cooling water injection device (7) provided with an injection nozzle (71) arranged in the tapered portion (11) of the reactor (1) is provided. The cooling water injection nozzle (71) is arranged at the lower end portion of the tapered portion (11) of the reactor (1), facing upward in the axial direction of the reactor (1).

Below the cyclone (5) is a solids tank (2
0) is provided. The solids tank (20) is provided with a screw conveyor (8) for taking out some solids that are not recycled to the reactor as by-products out of the system. Above the cyclone (5), there is arranged a conduit (21) for sending the exhaust gas from which the solids have been removed to an electrostatic precipitator (9). A screw conveyor (22) is provided below the electric precipitator (9) to take out dust and the like separated from exhaust gas as by-products to the outside of the system.

The solid material recirculation path (6) has a screw feeder (61) having an inlet connected to the solid matter tank (20), and one end connected to an outlet of the screw feeder (61), and the other end connected to the reactor.
(1) and a conduit (62) connected to the lower part of the cylindrical portion (12).

In the above apparatus, the exhaust gas discharged from the coal-fired boiler flows into the reactor (1) from the exhaust gas inlet (2) and flows upward in the reactor (1). The exhaust gas stream first contacts the cooling water injected from the injection nozzle (71) at the tapered portion (11) of the reactor (1), and its temperature is reduced to about 70 to 250 ° C. This watery exhaust gas stream is recirculated
The solids such as the reaction product and the unreacted absorbent which are recirculated into the reactor (1) through (6) come into contact with each other, whereby the surface of the solid becomes wet. Next, the cylindrical part (1
At the lower part of 2), the absorbent slurry injected obliquely downward from the injection nozzle (42) comes into contact with the exhaust gas flow and countercurrent,
Near this confluence, a violent turbulent state is formed in which the exhaust gas, the absorbent and the solid are mixed. And while the absorbent slurry is dried by the heat of the exhaust gas, the sulfur oxides contained in the exhaust gas, acid gases such as hydrogen chloride,
An absorption reaction occurs with the absorbent mainly on the surface of the wet solid material which is covered with the water film, and is absorbed by the absorbent. In the case of the apparatus of the present invention, the contact between the exhaust gas and the absorbent is violent in the reactor (1), so that the efficiency of acid gas absorption is higher than in the prior art. In addition, the absorbent and solids are homogeneously dispersed in the exhaust gas, and the absorbent slurry floats in the reactor (1) after coming into contact with the exhaust gas flow, so that the slurry near the axis of the reactor Since the residence time of the absorbent in the reactor is increased, and thus the residence time of the absorbent as a whole is increased, the utilization rate of the absorbent is increased as compared with the prior art.

Next, the exhaust gas leaves the reactor (1) from the exhaust gas outlet (3) and is sent to the cyclone (5) where the dried reaction product, unreacted absorbent and ash contained in the exhaust gas are contained. Etc. are separated. The exhaust gas from which solids have been removed by the cyclone (5) passes through a conduit (21) and is collected by an electrostatic precipitator.
(9), where dust and ash particles are removed and purified, and then released into the atmosphere from the chimney. Electric dust collector
The dust and the like separated from the exhaust gas in (9) are taken out of the system by a screw conveyor (22) as by-products.

B. Second Embodiment This embodiment is shown in FIG.

The apparatus for removing acidic gas from exhaust gas shown in FIG.
The reactor (1) is disposed vertically downward near the axis of the reactor (1) at the center of the height in the cylindrical portion (12). Others are the same as the first embodiment.

C. Third Embodiment This embodiment is shown in FIG.

The apparatus for removing acidic gas from exhaust gas shown in FIG. 3 is not provided with a cooling water injection device into the lower end of the reactor. Others are the same as the first embodiment.

C. Fourth Embodiment This embodiment is shown in FIG.

The apparatus for removing acidic gas from exhaust gas shown in FIG. 4 is not provided with a device for injecting cooling water into the lower end of the reactor. Others are the same as the second embodiment.

[0035]

According to the method and the apparatus for removing acid gas from exhaust gas of the present invention, the exhaust gas and the absorbent are vigorously contacted in the reactor, and the absorbent and solids are uniformly dispersed in the exhaust gas. In addition, since the absorbent slurry floats inside the reactor after coming into contact with the exhaust gas stream and the countercurrent, it rises, so that the residence time of the absorbent in the reactor near the axis of the reactor is shorter than in the conventional technology. As a result, the residence time of the absorbent as a whole in the reactor becomes longer, so that the acid gas absorption efficiency and the utilization rate of the absorbent can be improved.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a first embodiment of the present invention.

FIG. 2 is a flowchart showing a second embodiment of the present invention.

FIG. 3 is a flowchart showing a third embodiment of the present invention.

FIG. 4 is a flowchart showing a fourth embodiment of the present invention.

[Explanation of symbols]

 (1) ... reactor (2) ... exhaust gas inlet (3) ... exhaust gas outlet (4) ... absorbent slurry injection device (42) ... absorbent slurry injection nozzle (5) ... cyclone (6) ... solid matter recirculation path

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Yoshimasa Miura 5-3-28 Nishikujo, Konohana-ku, Osaka-shi Inside Hitachi Zosen Corporation (72) Inventor Hirotoshi Yanagi 5-28, Nishikujo, Konohana-ku, Osaka-shi No. Within Hitachi Zosen Corporation (72) Inventor Takeshi Katagiri 5-3-28 Nishikujo, Konohana-ku, Osaka-shi Within Hitachi Zosen Corporation (72) Inventor Katsutoshi Matsunaga 5-28 Nishikujo, Konohana-ku, Osaka Hitachi Inside Shipbuilding Co., Ltd. (72) Inventor Hironaka Tanaka 5-28 Nishikujo, Konohana-ku, Osaka City Inside Hitachi Shipbuilding Co., Ltd.

Claims (2)

[Claims] 1. An absorbent slurry is injected into a vertical reactor in which exhaust gas is flowing upward, and while absorbing the exhaust gas, the acid gas contained in the exhaust gas is absorbed by the absorbent while drying the absorbent slurry. Separating dried reaction products, unreacted absorbents and other solids contained in the exhaust gas discharged from the reactor, and recirculating a part of the separated solids to the reactor. A method for removing an acid gas in an exhaust gas, comprising: injecting an absorbent slurry downward into a reactor so as to contact an exhaust gas flow and a countercurrent. 2. A vertical reactor having an exhaust gas inlet at a lower end and an exhaust gas outlet at an upper end, means for injecting an absorbent slurry into the reactor, and a dry solid contained in exhaust gas discharged from the reactor. And a recirculation path for recirculating a part of the separated solid matter to the reactor, wherein the injection nozzle of the absorbent slurry injection means comprises a reactor. An acidic gas removal device for exhaust gas, wherein the device is disposed downward in the inside.