JPH11104440A - 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 retention time of a solid substance in a reactor is lengthened and the concn. of the solid substance is made high over approximately the whole length in the reactor and an absorbent and the solid substance are homogeneously dispersed in exhaust gas. 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, as a reactor, the one wherein the whole or the major part is formed into a tapered shape which becomes narrow downward is used to decrease gradually the speed of the stream of the exhaust gas rising upward in the reactor 1.

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 acidic gases such as sulfur oxides in exhaust gas of this kind, for example, as disclosed in Japanese Patent Publication No. 6-63209, Injects an absorbent slurry such as slaked lime slurry into a vertical reactor flowing upwards, while drying the absorbent slurry with the heat of the exhaust gas while converting the acidic gas such as sulfur oxides contained in the exhaust gas into the absorbent. Absorb,
A so-called semi-dry method comprising separating a dried reaction product, unreacted slaked lime and other solids contained in the exhaust gas discharged from the reactor, and recirculating a part of the separated solids to the reactor. The outflow process is conventionally known.

There is a need for this semi-dry deflow process to further improve acid gas absorption efficiency and absorbent utilization. An absorption reaction between an acid gas such as a sulfur oxide and an absorbent such as slaked lime is mainly performed on a surface of a solid material floating in a reactor. Therefore, in order to increase the acid gas absorption efficiency and the absorbent utilization rate, the residence time of the solids in the reactor is lengthened, and the solids concentration in the reactor is increased, so that the solids float in the reactor. It is necessary to increase the total surface area of the solids. It is also important to uniformly disperse the absorbent and the solids in the exhaust gas flowing in the reactor in order to increase the efficiency of absorbing the acidic gas and the utilization rate of the absorbent.

[0004] However, the reactor used in the conventional semi-dry deflow process is formed in a tapered shape in which the lower end portion becomes thinner downward, and the remaining portion is formed in a cylindrical shape. The exhaust gas flowing in the reactor became turbulent due to rapid deceleration at the lower end of the reactor, but approached a laminar flow upward. Therefore, the residence time of the solid in the reactor is short,
The solids concentration in the reactor, especially at the top, was low and the absorbent and solids were not homogeneously dispersed in the exhaust gas.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, to increase the residence time of solids in a reactor, to increase the solids concentration over almost the entire length of the reactor, and to use an absorbent and solids. Is homogeneously dispersed in the exhaust gas to improve acid gas absorption efficiency and absorbent 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. In the method for removing acid gas in exhaust gas, which comprises recirculating a part of the gas to the reactor, a reactor formed in a tapered shape in which the whole or most of the gas becomes narrower downward, and ascending in the reactor The exhaust gas flow is gradually decelerated as going upward.

Further, the apparatus for removing acidic gas from exhaust gas according to the present invention has 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 reactor. A device for separating dried solids contained in the exhaust gas discharged from the reactor, and a device for removing acid gas in the exhaust gas comprising means for recirculating a part of the separated solids to the reactor; Is formed in a tapered shape in which the entirety or a large part thereof becomes thinner downward.

According to the present invention, the above-mentioned reactor configuration causes the exhaust gas flow rising in the reactor to be gradually decelerated as going upward, so that the exhaust gas flow becomes turbulent over almost the entire length in the reactor. A high concentration turbulent layer is formed by suspended solids having different particle size distributions over almost the entire length of the reactor. Therefore, compared with the case of using a conventional cylindrical reactor, even if the solids circulation amount of the entire system is the same, the residence time of the solids in the reactor is long, and the solids concentration in the reactor is low. High, and the absorbent and solids are homogeneously dispersed in the exhaust gas.

The reactor is generally circular in cross section, but may be polygonal in cross section.

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

Means for injecting the adsorbent slurry into the reactor include, for example, an injection device provided with an injection nozzle, a pressure pump and the like. The absorbent slurry is usually injected upward from the lower end in 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 recycled material 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.

A 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. Recycled solids are usually fed to the bottom of the reactor.

As a result of part of the solids being recycled to the reactor, the solids suspended in the reactor and the absorbent 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 . The feature of the present invention is that the solid concentration is particularly high even in the upper part of the reactor.

[0017]

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

Referring to FIG. 1, an apparatus for removing acidic gas in 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;
An injection device (4) for injecting the absorbent slurry into (1), a cyclone (5) for separating dry solids contained in the exhaust gas discharged from the reactor (1), and a cyclone (5) Recirculation path (6) that recirculates some of the solids collected to the reactor (1)
And

The reactor (1) has a portion (1) excluding its upper end.
1) has a circular cross section and is formed in a tapered shape that becomes thinner downward, and the lower end of the tapered portion (11) serves as an exhaust gas inlet (2). The upper end of the reactor is composed of an annular portion (12) and a cone portion (13) thereon, and the upper end of the cone portion (13) serves as an exhaust gas outlet (3).

The absorbent slurry is an aqueous slurry of slaked lime. This slurry is prepared by digesting quicklime with water in a digester (7).

The injection device (4) is provided with a pressurizing pump (41) for pressurizing the absorbent slurry, an injection nozzle (42), and a blower for supplying injection air (43). The injection nozzle (42) 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), 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 the 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 the tapered portion (11) of the reactor (1) increases as it goes upward. The taper (11)
The exhaust gas flow inside is gradually decelerated as going upward. As a result, turbulence of the exhaust gas flow occurs over the entire length in the tapered portion (11).

Due to the turbulence of the exhaust gas flow, the injection nozzle
(42) an absorbent slurry injected into the reactor (1),
The reaction product recirculated into the reactor (1) through the recirculation path (6) and solids such as unreacted absorbent are mixed, and the absorbent and solids are homogeneously dispersed in the exhaust gas. . As a result, a high-concentration turbulent layer is formed by suspended solids having different particle size distributions over almost the entire length of the reactor (1). Then, while the absorbent slurry is dried by the heat of the exhaust gas, the acidic gas such as sulfur oxides and hydrogen chloride contained in the exhaust gas is absorbed mainly on the surface of the wet solid material covered with a film of water. It causes an absorption reaction with the agent and is absorbed by the absorbent.

The exhaust gas discharged from the exhaust gas outlet (3) at the upper end of the reactor (1) is sent to a cyclone (5) where the dried reaction products, unreacted absorbent and ash etc. contained in the exhaust gas are discharged. Solids are separated. The exhaust gas from which solids have been removed by the cyclone (5) is sent to an electric precipitator (9) via a conduit (21), where dust and ash particles are removed and purified. Released during. Dust and the like separated from the exhaust gas by the electric dust collector (9) are taken out of the system as a by-product by the screw conveyor (22).

About 99% of the solids separated by the cyclone (5) are recycled to the reactor (1) via the recycle line (6). The remaining about 1% of the solid matter is taken out of the system by a screw conveyor (8) as a by-product.

[0028]

According to the method and apparatus for removing acid gas from exhaust gas of the present invention, a turbulent flow of an exhaust gas flow and a high-concentration turbulent layer formed by suspended solids having a different particle size distribution over substantially the entire length of the reactor. As a result, as compared with the case of using a conventional cylindrical reactor, the residence time of solids in the reactor is increased, and the solid concentration in the reactor is increased. Since the substances are homogeneously dispersed in the exhaust gas, the efficiency of absorbing the acidic gas and the utilization rate of the absorbent can be increased.

[Brief description of the drawings]

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

[Explanation of symbols]

 (1)… Reactor (11)… Tapered section (2)… Exhaust gas inlet (3)… Exhaust gas outlet (4)… Absorbent slurry injection device (5)… Cyclone (6)… Solids 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 5-3-28 Nishikujo, Konohana-ku, Osaka City

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. In the acid gas removal method, the reactor is characterized in that the whole or most of the reactor is formed into a tapered shape that becomes thinner as it goes downward, and the exhaust gas flow ascending in the reactor is gradually decelerated as it goes upward. To remove acid gas from exhaust gas. 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 solids to the reactor, wherein the entire or most of the reactor goes down. An acidic gas removal device for exhaust gas, wherein the device is formed in a tapered shape.