JP3395035B2 - Method and apparatus for removing acid gas from exhaust gas - Google Patents

Description

Description: 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 or a refuse-burning furnace. The present invention relates to a method and an apparatus for removing and eliminating the harmful exhaust gas discharged into the atmosphere. 2. Description of the Related Art As means for removing sulfur oxides and the like in exhaust gas, for example, as disclosed in Japanese Patent Publication No. 6-63209, exhaust gas is directed upward. An absorbent slurry such as slaked lime is injected into the flowing vertical reactor, and while absorbing the exhaust gas, the absorbent slurry absorbs acidic gases such as sulfur oxides contained in the exhaust gas while drying the absorbent slurry. A so-called semi-dry degassing method comprising separating dried reaction products, 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. Flow processes are conventionally known. [0003] With respect to this semi-dry deflow process, there is a demand for further improving the efficiency of acid gas absorption. The absorption reaction between an acid gas such as sulfur oxide and an absorbent such as slaked lime is mainly performed on the surface of a solid material floating in the reactor, and the surface of the solid material is covered with a film of water. It is easy to happen in the state. It is also important to mix the absorbent slurry and the solid homogeneously in order to increase the efficiency of acid gas absorption. [0004] However, in the case of the conventional semi-dry deflow process, the surface of the solid material is wetted by contact with the absorbent slurry during the dispersion of the absorbent slurry injected into the reactor into the exhaust gas. Therefore, there is a time lag between the contact of each solid with the absorbent slurry and the surface thereof being wet, and it takes time until all the surfaces of the solids become wet. Further, the solid matter and the absorbent slurry were mixed in the reactor, but it was difficult to mix them uniformly. [0005] It is an object of the present invention to solve the above-mentioned problems, to shorten the time required for all solids to become wet in the reactor, and to make the absorbent slurry and the solids homogeneous. To improve the acid gas absorption efficiency. According to the present invention, there is provided a method for removing an acid gas from an exhaust gas, comprising: supplying an absorbent slurry into a vertical reactor in which the exhaust gas is flowing upward; The acidic gas contained in the exhaust gas is absorbed by the absorbent while drying the slurry, and the dried reaction products, unreacted absorbent and other solid substances contained in the exhaust gas discharged from the reactor are separated and separated. and the acid gas removal process in the exhaust gas which comprises recirculating to the reactor a portion of the solid, recycled solids and previously solids recycle than this
The method is characterized in that the absorbent slurry introduced into the passage is mixed in the solid recirculation passage and the resulting mixture is supplied to the reactor. 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 supplying an absorbent slurry to the reactor, and a reactor. In a separation device for separating dried solids contained in the exhaust gas discharged from the, and an acid gas removal device in the exhaust gas equipped with a recirculation path for recirculating a part of the separated solids to the reactor, At least a part of the solid recirculation path is constituted by a screw feeder, and from the recirculated solid inlet in the screw feeder .
Also, an introduction pipe for introducing the absorbent slurry is provided on the starting end side . According to the present invention, the recirculated solids are mixed with the absorbent slurry in the recirculation path, and the resulting mixture is supplied to the reactor.
These surfaces are recirculated to the reactor in a wet state in contact with the absorbent slurry. In addition, since the recirculated solids and the absorbent slurry are stirred and mixed by the screw feeder, both are more homogeneously mixed as compared with the prior art mixed in the reactor. Therefore, the time required for the absorbent to uniformly spread on the surface of the wet solid is shortened. [0009] 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 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 amount of the fresh absorbent supplied 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 part of the solid matter to the reactor may be constituted by a screw feeder alone or may be constituted by a screw feeder and a conduit. Also, a solid matter tank may be provided between the cyclone and the solid matter recirculation path. The absorbent slurry introduction pipe to the screw feeder is connected to the start end side of the recirculation solids inlet in the screw feeder. Therefore, the recycle solids inlet is provided at the middle of the length of the screw feeder . The mixture of the recirculated solid and the absorbent slurry mixed and stirred in the screw feeder is usually fed to the lower part of the reactor. The mixture of recirculated solids and absorbent slurry fed into the reactor is homogeneously dispersed in the exhaust gas by the exhaust gas stream. Solids concentration in the reactor is preferably maintained at 500 to 1000 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 and cooled, for example, to about 70-250 ° C.
Similarly, in the apparatus of the present invention, preferably, a means for injecting cooling water for cooling exhaust gas is provided at a lower end portion in the reactor. The cooling water is usually injected upward in the axial direction of the reactor. The acidic gas absorption efficiency increases as the operating temperature in the reactor decreases, so if the exhaust gas stream is cooled by contact with cooling water before contacting the exhaust gas stream with the absorbent slurry as described above, the acid gas absorption efficiency can be improved. Can be further improved. Next, a preferred embodiment of the present invention will be described with reference to the drawings. A. First Embodiment This embodiment is shown in FIG. In FIG.
The 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 the lower end and an exhaust gas outlet (3) at the upper end, and an exhaust gas discharged from the reactor (1). A cyclone (5) for separating dried solids contained in the water, and a recirculation path (6) for recirculating a part of the solids separated by the cyclone (5) to the reactor (1). . The solid material recirculation path (6) has a cyclone inlet.
A screw feeder (61) leading to the lower end of (5) and a conduit (62) having one end connected to the outlet of the screw feeder (61) and the other end connected to the lower part of the cylindrical portion (12) of the reactor (1). ). An introduction pipe (4) for introducing the absorbent slurry is provided in the screw feeder (61). The slurry introduction pipe (4) is connected to a start end side of a solid circulating material inlet provided at a middle portion of the length of the screw feeder (61). The lower end portion (11) of the reactor (1) has a circular cross section and is formed in a tapered shape which becomes thinner downward, and the remaining portion (12) is formed in a cylindrical shape. . Further, a cooling water injection device (7) having 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). Cyclone (5) and screw feeder (61)
Between them, a solid matter tank (20) 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 absorbent slurry comprises an aqueous slurry of slaked lime. This slurry is prepared by digesting quicklime with water in a digester (not shown), and is introduced from the digester into the screw feeder (61) via the introduction pipe (4). 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. On the other hand, in the screw feeder (61), the absorbent slurry introduced from the introduction pipe (4) and the circulating solid from the solid tank (20) are stirred and mixed, whereby almost all of the recirculated solid is mixed. The surface becomes wet and the recirculated solids and the absorbent slurry are homogeneously mixed. These mixtures are fed into the reactor (1) from the screw feeder (61) via the conduit (62) and dispersed in the exhaust gas. In the reactor (1), while the absorbent slurry is dried by the heat of the exhaust gas and the cooling water is evaporated, acid gases such as sulfur oxides and hydrogen chloride contained in the exhaust gas are mainly converted into a water film. The absorbent reacts with the absorbent on the surface of the covered and wet solid material, and is absorbed by the absorbent. In the case of the present invention, the surface of almost all solid objects is
Since it is in a wet state in advance by stirring and mixing with the absorbent slurry in the screw feeder (61), it is characterized in that a higher acid gas absorption efficiency can be obtained 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. About 99% of the solids separated by the cyclone (5) are recycled to the reactor (1) via the solids tank (20) and the recycle line (6). About 1% remaining solids
Is taken out of the system as a by-product by the screw conveyor (8). B. Second Embodiment This embodiment is shown in FIG. The apparatus for removing acidic gas in exhaust gas shown in FIG. 2 is not provided with a cooling water injection device into the lower end of the reactor. Others are the same as the first embodiment. According to the method and the apparatus for removing acid gas in exhaust gas of the present invention, the recycle solid is recycled to the reactor with the surface being wetted beforehand, and the recycle solid is removed. Since the absorbent slurry is homogeneously mixed by the screw feeder, the efficiency of acid gas absorption 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. [Explanation of symbols] (1)… Reactor (2)… exhaust gas inlet (3)… Exhaust gas outlet (5) Cyclone (6)… solid matter recirculation path (61)… Screw feeder (4)… absorbent slurry introduction pipe

Continuation of the front page (72) Inventor Hirotoshi Yanagi 5-3-28 Nishikujo, Konohana-ku, Osaka-shi Inside Tachibashi Shipbuilding Co., Ltd. Shipbuilding Co., Ltd. (72) Inventor Katsunori Matsunaga 5-3-28 Nishikujo, Konohana-ku, Osaka-shi Tachibashi Shipbuilding Co., Ltd. (72) Inventor Hironaka Tanaka 5-28, Nishikujo, Konohana-ku, Osaka-shi (56) References JP-A-5-309229 (JP, A) WO 96/16722 (WO, A1) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01D 53 / 34

Claims (1)

(57) [Claim 1] A vertical reactor having an exhaust gas inlet at a lower end and an exhaust gas outlet at an upper end, means for supplying an absorbent slurry to the reactor, and exiting the reactor. An apparatus for removing acidic gas in exhaust gas, comprising: a separation device for separating dried solid matter contained in the exhaust gas; and a recirculation path for recirculating a part of the separated solid matter to the reactor. At least a part of the circulation path is constituted by a screw feeder, and an introduction pipe for introducing the absorbent slurry is provided on the start end side of the recirculation solid material inlet in the screw feeder, wherein the exhaust gas is discharged. Acid gas removal equipment.