JP3502458B2 - Wet flue gas desulfurization equipment - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wet flue gas desulfurization apparatus, and more particularly to a wet flue gas desulfurization apparatus suitable for desulfurizing exhaust gas discharged from a coal burning combustion furnace and containing fly ash in a relatively high concentration. The present invention relates to a smoke desulfurization device.

[0002]

_2. Description of the Related Art In order to remove environmental pollutants such as SO ₂ and dust from exhaust gas, an absorption liquid mainly containing dissolved and / or suspended limestone is subjected to a gas-liquid contact reaction with exhaust gas containing sulfurous acid gas to form sulfurous acid. A wet flue gas desulfurization method of desulfurizing exhaust gas by immobilizing gas as gypsum is often used. Among them, a jet bubbling reaction tank (Japanese Patent Publication No. 60-4726 and Japanese Patent Publication No. 60-
The wet flue gas desulfurization apparatus using the above-mentioned No. 51372 gazette) is widely adopted as an apparatus which has a high removal rate of environmental pollutants and is economically excellent. Conventionally, a wet flue gas desulfurization apparatus using a jet bubbling reaction tank is generally provided in a preceding stage of the jet bubbling reaction tank with a dust removal tower equipped with a cooling liquid circulation pump, and first, exhaust gas is introduced into the dust removal tower,
Here, the exhaust gas was introduced into the jet bubbling reaction tank after being brought into contact with the spray droplets of the cooling liquid to remove dust and cool the exhaust gas. In particular, in the case of desulfurizing exhaust gas discharged from a coal-fired combustion furnace and containing fly ash in a relatively high concentration, dust removal by a dust removal tower has been performed almost without exception.

Meanwhile, the wet flue gas desulfurization apparatus having the dust removing tower has the following disadvantages. First, since the droplet size of the cooling liquid sprayed in the dust removal tower is larger than the particle size of dust particles in the exhaust gas, the efficiency of dust capturing of the cooling liquid is low. Therefore, in order to cool the exhaust gas and remove dust, it was necessary to spray a large amount of cooling liquid. Therefore, the separator becomes large to separate a large amount of cooling liquid from the exhaust gas,
Furthermore, since the separated cooling liquid is circulated and reused, the cooling liquid circulation pump becomes large and the equipment cost is increased. In addition, the power cost to operate a large cooling liquid circulation pump also increased. Secondly, since pressure loss of exhaust gas occurs in the dust removing tower, it is necessary to increase the blowing pressure of exhaust gas by a pressure commensurate with the pressure loss, which increases power cost.

Therefore, as shown in FIG. 2, a wet flue gas desulfurization apparatus 100 has been developed in which the dust removing tower is omitted and the exhaust gas is directly introduced into the jet bubbling reaction tank. The wet flue gas desulfurization apparatus 100 includes a jet bubbling reaction tank 12 that desulfurizes exhaust gas and removes dust, a centrifugal separator 14, and a thickener 1.
6 and other necessary equipment such as an untreated exhaust gas / desulfurization exhaust gas heater (not shown). Jet bubbling reaction tank (hereinafter simply referred to as reaction tank) 1
In the case of 2, a slurry-like absorption liquid in which limestone is mainly dissolved and / or suspended in water is stored in the lower portion of the tank, and the exhaust gas containing the sulfur dioxide gas introduced and the absorption liquid are subjected to a gas-liquid contact reaction to generate sulfur dioxide gas. It is a device that desulfurizes exhaust gas and removes dust by fixing it as gypsum.

An outline of the reaction tank 12 will be described below with reference to FIG. The details are described in JP-A-64-18429.
Japanese Patent Publication No. 3-70532 and Japanese Patent Publication No. 3-70532. As shown in FIG. 3, the reaction tank 12 includes an exhaust gas outlet chamber 26, an exhaust gas inlet chamber 24 having an absorbing liquid injection nozzle 22 therein, and an exhaust gas inlet chamber 24 at an upper end thereof in order from the top in the tank.
And an exhaust gas dispersion pipe 20 that communicates with and hangs downward from the pipe. Further, a jet nozzle 28 and a stirrer 30 for jetting an oxygen-containing gas such as air are provided below the exhaust gas dispersion pipe 20, and an absorption liquid introduction pipe 32 and a discharge pipe 34 are provided.
Are connected to the reaction tank 12. In the upper part of the reaction tank 12, the introduction duct 36 and the discharge duct 38 are connected to the exhaust gas inlet chamber 24 and the exhaust gas outlet chamber 26, respectively, and a cooling water injection nozzle 40 is arranged in the introduction duct 36. An absorption liquid supply pipe 42 and a cooling water supply pipe 44 are connected to the absorption liquid injection nozzle 22 and the cooling water injection nozzle 40, respectively. Reference numeral 46 denotes an air introducing pipe, and 48 denotes an absorbing liquid.

When the reaction tank 12 is operated, the exhaust gas is introduced into the reaction tank 12 from the introduction duct 36 while the cooling water is ejected from the nozzle 40 and the absorbing liquid is ejected from the nozzle 22 in the form of fine particles. The exhaust gas comes into gas-liquid contact with the cooling water and the fine particles of the absorbing liquid in the exhaust gas inlet chamber 24, and the pollutants in the exhaust gas are captured and absorbed by the fine particles, and the exhaust gas is humidified and cooled. Furthermore, the exhaust gas is
Along with the fine particles, they pass through the exhaust gas dispersion pipe 20, and are dispersed and introduced into the absorption liquid through a large number of small openings in the lower part of the exhaust gas dispersion pipe 20, for example, a large number of pores, and gas-liquid two-phase continuous consisting of fine bubbles of the exhaust gas and the absorption liquid. Forming a jet bubbling layer which is a gas-liquid contact layer. The remaining pollutants in the exhaust gas are
In the jet bubbling layer, the liquid is captured and absorbed by the absorbing liquid, and the liquid particles entrained in the exhaust gas are also captured and absorbed by the absorbing liquid. In the jet bubbling layer, the SO ₂ component reacts with limestone, water, and oxygen to form gypsum, and is sent out as gypsum slurry from the bottom of the reaction tank 12 through the discharge pipe 34 to the centrifugal separator 14 by the gypsum slurry discharge pump 62. . On the other hand, the exhaust gas from which the pollutants have been removed is withdrawn from the reaction tank 12 from the jet bubbling layer, through the passage 52 and the exhaust gas outlet chamber 26, and through the outlet duct 38.

The gypsum slurry is solid-liquid separated into a solid gypsum component and a liquid residual liquid by the centrifugal separator 14. The residual liquid is sent to the thickener 16 and separated into a concentrated liquid and a supernatant liquid. The concentrated liquid is sent out by the concentrated liquid pump 64, and is sent directly to the reaction tank 12 through the absorption liquid introduction pipe 32. Also,
The supernatant liquid is once introduced into the settling tank 70, then sent by the drainage pump 72, and a part of the supernatant liquid flows into the limestone slurry generator 66 through the return pipe 73 and is used for slurry preparation. It is returned to the reaction tank 12 by the pump 68, and the rest is sent to a wastewater treatment device (not shown). On the other hand, the gypsum component is delivered as a raw material for cement production or gypsum board production.

[0008]

However, in the above-mentioned wet flue gas desulfurization apparatus, when desulfurizing the exhaust gas discharged from the coal-fired combustion furnace and containing fly ash in a relatively high concentration, the centrifugal separator 14 is used. There was a problem that the quality of gypsum, especially the purity of gypsum (conversely speaking, the content of fly ash in gypsum) and the water content varied. When the purity and water content of gypsum fluctuate, it is often not preferable as a raw material for cement production or gypsum board production, and there has been a demand for production of gypsum of which quality does not fluctuate. Therefore,
The object of the present invention is a wet flue gas desulfurization apparatus capable of maintaining the purity and water content of gypsum constant even when desulfurizing exhaust gas discharged from a coal-fired combustion furnace and containing fly ash at a relatively high concentration. Is to provide.

[0009]

Means for Solving the Problems The present inventor has studied the cause of fluctuations in the purity and water content of gypsum in a conventional wet-type flue gas desulfurization apparatus omitting a dust removal tower, and has obtained the following findings. . First, as a result of examining the relationship between the fly ash content rate in gypsum, the gypsum water content rate, and the gypsum purity, it was found that the relationship is as shown in FIG. According to this, when the fly ash content in the gypsum increases, the increase rate of water content of gypsum increases, and the purity of gypsum decreases. In addition, in FIG. 4, the horizontal axis shows the fly ash content rate [wt%] in gypsum,
The gypsum water content increase rate [wt%] and gypsum purity [wt%] are plotted on the left and right vertical axes, respectively. The gypsum water content increase rate means the rate at which the water content of gypsum increases with the increase of the fly ash content rate, based on when the fly ash content rate in the gypsum is 0. Secondly, if the thickener 16 has a high sedimentation performance and the thickener 16 can completely separate the fly ash to the concentrated liquid side, as can be seen from FIG. 2, the fly in the residual liquid discharged from the centrifugal separator 14 is understood. The ash returns to the reaction tank 12 again together with the concentrated liquid. Therefore, the fly ash introduced into the wet flue gas desulfurization device together with the exhaust gas has to stay in the wet flue gas desulfurization device except for being discharged out of the system together with the gypsum component separated by the centrifugal separator 14. . In this case, the fly ash content in the absorption liquid in the reaction tank 12 does not depend on the fly ash content rate in the exhaust gas, that is, the variation of the inflow amount of the fly ash, and there is no means for controlling the fly ash discharge amount. The rate is variable and therefore the fly ash content in the gypsum is variable.

Based on the knowledge obtained, in order to achieve the above object, the jet bubbling reaction tank according to the present invention mainly comprises an absorbing liquid in which limestone is dissolved and / or suspended in water and an exhaust gas containing sulfurous acid gas. Gaseous components and residual liquid are separated from the gas-liquid contact tank that desulfurizes the exhaust gas and removes dust by immobilizing sulfur dioxide as gypsum through a gas-liquid contact reaction and the gypsum slurry extracted from the gas-liquid contact tank. It is equipped with a solid-liquid separator and a liquid-liquid separator that separates the residual liquid flowing out of the solid-liquid separator into a concentrated liquid and a supernatant liquid, and desulfurizes exhaust gas containing fly ash in a relatively high concentration to remove dust. In the wet flue gas desulfurization device, the bypass pipe for guiding the gypsum slurry from the upstream side of the solid-liquid separator to the liquid-liquid separator and the flow control valve provided in the bypass pipe are provided, and It is characterized in that depending on the content and to adjust the opening degree of the flow rate control valve.

The solid-liquid separator used in the present invention is a known solid-liquid separator, and for example, a centrifugal separator can be used.
The liquid-liquid separator is also a known liquid-liquid separator, for example, a thickener or clarifier that separates a concentrated liquid and a supernatant by sedimentation, a liquid that separates a concentrated liquid and a supernatant by centrifugation. A separation cyclone can be used. In particular,
Liquid-liquid separation cyclones are effective alternatives to thickeners. In the present specification, the supernatant liquid discharged from the liquid-liquid separator means
Concentrated liquid that contains a relatively small amount of solids, semi-solids, suspensions, etc. (hereinafter collectively referred to as solids) in the residual liquid that came out of the solid-liquid separator The liquid refers to a liquid containing a relatively large amount of solid matter as compared with the supernatant.

A preferred embodiment of the present invention is characterized in that the gas-liquid contact tank is a jet bubbling reaction tank.

[0013]

The liquid-liquid separation device is designed so that the residual liquid can be separated at a predetermined flow rate. From the operating principle of this type of separation device, basically, the concentration liquid withdrawal flow rate is kept constant. As long as the flow rate increases, the content of solids on the supernatant side increases to some extent as the inflow increases. In the present invention, utilizing this operating principle, when the content of fly ash in the exhaust gas becomes high, the flow control valve of the bypass pipe is opened to bypass the solid-liquid separator and gypsum containing fly ash. Flow the slurry into the liquid-liquid separator. When the amount of inflow increases, the content of solids, that is, fly ash and gypsum in the supernatant discharged from the liquid-liquid separator increases, and the amount of fly ash discharged to the outside of the system increases. Therefore, by adjusting the opening of the flow rate control valve according to the fly ash content in the exhaust gas, the amount of fly ash discharged to the outside of the system is controlled,
Therefore, the fly ash content in the absorbing liquid in the gas-liquid contact tank is controlled to be constant. Thereby, the fly ash content in the gypsum can be kept constant, so that the gypsum water content and the gypsum purity can be kept constant.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in more detail based on embodiments with reference to the accompanying drawings. FIG. 1 is a schematic flow sheet showing the configuration of an embodiment of a wet flue gas desulfurization apparatus 10 according to the present invention. 2 and 3 among the devices and parts shown in FIG.
The same parts as those in FIG.
Like FIG. 2, FIG. 1 is a flow sheet showing only the main part of the present invention, and the description of devices and control devices not directly related to the present invention is omitted. The wet flue gas desulfurization apparatus 10 of this embodiment is provided with a first bypass pipe 74 and a second bypass pipe 76 in addition to the configuration of the wet flue gas desulfurization apparatus 100 shown in FIG.

The first bypass pipe 74 is provided with a flow rate control valve 78 and is connected to the inlet of the thickener 16 bypassing the centrifugal separator 14 from the upstream of the centrifugal separator 14.
The second bypass pipe 76 is provided with a flow rate control valve 80, and bypasses the thickener 16 from the downstream of the centrifugal separator 14 and communicates with the sedimentation tank 70.

The thickener 16 is a device for separating the concentrated liquid and the supernatant liquid by sedimentation separation, and is designed so that the residual liquid can be separated at a predetermined flow rate. From the operating principle of this type of separation device, Obviously, basically, as long as the withdrawal flow rate of the concentrated solution is kept constant, if the inflow rate increases, the content of the solid matter on the supernatant side increases to some extent. In the present embodiment, the operating principle of the thickener 16 is used to open the flow rate control valve 78 of the first bypass pipe 74 immediately or at a certain time difference when the content of fly ash in the exhaust gas increases. The gypsum slurry is introduced directly into the thickener 16, thereby increasing the amount of fly ash flowing out together with the supernatant. As a result, the fly ash content of the absorbing liquid retained in the jet bubbling reaction tank 12, that is, the fly ash content contained in the gypsum slurry can be maintained constant.

The second bypass pipe 76 is an emergency means. When the gypsum slurry flows through the first bypass pipe 74 to the thickener 16 at a large flow rate, the flow rate significantly exceeds the capacity of the thickener 16, and a large amount of gypsum and fly ash are mixed in the supernatant liquid. There is also. This will hinder the operation of the wastewater treatment device.
By opening the flow rate control valve 80 of the bypass pipe 76 and adjusting the opening of the flow rate control valve 80, the residual liquid of the centrifugal separator 14 bypasses the thickener 16 and drops directly into the settling tank 70, and the amount of inflow to the thickener 16 is increased. Adjust.

A liquid-liquid cyclone may be used instead of the thickener 16. The liquid-liquid cyclone is a device that separates the concentrated liquid and the supernatant liquid by centrifugation, and like the thickener, as long as the withdrawal flow rate of the concentrated liquid is kept constant, there will be some degree of difference as the inflow increases. , The content of solids on the supernatant side increases. Therefore, it is also possible to directly introduce the gypsum slurry into the liquid-liquid cyclone via the first bypass pipe 74, thereby increasing the amount of fly ash flowing out together with the supernatant liquid.

[0019]

According to the constitution of the present invention, the solid-liquid separator is bypassed and a bypass pipe for guiding the gypsum slurry from the upstream to the liquid-liquid separator is provided, and a flow control valve provided in the bypass pipe. By controlling the content of fly ash in the gas-liquid contact tank by adjusting the opening of the flow control valve according to the content of fly ash in the exhaust gas, the fly ash content in the gypsum can be adjusted. Can be constant. By using this wet flue gas desulfurization device, it is possible to maintain the water content and the gypsum purity of the gypsum produced as a by-product,
Gypsum produced as a by-product can be effectively used. Further, as long as the specifications of gypsum permit, the content of fly ash in the gypsum can be maintained at the maximum, so that the load on the wastewater treatment equipment and the load on the dry electrostatic precipitator for dust removal can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic flow sheet showing the configuration of an embodiment of a wet flue gas desulfurization apparatus according to the present invention.

FIG. 2 is a schematic flow sheet showing the configuration of a conventional wet type flue gas desulfurization apparatus in which a dust removing tower is omitted.

FIG. 3 is a schematic diagram showing a configuration of a jet bubbling reaction tank.

FIG. 4 is a graph showing the relationship between the gypsum water content and the gypsum purity with respect to the fly ash content in gypsum.

[Explanation of symbols]

100 Conventional wet flue gas desulfurization equipment without the dust removal tower 12 Jet bubbling reaction tank 14 Centrifuge 16 Thickener 20 Exhaust gas dispersion pipe 22 Absorption liquid injection nozzle 24 Exhaust gas inlet chamber 26 Exhaust gas outlet chamber 28 ejection nozzle 30 stirrer 32 Absorption liquid introduction tube 34 Absorbing liquid discharge pipe 36 Introduction duct 38 Outlet duct 40 Cooling water injection nozzle 42 Absorbing liquid supply pipe 44 Cooling water supply pipe 46 Oxygen-containing gas introduction pipe 48 Absorbing liquid holding part 52 passage 62 gypsum slurry discharge pump 64 Concentrate pump 66 Limestone slurry generator 68 Limestone slurry pump 70 Settling pond 72 drainage pump 73 Return tube 74 First bypass pipe 76 Second bypass pipe 78 Flow control valve 80 Flow control valve

─────────────────────────────────────────────────── --Continued from the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) B01D 53/14-53/18 B01D 53/34-53/85 C01F 11/46

Claims (2)

(57) [Claims] 1. An exhaust gas is desulfurized by mainly subjecting an absorbing solution mainly obtained by dissolving and / or suspending limestone to water and an exhaust gas containing sulfurous acid gas to a gas-liquid contact reaction to immobilize the sulfurous acid gas as gypsum, In addition, a gas-liquid contact tank for removing dust, a solid-liquid separator for separating gypsum components and residual liquid from the gypsum slurry extracted from the gas-liquid contact tank, and a residual liquid flowing out of the solid-liquid separator for a concentrated liquid and a supernatant liquid. In a wet-type flue gas desulfurization device that desulfurizes exhaust gas containing fly ash in a relatively high concentration and removes dust, it is equipped with a liquid-liquid separator that separates liquid and liquid from the upstream side by bypassing the solid-liquid separator. A bypass pipe that guides the gypsum slurry to the device, and a flow control valve provided in the bypass pipe are provided, and the opening of the flow control valve is adjusted according to the content of fly ash in the exhaust gas. Wet flue gas desulfurization Location. 2. The wet flue gas desulfurization apparatus according to claim 1, wherein the gas-liquid contact tank is a jet bubbling reaction tank.