JP6046526B2 - Selenium recovery system and method for recovering selenium in exhaust gas - Google Patents

Description

  The present invention relates to a selenium recovery system and a selenium recovery method in exhaust gas. In particular, it is useful in recovering selenium in exhaust gas discharged from a glass melting furnace related to glass containing selenium.

  Selenium or a selenium compound (hereinafter sometimes abbreviated as “Se”), particularly metal selenium, has semiconducting properties and photoconductivity, so that it can be used for a photosensitive drum of a copying machine or have optical characteristics. Used as a colorant and decolorizer for various optical glasses. Here, the metal Se has a very low boiling point of 688 ° C. as compared with other metals, and some of them evaporate in the glass melting furnace. These are treated by a general exhaust gas treatment. At this time, as for Se contained in wastewater from the manufacturing process, many techniques for separating Se in wastewater have been studied for the purpose of wastewater control measures. On the other hand, the exhaust gas is not generally treated only with Se, but it has a high recovery effect in consideration of the resource value as a rare metal, and research on Se recovery technology in exhaust gas has recently progressed. It is out.

  For example, an apparatus for removing selenium in exhaust gas as shown in FIG. 5 has been proposed so that selenium in exhaust gas can be efficiently collected and removed from the exhaust gas. Specifically, the exhaust gas flue 116 and the heating furnace 117 are arranged around a heating furnace 117 provided adjacent to the exhaust gas flue 116 and a rotary shaft 118 provided between the heating furnace 117 and the exhaust gas flue 116. A disk-shaped adsorbent 120 that rotates across and adsorbs the selenium component in the flue gas flue 116 and separates it in the heating furnace 117, and selenium recovery means 114 that absorbs the separated selenium component with water (for example, Patent Document 1). Here, A is exhaust gas, 113 is a selenium collection unit, 121 is a selenium adsorption unit, 122 is a selenium desorption unit, 123 is a drive unit, 124 is a burner, 125 is a spray nozzle, 126 is a circulation pump, and 127 is a gas flow Road 130 is a selenium absorption tower.

JP 2001-104748 A

However, such a selenium removal device in exhaust gas has the following problems.
(I) The adsorbent used for the adsorption treatment of Se is expensive and requires high-temperature treatment to desorb and regenerate the adsorbed Se. In long-term use, it was difficult to use the actual device. In addition, Se adsorbed on such a treatment system gradually remains and increases in the amount of adhesion, which makes it difficult to peel off.
(Ii) Especially in glass manufacturing processes containing sulfur compounds, there was a problem of the generation of sulfuric acid mist (SO ₃ ) accompanying such high-temperature treatment, and the corrosion and blockage in the flow path accompanying sulfuric acid mist. .
(Iii) In addition, since selenium oxide (SeO ₂ ), which is presumed to be present in the exhaust gas, has high water solubility, removal treatment with an aqueous solution is actually used, but once dissolved Se is separated. As described above, a separate processing device is required as in the case of Se treatment in the waste water, and the exhaust gas processing device becomes very complicated.
(Iv) Furthermore, when the sulfur compound present in the exhaust gas is recovered as a sulfate component, separation from selenium in the recovery process is very difficult, and the reduction of selenium contamination in the recovered sulfate is significant. It was an issue. In particular, in the exhaust gas from a glass melting furnace for treating alkali glass or the like, sulfate components such as sodium sulfate in the exhaust gas are recovered and often used again as a material such as alkali glass. Separation of selenium dissolved in effluent containing sulfites of alkali metals such as mirabilite was an important issue.

  In view of the above-mentioned problems of the prior art, it is an object of the present invention to efficiently separate selenium from an exhaust gas containing a sulfur compound and continuously recover the separated selenium. It is to provide a selenium recovery system and a recovery method. In particular, when recovering selenium together with sulfates in an apparatus that recovers sulfate components (eg, mirabilite) contained in exhaust gas from glass melting furnaces containing selenium, high selenium recovery efficiency is ensured. An object of the present invention is to provide a selenium recovery system and a recovery method that can be used.

  As a result of intensive studies to solve the above problems, the present inventor has found that the above object can be achieved by the following selenium recovery system and recovery method, and has completed the present invention.

That is, the selenium recovery system according to the present invention targets at least selenium or an exhaust gas containing a selenium compound and a sulfur compound, and at least cooling water is added to the exhaust gas, the exhaust gas temperature is equal to or higher than the melting point of selenium, an alkali metal or A cooling section that is cooled to a temperature lower than the production temperature of the alkaline earth metal sulfate or sulfite, and a neutralizing agent containing an alkali metal compound or an alkaline earth metal compound is added to the exhaust gas; A neutralization treatment portion for neutralizing acidic components in exhaust gas containing sulfate or sulfite of an alkali metal or alkaline earth metal derived therefrom, dust in the exhaust gas and the cooling portion or neutralization treatment portion A dust collection processing unit for collecting solid components generated in any one of the above, and the neutralization processing unit or dust collection The exhaust gas treated in any of the treatment parts is introduced, and has a selenium precipitation part for precipitating selenium or a selenium compound on the surface set below the melting point of the selenium, and deposited on the surface of the selenium precipitation part Selenium or a selenium compound is taken out, and a sulfate component is taken out from the solid component collected in the dust collection processing section.
In particular, the exhaust gas from a glass melting furnace containing at least selenium or a selenium compound and a sodium compound and a sulfur compound is targeted, at least,
Cooling water is added to the exhaust gas, and a neutralizing agent containing a sodium compound added in a neutralization treatment section located at a later stage of the cooling section and having an exhaust gas temperature equal to or higher than the melting point of selenium, and sodium compounds and sulfur compounds in the exhaust gas A cooling section that is cooled to a temperature that produces sodium sulfate or sodium sulfite;
A neutralization treatment unit in which a neutralizing agent containing a sodium compound is added to the exhaust gas, and neutralization treatment of an acidic component in the exhaust gas containing sodium sulfate salt or sodium sulfite salt derived from the sulfur compound is performed,
A dust collection processing unit for collecting dust in the exhaust gas and solid components generated in either the cooling unit or the neutralization processing unit;
The exhaust gas treated in either the neutralization treatment part or the dust collection treatment part is introduced, and has a selenium precipitation part for precipitating selenium or a selenium compound on the surface set to be equal to or lower than the melting point of the selenium,
Selenium recovery in which selenium or a selenium compound precipitated on the surface of the selenium precipitation part is taken out, and a sulfate component containing sodium sulfate or a sulfite containing sodium sulfite is taken out from the solid component collected in the dust collection treatment part A system is preferred.

In addition, the present invention is a method for recovering selenium, characterized by having at least the following steps for exhaust gas containing at least selenium or a selenium compound and a sulfur compound.
(1) A cooling treatment step in which cooling water is added to the exhaust gas, and the exhaust gas temperature is cooled to be not lower than the melting point of selenium and not higher than the formation temperature of an alkali metal or alkaline earth metal sulfate or sulfite (2) A neutralizing agent containing an alkali metal compound or an alkaline earth metal compound is added to the exhaust gas, and neutralization treatment of acidic components in the exhaust gas containing an alkali metal or alkaline earth metal sulfate or sulfite derived from the sulfur compound The neutralization treatment step (3) in which the dust in the exhaust gas and the solid component generated in any one of the steps (1) and (2) are collected (4) The step (1 ) To (3) or the selenium precipitation in which the exhaust gas treated in some of them is subjected to a surface temperature below the melting point of the selenium. Selenium or a selenium compound is precipitated on the surface of the selenium precipitation part, and the precipitated selenium is recovered (5) The selenium salt or sulfite from the solid component collected in the step (3) Sulfate component recovery process from which salt components are removed
In particular, a selenium recovery method having at least the following steps for exhaust gas from a glass melting furnace containing at least selenium or a selenium compound and a sodium compound and a sulfur compound is preferred.
(1) Cooling water is added to the exhaust gas, the exhaust gas temperature is equal to or higher than the melting point of selenium, and a neutralizing agent containing a sodium compound added in a neutralization treatment step after the cooling step, and a sodium compound and a sulfur compound in the exhaust gas, Cooling process that is cooled to a temperature that produces sodium sulfate or sodium sulfite
(2) A neutralization treatment step in which a neutralizing agent containing a sodium compound is added to the exhaust gas, and neutralization treatment of an acidic component in the exhaust gas containing sodium sulfate salt or sodium sulfite salt derived from the sulfur compound is performed.
(3) Dust collection processing step in which dust in the exhaust gas and solid components generated in any of the steps (1) and (2) are collected
(4) The exhaust gas treated by the steps (1) to (3) or some of them is brought into contact with a selenium precipitation part whose surface temperature is set to be equal to or lower than the melting point of the selenium, and the selenium precipitation Selenium recovery process in which selenium or a selenium compound is precipitated on the surface of the part and the precipitated selenium is recovered
(5) A sulfate component recovery step in which the sulfate or sulfite component is taken out from the solid component collected in the step (3).

Conventionally, in a recovery process of a sulfur compound derived from a glass raw material (for example, sulfate such as mirabilite) contained in exhaust gas from a glass melting furnace, selenium or a selenium compound (Se) derived from the same raw material is recovered together with the sulfate. It was very difficult. Based on the following knowledge in the verification process, the present invention can perform an efficient selenium separation process and continuous recovery process from exhaust gas by using the selenium recovery system and recovery method configured as described above. In addition, it has been found that sulfates or sulfites of alkali metals or alkaline earth metals (hereinafter sometimes referred to as “sulfate components”) can be recovered with high purity.
(A) In the treatment part (selenium precipitation part) in which the selenium compound (Se) such as metal selenium or selenium oxide contained in the exhaust gas after the neutralization treatment is set to be equal to or lower than the melting point of selenium (about 190 to 200 ° C.) , Se is deposited as a precipitate.
(B) Such precipitation of Se can obtain a larger amount of precipitation under conditions where the sulfur component contained in the exhaust gas is decreased, particularly under conditions where a sulfate component is generated.
(C) Sulfate component produced after neutralization under temperature conditions (for example, about 240 to 280 ° C.) above the melting point of selenium and below the production temperature of the sulfate component (eg sodium sulfate production temperature: about 900 ° C.) By collecting as dust and dust deposits in the dust collection processing section, it is possible to obtain a higher recovery efficiency of the sulfur compound.
(D) In the recovery of sulfate components, different types of collectors such as an electrostatic precipitator (hereinafter sometimes referred to as “EP”) and a filtration dust collector (such as a bag filter, hereinafter sometimes referred to as “BF”) are used. By collecting together with dust having different particle diameters by the dust means, higher collection efficiency can be obtained.
In particular, in a process for producing alkali glass containing sodium nitrate (Na ₂ SO ₄ ) and Se as a part of raw materials, it is dissolved by performing a neutralization treatment using a neutralizing agent containing a sodium compound (for example, sodium hydroxide). High-purity sodium sulfate can be recovered from the exhaust gas from the furnace, and Se can be recovered more efficiently.

According to the present invention, in the selenium recovery system, as the selenium precipitation part, a low-temperature part adjusted to a melting point of selenium or less is formed on the outer surface inserted into the exhaust gas flow path. The selenium compound is precipitated, and the low temperature part has a configuration capable of being extracted from the exhaust gas flow path, thereby collecting selenium or the selenium compound.
As described above, Se contained in the exhaust gas after the neutralization treatment can be taken out as a precipitate at a predetermined temperature. The present invention has a structure that can be extracted from the exhaust gas flow path as an optimum configuration for forming a low temperature portion where selenium precipitates, and by forming the low temperature portion on the outer surface through the refrigerant circulation portion, Se is efficiently produced. It was possible to precipitate.

According to the present invention, in the selenium recovery system, as the dust collection processing unit, an electric dust collection device is provided on the upstream side of the exhaust gas flow, a filtration type dust collection device is provided on the downstream side, and the selenium precipitation unit is provided. , Exhaust gas connected to the inside of the electrostatic precipitator, the inside of the filter-type dust collector, the exhaust gas passage on the downstream side of the electrostatic dust collector, or the exhaust gas passage on the downstream side of the filter-type dust collector It is provided in any one or some of the treatment equipment or the chimney .
Further, the present invention provides the above selenium recovery method, wherein the step (3) comprises the following two steps:
(3a) An electric dust collection step in which solid components in the exhaust gas are collected by electric dust collection while the exhaust gas temperature is maintained above the melting point of selenium (3b) In a state where the exhaust gas temperature is maintained above the melting point of selenium The filtration type dust collecting process in which the solid component in the exhaust gas is collected by the filter medium is applied to the exhaust gas treated in any one or some of the processes (2), (3a), (3b). It is characterized by being performed.
The solid component mainly composed of a sulfate component produced by the neutralization treatment includes various shapes ranging from fine particles to large particles exceeding 100 μm. The present invention makes it possible to take out a solid component having a wide range of particle diameters from exhaust gas by providing a plurality of dust collecting means having such solid components having characteristics. In addition, in the recovery of Se, the smaller the sulfate component in the exhaust gas, the better. On the other hand, depending on the properties in the exhaust gas, there are cases where it is relatively difficult to be influenced by the sulfate component in the exhaust gas. That is, the recovery efficiency of Se on the upstream side of the exhaust gas flow path in which the Se concentration is high, and the recovery efficiency of Se on the downstream side where the amount of sulfate component in the exhaust gas by such a dust collection treatment means is small, May vary depending on the nature of the exhaust gas. The present invention makes it possible to ensure higher recovery efficiency by setting one or more optimum Se recovery points that meet exhaust gas conditions.

The present invention provides a solution containing an alkali metal or alkaline earth metal sulfate or sulfite containing sodium sulfate or sodium sulfite generated in the cooling section and / or neutralization section in the selenium recovery system. A pH measuring device for measuring the pH of the cooling water, and controlling the addition amount of the cooling water, the addition amount of the neutralizing agent, and the temperature of the exhaust gas so that the pH value falls within a predetermined range. And
In addition, the present invention provides an alkali metal or alkaline earth metal sulfate or sulfite containing sodium sulfate or sodium sulfite generated in the following step (2a) after the step (2) in the above selenium recovery method. PH measurement step (2b) for measuring the pH of the salt-containing solution The amount of cooling water added, the amount of neutralizing agent added, and the temperature of the exhaust gas are controlled so that the pH value falls within a predetermined range. It has a pH adjustment process.
As described above, in the exhaust gas treatment, the formation of the sulfate component by the neutralization treatment effectively precipitates Se to the low temperature part of the selenium precipitation part, and is effective in recovering Se contained in the product. understood. The present invention makes it possible to create more optimal conditions for Se recovery by appropriately measuring the treatment state in the neutralization treatment and using this as a control index. Moreover, these conditions made it possible to create optimum recovery conditions even in the recovery process of sulfate components. Specifically, the pH of the solution containing the sulfate component generated after the neutralization treatment is measured, and the added amount of cooling water and the added amount of the neutralizing agent so that the pH value is in a neutral to weak alkaline range. And the temperature of the exhaust gas is controlled.

According to the present invention, in the selenium recovery system, a sulfate recovery unit is provided in the dust collection processing unit, and the alkali metal or alkaline earth metal sulfate or sulfite generated in the cooling unit and / or the neutralization processing unit is provided. The solid component containing the salt is recovered, the sulfate or sulfite component in the recovered solid component is measured, and the amount of the cooling water added so that the recovered amount of the sulfur component falls within a predetermined range, The addition amount of the neutralizing agent and the temperature of the exhaust gas are controlled.
In addition, the present invention provides a solid component containing a sulfate or sulfite of an alkali metal or alkaline earth metal recovered in the step (5) in the above selenium recovery method.
(5a) Sulfur component measurement step for measuring sulfate or sulfite component in the recovered solid component (5b) The amount of cooling water added so that the recovered amount of the sulfur component is within a predetermined range, It has the sulfur component adjustment process which controls the addition amount of a neutralizing agent, and the temperature of the said waste gas.
As described above, it has been found that efficient separation of sulfate components is an important factor for efficient selenium recovery from exhaust gas. That is, the recovery amount of the sulfate component (sulfur component) means that it is an index for efficient recovery of selenium. The present invention measures the recovery amount of the sulfate component actually recovered after the neutralization treatment and uses this as a control index to create a more optimal condition in the recovery treatment of Se and the sulfate component. It was possible.

Schematic illustrating the basic configuration of a selenium recovery system according to the present invention Schematic which shows the 2nd structural example of the collection | recovery system of selenium based on this invention. Schematic which shows the 3rd structural example of the collection | recovery system of selenium based on this invention. Schematic illustrating experimental data in an embodiment according to the present invention Schematic illustrating a selenium removal device in exhaust gas according to the prior art

  The selenium recovery system according to the present invention (hereinafter referred to as “the present system”) targets at least exhaust gas containing selenium or a selenium compound (Se) and a sulfur compound (SOx), and at least the exhaust gas is cooled to a predetermined temperature range. Cooling section, neutralization section where the exhaust gas is neutralized, dust collection section where the solid components contained in the exhaust gas after neutralization are collected, and neutralization section or dust collection process A selenium precipitation part for precipitating selenium or a selenium compound in the exhaust gas treated in any of the parts, and the Se component deposited on the surface of the selenium precipitation part is taken out and collected in the dust collection treatment part The sulfate component is taken out of the product. Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<Basic configuration of this system>
FIG. 1 shows a basic schematic overall configuration of the present system (first configuration example). Exhaust gas discharged from an exhaust gas generation facility (for example, a glass melting furnace, hereinafter sometimes referred to as “melting furnace”) 1 is a cooling unit 2, a neutralization processing unit 3, a dust collection processing unit (electric dust collector [EP] 4). Is purified via a ventilator 5 and a filter-type dust collector [BF] 6 is exemplified) and discharged from a discharge unit (chimney) 7. This system is intended for exhaust gas containing Se and SOx, such as exhaust gas from a glass melting furnace, and aims to efficiently recover Se and sulfur compounds derived from raw materials (eg, sulfate components such as sodium nitrate). Configured as The exhaust gas introduced into this system is cooled to the desired exhaust gas temperature, the cooling part 2 is neutralized, the neutralization part 3 where the sulfate component is generated, and the solid component containing the sulfate component is separated In the selenium collection unit 8 provided in the chimney 7 to be separated, the precipitates containing Se are separated. In the first configuration example, a configuration in which the selenium recovery unit 8 is provided in the chimney 7 is illustrated, but as will be described later, the present invention is not limited to this, and the neutralized exhaust gas can be targeted. It can be provided in the exhaust gas flow path or in each processing section.

  In the present invention, the exhaust gas to be treated contains at least Se and SOx, for example, exhaust gas discharged from glass melting furnaces related to various optical glasses containing Se as a colorant or decolorizer. Specifically, in order to obtain the optical characteristics of the glass for flat panels, Se is contained, and a glass material containing mirabilite as a base material is used. From the glass melting furnace in the production process, exhaust gases containing these Se, SOx and sodium (Na) compounds are discharged, and by collecting such materials that require waste treatment and using them again as raw materials, A production system with a small environmental load can be configured.

  When the melting furnace 1 is, for example, a glass melting furnace, a glass component containing a desired component is taken out as a product, and high-temperature exhaust gas containing components derived from raw materials (Se, SOx, etc.) is introduced into the system. The The exhaust gas introduced into the cooling unit 2 is cooled to a temperature equal to or higher than the melting point of selenium and equal to or lower than the generation temperature of the sulfate component, and is introduced into the neutralization processing unit 3 to be neutralized. The exhaust gas derived from the neutralization processing unit 3 is introduced into EP4 and subjected to gas-solid separation processing. The solid component derived from EP4 is taken out as a sulfate component which is a main component. The exhaust gas derived from EP4 is introduced into the BF 6 by the exhaust fan 5, and further fine dust is collected and subjected to gas-solid separation processing. The solid component derived from BF6 is taken out as a sulfate component which is a main component. The exhaust gas derived from the BF 6 is introduced into the chimney 7 and the contained Se is taken out by the selenium recovery unit 8.

  In the cooling unit 1, cooling water is added to the exhaust gas at a high temperature (for example, about 500 ° C.), and the exhaust gas is cooled so that the exhaust gas temperature is not lower than the melting point of selenium and not higher than the generation temperature of the sulfate component (for example, about 240 to 280 ° C.). The As the cooling water, city water or industrial water cooled to room temperature or about 0 to 20 ° C. can be used, and soft water is preferably used in order to reduce clogging of the cooling water supply unit (for example, a nozzle). . As in the configuration example shown in the figure, the exhaust gas can be efficiently cooled by adding it to the exhaust gas in a spray form. The cooling temperature is not less than 218 ° C., which is the melting point of selenium, and not more than the formation temperature of the sulfate component (eg, formation temperature of sodium sulfate: about 900 ° C.), preferably about 240-280 ° C. so that Se in the exhaust gas remains. Furthermore, about 250-270 degreeC is preferable. By setting a temperature condition that utilizes the difference in physical properties between Se and sulfate components, Se and sulfate components can be effectively separated without using special equipment or materials in subsequent processing. it can. The exhaust gas cooled by the cooling unit 2 is introduced into the neutralization processing unit 3 disposed at the top, and a part of the sulfate component contained in the original exhaust gas is dissolved in the cooling water and cooled. Stored in part 2. In addition, since it is the conditions over 200 degreeC, the solution after a process hardly generate | occur | produces, but in order to confirm the effect of a neutralization process so that it may mention later, a part liquid layer is formed and pH of a solution is adjusted. It is preferable to measure.

  In the neutralization process part 3, a neutralizing agent is added to the exhaust gas cooled by the cooling part 2, the neutralization process of the acidic component in exhaust gas is performed, and a sulfate component is produced | generated from a sulfur compound. Like the cooling unit 2, the exhaust gas can be added to the exhaust gas in a sprayed manner to efficiently neutralize the exhaust gas. The exhaust gas neutralized by the neutralization processing unit 3 is fed to EP4. The neutralizing agent neutralizes Se, SOx, gaseous sulfates and sulfites contained in the original exhaust gas. The state of the neutralization treatment is detected by the hydrogen ion concentration (pH), for example, if there is a liquid layer at the bottom of the cooling unit 2, as will be described later, and the amount of neutralizing agent added is adjusted using the pH value as an index can do. In addition, in the 1st structural example, although the neutralization process part 3 was illustrated as integral with the cooling part 2, these can also be comprised as a different body. Moreover, in the structure which can form a liquid layer in the lower part of the cooling unit 2 or the neutralization processing unit 3, the cooling unit uses the solution in the liquid layer (cooling water or mixed water with the neutralized liquid) as cooling water. 1 can be formed. A zero emission type exhaust gas treatment system can be formed without generating waste liquid.

[About neutralizing agent]
In this system, it is preferable to use an agent containing an alkali metal compound or an alkaline earth metal compound as a part of the neutralizing agent. For example, hydroxides such as sodium hydroxide, potassium hydroxide, calcium hydroxide, and magnesium hydroxide, sodium carbonate, potassium carbonate, carbonates such as calcium carbonate and magnesium carbonate, sodium bicarbonate, potassium bicarbonate, calcium bicarbonate, Mention may be made, for example, of a drug mainly composed of a hydrogen carbonate such as magnesium hydrogen carbonate or an oxide such as sodium oxide, potassium oxide, calcium oxide or magnesium oxide. In the neutralization treatment, a sulfate component is generated by reaction with sulfur oxides in the exhaust gas, and is separated as a solid component mainly composed of the sulfate component in the dust collection treatment. Pure alkali metal or alkaline earth metal sulfates can be recovered. Further, as described above, Se can be efficiently recovered by efficiently recovering the sulfate component in the recovery process of Se from the exhaust gas containing the sulfur compound. The role is big. In particular, it is possible to more efficiently collect Se by performing a rough dust collection process for a relatively large particle diameter component by EP4 and a dense dust collection process for fine particles by BF6. . Specifically, for example, in a process for producing alkali glass containing sodium nitrate (Na ₂ SO ₄ ) and Se as a part of the raw material, a neutralizing treatment is performed using a neutralizing agent containing sodium hydroxide, thereby providing a melting furnace. In addition to recovering high-purity mirabilite from the exhaust gas from, Se can be recovered more efficiently.

[Dust collection section]
As the dust collection processing unit, in the present system, a configuration in which an electrostatic dust collection device (EP) 4 and a filtration dust collection device (BF) 6 are connected via an exhaust fan 5 is illustrated. The solid component mainly composed of a sulfate component produced by the neutralization treatment includes various shapes ranging from fine particles to large particles exceeding 100 μm. In this system, by providing EP4 on the upstream side of the flow of exhaust gas and providing BF6 on the downstream side with respect to such a solid component, particles having a predetermined size (for example, several tens of μm) or more are collected by EP4. Smaller particles are collected by BF6. By providing a plurality of dust collection means having different characteristics, the sulfate component contained in the solid component having a wide range of particle diameters could be extracted from the exhaust gas. In addition, although the structure provided with the two dust collection processing means which have different characteristics called EP4 and BF6 was illustrated here, according to the property of exhaust gas, only one of these, the structure which united these, these Can be used, or a configuration such as a combination with means having a gas-solid separation function such as a cyclone type can be used.

  In EP4, the exhaust gas derived from the neutralization processing unit 3 is subjected to gas-solid separation processing by an electric dust collecting means at a relatively high temperature condition of about 240 ° C. or higher. The dust that is separated and taken out has a relatively large particle size of about several tens of μm or more, and a solid component mainly composed of a sulfate component is formed. At this time, by separating the sulfate component, high recovery efficiency for Se in the exhaust gas can be ensured in the subsequent processing. The exhaust gas derived from EP 4 is fed to the BF 6 by the exhaust fan 5. In addition to Se, the dust includes materials derived from raw materials supplied to the exhaust gas generation facility. Examples of the exhaust gas from the glass melting furnace include sodium compounds, calcium compounds, silica components, fluorine compounds, and the like.

  In BF6, gas-solid separation processing is performed by a filter medium. The dust taken out by separation is a fine powder or granular material having a particle size of about 10 to several tens of μm, and a solid component mainly composed of a sulfate component is formed. By separating the fine sulfate component, it is possible to further secure high recovery efficiency for Se in the exhaust gas. The exhaust gas derived from the BF 6 is discharged through the chimney 7. As a filter medium used in BF6, glass, Teflon (registered trademark), or the like is used, but it is preferable to use ceramics, metal mesh, or the like under a high temperature condition of about 240 ° C. or higher. Further, in the dust, like the dust from EP4, a material derived from the raw material supplied to the exhaust gas generation facility is included in addition to Se. Examples of the exhaust gas from the glass melting furnace include sodium compounds, calcium compounds, silica components, fluorine compounds, and the like.

  Here, the sulfate recovery unit 41 or / and 61 is provided in EP4 or / and BF6, and the solid component containing the sulfate component generated in the cooling unit 2 and / or the neutralization processing unit 3 is recovered and recovered. The sulfate component in the solid component is measured, and the amount of cooling water added, the amount of neutralizer added, and the temperature of the exhaust gas are controlled so that the recovered amount of the sulfate component (sulfur component) falls within a predetermined range. It is preferable. By measuring the recovery amount of the sulfate component recovered after the neutralization treatment, and using this as an index for feedback control of the cooling treatment and the neutralization treatment, a more optimal condition for the recovery treatment of Se and the sulfate component is created. be able to.

[Selenium precipitation part]
In the selenium precipitation part 8, the exhaust gas derived from BF6 is treated at a low temperature below the melting point of selenium (for example, about 190 to 200 ° C.), Se is generated on the outer surface of the selenium precipitation part 8, and crystalline precipitates are formed. It is formed. By such precipitation treatment, Se having high purity with little mixing of sulfate components is taken out. The exhaust gas in contact with the selenium precipitation part 8 is further purified and discharged through the chimney 7. Thus, by setting the temperature to be equal to or lower than the melting point of selenium and having no significant temperature difference than the melting point, Se contained in the exhaust gas after the neutralization treatment is formed in the low temperature portion formed on the outer surface. Can be concentrated on the surface. Further, the precipitate thus generated gradually grows with this as a nucleus, and the growth rate can be maintained by cold heat from the refrigerant. Furthermore, such precipitation of Se can obtain a larger amount of precipitation under the condition where the sulfur component contained in the exhaust gas is reduced, particularly under the condition where the sulfate component is generated. In the first configuration example, a case where the exhaust gas flow path is provided in the chimney 7 which is the final stage of the exhaust gas treatment is illustrated.

  As a configuration of the selenium precipitation portion 8, for example, a refrigerant having a temperature of about 150 ° C. or less circulates, and a low temperature portion adjusted to be equal to or lower than the melting point of selenium (for example, about 190 to 200 ° C.) is formed on the outer surface inserted into the exhaust gas passage In addition, Se can be efficiently recovered by using a configuration in which the low temperature portion can be extracted from the exhaust gas passage. Specifically, it is inserted into the exhaust gas flow path inside the chimney 7 or the like, and when the deposit is collected, a pluggable device that can extract the attached deposit or remove it, or the exhaust gas flow path is branched, and a part of the exhaust gas Alternatively, a device or the like in which the entire amount is circulated and a detachable bypass channel is provided, and the selenium precipitation portion 8 is attached to the bypass channel can be used. However, the selenium recovery unit 8 is not limited to the configuration installed in such a chimney 7, and as shown in a configuration example described later, an exhaust gas flow channel or each processing unit capable of targeting a neutralized exhaust gas Can be provided.

<Selenium recovery method using this system>
The selenium recovery method using this system has at least the following processes.
(1) Cooling process in which cooling water is added to the exhaust gas, and the exhaust gas temperature is cooled so as to be not lower than the melting point of selenium and not higher than the production temperature of the sulfate component. (2) An alkali metal compound or alkaline earth metal compound is added to the exhaust gas. Neutralization treatment step in which neutralizing treatment is added and neutralization treatment of acidic components in exhaust gas containing sulfate components derived from sulfur compounds is performed (3) Dust in exhaust gas and steps (1), (2) Dust collection treatment step (4) in which solid components generated in any of the steps are collected (4) The exhaust gas treated in steps (1) to (3) or some of them has a surface temperature of the selenium A selenium recovery step in which the selenium precipitate is set in contact with a selenium precipitation part set below the melting point of the selenium, and selenium or a selenium compound is precipitated on the surface of the selenium precipitation part. ) Sulfate component recovery step in which the sulfate component is taken out from the solid component collected in step (3). For each step, the exhaust gas from the melting furnace for the glass raw material containing sodium nitrate and Se is recovered in the first configuration example. The case where it is introduced into the system will be described in detail as an example.

(1) Cooling step of exhaust gas Cooling water is added to the exhaust gas, and the exhaust gas is cooled so that the exhaust gas temperature is not lower than the melting point of selenium and not higher than the generation temperature of the sulfate component. Specifically, for example, city water or industrial water cooled to room temperature or about 0 to 20 ° C. is added to the exhaust gas at about 500 ° C. introduced into the cooling unit 2 in a spray state, and the exhaust gas temperature is increased. Is preferably cooled to about 240-280 ° C, more preferably about 250-270 ° C. The cooling water that has not been evaporated is subjected to gas-liquid contact with the exhaust gas, and then Se, SOx, gaseous sulfate components, and the like contained in the exhaust gas dissolved in the cooling water are stored at the bottom of the cooling unit 2. The exhaust gas from which these components are separated is introduced into the neutralization processing unit 3. In the cooling unit 2, the following reactions occur in the gas phase and the liquid phase.
(1-1) Reaction associated with contact between exhaust gas and cooling water (including contact with primary neutralizer) Na ₂ SO ₃ + SO ₂ → 2NaHSO ₃
2Na ₂ SO ₃ + SO ₃ → 2NaHSO ₃ + Na ₂ SO ₄ .. Formula 2
(1-2) Reaction associated with contact between O _{2 in} exhaust gas and cooling water (including contact with primary neutralizer) 2Na ₂ SO ₃ + O ₂ → 2Na ₂ SO ₄

(2) Neutralizing treatment step of exhaust gas To the cooled exhaust gas, for example, a neutralizing agent containing an alkali metal compound such as sodium hydroxide or an alkaline earth metal compound such as calcium hydroxide is added and discharged from, for example, a glass melting furnace In the case of exhaust gas, neutralization treatment of the exhaust gas is performed by reacting with an acidic component such as sulfur oxide (SOx), fluorine compound or nitrogen oxide (NOx) derived from glass raw material. SOx, gaseous sulfate components, etc. contained in the exhaust gas are produced by neutralization reaction in the presence of moisture, part of which is dissolved in the cooling water or neutralizing agent that has not been evaporated, and the waste liquid (liquid The solution in the layer is stored at the bottom of the cooling unit 2. Specifically, in the neutralization treatment of exhaust gas, the following reactions occur together with the reactions of the above formulas 1 to 3.
NaHSO ₃ + NaOH → Na ₂ SO ₃ .. Formula 4
At this time, the state of the neutralization treatment can be detected by measuring the pH of the drainage (solution in the liquid layer). Moreover, the addition amount of cooling water and a neutralizing agent can be adjusted using this pH value as a parameter | index. Specifically, the pH is measured using a glass electrode pH meter (manufactured by Toa DKK Co., HDM-136A), and the standard value for neutralization is adjusted to, for example, pH 8.0 ± 1.0. Is done.

At this time, in the following process (2a), a pH measurement step (2b) for measuring the pH of the drained solution (solution in the liquid layer) containing the generated sulfate component is within a predetermined range (for example, pH 8.0 ± 1 0.0), it is preferable to have a pH adjusting step for controlling the addition amount of the cooling water, the addition amount of the neutralizing agent, and the temperature of the exhaust gas. Optimal recovery conditions can be created in the recovery process of sulfate components.

(3) Dust collection processing step of exhaust gas The neutralized exhaust gas is subjected to gas-solid separation processing by EP4. By the electric dust collection treatment under a relatively high temperature condition of about 240 ° C. or higher, a relatively large solid component having a particle size of about several tens of μm or more contained in the exhaust gas is efficiently separated as dust. Further, the exhaust gas derived from EP4 is fed to BF6, and further fine particles are subjected to gas-solid separation processing. It is efficiently separated as dust having a particle size of about 10 to several tens of μm whose main component is a sulfate component derived from raw materials. The dust separated in EP4 and BF6 is taken out as a solid component whose main component is a sulfate component derived from the raw material.

At this time, it is preferable to have the following processes.
(3a) Sulfur component recovery step for recovering the solid component containing the generated sulfate component (3b) Sulfur component measurement step for measuring the sulfate component in the recovered solid component (3c) The recovery amount of the sulfur component is predetermined Component adjustment process for controlling the amount of cooling water added, the amount of neutralizing agent containing an alkali metal compound or alkaline earth metal compound, and the temperature of the exhaust gas so as to be within the range of

(4) Selenium recovery step The exhaust gas from which the sulfate component is separated as a solid component is brought into contact with the selenium precipitation part 8 whose surface temperature is set to be equal to or lower than the melting point of selenium (for example, about 190 to 200 ° C.). Se is precipitated and the precipitated Se is taken out as a precipitate. In the neutralized exhaust gas, a sulfate component is present as a main component together with Se, and in the low temperature precipitation recovery of Se, it is preferable that the coexisting sulfate component is reduced. In the first configuration example, an example in which the exhaust gas derived from BF6, which is the condition with the least amount of coexisting components, is recovered by the selenium precipitation portion 8 provided in the chimney 7 is shown. However, as in other configuration examples to be described later, by providing a selenium precipitation portion 8 in the exhaust gas passage after the neutralization process or in each processing stage, Se is recovered separately from the sulfate component that can be recovered as a solid component. Is possible.

(5) Recovery step of sulfate component The solid component separated in step (3) contains a sulfate component as a main component and includes solid components having a wide range of particle sizes. In addition, since the dust is collected in a high temperature state, the sulfate component in such a solid component can be taken out as a high purity component with little moisture. In addition, in order to extract a higher-purity sulfate component from such a solid component (dust), a solution in which the sulfate component is dissolved by removing other components in a high-temperature reduced pressure state and immersing it again in clean water. A method such as removal of other components by crystallization treatment from the above can be used.

At this time, for the solid component containing the recovered sulfate component,
(5a) Sulfur component measurement step for measuring sulfate or sulfite component in the solid component (5b) Cooling water addition amount and neutralizing agent addition amount so that the recovery amount of the sulfur component is within a predetermined range And a sulfur component adjusting step for controlling the temperature of the exhaust gas. By measuring the recovery amount of the sulfate component (sulfur component) recovered after the neutralization treatment, and using this as an index for feedback control of the cooling treatment and neutralization treatment, it is more optimal in the recovery treatment of Se and sulfate components Can create the right conditions.

[Other configuration examples of this system]
This system is based on the above first configuration example, and several embodiments are possible. Specifically, the configuration illustrated in FIG. 2 can be given (second configuration example). In addition to the selenium precipitation part 8c provided in the chimney 7 of the first configuration example, the selenium precipitation part 8a provided in the EP4 and the selenium precipitation part 8b provided in the BF6 are exemplified as the site for depositing and collecting Se. In EP4, the sulfate component produced by the neutralization treatment is removed while adhering to dust having a large particle size, and the high temperature state is maintained, so the surface of the selenium precipitation portion 8a having a large temperature difference. Se is likely to precipitate on the surface, and Se can be recovered. In BF6, the sulfate component is removed together with dust having a fine particle size, and the decrease in the sulfate component combined with EP4 causes very few factors to inhibit the precipitation of Se. Se is precipitated, and Se can be collected. Se can be collected in any one or two or more selenium precipitation portions.

  At this time, when the content of the sulfur compound in the exhaust gas is small and the generation of solid components including a sulfate component is small, the exhaust gas is supplied from the neutralization processing unit 3 to the dust collection processing unit (EP4 or / and BF6). It can be set as the structure which the waste gas introduce | transduced can contact a selenium precipitation part. This is because a factor that inhibits the precipitation of Se due to the adhesion or mixing of Se to the solid component or the influence of the adhesion or mixing of the solid substance to the precipitated Se is small.

  In the second configuration example, cooling water and neutralizing agent supply flow rate adjustment valves V2 and V3 connected to the sprayers provided in the cooling unit 2 and the neutralization processing unit 3 are provided, and the bottom of the cooling unit 2 is provided. A pH measuring device S for measuring the pH of the liquid layer is provided. The amount of cooling water added can be adjusted by the supply flow rate adjusting valve V2 using the temperature in the cooling unit 2 as an index. The addition amount of the neutralizing agent can be adjusted by the supply flow rate adjusting valve portion V3 using the pH value as an index. As the pH measuring device S, for example, a glass electrode type pH meter can be used. Further, as illustrated in FIG. 2, a liquid layer 21 is formed below the cooling unit 2 or the neutralization processing unit 3, and the solution in the liquid layer 21 (mixed solution with cooling water or neutralized liquid) is used. It is preferable to form a circulation system that supplies cooling water (and a neutralizing agent) to the cooling unit 1. By supplying the solution in the liquid layer 21 to the injection unit 24 through the circulation channel 23 by the circulation pump 22, it can be used as cooling water having a neutralization function by the remaining neutralizing agent, A zero emission type exhaust gas treatment system can be formed without generating waste liquid. A circulation system can also be formed for the neutralizing agent supply flow path (not shown). In addition, it can be set as the structure which introduces the cooling water (and neutralizing agent) for replenishment into the liquid layer 21 instead of the circulation flow path 23. FIG.

  The following shows the results of qualitative and quantitative verification of the collected Se and mirabilite using this system in an alkali glass manufacturing process.

[Operating conditions of this system at the time of verification]
Using this system according to the first configuration example, exhaust gas containing soot and dust in the exhaust gas shown in Table 1 (a) below is introduced into the cooling unit 2, and the temperature of the exhaust gas or dust and the extracted dust in each processing unit are introduced. A composition containing Se was confirmed. The composition of precipitates and the like adhering to the probe was measured with a fluorescent X-ray measurement apparatus (Rigaku Corporation, model RIX3100), and the crystal structure was measured with an X-ray diffractometer (Rigaku Corporation, model RINT2500VL).

〔inspection result〕
As a verification result, the temperature and composition of each part in FIG.
(A) Solid component in exhaust gas introduced into this system (b) Solid component in water supplied from neutralization processing unit 3 (c) Dust extracted from EP4 (d) Dust extracted from BF6 (e) BF6 Deposit (f) deposited near the duct after filtration (f) Deposit deposited on the probe and deposited on the probe. FIG. 4 shows an example of a measurement pattern in the X-ray diffraction measurement of the deposit deposited inside the exhaust gas passage. To do. 4A shows (e) deposits in the vicinity of the duct after filtration of BF, and FIG. 4B shows (f) deposits on the outer surface of the probe inserted into the duct. In the measurement by the fluorescent X-ray measurement method, since the property cannot be distinguished from a metal and an oxide, in Table 1 below, Se is displayed as “SeO ₂ ”. It was found to be metal Se (zero valence).

  At this time, (f) Quantitative grasp of deposits mainly composed of Se having the composition shown in Table 1 above in the probe (selenium precipitation portion) inserted in the duct was performed. 0.15% of Se could be recovered on the surface of the precipitation portion of the probe having a contact surface area of about 4% with respect to the cross-sectional area of the duct. It was verified that the Se recovery rate can be improved in the Se dry recovery by increasing the effective contact surface area using a multi-probe probe or the like.

  As described above, according to the present invention, it was confirmed that Se and sulfate components (sulfur compounds) in exhaust gas can be effectively separated and each can be efficiently recovered.

1 Exhaust gas generation equipment (melting furnace)
2 Cooling unit 3 Neutralization processing unit 4 Dust collection processing unit, electrostatic precipitator (EP)
5 Ventilator 6 Dust collection section, filtration dust collector, bag filter (BF)
7 Discharge part (duct and chimney)
8 Selenium precipitation part

Claims (9)

At least for selenium or a flue gas from a glass melting furnace containing a selenium compound and a sodium compound and a sulfur compound,
Cooling water is added to the exhaust gas , and a neutralizing agent containing a sodium compound added in a neutralization treatment section located at a later stage of the cooling section and having an exhaust gas temperature equal to or higher than the melting point of selenium, and sodium compounds and sulfur compounds in the exhaust gas A cooling section that is cooled to a temperature that produces sodium sulfate or sodium sulfite ;
A neutralization treatment unit in which a neutralizing agent containing a sodium compound is added to the exhaust gas, and neutralization treatment of an acidic component in the exhaust gas containing sodium sulfate salt or sodium sulfite salt derived from the sulfur compound is performed,
A dust collection processing unit for collecting dust in the exhaust gas and solid components generated in either the cooling unit or the neutralization processing unit;
The exhaust gas treated in either the neutralization treatment part or the dust collection treatment part is introduced, and has a selenium precipitation part for precipitating selenium or a selenium compound on the surface set to be equal to or lower than the melting point of the selenium,
Selenium or a selenium compound deposited on the surface of the selenium precipitation part is taken out, and a sulfate component containing sodium sulfate or a sulfite containing sodium sulfite is taken out from the solid component collected in the dust collection treatment part. A selenium recovery system in exhaust gas.   As the selenium precipitation portion, a low temperature portion adjusted to be equal to or lower than the melting point of selenium is formed on the outer surface inserted into the exhaust gas flow path, and selenium or a selenium compound is precipitated in the low temperature portion, and the low temperature portion is The selenium recovery system in exhaust gas according to claim 1, wherein selenium or a selenium compound is recovered by having a configuration capable of being extracted from the exhaust gas flow path. As the dust collection processing unit, an electric dust collector is provided on the upstream side of the flow of exhaust gas, a filtration type dust collector is provided on the downstream side, and the selenium precipitation unit is disposed inside the electric dust collector, the filtration type Provided in the dust collector, in the exhaust gas passage on the downstream side of the electric dust collector, or in the exhaust gas treatment facility or chimney connected to the exhaust gas passage on the downstream side of the filtration dust collector The selenium recovery system in exhaust gas according to claim 1 or 2, wherein A pH measuring device for measuring the pH of a solution containing an alkali metal or alkaline earth metal sulfate or sulfite containing sodium sulfate or sodium sulfite generated in the cooling section and / or neutralization section; The addition amount of the cooling water, the addition amount of the neutralizing agent, and the temperature of the exhaust gas are controlled so that the pH value falls within a predetermined range. System for recovering selenium in exhaust gas.   A sulfate recovery unit is provided in the dust collection processing unit, and a solid component containing sulfate or sulfite of alkali metal or alkaline earth metal generated in the cooling unit and / or neutralization processing unit is recovered and recovered. Further, the sulfate or sulfite component in the solid component is measured, and the amount of the cooling water added, the amount of the neutralizing agent added, and the temperature of the exhaust gas so that the recovered amount of the sulfur component falls within a predetermined range. The selenium recovery system in exhaust gas according to any one of claims 1 to 4, wherein the selenium recovery system is controlled. A method for recovering selenium in exhaust gas, comprising at least the following steps for exhaust gas from a glass melting furnace containing at least selenium or a selenium compound and a sodium compound and a sulfur compound.
(1) Cooling water is added to the exhaust gas, the exhaust gas temperature is equal to or higher than the melting point of selenium, and a neutralizing agent containing a sodium compound added in a neutralization treatment step after the cooling step, and a sodium compound and a sulfur compound in the exhaust gas, There is added neutralizing agent comprising a sodium compound in the cooling step (2) the exhaust gas is cooled to a temperature to generate the sodium salt or sodium sulfite sulfate, the sodium sulfate salt or sulfite derived from sulfur compounds Neutralization treatment process in which neutralization treatment of acidic components in exhaust gas containing sodium salt is performed (3) Dust in the exhaust gas and solid components generated in any of the steps (1) and (2) are collected Dust collection treatment step (4) The exhaust gas treated by the steps (1) to (3) or some of them A selenium recovery step (5) in which the surface temperature is brought into contact with the selenium precipitation part set to be equal to or lower than the melting point of the selenium, selenium or a selenium compound is precipitated on the surface of the selenium precipitation part, and the precipitated selenium is recovered A sulfate component recovery step in which the sulfate or sulfite component is taken out from the solid component collected in (3) The step (3) is composed of the following two steps,
(3a) An electric dust collection step in which solid components in the exhaust gas are collected by electric dust collection while the exhaust gas temperature is maintained above the melting point of selenium (3b) In a state where the exhaust gas temperature is maintained above the melting point of selenium The filtration type dust collecting process in which the solid component in the exhaust gas is collected by the filter medium is applied to the exhaust gas treated in any one or some of the processes (2), (3a), (3b). The method for recovering selenium in exhaust gas according to claim 6, wherein the method is performed. After the step (2), the following step (2a) is a pH measurement step (2b) for measuring the pH of the solution containing the sulfate or sulfite of an alkali metal or alkaline earth metal containing sodium sulfate or sodium sulfite. 7) A pH adjusting step of controlling the added amount of the cooling water, the added amount of the neutralizing agent, and the temperature of the exhaust gas so that the pH value falls within a predetermined range. 8. A method for recovering selenium in exhaust gas according to item 7. For the solid component containing the alkali metal or alkaline earth metal sulfate or sulfite recovered in the step (5),
(5a) Sulfur component measurement step for measuring sulfate or sulfite component in the recovered solid component (5b) The amount of cooling water added so that the recovered amount of the sulfur component is within a predetermined range, The method for recovering selenium in exhaust gas according to any one of claims 6 to 8, further comprising a sulfur component adjusting step for controlling the amount of neutralizing agent added and the temperature of the exhaust gas.

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