JP5851440B2 - 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 Se, has a semiconducting property and a photoconductivity. Therefore, it is used for a photosensitive drum of a copier or has an optical characteristic. 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 a challenge. 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 so that the exhaust gas temperature is equal to or lower than the melting point of selenium. A cooling section to be cooled, a primary neutralizer added to the exhaust gas, neutralization treatment of acidic components in the exhaust gas, and a sulfate and a sulfite generated from the sulfur compound by the neutralization treatment 1 A primary neutralization treatment section in which the secondary drainage is neutralized, and an oxidant is added to the primary drainage derived from the primary neutralization treatment section, and the sulfite in the primary drainage A secondary neutralizing agent is added to the oxidation treatment unit in which the oxidation treatment including conversion to sulfate is performed, and the primary drainage in which the oxidation treatment is performed or the secondary drainage in which the oxidation treatment is performed. Neutralizing the treated secondary drainage A secondary neutralization treatment section and a filtration treatment section in which the secondary drainage liquid derived from the secondary neutralization treatment section is subjected to liquid-solid separation treatment with a silica-based filter medium, and the filtration treatment The solid component derived from the section is taken out as sludge containing selenium.

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) Cooling treatment step in which cooling water is added to the exhaust gas and cooled so that the exhaust gas temperature is equal to or lower than the melting point of selenium. (2) A primary neutralizing agent is added to the exhaust gas, and is generated from the sulfur compound. Primary neutralization treatment step in which primary drainage containing sulfate and sulfite is neutralized (3) An oxidizing agent is added to the primary drainage generated in step (2), Oxidation treatment step (4) in which oxidation treatment including conversion of sulfite to sulfate is performed. Simultaneously with the oxidation treatment in the step (3), or a secondary neutralizing agent is added to the effluent generated by the oxidation treatment. A secondary neutralization treatment step for adding and generating a neutralized secondary drainage (5) A filtration treatment step in which the secondary drainage generated in the step (4) is subjected to liquid-solid separation treatment by a filter medium. (6) The solid component separated in the step (5) is selenium. Sludge removal step to be taken out as a non-sludge

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. I found.
(A) Most of selenium compounds such as selenium oxide dissolved in the primary effluent are converted to insoluble Se containing metal selenium by oxidation treatment under the oxidizing atmosphere conditions of the primary effluent.
(B) Such insoluble Se can obtain higher separation efficiency by a silica-based filter medium (for example, diatomaceous earth).

In the selenium recovery system, the liquid component derived from the filtration unit is subjected to a heat treatment, and a crystallization component including a sulfate component dissolved in the liquid component is generated. It has a processing part, and the sulfur compound is taken out as a sulfate component mainly composed of a crystallization component in the crystallization processing part.
In addition to the knowledge regarding the efficient separation and continuous recovery of selenium from exhaust gas as described above in the verification process, by using the selenium recovery system with such a configuration, based on the following knowledge, sulfate It has been found that the components can be recovered with high purity.
(C) A higher recovery efficiency of the sulfur compound can be obtained by converting the sulfite produced from the sulfur compound contained in the primary drainage liquid into a sulfate by oxidation treatment and collecting it as a sulfate.
(D) The sulfate converted by the oxidation treatment is further subjected to a secondary neutralization treatment, thereby increasing the amount of high-purity crystalline sulfate obtained by the crystallization treatment.

The present invention has the above-described selenium recovery system, further comprising a concentration processing unit that concentrates a liquid component derived from the filtration processing unit or the crystallization processing unit, and the concentration processing unit is connected to a vacuum decompression unit. In addition, it is characterized by being concentrated and separated by vacuum evaporation under heating conditions, and subjected to a drying process, and the sulfur compound is taken out as a sulfate that has been subjected to a drying process.
With this configuration, the liquid component separated from sludge is concentrated and separated by vacuum evaporation under heating conditions, and dried to obtain a highly purified sulfate that has been dried. It can be recovered well. Further, after the concentrated liquid component is separated by a centrifugal separator or the like, the sulfate dissolved in the liquid component during filtration of the sulfate and the secondary drainage can be taken out as the remaining component. As a result, it is possible to efficiently recover selenium from exhaust gas and to efficiently recover the sulfate component. Also, such a recovery system or recovery method makes it possible to form a zero emission type exhaust gas treatment system that does not emit waste liquid outside the system.

Further, the present invention provides the selenium recovery method, wherein the liquid component separated in the step (5) is
(7) heat treated, generation processing of crystal析成component comprising sulfate dissolved in the liquid component is performed, the crystallization process of the sulfur compounds are removed as the sulphate component mainly containing crystal析成min Alternatively, the liquid component separated by the step (5) or the step (7) is
(8) is concentrated separated by vacuum evaporation treatment under the heating conditions, the drying process is performed, the sulfur compound, characterized by having a concentration separation step which is taken out as a dry treated sulfate.
By using such a recovery method, in addition to an efficient separation process and continuous recovery process of selenium from exhaust gas, a sulfate component is recovered with high purity based on the findings of (c) and (d) above. It became possible. In addition, it is possible to obtain a highly purified sulfate that has been dried, and to efficiently recover the sulfur compound in the exhaust gas.

In the selenium recovery system, the oxidation treatment unit and / or the secondary neutralization treatment unit supply air into the liquid layer using the air as the oxidizing agent, and measure the pH of the liquid layer. And an ORP measuring device for measuring the oxidation-reduction potential, and the addition amount of the oxidizing agent and the secondary neutralizing agent is controlled so that the pH or ORP falls within a predetermined range. To do.
Further, the present invention provides the method for recovering selenium as described above, wherein in the step (3) and / or step (4), air is used as the oxidant to supply the liquid layer, and the pH of the liquid layer or The addition amount of the oxidizing agent and the secondary neutralizing agent is controlled so that the ORP falls within a predetermined range.
As described above, it was found that in the treatment of the primary drainage, the oxidizing atmosphere conditions of the drainage in the oxidation treatment are effective for the generation of insoluble Se or the recovery by the silica-based filter medium. The present invention makes it possible to create a more optimal condition for Se recovery by measuring the ORP of secondary drainage and using this as a control index. It was also found that the conditions for the oxidation treatment and the secondary neutralization treatment are greatly affected in the recovery treatment of the sulfate component. The present invention makes it possible to create more optimal sulfate component recovery processing conditions by measuring the pH or ORP of the secondary effluent and using this as a control index. As the oxidizing agent used for the oxidation treatment, easily available air can be used.

In the above selenium recovery system, the primary neutralizing agent and / or the secondary neutralizing agent may include an alkali metal in the primary neutralizing agent and / or the secondary neutralizing agent. An agent containing a compound is used to produce an alkali metal sulfate or sulfite, and the alkali metal sulfate is taken out from the crystallization treatment section.
As described above, it was found that Se can be efficiently recovered by efficiently recovering the sulfate component in the process of recovering Se from the exhaust gas containing the sulfur compound. In particular, it was found that Se can be recovered more efficiently by preparing a high-purity sulfate that can be crystallized during the recovery process (preparation of secondary drainage). That is, it is preferable to produce an alkali metal sulfate that forms a liquid component as a secondary drainage liquid and can be crystallized by a subsequent heating and evaporation process, and is preferably a primary neutralizer and / or a secondary neutralizer. Such a condition was made possible by using a chemical containing an alkali metal compound in the part.

In the selenium recovery system, a part of the solution derived from the filtration processing unit or the crystallization processing unit is again introduced into the primary neutralization processing unit to form a circulation system. It is characterized by that.
In the secondary drainage, the main component is separated into Se and sulfate in the filtration treatment, and is separated into high-purity sulfate and residual components in the crystallization treatment. In any case, components contained in the exhaust gas before treatment are contained as untreated components. In the present invention, by introducing such untreated components into the primary neutralization treatment section and forming a circulation system, it is possible to efficiently recover selenium from the exhaust gas, and efficiently use the sulfate components. It became possible to collect. In addition, such a recovery system makes it possible to form a zero emission type exhaust gas treatment system that does not emit waste liquid outside the system.

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

  A selenium recovery system according to the present invention (hereinafter referred to as “the present system”) is directed to an exhaust gas containing at least selenium or a selenium compound (Se) and a sulfur compound (SOx), and includes at least a cooling unit in which the exhaust gas is cooled. A primary neutralization treatment section for performing neutralization treatment of the exhaust gas and neutralization treatment of the primary drainage produced by the neutralization treatment, an oxidation treatment section for carrying out oxidation treatment of the primary drainage, and an oxidation treatment A secondary neutralization treatment unit for performing neutralization treatment of the primary drainage liquid or the secondary drainage subjected to oxidation treatment, and a filtration processing unit for subjecting the secondary drainage to liquid-solid separation treatment. The solid component derived from the filtration processing unit is extracted as sludge containing selenium. Further, the liquid component derived from the filtration processing unit is subjected to heat treatment, and the crystallization processing unit is configured to perform generation processing of a crystallization component including a sulfate dissolved in the liquid component. In the part, the sulfur compound can be taken out as a sulfate component mainly composed of a crystallization component. Furthermore, it has a concentration processing unit for concentrating the liquid component derived from the crystallization processing unit, the concentration processing unit is connected to a vacuum decompression means, concentrated and separated by a vacuum evaporation process under heating conditions, and dried. The sulfur compound can be taken out as a sulfate that has been subjected to a treatment. Alternatively, instead of the crystallization processing unit, it has a concentration processing unit connected to a vacuum decompression means and subjected to vacuum evaporation under heating conditions, and the liquid component derived from the filtration processing unit is concentrated and separated in the concentration processing unit By being dried, the sulfur compound can be taken out as a dried sulfate. 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). The exhaust gas is introduced into the cooling unit 1, cleaned and discharged through the primary neutralization processing unit 2, and primary drainage is generated. The primary drainage liquid derived from the primary neutralization processing unit 2 is introduced into the secondary neutralization processing unit 4 through the oxidation processing unit 3 to generate secondary drainage. The secondary drainage liquid derived from the secondary neutralization processing unit 4 is introduced into the filtration processing unit 5 and subjected to liquid-solid separation processing. The solid component derived from the filtration processing unit 5 is taken out as sludge containing Se. Furthermore, by introducing the liquid component derived from the filtration processing unit 5 into the crystallization processing unit 6, the sulfate component can be taken out as a crystallization component.

  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.

  In the cooling unit 1, cooling water is added to the exhaust gas, and the exhaust gas temperature is cooled to be equal to or lower than the melting point of selenium. 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. Moreover, as shown by the broken line portion, a high cooling effect can be obtained by providing a cooling grid or net in the exhaust gas flow passage. The cooling temperature is preferably 218 ° C. or lower, preferably about 100 ° C. or lower, more preferably about 80 ° C. or lower, which is the melting point of selenium, so as to prevent Se from remaining in the exhaust gas. By setting the temperature to about 100 ° C. or lower, the subsequent processing can be performed without using special equipment or materials. The exhaust gas cooled by the cooling unit 1 is introduced into the primary neutralization processing unit 2 disposed in the upper part, and Se or SOx contained in the original exhaust gas or gaseous sulfate and sulfite. Etc. (for example, sodium sulfite or the like in the case where salt glass or the like is used as the glass raw material) is dissolved in the cooling water and stored in the primary drainage tank 11. In the illustrated configuration example, a configuration in which new cooling water is always supplied is illustrated. However, as in a second configuration example described later, the primary drainage stored in the primary drainage tank 11 is circulated and cooled. It can also be used as water.

  In the primary neutralization processing unit 2, a primary neutralizing agent is added to the exhaust gas cooled in the cooling unit 1, and neutralization treatment of acidic components in the exhaust gas and sulfuric acid generated from sulfur compounds by the neutralization treatment The primary drainage containing salt and sulfite is neutralized. The primary neutralizing agent will be described later together with the secondary neutralizing agent used in the secondary neutralization processing unit 4. As with the cooling unit 1, the exhaust gas can be efficiently neutralized by adding it to the exhaust gas in the form of a spray and providing a grid or net in the exhaust gas flow passage. The exhaust gas neutralized by the primary neutralization processing unit 2 is cleaned and discharged from the upper part of the primary neutralization processing unit 2, and is exhausted from the chimney through a dust collector and a wind exhauster (not shown). (Not shown). The primary neutralizing agent neutralizes Se, SOx or gaseous sulfates and sulfites contained in the original exhaust gas and stores them in the primary drainage tank 11 as primary drainage. . The state of the primary neutralization treatment can be detected by, for example, providing a pH measuring device (for example, a glass electrode type pH meter) that measures the hydrogen ion concentration (pH) of the liquid layer. The amount of primary neutralizing agent added can be adjusted using the pH value as an index. The stored primary drainage is fed to the oxidation processing unit 3 by the feed pump P1, and the feed flow rate is adjusted by the control valve V1. In the first configuration example, the primary neutralization processing unit 2 is illustrated as a separate body from the cooling unit 1. However, as in a second configuration example described later, these are configured as a primary processing unit that integrates them. You can also.

In the oxidation treatment unit 3, an oxidizing agent is added to the primary effluent derived from the primary neutralization treatment unit 2, and an oxidation treatment including conversion of sulfite in the primary effluent to sulfate is performed. . As the oxidizing agent, easily available air can be used. However, the agent is not limited to this as long as it has an oxidation function capable of an oxidation treatment including conversion of sulfite to sulfate, and oxygen gas, oxygen-enriched gas, gas containing ozone, or the like is used. be able to. A specific reaction in the oxidation treatment will be described later. By supplying the foam from the lower part of the oxidation treatment unit 3 and stirring the entire liquid layer inside the oxidation treatment unit 3 by the stirring means 31, uniform and efficient oxidation treatment can be performed. Oxidized effluent is fed to the secondary neutralization processing unit 4. The state of the oxidation treatment can be detected by, for example, providing an ORP measuring device that measures an oxidation-reduction potential (ORP) in the liquid layer. Moreover, the addition amount of an oxidizing agent can be adjusted using ORP as an index. With such a function, the following effects can be obtained.
(A) Most of selenium compounds such as selenium oxide dissolved in the primary effluent are converted to insoluble Se containing metal selenium by oxidation treatment under the oxidizing atmosphere conditions of the primary effluent.
(C) A higher recovery efficiency of the sulfur compound can be obtained by converting the sulfite produced from the sulfur compound contained in the primary drainage liquid into a sulfate by oxidation treatment and collecting it as a sulfate.

In the secondary neutralization processing unit 4, a secondary neutralizing agent is added to the effluent that has been subjected to the oxidation treatment, and a secondary neutralization treatment is performed. The secondary neutralizing agent will be described later together with the primary neutralizing agent. By stirring the entire liquid layer inside the secondary neutralization processing unit 4 with the stirring means 41, a uniform and efficient secondary neutralization process can be performed. The state of the secondary neutralization treatment can be detected by, for example, a pH measuring device as described above, and the amount of the secondary neutralizing agent added can be adjusted using the pH value as an index. With such a function, the following effects can be obtained.
(D) The sulfate converted by the oxidation treatment is further subjected to a secondary neutralization treatment, thereby increasing the amount of high-purity crystalline sulfate obtained by the crystallization treatment.
The secondary drainage subjected to the secondary neutralization process is fed to the filtration processing unit 5 by the feed pump P4, and the feed flow rate is adjusted by the control valve V4. In the first configuration example, the secondary neutralization processing unit 4 is illustrated as a separate body from the oxidation processing unit 3, but these are integrated to form a secondary processing unit as in the second configuration example described later. Secondary neutralization treatment can be performed simultaneously with the oxidation treatment on the primary drainage.

[About neutralizing agent]
In this system, it is preferable to use an agent containing an alkali metal compound as a part of the primary neutralizer and / or the secondary neutralizer. For example, hydroxides such as sodium hydroxide and potassium hydroxide, carbonates such as sodium carbonate and potassium carbonate, bicarbonates such as sodium bicarbonate and potassium bicarbonate or oxides such as sodium oxide and potassium oxide are the main components. Can be mentioned. In the neutralization treatment and oxidation treatment, an alkali metal sulfate is produced by reaction with sulfur oxides in the exhaust gas, and after separation as a liquid component in the filtration treatment, an alkali metal sulfate is produced in the crystallization treatment, By taking this out, it is possible to recover a highly pure alkali metal sulfate. Further, as described above, Se can be efficiently recovered by efficiently recovering the sulfate component in the process of recovering Se from the exhaust gas containing the sulfur compound. In particular, Se can be recovered more efficiently by preparing a high-purity sulfate that can be crystallized during the recovery process (preparation of secondary drainage). 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 primary neutralizing agent and / or a secondary neutralizing agent containing sodium hydroxide are used. By performing the secondary neutralization treatment and / or the secondary neutralization treatment, it is possible to collect high-purity mirabilite from the exhaust gas from the melting furnace, and it is possible to more efficiently collect Se.

  However, chemicals partially containing alkaline earth metal compounds, for example, hydroxides such as calcium hydroxide and magnesium hydroxide, carbonates such as calcium carbonate and magnesium carbonate, bicarbonates such as calcium bicarbonate and magnesium bicarbonate Or it is also possible to use the chemical | medical agent which has oxides, such as calcium oxide and magnesium oxide, as a main component as a neutralizing agent. When such chemicals are used, insoluble calcium sulfate and magnesium sulfate are produced during the neutralization treatment, but this may be affected by removing Se as a precipitate or a solid component of the filtration treatment. In addition, only the crystallization component derived from the exhaust gas (for example, sodium nitrate which is a raw material of glass) can be taken out with high purity.

In the filtration processing unit 5, the secondary drainage liquid derived from the secondary neutralization processing unit 4 is subjected to liquid-solid separation processing by the filter medium. The separated solid component is taken out as sludge containing selenium. At this time, since high-purity sulfate is present in the solution up to the final stage of separation and recovery of Se, high recovery efficiency of Se can be ensured. As the filter medium, it is preferable to use a filter cloth, a granular material, a powdery body, or the like mainly composed of silicon or silicon oxide, such as diatomaceous earth or a zeolite-based filter medium. The silica-based filter medium has an adsorption capacity for Se, and the following effects can be obtained by such a function.
(B) Insoluble Se can obtain higher separation efficiency from the secondary drainage by a silica-based filter medium (for example, diatomaceous earth).
In addition to Se, the sludge contains 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. The separated liquid component is fed to the crystallization processing unit 6 by the feed pump P5, and the feed flow rate is adjusted by the control valve V5. Further, as will be described later, by branching and feeding a part of the separated liquid component, mixing with the primary neutralizing agent and forming a circulation system to be introduced into the primary neutralization processing unit 2, The recovery rate of Se can be improved. Further, by configuring such a circulation system, it has become possible to form a zero emission type exhaust gas treatment system that does not emit waste liquid outside the system.

  In the crystallization processing unit 6, the liquid component derived from the filtration processing unit 5 is subjected to heat treatment, and a crystallization component including a sulfate dissolved in the liquid component is generated. A highly pure sulfate component is taken out by the crystallization treatment. Specifically, the crystallization treatment unit 6 is connected to a vacuum decompression means (not shown), and the sulfate component crystallized by the vacuum evaporation treatment under heating conditions is taken out. With such a configuration, high-purity crystallization sulfate can be efficiently recovered. Examples of the heat treatment include heating by a heater provided around the crystallization treatment unit 6, heating by steam introduced into the inside, and heating purge.

  Furthermore, it is preferable to provide a concentration processing unit (not shown) in which the liquid component separated in the crystallization processing unit 6 is concentrated. Specifically, a concentration processing unit having a heating unit (not shown) and connected to a vacuum decompression unit (not shown) is suitable. The liquid component derived from the crystallization treatment unit 6 is concentrated and separated by vacuum evaporation under heating conditions, and is subjected to a drying process, whereby sulfur compounds in the exhaust gas can be taken out as a sulfate that has been dried. it can. A high-purity sulfate component is taken out by the crystallization treatment, and a residual component containing Se dissolved in the liquid component after the filtration treatment is taken out by the concentration step. Further, after the liquid component separated in the crystallization treatment unit 6 is further concentrated and separated by a centrifugal separator (not shown), the residual component containing sulfate and Se is taken out by a drying process. . With such a configuration, sulfate and Se can be efficiently recovered from the remaining components in addition to highly purified crystallization sulfate. Further, it is possible to form a zero emission type exhaust gas treatment system that does not generate waste liquid outside the system. Examples of the heat treatment include heating by a heater provided around the concentration processing unit, heating by steam introduced into the inside, and heating purge.

  Alternatively, a configuration in which the concentration processing unit (not shown) is provided in place of the crystallization processing unit 6 is also possible. Rather than taking out the sulfur compound as a specific compound such as mirabilite, the sulfur compound in the exhaust gas can be taken out efficiently by taking out various sulfur compounds mainly composed of sulfate or the like in a concentrated form. Specifically, the liquid component derived from the filtration processing unit 5 is concentrated and separated in the concentration processing unit and dried, so that the sulfur compound can be taken out as a dried sulfate or the like. At the same time, it can be taken out as a residual component containing Se dissolved in the liquid component after the filtration treatment. In addition to high purity sulfur compounds such as sulfate, Se can be efficiently recovered. Further, it is possible to form a zero emission type exhaust gas treatment system that does not generate waste liquid outside the system.

[Selenium recovery method using this system]
The selenium recovery method using this system has at least the following processes.
(1) Cooling treatment step in which cooling water is added to the exhaust gas and cooled so that the exhaust gas temperature is equal to or lower than the melting point of selenium. (2) A primary neutralizing agent is added to the exhaust gas, and is generated from the sulfur compound. Primary neutralization treatment step in which primary drainage containing sulfate and sulfite is neutralized (3) An oxidizing agent is added to the primary drainage generated in step (2), Oxidation treatment step (4) in which oxidation treatment including conversion of sulfite to sulfate is performed. Simultaneously with the oxidation treatment in the step (3), or a secondary neutralizing agent is added to the effluent generated by the oxidation treatment. A secondary neutralization treatment step for adding and generating a neutralized secondary drainage (5) A filtration treatment step in which the secondary drainage generated in the step (4) is subjected to liquid-solid separation treatment by a filter medium. (6) The solid component separated in the step (5) is selenium. Sludge removal process is taken out as a no sludge Hereinafter, each step will be described in detail as an example of the exhaust gas from the melting furnace of a glass raw material containing sodium sulfate and Se.

(1) Cooling treatment process of exhaust gas Cooling water is added to the exhaust gas, and the exhaust gas is cooled so that the exhaust gas temperature is equal to or lower than the melting point of selenium. Specifically, with respect to the exhaust gas of about 250 to 300 ° C. introduced into the cooling unit 1, for example, city water or industrial water cooled to room temperature or about 0 to 20 ° C. is added in a spray state, The exhaust gas temperature is preferably cooled to about 100 ° C. or lower, more preferably about 80 ° C. or lower. The water in the cooled exhaust gas and the substance having a boiling point of about 100 ° C. or less are condensed and stored in the primary drainage tank 11 together with the cooling water and the condensed water. Further, Se and SOx contained in the exhaust gas or gaseous sulfate and sulfite are dissolved in the cooling water and stored in the primary drainage tank 11. The exhaust gas from which such components are separated is introduced into the primary neutralization processing unit 2. In the cooling unit 1, the following reaction occurs.
(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) Primary neutralization treatment step of exhaust gas If the primary exhaust agent containing an alkali metal compound such as sodium hydroxide is added to the cooled exhaust gas, for example, if it is exhaust gas discharged from a glass melting furnace, glass Primary neutralization treatment of exhaust gas is performed by reacting with an acidic component such as sulfur oxide (SOx), fluorine compound or nitrogen oxide (NOx) derived from raw materials. SOx, gaseous sulfates, sulfites, and the like contained in the exhaust gas are stored in the primary drainage tank 11 as water-soluble substances generated by the neutralization reaction in the presence of moisture. At the same time, the primary drainage stored in the primary drainage tank 11 is neutralized, and primary drainage containing the sulfate and sulfite is generated. Specifically, in the primary 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 primary neutralization treatment can be detected by measuring the pH of the primary drainage. The amount of primary neutralizing agent added can be adjusted using the pH value as an index. The primary waste liquid subjected to the primary neutralization treatment is fed to the oxidation treatment unit 3 by the feed pump P1, and the feed flow rate is adjusted by the control valve V1.

(3) Oxidation treatment step of primary drainage To the primary drainage generated in step (2), an oxidizing agent such as air is added, for example, to sulfite sulfate in the drainage under oxidizing atmosphere conditions. An oxidation treatment including conversion of is performed. At the same time as the oxidizing agent is supplied so as to form foam in the liquid layer, the stirring of the entire liquid layer by the stirring means 31 enables uniform and efficient oxidation treatment. At this time, the state of the oxidation treatment can be detected by measuring the ORP of the liquid layer in the oxidation treatment unit 3. Further, the addition amount of the oxidizing agent can be adjusted using the ORP value as an index. By such oxidation treatment, most of the selenium compound such as selenium oxide dissolved in the primary effluent is converted into insoluble Se containing metal selenium. In the oxidation treatment unit 3, for example, sodium sulfite or sodium hydrogen sulfite in the primary drainage is oxidized by air, and the following reaction occurs.
2Na ₂ SO ₃ + O ₂ → Na ₂ SO ₄ .. Formula 3
2NaHSO ₃ + O ₂ → Na ₂ SO ₄ + H ₂ SO ₄ .. Formula 5
Oxidized effluent is fed to the secondary neutralization processing unit 4.

(4) Secondary neutralization treatment step of primary drainage Secondary neutralizing agent containing an alkali metal compound such as sodium hydroxide in the drainage generated simultaneously with the oxidation treatment in step (3) or by the oxidation treatment To produce a neutralized secondary drainage. Specifically, by the change in pH value caused by the reaction shown in the above formula 3 (the pH of sodium sulfite is about 9, the pH of sodium sulfate is about 7) or the reaction shown in formula 5 In response to the change in pH value due to the generated sulfuric acid, a neutralized secondary drainage solution is generated using a secondary neutralizing agent such as sodium hydroxide. For the latter, the following reaction occurs.
H ₂ SO ₄ + 2NaOH → Na ₂ SO ₄ .. Formula 6
At this time, the state of the secondary neutralization treatment can be detected by measuring the pH of the secondary drainage. Moreover, the addition amount of a secondary neutralizing agent can be adjusted using this pH value as a parameter | index. The secondary drainage is fed to the filtration processing unit 5 by the feed pump P4, and the feed flow rate is adjusted by the control valve V4.

(5) Filtration treatment process of secondary drainage The secondary drainage generated in the step (4) is subjected to liquid-solid separation treatment by a filter medium. By using a silica-based filter medium such as diatomaceous earth, it is possible to obtain a higher separation efficiency from the secondary drainage for insoluble Se without being affected by other components in the separated solid component. Further, the separated liquid component contains high-purity sulfate as a main component, and contains partially soluble Se and the like. The liquid component is fed to the crystallization processing unit 5 by the feed pump P5, and the feed flow rate is adjusted by the control valve V5.

(6) Sludge removal step The solid component separated in step (5) is taken out as sludge containing Se. Specifically, a solid component having a composition as exemplified in the following Table 1 is separated and taken out as sludge. Examples of materials derived from raw materials such as exhaust gas generation equipment include sodium compounds, calcium compounds, silica components (silicon oxide), fluorine compounds, and the like.

Moreover, it is preferable that the selenium collection | recovery method using this system has the following processes.
(7) the above step (5) the liquid component separated by the, heat treated, generation processing of crystal析成component comprising sulfate dissolved in the liquid component is performed, the sulfur compounds, mainly crystallized析成min further crystallization process is taken out as the sulphate component to the liquid component separated by said step (7) preferably has the following process.
(8) is concentrated separated by vacuum evaporation treatment under the heating conditions, the drying process is performed, the sulfur compound, concentration and separation steps is taken out as a dry treated sulfate or instead of the above step (7), the following process It is preferable to have.
(8 ') is a liquid component separated by the above step (5), and concentrated separated by vacuum evaporation treatment under the heating conditions, the drying process is performed, the sulfur compound is taken out as a dry treated sulfate and concentrated Separation process

(7) Crystallization treatment step The liquid component separated in the step (5) is subjected to a heat treatment, and a generation treatment of a crystallization component containing a sulfate dissolved in the liquid component is performed. The sulfate component is removed. In the crystallization component generation process, the liquid component is introduced into the crystallization processing unit 6 and subjected to heat treatment, whereby the liquid component is separated into a solid crystallization portion and a liquid concentrated residual component. The The crystallized portion can be taken out as it is, and further, a high-purity sulfate can be obtained by continuing the heat treatment. At this time, a vacuum decompression means (not shown) is connected to the crystallization treatment unit 6 to form a decompression vessel, so that the crystallization treatment can be performed more quickly and effectively, and crystallization with higher purity can be performed. (Crystallized mirabilite) can be obtained.

(8) Concentration treatment step (secondary treatment)
The liquid concentrated residual component separated in the step (7) is preferably subjected to a concentration treatment as a secondary treatment after the crystallization treatment. Specifically, the remaining components are further concentrated and separated by a centrifuge (not shown), and then subjected to evaporation and drying treatment under heating conditions, for example, reduced pressure to 150 Pa or less, and sulfate and Se. The remaining components including are removed. It is possible to form a zero emission type exhaust gas treatment system that does not emit waste liquid outside the system.

(8 ') Concentration treatment step (primary treatment)
Alternatively, instead of the above step (7), as the primary process after the sludge removal step (6), the remaining component enriched in separated form the liquid by the step (5) is concentrated by vacuum evaporation treatment under the heating conditions separated, dried process is performed, the sulfur compounds are removed as a dry treated sulfate. At this time, after further concentrated and separated by a centrifuge (not shown), a residual component containing sulfate and Se can be further extracted by performing a drying treatment. It is possible to form a zero emission type exhaust gas treatment system that does not emit waste liquid outside the system.

[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). The primary processing unit 10 in which the cooling unit 1 and the primary neutralization processing unit 2 are integrated in the first configuration example, the secondary processing unit 30 in which the oxidation processing unit 3 and the secondary neutralization processing unit 4 are integrated, and the primary It has the neutralizing agent tank 20 which bears supply of the neutralizing agent common to the process part 10 and the secondary process part 30, It is characterized by the above-mentioned. The integrated configuration makes it possible to make maximum use of the gas-liquid contact space, reduce the volume of the space, and reduce the size of the apparatus.

  The primary processing unit 10 does not always supply new cooling water, but circulates the primary drainage stored in the primary drainage tank 11 and uses it as cooling water. The energy required to cool the exhaust gas with a small heat capacity corresponding to the amount of newly supplied exhaust gas can be handled by the minimum supply of new cooling water with a large heat capacity, and an energy efficient system must be constructed. Can do. In addition, the primary processing unit 10 supplies the primary effluent, to which the primary neutralizing agent has been added by one spraying means, in the form of spray as cooling water, thereby cooling including the primary neutralizing agent simultaneously with the cooling function. Contact between water and exhaust gas can be achieved and primary neutralization treatment can be performed. Specifically, the primary drainage liquid stored in the primary drainage tank 11 is partly fed to the secondary processing unit 30 by the feed pump P1, and the feed flow rate is controlled by the control valve V1. While being adjusted, a part thereof is used as cooling water via the circulation flow path 12. A part of the primary neutralizing agent is fed from the neutralizing agent tank 20 to the primary processing unit 10 by the feeding pump P2, and the feeding flow rate is adjusted by the control valve V2.

  In the secondary processing unit 30, the oxidizing process and the neutralizing process of the primary drainage are performed at the same time. It is possible to adjust the amount of supply of the summing agent. That is, the drainage liquid having a predetermined ORP value during the oxidation process may slightly vary from the predetermined value by the subsequent secondary neutralization process depending on the properties of the primary drainage liquid. Such a situation can be avoided. Here, a detector 32 including an ORP measuring device and / or a pH measuring device is provided in the secondary processing unit 30. Part of the secondary neutralizer is fed from the neutralizer tank 20 to the secondary processing unit 30 by the feed pump P2, and the feed flow rate is adjusted by the control valve V3. The state of the oxidation treatment is detected by an ORP measuring device, and the amount of oxidant added is adjusted using the ORP value as an index. The state of the secondary neutralization treatment is detected by a pH meter, and the amount of secondary neutralizer added is adjusted using the pH value as an index.

  The common use of the neutralizing agent in the neutralizing agent tank 20 prevents the diversification of products or coexisting components in each treatment, makes it possible to limit the treatment conditions, and to improve the recovery rate. For example, since Na derived from raw materials is contained in the exhaust gas from a glass melting furnace using mirabilite as a raw material, by using sodium hydroxide as a neutralizing agent, sufficient Na is ensured for the production of sodium sulfate. Can do. In addition, by managing the neutralization index (pH), it is possible to avoid supply of excess sodium hydroxide, that is, the Na component.

  Moreover, a configuration as illustrated in FIG. 3 can be given (third configuration example). In the system based on the first configuration example, a part of the solution derived from the filtration processing unit 5 or the crystallization processing unit 6 is again introduced into the primary neutralization processing unit 2 to form a circulation system. It is characterized by. By returning the liquid component containing Se partially dissolved in the filtration processing unit to the primary neutralization processing unit 2, it is possible to improve the selenium recovery rate. In addition, since the liquid component before the crystallization treatment contains a large amount of sulfate, a primary drainage and a secondary drainage containing a high concentration of sulfate can be obtained, and a highly efficient crystallization treatment is performed. In addition, the supply amount of the oxidizing agent and the neutralizing agent can be reduced.

  Furthermore, by returning the residual component containing Se separated in the crystallization treatment unit 6 to the primary neutralization treatment unit 2, it is possible to improve the Se recovery rate. In addition, the main component of the secondary effluent is separated into Se and sulfate in the filtration treatment, and is separated into high-purity sulfate and residual components in the crystallization treatment. In any case, components contained in the exhaust gas before treatment are contained as untreated components. By introducing such untreated components into the primary neutralization processing unit 2 and forming a circulation system, Se and sulfate components can be efficiently recovered. Further, by configuring such a circulation system, it is possible to form a zero emission type exhaust gas treatment system that does not generate waste liquid outside the system.

  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, the exhaust gas containing dust in the exhaust gas shown in Table 1 (a) below is introduced into the cooling unit 1 and the composition and crystal of the sludge containing Se taken out from the filtration unit 5 The composition of the precipitation and the composition of the remaining components generated in the crystallization treatment unit 6 were confirmed. Here, pH and ORP are measured using a glass electrode type pH / ORP measuring instrument (K-10 / D-54 manufactured by Horiba Seisakusho), and the reference value for neutralization treatment is set to pH 7.5 ± 0.5. The reference value for the oxidation treatment was adjusted to ORP 0 mV or less. The composition of sludge and the like was measured with a fluorescent X-ray measuring device (manufactured by Rigaku Corporation, model RIX3100), and the crystal structure was measured with an X-ray diffractometer (manufactured by Rigaku Corporation, model RINT 2500VL).

〔inspection result〕
As a verification result, the composition of (b) sludge, (c) crystallized mirabilite, and (d) residual component is shown in Table 1 below (each measured value is expressed in weight%). In FIG. 4, the X-ray-diffraction measurement result of sludge is illustrated. In the measurement by the fluorescent X-ray measurement method, since the property cannot distinguish between the metal and the oxide, in Table 1 below, Se is displayed as “SeO ₂ ”, but the actual product is obtained from the X-ray diffraction measurement. It was found to be metal Se (zero valence). In addition, the amount of Se contained in the crystallization mirabilite was greatly reduced as compared to the case where (x) the crystallization treatment was performed without performing the oxidation treatment and the secondary neutralization treatment as in the conventional system. . It was verified that Se can be efficiently taken out as a component of sludge. At the same time, a very high purity crystallized mirabilite was obtained.

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

DESCRIPTION OF SYMBOLS 1 Cooling part 11 Primary drainage tank 2 Primary neutralization process part 3 Oxidation process part 31,41 Stirring means 4 Secondary neutralization process part 5 Filtration process part 6 Crystallization process part P1, P4, P5 Feeding pump V1 , V4, V5 control valve

Claims (9)

For exhaust gas containing at least selenium or a selenium compound and a sulfur compound,
A cooling unit to which cooling water is added to the exhaust gas and cooled so that the exhaust gas temperature is equal to or lower than the melting point of selenium;
A primary neutralizing agent is added to the exhaust gas, neutralization treatment of acidic components in the exhaust gas, and neutralization treatment of a primary effluent containing sulfate and sulfite generated from the sulfur compound by the neutralization treatment A primary neutralization processing unit,
An oxidation treatment unit in which an oxidant is added to the primary effluent derived from the primary neutralization treatment unit, and an oxidation treatment including conversion of sulfite in the primary effluent to sulfate is performed;
A secondary neutralizer is added to the primary effluent subjected to the oxidation treatment or the secondary effluent subjected to the oxidation treatment, and the secondary effluent subjected to the oxidation treatment is neutralized. A sum processing unit;
A secondary drainage derived from the secondary neutralization treatment unit has a filtration treatment unit that is subjected to liquid-solid separation treatment with a silica-based filter medium;
A selenium recovery system in exhaust gas, wherein the solid component derived from the filtration unit is taken out as sludge containing selenium.   The liquid component derived from the filtration processing unit has a crystallization processing unit in which a heat treatment is performed to generate a crystallization component including a sulfate dissolved in the liquid component. In the crystallization processing unit, The selenium recovery system in exhaust gas according to claim 1, wherein the sulfur compound is taken out as a sulfate component mainly composed of a crystallization component.   A concentration processing unit for concentrating the liquid component derived from the filtration processing unit or the crystallization processing unit, the concentration processing unit being connected to a vacuum decompression unit, and concentrated and separated by vacuum evaporation under heating conditions; The system for recovering selenium in exhaust gas according to claim 1 or 2, wherein the sulfur compound is taken out as a sulfate that has been subjected to a drying treatment, and then subjected to a drying treatment.   In the oxidation treatment unit or / and the secondary neutralization treatment unit, air is supplied into the liquid layer using air as the oxidizing agent, and a pH measuring device for measuring the pH of the liquid layer, or a redox potential is measured. An ORP measuring device is provided, and the addition amount of the oxidizing agent and the secondary neutralizing agent is controlled so that the pH or ORP is within a predetermined range. Selenium recovery system in exhaust gas.   In the said primary neutralization process part and / or the said secondary neutralization process part, the chemical | medical agent containing an alkali metal compound is used for a part of primary neutralizer and / or secondary neutralizer, and an alkali metal sulfate Or while producing | generating a sulfite, the selenium collection | recovery system in the waste gas in any one of Claims 1-4 from which the sulfate of an alkali metal is taken out from the said crystallization process part.   A part of the solution derived from the filtration processing unit or the crystallization processing unit is again introduced into the primary neutralization processing unit to form a circulation system. A selenium recovery system in the exhaust gas described. A method for recovering selenium in exhaust gas, comprising at least the following steps for exhaust gas containing at least selenium or a selenium compound and a sulfur compound.
(1) Cooling treatment step in which cooling water is added to the exhaust gas and cooled so that the exhaust gas temperature is equal to or lower than the melting point of selenium. (2) A primary neutralizing agent is added to the exhaust gas, and is generated from the sulfur compound. Primary neutralization treatment step in which primary drainage containing sulfate and sulfite is neutralized (3) An oxidizing agent is added to the primary drainage generated in step (2), Oxidation treatment step (4) in which oxidation treatment including conversion of sulfite to sulfate is performed. Simultaneously with the oxidation treatment in the step (3), or a secondary neutralizing agent is added to the effluent generated by the oxidation treatment. A secondary neutralization treatment step for adding and generating a neutralized secondary drainage (5) A filtration treatment step in which the secondary drainage generated in the step (4) is subjected to liquid-solid separation treatment by a filter medium. (6) The solid component separated in the step (5) is selenium. Sludge removal step to be taken out as a non-sludge The liquid component separated in the step (5) is
(7) heat treated, generation processing of crystal析成component comprising sulfate dissolved in the liquid component is performed, the crystallization process of the sulfur compounds are removed as the sulphate component mainly containing crystal析成min Alternatively, the liquid component separated by the step (5) or the step (7) is
(8) is concentrated separated by vacuum evaporation treatment under the heating conditions, the drying process is performed, the sulfur compound, according to claim 7, characterized in that it has a concentration separation step which is taken out as a dry treated sulfate A method for recovering selenium in exhaust gas. In step (3) and / or step (4), air is used as the oxidant to be supplied into the liquid layer, and the oxidant and ORP are adjusted so that the pH or ORP of the liquid layer falls within a predetermined range. The method for recovering selenium in exhaust gas according to claim 7 or 8, wherein the amount of secondary neutralizer added is controlled.

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