JP7377639B2 - Mercury recovery equipment and mercury recovery method - Google Patents

Description

The present disclosure relates to a mercury recovery device and a mercury recovery method.

When thermally recycling waste plastic in the cement manufacturing process, chlorine contained in the waste plastic causes equipment trouble due to abnormal formation of coating. For this reason, attempts have been made to reformulate biomass ash and waste plastics into fuel with reduced chlorine content by carbonizing them in a desalination furnace. In this method, exhaust gas containing chlorine or hydrogen chloride is generated during reforming. Patent Document 1 proposes such equipment for cleaning exhaust gas.

On the other hand, organic waste may contain trace amounts of heavy metal components such as mercury derived from automobile HID lights in addition to organic components such as plastics. When such organic waste is heated, mercury vapor is generated, and there is concern that the exhaust gas may pollute the atmosphere. Therefore, as a method for cleaning exhaust gas containing mercury, a technique is known in which chlorine gas and vaporized mercury are reacted and recovered as water-soluble mercury chloride (for example, see Patent Document 2).

Japanese Patent Application Publication No. 2011-183269 Japanese Unexamined Patent Publication No. 61-222525

However, in the invention of Patent Document 2, the combustion of waste and the reaction of mercury are performed in the same furnace, so depending on the quality of the waste, combustion may become unstable and the reaction between gaseous mercury and chlorine may not proceed smoothly. This is a concern. There is also concern that the combustion temperature conditions will become lower and that organic chlorine compounds such as dioxins will be generated during combustion. Therefore, an object of the present disclosure is to provide a mercury recovery method and a mercury recovery device that can recover mercury contained in waste in a sufficiently stable manner.

As a result of studies by the present inventors, the chlorine component and mercury generated by heating organic waste containing chlorine and mercury in a desalination furnace were removed by burning the organic gas generated at the same time in the desalination furnace. It has been found that by heating, mercury can be converted to water-soluble mercury chloride, which can be absorbed into an absorption liquid and recovered without using a separate fuel source.

That is, the mercury recovery device according to one aspect of the present disclosure heats organic waste containing chlorine and mercury in a low-oxygen atmosphere in which the oxygen concentration is lower than that of air, and collects organic waste containing combustible organic components, mercury, and chlorine components. A desalination furnace that generates cracked gas, a combustion furnace that burns the cracked gas to obtain combustion gas containing mercury(II) chloride, and recovers solid content containing at least one of dust and metallic mercury contained in the combustion gas. It includes a recovery section and an absorption section that causes an absorption liquid to absorb mercury chloride (II) contained in the combustion gas.

The above-mentioned mercury recovery apparatus includes a desalination furnace that heats in a low-oxygen atmosphere and a combustion furnace that burns cracked gas generated in the desalination furnace. In this way, since the heat treatment is carried out in two stages: the desalination furnace and the combustion furnace, mercury chloride (II) can be stably produced from organic waste containing chlorine and mercury. Since the absorber has an absorbing portion that causes the absorbent to absorb mercury (II) chloride contained in the combustion gas, it is possible to stably recover mercury from organic waste. Furthermore, since the combustion gas includes a recovery section that recovers solid content including at least one of dust and metallic mercury contained in the combustion gas, it is possible to further reduce solid content such as fine dust released into the atmosphere. Since metallic mercury may adhere to such fine dust, it is possible to further reliably reduce the release of mercury. Moreover, blockage in each device, piping, etc. can be suppressed. Therefore, mercury contained in waste can be recovered in a sufficiently stable manner.

The organic waste contains plastic, and in the desalination furnace, it is preferable to obtain charred material containing carbon derived from the plastic. This makes it possible to obtain a fuel source with reduced chlorine components and mercury from organic waste. Therefore, the mercury recovery device of the present disclosure can also be called a fuel production device.

Preferably, the desalination furnace has a supply section for supplying pulverized coal. When pulverized coal is supplied from the supply section, the pulverized coal will adhere to the surface of the molten organic waste and the generated charcoal, and the organic waste and charcoal will be fused to the furnace wall of the desalination furnace. It can be suppressed.

The combustion temperature of the combustion furnace is preferably 850°C or higher. This makes it possible to suppress the production of organic chlorine compounds such as dioxins.

It is preferable to include a circulation channel for returning a part of the absorption liquid drawn out from the absorption part to the absorption part. As a result, mercury (II) chloride is sufficiently concentrated in the absorption liquid, and the amount of waste liquid finally discharged can be reduced.

The mercury recovery device may include a temperature reduction section that cools the combustion gas by bringing the combustion gas into contact with the absorption liquid. In this case, the combustion gas cooled in the temperature reduction section may be supplied to the recovery section or the absorption section. Thereby, the absorption efficiency of mercury chloride (II) by the absorption liquid can be improved.

The collection section may include a wet scrubber. Thereby, solid content such as dust and metallic mercury contained in the combustion gas can be efficiently captured. The wet scrubber may be a venturi scrubber. As a result, even if the concentration of dust and metal mercury contained in the combustion gas is high, the dust and metal mercury can be captured with a simple device configuration.

The mercury recovery device has a flow path for supplying a waste liquid containing hydrochloric acid discharged from at least one of the absorption section and the temperature reduction section that cools the combustion gas by bringing the combustion gas into contact with the absorption liquid to the recovery section. May have. By reusing the waste liquid in this manner, mercury(II) chloride can be further concentrated in the waste liquid. Therefore, operating costs can be reduced.

The mercury recovery device may include a solid-liquid separation section that separates at least a portion of the solid content contained in the waste liquid. This makes it possible to prevent each device from becoming clogged with solid matter. The flow path may supply a waste liquid obtained by separating at least a portion of the solid content in the solid-liquid separation section to the recovery section. Thereby, the stability of the recovery section can be improved.

The above-mentioned mercury recovery device preferably includes a precipitation section that obtains a mercury-containing precipitate from the waste liquid discharged from the absorption section. By recovering mercury as a precipitate through solid-liquid separation, the amount of industrial waste can be reduced.

Preferably, the precipitation section includes a precipitation tank that obtains a mercury-containing precipitate from the absorption liquid by co-precipitation of mercury(II) chloride and at least one of ferrous hydroxide and ferric hydroxide. This makes it possible to sufficiently recover mercury as a solid substance and sufficiently reduce the impact on the environment.

Preferably, the precipitation section includes a supply section that supplies an alkali containing at least one of sodium hydroxide, potassium hydroxide, and calcium hydroxide. Thereby, the pH of the absorption liquid can be adjusted to efficiently obtain a mercury-containing precipitate.

A mercury recovery method according to one aspect of the present disclosure includes heating organic waste containing chlorine and mercury in a low-oxygen atmosphere with an oxygen concentration lower than that of air to decompose the organic waste containing combustible organic components, mercury, and chlorine components. A desalination process to generate gas, a combustion process to obtain combustion gas containing mercury(II) chloride by burning the decomposed gas, a recovery process to recover dust and metallic mercury contained in the combustion gas, and a combustion process to collect the dust and metal mercury contained in the combustion gas. and an absorption step of absorbing the mercury(II) chloride contained in the absorption liquid.

The above-described mercury recovery method includes a heating step of heating in a low-oxygen atmosphere and a combustion step of burning decomposed gas generated in the heating step. In this way, since the heat treatment is performed in two stages, the heating step and the combustion step, mercury chloride (II) can be stably produced from organic waste containing chlorine and mercury. Since the method includes an absorption step in which mercury (II) chloride contained in the combustion gas is absorbed into the absorption liquid, mercury in organic waste can be stably recovered. Furthermore, since the present invention includes a recovery process for recovering dust and metallic mercury contained in the combustion gas, it is possible to further reduce solid content such as fine dust released into the atmosphere. Since metallic mercury may adhere to such fine dust, it is possible to further reliably reduce the release of mercury. Moreover, blockage in each device, piping, etc. can be suppressed. Therefore, mercury contained in waste can be recovered in a sufficiently stable manner.

The above-mentioned mercury recovery method involves co-precipitation of mercury (II) chloride absorbed in the absorption liquid in the absorption step with at least one of ferrous hydroxide and ferric hydroxide to precipitate mercury-containing from the absorption liquid. It is preferable to further include a precipitation step for obtaining a product. This makes it possible to sufficiently recover mercury and sufficiently reduce the impact on the environment.

According to the mercury recovery device and mercury recovery method of the present disclosure, mercury contained in waste can be recovered in a sufficiently stable manner.

FIG. 1 is a diagram schematically showing a mercury recovery device. 1 is a diagram schematically showing an example of the structure of a firing furnace. It is a figure which shows typically an example of the structure of a temperature reduction part. It is a figure showing arrangement of each nozzle when a temperature reduction tower is seen from above. It is a figure which shows typically an example of a collection|recovery part. It is a figure which shows typically an example of the structure of an absorption part.

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings, as the case may be. However, the following embodiments are examples for explaining the present disclosure, and are not intended to limit the present disclosure to the following contents. In the description, the same reference numerals will be used for the same elements or elements having the same function, and redundant description will be omitted in some cases. In addition, the positional relationships such as top, bottom, left, and right are based on the positional relationships shown in the drawings unless otherwise specified. Furthermore, the dimensional ratio of each element is not limited to the ratio shown in the drawings.

FIG. 1 is a diagram schematically showing a mercury recovery device according to an embodiment. The mercury recovery equipment shown in Figure 1 heats organic waste containing chlorine and mercury in a low-oxygen atmosphere with an oxygen concentration lower than that of air, producing decomposition gas containing combustible organic components, mercury, and chlorine components. A salt furnace 10, a combustion furnace 20 that burns cracked gas to obtain a combustion gas containing soluble mercury(II) chloride, a temperature reduction section 30 that cools the combustion gas with an absorption liquid, and a combustion gas that is cooled in the temperature reduction section 30. a recovery unit 50 that recovers dust and metallic mercury from the combustion gas; an absorption unit 60 that causes an absorption liquid to absorb mercury chloride (II) contained in the combustion gas; and a precipitation tank 40 that obtains a mercury-containing precipitate from the absorption liquid. and.

A first supply section 12 that supplies organic waste containing chlorine and mercury, and a second supply section 14 that supplies pulverized coal are connected to the desalination furnace 10. Organic waste includes waste containing plastic. The organic waste may be a mixture of waste plastic containing chlorine and waste containing mercury. Examples of waste containing mercury include automobile shredder dust. In particular, parts such as automobile HID lights contain high concentrations of mercury.

The pulverized coal supplied from the second supply section 14 adheres to the surface of the organic waste or fuel in a molten state. Thereby, it is possible to suppress the organic waste and fuel from being fused to the furnace wall of the desalination furnace 10. The heating temperature in the desalination furnace 10 is, for example, 200°C or higher, preferably 250 to 500°C, more preferably 250 to 400°C. As the heat source, for example, exhaust gas from a cement kiln can be used. By supplying such exhaust gas, organic waste, and pulverized coal as necessary to the desalination furnace 10, decomposed gas containing a chlorine component (chlorine or hydrogen chloride) and mercury, and a chlorine component and mercury are removed. carbide with reduced content is obtained. Carbide contains carbon derived from waste plastics.

The carbide discharged from the lower discharge part 16 of the desalination furnace 10 may be supplied as solid fuel to, for example, a cement kiln. On the other hand, cracked gas discharged from the upper discharge section 18 of the desalination furnace 10 is supplied to the combustion furnace 20. The cracked gas contains chlorine components (chlorine and hydrogen chloride), gaseous mercury, and combustible organic components. Since the desalination furnace 10 has a low oxygen atmosphere, oxidation of mercury can be suppressed and gaseous mercury can be efficiently produced. From the viewpoint of sufficiently suppressing mercury oxidation, the oxygen concentration in the desalination furnace 10 is preferably 12% by volume or less. The oxygen concentration in the desalination furnace 10 can be measured using a commercially available oxygen sensor. The combustion furnace 20 includes a burner for burning the cracked gas using air.

FIG. 2 is a diagram schematically showing an example of the structure of the combustion furnace 20. The combustion furnace 20 includes a burner 22 that burns cracked gas in the presence of primary air, a secondary air supply section 24 that supplies secondary air into the combustion furnace 20, and an exhaust section 26 that discharges combustion gas. . By combustion of the cracked gas in the combustion furnace 20, gaseous mercury is oxidized and reacts with chlorine gas or hydrogen chloride gas to produce water-soluble mercury(II) chloride. The combustion gas discharged from the discharge section 26 contains mercury(II) chloride.

The burner 22 discharges cracked gas downward. As a result, the flame from the burner 22 is directed downward. Combustion gas generated by combustion of the cracked gas is discharged from a discharge section 26 provided below the combustion furnace 20. The combustion temperature in the combustion furnace 20 is, for example, 850° C. or higher, preferably 900° C. or higher, and more preferably 1,000° C. or higher, from the viewpoint of suppressing the generation of organic chlorine compounds such as dioxins.

In the combustion furnace 20, combustible organic components generated in the desalination furnace 10 are burned. In this way, combustible organic components are decomposed and effectively used as a thermal energy source. Furthermore, since gas is used as a thermal energy source, mercury (II) chloride can be generated with almost no incineration ash.

Returning to FIG. 1, the combustion gas containing mercury chloride (II) obtained in the combustion furnace 20 is introduced into the temperature reduction section 30. In the temperature reduction section 30, the combustion gas comes into contact with water and is cooled to, for example, 80°C or lower, preferably 70 to 75°C.

FIG. 3 is a diagram schematically showing a temperature reduction tower that is an example of the temperature reduction section 30. FIG. 3 is a side view of the cooling tower. The cooling tower includes a main body 30A, a nozzle 28 that supplies combustion gas to the lower part of the main body 30A, and nozzles 31 (nozzles 31A, 31B, 31C) that supply an absorption liquid that cools the combustion gas supplied from the nozzle 28. , 31D, 31E, 31F) and a nozzle 33 for supplying an oxidizing agent or an absorption aid. As the absorption liquid, water or a fluid containing water and an oxidizing agent can be used. Hereinafter, the case where water is used as the absorption liquid will be explained as an example.

The oxidizing agent contains at least one selected from the group consisting of hypochlorous acid, chlorine, hydrogen peroxide, potassium permanganate, nitric acid, and sulfuric acid. As an absorption aid, hydrochloric acid or the like can be used. By supplying such an oxidizing agent or absorption aid, the recovery rate of mercury can be improved. The oxidizing agent may be dissolved in water and supplied from the nozzles 31A, 31B, 31C, 31D, 31E, and 31F. The nozzles 31A, 31B, 31C, 31D, 31E, 31F, and the nozzle 33 may each have a plurality of discharge ports at their tips, thereby dispersing water and the oxidizing agent in the form of a spray or mist. This makes it possible to improve the efficiency of contact with combustion gas.

Four nozzles 31A, 31B, 31C, 31D, and 31F are installed radially such that their tips point toward the center of the main body 30A. FIG. 4A is a diagram showing the positional relationship between the nozzle 31A (31B) and the nozzle 28 that supplies combustion gas when the temperature reduction tower is viewed from above. As shown in FIG. 4(A), the nozzle 31A (31B) is installed so that the direction from its base end to its tip forms an angle of 45° or 135° with respect to the direction in which combustion gas is introduced into the nozzle 28. be done.

FIG. 4(B) is a diagram showing the positional relationship between the nozzle 31D (31F) and the nozzle 28 when the temperature reduction tower is viewed from above. The nozzle 31D (31F) is installed so that the direction from its base end to its tip forms an angle of 0°, 90°, or 180° with respect to the direction in which combustion gas is introduced into the nozzle 28. In this way, in addition to providing a plurality of nozzles radially at the same height, by arranging the nozzles provided at different heights so as to be offset along the circumferential direction of the main body 30A, the cooling of the combustion gas is improved. Variations can be reduced and the contact efficiency between combustion gas and water can be improved.

The discharge ports provided at the tips of the nozzles 31A, 31B, 31C, 31D, and 31F may discharge water so that the discharged water and the combustion gas come into countercurrent contact. Thereby, variations in cooling of the combustion gas can be further reduced, and the efficiency of contact between the combustion gas and water can be further improved. Further, by discharging water so that the nozzles installed above are in countercurrent contact with each other, water can easily flow down the inner wall of the main body portion 30A. This allows the water to function as a lining, reducing corrosion of the inner walls. Note that the number and orientation of each nozzle are not limited to those shown in the drawings.

The combustion gas introduced into the cooling tower rises within the main body 30A while coming into contact with water supplied from nozzles 31A, 31B, 31C, 31D, 31E, and 31F. At this time, a part of mercury(II) chloride contained in the combustion gas may be absorbed by water. The absorption liquid obtained by absorbing mercury(II) chloride flows downward and is stored at the bottom of the main body 30A. The absorption liquid may absorb hydrochloric acid in addition to mercury(II) chloride. The cooled combustion gas is discharged from the flow path 32 connected to the upper part of the main body 30A. On the other hand, the absorption liquid stored at the bottom of the main body 30A is led out as a waste liquid from a flow path 34 connected to the bottom of the main body 30A.

Returning to FIG. 1, the combustion gas discharged from the flow path 32 is introduced into the recovery section 50. The recovery unit 50 recovers solid content including dust and metallic mercury contained in the combustion gas. By providing the recovery unit 50, it is possible to reduce the solid content contained in the clean gas that is finally released into the atmosphere.

The collection unit 50 may be a wet scrubber, a dust collector, or a filter. Among these, wet scrubbers are preferred from the viewpoint of ease of maintenance work and safety. The wet scrubber may be a venturi scrubber or a tornado scrubber. In the case of a wet scrubber, solids contained in the combustion gas collide with, for example, mist and are captured by the mist. This mist may be collected as an agglomerated liquid obtained by agglomerating the mist, or may be introduced into the absorption section 60 on the downstream side in the form of a mist to which solid content has adhered. When collecting the coagulated liquid, it may be collected using a pipe (not shown) provided in the collecting section 50.

When the recovery unit 50 is a wet scrubber, the liquid (scrubbing liquid) supplied to the wet scrubber may be industrial water or an acidic liquid containing an acid such as hydrochloric acid. The acidic liquid may be a waste liquid discharged from the temperature reduction section 30 or the absorption section 60. By using such waste liquid, industrial waste can be reduced. Furthermore, by using an acidic liquid, metallic mercury can be oxidized and absorbed into the waste liquid.

FIG. 5 is a diagram schematically showing a venturi scrubber that is an example of the collection section 50. In this example, the venturi scrubber is arranged so that the fluid flows vertically downward, but the direction in which the venturi scrubber is installed is not particularly limited. A flow path 32 that supplies combustion gas from the temperature reduction section 30 is connected to the upstream side of the venturi scrubber. A flow path 56 is connected to the throat portion 51 of the venturi scrubber. Pressurized waste liquid is supplied from the flow path 56 as a scrubbing liquid. The scrubbing liquid turns into mist in the throat portion 51 and collides with solid content including dust and metallic mercury contained in the combustion gas. The solid content collided with the mist-like scrubbing liquid is absorbed by the scrubbing liquid and flows out together with the combustion gas from a flow path 58 connected to the downstream side of the Venturi scrubber.

The recovery unit 50 can absorb and recover solid content remaining in the combustion gas without being absorbed by the absorption liquid in the temperature reduction unit 30 into the scrubbing liquid. The scrubbing liquid that has absorbed the solid content is introduced into the absorption section 60 together with the combustion gas in a mist form. In the absorption section 60, the absorption liquid and the scrubbing liquid that has absorbed combustion gas and solids come into countercurrent contact. Mercury (II) chloride and solid content contained in the combustion gas are absorbed into the absorption liquid.

FIG. 6 is a diagram schematically showing the structure of an absorption tower, which is an example of an absorption section. The absorption tower includes a main body 60A. A channel 58 for supplying combustion gas containing mercury chloride (II) chloride and a scrubbing liquid in the form of a mist is connected to the lower part of the main body 60A, and a channel 58 for supplying combustion gas containing mercury chloride (II) chloride and a scrubbing liquid in the form of a mist is connected to the top part of the main body 60A. A flow path 64 for discharging cleaning gas is connected thereto. Moreover, a nozzle for introducing water as an absorption liquid and a nozzle for introducing waste liquid are provided at the upper part of the main body 60A. The water introduced from the nozzle comes into contact with the combustion gas and mist scrubbing liquid supplied from the flow path 58 within the main body 60A.

Although the cleaning gas led out from the flow path 64 has sufficiently reduced harmful components, it may be discharged into the atmosphere after passing through an auxiliary mercury adsorption device such as activated carbon. Since the cleaning gas has sufficiently reduced solid content such as dust and metallic mercury, clogging of the mercury adsorption device can be sufficiently suppressed.

The main body portion 60A includes a filling layer 62 filled with a filler in the center portion. Examples of the filling include pole rings. By providing the packed bed 62, the efficiency of contact between water and combustion gas can be increased. Water (absorbing liquid) that has absorbed the mist containing mercury chloride (II) and solids in the combustion gas is stored at the bottom and is led out from the flow path 66 as a waste liquid. The effluent may contain hydrochloric acid and solids in addition to mercury(II) chloride.

As shown in FIGS. 1 and 6, a part of the waste liquid discharged from the flow path 66 is circulated through the flow path 68 (circulation flow path) to the absorption section 60. By circulating a portion of the wastewater in this way, mercury chloride (II) chloride and solid content can be sufficiently concentrated in the wastewater, reducing the amount of wastewater that is ultimately released. can. Note that the connection position of the flow path 68 in the absorption tower is not limited to the position shown in FIG. 6, and may be at another position, or the waste liquid may be supplied from at least one of the nozzles to which water is supplied. .

As shown in FIG. 1, a part of the waste liquid containing mercury(II) chloride and solids derived from the temperature reduction section 30 and the absorption section 60 passes through the flow path 36 and the flow path 65, respectively. The liquid is introduced into the liquid separation section 70. In the solid-liquid separation section 70, at least a portion of the solid content contained in the waste liquid is removed. The solid-liquid separation section 70 may be, for example, a filter equipped with a filter. By providing the solid-liquid separation section 70, the solid content in the waste liquid is reduced. A portion of the waste liquid with reduced solid content flows through the flow path 56 and is introduced into the recovery section 50. Since this waste liquid has a reduced solid content, clogging of the flow path 56 can be suppressed. Therefore, even if a Venturi scrubber is used as the recovery section 50, blockage in the nozzle and throat section 51 that supplies the waste liquid is suppressed, and mercury recovery can be continued more stably.

Another part of the waste liquid with reduced solid content, which is led out from the solid-liquid separation section 70, is supplied to the temperature reduction section 30 via the flow path 54. The effluent contains acids such as hydrochloric acid. Therefore, mercury (II) chloride can be concentrated in the waste liquid discharged from the temperature reduction section 30, and the load on the absorption section 60 can be reduced. Note that the connection position of the flow path 54 in the temperature reduction tower is not limited to the position shown in FIG. A liquid may also be supplied.

A part of the waste liquid containing mercury(II) chloride and solid content (mercury and dust), which is led out from the temperature reduction section 30 and the absorption section 60 through the flow path 34 and the flow path 66, is transferred to the precipitation tank 40 (sedimentation section). 40). A waste liquid, a ferrous salt compound or a ferric salt compound, an alkali, and a polymer flocculant are introduced into the settling tank 40 . Here, the "ferrous salt compound or ferric salt compound" may be either one or both. In the precipitation tank 40, the pH is adjusted to, for example, 8 to 12, preferably 9 to 11, by introducing an alkali. Further, as a polymer flocculant, for example, a high anionic polymer flocculant is introduced. As a result, mercury is co-precipitated with at least one of ferrous hydroxide and ferric hydroxide, and a precipitate containing mercury is obtained.

Alkali include potassium hydroxide, sodium hydroxide and calcium hydroxide. A basic waste liquid containing at least one of sodium hydroxide, potassium hydroxide, and calcium hydroxide may be used as the alkali. Ferrous salt compounds include ferrous chloride, ferrous chloride dihydrate, ferrous sulfate, ferrous sulfate tetrahydrate, ferrous sulfate pentahydrate, and ferrous sulfate heptahydrate. and polyferrous sulfate. Examples of ferric salt compounds include ferric chloride, ferric chloride hexahydrate, ferric sulfate, ferric sulfate trihydrate, ferric sulfate hexahydrate, and ferric sulfate. Examples include heptahydrate, polyferric sulfate, and the like.

In the precipitation tank 40, solid-liquid separation is performed to separate the precipitate and the residual liquid. The precipitate is recovered as sludge. On the other hand, the aqueous solution (waste liquid) obtained by solid-liquid separation in the settling tank 40 can be discharged to the outside because mercury is sufficiently reduced. Note that a plurality of settling tanks may be installed.

The mercury recovery device of this embodiment performs heat treatment in two stages: the desalination furnace 10 and the combustion furnace 20, so mercury chloride (II) is stably generated from organic waste containing chlorine and mercury. can be done. Then, mercury chloride (II) contained in the combustion gas is absorbed by an absorption liquid in the absorption section 60 and made into a waste liquid, and the mercury is recovered as a precipitate from the waste liquid in the precipitation tank 40. Further, solid contents such as metallic mercury and dust contained in the combustion gas are recovered by a recovery section 50, and the solid contents are separated by a solid-liquid separation section 70. In this way, mercury in organic waste can be recovered in a sufficiently stable manner.

Next, one embodiment of a method for recovering mercury from organic waste will be described. The mercury recovery method of this embodiment can be performed using the above-mentioned mercury recovery apparatus. Therefore, the description of the mercury recovery device also applies to the mercury recovery method. Further, the description of the mercury recovery method described below is also applied to the above-mentioned mercury recovery apparatus.

The mercury recovery method of this embodiment heats organic waste containing chlorine and mercury in a low-oxygen atmosphere with an oxygen concentration lower than that of air to produce decomposed gas containing combustible organic components, mercury, and chlorine components. a desalination process for producing carbide; a combustion process for burning the decomposed gas to obtain a combustion gas containing mercury(II) chloride; and recovering solid content containing at least one of dust and metallic mercury contained in the combustion gas. and an absorption step in which mercury (II) chloride contained in the combustion gas is absorbed into an absorption liquid. Further, incidental to these steps, a temperature reduction step of cooling the combustion gas by bringing the combustion gas into contact with an absorption liquid, and a solid-liquid separation step of separating at least a portion of the solid content contained in the waste liquid, The method may also include a precipitation step of insolubilizing water-soluble mercury in the absorption liquid and recovering it as a precipitate.

In the desalination process, organic waste containing waste plastic containing chlorine and waste containing mercury is heated in a low oxygen atmosphere in the desalination furnace 10 . This separates the cracked gas containing chlorine components such as chlorine and hydrogen chloride, mercury, and combustible organic components from the organic waste. Since the desalination process heats organic waste in a low-oxygen atmosphere, oxidation of mercury can be suppressed and gaseous mercury can be efficiently produced. In the desalination step, pulverized coal may be heated together with the organic waste. The solid carbide obtained in the desalination process may be used as fuel for cement manufacturing equipment. The heating temperature in the desalting step is, for example, 200°C or higher, preferably 250 to 500°C, more preferably 300 to 350°C.

In the combustion process, the cracked gas obtained in the heating process is burned in the combustion furnace 20. In the combustion process, gaseous mercury is oxidized and reacts with chlorine or hydrogen chloride gas to produce water-soluble mercury(II) chloride. The cracked gas obtained in the desalination furnace 10 is mixed in a distribution stage until it is supplied to the combustion furnace 20 so that the composition is sufficiently uniform. By burning the cracked gas in which the compositional variations have been sufficiently reduced in this way in the combustion furnace 20, the mercury contained in the cracked gas can be caused to react sufficiently evenly. Therefore, unreacted mercury can be sufficiently reduced.

The combustion temperature in the combustion step is, for example, 850°C or higher, preferably 900°C or higher, and more preferably 1,000°C or higher. By setting the temperature within such a range, generation of organic chlorine compounds such as dioxins can be sufficiently suppressed. In the combustion process, combustible organic components contained in the cracked gas generated in the heating process are burned. In this way, combustible organic components are treated while being used effectively as a thermal energy source. Furthermore, since gas is used as a thermal energy source, the reaction can proceed without substantially generating incineration ash.

In the temperature reduction step, the combustion gas is brought into contact with the absorption liquid and cooled, for example, in the temperature reduction section 30. The absorption liquid may be water or water containing an oxidizing agent. By containing an oxidizing agent, unreacted metallic mercury is oxidized, unreacted hydrogen chloride and mercury react and are converted to mercury chloride, and mercury chloride can be absorbed by the absorption liquid. This makes it possible to further reduce the mercury concentration in the combustion gas. In the temperature reduction process, not only the absorption liquid but also the waste liquid generated in the temperature reduction process and the absorption process described later may be circulated and brought into contact with the combustion gas. This allows mercury(II) chloride to be further concentrated in the waste liquid.

In the recovery step, the solid content contained in the combustion gas is recovered in the recovery section 50. The solid content includes at least one of metallic mercury and dust. When the recovery process is performed using a wet scrubber, the waste liquid generated in the temperature reduction process and/or the absorption process described below may be used as the scrubbing liquid. By recovering at least a portion of the solid content into mist or the like in the recovery process, the solid content released into the atmosphere can be sufficiently reduced.

In the solid-liquid separation step, the solid content contained in the waste liquid is separated from the waste liquid in the solid-liquid separation section 70 . Thereby, the solid content contained in the waste liquid can be reduced. Such waste liquid can be suitably reused in the recovery process and the temperature reduction process. The recycled wastewater may contain acids such as hydrochloric acid.

In the absorption process, combustion gas containing mercury chloride is absorbed into an absorption liquid in the absorption section 60. Water such as industrial water can be used as the stock solution of the absorption liquid. In addition to water, an oxidizing agent may be added. Examples of the oxidizing agent include hypochlorous acid, hydrochloric acid, hydrogen peroxide, potassium permanganate, nitric acid, and sulfuric acid.

The absorption section 60 may have a plurality of absorption towers in parallel or in series. In order to increase the contact area between the combustion gas flowing in the absorption tower and the absorption liquid, a packing may be installed in the tower, or a spray device that supplies the absorption liquid in the form of a mist may be used. By circulating at least a portion of the absorption liquid within the absorption tower, it becomes possible to increase the concentration of mercury chloride in the absorption liquid and to improve the efficiency of mercury recovery from the absorption liquid.

It is also possible to convert metallic mercury into soluble mercury chloride in the absorption section 60. For this purpose, for example, an oxidizing agent may be dispersed within the absorption tower. By oxidizing unreacted metallic mercury in the absorption tower, unreacted hydrogen chloride and mercury react and are converted to mercury chloride, which can be absorbed into the absorption liquid. This makes it possible to further reduce the mercury concentration in the gas.

There are no particular restrictions on the contact conditions between the combustion gas and the absorption liquid in the absorption section 60, and they may be appropriately selected depending on the composition of the combustion gas and the amount of the combustion gas. The cleaning gas obtained from the absorption section 60 may be introduced into an auxiliary mercury adsorption device installed downstream of the absorption section. Specific examples of mercury adsorption devices include adsorption devices using activated carbon.

The waste liquid that has absorbed water-soluble mercury in the temperature reducing section 30 and the absorption section 60 is transported to the settling tank 40. In the precipitation tank 40, mercury is recovered through a precipitation process. In the precipitation step, a ferrous salt compound or a ferric salt compound is added to the absorption liquid in the precipitation tank 40. In the precipitation step, if necessary, alkali is added to adjust the pH to 8 to 12, preferably 9 to 11, and then a polymer flocculant is added. In this insolubilization step, the ferrous salt compound or ferric salt compound incorporates a mercury component such as mercury(II) chloride and co-precipitates. Thereby, mercury dissolved in the absorption liquid can be recovered as a precipitate.

Examples of ferrous salt compounds include ferrous chloride, ferrous chloride dihydrate, ferrous sulfate, ferrous sulfate tetrahydrate, ferrous sulfate pentahydrate, and ferrous sulfate. Examples include heptahydrate, polyferrous sulfate, and the like. Examples of ferric salt compounds include ferric chloride, ferric chloride hexahydrate, ferric sulfate, ferric sulfate trihydrate, ferric sulfate hexahydrate, and ferric sulfate. Examples include heptahydrate, polyferric sulfate, and the like. Examples of the polymer flocculant include high anionic polymer flocculants. The polymer flocculant has the effect of promoting the flocculation of precipitates containing iron hydroxide as a main component and facilitating solid-liquid separation.

Examples of the alkali used in the liquid phase pH adjuster include sodium hydroxide, potassium hydroxide, and calcium hydroxide. A basic waste liquid may be used as the pH adjuster. By using basic waste liquid, it is possible to reduce the amount of industrial chemicals used and to consolidate waste liquid processing equipment. Examples of the basic waste liquid that can be used include those containing at least one of sodium hydroxide, potassium hydroxide, and calcium hydroxide. Further, for pH adjustment, an acid such as sulfuric acid or hydrochloric acid may be used together with an alkali.

According to the mercury recovery method of this embodiment, mercury can be recovered from organic waste while suppressing extra fuel costs and chemical costs and without generating harmful organic chlorine compounds. Furthermore, by using basic waste liquid as an alkali in the precipitation step, the amount of industrial chemicals used can be reduced.

Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above embodiments. For example, in another embodiment, the recovery section 50 may be provided on the downstream side of the flow path 64, and the combustion gas after mercury (II) chloride has been absorbed in the absorption section 60 may be introduced. Thereby, the solid content that could not be captured by the absorption section 60 can be recovered by the recovery section 50. In this case, the mist containing solids generated in the recovery section 50 may be introduced into the solid-liquid separation section 70 or directly into the temperature reduction section 30 and the absorption section 60. In yet another embodiment, the solid-liquid separation section 70 may be provided separately in the channel 54 and the channel 56, or may be provided in the channel 66 and the channel 34. In yet another embodiment, the temperature reduction section 30 may be, for example, a heat exchanger, or the temperature reduction section 30 may not be provided.

According to the mercury recovery device and mercury recovery method of the present disclosure, mercury contained in waste can be recovered in a sufficiently stable manner.

DESCRIPTION OF SYMBOLS 10... Desalination furnace, 12, 14... Supply part, 16... Lower discharge part, 18... Upper discharge part, 20... Combustion furnace, 22... Burner, 24... Secondary air supply part, 26... Discharge part, 28... Nozzle , 30... Temperature reduction section, 30A... Main body section, 32... Channel, 34... Channel, 36... Channel, 40... Sedimentation tank (sedimentation section), 50... Recovery section, 51... Throat section, 60... Absorption section , 60A... Main body part, 62... Filled bed, 70... Solid-liquid separation part.

Claims (16)

a desalination furnace that heats organic waste containing chlorine and mercury in a low-oxygen atmosphere with an oxygen concentration lower than that of air to produce decomposed gas containing flammable organic components, mercury and chlorine components;
A combustion furnace comprising a burner, in which the cracked gas generated in the desalination furnace is combusted to obtain combustion gas containing mercury(II) chloride;
a recovery unit that recovers solid content containing at least one of dust and metallic mercury contained in the combustion gas;
an absorption unit that causes an absorption liquid to absorb the mercury(II) chloride contained in the combustion gas;
A mercury recovery device equipped with The organic waste contains plastic;
The mercury recovery apparatus according to claim 1, wherein the desalination furnace obtains carbide containing carbon derived from the plastic. The mercury recovery apparatus according to claim 1 or 2, wherein the desalination furnace has a supply section that supplies pulverized coal. The mercury recovery device according to any one of claims 1 to 3, wherein the combustion temperature of the combustion furnace is 850° C. or higher. The mercury recovery device according to any one of claims 1 to 4, further comprising a circulation channel for returning a portion of the absorption liquid drawn out from the absorption unit to the absorption unit. Claim 1, further comprising a temperature reduction section that cools the combustion gas by bringing the combustion gas into contact with an absorption liquid, and the combustion gas cooled in the temperature reduction section is supplied to the recovery section or the absorption section. The mercury recovery device according to any one of items 5 to 5. The mercury recovery device according to any one of claims 1 to 6, wherein the recovery section includes a wet scrubber. The mercury recovery apparatus according to claim 7, wherein the wet scrubber is a Venturi scrubber. A flow path for supplying a waste liquid containing hydrochloric acid discharged from at least one of the absorption section and a temperature reduction section that cools the combustion gas by bringing the combustion gas and the absorption liquid into contact with each other, to the recovery section. The mercury recovery device according to any one of claims 1 to 8, comprising: The mercury recovery apparatus according to claim 9, further comprising a solid-liquid separation section that separates at least a portion of solid content contained in the waste liquid from the waste liquid. The mercury recovery apparatus according to claim 10, wherein the flow path supplies the waste liquid obtained by separating at least a portion of the solid content in the solid-liquid separation section to the recovery section. The mercury recovery device according to any one of claims 1 to 11, comprising a precipitation section that obtains a mercury-containing precipitate from the waste liquid discharged from the absorption section. 12. The precipitation section includes a precipitation tank for obtaining the precipitate containing mercury from the wastewater by co-precipitation of mercury(II) chloride and at least one of ferrous hydroxide and ferric hydroxide. The mercury recovery device described in . The mercury recovery apparatus according to claim 12 or 13, wherein the precipitation section includes a supply section that supplies an alkali containing at least one of sodium hydroxide, potassium hydroxide, and calcium hydroxide. A desalination process in which organic waste containing chlorine and mercury is heated in a desalination furnace in a low-oxygen atmosphere with an oxygen concentration lower than that of air to generate decomposed gas containing flammable organic components, mercury, and chlorine components. and,
A combustion step in which the decomposed gas generated in the desalination furnace is combusted in a combustion furnace equipped with a burner to obtain a combustion gas containing mercury(II) chloride;
a recovery step of recovering solid content containing at least one of dust and metallic mercury contained in the combustion gas;
A mercury recovery method comprising the step of absorbing the mercury (II) chloride contained in the combustion gas into an absorption liquid. A precipitation step of obtaining a mercury-containing precipitate by co-precipitating the mercury(II) chloride absorbed in the absorption liquid in the absorption step with at least one of ferrous hydroxide and ferric hydroxide. The mercury recovery method according to claim 15.

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