Eliminator unit, scrubber device equipped therewith, and exhaust gas treatment method using the scrubber device.

Abstract

The present invention provides an eliminator unit capable of suppressing the loss of salt crystal particles due to exhaust gas discharged from a drying apparatus, and a scrubber apparatus equipped with the same. [Solution] An eliminator unit for separating and recovering dust containing water-soluble salt crystal particles and mist containing substances derived from the crystal particles from exhaust gas, comprising: a collision plate type eliminator 13 in which a plurality of plate-shaped members 13a arranged at equal intervals in the horizontal plane and not bent in the vertical direction are arranged within a rectangular frame serving as a support member 13b; and exhaust gas 1 Nm³ in a preferably fan-shaped spray pattern directed toward the plurality of plate-shaped members 13a so as to constantly form a water film on the front and back surfaces of the plurality of plate-shaped members 13a. 3 It has a spray nozzle 14 that sprays water at a rate of 15 to 50 mL per unit.

Description

[Technical Field]

[0001] The present invention relates to an eliminator unit, a scrubber device provided with the eliminator unit, and an exhaust gas treatment method using the scrubber device. [Background Art]

[0002] Nickel sulfate is used in various applications including as a raw material for nickel plating and catalysts, as well as electrode materials such as positive electrode active materials for lithium ion secondary batteries. As methods for producing nickel sulfate, known methods include, for example, treating a nickel-cobalt mixed sulfide as an intermediate raw material produced by a high-pressure acid leaching method also referred to as the HPAL method, or a nickel matte as an intermediate raw material produced by pyrometallurgy, via a wet process.

[0003] For example, Patent Document 1 discloses a technique for producing nickel sulfate crystals, in which a slurry prepared by adding water to a nickel-cobalt mixed sulfide (mixed sulfide: MS) as an intermediate raw material is leached under high temperature and high pressure conditions to produce a crude nickel sulfate aqueous solution, then impurities are removed by various purification methods such as an oxidation neutralization method and a solvent extraction method, and the obtained high-purity nickel sulfate aqueous solution is crystallized. The nickel-cobalt mixed sulfide can be produced by adding sulfuric acid to a raw material nickel oxide ore, performing acid leaching treatment under high temperature and high pressure conditions, neutralizing the obtained leachate containing nickel and cobalt to remove impurities such as iron, then adding a sulfiding agent such as hydrogen sulfide gas to perform sulfiding treatment. [Prior Art Documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2024-170245 [Summary of the Invention] [Problems to be Solved by the Invention]

[0005] As in the nickel sulfate manufacturing method described above, continuous crystallization apparatuses are generally used when industrially producing crystalline products such as nickel sulfate from high-purity nickel aqueous solutions. A continuous crystallization apparatus is a device that continuously introduces a solution containing the substance to be crystallized into a crystallization vessel and supersaturates the solution, thereby using the degree of supersaturation as a driving force to precipitate the substance as a solid phase. Various methods are known for achieving this supersaturation, including evaporation, which involves heating the solution to the boiling point of the solvent and evaporating it; cooling, which involves cooling the solution; and pH control, which involves changing the pH of the solution. Of these, evaporation is generally preferred when precipitating nickel compounds such as nickel sulfate from high-purity nickel aqueous solutions.

[0006] In the evaporation method described above, the vapor generated by the evaporation of water from the aqueous solution is continuously discharged from the top of the crystallization vessel, while the slurry containing the precipitated crystals is concentrated by sedimentation separation and continuously withdrawn from the bottom of the crystallization vessel as a concentrated slurry. The concentrated slurry withdrawn from the bottom of the crystallization vessel in this way is separated into solid-liquid components: the mother liquor on the liquid phase side and the crystal particles on the solid phase side, using a dehydrator such as a centrifuge. The mother liquor on the liquid phase side is generally returned to the crystallization vessel. On the other hand, the crystal particles on the solid phase side are in a wet state with the mother liquor adhering to their surface, so they are introduced into a drying device and dried before being produced as crystals.

[0007] For drying the above-mentioned crystalline particles, drying devices that utilize hot air as a heat transfer medium are preferably used, such as a fluidized bed dryer that dries the material to be dried by blowing hot air from below onto the material on a screen to form a fluidized bed, a rotary dryer that dries the material by introducing it into an inclined rotating cylinder and blowing hot air onto it while it rolls, an airflow dryer that dries the material by introducing it into a hot airflow and dispersing it into powder form, and a transfer-type hot air dryer that dries the material by blowing hot air onto the material placed on an endless wire mesh or porous belt that moves horizontally.

[0008] As described above, drying equipment that uses hot air as a heat transfer medium works by bringing hot air into contact with crystalline particles to evaporate the moisture on the particle surface. As a result, particularly fine crystalline particles can be blown up by the hot air inside the drying equipment, becoming dust, which is then carried over into the exhaust gas containing vapor produced by the evaporation of moisture and discharged from the drying equipment. The exhaust gas from the drying equipment can be reused as a dry heat transfer medium after the moisture has been removed by a dehumidifier or the like. However, in industrial drying processes, heated air is generally used as the heat transfer medium, so it is usually released into the atmosphere after appropriate dust removal. Therefore, even with appropriate dust removal, a minute amount of dust will still be contained in the exhaust gas, and the release of crystalline particle dust into the atmosphere along with the exhaust gas has sometimes been a problem.

[0009] Conventionally, exhaust gas discharged from a drying device is introduced into a wet scrubber, where water is used as the collection medium to absorb the crystalline particle dust into the water, thereby recovering the crystalline particle dust in the form of an aqueous solution containing the salt of the crystalline particles. Furthermore, if necessary, a mist eliminator or demister is installed downstream of the wet scrubber to separate and collect water droplets and mist contained in the exhaust gas after cleaning by the wet scrubber using the inertial effect.

[0010] As described above, by using wet scrubbers or mist eliminators, it is possible to recover some of the crystalline particle dust discharged from the drying equipment along with the exhaust gas. However, even in the exhaust gas after dust removal from these wet scrubbers or mist eliminators, although the amount is far less than that of the exhaust gas before introduction into the wet scrubber, a small amount of dust containing crystalline particles and mist containing substances derived from these crystalline particles is still present, which sometimes leads to problems with the loss of salts that make up the crystalline particles.

[0011] The present invention has been made in view of the above circumstances, and aims to provide an eliminator unit and a scrubber device equipped therewith that can suppress the loss of salt constituting crystal particles due to exhaust gas discharged from a drying device. [Means for solving the problem]

[0012] To achieve the above objective, the eliminator unit according to the present invention is an eliminator unit that separates and recovers dust containing water-soluble salt crystal particles and mist containing substances derived from said crystal particles from exhaust gas, and is characterized by having a collision plate type eliminator in which a plurality of plate-shaped members that are arranged at equal intervals in the horizontal plane and have no bends in the vertical direction are arranged in a rectangular frame, and a spray nozzle that sprays water toward the plurality of plate-shaped members such that a water film is constantly formed on the front and back surfaces of the plurality of plate-shaped members. [Effects of the Invention]

[0013] According to the present invention, it is possible to suppress the loss of salt constituting the crystal particles due to exhaust gas discharged from the drying apparatus. [Brief explanation of the drawing]

[0014] [Figure 1] This is a block flow diagram of a method for producing nickel sulfate to which a scrubber apparatus equipped with an eliminator unit according to an embodiment of the present invention is preferably applied. [Figure 2] Figure 1 is a process flow diagram of a crystallization apparatus and scrubber apparatus preferably used in the crystallization process. [Figure 3] Figure 2 shows a longitudinal cross-sectional view and an AA cross-sectional view of a specific example of a scrubber apparatus. [Figure 4] Figure 3 is a partial perspective view of the eliminator unit of the scrubber device. [Figure 5] This is a schematic plan view showing how mist and dust are collected on the front and back surfaces of multiple plate-like members included in the eliminator of the eliminator unit shown in Figure 4. [Figure 6] This is a plan view of specific examples of various plate materials suitably used for the number of plate-like members included in the eliminator of the eliminator unit of an embodiment of the present invention. [Figure 7]It is a perspective view of an annular pipe provided with an eliminator provided so as to surround a venturi tube in the scrubber device of Fig. 3, and a plurality of spray nozzles that spray water onto the plurality of plate-shaped members of the eliminator. MODE FOR CARRYING OUT THE INVENTION

[0015] 1. Method for Producing Nickel Sulfate First, a method for producing nickel sulfate to which a scrubber device provided with an eliminator unit according to an embodiment of the present invention is suitably applied will be described. As shown in Fig. 1, the method for producing nickel sulfate comprises: a slurry preparation step S1 of slurrying a nickel sulfide raw material to prepare a nickel sulfide slurry; a leaching step S2 of subjecting the nickel sulfide slurry to oxidative leaching treatment under high temperature and high pressure to obtain a crude nickel sulfate aqueous solution as a leachate; a deferrization step S3 of removing iron as an impurity contained in the leachate by oxidative neutralization treatment; a solvent extraction step S4 of removing impurities such as cobalt contained in the crude nickel sulfate aqueous solution after the oxidative neutralization treatment by solvent extraction; and a crystallization step S5 of introducing the high-purity nickel sulfate aqueous solution obtained in the solvent extraction step S4 into a crystallizer to produce nickel sulfate crystals. Each of these steps will be specifically described below.

[0016] 1.1 Slurry Preparation Step S1 As a raw material for nickel sulfate, nickel sulfides such as nickel matte containing Ni₃S₂ as a main component and nickel-cobalt mixed sulfide (MS) are used. For example, nickel matte can be produced by pyrometallurgical smelting of nickel oxide ore, while nickel-cobalt mixed sulfide can be produced by subjecting nickel oxide ore to high pressure acid leaching and then to sulfidation treatment. The former nickel matte generally has a nickel grade of about 75 to 80% and a sulfur grade of about 20 to 25%, and the latter nickel-cobalt mixed sulfide generally has a nickel grade of about 50 to 60% by mass, a cobalt grade of about 4 to 6% by mass, and a sulfur grade of about 30 to 35% by mass.

[0017] In the slurry preparation step S1, after crushing and classifying the nickel matte or nickel-cobalt mixed sulfide described above, water is added to form a slurry, thereby preparing a nickel sulfide slurry. There is no particular limitation on the solid content concentration of this nickel sulfide slurry, but 100 to 300 g / L is preferable.

[0018] 1.2 Leaching Step S2 In the leaching step S2, the nickel sulfide slurry prepared in the preceding slurry preparation step S1 is introduced into a horizontally long pressure vessel called an autoclave, and high-pressure air is blown into the vessel to perform oxidative leaching treatment under high temperature and high pressure conditions of about 150 to 180°C and a pressure of about 1 to 2 MPaG, thereby producing a leachate which is an aqueous nickel sulfate solution.

[0019] 1.3 Iron Removal Step S3 The leachate produced in the leaching step S2 contains, for example, about 100 to 120 g / L of nickel, about 10 g / L of cobalt, and further contains iron as an impurity. Therefore, in the iron removal step S3, for example, air is blown into the leachate as an oxidizing agent to convert Fe 2+ to Fe 3+ While oxidizing to, a neutralizing agent such as slaked lime, calcium carbonate, or sodium hydroxide is added to preferably cause an oxidative neutralization reaction at a pH of about 2.6 to 5.9, thereby producing a neutralized precipitate containing Fe(OH)₃. A crude nickel sulfate aqueous solution is obtained by subjecting the slurry containing the thus-produced neutralized precipitate to solid-liquid separation using a filter press or the like.

[0020] 1.4 Solvent Extraction Step S4 In solvent extraction step S4, impurities such as cobalt contained in the crude nickel sulfate aqueous solution are removed by performing extraction using a phosphoric acid-based extractant, such as mono-2-ethylhexyl 2-ethylhexyl phosphonic acid. This yields a high-purity nickel sulfate aqueous solution. In this solvent extraction step S4, the organic solvent containing the above-mentioned phosphoric acid-based extractant is circulated in the following order: extraction stage, washing stage, exchange stage, nickel recovery stage, cobalt recovery stage, and back-extraction stage. The pH is adjusted so that the pH value decreases in this order, thereby efficiently removing impurities from the crude nickel sulfate aqueous solution and recovering the removed cobalt.

[0021] 1.5 Crystallization process S5 In the crystallization step S5, the high-purity nickel sulfate aqueous solution obtained in the preceding solvent extraction step S4 is charged into the evaporator of the crystallization apparatus, and the water in the high-purity nickel sulfate aqueous solution is continuously evaporated under reduced pressure to create a supersaturated state, thereby crystallizing nickel sulfate crystals. Next, a crystallization apparatus preferably used in this crystallization step S5 will be described.

[0022] 2. Crystallization apparatus For crystallization of nickel sulfate crystals from an aqueous nickel sulfate solution, a crystallization apparatus having an evaporator that causes crystallization by creating a supersaturated state through evaporation of water in the nickel sulfate aqueous solution is preferably used. While not limited to specific types, continuous crystallization apparatuses with such evaporators include DTB (draft tube & baffle) type, DP (double propeller) type, and Crystal Oslo type. As illustrated in Figure 2, a DTB type crystallization apparatus has a vertical, approximately cylindrical evaporator (also called a crystallization vessel) 1. This evaporator 1 is divided into a main body 1b and a settling section 1c located on the lower outside by a baffle 1a with an open lower end. A draft tube 1d is provided concentrically within the main body 1b. A stirrer 2 is provided within the draft tube 1d, causing the slurry-like nickel sulfate aqueous solution containing crystals to circulate inside and outside the draft tube 1d. Crystals that have grown significantly during this circulation settle to the bottom of the evaporator 1 by gravity and are discharged via classification legs 1e. Meanwhile, some of the nickel sulfate aqueous solution containing microcrystals is withdrawn from the settling section 1c, heated in the heat exchanger 3, and then returned to the bottom of the evaporator 1 along with the aqueous solution containing the material to be crystallized, which is supplied from the stock tank 4. A vacuum pump 6 is connected to the top of the evaporator 1 via a condenser 5, thereby maintaining a reduced pressure inside the evaporator 1.

[0023] The DP type crystallizer is a modified version of the DTB type crystallizer, in which a stirrer is installed outside the draft tube to allow the slurry-like aqueous solution containing crystals to circulate more efficiently inside and outside the draft tube. The Crystal Oslo type crystallizer has a structure in which the evaporator and classification tank are separated into upper and lower sections. The supersaturated aqueous solution in the upper evaporator is sent to the lower classification tank through a descending pipe in the center of the apparatus. In this case, the crystals that have grown in the classification tank are discharged from the bottom. Among the various types of crystallizers described above, the DTB type is preferred. In any of the above types of crystallizers, the concentrated slurry containing nickel sulfate crystals, which is extracted from the bottom of the crystallizer, is separated into solid-liquid crystals on the solid phase side and mother liquor on the liquid phase side by a dehydrator 7 such as a centrifuge. The mother liquor, which is the nickel sulfate aqueous solution separated into solid and liquid on the liquid phase side, is returned to the stock tank 4. On the other hand, the dehydrated crystals recovered as the solid phase are in a wet state with mother liquor adhering to their surface, so they are introduced into the dryer 8, where they are dried to produce granular nickel sulfate crystals with a particle size of about 1 mm.

[0024] While there are no particular limitations on the type of dryer 8 described above, drying devices that use hot air as a heat transfer medium, such as the aforementioned fluidized bed dryers, rotary dryers, airflow dryers, and transfer-type hot air dryers, are preferably used. This type of drying device has a hot air generator that includes a fan that takes in air and pressurizes it, and a heater that heats the pressurized air. The dehydrated nickel sulfate crystals introduced into the dryer 8 are heated by exposure to the hot air supplied from the hot air generator, and the moisture evaporates, resulting in a drying process. The exhaust gas containing the vapor produced by this evaporation is discharged from the dryer 8. At this time, some of the nickel sulfate crystal particles are blown up by the hot air and become crystal particle dust, which is carried over into the vapor-containing exhaust gas and discharged from the dryer 8. In order to recover the nickel sulfate crystal particle dust contained in the exhaust gas discharged from the dryer 8, the exhaust gas is introduced into a dust removal device that includes a cyclone and a scrubber device, where the nickel sulfate crystal particle dust contained in the exhaust gas is recovered. Next, I will explain this dust removal device in detail.

[0025] 3.Dust removal equipment As shown in Figure 2, the exhaust gas discharged from the dryer 8 is first introduced into a cyclone 9, a device that separates gas from solid by centrifugal force through high-speed swirling of dust-containing gas within a cylinder. Here, mainly coarse crystalline nickel sulfate particles contained in the exhaust gas are recovered. The recovery rate can be increased by periodically returning the recovered nickel sulfate crystalline particles to the raw liquid tank 4.

[0026] The exhaust gas after primary dust removal, processed by the cyclone 9, is then introduced to the subsequent scrubber device 10. The scrubber device 10 includes a wet scrubber section that collects dust containing nickel sulfate crystalline particles, a water-soluble salt, contained in the primary dust removal exhaust gas, using water as the collection medium, and an eliminator unit located downstream of the wet scrubber section that uses its inertia to separate, remove, and recover mist of the wash water carried over from the exhaust gas after washing in the wet scrubber section, as well as very small amounts of crystalline dust particles that were not captured by the water in the wet scrubber section. The gas outlet at the top of the scrubber device 10 is connected to an exhaust gas fan 20 for exhaust gas suction.

[0027] The type of wet scrubber section included in the scrubber device 10 described above is not particularly limited as long as it can efficiently collect dust containing water-soluble salt crystal particles in the exhaust gas by wet means, as described above. Examples include the Venturi type, which collects dust by contacting water droplets generated by spraying water into the throat of a Venturi tube into which the exhaust gas is introduced; the Rotocron type, which collects dust by passing the exhaust gas at high speed through an inverted S-shaped flow path provided at the water level surface of water stored in a container; and the Cyclone type, which collects dust by introducing exhaust gas tangentially from the bottom of a cylindrical body and spraying water from the center of the axis into the inside of the body while it is swirling. Among these, the Venturi type is preferred because it can collect even extremely fine particles with high efficiency. The following explanation will use the case of using a Venturi type scrubber as an example with reference to Figure 3.

[0028] As shown in Figure 3, the scrubber device 10 is provided with a Venturi tube 12, which has a substantially square cross-section perpendicular to the flow direction, protruding from the top to the bottom of the cylindrical container 11 at the central axis inside the container 11. The tip opening of this Venturi tube 12 faces the water surface of the stored water at the bottom of the cylindrical container 11, and a scrubber nozzle 12a is provided just before the throat of the Venturi tube 12 to discharge exhaust gas cleaning water downwards. From this scrubber nozzle 12a, exhaust gas 1 Nm 3 It is preferable to release an exhaust gas cleaning water volume of 2.6 to 3.0 L per unit. This amount of exhaust gas cleaning water is equivalent to 1 Nm of exhaust gas. 3 If the volume is less than 2.6L per unit, the number of droplets will decrease, which may reduce the total surface area of ​​the droplets, and conversely, the exhaust gas volume may decrease by 1Nm³. 3 If the volume exceeds 3.0 L per unit, the diameter of the droplets increases, which may reduce the total surface area of ​​the droplets. With this configuration, the primary dust-removed exhaust gas discharged from the preceding cyclone 9 and introduced from the upper inlet of the venturi tube 12 can be efficiently brought into contact with the droplet-shaped cleaning water discharged from the scrubber nozzle 12a within the venturi tube 12. As a result, dust containing water-soluble salt crystal particles contained in the primary dust-removed exhaust gas is collected in this droplet-shaped cleaning water.

[0029] As described above, the droplet-shaped washing water that collects dust exits the tip opening of the Venturi tube 12, separates from the exhaust gas after washing, and continues straight ahead, temporarily storing at the bottom of the cylindrical container 11. It is then drawn out from the bottom nozzle and supplied again to the scrubber nozzle 12a via an external circulation line equipped with a circulation pump. A branch line is provided on the discharge side of this circulation pump, with its end connected to the stock solution tank 4. The liquid level of the washing water stored at the bottom of the cylindrical container 11 is controlled to a constant level by the opening of a control valve on this branch line. This allows the nickel sulfate crystalline particles recovered by the scrubber device 10 to be repeatedly returned to the stock solution tank 4, thereby minimizing the loss of salts that constitute the crystalline particles.

[0030] Meanwhile, the exhaust gas after cleaning, from which dust has been removed, changes direction by approximately 180° after exiting the tip opening of the Venturi tube 12 and rises inside the cylindrical container 11. As mentioned above, this exhaust gas after cleaning contains mist of the cleaning water carried over and very small amounts of crystalline dust particles that were not captured by the water in the scrubber section. An eliminator unit is provided inside the cylindrical container 11, surrounding the Venturi tube 12, so as to block the roughly annular flow path between the inner wall of the cylindrical container 11 and the outer wall of the Venturi tube 12 through which this rising exhaust gas after cleaning flows.

[0031] Referring to Figure 4, the eliminator unit will be described in detail. One element of the eliminator unit, the multiple eliminators 13, each have multiple plate-shaped members 13a arranged at equal intervals in the horizontal plane, and a rectangular frame-shaped support member 13b that supports these multiple plate-shaped members 13a. The other element of the eliminator unit, the spray nozzle 14, is provided to constantly spray water onto the multiple plate-shaped members 13a so that a water film is constantly formed on the front and back surfaces of these multiple plate-shaped members 13a. With this configuration, as shown in Figure 5, it becomes possible to absorb the mist and dust contained in the exhaust gas after cleaning, which is collected by impacting the front and back surfaces of the multiple plate-shaped members 13a due to inertia, into the water film on the front and back surfaces. Preferably, the spray nozzle 14 is arranged to spray water toward the upper ends of the multiple plate-shaped members 13a.

[0032] Conventional eliminators did not actively maintain a wet state by constantly spraying water, but were used simply as devices to function as impact plates. The reason for not intentionally maintaining a wet state was that the mist generated by the wet scrubber was the target of removal. However, it frequently occurred that crystalline salt particles could not be sufficiently removed by the eliminator. As a result of diligent investigation and research by the inventors, it was found that if the exhaust gas after cleaning contains a very small amount of crystalline dust particles that were not captured by the water in the scrubber section, conventional eliminators have difficulty removing the dust. Therefore, by installing an eliminator unit downstream of the wet scrubber, which has an impact plate type eliminator 13 and spray nozzles 14 that spray water onto the multiple plate-like members 13a so that a water film is constantly formed on the front and back surfaces of the multiple plate-like members 13a of the eliminator 13, it became possible to effectively remove the above-mentioned very small amount of crystalline dust particles. Here, "spraying water so that a water film is constantly formed" means "spraying water continuously without interruption."

[0033] The specific shape of the multiple plate-like members 13a described above is not particularly limited as long as it is a collision plate system that can sharply bend the straight flow of the exhaust gas after cleaning, causing the mist and dust contained in the exhaust gas after cleaning to collide with the wall surface due to their inertia and be collected. For example, as shown in Figure 6(a), it may be a shape that bends in a zigzag pattern at multiple points in a plan view, as shown in Figure 6(b), or it may be a shape that curves in a wave-like pattern at multiple points in a plan view, as shown in Figure 6(c), with a collection effect at the top of Figure 6(b). The shape may have fin-like protrusions to increase the efficiency, or as shown in Figure 6(d), it may have alternating isosceles trapezoidal and inverted isosceles trapezoidal shapes in plan view, or as shown in Figure 6(e), multiple strip-shaped plates may be arranged vertically and horizontally so that their front and back surfaces are inclined at a certain angle with respect to the direction of travel of the exhaust gas after cleaning in plan view, or as shown in Figure 6(f), multiple strip-shaped plates may be arranged vertically and horizontally so that their front and back surfaces are alternately inclined left and right in plan view with respect to the direction of travel of the exhaust gas after cleaning.

[0034] Regardless of the shape of the plate-like member 13a used, each plate-like member 13a is made without any curvature in the vertical direction. This allows the water film formed on the front and back surfaces of each plate-like member 13a to flow smoothly down along these surfaces, like a wet wall tower, and drip or flow out from the lower end of the plate-like member 13a. As a result, the water film can be constantly replaced by clean spray water continuously sprayed from the spray nozzle 14. Consequently, the propulsion force for dust containing water-soluble salt crystal particles and mist containing substances derived from these crystal particles, which are contained in the exhaust gas after cleaning, to be absorbed and dissolved by the water film on the front and back surfaces of the plate-like member 13a can be increased, allowing for the recovery of water-soluble salt with higher efficiency.

[0035] As mentioned above, the support member 13b not only supports the multiple plate-shaped members 13a, but also prevents the exhaust gas after cleaning from bypassing these plate-shaped members 13a. For this reason, the lowermost part of the support member 13b is joined to the inner edge of the annular lower partition plate 15 provided on the inner wall surface of the cylindrical container 11, or is integrated with the lower partition plate 15. On the other hand, the uppermost part of the support member 13b is joined to the outer edge of the upper partition plate 16 provided on the outer wall surface of the Venturi tube 12, or is integrated with the upper partition plate 16. Furthermore, the sides of adjacent support members 13b are connected to each other or sealed with plate material or the like to prevent gaps. Figure 3(b) shows an example in which 10 eliminators 13 are provided on the outside of the Venturi tube 12 at equal intervals in the circumferential direction without gaps, but the number of eliminators 13 is not limited to this, and three or more are preferable considering ease of handling during maintenance and manufacturing costs.

[0036] The spray nozzles 14, which are responsible for spraying water onto the multiple plate-shaped members 13a, are preferably provided one per eliminator 13, as shown in Figure 7, and are preferably capable of spraying water onto the upper ends of the multiple plate-shaped members 13a all at once in a fan-shaped spray pattern. Note that in Figure 7, one of the eliminators 13 on the front side has been removed for illustrative purposes. As mentioned above, the spray water sprayed by the spray nozzles 14 flows smoothly down along the front and back surfaces of the plate-shaped members 13a due to gravity, so even if the amount of spray water sprayed from the spray nozzles 14 is small, it is possible to maintain a constantly wet state by spraying water onto the upper ends of the multiple plate-shaped members 13a, thereby forming a water film on preferably the entire front and back surfaces.

[0037] The spraying of water by the spray nozzle 14 described above is preferably performed from the upstream side with respect to the exhaust gas flow direction in the multiple plate-shaped members 13a. This can be achieved by providing an annular pipe 14a concentrically with the cylindrical container 11 inside the multiple eliminators 13, as shown in Figure 7, and positioning the spray nozzle 14 in this annular pipe 14a opposite the widthwise center of the upper end of each of the multiple eliminators 13. In this case, in order to avoid physical interference with the upper partition plate 16 mentioned above, the annular pipe 14a is positioned slightly below the upper ends of the multiple plate-shaped members 13a, so the spray water is sprayed diagonally upward from the spray nozzle 14.

[0038] The amount of water sprayed from the spray nozzle 14 described above is equivalent to 1 Nm of exhaust gas. 3A spray volume of 15 to 50 mL per unit is preferred, and 20 to 35 mL is more preferred. If this spray volume is less than 15 mL, there is a risk that the recovery of dust containing water-soluble salt crystal particles and mist containing substances derived from these crystal particles will be insufficient. Conversely, if this amount exceeds 50 mL, the recovery rate of the above-mentioned crystal particle dust and mist will hardly improve any further, which is undesirable from the standpoint of operating costs. Furthermore, as shown in Figure 2, the cleaning water extracted from the scrubber device 10 by liquid level control is returned to the stock tank 4, so the supply amount of cleaning water to the stock tank 4 will increase excessively, which may lead to a decrease in the salt concentration of the stock solution, an increase in the energy consumption of the heat source supplied to the heat exchanger, or a decrease in the crystallization capacity of the crystallization device itself. Note that the exhaust gas volume used as a reference here is the volume under standard conditions.

[0039] A demister 17 may be provided at the top of the cylindrical container 11 located downstream of the eliminator 13. This allows for the collection of mist and dust that have passed through the eliminator 13, thereby further increasing the recovery rate of water-soluble salts. The demister 17 is generally made of a mat-like layer of metal or resin wire mesh with a thickness of approximately 100 to 150 mm. The mist collected in the demister 17 grows on the surface of the wire mesh to form large droplets, which then fall due to gravity.

[0040] The demister 17 may be washed with water periodically or as needed for cleaning. This cleaning can be effectively performed by spraying water onto the demister 17 from above, below, or both above and below using a spray nozzle with a conical spray pattern. The resulting washing wastewater and the larger droplets collected by the demister 17 can be collected together with the water film dripping or flowing out from the eliminator 13 and the washing water from the wet scrubber. The exhaust gas exiting the demister 17 is then removed as dust and extracted as exhaust gas from the top discharge nozzle of the cylindrical container 11 by the exhaust gas fan 20 before being released into the atmosphere.

[0041] The above description of an eliminator and a scrubber device equipped with the eliminator, using the case where the water-soluble salt crystal particles contained in the exhaust gas are nickel sulfate, is not limited to the above embodiments, and various alternative and modified examples are possible. For example, the water-soluble salt crystal particles may be copper sulfate or the like. The present invention will now be described more specifically with reference to examples, but the present invention is not limited in any way by the following examples. [Examples]

[0042] As an example, nickel sulfate crystals were produced from a nickel-cobalt mixed sulfide along the block flow shown in Figure 1. In this process, a crystallization apparatus and scrubber apparatus as shown in Figure 2 were used for the crystallization step. As shown in Figure 3, ten eliminators 13 were evenly arranged circumferentially around a Venturi tube 12 inside a cylindrical container 11, and an annular pipe 14a was provided inside them. The multiple plate-like members 13a of each eliminator 13 were made of vertically straight plate material that was bent in a zigzag pattern at multiple points, as shown in Figure 6(a), and arranged at equal intervals in the horizontal plane.

[0043] Exhaust gas 1 Nm from the scrubber nozzle 12a of the venturi tube 12 3 2.8 liters of exhaust gas cleaning water were discharged per unit. In addition, ten uniform fan-shaped nozzles (model number VEP) manufactured by Ikeuchi Co., Ltd., which form a fan-shaped spray pattern, were arranged evenly around the annular pipe 14a as spray nozzles 14. At that time, the angle of the spray nozzles 14 was adjusted so that the fan-shaped spray pattern spread horizontally diagonally upwards in order to spray water onto the upper ends of multiple plate-shaped members 13a of the corresponding eliminator 13 all at once.

[0044] The above-mentioned annular pipe 14a receives exhaust gas 1 Nm³ discharged from the crystallization apparatus. 3Industrial water was continuously supplied at a flow rate of 28 mL per unit. Furthermore, to clean the demister 17, industrial water was supplied from above and below it at a flow rate of 80 L / min for 2 minutes at a frequency of once every 240 minutes. Nickel sulfate crystals were produced over a certain period of time under the conditions of the above embodiment that satisfy the requirements of the present invention.

[0045] As a comparative example, nickel sulfate crystals were produced over a certain period of time in the same manner as in the above embodiment, except that the constant supply of industrial water from the annular pipe 14a was stopped, and instead the same amount of industrial water was directly supplied to the bottom of the cylindrical container 11 as makeup water. At the timing of cleaning the demister 17, a portion of the industrial water at the flow rate of 80 L / min was withdrawn and sprayed onto the multiple plate-shaped members 13a of the eliminator 13 from a separately provided spray nozzle to perform cleaning. While nickel sulfate crystals were produced under the conditions of the above embodiment and comparative example, the analysis values ​​of the exhaust gas sampled multiple times at the outlet side of the exhaust gas fan 20 were averaged, and it was found that under the conditions of the embodiment, the amount of nickel lost due to the exhaust gas was reduced by 34% compared to the conditions of the comparative example. [Explanation of Symbols]

[0046] 1 Evaporator 1a Baffle 1b Main body 1c Settling section 1D draft tube 1e Classified leg 2. Agitator 3 Heat exchanger 4 Stock solution tank 5. Capacitor (condenser) 6. Vacuum pump 7 Dehydrator 8 Dryer 9 Cyclone 10 Scrubber device 11 Cylindrical container 12 Venturi tubes 12a Scrubber Nozzle 13 Eliminator 13a Plate-shaped member 13b Support member 14 Spray nozzles 14a Annular pipe 15 Lower partition plate 16 Upper partition plate 17 Demister 20 Exhaust gas fan

Claims

1. An eliminator unit for separating and recovering dust containing water-soluble salt crystal particles and mist containing substances derived from the crystal particles from exhaust gas, comprising: a collision plate type eliminator in which a plurality of plate-shaped members, which are arranged at equal intervals in the horizontal plane and have no bends in the vertical direction, are arranged within a rectangular frame; and a spray nozzle that sprays water toward the plurality of plate-shaped members such that a water film is constantly formed on the front and back surfaces of the plurality of plate-shaped members.

2. The eliminator unit according to claim 1, wherein the spray nozzle sprays water onto the upper ends of the plurality of plate-shaped members in a fan-shaped spray pattern.

3. The amount of water sprayed from the spray nozzle is the exhaust gas 1 Nm ３ The eliminator unit according to claim 2, wherein the volume is 15 to 50 mL per unit.

4. A scrubber apparatus comprising: a wet scrubber for cleaning exhaust gas containing dust containing water-soluble salt crystal particles; and an eliminator unit according to claim 1 for separating and recovering a mist containing a portion of the dust and a substance derived from the crystal particles contained in the exhaust gas after cleaning that has passed through the wet scrubber.

5. The scrubber apparatus according to claim 4, wherein the wet scrubber is a venturi type scrubber equipped with a venturi tube inside a vertical container, and at least three eliminators are evenly provided in the circumferential direction so as to surround the venturi tube.

6. The amount of exhaust gas cleaning water in the Venturi type scrubber is 1 Nm of exhaust gas. ３ The scrubber apparatus according to claim 5, wherein the volume is 2.6 to 3.0 L per unit.

7. The scrubber device according to claim 5, wherein one spray nozzle is provided for each of at least three of the eliminators in an annular pipe for water supply provided inside at least three of the eliminators.

8. A method for treating exhaust gas, comprising separating and recovering dust containing water-soluble salt crystal particles and mist containing substances derived from such crystal particles from the exhaust gas using a collision plate type eliminator, wherein water is sprayed onto a plurality of plate-shaped members contained in the eliminator so as to constantly form a water film, thereby absorbing the dust and mist collected by collision with the plurality of plate-shaped members into the water film.

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