JP7548064B2 - Gravity settling type dust collector, dust collection method, dust collection equipment, and method for producing zinc oxide ore - Google Patents

Description

The present invention relates to a gravity settling type dust collector, a dust collection method, and a dust collection facility that can be used for exhaust gas treatment in a zinc oxide ore manufacturing plant, and further to a zinc oxide ore manufacturing method that uses the above-mentioned device, method, or facility.

Zinc oxide ore is widely used as a raw material for zinc ingots at zinc smelters. The raw material for this zinc oxide ore is widely used steel dust, a by-product generated from steelmaking furnaces such as blast furnaces and electric furnaces in the steel industry, which contains a relatively large amount of zinc in addition to iron components.

In zinc oxide ore manufacturing plants that use steel dust as a raw material, the steel dust and a reducing agent such as carbon are heated in a reduction roasting furnace, and the high-temperature exhaust gas discharged is introduced into a dust collection facility installed downstream of the reduction roasting furnace to recover the dust-like zinc components (crude zinc oxide dust) contained in the exhaust gas.

The dust collection equipment that recovers crude zinc oxide dust from the high-temperature exhaust gas discharged in the reduction roasting process is usually configured with a gravity settling type dust collector that performs preliminary dust collection, an electric dust collector, and a bag filter connected in this order from the upstream side of the dust collection equipment.

The high-temperature exhaust gas discharged from the reduction roasting furnace is introduced into the gravity settling type dust collector that constitutes the above-mentioned dust collection equipment. A gravity settling type dust collector (see Patent Document 1) that flows the exhaust gas laterally in the internal space of the dust collection chamber and causes the dust in the exhaust gas to settle by gravity is widely used as a gravity settling type dust collector that performs preliminary dust collection processing on such high-temperature exhaust gas.

Here, steel dust contains a relatively large amount of chlorine. Therefore, dioxins may be generated during the reduction roasting process in the reduction roasting furnace. Therefore, in the above-mentioned dust collection equipment that processes the exhaust gas discharged in the reduction roasting process, the exhaust gas is cooled by spraying cooling water, etc., in order to suppress the generation of dioxins (see Patent Document 2).

However, in the above-mentioned type of gravity settling dust collector, which allows the dust in the exhaust gas to settle by gravity while the exhaust gas flows laterally in the internal space of the dust collection chamber, a mixture of the cooling water for cooling the exhaust gas and the dust in the exhaust gas can adhere to the inner wall surface of the dust collector and grow into a mass with a diameter of about 500 mm. Such huge masses can, for example, fall onto the conveyor device installed below the dust collection chamber, causing damage or breakdown of the device, and can cause various breakdowns and damage that interfere with the normal operation of the gravity settling dust collector.

For example, Patent Document 3 discloses a gravity settling dust collector that introduces exhaust gas into the dust collection chamber by spraying it downward from an inner tube located inside the outer shell of the dust collection chamber, and then causes the exhaust gas to rise again after the dust has fallen and is discharged; in other words, it removes dust by causing the exhaust gas to flow mainly vertically. The same document also discloses that in this type of dust collector, the nozzles that spray the cooling water are positioned at an appropriate distance from the bottom end and the inner wall surface on the top side of the inner tube that introduces the gas, and that this makes it possible to prevent the sprayed water from adhering to the inner wall surface of the dust collector as a liquid without evaporating.

However, Patent Document 3 does not mention any means for preventing the cooling water containing crude zinc oxide dust from adhering to the inner wall surface of a gravitational settling type dust collector that causes high-temperature exhaust gas to flow laterally in the internal space of the dust collection chamber while maintaining the cooling effect of the high-temperature exhaust gas.

On the other hand, Patent Document 4 discloses a method of operating a high-temperature furnace in which materials to be treated are treated at high temperatures in a high-temperature combustion furnace, and exhaust gas from the high-temperature furnace is rapidly cooled by forming a gap between the exhaust gas outlet and the duct and drawing the air outside the furnace into the duct together with the exhaust gas.

However, the operating method of Patent Document 4 involves mixing a large amount of air into the exhaust gas at the combustion furnace outlet to rapidly cool it, which increases the amount of exhaust gas and requires a large exhaust gas treatment facility, which in turn results in significant installation and operating costs. Therefore, it is not practical to apply this method to zinc oxide ore manufacturing plants that already have sufficiently large exhaust gas treatment facilities.

Utility Model Publication No. 63-20917 JP 2015-202474 A Japanese Unexamined Patent Publication No. 4-268007 Japanese Patent Application Publication No. 11-61232

The present invention aims to suppress the formation of dust-derived lumps adhering to the inner wall surface of the dust collection chamber in a gravity settling dust collector that causes high-temperature exhaust gas to flow laterally while allowing dust in the exhaust gas to settle by gravity.

The inventors of the present invention came up with the idea that the above-mentioned problems can be solved by arranging the cooling water spray section, which is installed in the dust collection chamber to cool the exhaust gas, in a specific position appropriately adjusted to the flow path of the exhaust gas in a gravity settling dust collector, which causes the dust in the exhaust gas to settle by gravity while the exhaust gas flows laterally in the dust collection chamber, and thus completed the present invention.

(1) A gravity settling type dust collector comprising: a substantially box-shaped dust collecting chamber; a gas inlet pipe for blowing exhaust gas to be treated into the dust collecting chamber from a front wall side of the dust collecting chamber; a gas exhaust pipe for discharging the treated exhaust gas from a rear wall side of the dust collecting chamber; and a cooling water injection unit, the gravity settling type dust collector causing dust in the exhaust gas to settle by gravity while causing the exhaust gas to flow laterally in an internal space of the dust collecting chamber, the gas inlet pipe being installed at an incline facing obliquely downward so that the exhaust gas can be blown obliquely downward from near a top wall on the front wall side of the dust collecting chamber, the cooling water injection unit being installed on an inner wall surface of the front wall below a gas inlet port of the gas inlet pipe, and the tip of the cooling water injection unit being located at a position separated from a high gas concentration region as defined below.
High gas concentration region: a partial spatial region within a dust collection chamber, which, in a vertical cross section when the dust collection chamber is viewed from the side wall side, occupies the range above an imaginary line that starts at the lower end of the gas inlet of the gas inlet pipe and extends diagonally downward along the gas inlet direction of the gas inlet pipe.

The gravity settling dust collector (1) is a type of gravity settling dust collector that allows high-temperature exhaust gas to flow laterally while allowing dust in the exhaust gas to settle by gravity, making it possible to suppress the formation of dust-derived lumps adhering to the inner wall surface of the dust collection chamber.

(2) The gravity settling type dust collector described in (1), in which the cooling water injection unit is a two-fluid nozzle that injects cooling water while crushing it with a high-velocity compressed air stream.

In the gravity settling dust collector of (2), the cooling water injection section is configured with a two-fluid nozzle that can further atomize the cooling water injection form. This promotes proper evaporation of the cooling water particles, and allows the above-mentioned effects of the gravity settling dust collector of (1) to be more stably expressed.

(3) A gravity settling dust collector as described in (1) or (2), in which the distance between the tip of the cooling water injection section and the outer edge of the high gas concentration area is greater than 0 mm and is 100 mm or less.

In the gravity settling dust collector of (3), the distance between the tip of the cooling water injection section is limited to a specific preferred range. This makes it possible to prevent clogging of the injection section due to dust in the exhaust gas adhering to the tip of the cooling water injection section, and also makes it possible to achieve both finer cooling water particles and appropriate contact between the cooling water particles and the gas flow, thereby maintaining a higher level of cooling effect while achieving the above-mentioned effects of the gravity settling dust collector of (1) or (2).

(4) A dust collection method from exhaust gas using a gravity settling type dust collector described in any one of (1) to (3), in which the exhaust gas contains dioxins, and the injection flow rate of the cooling water is adjusted to a flow rate that brings the temperature of the exhaust gas at the inlet of the gas exhaust pipe to a temperature range of 250°C to 280°C.

According to the dust collection method of (4), in performing exhaust gas treatment using a gravity settling dust collector in which high-temperature exhaust gas is caused to flow laterally while the dust in the exhaust gas is allowed to settle by gravity, it is possible to suppress the formation of agglomerates of dust that adhere to the inner wall surface of the dust collection chamber of the dust collector.

(5) A dust collection system comprising a pre-treatment dust collector that is a gravity settling type dust collector described in any one of (1) to (3) and a post-treatment dust collector that is connected downstream of the pre-treatment dust collector and includes a dry dust collector.

According to the dust collection equipment of (5), in a dust collection equipment in which a gravity settling type dust collector that causes high-temperature exhaust gas to flow laterally and causes dust in the exhaust gas to settle by gravity is arranged as a pre-treatment dust collector, it is possible to suppress the formation of dust-derived lumps adhering to the inner wall surface of the dust collection chamber of the pre-treatment dust collector.

(6) A method for producing zinc oxide ore, which includes a reduction roasting process for reducing and roasting a crude zinc oxide raw material, and a crude zinc oxide dust recovery process for separating and recovering zinc-containing crude zinc oxide dust from the exhaust gas discharged in the reduction roasting process, in which the crude zinc oxide dust recovery process separates and recovers the crude zinc oxide dust from the exhaust gas discharged in the reduction roasting process using the dust collection equipment described in (5).

According to the method for producing zinc oxide ore (6), by taking advantage of the above-mentioned effects of the dust collection equipment (5), it is possible to produce zinc oxide ore with higher productivity than conventional methods while sufficiently suppressing the risk of dioxin generation.

According to the present invention, in a gravity settling dust collector that causes dust in high-temperature exhaust gas to settle by gravity while flowing the gas laterally, it is possible to suppress the formation of agglomerates of dust that adhere to the inner wall surface of the dust collection chamber.

1 is a side view (partially see-through) showing a schematic configuration of a gravity settling type dust collector of the present invention. FIG. 1 is a front view showing a schematic configuration of a gravity settling type dust collector of the present invention. FIG. FIG. 2 is a partially enlarged view of FIG. 1 and is a drawing for explaining the installation position of the cooling water injection unit. FIG. 1 is a flow diagram showing the flow of a method for producing zinc oxide ore that can be carried out using the gravity settling type dust collector or dust collection equipment of the present invention. 1 is a block diagram showing a configuration of a dust collection facility including a gravity settling type dust collector of the present invention.

A preferred embodiment of the present invention will now be described. Figure 4 is a flow diagram showing the flow of a method for producing zinc oxide ore that can be suitably carried out using the gravity settling type dust collector, dust collection method, or dust collection equipment of the present invention. The gravity settling type dust collector, dust collection method, or dust collection equipment of the present invention can be particularly preferably used as a technical means for carrying out the process shown in Figure 4, i.e., a process for producing zinc oxide ore by reducing and roasting raw materials containing a certain amount or more of chlorine, such as steel dust.

<Gravity settling type dust collector, dust collection equipment, dust collection method>
The "gravity settling type dust collector" of the present invention is a dust collector that separates and collects particles mixed in gas by gravitational settling from a low-speed air current flowing laterally in the internal space of a dust collection chamber 11. A gravity settling type dust collector 1, which is one embodiment of the gravity settling type dust collector of the present invention, can be preferably used as a device constituting a "dust collection facility" that performs the crude zinc oxide dust recovery step S20 in a "zinc oxide ore manufacturing method" in which the four steps shown in Fig. 4, i.e., the reduction roasting step S10, the crude zinc oxide dust recovery step S20, the wet step S30, and the dry heating step S40, are sequentially performed.

[Dust collection equipment]
The above-mentioned "dust collection equipment", as exemplified as dust collection equipment 100 in Fig. 5, is a composite dust collection equipment including, in order from the side (upstream process side) of the reducing roasting furnace 4 where the reducing roasting process S10 is performed, a gravity settling type dust collector 1 arranged as a pretreatment dust collector, an electric dust collector 2 which is a dry dust collector connected to the downstream side of the gravity settling type dust collector 1, and a bag filter 3. The electric dust collector 2 is an equipment that introduces dust charged by corona discharge into an electric field and collects it on a dust collecting electrode, and the bag filter 3 is an equipment that collects dust remaining in the exhaust gas at the most downstream side of the equipment by filtering it with a filter cloth.

The gravity settling dust collector 1 is a dust collector that excels in collecting particles with a relatively large particle diameter. Therefore, the dust collection equipment 100 is configured such that the gravity settling dust collector 1 is disposed on the most upstream side as a dust collector that performs pre-processing to collect particles with a relatively large particle diameter prior to dust collection by the downstream electric dust collector 2 and the bag filter 3.

[Dust collection method]
The "dust collection method" of the present invention is also a process that can be used as a technical means for carrying out the crude zinc oxide dust recovery step S20 in the above-mentioned "zinc oxide ore manufacturing method". This "dust collection method" is a process that can be carried out using a dust collection facility 100 equipped with a gravity settling type dust collector 1.

[Gravity settling type dust collector]
1 and 2, the gravity settling type dust collector 1 includes a roughly box-shaped dust collection chamber 11 that causes the exhaust gas to flow laterally, a gas inlet pipe 12 that blows the exhaust gas into the dust collection chamber 11 from the front wall 111 side, a gas outlet pipe 13 that discharges the treated exhaust gas from the rear wall 112 side to the outside of the dust collection chamber 11, and a cooling water injection unit 14 installed inside the dust collection chamber 11. In addition, a flow conveyor 15 that transports and collects dust that has settled and separated from the exhaust gas is preferably installed on the bottom side of the dust collection chamber 11.

(Dust collection chamber, gas inlet pipe, gas exhaust pipe)
1 and 2, the dust collection chamber 11 is a substantially box-shaped structure surrounded by a front wall 111 on the gas inlet pipe 12 side, a back wall 112 on the gas exhaust pipe side, a top wall 113, and a pair of side walls 114 along the flow direction of the exhaust gas. A part of the front wall 111 on the top wall 113 side is preferably a front wall inclined part 115 that is inclined to join the gas inlet pipe 12 obliquely downward. A part of the bottom side of the side wall 114 is preferably a side wall inclined part 116 that is inclined in a manner converging toward the flow conveyor 15 at the bottom.

The gas introduction pipe 12 is installed at an angle facing diagonally downward so that exhaust gas can be blown diagonally downward from near the top wall 113 on the front wall 111 side of the dust collection chamber 11. The gas introduction pipe 12 is preferably installed in such a manner that it is joined to the front wall inclined portion 115 and forms a gas introduction port 121 that opens through the inclined portion.

The gas exhaust pipe 13 is installed at the end on the rear wall 112 side of the top wall 113 or in a nearby area so that the gas can be exhausted on the rear wall 112 side of the dust collection chamber 11.

In the gravity settling type dust collector 1 having the dust collection chamber 11, gas inlet pipe 12 and gas exhaust pipe configured as described above, the dust concentration distribution in the exhaust gas blown into the dust collection chamber 11 from the gas inlet pipe 12 is relatively higher in the region (region A in Figure 1) above an imaginary line (line d in Figure 1) that starts from the lower end of the gas inlet 121 at the end of the gas inlet pipe 12 and extends diagonally downward along the gas inlet direction of the gas inlet pipe 12, in a vertical cross section when the dust collection chamber 11 is viewed from the side wall 114 side, than in the region (region B in Figure 1) below the same imaginary line. In this specification, the above-mentioned region A, i.e., "a partial spatial region in the dust collection chamber, which occupies a range above a virtual line extending diagonally downward along the gas introduction direction of the gas introduction tube from the lower end of the gas introduction port of the dust collection chamber in a vertical cross section when the dust collection chamber is viewed from the side wall side" is defined as the "high gas concentration region" in the dust collection chamber. Also, the partial spatial region in the dust collection chamber excluding the "high gas concentration region" (region B in FIG. 1) is defined as the "low gas concentration region" in the dust collection chamber. Also, the gas introduction direction of the gas introduction tube mentioned above refers to the direction along the lower outer edge of the gas introduction tube (direction d in FIG. 3) defined by the inclination angle of the gas introduction tube in FIG. 3 (the angle of depression angle θ in FIG. 3).

(Cooling water injection part)
The structure of the cooling water injection unit 14 is not limited to a specific structure as long as it can inject the cooling water in a desired manner. However, in the gravity settling type dust collector 1, it is essential that the arrangement of the cooling water injection unit 14 is limited to a specific position range by a requirement derived from a unique technical idea. The "first requirement" of the arrangement of the cooling water injection unit 14 in the gravity settling type dust collector 1 is that it is installed on the inner wall surface of the front wall 111 of the dust collection chamber 11 below the gas inlet 121 of the gas introduction pipe 12. And the "second requirement" is that the tip of the cooling water injection unit 14 is located away from the "high gas concentration region" defined above.

In a gravity settling dust collector 1 equipped with a gas inlet pipe 12 that blows exhaust gas into the dust collection chamber diagonally downward from near the top wall 113 on the front wall 111 side, the arrangement of the cooling water injection unit 14 satisfies the above-mentioned "first requirement" and "second requirement", so that cooling water can be sprayed from the rear of the flow of high-temperature exhaust gas to be treated that flows roughly horizontally through the internal space of the dust collection chamber 11, and the injected cooling water can be diffused and reach the "high gas concentration region (region A)" in a sufficiently atomized state. This promotes the evaporation of moisture from the cooling water particles that come into contact with and absorb dust, and prevents the cooling water particles from reaching and adhering to the inner wall surface of the dust collection chamber 11 in liquid form, thereby reducing the generation of dust-derived agglomerates that grow while adhering to the inner wall surface.

In addition, by having the tip of the cooling water injection part 14 located away from the "high gas concentration region" defined above, i.e., by satisfying the above "second requirement," it is possible to prevent the tip of the cooling water injection part 14 from continuously coming into contact with high concentration gas, causing nozzle clogging and causing the cooling water to splash in the direction of the inner wall surface and wet the inner wall surface. This effect also makes it possible to reduce the generation of dust-derived agglomerates that grow while attached to the inner wall surface.

Here, in conventional gravity settling dust collectors, the cooling water injection section 14 is generally positioned with a priority given to ensuring that the cooling water reaches the area with the highest gas concentration as quickly as possible in order to increase cooling efficiency. A specific example of such a conventional cooling water injection section position is the gravity settling dust collector 1 of FIG. 1, in which the cooling water injection section is positioned in an area closer to the front wall 111 on the inner wall surface of the top wall 113, rather than in the position shown in the figure (not shown).

When the cooling water injection unit 14 is positioned as described above, there is a high probability that the cooling water will come into contact with the dust present in high concentrations before it can fully diffuse inside the dust collection chamber 11, and this type of contact will result in the formation of a large number of particles with crude zinc oxide dust trapped inside. This large number of particles containing such dust will reach the inner wall surface of the dust collection chamber 11 as a liquid without the water having fully evaporated, and will adhere to the surface, causing the formation of huge clumps of dust-derived material that will grow while attached to the inner wall surface.

In contrast, in the gravity settling dust collector 1 of the present invention, the cooling water injection section 14 is arranged so that its tip is located behind the "high gas concentration region" in the flow direction, i.e., the cooling water injection section 14 is located behind the gas flow and its tip does not enter the "high gas concentration region" (see Figure 3). As a result, the cooling water injected from the tip of the cooling water injection section 14 is first diffused to a certain degree or more in the region (region B) where the dust concentration is relatively low, i.e., atomized to a certain degree or more, and then reaches the "high gas concentration region (region A)" and comes into contact with the dust in the gas that is present at a high concentration. Therefore, compared to the general arrangement of the cooling water injection section described above, the moisture of the cooling water particles in the state in which dust has been taken in after contacting the dust can be evaporated more quickly.

In addition, the nozzle becomes clogged when the tip of the cooling water injection part 14 continues to come into contact with high concentration gas, and the cooling water splashes in the direction of the inner wall surface, wetting the inner wall surface, causing a large amount of dust particles to adhere to the surface, further promoting the formation of huge clumps of dust that grow while attached to the inner wall surface.

In contrast, in the gravity settling dust collector 1 of the present invention, as described above, the tip of the cooling water injection part 14 is positioned so that it does not enter the "high gas concentration area", which prevents the nozzle from clogging due to the tip of the cooling water injection part 14 continuing to come into contact with high concentration gas. As described above, this action also prevents the formation of large dust-derived agglomerates on the inner wall surface of the dust collection chamber 11.

Regarding the above-mentioned "second requirement" regarding the arrangement of the cooling water injection part 14, specifically, the distance between the tip of the cooling water injection part 14 and the outer edge of the "high gas concentration area" (distance S shown in FIG. 3) is preferably more than 0 mm and less than 100 mm, and more preferably 10 mm or more and less than 100 mm. By making this distance S at least more than 0 mm, it is possible to avoid the entire surface of the tip of the cooling water injection part 14 entering the "high gas concentration area" and the front surface of the tip being covered with high concentration gas, thereby preventing the generation of a large amount of large water particles containing dust. Furthermore, it is possible to reduce the risk of nozzle clogging due to the tip of the cooling water injection part 14 continuing to come into contact with high concentration gas. In addition, by making the distance S 10 mm or more, it is possible to promote the diffusion of the injected cooling water. In other words, it is possible to promote the atomization of the cooling water. On the other hand, by keeping the distance S at 100 mm or less, it is possible to suppress the generation of large dust-derived agglomerates on the inner wall surface of the dust collection chamber 11 while maintaining a high level of cooling effect.

The arrangement of the cooling water injection unit 14 may be any arrangement that satisfies both the above-mentioned "first requirement" and "second requirement," and other detailed arrangement conditions are not particularly limited. However, as a specific example of a preferred arrangement of the cooling water injection unit 14, as shown in FIG. 2, a pair of spray nozzles are arranged symmetrically side by side with the gas inlet 121 between them at the same height position that satisfies the above-mentioned two requirements.

The cooling water injection unit 14 can be configured with any conventionally known spray nozzle, etc., without any particular limitations, so long as it has the function of spraying cooling water in the desired manner. However, as the spray nozzle that constitutes the cooling water injection unit 14, it is particularly preferable to use a two-fluid nozzle that injects cooling water while crushing it with a high-speed airflow of compressed air.

The spray angle of the cooling water from the cooling water spray unit 14 is preferably adjusted so that the sprayed cooling water does not reach the inner wall surface of the side wall 114 of the dust collection chamber 11 as a liquid without evaporating. This adjustment can be performed, for example, by optimizing the position of the spray nozzle of the cooling water spray unit 14 and the spray angle of the cooling water. In order to obtain a desired spray angle, it is also a preferred embodiment of the present invention to prepare multiple spray nozzles with different spray angles in advance and adjust the spray angle by replacing the spray nozzle with the one that has the desired spray angle each time. The above "spray angle" refers to the size of the apex angle of the cone shape defined by the outer edge of the diffusion range of the sprayed water, with the spray nozzle of the cooling water spray unit 14 as the apex.

It is preferable that the "jet angle" of the cooling water jetting unit 14 is adjusted to a range in which the cooling water does not evaporate and does not reach the inner wall surface of the dust collection chamber 11 as a liquid. As long as such requirements are met, there is no restriction to a specific angle range. However, when the "jet angle" becomes a certain size or more, the distance until the cooling water jetted from the tip of the cooling water jetting unit 14 reaches the inner wall surface of the side wall 114 in the dust collection chamber 11 inevitably becomes short, so the maximum angle that can ensure this distance as a distance that the cooling water does not evaporate and reach the inner wall surface as a liquid becomes the upper limit value of the practically preferable "jet angle". On the other hand, when the "jet angle" becomes smaller than a certain size, the flux density of the jetted cooling water increases accordingly, and there is a high risk that the cooling water will not be sufficiently diffused before reaching the "high gas concentration region". Therefore, it is preferable to make the jet angle as large as possible within the above-mentioned preferable upper limit value range. As a general guideline, the preferable angle range of the jet angle of the cooling water from the cooling water jetting unit 14 is about 20° to 30°.

It is preferable to adjust the flow rate of the cooling water injected from the cooling water injection unit 14 to a flow rate at which the gas temperature of the treated exhaust gas at the inlet of the gas exhaust pipe 13 is in a temperature range in which the resynthesis of dioxins is suppressed. The dioxins resynthesized inside the dust collection chamber 11 of the gravity settling type dust collector 1 are adsorbed by the activated carbon injected into the exhaust gas discharged from the electric dust collector 2. However, if the amount of dioxins resynthesized becomes excessive, there is a concern that the adsorption load of the activated carbon will be overloaded, making it difficult to recover the dioxins. For this reason, it is preferable to adjust the flow rate of the cooling water injected in the gravity settling type dust collector 1 to a flow rate at which the gas temperature of the exhaust gas at the inlet of the gas exhaust pipe 13 is in a temperature range of 250°C to 280°C. By adjusting the flow rate of the cooling water injected from the cooling water injection unit 14 to such a flow rate, the resynthesis of dioxins can be reduced. In addition, by keeping the temperature of the treated exhaust gas within the above range, it is also possible to reduce the formation of dust-derived agglomerates that grow while adhering to the inner wall surface of the dust collection chamber 11.

The flow rate of the cooling water injected from the cooling water injection unit 14 can be adjusted, for example, by manually adjusting the adjustment valve while monitoring the gas temperature of the exhaust gas at the inlet of the gas exhaust pipe 13. However, this is not limited to this, and for example, a control unit for controlling the injection flow rate of the cooling water in a PLC (programmable logic controller) and a sensor for detecting the gas temperature of the exhaust gas at the inlet of the gas exhaust pipe may be provided to automatically control the adjustment valve.

<Method of manufacturing zinc oxide ore>
The basic flow of a general method for producing zinc oxide ore is as shown in Figure 4. Usually, zinc oxide ore is produced by a production method that sequentially performs a reduction roasting step S10 in which zinc-containing ore such as steel dust is reduced and roasted in a heating furnace such as a reduction roasting rotary kiln (RRK) to volatilize the zinc component, a crude zinc oxide dust recovery step S20 in which crude zinc oxide dust is recovered from exhaust gas discharged from the reduction roasting step, a wet step S30 in which halogens such as chlorine and cadmium are separated and removed from the crude zinc oxide dust to obtain a crude zinc oxide cake, and a dry heating step S40 in which the crude zinc oxide cake is dry heated in a dry heating rotary kiln (DRK) to obtain zinc oxide ore.

The "zinc oxide ore manufacturing method" according to the present invention is a process in which the separation and recovery of crude zinc oxide dust from exhaust gas, which is carried out in the crude zinc oxide dust recovery step S20 among the above steps, is carried out using a dust collection system 100 including the gravity settling type dust collector 1 of the present invention.

[Reduction roasting process]
The reduction roasting step S10 is a step of performing a reduction roasting process on zinc-containing ore such as steel dust. The reduction roasting process is usually performed by roasting the zinc-containing ore and the reducing material using a reduction roasting furnace such as a reduction roasting rotary kiln (RRK). The reduction roasting rotary kiln (RRK) is a rotary heating furnace that includes a kiln body that is a fire-resistant cylindrical pot, a burner unit provided near the discharge port side of the kiln body, and a drive gear that transmits a rotational force to the kiln body. In the manufacturing process of zinc oxide ore, a kiln body having a furnace length of about 50 m is often used.

The reducing roasting furnace is charged with raw materials in which steel dust has been pelletized in advance together with a reducing agent such as coke. The zinc in the steel dust is reduced and volatilized as zinc vapor by the action of carbon monoxide generated by the combustion of the coke, and the iron in the steel dust remains in the reducing roasting furnace as metallic iron and is discharged from the discharge end as clinker. The temperature of the exhaust gas discharged in the reducing roasting process is 500 to 700°C, and the gas flow rate is 25,000 to 27,000 Nm ³ /h. The typical composition of the exhaust gas is 5 vol% CO ₂ , 14 vol% O ₂ , 2 vol% CO, and 4 to 5 vol% H ₂ O. The zinc vapor volatilized in the reducing roasting furnace is reoxidized and transformed into zinc oxide, which becomes crude zinc oxide dust. The typical concentration of zinc oxide dust contained in the exhaust gas from the reducing roasting furnace is about 100 to 200 g/Nm ³ . Moreover, this crude zinc oxide dust generally contains about 8 to 20% of halogen impurities such as chlorine.

[Crude zinc oxide dust recovery process]
The crude zinc oxide dust recovery step S20 is a step of recovering crude zinc oxide dust from the zinc-containing exhaust gas discharged from the reduction roasting furnace 4 in which the reduction roasting step S10 is carried out.

In the crude zinc oxide dust recovery process S20, the exhaust gas discharged from the reduction roasting furnace 4 is passed sequentially through a gravity settling dust collector 1, an electric dust collector 2, and a bag filter 3 that constitute the dust collection equipment 100, to recover crude zinc oxide dust.

In the crude zinc oxide dust recovery process S20, the exhaust gas discharged from the reduction roasting furnace 4 is first introduced into the gravity settling dust collector 1. The exhaust gas containing the crude zinc oxide dust discharged in the reduction roasting process S10 is rapidly cooled naturally, but is further cooled by cooling water in the gravity settling dust collector 1. The exhaust gas cooled in this way is then sequentially introduced into the downstream electric dust collector 2 and the bag filter 3. In the process of introduction from the electric dust collector 2 to the bag filter 3, activated carbon is blown into the exhaust gas discharged from the electric dust collector 2. By attaching the activated carbon to the surface of the filter cloth of the bag filter 3 while the dioxins remaining in the exhaust gas are adsorbed, the dioxins in the exhaust gas can be further removed.

[Wet process]
The wet process S30 is a process in which water-soluble impurities such as chlorine and fluorine contained in the crude zinc oxide dust obtained in the crude zinc oxide dust recovery process S20 are separated and extracted into a treatment liquid, and further, impurities are removed from the crude zinc oxide dust by a water washing method through a solid-liquid separation process, thereby obtaining a crude zinc oxide cake.

[Drying and heating process]
The dry heating step S40 is a step for producing high-quality zinc oxide ore while further reducing the halogen concentration by calcining the crude zinc oxide cake obtained in the wet step S30. Usually, the calcination is carried out using a dry heating rotary kiln (DRK). A dry heating rotary kiln (DRK) is a rotary heating furnace having the same basic structure as an RRK, and in the process for producing zinc oxide ore, a main furnace length of about 30 m is often used.

In the drying and heating step S40, the size of the zinc oxide ore discharged from the DRK is generally 1 mm to 6 mm, and its general composition is 60% to 70% by mass zinc, 3% to 5% by mass lead, 0.5% to 1.5% by mass chlorine, and approximately 0.6% by mass or less fluorine (all on a dry weight basis).

In a crude zinc oxide production plant capable of carrying out the overall process shown in Figure 4, a test run was carried out to produce crude zinc oxide ore using the production method of the present invention. The operating conditions for the test runs of each Example and Comparative Example are as follows. In each run, the form of agglomeration on the inner wall surface of the dust collection chamber of the gravity settling dust collector was observed, and the dioxin concentration of the exhaust gas discharged from the bag filter was also measured. The measurement and observation results were as shown in Table 1 below.

[Example 1]
(Reduction roasting process)
Steel dust, which is a raw material for crude zinc oxide, was charged into a reduction roasting rotary kiln (RRK) together with a carbonaceous reducing agent such as coke and limestone, and reduction roasting treatment was carried out while controlling the temperature of the reduction roasting rotary kiln so that the maximum temperature of the treated material was 1000 to 1400°C.

(Crude zinc oxide dust recovery process)
The crude zinc oxide dust generated in the reduction roasting process was collected using a gravity settling type dust collector (dust collector for pre-treatment) and an electric dust collector and a bag filter (dust collector for post-treatment) connected downstream of the gravity settling type dust collector.

For the crude zinc oxide dust recovery process, a gravity settling dust collector with a length of 16 m in the longitudinal direction along the exhaust gas flow, a length of 4 m in the vertical direction, and a length of 3 m in the lateral direction was used. The cooling water injection section was configured by installing a pair of spray nozzles on the inner wall surface of the front wall. These spray nozzles were used to inject cooling water toward the exhaust gas flow from behind the flow of crude zinc oxide dust in the exhaust gas. The installation positions of both spray nozzles were at a height position 100 mm below the lower end of the gas inlet. The tips of the spray nozzles were positioned away from the "high gas concentration region". Specifically, the distance from the tip of the spray nozzle to the outer edge of the "high gas concentration region" (distance S shown in Figure 3) was set to 10 mm.

The spray nozzle used had a spray angle of 20°, and the spray flow rate of the cooling water was adjusted to a flow rate that would bring the exhaust gas temperature at the gas exhaust pipe inlet to 280°C. The spray flow rate at this time was 25 L/min on average.

Test operation was carried out under the above conditions for one month, and the dioxin concentration of the exhaust gas discharged from the bag filter was measured. If lumps of 500 mm or more were formed on the inner wall surface of the dust collection chamber during the test period, they were removed. The number of times that lump removal work was required during the operation period, and the measurement results of the dioxin concentration are shown in Table 1.

[Example 2]
Except for using a spray nozzle with a spray angle of 35°, the test operation, removal of lumps that had grown on the inner wall surface, and measurement of dioxin concentration were carried out under the same conditions as in Example 1. The number of times lump removal work was required during the operation period and the measurement results of dioxin concentration are shown in Table 1.

[Comparative Example]
Both spray nozzles were installed at a height position 100 mm below the lower end of the gas inlet. The tips of the spray nozzles were positioned so as to penetrate into the "high gas concentration region". Specifically, the spray nozzles were positioned so that a portion 10 mm from the tips penetrated into the "high gas concentration region". As for other conditions, the test operation, the removal of the lumps that had grown on the inner wall surface, and the measurement of the dioxin concentration were performed under the same conditions as in Example 2. The number of times the lump removal operation was required during the operation period and the measurement results of the dioxin concentration are shown in Table 1.

In Comparative Example 1, which shows a conventional embodiment, the dioxin concentration was 0.04 (ng-TEQ/ ^Nm3 ), which was significantly lower than the legal limit of 10 (ng-TEQ/ ^Nm3 ), but the crude zinc oxide dust adhered to the inner wall surface of the gravity settling type dust collector, and lumps were frequently formed. As a result, work to remove these lumps occurred 15 times per month.

On the other hand, in Example 2, although the crude zinc oxide dust adhered to the inner wall surface of the gravity settling dust collector and formed lumps, the number of operations required to remove these lumps was reduced to four times per month, significantly reducing the number of operations.

Furthermore, in Example 1, the crude zinc oxide dust no longer adheres to the inner wall surface of the gravity settling type dust collector, and the operation of removing the above-mentioned lumps is no longer necessary.

The above results show that the gravity settling dust collector of the present invention can be used in a zinc oxide ore manufacturing plant that uses crude zinc oxide containing a large amount of chlorine, such as steel dust, as a raw material to sufficiently suppress the generation of dioxins in the reduction roasting process, while significantly suppressing the adhesion of crude zinc oxide dust to the gravity settling dust collector that recovers crude zinc oxide dust from the exhaust gas discharged in the process, thereby significantly improving productivity while maintaining safety.

REFERENCE SIGNS LIST 1 Gravity settling type dust collector 11 Dust collection chamber 111 Front wall 112 Rear wall 113 Top wall 114 Side wall 115 Front wall inclined portion 116 Side wall inclined portion 12 Gas inlet pipe 121 Gas inlet 13 Gas exhaust pipe 14 Cooling water injection section 15 Flow conveyor 2 Electrical dust collector 3 Bag filter 100 Dust collection equipment S10 Reduction roasting process S20 Crude zinc oxide dust recovery process S30 Wet process S40 Drying heating process

Claims (6)

A roughly box-shaped dust collection chamber;
a gas introduction pipe for blowing the exhaust gas to be treated into the dust collection chamber from the front wall side of the dust collection chamber;
a gas exhaust pipe for exhausting the treated exhaust gas from a rear wall side of the dust collecting chamber;
A cooling water injection unit;
Equipped with
A gravity settling type dust collector that collects dust by causing dust in the exhaust gas to settle by gravity while causing the exhaust gas to flow laterally in an internal space of the dust collection chamber,
the gas introduction pipe is installed at an incline obliquely downward so that the exhaust gas can be blown into the dust collection chamber obliquely downward from the vicinity of a top wall on the front wall side of the dust collection chamber,
The cooling water jetting unit is installed on the inner wall surface of the front wall below the gas inlet of the gas inlet pipe, and a tip of the cooling water jetting unit is located at a position away from a high gas concentration region defined as follows:
Gravity settling type dust collector.
(High gas concentration region): A partial spatial region within the dust collection chamber, which, in a vertical cross section when the dust collection chamber is viewed from the side wall side, occupies the range above an imaginary line that starts at the lower end of the gas inlet of the gas inlet pipe and extends diagonally downward along the gas inlet direction of the gas inlet pipe. The cooling water injection unit is a two-fluid nozzle that injects cooling water while crushing it with a high-speed airflow of compressed air.
2. The gravity settling type dust collector according to claim 1. The distance between the tip of the cooling water injection part and the outer edge of the high gas concentration region is more than 0 mm and 100 mm or less.
3. A gravity settling type dust collector according to claim 1 or 2. A method for collecting dust from an exhaust gas using the gravity settling type dust collector according to any one of claims 1 to 3,
The exhaust gas is a gas containing dioxins,
The injection flow rate of the cooling water is adjusted to a flow rate at which the temperature of the exhaust gas at the inlet of the gas exhaust pipe is in the range of 250° C. or more and 280° C. or less.
Dust collection method. A pre-treatment dust collector which is the gravity settling type dust collector according to any one of claims 1 to 3, and a post-treatment dust collector which is connected downstream of the pre-treatment dust collector and includes a dry dust collector.
Dust collection equipment. A method for producing zinc oxide ore, comprising: a reduction-roasting step of reducing and roasting a crude zinc oxide raw material; and a crude zinc oxide dust recovery step of separating and recovering zinc-containing crude zinc oxide dust from exhaust gas discharged in the reduction-roasting step,
In the crude zinc oxide dust recovery step, separation and recovery of the crude zinc oxide dust from the exhaust gas discharged in the reduction roasting step is performed by the dust collection equipment according to claim 5.
How zinc oxide ore is produced.

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