Piping system for environmental dust collection and environmental dust collection method using the same

Abstract

To provide a piping system for environmental dust collection capable of preventing block of a bent part of the piping of the environmental dust collection, and an environmental dust collection method using therewith.SOLUTION: A piping system for environmental dust collection for transferring, to a dust collecting facility, in-furnace gas containing dust and leaking from a smelting furnace like a rotary kiln, has an inspection hole 21 at an upstream side or a downstream side proximal to the bent part B of a piping 20 for the environmental dust collection bent at an angle of 30 degrees or more and 60 degrees or less. An electromagnetic drive type knocker 22 is provided downstream proximal to the bent part B, preferably at a position downstream the inspection hole 21.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to an environmental dust collection piping system for transferring furnace gas containing dust leaking from a smelting furnace to dust collection equipment, and an environmental dust collection method using the environmental dust collection piping system.

Background Art

[0002] The Waelz process is known in which raw materials containing zinc oxides such as electric furnace dust and steel dust are subjected to reduction roasting treatment in a smelting furnace, and low-boiling zinc reduced and volatilized from the raw materials is re-oxidized and recovered as crude zinc oxide dust. A rotary kiln having a structure in which a cylindrical furnace body is placed horizontally is frequently used for the above-mentioned smelting furnace. Since both the charging end portion on the raw material charging side and the discharging end portion on the discharging side of the residue remaining in the furnace body after reduction roasting are open, both of these end portions are surrounded by fixed hoods. Since the furnace body rotates about its axis with respect to the fixed hoods at both ends, a gap is provided between the outer peripheral surfaces of both ends of the furnace body and the side walls on the furnace body side of each fixed hood. And in order to suppress the intrusion of outside air into the rotary kiln from this gap portion, or conversely, the leakage of the furnace gas in the rotary kiln to the outside, the gap portion has a seal structure.

[0003] The internal pressure of the rotary kiln in which the reduction roasting treatment by the above-mentioned Waelz process is usually maintained slightly on the negative pressure side, but the internal pressure may temporarily become higher than the outside air pressure due to fluctuations in operating conditions caused by disturbances. At that time, since the dust containing zinc oxide generated in the rotary kiln passes through the seal structure together with the furnace gas and leaks to the outside, it becomes a problem that the working environment around the rotary kiln deteriorates. Therefore, an end portion of an environmental dust collection pipe is connected to the seal portion of the above-mentioned rotary kiln, and the dust containing powdery zinc oxide leaked together with the furnace gas is recovered by an environmental dust collection equipment such as a bag filter through this environmental dust collection pipe.

[0004] The above structure prevents deterioration of the working environment around the rotary kiln even if dust containing fine zinc oxide leaks out from the seal portion of the rotary kiln along with the furnace gas. However, blockages in the piping due to zinc oxide-containing dust frequently occurred at bends in the environmental dust collection piping. When a blockage occurred in the piping, the worker had to either strike the blocked portion of the piping from the outside with a hammer or insert a jig through an inspection hole provided at the bend to remove the blockage. Thus, when a blockage occurred in the piping, it was necessary to perform time-consuming and complicated work, which placed an excessive burden on the worker.

[0005] Therefore, as described above, there is a need for a technology that can resolve the problem of blockage in pipes without requiring complicated work by workers, and various technologies have been proposed for this purpose. For example, Patent Document 1 discloses a technology in which a superabsorbent polymer is sprayed onto wet mineral raw materials before or during transport using pipes, etc. It is stated that this allows the wet mineral raw materials to be transported in a highly slippery mixture with the superabsorbent polymer, thereby preventing adhesion and blockage in the pipes. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2018-058017 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, the technology described in Patent Document 1 above targets coal and iron ore stored in raw material yards, etc., as the objects to be prevented from clogging or adhering to pipes. It is unlikely that the same effect will be achieved in preventing clogging by dust generated when powder produced by heat treatment inside a smelting furnace such as a rotary kiln leaks out along with the furnace gas. Furthermore, in the technology described in Patent Document 1, the recovered dust contains superabsorbent polymers, which cannot be reused as is, and the high cost of these superabsorbent polymers can be a problem. The present invention has been made in view of the above-mentioned problems of conventional smelting furnaces, and aims to provide an environmental dust collection piping system that can prevent clogging inside pipes at bends in the environmental dust collection piping, and an environmental dust collection method using the environmental dust collection piping system. [Means for solving the problem]

[0008] To achieve the above objective, the environmental dust collection piping system according to the present invention is an environmental dust collection piping system for transferring furnace gas containing dust leaking from a smelting furnace to a dust collection facility, characterized in that an inspection hole is provided immediately upstream or downstream of a bend in the piping that is bent at an angle of 30 degrees or more and 60 degrees or less, and a knocker is provided immediately downstream of the bend and downstream of the inspection hole.

[0009] Furthermore, the environmental dust collection method according to the present invention collects dust leaking from inside the smelting furnace with an average dust concentration of 0.4 g / m³. 3 The above describes an environmental dust collection method for transferring furnace gas containing a temperature of 100°C or higher to a dust collection facility via an environmental dust collection piping system, characterized in that an inspection hole is provided immediately upstream or downstream of a bend in the piping that is bent at an angle of 30 degrees or more and 60 degrees or less, and a position immediately downstream of the bend and downstream of the inspection hole is periodically struck with a knocker. [Effects of the Invention]

[0010] According to the present invention, it is possible to prevent blockage inside the pipe at bends in the environmental dust collection piping. [Brief explanation of the drawing]

[0011] [Figure 1] This is a side view of a rotary kiln to which the environmental dust collection piping system of the present invention is suitably applied. [Figure 2] This is a cross-sectional view of the seal area enclosed by the dotted circular section in Figure 1. [Figure 3] This is a side view of various specific examples of the environmental dust collection piping system of the present invention. [Figure 4] This is a perspective view of specific example (a) in Figure 3. [Modes for carrying out the invention]

[0012] First, as an example of a smelting furnace in which the environmental dust collection piping system according to the present invention is suitably employed, a rotary kiln in which a reduction roasting process is performed using the Wertz method will be described in detail with reference to Figure 1. The rotary kiln shown in Figure 1 mainly consists of a furnace body 1, which is a metal cylindrical body with its inner surface lined with refractory bricks (not shown) and is positioned horizontally, and an input-side hood 2 and an output-side hood 3 that surround the input-side end and the output-side end, respectively.

[0013] At least two annular tires 4 are provided concentrically on the outer circumference of the furnace body 1, spaced apart in the axial direction, and each is rotatably supported by two support rollers 5. The furnace body 1 is tilted slightly from the horizontal so that its discharge end is located below its charging end. An annular girth gear 6 is further provided concentrically on the outer circumference of the furnace body 1, and a motor-driven pinion gear 7 meshes with this girth gear 6.

[0014] With the above configuration, the raw materials charged together with a reducing agent such as coke from the inlet 8 on the charging end side are stirred within the rotating furnace body 1 and gradually move toward the discharge end side. At that time, the raw materials are subjected to a reducing roasting treatment by a high-temperature atmosphere, preferably around 1000 to 1400°C, more preferably around 1100 to 1200°C, generated by the combustion of the fuel introduced from the burner 9 located on the discharge end side of the furnace body 1 and the reducing agent charged from the inlet 8.

[0015] The reduction roasting process described above reduces and volatilizes the zinc oxide in the raw material, and the resulting zinc vapor is reoxidized to produce finely powdered zinc oxide. This finely powdered zinc oxide is discharged along with the furnace gas through the duct 10 of the charging-side hood 2 of the furnace body 1 and is recovered as crude zinc oxide dust in recovery equipment such as an electrostatic precipitator (not shown). On the other hand, the residue remaining in the furnace body 1 after the reduction roasting process is discharged as clinker from the bottom of the discharge-side hood 3.

[0016] In rotary kilns that handle powdered materials, such as the rotary kiln in which the Wertz process described above is performed, the charging hood 2 and the discharge hood 3 surrounding both ends of the furnace body 1 have a sealing structure in the gap between their respective furnace body side walls and the outer circumference of the furnace body 1, extending around the entire circumference of the furnace body 1. Furthermore, to prevent dust leaking out with the furnace gas from this sealing area from being blown around outside the rotary kiln, collection hoods 2a and 3a are provided on the furnace body side walls of the charging hood 2 and the discharge hood 3, respectively, so as to cover both ends of the furnace body 1 from above. The ends of the environmental dust collection piping 20 are connected to the sealing areas of the charging hood 2 and the discharge hood 3, as well as to their collection hoods 2a and 3a, in order to transfer the dust leaked out with the furnace gas to an environmental dust collection system.

[0017] Figure 2 shows a cross-sectional view of the sealing structure in the gap between the furnace body side wall of the discharge hood 3 and the outer circumference of the furnace body 1, along with the surrounding collection hood 3a and the end of the environmental dust collection piping 20. The sealing structure of the rotary kiln's charge-side hood 2 and its surroundings are almost identical to the structure shown in Figure 2, except for a horizontal reversal, so their explanation is omitted for brevity.

[0018] Specifically explaining the structure of FIG. 2, the seal structure of the gap between the furnace body side wall of the discharge side hood 3 and the outer periphery of the furnace body 1 is a labyrinth seal, which prevents the leakage of the furnace gas in the rotary kiln to the outside and, conversely, the intrusion of outside air into the furnace. However, when the internal pressure of the rotary kiln fluctuates and becomes higher than the outside air pressure, as indicated by the black arrow, the furnace gas containing dust may leak out of the rotary kiln through the labyrinth seal. In order to prevent the directly atmospheric discharge of the leaked furnace gas containing dust, the first branch pipe 20a of the environmental dust collection pipe 20 is connected to the outlet side portion of the labyrinth seal.

[0019] Most of the furnace gas containing dust passing through the above-mentioned labyrinth seal flows into the environmental dust collection pipe 20 through this first branch pipe 20a, but a part leaks to the outside through the gap between the outlet side portion of the labyrinth seal and the outer periphery of the furnace body 1. In order to recover the furnace gas containing dust leaked to the outside, the second branch pipe 20b of the environmental dust collection pipe 20 is connected to the environmental collection hood 3a. Further, in order to reduce the amount of dust passing through the labyrinth seal together with the furnace gas as much as possible, the third branch pipe 20c of the environmental dust collection pipe 20 is connected to the furnace body side wall of the discharge side hood 3.

[0020] As described above, the environmental dust collection pipe 20 having a plurality of branch pipes into which the furnace gas containing dust flows at its end is mainly composed of a pipe system including a straight pipe and a bent pipe. In this pipe system, as shown in FIGS. 3(a) and (b), an inspection hole 21 is provided on the immediate upstream side or downstream side of the bending portion B of the pipe bent at an angle θ of 30 degrees or more and 60 degrees or less. Further, a knocker 22 is provided at a position on the immediate downstream side of the bending portion B and downstream of the inspection hole 21. With such a structure, it is possible to prevent the blockage of the pipe inside at the bending portion B of the environmental dust collection pipe 20.

[0021] To explain in more detail, even if high-temperature furnace gas containing dust such as zinc oxide powder leaks from the seal portion, which is the opening to the outside of the smelting furnace, as in the rotary kiln performing the reduction roasting process by the Wertz method described above, the end of the environmental dust collection piping 20 can be connected to the outlet side of the seal portion or to the collection hood covering this portion, and the leaked furnace gas can be sucked in by a fan (not shown), thereby capturing the dust contained in the leaked furnace gas with environmental dust collection equipment such as a bag filter (not shown) installed at the end of the environmental dust collection piping 20. As a result, it becomes possible to release clean gas, with most of the dust removed, into the atmosphere.

[0022] Incidentally, depending on the processing conditions in the smelting furnace described above, the high-temperature furnace gas containing the dust described above may contain vapor. Even if such vapor-containing furnace gas leaks out, the possibility of condensation is low if the temperature of the gas flowing through the environmental dust collection piping 20 exceeds 100°C, at least from the opening where the leak in the smelting furnace occurs to the inspection hole 21, preferably throughout the entire environmental dust collection piping 20 up to the environmental dust collection equipment. Furthermore, if the flow velocity of the gas flowing through the environmental dust collection piping 20 is fast enough to transport the dust contained in the leaked furnace gas, problems such as accumulation or blockage of this dust within the environmental dust collection piping 20 are less likely to occur, and the dust contained in the leaked gas can be transported to the environmental dust collection equipment.

[0023] However, at points where the environmental dust collection piping 20 is bent at an angle of 30 degrees or more and 60 degrees or less, a region is created within the piping where the gas flow velocity decreases, so the average dust concentration of the leaked furnace gas is, for example, 0.4 g / m³. 3When the dust concentration is high, dust tends to accumulate in this region, and in some cases, this can cause blockages in the piping. In particular, when performing processes that produce chlorine volatilization reactions or reductive volatilization reactions in the above-mentioned smelting furnace, the volatilized reaction products remain in the air inside the furnace, resulting in a very high dust concentration in the space inside the smelting furnace. Therefore, if this furnace gas with a very high dust concentration leaks out from the openings of the smelting furnace, the above-mentioned blockage problem is likely to occur. The average dust concentration is the average value obtained by taking dust concentration measurements multiple times. Generally, the dust concentration can be calculated by drawing in exhaust gas through an inspection hole at a speed equal to the exhaust gas flow velocity using a suction nozzle, filtering and collecting the dust, and then calculating the dust concentration from the mass of the collected dust and the amount of gas.

[0024] Conventionally, if it was suspected that accumulation or blockage was occurring based on pressure gauges such as manometers installed in the environmental dust collection piping system, or the operating status of the environmental dust collection equipment, workers would manually insert a jig into the pipe through an inspection hole installed at a bend in the piping where accumulation was expected to occur, and remove the solid material causing the accumulation or blockage. This work was performed in areas where the surface temperature of the pipe was 100°C or higher, which placed a heavy burden on the workers.

[0025] Furthermore, since the inspection holes mentioned above need to be closed during normal operation, the flange openings of the inspection holes will be sealed with, for example, blind flanges with handles. In this case, a sealing member must be interposed between the opposing surfaces of the flanges, and there is a risk that air from the atmosphere may flow into the environmental dust collection piping 20 through a small gap between this sealing member and at least one of the flange surfaces. In this case, the temperature of the gas flowing inside the environmental dust collection piping 20 will be partially lowered, making condensation more likely to occur.

[0026] If the fluid handled in the piping system is at room temperature, a highly sealing gasket made of rubber or similar material can be used as a sealing element to prevent the inflow of air from the atmosphere. However, in the case of piping systems handling fluids at temperatures of 100°C or higher, a glass fiber gasket, for example, must be used. While glass fiber gaskets have improved heat resistance compared to the rubber gaskets mentioned above, their sealing performance is undeniably inferior. As a result, dust is more likely to adhere to areas where condensation occurs on the inner wall of the pipe due to air flowing into the pipe, making the aforementioned accumulation and blockage problems more likely to occur.

[0027] Furthermore, if the above-mentioned smelting furnace performs a process that includes a chloride volatilization reaction, such as a rotary kiln-type zinc smelting furnace that recovers zinc from steel dust by the Wertz process described above, the leaked furnace gas contains hygroscopic zinc chloride. Therefore, as mentioned above, if condensation occurs due to the inflow of air from the atmosphere, accumulation and blockage are more likely to occur inside the piping.

[0028] Even in such circumstances, in the environmental dust collection piping system of the embodiment of the present invention, as shown in Figure 3 for example, a knocker 22 is provided immediately downstream of the bend B in the environmental dust collection piping 20 and downstream of the inspection hole 21. This allows an external impact to be applied to the bend B of the environmental dust collection piping 20 before dust gradually accumulates inside the environmental dust collection piping 20 and blocks it, thereby allowing the accumulated dust-derived solid matter to be detached from the inner wall of the environmental dust collection piping 20.

[0029] As described above, the solid material detached by the impact force of the knocker 22 is propelled from the inner wall of the environmental dust collection piping 20 toward the center by this impact force, and is then transported to environmental dust collection equipment such as a dust collector by the high-velocity gas flow in the center. When selecting the model of the knocker 22, it is possible to refer to the hammer that was conventionally used by workers to apply impact force to the piping manually. That is, a knocker with an impact force of about the same magnitude as the impact force obtained by multiplying the weight of the hammer head by the distance from the grip to the head of the hammer should be adopted. For example, if a hammer with a head weight of 4.5 kg and a distance of 30 cm from the grip to the head was used, it is preferable to adopt a knocker 22 with an impact force of about 13.2 kg·m / s.

[0030] There are no particular limitations on the frequency at which the knocker 22 strikes the environmental dust collection piping 20. However, under operating conditions similar to those of actual operation, the amount of dust accumulation inside the piping at the bend B of the environmental dust collection piping 20 should be tested with various striking frequencies to determine a striking frequency at which no dust accumulation can be observed when looking through the inspection hole 21. In the case of an environmental dust collection piping system for a rotary kiln performing reductive roasting using the Wertz method, this striking frequency is preferably 1 strike / 10 minutes or more and 10 strikes / 10 minutes or less.

[0031] In the environmental dust collection piping system of the above-described embodiment of the present invention, it is preferable that the knocker 22 is electromagnetically driven. If an air knocker is used for the knocker 22, for example, if the environmental dust collection piping 20 is installed outdoors, the copper air supply piping commonly used for air knockers may corrode over time due to the high ambient temperature, potentially causing malfunctions. In addition, condensate may enter the air knocker through the air supply piping, which may also cause malfunctions. In contrast, if the knocker 22 is electromagnetically driven, it is preferable because only electrical wiring needs to be connected, and problems such as corrosion and condensate intrusion, as with the air supply piping, do not occur even if the installation location is an outdoor environment.

[0032] In the environmental dust collection piping system of the above embodiment of the present invention, it is preferable to attach the knocker 22 on a steel plate 23 with a thickness of 3 mm or more, which is attached to the surface of the environmental dust collection piping 20 by welding or the like. When the dust contains corrosive substances such as chlorine, as in the case of carrying out a reaction including a chlorine volatilization reaction in the above-mentioned smelting furnace, the corrosion rate of the environmental dust collection piping 20 increases in the places where this dust repeatedly accumulates, due to the high temperature of the environmental dust collection piping 20, which is 100°C or higher as described above. Even in such a situation, by attaching the knocker 22 on the steel plate 23 as described above, the strength to hold the knocker 22 is maintained even if some corrosion occurs in the environmental dust collection piping 20. If the thickness of the steel plate 23 is less than 3 mm, the above effect will be difficult to achieve. Generally, the upper limit of the thickness of the steel plate is about 15 mm.

[0033] Next, a method for collecting dust in an environmental dust collection system using the environmental dust collection piping system of the above embodiment of the present invention will be described. This environmental dust collection method collects dust leaking from inside the smelting furnace with an average dust concentration of 0.4 g / m³. 3 The above is an environmental dust collection method for transferring furnace gas containing temperatures of 100°C or higher to a dust collection facility via an environmental dust collection piping system, wherein an inspection hole 21 is provided immediately upstream or downstream of the bend B in the environmental dust collection piping 20 which is bent at an angle of 30 degrees or more and 60 degrees or less, and a knocker 22 is periodically struck at a position immediately downstream of the bend B and downstream of the inspection hole 21.

[0034] As a result, even if high-temperature furnace gas containing dust leaks from the seal portion, which is the opening to the outside of the smelting furnace, it can be transferred to environmental dust collection equipment such as a bag filter via the environmental dust collection piping 20, and clean gas from which dust has been almost completely removed can be released into the atmosphere by this environmental dust collection equipment. At that time, the furnace gas containing dust that leaked from the seal portion has an average dust concentration of 0.4 g / m³. 3 Even if the above conditions are met, condensation will be less likely to occur if the temperature inside the environmental dust collection piping 20 is 100°C or higher, thus preventing dust from adhering to the inner wall of the piping.

[0035] However, as mentioned above, in the inspection hole 21, the flange opening is sealed with, for example, a blind flange with a handle. Therefore, there is a risk that air from the atmosphere may flow into the environmental dust collection piping 20 through a small gap between the sealing member interposed between the opposing surfaces of these flanges and at least one flange surface. In this case, the temperature of the gas flowing inside the environmental dust collection piping 20 is partially lowered, making condensation more likely. Even in this case, by periodically striking the area downstream of the inspection hole 21 with the knocker 22, solid matter derived from dust that has adhered due to condensation can be detached from the inner wall of the piping and ejected to the center before blockage occurs.

[0036] In the environmental dust collection method of the embodiment of the present invention described above, a remarkable effect is obtained when the dust contains a compound containing zinc and chlorine. In particular, a remarkable effect is obtained when the dust contains 55% by mass or more of zinc and 3% by mass or more of chlorine. The reason for this is that zinc chloride is hygroscopic, and as described above, when condensation occurs due to the inflow of outside air from the inspection hole 21, accumulation and blockage are more likely to occur in the environmental dust collection piping 20. However, as described above, by periodically striking the area downstream of the inspection hole 21 with the knocker 22, the accumulated dust can be detached from the inner wall of the piping and ejected to the center before it is affected by zinc and chlorine, thereby preventing accumulation from progressing and eventually blocking the piping. [Examples]

[0037] [Examples] Using an environmental dust collection piping system with the structure shown in Figure 3(b), furnace gas at 120°C containing dust leaked from the labyrinth seal of the rotary kiln's discharge hood was drawn in, and the dust was collected by a bag filter. The average dust concentration of this leaked furnace gas was 0.8 g / m³. 3The piping for environmental dust collection had one bend at a 45-degree angle, and an inspection hole was provided immediately after this bend. Furthermore, 200 mm downstream from this inspection hole, a 9 mm thick steel plate was attached by welding, curved to follow the outer wall surface of the piping for environmental dust collection, and an electromagnetic knocker (electromagnetic magnetic hammer) manufactured by Nippon Magnetics Co., Ltd. was mounted on top of it.

[0038] Then, the Wertz process, which involves charging steel dust raw materials containing zinc oxide into a rotary kiln and performing reductive roasting to recover crude zinc oxide dust, was continued for 217 days. During this time, an electromagnetic knocker was operated at a frequency of 5 times every 10 minutes. During this operation, inspection holes were opened and the bends in the environmental dust collection piping were checked, and no dust accumulation or blockage was observed.

[0039] [Comparative Example] The system was operated for 217 days in the same manner as the above embodiment, except that an electromagnetic knocker was not installed. During these 217 days of operation, blockages occurred in the environmental dust collection piping at an average frequency of 0.7 times per day, and each time, it was necessary to clear the blockage by striking it with a hammer by a worker. The time required for clearing the blockage was 13 minutes per blockage on average. [Explanation of symbols]

[0040] 1 Furnace body 2. Insertion side hood 2a Circulation hood 3. Discharge side hood 3a Circulation hood 4 tires 5 Receiving roller 6 Garth Gear 7 Pinion Gear 8 Inlet 9 burners 10 ducts 20 Piping for environmental dust collection 20a First branch pipe 20b Second branch pipe 20c Third branch pipe 21 Inspection holes 22 Knocker 23 Iron Plate

Claims

1. An environmental dust collection piping system for transferring in-furnace gas containing dust leaking from a smelting furnace to a dust collection facility, characterized in that an inspection hole is provided immediately upstream or downstream of a bend in the piping that is bent at an angle of 30 degrees or more and 60 degrees or less, and a knocker is provided immediately downstream of the bend and downstream of the inspection hole.

2. The piping system for environmental dust collection according to claim 1, characterized in that the knocker is electromagnetically driven.

3. The environmental dust collection piping system according to claim 1 or 2, characterized in that the knocker is attached to a steel plate with a thickness of 3 mm or more that is welded to the surface of the piping.

4. Dust leaking from inside the smelting furnace, with an average dust concentration of 0.4 g / m³. ３ An environmental dust collection method that transfers furnace gas containing a temperature of 100°C or higher to a dust collection facility via an environmental dust collection piping system, characterized in that an inspection hole is provided on the upstream or downstream side immediately before a bend in the piping that is bent at an angle of 30 degrees or more and 60 degrees or less, and a position immediately downstream of the bend and downstream of the inspection hole is periodically struck with a knocker.

5. The environmental dust collection method according to claim 4, characterized in that the dust contains a compound containing zinc and chlorine.