Control method for exhaust gas draft of drying oven

Abstract

To provide a control method of exhaust gas draft in a drying furnace which is capable of effectively utilizing a high temperature gas in a slag cleaning furnace as drying hot air, with the in-furnace pressure of the drying furnace stabilized.SOLUTION: The sulfide concentrate that has been dried with hot air in a drying furnace 2 is blown into a self-fluxing furnace 4 together with air or oxygen-enriched air to oxidize and burn it to generate a matte layer and a slag layer in molten states, and after that, the slag layer in the self-fluxing furnace 4 is transferred to a slag cleaning furnace 5 for electrical heating, thereby separating matte included in the slag layer. In such a smelting system, when the slag cleaning furnace exhaust gas discharged from the slag cleaning furnace 5 is used as the hot air, the opening of a damper 25 that controls the exhaust gas draft of the drying furnace 5 is operated quickly, while the opening of the damper 25 is operated slowly when the slag cleaning furnace exhaust gas discharged from the furnace 5 is not used as the hot air.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for controlling exhaust gas draft in a drying furnace for drying wet raw materials, and more particularly to a method for controlling exhaust gas draft in a drying furnace for drying sulfide concentrates used as raw materials in dry non-ferrous metal smelting. [Background technology]

[0002] In dry nonferrous metal smelting, smelting is performed to recover high-grade nonferrous metals by heating raw ore and removing impurities in a molten state. For example, in dry copper smelting, copper concentrate (sulfide concentrate) consisting mainly of chalcopyrite with a copper content of about 30% obtained by pretreatment such as flotation is sequentially heated in a flash furnace and a smelting pot, as shown in Patent Document 1, to separate and remove the iron and silica contained in the copper concentrate as slag. The matte thus produced, with a copper content of about 60-65%, is further processed in a converter and a refining furnace to produce blister copper with a copper content of about 99%. The blister copper thus produced is cast into an anode and subjected to electrolytic refining to be shipped as electrolytic copper with a copper content of 99.99%.

[0003] In the flash smelting furnace, raw copper concentrate is blown into the concentrate burner at the top of the reaction tower through gas-solid contact with air or oxygen-enriched air, causing a combustion reaction. The resulting heat from the oxidation reaction of the copper concentrate is used to produce molten matte and slag. To improve combustion efficiency in the concentrate burner, the copper concentrate is preferably ignited immediately after being ejected from the concentrate burner and maintained at a high temperature. However, if the copper concentrate is wet, the gas-solid contact is hindered, or the temperature of the copper concentrate decreases due to the latent heat of vaporization of water, resulting in a decrease in the combustion reaction rate. Therefore, prior to smelting in the flash smelting furnace, the wet copper concentrate is loaded into a drying furnace, typically a rotary kiln, and dried by blowing combustion gas generated in a hot blast stove into the drying furnace.

[0004] Because the drying process described above consumes a large amount of thermal energy, various technologies have been proposed to improve efficiency. For example, Patent Document 2 discloses a technology in which high-temperature gas discharged from a flash smelting furnace is introduced into a waste heat boiler to generate steam, and nitrogen heated by heat exchange with the steam is introduced into a drying furnace, thereby drying wet sulfide concentrate charged as a raw material into the flash smelting furnace. This reduces the amount of combustion gas that serves as a heat source for the drying furnace, thereby reducing the amount of heavy oil fuel consumed in the hot stove that generates the combustion gas and making it possible to mitigate the problem of environmental pollution caused by sulfur dioxide generated by the combustion of the sulfur content in the heavy oil.

[0005] Furthermore, to prevent gases generated during the drying process from leaking into the surrounding area, drying ovens typically use exhaust fans such as blowers to suction out the gases inside the oven, maintaining a negative pressure inside the oven. However, this control can fluctuate significantly due to various external disturbances. As a result, the oven pressure can become too high, causing problems such as gas leakage into the surrounding area and the emission of smoke and ash. Conversely, the oven pressure can become too low, causing problems such as the collapse of the flue gas passage and backflow of gas. Therefore, in order to stabilize the oven pressure, Patent Document 3 proposes a technology for easily stabilizing the oven pressure by installing a damper in the exhaust gas passage connecting the oven (kiln) to the exhaust gas handling equipment and controlling its opening. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-241423 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-119525 [Patent Document 3] Patent Publication No. 2021-021512 Summary of the Invention [Problem to be solved by the invention]

[0007] As described above, when the combustion gas generated in the hot stove is blown into a drying furnace as hot air to dry a wet raw material such as copper concentrate, the temperature of the hot air and the amount of hot air generated suitable for the drying process can be determined from processing conditions such as the amount of wet raw material charged into the drying furnace per unit time and its moisture content. However, in general, hot stoves are sometimes unable to sufficiently increase the temperature of the combustion gas and the amount of the combustion gas generated due to restrictions such as the heat resistance temperature of refractories near their fuel burners, and this can become a bottleneck, restricting the amount of raw material such as copper concentrate that can be charged into the drying furnace.

[0008] In addition, since industrial heavy oil containing sulfur is generally used as fuel for combustion in the fuel burners of the hot stoves, the combustion gas generated in the hot stoves contains sulfur oxides (hereinafter referred to as SO X Therefore, this SO X After being used as hot air in a drying furnace such as a rotary kiln, the combustion gas containing the fuel oil leaves the drying furnace together with the dried solids and undergoes gas-solid separation in a cyclone, after which it is introduced via a suction fan into an exhaust gas treatment facility where it is subjected to a prescribed treatment before being released into the atmosphere. Therefore, due to environmental conservation considerations and limitations on the treatment capacity of the exhaust gas treatment facility, it has been difficult to increase the amount of heavy oil burned per unit time in the hot air stove. [Means for solving the problem]

[0009] The inventors noticed that the slag extracted from the flash smelting furnace is heated to high temperatures by the slag in the slag-heating furnace. Conventionally, this gas is released into the atmosphere as slag-heating furnace exhaust gas after being detoxified in a collection system. This gas could potentially serve as a heat source for the drying furnace. However, the slag-heating furnace is designed to stably process the slag by-product of the flash smelting furnace. It is not intended for the gas inside the slag-heating furnace to be used as a heat source for other equipment. Therefore, its composition, pressure, and other properties are unstable. Therefore, if the high-temperature gas present in the slag-heating furnace is introduced into a drying furnace such as a rotary kiln as a heat source, the operating conditions of the slag-heating furnace could cause the pressure inside the drying furnace to become unstable.

[0010] Therefore, the inventors further investigated a method for utilizing the high-temperature gas present in the smelting furnace in a manner that does not cause the above problems, and discovered that by introducing the high-temperature gas discharged from the smelting furnace into the drying furnace according to the operating status of the smelting furnace and switching the control mode of a damper installed in the flue through which the drying furnace exhaust gas discharged by suction from the drying furnace according to the operating status, the high-temperature gas present in the smelting furnace can be effectively used as hot air for drying wet raw materials such as copper concentrate while maintaining a stable pressure in the drying furnace, leading to the completion of the present invention. Note that the flow of the drying furnace exhaust gas discharged by suction from the drying furnace in the flue as described above is also called the exhaust gas draft.

[0011] That is, the method for controlling the exhaust gas draft of a drying furnace according to the present invention is a smelting facility in which sulfide concentrate that has been dried with hot air in a drying furnace is blown into a flash smelting furnace together with air or oxygen-enriched air and subjected to oxidative combustion to produce a molten matte layer and a slag layer, and then the slag layer from the flash smelting furnace is transferred to a smelting furnace and electrically heated to separate the matte contained in the slag layer, characterized in that when the smelting furnace exhaust gas discharged from the smelting furnace is used as the hot air, the opening of a damper that controls the exhaust gas draft of the drying furnace is quickly operated, and when the smelting furnace exhaust gas discharged from the smelting furnace is not used as the hot air, the opening of the damper is slowly operated. [Effects of the Invention]

[0012] According to the present invention, the high-temperature gas present in the smelting furnace can be effectively used as hot air for drying wet raw materials such as copper concentrate while maintaining the pressure inside the drying furnace stable. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a process flow diagram of a smelting facility including a hot stove, a drying furnace, a flash furnace, and a smelting furnace to which a method for controlling an exhaust gas draft according to an embodiment of the present invention is applied. FIG. [Figure 2]1 is a schematic flow diagram showing a specific example of a hot air supply piping system and an exhaust gas draft piping system to a drying furnace to which a method for controlling an exhaust gas draft according to an embodiment of the present invention is applied, and a control system for controlling these. FIG. [Figure 3] 1 is a flowchart showing a specific example of an algorithm for controlling the opening degree of a drying furnace exhaust gas damper, which is preferably executed in the exhaust gas draft control method according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, an embodiment of a method for controlling the exhaust gas draft of a drying furnace according to the present invention will be described with reference to the drawings, taking as an example a case where the material to be dried in the drying furnace is a wet copper concentrate used as a raw material for dry copper smelting. As shown in Fig. 1, wet copper concentrate with a moisture content (also called moisture content) of about 7 to 10% that has been pretreated at a mining site is generally transported by a dedicated ship, unloaded, and temporarily stored in a storage shed 1. The copper concentrate in this storage shed 1 is blended with copper concentrate from other lots as needed, and then charged into a rotary kiln-type drying furnace 2 (also called a flash dryer).

[0015] A rotary kiln is a rotary drying device with a cylindrical body that is rotatably mounted with its central axis slightly tilted from horizontal. Copper concentrate is loaded into the body from its upper end using a constant volume feeder such as a screw feeder. As the body rotates, the copper concentrate is stirred by a blade-like lifter installed inside and gradually moves toward the lower end. During this stirring and movement, the copper concentrate is efficiently dried by hot air introduced from the upper end of the body. Rotary drying devices that use steam as a heat source for drying are sometimes called rotary steam dryers to distinguish them from the rotary kilns described above.

[0016] The hot air introduced into the drying oven 2 is generated in a hot air stove 3 located adjacent to the drying oven 2. The hot air stove 3 is composed of a combustion chamber equipped with a fuel burner and a mixing chamber adjacent to the combustion chamber. The high-temperature combustion gas generated by the combustion of fossil fuels such as heavy oil by the fuel burner in the combustion chamber is mixed in the mixing chamber with outside air taken in from outside the system and the smelting furnace exhaust gas discharged from the smelting furnace (described later). This generates hot air with a temperature of about 400 to 600°C.

[0017] The copper concentrate that has been dried to a moisture content of approximately 0.2 to 0.4% in the drying furnace 2 as described above is then charged into the flash smelting furnace 4. The flash smelting furnace 4 is a device that uses the heat from the oxidation reaction of the copper concentrate itself to perform smelting and refining, making it possible to reduce fuel consumption compared to reverberatory furnaces and electric furnaces. Furthermore, as mentioned above, the amount of heat required to evaporate the moisture in the copper concentrate is reduced by the drying process in the preceding drying furnace 2, making it possible to further reduce fuel consumption in the flash smelting furnace 4.

[0018] The flash smelting furnace 4 is mainly composed of a cylindrical reaction tower (reaction shaft) equipped at its top with a concentrate burner for burning the copper concentrate, a settler that acts as a storage section for separating the matte and slag produced by the combustion of the copper concentrate into layers, and an uptake that acts as a flue gas passage connected to one end of the settler opposite to the end connected to the lower end of the reaction tower. The copper concentrate dried in the drying furnace 2 is blown into the flash smelting furnace 4 via the concentrate burner, along with air or oxygen-enriched air, and, if necessary, auxiliary fuel and silicic acid called flux. This causes the copper concentrate to instantly oxidize and burn, resulting in smelting and refining, producing matte (matte) composed of sulfides with a copper content of approximately 60 to 65%, and slag (calami) composed of iron oxide, silicic acid, and the like.

[0019] The matte and slag produced as described above are separated into a lower matte layer and an upper slag layer in the settler. The matte layer is extracted from the flash smelting furnace 4 and charged into a converter 6, where it is oxidized by blowing oxygen-enriched air into it, and iron and sulfur are removed to produce blister copper with a copper content of approximately 98-99%. However, there is a limit to how much the copper content of the slag layer can be reduced in the flash smelting furnace 4 due to the chemical dissolution of copper and the suspension (floating) of particulate matte. Therefore, using the slag layer extracted from the flash smelting furnace 4 as aggregate for concrete, etc., would result in a significant economic loss.

[0020] The slag layer from the flash smelting furnace 4 is then transferred to a slag furnace 5, where the copper contained in the slag layer is recovered. The slag furnace 5 generally has a structure in which multiple graphite rod-shaped electrodes are inserted into a furnace lined with heat-resistant bricks. When electricity is passed through these electrodes, the slag layer transferred from the flash smelting furnace 4 is heated by Joule heat, and the matte contained in the slag layer separates, forming a new matte layer below the slag layer. This lower matte layer is then extracted from the slag furnace 5 and treated in a converter 6, similar to the matte extracted from the flash smelting furnace 4. Meanwhile, the upper slag layer, which is in a molten state (or semi-fluid state) at approximately 1200 to 1300°C, is extracted from the slag furnace 5 and subjected to water granulation using a water granulator or similar device.

[0021] An upper space is formed inside the kiln 5, and the gas in this upper space is heated to about 500°C because it is in contact with the molten, high-temperature slag layer. However, since the gas in the upper space of the kiln 5 contains traces of sulfur components released from the slag and matte layers, the gas in the upper space of the kiln has traditionally been discharged as kiln exhaust gas and sent to a recycling system, where it is detoxified by absorbing the sulfur components with an alkali such as a caustic soda solution in a packed tower of the recycling system, and then released into the atmosphere through a chimney.

[0022] In an embodiment of the method for controlling exhaust gas draft, the high-temperature slag layer stably stored in a molten state in the slag furnace 5 is used as a heat source for drying copper concentrate, and the gas in the upper space of the slag furnace 5 is used as the heat medium. Specifically, as shown by the dotted line in Figure 1, a branch pipe 9 is provided branching off from a flue 8 for transporting the slag exhaust gas discharged from the upper space of the slag furnace 5 to a collection system, and the tip of this branch pipe 9 is connected to the hot stove 3. This allows a portion of the slag exhaust gas discharged from the upper space of the slag furnace 5 to be extracted through this branch pipe 9 and sent to the hot stove 3 as a heat transfer gas, making it possible to replace at least a portion of the air used as the heated gas in the hot stove 3 with the slag exhaust gas discharged from the slag furnace 5. As shown by the dashed line in Figure 1, the branch pipe 9 branching off from the flue 8 may be connected not to the hot air stove 3 but to a supply pipe that sends the hot air generated in the hot air stove 3 to the drying oven 2.

[0023] The smelting furnace exhaust gas discharged from the upper space of the smelting furnace 5 is pressurized by the suction fan 7 for the circulating system installed in the flue 8 before being sent to the circulating system. Therefore, the operating pressure of the hot stove 3 and the drying furnace 2, which are generally operated at negative pressure, may be lower than the pressure at the branch point of the branch pipe 9 located on the discharge side of the circulating system suction fan 7 in the flue 8. In this case, as shown in Figure 2, by installing a branch-side damper 10 in the branch pipe 9 and adjusting its opening, it is possible to adjust the amount of exhaust gas discharged from the smelting furnace 5 that is supplied to the hot stove 3. Alternatively, depending on the equipment configuration, the operating pressure of the circulating system may be lower than the operating pressure of the hot stove 3 or the drying furnace 2. In this case, instead of the branch-side damper 10, a flue-side damper 11 may be installed in the flue 8 downstream of the branch point of the branch pipe 9.

[0024] Alternatively, both a branch-side damper 10 and a flue-side damper 11 may be provided, and the amount of gas supplied to the hot stove 3 may be adjusted by adjusting the apertures of these dampers 10, 11. In this case, to increase the amount of gas supplied to the hot stove 3, the aperture of the branch-side damper 10 is adjusted in the open direction and the aperture of the flue-side damper 11 is adjusted in the closed direction, and to decrease the amount of gas supplied to the hot stove 3, these dampers 10, 11 are adjusted in the opposite direction. Note that a manual valve 12 is preferably provided on the primary side (upstream side) of the branch-side damper 10 in the branch pipe 9. A thermometer 13 and a flow meter 14 are also preferably provided in the branch pipe 9.

[0025] Typically, only the upper slag layer, which contains almost no volatile components and has separated in the flash smelting furnace 4, is charged into the slag furnace 5. Therefore, the slag exhaust gas discharged from the upper space of the slag furnace 5 is a mixture of the gas originally present in the upper space of the slag furnace 5 and the outside air drawn in from outside the slag furnace 5 by the suction fan 7 for the collection system. Therefore, as mentioned above, even if the slag contains only a small amount of sulfur, it can be handled together with the sulfur contained in heavy oil and copper concentrate, so there is no particular problem with introducing it directly into the drying furnace 2 as hot air. However, if it is desired to prevent oxygen from being introduced into the drying furnace 2, an inert gas such as nitrogen can be introduced into the upper space of the slag furnace 5 in advance as a heat transfer gas.

[0026] The hot air used for drying in the drying oven 2 contains particles so fine that they cannot be completely removed by a cyclone. Therefore, it is sucked in by the drying oven exhaust gas suction fan 21 and discharged from the drying oven 2 as drying oven exhaust gas. After that, it is preferably treated in an exhaust gas treatment facility 22 such as a bag filter or an electrostatic precipitator, and then released into the atmosphere through a chimney 23. At the outlet side of this exhaust gas treatment facility, there is a SO X A concentration meter 24 is installed to measure the SO concentration of the drying furnace exhaust gas immediately before it is released into the atmosphere. X The concentration is constantly monitored.

[0027] The exhaust gas draft control method according to the embodiment of the present invention is XSO in the exhaust gas from the drying furnace measured with a concentration meter 24 X When the concentration exceeds a predetermined threshold, the extraction of the slag furnace exhaust gas from the flue 8 is stopped, so that the slag furnace exhaust gas is not introduced into the drying furnace 2. As a result, if, for example, the matte layer of the flash smelting furnace 4 flows into the slag furnace 5 due to an erroneous operation, and this flowed-in matte layer is heated in the slag furnace 5, a larger amount of SO than the slag layer is released. X As a result, the SO X Even if the concentration becomes significantly higher than during normal operation, this high SO X This can prevent high-concentration smelting furnace exhaust gas from being released into the atmosphere via the drying furnace 2.

[0028] Specifically, during normal operation when the slag layer of the flash smelting furnace 4 is transferred to the slag furnace 5, the SO X The concentration is about 1000 to 2600 ppm by volume, so a part of this smelting furnace exhaust gas is extracted from the flue 8 and introduced into the drying furnace 2 as a heat transfer gas at a flow rate of about 3000 Nm 3 / h or less, SO X On the other hand, when the matte layer from the flash smelting furnace 4 flows into the smelting furnace 5 as described above, the SO X The concentration rises from 1000 to 2600 volume ppm to about 4500 to 6500 volume ppm. X If the exhaust gas from the slag furnace with this concentration continues to be introduced into the drying furnace 2, the above SO X Therefore, when a situation occurs in which the matte layer flows from the flash smelting furnace 4 into the smelting furnace 5, the extraction of the smelting furnace exhaust gas from the flue 8 is stopped, and all of the smelting furnace exhaust gas emitted from the smelting furnace 5 is sent to an environmental smoke collection system (also called an environmental collection system).

[0029] It is preferable that the withdrawal of the smelting furnace exhaust gas from the flue 8 is stopped automatically. X SO in the exhaust gas from the drying furnace measured with a concentration meter 24 XThe concentration value is input to a control means 30 such as a PLC (Program Logic Controller) or a DCS (Distributed Control System), and this SO X The control means 30 may be programmed to determine that the matte layer in the flash smelting furnace 4 has flowed into the smelting furnace 5 when the concentration value exceeds a predetermined threshold value, and to output a signal to fully close the branch side damper 10 provided in the branch pipe 9 and fully open the flue side damper 11 provided in the flue 8.

[0030] A drying oven exhaust gas damper 25 is provided on the suction side of the drying oven exhaust gas suction fan 21, and the flow rate of the drying oven exhaust gas discharged by suction from the drying oven 2 can be adjusted by the opening degree of this drying oven exhaust gas damper 25, thereby controlling the pressure inside the drying oven 2. Specifically, if the pressure inside the oven measured by a pressure gauge provided in the drying oven 2 is higher than a predetermined set value, a signal (also called an open command) is output to the drying oven exhaust gas damper 25 in a direction to increase the opening degree. Conversely, if the pressure inside the oven is equal to or lower than the predetermined set value, a signal (also called a close command) is output to the drying oven exhaust gas damper 25 in a direction to decrease the opening degree.

[0031] When smelting furnace exhaust gas is not introduced into the drying furnace 2 as described above, the only hot air introduced into the drying furnace 2 is that generated by the hot stove 3, resulting in fewer disturbances that fluctuate the furnace pressure. The main disturbances are due to the amount of copper concentrate charged and its moisture content, which are the material to be dried. Therefore, the exhaust gas draft can be stably controlled by slowly adjusting the opening of the drying furnace exhaust gas damper 25, i.e., by adjusting the rate of change in opening per unit time to a small value. In contrast, when smelting furnace exhaust gas is introduced into the drying furnace 2, the furnace pressure of the drying furnace 2 is affected by the operating status of the smelting furnace 5 in addition to the above disturbances. Therefore, the exhaust gas draft can be quickly stabilized by adjusting the opening of the drying furnace exhaust gas damper 25 quickly, i.e., by adjusting the rate of change in opening per unit time to a large value.

[0032] Therefore, in the method for controlling the exhaust gas draft of the drying oven 2 of the present invention, the control parameter for the opening of the drying oven exhaust gas damper 25 is switched depending on whether or not the smelting furnace exhaust gas is introduced as hot air into the drying oven 2. That is, when the smelting furnace exhaust gas discharged from the smelting furnace 5 is extracted through the branch pipe 9 and used as hot air for the drying oven 2, the opening of the drying oven exhaust gas damper 25 is controlled to operate quickly. When the extraction of the smelting furnace exhaust gas from the branch pipe 9 is stopped and the entire amount is treated in a collection system without being used as hot air for the drying oven 2, the opening of the drying oven exhaust gas damper 25 is controlled to operate slowly. The operating speed of the drying oven exhaust gas damper 25 can be as fast as can be achieved by a typical operating mechanism, such as a hydraulic cylinder or an electric motor. However, there is technical significance in switching the sensitivity of the control depending on the hot air source, so that the damper operates quickly when the smelting furnace exhaust gas is used as hot air compared to when it is not used, and operates slowly compared to when it is not used.

[0033] The opening degree of the drying furnace exhaust gas damper 25 can be controlled as described above by executing the algorithm shown in Fig. 3 in the control means 30. Specifically, first, in step S1, it is determined whether or not the smelting furnace exhaust gas is being used as hot air for the drying furnace 2. This determination is made by the SO X SO in the exhaust gas from the drying furnace measured with a concentration meter 24 X In some cases, it can be determined indirectly based on whether the density value exceeds a preset threshold value.

[0034] If the result of the above determination is that the smelting furnace exhaust gas is not being used as hot air, the control parameters used to control the opening of the drying furnace exhaust gas damper 25 (described later) are set to, for example, α = 2.00 and β = 1.35, as shown in step S2. On the other hand, if the smelting furnace exhaust gas is being used as hot air, the control parameters are set to, for example, α = 2.45 and β = 2.00, as shown in step S3. Note that the values ​​of the control parameters α and β are not limited to the above values ​​as long as they are greater when the smelting furnace exhaust gas is being used as hot air than when it is not being used as hot air, and it is preferable to adopt appropriate values ​​depending on the dynamic characteristics of the control system to which the control parameters are applied.

[0035] Next, in step S4, it is determined whether the internal pressure of the drying oven 2 should be urgently controlled. This step prepares for unexpected events, such as rainwater seeping into the oven and generating a large amount of steam, or the exhaust gas flow path becoming clogged with foreign matter. If the indicated value of the internal pressure is higher than, for example, -100 Pa, which serves as the criterion for this determination, it is determined that the internal pressure of the drying oven 2 is significantly too high, and as shown in step S5, an open command signal is output to the drying oven exhaust gas damper 25 to increase the opening by, for example, 5% from the current opening (for example, if the current opening is 30%, the opening will be increased to 35%). This causes a larger amount of gas to be sucked from the drying oven 2 than currently, thereby reducing the internal pressure of the drying oven 2 from its current state. On the other hand, if the indicated value of the internal pressure of the drying oven 2 is -100 Pa or lower, it is within the applicable range of the control parameters set in steps S2 and S3, and the process proceeds to step S6. The opening degree of the drying furnace exhaust gas damper 25 is 0% when fully closed and 100% when fully open.

[0036] In step S6, it is determined whether the difference obtained by subtracting the set value from the indicated value of the drying furnace internal pressure is +50 Pa or more. If this difference (deviation) is +50 Pa or more, the furnace internal pressure is higher than the set value, and an open command signal is output to the drying furnace exhaust gas damper 25 to increase the opening by α% from the current opening, as shown in step S7. On the other hand, if the difference (deviation) is less than +50 Pa, the process proceeds to the next step S8. The specific value of α% used in step S7 has already been determined in steps S1 to S3 described above, and the rate of change in the opening of the drying furnace exhaust gas damper 25 differs depending on whether or not the smelting furnace exhaust gas is being used as hot air.

[0037] That is, when smelting furnace exhaust gas is not being introduced into the drying furnace 2 as hot air, the pressure inside the drying furnace 2 does not fluctuate significantly, so the opening of the drying furnace exhaust gas damper 25 is slowly operated to further stabilize the pressure inside the furnace. Therefore, a signal for an opening command with an opening rate of 2.00% (e.g., if the current opening is 30.00%, a command to open to 32.00%) is output to the drying furnace exhaust gas damper 25. On the other hand, when smelting furnace exhaust gas is being introduced into the drying furnace 2 as hot air, this adds to the disturbance and causes the pressure inside the drying furnace 2 to fluctuate more significantly. Therefore, in order to further stabilize the pressure inside the furnace, the opening of the drying furnace exhaust gas damper 25 must be operated more quickly than in the case of the above-mentioned slow operation. Therefore, a signal for an opening command with an opening rate of 2.45% (e.g., if the current opening is 30.00%, a command to open to 32.45%) is output to the drying furnace exhaust gas damper 25.

[0038] In step S8, it is determined whether the difference obtained by subtracting the set value from the indicated value of the drying furnace internal pressure is greater than or equal to +30 Pa and less than 50 Pa. If the difference (deviation) is within this range, the furnace internal pressure is slightly higher than the set value, and an open command signal is output to the drying furnace exhaust gas damper 25 to increase the opening by β% from the current opening, as shown in step S9. On the other hand, if the difference (deviation) is not within this range, the process proceeds to step S10. The specific value of this β% has already been determined in steps S1 to S3 described above, and, as in step S7, the rate of change in the opening of the drying furnace exhaust gas damper 25 differs depending on whether or not the smelting furnace exhaust gas is being used as hot air.

[0039] That is, when smelting furnace exhaust gas is not being introduced as hot air into the drying furnace 2, a signal of an opening command with an opening change rate of 1.35% to operate slowly (for example, if the current opening is 30.00%, a command to operate in the opening direction up to 31.35%) is output to the drying furnace exhaust gas damper 25. On the other hand, when smelting furnace exhaust gas is being introduced as hot air into the drying furnace 2, a signal of an opening command with an opening change rate of 2.00% to operate quickly (for example, if the current opening is 30.00%, a command to operate in the opening direction up to 32.00%) is output to the drying furnace exhaust gas damper 25.

[0040] In step S10, it is determined whether the difference obtained by subtracting the set value from the indicated value of the pressure inside the drying oven is greater than or equal to -30 Pa and less than 30 Pa. If the difference (deviation) is within this range, it can be determined that the pressure inside the oven is approximately equal to the set value, and therefore, as shown in step S11, no signal is output to the drying oven exhaust gas damper 25, and the current opening degree is maintained. On the other hand, if the difference (deviation) is not within this range, the process proceeds to the next step S12.

[0041] In step S12, it is determined whether the difference obtained by subtracting the set value from the indicated value of the drying furnace internal pressure is greater than or equal to -50 Pa and less than -30 Pa. If the difference (deviation) is within this range, the furnace internal pressure is slightly lower than the set value, and therefore, as shown in step S13, a close command signal is output to the drying furnace exhaust gas damper 25 so that the opening degree is reduced by β% from the current opening degree. The specific value of this β% has already been determined in steps S1 to S3 described above, and, as in step S7, the opening degree change rate of the drying furnace exhaust gas damper 25 differs depending on whether or not the smelting furnace exhaust gas is being used as hot air.

[0042] That is, when smelting furnace exhaust gas is not being introduced as hot air into the drying furnace 2, a close signal with an opening change rate of 1.35% is output to the drying furnace exhaust gas damper 25 to operate slowly (for example, if the current opening is 30.00%, a signal to operate in the closing direction to 28.65%). On the other hand, when smelting furnace exhaust gas is being introduced as hot air into the drying furnace 2, a close command with an opening change rate of 2.00% is output to the drying furnace exhaust gas damper 25 to operate quickly (for example, if the current opening is 30.00%, a command to operate in the closing direction to 28.00%).

[0043] Furthermore, if the difference (deviation) obtained by subtracting the set value from the indicated value of the drying furnace pressure determined in step S12 is not within the range of -50 Pa or more and less than -30 Pa, the furnace pressure is lower than -50 Pa, and therefore a close command signal is output to the drying furnace exhaust gas damper 25 to open it α% smaller than the current opening, as shown in step S14.

[0044] That is, when smelting furnace exhaust gas is not being introduced as hot air into the drying furnace 2, a signal of a close command with an opening change rate of 2.00% is output to the drying furnace exhaust gas damper 25 to operate slowly (for example, if the current opening is 30.00%, a command to operate in the closing direction to an opening of 28.00%). On the other hand, when smelting furnace exhaust gas is being introduced as hot air into the drying furnace 2, a signal of a close command with an opening change rate of 2.45% is output to the drying furnace exhaust gas damper 25 to operate quickly (for example, if the current opening is 30.00%, a command to operate in the closing direction to an opening of 27.55%).

[0045] After step S5, S7, S9, S11, S13, or S14 is executed, the process proceeds to step S15, where a timer is started to count a predetermined time. The opening of the drying oven exhaust gas damper 25 executed in any of the above steps is maintained until the timer counts down, thereby stabilizing the pressure inside the oven, which fluctuates due to the opening and closing operation of the drying oven exhaust gas damper 25. The length of the predetermined time counted by the timer is adjusted as appropriate depending on the type and size of the valve used in the drying oven exhaust gas damper 25, the length and size of the flue in which the drying oven exhaust gas damper 25 is installed, and other factors, but is generally preferably about 20 seconds.

[0046] After the timer has finished counting in step S15, the process proceeds to step S16, where it is confirmed whether the switch for executing the above-mentioned exhaust gas draft control algorithm is ON or OFF. Normally, this switch is ON, so the process returns to step S1 and the above-mentioned exhaust gas draft control algorithm is repeated. On the other hand, if this switch is OFF, the control algorithm ends.

[0047] As explained above, with the exhaust gas draft control method according to the embodiment of the present invention, it is possible to effectively utilize the high-temperature gas present in the smelting furnace as hot air for drying wet raw materials such as copper concentrate while keeping the pressure inside the drying furnace stable. Furthermore, it is not necessary to make costly capital investments such as adding fuel burners to the hot stove 3 or to increase the consumption of heavy oil, which is the raw material for generating hot air. In addition, it is possible to reduce SO 2 derived from heavy oil. X Therefore, it becomes possible to dry a larger amount of sulfide concentrate at a low cost and at a high processing speed. [Example]

[0048] (Example) In a sulfide concentrate smelting plant with the equipment configuration shown in Figure 1, the hot air introduced into the rotary kiln type drying furnace 2, which dries the wet sulfide concentrate used as the raw material, is obtained by combining the hot air produced by burning heavy oil in the hot stove 3 with the exhaust gas discharged from the smelting furnace 5. In this case, as shown in Figure 2, the SO X The concentration meter 24 measures the SO concentration in the exhaust gas from the drying oven 2. X The value is input to the DCS as the control means 30, and the SO X The DCS was programmed to automatically close the branch-side damper 10 installed in the branch pipe 9 and output a signal to fully open the flue-side damper 11 when the value exceeded a threshold set at 70 ppm by volume lower than the target control value.

[0049] Furthermore, the opening of the drying furnace exhaust gas damper 25, which is installed on the suction side of the drying furnace exhaust gas suction fan 20, was controlled by the DCS so that the pressure inside the drying furnace 2, measured by a pressure gauge installed in the drying furnace, would be set to the set value of -100 Pa. In this case, the rate of change in the opening of the drying furnace exhaust gas damper 25 was changed according to whether or not the smelting furnace exhaust gas was used as hot air, according to the algorithm shown in Figure 3.

[0050] That is, when the smelting furnace exhaust gas was not used as hot air, the drying furnace exhaust gas damper 25 was set to open or close slowly by outputting an open or close command at an opening rate of 1.35% when the difference between the indicated value and the set value of the furnace pressure was 30 Pa or more but less than 50 Pa, and outputting an open or close command at an opening rate of 2.00% when the difference between the indicated value and the set value of the furnace pressure was 50 Pa or more. On the other hand, when the smelting furnace exhaust gas was used as hot air, the drying furnace exhaust gas damper 25 was set to open or close quickly by outputting an open or close command at an opening rate of 2.00% when the difference between the indicated value and the set value of the furnace pressure was 30 Pa or more but less than 50 Pa, and outputting an open or close command at an opening rate of 2.45% when the difference between the indicated value and the set value of the furnace pressure was 50 Pa or more. When the difference between the indicated value and the set value of the furnace pressure was less than 30 Pa, the opening change rate was set to 0% so that the current opening was maintained.

[0051] As a result of controlling the exhaust gas draft of the drying furnace 2 by the above method, when the exhaust gas from the smelting furnace was being introduced as hot air into the drying furnace 2, the pressure inside the furnace was stably controlled within the range of -350.2 to -89.8 Pa. On the other hand, when the exhaust gas from the smelting furnace was not being introduced as hot air into the drying furnace 2, the pressure inside the furnace was stably controlled within the range of -325.3 to -155.9 Pa. In addition, when the SO X SO measured by concentration meter 24 X The concentration never exceeded the control guideline value, even momentarily.

[0052] (Comparative Example) Regardless of whether or not the exhaust gas from the smelting furnace was used as hot air, the system was set so that an open or close command was output at an opening rate of 1.35% when the deviation between the indicated value and the set value of the furnace pressure was 30 Pa or more but less than 50 Pa, and so that an open or close command was output at an opening rate of 2.00% when the deviation between the indicated value and the set value of the furnace pressure was 50 Pa or more. Except for this, the exhaust gas draft of the drying furnace 2 was controlled in the same manner as in the above example.

[0053] As a result, SO XSO measured by concentration meter 24 X The concentration never exceeded the control guideline value, even momentarily. However, when the smelting furnace exhaust gas was being introduced as hot air into the drying furnace 2, the pressure inside the furnace fluctuated within the range of -524.1 to -83.3 Pa, and when the smelting furnace exhaust gas was not being introduced as hot air into the drying furnace 2, the pressure inside the furnace fluctuated within the range of -398.5 to -128.2 Pa. In both cases, the control of the exhaust gas draft of the drying furnace 2 became unstable compared to the above examples. [Explanation of symbols]

[0054] 1. Storage building 2 Drying oven 3 hot stove 4 Flash-melting furnace 5. Smelting furnace 6. Converter 7. Suction fans for environmental collection equipment 8 flue 9 Branch Pipe 10 Branch side damper 11 Flue-side damper 12 Manual valve 13 Thermometer 14 Flow meter 21 Drying furnace exhaust gas suction fan 22 Drying furnace exhaust gas treatment equipment 23 Chimney 24 SO X concentration meter 25 Drying furnace exhaust gas damper 30 Control Means

Claims

1. 1. A smelting facility in which sulfide concentrate that has been dried with hot air in a drying furnace is blown into a flash smelting furnace together with air or oxygen-enriched air to cause oxidative combustion to produce a molten matte layer and a slag layer, and then the slag layer from the flash smelting furnace is transferred to a smelting furnace and electrically heated to separate the matte contained in the slag layer, the method comprising: promptly operating a damper that controls the exhaust gas draft of the drying furnace when the smelting furnace exhaust gas discharged from the smelting furnace is used as the hot air; and slowly operating the damper when the smelting furnace exhaust gas discharged from the smelting furnace is not used as the hot air.

2. 2. The method for controlling an exhaust gas draft of a drying furnace according to claim 1, wherein the exhaust gas from the smelting furnace is used as the hot air except when the matte layer from the flash smelting furnace flows into the smelting furnace.

3. SO of the exhaust gas from the drying furnace Ｘ 3. The method for controlling exhaust gas draft of a drying furnace according to claim 2, wherein when the concentration exceeds a predetermined threshold, the matte layer of the flash smelting furnace is treated as having flowed into the smelting furnace.

Images