Method for heating a smelting furnace

Abstract

To provide a temperature raising method capable of shortening a temperature raising time without generating local overheating in a furnace, by smoothly igniting a shaft burner, and stabilizing a burner flame even after ignition of the shaft burner.SOLUTION: A method for raising a temperature at the time of startup of a smelting furnace for smelting non-ferrous metals, such as a self-melting furnace used in a smelting process of pyrometallurgical copper smelting, wherein after the inside of the smelting furnace is substituted by air of higher oxygen concentration than the air introduced via a gas introduction part formed of a window box for example in the smelting furnace, a burner of the smelting furnace is ignited.SELECTED DRAWING: Figure 1

Description

【Technical Field】 【0001】 The present invention relates to a method for raising the temperature of a smelting furnace, and particularly to a method for raising the temperature when starting up a smelting furnace used in the smelting process of non-ferrous metal smelting typified by copper smelting. 【Background Art】 【0002】 A dry copper smelting process using copper concentrate with a copper grade of about 30% obtained by beneficiating mined ore as a raw material includes a smelting process of generating a matte with a copper grade of about 60 - 65% by oxidizing and melting the copper concentrate charged into a smelting furnace, a copper making process of generating blister copper with a copper grade of about 99.8% by further oxidizing the obtained matte, and a refining process of generating refined copper (pure copper) with a copper grade of 99.99% or more by electrolytically refining the obtained blister copper. 【0003】 Generally, an Outokumpu type self-smelting furnace is frequently used in the above-mentioned smelting furnace. The self-smelting furnace mainly includes a vertical cylindrical reaction shaft that oxidizes copper concentrate introduced from an upper burner with air or oxygen-enriched air, a settler located below the reaction shaft that separates the matte and slag generated by the oxidation reaction based on the specific gravity difference, and an uptake located on the opposite side of the reaction shaft side above the settler that discharges high-temperature exhaust gas at about 1300°C containing SO2 generated during the oxidation reaction. 【0004】 As described above, since high-temperature exhaust gas containing high-concentration SO2 gas is stably discharged from the uptake of the self-smelting furnace, this exhaust gas is heat-recovered by a waste heat boiler and then sent to a sulfuric acid manufacturing plant as a raw material for sulfuric acid. In the waste heat boiler, steam is generated by the recovered heat and used as power for a turbine generator of auxiliary equipment. Since this turbine generator is periodically inspected by a government agency about once every two years, the self-smelting furnace also stops operating in accordance with this timing. Then, the refractory of the self-smelting furnace is inspected during this operation stop period, and repairs are made as necessary. 【0005】 When starting up the self-smelting furnace after the above-mentioned shutdown period, it is necessary to heat the furnace over a period of about a week before charging in the raw material, copper concentrate. The reason for this is that if the furnace is heated without sufficient time, the refractory material will expand rapidly, which may damage the bricks, especially in the parts that were replaced during the shutdown period, or cause excessive flow of molten metal into the gaps created between the bricks due to the rapid expansion. In addition, if copper concentrate is introduced from the burner without sufficiently heating the self-smelting furnace, there is a risk that the copper concentrate will not ignite properly due to insufficient heat. 【0006】 The method of raising the temperature of the above-mentioned self-smelting furnace during startup is generally employed by burning heavy oil using a burner installed at the top of the reaction shaft (hereinafter also referred to as a shaft burner or concentrate burner) and multiple burners installed in the settler (hereinafter also referred to as settler burners). For example, Patent Document 1 discloses a technology for heating the self-smelting furnace body when it is shut down, or when it is started up after repairs, using a concentrate burner that burns copper concentrate, flux, and other charges introduced together with fuel and air or oxygen-enriched air during copper smelting. Specifically, powdered coke is introduced from the concentrate burner along with air or oxygen-enriched air, and a portion of the powdered coke is scattered in an unburned state in the settler and burned, thereby maintaining or raising the temperature of the entire furnace to a predetermined temperature. [Prior art documents] [Patent Documents] 【0007】 [Patent Document 1] Japanese Patent Publication No. 2000-199019 [Overview of the Initiative] [Problems that the invention aims to solve] 【0008】 It is stated that by using the technology described in Patent Document 1, the entire furnace of a self-smelting furnace can be heated or warmed simply by supplying powdered coke together with air from a concentrate burner located at the top of the reaction shaft, without the need to specifically install burners for heating and warming, which is advantageous in terms of equipment management, and also reduces damage to bricks due to localized heating and cracking of bricks due to uneven thermal expansion. Furthermore, it is stated that when warming a molten metal while it is held in the settler during operation, using powdered coke can increase the amount of steam generated by the waste heat boiler to about 30% to 50% of the normal operating amount compared to when heavy oil is used, and when warming using powdered coke after furnace repair, about three times the amount of steam can be obtained compared to when heavy oil is used alone. 【0009】 However, the technology described in Patent Document 1 uses powdered coke in addition to heavy oil, which is commonly used as an auxiliary fuel during normal operation. Therefore, separate equipment is required for storage, quantitative dispensing, and transportation of powdered coke, which increases equipment costs and makes handling it cumbersome. 【0010】 Furthermore, generally speaking, when starting up a self-smelting furnace in an atmospheric environment, the furnace interior is heated from a cooled state, so in the initial stages of startup, the radiant heat from the furnace walls is low, making it difficult to ignite the shaft burner. Even if ignition occurs, the burner flame may not stabilize, resulting in unburned heavy oil entering the furnace. In addition, even after ignition of the shaft burner, incomplete combustion in the shaft burner and multiple settler burners makes it difficult for the flame to extend, resulting in the gas temperature not rising sufficiently, which can lead to problems such as localized overheating inside the furnace or a decrease in the heating rate. Under these circumstances, if the heavy oil supply flow rate is increased to forcibly approach the ideal heating curve, there is a risk of incomplete combustion in the burner. For this reason, the heavy oil supply flow rate cannot be increased until the temperature of the refractory material inside the furnace has risen to a certain level, which has been a problem as it takes a long time to heat up. 【0011】 This invention has been made in view of the above circumstances, and aims to provide a heating method that can shorten the heating time without causing localized overheating in the furnace by smoothly igniting the shaft burner during the initial heating of the smelting furnace and stabilizing the burner flame after ignition of the shaft burner. [Means for solving the problem] 【0012】 To achieve the above objective, the method for raising the temperature of a smelting furnace according to the present invention is a method for raising the temperature of a smelting furnace used for smelting non-ferrous metals during startup, wherein the inside of the smelting furnace is replaced with a gas having a higher oxygen concentration than the air introduced into the smelting furnace through a gas introduction section. And once the substitution is complete and the high-oxygen-concentration gas has spread throughout the entire smelting furnace, This method is characterized by igniting the burner of the smelting furnace. [Effects of the Invention] 【0013】 According to the present invention, the shaft burner can be ignited smoothly when raising the temperature during startup of the smelting furnace, and the burner flame can be stabilized even after the shaft burner is ignited, thereby shortening the temperature rise time without causing localized overheating inside the furnace. [Brief explanation of the drawing] 【0014】 [Figure 1] This is a schematic flow diagram of a self-melting furnace and its exhaust gas treatment equipment that are heated by the heating method of an embodiment of the present invention. [Figure 2] This is a longitudinal cross-sectional view of a specific example of a shaft burner equipped in the self-melting furnace shown in Figure 1. [Figure 3] This graph shows the heating profile of a self-melting furnace that has been heated up in an embodiment of the present invention. [Modes for carrying out the invention] 【0015】 The following describes in detail an embodiment of the heating method for a smelting furnace according to the present invention. This embodiment of the heating method for a smelting furnace is intended for smelting furnaces that smelt non-ferrous metals such as copper, zinc, lead, nickel, and tin. It is a method for heating a smelting furnace from a state where the inside of the furnace has cooled down in order to restart operations of the smelting furnace, which has been shut down by stopping the charging of raw materials for inspection, repair, or repair of ancillary equipment. The method is characterized by replacing the inside of the smelting furnace with a gas with a higher oxygen concentration than the air introduced into the smelting furnace through a gas introduction section, and then igniting the burner of the smelting furnace. 【0016】 To explain in more detail, first, a gas with a higher oxygen concentration than air (hereinafter referred to as high-oxygen-concentration gas) is introduced into the furnace of the smelting furnace through its gas introduction section, and the inside of the furnace is replaced with this high-oxygen-concentration gas. Examples of oxygen production equipment such as PSA (Pressure Swing Adsorption) type oxygen gas generators and cryogenic air separators can be used as sources for this high-oxygen-concentration gas. 【0017】 The high-oxygen gas preferably has an oxygen concentration of 80% by volume or higher. If the oxygen concentration is less than 80% by volume, the oxygen concentration when the furnace is replaced will be lower than the desired oxygen concentration, which may make it difficult to ignite the burner smoothly or cause the burner flame to become unstable after ignition, potentially hindering the full effectiveness of the present invention. 【0018】 Once the above substitution is complete and the entire furnace is filled with high-oxygen gas, the burner is ignited. In the case of a self-smelting furnace, the burner ignited here is a shaft burner, for example, one that uses heavy oil as fuel, located on the ceiling of the reaction shaft. Furthermore, if necessary, in addition to this shaft burner, settler burners, preferably about 6 to 12 of them, located in the settler of the self-smelting furnace, may also be ignited. 【0019】 When the above burner is ignited, oxygen is present in the furnace at a higher concentration than air overall. Therefore, even when starting up from a state where the inside of the furnace has been cooled, the burner can be easily ignited. Also, after the burner is ignited, the shape of the flame can be stabilized. As a result, the gas temperature inside the furnace can be made almost uniform throughout, so that the temperature of the furnace wall can be raised almost evenly overall without local heating. Thus, problems such as the burner not smoothly igniting or the flame becoming unstable even after ignition when starting up a smelting furnace in an air atmosphere as in the past are less likely to occur. Therefore, the problem that the heavy oil introduced into the burner does not catch fire and instead drips as it is and accumulates at the bottom of the furnace due to the burner not igniting hardly occurs. Also, problems of local overheating caused by the flame shape becoming too short or unstable after ignition are less likely to occur. 【0020】 Note that the state where the above high-oxygen-concentration gas has spread throughout the furnace means a state where the oxygen concentration exceeds at least 21% by volume in all places inside the furnace. For example, in a self-smelting furnace, it may be determined that the gas has spread when the oxygen concentration is detected to exceed 21% by volume in a gas concentration meter provided at the exhaust gas outlet of the uptake. Or, it may be determined that the gas has spread when the time obtained by dividing the volume of the furnace by the supply flow rate of the high-oxygen-concentration gas has elapsed since the start of the supply of the high-oxygen-concentration gas into the furnace. Or, it may be determined that the gas has spread when both of these conditions are satisfied. 【0021】 After ignition of the burner described above, it is preferable to increase the temperature such that the temperature measured by a thermometer provided in advance in the refractory installed in the furnace or by a thermometer for measuring the gas temperature in the furnace rises along a pre-prepared temperature increase curve, and this can be adjusted by the supply flow rate of the heavy oil supplied to the burner. Generally, thermometers are provided at about four to eight locations, for example, in the refractory installed as a lining material in the furnace of a smelting furnace. Also, in order to measure the gas temperature in the furnace, thermometers are provided at two locations, for example, in the center of the settler and at the lower part of the uptake. Therefore, it becomes possible to accurately grasp the temperature increase state in the furnace based on the indicated values of these thermometers. 【0022】 The temperature increase method according to the embodiment of the present invention can be preferably applied to a non-ferrous metal smelting furnace and can be preferably applied to the Outokumpu-type self-smelting furnace described above, but is not limited thereto. It can be applied to various-shaped furnaces such as an Ausmelt TSL (Top Submerged Lance) furnace in which a lance into which fuel, air, etc. are introduced is inserted from the top into a vertically substantially cylindrical furnace and the tip of the lance is immersed in the slag layer for smelting, and a reverberatory furnace having a rectangular, wide and shallow hearth with a burner at one end and an arch-shaped ceiling and performing smelting using the reflection from the ceiling. 【0023】 FIG. 1 schematically shows a self-smelting furnace 1 composed of a reaction shaft 11, a settler 12, and an uptake 13. In this self-smelting furnace 1, one shaft burner 20 is provided at the top of the reaction shaft 11, and a total of twelve settler burners 30 are provided in the settler 12, five on each of the two side walls parallel to the longitudinal direction thereof and two on the side wall on the reaction shaft side. The high-temperature exhaust gas discharged from the reaction shaft 11 is sent to a sulfuric acid production plant 3 after heat recovery by a waste heat boiler 2. The high-pressure steam generated by heat recovery in the waste heat boiler 2 is sent to a steam turbine 4 and used as a power source there. 【0024】 The gas introduction section is not particularly limited as long as it can introduce high-oxygen-concentration gas into the furnace at the desired supply flow rate, but in the case of the self-smelting furnace 1, it is preferable to use the wind box of the shaft burner 20. Specifically, as shown in Figure 2, the shaft burner 20 provided at the top of the reaction shaft 11 mainly consists of a substantially cylindrical burner cone 21 that penetrates the top of the reaction shaft 11, a substantially conical wind box 22 provided concentrically with the burner cone 21 and communicating with the upper end of the burner cone 21, a cylindrical concentrate chute 23 that serves as a supply pipe for copper concentrate and flux, an oxyfuel burner 24 provided concentrically inside the concentrate chute 23 and serving as a fuel for introducing fuel such as heavy oil, and a wind speed regulator 25 provided so as to be able to reciprocate axially around the concentrate chute 23. 【0025】 During normal operation, concentrate supplied from the upper end of the concentrate chute 23 is introduced into the burner cone 21 by free fall, while reaction air is blown into the burner cone 21 through a slit between the wind box 22 and the wind speed regulator 25. As a result, the concentrate and reaction air are introduced into the reaction shaft 11 in a mixed state within the burner cone 21. By using the wind box 22 and the burner cone 21 connected to its lower end as the introduction point for the high-oxygen concentration gas, the high-oxygen concentration gas introduced into the self-smelting furnace 1 flows in one direction through the furnace in the order of reaction shaft 11, settler 12, and uptake 13, and is discharged from the upper outlet of the uptake 13, thus efficiently replacing the inside of the furnace with high-oxygen concentration gas. 【0026】 In the heating method of the embodiment of the present invention, it is preferable to set the air supply flow rate introduced into the burner for heating the furnace to less than the theoretical combustion air amount of the fuel introduced into the burner (i.e., less than 100% of the theoretical combustion air amount). As a result, the burner undergoes incomplete combustion, and some of the unburned fuel spreads throughout the smelting furnace. This unburned fuel spread throughout the furnace can then be burned away from the burner, thus allowing the furnace to be heated more uniformly. It is preferable that the lower limit of the air supply flow rate is 70% or more of the theoretical combustion air amount. If this supply flow rate is less than 70% of the theoretical combustion air amount, combustion in the burner itself becomes difficult. 【0027】 As described above, by adopting the heating method of the embodiment of the present invention, the burner can be ignited smoothly when heating up the smelting furnace during startup, and the flame shape of the burner can be stabilized after ignition, so that the temperature can be raised in a relatively short time without causing localized overheating inside the furnace. In particular, the heating method of the embodiment of the present invention is more effective when heating up when the inside of the smelting furnace is at approximately room temperature to about 300°C due to a long period of shutdown of the smelting furnace. Examples of such long-term shutdowns include when large-scale repairs are made to the refractory materials of the smelting furnace, or when operations are shut down in conjunction with periodic inspections of waste heat boilers or steam turbine power generation equipment attached to the smelting furnace. [Examples] 【0028】 [Examples] To restart operations of a self-smelting furnace 1 for copper smelting, which has the structure shown in Figure 1, after being shut down for a long period of time, a high-oxygen-concentration gas with an oxygen concentration of 85-91% by volume was first introduced into the self-smelting furnace 1 while the internal temperature of the furnace had cooled down. This high-oxygen-concentration gas was generated by a PSA (Pressure Swing Adsorption) type oxygen gas generator and introduced into the self-smelting furnace 1 via the burner cone 21 by introducing it into the window box 22 of the shaft burner 20, which is located on the ceiling of the reaction shaft 11 as shown in Figure 2. 【0029】 Approximately two hours, calculated by dividing the volume of the self-smelting furnace 1 by the supply flow rate of the high-oxygen concentration gas, had elapsed since the start of the introduction of the high-oxygen concentration gas. Therefore, it was determined that the high-oxygen concentration gas had spread throughout the self-smelting furnace 1, and the introduction of the high-oxygen concentration gas was stopped. Instead, heavy oil and air were supplied to the shaft burner 20 and ignited. At this time, the air supply flow rate was set to 80% of the theoretical combustion air volume for the heavy oil. As a result, ignition was achieved smoothly. Subsequently, eight of the twelve Settler burners 30 were also ignited under the same condition of 80% of the theoretical combustion air volume, and ignition was achieved smoothly. 【0030】 After igniting the shaft burner 20 and the settler burner 30 described above, the shape of the burner flames was visually inspected through the viewing window of the self-melting furnace 1 and found to be stable without any significant shortening. As a result, problems such as localized overheating and heavy oil dripping and accumulating at the bottom of the furnace due to improper ignition did not occur. Furthermore, by adjusting the heavy oil supply flow rate while monitoring the reading of the thermometer installed in the center of the settler, it was possible to raise the temperature throughout the furnace almost uniformly and at almost the same rate without deviating significantly from the pre-planned temperature rise curve. The self-melting furnace 1 was heated twice under the same conditions as described above at different times. As a result, the burners could be ignited smoothly in these two heating cycles as well, and the shape of the burner flames after ignition was stabilized, so problems such as localized overheating and heavy oil dripping did not occur. 【0031】 [Comparative Example] The self-melting furnace 1 was heated in the same manner as in the above embodiment, except that the process of replacing the inside of the self-melting furnace 1 with high-oxygen concentration gas introduced from the wind box 22 before igniting the burners was not performed. As a result, it was difficult to ignite the burners smoothly, and even when ignited, the shape of the flames became unstable. In addition, when ignition was not performed smoothly, heavy oil dripped from the burners and accumulated at the bottom of the furnace. This problem occurred not only with the shaft burner 20 but also with the eight settler burners 30 that were ignited. 【0032】 Furthermore, after igniting the shaft burner 20 and the settler burner 30, visual inspection of the flame shape of these burners through the viewing window revealed that some had short flames or unstable flame shapes, resulting in localized overheating inside the furnace. Moreover, because the unstable flame shape of the burners could lead to excessive incomplete combustion, the heavy oil supply flow rate could not be increased until the temperature of the refractory material inside the furnace rose to a certain level, forcing a slow heating process. As a result, variations in temperature and heating rate depending on the location within the furnace were observed. 【0033】 Figure 3 and Table 1 show the results of the heating process when attempting to raise the temperature along a predetermined heating curve by adjusting the heavy oil supply flow rate while observing the reading of a thermometer installed in the center of the settler for the three heating cycles (Cases 1-3) performed in the above examples and the one heating cycle (Case 4) performed in the comparative example. 【0034】 [Table 1] 【0035】 As can be seen from Table 1 above, Cases 1 to 3 of the examples all showed a heating rate 1.13 to 1.34 times faster than Comparative Example Case 4. Furthermore, the heating rate per unit amount of heavy fuel oil in Cases 1 to 3 was 1.38 to 1.77 times faster than in Case 4. Therefore, it can be seen that by heating the self-melting furnace using a method that satisfies the requirements of the present invention, heating can be achieved more quickly and efficiently than in conventional methods. [Explanation of symbols] 【0036】 1 Flash-melting furnace 2. Waste heat boiler 4 Steam Turbine 11 Reaction Shaft 12 Settler 13 Uptake 20 Shaft Burners 21 Burner Cone 22 Window Box 23. Ore Chute 24 Oxy Fuel Burner 25 Wind speed regulator 30 Settler Burner

Claims

[Claim 1] A method for raising the temperature of a smelting furnace used for smelting non-ferrous metals, characterized in that the inside of the smelting furnace is replaced with a gas having a higher oxygen concentration than the air introduced into the smelting furnace through a gas introduction section, and the burner of the smelting furnace is ignited when the replacement is complete and the gas with the higher oxygen concentration has spread throughout the entire smelting furnace. [Claim 2] A method for raising the temperature of a smelting furnace according to claim 1, characterized in that the smelting furnace is a self-smelting furnace and the gas introduction section is a wind box. [Claim 3] The method for raising the temperature of a smelting furnace according to claim 1 or 2, characterized in that the temperature increase during startup is from a state in which the inside of the furnace has been cooled. [Claim 4] A method for raising the temperature of a smelting furnace according to any one of claims 1 to 3, characterized in that the supply flow rate of air introduced into the burner is less than the theoretical combustion air amount of the fuel introduced into the burner.

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