JP4295134B2 - Refining furnace operation method - Google Patents

Description

  The present invention relates to a copper refining operation method for obtaining refined crude copper suitable for copper electrolytic refining by refining copper concentrate and a copper raw material using a flash smelting furnace, a converter, and a refining furnace. In particular, the present invention relates to a method of reducing a hydrocarbon gas as a reducing agent by blowing it into a molten copper together with an oxygen-containing gas such as air in a reduction treatment step after an oxidation step in a refining furnace.

  In general, various processes are carried out as a copper smelting process, but a typical process is to make a mat in a flash smelting furnace and treat the mat in a converter to have a copper content of about 98.5 mass%. There is a process in which the crude copper is obtained, the crude copper is further refined to increase the copper content to about 99.3 mass% to 99.5 mass%, the anode is cast, and finally electrolytic purification is performed.

  In this case, as a specific method for dry refining of crude copper, there are an oxidation step for mainly oxidizing and removing S by blowing air into the molten copper, and it is dissolved in the crude copper from the converter, during the oxidation treatment step In order to remove (deoxidize) 0.6 to 1.0 mass% of oxygen that is also dissolved, it usually consists of a reduction step in which oxygen is reduced to 0.01 to 0.1 mass% by blowing a reducing agent into the molten metal. is there. As a reducing agent in the latter reduction process, petroleum-based liquefied hydrocarbon gas (LPG) is recently often blown together with cracking air.

  After the reduction process in the refining furnace as described above, the molten metal is usually discharged from the refining furnace, and the molten metal is led to a casting machine through a trough or the like and cast into an anode for electrolytic purification. Therefore, the tapping temperature from the refining furnace should be as close as possible to the temperature that allows for the temperature drop between the refining furnace and the casting machine (hereinafter referred to as the “target tapping temperature”) to the optimum casting temperature, or the minimum allowable temperature in the casting machine. It is necessary to set the casting temperature to be equal to or higher than the temperature expected from the amount of temperature drop between the refining furnace and the casting machine (this is described as “target minimum hot water temperature”).

  The target tapping temperature varies depending on the length and structure of the soot from the refining furnace to the casting machine, or the level of tapping, but is generally set to about 1160 to 1200 ° C. Therefore, the target minimum tapping temperature is 1160 ° C. The above is the usual case.

  On the other hand, the molten metal temperature immediately before the start of reduction of the crude copper in the refining furnace varies depending on the amount of molten metal in the furnace, the structure of the furnace, the pouring temperature from the converter, the heat insulation conditions before the oxidation process, the treatment conditions of the oxidation process, etc. Generally, it is often about 1100 to 1130 ° C. Therefore, when the target minimum hot water temperature is set to 1160 ° C., a temperature increase of 30 to 60 ° C. is required in the reduction step, and this required temperature increase amount is usually different for each operation.

  As described above, there are two purposes for the reduction process in the refining furnace, one is deoxidation of crude copper, and one is heating the molten metal for the casting process, which is a subsequent process. Specifically, in the reduction process, in the former, the oxygen concentration in the molten metal is reduced to 0.01 to 0.1 mass%, and in the latter, the molten metal temperature is heated to 1160 ° C. or higher.

  As means for achieving the purpose of the reduction step as described above, there is a disclosure (Patent Document 1) of Japanese Patent Application Laid-Open No. 2000-290735 (Applicant: Nikko Metal Co., Ltd., “Reduction treatment method in dry refining of crude copper”). Measure the molten metal temperature before starting the reduction, and adjust the flow rate ratio between the reducing agent (hydrogen carbonate gas) and the oxygen-containing gas such as air so that the proportion of the oxygen-containing gas increases as the molten metal temperature decreases. A method of increasing the temperature to the target minimum hot water temperature after the reduction by processing is disclosed.

  Here, when shortening the reduction process time is considered, it is generally considered that the flow rate of the oxygen-containing gas such as a reducing agent (hydrogen carbonate gas) and air is increased. However, if the flow rate of the reducing agent alone is increased, the reduction process time will be shortened, but the temperature rise of the molten metal during the reduction will be insufficient, the molten metal temperature after reduction will not reach the target temperature, and after reduction with a heavy oil burner etc. There is a high possibility that the molten metal needs to be heated. Further, if the flow rate of oxygen-containing gas such as reducing agent and air is increased unnecessarily, it is expected that the splash of molten metal into the exhaust gas duct will increase and hinder the operation. In addition, the flow rate of the oxygen-containing gas such as the reducing agent or air may not be increased so much due to the limit of the facility capacity.

  On the other hand, as a method of reducing crude copper in which the air ratio is changed during the reduction process, there is a disclosure of Japanese Patent Application Laid-Open No. 2000-178665 (Applicant: Mitsui Kinzoku Mining Co., Ltd.) (Patent Document 2). The air ratio is adjusted according to the sulfur concentration of the crude copper, and the timing at which the air ratio is lowered during the reduction process is also determined by the degree of reduction in the sulfur concentration of the crude copper. Is different.

JP 2000-290735 A JP 2000-178665 A

  The present invention has been made against the background described above, and enables reduction of the time of the reduction process without significantly increasing the amount of blowing of oxygen-containing gas such as conventional reducing agents and air, and the molten metal temperature at the end of reduction. The purpose of this is to ensure that the temperature is reliably and stably kept above the target minimum hot water temperature and to prevent an increase in energy costs.

  The present inventors have earnestly investigated the relationship between the flow rate of an oxygen-containing gas such as hydrogen carbonate gas and air blown into the crude copper melt for reduction treatment and the behavior of oxygen and sulfur to be removed in the reduction process. As a result of investigation, focusing on the fact that the oxygen and sulfur removal reaction is promoted by increasing the flow rate of oxygen-containing gas such as air (hereinafter referred to as “air” as a representative example) at the beginning of the reduction. It was found that the removal rate of both was the highest in the initial 30 minutes, and that this removal reaction was closely related to the stirring power of the molten metal.

:
The present invention solves the above problems,
(1) In a copper refining furnace, air is blown at an air ratio of 0.07 to 0.15 to the reducing gas at the initial stage of the reduction process (less than half of the total reduction time), the molten metal is forcibly stirred, and the reducing gas Promote the reaction of oxygen,
Thereafter, the refining furnace operating method is characterized by operating by reducing the air ratio by 0.03 to 0.04 compared to the initial stage to shorten the refining furnace operating time. It is.

(2) In a copper refining furnace, air is blown at an air ratio of 0.07 to 0.15 with respect to the reducing gas at the initial stage of the reduction process (less than half the total reduction time), the molten metal is forcibly stirred, A refining furnace operation method that promotes the oxygen reaction and then operates the air ratio by 0.03-0.04 lower than the initial stage to shorten the refining furnace operating time.
It is.

According to the present invention,
(1) The reduction treatment time can be shortened by 10 to 20% (10 to 20 minutes when the average operation time is 110 minutes).
(2) In addition, the basic unit of hydrocarbon gas (LPG in the present invention) during reduction can be reduced from 3.4 kg / t to 3.2 kg / t.

(3) The molten metal temperature after the reduction process can be stably maintained at the target minimum hot water temperature (1160 ° C) or higher and there is no need to heat the molten metal with a heavy oil burner after the reduction process. There is a prevention effect.

  First, the purification process of crude copper in the refining furnace including the reduction treatment of the present invention will be described.

In a refining furnace, for example, a cylindrical horizontal tilting type refining furnace, crude copper discharged from a converter in a previous process is received in a refining furnace using a ladle or the like. Of course, the molten copper for two or more converters may be sequentially received in the refining furnace.
After the predetermined amount of the molten copper from the converter is received in the refining furnace as described above, an oxidation step for oxidizing and removing S in the molten metal is performed. This oxidation step is usually performed by blowing a gas oxidant such as air from a tuyere below the molten metal in the refining furnace, but is not particularly limited in the present invention. Prior to the oxidation step, it is usual to perform a process (calami scraping) for scraping off oxides such as iron oxide floating on the molten metal.

  After the oxidation step is completed as described above, the reduction step is performed. This reduction step exists in the crude copper sent from the converter, and is for removing (deoxidizing) oxygen dissolved by the oxidation treatment. However, simultaneously with deoxidation, S is also removed by an oxidation reaction with oxygen in the air entrained by stirring or with oxygen dissolved in the molten metal.

This reduction step is performed by blowing a reducing agent (hydrocarbon-based gas) into the refining furnace together with air from the tuyere below the hot water surface. As a typical reducing agent, there is one obtained by vaporizing petroleum liquefied hydrocarbon (LPG) containing butane (C ₄ H ₁₀ ) as a main component, and LPG is generally used in the method of the present invention. However, the present invention is not limited to this, and natural gas or the like may be used. The oxygen-containing gas is typically air, but other oxygen-enriched air or any gas containing a large amount of oxygen (of course, it is necessary that components other than oxygen do not affect the molten copper. ) May be used.

In this reduction process, the air is used to increase the deoxidation rate by partially burning hydrocarbon gas and decomposing it into CO, H ₂ and C _m H _n (m ≦ 4; n ≦ 10). When air is blown into the molten metal, oxygen in the blown air reacts with a hydrocarbon gas (for example, C ₄ H ₁₀ ) as follows.

C ₄ H ₁₀ + O ₂ → CO + H ₂ + C _m H _n (m ≦ 4; n ≦ 10)
By this reaction, CO, H ₂ and C _m H _n (m ≦ 4; n ≦ 10) contribute to reducing and removing oxygen in the molten metal. Note that the above reaction is a partial combustion reaction, and as the amount of blown oxygen increases, the calorific value increases, and the amount of rise in molten metal temperature during the reduction treatment increases.

  Therefore, in the present invention, as in JP-A-2000-290735, the melt temperature immediately before the start of the reduction process after the end of the oxidation process (before the start of the blowing of hydrocarbon gas and air) is measured, Accordingly, the flow rate ratio of the hydrocarbon gas and air is adjusted. Specifically, when the melt temperature before the start of reduction is low, the ratio of air is increased to increase the amount of temperature increase during the reduction process. Conversely, when the melt temperature before the start of reduction is high, The ratio is lowered to suppress the amount of temperature increase during the reduction process, thereby controlling the molten metal temperature at the end of the reduction process to approach the target hot water temperature.

That is, in the present invention, in the initial stage of the reduction process (less than half of the total reduction time), air is blown into the reducing gas at an air ratio of 0.07 to 0.15 to forcibly agitate the molten metal.
More specifically, in the present invention, as shown in FIG. 1, only 1.5 to 2.0 times the conventional air (corresponding to an air ratio of 0.07 to 0.15 with respect to the reducing gas) is blown in within 30 minutes of the initial reduction. As a result, the molten metal stirring ability at the initial stage of reduction is increased, and the deoxidation and desulfurization reactions are promoted. This is because the O and S removal rates are greatest within the first 30 minutes of reduction.
The definition of the air ratio here is as follows.
Air ratio = the amount of air actually used / theoretical amount of air required for complete combustion of the reducing agent For example, in the case of LPG gas, about 12 Nm ³ of air is required for complete combustion of LPG1Kg, and it is actually injected into 1 kg of LPG. If the air volume is 6Nm ³ , the air ratio is 0.5.
Another object is to raise the molten metal temperature at the beginning of the reduction. This is because the increase in the molten metal temperature at the early stage of reduction reduces the viscosity of the molten metal and is effective in improving the reaction rate.

It should be noted that the air ratio is 0.03 to 0.15 from 30 minutes after the start of reduction to the end of reduction, and the operating conditions of the reducing agent blown from the tuyere and the air flow rate are not different between the present invention and the prior art.
As a result, in the present invention, since the molten metal stirring ability and the hot water temperature increase amount within the initial 30 minutes of the reduction treatment increased, the deoxidation reaction was promoted, and the reduction time of one operation was reduced from the conventional 110 minutes to 90 to 100 minutes. At the same time, the basic unit of reducing agent (eg LPG) was reduced from 3.4 kg / t to 3.2 kg / t.

  As described above, even if the amount of air is greatly increased within the first 30 minutes of reduction start, the molten metal temperature at the end of reduction can be secured at a predetermined temperature (the target hot water temperature or the target minimum hot water temperature or higher). There is no change that it is unnecessary to heat the molten metal again with a heavy oil burner after the reduction is completed.

  In the above, the specific means for measuring the molten metal temperature before the start of reduction is arbitrary, and may be performed using, for example, a consumable thermocouple. Also, the adjustment of the flow rate ratio between hydrocarbon gas and air in accordance with the measured melt temperature before the start of reduction can be adjusted manually by the operator or automatically based on predetermined tables and relational expressions. It is also possible to make adjustments.

Since the hydrocarbon gas is originally injected to reduce oxygen in the molten metal, the amount of air to be injected together with the hydrocarbon gas is such that the hydrocarbon gas completely burns, and CO ₂ and H ₂ In order not to become only O, it must be less than the theoretical air combustion amount of hydrocarbon gas. Specifically, it is desirable to determine the amount of blown air to be within a range of 3 to 30% of the theoretical air combustion amount (air ratio 0.03 to 0.30), and therefore hydrocarbons depending on the melt temperature before the start of reduction. In determining the flow rate ratio of the system gas and air, it is desirable to determine the air injection rate within the range of 0.03 to 0.30 in accordance with the component composition of the hydrocarbon-based gas.
(Confirmation test for oxygen and sulfur concentration changes in the refining furnace)

  Using a cylindrical horizontal tilting type 400 ton refining furnace, 410 tons of crude copper having a Cu purity of 98.5 mass% was purified as follows. That is, after receiving 205 tons of the first molten copper from the converter in the refining furnace kept warm by the combustion of the heavy oil burner in advance, 205 tons of the second furnace from the converter was received. Crude copper will be 400 tons by scraping. The refinery furnace is kept warm with a heavy oil burner while receiving crude copper.

After accepting the second round of molten copper from the converter in this way, scrubbing and then oxidizing the air from the tuyere below the surface at a flow rate of 500 Nm ³ / h for 2.0 hours from the start Infused. After the oxidation process, as a reduction process, gas (LPG) vaporized from petroleum liquefied hydrocarbons containing butane as the main component and air were blown from the tuyere below the hot water surface.

Here, in order to investigate changes in O and S concentrations in the molten copper during the reduction treatment, the melts during the reduction treatment were sampled, and changes over time in the O and S concentrations were measured. FIG. 2 shows an example of changes in O concentration and S concentration in the molten metal when 400 tons of crude copper is reduced at an LPG flow rate of 800 kg / h and an air flow rate of 1200 Nm ³ / h.

  As can be seen from FIG. 2, both O and S have the most significant density drop in the initial 30 minutes (the gray colored portion in the figure). Such sampling survey was conducted several times. The obtained changes in O and S concentrations were almost the same as those in FIG.

  The reduction reaction of the molten copper in the refining furnace is a gas-liquid reaction, the reaction rate is fast, and it is generally said that it is mass transfer-controlled. Therefore, from this result, it is presumed that the reduction reaction is promoted by increasing the stirring ability of the molten metal within the first 30 minutes of the reduction treatment, in which the removal rate of O and S is particularly high.

  In order to confirm the effect of increased air flow rate (increase in stirring capacity of molten metal) in the reduction process, the reduction process was performed by increasing the air flow rate compared to the conventional reduction conditions (described later in Table 2) to reduce the reduction time and LPG intensity. The effect was investigated. In addition, the time slot | zone which increases an air flow rate was changed from the reduction | restoration start-30 minutes of this invention to the reduction | restoration start-45 minutes as the comparative example 1, and the reduction | restoration start-end as the comparative example 2, and the influence was investigated.

From Table 1, in Comparative Examples 1 and 2, the reduction time was 110 minutes or more, and the LPG basic unit was 3.11 kg / t or more, but in the example of the present invention in which the air flow rate was increased only for 30 minutes from the start of reduction, The time was the shortest at 90 minutes, and the LPG basic unit was the lowest at 2.99 kg / t.
Even in the conditions shown in the present invention of Example 1, the 0 concentration decreased from 0.6 to 1.0 mass% to 0.1 mass% or less and the S concentration decreased from 60 to 80 ppm to 30 ppm or less by the reduction treatment.

In order to confirm the effect of Example 1 in actual operation, the operation in the following refining furnace was performed for 3 months, and the results of reduction time and LPG basic unit were compared with the conventional results.
That is, before starting the reduction treatment, the molten metal temperature is measured by a consumable thermocouple, and the LPG blowing flow rate and the air flow rate of the present invention are determined according to the molten metal temperature as shown in Table 2, and the reduction treatment is performed. It was.
In the present invention, the conventional air ratio in the reduction treatment is 0.03 to 0.15, and in the present invention, the air ratio within the initial 30 minutes of the reduction treatment is increased by 0.03 to 0.04.
In Table 2, in each case where the melt temperature before the reduction start was 1115 ° C. to 1130 ° C. or higher, the LPG flow rate was changed midway, and the LPG / air flow rate ratio was changed.
The test results are shown in Table 3.

According to Table 3, for each case where the molten metal temperature before reduction is from 1110 ° C to 1130 ° C or higher, the LPG of the present invention and the air flow rate condition showed a reduction time reduction effect in all temperature ranges compared to the conventional case. .
The average reduction time was reduced by approximately 15% from the conventional 114 minutes to 97 minutes, and the LPG basic unit could be reduced from the conventional 3.36 kg / t to 3.23 kg / t.
By the reduction treatment, the 0 concentration decreased from 0.6 to 1.0 mass% to 0.1 mass% or less, and the S concentration decreased from 60 to 80 ppm to 30 ppm or less, and the quality of the purified crude copper was the same as before.

1 shows one embodiment of a simple embodiment of the present invention. It is a graph which shows the time-dependent change of O and S density | concentration in the crude copper molten metal in the reduction process of a refinement | purification furnace.

Claims (1)

In a copper refining furnace, air is blown at an air ratio of 0.07 to 0.15 with respect to the reducing gas at the initial stage of the reduction process (less than half of the total reduction time), the molten metal is forcibly stirred, and the reaction between the reducing gas and oxygen Promote
Thereafter, the refining furnace operating method is characterized by operating by reducing the air ratio by 0.03 to 0.04 compared to the initial stage to shorten the refining furnace operating time.

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