Operating method of rotary kiln

Abstract

To reduce fuel cost in a rotary kiln whose interior is heated by combustion heat of a fossil fuel such as fuel oil and dust coal while avoiding excessive advance of reduction treatment in a reduction furnace on a downstream side of the rotary kiln.SOLUTION: A method for operating a rotary kiln 1 which is a heating furnace configured to heat the interior thereof by combustion heat of a fossil fuel, and in which a reduction furnace that carries out reduction treatment is connected on a downstream process side. A part of the fossil fuel loaded into the rotary kiln 1 is replaced with RPF.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an operating method of a rotary kiln. More specifically, the present invention relates to an operating method of a rotary kiln that can be preferably applied to the operation of a rotary kiln for drying nickel oxide ore as a raw material in ferronickel smelting.

Background Art

[0002] In ferronickel smelting, which is an alloy of iron and nickel, nickel oxide ore used as a raw material is an ore containing about 1% to 3% by weight of nickel. Since this ore contains about 20% to 25% by weight of moisture, before being subjected to a grinding process and charged into an electric furnace for reduction and melting processes, a drying process is performed to remove this moisture.

[0003] In ferronickel smelting, this drying process is usually performed in such a manner that the ore is fired using a rotary kiln to remove the moisture in the ore and, at the same time, to cause partial reduction to proceed. Then, this ore stays in the rotary kiln for about 2 to 3 hours and is then sequentially charged into the electric furnace.

[0004] In the above drying process, as heat sources for removing the moisture in the ore and for performing the partial reduction process of the ore, mainly, the combustion heat of fossil fuels such as heavy oil and pulverized coal burned by a burner provided at the discharge end of the rotary kiln, and the combustion heat of coal charged into the rotary kiln are used.

[0005] The above coal is usually charged from the charging end of the rotary kiln. However, in order to reduce the usage amount of expensive heavy oil and pulverized coal, in recent years, an operating method of charging coal not from the charging end but from a reducing agent (fuel) supply port provided in the middle of the rotary kiln has also been implemented (see Patent Document 1).

[0006] In the above operation method, by charging coal into the middle of the rotary kiln, coal is supplied to the high-temperature part of the rotary kiln, and the volatile matter contained in the coal can be burned more efficiently than before. However, the volatile matter contained in coal is limited, and the reduction amount of the use of heavy oil and pulverized coal has been limited to a certain range.

[0007] As another conventional method for reducing the use amount of heavy oil and pulverized coal, there is a method of mixing wood pellets into coal and charging them into the rotary kiln (see Patent Document 2). However, wood pellets contain a large proportion of fixed carbon contributing as a reducing agent, about 16% or more and 23% or less. When a large amount is used only for the purpose of raising the temperature inside the rotary kiln, the degree of reduction in the electric furnace for reduction treatment on the downstream side of the rotary kiln may excessively increase, and the quality of the final product may not be properly maintained.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] An object of the present invention is to reduce the fuel cost while avoiding excessive progress of the reduction treatment in the reduction furnace on the downstream side of the rotary kiln in a rotary kiln that is internally heated by the combustion heat of fossil fuels such as heavy oil and pulverized coal.

Means for Solving the Problems

[0010] The inventors of the present invention have conceived that, in a rotary kiln in which a reduction furnace is further connected to the downstream side, by replacing a part of fossil fuels such as heavy oil and pulverized coal input as a heat source with "RPF (Refuse derived paper and plastics densified Fuel)" instead of wood pellets, which were the main conventional alternative fuels, the above problems can be solved, and thus the present invention has been completed. Specifically, the present invention provides the following.

[0011] (1) An operating method of a rotary kiln, which is a heating furnace that heats the inside by the combustion heat of fossil fuels, and in which a reduction furnace for performing a reduction treatment is connected to the downstream process side, wherein a part of the fossil fuels input into the rotary kiln is replaced with RPF.

[0012] According to the operating method of the rotary kiln of (1), in a rotary kiln that heats the inside by the combustion heat of fossil fuels such as heavy oil and pulverized coal, it is possible to reduce the fuel cost while avoiding excessive progress of the reduction treatment in the reduction furnace on the downstream side of the rotary kiln.

[0013] (2) The rotary kiln dries the object to be fired and performs a partial reduction treatment with a reducing agent. The total amount of the fixed carbon content of the RPF input into the rotary kiln and the fixed carbon content of the reducing agent other than the RPF is adjusted to be the amount of fixed carbon required for the reduction treatment performed in the rotary kiln and the reduction furnace. The operating method of the rotary kiln according to (1).

[0014] According to the operating method of the rotary kiln of (2), in the operating method of the rotary kiln according to (1), by optimizing the fixed carbon contained in "RPF" to an amount that is neither excessive nor insufficient for maintaining an appropriate reduction degree, it is possible to more precisely maintain an appropriate reduction degree in the downstream process while reducing the fuel cost.

[0015] (3) The operation method of the rotary kiln according to (1) or (2), wherein the input amount of the RPF is adjusted so that the effective utilization rate of the RPF is 80% or more.

[0016] According to the operation method of the rotary kiln in (3), in the operation method of the rotary kiln according to (1) or (2), by optimizing the calorific value of "RPF" to be exactly the amount required to maintain an appropriate furnace temperature without excess or deficiency, it is possible to more precisely maintain an appropriate furnace temperature while reducing fuel costs.

[0017] (4) The operation method of the rotary kiln according to (2), wherein the RPF is charged into the rotary kiln in a state of being mixed with the reducing agent other than the RPF.

[0018] According to the operation method of the rotary kiln in (4), since "RPF" can be burned more efficiently, it is possible to save more fossil fuels while maintaining the required calorific value.

[0019] (5) The operation method of the rotary kiln according to any one of (1) to (4), wherein the rotary kiln is a rotary kiln that dries the nickel oxide ore as a raw material and performs a partial reduction treatment in ferronickel smelting.

[0020] According to the operation method of the rotary kiln in (5), by enjoying the above effects of the operation method of the rotary kiln according to any one of (1) to (4), it is possible to contribute to the improvement of economic efficiency by reducing the raw material cost in the production of ferronickel smelting.

Advantages of the Invention

[0021] According to the present invention, in a rotary kiln that heats the inside by the combustion heat of fossil fuels such as heavy oil and pulverized coal, it is possible to reduce fuel costs while avoiding excessive progress of the reduction treatment in the reduction furnace on the downstream side of the rotary kiln.

Brief Description of the Drawings

[0022]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0023] Hereinafter, specific embodiments of the "operation method of a rotary kiln" of the present invention will be described. It should be noted that the present invention is not limited to the following embodiments, and can be implemented in other forms and modes other than the following as long as the gist of the present invention is not changed.

[0024] The "operation method of a rotary kiln" of the present invention is a process that can be widely implemented in various rotary kilns that are heating furnaces heated internally by the combustion heat of fossil fuels such as heavy oil and pulverized coal, and in which a reduction furnace for performing a reduction process is connected to the downstream process side. The "heating furnace heated internally by the combustion heat of fossil fuels" may be a heating furnace intended for drying the charged material, but it is preferably a heating furnace intended to perform a partial reduction process together with the above drying process.

[0025] It should be noted that in this specification, the "heating furnace to which a reduction furnace for performing a reduction process is connected to the downstream process side" means that the high-temperature exhaust from the heating furnace (rotary kiln) installed on the upstream process side is installed on the downstream process side. It means that the two facilities are installed so as to operate in conjunction with each other in such a manner that they are input into the "reduction furnace". For example, even if a heating furnace such as a rotary kiln and a reduction furnace such as an electric furnace that operate in conjunction in the above manner are connected via a conveying device such as a belt conveyor, it is naturally a "heating furnace to which a reduction furnace for performing a reduction process is connected to the downstream process side" and is an object to which the present invention is applied.

[0026] As a preferred implementation target of the "operation method of rotary kiln" of the present invention, in the "overall process of ferronickel smelting" described in detail below, a "rotary kiln for drying and reduction" installed upstream of the reduction furnace (electric furnace) and performing the ore drying and partial reduction processes can be mentioned.

[0027] <Overall Process of Ferronickel Smelting> The "overall process of ferronickel smelting" is a metal smelting process that uses nickel oxide ore (nickel oxide ore) as a raw material and has at least "partial reduction process" and "smelting reduction process" as essential processes. In this process, ferronickel with a nickel grade of about 20% by weight can be produced. Also, in this process, if necessary, a drying process prior to the above partial reduction process and a desulfurization process following the above smelting reduction process are further performed.

[0028] In addition, in the above "overall process of ferronickel smelting", as the nickel oxide ore (nickel oxide ore) used as a raw material, for example, in terms of dry ore, the Ni grade is 2.1% by weight or more and 2.5% by weight or less, the Fe grade is 11% by weight or more and 23% by weight or less, the MgO grade is 20% by weight or more and 28% by weight or less, SiO 2 The grade is 29% by weight or more and 39% by weight or less, the CaO grade is less than 0.5% by weight, and the ignition loss is 10% by weight or more and 15% by weight or less. Garnierite ore is preferably used.

[0029] [Partial Reduction Process] The partial reduction process is a process of completely removing the moisture (adherent water, crystal water) in the nickel oxide ore and generating partially reduced nickel oxide ore (nickel oxide sinter). In the partial reduction process, a reducing agent (coal) is added, and these are charged into a rotary kiln for drying and reduction and fired at a firing temperature of about 800°C or more and 900°C or less to completely remove the moisture and perform a partial reduction treatment. The above firing is performed by heating the inside of the rotary kiln with the combustion heat of fossil fuels such as heavy oil and pulverized coal.

[0030] In the above drying and partial reduction processes, as shown in FIG. 1, the combustion heat of fossil fuels such as heavy oil and pulverized coal burned by the burner 14 provided at the discharge end 13 of the rotary kiln 1 is utilized. The ore subjected to the drying and partial reduction processes becomes sintered ore and is discharged from the discharge end 13, and is conveyed by a conveying means to a reduction furnace such as an electric furnace connected to the downstream process side.

[0031] By performing such a partial reduction process according to the "operation method of the rotary kiln" of the present invention, it is possible to reduce the fuel cost while avoiding excessive progress of the reduction process in the electric furnace where the subsequent smelting reduction process is performed.

[0032] [Smelting reduction process] The smelting reduction process is a process in which nickel oxide sintered ore produced in the partial reduction process is charged into an electric furnace, melted and reduced in the furnace to produce ferronickel (metal) and slag. The ferronickel melt produced in this process mainly contains iron and contains nickel at a grade of about 16% by weight or more and 25% by weight or less according to the set amount of the carbonaceous reducing agent. Although the illustration of the electric furnace is omitted, a specific example of the electric furnace for performing smelting reduction can be a known "three-phase AC electrode type circular electric furnace".

[0033] <Operation method of the rotary kiln> The "operation method of the rotary kiln" of the present invention is, for example, a rotary kiln which is a "heating furnace in which a reduction furnace for performing a reduction process is connected to the downstream process side", such as a "rotary kiln for drying and reduction" used in the above-mentioned "overall process of ferronickel smelting". The main feature of the operation method of the rotary kiln is that a part of the above-mentioned fossil fuel charged into the rotary kiln is replaced with "RPF (Refuse derived paper and plastics densified Fuel)".

[0034] [RPF] "RPF" is an abbreviation for "Refuse derived paper and plastics densified Fuel", which is a solid fuel of industrial waste system formed by mixing waste paper, waste plastics and wood chips and molding them. The carbon content after the volatile matter has escaped (hereinafter also referred to as "fixed carbon") is about 5% or more and 10% or less, which is lower than that of wood pellets, and it is a fuel rich in volatile matter compared with wood pellets.

[0035] Therefore, by using "RPF" as fuel, its rich volatile matter can be burned to obtain a combustion heat almost equivalent to that of coal, and the inside of the rotary kiln can be efficiently heated. Moreover, when using "RPF" as fuel, unlike conventional alternative fuels such as "wood pellets", there is almost no need to consider the risk of excessive introduction of "fixed carbon" into the downstream reduction furnace, so a larger amount than "wood pellets" can be introduced into the upstream rotary kiln. Therefore, "RPF" can effectively reduce the usage amount of fossil fuels such as heavy oil and pulverized coal in a "heating furnace with a reduction furnace for reduction treatment connected to the downstream process side".

[0036] In addition, in the "operation method of the rotary kiln" of the present invention, the input amount of "RPF" into the rotary kiln is preferably adjusted so that the total of the fixed carbon amount of "RPF" and the fixed carbon amount of a reducing agent other than RPF (coal in this example) is equal to the fixed carbon amount required for ore reduction. Therefore, when it is desired to increase the input amount of "RPF", the input amount of a reducing agent other than RPF (coal in this example) may be decreased by an amount corresponding to the increased fixed carbon amount of "RPF".

[0037] However, if the input amount of "RPF" is increased beyond a certain limit, it may become difficult to effectively utilize the combustion heat of "RPF". Therefore, it is preferable to adjust the input amount of "RPF" within the range where the combustion heat of "RPF" can be effectively utilized. In this specification, the degree to which the combustion heat of "RPF" is effectively utilized is evaluated by the "RPF effective utilization rate" defined by the following formula (1). This "RPF effective utilization rate" is defined as the ratio of the combustion heat generated by the fuel (heavy oil + pulverized coal) reduced by the input "RPF" to the combustion heat generated by the input "RPF".

[0038] (RPF effective utilization rate) =(Heat quantity of the reduced fuel (heavy oil + pulverized coal)) / (Heat quantity of the input RPF) ··· (1)

[0039] From the above, in the "operation method of the rotary kiln" of the present invention, the input amount of "RPF" into the rotary kiln is preferably adjusted within the input amount range such that the total amount of the fixed carbon content of the RPF and other reducing agents input into the rotary kiln is kept constant and the above "RPF effective utilization rate" is 80% or more.

[0040] In the "operation method of rotary kiln" of the present invention, the optimum value of the input amount of "RPF" into the rotary kiln can be specifically determined by methods such as conducting tests to obtain the relationship between the reduction amount of heavy oil or pulverized coal with respect to the input amount of "RPF" and the "effective utilization rate of RPF". As a specific example of adjusting the input amount of "RPF" into the rotary kiln, for example, when firing 50 t / h of ore in a rotary kiln with a total length of 100 m, the input amounts of both can be adjusted so that the input amount into the rotary kiln is 0.25 t / h for "RPF" and 5.0 t / h for coal as a reducing agent, whereby the "effective utilization rate of RPF" can be made 93.4%. Also, in the same rotary kiln, by adjusting the input amounts of both so that the input amount of "RPF" is 0.5 t / h and the input amount of coal is 4.9 t / h, the "effective utilization rate of RPF" can be made 86.2%. Thus, under the condition of firing 50 t / h of ore in a rotary kiln with a total length of 100 m, which is also a standard operating condition in the "overall process of ferronickel smelting", by setting the input amount of RPF to be 0.25 wt / hr or more and 1.0 wt / hr or less, preferably 0.25 wt / hr or more and 0.5 wt / hr or less, the advantageous effects of the present invention can be enjoyed, and the fuel cost can be reduced while maintaining the product quality.

[0041] Also, "RPF" usually circulates as cylindrical pellets. In the "operation method of rotary kiln" of the present invention, as pellets of the above shape, the diameter is 15 mm or more and 40 mm or less, the length is 10 mm or more and 110 mm or less, and the density is 0.3 to 0.4 cm 3Those can preferably be used. Regarding the pellets having the above shape, it is more preferable that the balance of the overall shape is adjusted such that the diameter becomes larger and the length becomes shorter. As an example, when the above pellets have a diameter of 15 mm or more and less than 25 mm, the length is preferably 60 mm or more and 110 mm or less, and when the diameter is 25 mm or more and 40 mm or less, the length is more preferably 10 mm or more and less than 60 mm. By adjusting the shape and size of the pellets in this way, the size of the "RPF" can be averaged and burned more efficiently.

[0042] [Input of fuel (reductant) into the rotary kiln] The rotary kiln 1 shown in FIG. 1 is an example of a "rotary kiln for drying and reduction", which is a rotary kiln that can be preferably operated by the above-mentioned "overall process of ferronickel smelting". When the "operating method of the rotary kiln" of the present invention is implemented in this rotary kiln 1, "RPF" and "reductants other than RPF such as coal", preferably a mixture of these (hereinafter, these are also collectively referred to as "reductant r") are fed from a reductant (fuel) supply port 12 provided at the charging end 11 of the rotary kiln 1 or at a location corresponding to the vicinity of the middle position of the conveying path of the rotary kiln. The operating method of the rotary kiln of the present invention is a process that actively utilizes the combustion heat of "RPF" by burning the "RPF" thus fed in the rotary kiln 1 to reduce the amount of fossil fuels such as heavy oil and pulverized coal fed as fuel.

[0043] [Rotary kiln] The rotary kiln 1, which is a preferred object of the present invention, is a large cylindrical rotary heating furnace as shown in Fig. 1. Further, the rotary kiln 1 is provided so as to incline downward from its charging end 11 toward the discharging end 13. In the rotary kiln 1, raw ore is charged from the charging end 11, and the ore moves in the rotating body portion toward the discharging end 13. Further, in the rotary kiln 1, usually, a heating burner 14 such as a heavy oil burner is installed on the discharging end 13 side, and the combustion heat of the fossil fuel burned by the burner 14 flows in the direction opposite to that of the ore, thereby heating the ore in countercurrent. Further, as shown in Fig. 1, in the rotary kiln 1, granular reducing agent r and the like quantitatively cut out from the hopper 2 are charged into the rotary kiln 1 from the reducing agent (fuel) supply port 12 via the charging conveyor 3.

[0044] The size of the rotary kiln 1 is not particularly limited, but as a rotary kiln for drying and reduction used in ferronickel smelting, those having an inner diameter of about 4.5 m or more and 6.5 m or less and a total length of about 100 m or more and 150 m or less are preferably used. In a rotary kiln having an inner diameter of less than 4.5 m or a total length of less than 100 m, it becomes difficult to sufficiently secure the time required to dry the ore and perform partial reduction treatment in the rotary kiln, and there is a concern that effective treatment cannot be performed. On the other hand, in a rotary kiln having an inner diameter exceeding 6.5 m or a total length exceeding 150 m, the capital investment for installing the rotary kiln and the cost for maintenance increase, which is not preferable from the viewpoint of economy.

[0045] The temperature inside the rotary kiln 1 is not particularly limited, but it is preferable to maintain the ore temperature at the discharging end 13 at about 700°C or more and 900°C or less, and further, the exhaust gas temperature at the charging end 11 at about 250°C or more and 400°C or less. By maintaining the above temperature at or above each of the above lower limit temperatures, the volatile components and fixed carbon in the charged reducing agent r can be sufficiently burned. Further, by maintaining the above temperature at or below each of the above upper limit temperatures, the generation of beko on the inner wall of the rotary kiln 1 can be prevented.

[0046] Also, the rotation speed of the rotary kiln 1 is not particularly limited, but it is preferably about 0.5 rpm or more and 1.5 rpm or less. When the rotation speed of the rotary kiln 1 is less than 0.5 rpm, the stirring force inside the rotary kiln 1 becomes weak, and the charged reducing agent r slowly slides in the circumferential direction while being buried in the ore used as the raw material, and gradually moves from the charging end 11 side to the discharging end 13 side. In such a case, there is a concern that the contact between the surface of the reducing agent r and the air inside the rotary kiln 1 becomes insufficient, and it becomes difficult to burn the volatile components and fixed carbon in the charged reducing agent r. On the other hand, when the rotation speed of the rotary kiln exceeds 1.5 rpm, the stirring force inside the rotary kiln 1 becomes strong, and the ore of the raw material charged into the rotary kiln 1 rises in the rotary kiln 1 and is discharged from the charging end 11 together with the exhaust gas as dust, and there is a concern that the actual yield of the sinter obtained from the discharging end 13 decreases.

[0047] FIG. 2 is another example of a rotary kiln in which the present invention can be implemented in a preferred embodiment, and is a cross-sectional configuration diagram of a rotary kiln having a scoop feeder 17 for charging "RPF" and "reducing agents other than RPF such as coal". The scoop feeder 17 is provided at a position in the middle of the moving direction of the ore (the longitudinal direction of the rotary kiln body) in the rotary kiln 1A. As shown in FIG. 2, the rotary kiln 1A is composed of a rotating body portion 15 and an outer shell 16 covering the body portion 15, and a scoop feeder 17 is provided at a predetermined position of the body portion 15.

[0048] In the rotary kiln 1A having the scoop feeder 17, the ore o as the raw material is charged into the body portion 15, and the ore o moves from the charging end 11 to the discharging end 13 as the body portion 15 rotates. Also, in this rotary kiln 1A, a space portion 16R is formed by the body portion 15 and the outer shell 16, and the reducing agent r is charged into the space portion 16R through the reducing agent (fuel) supply port 12A provided in the outer shell 16.

[0049] The scoop feeder 17 is formed of, for example, an L-shaped pipe. With a tip portion 171 having an L-shaped bent portion, the reducing agent r is scooped up and passed through the pipe forming the L-shaped straight portion 172 and supplied into the interior of the body portion 15. More specifically, the scoop feeder 17 is fixed to the body portion 15 at a predetermined location, and the tip portion 171 having the L-shaped bent portion is located within the space portion 16R formed by the body portion 15 and the outer shell 16. In this scoop feeder 17, as the body portion 15 to which the scoop feeder 17 is fixed rotates, the reducing agent r loaded in the space portion 16R is scooped up through the tip portion 171 and taken into the scoop feeder 17. Then, when this scoop feeder 17 is positioned above the body portion 15 as the body portion 15 rotates, due to the action of gravity, the reducing agent r taken into the scoop feeder 17 passes through the pipe forming the L-shaped straight portion 172 and is supplied into the interior of the body portion 15.

[0050] In addition, in the rotary kiln 1 (1A), the installation position of the reducing agent (fuel) supply port 12 (12A) in the moving direction of the ore (the longitudinal direction of the main body of the rotary kiln) is preferably directly above or in the vicinity of the position where the temperature inside the main body of the rotary kiln is 900°C or higher and about 1200°C or lower. In the rotary kiln 1A, by introducing the reducing agent r from this position, the volatile components and fixed carbon of the reducing agent r can be efficiently burned.

[0051] Furthermore, among the above-described positions, the installation position of the reducing agent (fuel) supply port 12 (12A) is more preferably set to be from the position "separated from the discharge end 13 by a length of 2 / 10 of the total length of the rotary kiln" to the position "separated from the discharge end 13 by a length of 5 / 10 of the total length of the rotary kiln". When the position where the reducing agent r is introduced is closer to the discharge end 13 than the position "separated from the discharge end 13 by a length of 2 / 10 of the total length of the rotary kiln", the residence time of the introduced reducing agent r in the rotary kiln 1 becomes short, resulting in insufficient heating time and insufficient heating. There is a concern that it may be difficult to burn the volatile components and fixed carbon in the RPF. On the other hand, when it is closer to the charging end 11 than the position "separated from the discharge end 13 by a length of 5 / 10 of the total length of the rotary kiln", since the reducing agent r is introduced into a portion where the temperature in the rotary kiln 1 is low, the reducing agent r is dispersed in the ore layer where the moisture has not been completely removed, and its surface is covered with ore containing moisture. Therefore, even if it is heated during the process of moving toward the discharge end 13, it is difficult to sufficiently bring the reducing agent r into contact with air, and there is a concern that it may be difficult to sufficiently burn the volatile components and fixed carbon in the RPF.

[0052] As an example, in the case of a rotary kiln 1 with a total length of 100 m, inside the rotary kiln, the ore charged from the charging end 11 gradually moves toward the discharge end 13 while being heated to about 200 °C near 30 m from the charging end 11 and heated to 900 °C or more and 1200 °C or less between 80 m. And in such a rotary kiln 1, if the scoop feeder 17 is provided at a position 50 m from the charging end 11, by introducing through this scoop feeder 17, the region from 50 m to 80 m from the charging end 11 can be quickly heated up, so that the region heated to 900 °C or more and 1200 °C or less can be expanded.

Example

[0053] Hereinafter, the present invention will be described more specifically by showing examples based on test operations, but the present invention is not limited to the following examples.

[0054] [Example 1] In ferronickel smelting, a rotary kiln (a rotary kiln for drying and reduction) with an inner diameter of 4.8 m and a length of 105 m was used to perform a firing and drying treatment on the ore. In this firing and drying treatment, a reducing agent composed of "RPF" and coal was used as the reducing agent. The input of the above reducing agent into the rotary kiln rotating at a rotation speed of 1.5 rpm was carried out through a scoop feeder provided at a position 2 / 10 of the total length away from the discharge end of the rotary kiln after premixing "RPF" and coal. Here, the diameter of the "RPF" used for input was 30 mm, the length was 10 to 40 mm, and the density was 0.4 g / cm 3 and the input amount of "RPF" was 0.25 t / h and the input amount of coal was 5.0 t / h with respect to the ore processing amount of 50 t / h.

[0055] The firing power of the burner was adjusted so that the ore temperature at the discharge end of the rotary kiln was 800 °C or higher and 900 °C or lower, and the above operation was continued. The usage amounts of heavy oil and pulverized coal used for the burner were 80 L / h for heavy oil and 3.4 t / h for pulverized coal.

[0056] Next, after performing the drying and reduction treatment of the ore by the above procedure to obtain sinter, the obtained sinter was charged into an electric furnace and reduced and melted by inputting 500 kwh / Dry-ton of electric power to produce ferronickel. When the iron grade in the slag generated in this process was confirmed, the iron grade was 7% or higher and 9% or lower within the management target value range.

[0057] [Example 2] A test operation was carried out in the same manner as in Example 1 except that the input amount of "RPF" was 1 t / h and the input amount of coal was 4.8 t / h. The usage amounts of heavy oil and pulverized coal used for the burner were 42 L / h for heavy oil and 2.97 t / h for pulverized coal. When the iron grade in the slag generated in the electric furnace was confirmed, the iron grade was 7% or higher and 9% or lower within the management target value range.

[0058] [Comparative Example 1] The test operation was carried out in the same manner as in Example 1, except that "RPF" was not used and only coal was used as the reducing agent with an input amount of 5.1 t / h. The amounts of heavy oil and pulverized coal used in the burner were 94 L / h for heavy oil and 3.57 t / h for pulverized coal. When the iron grade in the slag generated in the electric furnace was confirmed, the iron grade was within the range of 7% or more and 9% or less, which is within the management target value range.

[0059] In Example 1 and Example 2 using a reducing agent containing "RPF", compared with Comparative Example 1 without using "RPF", in Example 1, the amount of heavy oil used was reduced by 14 L / h and the amount of pulverized coal used was reduced by 0.17 t / h. In Example 2, the amount of heavy oil used was reduced by 52 L / h and the amount of pulverized coal used was reduced by 0.60 t / h. Also, the iron grade in the slag all changed within the range of 7% or more and 9% or less, and no variation in the degree of reduction due to replacing a part of the reducing agent that also acts as a heat source with "RPF" was observed. From the above, it was confirmed that the operation method of the rotary kiln of the present invention is a process that can suppress the increase in the degree of reduction in the electric furnace and reduce the amounts of heavy oil and pulverized coal used as fuels.

Explanation of Symbols

[0060] 1 Rotary kiln 11 Charging end 12, 12A Reducing agent (fuel) supply port 13 Discharge end 14 Burner 15 Body part 16 Outer shell 16R Space part 17 Scoop feeder 171 Tip part 172 Straight part 2 Hopper 3 Feeding conveyor

Claims

1. A heating furnace that heats its interior by the combustion heat of fossil fuels, and a reduction furnace that performs a reduction process is connected to the downstream process side. By operating a rotary kiln, the nickel oxide ore of the raw material is dried and a partial reduction process is performed. In the reduction furnace, ferronickel metal and slag are generated by melting and reducing the nickel oxide sinter obtained by operating the rotary kiln. A method for smelting ferronickel, replacing a part of the fossil fuel input into the rotary kiln with RPF, A method for smelting ferronickel.

2. The rotary kiln is a rotary kiln that dries the object to be fired and performs a partial reduction process with a reducing agent, The total amount of the fixed carbon content of the RPF input into the rotary kiln and the fixed carbon content of the reducing agent other than the RPF is adjusted to be the amount of fixed carbon required for the reduction process performed in the rotary kiln and the reduction furnace. The method for smelting ferronickel according to claim 1.

3. Adjusting the input amount of the RPF so that the effective utilization rate of the RPF is 80% or more, The method for smelting ferronickel according to claim 1 or 2.

4. The RPF is input into the rotary kiln in a state of being mixed with the reducing agent other than the RPF, The method for smelting ferronickel according to claim 2.

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