Rotary kiln operation method for ferronickel smelting

Abstract

The present invention provides an appropriate method for charging waste plastics, which contribute to reduction, in addition to coal, which is a reducing agent, using nickel ore or both nickel ore and nickel-containing substances as the main raw materials. [Solution] A rotary kiln operating method for smelting ferronickel using only a rotary kiln 10 in which the flows of raw materials and gas are countercurrent, without the need for melting equipment, in which nickel ore or both nickel ore and a nickel-containing substance as a nickel source, a slag melting material, and coal are charged into the raw material charging side of the rotary kiln, and hot air and waste plastics are blown into the calcined product discharge side of the rotary kiln using a heating burner 11 and a waste plastic blowing burner 12, and calcined product is obtained from the calcined product discharge side, and nickel is reduced by the coal charged from the raw material charging side and the waste plastics 21 blown into the calcined product discharge side.

Description

[Technical Field]

[0001] The present invention provides a technology for utilizing waste plastics when reducing and smelting Ni using nickel ore and nickel-containing substances as main raw materials and coal as a reducing agent in ferronickel smelting using only a rotary kiln without a melting step. [Background technology]

[0002] Ferronickel alloys are widely used as a nickel source for nickel-containing austenitic stainless steels, duplex stainless steels, alloy steels, etc. Ferronickel alloys have traditionally been produced by reducing Ni and Fe contained in nickel oxide ore.

[0003] Conventionally, in order to reduce Ni and Fe in a rotary kiln, a method has been widely used in which a reducing agent mainly made of coal is charged into the raw material charging side of the rotary kiln together with the nickel ore to be reduced, and this technology is also applied in Patent Document 1. In this reaction, as shown in the following formula, carbon (C) contained in the coal combines with oxygen (O2) from the air introduced into the rotary kiln to generate carbon monoxide (CO), which acts as a reducing gas to reduce some of the Ni oxides and Fe oxides contained in the Ni ore and Ni-containing material, generating ferronickel and carbon dioxide (CO2). 2C+O2 → 2CO NiO+CO → Ni+CO2 Fe2O3+CO → 2FeO+CO2 FeO+CO → Fe+CO2

[0004] Currently, in order to reduce costs and CO2 emissions in reduction smelting, it is recognized that reducing the amount of coal used, which has been widely used in the past, is an issue that must be addressed in nickel smelting as well.

[0005] Examples of using waste plastics as a heat source instead of fossil fuels include the cement kiln described in Patent Document 2 and the hot air furnace described in Patent Document 3. In Patent Document 2, in addition to a burner that injects the main fuel into the rotary kiln, a burner is provided for injecting combustible waste such as waste plastics, which is then injected into the rotary kiln together with the fossil fuel. This method burns combustible waste and uses it as a heat source, but does not provide the injection conditions suitable for Ni reduction required in the present invention.

[0006] In a nickel smelting process that involves a melting step after the rotary kiln, Patent Document 4 proposes a technology in which RPF is charged through a reducing agent (fuel) supply port located at the middle position in the longitudinal direction of the rotary kiln, thereby substituting part of the coal as a reducing agent. Furthermore, in a similar ferronickel smelting process, Patent Document 5 proposes a technology in which a scrap tire shredder is charged through a reducing agent (fuel) supply port, thereby substituting part of the coal as a reducing agent. Both technologies are applied to partial reduction in a rotary kiln that involves a melting reduction step in an electric furnace, and when ferronickel smelting is performed using only a rotary kiln without an electric furnace, there is no mention of at what position in the longitudinal direction of the rotary kiln the reducing agent should be charged to obtain a reduction effect.

[0007] Furthermore, the reducing material supply ports described in Patent Documents 4 and 5 can be installed in relatively low-temperature areas without any problems. However, even if an attempt is made to provide a reducing material charging hole in a rotary kiln to target an area where Ni reduction is occurring, it may be difficult to install the charging hole due to high temperatures or the generation of slag. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2024-47981 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-87047 [Patent Document 3] Japanese Patent Application Publication No. 3-10026 [Patent Document 4] Japanese Patent Publication No. 2022-180818 [Patent Document 5] Japanese Patent Publication No. 2023-81117 Summary of the Invention [Problem to be solved by the invention]

[0009] As described above, in a ferronickel smelting process in which nickel reduction is completed using only a rotary kiln without a melting step, it is necessary to raise the temperature of the raw materials in the rotary kiln to a temperature at which nickel and iron are reduced and a slag phase consisting of a solid phase and a liquid phase is formed, and to coarsen the ferronickel particles to a size that allows them to be recovered before they are discharged from the rotary kiln. This process has the advantage that it does not involve a melting step using an electric furnace, and therefore does not require the site and cost required to install an electric furnace, and does not require the operating costs.

[0010] On the other hand, in order to reduce the cost of coal required for reduction and heating, and CO2 emissions, it is necessary to make effective use of waste plastics that are currently incinerated or landfilled. A typical manufactured product of plastics is polyethylene (CH2CH2). n , Polypropylene (CH2CHCH3) n , polystyrene [CH2CH(C6H5)] n These are the various types of carbon and hydrogen (H) contained in waste plastics, which can become a source of reducing gases such as CO and H2 gas inside the rotary kiln.

[0011] Therefore, the present invention aims to provide an appropriate method for charging waste plastics that contribute to reduction in addition to coal as a reducing agent, using nickel ore or both nickel ore and nickel-containing substances as the main raw materials. Note that the nickel-containing substances referred to here refer to recycled products containing 1% or more of Ni, such as spent nickel catalysts from petroleum refining, waste batteries, and electronic chips such as MLCCs (multilayer capacitors). [Means for solving the problem]

[0012] The inventors conducted an experiment using a rotary kiln with a diameter of 4.2 m and a length of 72 m to clarify the appropriate range of conditions for the waste plastic charging method. A schematic diagram of the experiment is shown in FIG. 1. The ferronickel smelting apparatus 1 of the present invention has a rotary kiln 10. The left end of the rotary kiln 10 is the raw material charging side, and the right end is the side where the raw material is calcined and discharged (hereinafter referred to as the calcined product discharge side). The raw material 20 charged from the raw material charging side consists of a blend of crushed nickel ore, nickel-containing material, limestone as a slag melting material, and coal. The limestone was in the form of uncalcined calcium carbonate and was set at 60 kg / ton of nickel source (per ton of nickel ore and nickel-containing material). Anthracite was used as the reducing agent, and the coal content was adjusted to a range of 100 to 150 kg / ton of nickel source. These raw materials were mixed, the moisture content was adjusted to about 15%, and then the mixture was formed into briquettes and charged into the rotary kiln 10.

[0013] The rotary kiln 10 used in the test was equipped with a burner 11 that injects either pulverized coal or heavy oil into the calcined material discharge side, where raw materials 20 are calcined and discharged, and the raw materials 20 are heated by the combustion heat. Note that the effects of the present invention are not impaired even if a gas fuel such as LNG is used as a heat source other than the above. In addition, a burner 12 that injects waste plastic 21 into the rotary kiln was equipped on the calcined material discharge side, and the waste plastic was injected so that it would fall at various distances.

[0014] The rotary kiln 10 operates an exhaust fan installed in the exhaust gas system to introduce air into the furnace from the calcination material discharge side, and exhaust gas and heat from combustion in the burner 11 flow toward the raw material charging port. Inside the rotary kiln, as shown by the opposing arrows, gas flows in the opposite direction to the flow of raw materials 20, and the calcination material discharge side becomes a higher temperature area in the longitudinal direction. As the high-temperature gas flows toward the raw material charging side and the raw materials 20 tumble inside the rotary kiln, heat is transferred to the raw materials 20, not only to the surface of the raw materials but also to the interior of the raw material layer.

[0015] The newly produced Ni and Fe, reduced inside the rotary kiln, initially forms small ferronickels, but as it moves through the furnace toward the burnt material discharge side, the temperature rises, causing some of the surrounding oxides to melt and form slag. Once molten slag is formed, the ferronickels become more mobile and undergo repeated coalescence and growth. They grow to a size that can be recovered, and are finally discharged from the rotary kiln 10 as clinker, a mixture with slag. Therefore, it is important that the speed of movement through the furnace is not too fast for growth to be effective, and if it is too slow, it becomes difficult to ensure industrial production volumes. In this test, the rotation speed was adjusted so that the material would move through the 72 m rotary kiln in approximately 10 hours.

[0016] The waste plastic 21 blown into the burned material discharge side reacts with oxygen in the air introduced into the rotary kiln, and in the high temperature range exceeding 1000°C, which is the operating temperature of the rotary kiln 10, it turns into CO and H2 gas according to the following reaction formula. Waste plastic ((CH2CH2) n etc.) + O2 → CO + H2

[0017] If the waste plastic 21 blown into the rotary kiln has a certain size, it will not burn out immediately but will be taken into the burned material in the rotary kiln, generating the above-mentioned reducing gas from inside the raw material, thereby achieving the effect of a reducing agent.

[0018] The air introduced into the rotary kiln from the discharge side of the fired material also reacts with the fuel (coal, heavy oil, LNG) from the burner, generating heat (exothermic reaction). There, the following reactions occur, turning the air into CO2 and CO: C(fuel) + O2(air) → CO2 2C (fuel) + O2 (air) → 2CO

[0019] However, the CO gas flows through the open space above the raw material layer in the rotary kiln, and its function as a gas medium to transfer heat to the raw materials is small, as it has little effect on reducing Ni oxides in the raw materials. The heat transfer caused by this gas flow raises the temperature of the raw materials in the rotary kiln toward the raw material charging side, and the gas temperature also gradually decreases.

[0020] Plastics have lower ignition temperatures (in the presence of oxygen) and pyrolysis temperatures (in the absence of oxygen) than coal, and if they are charged together with the raw materials from the raw material charging side, they will burn out or pyrolyze quickly. This shows that it is preferable to have them reach a position that is more effective for Ni recovery directly. However, even if we try to install a reducing material charging hole in the rotary kiln to target the area where Ni reduction is occurring, it is difficult to install the charging hole due to the high temperature and the generation of slag.

[0021] Under the above conditions, experiments were conducted in which nickel ore, or a blend of nickel ore and a nickel-containing substance, was reduced using coal and waste plastics injected from the calcined product discharge side. As a result, it was found that by following the injection conditions according to the present invention, it is possible to reduce and smelt nickel using coal, which is a reducing agent contained in the raw material, and waste plastics, which is injected from the calcined product discharge side, and that it is possible to reduce the amount of coal used as a reducing agent while maintaining an industrially sufficient Ni yield.

[0022] That is, the present invention is a method for operating a rotary kiln in which ferronickel is smelted only in a rotary kiln in which the flows of raw materials and gas are countercurrent, without the need for melting equipment, in which nickel ore or both nickel ore and a nickel-containing substance as a nickel source, a slag melting material, and coal are charged into the raw material charging side of the rotary kiln, and hot air and waste plastics are blown into the calcined material discharge side of the rotary kiln by a heating burner and a waste plastic injection burner, and a calcined material is obtained from the calcined material discharge side, and nickel is reduced by the coal charged from the raw material charging side and the waste plastics blown into the calcined material discharge side, and in this method for operating a rotary kiln in which nickel is smelted, the Ni recovery rate is satisfied, the effect of reducing the basic unit of the reducing agent is also obtained, and continuous stable operation is possible.

[0023] In the rotary kiln operating method, it is preferable that the waste plastics are blown in so that they fall within a range of 2 to 15 m from the burned material discharge side.

[0024] Furthermore, in the rotary kiln operation method, it is preferable that the average size of the waste plastic is a diameter of 5 to 25 mm and a length of 5 to 70 mm.

[0025] Furthermore, in the rotary kiln operation method, it is preferable that the surface temperature of the burned material at a position 5 m from the burned material discharge side is in the range of 1100 to 1400°C. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a schematic diagram of a rotary kiln used in ferronickel smelting according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0027] The ranges of the rotary kiln operating conditions of the present invention will be explained below. Reduction by coal fed from the nickel source charging side and waste plastics blown in from the burnt product discharge side By charging coal as a reducing agent together with the raw materials from the raw material charging side and waste plastics from the calcined material discharge side, it was possible to obtain a stable and sufficient Ni yield and produce ferronickel of excellent quality. Plastics have lower ignition temperatures (in the presence of oxygen) and pyrolysis temperatures (in the absence of oxygen) than coal, and if they are charged together with the raw materials from the raw material charging side, they burn out early or undergo pyrolysis, not contributing to reduction, and the waste plastic charging is not effectively utilized. For this reason, charging from the raw material charging side is not effective, and it is preferable to inject from the calcined material discharge side under the injection conditions described below.

[0028] Waste plastic injection position: 2 to 15 m When the waste plastic injection position is within the above range, a stable and sufficient Ni yield can be obtained, and ferronickel of excellent quality can be produced. If the waste plastic is injected further than 2 m, the waste plastic immediately falls and is discharged outside the furnace, and it does not fully function, resulting in insufficient generation of reducing gas, and as a result, insufficient reduction of Ni and a decrease in yield are observed. On the other hand, if the waste plastic is injected at a position beyond 15 m, no gas is generated in the area on the calcined product discharge side from the falling position, resulting in insufficient reduction of Ni and a decrease in yield are observed. Therefore, the injection distance is set to 2 to 15 m.

[0029] Temperature 5m from the firing point: 1100-1400℃ When the temperature at the 5m position from the burnt material discharge side is within the above range, a stable and sufficient Ni yield can be obtained, and ferronickel of excellent quality can be produced. If the temperature is below 1100°C, the growth of ferronickel becomes insufficient, and a decrease in yield is observed. On the other hand, if the temperature exceeds 1400°C, the load on the furnace body becomes large, resulting in frequent replacement of refractories. Therefore, the temperature at the 5m position is set to 1100 to 1400°C.

[0030] Average size of waste plastic: 5-25mmφ (diameter) x 5-70mmL (length) When the average dimensions of the waste plastics are within the above range, a stable and sufficient Ni yield can be obtained, and high-quality ferronickel can be produced. If the dimensions are smaller than 5 mmφ x 5 mmL, the waste plastics burn out immediately when injected into the rotary kiln. They are not absorbed into the raw material layer and do not contribute to reduction. This results in insufficient contact between the raw material and the reducing gas, resulting in insufficient Ni reduction and a reduced yield. On the other hand, if the dimensions exceed 25 mmφ x 70 mmL, the waste plastics are heavy, requiring significant energy to blow far with a blower, and the amount that can be injected into the rotary kiln is limited. If the injection volume is small, the spatial density relative to the raw material in the kiln is low, and reducing gas is generated only from limited locations, resulting in insufficient contact between the reducing gas and the raw material. This results in insufficient Ni reduction and a reduced yield. Therefore, the average dimensions were set to 5-25 mmφ (diameter) x 5-70 mmL (length). [Example]

[0031] The following examples are presented to clarify the effects of the present invention. A rotary kiln with a diameter of 4.2 m, a length of 72 m, and a tilt angle of 1° was used for the operation. The rotation speed of the rotary kiln was controlled within a range of 40 to 50 rph. The raw materials were heated using a pulverized coal burner on the burned material discharge side of the rotary kiln, and waste plastic was then injected. The raw materials consisted primarily of crushed nickel oxide ore and nickel-containing materials, and also contained coal as a reducing agent and limestone as a slag melting agent. The moisture content was adjusted to approximately 15%, and the materials were formed into briquettes, which were then charged into the rotary kiln at a feed rate of 17 tons / hr. The limestone consumption rate was adjusted between 10 and 100 kg / ton of nickel source, while monitoring the condition of the slag in the furnace.

[0032] The nickel oxide ore used had a chemical composition of 36-52% SiO2, 0.2-3% Al2O3, 6-20% Fe, 17-30% MgO, 1.5-3% Ni, 0.5% or less Co, 2% or less Cr2O3, and 0.005% or less P. The nickel-containing materials used included spent nickel catalysts from petroleum refineries, spent batteries, and electronic chips such as multilayer capacitors (MLCCs). In addition to Ni, these materials contained SiO2, Al2O3, TiO2, BaO, Co, Fe, Cr, Mn, Sn, and other elements. The Ni concentration was 1-50%.

[0033] The coal added as a reducing agent had a fixed-C content of 70-80%, an ash content of 10-15% consisting of SiO2, Al2O3, CaO, etc., and an Ig-loss content of 10%. The waste plastics injected had a total-C content of 60-80%, a total-H content of 8-13%, and consisted of RPF of various sizes. A roots blower was used for injection.

[0034] In the evaluation, the weight ratio of Ni recovered as ferronickel from the burned material (a mixture of ferronickel and slag) relative to the weight of Ni charged into the rotary kiln, as well as the reduction ratio of coal usage as a reducing agent accompanying the injection of waste plastics, were used as indicators, and in addition, the feasibility of stable operation of the rotary kiln was also taken into consideration. Ferronickel was recovered through a process of crushing the recovered burned material and a process of separating the metal and slag from the crushed material in water due to the difference in specific gravity.

[0035] The results are shown in Table 1. The measurement and evaluation methods for each item were as follows. 1) The blowing reach The reach distance from the burned material discharge side according to the blowing conditions of the Roots blower into which the waste plastic is blown was measured offline in advance, and the reach distance was determined based on those conditions. The longitudinal variation of the reach of the waste plastic was within a range of 1 m. For example, "1 to 2 m" means that the reach was within a range of more than 1 m but less than 2 m. 2) Waste plastic residence time Waste plastic was blown into the rotary kiln and visually observed as it moved toward the burned material discharge side while emitting flames. The time from when the dropped waste plastic emitted flames until it stopped emitting flames was measured and recorded as the residence time. If the waste plastic was discharged from the rotary kiln while still emitting flames, the residence time was recorded as the time until it was discharged. 3) Temperature at 5m point The temperature was measured using a radiation thermometer at a point 5 m from the firing product discharge side. 4) Average size of waste plastic The dimensions of a total of 20 RPFs were measured randomly for each test run, and the average value was used as the average dimension. 5) Evaluation (a) Reduction rate of reducing agent after injection: The reduction rate of reducing agent (anthracite) after starting injection of waste plastic. 〇: Reduction effect of 5% or more, ×: No reduction effect (a) Ni recovery rate: The ratio of the weight of Ni recovered to the weight of Ni charged during 24 hours of operation. ○: Ni recovery rate of 90% or more, ×: Ni recovery rate of less than 90% (c) Operational stability: Evaluation of operational continuity, such as whether there is any damage to the rotary kiln and whether there is any unreacted plastic mixed in the discharged burned material. 〇: Stable operation, ×: Problems with continuing operation

[0036] [Table 1]

[0037] Each example of the invention will be described below. Nos. 1 to 15 satisfied all ranges and were therefore rated as ◯ for both Ni recovery and quality.

[0038] Comparative Example: In No. 16, waste plastic was charged through the raw material charging port, but it was thermally decomposed immediately after charging and did not contribute to reduction.

[0039] In Nos. 17 and 18, the temperature at the 5m point exceeded the specified range, causing significant damage to the refractory in the rotary kiln, which required the operation to be stopped and the refractory replaced, making it difficult to continue stable Ni smelting. Although a small reduction in the amount of reducing agent was observed, it was not sufficient.

[0040] In Nos. 19 and 20, the temperature at the 5m point was lower than the specified range, which resulted in poor growth of ferronickel and a significantly poor Ni recovery rate. The effect of reducing the amount of reducing agent was also not achieved.

[0041] In No. 21, the average size of the waste plastic was large, and it was discharged from the furnace before it was completely burned, which meant that it did not contribute enough to the reduction, and the Ni recovery rate was extremely poor. The effect of reducing the amount of reducing agent was not achieved. In addition, a large amount of waste plastic was mixed into the calcined product, making stable operation of the ferronickel recovery process impossible.

[0042] In Nos. 22 and 23, the average size of the waste plastic was small, and it burned out before being incorporated into the raw materials in the furnace, resulting in insufficient contribution to reduction and a significantly poor recovery rate of Ni. The reduction effect of the reducing agent was also not achieved.

[0043] In Nos. 24 and 25, the injected waste plastic reached a position too close to the source, so it was immediately discharged before being incorporated into the raw material and burned out, resulting in insufficient contribution to reduction and a significantly poor Ni recovery rate. The effect of reducing the amount of reducing agent was also not achieved. Furthermore, a large amount of waste plastic was mixed into the fired product, making stable operation impossible in the ferronickel recovery process.

[0044] In No. 26 and No. 27, the injected waste plastic reached too far inside the furnace, so it burned out as it moved through the furnace, resulting in insufficient contribution to reduction and a significantly poor Ni recovery rate. The effect of reducing the amount of reducing agent was also not achieved. [Industrial Applicability]

[0045] This invention provides an operating technology that uses less coal than conventional nickel smelting. It also leads to the effective use of waste plastics, contributing to the utilization of waste materials. Furthermore, it enables the inexpensive production of ferronickel, reducing the cost of stainless steel, which is made from ferronickel. [Explanation of symbols]

[0046] 1: Ferronickel smelting equipment, 10: Rotary kiln, 11: Burner, 12: Waste plastic injection burner, 13: Radiation thermometer, 20: Raw material, 21: Waste plastic.

Claims

1. A rotary kiln operation method for smelting ferronickel using only a rotary kiln in which raw materials and gas flow in a countercurrent manner without using a melting facility, comprising: Nickel ore as a nickel source, or both nickel ore and a nickel-containing substance, a slag melting material, and coal are charged into the raw material charging side of the rotary kiln; A heating burner and a waste plastic blowing burner are used to blow hot air and waste plastic into the burned material discharge side of the rotary kiln, The fired product is obtained from the fired product discharge side, A rotary kiln operating method for ferronickel smelting, characterized in that nickel is reduced by coal charged from the raw material charging side and waste plastics injected from the burned product discharge side.

2. 2. The rotary kiln operating method for ferronickel smelting according to claim 1, wherein the waste plastics are blown in so that the waste plastics fall within a range of 2 to 15 m from the burned product discharge side.

3. 2. The rotary kiln operating method for ferronickel smelting according to claim 1, wherein the average size of the waste plastic is a diameter of 5 to 25 mm and a length of 5 to 70 mm.

4. 2. The rotary kiln operating method for ferronickel smelting according to claim 1, wherein the surface temperature of the burnt material at a position 5 m from the burnt material discharge side is in the range of 1100 to 1400°C.

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