A fast-reducing composite pellet and its preparation method and reduction process

Abstract

The present invention discloses a fast-reducing composite pellet, a preparation method, and a pellet reduction process. The composite pellet comprises a core containing a reducing agent with a high volatile content, an intermediate calcium carbonate layer, and an iron-containing shell layer. During the reduction roasting process of the pellet, the core layer decomposes to release a large amount of H2, CO, and CH4, which participate in the reduction of iron oxides. The calcium carbonate layer then undergoes a decomposition reaction to release CO2, which reacts with the carbon in the core to produce more CO through a Boudall reaction. As the CO diffuses outward, it reduces the iron oxides in the shell layer. This allows the iron oxides inside and outside the iron-containing shell layer of the pellet to undergo reduction reactions simultaneously, resulting in a faster reduction rate and higher reduction strength than conventional pellets or pellets with internal carbon.

Description

Technical Field

[0001] The present invention relates to a pellet reduction technology, in particular to a fast-reduced composite pellet and a preparation method and a pellet reduction process, belonging to the technical field of iron-containing pellet reduction. Background Art

[0002] The main processes for extracting metallic iron from iron-containing minerals (primarily iron oxides) include the blast furnace process, direct reduction, and molten reduction. From a metallurgical perspective, ironmaking is the reverse of the process of rusting and subsequent mineralization. Simply put, it involves reducing pure iron from iron-containing compounds. Pig iron is produced by reducing iron ore with a reducing agent at high temperatures. The main raw materials for ironmaking are iron ore and coke; the coke provides heat and produces the reducing agent, carbon monoxide.

[0003] Blast furnace smelting is a continuous process that reduces iron ore to pig iron. Solid raw materials, such as iron ore, coke, and flux, are fed into the blast furnace in batches according to specified proportions via a top charging device, maintaining a constant charge level at the furnace throat. Coke and ore form alternating layers within the furnace. Ironmaking using the blast furnace method is often associated with technical challenges such as long production cycles, low efficiency, high energy consumption, and significant pollutant generation.

[0004] Direct reduced iron (DRI) is a supplement to scrap steel in the mini-process steelmaking process and an ideal raw material for smelting high-quality specialty steel. In recent years, the production of DRI has rapidly expanded worldwide. Due to the scarcity of iron ore and natural gas resources, the development of DRI in my country has been relatively slow. Research and practical applications have focused on coal-based DRI processes, which utilize non-coking coal to produce DRI or metallic iron. Existing coal-based DRI processes typically use oxidized pellets or cold-consolidated pellets as raw materials, reacting in a rotary kiln to produce DRI. In coal-based rotary kiln DRI processes, the time from charge entry to product discharge is 6-8 hours, resulting in a long production cycle and low efficiency. The productivity of a rotary kiln DRI process—the amount of product produced per unit time—is generally dependent on the kiln size and structure, raw material and fuel conditions, kiln temperature and temperature distribution, atmosphere, and charge level. The reduction rate of the pellets is a fundamental factor influencing the DRI production cycle and efficiency.

[0005] In order to increase the reduction rate of direct reduction, researchers and practitioners have proposed some technical measures, including some measures in kiln design (such as CN110229939A, a two-stage rotary kiln non-coking ironmaking device) and pelletizing ingredients (such as CN106591572A, a method for strengthening the preparation and reduction of carbon-containing pellets in iron ore). However, their practicality in industrial applications is relatively poor, and most of them are still in the experimental stage and have not yet been promoted and applied. Summary of the Invention

[0006] In response to the shortcomings of the prior art, the present invention provides a fast-reducing composite pellet, a preparation method thereof, and a pellet reduction process. The composite pellet comprises three layers: an inner core pellet layer (reduced core) comprising a mixture of a reducing agent and a binder containing a high volatile content; a middle pellet layer comprising a calcium carbonate (CaCO3) layer; and an outer pellet layer (iron-containing material layer) comprising a mixture of iron concentrate and a binder. During the pellet reduction roasting process, the inner core pellet layer first decomposes to release a large amount of reducing gases (such as H2, CO, and CH4) to participate in the reduction of iron oxides. The middle pellet layer then undergoes a decomposition reaction to release CO2, which reacts with carbon in the inner core pellet layer to produce more CO. As the CO2 diffuses outward, it reduces the iron oxides in the outer pellet layer. This results in simultaneous reduction reactions of the iron oxides in both the outer and inner layers of the pellet, resulting in a faster reduction rate and higher reduced pellet strength than conventional pellets or pellets with internal carbon content.

[0007] To achieve the above objectives, the technical solutions adopted by the present invention are specifically described as follows:

[0008] According to a first embodiment of the present invention, a fast-reducing composite pellet is provided.

[0009] A fast-reducing composite pellet comprises a reduced core, a calcium carbonate layer covering the reduced core, and an iron-containing material layer covering the calcium carbonate layer.

[0010] Preferably, the reduced spherical core comprises a reducing agent and a binder I. The reducing agent is selected from one or more of bituminous coal, lignite, biomass, and organic solid waste. The binder I is present in an amount of 0.05-0.3% by weight, preferably 0.08-0.2% by weight, of the total mass of the reducing agent.

[0011] Preferably, the iron-containing material layer L3 comprises an iron-containing raw material and a binder II, wherein the content of the binder II is 0.8-3% by weight of the total mass of the iron-containing raw material, preferably 1-2%.

[0012] Preferably, the binder I and the binder II are each independently one or more of bentonite, humic acid, and humate.

[0013] Preferably, the diameter of the reduced spherical core L1 is 2-6 mm, preferably 3-5 mm. The thickness of the calcium carbonate layer L2 is 1-3 mm, preferably 1.5-2 mm. The thickness of the iron-containing material layer L3 is 3-7 mm, preferably 4-6 mm.

[0014] According to a second embodiment of the present invention, a method for preparing rapidly reduced composite pellets is provided.

[0015] A method for preparing a rapidly reduced composite pellet or a method for preparing the composite pellet according to the first embodiment, the method comprising the following steps:

[0016] 1) The reducing agent and the binder I are uniformly mixed, and then granulated using a first pelletizing device to obtain reduced ball cores.

[0017] 2) placing the reduced ball core in a second ball-making device, then adding lime milk and granulating to obtain mother balls coated with a lime milk layer.

[0018] 3) The iron-containing raw material and the binder II are uniformly mixed to form an iron-containing mixture. The mother balls coated with the lime milk layer are placed in a third pelletizing device, and then the iron-containing mixture is added for granulation to obtain green pellets.

[0019] 4) Drying the green pellets with a drying medium containing CO2 to obtain rapidly reduced composite pellets.

[0020] Preferably, in step 1), the reducing agent is selected from one or more of bituminous coal, lignite, biomass, and organic solid waste. The binder I is selected from one or more of bentonite, humic acid, and humate. The amount of binder I added is 0.05-0.3% by weight of the total reducing agent, preferably 0.08-0.2%.

[0021] Preferably, in step 1), the volatile content of the reducing agent is ≥25 wt %, preferably the volatile content of the reducing agent is ≥30 wt %.

[0022] Preferably, in step 1), the diameter of the reduced spherical core is 2 to 6 mm, preferably 3 to 5 mm.

[0023] Preferably, in step 2), the diameter of the mother ball coated with the lime milk layer is 4 to 12 mm, preferably 6 to 9 mm.

[0024] Preferably, in step 3), the binder II is selected from one or more of bentonite, humic acid, and humate. The amount of binder II added is 0.8-3%, preferably 1-2%, of the total mass of the iron-containing raw material. The diameter of the green pellets is 10-25 mm, preferably 12-20 mm.

[0025] Preferably, in step 4), the CO2-containing drying medium is selected from one or more of hot air to which CO2 is added, hot exhaust gas from various blast furnace steelmaking processes, and hot exhaust gas from a direct reduction process. The CO2 content in the CO2-containing drying medium is 5 to 20 wt%, preferably 8 to 15 wt%.

[0026] Preferably, step 1) is specifically as follows: first, the reducing agent and the binder I are crushed to a particle size of -0.074mm≥60% (preferably -0.074mm≥70%), and then mixed in proportion. After mixing evenly, the mixture is sent to a first pelletizing device (such as a pelletizing disc, a cylinder, or a pelletizing machine) for granulation to obtain reduced ball cores.

[0027] Preferably, step 2) comprises mixing and digesting quicklime and water in a mass ratio of 1:1 to 2.5 (preferably 1:1.2 to 1.8) to produce lime milk. The reduced ball cores are placed in a second pelletizing device (e.g., a pelletizing disk or cylinder), and then lime milk is added for granulation to obtain mother balls coated with a lime milk layer.

[0028] Preferably, step 3) comprises the following steps: first, crushing the iron-containing raw material and the binder II to a particle size of -0.074 mm ≥ 75% (preferably -0.074 mm ≥ 80%), and then uniformly mixing them in proportion to obtain an iron-containing mixture. The mother balls coated with the lime milk layer are placed in a third pelletizing device (e.g., a pelletizing disk or cylinder), and then adding the iron-containing mixture to granulate the pellets to obtain green pellets.

[0029] Preferably, step 4) is specifically as follows: placing the green pellets in a drying device, and then introducing a drying medium containing CO2 for drying, the temperature of the drying medium is 150-300°C (preferably 180-260°C), the drying time is 10-100 minutes (preferably 30-80 minutes), and after drying, rapidly reduced composite pellets are obtained.

[0030] According to a third embodiment of the present invention, a reduction process for rapidly reduced composite pellets is provided.

[0031] A reduction process for rapidly reducing composite pellets, or a reduction process for composite pellets as described in the first embodiment, or a reduction process for composite pellets prepared by the method described in the second embodiment, wherein the reduction process is specifically:

[0032] The rapidly reduced composite pellets and carbonaceous fuel are subjected to reduction roasting treatment in a rotary kiln to obtain reduced composite pellets.

[0033] Preferably, the amount of carbonaceous fuel added is such that the C / Fe mass ratio (generally referring to the ratio of the total mass of carbon in the coal added during the roasting process to the total Fe content in the composite pellets) is 1 to 1.5:1, preferably 1 to 1.2:1. The reduction roasting temperature is 850-1100°C, preferably 950-1000°C. The reduction roasting time is 0.5-1.5 hours, preferably 0.8-1.2 hours.

[0034] In the prior art, in the coal-based rotary kiln direct reduction process, it takes 6-8 hours from the time the pellets enter the kiln to the time the products exit the kiln, resulting in a long production cycle and low production efficiency. The productivity of a general rotary kiln direct reduction process is usually related to the size and structure of the kiln, the conditions of raw materials and fuel, the temperature and temperature distribution in the kiln, the atmosphere, and the charge amount, and is also closely related to the structure of the pellets themselves, such as the carbon content, carbon form, particle size, etc. The diffusion direction of the reducing agent inside the pellets is one of the key factors affecting the reduction reaction. Generally, the reducing agent needs to diffuse from the outside of the pellets to the inside of the pellets, and the CO2 or H2O generated after reduction diffuses from the inside of the pellets to the outside. The product gas that diffuses to the outside increases the difficulty of the reducing agent diffusing into the interior of the pellets, which in turn leads to slow reduction efficiency.

[0035] In the present invention, the composite pellets for rapid reduction have a multi-layer structure, the diameter of the pellets is 10 mm to 25 mm (preferably 12 mm to 20 mm), and the cross-sectional structure is as shown in the attached figure. Figure 1 As shown. The composite pellets include three material layers, the inner core pellet layer (L1) is a mixture of a reducing agent and a binder containing a high volatile content, the middle pellet layer (L2) is a calcium carbonate layer (CaCO3), and the outer pellet layer (L3) is a mixture of iron concentrate and a binder. Among them, the diameter of the inner core pellet L1 layer is 2 to 6 mm (preferably 3 to 5 mm), the thickness of the middle layer L2 is 1 to 3 mm (preferably 1.5 to 2 mm), and the thickness of the L3 layer is 3 to 7 mm (preferably 4 to 6 mm). The reducing agent in the L1 layer can be one or more of bituminous coal, lignite, biomass, and organic solid waste, and the binder in the L1 layer and the L3 layer can be an organic or inorganic binder such as bentonite, humic acid, and humate. The composite pellets with this three-layer structure can simultaneously reduce iron oxides from the inside and outside of the iron-containing material layer (L3) during reduction roasting, and have a faster reduction speed and higher reduced ball strength than ordinary pellets or internal carbon pellets.

[0036] In the present invention, when the composite pellets are subjected to high-temperature reduction in the kiln, the iron oxides in the outer layer L3 of the pellets begin to react with the reducing agent in the kiln from the outside to the inside. When the pellet temperature reaches above 810°C, the CaCO3 in the middle layer L2 of the composite pellets decomposes to release CO2 (CaCO3=CaO+CO2 ), CO2 reacts with the reducing agent (such as C) in the L1 layer to produce Boudall reaction (CO 2(g) +C (s) =2CO + (g) +2e -) generates CO, which diffuses outward and reduces the iron oxides in the L3 layer. The generated CO2 undergoes a Bourdeau reaction again, repeating the iron oxide reduction cycle. Therefore, when the multi-layer composite pellets of the present invention are reduced in a reduction furnace, the CO2 released by the decomposition of calcium carbonate in the L2 layer acts as an initiator for the iron oxide reduction reaction within the pellets, causing the iron oxides in both the outer and inner layers to undergo reduction reactions simultaneously, thereby increasing the reduction rate.

[0037] In the present invention, one or more materials such as bituminous coal, lignite, biomass, organic solid waste, etc., which are rich in volatiles, are pre-granulated into balls (i.e., L1) as reducing agents and binders, and are placed as ball cores in the core of the composite pellets. When the composite pellets are reduced in the reduction furnace, the core of the pellets begins to decompose a large amount of reducing gas containing components such as H2, CO, and CH4 when the temperature reaches above 500°C. At this time, because the L2 layer of calcium carbonate shell seals the core layer L1, the reducing gas cannot diffuse outward immediately, thereby preventing the reducing gas from precipitating before the iron oxides begin to be significantly reduced. When the temperature reaches above 810°C, the L2 layer begins to decompose, and the reducing gas diffuses outward in large quantities, reducing the iron oxides in the L3 layer. Since the reducing ability of H2 is much higher than that of CO, the reducing gas released from the L1 layer of the core of the pellets greatly promotes the reduction of the iron oxides inside the composite pellets, thereby increasing the overall reduction rate of the pellets.

[0038] In the present invention, a drying medium rich in CO2 is used to dry the green pellets. During the drying process, the carbonation reaction of lime milk (Ca(OH)2) is very easy to proceed (Ca(OH)2+CO2=CaCO3+H2O, ), the lime milk layer in the middle material layer of the green ball undergoes a carbonation reaction to generate CaCO3, thereby forming a calcium carbonate L2 layer. After drying, fast-reduced composite pellets are obtained. The CO2-rich drying medium can be hot air with added CO2, hot exhaust gas from various blast furnace steelmaking processes, and direct reduction processes. Generally, the CO2 content of the CO2-rich drying medium is 5-15wt%, preferably 8-12wt%.

[0039] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0040] 1: The fast-reduction composite pellets proposed in the present invention have a multi-layer structure, consisting of a reducing agent core, a calcium carbonate shell, and an iron-containing material layer, from the center of the pellet outward. The iron-containing material layer does not require internal carbon. During high-temperature reduction of the composite pellets, the CO2 released by the decomposition of the calcium carbonate in the middle layer of the pellets acts as an initiator for the reduction reaction of the iron oxides within the pellets. It reacts with the reducing agent in the core layer of the pellets to form CO. As the CO2 diffuses outward, it reduces the iron oxides from the inside out, thereby reducing the iron oxides inside and outside the pellets simultaneously. This improves the reduction efficiency, resulting in a faster reduction speed than conventional pellets and a higher reduction intensity than pellets with internal carbon.

[0041] 2. The composite pellets of this invention have a calcium carbonate shell as the middle layer. During the composite pellet reduction and heating process, the H2-containing reducing gas released by the reducing agent in the pellet core is trapped, preventing immediate outward diffusion and preventing the reducing gas from escaping before the iron oxides in the outer layer of the pellets begin to be significantly reduced. However, when the reduction temperature rises above 810°C, the calcium carbonate shell in the middle layer begins to decompose, releasing reducing gases such as H2, which diffuse outward in large quantities and reduce the outer iron oxides. Because H2 has a much higher reducing power than CO, the H2-containing reducing gas significantly promotes the reduction of the iron oxides within the composite pellets.

[0042] 3: The present invention proposes a fast-reducing composite pellet and a preparation method. First, materials such as bituminous coal, lignite, biomass, organic solid waste, etc. containing a large amount of volatile matter are made into ball cores by ball making or agglomeration. Then, lime milk is added to make ball cores to make mother balls coated with a lime milk layer. Then, a mixture of iron ore concentrate and a binder is further balled to form composite pellet green balls. Finally, the lime milk in the middle material layer of the pellet is carbonated by drying with hot air or hot tail (waste) gas containing a large amount of CO2 to obtain fast-reducing composite pellets. The process is simple and the operability is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 Schematic diagram of the structure of the composite pellets for rapid reduction of the present invention.

[0044] Figure 2 The figure is a flow chart of the preparation process of the fast-reducing composite pellets of the present invention.

[0045] Reference numerals: L1: reduced core; L2: calcium carbonate layer; L3: iron-containing material layer. DETAILED DESCRIPTION

[0046] The technical solutions of the present invention are illustrated below with examples, and the scope of protection requested by the present invention includes but is not limited to the following embodiments.

[0047] A fast-reducing composite pellet, such as Figure 1As shown, the composite pellet includes a reduced core L1, a calcium carbonate layer L2 covering the reduced core L1, and an iron-containing material layer L3 covering the calcium carbonate layer L2.

[0048] Preferably, the reducing spherical core L1 includes a reducing agent and a binder I. The reducing agent is selected from one or more of bituminous coal, lignite, biomass, and organic solid waste. The binder I is present in an amount of 0.05-0.3% by weight, preferably 0.08-0.2% by weight, of the total reducing agent.

[0049] Preferably, the iron-containing material layer L3 comprises an iron-containing raw material and a binder II, wherein the content of the binder II is 0.8-3% by weight of the total mass of the iron-containing raw material, preferably 1-2%.

[0050] Preferably, the binder I and the binder II are each independently one or more of bentonite, humic acid, and humate.

[0051] Preferably, the diameter of the reduced spherical core L1 is 2-6 mm, preferably 3-5 mm. The thickness of the calcium carbonate layer L2 is 1-3 mm, preferably 1.5-2 mm. The thickness of the iron-containing material layer L3 is 3-7 mm, preferably 4-6 mm.

[0052] A method for preparing a fast-reducing composite pellet, such as Figure 2 As shown, the method includes the following steps:

[0053] 1) The reducing agent and the binder I are uniformly mixed, and then granulated using a first pelletizing device to obtain reduced spherical cores L1.

[0054] 2) The reduced ball core L1 is placed in a second ball-forming device, and then lime milk is added and granulated to obtain mother balls coated with a lime milk layer.

[0055] 3) The iron-containing raw material and the binder II are uniformly mixed to form an iron-containing mixture. The mother balls coated with the lime milk layer are placed in a third pelletizing device, and then the iron-containing mixture is added for granulation to obtain green pellets.

[0056] 4) Drying the green pellets with a drying medium containing CO2 to obtain rapidly reduced composite pellets.

[0057] Preferably, in step 1), the reducing agent is selected from one or more of bituminous coal, lignite, biomass, and organic solid waste. The binder I is selected from one or more of bentonite, humic acid, and humate. The amount of binder I added is 0.05-0.3% by weight of the total reducing agent, preferably 0.08-0.2%.

[0058] Preferably, in step 1), the volatile content of the reducing agent is ≥25 wt %, preferably the volatile content of the reducing agent is ≥30 wt %.

[0059] Preferably, in step 1), the diameter of the reduced spherical core L1 is 2 to 6 mm, preferably 3 to 5 mm.

[0060] Preferably, in step 2), the diameter of the mother ball coated with the lime milk layer is 4 to 12 mm, preferably 6 to 9 mm.

[0061] Preferably, in step 3), the binder II is selected from one or more of bentonite, humic acid, and humate. The amount of binder II added is 0.8-3%, preferably 1-2%, of the total mass of the iron-containing raw material. The diameter of the green pellets is 10-25 mm, preferably 12-20 mm.

[0062] Preferably, in step 4), the CO2-containing drying medium is selected from one or more of hot air to which CO2 is added, hot exhaust gas from various blast furnace steelmaking processes, and hot exhaust gas from a direct reduction process. The CO2 content in the CO2-containing drying medium is 5 to 20 wt%, preferably 8 to 15 wt%.

[0063] Preferably, step 1) is specifically as follows: first, the reducing agent and the binder I are crushed to a particle size of -0.074mm≥60% (preferably -0.074mm≥70%), and then mixed in proportion. After mixing evenly, the mixture is sent to the first pelletizing equipment (such as a pelletizing disc, a cylinder, or a pelletizing machine) for granulation to obtain the reduced ball core L1.

[0064] Preferably, step 2) comprises mixing and digesting quicklime and water in a mass ratio of 1:1 to 2.5 (preferably 1:1.2 to 1.8) to produce lime milk. The reduced cores L1 are placed in a second pelletizing device (e.g., a pelletizing disk or cylinder), and then lime milk is added for granulation to obtain mother balls coated with a lime milk layer.

[0065] Preferably, step 3) comprises the following steps: first, crushing the iron-containing raw material and the binder II to a particle size of -0.074 mm ≥ 75% (preferably -0.074 mm ≥ 80%), and then uniformly mixing them in proportion to obtain an iron-containing mixture. The mother balls coated with the lime milk layer are placed in a third pelletizing device (e.g., a pelletizing disk or cylinder), and then adding the iron-containing mixture to granulate the pellets to obtain green pellets.

[0066] Preferably, step 4) is specifically as follows: placing the green pellets in a drying device, and then introducing a drying medium containing CO2 for drying, the temperature of the drying medium is 150-300°C (preferably 180-260°C), the drying time is 10-100 minutes (preferably 30-80 minutes), and after drying, rapidly reduced composite pellets are obtained.

[0067] A reduction process for rapidly reduced composite pellets, the reduction process specifically comprising: subjecting the rapidly reduced composite pellets and carbonaceous fuel to reduction roasting treatment in a rotary kiln to obtain reduced composite pellets.

[0068] Preferably, the carbonaceous fuel is added in an amount such that the C / Fe mass ratio is 1 to 1.5:1, preferably 1 to 1.2:1. The reduction roasting temperature is 850-1100°C, preferably 950-1000°C. The reduction roasting time is 0.5-1.5 hours, preferably 0.8-1.2 hours.

[0069] Example 1

[0070] First, the bituminous coal and sodium humate are crushed to a particle size of -0.074 mm or more, and then the bituminous coal and 0.1% of the sodium humate based on the dry weight of the bituminous coal are mixed and uniformly mixed to obtain a reduction mixture;

[0071] First, the iron ore concentrate and bentonite are crushed to a particle size of -0.074 mm or more, and then the iron ore concentrate and 1.0% bentonite based on the dry weight of the iron ore are mixed and uniformly mixed to obtain an iron-containing mixture;

[0072] Quicklime and water are mixed and digested in a mass ratio of 1:1.8 to obtain lime milk;

[0073] The reduction mixture is first added to a first pelletizing disk to produce core balls with an average diameter of about 4 mm; the core balls and lime milk are then added to a second pelletizing disk to produce mother balls coated with a lime milk layer with an average diameter of about 7 mm; the mother balls coated with the lime milk layer and the iron-containing mixture are then added to a third pelletizing disk to produce composite green pellets with an average diameter of about 16 mm; and the composite green pellets are finally dried in hot air at 200° C. (CO2 content of 10 wt%) for 60 minutes to obtain rapidly reduced composite pellets.

[0074] The rapidly reduced composite pellets were reduction-roasted with lump coal at a C / Fe mass ratio of 1:1 in a rotary kiln at a temperature of 1000°C for 60 minutes to obtain reduced pellets with a metallization rate of 90.1% and an average strength of 642N per reduced ball.

[0075] Example 2

[0076] First, the bituminous coal and sodium humate are crushed to a particle size of -0.074 mm or more, and then the bituminous coal and 0.1% of the sodium humate based on the dry weight of the bituminous coal are mixed and uniformly mixed to obtain a reduction mixture;

[0077] First, the iron ore concentrate and bentonite are crushed to a particle size of -0.074 mm or more, and then the iron ore concentrate and 1.0% bentonite based on the dry weight of the iron ore are mixed and uniformly mixed to obtain an iron-containing mixture;

[0078] Quicklime and water are mixed and digested in a mass ratio of 1:1.8 to obtain lime milk;

[0079] The reduction mixture is first added to a first pelletizing disk to produce core balls with an average diameter of about 4 mm; the core balls and lime milk are then added to a second pelletizing disk to produce mother balls coated with a lime milk layer with an average diameter of about 7 mm; the mother balls coated with the lime milk layer and the iron-containing mixture are then added to a third pelletizing disk to produce composite green pellets with an average diameter of about 16 mm; and the composite green pellets are finally dried in hot air at 200° C. (CO2 content of 10 wt%) for 60 minutes to obtain rapidly reduced composite pellets.

[0080] The rapidly reduced composite pellets were reduction-roasted with lump coal at a C / Fe mass ratio of 1.2:1 in a rotary kiln at a temperature of 1000°C for 60 minutes to obtain reduced pellets with a metallization rate of 92.6% and an average strength of 655N per reduced ball.

[0081] Example 3

[0082] First, the bituminous coal and sodium humate are crushed to a particle size of -0.074 mm or more, and then the bituminous coal and 0.1% of the sodium humate based on the dry weight of the bituminous coal are mixed and uniformly mixed to obtain a reduction mixture;

[0083] First, the iron ore concentrate and bentonite are crushed to a particle size of -0.074 mm or more, and then the iron ore concentrate and 1.0% bentonite based on the dry weight of the iron ore are mixed and uniformly mixed to obtain an iron-containing mixture;

[0084] Quicklime and water are mixed and digested in a mass ratio of 1:1.8 to obtain lime milk;

[0085] The reduction mixture is first added to a first pelletizing disk to produce core balls with an average diameter of about 4 mm; the core balls and lime milk are then added to a second pelletizing disk to produce mother balls coated with a lime milk layer with an average diameter of about 7 mm; the mother balls coated with the lime milk layer and the iron-containing mixture are then added to a third pelletizing disk to produce composite green pellets with an average diameter of about 16 mm; and the composite green pellets are finally dried in hot air at 200° C. (CO2 content of 10 wt%) for 60 minutes to obtain rapidly reduced composite pellets.

[0086] The rapidly reduced composite pellets were reduction-roasted with lump coal at a C / Fe mass ratio of 1.5:1 in a rotary kiln at a roasting temperature of 1000°C for 60 minutes to obtain reduced pellets with a metallization rate of 93.3% and an average strength of 660N per reduced ball.

[0087] Example 4

[0088] First, the bituminous coal and sodium humate are crushed to a particle size of -0.074 mm or more, and then the bituminous coal and 0.1% of the sodium humate based on the dry weight of the bituminous coal are mixed and uniformly mixed to obtain a reduction mixture;

[0089] First, the iron ore concentrate and bentonite are crushed to a particle size of -0.074 mm or more, and then the iron ore concentrate and 1.0% bentonite based on the dry weight of the iron ore are mixed and uniformly mixed to obtain an iron-containing mixture;

[0090] Quicklime and water are mixed and digested in a mass ratio of 1:1.8 to obtain lime milk;

[0091] The reduction mixture is first added to a first pelletizing disk to produce core balls with an average diameter of about 4 mm; the core balls and lime milk are then added to a second pelletizing disk to produce mother balls coated with a lime milk layer with an average diameter of about 7 mm; the mother balls coated with the lime milk layer and the iron-containing mixture are then added to a third pelletizing disk to produce composite green pellets with an average diameter of about 16 mm; and the composite green pellets are finally dried in hot air at 200° C. (CO2 content of 10 wt%) for 60 minutes to obtain rapidly reduced composite pellets.

[0092] The rapidly reduced composite pellets were reduction-roasted with lump coal at a C / Fe mass ratio of 1.2:1 in a rotary kiln at a temperature of 1000°C for 40 minutes to obtain reduced pellets with a metallization rate of 85.4% and an average strength of 621N per reduced ball.

[0093] Example 5

[0094] First, the bituminous coal and sodium humate are crushed to a particle size of -0.074 mm or more, and then the bituminous coal and 0.1% of the sodium humate based on the dry weight of the bituminous coal are mixed and uniformly mixed to obtain a reduction mixture;

[0095] First, the iron ore concentrate and bentonite are crushed to a particle size of -0.074 mm or more, and then the iron ore concentrate and 1.0% bentonite based on the dry weight of the iron ore are mixed and uniformly mixed to obtain an iron-containing mixture;

[0096] Quicklime and water are mixed and digested in a mass ratio of 1:1.8 to obtain lime milk;

[0097] The reduction mixture is first added to a first pelletizing disk to produce core balls with an average diameter of about 4 mm; the core balls and lime milk are then added to a second pelletizing disk to produce mother balls coated with a lime milk layer with an average diameter of about 7 mm; the mother balls coated with the lime milk layer and the iron-containing mixture are then added to a third pelletizing disk to produce composite green pellets with an average diameter of about 16 mm; and the composite green pellets are finally dried in hot air at 200° C. (CO2 content of 10 wt%) for 60 minutes to obtain rapidly reduced composite pellets.

[0098] The rapidly reduced composite pellets were reduction-roasted with lump coal at a C / Fe mass ratio of 1.2:1 in a rotary kiln at a temperature of 950°C for 60 minutes to obtain reduced pellets with a metallization rate of 86.1% and an average strength of 629N per reduced ball.

[0099] Example 6

[0100] First, the bituminous coal and sodium humate are crushed to a particle size of -0.074 mm or more, and then the bituminous coal and 0.1% of the sodium humate based on the dry weight of the bituminous coal are mixed and uniformly mixed to obtain a reduction mixture;

[0101] First, the iron ore concentrate and bentonite are crushed to a particle size of -0.074 mm or more, and then the iron ore concentrate and 1.0% bentonite based on the dry weight of the iron ore are mixed and uniformly mixed to obtain an iron-containing mixture;

[0102] Quicklime and water are mixed and digested in a mass ratio of 1:1.8 to obtain lime milk;

[0103] The reduction mixture is first added to a first pelletizing disk to produce core balls with an average diameter of about 4 mm; the core balls and lime milk are then added to a second pelletizing disk to produce mother balls coated with a lime milk layer with an average diameter of about 7 mm; the mother balls coated with the lime milk layer and the iron-containing mixture are then added to a third pelletizing disk to produce composite green pellets with an average diameter of about 16 mm; and the composite green pellets are finally dried in hot air at 200° C. (CO2 content of 10 wt%) for 60 minutes to obtain rapidly reduced composite pellets.

[0104] The rapidly reduced composite pellets were reduction-roasted with lump coal at a C / Fe mass ratio of 1.2:1 in a rotary kiln at a roasting temperature of 1100°C for 60 minutes to obtain reduced pellets with a metallization rate of 93.0% and an average strength of 661N per reduced ball.

[0105] Example 7

[0106] First, the bituminous coal and sodium humate are crushed to a particle size of -0.074 mm or more, and then the bituminous coal and 0.1% of the sodium humate based on the dry weight of the bituminous coal are mixed and uniformly mixed to obtain a reduction mixture;

[0107] First, the iron ore concentrate and bentonite are crushed to a particle size of -0.074 mm or more, and then the iron ore concentrate and 1.0% bentonite based on the dry weight of the iron ore are mixed and uniformly mixed to obtain an iron-containing mixture;

[0108] Quicklime and water are mixed and digested in a mass ratio of 1:1.8 to obtain lime milk;

[0109] The reduction mixture is first added to a first pelletizing disk to produce core balls with an average diameter of about 4 mm; the core balls and lime milk are then added to a second pelletizing disk to produce mother balls coated with a lime milk layer with an average diameter of about 7 mm; the mother balls coated with the lime milk layer and the iron-containing mixture are then added to a third pelletizing disk to produce composite green pellets with an average diameter of about 16 mm; and the composite green pellets are finally dried in hot air at 200° C. (CO2 content of 10 wt%) for 60 minutes to obtain rapidly reduced composite pellets.

[0110] The rapidly reduced composite pellets were reduction-roasted with lump coal at a C / Fe mass ratio of 1.2:1 in a rotary kiln at a roasting temperature of 1000°C for 75 minutes to obtain reduced pellets with a metallization rate of 92.9% and an average strength of 658N per reduced ball.

[0111] Comparative Example 1

[0112] First, bituminous coal and sodium humate are crushed to particle sizes of -0.074 mm or more, and then the bituminous coal and 0.1% of sodium humate based on the dry weight of the bituminous coal are mixed and evenly mixed to obtain a reduction mixture; iron concentrate and bentonite are crushed to particle sizes of -0.074 mm or more, and then the iron concentrate and 1.0% of bentonite based on the dry weight of the iron concentrate are mixed and evenly mixed to obtain an iron-containing mixture; quicklime and water are mixed and digested in a mass ratio of 1:1.8 to obtain lime milk; finally, the reduction mixture, the iron-containing mixture and the lime milk are mixed to obtain a pellet mixture.

[0113] The pellet mixture is added to a third pelletizing disk to obtain composite green pellets having an average diameter of about 16 mm; the composite green pellets are finally dried in hot air (with a CO2 content of 10 wt%) at 200° C. for 60 minutes to obtain composite pellets;

[0114] The composite pellets were reduction-roasted with lump coal of C / Fe mass ratio of 1.2:1 in a rotary kiln at a temperature of 1000°C and a time of 60 min to obtain reduced pellets with a metallization rate of 81.8% and an average strength of 608 N per reduced ball.

[0115] Comparative Example 2

[0116] First, the bituminous coal and sodium humate are crushed to a particle size of -0.074 mm or more, and then the bituminous coal and 0.1% of the sodium humate based on the dry weight of the bituminous coal are mixed and uniformly mixed to obtain a reduction mixture;

[0117] First, the iron ore concentrate and bentonite are crushed to a particle size of -0.074 mm or more, and then the iron ore concentrate and 1.0% bentonite based on the dry weight of the iron ore are mixed and uniformly mixed to obtain an iron-containing mixture;

[0118] The reducing mixture is first added to the first pelletizing disk to produce cores with an average diameter of about 4 mm. The cores and the iron-containing mixture are then added to the third pelletizing disk to produce composite green pellets with an average diameter of about 15.6 mm. Finally, the composite green pellets are dried in hot air (with a CO2 content of 10 wt%) at 200°C for 60 minutes to obtain composite pellets.

[0119] The composite pellets were reduction-roasted with lump coal with a C / Fe mass ratio of 1.2:1 in a rotary kiln at a temperature of 1000°C for 60 minutes to obtain reduced pellets with a metallization rate of 77.4% and an average strength of 536N per reduced ball.

[0120] Comparative Example 3

[0121] First, the iron ore concentrate and bentonite are crushed to a particle size of -0.074 mm or more, and then the iron ore concentrate and 1.0% bentonite based on the dry weight of the iron ore are mixed and uniformly mixed to obtain an iron-containing mixture;

[0122] The iron-containing mixture is added to the third pelletizing disk to obtain composite green pellets with an average diameter of about 15.5 mm; finally, the composite green pellets are dried in hot air (CO2 content is 10wt%) at 200°C for 60 minutes to obtain composite pellets; the composite pellets are reduction-roasted with lump coal with a C / Fe mass ratio of 0.5:1 in a rotary kiln at a roasting temperature of 1000°C and a roasting time of 60 minutes to obtain reduced pellets with a metallization rate of 80.9% and a reduced ball strength of 312N / piece.

[0123] Comparative Example 4

[0124] First, the iron ore concentrate and bentonite are crushed to a particle size of -0.074 mm or more, and then the iron ore concentrate and 1.0% bentonite based on the dry weight of the iron ore are mixed and uniformly mixed to obtain an iron-containing mixture;

[0125] The iron-containing mixture is added to the third pelletizing disk to obtain composite green pellets with an average diameter of about 15.5 mm; finally, the composite green pellets are dried in hot air (CO2 content is 10wt%) at 200°C for 60 minutes to obtain composite pellets; the composite pellets are reduction-roasted with lump coal with a C / Fe mass ratio of 1.2:1 in a rotary kiln at a roasting temperature of 1000°C and a roasting time of 60 minutes to obtain reduced pellets with a metallization rate of 82.7% and a reduced ball strength of 516N / piece.

[0126] Comparative Example 5

[0127] First, the iron ore concentrate and bentonite are crushed to a particle size of -0.074 mm or more, and then the iron ore concentrate and 1.0% bentonite based on the dry weight of the iron ore are mixed and uniformly mixed to obtain an iron-containing mixture;

[0128] The iron-containing mixture is added to the third pelletizing disk to obtain composite green pellets with an average diameter of about 15.5 mm; finally, the composite green pellets are dried in hot air (CO2 content is 10wt%) at 200°C for 60 minutes to obtain composite pellets; the composite pellets are reduction-roasted with lump coal with a C / Fe mass ratio of 2.0:1 in a rotary kiln at a roasting temperature of 1000°C and a roasting time of 60 minutes to obtain reduced pellets with a metallization rate of 83.6% and a reduced ball strength of 652N / piece.

[0129] Comparative Example 6

[0130] First, the bituminous coal and sodium humate are crushed to a particle size of -0.074 mm or more, and then the bituminous coal and 0.1% of the sodium humate based on the dry weight of the bituminous coal are mixed and uniformly mixed to obtain a reduction mixture;

[0131] First, the iron ore concentrate and bentonite are crushed to a particle size of -0.074 mm or more, and then the iron ore concentrate and 1.0% bentonite based on the dry weight of the iron ore are mixed and uniformly mixed to obtain an iron-containing mixture;

[0132] Quicklime and water are mixed and digested in a mass ratio of 1:1.8 to obtain lime milk;

[0133] The reduction mixture is first added to a first pelletizing disk to produce core balls with an average diameter of about 4 mm; the core balls and lime milk are then added to a second pelletizing disk to produce mother balls coated with a lime milk layer with an average diameter of about 7 mm; the mother balls coated with the lime milk layer and the iron-containing mixture are then added to a third pelletizing disk to produce composite green pellets with an average diameter of about 16 mm; and the composite green pellets are finally dried in hot air at 200° C. (CO2 content of 10 wt%) for 60 minutes to obtain rapidly reduced composite pellets.

[0134] The rapidly reduced composite pellets were reduction-roasted with lump coal at a C / Fe mass ratio of 0.5:1 in a rotary kiln at a temperature of 950°C for 60 minutes to obtain reduced pellets with a metallization rate of 80.2% and an average strength of 602N per reduced ball.

Claims

1. A fast-reducing composite pellet, characterized by: The composite pellet comprises a reduced core (L1), a calcium carbonate layer (L2) covering the reduced core (L1), and an iron-containing material layer (L3) covering the calcium carbonate layer (L2). The reducing spherical core (L1) includes a reducing agent and a binder I; the reducing agent is selected from one or more of bituminous coal, lignite, biomass, and organic solid waste; and the iron-containing material layer (L3) includes an iron-containing raw material and a binder II.

2. The composite pellet according to claim 1, characterized in that: The content of binder I is 0.05-0.3% of the total mass of the reducing agent; and / or The content of binder II is 0.8-3% of the total mass of the iron-containing raw material.

3. The composite pellet according to claim 2, characterized in that: The content of binder I is 0.08-0.2% of the total mass of the reducing agent; and / or The content of binder II is 1-2% of the total mass of the iron-containing raw material.

4. The composite pellet according to any one of claims 1 to 3, characterized in that: Binder I and binder II are independently one or more of bentonite, humic acid, and humate.

5. The composite pellet according to any one of claims 1 to 3, characterized in that: The diameter of the reduced spherical core (L1) is 2-6 mm; the thickness of the calcium carbonate layer (L2) is 1-3 mm; and the thickness of the iron-containing material layer (L3) is 3-7 mm.

6. The composite pellet according to claim 5, characterized in that: The diameter of the reduced spherical core (L1) is 3-5 mm; the thickness of the calcium carbonate layer (L2) is 1.5-2 mm; and the thickness of the iron-containing material layer (L3) is 4-6 mm.

7. A method for preparing a fast-reducing composite pellet, characterized in that: The method comprises the following steps: 1) uniformly mixing the reducing agent and the binder I, and then granulating them using a first pelletizing device to obtain reduced spherical cores (L1); 2) placing the reduced ball core (L1) in a second ball-forming device, then adding lime milk and granulating to obtain mother balls coated with a lime milk layer; 3) uniformly mixing the iron-containing raw material and the binder II to form an iron-containing mixture; The mother balls coated with the lime milk layer are placed in a third pelletizing device, and then iron-containing mixed materials are added for granulation to obtain green pellets; 4) Drying the green pellets with a drying medium containing CO2 to obtain rapidly reduced composite pellets; In step 1), the reducing agent is selected from one or more of bituminous coal, lignite, biomass, and organic solid waste.

8. The method according to claim 7, wherein: In step 1), the binder I is selected from one or more of bentonite, humic acid, and humate; the added amount of the binder I is 0.05-0.3% of the total mass of the reducing agent.

9. The method according to claim 8, characterized in that: The addition amount of binder I is 0.08-0.2% of the total mass of the reducing agent.

10. The method according to claim 8 or 9, characterized in that: The volatile content of the reducing agent is ≥ 25wt%; and / or The diameter of the reduced spherical core (L1) is 2-6 mm.

11. The method according to claim 10, characterized in that: The volatile content of the reducing agent is ≥30wt%; and / or The diameter of the reduced spherical core (L1) is 3-5 mm.

12. The method according to any one of claims 7 to 9 and 11, characterized in that: In step 2), the diameter of the mother ball coated with the lime milk layer is 4 to 12 mm; and / or In step 3), the binder II is selected from one or more of bentonite, humic acid, and humate; the amount of binder II added is 0.8-3% of the total mass of the iron-containing raw material; and the diameter of the green pellets is 10-25 mm.

13. The method according to claim 12, wherein: In step 2), the diameter of the mother ball coated with the lime milk layer is 6 to 9 mm; and / or In step 3), the amount of binder II added is 1-2% of the total mass of the iron-containing raw material; and the diameter of the green pellets is 12-20 mm.

14. The method according to any one of claims 7 to 9, 11 and 13, characterized in that: In step 4), the CO2-containing drying medium is selected from one or more of hot air with added CO2, hot tail gas from various processes of blast furnace steel smelting, and hot tail gas from direct reduction process; the CO2 content in the CO2-containing drying medium is 5~20wt%.

15. The method according to claim 14, characterized in that: The content of CO2 in the CO2-containing drying medium is 8~15wt%.

16. The method according to any one of claims 7 to 9, characterized in that: Step 1) specifically comprises: first crushing the reducing agent and the binder I into particle sizes of -0.074 mm ≥ 60%, then mixing them in proportion, and after mixing evenly, sending them to a first pelletizing device for pelletizing to obtain reduced ball cores (L1); and / or Step 2) specifically comprises: mixing quicklime and water in a mass ratio of 1:1 to 2.5 to obtain lime milk; placing the reduced ball core (L1) in a second pelletizing device, and then adding lime milk to granulate to obtain mother balls coated with a lime milk layer; and / or Step 3) is specifically as follows: first, the iron-containing raw material and the binder II are crushed to a particle size of -0.074 mm ≥ 75%, and then mixed in proportion to obtain an iron-containing mixture; the mother ball coated with the lime milk layer is placed in a third pelletizing device, and then the iron-containing mixture is added for granulation to obtain green pellets; and / or Step 4) is specifically as follows: placing the green pellets in a drying device, and then introducing a drying medium containing CO2 for drying. The temperature of the drying medium is 150-300°C, and the drying time is 10-100 minutes. After drying, rapidly reduced composite pellets are obtained.

17. The method according to claim 16, wherein: Step 1) specifically comprises: first crushing the reducing agent and the binder I into particle sizes of -0.074 mm ≥ 70%, then mixing them in proportion, and after mixing evenly, sending them to a first pelletizing device for pelletizing to obtain reduced ball cores (L1); and / or Step 2) specifically comprises: mixing quicklime and water in a mass ratio of 1:1.2-1.8 to obtain lime milk; placing the reduced ball core (L1) in a second pelletizing device, and then adding lime milk to granulate to obtain mother balls coated with a lime milk layer; and / or Step 3) is specifically as follows: first, the iron-containing raw material and the binder II are crushed to a particle size of -0.074 mm ≥ 80%, and then mixed in proportion to obtain an iron-containing mixture; the mother ball coated with the lime milk layer is placed in a third pelletizing device, and then the iron-containing mixture is added for granulation to obtain green pellets; and / or Step 4) is specifically as follows: placing the green pellets in a drying device, and then introducing a drying medium containing CO2 for drying. The temperature of the drying medium is 180-260°C, and the drying time is 30-80 minutes. After drying, fast-reduced composite pellets are obtained.

18. A reduction process for the composite pellets according to any one of claims 1 to 6 or the composite pellets prepared by the method according to any one of claims 7 to 17, characterized in that: The reduction process is specifically as follows: The rapidly reduced composite pellets and carbonaceous fuel are subjected to reduction roasting treatment in a rotary kiln to obtain reduced composite pellets; the amount of the carbonaceous fuel added is such that the C / Fe mass ratio is 1-1.5:

1.

19. The reduction process of composite pellets according to claim 18, characterized in that: The temperature of reduction roasting is 850-1100° C.; the time of reduction roasting is 0.5-1.5 h.

20. The reduction process of composite pellets according to claim 19, characterized in that: The amount of the carbonaceous fuel added is such that the C / Fe mass ratio is 1 to 1.2:1; The temperature of the reduction roasting is 950-1000° C.; the time of the reduction roasting is 0.8-1.2 h.

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