Method for utilizing a pellet return

Abstract

The application provides a kind of pellet return utilization method, through the method steps provided by the application, the pellet return is used for fluidized reduction ironmaking raw material, only needs moderate processing, and does not need to be finely ground to the concentrate particle size level required for pelletizing, thereby avoiding excessive wear of equipment, reducing grinding cost.Moreover, when used for fluidized bed reduction ironmaking, the pellet return has high cold and hot strength, good reducibility, and does not produce crystallization water decomposition endotherm and thermal explosion problem, thus having more excellent metallurgical properties than conventional iron ore powder raw material for fluidized bed, can effectively avoid particle pulverization, reduce sticking and loss of flow, and can reduce energy consumption, improve the production stability of fluidized bed.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgy technology, and mainly relates to a method for utilizing recycled pellet ore. Background Technology

[0002] Iron ore pellets are a high-quality raw material for ironmaking in the steel industry. They are widely used and have seen significant development due to their high grade, uniform particle size, good strength, convenient transportation and storage, and excellent high-temperature softening, high-temperature reducing expansion, and dripping properties. Currently, there are three main industrial processes for large-scale production of oxidized iron ore pellets: vertical shaft furnace, chain grate-rotary kiln, and belt roaster. Among these, the chain grate-rotary kiln process dominates the current pelletizing process. During pellet production, some breakage and pulverization are inevitable due to transportation, collision, and drying. These mainly occur during green pellet screening, drying, preheating, kiln tail, and finished product screening stages, collectively referred to as return material or return ore. Vertical shaft furnace pelletizing processes generate a relatively large amount of return material, sometimes exceeding 10%. The chain grate-rotary kiln process typically produces less than 5%, and the belt roaster process produces even less. This includes some dust from dust removal and some larger particle size return material. Typically, the return material generated during the green pellet screening and drying stages can be easily reused for pelletizing. However, return material generated during preheating and finished product screening—such as the dry return material generated during high-temperature preheating of pellets in the chain grate-rotary kiln process, or the undersize material smaller than 8mm after finished pellet screening—is too large to be directly returned for pelletizing. Furthermore, due to high-temperature roasting, its hardness is very high, and re-grinding results in high grinding costs and severe equipment wear, often leading to poor processing results. Many large particles remain uncrushed, or the particle size after crushing is still too large, resulting in poor pelletizing performance and causing stratification of the finished pellets, severely affecting the quality of the pellets. These return materials can only be stockpiled or sold at low prices to other concentrators or sintering plants. There is also research on briquetting them, but the resulting briquettes often have poor strength and metallurgical properties, failing to meet the requirements of blast furnace smelting. Therefore, researching and exploring new ways and methods to utilize pellet return material is crucial. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the present invention aims to provide a method for utilizing recycled pellets in fluidized bed ironmaking. On the one hand, this method eliminates the need for excessive grinding of recycled pellets with large particle size and high hardness, reducing grinding costs and equipment wear, while also avoiding the adverse effects of recycled pellets on the pelleting process and product quality. On the other hand, using recycled pellets as raw materials in fluidized bed ironmaking can effectively reduce pulverization during the fluidization reaction, inhibit agglomeration and flow loss, reduce the burden on the dust recovery system, and improve the stability of fluidized bed production.

[0004] The objective of this invention is achieved through the following technical solution:

[0005] A method for utilizing recycled pellet ore includes the following steps:

[0006] (1) Transport the pellet return material to the return material bin for storage and standby. The pellet return material is the pellet ore with unqualified particle size screened out from the finished pellet ore in the pellet production process, or the dry return material generated in the pellet preheating link.

[0007] (2) Obtain the pre-treated material with a particle size of 0.1 - 5 mm by crushing and screening the pellet return material, and transport it to the pre-treated material bin for storage and standby.

[0008] (3) Use the pre-treated material obtained in step (2) as the raw material for fluidized direct reduction ironmaking, add it to the fluidized bed reduction system for reduction reaction, and obtain a reduction product with a metallization rate not less than 90%.

[0009] (4) Carry out hot pressing treatment on the fluidized bed reduction product in step (3) under nitrogen protection to obtain a hot pressed block product.

[0010] Further, in step (1), the pellet production process is a conventional pellet ore production process; the dry return material is the dry return material generated in the grate-kiln pellet production process in the grate-kiln link; the content of TFe in the chemical composition of the pellet return material is not less than 60%.

[0011] Further, the conventional pellet ore production process is one of shaft furnace, grate-kiln, and traveling grate type pelletizer.

[0012] Further, the fine powder under 0.1 mm obtained in the screening process is returned to the pellet raw material for re-pelletizing, and the oversize material over 5 mm is transported to the return material bin or returned to the crusher for re-treatment.

[0013] Further, the screening process is multi-stage screening, and the pre-treated materials with different particle size ranges are reserved separately. The different particle size ranges are 5 kinds of particle size ranges such as A, B, C, D, and E, where 0.1 mm < A ≤ 1 mm, 1 mm < B ≤ 2 mm, 2 mm < C ≤ 3 mm, 3 mm < D ≤ 4 mm, 4 mm < E ≤ 5 mm, and the average particle strength is 20 N / mm 2 above.

[0014] Further, the fluidized bed reduction system consists of 2 - 4 stages of fluidized beds. The pre-treated material is used as a single furnace charge or formulated into a mixed furnace charge with other ironmaking raw materials. The pre-treated material is selected from a certain particle size range or used in combination with multiple particle size ranges in proportion.

[0015] Further, the fluidized bed reduction gas is hydrogen or mixed gas, and the volume content of CO and H2 in the mixed gas is above 95%.

[0016] Furthermore, the reaction temperature of the fluidized bed reduction system is controlled at 550℃~800℃, the reaction time is controlled at 30~120min, and the reaction pressure is controlled at 200~800kPa.

[0017] Furthermore, the density of the hot-pressed block is not less than 4.5 g / cm³. 3 .

[0018] The recycled material generated during the preheating and finished product screening stages of pellet production has a very high hardness due to high-temperature roasting. If it is to be returned to the raw material for pelletizing, it must be re-milled (≤0.074mm proportion above 90%, ≤0.044mm proportion above 60%), resulting in high grinding costs and severe equipment wear. Often, the processing effect is poor; many large particles are difficult to crush, or the particle size after milling still fails to reach the pelletizing concentrate level, leading to poor pelletizing performance and subsequent stratification of the pellets, seriously affecting pellet quality and production stability. It can only be stockpiled or sold at low prices to other concentrators or sintering plants. There is also research on briquetting it, but the resulting briquettes often have poor strength and metallurgical properties, failing to meet the requirements of blast furnace smelting. There is a strong desire to explore new ways and methods to utilize recycled pellet material.

[0019] On the other hand, fluidized bed reduction ironmaking process was once regarded as the most reasonable method among gas-based reduction processes because it can directly use fine ore without coke, has advantages such as large gas-solid phase contact area and good heat and mass transfer conditions. However, some shortcomings in actual production have limited the development of fluidized bed ironmaking technology. In fluidized bed reduction ironmaking technology, the reduction device typically used is a gas-solid fluidized bed. The reducing gas and iron ore within a certain particle size range will generate strong disturbances within the bed. The iron ore particles will constantly collide and rub against each other, causing particle wear and easily leading to a gradual reduction in particle size. During fluidized bed reduction, the material usually reacts at 500℃ to 850℃. Since iron ore particles often contain water of crystallization and carbonate minerals, problems such as decomposition and endothermic reactions will occur. Furthermore, during the heating process, due to the effect of thermal stress and the precipitation of water of crystallization, explosions may occur, causing the iron ore particles to become more powdery. This changes the designed particle size of the material, and the generation of a large amount of fine powder will exacerbate the agglomeration tendency, lose the fluidized state, and form a fixed bed. The reducing gas changes from turbulent flow to flowing away through the voids in the particles, drastically reducing the gas-solid contact area. In severe cases, the reaction almost stops, and the ore powder cannot be automatically discharged, causing production to stop. Furthermore, finer iron ore powder particles are easily carried out of the fluidized bed in large quantities by high-temperature, high-speed reducing gases, leading to fine powder separation, clogging of equipment pipelines, thus affecting the stable operation of the fluidized bed and causing loss of reducing raw materials, and increasing the burden on the recovery system.

[0020] This invention utilizes recycled pellets as raw material for fluidized bed reduction ironmaking. It requires only moderate processing, eliminating the need for grinding to the required concentrate particle size for pelletizing, thus avoiding excessive equipment wear and reducing grinding costs. Furthermore, when used in fluidized bed reduction ironmaking, recycled pellets, compared to conventional fluidized bed raw material powder, are high-temperature treated "clinker" with extremely high physical strength in both hot and cold states. This significantly reduces mechanical wear caused by particle collisions and friction during the fluidized bed reaction. In addition, the recycled pellets are obtained by pelletizing and roasting -200 mesh fine powder, primarily hematite, with numerous micropores, good reducibility, and no water of crystallization, thus avoiding decomposition and endothermic reactions, as well as thermal explosion caused by water of crystallization. Therefore, compared to conventional iron ore powder raw materials for fluidized bed production, the technical solution provided by this invention effectively avoids particle pulverization, reduces adhesion and flow loss, and equipment blockage, while also reducing energy consumption and improving the stability of fluidized bed production.

[0021] The beneficial effects of this invention are as follows:

[0022] The present invention provides a method for utilizing recycled pellets as raw material in fluidized bed reduction ironmaking. This method requires only moderate processing, eliminating the need for grinding to the concentrate particle size required for pelletizing, thus avoiding excessive equipment wear and reducing grinding costs. Furthermore, when used in fluidized bed reduction ironmaking, the recycled pellets exhibit high strength in both hot and cold states, good reducibility, and do not cause endothermic decomposition of crystal water or thermal explosion. Therefore, compared to conventional iron ore powder raw materials for fluidized bed production, they possess superior metallurgical properties, effectively preventing particle pulverization, reducing adhesion and flow loss, and lowering energy consumption while improving the stability of fluidized bed production. Detailed Implementation

[0023] The present invention will be further illustrated below through examples.

[0024] The present invention discloses a method for utilizing recycled pellet ore, comprising the following steps:

[0025] (1) The pellet return material is transported to the return material silo for storage and standby. The pellet return material is the unqualified pellets screened out from the finished pellets in the pellet production process, or the dry return material generated in the pellet preheating stage. The pellet production process is a conventional pellet production process such as vertical shaft furnace, chain grate-rotary kiln, / or belt roaster; the dry return material is the dry return material generated in the chain grate stage of the chain grate-rotary kiln pellet production process; the mass percentage of TFe content in the chemical composition of the pellet return material is not less than 60%.

[0026] (2) Pretreat the pellet return material. Through crushing and screening processes, obtain pretreated materials with different particle size ranges of 0.1 - 5 mm, transport them to the pretreated material silo for storage and standby. The fine powder passing through the sieve with a size less than 0.1 mm is returned to the pellet raw material for re - pelletizing, and the over - sized material with a size greater than 5 mm is transported to the return material silo or returned to the crusher for further processing. The crushing of the pellet return material uses conventional crushing equipment such as roll crushers and jaw crushers. The screening is multi - stage screening to obtain pretreated materials with different particle size ranges for standby respectively. The different particle size ranges are 5 kinds of particle size ranges such as A, B, C, D, and E, where 0.1 mm < A ≤ 1 mm, 1 mm < B ≤ 2 mm, 2 mm < C ≤ 3 mm, 3 mm < D ≤ 4 mm, 4 mm < E ≤ 5 mm, and the average particle strength is 20 N / mm 2 or more.

[0027] (3) Use the pretreated materials obtained in step (2) as the raw materials for fluidized direct reduction ironmaking. Select pretreated materials with appropriate particle size ranges according to the requirements of the fluidized reduction system, and add them to the fluidized bed reduction system for reduction reaction to obtain reduction products with a metallization rate not less than 90%. The fluidized bed reduction system consists of 2 - 4 - stage fluidized beds. The pretreated materials can be used as a single furnace charge or formulated into a mixed furnace charge with other ironmaking raw materials in a certain proportion. The pretreated materials can be selected from a certain particle size range or used in combination of multiple particle size ranges in proportion. The reducing gas for the fluidized bed is hydrogen or mixed coal gas, and the volume content of CO and H2 in the mixed coal gas is more than 95%. The reaction temperature of the fluidized bed reduction system is controlled at 550 - 800 °C, the reaction time is controlled at 30 - 120 min, and the reaction pressure is controlled at 200 - 800 kPa.

[0028] (4) The fluidized bed reduction products in step (3) are subjected to hot pressing treatment under nitrogen protection to obtain hot - pressed blocks of products. The density of the hot - pressed blocks is not less than 4.5 g / cm 3 .

[0029] The following is illustrated with specific examples:

[0030] Example 1

[0031] Unqualified pellets from a vertical shaft furnace at a pellet plant are transported to a return material silo for storage. The collected return pellets are crushed using a roller crusher, and pre-treated material with a particle size range of 0.1–5 mm is obtained through a vibrating screen and transported to a pre-treated material silo for storage. Fine powder smaller than 0.1 mm is returned to the pellet batching room, mixed with other raw materials, and re-pelletized. Larger particles larger than 5 mm are returned to the crusher for further processing. Tables 1-1 and 1-2 show the chemical composition of the obtained pre-treated material. The 1-2 mm pretreated material was preheated and added to a two-stage fluidized bed reduction system for reduction reaction. The reducing gas was hydrogen. After pre-reduction in a first-stage fluidized bed (reaction temperature 800℃, reaction time 15 min, reaction pressure 300 kPa) and final reduction in a second-stage fluidized bed (reaction temperature 700℃, reaction time 15 min, reaction pressure 600 kPa), the reactant material had good fluidization performance and no agglomeration was observed. Finally, a reduced product with a metallization rate of 90.5% was obtained.

[0032] The obtained reduced product was hot-pressed under nitrogen protection to obtain a product with a density of approximately 4.9 g / cm³. 3 Hot-pressed briquettes. This method requires only moderate processing of returned pellets, avoiding excessive equipment wear and reducing grinding costs. When used in fluidized bed reduction ironmaking, it effectively reduces particle pulverization and agglomeration loss, lowers energy consumption, and improves the stability of fluidized bed production.

[0033] Table 1-1 Composition of pretreated pellet return material

[0034]

[0035] Table 1-2 Particle size and particle strength of pellet return pretreated material

[0036]

[0037] Example 2

[0038] Unqualified finished pellets produced by a chain grate rotary kiln at a pellet plant are transported back to a return material silo for storage. The collected return pellets are crushed using a jaw crusher, and pre-treated material with a particle size range of 0.1-5mm is obtained through a vibrating screen and transported to a pre-treated material silo for storage. Fine powder smaller than 0.1mm is returned to the pellet batching room, mixed with other raw materials, and re-pelletized. Larger particles larger than 5mm are returned to the return material silo. Tables 2-1 and 2-2 show the chemical composition and particle size distribution of the obtained pre-treated material. The pretreated material (0.1–3 mm) was added to a three-stage fluidized bed reduction system for reduction reaction. The reaction temperature was 550–700℃, the reaction time was 60 min, and the reaction pressure was 600–800 kPa. The reducing gas was a mixed coal gas obtained from natural gas reforming (CO and H2 volume content approximately 96%). After reduction by the three-stage fluidized bed system, the reactants exhibited good fluidization performance and no agglomeration was observed. The obtained reduced product was then hot-pressed under nitrogen protection to obtain a metallization rate of 92% and a density of approximately 5 g / cm³. 3 Hot-pressed briquettes. This method requires only moderate processing of returned pellets, avoiding excessive equipment wear and reducing grinding costs. When used in fluidized bed reduction ironmaking, it effectively reduces particle pulverization and agglomeration loss, lowers energy consumption, and improves the stability of fluidized bed production.

[0039] Table 2-1 Composition of pretreated pellet return material

[0040]

[0041] Table 2-2 Particle size and particle strength of pretreated pellet return material

[0042]

[0043] Example 3

[0044] In a pellet plant, approximately 4% dry return material is generated during the preheating stage of the chain grate rotary kiln. Previously, directly returning this material to the raw material for pelletizing had several adverse effects. This dry material is now collected and transported to a return material silo. A double-roll crusher further crushes the collected pellets, and a vibrating screen separates the material into pre-treated particles ranging from 0.1mm to 5mm. These pre-treated particles are then transported to a pre-treated material silo for storage. Fine powder smaller than 0.1mm is returned to the pelletizing batching room, where it is mixed with other raw materials, milled, and re-pelletized. Larger particles larger than 5mm are returned to the crusher for further processing. Tables 3-1 and 3-2 show the results. The chemical composition and particle size distribution of the obtained pretreated material were determined. The 2–5 mm pretreated material was added to a four-stage fluidized bed reduction system for reduction reaction. The reaction temperature was 550–800℃, the reaction time was 120 min, and the reaction pressure was 200–500 kPa. The reducing gas was a mixed coal gas (CO and H2 volume content approximately 98%). After reduction in the four-stage fluidized bed system, the reactants exhibited good fluidization performance and no agglomeration was observed. The obtained reduced product was then hot-pressed under nitrogen protection to obtain a metallization rate of 93% and a density of approximately 5.1 g / cm³. 3 Hot-pressed briquettes. This method requires only moderate processing of returned pellets, avoiding excessive equipment wear and reducing grinding costs. When used in fluidized bed reduction ironmaking, it effectively reduces particle pulverization and agglomeration loss, lowers energy consumption, and improves the stability of fluidized bed production.

[0045] Table 3-1 Composition of pretreated pellet return material

[0046]

[0047] Table 3-2 Particle size and particle strength of pretreated pellet return material

[0048]

[0049] Example 4

[0050] Unqualified finished pellets produced by a belt roaster at a pellet plant are transported back to a return material silo for storage. The collected return pellets are crushed using a jaw crusher, and pre-treated material with a particle size range of 0.1–5 mm is obtained through a vibrating screen and transported to a pre-treated material silo for storage. Fine powder smaller than 0.1 mm is returned to the pellet batching room, mixed with other raw materials, and re-pelletized. Larger particles larger than 5 mm are returned to the crusher for further processing. Tables 4-1 and 4-2 show the chemical composition and particle size distribution of the obtained pre-treated material. The 0.1–1 mm pretreated material was added to a two-stage fluidized bed reduction system at a ratio of 40% together with iron ore powder for reduction reaction. The reducing gas was hydrogen. After pre-reduction in a first-stage fluidized bed (reaction temperature 750℃, reaction time 20 min, reaction pressure 400 kPa) and a second-stage fluidized bed (reaction temperature 650℃, reaction time 40 min, reaction pressure 500 kPa), the obtained reduced product was hot-pressed under nitrogen protection to obtain a metallization rate of 90.6% and a density of approximately 5.2 g / cm³. 3 Hot-pressed briquettes. This method requires only moderate processing of returned pellets, avoiding excessive equipment wear and reducing grinding costs. When used in fluidized bed reduction ironmaking, it effectively reduces particle pulverization and agglomeration loss, lowers energy consumption, and improves the stability of fluidized bed production.

[0051] Table 4-1 Composition of pretreated pellet return material

[0052]

[0053] Table 4-2 Particle size and particle strength of pretreated pellet return material

[0054]

[0055] Example 5

[0056] Unqualified returned ore (particle size <8mm) from finished pellets produced by a vertical shaft furnace in a pellet plant is transported to a return material silo for storage. The collected returned pellets are moderately crushed using a double-roll crusher. Pre-treated material with a particle size range of 0.1–5mm is obtained through a vibrating screen and transported to a storage silo for further processing. Fine powder smaller than 0.1mm is returned to the pellet batching room, mixed with other raw materials, and re-pelletized. Larger particles larger than 5mm are returned to the crusher for further processing. Tables 5-1 and 5-2 show the chemical composition and particle size distribution of the obtained pre-treated material. The pre-treated material is added at a ratio of 10% to iron ore powder to a four-stage fluidized bed reduction system for reduction reaction. The reaction temperature is 550–800℃, the reaction time is 60 min, the reaction pressure is 400–600 kPa, and the reducing gas is hydrogen. After reduction by the four-stage fluidized bed system, the obtained reduced product is hot-pressed under nitrogen protection to obtain a metallization rate of 92.3% and a density of approximately 4.6 g / cm³. 3Hot-pressed briquettes. This method requires only moderate processing of returned pellets, avoiding excessive equipment wear and reducing grinding costs. When used in fluidized bed reduction ironmaking, it effectively reduces particle pulverization and agglomeration loss, lowers energy consumption, and improves the stability of fluidized bed production.

[0057] Table 5-1 Composition of pretreated pellet return material

[0058]

[0059] Table 5-2 Particle size and particle strength of pretreated pellet return material

[0060]

[0061] Example 6

[0062] Unqualified finished pellets from a pellet plant's chain grate rotary kiln were transported back to a return material silo for storage. The collected return pellets were moderately crushed using a jaw crusher, and pre-treated material with a particle size range of 0.1–5 mm was obtained through a vibrating screen and transported to a storage silo for further processing. Fine powder smaller than 0.1 mm was returned to the pellet batching room, mixed with other raw materials, and re-pelletized. Larger particles larger than 5 mm were returned to the crusher for further processing. Tables 6-1 and 6-2 show the chemical composition and particle size distribution of the obtained pre-treated material. The 0.1–1 mm and 1–2 mm pre-treated materials were added to a three-stage fluidized bed reduction system at ratios of 20% and 80%, respectively, for reduction reaction. The reaction temperature was 650–750℃, the reaction time was 100 min, and the reaction pressure was 400–500 kPa.

[0063] The reducing gas was a mixed coal gas (CO and H2 volume content approximately 96%) obtained from natural gas reforming. After fluidized bed reduction at 650–790℃, the reactants exhibited good fluidization properties and no agglomeration occurred. The resulting reduced product was then hot-pressed under nitrogen protection to achieve a metallization rate of 92% and a density of approximately 5 g / cm³. 3 Hot-pressed briquettes. This method requires only moderate processing of returned pellets, avoiding excessive equipment wear and reducing grinding costs. When used in fluidized bed reduction ironmaking, it effectively reduces particle pulverization and agglomeration loss, lowers energy consumption, and improves the stability of fluidized bed production.

[0064] Table 6-1 Composition of pretreated pellet return material

[0065]

[0066] Table 6-2 Particle size and particle strength of pretreated pellet return material

[0067]

[0068] As can be seen from the above, the pellet return material utilization method provided by this invention uses the pellet return material as raw material for fluidized bed reduction ironmaking. It only requires moderate processing and does not need to be ground to the concentrate particle size required for pelletizing, thereby avoiding excessive equipment wear and reducing grinding costs. Furthermore, when used in fluidized bed reduction ironmaking, the pellet return material exhibits high cold and hot strength, good reducibility, and does not produce endothermic decomposition of crystal water or thermal explosion problems. Therefore, it has superior metallurgical properties compared to conventional iron ore powder raw materials for fluidized bed production, effectively preventing particle pulverization, reducing adhesion and flow loss, and lowering energy consumption while improving the stability of fluidized bed production.

[0069] To illustrate the present invention, the present invention has been appropriately and sufficiently described above through embodiments. The above embodiments are only for illustrating the present invention and are not intended to limit the present invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Any modifications, equivalent substitutions, improvements, etc., should be included within the protection scope of the present invention. The patent protection scope of the present invention should be defined by the claims.

Claims

1. A method for utilizing a pellet return, characterized in that The method comprises the following steps: (1) transporting the pellet return material to a return material storage for standby, wherein the pellet return material is pellet ore with unqualified particle size screened out from finished pellet ore in a pellet production process, or dry return material generated in a pellet preheating link; (2) transporting the pellet return material through crushing and screening to obtain pretreatment material with particle size of 0.1-5 mm to a pretreatment material storage for standby; (3) taking the pretreatment material obtained in step (2) as fluidized direct reduction ironmaking raw material, adding the pretreatment material to a fluidized bed reduction system for reduction reaction, and obtaining a reduction product with metallization rate not less than 90%; (4) performing hot pressing treatment on the reduction product in step (3) under nitrogen protection to obtain a product hot pressed block.

2. A method of handling a pellet return according to claim 1, characterized in that, The pellet production process in step (1) is a conventional pellet ore production process; the dry return material is dry return material generated in a chain grate link in a chain grate-rotary kiln pellet production process; and the TFe content in the chemical composition of the pellet return material is not less than 60%.

3. A method of handling a pellet return according to claim 2, characterized in that, The conventional pellet ore production process is one of a shaft furnace, a chain grate-rotary kiln and a belt-type roaster.

4. A method of handling a pellet return according to claim 1, characterized in that, In the screening process, undersize fine powder with particle size less than 0.1 mm is returned to pellet raw material for re-pelletizing, and oversize material with particle size greater than 5 mm is transported to a return material storage or re-processed by a crusher.

5. The method of claim 1, wherein the recycled pellets are used as a raw material for producing a pellet. The screening process is multi-stage screening, and the pretreated materials in different particle size ranges are obtained for standby respectively, the different particle size ranges are A, B, C, D, E and the like five particle size ranges, wherein 0.1mm 2 The above.

6. A method of utilizing a pellet return according to claim 1 and 5, characterized in that, The fluidized bed reduction system is composed of 2-4 stages of fluidized beds, the pretreatment material is used as single furnace charge or is mixed with other ironmaking raw materials to form mixed furnace charge, and the pretreatment material is selected from a certain particle size range or multiple particle size ranges and is used in proportion.

7. A method of handling a pellet return according to claim 1, characterized in that, The fluidized bed reduction gas is hydrogen or mixed gas, and the volume content of CO and H2 in the mixed gas is more than 95%.

8. A method of handling a pellet return according to claim 1, characterized in that, The reaction temperature of the fluidized bed reduction system is 550-800 ℃, the reaction time is 30-120 min, and the reaction pressure is 200-800 kPa.

9. A method of handling a pellet return according to claim 1, characterized in that, The hot briquet density is not less than 4.5 g / cm 3 .

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