Ironmaking process and ironmaking equipment suitable for low-grade iron ore

Abstract

The invention relates to the technical field of metal smelting, and provides an ironmaking process and ironmaking equipment suitable for low-grade iron ore, and the ironmaking process comprises the following steps: mixing low-grade iron ore powder, pulverized coal and an adhesive according to a preset proportion, and making the mixture into cold-pressed balls; the cold-pressed balls are subjected to reduction treatment, so that iron oxide in the cold-pressed balls is subjected to a reduction reaction and aggregated to generate iron beads, gangue phases in the cold-pressed balls are subjected to a reaction to generate slag phases, and the slag phases comprise calcium silicate; the reduced cold-pressed balls are subjected to heat preservation treatment, so that calcium silicate in the slag phase is subjected to crystal transformation; cooling the cold-pressed balls subjected to heat preservation, so that calcium silicate in the slag phase is subjected to crystal transformation again to be broken, and the iron beads are stripped from the broken slag phase; and impurity powder formed by fragmentation of the iron shots and the slag phase is screened and separated. According to the method, the problem that an existing direct reduction ironmaking technology is high in dependence degree on the high-grade iron ore can be solved, and high-quality utilization of the low-grade iron ore is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of metal smelting, and in particular to an iron-making process and iron-making equipment suitable for low-grade iron ore. Background Art

[0002] In the context of promoting industrial upgrading and environmental protection and emission reduction, the steel industry faces severe opportunities and challenges. In order to achieve high-quality development, steel companies must pay attention to energy conservation and emission reduction and clean production, and comprehensively reduce the emission of SOx, NOx, CO2 and smoke and dust in the sintering and coking links, so as to build a green and sustainable industrial system. Compared with the traditional blast furnace ironmaking method, non-blast furnace direct reduction ironmaking technology has obvious advantages in environmental protection and energy saving, which greatly reduces the dependence on coking coal in the ironmaking process, reduces energy consumption and pollutant emissions, and provides a solid foundation for the sustainable development of the steel industry.

[0003] The direct reduction ironmaking technology uses non-coking coal and high-grade iron ore powder as raw materials. Its process end product is high metallization rate pellets with pure chemical composition and extremely low impurity content. These pellets are not only the main raw materials for electric furnace steelmaking, but can also be used in converter steelmaking. The direct reduction ironmaking process mainly includes two categories: gas-based and coal-based. The mainstream processes of gas-based direct reduction are MIDREX (typical vertical furnace method) and HYL (typical reactor method); the coal-based direct reduction ironmaking process mainly includes rotary kiln and rotary hearth furnace. Compared with traditional blast furnace ironmaking, the method of using non-coking coal eliminates high-energy consumption and high-pollution links such as coking and sintering, showing the advantages of high quality, low consumption and environmental protection. However, since high gangue content will increase the power consumption and refractory consumption of steelmaking during the steelmaking process, the iron ore grade is required to be relatively high.

[0004] In recent years, direct reduction ironmaking technology has made significant progress, but the existing process has high requirements for the iron-containing ore powder entering the furnace, and the ore grade is required to be above 66%. Direct reduced iron produced from low-grade ore cannot be used in steelmaking furnaces due to the high content of gangue and impurities. Therefore, the direct reduction process is highly dependent on high-grade ore, which greatly increases production costs. The development of direct reduction technology and the shortage of high-grade iron ore resources are in sharp conflict. Under these conditions, the development of new ironmaking processes with strong adaptability to raw materials and furnace materials, high energy utilization, low investment cost, and flexible operation has become one of the topics of concern for steel companies. Summary of the invention

[0005] The purpose of the present invention is to provide an ironmaking process and ironmaking equipment suitable for low-grade iron ore, so as to solve the problem that the current direct reduction ironmaking technology is highly dependent on high-grade iron ore and realize the high-quality utilization of low-grade iron ore.

[0006] The above technical objectives of the present invention are mainly achieved through the following technical solutions:

[0007] In one aspect, the present invention provides an ironmaking process applicable to low-grade iron ore, comprising the following steps:

[0008] Step S1: mixing low-grade iron ore powder, coal powder and a binder in a predetermined proportion and forming the mixture into cold-pressed balls;

[0009] Step S2: performing a reduction treatment on the cold pressed balls at a predetermined first temperature and a first time, so that the iron oxides in the cold pressed balls undergo a reduction reaction and aggregate to form iron beads, and the gangue phase in the cold pressed balls reacts to form a slag phase, wherein the slag phase contains calcium silicate generated by the reaction;

[0010] Step S3: performing heat preservation treatment on the reduced cold pressed balls under a predetermined second temperature and second time condition, so that the calcium silicate in the slag phase undergoes a crystal transformation;

[0011] Step S4: cooling the cold pressed balls after heat preservation at a predetermined cooling rate, so that the calcium silicate in the slag phase undergoes crystal transformation again and breaks, so that the iron balls are peeled off from the broken slag phase;

[0012] Step S5: sieving and separating the iron beads and the impurity powder formed by crushing.

[0013] The ironmaking process suitable for low-grade iron ore described in the present invention realizes high-quality utilization of low-grade iron ore resources, and the terminal product realizes iron-slag separation. The obtained metal iron beads have a high metallization rate and can be directly used in an electric furnace or a converter, achieving a near-zero slag content and improving the purity of the steelmaking process.

[0014] In a preferred embodiment of the present invention, after the cold-pressed balls are made, the coal powder is sprayed on the surface of the cold-pressed balls.

[0015] In this embodiment, during the reduction process of the cold-pressed balls in the rotary kiln to form iron beads, since coal powder is sprayed on the surface of the cold-pressed balls, the coal powder wrapped on the outer surface first participates in the reaction, forming a solid iron shell on the outer surface of the cold-pressed balls, which can effectively inhibit the adhesion between the charge materials.

[0016] In a preferred embodiment of the present invention, the mass percentage of coal powder in the mixture is y;

[0017] y=(0.11x+0.76z) / d

[0018] Among them, x is the mass percentage of Fe2O3 in the iron ore powder; z is the mass percentage of total iron in the iron ore powder; d is the mass percentage of fixed carbon in the coal powder.

[0019] In this embodiment, the ratio of coal powder needs to be strictly controlled according to the components of each raw material during the pelletizing process. This is mainly because a low coal ratio leads to incomplete reduction, and a high coal ratio leads to excessive melting of the iron beads generated by the reduction, which makes it difficult for the charge in the kiln to stick and for the subsequent separation of slag and iron. The ratio of coal powder in the batching process is determined by the ore grade, and the coal ratio should ensure that the iron oxide is reduced to elemental iron while meeting the carburizing requirements.

[0020] In a preferred embodiment of the present invention, the first time is 65 min-75 min, and the first temperature is 1227° C.-1250° C.

[0021] In this embodiment, it is necessary to strictly control the temperature in the rotary kiln and the reaction time of the cold-pressed balls in the rotary kiln. If the reduction temperature is too low or the time is too short, the reduction will be incomplete, resulting in a lower iron formation rate. If the reduction temperature is too high or the time is too long, the metallic iron will melt and wrap the slag, making it difficult to separate the iron slag in the subsequent process.

[0022] In a preferred embodiment of the present invention, during the process of the iron oxides in the cold-pressed balls undergoing reduction reaction and generating iron, the iron oxides in the iron ore powder are reduced and carburized to generate iron, and part of the melted iron is aggregated into iron beads, which are distributed in the internal voids of the cold-pressed balls and on the surface of the cold-pressed balls;

[0023] In the process of the gangue phase in the cold-pressed balls reacting to generate the slag phase, CaO and SiO2 in the gangue phase react to generate 3CaO·SiO2 and 2CaO·SiO2, thereby forming the slag phase containing the calcium silicate.

[0024] In a preferred embodiment of the present invention, the second temperature is 1100° C.-1150° C., and the second time is 30 min-40 min.

[0025] In this embodiment, the temperature in the holding furnace and the holding time of the cold-pressed balls in the holding furnace need to be strictly controlled to ensure that the tricalcium silicate (3CaO·SiO2) in the slag phase can fully undergo crystal transformation.

[0026] In a preferred embodiment of the present invention, during the heat preservation process of the cold pressed balls, the 3CaO·SiO2 in the slag phase undergoes a crystal transformation into α-2CaO·SiO2.

[0027] In a preferred embodiment of the present invention, the cooling rate of the cold-pressed balls in the crushing furnace is 50°C / min-60°C / min.

[0028] In this embodiment, the cooling rate of the cold-pressed balls in the crushing furnace needs to be strictly controlled to ensure that the calcium silicate in the cold-pressed balls undergoes a rapid crystal transformation. Due to the material characteristics of calcium silicate itself, strong internal stress will be generated during the rapid transformation of the crystal structure, causing vicious expansion and a large number of cracks, and finally causing the slag phase to break into fine powder, thereby forming iron beads and impurity powder.

[0029] In a preferred embodiment of the present invention, during the cooling of the cold-pressed balls, the calcium silicate in the slag phase undergoes a crystal transformation: α-2CaO·SiO2 transforms into β-2CaO·SiO2, and then transforms from β-2CaO·SiO2 into γ-2CaO·SiO2.

[0030] In a preferred embodiment of the present invention, the diameter of the iron bead is greater than 3 mm, and the metallization rate of the iron bead (the mass percentage of elemental iron in the iron bead to the total iron in the iron bead) is greater than or equal to 95%.

[0031] In a preferred embodiment of the present invention, during the cooling of the cold-pressed balls, a combined cooling method of air cooling and water cooling is adopted to accelerate the cooling rate of the cold-pressed balls.

[0032] In this embodiment, the cold pressed balls are cooled rapidly by introducing low temperature nitrogen into the pulverizing furnace and laying water cooling pipes in the pulverizing furnace.

[0033] In a preferred embodiment of the present invention, the ironmaking process applicable to low-grade iron ore further comprises:

[0034] The process of reducing the cold pressed balls is carried out in a rotary kiln, and fuel is passed through the rotary kiln, and the fuel is burned to provide heat and generate smoke;

[0035] The flue gas is mixed with CH4 and reformed to generate CO and H2, and the CO and H2 are introduced into the rotary kiln and reused as fuel.

[0036] In this embodiment, the low-quality waste flue gas generated in the rotary kiln is reformed into high-quality coal gas through reforming regeneration in the reforming furnace, and carbon emissions are reduced by re-converting CO2 in the flue gas. Compared with the existing process, CO2 emissions are reduced by 30%-40%.

[0037] In a preferred embodiment of the present invention, the flue gas generated by the rotary kiln contains CO2 and H2O; during the reforming process of the flue gas, CO2 and H2O react with CH4 to generate CO and H2; CO and H2 are mixed with CH4 and introduced into the rotary kiln as fuel.

[0038] In this embodiment, natural gas whose main component is CH4 is used as a gas source, which is used for combustion heat supply in the rotary kiln on the one hand, and for reforming the flue gas in the reforming furnace on the other hand.

[0039] In a preferred embodiment of the present invention, in the process of separating the iron beads from the impurity powder formed by crushing, slag-iron separation can be achieved by screen filtration or magnetic separation.

[0040] On the other hand, the present invention also provides an ironmaking equipment suitable for low-grade iron ore, comprising:

[0041] Mixing device for mixing low-grade iron ore powder, coal powder and adhesive;

[0042] A ball press for cold-pressing the mixed material into cold-pressed balls, wherein the mixing device is connected to the ball press;

[0043] A rotary kiln for reducing iron oxides in the cold-pressed balls, wherein the ball press is connected to the rotary kiln, and the cold-pressed balls are reduced to form iron balls in the rotary kiln;

[0044] A heat preservation furnace for keeping the cold pressed balls warm, the rotary kiln being connected to the heat preservation furnace;

[0045] A crushing furnace is used to cool the cold pressed balls, the insulation furnace is connected to the crushing furnace, during the cooling process of the cold pressed balls in the crushing furnace, the iron balls are peeled off from the impurity powders produced by the cold pressed balls, and a screen is provided in the crushing furnace for separating the iron balls from the impurity powders.

[0046] The ironmaking equipment suitable for low-grade iron ore described in the present invention realizes high-quality utilization of low-grade iron ore resources through a reduction-slag-iron separation system composed of a rotary kiln, a holding furnace and a crushing furnace, and the terminal product realizes iron-slag separation. The obtained metal iron beads have a high metallization rate and can be directly used in an electric furnace or a converter, achieving near-zero slag content and improving the purity in the steelmaking process.

[0047] In a preferred embodiment of the present invention, the kiln head of the rotary kiln is connected to the ball press, and the kiln tail of the rotary kiln is connected to a gas supply pipeline, and the gas supply pipeline can supply fuel gas to the rotary kiln;

[0048] The rotary kiln is tilted so that the kiln head is higher than the kiln tail, and the movement direction of the cold-pressed balls in the rotary kiln is opposite to the movement direction of the fuel gas.

[0049] In this embodiment, the cold-pressed balls move slowly forward in the kiln by relying on the inclination and rotation of the rotary kiln cylinder, and are gradually heated by the reverse hot air flow to complete the reduction and carburizing reaction processes. The cold-pressed balls generated after reduction are discharged from the tail end of the kiln.

[0050] In a preferred embodiment of the present invention, the rotary kiln is provided with an angle adjustment mechanism capable of adjusting its inclination angle, and the time for the cold-pressed balls to move from the kiln head to the kiln tail is controlled by the angle adjustment mechanism.

[0051] In this embodiment, the reaction time of the cold-pressed balls in the rotary kiln is strictly controlled by the angle adjustment mechanism. If the reduction time is too short, the reduction will be incomplete, resulting in a lower iron formation rate. If the reduction time is too long, the metallic iron will melt and wrap the slag, making it difficult to separate the iron slag in the subsequent process.

[0052] In a preferred embodiment of the present invention, an oxygen cabinet, a gas cabinet and a blowing mechanism are provided on the gas supply pipeline, and a gas spray gun is connected to the end of the gas supply pipeline located in the rotary kiln.

[0053] In this embodiment, there is natural gas in the gas tank on the gas supply line, and the raw materials used in the rotary kiln are natural gas and oxygen. A high nitrogen content in the air will affect the calorific value of the gas and the nitrogen enrichment in the reforming cycle will affect the utilization efficiency, so oxygen is selected as a combustion aid; at the same time, the temperature in the rotary kiln is strictly controlled by the injection mechanism on the gas supply line. If the reduction temperature is too low, the reduction will be incomplete, resulting in a lower iron formation rate. If the reduction temperature is too high, the metallic iron will melt and wrap the slag, making it difficult to separate the iron slag in the subsequent process.

[0054] In a preferred embodiment of the present invention, the fume outlet of the rotary kiln is connected to a recovery pipeline, and the outlet end of the recovery pipeline is connected to the gas supply pipeline;

[0055] Along the flow direction of the flue gas in the recovery pipeline, the recovery pipeline is provided with:

[0056] A reforming furnace for reducing CO2 and H2O in flue gas, wherein CH4 is passed through the reforming furnace, and in the reforming furnace, CO2 and H2O react with CH4 to produce CO and H2;

[0057] A dust collector used to filter dust from flue gas.

[0058] In this embodiment, the low-quality waste flue gas generated in the rotary kiln is reformed into high-quality coal gas through the reforming regeneration of the reforming furnace on the recovery pipeline, and the carbon emissions are reduced by re-converting the CO2 in the flue gas. Compared with the existing process, CO2 emissions are reduced by 30%-40%.

[0059] In a preferred embodiment of the present invention, the heat-insulating furnace and the pulverizing furnace are both connected to nitrogen tanks via pipelines, and the nitrogen tanks can respectively introduce nitrogen into the heat-insulating furnace and the pulverizing furnace.

[0060] In this embodiment, nitrogen is introduced into the insulation furnace through a nitrogen tank to prevent the reduced iron in the cold-pressed balls from being re-oxidized during the insulation process; nitrogen is introduced into the crushing furnace through a nitrogen tank to purge and cool the high-temperature charge in the crushing furnace.

[0061] In a preferred embodiment of the present invention, a nitrogen circulation pipeline is connected between the insulation furnace and the pulverizing furnace, and the nitrogen circulation pipeline includes a first nitrogen pipeline and a second nitrogen pipeline; the high-temperature nitrogen generated in the pulverizing furnace can enter the insulation furnace through the first nitrogen pipeline; the high-temperature nitrogen in the insulation furnace can enter the pulverizing furnace through the second nitrogen pipeline, and a power generation mechanism is provided on the second nitrogen pipeline.

[0062] In this embodiment, nitrogen preheating and waste heat recovery of the charge are simultaneously completed in the pulverizing furnace, and then the high-temperature nitrogen is introduced into the bottom of the insulation furnace through the first nitrogen pipeline as a protective gas, thereby reducing the temperature fluctuation in the insulation furnace; at the same time, the high-temperature nitrogen in the insulation furnace is recovered through the power generation mechanism for waste heat recovery.

[0063] In a preferred embodiment of the present invention, a ball valve is provided in the insulation furnace, and the residence time of the cold-pressed balls in the insulation furnace is controlled by the ball valve.

[0064] In this embodiment, the cold pressing ball is strictly kept in the holding furnace for a holding time through the ball valve to ensure that the tricalcium silicate in the slag phase can fully undergo crystal transformation.

[0065] In a preferred embodiment of the present invention, a water cooling pipe is provided at the bottom of the pulverizing furnace.

[0066] In this embodiment, the cooling water in the water cooling pipe can water-cool the charge in the pulverizing furnace, and cooperate with the air cooling of nitrogen to achieve rapid cooling of the charge.

[0067] In a preferred embodiment of the present invention, a vibration mechanism connected to the screen is provided in the pulverizing furnace, and the vibration mechanism can drive the screen to vibrate to separate the iron balls from the impurity powder and move the iron balls toward the outlet of the pulverizing furnace.

[0068] In this embodiment, the screen is driven to vibrate by a vibration mechanism, which can quickly separate the iron beads from the impurity powder on the one hand, and drive the iron beads to move toward the outlet of the crushing furnace on the other hand.

[0069] In a preferred embodiment of the present invention, a coal powder injection mechanism is provided in the ball press machine, and the coal powder injection mechanism can spray coal powder onto the cold pressed balls to form the cold pressed balls coated with coal powder.

[0070] In this embodiment, during the reduction of cold-pressed balls to generate metallic iron in a rotary kiln, coal powder is sprayed on the surface of the cold-pressed balls, and the coal powder wrapped on the outer surface first participates in the reaction, forming a solid iron shell on the outer surface of the cold-pressed balls, which can effectively inhibit the adhesion between the charge materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the prior art descriptions. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0072] The accompanying drawings described herein are only for explanation purposes and are not intended to limit the scope of the present invention in any way. In addition, the shapes and proportional dimensions of the various components in the figures are only schematic, used to help understand the present invention, and are not specifically limited to the shapes and proportional dimensions of the various components of the present invention. Those skilled in the art can select various possible shapes and proportional dimensions to implement the present invention according to the teachings of the present invention.

[0073] Figure 1 This is a flow chart of the ironmaking process applicable to low-grade iron ore according to the present invention;

[0074] Figure 2 Another process flow chart of the ironmaking process applicable to low-grade iron ore according to the present invention;

[0075] Figure 3 The figure is a schematic diagram of the structure of the ironmaking equipment suitable for low-grade iron ore according to the present invention.

[0076] Description of reference numerals:

[0077] 1. Mixing device; 2. Ball press; 3. Rotary kiln; 4. Gas spray gun; 5. Spraying mechanism; 6. Gas cabinet; 7. Oxygen cabinet; 8. Flue gas outlet; 9. Reforming furnace; 10. Dust collector; 11. Fan; 12. Holding furnace; 13. Ball valve; 14. Nitrogen sealing mechanism; 15. Crushing furnace; 16. Power generation mechanism; 17. Nitrogen spray gun; 18. Nitrogen tank; 19. Slag receiving port; 20. Iron outlet; 21. Gas supply pipeline; 22. Recovery pipeline; 23. First nitrogen pipeline; 24. Second nitrogen pipeline. DETAILED DESCRIPTION

[0078] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0079] It should be noted that when an element is referred to as being "disposed on" another element, it may be directly on the other element or there may be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only and are not intended to be the only embodiment.

[0080] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0081] Implementation method 1:

[0082] like Figure 1 and Figure 2 As shown, the present invention provides an ironmaking process suitable for low-grade iron ore, which comprises the following steps:

[0083] Step S1: mixing low-grade iron ore powder, coal powder and a binder in a predetermined proportion and forming the mixture into cold-pressed balls;

[0084] Step S2: The cold pressed balls are fed into the rotary kiln 3, and the cold pressed balls are subjected to reduction treatment in the rotary kiln 3 under the predetermined first temperature and first time conditions, so that the iron oxides in the cold pressed balls undergo a reduction reaction and aggregate to form iron beads, and the gangue phase in the cold pressed balls reacts to form a slag phase, and the slag phase contains calcium silicate generated by the reaction;

[0085] Step S3: sending the reduced cold-pressed balls into the holding furnace 12, and performing a holding treatment on the cold-pressed balls at a predetermined second temperature and a second time, so that the calcium silicate in the slag phase undergoes a crystal transformation;

[0086] Step S4: sending the cold pressed balls which have been kept warm into a crushing furnace 15, and cooling the cold pressed balls at a predetermined cooling rate, so that the calcium silicate in the slag phase undergoes a crystal transformation again and breaks, thereby separating the iron balls from the crushed slag phase;

[0087] Step S5: Separating the impurity powder formed by crushing the iron beads and the slag phase.

[0088] The ironmaking process applicable to low-grade iron ore of the present invention realizes high-quality utilization of low-grade iron ore resources, and the terminal product realizes iron-slag separation. The obtained metal iron beads have a high metallization rate and can be directly used for electric furnace steelmaking or converter steelmaking, achieving near-zero slag content and improving the purity of the steelmaking process.

[0089] The specific process of each step of the ironmaking process applicable to low-grade iron ore of the present invention and the corresponding preferred implementation methods will be further described below.

[0090] In step S1, the pretreatment of the ironmaking material is carried out, which mainly includes two processes: mixing and briquetting.

[0091] Specifically, during the mixing process, the proportion of each raw material is calculated according to the components in each raw material, and then the low-grade iron ore powder, coal powder and adhesive are mixed together through the mixing device 1. Among them, the main component of the low-grade iron ore powder is iron oxide, and the main impurity is gangue. The gangue impurity content in the low-grade iron ore powder is relatively high, and the iron grade in the low-grade iron ore powder is usually below 50%. The present invention can use the above-mentioned low-grade iron ore powder as the main raw material for producing reduced iron, and realize high-quality utilization; the main component of coal powder is carbon, which is used as a reducing agent to reduce the iron oxide in the iron ore powder to iron under high temperature conditions; the adhesive is used as an auxiliary material for bonding the iron ore powder and the coal powder before the reaction, and the adhesive can be clay minerals, bentonite, etc.

[0092] Preferably, the mass percentage of coal powder in the mixture is y;

[0093] y=(0.11x+0.76z) / d

[0094] Wherein, x is the mass percentage of Fe2O3 in the iron ore powder; z is the mass percentage of total iron (Fe) in the iron ore powder; d is the mass percentage of fixed carbon (C) in the coal powder.

[0095] In the process of pelletizing, the proportion of coal powder needs to be strictly controlled according to the components of each raw material. This is mainly because the low coal ratio (y) leads to incomplete reduction, and the high coal ratio leads to excessive melting of the iron beads generated by reduction, which causes the charge in the kiln to stick and make subsequent separation of slag and iron difficult. The proportion of coal powder in the batching process is determined by the ore grade, and the coal ratio should ensure that the iron oxide is reduced to elemental iron while meeting the carburizing requirements.

[0096] Furthermore, during the ball pressing process, the mixture mixed in a predetermined ratio is introduced into the roller ball press 2, and the mixture is cold pressed and balled by the roller ball press 2, thereby producing cold pressed balls with iron ore powder and coal powder as main components.

[0097] Preferably, during the process of the roller briquetting machine 2 forming the mixed material into cold pressed balls, a layer of coal powder is sprayed on the surface of the formed cold pressed balls.

[0098] During the process of reducing the cold-pressed balls to generate metallic iron in the rotary kiln 3, since the coal powder is sprayed on the surface of the cold-pressed balls, the coal powder wrapped on the outer surface first participates in the reaction, and then a solid iron shell is formed on the outer surface of the cold-pressed balls, which can effectively inhibit the adhesion between the charge materials.

[0099] In step S2, the iron oxides in the cold-pressed balls are reduced.

[0100] Specifically, the pressed cold-pressed balls are added into the cylinder of the rotary kiln 3 through the kiln head of the rotary kiln 3. Since the cylinder of the rotary kiln 3 is installed at an angle, the cold-pressed balls move forward slowly in the rotary kiln 3 by relying on the inclination and rotation of the cylinder. The fuel is sprayed into the rotary kiln 3 from the kiln tail, and high-temperature hot flue gas is generated after combustion. The hot flue gas and the material flow through the entire kiln in the reverse direction. The heat generated heats the cold-pressed balls, realizing the processes of iron oxide reduction and carburizing reaction. The cold-pressed balls are unloaded from the kiln tail after reduction.

[0101] Preferably, in step S2, the temperature in the rotary kiln 3 and the reaction time of the cold-pressed balls in the rotary kiln 3 need to be strictly controlled. If the reduction temperature is too low and the time is too short, the reduction will not be complete, which will reduce the iron generation rate. If the reduction temperature is too high and the time is too long, the metal iron will melt and wrap the slag, making it difficult to separate the iron slag in the subsequent process. Therefore, the reaction temperature of the cold-pressed balls in the rotary kiln 3 is controlled to be 1227°C-1250°C, and the reaction time is controlled to be 65min-75min.

[0102] Under the above temperature and time conditions, in the rotary kiln 3, the iron oxides in the iron ore powder in the cold-pressed balls are reduced and carburized, and then partially melted and aggregated into iron beads, which are distributed in the internal gaps and surfaces of the cold-pressed balls. At the same time, the CaO and SiO2 in the gangue phase in the cold-pressed balls react to form tricalcium silicate (3CaO·SiO2) and dicalcium silicate (2CaO·SiO2), thereby forming a slag phase mainly composed of calcium silicate.

[0103] In step S3, the reduced cold-pressed balls are kept warm so that the calcium silicate in the slag phase undergoes a crystal transformation.

[0104] Specifically, the reduced cold-pressed balls directly enter the insulation furnace 12 through the outlet at the end of the rotary kiln 3. The insulation furnace 12 is electrically heated, and heating rods are provided on both sides of the furnace body. The insulation furnace 12 is filled with nitrogen to prevent the re-oxidation of the reduced iron.

[0105] Preferably, in step S3, the temperature in the holding furnace 12 and the holding time of the cold pressed balls in the holding furnace 12 need to be strictly controlled to ensure that the tricalcium silicate (3CaO·SiO2) in the slag phase can fully undergo a crystal transformation. Therefore, the holding temperature of the cold pressed balls in the holding furnace 12 is controlled to be 1100°C-1150°C, and the holding time is controlled to be 30min-40min.

[0106] Under the above temperature and time conditions, in the holding furnace 12, the tricalcium silicate (3CaO·SiO2) in the slag phase undergoes a crystal transformation into α-2CaO·SiO2.

[0107] In step S4, the cold-pressed balls are rapidly cooled, so that iron beads and impurity powder are generated from the cold-pressed balls due to the fragmentation of the slag phase.

[0108] Specifically, the cold pressed balls after insulation enter the crushing furnace 15 through the outlet of the insulation furnace 12. The crushing furnace 15 adopts a combination of air cooling and water cooling to accelerate the cooling rate of the cold pressed balls. A combination of introducing low-temperature nitrogen into the crushing furnace 15 and laying a water-cooling pipe in the crushing furnace 15 can achieve rapid cooling of the cold pressed balls. During the cooling process, the calcium silicate in the slag phase undergoes a rapid crystal transformation (α-β-γ). Due to the material characteristics of calcium silicate itself, strong internal stress will be generated during the rapid transformation of the crystal structure, causing malignant expansion and a large number of cracks, which eventually causes the slag phase to break into fine powder (usually less than 1 mm in diameter).

[0109] Preferably, the cooling rate of the cold-pressed balls in the pulverizing furnace 15 needs to be strictly controlled to ensure that the calcium silicate in the cold-pressed balls undergoes a rapid crystal transformation. Therefore, the cooling rate of the cold-pressed balls in the pulverizing furnace 15 needs to be controlled to be 50°C / min-60°C / min.

[0110] Under the above cooling rate conditions, in the crushing furnace 15, the calcium silicate in the slag phase undergoes a rapid crystal transformation, α-2CaO·SiO2 is transformed into β-2CaO·SiO2, and then from β-2CaO·SiO2 to γ-2CaO·SiO2; the slag phase is broken into fine powder, thereby stripping the iron beads with a diameter greater than 3 mm produced in the reduction process from the slag phase, and the metallization rate of the iron beads (the mass percentage of elemental iron in the iron beads to the total iron in the iron beads) is greater than or equal to 95%.

[0111] In step S5, the iron beads and impurity powder are separated.

[0112] In one embodiment, the slag-iron separation is achieved by sieve filtration. Specifically, the crushing furnace 15 uses a vibrating sieve to gradually move the charge to the right, and the mesh diameter of the sieve is 3 mm. The fine impurity powder is sieved down and recovered through the slag receiving port 19, while the metal iron beads with a diameter greater than 3 mm are transported to the iron outlet 20 through the sieve to achieve slag-iron separation.

[0113] In another embodiment, the slag-iron separation is achieved by magnetic separation. Specifically, the iron beads are adsorbed from the impurity powder by the magnetic attraction of the magnet to the iron beads.

[0114] According to one embodiment of the present invention, the ironmaking process applicable to low-grade iron ore also includes: mixing the high-temperature flue gas generated in the rotary kiln 3 with CH4 and passing it into the reforming furnace 9 for reforming to produce CO and H2, and passing the CO and H2 into the rotary kiln 3 for reuse as fuel.

[0115] Through the reforming and regeneration of the reforming furnace 9, the low-quality waste flue gas generated in the rotary kiln 3 is reformed into high-quality coal gas. The carbon emission is reduced by re-converting the CO2 in the flue gas. Compared with the existing process, the CO2 emission is reduced by 30%-40%. At the same time, the waste heat in the high-temperature flue gas can also be recovered.

[0116] Specifically, the rotary kiln 3 uses natural gas as the main fuel. The flue gas generated by the rotary kiln 3 contains CO2 and H2O. The flue gas is discharged from the kiln head and directly enters the reforming furnace 9. At the same time, natural gas is introduced into the rotary kiln 3. Since the flue gas has a high temperature (≥1200°C), the CO2 and H2O in the flue gas react with the CH4 in the natural gas under high temperature conditions to generate CO and H2. The reaction process is as follows:

[0117] CH4+CO2=2CO+2H2;

[0118] CH4+H2O=CO+3H2;

[0119] The natural gas with CH4 as the main component is used as the gas source, which is used for combustion and heating in the rotary kiln 3 on the one hand, and for reforming the flue gas in the reforming furnace 9 on the other hand. The CO and H2 generated in the reforming furnace 9 are mixed with CH4 and introduced into the rotary kiln 3 as fuel. While completing the recovery of flue gas waste heat resources, the heat loss in the kiln is reduced, and the emission of CO2 can also be reduced.

[0120] Implementation method 2:

[0121] like Figure 3As shown, the present invention also provides an ironmaking equipment suitable for low-grade iron ore, which includes: a mixing device 1 for mixing low-grade iron ore powder, coal powder and adhesive; a ball press machine 2 for cold pressing the mixture into cold-pressed balls, the mixing device 1 is connected to the ball press machine 2; a rotary kiln 3 for reducing iron oxides in the cold-pressed balls, the ball press machine 2 is connected to the rotary kiln 3, and the cold-pressed balls are reduced in the rotary kiln 3 to produce iron beads; an insulation furnace 12 for keeping the cold-pressed balls warm, the rotary kiln 3 is connected to the insulation furnace 12; a pulverizing furnace 15 for cooling the cold-pressed balls, the insulation furnace 12 is connected to the pulverizing furnace 15, the cold-pressed balls produce iron beads and impurity powder during the cooling process in the pulverizing furnace 15, and a screen for separating the iron beads and impurity powder is provided in the pulverizing furnace 15.

[0122] The ironmaking equipment suitable for low-grade iron ore described in the present invention realizes high-quality utilization of low-grade iron ore resources through the reduction-slag iron separation system composed of the rotary kiln 3, the insulation furnace 12 and the crushing furnace 15, and the terminal product realizes iron-slag separation. The obtained metal iron beads have a high metallization rate and can be directly used for electric furnace steelmaking or converter steelmaking, achieving near-zero slag content and improving the purity in the steelmaking process.

[0123] The specific structure of each part of the ironmaking equipment suitable for low-grade iron ore described in the present invention, as well as the position and connection relationship between the various parts will be explained below.

[0124] like Figure 3 As shown, the ironmaking equipment has a mixing device 1, which can achieve the mixing of multiple materials. The mixing device 1 is provided with multiple material boxes, each of which can contain a material; in this embodiment, the three material boxes are used to contain low-grade iron ore powder, coal powder and adhesive respectively. The outlets at the bottom of the material boxes are connected to the mixing box, and the opening degree of the outlets at the bottom of each material box is controlled to control the mixing ratio of various materials.

[0125] like Figure 3 As shown, the ironmaking equipment has a briquette press 2, which can realize cold pressing and briquetting of the mixed material. The briquette press 2 is arranged below the mixing device 1, and the mixed material enters between two pairs of rollers of the briquette press 2 and is pressed into cold pressed balls.

[0126] like Figure 3As shown, the ironmaking equipment has a rotary kiln 3, which can achieve the reduction of iron oxides under high temperature environment. The kiln head of the rotary kiln 3 is connected to the ball press 2, and the cold pressed balls produced by the ball press 2 can enter the cylinder of the rotary kiln 3 through the kiln head; the kiln tail of the rotary kiln 3 is connected to the gas supply pipeline 21, and the gas supply pipeline 21 can pass fuel gas into the rotary kiln 3; the cylinder of the rotary kiln 3 is inclined so that the kiln head is higher than the kiln tail, and the movement direction of the cold pressed balls in the rotary kiln 3 is opposite to the movement direction of the fuel gas. The cold pressed balls move forward slowly in the kiln by relying on the inclination and rotation of the cylinder of the rotary kiln 3, and are gradually heated by the reverse hot air flow, completing the reduction reaction and carburizing reaction and other processes, and the reduced cold pressed balls are unloaded from the kiln tail.

[0127] like Figure 3 As shown, the ironmaking equipment has a holding furnace 12, which can keep the cold pressed balls warm. The entrance of the holding furnace 12 is connected to the kiln tail of the rotary kiln 3, and the cold pressed balls after reduction directly enter the holding furnace 12 through the outlet of the kiln tail for keeping warm. The holding furnace 12 adopts electric heating, and there are heating rods on both sides of the furnace body. The temperature in the furnace is maintained in the range of 1100℃-1150℃ through the heating effect of the heating rods.

[0128] like Figure 3 As shown, the ironmaking equipment also has a crushing furnace 15, which can realize the rapid cooling of the cold-pressed balls and the separation of slag and iron. The inlet of the crushing furnace 15 is connected to the outlet of the insulation furnace 12, and the cold-pressed balls after insulation directly enter the crushing furnace 15 through the outlet of the insulation furnace 12. The crushing furnace 15 can cool the cold-pressed balls by air cooling and / or water cooling to decompose them into metal iron beads and impurity powder; a screen with an aperture of 3mm is provided in the crushing furnace 15, and the fine impurity powder is sieved down and recovered through the slag receiving port 19, while the metal iron beads with a diameter greater than 3mm enter the iron outlet 20 to realize the separation of slag and iron, and finally obtain metal iron beads with a metallization rate greater than or equal to 95%, realizing the high-quality utilization of low-grade ores.

[0129] The structure and technical effects of the preferred embodiment of the ironmaking equipment suitable for low-grade iron ore described in the present invention will be further described below.

[0130] According to one embodiment of the present invention, a coal powder injection mechanism 5 is provided in the briquetting machine 2, and the coal powder injection mechanism 5 can spray coal powder onto the cold-pressed balls to form cold-pressed balls coated with coal powder.

[0131] During the process of reducing the cold-pressed balls to generate metallic iron in the rotary kiln 3, since the surface of the cold-pressed balls is sprayed with coal powder, the coal powder wrapped on the outer surface first participates in the reaction, and a solid iron shell is formed on the outer surface of the cold-pressed balls, which can effectively inhibit the adhesion between the charge materials.

[0132] According to one embodiment of the present invention, the rotary kiln 3 is provided with an angle adjustment mechanism capable of adjusting its tilt angle, and the angle adjustment mechanism is used to control the time for the cold pressed balls to move from the kiln head to the kiln tail.

[0133] If the reduction time is too short, the reduction will be incomplete, resulting in a lower iron formation rate. If the reduction time is too long, the metallic iron will melt and wrap the slag, making it difficult to separate the iron slag in the subsequent process. Therefore, an angle adjustment mechanism is provided to control the reaction time of the cold-pressed balls in the rotary kiln 3 to be between 65min and 75min.

[0134] According to one embodiment of the present invention, Figure 3 As shown, an oxygen tank 7, a gas tank 6 and a spraying mechanism 5 are provided on the gas supply pipeline 21, and a gas spray gun 4 is connected to the end of the gas supply pipeline 21 located in the rotary kiln 3.

[0135] The gas tank 6 on the gas supply line 21 contains natural gas, and the raw materials used by the rotary kiln 3 are CH4 in the natural gas and oxygen in the oxygen tank 7; the high nitrogen content in the air will affect the calorific value of the gas, and the nitrogen enrichment during the reforming cycle will affect the utilization efficiency, so oxygen is selected as the combustion aid.

[0136] If the reduction temperature is too low, the reduction will be incomplete, resulting in a lower iron formation rate. If the reduction temperature is too high, the metallic iron will melt and wrap the slag, making it difficult to separate the iron slag in the subsequent process. Therefore, the injection rate of the gas injection gun 4 is controlled by the injection mechanism 5 on the gas supply pipeline 21, so that the temperature in the rotary kiln 3 is between 1227°C and 1250°C.

[0137] According to one embodiment of the present invention, Figure 3 As shown, the flue gas outlet 8 of the rotary kiln 3 is connected to a recovery pipeline 22, and the outlet end of the recovery pipeline 22 is connected to the gas supply pipeline 21; along the flow direction of the flue gas in the recovery pipeline 22, the recovery pipeline 22 is provided with: a reforming furnace 9 for reducing CO2 and H2O in the flue gas, CH4 is passed through the reforming furnace 9, and in the reforming furnace 9, CO2 and H2O react with CH4 to produce CO and H2; and a dust collector 10 for filtering dust in the flue gas.

[0138] Through the reforming regeneration of the reforming furnace 9 on the recovery pipeline 22, the low-quality waste flue gas generated in the rotary kiln 3 is reformed into high-quality coal gas, and the re-conversion of CO2 in the flue gas reduces carbon emissions. Compared with the existing process, CO2 emissions are reduced by 30%-40%.

[0139] Specifically, Figure 3 As shown, the inlet end of the recovery pipeline 22 is connected to the kiln head of the rotary kiln 3, and the high-temperature flue gas generated in the rotary kiln 3 enters the recovery pipeline 22; the outlet end of the recovery pipeline 22 is connected to the gas supply pipeline 21, and the coal gas generated by the flue gas after reforming and dust removal enters the gas supply pipeline 21.

[0140] The flue gas first enters the reforming furnace 9, and the gas tank 6 is connected to the reforming furnace 9 through a pipeline to introduce CH4 into the reforming furnace 9; the high-temperature flue gas and CH4 enter from the inlet at the bottom of the reforming furnace 9 respectively. The reforming furnace 9 is provided with a spiral ascending pipeline and filled with a porous resistance ball to slow down the airflow speed and ensure that the flue gas and natural gas are fully mixed. Because the flue gas has a high temperature (≥1200℃), CO2 and H2O in the flue gas react with CH4 in the natural gas under high temperature conditions to generate CO and H2.

[0141] Maintaining the mixing ratio of flue gas and natural gas at 0.5-0.6, the conversion rate is the highest, about 65%-70%; in addition, Fe and CaO in flue gas dust will also promote the improvement of conversion rate to a certain extent, based on which low-quality flue gas is converted into high-quality coal gas. After the flue gas dust rises to a certain height with the airflow, it falls to the bottom of the reforming furnace 9 under the action of gravity under the conditions of pipeline obstruction and reduced gas flow rate, completing the rough dust removal of the flue gas.

[0142] Afterwards, the reformed and roughly dedusted coal gas enters the dust collector 10 for further dedusting, then enters the gas supply pipeline 21, enters the coal gas injection gun 4 through the injection mechanism 5, and is then injected into the rotary kiln 3 for re-combustion and utilization.

[0143] The flue gas is reformed to produce coal gas, which can reduce the emission of CO2 in the flue gas on the one hand; on the other hand, since CH4 absorbs heat when it is cracked under high temperature conditions (1 mol of CH4 absorbs 1760 kJ of heat), directly injecting CH4 into the rotary kiln 3 through the coal gas injection gun 4 for combustion will partially crack and cause heat loss in the kiln. Through the reforming process, part of CH4 is converted into CO and H2 by utilizing the waste heat of the flue gas for direct combustion and heat release, thus completing the recovery of flue gas waste heat resources and reducing the heat loss in the kiln.

[0144] Further, such as Figure 3 As shown, a fan 11 for driving the gas flow is provided on the recovery pipeline 22 ; a fan 11 for driving the natural gas to flow toward the reforming furnace 9 is also provided on the pipeline between the reforming furnace 9 and the gas tank 6 .

[0145] According to one embodiment of the present invention, Figure 3 As shown, the holding furnace 12 and the crushing furnace 15 are both connected to a nitrogen tank 18 through a pipeline, and the nitrogen tank 18 can respectively introduce nitrogen into the holding furnace 12 and the crushing furnace 15. Nitrogen is introduced into the holding furnace 12 through the nitrogen tank 18 to prevent the reduced iron in the cold-pressed balls from being reoxidized during the holding process; nitrogen is introduced into the crushing furnace 15 through the nitrogen tank 18 to purge and cool the high-temperature furnace charge in the crushing furnace 15.

[0146] Specifically, the nitrogen tank 18 is connected to the top of the insulation furnace 12 through a pipeline. In order to prevent the gas in the rotary kiln 3 from entering the insulation furnace 12 during the unloading process, a nitrogen sealing mechanism 14 is provided on the upper part of the furnace body of the insulation furnace 12; the nitrogen tank 18 is connected to the nitrogen spray gun 17 in the crushing furnace 15 through a pipeline, and the low-temperature nitrogen is sprayed onto the charge in the crushing furnace 15 through the nitrogen spray gun 17.

[0147] According to one embodiment of the present invention, Figure 3 As shown, a nitrogen circulation pipeline is connected between the holding furnace 12 and the crushing furnace 15, and the nitrogen circulation pipeline includes a first nitrogen pipeline 23 and a second nitrogen pipeline 24; the high-temperature nitrogen generated in the crushing furnace 15 can enter the holding furnace 12 through the first nitrogen pipeline 23; the high-temperature nitrogen in the holding furnace 12 can enter the crushing furnace 15 through the second nitrogen pipeline 24, and a power generation mechanism 16 is provided on the second nitrogen pipeline 24.

[0148] Nitrogen preheating and waste heat recovery of the charge are completed simultaneously in the crushing furnace 15, and then the high-temperature nitrogen is introduced into the bottom of the insulation furnace 12 as a protective gas through the first nitrogen pipeline 23, thereby reducing the temperature fluctuation in the insulation furnace 12; at the same time, the high-temperature nitrogen in the insulation furnace 12 is recovered through the power generation mechanism 16 for waste heat recovery, and the low-temperature nitrogen generated by the waste heat recovery is introduced into the crushing furnace 15 to cool the charge.

[0149] According to one embodiment of the present invention, Figure 3 As shown, a ball valve 13 is provided in the holding furnace 12, and the residence time of the cold pressed balls in the holding furnace 12 is controlled by the ball valve 13 to ensure that the tricalcium silicate in the slag phase can fully undergo crystal transformation. In this embodiment, the residence time of the cold pressed balls in the holding furnace 12 is controlled by the ball valve 13 to be between 30 minutes and 40 minutes.

[0150] According to one embodiment of the present invention, a water cooling pipe is provided at the bottom of the pulverizing furnace 15; the cooling water in the water cooling pipe can water-cool the charge in the pulverizing furnace 15, and cooperate with the air cooling of nitrogen to achieve rapid cooling of the charge.

[0151] According to one embodiment of the present invention, a vibration mechanism connected to the screen is provided in the pulverizing furnace 15, and the vibration mechanism can drive the screen to vibrate so as to separate the iron beads from the impurity powder, and at the same time make the iron beads move toward the outlet of the pulverizing furnace 15. The vibration mechanism drives the screen to vibrate, which can quickly separate the iron beads from the impurity powder on the one hand, and drive the iron beads to move toward the outlet of the pulverizing furnace 15 on the other hand. In this embodiment, the diameter of the mesh in the screen is 3mm, and the fine impurity powder is sieved down and recovered through the slag receiving port 19, while the diameter of the metal iron beads is greater than 3mm and enters the iron outlet 20 to achieve slag iron separation.

[0152] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An ironmaking process suitable for low-grade iron ore, characterized in that: include: Mixing low-grade iron ore powder, coal powder and a binder in predetermined proportions and forming the mixture into cold-pressed balls; Under the conditions of a predetermined first temperature and a first time, the cold pressed balls are subjected to a reduction treatment, so that the iron oxides in the cold pressed balls undergo a reduction reaction and aggregate to form iron beads, and the gangue phase in the cold pressed balls reacts to form a slag phase, wherein the slag phase contains calcium silicate; Under predetermined second temperature and second time conditions, the reduced cold pressed balls are subjected to heat preservation treatment so as to cause the calcium silicate in the slag phase to undergo a crystal transformation; Cooling the cold pressed balls after heat preservation at a predetermined cooling rate, so that the calcium silicate in the slag phase undergoes crystal transformation again and breaks, so that the iron balls are peeled off from the broken slag phase; The iron beads and impurity powder formed by crushing the slag phase are separated.

2. The ironmaking process applicable to low-grade iron ore according to claim 1, characterized in that: After the cold pressed balls are made, the coal powder is sprayed on the surface of the cold pressed balls.

3. The ironmaking process applicable to low-grade iron ore according to claim 1, characterized in that: The mass percentage of coal powder in the mixture is y; y=(0.11x+0.76z) / d Among them, x is the mass percentage of Fe2O3 in the iron ore powder; z is the mass percentage of total iron in the iron ore powder; d is the mass percentage of fixed carbon in the coal powder.

4. The ironmaking process applicable to low-grade iron ore according to claim 1, characterized in that: The first time is 65 min-75 min, and the first temperature is 1227° C.-1250° C.

5. The ironmaking process applicable to low-grade iron ore according to claim 4, characterized in that: In the process of the iron oxides in the cold-pressed balls undergoing a reduction reaction and forming the iron beads, the iron oxides in the iron ore powder are reduced and carburized to form iron, and part of the melted iron is aggregated into the iron beads, which are distributed in the internal spaces of the cold-pressed balls and on the surface of the cold-pressed balls; In the process of the gangue phase in the cold-pressed balls reacting to generate the slag phase, CaO and SiO2 in the gangue phase react to generate 3CaO·SiO2 and 2CaO·SiO2, thereby forming the slag phase containing the calcium silicate.

6. The ironmaking process applicable to low-grade iron ore according to claim 1, characterized in that: The second temperature is 1100° C.-1150° C., and the second time is 30 min-40 min.

7. The ironmaking process applicable to low-grade iron ore according to claim 6, characterized in that: During the heat preservation process of the reduced cold-pressed balls, the 3CaO·SiO2 in the slag phase undergoes a crystal transformation into α-2CaO·SiO2.

8. The ironmaking process applicable to low-grade iron ore according to claim 1, characterized in that: During the cooling process of the cold pressed balls after heat preservation, the predetermined cooling rate is 50° C. / min-60° C. / min.

9. The ironmaking process applicable to low-grade iron ore according to claim 8, characterized in that: During the cooling process of the cold-pressed balls after heat preservation, the calcium silicate in the slag phase undergoes a crystal transformation: α-2CaO·SiO2 transforms into β-2CaO·SiO2, and then transforms into γ-2CaO·SiO2.

10. The ironmaking process applicable to low-grade iron ore according to claim 1 or 9, characterized in that: The diameter of the iron bead is greater than 3 mm, and the metallization rate of the iron bead is greater than or equal to 95%.

11. The ironmaking process applicable to low-grade iron ore according to claim 1, characterized in that: In the process of cooling the cold pressed balls after heat preservation, a combined cooling method of air cooling and water cooling is adopted to accelerate the cooling rate.

12. The ironmaking process applicable to low-grade iron ore according to claim 1, characterized in that: Also includes: The process of reducing the cold-pressed balls is carried out in a rotary kiln (3), wherein fuel is passed through the rotary kiln (3), and the fuel is burned to provide heat and generate smoke; The flue gas is mixed with CH4 and reformed to generate CO and H2, and the CO and H2 are introduced into the rotary kiln (3) and reused as fuel.

13. The ironmaking process applicable to low-grade iron ore according to claim 12, characterized in that: The flue gas generated by the rotary kiln (3) contains CO2 and H2O; during the process of reforming the flue gas, CO2 and H2O react with CH4 to generate CO and H2; CO and H2 are mixed with CH4 and introduced into the rotary kiln (3) as fuel.

14. The ironmaking process applicable to low-grade iron ore according to claim 1, characterized in that: In the process of separating the iron beads and the impurity powder formed by crushing the slag phase, slag-iron separation can be achieved by screen filtration or magnetic separation.

15. An ironmaking equipment suitable for low-grade iron ore, characterized in that: include: A mixing device (1) for mixing low-grade iron ore powder, coal powder and a binder; A ball press (2) for cold-pressing the mixed material into cold-pressed balls, wherein the mixing device (1) is connected to the ball press (2); A rotary kiln (3) for reducing the iron oxides in the cold-pressed balls, the ball press (2) being connected to the rotary kiln (3), and the cold-pressed balls being reduced in the rotary kiln (3) to form iron balls; A heat preservation furnace (12) for keeping the cold pressed balls warm, the rotary kiln (3) being connected to the heat preservation furnace (12); A pulverizing furnace (15) is used to cool the cold pressed balls. The heat preservation furnace (12) is connected to the pulverizing furnace (15). During the cooling process of the cold pressed balls in the pulverizing furnace (15), the iron balls are separated from the generated impurity powder. A screen is provided in the pulverizing furnace (15) for separating the iron balls from the impurity powder.

16. The ironmaking equipment suitable for low-grade iron ore according to claim 15, characterized in that: The kiln head of the rotary kiln (3) is connected to the briquetting machine (2), and the kiln tail of the rotary kiln (3) is connected to a gas supply pipeline (21), and the gas supply pipeline (21) can supply fuel gas to the rotary kiln (3); The rotary kiln (3) is arranged to be inclined so that the kiln head is higher than the kiln tail, and the movement direction of the cold-pressed balls in the rotary kiln (3) is opposite to the movement direction of the fuel gas.

17. The ironmaking equipment suitable for low-grade iron ore according to claim 16, characterized in that: The rotary kiln (3) is provided with an angle adjustment mechanism capable of adjusting its tilt angle, and the time for the cold-pressed balls to move from the kiln head to the kiln tail is controlled by the angle adjustment mechanism.

18. The ironmaking equipment suitable for low-grade iron ore according to claim 16, characterized in that: The gas supply pipeline (21) is provided with an oxygen cabinet (7), a gas cabinet (6) and a spraying mechanism (5), and the end of the gas supply pipeline (21) located in the rotary kiln (3) is connected to a gas spray gun (4).

19. The ironmaking equipment suitable for low-grade iron ore according to claim 16, characterized in that: The smoke outlet (8) of the rotary kiln (3) is connected to a recovery pipeline (22), and the outlet end of the recovery pipeline (22) is connected to the gas supply pipeline (21); Along the flow direction of the flue gas in the recovery pipeline (22), the recovery pipeline (22) is provided with the following in sequence: A reforming furnace (9) for reducing CO2 and H2O in flue gas, wherein CH4 is passed through the reforming furnace (9), and in the reforming furnace (9), CO2 and H2O react with CH4 to produce CO and H2; A dust collector (10) is used for filtering dust in flue gas.

20. The ironmaking equipment suitable for low-grade iron ore according to claim 15, characterized in that: The heat-insulating furnace (12) and the pulverizing furnace (15) are both connected to a nitrogen tank (18) via a pipeline, and the nitrogen tank (18) can respectively introduce nitrogen into the heat-insulating furnace (12) and the pulverizing furnace (15).

21. The ironmaking equipment suitable for low-grade iron ore according to claim 20, characterized in that: A nitrogen circulation pipeline is connected between the holding furnace (12) and the pulverizing furnace (15), and the nitrogen circulation pipeline includes a first nitrogen pipeline (23) and a second nitrogen pipeline (24); The high-temperature nitrogen generated in the pulverizing furnace (15) can enter the holding furnace (12) through the first nitrogen pipeline (23); The high-temperature nitrogen in the heat-insulating furnace (12) can enter the pulverizing furnace (15) through the second nitrogen pipeline (24), and a power generation mechanism (16) is provided on the second nitrogen pipeline (24).

22. The ironmaking equipment suitable for low-grade iron ore according to claim 15, characterized in that: A ball valve (13) is provided in the heat preservation furnace (12), and the residence time of the cold-pressed balls in the heat preservation furnace (12) is controlled by the ball valve (13).

23. The ironmaking equipment suitable for low-grade iron ore according to claim 15 or 20, characterized in that: The furnace bottom of the pulverizing furnace (15) is provided with a water cooling pipe.

24. The ironmaking equipment suitable for low-grade iron ore according to claim 15, characterized in that: A vibration mechanism connected to the screen is provided in the pulverizing furnace (15), and the vibration mechanism can drive the screen to vibrate so as to separate the iron balls from the impurity powder and move the iron balls toward the outlet of the pulverizing furnace (15).

25. The ironmaking equipment suitable for low-grade iron ore according to claim 15, characterized in that: The briquetting machine (2) is provided with a coal powder injection mechanism (5), and the coal powder injection mechanism (5) can spray coal powder onto the cold pressed balls to form a layer of coal powder wrapped around the surface of the cold pressed balls.

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