Method for producing low metamorphic coal into semicoke for iron ore sintering

Abstract

The application discloses a method for producing low-metamorphic coal into semi-coke for iron ore sintering, which comprises the following steps: washing low-metamorphic coal to obtain raw materials, and performing coal pyrolysis on the raw materials to obtain semi-coke particles, and screening semi-coke particles with a particle size of 12-15 mm for high sintering. The semi-coke produced by the method has an optimized microstructure and element composition, and its combustion performance and calorific value are closer to those of coke powder for sintering, so that the vertical sintering speed is basically unchanged before and after the process of replacing coke powder with semi-coke in a high proportion, thereby ensuring the performance of sintered ore, and the amount of nitrogen oxides generated is obviously reduced.

Description

Technical Field

[0001] This invention belongs to the field of semi-coke production and iron ore sintering technology, specifically relating to a method for producing semi-coke for iron ore sintering from low-rank coal. Background Technology

[0002] Solid fuel costs account for approximately 30% to 40% of the total processing cost of iron ore sintering. Reducing solid fuel costs is an effective way to lower overall processing costs in sintering. Traditionally, coke powder is the primary solid fuel for sintering. However, with the continuous rise in coke powder prices in recent years, the use of new alternative fuels such as anthracite and semi-coke has become inevitable, either to reduce solid fuel costs or due to resource constraints. However, the use of anthracite as a substitute in steel enterprises has generally resulted in problems such as excessive nitrogen oxide emissions and reduced sintering capacity.

[0003] Semi-coke is a solid carbon fuel produced by medium- and low-temperature pyrolysis of low-rank coal. It has the characteristics of high calorific value, low ash, low sulfur and low phosphorus. Using it as a sintering fuel can not only expand the sources of sintering fuel, but also reduce the cost of sintering fuel, and has good potential for promotion.

[0004] Fuel plays a crucial role in the sintering process, and different types of fuel significantly impact the yield and quality of sintered ore. Compared to sintered coke powder, while semi-coke has advantages such as lower enrichment of harmful elements and lower price, it also has significant drawbacks, including lower fixed carbon content and higher volatile matter content. This leads to a series of problems when semi-coke is used as a substitute fuel in sintering. Its excellent combustion performance means that the large amount of heat released during combustion cannot be absorbed by the sintering bed before entering the flue gas. The rapid combustion of the fuel causes a mismatch between the combustion rate and heat transfer rate during sintering, weakening its automatic heat storage capacity and affecting the formation of the liquid phase. The high volatile matter content further re-condenses in the lower part of the sintering bed, thus affecting the permeability of the bed. In addition, the poor strength and shatter resistance of semi-coke, as well as its unreasonable particle size distribution, exacerbate the unevenness of the sintered cross-section. These numerous problems with semi-coke as a sintering fuel ultimately have a significant impact on the quality indicators of the sintered ore. Given the characteristics of semi-coke, it can currently only be added in a certain proportion (20% to 30%) during the sintering process. Obviously, without changing the performance of semi-coke, it is difficult to achieve large-scale application of semi-coke in the sintering field by simply adding it in this way.

[0005] Large-scale production of semi-coke primarily utilizes vertical internal heating furnace dry distillation, a process mainly for producing coal tar and semi-coke for ferroalloys / calcium carbide. However, this process fails to consider the specific requirements of sintering fuel in terms of raw material selection, particle size control, and pyrolysis condition control. Therefore, finding optimal dry distillation conditions that meet both the quality requirements of sintering fuel and ensure a sufficiently high tar yield is crucial for improving the applicability of semi-coke in the iron ore sintering field. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for producing semi-coke for iron ore sintering from low-rank coal, which addresses the shortcomings of the prior art. This method solves the technical problem that semi-coke sintering cannot be applied on a large scale. By optimizing the microstructure and combustion reactivity of semi-coke through the selection of raw coal and the control of pyrolysis conditions, the combustion behavior of semi-coke in the sintering bed is optimized.

[0007] The present invention adopts the following technical solution:

[0008] A method for producing semi-coke for iron ore sintering from low-rank coal involves washing the low-rank coal to obtain raw material, then performing coal pyrolysis on the raw material to obtain semi-coke particles, and finally screening semi-coke particles with a particle size of 12-15 mm for high-temperature sintering.

[0009] Specifically, the ash content in the raw materials should be less than 5.5%, and the specific surface area should be less than 2.0 m². 2 / g, microcrystalline structure parameter d 002 It is less than 0.345 nm and the dry basis nitrogen content is less than 0.90%.

[0010] Specifically, in coal pyrolysis, the flow ratio of return gas to incoming air is controlled as (1.80~1.90): 1.

[0011] Furthermore, the optimal flow ratio of return gas to furnace air is 1.85:1.

[0012] Specifically, in coal pyrolysis, the coke pushing speed is controlled at 660–840 r / min.

[0013] Furthermore, the focus pushing speed is 720 r / min.

[0014] Specifically, in coal pyrolysis, the temperature inside the dry distillation furnace is controlled at 730–750℃.

[0015] Furthermore, the temperature inside the dry distillation furnace is 740℃.

[0016] Specifically, semi-coke particles with a particle size of 12-15mm are crushed and used as semi-coke for sintering. The mass of semi-coke with a particle size of 1-3mm is greater than 65% of the total mass of semi-coke after crushing, and the mass of semi-coke with a particle size of less than 1mm is less than 25% of the total mass of semi-coke after crushing.

[0017] Another technical solution of the present invention is a semi-coke for iron ore sintering.

[0018] Compared with the prior art, the present invention has at least the following beneficial effects:

[0019] This invention discloses a method for producing semi-coke for iron ore sintering from low-rank coal. It optimizes the raw coal by utilizing industrial analysis, pore structure, carbon chemical structure parameters, and nitrogen content; it optimizes the coal coke pyrolysis process to reduce the combustion performance and nitrogen content of the semi-coke; and it achieves particle homogenization by crushing the semi-coke particles, thereby improving the stability of combustion and heat supply during sintering. Using 12-15mm particles not only reduces the combustion reactivity of the semi-coke but also ensures high fixed carbon and calorific value. Simultaneously, the composition and performance of products larger than 15mm are not affected. This optimizes the microstructure and elemental composition of the semi-coke, making its combustion performance and calorific value closer to that of coke powder for sintering. The vertical sintering rate remains essentially unchanged before and after the high-proportion replacement of coke powder with semi-coke, thus ensuring the performance of the sintered ore while significantly reducing nitrogen oxide generation.

[0020] Furthermore, the ash content in the washed coal is less than 5.5%, and the specific surface area is less than 2.0 m². 2 / g, microcrystalline structure parameter d 002 With a particle size less than 0.345 nm and a dry basis nitrogen content of less than 0.90%, the low ash content of the coal ensures that the calorific value, specific surface area, and microcrystalline structure of the semi-coke affect its combustion reactivity, while the nitrogen content affects the formation of nitrogen oxides during the combustion process of the semi-coke.

[0021] Furthermore, the ratio of return gas to furnace air flow is controlled to 1.80–1.90, and the content of oxidizing atmosphere and medium temperature in the dry distillation gas are optimized to ensure that the external temperature conditions for semi-coke pyrolysis meet the requirements.

[0022] Furthermore, optimizing the coke pushing speed and residence time of semi-coke in the dry distillation furnace can improve the thermal condensation reaction during pyrolysis, enhance the mechanical strength of semi-coke, and promote the orderly development of carbon chemical structure.

[0023] Furthermore, the temperature setting inside the dry distillation furnace can not only reduce the porosity of semi-coke and further reduce its specific surface area, but also suppress secondary tar reactions to the greatest extent, ensuring a high coal tar yield during pyrolysis.

[0024] In summary, the semi-coke produced by this invention optimizes the microstructure and elemental composition of semi-coke, making its combustion performance and calorific value closer to that of coke powder for sintering. The vertical sintering rate remains basically unchanged before and after the process of high-proportion replacement of coke powder with semi-coke, thereby ensuring the performance of sintered ore, while the amount of nitrogen oxides generated is significantly reduced.

[0025] The technical solution of the present invention will be further described in detail below through embodiments. Detailed Implementation

[0026] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0028] Unless otherwise specified, all the technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0029] In this invention, unless otherwise specified, percentage (%) or parts refer to weight percentage or parts relative to the composition.

[0030] Unless otherwise specified, the components or preferred components involved in this invention can be combined with each other to form new technical solutions.

[0031] In this invention, unless otherwise specified, the numerical range "a~b" represents an abbreviation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "6~22" means that all real numbers between "6~22" have been listed in this document, and "6~22" is simply an abbreviation of these numerical combinations.

[0032] The "scope" disclosed in this invention can be in the form of a lower limit and an upper limit, and can be one or more lower limits and one or more upper limits, respectively.

[0033] In this invention, the term "and / or" as used herein refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes such combinations.

[0034] In this invention, unless otherwise stated, the various reactions or operation steps may be performed sequentially or in a particular order. Preferably, the reaction methods described herein are performed sequentially.

[0035] Unless otherwise stated, the technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods or materials similar to or equivalent to those described herein may also be used in this invention.

[0036] This invention provides a method for producing semi-coke for iron ore sintering from low-rank coal. The method optimizes the microstructure and elemental composition of the semi-coke, making its combustion performance and calorific value closer to that of coke powder used in sintering. The vertical sintering rate remains essentially unchanged before and after the high-proportion replacement of coke powder with semi-coke, thus ensuring the performance of the sintered ore, while significantly reducing nitrogen oxide generation. The production steps of this method are as follows: First, the raw coal is optimized using industrial analysis, pore structure, carbon chemical structure parameters, and nitrogen content. Second, the coal pyrolysis process is optimized by controlling conditions such as the return gas / feed air flow ratio in the dry distillation furnace burner, the maximum temperature in the dry distillation furnace, and the coke pusher speed, thereby reducing the combustion performance and nitrogen content of the semi-coke. Finally, the semi-coke particles are crushed to achieve particle homogenization, improving the stability of combustion and heating during the sintering process.

[0037] This invention discloses a method for producing semi-coke for iron ore sintering from low-rank coal, comprising the following steps:

[0038] S1. Low-rank coal is washed to obtain coal with an ash content of less than 5.5% and a specific surface area of ​​less than 2.0 m². 2 / g, microcrystalline structure parameter d 002 With a particle size of less than 0.345 nm and a dry basis nitrogen content of less than 0.90%, it is used as a raw material in this production process.

[0039] Further screening of various washed coals was conducted using the following methods: industrial analysis was performed according to the national standard GB / T 212-2008 to determine the ash content; the specific surface area was determined using the nitrogen adsorption method; the diffraction angle of the 002 peak of the raw coal was determined by X-ray diffraction, and the microcrystalline structure parameter d002 was calculated according to the Bragg equation; and the dry basis nitrogen content in the coal was determined according to the national standard GB / T 31391-2015.

[0040] S2. Control the flow ratio of recycled gas to incoming air in the burner of the pyrolysis furnace to 1.80-1.90; control the pushing speed of the coke pusher to 660-840 r / min; control the temperature of the inner wall of the pyrolysis furnace to 730-750℃, and carry out coal pyrolysis treatment to obtain semi-coke particles.

[0041] S3. Particles with a size of 12-15 mm obtained from screening step S2 are crushed and used as semi-coke for high-temperature sintering.

[0042] Among them, the mass of semi-coke with a particle size of 1-3mm is greater than 65% of the total mass of semi-coke after crushing, and the mass of semi-coke with a particle size of less than 1mm is less than 25% of the total mass of semi-coke after crushing.

[0043] Through numerous basic experiments, this invention clarifies the microstructure that semi-coke used for sintering should possess, and also obtains the dry distillation conditions required for preparing high-quality sintered semi-coke.

[0044] Example 1

[0045] S1. Low-rank coal is washed to obtain coal with an ash content of less than 5.5% and a specific surface area of ​​less than 2.0 m². 2 / g, microcrystalline structure parameter d 002 With a particle size of less than 0.345 nm and a dry basis nitrogen content of less than 0.90%, it is used as a raw material in this production process.

[0046] S2. Control the flow ratio of recycled gas to incoming air in the burner of the pyrolysis furnace to 1.80-1.90; control the pushing speed of the coke pusher to 660 r / min; control the inner wall temperature of the pyrolysis furnace to 730℃, and carry out coal pyrolysis treatment to obtain semi-coke particles.

[0047] S3. Among the semi-coke particles obtained in step S2, those with a particle size of 12mm are crushed and used as semi-coke for high-temperature sintering. The mass of semi-coke with a particle size of 1mm is greater than 65% of the total mass of semi-coke after crushing, and the mass of semi-coke with a particle size of less than 1mm is less than 25% of the total mass of semi-coke after crushing.

[0048] Example 2

[0049] S1. Low-rank coal is washed to obtain coal with an ash content of less than 5.5% and a specific surface area of ​​less than 2.0 m². 2 / g, microcrystalline structure parameter d 002 With a particle size of less than 0.345 nm and a dry basis nitrogen content of less than 0.90%, it is used as a raw material in this production process.

[0050] S2. Control the flow ratio of recycled gas to incoming air in the burner of the dry distillation furnace to 1.84; control the pushing speed of the coke pusher to 700 r / min; control the inner wall temperature of the dry distillation furnace to 735℃, and carry out coal pyrolysis to obtain semi-coke particles.

[0051] S3. Among the semi-coke particles obtained in step S2, those with a particle size of 13mm are crushed and used as semi-coke for high-temperature sintering. The mass of semi-coke with a particle size of 2mm is greater than 65% of the total mass of semi-coke after crushing, and the mass of semi-coke with a particle size of less than 1mm is less than 25% of the total mass of semi-coke after crushing.

[0052] Example 3

[0053] S1. Low-rank coal is washed to obtain coal with an ash content of less than 5.5% and a specific surface area of ​​less than 2.0 m². 2 / g, microcrystalline structure parameter d 002 With a particle size of less than 0.345 nm and a dry basis nitrogen content of less than 0.90%, it is used as a raw material in this production process.

[0054] S2. Control the flow ratio of recycled gas to incoming air in the burner of the dry distillation furnace to 1.88; control the pushing speed of the coke pusher to 750 r / min; control the inner wall temperature of the dry distillation furnace to 740℃, and carry out coal pyrolysis to obtain semi-coke particles.

[0055] S3. Among the semi-coke particles obtained in step S2, those with a particle size of 14mm are crushed and used as semi-coke for high-temperature sintering. The mass of semi-coke with a particle size of 2mm is greater than 65% of the total mass of semi-coke after crushing, and the mass of semi-coke with a particle size of less than 1mm is less than 25% of the total mass of semi-coke after crushing.

[0056] Example 4

[0057] S1. Low-rank coal is washed to obtain coal with an ash content of less than 5.5% and a specific surface area of ​​less than 2.0 m². 2 / g, microcrystalline structure parameter d 002 With a particle size of less than 0.345 nm and a dry basis nitrogen content of less than 0.90%, it is used as a raw material in this production process.

[0058] S2. Control the flow ratio of recycled gas to incoming air in the burner of the dry distillation furnace to 1.90; control the pushing speed of the coke pusher to 840 r / min; control the inner wall temperature of the dry distillation furnace to 750℃, and carry out coal pyrolysis treatment to obtain semi-coke particles.

[0059] S3. Among the semi-coke particles obtained in step S2, those with a particle size of 15mm are crushed and used as semi-coke for high-temperature sintering. The mass of semi-coke with a particle size of 3mm is greater than 65% of the total mass of semi-coke after crushing, and the mass of semi-coke with a particle size of less than 1mm is less than 25% of the total mass of semi-coke after crushing.

[0060] Semi-coke producers select the carbonized coal with the composition shown in Table 1 from a wide range of washed coals. In addition, the specific surface area of ​​the carbonized coal is 1.8 m². 2 / g, microcrystalline structure parameter d 002 The wavelength is 0.336 nm, which meets the requirements for raw material screening.

[0061] Table 1. Industrial and elemental analysis results of washed coal / %

[0062]

[0063]

[0064] During the dry distillation process, the ratio of return gas to incoming air in the burner of the dry distillation furnace is controlled to 1.82, the coke pushing speed of the coke pusher is controlled to 770 r / min, the maximum temperature of the inner wall of the dry distillation furnace is controlled to 736℃, and particles with a size of 12-15 mm are selected from the semi-coke products as semi-coke for iron ore sintering. The performance indicators of the produced semi-coke are shown in Table 2.

[0065] Table 2 Performance Indicators of Semi-coke

[0066] <![CDATA[M t / %]]> <![CDATA[M ad / %]]> <![CDATA[A d / %]]> <![CDATA[V daf / %]]> <![CDATA[FC ad / %]]> <![CDATA[S t,d / %]]> <![CDATA[Q gr.d / kcal / kg]]> 18.3 1.74 7.1 6.42 84.02 0.24 7580

[0067] The semi-coke was crushed into semi-coke powder with a particle size of 2-4 mm, accounting for 90% of the total. It was then mixed with the existing coke powder at a ratio of 1:1 (fuel ratio 4.9%). The sintering indicators are shown in Table 3.

[0068] Table 3. Indicators of sintered ore after adding semi-coke

[0069]

[0070] The above embodiments demonstrate that the method of the present invention can produce semi-coke products with combustion performance similar to coke powder and stable sinter quality after use, thereby improving the applicability of semi-coke in iron ore sintering.

[0071] In summary, this invention provides a method for producing semi-coke for iron ore sintering from low-rank coal. The semi-coke prepared by this method is suitable as an alternative fuel for sintering coke powder, thereby reducing the release of polluting gases and saving costs.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for producing semi-coke for iron ore sintering from low-rank coal, characterized in that, Low-rank coal is washed to obtain raw material with an ash content of less than 5.5% and a specific surface area of ​​less than 2.0 m². 2 / g, microcrystalline structure parameter d 002 The raw material is pyrolyzed to obtain semi-coke particles with a particle size of less than 0.345 nm and a dry basis nitrogen content of less than 0.90%. During the pyrolysis process, the flow ratio of return gas to incoming air is controlled at (1.80~1.90):1, the coke pushing speed is controlled at 660~840 r / min, and the temperature inside the dry distillation furnace is controlled at 730~750℃. Semi-coke particles with a particle size of 12~15 mm are screened. The semi-coke particles with a particle size of 12~15 mm are crushed and used as semi-coke for sintering. The mass of semi-coke with a particle size of 1~3 mm is greater than 65% of the total mass of semi-coke after crushing, and the mass of semi-coke with a particle size of less than 1 mm is less than 25% of the total mass of semi-coke after crushing.

2. The method according to claim 1, characterized in that, The flow ratio of return gas to furnace air is 1.85:

1.

3. The method according to claim 1, characterized in that, The focus pushing speed is 720 r / min.

4. The method according to claim 1, characterized in that, The temperature inside the dry distillation furnace is 740℃.

5. Semi-coke for iron ore sintering prepared by the method according to claim 1.

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