阅读说明：本技术 一种转炉快速造渣用部分煅烧石灰石及其制备方法 (Partially calcined limestone for rapid slagging of converter and preparation method thereof ) 是由 李光强 刘昱 田雨丰 李腾飞 陈牒斌 黄世辉 于 2021-02-05 设计创作，主要内容包括：本发明涉及一种转炉快速造渣用部分煅烧石灰石及其制备方法,制备的部分煅烧石灰石的表层石灰层为高活性石灰,内层核心成分为碳酸钙。制备方法为以含碳酸钙石灰石为原料,经破碎、清洗和筛选,得到15～20mm的块状石灰石,在200～300℃加热炉内保温2～3h后,在3～6转/min的回转窑内,800～900℃煅烧0.5～0.8h制得部分煅烧石灰石。在转炉中应用制备的部分煅烧石灰石造渣,溶解过程避开了直接用石灰石造渣时溶解初期存在的停滞阶段,初期溶解速率更快；且当CO-2残余量在质量％为25～30时分解需要的热量减小32％以上,利于维持转炉热平衡,应用部分煅烧石灰石造渣使用范围可扩大到生产碳含量更高的钢种。(The invention relates to partially calcined limestone for quick slagging of a converter and a preparation method thereof. The preparation method comprises the steps of taking calcium carbonate-containing limestone as a raw material, crushing, cleaning and screening to obtain 15-20 mm blocky limestone, keeping the temperature in a heating furnace at 200-300 ℃ for 2-3 h, and calcining in a rotary kiln at 3-6 r/min at 800-900 ℃ for 0.5-0.8 h to obtain partially calcined limestone. The prepared partially calcined limestone is applied to the converter for slagging, so that a stagnation stage existing in the initial dissolution stage when the limestone is directly used for slagging is avoided in the dissolution process, and the initial dissolution rate is higher; and when CO is present 2 When the residual amount is 25-30% by mass, the heat required for decomposition is reduced by more than 32%, the heat balance of the converter is favorably maintained, and the application range of partial calcined limestone slagging can be expanded to produce steel with higher carbon content.)

1. The utility model provides a converter is partial calcination lime stone for quick slagging which characterized in that: the partially calcined limestone is prepared by partially calcining a limestone raw material with the mass percentage of more than 98.8 calcium carbonate, decomposing the surface layer into a surface lime layer, wherein the component is porous active calcium oxide, the core of the inner layer is still unreacted core limestone and the component is calcium carbonate; the apparent porosity of the surface lime layer is 38.88-52.5%.

2. The partially calcined limestone for rapid slagging in converters according to claim 1, characterized in that: the limestone core of the partially calcined limestone is subjected to decomposition reaction in the converter slagging process: CaCO₃＝CaO+CO₂When CO is present₂When the residual amount is 25-30 mass percent, escaping CO₂The method is used for removing the calcium silicate isolation layer on the surface in the limestone dissolution process and accelerating the dissolution of limestone.

3. A method for preparing partially calcined limestone for rapid converter slagging according to claim 1, characterized in that the method comprises the following steps:

firstly, limestone with the mass percentage content of more than 98.8 calcium carbonate is used as a raw material, primary crushing is carried out by a crusher to obtain limestone with the granularity of 50-100 mm, and secondary crushing is carried out to obtain limestone with the granularity of 15-20 mm;

secondly, cleaning the limestone subjected to secondary crushing by using a stone scrubber, grading by using a vibrating screen, and screening to obtain blocky limestone with the particle size of 15-20 mm;

thirdly, putting the block limestone pretreated in the second step into a heating furnace, and preheating for 2-3 hours at the temperature of 200-300 ℃ to remove moisture;

and fourthly, putting the limestone with the moisture removed into a rotary kiln at 800-900 ℃ for 0.5-0.8 h, and controlling the rotating speed of the rotary kiln at 3-6 r/min to prepare partially calcined limestone.

Technical Field

The invention relates to partially calcined limestone for quick slagging of a converter and a preparation method thereof, belonging to the technical field of slagging in the steelmaking process of the converter.

Background

In the converter steelmaking process, in order to realize the purpose of massive dephosphorization in the early stage, the slag with certain alkalinity, oxidability and good fluidity needs to be rapidly produced. For a century, the traditional method is to use calcined pure lime for slagging, the lime is the main slagging agent for converter steelmaking, and the lime is prepared by burning limestone under certain conditions.

Increasing the lime activity is beneficial for accelerating the dissolution of lime in the converter slag, but has limited effect. Because the calcium silicate isolation layer is formed on the surface of lime in the process of dissolving the lime in the converter slag, and mass transfer in the dissolving process is seriously hindered, two measures are mainly taken to accelerate the dissolution of the lime in the converter slag, namely, the size of blocky lime is reduced, so that the mass transfer distance in the lime dissolving process is shortened, but the lime with too small size is taken away by gas flowing reversely in the converter, and the distribution loss of the lime is caused. Another measure is to destroy the calcium silicate barrier formed on the surface of lime, e.g. by using limestone instead of lime for slagging, by using CO generated during the decomposition of limestone₂The silicate layer on the surface of the lime is destroyed, and the lime dissolution rate is further improved.

Therefore, in the last decade, a technology of slagging by using blocky limestone instead of calcined lime is continuously proposed by professionals, after the limestone is directly put into a converter, a rapid heating and calcining process is carried out by using high-temperature molten iron in the converter, the blocky limestone is rapidly decomposed into lime and generates a large amount of gas, the condition of slagging and dephosphorization of the converter is met, and the formation of the large amount of gas improves the dynamic condition. For example, the application number is 201210139432.1 in 'a method for slagging by replacing partial limestone with lime for a top-bottom combined blown converter' and 'a method for slagging and steelmaking by using limestone in steelmaking of semisteel by a top-bottom combined blown converter' disclosed by the Chinese intellectual Property office in 2012, and the application number is 201910308981.9; the above-mentioned techniques are all that limestone is directly used for slagging in steel-making. However, in recent years, it has been found that limestone has some disadvantages in place of lime, and since the dissolution process of limestone first undergoes a decomposition process, the decomposition of limestone is an endothermic reaction, and the furnace temperature in the initial stage of the converter is relatively low, the limestone may have a stagnation stage lasting for a long time in the initial stage of the dissolution process, so that the initial dissolution rate of limestone is slow. More importantly, the heat balance of the smelting process of the converter can be influenced by the large amount of heat absorption in the decomposition process of the limestone, and more carbon in molten steel needs to be consumed to generate heat, so that the method for directly adding the limestone for slagging is only suitable for smelting steel with low carbon content, and the reasonable adding amount of other slagging agents can be influenced by the overlarge addition amount of the limestone under the condition that the surplus heat of a converter molten pool is limited.

Disclosure of Invention

The invention aims to overcome the defects of the traditional lime slagging technology and the technology of replacing lime slagging with limestone in recent years, and provides the partially calcined limestone for quick slagging of the converter and the preparation method thereof, and the preparation method provided by the invention is simple and easy to operate, and the preparation process is more energy-saving and environment-friendly; the prepared partially calcined limestone can keep the highest activity and apparent porosity of a surface lime layer; when the method is used, the heat consumption in the dissolving process of the converter slag is less, the dissolving speed is higher, the method is more favorable for maintaining the heat balance of the converter, the furnace condition can be ensured, the requirement of the end temperature of the converter can be met, and the application range can be expanded to produce steel with higher carbon content.

In order to achieve the purpose, the invention adopts the technical scheme that: providing partially calcined limestone for rapid slagging of a converter, wherein the partially calcined limestone is prepared by partially calcining a limestone raw material of calcium carbonate with the mass percentage of more than 98.8, the surface layer of the partially calcined limestone is decomposed into a surface lime layer, the component of the partially calcined limestone is porous activated calcium oxide, the core of the inner layer is still unreacted core limestone, and the component of the partially calcined limestone is calcium carbonate; the apparent porosity of the surface lime layer is 38.88-52.5%.

The limestone core of the partially calcined limestone is subjected to decomposition reaction in the converter slagging process: CaCO₃＝CaO+CO₂When CO is present₂When the residual amount is 25-30 mass percent, escaping CO₂The method is used for removing the calcium silicate isolation layer on the surface in the limestone dissolution process and accelerating the dissolution of limestone.

The invention also provides a preparation method of the partially calcined limestone for quick slagging of the converter, which comprises the following steps:

firstly, limestone with the mass percentage content of more than 98.8 calcium carbonate is used as a raw material, primary crushing is carried out by a crusher to obtain limestone with the granularity of 50-100 mm, and secondary crushing is carried out to obtain limestone with the granularity of 15-20 mm;

secondly, cleaning the limestone subjected to secondary crushing by using a stone scrubber, grading by using a vibrating screen, and screening to obtain blocky limestone with the particle size of 15-20 mm;

thirdly, putting the block limestone pretreated in the second step into a heating furnace, and preheating for 2-3 hours at the temperature of 200-300 ℃ to remove moisture;

and fourthly, putting the limestone with the moisture removed into a rotary kiln at 800-900 ℃ for 0.5-0.8 h, and controlling the rotating speed of the rotary kiln at 3-6 r/min to prepare partially calcined limestone.

Compared with the prior art, the partially calcined limestone for rapid slagging of the converter and the preparation method thereof have the advantages that:

compared with the traditional lime calcining process, the partially calcined limestone for slagging prepared by the method can reduce the calcining time of the limestone in a lime kiln, thereby reducing the energy consumption and CO consumption in the calcining process₂And discharging, and simultaneously keeping the highest activity of the surface lime as much as possible. While the traditional lime needs to be completely calcined, when the lime is calcined inside, the surface of the lime is burnt and the activity is reduced.

Compared with the lime prepared conventionally, the partially calcined limestone prepared by the method of the invention has high activity on the surface lime, so that the dissolution rate of the partially calcined limestone in the converter slag can be accelerated, and the quality of the partially calcined limestone contained in the partially calcined limestone is higher25-30% of carbon dioxide, escaping CO₂Can destroy the calcium silicate isolation layer formed in the surface lime dissolving process, thereby ensuring that the later dissolving rate is not influenced, and greatly improving the dissolving rate of the whole slagging process.

Compared with the method for directly feeding limestone into the converter, the partially calcined limestone for rapidly slagging in the converter and the preparation method thereof have the advantages that the surface layer of the partially calcined limestone is decomposed and high-activity lime is maintained, the apparent porosity is as high as 38.88-52.5%, so that a stagnation stage experienced at the initial stage of a limestone dissolving process is avoided in the dissolving process of the partially calcined limestone in the converter slag, and the initial dissolving rate is higher. When the mass percentage of the residual carbon dioxide is 25-30, the heat required by decomposition is reduced by more than 32%, which is more beneficial to maintaining the heat balance of the converter, so that the partially calcined limestone is used for slagging, and the application range can be expanded to produce steel grades with higher carbon content.

Drawings

FIG. 1 is a schematic diagram of the structure of partially calcined limestone prepared according to the present invention.

FIG. 2 is a TG-DSC graph of raw limestone for making partially calcined limestone in accordance with the present invention.

FIG. 3 is an SEM image of a lime layer on the surface of partially calcined limestone.

FIG. 4 is a block diagram illustrating the specific steps of preparing partially calcined limestone in accordance with the present invention.

Fig. 5 is a graph of the dissolution rate of lime, limestone and partially calcined limestone of the present invention in converter slag.

Fig. 6 is an SEM image of the slag/lime interface microstructure when the converter slag is dissolved for 3min using conventional lime.

Fig. 7 is an EDS surface scan picture of the microstructure of the slag/lime interface when the converter slag is dissolved for 3min with conventional lime.

FIG. 8 is an SEM image of the slag/lime interface microstructure when limestone is used to dissolve the converter slag for 3 min.

FIG. 9 is an SEM image of the CaO-FeO layer/lime interface microstructure of partially calcined limestone according to the present invention when the converter slag is dissolved for 3 min.

In the above figures: 1-surface lime layer; 2-unreacted nuclear limestone.

Detailed Description

The partially calcined limestone for converter rapid slagging and the preparation method thereof according to the present invention will be described in further detail with reference to the accompanying drawings, but the practice of the present invention is not limited thereto.

Example 1: the invention provides partially calcined limestone for rapid slagging in a converter, the structure and physical properties of which are shown in figures 1, 2 and 3, and figure 1 is a schematic structural diagram of the partially calcined limestone. It can be seen from the figure that after partial calcination of the limestone raw material, the surface layer of the limestone is already decomposed into a surface lime layer 1 with porous activated calcium oxide, and the inner core is still unreacted core limestone 2 with calcium carbonate.

FIG. 2 is a TG-DSC graph of raw limestone. It can be seen from the figure that the weight loss of the raw material after calcination can reach 43.5 wt%, and the calculated mass percentage of calcium carbonate in the raw material is more than 98.8.

FIG. 3 is an SEM image showing the vicinity of the surface layer of partially calcined limestone, in which it can be seen that the surface layer of lime 1 has many cracks and numerous micropores distributed therein; the apparent porosity of the surface layer lime layer 1 is measured to be 38.88-52.5%.

The embodiment provides a preparation method of the partially calcined limestone for rapid slagging of the converter, and the specific steps of the preparation method are as follows, with reference to fig. 4:

firstly, limestone with the mass percentage content of more than 98.8 calcium carbonate is used as a raw material, primary crushing is carried out by a crusher to obtain limestone with the granularity of 50-100 mm, and secondary crushing is carried out to obtain limestone with the granularity of 15-20 mm;

secondly, cleaning the limestone subjected to secondary crushing by using a stone scrubber, grading by using a vibrating screen, and screening to obtain blocky limestone with the particle size of 15-20 mm;

thirdly, putting the block limestone pretreated in the second step into a heating furnace, and preserving heat for 3 hours at the temperature of 200 ℃ to preheat so as to remove moisture;

and fourthly, putting the limestone with the moisture removed into a rotary kiln at 800 ℃ for 0.8h, and controlling the rotating speed of the rotary kiln at 3 revolutions per minute to obtain the partially calcined limestone shown in the figure 1.

The use result shows that the quick slagging of the partially calcined limestone prepared by the invention is superior to the traditional completely calcined lime and the slagging of the limestone directly input. See the dissolution rate curve of fig. 5. The three curves are respectively a schematic diagram of dissolution rate curves of limestone, partially calcined limestone prepared by the invention and fully calcined lime in converter slag. As can be seen from the figure, if limestone is used, the dissolution rate in the initial stage of the converter slag is slow; if lime is used for dissolving in the converter slag, the dissolution rate is slowed down due to the formation of a calcium silicate layer; only the partially calcined limestone prepared by the method can ensure the rapid dissolution in the initial stage and also can ensure the dissolution rate in the later stage, and the dissolution rate is improved by nearly 1 time within 3 min.

Referring to fig. 6 and 7, SEM and EDS images of the slag/lime interface microstructure of conventional fully calcined lime at 3min of converter slag dissolution are given; as can be seen from the figure, when lime is dissolved in the converter slag, a calcium silicate reaction layer is formed at the slag/lime interface, which hinders mass transfer and slag penetration during lime dissolution, thereby slowing down the lime dissolution rate.

Fig. 8 and 9 show SEM images of the slag/lime interface microstructures when limestone is directly input and partially calcined limestone prepared by the present invention is dissolved in converter slag for 3min, respectively, in the process of dissolving limestone and partially calcined limestone, no calcium silicate isolation layer is formed with the interface layer of slag, and FeO can more easily permeate into the lime layer formed by surface decomposition, thereby accelerating the dissolution thereof.

As can be seen from the above figures, the partially calcined limestone for rapid slagging in a converter and the method for preparing the same according to the present invention can accelerate the dissolution rate in the converter slag and when CO is added, since the lime layer on the surface of the partially calcined limestone maintains higher activity than the limestone directly charged into the converter, and the dissolution rate can be accelerated when the limestone is charged into the converter₂When the residual amount is 25-30 mass percent, escaping CO₂The calcium silicate isolation layer formed in the limestone surface dissolving process can be damaged, so that the later dissolving rate can be ensured not to be influenced, the dissolving rate of the whole slagging process can be greatly improved, the heat required by decomposition is reduced by more than 32%, and the converter heat balance is favorably maintained, so that the partially calcined limestone prepared by the method is used for slagging, and the application range can be expanded to produce steel grades with higher carbon content.

Example 2: the invention provides a partially calcined limestone for rapid slagging in a converter and a preparation method thereof, wherein the structure, the preparation method and the use effect on the converter of the partially calcined limestone are basically the same as those of embodiment 1, except that the block limestone pretreated in the third preparation step is placed in a heating furnace, heat preservation is carried out for 2 hours at 300 ℃ for preheating to remove moisture, the limestone after moisture removal is placed in a rotary kiln at 900 ℃ for 0.5 hour in the fourth preparation step, and the rotating speed of the rotary kiln is controlled at 6 revolutions per minute to obtain the partially calcined limestone.

Example 3: the invention provides a partially calcined limestone for converter rapid slagging and a preparation method thereof, wherein the structure, the preparation method and the use effect on a converter of the partially calcined limestone are basically the same as those of embodiment 1, except that in the fourth preparation step, the limestone with water removed is put into a rotary kiln at the temperature of 840 ℃ for 0.7h, and the rotating speed of the rotary kiln is controlled at 4 r/min, so that the partially calcined limestone is obtained.

The partially calcined limestone for rapid slagging of the converter and the preparation method thereof have the advantages that the preparation method is simple and easy to operate, the surface lime layer of the prepared partially calcined limestone is high-activity lime, and the core component of the inner layer is still unreacted nuclear limestone, namely calcium carbonate. The partial calcined limestone is used for slagging in a converter, the dissolution process avoids the stagnation stage in the initial stage of directly dissolving the limestone, the initial dissolution rate is faster, the heat required by decomposition is reduced by more than 32 percent, the heat balance of the converter is favorably maintained, and the application range can be expanded to produce steel grades with higher carbon content.