Converter operation method

Abstract

To substitute or reduce fossil fuel used for the heat rise of molten steel and to secure the calorific power of a converter gas.SOLUTION: A converter operation method comprises: a step of feeding heat rise auxiliary raw material in which a volatile component content is above 20% to less than 40% into a converter stored with molten steel; a step of feeding oxygen to the auxiliary raw material fed into the furnace; and a step of recovering a gas generated by a reaction between the auxiliary raw material, the molten steel, and the oxygen from the converter so as to be utilized as a heat source.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a converter operation method In the law in particular.

Background Art

[0002] In recent years, from the perspective of environmental protection, reduction of CO2 emissions has become an important issue even in iron manufacturing processes. Accordingly, as described in Patent Document 1 for example, a technology has been proposed that achieves carbon neutrality by replacing fossil fuels such as coal with so-called biomass carbonaceous materials produced from plant-derived raw materials as the carbonaceous materials charged into the furnace.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0004] As an initiative for reducing CO2 emissions in iron manufacturing processes separate from the above, increasing the usage ratio of reduced iron, specifically iron scrap, in steelmaking raw materials is under investigation. Unlike blast furnace hot metal, iron scrap is at room temperature or preheated in advance, but since its temperature is lower than that of blast furnace hot metal, an increase in the usage ratio of iron scrap in steelmaking raw materials leads to an increase in the required amount of heat-raising carbonaceous material charged into the converter. Conventionally, amorphous graphite has been used as such heat-raising carbonaceous material, but since it is a fossil fuel that increases CO2 emissions, and the producing regions of low-sulfur amorphous graphite with low refining load are limited, the use of biomass carbonaceous material as the heat-raising carbonaceous material is also under investigation. However, since biomass carbonaceous materials generally have a high volatile content and a low fixed carbon content, they are used after the volatile content is reduced by heating or the like in order to improve the heat raising efficiency.

[0005] Furthermore, an increase in the proportion of scrap iron used in steelmaking raw materials leads to a decrease in the proportion of blast furnace molten iron used, resulting in reduced operation of blast furnaces and coke ovens used in the ironmaking process, and consequently, a decrease in the production of by-product gases such as blast furnace gas and coke oven gas. Since by-product gases are used as a heat source in other processes within the steelworks, a decrease in production necessitates the procurement of heat sources such as natural gas, which is undesirable from a cost perspective or from the perspective of reducing CO2 emissions. Converter gas is also produced as a by-product gas in converters, but a decrease in the proportion of blast furnace molten iron used reduces the amount of carbon generated by decarburization blowing in converters. As a result, the calorific value of converter gas during combustion decreases, which may make it insufficient for use as a heat source.

[0006] Therefore, the present invention relates to a converter operation method that can replace or reduce fossil fuels used for heating molten steel and ensure the calorific value of the converter gas. Law The purpose is to provide it. [Means for solving the problem]

[0007] [1] A method for operating a converter, comprising the steps of: supplying a heat-raising auxiliary material having a volatile matter content greater than 20% by mass and 40% by mass or less into a converter in which molten steel is stored; supplying oxygen to the auxiliary material supplied into the furnace; and recovering the gas generated by the reaction of the auxiliary material, the molten steel and the oxygen from the converter and using it as a heat source. [2] The above auxiliary raw material is carbonized material obtained by carbonization treatment of waste plastic or biomass, or waste plastic that has not been carbonized, the method of operating the converter as described in [1]. [3] The above auxiliary raw materials have a sulfur content of 0.02% by mass or less and an ash content of 5% by mass or less, the method of operating a converter according to [1] or [2]. [4] The method for operating a converter according to any one of [1] to [3], wherein the above-mentioned auxiliary heat-boosting raw material includes a first auxiliary heat-boosting raw material and a second auxiliary heat-boosting raw material, wherein the volatile content of the first auxiliary heat-boosting raw material is greater than the volatile content of the second auxiliary heat-boosting raw material, and further comprises a step of selecting whether to supply the first auxiliary heat-boosting raw material or the second auxiliary heat-boosting raw material into the converter according to the amount of production per hour required by the converter. [5] A method for operating a converter according to any one of items [1] to [4], further comprising the step of selecting whether to supply the above-mentioned auxiliary heat-boosting raw material into the converter or to supply the above-mentioned auxiliary heat-boosting raw material having a volatile content of 20% by mass or less into the converter, depending on the amount of production per hour required by the converter. [6] A secondary raw material for heating a converter, having a volatile matter content greater than 20% by mass and 40% by mass or less, a sulfur content of 0.02% or less, and an ash content of 5% or less. [Effects of the Invention]

[0008] According to the above configuration, even biomass charcoal materials with a high volatile content can be used as auxiliary raw materials for heating, thus replacing or reducing the use of fossil fuels for heating molten steel. Furthermore, by including volatile components within an appropriate range in the auxiliary raw materials for heating, the amount of CO gas generated by reaction with oxygen in the converter increases. This ensures that the calorific value of the converter gas is secured and can be used as a heat source in other processes, thereby reducing costs and CO2 emissions. [Brief explanation of the drawing]

[0009] [Figure 1] This figure shows a schematic configuration of a converter facility in which the operating method according to one embodiment of the present invention is implemented. [Figure 2] This graph shows the relationship between the volatile content of the auxiliary raw materials used for heating and the change in molten steel temperature. [Modes for carrying out the invention]

[0010] Preferred embodiments of the present invention will be described in detail below with reference to the attached drawings. In this specification and drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant descriptions will be omitted.

[0011] Figure 1 shows a schematic configuration of a converter facility in which an operating method according to one embodiment of the present invention is implemented. The converter facility 10 includes a converter 11, a lance 12, a flue 13, and a feeding device 14. Since the general configuration of a converter facility is already known, parts of the converter facility 10 that are not related to the operating method described below are not shown or described. In the converter facility 10, the lance 12 inserted from the furnace opening of the converter 11 supplies oxygen-containing gas to the molten steel in the converter 11 (acid supply). When carbon in the molten steel reacts with oxygen, it becomes CO gas or CO2 gas, and these gases are discharged from the flue 13 as converter gas (LDG). The feeding device 14 supplies auxiliary materials such as carbon material into the converter 11. If the auxiliary material is in powder form, it can also be blown into the converter 11 together with the oxygen-containing gas using the lance 12. In addition, a bottom-blowing nozzle may be used in conjunction with the lance 12 for acid supply.

[0012] In this embodiment, the auxiliary raw materials introduced (or blown) into the converter 11 in the converter equipment 10 described above include a heat-boosting auxiliary raw material having a volatile matter content greater than 20% by mass and 40% by mass or less. Preferably, the heat-boosting auxiliary raw material has a sulfur content of 0.02% by mass or less and an ash content of 5% by mass or less. The portion of the heat-boosting auxiliary raw material other than volatile matter, sulfur, and ash is fixed carbon. Volatile matter and ash are defined by JIS M0104 "Terminology for Coal Utilization Technology" and can be quantified according to JIS M8812 "Coal and Coke - Industrial Analysis Methods". Sulfur is defined as total sulfur in JIS M0104 and can be quantified according to JIS M8813 "Coal and Coke - Elemental Analysis Methods". In this specification, the content is defined as the dry mass relative to the total auxiliary raw material.

[0013] While the above definitions generally apply to carbon materials such as coal, coke, charcoal, and briquettes, in this embodiment, materials that are not necessarily called carbon materials but contain volatile matter, ash, and sulfur as defined and quantified above can be used as auxiliary materials for heating. For example, the auxiliary materials for heating may be carbonized material obtained by carbonization of waste plastic or biomass, or waste plastic that has not undergone carbonization.

[0014] As described above, in the converter, the oxygen supplied by the acid supply causes the reactions shown in equations (1) to (3) below. Equation (1) is the oxidation reaction of iron in molten steel, and equations (2) and (3) are the oxidation reactions (decarburization reactions) of carbon in molten steel. The decarburization reactions in equations (2) and (3) are endothermic reactions, and therefore proceed while consuming the heat of the blast furnace molten iron, which is the raw material for molten steel. Although the exothermic reaction in equation (1) occurs, overall, with only acid supply, the temperature of the molten steel decreases as the decarburization reaction progresses. Fe+1 / 2O2→FeO+1150[kcal / kg-Fe] ···(1) C (in molten steel) +1 / 2O2→CO-2200[kcal / kg-C] ···(2) C (in molten steel) + O2 → CO2-7840[kcal / kg-C] ···(3)

[0015] The auxiliary raw material for heating increases the temperature of the molten steel by supplying fixed carbon (C) into the converter, which reduces the FeO produced in the reaction of equation (1) as shown in equation (4) below, and consequently promotes the iron oxidation reaction of equation (1), which is an exothermic reaction. Equation (4) is an endothermic reaction, but since the amount of heat released in equation (1) is greater than the amount of heat absorbed in equation (4), the difference is used to heat the molten steel and allow the decarburization reactions of equations (2) and (3) above to proceed. FeO+C→Fe+CO-680[kcal / kg-Fe] ···(4)

[0016] In addition, a typical volatile component contained in the auxiliary raw materials for heating is carbon-based linear C n H 2nis vaporized in the high-temperature converter, thermally decomposed as shown in the following formula (5), and then oxidized by the oxygen supplied via oxygen blowing, as shown in formula (6) and formula (7). Unlike the above formulas (2) and (3), formula (6) and formula (7) are reactions of free carbon and thus are exothermic reactions, and the calorific value exceeds the endothermic value during vaporization and thermal decomposition of volatile matter. Therefore, when the auxiliary raw material for temperature rise is supplied to the molten steel together with oxygen blowing, in combination with the above reaction of fixed carbon (reducing FeO to promote the oxidation reaction of iron), the molten steel also rises in temperature through the reaction of volatile matter. C n H 2n →nC+nH₂···(5) C+1 / 2O₂→CO ···(6) C+O₂→CO₂···(7)

[0017] The combustible CO gas generated by the reactions of the above formula (2), formula (4) and formula (7) accompanying oxygen blowing to molten steel in the converter and the supply of the auxiliary raw material for temperature rise is discharged as converter gas (LDG), and used as a heat source in other processes within the steelworks.

[0018] Here, since the reaction of formula (4) by fixed carbon (the reaction of formula (1) promoted by said reaction) has higher temperature rise efficiency, conventionally, carbonaceous materials with increased fixed carbon content obtained by artificially reducing the volatile matter content through heating or the like have been used as auxiliary raw materials for temperature rise. However, when the usage ratio of iron scrap used together with blast furnace hot metal as a raw material for molten steel increases, since iron scrap has a lower carbon content than blast furnace hot metal, the CO gas generated by the decarburization reaction of formula (2) decreases. Furthermore, when the volatile matter content of the auxiliary raw material for temperature rise is lowered, the amount of oxygen blowing, that is, the amount of oxygen supplied by oxygen blowing, increases relative to the amount of carbon generated by the thermal decomposition of formula (5), as a result, the reaction of formula (7) becomes dominant over the reaction of formula (6) (or the CO gas generated in formula (6) undergoes secondary combustion in the converter), and the generated CO gas is further reduced. In that case, the calorific value during combustion of the converter gas decreases due to the reduction of CO gas as a combustible component, and the demand as a heat source may not be satisfied.

[0019] Therefore, in this embodiment, the volatile content of the auxiliary raw material for heat generation is made greater than 20% by mass by deliberately not reducing the volatile content of the original carbon material, for example. In this case, although the efficiency of heat generation decreases due to the relative decrease in the fixed carbon content, the amount of carbon produced by the thermal decomposition in equation (5) becomes larger relative to the amount of acid supplied, resulting in the reaction in equation (6) becoming dominant over the reaction in equation (7) (or the secondary combustion of the CO gas produced in equation (6) in the converter is suppressed), and more CO gas can be generated. Even if the amount of auxiliary raw material required for heat generation increases or the blowing time becomes longer due to the decrease in the efficiency of heat generation, if the calorific value of the converter gas during combustion can be increased by the increase in the combustible component CO gas to meet the demand as a heat source, then the procurement of heat sources such as natural gas becomes unnecessary, which is advantageous from the standpoint of cost or CO2 emission reduction. In addition, if the process of artificially reducing the volatile content of the original carbon material becomes unnecessary, that is also an advantage.

[0020] However, if the volatile content of the auxiliary raw material for heating is too high, the amount of carbon produced by the thermal decomposition in equation (5) will be excessive relative to the amount of acid supplied, resulting in unreacted carbon remaining. In this case, the exothermic reaction will not occur, which exceeds the heat absorbed during the vaporization and thermal decomposition of the volatile components. As a result, the molten steel will not be heated by the reaction of the volatile components, and conversely, the temperature of the molten steel will decrease. In the case of a typical acid supply rate in a converter, by setting the volatile content of the auxiliary raw material for heating to 40% by mass or less, it is possible to increase the amount of CO gas produced while heating the molten steel by the reaction of the volatile components.

[0021] In this embodiment, the amount of CO gas contained in the converter gas can be increased by increasing the volatile content of the auxiliary material for heating. However, as mentioned above, increasing the volatile content increases the blowing time. Therefore, instead of always using an auxiliary material for heating with a high volatile content, the auxiliary material for total heat may be selectively used depending on the required production volume per unit time (converter tapping volume). In operations requiring high production volume, an auxiliary material for heating with a low volatile content is selected to prioritize securing the converter tapping volume over the calorific value of the converter gas. In operations that do not require high production volume, an auxiliary material for heating with a high volatile content is selected to ensure the calorific value of the converter gas.

[0022] In the above example, a heat-raising auxiliary material with a high volatile content used in operations where high production volume is not required is designated as the first heat-raising auxiliary material, and a heat-raising auxiliary material with a low volatile content used in operations where high production volume is required is designated as the second heat-raising auxiliary material. In this case, both the first and second heat-raising auxiliary materials may be heat-raising auxiliary materials according to the embodiment of the present invention, or only the first heat-raising auxiliary material may be a heat-raising auxiliary material according to the embodiment of the present invention. In the former case, for example, the volatile content of the first heat-raising auxiliary material is close to 40% by mass, and the volatile content of the second heat-raising auxiliary material is close to 20% by mass. In the latter case, the volatile content of the first heat-raising auxiliary material is greater than 20% by mass, and the volatile content of the second heat-raising auxiliary material is 20% by mass or less.

[0023] Furthermore, from the viewpoint of reducing the burden of desulfurization treatment of molten steel in subsequent processes, it is preferable that the sulfur content in the auxiliary raw materials be 0.02% by mass or less. When the sulfur content is within this range, the sulfur is more likely to be absorbed into the slag or volatilized rather than dissolved in the molten steel, and therefore has little effect on the desulfurization treatment. Similarly, from the viewpoint of reducing the burden of desiliconization treatment, it is preferable that the ash content in the auxiliary raw materials be 5% or less. When the ash content is within this range, the silicon contained in the ash is more likely to be absorbed into the slag or volatilized rather than dissolved in the molten steel, and therefore has little effect on the desiliconization treatment. [Examples]

[0024] To verify the effectiveness of the converter operation method according to the present embodiment described above, the following actual-machine tests were conducted.

[0025] First, in a converter using blast furnace molten iron as the raw material for molten steel, an average of approximately 1% of the weight of molten iron was added as a heat-boosting auxiliary material, and the ratio of CO gas to CO2 gas in the recovered converter gas was measured. The heat-boosting auxiliary materials used and their components are shown in Table 1. In Table 1, "CN charcoal" is a charcoal material made from woody biomass that has been carbonized and carbonized, with a binder added and molded to a predetermined size. The content of each component is shown in mass percent.

[0026] [Table 1]

[0027] Actual test results confirmed that the proportion of CO gas in the converter gas increased with CN coal (2) and CN coal (3) having a volatile matter content greater than 20% by mass. From these results, it can be seen that the amount of CO gas generated can be increased by increasing the volatile matter content of the auxiliary raw material for heat advancement to more than 20% by mass.

[0028] Figure 2 is a graph showing the relationship between the volatile content of the heat-raising auxiliary material and the change in molten steel temperature. In the same actual machine test as described above, the change in molten steel temperature (ΔT) before and after the addition of the heat-raising auxiliary material was calculated for three cases where the volatile content of CN carbon was 17 mass%, 22.8 mass%, and 43 mass%. From the results, it was found that the higher the volatile content of the heat-raising auxiliary material, the smaller the increase in molten steel temperature, and when the volatile content exceeded 40 mass%, the change in molten steel temperature became negative, meaning that the molten steel was being cooled.

[0029] Preferred embodiments of the present invention have been described in detail above with reference to the attached drawings, but the present invention is not limited to these examples. It will be obvious to those skilled in the art to which the present invention belongs that various modifications or alterations can be conceived within the scope of the technical idea described in the claims, and these will naturally also be understood to fall within the technical scope of the present invention. [Explanation of Symbols]

[0030] 10...Converter equipment, 11...Converter, 12...Lance, 13...Flue, 14...Input device.

Claims

1. The volatile matter content in the converter where the molten steel is stored is greater than 20% by mass and less than or equal to 35.6% by mass. The process of supplying auxiliary raw materials for heating, A step of supplying oxygen to the auxiliary material supplied into the furnace, The gas generated by the reaction of the auxiliary raw materials, the molten steel, and the oxygen is released from inside the converter. The process of recovering and using it as a heat source A method of operating a converter, including [the specified part of the text].

2. The aforementioned auxiliary raw materials have a sulfur content of 0.02% by mass or less and an ash content of 5% by mass or less. The method for operating a converter as described in claim 1, as shown below.

3. The aforementioned auxiliary heat-boosting raw material includes a first auxiliary heat-boosting raw material and a second auxiliary heat-boosting raw material, and the first The volatile content of the auxiliary heat-raising material is greater than the volatile content of the second auxiliary heat-raising material. Depending on the amount of production per unit time required by the converter, the first heat-boosting auxiliary raw material or The process further includes a step of selecting which of the second heat-boosting auxiliary materials to supply into the converter. A method for operating a converter according to claim 1 or claim 2.

Images