Furnace top ignition method

Abstract

The present invention provides a furnace apex firing method that suppresses abnormal combustion of blast furnace gas during apex firing, enabling safe and stable apex firing. [Solution] A furnace top ignition method in which blast furnace gas is ignited on the surface of raw materials filled in the blast furnace after the blast furnace has been shut down, comprising: a water ingress determination step (step S1) in which the presence or absence of water ingress into the blast furnace is confirmed based on the hydrogen gas concentration contained in the blast furnace gas; a dilution inert gas introduction step (step S3) in which dilution inert gas is introduced into the blast furnace so that the concentrations of combustible gas and inert gas contained in the blast furnace gas satisfy the following formulas; and an air introduction step (step S5) in which air is introduced into the blast furnace after the dilution inert gas has been introduced into the blast furnace. Inert gas concentration x>100α / (α+β) ···(1) Combustible gas concentration y<100β / (α+β) ···(2)

Description

Technical Field

[0001] The present invention relates to a method for ignition at the top of a furnace.

Background Art

[0002] In a blast furnace, high-temperature air, that is, high-temperature oxygen gas, is blown into the blast furnace from a blowing facility called tuyere, and high-temperature reducing gas is generated by the reaction of the oxygen gas, coke, and pulverized coal. In the blast furnace, the temperature of the iron ore is raised, reduced, and melted by the above-mentioned high-temperature reducing gas, and pig iron and slag are discharged outside the furnace from the tapping hole installed below the tuyere. In this blast furnace, in order to perform construction work or regular maintenance, there may be a case where a blow-off is performed to temporarily stop the blowing of high-temperature air into the blast furnace.

[0003] In order to perform construction work or maintenance around the furnace body of the blast furnace during a blow-off, it is a prerequisite for performing the construction work or maintenance that the gas in the blast furnace (hereinafter referred to as blast furnace gas) does not leak out around the furnace body. Therefore, conventionally, air is supplied to the surface of the raw materials in the blast furnace, and the blast furnace gas is ignited and burned (hereinafter referred to as top-of-furnace ignition). By doing so, the blast furnace gas is burned on the surface of the raw materials in the blast furnace to generate an upward airflow, thereby preventing the leakage of the blast furnace gas from the furnace body opening. In addition, by performing top-of-furnace ignition, abnormal combustion of the blast furnace gas during a blow-off is prevented. Abnormal combustion means, for example, unstable combustion in which the blast furnace gas spontaneously ignites or misfires on the surface of the raw materials in the blast furnace, or combustion that generates dust. The components of the blast furnace gas mainly include nitrogen gas, carbon monoxide gas, carbon dioxide gas, and hydrogen gas.

[0004] Regarding the procedure for performing a blast furnace top ignition, for example, Patent Document 1 discloses a method for performing a blast furnace top ignition while analyzing the composition of the blast furnace gas. In the method disclosed in Patent Document 1, the concentrations of carbon monoxide and hydrogen gas in the blast furnace gas are analyzed, and it is calculated whether these analytical values ​​fall within the range of gas composition in the blast furnace gas that causes abnormal combustion when a blast furnace top ignition is performed (hereinafter referred to as the abnormal combustion range). If each analytical value is outside the abnormal combustion range, air is introduced into the blast furnace from the top to perform a blast furnace top ignition.

[0005] Patent Document 2 discloses a technique in which, after reducing the furnace height and shutting down the blast furnace, an inert gas is immediately introduced into the blast furnace from the top, and then the concentrations of carbon monoxide and hydrogen gas in the blast furnace gas are analyzed using multiple gas analyzers installed circumferentially around the blast furnace. The technique is then used to confirm that the analyzed values ​​of each gas concentration are outside the abnormal combustion range before firing at the top of the furnace. It also discloses a technique to detect the presence or absence of water ingress in the furnace based on the hydrogen gas concentration, and if water ingress is detected, firing at the top of the furnace is performed after stopping the water ingress. Note that reducing the furnace height means lowering the height of the raw material filling in the blast furnace (referred to as the stock line). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent No. 10-204510 [Patent Document 2] Japanese Unexamined Patent Publication No. 56-166313 [Overview of the project] [Problems that the invention aims to solve]

[0007] The technologies disclosed in Patent Documents 1 and 2 do not consider abnormal combustion of blast furnace gas when air is introduced into the blast furnace, and calculate whether or not it is outside the abnormal combustion range based only on the concentrations of carbon monoxide and hydrogen gas. Therefore, even if the gas composition of the blast furnace gas is outside the abnormal combustion range when air is introduced into the blast furnace from the top, the gas composition of the blast furnace gas may fall within the abnormal combustion range as the oxygen gas concentration inside the blast furnace increases.

[0008] Furthermore, Patent Document 1 does not specify the need to check for water ingress inside the blast furnace before apex firing. Therefore, for example, if water ingress continues inside the blast furnace even after apex firing, the furnace temperature may decrease due to the ingress. Also, water may be reduced to produce hydrogen gas, and an increase in hydrogen gas concentration may lead to abnormal combustion.

[0009] Furthermore, in the technology disclosed in Patent Document 2, an inert gas is immediately introduced into the blast furnace after the blast is shut off. Therefore, if the amount of water ingress into the blast furnace is small, the hydrogen gas generated by the reduction of water by the inert gas may be diluted, and it may not be possible to detect the ingress by gas analysis. In that case, similar to Patent Document 1, the furnace temperature may decrease due to the ingress. Also, the reduction of water generates hydrogen gas, and the hydrogen gas concentration may increase, potentially leading to abnormal combustion.

[0010] The present invention was made to solve the above problems, and aims to provide a furnace apex firing method that suppresses abnormal combustion of blast furnace gas when performing apex firing and enables safe and stable apex firing. [Means for solving the problem]

[0011] The means to solve the above problems are as follows: [1] A furnace top ignition method for igniting blast furnace gas on the surface of raw materials filled in a blast furnace after the blast furnace has been shut down, comprising: a flood detection step for checking whether or not there is flooding into the blast furnace based on the hydrogen gas concentration contained in the blast furnace gas; a dilution inert gas introduction step for introducing a dilution inert gas into the blast furnace to dilute the blast furnace gas so that the concentrations of flammable gas and inert gas contained in the blast furnace gas satisfy the following formula, after confirming in the flood detection step that there is no flooding into the blast furnace; and an air introduction step for introducing air into the blast furnace after introducing the dilution inert gas into the blast furnace in the dilution inert gas introduction step. Inert gas concentration x>100α / (α+β) ···(1) Combustible gas concentration y<100β / (α+β) ···(2) α is the concentration of the inert gas at the critical point (vol%). β is the concentration of the flammable gas at the critical point (vol%). y is the concentration of the flammable gas (vol%). x is the concentration of the inert gas (vol%). [2] The furnace apex firing method according to [1], wherein in the dilution inert gas introduction step, an inert gas volume of 1 / 10 or more of the internal volume of the blast furnace under standard conditions is introduced into the blast furnace per unit time. [3] The furnace apex firing method according to [1] or [2], wherein the air introduction step involves introducing air into the blast furnace such that the following equation is satisfied. y < (β / α)x ···(3) [4] The furnace top firing method according to any one of [1] to [3], wherein in the flooding determination step, it is determined that there is no flooding into the blast furnace when the hydrogen gas concentration is 3.0 vol% or less and there is no increase in the hydrogen gas concentration. [5] A furnace apex ignition method according to any one of [1] to [4], further comprising an ignition source introduction step of introducing an ignition source into the blast furnace if, in the air introduction step, air is introduced into the blast furnace and the blast furnace gas does not ignite due to spontaneous combustion on the surface of the raw materials. [Effects of the Invention]

[0012] According to the present invention, abnormal combustion of blast furnace gas during apex firing can be suppressed, and apex firing can be performed safely and stably.

Brief Description of the Drawings

[0013] [Figure 1] It is a diagram showing a blast furnace facility to which the top ignition method according to this embodiment can be applied. [Figure 2] It is a diagram showing the abnormal combustion range superimposed on a diagram showing the relationship between the gas concentration of combustible gas and the gas concentration of inert gas in blast furnace gas in the blast furnace. [Figure 3] It is a flowchart for explaining the top ignition method according to this embodiment. [Figure 4] It is a diagram for explaining the change in gas composition in the blast furnace when the top ignition method according to this embodiment is executed. [Figure 5] It is a diagram for explaining the change in gas composition in the blast furnace of the comparative example.

Modes for Carrying Out the Invention

[0014] Hereinafter, the present invention will be specifically described through embodiments of the present invention (hereinafter referred to as "this embodiment"). The embodiments described below show a preferred example of the present invention, and the present invention is not limited by this embodiment in any way.

[0015] The top ignition method according to this embodiment is characterized in that, at the time of blast furnace shutdown, in order to perform top ignition safely and stably, top ignition is performed at a combustion ratio that greatly deviates from the theoretical combustion ratio. First, an explanation of top ignition is as follows. Top ignition means igniting blast furnace gas on the surface of the raw materials filled in the blast furnace (hereinafter referred to as the stock line) at the time of blast furnace shutdown to burn the blast furnace gas. This is to generate an upward gas flow to prevent the leakage of blast furnace gas from the furnace body opening. Note that blast furnace shutdown means temporarily stopping the blowing into the blast furnace. Therefore, at the time of blast furnace shutdown, the raw materials are stocked in the blast furnace, and the raw materials maintain a high temperature state, and blast furnace gas is generated.

[0016] When burning blast furnace gas, the closer the combustion ratio, which is the ratio of the amount of combustible gas contained in the blast furnace gas to the amount of air, is to the theoretical combustion ratio, the larger the combustion scale of the combustible gas becomes, and there is a possibility of generating dust. The theoretical combustion ratio means the ratio of the amount of combustible gas to the amount of air when the combustible gas is completely burned. In the present embodiment, unstable combustion in which the blast furnace gas ignites or misfires, or combustion of the blast furnace gas that may generate dust is referred to as abnormal combustion. In order to suppress such abnormal combustion, top ignition is performed at a combustion ratio that greatly deviates from the theoretical combustion ratio.

[0017] FIG. 1 is a diagram showing a blast furnace facility to which the top ignition method according to the present embodiment can be applied. As shown in FIG. 1, a charging device 3 for charging raw materials into the blast furnace 1 is provided at the top 2 of the blast furnace 1. The charging device 3 shown in FIG. 1 is a bell-less type, and while rotating the rotary chute 4, the raw materials are dropped along the rotary chute 4 and charged. Note that the charging device 3 may be a bell-type charging device instead of the bell-less type shown in FIG. 1.

[0018] A plurality of blast furnace gas riser pipes (hereinafter referred to as riser pipes) 5 for recovering blast furnace gas to the outside are connected to the top 2. The blast furnace gas contains combustible gas and inert gas. Examples of the inert gas include nitrogen gas and carbon dioxide gas. Examples of the combustible gas include carbon monoxide gas and hydrogen gas.

[0019] In the example shown in FIG. 1, a sampling pipe 6 for sampling blast furnace gas from the riser pipe 5 is connected to at least one of the plurality of riser pipes 5. An air filter 7 for removing solids contained in the blast furnace gas is provided in the sampling pipe 6. A gas analyzer 8 is provided on the downstream side of the air filter 7 in the flow direction of the blast furnace gas in the sampling pipe 6. Note that the sampling pipe may be installed in the belly of the blast furnace when reducing the scale and stopping the blast.

[0020] The gas analyzer 8 is a device that continuously analyzes the component concentrations of blast furnace gas. The gas analyzer 8 outputs the gas components, gas concentrations, and the time-dependent changes in each gas component and gas concentration contained in the blast furnace gas to the control device described later as analysis results. Examples of gas analyzers 8 include conventionally known gas analyzers such as gas chromatographs, mass spectrometers, or absorbance analyzers, as well as galvanic analyzers.

[0021] A nitrogen gas supply source (not shown) is connected to the gas analyzer 8 via a purge line 9. This is to discharge any blast furnace gas remaining inside the gas analyzer 8 to the outside using nitrogen gas when analyzing blast furnace gas. Upstream of the gas analyzer 8 in the direction of nitrogen gas flow in the purge line 9, a first shut-off valve 10 is provided to supply nitrogen gas to the gas analyzer 8 and to shut off the supply of nitrogen gas. A pressure regulating valve (not shown) may be provided upstream of the first shut-off valve 10 in the direction of nitrogen gas flow in the purge line 9.

[0022] Furthermore, in the example shown in Figure 1, when the blast furnace 1 is shut down, a dilution inert gas introduction pipe 11 is connected to the furnace top 2 to introduce a dilution inert gas into the blast furnace 1 to dilute the blast furnace gas. Nitrogen gas can be used as the dilution inert gas. The dilution inert gas introduction pipe 11 may be connected to the nitrogen gas supply source mentioned above. A flow meter 12 is provided between the nitrogen gas supply source and the furnace top 2 in the direction of nitrogen gas flow in the dilution inert gas introduction pipe 11 to measure the flow rate of nitrogen gas introduced into the blast furnace 1. The flow meter 12 shown in Figure 1 is a differential pressure type flow meter. The flow meter 12 has an orifice 13 installed in the dilution inert gas introduction pipe 11 and a differential pressure transmitter 14 that measures the pressure difference, i.e., pressure loss, before and after the orifice 13 in the direction of nitrogen gas flow. The flow meter 12 measures the flow rate of nitrogen gas introduced into the blast furnace 1 based on the pressure loss measured by the differential pressure transmitter 14. A second shut-off valve 15 is provided downstream of the flow meter 12 in the direction of nitrogen gas flow in the dilution inert gas introduction pipe 11 to supply nitrogen gas to the blast furnace 1 and to shut off the supply of nitrogen gas. A pressure regulating valve (not shown) may be provided upstream of the second shut-off valve 15 in the direction of nitrogen gas flow in the dilution inert gas introduction pipe 11.

[0023] Furthermore, the blast furnace equipment shown in Figure 1 has an air inlet pipe 16 that introduces air into the blast furnace 1 when the furnace is ignited at its apex. The air inlet pipe 16 is charged into the blast furnace 1 from a manhole (not shown) located at the top of the furnace 2 when the furnace is ignited at its apex, and air is supplied into the blast furnace 1 via the air inlet pipe 16 by a blower or compressor.

[0024] The blast furnace equipment shown in Figure 1 is equipped with a gas analyzer 8 and a control device 17 that controls the supply of inert gas and air to the blast furnace 1. The control device 17 has an input unit 18, an output unit 20, a storage unit 19, and a determination unit 21. The control device 17 is mainly composed of a microcomputer, for example. The control device 17 functions as the input unit 18, output unit 20, and determination unit 21 by executing a program read from the storage unit 19.

[0025] The input unit 18 is operated by an operator and, for example, inputs various analytical conditions to the control device 17 when analyzing blast furnace gas using the gas analyzer 8.

[0026] The storage unit 19 may be, for example, an updatable flash memory, a hard disk that is built-in or connected via a data communication terminal, an information recording medium such as a memory card, and a device for reading and writing such recording media. The storage unit 19 stores programs for the control device 17 to execute each function, data used by such programs, and so on. It also stores various analysis conditions for analyzing blast furnace gas by the gas analyzer 8 input from the input unit 18, the analysis results from the gas analyzer 8, and the gas composition range of blast furnace gas that may cause abnormal combustion (hereinafter referred to as the abnormal combustion range).

[0027] The determination unit 21 determines whether the gas concentration of combustible gases contained in the blast furnace gas is outside the abnormal combustion range when performing apex firing, based on the analysis results from the gas analyzer 8, the abnormal combustion range, and the programs and data stored in the memory unit 19. The abnormal combustion range can be calculated in advance for each type of combustible gas based on Le Chatelier's principle. The determination unit 21 also determines whether there is an increase in the concentration of combustible gases in the blast furnace gas based on the analysis results from the gas analyzer 8. This is to determine whether or not there is water ingress into the blast furnace 1 when the blast furnace 1 is shut down. If there is water ingress into the blast furnace 1, water is reduced inside the blast furnace 1 to produce hydrogen gas, and the hydrogen gas concentration inside the blast furnace 1 increases. Therefore, the presence or absence of water ingress into the blast furnace 1 can be determined based on whether or not there is an increase in hydrogen gas concentration. In other words, the determination unit 21 monitors the trend of hydrogen gas concentration to determine whether or not there is water ingress into the blast furnace 1. The abnormal combustion range will be described later.

[0028] The output unit 20 outputs various analysis conditions for analyzing blast furnace gas stored in the memory unit 19 to the gas analyzer 8. The output unit 20 also outputs the analysis results from the gas analyzer 8 and the determination results from the determination unit 21 to a notification means (not shown) to notify the operator. The notification means may include a monitor, speaker, light-emitting device, or a combination thereof. The control device 17 described above may be located in the gas analyzer 8, or it may be located in a higher-level control device that controls the entire blast furnace facility.

[0029] Here, abnormal combustion and the abnormal combustion range will be explained. In this embodiment, abnormal combustion refers to unstable combustion in which the blast furnace gas ignites or goes out of flame when the furnace apex is ignited, or combustion of the blast furnace gas that produces dust, as described above. The abnormal combustion range refers to the gas composition range of the blast furnace gas that causes abnormal combustion. Figure 2 is a diagram showing the relationship between the gas concentration of combustible gas and the gas concentration of inert gas in the blast furnace gas inside the blast furnace 1, with the abnormal combustion range superimposed on it. The area within the triangle enclosed by the thick solid line in Figure 2 is the abnormal combustion range.

[0030] The abnormal combustion range, that is, the upper limit UL and lower limit LL of the concentration (vol%) of the combustible gas in the mixture of blast furnace gas and air when abnormal combustion occurs, can be calculated based on Le Chatelier's formula (4) shown below. The vertical axis of Figure 2 shows the concentration of combustible gas, which is the sum of carbon monoxide and hydrogen gas. The horizontal axis shows the concentration of inert gas, which is the sum of nitrogen and carbon dioxide gas. Note that at the origin of Figure 2, the proportion of air is 100%, and the proportion of air decreases as you move away from the origin.

[0031]

number

[0032] In equation (4), L is the upper limit UL and lower limit LL of the concentration (%) of the combustible gas in the mixed gas described above when abnormal combustion occurs. In equation (4), Li is the minimum and maximum concentration (%) of the combustible gas component i forming the mixed gas when abnormal combustion occurs. When the combustible gas component i is carbon monoxide gas, Li has a maximum value of 74.0% and a minimum value of 12.5%. When the combustible gas component i is hydrogen gas, Li has a maximum value of 75.0% and a minimum value of 4.0%. In equation (4), Vi is the concentration (%) of the combustible gas component i in the mixed gas, and in this embodiment, it is the measured value of the combustible gas component i by the gas analyzer 8.

[0033] When calculating the upper limit UL of the concentration (%) of a combustible gas in a gas mixture when abnormal combustion occurs, the maximum value of the concentration (%) of the combustible gas component i when abnormal combustion occurs is used as Li in equation (4). That is, if the combustible gas component i is carbon monoxide, 74.0% is used as Li in equation (4), and if the combustible gas component i is hydrogen gas, 75.0% is used as Li in equation (4). Conversely, when calculating the lower limit LL of the concentration (%) of a combustible gas in a gas mixture when abnormal combustion occurs, the minimum value of the concentration (%) of the combustible gas component i when abnormal combustion occurs is used as Li in equation (4). That is, if the combustible gas component i is carbon monoxide, 12.5% ​​is used as Li in equation (4), and if the combustible gas component i is hydrogen gas, 4.0% is used as Li in equation (4).

[0034] Here, the upper limit UL represents the maximum concentration of combustible gas in the blast furnace gas at which abnormal combustion can occur. The lower limit LL represents the minimum concentration of combustible gas in the blast furnace gas at which abnormal combustion can occur. The upper limit lines shown in Figure 2 are lines connecting each upper limit UL, and the lower limit lines are lines connecting each lower limit LL. In Figure 2, the intersection of the upper limit lines and the lower limit lines is referred to as the critical point for abnormal combustion.

[0035] When performing a top-of-fuel ignition during a blast furnace shutdown, abnormal combustion may occur if the gas composition of the blast furnace gas falls within the abnormal combustion range shown in Figure 2. Therefore, in this embodiment, when performing a top-of-fuel ignition during a blast furnace shutdown, the gas composition of the blast furnace gas is adjusted as described below. Figure 3 is a flowchart illustrating the top-of-fuel ignition method according to this embodiment. The top-of-fuel ignition method according to this embodiment, shown in the flowchart in Figure 3, is performed when the blast furnace 1 is shutdown and a top-of-fuel ignition is performed.

[0036] In the example shown in Figure 3, the first step is to check whether or not water has entered the blast furnace 1 (Step S1). Even when the blast furnace 1 is shut down, raw materials are stored inside, maintaining a high temperature. Therefore, if water enters the blast furnace 1, the water is reduced and hydrogen gas is produced. This causes the hydrogen gas concentration inside the blast furnace 1 to gradually increase, potentially bringing the gas composition of the blast furnace gas into the abnormal combustion range. This check is performed to avoid this. It is also to suppress the decrease in furnace temperature due to water ingress.

[0037] In step S1, for example, the control device 17 controls the gas analyzer 8, and samples the blast furnace gas at regular time intervals to measure the hydrogen gas concentration contained in the blast furnace gas using the gas analyzer 8. The measured hydrogen gas concentrations are arranged in chronological order, and if each hydrogen gas concentration is 3.0 vol% (hereinafter simply referred to as %) or less, and each hydrogen gas concentration is the same as the others, it is determined that no water ingress has occurred in the blast furnace 1. Also, if each hydrogen gas concentration is 3.0% or less, and the hydrogen gas concentration decreases over time, it is determined that no water ingress has occurred in the blast furnace 1. On the other hand, if even one of the hydrogen gas concentrations exceeds 3.0%, it is determined that water ingress has occurred in the blast furnace 1. Furthermore, even if each hydrogen gas concentration is 3.0% or less, if the hydrogen gas concentration increases even slightly over time, it is determined that water ingress has occurred in the blast furnace 1.

[0038] If water ingress into the blast furnace 1 is confirmed in step S1 (No in step S1), the location of the water ingress into the blast furnace 1 is investigated, and water-stopping treatment is performed on the location of the water ingress (step S2). Examples of locations of water ingress into the blast furnace 1 include cooling staves (not shown) that cool the furnace body of the blast furnace 1, and cooling equipment such as piping that supplies cooling water to the cooling staves. Steps S1 and S2 are then repeated until it is confirmed that there is no water ingress into the blast furnace 1. Step S1 described above corresponds to the water ingress determination process in this embodiment.

[0039] If it is confirmed that there is no water ingress into the blast furnace 1 (Yes in step S1), an inert gas for dilution is introduced into the blast furnace 1 (step S3). This is to expel air from the top 2 of the blast furnace 1 and to reduce the concentration of flammable gas in the blast furnace gas, thereby suppressing abnormal combustion immediately after the shutdown of the blast furnace. It is also to reduce the degree of abnormal combustion in the event that abnormal combustion occurs. Nitrogen gas can be used as the inert gas for dilution.

[0040] In step S3, for example, the control device 17 opens the second shut-off valve 15 to introduce nitrogen gas into the blast furnace 1 at a volume of 1 / 10 or more of the internal volume of the blast furnace 1 per unit time (hour) under standard conditions (20°C, 1013 hPa). That is, 10,000 Nm³ 3 Nitrogen gas is introduced into the blast furnace 1 at a flow rate of approximately / h. The amount of nitrogen gas introduced is such that the gas composition of the blast furnace gas falls within the range where air can be mixed, as described later. In other words, nitrogen gas is introduced into the blast furnace 1 at the above flow rate until the gas composition of the blast furnace gas falls within the range where air can be mixed. Step S2 described above corresponds to the dilution inert gas introduction step in this embodiment.

[0041] Here, we will explain the change in the gas composition of the blast furnace gas due to the introduction of nitrogen gas into the blast furnace 1. Figure 4 is a diagram illustrating the change in the gas composition of the blast furnace gas inside the blast furnace 1 when the furnace top firing method according to this embodiment is implemented. The gas composition indicated by the symbol "A" in Figure 4 is the gas composition of the blast furnace gas immediately after the shutdown of the blast furnace 1. As described above, when the blast furnace 1 is shut down, the presence or absence of water ingress into the blast furnace 1 is checked, and if it is confirmed that there is no water ingress, nitrogen gas is introduced into the blast furnace 1 as an inert gas. As nitrogen gas is introduced, as shown in Figure 4, the concentration of combustible gas in the blast furnace gas gradually decreases, and the concentration of inert gas in the blast furnace gas gradually increases. It is preferable to introduce nitrogen gas while monitoring the gas components inside the furnace.

[0042] Following step S3, it is confirmed whether the gas composition of the blast furnace gas falls within the range in which air can be mixed (step S4). This can be done based on the analysis results from the gas analyzer 8. The range in which air can be mixed is the range of gas composition of the blast furnace gas in which, even if air is introduced into the blast furnace 1 to achieve apex ignition, the mixture of blast furnace gas and air can be prevented from entering the abnormal combustion range. This range in which air can be mixed can be determined in advance by experiment or calculation.

[0043] The range in which air can be mixed is, for example, the range below the line in Figure 4 that passes through the origin where the concentrations of both the flammable gas and the inert gas are both 0.0%, and the critical point of the abnormal combustion range. This line is shown in Figure 4 as a thick dashed line. The line described above can be expressed by the following equation (3). y=(β / α)x ···(3) y is the concentration of the flammable gas (%). x is the concentration of the inert gas (%). α is the concentration of the inert gas at the critical point (%). β is the concentration of the flammable gas at the critical point (%).

[0044] Here, if we let γ be the concentration (%) of the combustible gas when it undergoes complete combustion in air, that is, if we let γ be the concentration (%) of the combustible gas at the theoretical combustion ratio, then γ can be expressed by the following equation (5). γ=100 / (1+4.773 / 4(4CO% / 100+(2H2% / 100-2CO% / 100))) ···(5) CO% represents the carbon monoxide gas concentration, and H2% represents the hydrogen gas concentration.

[0045] Since the straight line representing the theoretical combustion ratio (y = -1 / γ × x + γ) shown in Figure 2 passes through the critical point (α, β), the concentration α of the inert gas at the critical point can be expressed by the following equation (6). α = (1 - β / γ) × 100 ... (6)

[0046] The change in the gas composition of the blast furnace gas when nitrogen gas is introduced into blast furnace 1 can be approximated by the following equation (7). y = -x + 100 ... (7)

[0047] Furthermore, the intersection of equation (3) and equation (7) can be expressed as (100α / (α+β), 100β / (α+β)). Therefore, the conditions under which the gas composition of the blast furnace gas falls within the range where air can be mixed in by introducing nitrogen gas into blast furnace 1 can be expressed by the following equations (1) and (2). Inert gas concentration x(%)>100α / (α+β) ···(1) Combustible gas concentration y(%)<100β / (α+β) ···(2)

[0048] Returning to the explanation of Figure 3, if the concentrations α and β of each gas in the blast furnace gas, as analyzed by the gas analyzer 8, satisfy equations (1) and (2) described above and fall within the range in which air can be mixed in (Yes in step S4), the process proceeds to step S5. On the other hand, if the concentrations α and β of each gas do not satisfy equations (1) and (2) and do not fall within the range in which air can be mixed in (No in step S4), the introduction of inert gas into the blast furnace 1 continues until equations (1) and (2) are satisfied.

[0049] In step S5, the introduction of inert gas is stopped, and air, i.e., oxygen gas, is introduced into the blast furnace 1 to ignite the furnace apex. For example, the control device 17 closes the second shut-off valve 15. Alternatively, the manhole at the furnace apex 2 is opened, an air introduction pipe 16 is inserted into the furnace apex 2 from the manhole, and air is introduced into the blast furnace 1 through the air introduction pipe 16. The amount of air introduced into the blast furnace 1 and the flow rate should be such that the concentrations x and y of each gas are within the range where air can be mixed. For example, air may be introduced into the blast furnace 1 while monitoring the concentrations x and y of each gas using a gas analyzer 8. Or, since the abnormal combustion range and the range where air can be mixed can be calculated in advance, the amount of air and the flow rate that will result in the concentrations x and y of each gas being within the range where air can be mixed can be calculated based on these values. Then, the calculated amount of air may be used as a target value, and air may be introduced into the blast furnace 1 at the calculated flow rate until the target amount of air is reached.

[0050] The gas composition of the blast furnace gas indicated by the symbol "B" in Figure 4 is the gas composition of the blast furnace gas when the introduction of inert gas is stopped and air is introduced into blast furnace 1. As shown in Figure 4, the concentrations x and y of each gas in the blast furnace gas gradually decrease with the introduction of air and never fall outside the range in which air can be mixed. Although not shown in the figure, the oxygen gas concentration gradually increases with the introduction of air.

[0051] Even when the blast furnace is shut off, the raw materials inside the blast furnace 1 maintain a high temperature. Therefore, when the oxygen gas concentration at the top of the furnace 2 reaches the concentration at which the combustible gas spontaneously ignites, the combustible gas in the stock line spontaneously ignites, generating a top flammage. The gas composition of the blast furnace gas that generates a top flammage due to spontaneous ignition can be determined in advance through experimentation. The gas composition of the blast furnace gas that generates a top flammage is indicated by the symbol "C" in Figure 4. Step S4 described above corresponds to the air introduction process in this embodiment.

[0052] Next, it is checked whether or not the furnace apex ignition has occurred (step S6). This can be checked visually, for example, from the manhole at the top of the furnace 2. Even if the gas composition of the blast furnace gas at the top of the furnace 2 is gas composition C, which causes a furnace apex ignition by spontaneous combustion, if a furnace apex ignition cannot be confirmed (No in step S6), an ignition source is introduced into the blast furnace 1 from the manhole to forcibly create a furnace apex ignition (step S7). Examples of ignition sources include smoke flares and torches. Step S6 is repeated until a furnace apex ignition can be confirmed. If a furnace apex ignition can be confirmed (Yes in step S6), the furnace apex ignition method according to this embodiment, as shown in the flowchart in Figure 3, is terminated. Note that step S6 described above corresponds to the ignition source introduction step in this embodiment.

[0053] (Effects / Actions) According to this embodiment, the presence or absence of water ingress is checked during the shutdown of the blast furnace 1, and if there is no water ingress, the furnace apex ignition is performed. Therefore, there is no increase in hydrogen gas concentration due to water ingress, and abnormal combustion caused by an increase in hydrogen gas concentration can be avoided. Furthermore, if there is no water ingress, an inert gas is introduced to maintain the concentrations x and y of each gas within the range in which air can be mixed. Therefore, abnormal combustion immediately after shutdown can be suppressed. Moreover, even when air is introduced for furnace apex ignition thereafter, the concentrations x and y of each gas are maintained within the range in which air can be mixed. Therefore, according to this embodiment, abnormal combustion of blast furnace gas when furnace apex ignition is performed can be suppressed, and furnace apex ignition can be performed safely and stably. [Examples]

[0054] (Example of an invention) A blast furnace setup similar to the one shown in Figure 1 was used for apex firing. The internal volume of the blast furnace in this example was 5000 m³. 3 Therefore, during the shutdown of the blast furnace, after confirming that there is no water ingress, 10,000 Nm of water is injected into the blast furnace. 3Nitrogen gas was then introduced. In other words, after confirming that the gas composition of the blast furnace gas was within the range where air mixing was permitted, air was introduced into the blast furnace in place of the inert gas in order to achieve apex ignition. In this embodiment, apex ignition was achieved safely and stably without abnormal combustion occurring, and without the flame flickering on and off when apex ignition was achieved.

[0055] (Comparative example) During the blast furnace shutdown described above, without checking for water ingress into the furnace, i.e., while water ingress was occurring, inert gas was immediately introduced after the shutdown. After confirming that the gas composition of the blast furnace gas was within the range where air mixing is permitted, air was introduced into the blast furnace in place of the inert gas in order to ignite the furnace at its peak. Figure 5 is a diagram illustrating the change in the gas composition of the blast furnace gas in the comparative example blast furnace. As shown in Figure 5, an increase in the concentration of flammable gas, i.e., hydrogen gas, was observed after the introduction of air. Eventually, the concentrations of both the flammable gas and the inert gas entered the abnormal combustion range, and abnormal combustion occurred. The gas composition of the blast furnace gas at the time of abnormal combustion is indicated by the symbol "D" in Figure 5. In the comparative example blast furnace, after identifying the water ingress points and performing water-stopping treatment, inert gas and air were introduced in the same manner as in the example. As a result, ignition at the furnace peak was achieved safely and stably, similar to this embodiment and the example. [Explanation of Symbols]

[0056] 1 blast furnace 2 Furnace top 3 Charging device 4. Rotating chute 5. Blast furnace gas riser tubes 6 sampling tubes 7. Air filter 8. Gas analyzer 9. Purge Line 10. First shut-off valve 11 Dilution inert gas introduction tube 12 Flow meter 13 Orifice 14. Differential pressure transmitter 15. Second shut-off valve 16 Air inlet pipe 17 Control device 18 Input section 19 Memory section 20 Output section 21 Judgment section

Claims

1. A furnace top ignition method in which blast furnace gas is ignited on the surface of the raw materials filled inside the blast furnace after the blast furnace has been shut down, A flood detection process that confirms whether or not water has entered the blast furnace based on the hydrogen gas concentration contained in the blast furnace gas, After confirming in the aforementioned flood detection step that there is no flooding into the blast furnace, a dilution inert gas introduction step is performed, in which a dilution inert gas is introduced into the blast furnace to dilute the blast furnace gas so that the concentrations of the flammable gas and the inert gas contained in the blast furnace gas satisfy the following formulas. A furnace apex firing method comprising an air introduction step of introducing air into the blast furnace after introducing a dilution inert gas into the blast furnace in the dilution inert gas introduction step. Inert gas concentration x>100α / (α+β)...(1) Combustible gas concentration y<100β / (α+β)...(2) α is the concentration of the inert gas at the critical point (vol%). β is the concentration of the flammable gas at the critical point (vol%). y is the concentration of the flammable gas (vol%). x is the concentration of the inert gas (vol%).

2. The furnace apex firing method according to claim 1, wherein in the dilution inert gas introduction step, an inert gas volume of 1 / 10 or more of the internal volume of the blast furnace under standard conditions is introduced into the blast furnace per unit time.

3. The furnace apex firing method according to claim 1 or 2, wherein the air introduction step involves introducing air into the blast furnace such that the following formula is satisfied. y<(β / α)x...(3)

4. The furnace top firing method according to claim 1 or 2, wherein in the ingress determination step, it is determined that there is no ingress of water into the blast furnace when the hydrogen gas concentration is 3.0 vol% or less and there is no increase in the hydrogen gas concentration.

5. The furnace top firing method according to claim 3, wherein in the ingress determination step, it is determined that there is no ingress of water into the blast furnace when the hydrogen gas concentration is 3.0 vol% or less and there is no increase in the hydrogen gas concentration.

6. The furnace apex ignition method according to claim 1 or 2, further comprising an ignition source introduction step of introducing an ignition source into the blast furnace if, in the air introduction step, air is introduced into the blast furnace and the blast furnace gas does not ignite due to spontaneous combustion on the surface of the raw materials.

7. The furnace apex ignition method according to claim 3, further comprising an ignition source introduction step of introducing an ignition source into the blast furnace if, in the air introduction step, air is introduced into the blast furnace and the blast furnace gas does not ignite due to spontaneous combustion on the surface of the raw materials.

8. The furnace apex ignition method according to claim 4, further comprising an ignition source introduction step of introducing an ignition source into the blast furnace if, in the air introduction step, air is introduced into the blast furnace and the blast furnace gas does not ignite due to spontaneous combustion on the surface of the raw materials.

9. The furnace apex ignition method according to claim 5, further comprising an ignition source introduction step of introducing an ignition source into the blast furnace if, in the air introduction step, air is introduced into the blast furnace and the blast furnace gas does not ignite due to spontaneous combustion on the surface of the raw materials.

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