Method for stopping blast furnace and lowering material surface

Abstract

The present application relates to the technical field of blast furnace smelting, and particularly relates to a method for lowering the material surface of a blast furnace during shutdown, comprising the following steps: during the process of lowering the material surface, liquid carbon dioxide is sprayed on the top of the blast furnace to control the temperature of the top of the blast furnace below 350 DEG C, while the volume percentage of carbon dioxide in the blast furnace is kept above 35%, the volume percentage of hydrogen is kept below 4%, and the volume percentage of oxygen is kept below 1%. The present application can eliminate the generation of hydrogen by spraying liquid carbon dioxide on the top of the blast furnace to replace water spraying on the top of the blast furnace. Meanwhile, the volume percentage of carbon dioxide is kept above 35% during the whole process of lowering the material surface, and there is no water-gas reaction between water and coke in the ore reduction stage, so that the oxygen content of the material surface is very low, which can be below 0.5%, and the probability of gas explosion is greatly reduced. Furthermore, even if the material surface is lowered below the bosh, the wind-oxygen excess stage is entered, but the density of oxygen is very light, which can quickly float upwards, while carbon dioxide can quickly sink, and then cover the surface of the furnace charge to prevent the combustion of gas.

Description

Technical Field

[0001] This invention relates to the field of blast furnace smelting technology, and specifically to a method for shutting down a blast furnace and reducing the burden level. Background Technology

[0002] Currently, blast furnaces are designed for a lifespan of 15-20 years. After a certain number of years of operation, they require major overhaul and shutdown. Existing technologies commonly employ the empty charge line method for blast furnace shutdown. This involves significantly reducing the ore-to-fuel ratio within the blast furnace, stopping charging, while continuing blast. This allows the coke at the bottom of the blast furnace to gradually burn off, the ore to melt as it descends, and the blast furnace burden to gradually move downwards, emptying the space above the tuyeres. During shutdown, the temperature at the furnace top is controlled by water injection and blast volume. Blast is stopped when the charge line drops to near the tuyeres.

[0003] However, the empty charge line shutdown method has the following disadvantages: First, during the process of adding water to the furnace top, if the water cannot be rapidly vaporized, the water droplets will react with the hot coke to form a water-gas reaction, namely, 2H2O=2H2+O2(1), 2C+O2=2CO(2). The hydrogen and oxygen generated by water decomposition are quickly blown away from the surface of the coke layer by the lower blast. Therefore, the water-gas reaction of adding water to the furnace top actually only carries out the first step of water decomposition to generate hydrogen and oxygen. The second step of the reaction is unlikely to take place, which results in the gas containing a large amount of hydrogen and oxygen. The more water that falls onto the surface of the coke layer, the higher the volume percentage of hydrogen and oxygen in the gas, and the easier it is to cause an explosion. Safety during shutdown is not guaranteed. Second, when the charge enters the furnace belly, the ore reduction reaction gradually stops, the permeability of the charge becomes better, and some O2 in the blast passes through the charge layer into the gas layer and burns with CO and H2 in the gas. The greater the air volume and the faster the gas flow, the more O2 enters the gas bed, increasing the risk of gas explosions and impacting the safety of the shutdown process. This is actually the main reason affecting shutdown safety. Previously, the primary measure to prevent this during shutdown was to directly cut off the gas supply when the burden level entered the furnace belly. The disadvantages of this method are that the gas supply is cut off too early, affecting gas recovery; the burden level is too high, resulting in a large amount of cleanup work after shutdown; and it also has a significant impact on the surrounding environment. Therefore, existing empty-burden line shutdown technologies have strict technical requirements for the volume percentages of hydrogen and oxygen during shutdown. If the volume percentages of oxygen and hydrogen exceed these limits during shutdown, the furnace top vent valves must be fully or partially opened to directly release the gas into the atmosphere. The resulting large amounts of smoke, gas, dust particles, and noise waves affect a radius of approximately 5 kilometers, polluting the surrounding environment. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defects of the existing empty charge line method for blast furnace shutdown, which has the disadvantages of high hydrogen and oxygen content in the gas, which easily causes detonation and premature gas cutting, which pollutes the surrounding environment. The present invention provides a method for blast furnace shutdown and charge level reduction to solve the above problems.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for shutting down a blast furnace and lowering the burden level includes: during the lowering process, spraying liquid carbon dioxide from the furnace top to control the furnace top temperature below 350°C, while maintaining the volume percentage of carbon dioxide in the furnace at ≥35%, the volume percentage of hydrogen at ≤4%, and the volume percentage of oxygen at ≤1%.

[0007] Preferably, the external carbon dioxide flow rate during the material level reduction process is obtained by the following formula: External carbon dioxide flow rate t / h = molar volume constant × [Q_gas × (CO% + CO2% × 2 + O2% × 2) × 1000 / molar volume constant - 2 × (Q_gas × N2% - Q_gas)] 外氮 [(79% × 0.21 × 1000 / molar volume constant)] / 2 / 1000 × 2 / 1000, where Q_gas is the blast furnace top gas volume, CO% is the measured volume percentage of CO in the top gas composition, CO2% is the measured volume percentage of CO2 in the top gas composition, O2% is the measured volume percentage of O2 in the top gas composition, N2% is the measured volume percentage of N2 in the top gas composition, Q_gas 外氮 This refers to the flow rate of nitrogen in the static pressure system of the furnace body.

[0008] Preferably, after the material level is lowered to below the center line of the tuyeres, the last batch of iron is produced until the blast furnace is shut down;

[0009] And / or, preliminary preparations are also carried out before the material is lowered.

[0010] Preferably, the preliminary preparation work includes the following steps:

[0011] (1) Before shutting down the furnace and reducing the amount of fuel, gradually reduce the edge load and at the same time reduce the cooling wall water flow to flush the furnace wall;

[0012] (2) Adjust the coke load, molten iron temperature and slag composition to allow the slag basicity to decrease slowly, the molten iron temperature to increase slowly, and the blast furnace airflow distribution to be gradually adjusted to a state close to that during the shutdown period.

[0013] (3) Add furnace charge for shutdown;

[0014] (4) Pre-shutdown wind.

[0015] Preferably, in step (1), the edge load and cooling wall water flow rate are gradually reduced in six steps over three days before the furnace is shut down and the feed is reduced;

[0016] And / or, the edge load is reduced to 1.3-1.5;

[0017] And / or, the cooling wall water flow rate is reduced to 3700-3900 m³ / h. 3 / h.

[0018] Preferably, in step (2), the coke load, coke-to-coke ratio, and coal ratio are gradually reduced in six steps, while manganese ore, fluorite, silica, and serpentine are added to adjust the slag-iron composition; wherein, the coke load gradually decreases from 5.1-5.5 to 2.8-3.2, the coke consumption gradually increases from 350-370 kg / t to 460-540 kg / t, the coal ratio gradually decreases from 170-190 kg / t to below 60 kg / t, and the amount of coke-to-coke ratio gradually decreases from 1.1-1.3 t to 0 t; and the quality of Si in the molten iron is controlled. The mass percentage of iron was gradually increased from 0.35-0.45% to 0.85-0.95%, the mass percentage of manganese was gradually increased from below 0.1% to 0.35-0.45%, the molten iron temperature was ≥1500℃, the slag basicity was gradually decreased from 1.10-1.20 to 0.93-0.97, the Al2O3 in the slag was gradually decreased from 15.2-15.8% to 13.9-14.1%, and the MgO / Al2O3 ratio was gradually increased from 0.45-0.55 to 0.55-0.65.

[0019] Preferably, in step (3), the shutdown charge structure requires that the total proportion of lump ore and pellets not exceed 20%, of which the proportion of lump ore does not exceed 10%, pulverized coal injection is stopped, all-coke smelting is carried out, coke load is <3.0, and coke consumption is >600kg / t; manganese ore, fluorite, silica and serpentine are added to adjust the slag and iron composition; wherein, the mass percentage of Si in the molten iron is controlled to reach 0.95%-1.05%, the mass percentage of manganese is ≥0.4%, the temperature of molten iron is ≥1500℃, the slag basicity is <0.95, the Al2O3 in the slag is ≤15.0%, and the MgO / Al2O3 is ≥0.55; and after the last batch of shutdown charge is laid out, water slag is used to cover the surface of the coke.

[0020] Preferably, the thickness of the slag is taken as the standard when the material level drops to the waist of the furnace, and the weight of the slag is determined by the formula m = πd. 2 The value is calculated as δρ / 4, where m is the weight of the slag, π is 3.1415, d is the diameter of the furnace waist, δ is the thickness of the slag in the furnace waist, and ρ is the density of the slag.

[0021] And / or, the thickness of the slag in the furnace waist is not less than 300 mm.

[0022] Preferably, the specific process of step (4) pre-shutdown is as follows:

[0023] ① Install a liquid carbon dioxide spraying system on the furnace top, with at least 8 spray guns, ensuring that the maximum flow rate of the spray guns is ≥67t / h;

[0024] ②Inspect the static pressure holes in the furnace body and connect them with inert gas;

[0025] ③Inspect the large venting device on the furnace top, and weld and reinforce the furnace shell;

[0026] ④ Repair damaged cooling equipment and replace leaking vent sleeves;

[0027] ⑤ Modify the probe encoder, lengthen the probe, and reinforce the probe wire rope connector;

[0028] ⑥ Inspect the radar probe.

[0029] Preferably, the maximum flow rate of the spray gun is 1 / n of the maximum flow rate of the required liquid carbon dioxide, where n is the number of spray guns, and the maximum flow rate of the required liquid carbon dioxide is calculated based on the highest volume percentage of carbon dioxide in the coal gas being 50%.

[0030] In this invention, the method for calculating the flow rate of carbon dioxide introduced during the shutdown and lowering of the burden level is as follows: Assuming the blast furnace top gas flow rate is Q_gas and the blast furnace air flow rate is Q_air flow rate, according to the nitrogen balance: Q_air flow rate × 79% = Q_gas × N2%, if the static pressure system of the furnace body is connected to inert gas N2, then the nitrogen balance formula can be transformed into Q_air flow rate × 79% + Q_air flow rate. 外氮 = Q gas × N2%, where Q gas quantity can be obtained from the furnace top gas flow meter, and N2% is the volume percentage of N2 in the measured furnace top gas composition. 外氮 The flow rate of nitrogen in the static pressure system of the furnace body can be found through a flow meter;

[0031] 1) First, calculate the number of moles of oxygen atoms brought into the furnace from the air = 2 × Q air volume × 0.21 × 1000 / molar volume constant = 2 × (Q gas × N2% - Q 外氮 ) / 79%×0.21×1000 / molar volume constant;

[0032] 2) According to the oxygen balance, the number of moles of oxygen atoms brought into the furnace by the air + the number of moles of oxygen brought in by the external liquid carbon dioxide = the number of moles of O atoms carried by CO + CO2 + O2 in the gas = Q gas × (CO% + CO2% × 2 + O2% × 2) × 1000 / molar volume constant, where CO% is the volume percentage of CO in the measured top gas composition, CO2% is the volume percentage of CO2 in the measured top gas composition, and O2% is the volume percentage of O2 in the measured top gas composition.

[0033] 3) The flow rate of externally introduced carbon dioxide, t / h, = molar volume constant × [(number of moles of O atoms carried by CO + CO2 + O2 in the gas) - number of moles of oxygen atoms carried into the furnace by the air] / 2 / 1000 × 2 / 1000. In summary, the flow rate of externally introduced carbon dioxide, t / h, = molar volume constant × [Q_gas × (CO% + CO2% × 2 + O2% × 2) × 1000 / molar volume constant - 2 × (Q_gas × N2% - Q_gas)]. 外氮 [(79% × 0.21 × 1000 / molar volume constant)] / 2 / 1000 × 2 / 1000. Wherein, 0.5 m³ of liquid carbon dioxide is produced from 1 kg of liquid carbon dioxide. 3 Gas calculations.

[0034] The technical solution of this invention has the following advantages:

[0035] 1. A method for shutting down a blast furnace and lowering the burden level, comprising: during the lowering process, spraying liquid carbon dioxide from the furnace top to control the furnace top temperature below 350°C, while maintaining the volume percentage of carbon dioxide in the furnace at ≥35%, the volume percentage of hydrogen at ≤4%, and the volume percentage of oxygen at ≤1%. This invention, by mimicking the principle of a carbon dioxide fire extinguisher, uses the spraying of liquid carbon dioxide from the furnace top in conjunction with the shutdown of coal supply at the bottom instead of water spraying from the furnace top, thus preventing the generation of hydrogen. Simultaneously, maintaining the volume percentage of carbon dioxide above 35% throughout the entire lowering process serves two purposes: firstly, because carbon dioxide has a high density, approximately 1.5 times that of air, the liquid carbon dioxide sprayed from the furnace top immediately vaporizes, replacing the coal gas in the furnace and covering the surface of the burden, reducing the oxygen concentration on the burden surface and creating a suffocating effect to prevent detonation; secondly, when the liquid carbon dioxide is sprayed from the storage container, it rapidly vaporizes into gas, attracting some heat from the surroundings, thus playing a cooling role and lowering the furnace top gas temperature and the burden surface temperature. Compared to traditional top-mounted water-cooling method for lowering the burden level, this method eliminates the water-gas reaction between water and coke during the ore reduction stage, and maintains a very low oxygen volume percentage on the burden surface, reaching <0.5%, thus significantly reducing the probability of gas detonation. Secondly, even when the burden level is lowered below the furnace belly, entering a stage of excess oxygen and blast, oxygen, being very light, rises rapidly while carbon dioxide sinks quickly, covering the burden surface and preventing gas combustion. Therefore, this method avoids gas detonation during blast furnace shutdown processes and also prevents pollution of the surrounding environment from dust, exhaust gases, and noise.

[0036] 2. In a method for reducing the burden level during blast furnace shutdown according to the present invention, in order to prevent carbon dioxide from reacting with coke in a carbon gasification reaction, after the last batch of shutdown burden is laid out, water slag is used to cover the surface of the coke, thereby reducing the volume percentage of carbon monoxide in the gas and increasing the volume percentage of carbon dioxide, so as to give full play to the flame retardant effect of carbon dioxide.

[0037] 3. In a method for shutting down a blast furnace and reducing the burden level according to the present invention, by adding manganese ore, the mass percentage of Mn element in the molten iron is increased to 0.35-0.45% (the mass percentage of manganese in normal molten iron is about 0.2%), and the slag basicity is controlled at a lower level of 0.93-0.97, which is more conducive to reducing the viscosity of slag and iron and accelerating the smooth discharge of molten iron and slag.

[0038] 4. In the method of blast furnace shutdown and burden reduction of the present invention, the present invention combines reducing the edge load in advance and reducing the flow rate of soft water in the cooling wall to flush the furnace wall, ensuring the regularity of the furnace shape during the shutdown process, reducing the fluctuation of edge airflow and furnace temperature, ensuring the smooth progress of the shutdown process, and reducing the cleaning work of slag on the furnace wall after shutdown.

[0039] 5. In the method for blast furnace shutdown and burden reduction of the present invention, the entire process only requires one blast furnace pre-shutdown, which optimizes the shutdown process of the blast furnace burden reduction line and improves the efficiency of blast furnace shutdown. Detailed Implementation

[0040] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0041] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0042] In Examples 1-2 of this invention, the composition of the gas during normal production is: 24.34% CO, 22.35% CO2, 49.31% N2, 3.51% H2, and 0.49% O2.

[0043] Example 1

[0044] This embodiment provides a method for shutting down a blast furnace and lowering the burden level, including the following steps:

[0045] (1) The edge load is gradually reduced in six steps, while the cooling wall water flow rate is reduced to flush the furnace wall. The specific process is shown in Table 1:

[0046] Table 1

[0047]

[0048] Wherein, edge load = (number of edge ore rings / number of edge coke rings) × (total number of coke rings / total number of ore rings) × coke load; the blast furnace throat is divided into 11 equal rings by the equal area method, that is, 11 positions (the outermost is 11, the innermost is 1), of which positions 11-9 belong to the edge area, positions 8-7 belong to the ring area, and positions 6-1 belong to the central area.

[0049] (2) About three days before shutting down the blast furnace and reducing the amount of raw materials, adjust the coke load, molten iron temperature, and slag composition to gradually decrease the slag basicity, slowly increase the molten iron temperature, and gradually adjust the blast furnace airflow distribution to a state close to that during the shutdown period. This involves gradually reducing the coke load, coke-to-coal ratio, and coal ratio in six steps, while simultaneously adding manganese ore, fluorite, silica, and serpentine to adjust the slag-iron composition. The molten iron temperature is set at 1510-1520℃. Specific processes and data are shown in Table 2.

[0050] Table 2

[0051] Mining batch t / p 70 67 63 60 57 54 51 scorched batch t / p 13.4 13.6 13.9 14.3 14.9 17.1 20.3 Jiao Ding t / p 1.1 1.1 0.5 0.5 0.25 0 0 Coal quantity t / h 45 40 35 30 20 10 0 Coke load 5.25 4.88 4.56 4.22 3.84 3.17 2.52 Coal ratio kg / t 176.3 156.3 149.2 127.3 84.7 42.3 0 Coke consumption kg / t 367 372 397 406 415 467 659 manganese ore t / p 0.3 0.6 0.85 1 1.2 1.35 1.5 Fluorite t / p 0.1 0.2 0.3 0.4 0.6 0.8 0.8 silica t / p 0.2 0.4 0.6 0.8 0.8 0.8 0.8 Serpentine t / p 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Slag alkalinity 1.132 1.085 1.040 1.025 0.982 0.966 0.861 <![CDATA[Al2O3%]]> 15.28 14.94 14.65 14.64 14.10 14.10 14.03 MgO% 7.69 7.82 7.97 7.96 8.34 8.51 8.52 <![CDATA[MgO / Al2O3]]> 0.50 0.52 0.54 0.54 0.59 0.60 0.59 Si% 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Mn% 0.08 0.15 0.23 0.27 0.32 0.36 0.47

[0052] (3) Add shutdown charge. The shutdown charge structure requires a total ratio of lump ore and pellets of 18%, with lump ore accounting for less than 8%. Pulverized coal injection is stopped, all-coke smelting is carried out, coke load is below 3.0, and coke consumption is above 600 kg / t. Based on the current production status, manganese ore, fluorite, silica, and serpentine are added to adjust the slag-iron composition. Specifically, the mass percentage of [Si] in the molten iron is controlled at 0.95-1.05%, the mass percentage of manganese at 0.45-0.50%, the molten iron temperature at 1510-1520℃, the slag basicity at 0.85-0.90, Al2O3 at 14.0-14.5%, and MgO / Al2O3 at 0.55-0.60. After the last batch of shutdown charge is laid out, water slag is used to cover the coke surface. The thickness of the water slag is 300 mm when the charge level is lowered to the furnace waist. The weight of the water slag is calculated using the formula m = πd. 2 The value is calculated as δρ / 4, where m is the weight of the slag (52.4t), π is 3.1415, d is the diameter of the furnace waist (13.5m), δ is the thickness of the slag in the furnace waist (300mm), and ρ is the density of the slag (1220kg / m³). 3 ).

[0053] (4) Pre-shutdown ventilation. The specific process is as follows: ① Install a liquid carbon dioxide spraying system on the furnace top, with 8 spray guns and a maximum flow rate of 67 t / h; ② Inspect the static pressure holes in the furnace body and connect inert gas; ③ Inspect the large venting device on the furnace top, weld and reinforce the furnace shell; ④ Repair damaged cooling equipment and replace leaking vent sleeves; ⑤ Modify the probe encoder, lengthen the probe, and reinforce the probe wire rope connector; ⑥ Inspect the radar probe. The maximum flow rate of the spray guns is one-eighth of the maximum required flow rate of liquid carbon dioxide, and the maximum required flow rate of liquid carbon dioxide is calculated based on a maximum volume percentage of 50% carbon dioxide in the gas.

[0054] (5) Shutdown and lowering of the burden level. The furnace top temperature is controlled below 350℃ by spraying liquid carbon dioxide onto the furnace top, while maintaining the carbon dioxide volume percentage in the furnace at 50%. The burden level is lowered to below the center line of the tuyeres, and the last iron is tapped, until the blast furnace is shut down. The flow rate of the externally introduced carbon dioxide is calculated through nitrogen and oxygen balance.

[0055] The method for calculating the flow rate of carbon dioxide introduced during the shutdown and lowering of the material level is as follows:

[0056] Assuming the blast furnace top gas flow rate is Qgas and the blast furnace air flow rate is Qair, according to the nitrogen balance: Qair × 79% + Qair 外氮 = Q gas × N2%, where the amount of Q gas can be obtained from the top gas flow meter (top gas generation is 560,000 m³). 3 / h), N2% is the volume percentage of N2 in the measured top gas composition (35%), and the inert gas flow rate is 0 m³ / h. 3 / h, substituting into the formula, we get Q air volume = (Q gas × N2%) - Q 外氮 ) / 79% = 248101.27m 3 / h≈248101m 3 / h;

[0057] 1) First, calculate the number of moles of oxygen atoms brought into the furnace from the air: 2 × Q air volume × 0.21 × 1000 / molar volume constant; Q air volume is 248101.27 m³ / s. 3 Substituting the values ​​of / h and the molar volume constant of 22.4 L / mol into the formula, we obtain the number of moles of oxygen atoms carried into the furnace by the wind as 4,651,899 mol / h.

[0058] 2) According to the oxygen balance: the number of moles of oxygen atoms carried into the furnace by the air + the number of moles of oxygen carried by liquid carbon dioxide = the number of moles of O atoms carried by CO + CO2 + O2 in the gas = Q_gas × (CO% + CO2% × 2 + O2% × 2) × 1000 / molar volume constant; where, the number of moles of O atoms carried by CO + CO2 + O2 in the gas = 560000 × [14.4% + 50% × 2 + 0.3% × 2] × 1000 / 22.4 = 28750000 mol / h, from which we can obtain the number of moles of oxygen carried by liquid carbon dioxide = 28750000 - 4651899 = 24098101 mol / h;

[0059] 3) The flow rate of externally introduced carbon dioxide t / h = molar volume constant × [number of moles of O atoms carried by CO + CO2 + O2 in the gas - number of moles of oxygen atoms carried into the furnace by the air] / 2 / 1000 × 2 / 1000 = 539.8t / h ≈ 540t / h.

[0060] In this embodiment, when the furnace is shut down using carbon dioxide, the gas composition is: 14.4% CO, 50% CO2, 35% N2, 0.3% H2, and 0.3% O2. The specific shutdown and feed level control parameters are shown in Table 3.

[0061] Table 3

[0062] <![CDATA[Top gas generation volume(m 3 / h)]]> 560000 <![CDATA[Volume of nitrogen in gas (m 3 / h)]]> 196000 <![CDATA[Air volume (m 3 / h)]]> 248101 <![CDATA[Air volume (m 3 / min)]]> 4135 Molar volume constant (L / mol) 22.4 Moles of oxygen atoms in wind (mol / h) 4651899 The number of moles of O atoms in the CO+CO2+O2 mixture of coal gas (mol / h) 28750000 Number of moles of introduced oxygen atoms (mol / h) 24098101 Moles of carbon dioxide introduced (mol / h) 12049051 <![CDATA[Volume of externally introduced carbon dioxide (m 3 / h)]]> 269899 Liquid carbon dioxide main pipe flow rate (t / h) 540 Flow rate of a single spray gun (t / h) 67

[0063] In this embodiment, the shutdown is safe and stable. There is no water-gas reaction between water and coke during the ore reduction stage, which avoids gas explosion during the shutdown process of the blast furnace charging line, and also avoids pollution of the surrounding environment by dust, exhaust gas and noise.

[0064] Example 2

[0065] The difference between this embodiment and Embodiment 1 is that the volume percentage of carbon dioxide in the furnace is maintained at 35%, while other conditions are the same as in Embodiment 1.

[0066] In this embodiment, when the furnace is shut down using carbon dioxide, the gas composition is: 15.1% CO, 35% CO2, 49.3% N2, 0.3% H2, and 0.3% O2. The specific shutdown and feed level control parameters are shown in Table 4.

[0067] Table 4

[0068] <![CDATA[Top furnace gas generation amount (m 3 / h)]]> 450000 <![CDATA[Nitrogen volume in gas (m 3 / h)]]> 221850 <![CDATA[Air volume (m 3 / h)]]> 280823 <![CDATA[air volume (m 3 / min)]]> 4680 Molar volume constant (L / mol) 22.4 Moles of oxygen atoms in wind (mol / h) 5265427 The number of moles of O atoms in the CO+CO2+O2 mixture of coal gas (mol / h) 17216518 Number of moles of introduced oxygen atoms (mol / h) 11951091 Moles of carbon dioxide introduced (mol / h) 5975545 <![CDATA[Volume of externally introduced carbon dioxide (m 3 / h)]]> 133852 Liquid carbon dioxide main pipe flow rate (t / h) 268 Flow rate of a single spray gun (t / h) 33

[0069] In this embodiment, the shutdown is safe and stable. There is no water-gas reaction between water and coke during the ore reduction stage, which avoids gas explosion during the shutdown process of the blast furnace charging line, and also avoids pollution of the surrounding environment by dust, exhaust gas and noise.

[0070] Comparative Example 1

[0071] The difference between this comparative example and Example 1 is that the volume percentage of carbon dioxide in the furnace is maintained at 30%, while other conditions are the same as in Example 1.

[0072] In this comparative example, when carbon dioxide was used for shutdown, the gas composition was: 22% CO, 30% CO2, 33% N2, 12% H2, and 3.0% O2. While the volume percentage of CO2 in the blast furnace gas was not high during the shutdown process, the volume percentage of CO was greater than 20%, the volume percentage of O2 was greater than or equal to 3.0%, and the volume percentage of H2 was greater than 10%. Within the sealed container of the blast furnace, once the burden level drops to the belly of the furnace, a large amount of CO and H2 will be generated. Simultaneously, because the temperature above the burden level reaches over 1000℃, an explosive reaction of the gas or hydrogen is highly likely to occur, affecting the safety of the shutdown process.

[0073] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for shutting down a blast furnace and lowering the burden level, characterized in that, include: During the process of lowering the material level, the furnace top temperature is controlled below 350℃ by spraying liquid carbon dioxide on the furnace top, while maintaining the volume percentage of carbon dioxide in the furnace top gas at ≥35%, the volume percentage of hydrogen at ≤0.3%, and the volume percentage of oxygen at ≤0.3%.

2. The method according to claim 1, characterized in that, The external carbon dioxide flow rate during the material level lowering process is obtained by the following formula: External carbon dioxide flow rate t / h = molar volume constant × [Q_gas × (CO% + CO2% × 2 + O2% × 2) × 1000 / molar volume constant - 2 × (Q_gas × N2% - Q_gas)] 外氮 [(79%×0.21×1000 / molar volume constant) / 2 / 1000×2 / 1000], where Q_gas is the blast furnace top gas volume, CO% is the measured volume percentage of CO in the top gas composition, CO2% is the measured volume percentage of CO2 in the top gas composition, O2% is the measured volume percentage of O2 in the top gas composition, N2% is the measured volume percentage of N2 in the top gas composition, Q_gas is the volume percentage of CO2 in the top gas composition, and Q_gas is the volume percentage of CO2 in the top gas composition. 外氮 This refers to the flow rate of nitrogen in the static pressure system of the furnace body.

3. The method according to claim 1 or 2, characterized in that, After the material level is lowered to below the center line of the tuyeres, the last batch of iron is produced until the blast furnace is shut down. And / or, preliminary preparations are also carried out before the material is lowered.

4. The method according to claim 3, characterized in that, The preliminary preparations include the following steps: (1) Before shutting down the furnace and reducing the amount of fuel, gradually reduce the edge load and at the same time reduce the flow rate of cooling wall water to flush the furnace wall; (2) Adjust the coke load, molten iron temperature and slag composition to allow the slag basicity to decrease slowly, the molten iron temperature to increase slowly, and the blast furnace airflow distribution to be gradually adjusted to a state close to that during the shutdown period. (3) Add furnace charge; (4) Pre-stop wind.

5. The method according to claim 4, characterized in that, In step (1), the edge load and cooling wall water flow rate are gradually reduced in six steps over three days before the furnace is shut down and the material is reduced. And / or, the edge load is reduced to 1.3-1.5; And / or, the cooling wall water flow rate is reduced to 3700-3900 m³ / h.

6. The method according to claim 4 or 5, characterized in that, In step (2), the coke load, coke-to-coke ratio, and coal ratio are gradually reduced in six steps, while manganese ore, fluorite, silica, and serpentine are added to adjust the slag-iron composition. Specifically, the coke load gradually decreases from 5.1-5.5 to 2.8-3.2, the coke consumption gradually increases from 350-370 kg / t to 460-540 kg / t, the coal ratio gradually decreases from 170-190 kg / t to below 60 kg / t, and the amount of coke-to-coke ratio gradually decreases from 1.1-1.3 t to 0. The following parameters were adjusted: the mass percentage of Si in the molten iron was gradually increased from 0.35-0.45% to 0.85-0.95%, the mass percentage of manganese was gradually increased from below 0.1% to 0.35-0.45%, the molten iron temperature was ≥1500℃, the slag basicity was gradually decreased from 1.10-1.20 to 0.93-0.97, the Al2O3 content in the slag was gradually decreased from 15.2-15.8% to 13.9-14.1%, and the MgO / Al2O3 ratio was gradually increased from 0.45-0.55 to 0.55-0.

65.

7. The method according to claim 5 or 6, characterized in that, In step (3), the shutdown charge structure requires that the total proportion of lump ore and pellets not exceed 20%, of which the proportion of lump ore not exceed 10%. Coal injection is stopped, and the entire coke is smelted. The coke load is <3.0, and the coke consumption is >600 kg / t. Manganese ore, fluorite, silica and serpentine are added to adjust the slag and iron composition. Among them, the mass percentage of Si in the molten iron is controlled to reach 0.95%-1.05%, the mass percentage of manganese is ≥0.4%, the temperature of molten iron is ≥1500℃, the slag basicity is <0.95, the Al2O3 in the slag is ≤15.0%, and the MgO / Al2O3 is ≥0.

55. After the last batch of shutdown charge is laid out, water slag is used to cover the surface of the coke.

8. The method according to claim 7, characterized in that, The thickness of the slag when the material level drops to the furnace waist is taken as the standard, and the weight of the slag is calculated using the formula m=πd. 2 The value is calculated as δρ / 4, where m is the weight of the slag, π is 3.1415, d is the diameter of the furnace waist, δ is the thickness of the slag in the furnace waist, and ρ is the density of the slag. And / or, the thickness of the slag in the furnace waist is not less than 300 mm.

9. The method according to any one of claims 5-8, characterized in that, The specific process of step (4) pre-shutdown is as follows: ① Install a liquid carbon dioxide spraying system on the furnace top, with at least 8 spray guns, ensuring that the maximum flow rate of the spray guns is ≥67 t / h; ②Inspect the static pressure holes in the furnace body and connect them with inert gas; ③Inspect the large venting device on the furnace top, and weld and reinforce the furnace shell; ④ Repair damaged cooling equipment and replace leaking vent sleeves; ⑤ Modify the probe encoder, lengthen the probe, and reinforce the probe wire rope connector; ⑥ Inspect the radar probe.

10. The method according to claim 9, characterized in that, The maximum flow rate of the spray gun is 1 / n of the maximum flow rate of the required liquid carbon dioxide, where n is the number of spray guns, and the maximum flow rate of the required liquid carbon dioxide is calculated based on the highest volume percentage of carbon dioxide in the coal gas being 50%.

Images