A control method for rapid and safe restoration of blast furnace within 48 hours of shutdown

Abstract

The present invention belongs to the technical field of iron and steel metallurgy, and specifically relates to a control method for fast and safe re-blowing of a blast furnace within 48 hours of wind-down. The control method includes the following aspects for control and adjustment: (1) preparation before wind-down; keeping the furnace condition stable and running smoothly one week before wind-down; raising the physical heat of molten iron by 5 to 10°C on the basic value of 1510°C 24 hours before wind-down, and limiting it to no more than 1520°C; (2) control of wind-down material composition and addition time; (3) wind-down operation control; (4) operation control after re-blowing. The control method can achieve the goal of safe, fast and efficient re-blowing of the blast furnace.

Description

Technical Field

[0001] The invention belongs to the technical field of iron and steel metallurgy, and specifically relates to a control method for quickly and safely resuming the ventilation of a blast furnace within 48 hours of a ventilation shutdown. Background Art

[0002] The blast furnace is the main smelting equipment in the long process iron-making process. Due to the complex reactions inside the blast furnace and low detectability, research on blast furnace iron-making has remained in the exploratory stage for a long time.

[0003] Resting and resuming the blowing are common operations of blast furnaces. A blast furnace can be regarded as a continuously operating coal gas countercurrent reactor. The main principle is to use forced blasting to burn fuels such as coke and coal to generate heat and reducing gases (CO, H2, etc.). After contacting with iron ore, a reduction reaction occurs, the metallic iron is reduced, and after melting, it is discharged in liquid form, completing the smelting cycle. Resting the blowing refers to the operation of cutting off the blowing to temporarily stop the reaction process inside the blast furnace if special circumstances such as equipment and production require interruption of production. In contrast, resuming the blowing is the operation of re-blasting to restore the reaction inside the blast furnace.

[0004] Blast furnace smelting requires heat. If there is no reasonable control during the wind-down operation, the blast furnace will cool down quickly and the liquid slag will solidify. When the wind is restored, the reaction in the furnace cannot proceed normally, or the slag cannot be converted from solid to liquid due to the low temperature and cannot be discharged. The industry calls this a serious case of furnace freezing, and this accident is irreversible. In addition to consuming a large amount of fuel for heating, there are no good measures, resulting in significant economic losses. Minor freezing will greatly prolong the recovery time of the blast furnace, which is manifested as long-term low air volume blasting, disordered reaction process, poor slag discharge, etc., which is also a huge waste. Therefore, the key factor lies in the operational technical plan adopted during the wind-down.

[0005] The existing re-airing method is to gradually restore the blast furnace to a normal smelting state by reducing the re-airing air volume and extending the re-airing time. The existing technology has the following defects: due to the slow recovery speed of the air volume, the entire re-airing cycle is prolonged, which in turn leads to reduced production efficiency and cannot meet normal production needs.

[0006] Patent CN103276124 discloses an environmentally friendly method for shutting down and resuming air in a blast furnace, and proposes: 1. Shut down air and stop gas: stop oxygen and coal 20 minutes before shutting down air; gradually reduce air in the fan room to the minimum, and control the furnace top temperature within 250°C; open the air release valve, release air to the hot air pressure ≤25kPa, fully open the regulating valve of the pressure regulating valve group, and confirm that the gravity dust collector is in the open position; open the clean coal gas release valve for dry dust removal and 2-3 blind eye glasses valves after the box release; open the furnace top to release. 2. Re-airing: After the conditions for re-airing are met, close the blast furnace roof venting, confirm that the gravity dust collector is fully opened; open the clean gas venting valve for dry dust removal and 2-3 box venting; close the blast furnace venting valve; re-air the hot blast furnace; supply air from the blower room, and the hot air pressure is lower than 50kPa; after the air pressure is sent to the blast furnace, bleed air, turn over the glasses valve, close the dry dust removal clean gas venting valve and box venting; after the dry dust removal operation is completed, the blast furnace is operated normally with air.

[0007] The above patent has the following deficiencies: 1. It does not make any corrections or preventive measures for the furnace conditions. However, it is known from production practice that the re-airing process of a blast furnace cannot be achieved without completely controlling the reaction rate, and the economy and efficiency of re-airing cannot be guaranteed. 2. The patent does not provide a clear and precise control limit, which has limited guiding significance in the actual production process and cannot achieve effective control in operation.

[0008] It can be seen that blast furnace smelting production urgently needs an effective rest and resumption air control method that can enable the blast furnace to quickly and smoothly go from stop to start. Summary of the invention

[0009] The purpose of the present invention is to provide a control method suitable for quickly and safely re-airing a blast furnace within 48 hours of a shutdown in view of the above-mentioned defects. The control method can achieve the goal of safely, quickly and efficiently re-airing the blast furnace.

[0010] With the advancement of smelting technology and the further improvement of requirements for safety, cost, quality, etc., higher requirements are also put forward for shutdown and resumption of ventilation operations: ① How to ensure operational safety, including personnel and equipment; ② How to efficiently complete the shutdown and resumption of ventilation of the blast furnace, such as shortening the shutdown and resumption of ventilation time as much as possible, thereby increasing the normal smelting working time; ③ How to be more economical, such as using as little fuel as possible, recovering coal gas as quickly as possible, and advancing the iron-making time.

[0011] Based on the above-mentioned purpose of the invention, the inventors have found through extensive research that among the many factors that affect the re-airing of the blast furnace, the control measures, adjustment means and standards described in the present invention can be used to realize the blast furnace going from stop to start in a stable state with short time, low consumption and fast iron output.

[0012] The specific technical solutions are as follows:

[0013] The method for controlling the rapid and safe re-airing of a blast furnace within 48 hours of a shutdown includes controlling and adjusting the following aspects:

[0014] (1) Preparation before the wind break:

[0015] Keep the furnace condition stable and running smoothly one week before the wind breaks;

[0016] The day before the wind down, the physical heat of the molten iron should be increased by 5-10℃ from the basic value of 1510℃, and shall not exceed 1520℃.

[0017] From the heat balance calculation, after the blast furnace reaction is terminated, the main heat loss is the heat taken away by the cooling of the furnace body. According to empirical calculations, the heat loss of the blast furnace within 48 hours needs to be compensated by increasing the physical heat by 5 to 10°C, that is, by adding more fuel to heat up the furnace body. If not supplemented, the blast furnace will tend to cool, making subsequent recovery more difficult. However, if the temperature is blindly increased, the viscosity of the slag iron in the blast furnace will increase and the fluidity will decrease, which is unfavorable. It will also increase additional consumption, so the upper limit is set at 1520°C.

[0018] (2) Control of the composition of the rest air material and the time of adding it:

[0019] A. Clean coke: The total amount of clean coke added is calculated at 1.7-1.8 t / h and added in 4 times;

[0020] ① The time for adding the first batch of clean coke is 3.5 hours before the wind stop + the length of one smelting cycle as the time control node;

[0021] ② The time for adding the second batch of clean coke is controlled by the length of a smelting cycle before the wind is shut down, ensuring that it reaches the tuyere when the wind is shut down;

[0022] ③ The third batch of clean coke should be added 6 hours before the wind is shut down; the amount added is 1t / h, ensuring that it reaches the middle of the furnace waist when the wind is shut down;

[0023] ④ The fourth batch of clean coke is added after the third batch of clean coke, and after an interval of 5 to 6 batches of light-load materials; the amount added is 0.5t / h.

[0024] In addition, according to the change of airflow, the center focus is added 1 to 2 times as appropriate, 2t / time.

[0025] The above-mentioned adding time is determined according to the smelting cycle, and a smelting cycle of 8 hours is taken as an example for specific description below.

[0026] The purpose of the first batch of clean coke and the second batch of clean coke is to ensure that the furnace body has sufficient heat before the wind is shut down. A certain furnace heat before the wind is shut down is a prerequisite for successful operation. In the process of adding light load materials to prepare for the wind shut down, due to the increase in fuel and the decrease in iron, a large amount of hot gas escapes with the air flow without reaction, causing the overall heat to decrease and the fuel consumption to increase. This is called the "decreased gas utilization rate" phenomenon.

[0027] To address this issue, the first batch of clean coke is added 8 hours + 3.5 hours of the smelting cycle before the shutdown (3.5 hours is the time it takes for the charge to reach the soft melting zone from the furnace top), that is, 11.5 hours before the shutdown, to make up for the heat loss in this part.

[0028] The purpose of the second batch of clean coke is to allow the coke to enter the tuyere and burn after a smelting cycle is completed. The purpose is to increase the heat of the last batch of iron as much as possible and increase the heat storage of the entire furnace.

[0029] The third batch of clean coke needs to reach the middle of the furnace waist. The furnace waist is considered to be the end point of the reduction reaction, and there is no solid metal material below the furnace waist. Because the blast furnace needs to lose a certain amount of heat during the wind-down period, so that the clean coke reaches the furnace waist, it can burn more coke as soon as the blast furnace is restored, increase the furnace temperature, and accelerate the melting of slag iron. On the other hand, when the clean coke reaches the furnace waist, it can improve the air permeability of the furnace waist and belly, creating conditions for the subsequent rapid increase in air volume and the dripping of slag iron.

[0030] Combination Figure 1 It can be seen that the charge is mainly divided into coke and metal. When loading, the charge is alternately fed into the blast furnace in the mode of one batch of coke + one batch of metal, forming a stacked shape inside. After the reaction starts, the iron element in the metal is reduced, and the macroscopic performance is melting-breaking-condensing into droplets, and finally passing through the gaps between the coke and entering the furnace. Except for a part of the coke burning and reacting, most of the coke still maintains its original properties. Each layer forms a skeleton to support the weight of the entire charge. At the waist of the furnace, the metal is completely reduced, leaving only coke; going down, the coke is constantly melted, and finally the strength disappears, and it collapses into the furnace in small pieces. Therefore, the entire belly is empty, and the furnace is full of liquid slag iron. Therefore, when the net coke reaches the middle of the waist of the furnace, there is no metal at this time, and the coke can react and burn with the oxygen transported from below to increase the heat. If the position is too high, the oxygen will first contact the metal, but the metal cannot replenish heat. If the position is too low, which is equivalent to the coke still burning, the coke will fall into the furnace through the furnace belly. In addition to causing waste, a large amount of unburned coke will be mixed with the slag and iron, destroying the fluidity of the furnace, blocking the iron mouth, and causing major safety hazards.

[0031] The fourth batch of clean coke is actually the split of the third batch of clean coke. In the prior art, the clean coke is added at a rate of 1.5 t / h at one time. However, the inventors found through research that if this batch of clean coke is added too concentratedly, although the overall heat is guaranteed during the coke combustion, the [Si] content in the molten iron will increase rapidly, which is not conducive to blast furnace smelting. Therefore, after optimized splitting, the total amount of clean coke added is guaranteed to remain unchanged, and concentration can be avoided.

[0032] B. Ingredients adjustment:

[0033] ① Adjust the load: adjust the coke ratio to 380-400kg / t until the wind-off is completed; in the actual production process, the upper and lower limits can be set according to the furnace performance, wind-off time and external conditions. Although the method of adding clean coke has been adopted to make up for the heat loss, the clean coke only works during the combustion time. Once all the combustion is completed, there may still be a problem of insufficient heat in the future. From this perspective, increasing the overall amount of coke added is an effective method, but at the same time, the cost needs to be taken into account. Therefore, the strategy adopted is to use clean coke as the main method and increase the coke ratio appropriately as the auxiliary method.

[0034] ② Adjust the basicity of the ingredients: the binary basicity CaO / SiO2 is 1.20-1.30. Due to the increase in the coke ratio and the effect of the net coke, the [Si]% in the molten iron after re-airing will increase. Although [Si] is not a harmful element, high silicon will make the slag viscous and reduce fluidity. The sign of successful re-airing is the ability to quickly discharge the slag. Obviously, high silicon is not conducive to the rapid recovery of the furnace condition. It is difficult to directly reduce the [Si]% content, but the slag basicity can be reduced and the SiO2 content in the slag can be increased. In this way, [Si] will be easier to enter the slag instead of the molten iron, thereby indirectly achieving the purpose.

[0035] C. Light load material:

[0036] ① Light-load material first stage: coke ratio is controlled at 400kg / t, batching [Si] is controlled at 0.5wt%, basicity is controlled at 1.22-1.24, and 15 batches of material are added;

[0037] ② The second stage of light-load material: the coke ratio is controlled at 400kg / t, the batching [Si] is controlled at 0.4wt%, the basicity is controlled at 1.25-1.28, and it is added until the wind stops.

[0038] (3) Wind-off operation control:

[0039] ① For the last batch of iron, the [Si] in the molten iron is controlled at 0.5-0.6wt% and the molten iron temperature is greater than 1520℃ to ensure sufficient heat in the furnace before the wind is shut down and to ensure clean slag iron is discharged.

[0040] ② Try not to reduce coal or reduce coal as little as possible before stopping the wind, and control the flame temperature at 2150-2250℃.

[0041] (4) Operation control after re-airing:

[0042] ① The coal replenishment time is controlled within 2 to 3 hours; the coal replenishment amount is based on the fuel ratio of 520kg / t;

[0043] ② When the maximum coal injection rate is 65t / h, and the fuel ratio is less than 520kg / t, the difference in coal volume is calculated as 1 ton / 100m 3 Proportional control of air volume;

[0044] ③ After replenishing the coal, maintain the fuel ratio at 510-520kg / tFe according to the change in gas utilization rate and restore the furnace condition.

[0045] In the present invention, the amount of the first batch of net coke added in step (2) of the method for controlling the rapid and safe resumption of blast furnace air within 48 hours of shutdown is 10 tons.

[0046] In the present invention, the amount of the second batch of net coke added in step (2) of the method for controlling the rapid and safe resumption of blast furnace air within 48 hours of shutdown is 10 tons.

[0047] In the present invention, the raw ore proportion of the ingredients in step (2) of the method for controlling the rapid and safe resumption of blast furnace air within 48 hours of shutdown is controlled at 10%.

[0048] The above method is applicable to the rapid and safe re-airing control of blast furnace within 48 hours of wind stop. 3 Blast furnace applications.

[0049] The beneficial effects of the present invention are as follows: the present invention enables the blast furnace to smoothly switch from stopping to starting, with short time, low consumption and fast iron tapping, through the precise control measures and adjustment technical means and standards; in particular, through technical means such as adjusting the furnace temperature, heat, load conditions before the wind stop, and the timing and position of adding fuel, the economy and efficiency of the blast furnace re-winding are guaranteed.

[0050] As a reaction vessel, the blast furnace is shut down by cutting off the air to prevent the reaction. However, since the blast furnace itself cannot be absolutely airtight and the heat is continuously taken away as the furnace cools, the temperature inside the blast furnace will gradually drop. Ironmaking is mainly based on reduction reaction, which is an endothermic reaction. Therefore, in the low temperature zone, even if the wind, oxygen and fuel are restored (re-air operation), it is difficult for the reaction to proceed efficiently, which is called "blast furnace difficulty". The control method of the present invention can ensure the effectiveness and consistency of the operation in "re-airing within 48 hours of shut-down".

[0051] Compared with the prior art, the control method described in the present invention: 1. clarifies the operating limits and furnace conditions used; 2. On a general basis, it stipulates clear operating control limits to achieve high efficiency and economy; 3. clarifies control standards to ensure safety and controllability.

[0052] The control method of the present invention has the following advantages: (1) ensuring safe and smooth rest and resumption of air; (2) optimizing consumption and rapid iron tapping; (3) the temperature of the molten iron after resumption of air reaches 1500°C in the third furnace. In addition, the control method of the present invention has universality and consistent effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 This is a schematic diagram of blast furnace smelting. DETAILED DESCRIPTION

[0054] The technical solution of the present invention is described in detail below in conjunction with actual production.

[0055] Example 1

[0056] 3000m 3 The scheduled maintenance of the blast furnace was 40 hours (7:30 on October 30th to 19:30 on October 31st), and the actual maintenance time was 40 hours and 28 minutes (7:22 on October 30th to 17:50 on October 31st).

[0057] The main items of the wind-out project include: replacement of the material distribution chute, addition of infrared imagers, replacement of the middle sleeve, furnace-based gas treatment, etc. The wind-out process is safe and controllable, the air is added smoothly after the wind is restored, and the furnace condition is steadily restored.

[0058] (1) Preparation before the wind break:

[0059] Before the shutdown, all parameters of the furnace condition were running well and the pressure-volume relationship was loose.

[0060] The furnace temperature is controlled within the temperature control range of 1515℃-1520℃ according to the middle and upper limit levels 24 hours before the shutdown. The heat is sufficient to ensure the good working condition of the furnace before the shutdown.

[0061] (2) Control of the composition of the rest air material and the time of adding it:

[0062] At 20:00 on October 29 (furnace entry time), the first batch of net coke of 10 tons was added, according to the normal angle and distribution time. The load was adjusted: ore batch 107 tons, coke ratio increased by 10kg / t on the original basis, batch basicity controlled at 1.30, [Si] at 0.35wt%, and raw ore ratio reduced to 10%.

[0063] The second batch of 10 tons of net coke was added at 23:30 on October 29th, according to the normal angle and laying time.

[0064] At 1:30 am on October 30 (time of entering the furnace), the third batch of 2 barrels of net coke (totaling 36 tons) were added.

[0065] After 6 batches of light-load materials are added, the fourth batch of 10 tons of clean coke is added according to the normal angle and distribution time.

[0066] On the night shift at 1:30 am on October 30 (furnace entry time), the first section of light load material was adjusted: 102 tons of ore batch, coke ratio was controlled at 400 kg / t, [Si] was controlled at 0.5wt%, basicity was controlled at 1.22 (the batching fuel ratio was 535 kg / t), and the proportion of raw ore in the batching was controlled at 10%.

[0067] After 15 batches of light-loaded material in the first stage, the second stage of light-loaded material was adjusted: ore batch 102 tons, coke ratio controlled at 400kg / t, [Si] controlled at 0.4wt%, basicity controlled at 1.27 (batch fuel ratio according to 535kg / t), raw ore proportion in batching controlled at 10%. The second stage of light-loaded material was up to the wind stop.

[0068] The above two sections of light-load materials total 28.5 batches.

[0069] (3) Wind-off operation control:

[0070] ① For the last batch of iron, the [Si] in the molten iron is controlled at 0.5-0.6wt% and the molten iron temperature is greater than 1520℃ to ensure sufficient heat in the furnace before the wind is shut down and to ensure clean slag iron is discharged.

[0071] ② Try not to reduce coal or reduce coal as little as possible before stopping the wind, and control the flame temperature at 2150-2250℃.

[0072] (4) Operation control after re-airing:

[0073] The air was restored at 19:56 on October 31st. After the air was restored at 20:07, the average top temperature was 112°C and the raw gas inlet temperature was 90°C, and the gas introduction operation was carried out.

[0074] Gradually restore the air volume and increase it to 6000m at 20:50 3 / min, and it took 44 minutes to reach full wind.

[0075] During the air volume recovery process, the pressure-volume relationship is appropriate, the probe works normally, and material discharge is smooth.

[0076] After 17 hours, the temperature of the cast iron cooling wall was basically stable.

[0077] The highest temperature after re-airing was 1460℃, the cumulative iron-making time was 166 minutes, and the highest heat was 1500℃.

[0078] The maximum temperature of the second furnace of molten iron is 1520℃.

[0079] The third furnace has the function of re-airing and coal supplementation, and the maximum heat temperature of molten iron is 1540℃.

[0080] The temperature of the molten iron reached above 1500℃ 4 hours after the re-airing, meeting the requirement of 1500℃ for the third furnace of the re-airing scheme. The maintenance process was safe and controllable, and all equipment was successfully tested and put into use at one time.

Claims

1. A control method for rapid and safe restoration of blast furnace wind within 48 hours of wind stoppage, characterized in that: The following aspects are included for control and adjustment: (1) Preparation before the wind break: Keep the furnace condition stable and running smoothly one week before the wind breaks; 24 hours before the wind is shut down, the physical heat of the molten iron should be increased by 5-10℃ from the basic value of 1510℃, and the temperature should not exceed 1520℃; (2) Control of the composition of the resting material and the time of adding it: A. Clean coke: The total amount of clean coke added is calculated at 1.7-1.8 t / h and added in 4 times; ① The time for adding the first batch of clean coke is 3.5 hours before the wind stop + the length of one smelting cycle as the time control node; the amount of the first batch of clean coke added is 10 tons; ② The time for adding the second batch of clean coke is based on the length of one smelting cycle before the wind stoppage as the time control node; the amount of the second batch of clean coke added is 10 tons; ③ The third batch of clean coke should be added 6 hours before the wind is shut down; the amount added is 1t / h; ④ The fourth batch of clean coke is added after the third batch of clean coke, and after 5 to 6 batches of light-load materials; the addition amount is 0.5t / h; B. Ingredients adjustment: ① Adjust the load: adjust the coke ratio to 380-400kg / t until the wind stop is completed; ② Adjust the basicity of ingredients: the binary basicity CaO / SiO2 is controlled at 1.20-1.30; C. Light load material: ① Light-load material first stage: coke ratio is controlled at 400kg / t, batching [Si] is controlled at 0.5wt%, basicity is controlled at 1.22-1.24, and 15 batches of material are added; ② The second stage of light-load material: the coke ratio is controlled at 400kg / t, the batching [Si] is controlled at 0.4wt%, the basicity is controlled at 1.25-1.28, and added to the rest air; (3) Wind-off operation control: ① In the last batch of iron, the [Si] in the molten iron is controlled at 0.5-0.6wt%, and the molten iron temperature is greater than 1520℃; ②Control the flame temperature at 2150-2250℃ before stopping the wind; (4) Operation and control after re-airing: ① The coal replenishment time is controlled within 2 to 3 hours; the coal replenishment amount is based on the fuel ratio of 520kg / t; ② When the maximum coal injection rate is 65t / h, and the fuel ratio is less than 520kg / t, the difference in coal volume is calculated as 1 ton / 100m 3 Proportional control of air volume; ③ After the coal is replenished, the fuel ratio is maintained at 510-520 kg / tFe according to the change of gas utilization rate to restore the furnace condition; The control method for rapid and safe re-airing of a blast furnace within 48 hours of wind stop is applicable to 3000m 3 blast furnace.

2. The control method for rapid and safe restoration of blast furnace after a 48-hour shutdown according to claim 1 is characterized in that: The raw ore ratio in step (2) is controlled at 10%.

3. The control method for rapid and safe re-airing of a blast furnace within 48 hours of a shutdown as claimed in claim 1 or 2 is used at 3000m 3 Blast furnace applications.

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