A heat preservation method for preventing freezing of a blast furnace hearth

Abstract

The application discloses a heat preservation method for preventing freezing of a blast furnace hearth, and comprises the following steps: after receiving an emergency stop command, under the premise that the blast furnace has tapping conditions, organizing furnace front tapping and taking a blast reducing operation; judging a stop preparation time, if the stop preparation time is sufficient, executing step 301, otherwise, executing step 302; step 301, adding N tons of coke into the blast furnace, and then loading the blast furnace according to a normal production burden proportion; step 302, adding coke into the blast furnace, and then adding ore into the blast furnace; confirming that the blast furnace has completed iron discharge, and plugging the iron notch of the blast furnace; drawing out residual coal gas in the blast furnace, and then plugging the tuyere of the blast furnace; closing the water outlet of the blast furnace top, closing a part of pump bodies, and reducing the water inflow of the cooling water of the blast furnace bottom; and reducing the steam flow of the blast furnace top. Through the measures of greatly reducing the cooling intensity of the blast furnace body and plugging the tuyere, the risk of large cooling and freezing of the blast furnace hearth is minimized.

Description

Technical Field

[0001] This invention relates to the field of blast furnace ironmaking technology, and in particular to a heat preservation method for preventing the blast furnace hearth from freezing. Background Technology

[0002] When a blast furnace is forced to shut down due to a sudden major accident, there is no time to change the fuel, insufficient time to add clean coke (shutdown fuel), and the blast furnace restart time is uncertain. After continuous heat loss from the hearth, the blast furnace is very prone to sudden cooling or even hearth freezing upon restarting. During the process of restoring the blast furnace to its normal operating condition, this not only significantly increases smelting costs but also easily induces serious accidents such as suspended fuel, collapse, excessive flow, and burn-through of the tuyeres, severely threatening the safe and stable operation of the blast furnace. Currently, there are only auxiliary recovery technologies for hearth freezing; there are no technologies to prevent hearth freezing caused by emergency blast furnace shutdowns. Summary of the Invention

[0003] The purpose of this invention is to provide a heat preservation method for preventing freezing of the blast furnace hearth, which can prevent freezing of the blast furnace hearth during emergency shutdown.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A method for preventing freezing of the blast furnace hearth is provided, comprising the following steps:

[0006] Step 100: Upon receiving an emergency shutdown order, and provided that the blast furnace is ready for tapping, organize tapping at the furnace front and implement blast reduction operations.

[0007] Step 200: Determine the wind cessation time. If the wind cessation preparation time is sufficient, proceed to step 301; otherwise, proceed to step 302.

[0008] In step 301, N tons of coke are added to the blast furnace. The blast furnace consumes M tons of coke per hour under normal shutdown conditions, where N = 8 * M. Then, the blast furnace is charged according to the normal production charge ratio.

[0009] Step 302: Add coke into the blast furnace, and then add ore into the blast furnace;

[0010] Step 400: Confirm that the blast furnace iron discharge is complete, and seal the blast furnace taphole; perform a blast furnace shutdown operation. After the blast furnace shutdown operation is completed, after an interval of 10 minutes, open the hot blast stove backflow valve to perform a backflow operation, extract the residual gas in the blast furnace, and then disassemble all tuyeres and seal the blast furnace tuyeres; manually close the inlet valve of the blast furnace top cooling water. The blast furnace is connected to multiple pumps. Close some of the pumps to reduce the inlet flow rate of the cooling water at the bottom of the blast furnace; reduce the steam flow rate at the top of the blast furnace.

[0011] As a preferred method for heat preservation to prevent freezing of the blast furnace hearth, the blast furnace top is equipped with multiple vent valves, and the method further includes the following steps:

[0012] Step 500: After the blast furnace has been shut down for two hours, a portion of the vent valves are closed, and the steam flow rate at the top of the blast furnace is reduced again.

[0013] A preferred method for heat preservation to prevent freezing of the blast furnace hearth also includes the following steps:

[0014] Step 600: After the blast furnace has been shut down for four hours, the flow rate of the cooling water inlet to the blast furnace is reduced again.

[0015] As a preferred method for heat preservation to prevent freezing of the blast furnace hearth, the cooling water flow rate required for normal production of the blast furnace is B, and step 400 includes:

[0016] Reduce the inlet flow rate of the cooling water in the blast furnace to (1 / 2)*B;

[0017] Step 600 includes:

[0018] Reduce the inlet flow rate of the cooling water at the bottom of the blast furnace to (1 / 4)*B to (1 / 3)*B.

[0019] As a preferred method for preventing freezing of the blast furnace hearth, during an emergency shutdown, the sealing of the tuyeres should be checked every hour. If the tuyeres are found to be dark (without light), further investigation should be conducted to find the leak and replace them immediately.

[0020] As a preferred method for heat preservation to prevent freezing of the blast furnace hearth, the blast furnace is provided with multiple tuyeres at certain intervals;

[0021] During the emergency ventilation shutdown, one of the aforementioned vents shall be opened every hour.

[0022] If red burning or bright light can be observed through the air vent, then the air vent should be blocked; otherwise, close the water inlet valve adjacent to the air vent, check for leaks, and repair or replace the cooling equipment at the leak point.

[0023] As a preferred method for heat preservation to prevent freezing of the blast furnace hearth, the reduced airflow operation includes:

[0024] Reduce the air volume to 60% to 80% of the air volume required for normal production.

[0025] As a preferred method for heat preservation to prevent freezing of the blast furnace hearth, step 301 further includes:

[0026] After the coke load in the blast furnace is reduced by 0.2-0.3 t / t, the blast furnace is then charged again according to the normal production feed ratio.

[0027] As a preferred method for preventing freezing of the blast furnace hearth, the tuyeres are sealed with water-soaked mud, the thickness of which is 4cm to 5cm.

[0028] As a preferred method for preventing blast furnace hearth freezing, the pump used when shutting down a portion of the blast furnace during normal production within 30 minutes of completing the emergency shutdown operation reduces the cooling intensity of the upper part of the blast furnace body and reduces the inflow rate of cooling water to the bottom of the blast furnace.

[0029] The beneficial effects of this invention are as follows: by significantly reducing the cooling intensity of the blast furnace body and sealing the tuyeres, the heat loss inside the blast furnace, especially in the high-temperature area of ​​the hearth, is effectively reduced, minimizing the risk of the hearth cooling down and freezing; the amount of coke in the blast furnace is increased as much as possible, and after adding coke, ore is added. The weight of the ore is much greater than that of the coke, and the ore can compact the coke, which can isolate the coke from contact with air and delay the combustion of the coke. Detailed Implementation

[0030] To make the technical problems solved by the present invention, the technical solutions adopted, and the technical effects achieved clearer, the technical solutions of the embodiments of the present invention will be further described in detail below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] In the description of this invention, unless otherwise explicitly specified and limited, the terms "connected," "linked," and "fixed" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0032] The present invention provides a heat preservation method for preventing freezing of the blast furnace hearth, comprising the following steps:

[0033] Step 100: Upon receiving an emergency shutdown order, and provided that the blast furnace is ready for tapping, organize tapping at the furnace front and implement blast reduction operations.

[0034] Step 200: Determine the wind cessation time. If there is sufficient preparation time for the wind cessation, proceed to step 301; otherwise, proceed to step 302.

[0035] Step 301: Add N tons of coke to the blast furnace. The blast furnace consumes M tons of coke per hour under normal shutdown conditions. N = 8 * M. Then, charge the blast furnace according to the normal production charge ratio.

[0036] Step 302: Add coke into the blast furnace, and then add ore into the blast furnace;

[0037] Step 400: Confirm that the blast furnace iron discharge is complete and seal the blast furnace taphole; then proceed with the blast furnace shutdown operation. After the blast furnace shutdown operation is completed, after an interval of 10 minutes, open the hot blast stove backflow valve to perform a backflow operation, extract the residual gas in the blast furnace, then disassemble all tuyeres and seal the blast furnace tuyeres; manually close the water inlet valve at the top of the blast furnace. The blast furnace is connected to multiple pumps; close some of the pumps to reduce the cooling water inlet flow rate at the bottom of the blast furnace; reduce the steam flow rate at the top of the blast furnace.

[0038] The tuyere blowing pipe is an essential structure on the blast furnace. It is installed at the tuyere of the blast furnace to enhance the penetration of the airflow from the tuyere into the center of the blast furnace.

[0039] Based on the different physical states of the raw materials and fuels fed into the blast furnace, the blast furnace smelting process can be roughly divided into five zones: the blocky zone, the soft molten zone, the dripping zone, the tuyere zone, and the slag and iron accumulation zone in the hearth. The hearth is the final stage of blast furnace smelting, and the completeness of the blast furnace smelting process is ultimately reflected in the working state of the hearth. The hearth is the source of the reducing gas and heat required in the smelting process. The initial distribution of the gas in the hearth not only determines the temperature and heat distribution across the hearth cross-section but also has a decisive influence on the gas flow and temperature distribution along the entire blast furnace cross-section. This is crucial to the blast furnace smelting process, and the thermal state of the blast furnace hearth is of paramount importance.

[0040] During shutdown, the main heat losses in the blast furnace include:

[0041] (1) The heat removed by the cooling system;

[0042] (2) To ensure that the heat carried away by the steam or nitrogen gas introduced into the blast furnace under positive pressure is carried away.

[0043] In response to the main pathways of heat loss during blast furnace shutdowns, this solution effectively reduces heat loss inside the blast furnace, especially in the high-temperature hearth, by significantly reducing the cooling intensity of the blast furnace body and sealing the tuyeres. This minimizes the risk of the blast furnace hearth cooling down and freezing. Steps 301 and 302 of this solution can maximize the amount of coke in the blast furnace. After adding coke, ore is added. The weight of the ore is much greater than that of the coke, which can compact the coke, effectively isolating the coke from contact with air and delaying coke combustion.

[0044] Furthermore, the blast furnace top is equipped with multiple venting valves, and the insulation method to prevent the blast furnace hearth from freezing also includes the following steps:

[0045] Step 500: Two hours after the blast furnace is shut down in an emergency, close some of the vent valves and reduce the steam flow rate at the top of the blast furnace again.

[0046] By closing some of the vent valves, the amount of gas emitted from the top of the blast furnace can be reduced, thus reducing heat loss. Since the number of vent valves that are open is relatively small, it is necessary to reduce the steam flow rate at the top of the blast furnace to ensure the balance of gas pressure inside the blast furnace. It is understandable that the temperature of the steam is much lower than the temperature inside the blast furnace, so reducing the steam flow rate into the blast furnace is also beneficial to maintaining the temperature inside the blast furnace.

[0047] Furthermore, the insulation method for preventing blast furnace hearth freezing also includes the following steps:

[0048] Step 600: Four hours after the blast furnace is shut down in an emergency, reduce the inlet flow rate of the cooling water in the blast furnace again.

[0049] Understandably, the timing of restarting the blast furnace is difficult to determine in the event of an emergency shutdown. Four hours after an emergency shutdown, the temperature inside the blast furnace will drop further. At this point, reducing the flow rate of the cooling water into the blast furnace can further reduce heat loss and also reduce the impact of excessive heat loss from the hearth on the blast furnace restart operation.

[0050] Furthermore, the cooling water flow rate required for normal blast furnace production is B. Step 400 includes: reducing the inlet flow rate of cooling water at the bottom of the blast furnace to (1 / 2)*B; Step 600 includes: reducing the inlet flow rate of cooling water at the bottom of the blast furnace to (1 / 4)*B to (1 / 3)*B.

[0051] Furthermore, during an emergency shutdown, the tuyere seals are checked every hour. If any leaks are found, the tuyeres are repaired. By checking the tuyere seals every hour and repairing any leaks, the situation inside the blast furnace can be investigated promptly, allowing for timely intervention and preventing excessive heat loss from the blast furnace due to tuyere leaks.

[0052] Furthermore, the blast furnace is equipped with multiple tuyeres. During an emergency shutdown, one tuyer is opened every hour in a clockwise or counterclockwise direction. If red-hot coals or bright light can be observed through the tuyer, the tuyer is sealed. Otherwise, the water inlet valves of the two adjacent tuyeres are closed, and leaks are identified and the cooling equipment at the leaking point is replaced. The heat carried away by leaking coolers into the furnace is a major pathway for heat loss during blast furnace shutdowns. By opening blocked tuyeres every hour, leaking coolers can be detected promptly, allowing for timely replacement and preventing hearth freezing due to untimely handling of large leaks.

[0053] Furthermore, the blast furnace's blast reduction operation after receiving an emergency shutdown order includes reducing the blast volume to 60% to 80% of the blast volume required for normal production.

[0054] Specifically, step 301 also includes: after reducing the coke load in the blast furnace by 0.2-0.3 t / t, the blast furnace is then charged with the normal production feed ratio.

[0055] Furthermore, water-bubbling mud is used to seal the air vents, with a thickness of 4cm to 5cm.

[0056] Furthermore, within 30 minutes of completing the blast furnace shutdown operation, a portion of the pumps are shut down to reduce the cooling intensity in the upper region of the blast furnace and to reduce the inflow rate of cooling water to the furnace bottom. The pumps include high-pressure pumps and medium-pressure pumps.

[0057] The complete steps of the heat preservation method for preventing freezing of the blast furnace hearth in this embodiment are as follows:

[0058] Step (1) After receiving the emergency shutdown order, the blast furnace should immediately organize the tapping of iron in front of the furnace if the conditions for tapping iron are met. According to the theoretical slag and iron discharge situation in the hearth, the blast furnace should immediately reduce the air volume to 60%-80% of the normal air volume to improve the heat level of the hearth and facilitate the clean discharge of slag and iron in the hearth in front of the furnace.

[0059] Step (2) Instruct the blast furnace charging microcomputer operator to stop charging other materials and add coke into the blast furnace as soon as possible. If time permits, add the amount of coke required for the blast furnace to shut down normally for 8 hours. After adding the coke, reduce the coke load by 0.2-0.3 t / t and charge according to the normal ratio. If time does not permit, add as much as you need, but you must ensure that the last half batch of charging material is ore.

[0060] Step (3) Calculate the actual iron output and theoretical iron output at the furnace front, confirm that the slag and iron in the furnace are discharged cleanly, and after the iron tap blows in large quantities, notify the furnace front to block the tap and carry out the blast furnace shutdown operation.

[0061] After the hot blast stove backflow is completed in step (4), immediately organize maintenance personnel to dismantle all tuyeres of the blast furnace, use water-soaked mud to block all tuyeres, with a thickness of 4-5cm, and keep the blast furnace warm.

[0062] After step (5) emergency shutdown, manually close the inlet valves of the furnace top water pump, furnace top cross temperature measuring gun cooling water and airtight box cooling water (i.e., the water inlet of the blast furnace top) to prevent water leakage into the furnace.

[0063] After step (6) shutting down the blast furnace, within 10 minutes, shut down 1 / 2 of the high-pressure pumps and 2 / 3 of the medium-pressure pumps required for normal production, and reduce the water flow rate of the furnace bottom water cooling pipe to 1 / 2 of the required for normal production, thereby reducing the cooling intensity of the blast furnace body and reducing heat loss.

[0064] After the emergency shutdown operation in step (7) is completed, the steam flow rate at the top of the furnace is reduced to half of the normal required flow rate.

[0065] Two hours after step (8), if the blast furnace re-blowing time is still uncertain, close some of the blast furnace top vent valves and leave only one vent valve open. At the same time, further reduce the amount of steam entering the furnace to ensure positive pressure inside the furnace while reducing the amount of heat carried away by the steam.

[0066] Step (9) The blast furnace is shut down for more than 4 hours in an emergency. The flow rate of the bottom water cooling pipe is further reduced to 1 / 4 to 1 / 3 of the normal production flow rate to reduce the heat carried away by the cooling water from the hearth.

[0067] Step (10) During the ventilation shutdown period, the shift foreman and pipe installer shall check the condition of the air vents every hour. If light is found to be passing through the air vents, mud shall be added in time to prevent heat loss.

[0068] Step (11) Check one blocked air vent every hour in a certain direction (clockwise or counterclockwise is convenient). If red burnt or bright light can be seen in the air vent, it can be sealed normally with mud. If the air vent is found to be dark, immediately close the small and medium sleeve water inlet valves of the two air vents next to the air vent to reduce water leakage into the furnace. Organize experienced pipe fitters to further confirm the water leakage point. If necessary, directly shut off the water inlet valve of the leaking cooler and immediately organize professional personnel to replace the leaking cooler.

[0069] Step (12) Notify the hot blast stove to start firing in advance before restarting the blast furnace to ensure that the blast temperature is maintained at a high level after restarting the blast furnace.

[0070] In the above steps, steps (4) to (7) can be performed in sequence, or the order can be changed, or they can be performed simultaneously without affecting the final result.

[0071] The following is based on a certain 1050m 3 An example of emergency shutdown and insulation of a blast furnace illustrates the above steps.

[0072] A steel plant 1050m 3 The blast furnace uses charging cars for charging and two tapholes for intermittent tapping. Due to a sudden oxygen production failure, the oxygen supply was interrupted, and the molten iron could not be processed. At 17:11, an emergency shutdown order was received. The main parameters before the shutdown were: blast volume 2300 m³ / h. 3 / min, oxygen-enriched 11500m 3 / h, ore batch weight 34.16t, coke batch weight 7.12t, normal shutdown coke addition is 3 tons / hour, blast furnace cooling water pump operation status is 2 high pressure pumps, 3 medium pressure pumps and 1 atmospheric pressure pump are running online, the taphole has just been opened for 10 minutes.

[0073] Upon receiving the instruction, the following measures were taken:

[0074] (1) After receiving the emergency shutdown order, the blast furnace immediately reduced the blast by 400m based on the theoretical slag and iron discharge situation in the hearth. 3 / min to 1900m 3 / min, which increases the heat level of the hearth and also helps to cleanly discharge slag and iron from the hearth in front of the furnace;

[0075] (2) Notify the blast furnace charging operator to stop feeding other materials and add 24t of coke into the blast furnace immediately. After adding the coke, the coke load drops from 4.8t / t to 4.5t / t. Feed according to the normal ratio. After 65 minutes of tapping iron, the air blows out. Notify the charging operator to stop feeding after feeding the last half batch of ore.

[0076] (3) Calculate the actual iron output and theoretical iron output at the furnace, confirm that the slag and iron in the furnace are discharged cleanly, and after the iron tap comes in again with a large burst of air, notify the furnace to block the tap and carry out the blast furnace shutdown operation. The emergency shutdown operation was completed at 18:12.

[0077] (4) After the hot blast stove is backflowed, immediately organize maintenance personnel to dismantle all the tuyere blowpipes of the blast furnace. During the dismantling of the tuyere blowpipes, prepare water-soaked mud. After the tuyere blowpipes are removed, use water-soaked mud to block all the tuyeres one by one, with a thickness of about 4cm, to keep the blast furnace warm.

[0078] (5) After an emergency shutdown, notify the on-site operators to manually close the inlet valves of the furnace top water pump, the furnace top cross temperature measuring gun cooling water and the airtight box cooling water (i.e. the water outlet of the blast furnace top) to prevent water leakage into the furnace.

[0079] (6) After the ventilation is stopped, one high-pressure pump and two medium-pressure pumps shall be shut down within 10 minutes, and the water inlet flow rate of the furnace bottom water-cooling pipe shall be reduced from 180m³ / h. 3 / h to 90m 3 / h, reducing the cooling intensity of the blast furnace body and reducing heat loss.

[0080] (7) After the emergency shutdown operation is completed, the steam flow rate at the top of the furnace is reduced to 1 / 2 of the normal required flow rate.

[0081] (8) If the blast furnace re-blowing time is still uncertain after 2 hours, close one blast furnace top vent valve and leave only one blast furnace top vent valve in the open state. At the same time, further reduce the amount of steam entering the furnace to reduce the heat carried away by the steam while ensuring positive pressure inside the furnace.

[0082] (9) If the blast furnace is shut down for an emergency of more than 4 hours, further reduce the flow rate of the bottom water cooling pipes by 60m³. 3 / h, reducing the amount of heat carried away from the furnace hearth by cooling water.

[0083] (10) During the shutdown period, the shift foreman and pipe installer shall check the condition of the air vents every hour. If light is found to be passing through the air vents, mud shall be added in time to prevent heat loss.

[0084] (11) Check the blocked air vents every hour in a certain direction. If red burnt or bright light can be seen in the air vent, it can be sealed normally with mud. If the air vent is found to be dark, immediately close the small and medium sleeve water inlet valves of the two air vents next to the air vent to reduce water leakage into the furnace. Organize experienced pipe fitters to further confirm the water leakage point. If necessary, directly shut off the water inlet valve of the leaking cooler and immediately organize professional personnel to replace the leaking cooler.

[0085] (12) Notify the hot blast stove to start firing in advance before restarting the blast furnace to ensure that the blast temperature is maintained at a high level after restarting the blast furnace.

[0086] After an interval of 15 hours and 16 minutes, the oxygen production system returned to normal, and the blast furnace was ready to resume operation. The blast furnace resumed operation according to the predetermined plan. Due to the adoption of extremely efficient blast furnace body, especially the heat preservation measures of the blast furnace hearth, the blast furnace resumed full-blow and full-oxygen operation 4 hours and 20 minutes after the resumption of operation. The first batch of iron slag and iron had good fluidity, the physical heat of molten iron was slightly low, and the chemical composition was basically within the normal range, which effectively reduced the risk of hearth cooling and freezing caused by the emergency shutdown of the blast furnace.

[0087] In the description herein, it should be understood that the terms "upper," "lower," "left," "right," and other orientations or positional relationships are used only for ease of description and simplification of operation, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. Furthermore, the terms "first" and "second" are used merely for descriptive distinction and have no special meaning.

[0088] In the description of this specification, references to terms such as "an embodiment," "example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example.

[0089] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style of the specification is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0090] The technical principles of the present invention have been described above with reference to specific embodiments. These descriptions are merely for explaining the principles of the invention and should not be construed as limiting the scope of protection of the invention in any way. Based on this explanation, those skilled in the art can readily conceive of other specific embodiments of the invention without inventive effort, and these embodiments will all fall within the scope of protection of the present invention.

Claims

1. A method for heat preservation to prevent freezing of the blast furnace hearth, characterized in that, Includes the following steps: Step 100: Upon receiving an emergency shutdown order, and provided that the blast furnace is ready for tapping, organize tapping at the furnace front and implement blast reduction operations. Step 200: Determine the wind cessation preparation time. If the wind cessation preparation time is sufficient, proceed to step 301; otherwise, proceed to step 302. In step 301, N tons of coke are added to the blast furnace. The blast furnace consumes M tons of coke per hour under normal shutdown conditions, N = 8 * M. Then, the blast furnace is charged according to the normal production charge ratio. In step 302, coke is added to the blast furnace, and then ore is added to the blast furnace, with the last half batch of feed being ore. Step 400: Confirm that the blast furnace iron discharge is complete, and seal the blast furnace taphole; perform blast furnace shutdown operation. After the blast furnace shutdown operation is completed, after an interval of 10 minutes, open the hot blast stove backflow valve to perform backflow operation, extract the residual gas in the blast furnace, and then disassemble all tuyeres and seal the blast furnace tuyeres; close the water outlet at the top of the blast furnace. The blast furnace is connected to multiple pumps. Close some of the pumps to reduce the inlet flow rate of cooling water at the bottom of the blast furnace; reduce the steam flow rate at the top of the blast furnace.

2. The heat preservation method for preventing freezing of the blast furnace hearth according to claim 1, characterized in that, The blast furnace is equipped with multiple venting valves on its top, and the process also includes the following steps: Step 500: After the blast furnace has been shut down for two hours, a portion of the vent valves are closed, and the steam flow rate at the top of the blast furnace is reduced again.

3. The heat preservation method for preventing freezing of the blast furnace hearth according to claim 2, characterized in that, It also includes the following steps: Step 600: After the blast furnace has been shut down for four hours, the flow rate of the cooling water inlet to the blast furnace is reduced again.

4. The heat preservation method for preventing freezing of the blast furnace hearth according to claim 3, characterized in that, The cooling water flow rate required for normal production of the blast furnace is B, and step 400 includes: Reduce the inlet flow rate of the cooling water in the blast furnace to (1 / 2)*B; Step 600 includes: Reduce the inlet flow rate of the cooling water at the bottom of the blast furnace to (1 / 4)*B to (1 / 3)*B.

5. The heat preservation method for preventing freezing of the blast furnace hearth according to any one of claims 1-4, characterized in that, During an emergency shutdown, the sealing of the air vents should be checked every hour. If a leak is found, the cooling equipment of the air vents should be replaced.

6. The heat preservation method for preventing freezing of the blast furnace hearth according to any one of claims 1-4, characterized in that, The blast furnace is provided with multiple tuyeres at intervals around its perimeter; During the emergency ventilation shutdown, one of the aforementioned vents shall be opened every hour. If a red burn or bright light can be observed through the air vent, then the air vent should be blocked; otherwise, close the water inlet valve adjacent to the air vent, and check for leaks and repair them.

7. The heat preservation method for preventing freezing of the blast furnace hearth according to any one of claims 1-4, characterized in that, The air reduction operation includes: Reduce the air volume to 60% to 80% of the air volume required for normal production.

8. The heat preservation method for preventing freezing of the blast furnace hearth according to any one of claims 1-4, characterized in that, Step 301 further includes: After the coke load in the blast furnace is reduced by 0.2-0.3 t / t, the blast furnace is then charged again according to the normal production feed ratio.

9. The heat preservation method for preventing freezing of the blast furnace hearth according to any one of claims 1-4, characterized in that, The air vent is sealed with water-based mud, the thickness of which is 4cm to 5cm.

10. The heat preservation method for preventing freezing of the blast furnace hearth according to any one of claims 1-4, characterized in that, Within 30 minutes of completing the blast furnace shutdown operation, a portion of the pumps are shut down to reduce the cooling intensity of the upper region of the blast furnace and to reduce the inflow rate of cooling water to the bottom of the blast furnace.