A control and regulation method for rapid cooling of blast furnace hot blast pipe

Abstract

The present application relates to a kind of high furnace hot blast pipe quick cooling control adjustment method, the method includes the following steps: step one, flow pipe diameter selection;Step two, cooling air volume one in two out;Step three, hot blast pipe and hot blast stove internal and external pressure balance adjustment, stabilize hot blast stove vault temperature;Step four, hot blast pipe two end flow balance adjustment;Step five, cooling end;The method has the characteristics of large cooling intensity, adjustment flexible, hot blast stove and hot blast pipe pressure balance hot blast stove cooling speed slow.

Description

Technical Field

[0001] This invention relates to a regulating method, specifically a method for rapid cooling of hot blast pipes in a blast furnace, belonging to the field of blast furnace ironmaking technology. Background Technology

[0002] The hot blast duct of a blast furnace refers to the pipeline from the hot blast valve outlet of the hot blast stove to the blast furnace casing. Its operating conditions are high temperature, high pressure, and high wind speed. Generally, the temperature of the hot blast branch pipe can reach 1350℃, the pressure is close to 500kPa, and the actual wind speed exceeds 50m / s. Due to the harsh working conditions, refractory material inside the hot blast duct often flakes off, requiring personnel to enter for inspection, cleaning, and repair work in severe cases. However, the hot blast duct is constructed with a large amount of refractory material, resulting in a large internal heat storage capacity, requiring a long time for personnel to enter and dissipate heat. Currently, two methods are generally used: natural cooling and forced cooling. Natural cooling is more friendly to the hot blast stove, but it involves a large workload and a long cooling time. Forced cooling is faster, but the hot blast stove needs to be kept warm for a short period.

[0003] The first method, natural cooling, involves removing the hot blast valve furthest from the blast furnace, lining the inside of the short pipe in the direction of the hot blast stove with bricks, and then sealing it with a blind plate. A gap is left at the original hot blast valve location, and the remaining hot blast valves are replaced with simulated hot blast valves. The blast furnace backflow pipe continuously draws cold air from the area near the gap left at the original hot blast valve to naturally cool the hot blast pipe. This method is labor-intensive and has a long cooling time, generally requiring more than 6 days to meet the requirements for hot blast pipe entry. However, it is friendly to the hot blast stove, allowing it to operate continuously for 10 days without insulation. The second method uses combustion air or other blowers connected to the manhole of the hot blast pipe. The air passes through the end pipe and finally reaches the backflow outlet to cool the hot blast pipe. Due to the positive pressure in the hot blast pipe, the hot blast valve and combustion air valve are not sealed, causing the temperature of the hot blast stove dome to drop rapidly. Typically, the hot blast stove can only operate continuously for 3-4 days without insulation. Summary of the Invention

[0004] This invention addresses the problems existing in the prior art by providing a control and regulation method for rapid cooling of blast furnace hot blast pipes. This method features high cooling intensity, flexible adjustment, pressure balance inside the hot blast stove and in the hot blast pipes, and slow cooling rate of the hot blast stove.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows: a control and regulation method for rapid cooling of blast furnace hot blast pipes, the method comprising the following steps:

[0006] Step 1: Selecting the flow rate pipe diameter;

[0007] The refractory material and construction parameters of the hot blast ducts were collected. The hot blast ducts were modeled and simulated. The required airflow for cooling was calculated based on the estimated time, and a suitable pipe diameter was selected according to the flow rate. The calculation process involved subtracting the hot blast duct repair time from the blast furnace shutdown time, leaving a one-day margin (to prevent calculation errors and unforeseen circumstances) as the planned cooling time. Different cooling airflow rates were then used in the model for simulation calculations based on this time, and the appropriate cooling airflow rate was selected based on time matching.

[0008] Step 2: Cooling airflow with one inlet and two outlets;

[0009] (1) During the blast furnace shutdown period, connect a pipe between the blast furnace mixing pipe and the hot blast stove combustion air regulating valve and combustion air combustion valve, open the manhole at the end of the hot blast stove direction hot blast main pipe and install a vent, and install a simple regulating device on the vent pipe.

[0010] (2) All air supply branch pipes of the blast furnace are blocked with blind plates, all air combustion valves of the hot blast stove are blocked with blind plates, all valves connected to the hot blast stove body are closed, the backflow valve is open, the mixing valve is open, and the venting valve is open.

[0011] (3) Start the hot blast stove combustion blower, adjust the air regulating valve and the combustion blower damper to achieve the required air flow. The air supplied by the combustion blower is separated into two paths through the mixing regulating valve, mixing valve and mixing chamber. One path cools the hot blast pipe in the direction of the blast furnace and the other path cools the hot blast pipe in the direction of the hot blast stove.

[0012] Step 3: Adjust the pressure balance inside and outside the hot air duct and hot air furnace to stabilize the temperature of the hot air furnace dome;

[0013] Since the valves of the hot blast stove cannot achieve absolute sealing, airflow will flow from high pressure to low pressure. It is necessary to control the pressure balance inside and outside the hot blast valve to ensure the normal cooling effect of the hot blast duct and to keep the temperature of the hot blast stove dome within a reasonable range. If the pressure inside the hot blast stove is greater than the pressure in the hot blast duct, hot air will flow out from the hot blast valve, affecting the cooling effect of the hot blast duct and increasing the cooling time. If the pressure relief rate of the flue valve or pressure relief valve is large, and the pressure in the hot blast duct is greater than the pressure inside the furnace, the poor sealing of the hot blast valve may cause the temperature of the hot blast stove dome to drop rapidly. It is necessary to install a heat preservation device in the hot blast stove to maintain the temperature of the hot blast stove dome.

[0014] (1) Calibrate the pressure gauges in the furnace and hot air duct, the pressure in the hot air furnace is P1, the pressure in the hot air duct is P2, control the pressure difference value, ΔP=P1-P2, -100Pa≤ΔP≤300Pa;

[0015] (2) Control method: If ΔP < -100Pa, open the hot air furnace pressure valve appropriately and adjust until -100Pa ≤ ΔP ≤ 300Pa; if ΔP ≥ 300Pa, open the hot air furnace pressure valve appropriately and adjust until -100Pa ≤ ΔP ≤ 300Pa.

[0016] (3) If adjusting the pressure valve to the maximum still cannot guarantee -100Pa≤ΔP≤300Pa, appropriately close the mixing air regulating valve to increase the pressure inside the hot blast stove.

[0017] (4) When the temperature at the outlet of the hot air duct drops below 200°C, the cooling operation should be temporarily stopped, or the cooling air volume should be reduced to an acceptable range, and a blind flange should be inserted on the outer flange side of the hot air valve.

[0018] (5) Open the pressure relief valve of each hot blast furnace appropriately so that ΔP < 0 Pa.

[0019] Step 4: Adjust the flow rate balance at both ends of the hot air duct;

[0020] (1) The hot air duct end on the hot air furnace side is fully open;

[0021] (2) Cooling is achieved using the maximum design flow rate;

[0022] (3) The temperature of the hot air duct at the end of the hot air duct on the hot air stove side is <200℃. After the hot air valve is inserted with a blind plate, the end vent valve is reduced so that the cooling rate V1 of the hot air duct on the hot air stove side is less than the cooling rate V2 of the hot air duct on the blast furnace side, i.e., V1 < V2.

[0023] (4) When the temperature t1 at the end of the hot blast pipe on the hot blast stove side is close to the temperature t2 at the outlet of the backflow valve on the hot blast pipe on the blast furnace side, i.e., t1 = t2;

[0024] (5) Increase the opening of the vent valve at the end of the hot air pipe on the hot air stove side so that the cooling rate V1 of the hot air pipe on the hot air stove side is close to the cooling rate V2 of the hot air pipe on the blast furnace side, i.e., V1 = V2.

[0025] Step 5: Cooling complete

[0026] (1) Backflow outlet temperature t2, combustion air temperature t0, t2 < (t0 + 25℃), fully open the diffuser valve, open the manholes in other parts of the hot air duct, effectively isolate the connecting pipe, and water seal the mixing duct.

[0027] (2) The backflow outlet temperature t2 < 50℃. Due to the chimney effect of the backflow valve and the vent pipe, the pipeline is naturally ventilated and personnel enter the pipeline to work.

[0028] If the backflow valve is not on the surrounding pipe, a vent pipe can be connected to the short pipe of the air supply branch of the remote cooling source. The total vent area is close to that of the backflow valve. During the cooling period, the backflow valve is kept closed. After the cooling is completed (t2 < (t0 + 25℃)), the backflow valve is opened to act as a chimney.

[0029] Compared with existing technologies, this invention has the following advantages: the cooling pipe is short and has low resistance, which can achieve a larger cooling air volume and can cool the hot air pipe to room temperature within 2-3 days; the pressure inside the pipe is balanced, and the cooling speed of the hot blast stove dome is slow, so the hot blast pipe cooling operation during the blast furnace shutdown for 10 days does not require the hot blast stove to be kept warm; the pipes at both ends can be adjusted more flexibly through backflow valves and end vent valves, so that the cooling rate at both ends can meet different requirements; without adding flow meters and regulating valves, the cooling air volume and air pressure can be precisely adjusted. Attached Figure Description

[0030] Figure 1 The process flow diagram of this invention.

[0031] In the diagram: 1-Cold air vent valve, 2-Flue valve I, 3-Flue valve II, 4-Cold air valve, 5-Hot blast stove, 6-Air combustion valve, 7-New connecting pipe, 8-Air regulating valve, 9-Air branch pipe flow meter, 10-End vent pipe, 13-Combustion fan, 14-Mixing air valve, 15-Mixing air regulating valve, 16-Mixing air chamber, 17-Backflow valve, 18-Blast furnace, 19-Air supply branch pipe. Detailed Implementation

[0032] To enhance understanding of the present invention, the embodiments will be described in detail below with reference to the accompanying drawings.

[0033] Example 1: See Figure 1 A method for controlling and regulating rapid cooling of blast furnace hot blast pipes, the method comprising the following steps:

[0034] Step 1: Selecting the flow rate pipe diameter;

[0035] Collect the refractory material and masonry parameters of the hot air duct, model and simulate the hot air duct, calculate the air flow required for cooling based on the estimated time, and select the appropriate pipe diameter based on the flow rate;

[0036] Step 2: Cooling airflow with one inlet and two outlets;

[0037] (1) During the blast furnace shutdown period, connect a pipe between the blast furnace mixing pipe and the hot blast stove combustion air regulating valve and combustion air combustion valve, open the manhole at the end of the hot blast stove direction hot blast main pipe and install a vent, and install a simple regulating device on the vent pipe.

[0038] (2) All air supply branch pipes of the blast furnace are blocked with blind plates, all air combustion valves of the hot blast stove are blocked with blind plates, all valves connected to the hot blast stove body are closed, the backflow valve is open, the mixing valve is open, and the venting valve is open.

[0039] (3) Start the hot blast stove combustion blower, adjust the air regulating valve and the combustion blower damper to achieve the required air flow. The air supplied by the combustion blower is separated into two paths through the mixing regulating valve, mixing valve and mixing chamber. One path cools the hot blast pipe in the direction of the blast furnace and the other path cools the hot blast pipe in the direction of the hot blast stove.

[0040] Step 3: Adjust the pressure balance inside and outside the hot air duct and hot air furnace to stabilize the temperature of the hot air furnace dome;

[0041] Since the valves of the hot blast stove cannot achieve absolute sealing, airflow will flow from high pressure to low pressure. It is necessary to control the pressure balance inside and outside the hot blast valve to ensure the normal cooling effect of the hot blast duct and to keep the temperature of the hot blast stove dome within a reasonable range. If the pressure inside the hot blast stove is greater than the pressure in the hot blast duct, hot air will flow out from the hot blast valve, affecting the cooling effect of the hot blast duct and increasing the cooling time. If the pressure relief rate of the flue valve or pressure relief valve is large, and the pressure in the hot blast duct is greater than the pressure inside the furnace, the poor sealing of the hot blast valve may cause the temperature of the hot blast stove dome to drop rapidly. It is necessary to install a heat preservation device in the hot blast stove to maintain the temperature of the hot blast stove dome.

[0042] (1) Calibrate the pressure gauges in the furnace and hot air duct, the pressure in the hot air furnace is P1, the pressure in the hot air duct is P2, control the pressure difference value, ΔP=P1-P2, -100Pa≤ΔP≤300Pa;

[0043] (2) Control method: If ΔP < -100Pa, open the hot air furnace pressure valve appropriately and adjust until -100Pa ≤ ΔP ≤ 300Pa; if ΔP ≥ 300Pa, open the hot air furnace pressure valve appropriately and adjust until -100Pa ≤ ΔP ≤ 300Pa.

[0044] (3) If adjusting the pressure valve to the maximum still cannot guarantee -100Pa≤ΔP≤300Pa, appropriately close the mixing air regulating valve to increase the pressure inside the hot blast stove.

[0045] (4) When the temperature at the outlet of the hot air duct drops below 200°C, the cooling operation should be temporarily stopped, or the cooling air volume should be reduced to an acceptable range, and a blind flange should be inserted on the outer flange side of the hot air valve.

[0046] (5) Open the pressure relief valve of each hot blast furnace appropriately so that ΔP < 0 Pa.

[0047] Step 4: Adjust the flow rate balance at both ends of the hot air duct;

[0048] (1) The hot air duct end on the hot air furnace side is fully open;

[0049] (2) Cooling is achieved using the maximum design flow rate;

[0050] (3) The temperature of the hot air duct at the end of the hot air duct on the hot air stove side is <200℃. After the hot air valve is inserted with a blind plate, the end vent valve is reduced so that the cooling rate V1 of the hot air duct on the hot air stove side is less than the cooling rate V2 of the hot air duct on the blast furnace side, i.e., V1 < V2.

[0051] (4) When the temperature t1 at the end of the hot blast pipe on the hot blast stove side is close to the temperature t2 at the outlet of the backflow valve on the hot blast pipe on the blast furnace side, i.e., t1 = t2;

[0052] (5) Increase the opening of the vent valve at the end of the hot air pipe on the hot air stove side so that the cooling rate V1 of the hot air pipe on the hot air stove side is close to the cooling rate V2 of the hot air pipe on the blast furnace side, i.e., V1 = V2.

[0053] Step 5: Cooling complete

[0054] (1) Backflow outlet temperature t2, combustion air temperature t0, t2 < (t0 + 25℃), fully open the diffuser valve, open the manholes in other parts of the hot air duct, effectively isolate the connecting pipe, and water seal the mixing duct.

[0055] (2) The backflow outlet temperature t2 < 50℃. Due to the chimney effect of the backflow valve and the vent pipe, the pipeline is naturally ventilated and personnel enter the pipeline to work.

[0056] If the backflow valve is not on the surrounding pipe, a vent pipe can be connected to the short pipe of the air supply branch of the remote cooling source. The total vent area is close to that of the backflow valve. During the cooling period, the backflow valve is kept closed. After the cooling is completed (t2 < (t0 + 25℃)), the backflow valve is opened to act as a chimney.

[0057] Example 2: See Figure 1 A method for rapid cooling of hot blast pipes in a blast furnace, the method comprising the following steps, using an effective volume of 4070 m³ 3 Taking the actual operation of the blast furnace as an example, this blast furnace is equipped with four hot blast stoves sharing one mixing chamber, and the backflow valve is on the hot blast duct:

[0058] Step 1: Selection of Flow Pipe Diameter

[0059] The refractory material and masonry parameters of the hot air duct were collected, and the hot air duct was modeled and simulated. Based on the estimated cooling time of 72 hours, the required air flow rate of 60,000 Nm at 25°C was calculated. 3 / h, select a connecting pipe diameter of 900mm based on the flow rate;

[0060] Step 2: Cooling airflow with one inlet and two outlets.

[0061] (1) After the blast furnace 18 is shut down, all 36 air supply branch pipes 19 are blocked with blind plates, all 4 hot blast stoves 5 are shut down and locked, the outer flanges of the 4 combustion air valves 6 are inserted with blind plates, the hot blast main manhole between No. 3 and No. 4 is opened and connected to the temporary end vent pipe 10. The end vent pipe 10 is equipped with a simple adjustment device and is fully opened. The end vent pipe 10 is equipped with a thermocouple.

[0062] (2) All valves connected to the hot blast stove body are closed, backflow valve 17 is open, mixing valve 14 is open, and venting valve 1 is open to cut off the connection between the hot blast stove and the blast furnace blower. The water seal of the mixing pipe is removed.

[0063] (3) Start the combustion blower 13, fully open the mixing valve 14 and the mixing regulating valve 15, determine the cooling flow rate using the flow rate of the air branch pipe flow meter 9 of the No. 1 hot air furnace, and adjust the opening of the damper of the combustion blower 13 and the No. 1 air regulating valve 15 to adjust the cooling air flow rate to 60000 Nm. 3 The cooling air passes through the combustion fan 13, the mixing valve 14, and the mixing regulating valve 15, and is split into two paths in the mixing chamber 16. One path cools the hot air pipe in the direction of the blast furnace, and the other path cools the hot air pipe in the direction of the hot blast stove. Compared with the one-in-one-out mode, the one-in-two-out mode has shorter pipes and lower friction resistance, which can achieve a larger air volume.

[0064] Step 3: Adjust the pressure balance inside and outside the hot air duct and hot air furnace to stabilize the temperature of the hot air furnace dome.

[0065] (1) Calibrate the pressure gauges in the furnace and hot air duct, the pressure in the hot air furnace is P1, the pressure in the hot air duct is P2, control the pressure difference value, ΔP=P1-P2, -100Pa≤ΔP≤300Pa;

[0066] (2) Adjust the pressure inside the hot air duct to 1600Pa. Since the condition of each hot air furnace is different, control the pressure inside the hot air furnace between 1500-1700Pa. If ΔP < -100Pa, open the hot air furnace pressure valve appropriately and adjust until -100Pa ≤ ΔP ≤ 300Pa. If ΔP ≥ 300Pa, open the hot air furnace pressure valve appropriately and adjust until -100Pa ≤ ΔP ≤ 300Pa.

[0067] (3) Even when the pressure valve of some hot blast stoves is opened to the maximum, it is still impossible to guarantee -100Pa≤ΔP≤300Pa. The mixing air regulating valve should be closed appropriately to increase the pressure inside the hot blast stove.

[0068] (4) Due to possible instrument errors, if the temperature of the dome of a hot blast stove drops faster than that of other hot blast stoves, ΔP should be increased appropriately. Similarly, if the temperature of the dome of a hot blast stove drops very slowly compared to that of other hot blast stoves, ΔP should be decreased appropriately.

[0069] (5) When the temperature of the hot air duct drops below 200°C, the cooling operation shall be temporarily stopped for 4 hours and a blind flange shall be inserted on the outer flange side of the hot air valve.

[0070] (6) Open the pressure relief valve of each hot air furnace appropriately so that ΔP < 0 Pa; in this case, the hot air valve blind plate does not need to be inserted very tightly to facilitate spot checks. The pressure inside the furnace is lower than the pressure of the hot air pipeline, so the hot air inside the hot air furnace will not overflow from the edge of the blind plate.

[0071] Step 4: Adjust the flow rate balance at both ends of the hot air duct;

[0072] (1) When the temperature of the hot air duct drops to 200℃, it takes 27 hours. After the hot air valve is inserted with a blind plate, the end vent valve is reduced so that the cooling rate of the hot air duct on the hot air stove side is V1 and the cooling rate of the hot air duct on the blast furnace side is V2, i.e., V1 < V2.

[0073] (2) When the temperature t1 at the end of the hot blast pipe on the hot blast stove side is close to the temperature t2 at the outlet of the backflow valve on the hot blast pipe on the blast furnace side, i.e., t1 = t2;

[0074] (3) Increase the opening of the vent valve at the end of the hot blast pipe on the hot blast stove side so that the cooling rate of the hot blast pipe on the hot blast stove side and the cooling rate of the hot blast pipe on the blast furnace side are close to V1=V2. This is mainly to ensure that the final cooling temperature of the hot blast pipes in the direction of the hot blast stove and the direction of the blast furnace is consistent.

[0075] Step 5: Cooling complete;

[0076] (1) When the backflow outlet temperature t2 is 50℃, fully open the valve of the diffuser 10, open the manholes of other parts of the hot air duct, effectively isolate the connecting pipe, close the mixing air regulating valve 15, close the mixing air valve 14, water seal the mixing air pipe, stop the combustion fan 13, and open one or more blind plates on the air supply branch pipe as needed, and naturally cool the pipe through the backflow valve 17.

[0077] (2) When personnel enter the pipeline for work, the measured temperature inside the pipeline far from the cooling source is less than 40℃ and the masonry temperature is less than 60℃.

[0078] Using this method, the actual cooling time of 71 hours was basically consistent with the calculation. If time is tight, the cooling gas intensity can be increased to reduce the cooling time. This method has a fast cooling speed, completing the cooling of the hot air duct in 71 hours. If time is tight, the cooling intensity can be increased to further reduce the cooling time. It can effectively reduce the temperature of the hot air furnace dome, ensuring that no insulation is needed for 10 days. The cooling time can be controlled more precisely; the actual cooling time of 71 hours differs from the calculated 72 hours by only 1 hour.

[0079] It should be noted that the above embodiments are not intended to limit the scope of protection of the present invention. Equivalent transformations or substitutions made based on the above technical solutions all fall within the scope of protection of the claims of the present invention.

Claims

1. A method for controlling and regulating rapid cooling of blast furnace hot blast pipes, characterized in that, The method includes the following steps: Step 1: Selecting the flow rate pipe diameter; Step 2: Cooling airflow with one inlet and two outlets; Step 3: Adjust the pressure balance inside and outside the hot air duct and hot air furnace to stabilize the temperature of the hot air furnace dome; Step 4: Adjust the flow rate balance at both ends of the hot air duct; Step 5: Cooling complete; The first step involves selecting the flow rate and pipe diameter. This involves collecting the refractory material and masonry parameters of the hot air duct, modeling and simulating the hot air duct, calculating the required air flow rate for cooling based on the estimated time, and selecting a suitable pipe diameter based on the flow rate. Step 2: Cooling airflow with one inlet and two outlets; (1) During the blast furnace shutdown period, connect a pipe between the blast furnace mixing pipe and the hot blast stove combustion air regulating valve and combustion air combustion valve, open the manhole at the end of the hot blast stove direction hot blast main pipe and install a vent, and install a simple regulating device on the vent pipe. (2) All blast furnace air supply branch pipes are blocked with blind plates, all hot blast stove air combustion valves are blocked with blind plates, all valves connected to the hot blast stove body are closed, backflow valves are open, mixing valves are open, and venting valves are open. (3) Start the combustion blower of the hot blast stove, adjust the air regulating valve and the damper of the combustion blower to achieve the required air flow. The air provided by the combustion blower is divided into two paths through the mixing regulating valve, the mixing valve and the mixing chamber. One path cools the hot blast pipe in the direction of the blast furnace and the other path cools the hot blast pipe in the direction of the hot blast stove. Step 3: Adjust the pressure balance inside and outside the hot air duct and hot air furnace to stabilize the temperature of the hot air furnace dome; details are as follows: (1) Calibrate the pressure gauges in the furnace and hot air duct, the pressure in the hot air furnace is P1, the pressure in the hot air duct is P2, control the pressure difference value, ΔP=P1-P2, -100Pa≤ΔP≤300Pa; (2) Control method: If ΔP < -100Pa, open the hot air furnace pressure valve appropriately and adjust until -100Pa ≤ ΔP ≤ 300Pa; if ΔP ≥ 300Pa, open the hot air furnace pressure valve appropriately and adjust until -100Pa ≤ ΔP ≤ 300Pa. (3) If adjusting the pressure valve to the maximum still cannot guarantee -100Pa≤ΔP≤300Pa, appropriately close the mixing air regulating valve to increase the pressure inside the hot blast stove; (4) When the temperature at the outlet of the hot air duct drops below 200°C, the cooling operation shall be temporarily stopped, or the cooling air volume shall be reduced to an acceptable range, and a blind flange shall be inserted on the outer flange side of the hot air valve. (5) Open the pressure relief valve of each hot blast stove appropriately so that ΔP < 0 Pa; Step 4: Adjust the flow rate balance at both ends of the hot air duct; details are as follows: (1) The vent at the end of the hot air duct on the side of the hot air furnace is fully open; (2) Cooling is achieved using the maximum design flow rate; (3) The temperature of the hot air duct at the end of the hot air duct on the hot air stove side is <200℃. After the hot air valve is inserted with a blind plate, the end vent valve is reduced so that the cooling rate V1 of the hot air duct on the hot air stove side is less than the cooling rate V2 of the hot air duct on the blast furnace side, i.e., V1 < V2. (4) When the temperature t1 at the end of the hot blast pipe on the hot blast stove side is close to the temperature t2 at the outlet of the backflow valve on the hot blast pipe on the blast furnace side, i.e., t1=t2; (5) Increase the opening of the vent valve at the end of the hot air pipe on the hot air stove side so that the cooling rate V1 of the hot air pipe on the hot air stove side is close to the cooling rate V2 of the hot air pipe on the blast furnace side, i.e., V1=V2. Step 5: Cooling complete, details are as follows: (1) Backflow outlet temperature t2, combustion air temperature t0, t2 < (t0 + 25℃), fully open the diffuser valve, open the manholes in other parts of the hot air duct, effectively isolate the connecting pipe, and water seal the mixing duct; (2) The temperature at the backflow outlet t2 is less than 50℃. Due to the chimney effect of the backflow valve and the vent pipe, the pipeline is naturally ventilated, and personnel enter the pipeline to work. If the backflow valve is not on the surrounding pipe, a vent pipe can be connected to the short pipe of the air supply branch of the remote cooling source. The total vent area is close to that of the backflow valve. During the cooling period, the backflow valve is kept closed, and after the cooling is completed, the backflow valve is opened to act as a chimney.

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