Silica bricks have good high temperature performance and instability at low temperature (below 600℃) during hot blast furnace cooling operation. Once the brick hot blast furnace is put into production, it cannot be cooled below 600℃, otherwise the masonry will collapse and collapse due to the sudden contraction of silica refractory bricks. At present, silica firebrick hot blast furnaces can perform better cooling operations. Due to the different furnace types and furnace sizes of silica firebrick hot blast furnaces in various steel enterprises, the cooling time of silica refractory brick hot blast furnaces has been successfully reduced from the initial 80 to 90 days to about 20 days. Although silica fire brick hot blast furnaces can be cooled by natural slow cooling, steel enterprises generally adopt the method of rapid cooling due to the construction period.
1. Cooling operation of silica brick hot blast furnace
(1) When the 3# hot blast furnace starts to cool down, the mixed air valve, cut-off valve and mixed air regulating valve are all closed. The 3# hot blast furnace is connected in parallel with the other 3 hot blast furnaces to supply air. The 3# hot blast furnace is used as mixed air and the 3# cold air valve is used as a mixed air regulating valve.
(2) To ensure the stability of the blast furnace air temperature, when the opening of the cold air valve of the 3# hot blast furnace reaches 80% of the valve plate stroke, the cold air valve of the 3# hot blast furnace is fully closed, and the pressure cut-off valve and pressure regulating valve are fully opened to continue to supply air. At this time, the mixed air valve is used for air temperature regulation; when another hot blast furnace with a higher top temperature is supplying air, the hot air valve and cold air valve of the 3# hot blast furnace are opened again, and the pressure valve is closed for parallel supply of air. At this time, the mixed air valve is closed, and the air supply is circulated in this way; the heat stored in the 3# hot blast furnace is taken out as much as possible, and the flue temperature is reduced to create conditions for the subsequent combustion air cooling furnace.
(3) When the temperature of the 3# hot blast furnace cannot guarantee the use of mixed air (generally the temperature is below 900℃), the 3# hot blast furnace is converted into a combustion-supporting air cooling furnace and the mixed air valve is opened.
(4) Operation of the air supply cooling furnace to the combustion-supporting air cooling furnace: put the 3# hot blast furnace in the stewing state, fully open the 1# and 2# flue valves, fully open the air valve, open the air regulating valve appropriately, use the combustion-supporting air cooling furnace, accurately control the opening of the air regulating valve according to the cooling furnace curve, and at the same time ensure the combustion-supporting air volume required for the burning of other hot blast furnaces (according to the burning air volume, adjust the air volume used for the cooling furnace at any time, mainly for burning).
(5) Control of the combustion-supporting air cooling furnace speed: above 600℃, control at 5~10℃/h, 600~300℃, control at 3~4℃/h, below 300℃, control at 2~3℃/h.
① The top temperature drops from 920℃ to 600℃, the cooling rate is 40℃/shift, and it takes 8 shifts.
②When the top temperature drops to 600℃, keep the temperature constant for 10 shifts.
③600～300℃ cooling time for 12 shifts.
④300℃ constant temperature for 12 shifts.
⑤300℃ down to 60℃ cooling time for 16 shifts.
(6) When the top temperature reaches 60℃, stop the combustion air cooling furnace, close the flue valve, air valve, and air regulating valve.
(7) Open the upper and lower manholes and cool the furnace by natural ventilation (before opening the manhole, perform the pressure holding test again and check the leakage rate of the 3# hot blast furnace to ensure that the leakage is the lowest before drilling the manhole.
2. Precautions for cooling the silica brick hot blast furnace
(1) When using the combustion-supporting air to cool the furnace, if there is a deviation from the cooling curve, such as the influence of the hot blast furnace burning, adjust the air volume according to the top temperature drop speed and control it as stable as possible during the constant temperature stage.
(2) When the combustion-supporting air volume cannot guarantee the air volume used for cooling the furnace, first ensure the air volume required for burning the furnace, appropriately extend the cooling time, and change the 3# hot blast furnace to a natural cooling furnace.
(3) When the temperature of the hot blast furnace flue reaches 400℃, stop the combustion air cooling furnace. After the furnace is simmered, open the lower cold air branch manhole, open the upper manhole, and use the axial flow fan to blow back to lower the flue temperature. When the flue temperature drops below 100℃, close the upper and lower manholes, and continue to cool the furnace with combustion air. Repeat this cycle. When the top temperature is lower than 60℃, open the upper and lower manholes and switch to natural cooling until the furnace is completely cooled.
