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After the refractory lining of the furnace has been completed following a long period of operation, the furnace shell must be inspected, corrected, and properly maintained. The key requirements include: (1) ensuring the shape and geometry of the furnace shell are accurate; (2) maintaining a minimal slope in the centerline of the shell and keeping the concentricity of the upper and lower openings consistent; (3) aligning the center of the furnace shell with the flue center and flue mouth; (4) calibrating the centerline of each spray hole and checking for deformation in the top iron shell; (5) performing internal grit blasting of the furnace shell to prepare it for further work.
The construction of the furnace wall and bottom must follow strict guidelines. The horizontal joints of the inner and outer linings should not be aligned, and vertical seams between the upper and lower layers of bricks must also be staggered, both inside and outside, as well as above and below. For the furnace bottom, the height and slope on both sides must be carefully controlled. The gap between the corundum bricks of the furnace wall and the hearth is filled with high-aluminum castable material, as shown in the bottom structure diagram.
The furnace, flue mouth, and throat structures are constructed using corundum-mullite fire mud along the inner diameter of the furnace shell. A layer of mullite lightweight bricks (half blocks [email protected]/64) is used to build up the structure, aiming to stagger the horizontal brick seams of the mullite stone bonded corundum bricks. After that, four more lightweight bricks are added. The internal diameter after this layer of light brickwork is 2860mm.
Inside the lightweight bricks, a fired mud is used to lay corundum bricks ([email protected]@61/67). Before placing the corundum bricks, a 10 mm asbestos slab is laid underneath. A good brick, specifically a knife-type corundum brick, is also installed. Every 10 blocks of corundum bricks, a 2 mm thick chrome refractory fiber paper is placed as a circumferential expansion joint. It is essential to ensure that the two types of bricks do not overlap in either their brick seams or vertical seams. During the installation of the corundum bricks, the center point and ellipticity of the furnace body must be checked and corrected if necessary. The internal diameter of the corundum brickwork is 2610mm.
The furnace bottom is shaped into four steps using lightweight bricks. The heights vary, with 315 mm across, 250 mm, 190 mm, and 125 mm below the hole. A moisture-proof paper is laid over the light bricks before applying corundum castable. The inclined surface, which tapers from 375 mm on one side to 125 mm below the manhole, is carefully built. Once the casting material has solidified, 12N1, 12N2, and 12N3 corundum bricks are laid on top, following the specified paving method. Any gaps between the bottomed corundum bricks (12N) and the furnace wall corundum bricks (1 brick) must not be filled with refractory bricks but instead compacted with corundum-based castables.
For the flue stacking bricks, special-shaped corundum bricks are used, and they must be constructed according to the provided specifications. The connection between the flue duct bricks and the horizontal flue bricks must be sealed to prevent any leakage. The construction begins on the fourth floor, where the flue mouth centerline is calibrated, and a lightweight brick with a backing (reserving the flue mouth) is erected. These are placed on both sides of the centerline, including 21, 20, and 19 flue tiles.
Next, a 1-brick wall is built from both sides on the fifth floor. On the sixth floor, 22 and 23 flue bricks are placed near each other, alongside 19 and 18 flue bricks. The height and center angle of these bricks are checked before building the sixth-floor furnace wall tile. On the seventh floor, 23 and 18 flue bricks are paired with 24 and 17 bricks, while the eighth floor uses 24 and 17 bricks with 25 and 16 bricks.
On the eighth-floor plane, the 25th and 16th flue bricks align with the horizontal centerline of the flue mouth. The roundness and center point of the flue mouth must be corrected, and the flue mouth molds are supported to prepare the upper brick layer. From the ninth to the twelfth floors, 16 and 25 bricks are built, followed by 17 and 24 flue bricks, 18 and 23 flue bricks, and finally 19, 20, 21, and 22 flue duct bricks. The brick lengths correspond to the lower half-circle.
Support brackets for the bricks are placed on the throat and furnace wall, ensuring proper alignment and no deviation from the calibration center. A lightweight brick with backing is built, followed by the 13th floor’s 6-throat bottom brick, the 14th floor’s 7A throat middle brick, and the 15th floor’s 7 bricks. Above the 7th throat corundum brick, 1-brick walls are constructed from the 16th to the 20th floors, following the same method as before.
On the 21st floor, the corundum brick is a processed brick, with the upper half cut off. The cut must leave a 40 mm expansion joint under the arch brick, and the cut brick must also be sloped about 25 mm away from the arch brick’s slope. Finally, corner bricks and roof bricks are installed, with asbestos panels (230 mm wide, 10 mm thick) placed inside the furnace shell, followed by [email protected] @ 20 mm lightweight bricks. A 40 mm chromium-containing fiber mat is laid on top of the corundum brick, then a 25 mm chrome fiber mat on the slope, and finally eight corundum corner bricks are installed. While laying the bricks, the center (radius) and internal diameter of the furnace are continuously checked.