Construction Practice of Refractory Castable Liner for Heating Furnace
In the application of monolithic refractory castables in heating furnaces, rational material selection, optimized lining structure, and the adoption of scientific construction techniques are crucial for extending the service life of the heating furnace and ensuring its safe operation.
The principle for selecting lining materials should be determined based on the type of heating furnace and the operating temperature conditions. Simultaneously, the combined use of high-temperature and low-temperature refractories should be considered to reduce project costs. While the design of the lining structure shares some common factors, significant differences arise depending on the type of material. The determination of construction techniques varies depending on the type of refractory material, the project objective, and the actual site conditions. Adopting scientific construction techniques can ensure project quality.
Optimization of Local Furnace Wall Construction
The general principle for furnace wall design is to construct a composite furnace wall using lightweight and heavy refractory materials, with thicknesses of 40–200 mm and 230–300 mm, respectively. Furnace wall structure and anchoring bricks.
The furnace lining consists of refractory fiber felt, calcium silicate board (or lightweight insulating bricks), and low-cement refractory castable. The refractory fiber felt is placed close to the furnace shell or between the lightweight bricks and the low-cement refractory castable lining. The thick-walled steel pipes used for fixing the reinforcing bars must be securely welded to the furnace shell steel plate. The length of the anchoring bricks should match the overall thickness of the furnace wall to meet construction requirements. The anchoring bricks are connected to the furnace shell via reinforcing bars and are movable; the distance between the cold end face of the anchoring brick and the furnace shell should be ≥40 mm. This allows for vertical movement with the rise and fall of the furnace wall, as well as horizontal movement with its expansion and contraction, ensuring the stability and service life of the furnace wall.
The anchor bricks in the low-cement refractory castable lining must be arranged in a straight line, i.e., horizontally and vertically, to allow the vibrator to move through the material during construction. Specifically, the arrangement requirements are as follows: starting from the working surface of the furnace bottom, install a row of anchor bricks at approximately 500 mm in height, followed by a row every 500–600 mm. The minimum distance between the top row of anchor bricks and the working surface of the furnace top should be 350–450 mm. The horizontal center-to-center spacing of the anchor bricks should also be 500–600 mm. When encountering holes, the distance between the working surface of the hole and the nearest surface of the anchor brick should be greater than 150 mm, and the area around the hole should be filled with low-cement refractory castable. In other words, the refractory fiber felt and insulation material must not be in direct contact with the high-temperature flame.
Optimization of Local Construction Process for Furnace Roof
The furnace roof lining material is basically the same as the furnace wall material, consisting of a combination of lightweight and heavyweight refractory materials with thicknesses of 50–150 mm and 200–300 mm, respectively. A partial construction drawing of the furnace roof using suspended bricks is provided. The suspended bricks are generally arranged in a straight line with a center-to-center distance of 300–350 mm. The lower limit of the center-to-center distance is used for suspended bricks in high-temperature areas, and the upper limit is used for lower areas, thus reducing heat loss from the top surface and surrounding area of the furnace roof anchor bricks. When encountering holes, a staggered arrangement is permissible. The center line of the suspended bricks around the furnace roof should maintain a certain distance from the working surface of the furnace wall.
The furnace roof anchor bricks are load-bearing components. There should be no cracks at the neck of the anchor brick; the dimensions at this point are generally 90 mm × (90–125) mm × 125 mm. The anchor section is serrated or wavy and embedded in the refractory material. The weight of a single suspended anchor brick is generally 9–14 kg.
To enhance radiative heat transfer and reduce heat loss from the furnace roof, a non-standard mold was used for integral casting, directly forming a high-temperature radiant at the top of the cast furnace roof. This method solved the problem of detachment of the high-temperature radiant when suspending it through holes in the pre-cast furnace roof. Simultaneously, the thickness of the heavy castable was optimized from 230 mm to 200 mm, and the insulation layer thickness was increased to further reduce heat loss from the furnace roof.
When using monolithic refractories for furnace construction, the furnace roof is generally flat, which is beneficial for design and construction. For new furnace designs, regardless of their complexity, monolithic refractories can be used. To improve the service life of the furnace roof, an anchor brick suspension system is used, allowing the furnace roof to be in a free state, separated from the low-cement castable of the furnace wall by compressed fiber felt. When the furnace roof moves up or down, it is buffered by horizontal expansion joints; the size of these joints depends on factors such as the height of the furnace wall, the degree of roof descent, and the operating temperature. Under no circumstances should the furnace roof directly contact the upper and side refractory materials of the furnace wall. In addition, the hanging anchor bricks around the furnace top should be away from the upper surface of the furnace wall, and the distance between their center line and the working surface of the furnace wall should generally be >200 mm.
Comments