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Insulation of Firing Tunnel Kiln
Insulation of the tunnel kiln is a crucial aspect of kiln construction, directly impacting its lifespan and therefore requiring utmost care. Tunnel kiln insulation primarily includes kiln wall insulation, kiln roof insulation, and pipe insulation. Among these, the kiln wall and kiln body insulation are the most critical. Poor roof insulation leads to significant heat loss through the insulation layer, preventing efficient utilization by the kiln and waste heat pipes, directly affecting product quality. Similarly, suboptimal roof insulation causes the temperature of lifting components and ordinary steel components to rise continuously under long-term loads, exacerbating corrosion and softening of the lifting hooks and steel structures, directly jeopardizing kiln safety. Likewise, the quality of kiln wall insulation and heat insulation directly impacts product quality and the kiln’s lifespan.
Insulation engineering is a meticulous task. To ensure quality at every stage of construction, strict attention to detail and frequent inspections are essential. Based on my experience, I will discuss construction methods for the kiln insulation of kiln walls and roof for your reference.
Kiln Wall Insulation
The kiln insulation work for kiln walls focuses on the area above the probe bricks. The construction procedure can be divided into two steps: laying insulating bricks and laying insulating felt.
Laying Insulating Bricks. The height, thickness, and total length of the insulating wall must conform to the design drawings. The laying method is the same as for clay refractory bricks, using refractory mortar. The masonry should be fully filled with mortar, with a mortar fullness of over 95%. When laying bricks, it is strictly forbidden to use a hammer to strike the bricks; instead, use a rubber mallet to gently tap the surface of the bricks to align them. It is strictly forbidden to cut bricks directly with a trowel; if processing is necessary, use a cutting machine to cut them neatly. To prevent the insulation bricks from directly contacting the open flame inside the kiln, the area around the observation hole should be constructed with refractory bricks. The overlapping bricks between the insulation wall and the insulation cotton, as well as the outer wall, should also be constructed with clay refractory bricks.
Insulation Cotton Laying. The ordered dimensions of the insulation cotton boards must meet both design requirements and the practical needs for easy installation. During installation, ensure that the cotton boards are in close contact, minimizing gaps at the joints. At the joints, it is best to use a high-temperature adhesive to ensure a tight seal and maintain the insulation effect.
Furthermore, cotton boards requiring processing should be neatly cut with a knife; never tear them by hand.
The construction procedure for kiln roof insulation is as follows: filling the V-shaped seams of the roof slab with high-alumina blankets or high-alumina cotton; applying high-temperature adhesive to the seams and then laying high-alumina blankets; laying the insulation blankets; applying sealant to the seams; spraying insulation coating; and installing and insulating the coal feeding pipes.
Filling the V-shaped seams of the roof slab with cotton. The V-shaped seams must be filled with high-alumina refractory cotton. During construction, pay attention to the following: the refractory cotton filling must be full and tight, and it should be filled in layers, with refractory adhesive applied afterward. For seams between boards that are very small or have no gaps, slightly open them to create a gap of about 5mm at the bottom, then fill with cotton. For seams that are too large, adjust them slightly to bring them closer together.
At the joints between the longitudinal and transverse seams of the ceiling panels, apply high-temperature adhesive. Then, fully lay and compact a 2-3cm thick, 30cm wide high-temperature high-alumina blanket to ensure complete integration between the seams.
Insulation Cotton Laying. The bottom layer of the insulation cotton should be made of a high-temperature-resistant aluminum silicate fiber needle-punched blanket. The surface layer can be aluminum silicate fiber blanket. To enhance its effectiveness, the cotton should be laid in a staggered pattern, both longitudinally and transversely. When laying the bottom layer, pay attention to the following: the area around the heat-resistant hoist and heat-resistant hanging parts must be compacted, and the joints should be staggered. The technical requirements for laying the insulation cotton can be summarized as: staggered laying, layered compaction, uniform spraying, and a smooth surface.
After the insulation cotton is laid, if the heat-resistant hanging parts are completely submerged in the cotton, a small amount of cotton should be removed from around the hanging parts to expose the top of the heat-resistant hook and the ordinary hanging rod to the air for natural heat dissipation.
Apply a sealant to all joints and gaps on the surface of the insulation cotton, smoothing it out to ensure a complete seal.
Using an insulating coating can bond the surface of the insulation cotton together, enhancing its insulation effect. The insulating coating is latex-like; after mixing with water, it is sprayed onto the surface of the cotton, maintaining a moderate consistency.
When installing the coal feeding pipe, its weight should not be directly applied to the refractory concrete slab. Use shims to slightly lift the pipe, allowing its weight to fall on the top slab, leaving a gap of approximately 10mm between its bottom and the concrete slab. After lifting, ensure the pipe’s position is fixed and does not move laterally. The pipe above the insulation cotton should be wrapped and securely bound with a high-temperature resistant aluminum silicate fiber needle-punched blanket. The portion embedded in the insulation cotton should be tightly packed around the pipe wall in layers of high-alumina cotton to prevent the high-temperature gas flow from the combustion chamber from escaping and causing crossfire. Finally, thoroughly pack the bottom and surrounding walls of the coal feeding pipe with high-alumina cotton from bottom to top to ensure a tight seal. Kiln insulation is the lifeblood of a kiln. Every small detail in the operation must be handled with utmost care and meticulous attention to detail to ensure the kiln’s lifespan.
How to Improve the Thermal Insulation Capacity of Insulating Bricks?
Heat transfer in insulating refractory materials such as insulating bricks involves two parts: heat transfer through the solid phase and heat transfer through the gas phase. At low temperatures, heat transfer is mainly through the solid phase. At high temperatures, heat transfer through the gas phase becomes crucial. To reduce the thermal conductivity of the solid phase, it is necessary to select a solid phase with low thermal conductivity and to reduce the contact area between solid particles. For example, the more complex the crystal structure, the more phonons are scattered, and the lower the thermal conductivity. Polycrystalline structures have relatively poor structural integrity and regularity, and coupled with the influence of grain boundary impurities and distortions, their thermal conductivity is lower than that of single crystals. Furthermore, pores can scatter phonons. Generally, increasing porosity can reduce thermal conductivity. Additionally, using spherical microparticles, so that heat can only be transferred through the tiny contact area between particles, can also significantly reduce the thermal conductivity of the solid. Therefore, the ways to improve the kiln insulation capacity of insulating bricks are:
① Increase porosity;
② Reduce pore size;
③ Increase the complexity of the microstructure at each stage;
④ Reduce solid-phase contact;
⑤ Add light-blocking substances to hinder radiative heat transfer.
