The lining structure of ceramic fiber used in petroleum refining and chemical heating furnace is mainly composed of ceramic fiber module and ceramic fiber blanket. The formation process of the composite lining structure is as follows:
1. Clean and rust-proof the steel plate of the furnace wall;
2. Carry out defense line according to design requirements and determine the position of anchor nails;
3. Install the defense line position and weld anchor nails;
4. Lay ceramic fiber blanket as backing insulation blanket and level it;
The high-aluminum ceramic fiber module and zirconium-containing ceramic fiber commonly used in the lining of the heating furnace of the petroleum refining and chemical equipment are both glassy ceramic fibers, which will shrink under long-term high temperature. This is determined by the properties of the ceramic fiber material itself. Microscopically, it is caused by the crystallization (crystallization) and grain growth of glassy ceramic fibers at high temperature. Glass is formed by supercooling (rapid cooling) of the melt. This state is not the lowest energy state. It has higher internal energy than crystals and is a metastable state.
From a thermodynamic point of view, it has a tendency to spontaneously transform into a low-energy state, and the atoms can automatically rearrange, that is, it has a tendency to crystallize and transform into a crystalline state.
From a kinetic point of view, due to the high viscosity of glassy materials at room temperature, the diffusion and rearrangement speed of internal atoms is low, and the speed of transformation from glassy state to crystalline state is very slow, which makes it have great relative stability at room temperature and is also a stable state.
Glassy ceramic fiber has the characteristics of short-range order and long-range disorder. With the increase of temperature, the viscosity of the fiber decreases, the atomic movement intensifies, the diffusion and regular arrangement speed of atoms increase, and the long-range disorder will transform into an ordered arrangement, that is, crystallization. The ordered regular rows are reduced, resulting in the volume shrinkage of a single ceramic fiber rod. Under the action of high temperature for a long time, the formed particles will grow, and the surface of the ceramic fiber rod will appear uneven, that is, the diameter will shrink. Continuous diameter shrinkage will lead to a shortening of the length of the ceramic fiber module, resulting in overall shrinkage.
After macroscopic shrinkage occurs, the ceramic fiber furnace lining will crack and gaps will appear under the action of a long-term flame atmosphere. After the gap appears, the flame and airflow take the opportunity to enter the gap, so that the ceramic fibers on both sides of the gap are directly in contact with the flame and airflow to work. As time goes by, the ceramic fibers on the contact surface shrink and expand perpendicular to the contact surface, causing the gap to become larger and larger. In this way, more and more flame airflow will enter, and it will continue to spread and develop around. After contacting the anchor nail, the anchor nail will oxidize and corrode under the action of long-term high-temperature airflow, and eventually break, causing the ceramic fiber module to fall off. At the same time, the ceramic fiber backing also shrinks and powders, and then breaks and falls off, eventually causing the entire ceramic fiber furnace lining to be damaged and fall off.
