Selection of Ceramic Fibers in Each Stage of Carbon Baking Kiln
The improved new carbon baking process system is further simplified. The baking kiln is changed from underground to above-ground type, and the heavy refractory lining is replaced with lightweight lining. Refractory fibers are mostly adopted as the lining materials for carbon baking kilns.
1. Low-temperature preheating stage
The carbon products are heated from room temperature to 200℃, and the maximum temperature shall not exceed 350℃.
2. Medium-temperature drastic change stage (Pyrolysis and Polycondensation Reaction)
The temperature of carbon products is between 200～700℃, and the internal temperature of the kiln is about 350～850℃. With the increase of temperature, the decomposition rate of coal tar pitch accelerates. At this stage, the binder basically completes carbonization and a large amount of volatile matter is discharged.
3. High-temperature carbonization stage (Graphitization stage)
At this stage, the temperature of carbon products ranges from 700℃ to 1000℃, and the internal temperature of the kiln is about 850～1300℃. When the temperature of baked products rises above 700℃, the decomposition and volatilization rate of coal tar pitch slows down, and the carbonization process of the binder is basically completed.
The firing temperature in the third stage is adjusted according to the type of sintered carbon material used.For carbon blocks, since they do not need to go through the graphitization process, the firing temperature only needs to reach 1300℃.For carbon electrodes that require graphitization treatment, the sintering temperature is relatively higher, at about 1200℃.For carbon resistors which require high resistivity, the firing temperature is relatively low, only reaching 1000℃.
Classification of Refractory Fiber Materials for Different Temperature Zones of Carbon Baking Kiln
(1) Low-temperature preheating stage: Ordinary ceramic fiber material.(2) Medium-temperature drastic change stage (pyrolysis and polycondensation reaction): Standard ceramic fiber material.(3) High-temperature carbonization stage (graphitization stage): Zirconia-containing ceramic fiber material or composite polycrystalline refractory fiber material.
Advantages of adopting ceramic fiber materials for thermal insulation lining of carbon baking kiln are mainly reflected in the following aspects:
(1) Light weight and low heat absorption rate, being 1/20 of heavy refractory bricks and 1/10 of lightweight refractory bricks.
(2) Extremely low thermal conductivity brings remarkable energy-saving effect.
(3) Simple construction without drying and maintenance required.
(4) Excellent resistance to rapid cooling and rapid heating.
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