Chlorination Furnace

The rate of degradation of the refractory lining in a chlorination furnace is primarily governed by the rate of carbothermal reduction occurring within the Al₂O₃-SiO₂ refractory material. The degradation process unfolds as follows:

(1) Within the interior of the brick, external CO gas diffuses inward through the material’s pores. It undergoes a carbothermal reduction reaction with SiO₂, generating SiO and CO₂ gases, which then diffuse outward. Upon reaching the brick’s surface, the SiO gas reacts with the surface carbon (C) and chlorine (Cl₂) to form SiCl₄ gas, which subsequently diffuses into the furnace chamber. Meanwhile, the carbothermal reduction reaction between CO gas and SiO₂ causes the material’s structure to loosen, thereby creating additional channels for external CO to penetrate deeper into the brick. This cycle repeats until the internal CO pressure within the brick drops to a level insufficient to sustain the carbothermal reduction reaction with SiO₂, or until the reaction temperature is no longer met.

(2) At the surface of the brick, SiO₂ reacts directly with carbon (C) via carbothermal reduction to produce SiO and CO. The resulting SiO then reacts with carbon (C) and chlorine (Cl₂) to form SiCl₄, which diffuses directly into the furnace chamber.

(3) In the presence of external TiO₂ inclusions (typically as fine particles), SiCl₄ gas—formed through the carbothermal reduction of SiO₂—continuously penetrates the brick’s interior via the aforementioned channels. This leads to the formation of an Al₂O₃-SiO₂-TiO₂ liquid phase (though no documented data exists regarding the specific influence of TiCl₄ on this phase diagram), thereby accelerating the structural disintegration of the material and resulting in a drastic decline in its abrasion resistance.

(4) Whether located within the interior or on the surface of the brick, the mullite particles generally retain their original morphology. This further substantiates the conclusion that the material’s degradation rate is controlled by the rate of carbothermal reduction, rather than by the rate of chlorination reactions (despite the fact that, from a thermodynamic perspective, mullite is the most susceptible component to chlorination).