The tapping ditch of a blast furnace includes several parts such as the main ditch, iron ditch, and slag ditch. The main tapping ditch of a large blast furnace is about 20 meters long, about 2.5 meters wide and deep, with a certain slope. It is roughly divided into two sections: the molten iron impact zone (flow zone) and the slag-iron separation zone. A slag dam is installed in the slag-iron separation zone to prevent slag from entering the tapping ditch. In the molten iron impact zone of the main tapping ditch, molten iron with slag rushes in at a speed of up to 8~12m/s, and then the flow rate slows down, the slag floats up, and the molten iron sinks. After slag-iron separation, the slag is discharged through the slag ditch, and the molten iron flows into the torpedo tank car through the iron ditch. When pre-treating molten iron in the tapping ditch, the pre-treating agent can be added to the molten iron at different locations. The pre-treating agent added will corrode the refractory material, making the service condition of the refractory material lining the tapping ditch worse.
The working state of the iron-outlet trough of a large blast furnace during iron-out and shutdown clearly shows the upper and lower slag lines and molten iron lines on the inner lining of the main iron-outlet trough, which causes severe local erosion in this area.
The damage of the slag line is caused by multiple processes:
(1) oxidation of SiC on the surface;
(2) slag infiltrates the surface to form a slag film;
(3) slag infiltration;
(4) oxidation of SiC in the slag infiltration area;
(5) melting of SiO2 and Al2O3 in the SiC oxidation area.
The damage of the iron line is also caused by multiple processes, namely:
(1) During the infiltration process, the attached slag on the surface of the refractory material falls off, forming a slag film at the interface between the refractory material and the molten iron, and there is a concentration gradient in this slag film, which causes the material to produce a local surface tension gradient;
(2) The carbon in the molten iron and slag film reacts with SiO2 to produce CO gas, causing a boiling effect, which further activates the movement of the slag film and accelerates the melting of the refractory material.
When the blast furnace is tapping iron, the speed of pouring out the molten iron mixed with slag is very fast, which makes the tapping channel bear great mechanical erosion and wear. In addition, cracks may appear in the tapping channel lining during drying and baking after construction.
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