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Working Environment And Application Of Magnesia-Chromium Brick In Flash Furnace Reaction Tower
Jan 22, 2019

The flash furnace is mainly composed of a reaction tower, a sedimentation tank and a rising flue. The reaction tower is the most important part in the flash furnace, and the gas-solid two-phase containing the concentrate powder is injected at a high speed and is in the upper part of the reaction tower. The chemical reaction is carried out and melted into a melt stream moving at a high speed downward, so that the refractory material in the reaction tower is subjected to severe high-speed erosion, erosion, wear and the like damage mechanism.


The reaction tower is cylindrical and is made of chrome-magnesia bricks, and is welded with steel plates except for the top of the tower. The diameter and height of the reaction tower are determined according to the furnace gas velocity in the reaction tower and the passage time of the furnace gas, and the furnace gas velocity in the reaction tower is generally 3 m/s. The higher the hot air temperature, the greater the concentration of oxygen in the air supply and the faster the reaction rate. The use of high temperature oxygen-enriched hot air can shorten the reaction time and reduce the height of the reaction tower. The height is lowered, the reaction time can be met, the heat loss of the reaction tower is reduced, the fuel is saved, and the lining is damaged to a certain extent by avoiding too much oil burning at the top of the tower.

The upper part of the reaction tower has a higher partial pressure of oxygen and a lower temperature, forming a protective layer of magnetic iron oxide on the wall of the tower. However, in the lower part of the reaction tower, the lining wears quickly due to the local high temperature and the flow of the molten reaction product along the surface of the lining. Therefore, the tower wall of 1.5~2m or less at the top of the reaction tower is made of electroformed chrome-magnesia brick, and the outside of the furnace body is intensively cooled, and several copper water jackets are arranged.

The electroformed chrome-magnesia brick is formed by melting a certain amount of refractory material into an electric furnace, and the main components are MgO, Cr2O3, Al2O3, etc., which have good high-temperature corrosion resistance.

The lower the contact surface temperature between the refractory lining and the melt, the slower the damage to the refractory brick. When the temperature of the contact surface is lower than a certain critical point, the melt condenses and the wear of the lining is greatly reduced, which is the reason why the brick lining is protected by water cooling. Since the outer surface of the lining is cooled by water to keep the temperature constant, when the brick lining wears, the temperature gradient at the wear point increases, and the heat conduction is enhanced. In the case where the thickness of the furnace wall is constant, the local heat loss becomes large, so that the melt having a low thermal conductivity is less than the heat transfer to the damaged place, and the contact surface temperature between the brick and the brick is lowered. If this temperature is lower than the temperature at which the magnetic iron oxide in the slag is supersaturated, a layer of dense slag having a protective effect is formed on the surface of the brick to stop the wear. The production practice proves that the upper wall of the reaction tower is corroded when it is just put into production, but when it is corroded to a certain extent, it is about half of the original brick thickness and remains stable, and no longer continues to corrode.

The oxidation reaction in the reaction column is carried out sufficiently, that is, when high-grade matte is produced, the melting point of the oxidized charge rises above the inner surface temperature of the lining, and a dense layer is formed on the wall of the reaction tower to reduce heat loss. When the low grade matte is smelted and the auxiliary tower is used to maintain the high temperature of the reaction tower, the lower furnace wall is susceptible to continuous scouring of the superheated molten product. The change of the charge and gas phase temperature in the reaction column along the height of the reaction column is shown in Fig. 1.

The tower body cooling has two kinds of stereo cooling and spray cooling. The three-dimensional cooling effect is better, but the structure is more complicated and the cost is higher; the spray cooling structure is simple and the cost is low, but due to the high-grade ice copper produced, the slag contains a high magnet, which makes the sedimentation tank difficult to operate.

The connection between the reaction tower and the ascending flue and the sedimentation tank is the two most vulnerable parts of the flash furnace. The joints are perpendicular to each other and are easily washed by high temperature airflow. In order to strengthen the structure of the joints, the finned water-cooled copper tubes are used as the skeleton. According to the thermal load of the copper tubes, the copper tubes are arranged at appropriate intervals, and the intermediate and surrounding fillings are filled with amorphous refractories to form a solid structure. The figure is shown in Figure 2.

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