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Ferroalloy furnace:how to solve the problem of rising temperature and redness of the furnace bottom

Views:6     Author:Site Editor     Publish Time: 2020-11-20      Origin:Site

Traditional ferroalloy submerged arc furnaces generally use pre-baked carbon blocks and wide and coarse-slit masonry linings, and adjust the primary current to control the electrode insertion depth in the furnace (that is, the electric furnace load). Take the main equipment of a company’s 2*25.5MVA submerged arc furnace as an example. Its lining adopts semi-graphite charcoal brick fine-seam masonry technology, but the redness of the furnace bottom appeared three months after the furnace was opened. Through fine furnace anatomy and cause analysis, find out the solution to the problem.

1# furnace was sent to the electric oven. After 6 days, the initial charge was put into operation. The first furnace iron was produced on the 7th day. With the continuous increase of furnace temperature, the secondary voltage was gradually increased on the 12th day, and the second furnace started to transmit electricity.

On the 43rd day of the operation of No. 1 furnace, a hard object was found to block the drainage of the steel braze during the tapping process, which improved after replacing the tap hole. There was more slag and less iron when the operation reached the 83rd day, and the phenomenon of iron deficiency often appeared. By the 90th day, the bottom temperature of the furnace was over 600 degrees Celsius, and the bottom temperature reached 1050℃ on the 95th day, and the bottom steel plate was close to Redness in five places near the center line.

A similar situation occurred in furnace No. 2 after that, the furnace bottom temperature rose from 425°C to above 550°C and the furnace had to be shut down.

Cause Analysis

When the bottom of the ferroalloy submerged arc furnace is red or worn, the main reasons are the lining material, the quality of the furnace, the daily operation and the furnace structure.

The smelting zone of the silico-manganese alloy electric furnace contains gas at the ends of the three electrodes to melt and gasify the surrounding solid materials to form a cavity-shaped crucible. The temperature in the cavity is as high as 2000-3000℃, and the hot surface of the crucible wall is about 1800-2000℃. The cold surface is about 1500~1800℃, and the solid material outside the crucible reaches 1500~1700℃ on the inner wall of the furnace lining.

The previously used fine-seam masonry technology, the refractory materials used when building the furnace are N42 clay bricks, L75 high alumina bricks, pre-baked (semi-graphite) carbon bricks, anhydrous carbon mortar, phosphate slurry, hard high alumina fine powder , Low-temperature coarse seam electrode paste, semi-graphite-silicon carbide brick. When the furnace was built, the actual thickness of these materials were 0.6345m for clay bricks, 0.335m for high alumina bricks, 1.206m for semi-graphite carbon bricks, 0.02m for asbestos fiberboard for heat insulation, and 0.03m for furnace shell steel plate.

Then we analyzed the thermal conductivity and interface temperature of the lining material.

The primary problem of a furnace wear accident in a ferroalloy electric furnace is the refractory lining in the furnace. The load softening point of high alumina bricks generally does not exceed 1200℃. If the working environment temperature exceeds 1200, it is necessary to add a layer of light carbon bricks to the contact surface of carbon bricks and high alumina bricks to reduce the temperature of the contact surface to 1200 Below ℃. At the same time, the masonry quality of the furnace lining is also one of the factors that affect the life. Various refractory materials will have different thermal expansion. It is necessary to set up an elastic buffer belt and the thickness should be appropriate. If it is too thin, it will not be able to compensate for the compliance of the refractory. If it is too thick, the furnace shell will not restrain the expansion of the refractory material and will easily expand the brick gap.

The baking of the furnace lining must follow the heating curve. The furnace lining is divided into two parts: the basic layer and the heat storage layer according to the thermal conductivity. The furnace curve should be formulated according to the characteristics of the lining, refractory material, thickness, construction location and baking method.

Other factors that affect the life of the furnace lining are the operation of the combined controller electric furnace, arc characteristics, current distribution, etc.

Analysis of furnace cleaning and conclusion

After the furnace was shut down for a week, the No. 1 furnace was cleaned, and a coke layer appeared at a position about 1 meter 3 from the furnace mouth, and its thickness was 60% higher than the normal value; 2.4 meters from the furnace mouth, the three-phase electrode area The charcoal brick body appears because the charcoal brick has risen, and the normal furnace depth is 3.6 meters.

The reason for the redness of the bottom of the furnace: the temperature stress of the brick lining occurred during the heating process, which caused bulging top cracking and iron penetration. The carbon brick triangle area is released by the concentrated heat to form "bulging".

The traditional wide-slit furnace construction technology can guarantee the lining service life of more than one year. In order to obtain a longer overall lining life, cold ramming can be used instead of pre-baked carbon block wide-slit masonry.

If the self-baking carbon block is made with fine seams, at least 3 years of furnace lining life can be guaranteed. The key to this method is the design and selection of furnace lining materials.

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