The electric furnace is the main equipment for the production of yellow phosphorus. The qualified phosphate rock, silica, and coke are made into a mixed furnace charge in a certain proportion and added to the electric furnace. The reduction reaction is carried out at 1300~1500℃, and the phosphorus-containing furnace gas produced is dust-removed and condensed, refined to get the finished yellow phosphorus, by-product slag, and ferrophosphorus are regularly discharged from the bottom of the furnace. Therefore, there are strict requirements on the insulation material, refractory material, and refractory brick structure in the furnace lining.
The furnace body of the phosphorus-making electric furnace is made of steel shell and refractory materials. The furnace charge undergoes a chemical reaction, and the resulting molten slag and phosphorus iron accumulate in the lower part of the furnace, forming slag corrosion.
Therefore, the furnace bottom and the furnace lining are refractory. Material requirements: high load softening temperature, good resistance to slag erosion, small expansion coefficient, good thermal stability, high compressive strength, general yellow phosphorus electric furnace lining refractory materials including high alumina bricks, carbon bricks, and cold stamping. The furnace top is mostly made of steel fiber refractory castable or high-strength refractory castable to make the furnace cover.
During the normal production process, the furnace lining will be corrupted by molten slag, and the degree of corrosion of the furnace lining is related to the maintenance cycle of the electric furnace. Therefore, generally speaking, the degree of corrosion of the furnace lining determines the service life of the phosphorus-making electric furnace and the overhaul interval time of the phosphorus-making device of the electric furnace.
Therefore, regarding key issues such as the quality of furnace lining refractory materials, construction and installation, and furnace lining masonry, the quality must be strictly controlled to prolong the service life of electric furnace phosphorus production and save production costs.
I. Analysis of the Causes of Damage to the Yellow Phosphorus Electric Furnace
When the phosphorus-making electric furnace is in normal operation, the slag temperature in the lower molten pool is about 1500℃ from the perspective of the furnace section. The high-temperature furnace gas conducts sufficient heat exchange through the material layer several meters thick from bottom to top to gradually reduce its temperature.
It rises to the upper space of the furnace to about 220~300 ℃. The temperature of the slag in the center of the molten furnace pool is about 1500 ℃. Due to the heat dissipation effect of the furnace body, the temperature gradually decreases from the center to the furnace wall and the bottom of the furnace. It is about 1000~1200 ℃ at the place where the furnace wall is hung.
The higher the temperature of the slag, the furnace wall, and the furnace bottom, the more corrosive the lining carbon brick will be. The furnace bottom and wall are generally cooled by natural air or circulating water, and the expected cooling effect of the furnace body must be achieved during daily production.
1.1Analysis of lining corrosion environment
Phosphate rock, silica, and coke are non-corrosive in themselves, but the proportion of silica, coke, and phosphate rock in the furnace charge is not suitable, and the coke particle size is too large, forming a chemical reaction in the furnace, which will lead to serious corrosion of the furnace lining during the production process.
The melting point of the slag determines the m(SiO2)/m(CaO) acid-base composition of the CaO-SiO2 system, which is judged by the acidity index Mk of the slag, when m(SiO2)=51.7%, m(CaO)=48.3 %, the melting point of CaSiO3 is the highest at 1540℃, and the acidity index of molten calcium silicate MK = 1.07. The slag with MK less than 1.07 is called basic slag, and the one with MK greater than 1.07 is called acidic slag.
However, the melting point of the slag whose acidity index is slightly larger or less than 1.07 is lower than that of CaSiO3, so the slag whose acidity index MK is close to 0.8 or 1.2 can be used in production operations. Because the acidic slag is highly corrosive to the furnace lining, it should not be used.
The basic slag operation is generally controlled at the slag acidity index MK = 0.75~0.85. Due to a small amount of impurities in the slag, its melting point is lowered, so the molten slag temperature controlled by the low melting point index is 1250~1450℃.
1.2 Erosion of furnace lining liquid
The high temperature at the end of the electrode affects the molten slag and ferrophosphorus. The carbon bricks at the bottom of the furnace are constantly tossed and washed, and pits are sometimes formed at the bottom of the molten pool in the triangular area of the electrode in the center of the furnace.
The iron penetrates the cracks of the bricks and floats the carbon bricks to ablate and melt them. The slag will also corrode the furnace wall carbon bricks, make the furnace shell steel plate red, and even burn through the furnace bottom and wall steel plate.
II Arrangement and masonry of refractory materials for the inner lining of yellow phosphorus electric furnace
(Schematic diagram of the configuration of refractories lining the yellow phosphorus electric furnace)
2.1 The Class shall construct the furnace bottom and furnace wall high-alumina brick masonry I masonry standard <1mm in the technical requirements standard for refractory brick masonry construction, and the dry masonry layer of high-alumina bricks shall be required to be full of mud. The finished brick surface should be cleaned before laying the next layer of bricks.
When the bricklaying is interrupted, or the bricks are reworked and demolished, and it is necessary to keep the chasm, it should be left as a stepped inclined chasm. The height difference between adjacent walls shall not exceed 1.2m. When laying masonry, a wooden or rubber mallet shall be used for alignment, and an iron hammer shall not be used to knock bricks.
2.2 The brick seam’s thickness in the carbon brick’s horizontal direction is about 20mm. Suppose west seam masonry or self-baked carbon bricks and hard ramming furnace technology are used. In that case, the product manual must be paid attention to when building the furnace, and the relevant technical requirements for furnace building must be followed.
2.3 When using cold or electrode paste as the binder to build the carbon brick furnace lining, it must first be heated on a low fire. The heating and melting temperature of the electrode paste is generally controlled at 180~190℃, and the pouring height into the brick joints is 80~100mm each time. It is compacted with a hammer and hammer so that the height after compaction is 40%~50% of the original height.
The vertical joints of the upper and lower layers of carbon bricks at the bottom of the furnace are vertically intersecting in space. The two layers of carbon bricks inside and outside the furnace wall are vertically built, and the width of the brick joints is about 40mm. Block it with a wooden board to prevent the electrode paste from flowing and forming pores to ensure the construction quality.
