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Discussion on the damage mechanism and preventive measures of converter bricks

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As social competition becomes more and more intense, reducing production costs has become the lifeblood of enterprises. Various copper smelters are constantly exploring ways to reduce the consumption of copper bricks per ton in converters. There are many factors that affect the damage of converter bricks, which are related to factors such as matte grade, refractory quality, masonry technology, blowing system and actual operation.

Damage to converter masonry and lining

Our factory has two 60t converters. The masonry structure includes 520mm eye furnace bricks, 9 layers of 520mm, and 14 layers of 460mm transition zones above the eye. Below the eye, we use 380mm bricks. We build refractory materials around the furnace mouth. The eye area and above are thicker to enhance erosion resistance.

Production practice shows that vulnerable parts of the converter lining are the furnace mouth, eye, and end wall. During blowing, the furnace endures severe mechanical scouring of high-temperature melt. It also faces severe erosion from slag and quartz flux. Periodic temperature fluctuations, mechanical collisions, and wear during furnace mouth cleaning and tuyere maintenance add to the stress.

The furnace mouth, tuyere, and end wall slag line are particularly vulnerable. These areas are the weakest links in masonry structure strength. They require the highest technical expertise in construction. The synchronous life of these parts largely represents the converter’s age.

When the furnace brick thickness in the tuyere area is less than 90mm, we must stop for digging and patching. If the masonry in other parts is less than 150mm, we must stop the furnace for an overhaul.

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Analysis of factors affecting converter life

There are many reasons for converter lining damage. In summary, they are mainly the result of three effects: mechanical force, thermal stress and chemical corrosion.

Influence of mechanical force

Damage to brick lining caused by energy of stirring melt

Due to the impact force of the blasted gas and the rising and expanding airflow, the melt is given a lot of stirring energy. When the gas-liquid two-phase mixed fluid impacts the melt surface, the melt is sprayed onto the brick lining by the gas-liquid two-phase fluid, causing a strong mechanical impact on the lining. At the same time, it also creates conditions for chemical erosion. Therefore, choosing a reasonable blast intensity is an important part of improving the converter life. Relatively suitable air supply intensity and air supply system are conducive to reducing the impact of the melt on the lining and extending the converter life.

Damage to tuyere bricks caused by cleaning the tuyere

During the blowing process, magnetic iron is inevitably generated. When the tuyere is poked, the melt in the tuyere area is backflowed, and nodules are easily generated at the tuyere. The tuyere needs to be cleaned continuously, and the mechanical vibration force has a great destructive effect on the brick lining in the tuyere area, causing the surface of the furnace bricks lining in the tuyere area to deteriorate under the action of the melt erosion. When the metamorphic layer expands to a certain extent, the brick body peels off, seriously affecting the life of the furnace.

Influence of thermal stress

The ability of refractory materials to resist damage caused by temperature changes during heating and cooling is called thermal shock resistance, which is an important indicator for measuring the quality of refractory materials. Most refractory materials are damaged at temperatures far below their refractoriness due to poor thermal shock resistance. The thermal damage of refractory materials is mainly related to the thermal stress generated by refractory materials during the production process. The converter is a periodic operation. It is inevitable that the converter temperature fluctuates due to the need for waiting for materials, filling the furnace mouth and equipment failure.

Effect of chemical erosion

Chemical erosion mainly includes two forms: melt erosion (slag, metal solution) and gas erosion. It manifests itself as dissolution, combination and penetration of magnesium refractory materials, which changes the structure of refractory materials, weakens their performance and causes damage.

Melt erosion

The melt contacts and penetrates through the pores, cracks and crystal interfaces of refractory materials. During the contact process, the refractory material dissolves into the melt, and soluble compounds with a volume density that is greatly different from that of the raw materials are formed on the surface of the refractory material. When the melt dissolves to a certain extent, penetration occurs. When the melt penetrates into the refractory material to a certain depth, a metamorphic layer with completely different properties from the raw material will be produced. Due to the different structures of the metamorphic layer and the raw material, the volume changes, and structural stress is generated, resulting in cracks in the raw material. Severe cracks cause the metamorphic layer to peel off or collapse. Under the erosion of the melt, a new metamorphic layer is produced. This cycle causes serious damage to the refractory material.

Gas erosion

Gas erosion generally refers to the reaction of SO2 and O2 in matte with alkaline oxides in refractory materials during the blowing process to form metal sulfates, which have a lower density than alkaline oxides. Due to the difference in volume density of the two phases, stress is generated, making the refractory materials loose and flaking, aggravating the damage of the refractory materials.

Measures to extend the life of the converter

Change the masonry method and improve the process standard:

Under normal circumstances, wet masonry will cause the furnace bricks to get damp, which is not conducive to 400℃ constant temperature dehydration. The converter masonry adopts a combination of dry and wet, that is, the upper and lower 4 layers of the tuyere area and the furnace mouth area are wet masonry, and the rest are dry masonry.

The tuyere bricks are changed from masonry at one end to masonry from the middle to both ends to avoid triangular joints and misalignment of the tuyere combined bricks.

The upper and lower furnace mouth arch furnace bricks are changed from masonry at one end to masonry from the center to both ends, and the symmetry is carried out, which is conducive to closing and locking on both sides to prevent uneven gaps and looseness between the two furnace bricks and falling off.

The distribution in the brick joints is full, uniform, consistent inside and outside, the expansion joints meet 2-3mm, the brick joints of each part are locked, the processed bricks are not more than one-third, and the processed bricks are not less than two-thirds of themselves.

The magnesium filler requires that the hand can be kneaded into a ball, fall from a height of one meter and see the scattered, the filling material is uniform in thickness and solidity.

Broken, broken corners and damp chrome-magnesia bricks must not be used.

Control the cold material of the converter to prevent high temperature corrosion

Tests have shown that when the chrome-magnesia brick is resistant to thermal vibration at 850℃, it will break after 18 times, causing damage to the furnace brick lining. Therefore, it is necessary to avoid high and low and violent fluctuations in furnace temperature to reduce and eliminate the damage to the brick lining caused by thermal stress. In production, the method of controlling the amount of cold material added is used to stabilize the furnace temperature.

Reasonably control the silicon content of converter slag to reduce chemical corrosion of neutral or weakly alkaline slag

Fayalite seriously corrodes periclase. It dissolves the surface of magnesia refractory materials and penetrates into the interior to dissolve them. Higher temperatures increase the solubility of MgO in converter slag. This forms forsterite with a low load softening temperature, reducing the performance of magnesia bricks.

Iron oxides can saturate periclase and chromite grains. This causes grain damage and leads to rapid deterioration of magnesia bricks. Converter slag with less than 18% silicon is alkaline. Slag with more than 28% silicon is acidic. Both seriously corrode the magnesia brick lining.

Converter slag with 19% to 24% silicon is neutral or weakly alkaline. It does not corrode the magnesia brick lining. In production, we strictly control the silicon content of converter slag. We stabilize it between 19% and 24%.

Improve the quality of personnel

Improve the quality and ability of furnace construction, converter operation, and production managers to ensure the quality of furnace construction. Improve the ability to respond to emergencies, and supervise and manage production scientifically and strictly.

Reasonable selection of air supply intensity and oxygen enrichment concentration

During the production process, it is inevitable that the furnace body and the fan do not match. It is strictly forbidden to use a large fan to supply air to the small furnace body to prevent violent scouring of the tuyere area and severe spraying of the melt. The oxygen enrichment concentration of the converter should not be higher than 27%. If the oxygen enrichment concentration is greater than 27%, the furnace bricks lining will be washed more.

Issues that should be noted

The following issues should also be noted in production:

(1) Formulate scientific standards for stopping, repairing and starting furnaces, such as brick lining removal standards and temperature increase standards, and strictly implement them.

(2) When starting a newly repaired furnace, “hanging furnace” and “copper infiltration” operations should be carried out to protect the furnace body.

(3) Strictly operate the process, and the control of furnace temperature at each stage and the judgment of the end point should be accurate. Prevent the occurrence of “over-blowing”, especially over-blowing in the second cycle, which is very harmful to the furnace body.

(4) Pay attention to the training of employees and improve the quality of all employees and the level of copper smelting technology.

Conclusion

By implementing the above measures, the energy consumption of copper bricks per ton is well controlled, costs are reduced, and annual benefits are created. As long as the masonry quality and process conditions are paid attention to, and the factors of thermal stress, mechanical force and chemical erosion that damage chrome-magnesia bricks are eliminated, the life of furnace bricks can be extended.

LMM YOTAI established in 2007. Our production technology comes from Japanese Yotai. As an experienced and international player in the refractories industry. We have succeeded in expanding both the breadth of its product range and the depth of its services. From raw material selection, refractory portofio & optimization, installation & services & recycle of used refractories on site to further reduce client’s Opex & Capex in refractory consumption per ton steel output, meanwhile improve product quality of client.

Our Product have been supplied to world’s top steel manufacturer Arcelormittal, TATA Steel, EZZ steel etc. We do OEM for Concast and Danieli for a long time

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