Cause Analysis And Prevention Measures Of Converter Lining Brick Damage in Steel Plant

As market competition becomes increasingly intense, reducing production costs has become crucial for enterprises. Various copper smelters are constantly exploring ways to reduce the consumption of refractory bricks per ton of copper in converters. There are numerous factors that lead to converter brick damage, including matte grade, refractory material quality, bricklaying technology, blowing system, and actual operating practices.

Converter Masonry and Lining Damage Condition

There are two sets of 60-ton converters in service. The converter masonry structure is designed as follows: the tuyere bricks are 520 mm thick. Above the tuyere area, there are 9 layers of 520 mm bricks and 14 layers of 460 mm bricks forming the transition zone. All bricks below the tuyere area have a thickness of 380 mm. Refractory materials are laid all around the furnace mouth, with thicker bricks used in the tuyere area and upper sections to improve corrosion resistance.

Production experience shows that the most vulnerable parts of the converter lining are the furnace mouth, tuyere area, and end wall. During the blowing process, the lining is subjected to severe mechanical scouring by high-temperature molten metal, intense corrosion from slag and silica flux, and periodic fluctuations in furnace temperature. It also experiences mechanical impact and abrasion during furnace-mouth cleaning and tuyere maintenance, resulting in extremely harsh working conditions. In particular, the slag line at the furnace mouth, tuyere area, and end wall is not only the most easily damaged part of the refractory lining but also represents the weakest links in masonry structural strength, as well as the areas requiring the highest construction standards. The simultaneous service life of these three key parts largely determines the overall campaign life of the converter.

According to on-site production experience, when the residual thickness of bricks in the converter tuyere area falls below 90 mm, the converter must be shut down for partial brick patching. When the residual brick thickness of other lining parts drops below 150 mm, a full furnace overhaul is required.

Analysis of Factors Affecting Converter Service Life

There are numerous causes of converter lining damage, which can be mainly summarized into three types: mechanical force, thermal stress, and chemical corrosion.

2.1 Influence of Mechanical Force

2.1.1 Damage to Brick Lining Caused by Molten Body Agitation Energy

The impact force of the blown-in gas, as well as the rising and expansion of airflow, delivers strong agitation energy to the molten material. When the gas-liquid mixture strikes the molten surface, the molten material is splashed onto the brick lining, causing severe mechanical impact on the furnace lining while also creating conditions for chemical erosion. Therefore, adopting a reasonable air-blowing intensity is a key measure to extend converter service life. An appropriate air supply volume and blowing system can effectively reduce the scouring impact of molten material on lining bricks and prolong the converter campaign life.

2.1.2 Damage to Tuyere Bricks during Tuyere Cleaning

Magnetite is inevitably formed during the blowing operation. Molten material flows back into the tuyeres during tuyere poking, resulting in nodulation inside the tuyeres that requires frequent cleaning. The mechanical vibration force causes severe damage to the tuyere-zone lining bricks, leading to deterioration of brick surfaces due to molten erosion. Once the deteriorated layer expands to a certain extent, brick spalling occurs, which greatly shortens the furnace service life.

2.2 Influence of Thermal Stress

Thermal shock resistance refers to the capability of refractories to resist damage caused by temperature changes during heating and cooling, and it serves as a core index to evaluate refractory quality. Most refractories fail due to poor thermal shock resistance even at temperatures far below their refractoriness. Thermal damage of refractories is primarily related to thermal stress generated during production. Converters operate intermittently. Production halts caused by material waiting, furnace-mouth repairs, and equipment failures inevitably lead to frequent furnace temperature fluctuations.

2.3 Influence of Chemical Corrosion

Chemical corrosion mainly includes molten corrosion (slag and molten metal) and gas corrosion. Such corrosion dissolves, reacts with, and penetrates magnesia refractories, changing their internal structure, weakening physical properties, and eventually causing damage.

2.3.1 Molten Corrosion

Molten substances make contact with and penetrate refractories through pores, cracks, and grain boundaries. Refractory components dissolve into the molten phase during contact, forming soluble compounds with significantly different bulk density on brick surfaces. Further dissolution promotes deep penetration. After molten material infiltrates to a certain depth inside bricks, deteriorated layers with completely different properties are formed. Structural differences between these deteriorated layers and the original bricks trigger volume variation and structural stress, resulting in internal cracks. Severe cracking causes peeling and breaking of the deteriorated layers. New deteriorated layers continue to form under continuous molten erosion in a repetitive cycle, leading to severe refractory damage.

2.3.2 Gas Corrosion

During the blowing process, sulfur dioxide and oxygen released from matte react with the basic oxides inside refractories to form metal sulfates. These sulfates have a lower density than the original basic oxides. The density difference between the two phases generates internal stress, making the refractories loose and prone to spalling, thus accelerating refractory deterioration.

Measures to Extend Converter Service Life

3.1 Optimize Masonry Methods and Upgrade Technical Standards

3.1.1 Mixed Dry and Wet Masonry Construction

Conventional wet masonry tends to dampen bricks, which is unfavorable for constant-temperature dehydration at 400℃. Therefore, a combined dry and wet masonry method is adopted for converters. Specifically, wet masonry is applied to the four layers above and below the tuyere area, as well as the furnace-mouth area, while dry masonry is used for all other positions.

3.1.2 Improved Tuyere Brick Laying Mode

Change the tuyere brick laying sequence from single-end construction to center-to-two-end construction to avoid triangular gaps and misalignment of the combined tuyere bricks.

3.1.3 Symmetrical Laying of Furnace-Mouth Arch Bricks

Adjust the laying method of the upper and lower furnace-mouth inverted arch bricks from single-end laying to symmetrical laying, starting from the center and moving towards both ends. This facilitates tight closing and locking on both sides and prevents bricks from falling due to uneven or loose joints.

3.1.4 Strict Control over Brick Joints and Expansion Gaps

Ensure full, even, and consistent filling inside and outside brick joints. Keep the expansion gap within 2–3 mm. Perform locking treatment at all brick junctions. The proportion of processed bricks shall not exceed one-third, and the intact portion of processed bricks shall be no less than two-thirds of the original brick volume.

3.1.5 Quality Requirements for Magnesite Filling Materials

The magnesite filler shall be hand-kneadable and dispersible when dropped from a height of one meter. The filler shall be laid with uniform thickness and consistent compactness.

3.1.6 Strict Raw Material Acceptance

The use of damaged, corner-broken, or damp chrome-magnesia bricks is strictly prohibited.

3.2 Control Cold Charge to Prevent High-Temperature Corrosion

Tests show that chrome-magnesia bricks fracture after only 18 thermal shock cycles at 850℃, resulting in damage to the furnace lining bricks. Hence, drastic and frequent furnace temperature fluctuations must be avoided to minimize thermal stress damage to the lining. In actual production, the amount of cold charge fed is regulated to stabilize the furnace temperature.

3.3 Properly Control Silicon Content in Converter Slag to Reduce Chemical Corrosion

Neutral or weakly alkaline slag can protect furnace lining bricks. Fayalite causes severe erosion of periclase, which not only dissolves the surface of magnesia refractories but also penetrates their interior for further dissolution. The higher the temperature, the higher the solubility of MgO in converter slag. At high temperatures, it forms forsterite with low refractoriness under load, which deteriorates the service performance of magnesia bricks. Iron oxides can also saturate periclase and chromite grains, destroy grain structures, and accelerate the failure of magnesia bricks.

Slag with silicon content below 18% is alkaline, while that above 28% is acidic. Both types severely erode magnesia furnace linings. When the silicon content ranges from 19% to 24%, the slag is neutral or weakly alkaline and causes no corrosion to magnesia bricks. In production, the silicon content of converter slag shall be strictly controlled and maintained steadily within 19–24%.

3.4 Improve Personnel Quality

Enhance the professional competence of furnace builders, converter operators, and production managers to ensure furnace masonry quality. Strengthen emergency response capabilities and implement scientific and rigorous supervision of production operations.

3.5 Reasonably Select Air Supply Intensity and Oxygen-Enriched Concentration

Mismatch between the converter furnace body and the air blower can occur during production. It is strictly forbidden to use high-power blowers for small-sized converters, in order to avoid severe scouring in the tuyere areas and violent splashing of molten materials. The oxygen-enriched concentration for converters shall not exceed 27%, as higher concentrations can cause intense abrasion damage to furnace lining bricks.

Matters Needing Attention

The following aspects shall be noted during production:

Formulate scientific standards for furnace shutdown, maintenance, and startup, such as lining brick removal standards and temperature rise standards, and enforce them strictly.

Carry out furnace coating and copper infiltration treatment before putting newly repaired converters into operation, to protect the furnace body.

Standardize process operations, accurately control furnace temperature at each stage, and determine the blowing endpoint. Avoid over-blowing, particularly during the second blowing cycle, which can cause severe damage to the converter.

Place emphasis on staff training to improve overall professional competence and technical skills in copper smelting.

Conclusion

By adopting the above measures, the refractory brick consumption per ton of copper can be effectively controlled, production costs reduced, and annual economic benefits achieved. As long as sufficient attention is paid to masonry quality and process conditions, and the thermal stress, mechanical force, and chemical corrosion factors that damage chrome-magnesia bricks are eliminated, the service life of furnace lining bricks can be greatly prolonged.