With the increase in the number of new dry production lines and the technological progress of the cement industry in recent years, refractory materials have become one of the indispensable bulk consumable materials in the cement industry production process (clinker calcination), and their direct costs account for approximately the clinker production cost. 1% to 2%, and its indirect impact is also very large. Therefore, personnel in cement production enterprises must know more about the basic knowledge of refractory materials, especially central control operators, who must be aware of the impact of production operations on refractory materials in order to better use refractory materials and avoid improper operation. And cause unnecessary loss of refractory materials. The following is a brief introduction to the types of effects of production operations on refractory materials in the kiln (here mainly refers to refractory bricks), the main damage to refractory materials in various areas of the kiln, and the use of refractory materials in the kiln for your reference.

  1 Type of damage

  The impact of production operations on refractory materials in the kiln can be roughly divided into the following four types, but the actual impact is often caused by several reasons coexisting at the same time.

  1.1 peeling

(1) Thermal spalling: Rapid thermal changes such as peeling off in the early stage of ignition or peeling off of the crust will bring internal thermal stress to the brick, and the resulting cracking phenomenon is called thermal spalling.

  (2) Mechanical spalling: The cracking phenomenon caused by mechanical stress such as the influence of a large kiln, the melting of joint iron plates, or the load of bricks is called mechanical spalling.

(3) Structural spalling: A metamorphic layer is formed due to the intrusion of foreign components such as liquid components, alkaline components or sulfur components of cement raw materials. The cracking phenomenon caused by differences in physical properties such as expansion is called structural spalling.

  1.2 Melt damage

 The high thermal load in the early stages of ignition or when the crust is peeled off, as well as the liquid phase components of the cement raw materials, will form low-melting point substances, causing melting damage to the refractory materials. Generally, magnesia-chromium bricks or chromium-free bricks in the firing area are more susceptible to melting damage, but improper production operations can also cause melting damage to spinel bricks in the cooling area or the area where the crust has fallen off, or even clay bricks in the calcining area.

  1.3 wear and tear

 Refers to the loss caused by cement raw materials to the surface layer of bricks. It is divided into mechanical wear that occurs in the calcined area and the area where the crust adheres and falls off, and high-temperature wear that occurs in the calcined area or cooling area and includes melting damage caused by the cement liquid component. When high-alumina clay bricks are used in the calcining area, they will react with the cement raw materials at a lower temperature than alkaline bricks to generate low-melting point products. Therefore, they sometimes adhere to the crust near the high thermal load. The side of the shedding area causes wear.

  1.4 Tissue embrittlement

  Refers to the embrittlement phenomenon caused by the structural destruction of bricks caused by thermal stress, mechanical stress and erosion by external components. Thermal stress mostly occurs in the crust adhesion and shedding areas and the firing area, which is caused by frequent temperature changes caused by the crust's adhesion and shedding; mechanical stress is caused by the kiln or the crust's adhesion and shedding and even the load of the bricks.

From the material point of view, alkaline bricks with high thermal expansion rates, such as magnesia chromium bricks, have a lot of impurities and a high linear change rate caused by repeated heating, so the embrittlement phenomenon is particularly obvious. Spinel bricks have high purity, low linear change rate caused by repeated heating, and good embrittlement resistance, so they are mostly suitable for areas where the crust is attached and peeled off. Compared with alkaline bricks, high-alumina clay bricks have a low thermal expansion rate and high bonding strength, so they are less likely to cause tissue embrittlement.

  2 Main damage conditions of refractory materials in various areas of the kiln

  2.1 Cooling area

  2.1.1 High temperature wear

 The impact of production operations on the refractory materials in the cooling area includes high-temperature wear caused by cement clinker. In the cooling area, since the adhesion of the crust is unstable and easily abraded by the sintered cement clinker, spinel bricks with higher high-temperature strength at around 1200°C are generally used. The temperature of clinker is about 1400°C, which usually does not cause melting damage. However, improper operation will increase the heat load and promote the formation of high-temperature wear.

  2.1.2 Mechanical damage

The effects of production operations on refractory materials in the cooling area include: mechanical stress caused by the kiln (mechanical stress caused by kiln centering, kiln torque, cylinder deformation, etc.), deformation of the fixed metal parts of the bricks at the blanking port, Damage caused by the friction between the bricks and the cylinder and the load of the bricks. Due to the poor rigidity of the cylinder at the blanking opening and the fact that the cylinder is prone to deformation and distortion, bricks adjacent to the fixed metal parts of the bricks are particularly susceptible to friction between the metal parts and the cylinder, cylinder deformation and Effect of deformation (biting) of metal parts.

  2.2 Firing area

  2.2.1 Melt damage

 The effects of production operations on refractory materials in the firing area include: high heat load generated during ignition or when the crust adheres and falls off, and melting damage caused by the liquid phase component of cement raw materials. The forms of melt damage are further divided into: ① Partial attachment and detachment of the crust resulting in water-like melt damage; ② Sliding melt damage caused by high-temperature wear and tear when the crust melts in a ring shape.

  2.2.2 Sulfur corrosion + spalling

 The impact of production operations on refractory materials includes sulfur corrosion on bricks caused by sulfur in raw materials and fuels. In the area where the crust is relatively stable deep in the firing area, sulfur corrosion in the reducing environment will cause damage and densification of the joint iron plates. The difference between the expansion rate of the crust and the stress of the kiln will cause mechanical damage. Sexual exfoliation.

  2.3 Area of crust attachment and detachment

   2.3.1 Jointed iron plates

 In addition to the sulfur corrosion of bricks caused by the sulfur in raw materials and fuels, the impact of production operations on refractory materials is also the problem of mechanical peeling caused by the corrosion of joint iron plates. The same phenomenon occurs when the seam iron plate is corroded due to sulfur corrosion as explained above. However, compared with the depth of the fired area where the crust is relatively stable, the crust in the area where the crust adheres and falls off is The skin adheres and falls off frequently, and the brick itself has a relatively high thermal load, making it more susceptible to sulfur corrosion in a reducing environment.

To reduce the damage to the jointed iron plate, the thickness of the iron plate can be set to 0.2mm to minimize its impact. By taking this measure, the mechanical damage caused by the melting damage of the iron plate can be greatly reduced. In addition, this can also reduce the thickness of the iron plate and the thickness of the bonding material, so that the construction can be carried out like bricklaying without mortar, forming a compact construction overall. At this time, the expansion allowance can be reduced to one for every eight bricks.

   2.3.2 Brittle peeling

In this area where the crust adheres and falls off more frequently, in addition to the structural embrittlement caused by thermal stress and mechanical stress, there is also the structural embrittlement caused by sulfur corrosion, which aggravates the structural embrittlement of the spinel bricks. damage.

Spinel bricks are basically a combination of magnesium components. In this combination, the trace components of the bricks, Ca, play an role. Sulfur corrosion causes the Ca component in the bonded tissue to react selectively, generating alkaline sulfate and CaSO4 double salt or CaSO4; in addition, due to the movement of the generated substances within the brick, the bonded tissue of the brick is destroyed, aggravating the Tissue embrittlement.

In addition, while sulfur corrosion causes structural damage to bricks, the deposition of alkaline sulfate, CaSO4, MgSO4 double salts and KCl will form a densified layer. When cracks occur at its boundaries, the resulting Peeling damage or peeling off of crust will cause the bricks to fall off.

  2.4 Calcination area

 The calcined area uses high-alumina bricks and clay bricks, which will cause differences in densification and expansion rates. The resulting structural peeling is the main manifestation of peeling damage.