- Time:Nov 07, 2023
With the continuous increase in cement production, the speed of CRKs is accelerating, and the calcination temperature is constantly rising. More and more production lines are simultaneously processing waste materials, hazardous waste, and other substances. All these factors pose significant challenges to the service life of refractory bricks inside the cement kiln.
In addition to the impact of changes in kiln speed, elevated temperature process conditions, and co-disposal of cement kilns, the damage to refractory bricks is also influenced by chemical factors.
I. Chemical Damage Mechanisms
1. Basic SaltPermeation
Basic salt permeation refers to the infiltration and condensation of alkali salt compounds in the brick's voids, forming a horizontal permeation layer of alkali salts within the brick. The damage caused by alkali salt permeation can be observed as distinct salt deposition layers on the residual brick surface. The upper transition zone is mainly infiltrated and deposited with KCl, while the lower transition zone is primarily infiltrated with K2SO4. The inconsistent properties between the permeation layer and the original brick layer make it prone to spalling under thermal shock. Refractory brick damage due to alkali salt permeation is characterized by visible color changes and significant differences in chemical composition between the layers after salt permeation.
To mitigate the damage caused by alkali salt permeation, it is necessary to select refractory bricks with good resistance to alkali and minimize the basic salt content introduced into the kiln.
2. Alkali Erosion
Alkali elements such as Na and K in the cement kiln react with Al2O3 and SiO2 in the refractory brick, leading to alkali spalling and subsequent brick damage.
Alkali salts erode the periclase and bonding phases in the high-temperature zone, causing a porous structure in this area. Extensive infiltration and erosion by cement clinker result in the formation of a dense altered layer. The deposition of alkali salts in the low-temperature zone increases the thickness of the dense altered layer. The dense and thick altered layer undergoes severe structural spalling during temperature fluctuations, particularly affecting magnesia-alumina spinel and magnesia-iron spinel.
To prevent damage caused by alkali erosion, it is essential to control the alkali-sulfur ratio (ASR) of refractory bricks at around. Choosing refractory materials with excellent alkali resistance and ensuring low porosity and impurity content in the refractory material can be beneficial.
3. Oxidation-Reduction Spalling
Oxidation-reduction spalling in refractory bricks is characterized by whitening on the working face or darkening on the non-working face (which can regain color after overburning). This type of damage occurs due to volume changes in Fe2+ and Fe3+ within the brick resulting from fluctuations in the kiln's oxidation and reduction atmospheres, leading to structural spalling. Refractory bricks containing iron elements, such as magnesia-iron bricks, are significantly affected by oxidation and reduction atmospheres.