2017年11月2日星期四

How to extend the life of refractory materials

refractory materials
refractory materials
How to extend the life of refractory materials. Generally divided into kiln kiln is divided into four bands, namely, decomposition zone, transition zone, firing zone and cooling zone. Four belt, firing with kiln lining the most critical, at home and abroad in the pre-decomposition kiln burning with the main use of alkaline refractory brick.
Thermal, mechanical and chemical factors contribute to the stress in the kiln lining and cause damage. With the kiln, operation and kiln lining in the kiln position of the different factors of the damage is also different. Which decisive role is the flame, kiln and kiln body deformation, they make the kiln bearing a variety of different stress.
For alkaline tiles, there are eight kinds of destructive factors, namely clinker melt infiltration, agglomeration of volatile components, reduction or reduction - oxidation, overheating, thermal shock, thermal fatigue, extrusion and grinding. However, these eight factors have different effects on the damage of different refractory brick lining in kiln, and the mechanism of damage to alkaline brick is described in this paper.
1, clinker melt infiltration:
Clinker melt mainly from the kiln and fuel, infiltration phase is mainly C2S, C4AF. The infiltration of C2S and C4AF in the metamorphic layer strongly dissolves magnesia and chrome ore in magnesia carbon bricks, precipitates secondary silicates such as CMS and magnesium rose pyroxene (C3MS2), and sometimes even precipitates potassium Stone; and the melt will be filled with brick lining pores, so that part of the brick layer of dense and embrittlement; combined with thermal stress and mechanical stress dual role, resulting in easy cracking refractory brick peeling. Due to C2S, C4AF above 550 ℃ began to form, and pre-decomposition kiln into the kiln material temperature has reached 800 ℃ ~ 860 ℃, so clinker melt penetration throughout the pre-decomposition kiln, the clinker melt on the pre-decomposition Kiln lining with a certain infiltration into the erosion effect.
2, the condensation of volatile components:
Pre-decomposition kiln, alkaline sulphate and chloride and other components volatile agglomeration, repeated circulation, resulting in the accumulation of these components in raw materials. By the production practice, the R2O, SO3 and CI- contents of the raw material in the warmest preheater of the kiln are often increased to 5 times, 3 to 5 times and 80 to 100 times respectively higher than that of the raw material. When the hot material enters the third part of the kiln cylinder (800 ° C to 1200 ° C), the volatile components in the material will aggregate in all the brick and brick layers, And the erosion of the adjacent components other than magnesite, resulting in brick thermal penetration stability of the infiltration layer is significantly reduced, the formation of expansion of potassium nepheline, garnet, the refractory brick lime damage, and thermal - mechanical stress Under the combined action of peeling off. The more the depth of the kiln lining is affected by the alkali salt, Selection.
3, reduction or reduction - oxidation reaction:
When the thermal system in the kiln is unstable, it is easy to produce the reduction flame or the incomplete combustion, so that the Fe3 + reduction or Fe2 + in the magnesia-chrome brick shrinks, and the migration and diffusion of Fe2 + in the magnesite crystal is stronger than Fe3 + More, which further exacerbated the volume shrinkage effect, so that the brick hole, the structure weakened, the intensity decreased. At the same time, the reduction of the kiln gas and the alternating atmosphere of the oxidation of the shrinkage and expansion of the volume effect occurs repeatedly, the brick will produce chemical fatigue. This process mainly occurs in the absence of kiln protection of magnesium chrome brick.
4, overheating:
When the kiln heat load is too high, so that the brick surface for a long time to lose the protection of the kiln, the hot surface layer of the matrix at high temperature melting and moving to the cold layer direction, leaving the brick lining layer of dense, hot surface layer is loose Porous (generally easy to occur in the firing area of ​​the firing zone), which is not resistant to abrasion, shock, vibration and thermal fatigue, easy to damage.
5, thermal shock:
When the kiln is not working properly or kiln leather is unstable, the alkaline tiles are susceptible to thermal shock. Kiln of the sudden collapse of the brick surface temperature caused by a sudden surge (or even up to thousands of degrees), leaving the brick to produce a lot of thermal stress. In addition, the frequent opening and closing of the kiln to produce alternating alternating heat within the brick. When the thermal stress, once beyond the structural strength of the brick lining, the brick suddenly cracks, and along the structure of the weakening of the Department continue to deepen the deepening, and finally the brick fragmentation. When the kiln skin falls, the broken brick in the hot surface layer is taken to keep the brick from damage. The thermal shock phenomenon can easily occur in the transition zone near the kiln.
6, thermal fatigue:
In the kiln operation, when the brick lining is not in the material layer, the surface temperature is lowered, and when the brick lining is exposed to the flame, the surface temperature is increased. Kiln each turn a week, brick lining surface temperature rise and fall range of up to 150 ℃ ~ 230 ℃, the impact of depth 15mm ~ 20mm. Such as pre-decomposition kiln speed of 3r / min, this periodic temperature rise and fall of up to 130,000 times per month. This repeated temperature rise and fall causes the thermal fatigue of the surface layer of the alkaline brick to accelerate the peeling of the brick.
7, squeeze:
Rotary kiln operation, the kiln refractory lining material by the pressure, tension, torque and shear mechanical stress, such as the combined effect. Among them, the rotation of the kiln, the oval of the kiln and the kiln fall, the bricks are subjected to the dynamic load; the weight of the refractory brick and the kiln and the thermal expansion of the brick itself make the brick bear the static load. In addition, between the lining brick and the kiln body, the relative movement between the brick lining and the brick lining, and the welds on the retaining ring and the kiln body, will cause the brick lining to withstand various mechanical stresses. When all these stresses exceed the structural strength of the brick, the brick is cracked. This phenomenon occurs in the kiln lining of the precalciner kiln.
8, wear:
Pre-decomposition kiln kiln discharge area without kiln leather protection, and clinker and large kiln leather and hard, will be on the part of the brick lining, resulting in more serious impact and abrasion damage.
In short, the impact of kiln lining consumption of more factors, but also more complex, and only continue to explore, the use of new technologies, new materials, improve the operation and management level, in order to achieve both reduce consumption, but also the kiln system balanced and stable operation.
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