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The main reason for the excessive damage of refractory materials in cement rotary kiln is these!
Dec 04, 2018

The operating rate of cement kiln is the focus of cement enterprises, and it is an important source of enterprise benefits. The reason for the low operating rate of pre-decomposed cement kiln is that in addition to equipment failure factors, more refractory materials in various parts of pre-decomposed cement kiln cannot. Satisfying the use requirements, resulting in frequent shutdowns of the kiln for replacement and repair.


1. Melt loss

The cement raw material undergoes a series of physical and chemical changes during the entire heating process from the decomposition of calcium carbonate to the mature minerals in the kiln, and produces a large amount of molten metal, slag, molten ash, these molten metals, slag, The molten ash reacts with the refractory material to form a low melting material which, when lost, causes the refractory material to melt.


Precaution:


(1) A refractory material having a low porosity, a small gas permeability, and a good firing;


(2) using a refractory material having a low melting degree of the melt and a high viscosity of the dissolved product;


(3) Use refractory materials that are not easily eroded by the melt as much as possible.


2, gas loss

The precalcining kiln makes full use of the waste heat preheating, so that the alkali, sulfate and chloride are volatilized and coagulated in the kiln, enriched in the kiln and recycled repeatedly, compared with the original raw material in the kiln of the hottest group preheater. In the material, R20 is increased by 5 times, SO3 is increased by 3 to 5 times, and it is in contact with refractory materials for a long time, causing chemical changes, causing erosion and destruction of refractory materials.


Precaution:


Refractory materials that react slowly with gases or gas condensates:


(2) using a refractory material with high gas permeability and high strength;


(3) Seal the joints.


3, structural spalling

Large-scale precalcining kiln adopts multi-ducted coal nozzles. The primary air volume is large, so the flame temperature is much improved. In addition, the kiln head is strengthened and sealed. The flame temperature in the kiln is about 1700~1800°C, which makes the kiln mouth and cooling zone. The temperature level of the firing zone, the filter belt, the decomposition zone and even the kiln door cover and the cooler is much higher than the corresponding part of the conventional kiln. When slag, dust, gas, or the like in contact with the heating surface invades the refractory material, a metamorphic layer is formed in the vicinity of the heating surface due to the action of these melting agents and heat, and the deteriorated portion is peeled off due to excessive shrinkage of the liquid phase, or deteriorated due to deterioration. The part is peeled off unlike the expansion of the undeteriorated part.


Precaution:


(1) The refractory material which is not easy to generate structural spallation, the same kind of refractory material, the high softening point of the load, the spalling property is relatively better;


(2) cooling the kiln wall is effective for reducing the thickness of the metamorphic layer;


(3) Appropriately control the amount of material added to reduce the stress on the refractory material.


4, mechanical spalling

Nissan 2000t precalciner kiln diameter is 4m, Nissan 4000 precalciner kiln diameter is 4.7 meters, the speed reaches 3~4 rev / min. The kiln diameter is increased, the kiln temperature is increased, and the rotation speed is increased. The refractory brick rotates with the cylinder at high temperature, plus the support of the supporting wheel, the weight of the kiln and the impact of the material in the kiln, the mechanical vibration and deformation are intensified, and the fire resistance is intensified. The destruction of the material is also exacerbated, causing the refractory material to peel.


Precaution:


(1) sufficiently leaving the expansion joint of the refractory material;


(2) Slowly heating and heating, especially when the cement kiln is ignited, the heating rate should be controlled;


(3) Select refractory materials with high temperature strength, corrosion resistance, thermal shock stability and easy adhesion to kiln skin.


5, permanent shrinkage

In order to ensure the output and efficiency of the cement enterprise, the cement kiln keeps running day and night, and the refractory material will shrink due to the thermal stress caused by the long-term high temperature heating and temperature difference, and the brick joint cracks and causes the falling off.


Precaution:


(1) cooling the kiln cylinder, especially the firing zone;


(2) A refractory material with a small permanent shrinkage is used.


6, hot stripping and softening damage

The thermal shock and refractory materials caused by the cyclic temperature difference per revolution of the cement kiln are subjected to quenching and rapid heat, the surface of the refractory material is peeled off due to the strain caused by the difference in surface and internal expansion, and the refractory material is subjected to the kiln at high temperature. The pressure of the material reduces the compressive strength of the refractory material, and the refractory material is crushed and collapses.


Precaution:


(1) Try to avoid rapid cooling and rapid heat;


(2) using a refractory material with high thermal shock resistance;


(3) A refractory material having a high softening point of load is used.


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