Cause Analysis and Countermeasures of Fire resistant lining damage in cement rotary kilnDate: 2019-06-20 Views:
The damage of refractory lining of rotary kiln often affects the continuity of production and is one of the common equipment accidents. The reasons include design structure, refractory material quality, masonry quality, operation and maintenance and so on. The comprehensive analysis of all kinds of lining damage accidents is helpful to find out some common causes. The pre-control measures are taken to avoid the occurrence of the accident to the greatest extent.
Effect of refractory lining on rotary kiln
Prevent the direct damage of high temperature flame or air flow to the kiln body, protect the kiln cylinder; prevent the erosion of harmful substances (CO,SO2) to the kiln body; prevent the material and air flow from eroding the kiln body; reduce the temperature of the kiln body and prevent the kiln body from being oxidized and eroded; have the function of heat storage and heat preservation; and can improve the performance of hanging kiln skin.
Form of damage to refractory lining
1. Common damage forms
The comprehensive effect of the mechanical stress, material friction, thermal stress, air flow and chemical attack of the refractory lining of the rotary kiln for the long-term bearing rotation often results in the following problems: firstly, the material lifting block is subjected to mechanical rotating gravity and the heart rate effect for a long time, the high-temperature effect and the impact friction of the stone lead to the distortion of the prefabricated block, the material falling off, the thickness reduction, the deformation and the falling of the refractory brick filled between the material-raising blocks, the other is the melting loss of the high-temperature sintered junction layer, the separation of the gravity during the rotation of the kiln body causes the material to be stripped, the lining is thinned, the temperature of the kiln body is increased, and the steel junction The structure changes to varying degrees to reduce the service life of kiln body.
2. The probability of all kinds of damage
German fire-resistant technology has carried out a lot of experimental research on the material after using, and statistics the probability that the main damage causes: the mechanical stress is 37%, due to the deformation of the cylinder and the thermal expansion of the brick, the chemical attack accounts for 36%, Due to the erosion of the clinker silicate and the alkali salt, the thermal stress is 27 percent, and the thermal stress is caused by the action of the overheating and the thermal shock.
With the different operation of the kiln type and the position of the kiln lining in the kiln, the above three factors play different roles, mainly depending on the deformation state of the flame, the kiln material and the kiln cylinder in operation, so that the lining bears various stresses.
Cause Analysis and Countermeasures of Refractory damage
1. Mechanical stress damage.
1. Thermal expansion and extrusion of refractory brick
When the kiln temperature rises to a certain extent, thermal expansion will produce pressure in the axial direction of the kiln, resulting in mutual extrusion between adjacent refractory brick. When the pressure is greater than the strength of refractory brick, it will lead to refractory brick surface peeling off. The following measures should be taken: dry refractory brick, reasonable side board, wet refractory brick leaving 2mm fire mud joint, leaving suitable brick retaining ring.
The stress of the iron plate is damaged
At the hot end of the refractory brick, the surface iron plate and the magnesium oxide in the magnesium brick are chemically reacted at high temperature to form the ferromagnesium compound, so that the volume is increased, the refractory brick is pressed and the horizontal fracture is caused. In this case, the practice of refractory brick facing iron should be changed or replaced with fire mud.
large-area twist and oblique dislocation of refractory brick
As the masonry is too loose, the kiln is frequently opened, resulting in the deformation of the kiln cylinder, and the relative movement of the kiln barrel and the cold surface of the lining brick causes the lining brick to be twisted and staggered and the brick surface is broken and the angle is dropped. The following measures shall be taken: when building, the large surface of the refractory brick shall be knocked out with a wooden hammer, the locking brick shall be locked, and the wedge iron shall be added for the second time; the stable thermal system shall be kept; and the deformation part of the kiln cylinder shall be leveled with high-temperature mortar.
elliptic stress extrusion
As the gap between the rotary kiln wheel belt pad is increased, the cylindrical body has a large ovality, resulting in the extrusion of refractory bricks. Periodically check the ovality of the cylinder. If the elliptic value exceeds 1/10 of the kiln diameter, replace the backing plate or increase the sizing block to adjust the clearance of the belt.
⑤ Stress extrusion of lock iron.
When locking brick, too much iron is too tight, which will lead to the formation of brick trench at the lock. The following measures should be taken: at the same lock, the number of locking iron should not exceed 3; the distance between locking iron should be scattered as far as possible; the loosening of inner and outer ports should be the same when locking brick; and the locking iron should be as far away as possible from the thin locking brick.
6 block brick ring extruded refractory brick
The brick (special-shaped brick) at the retaining ring is broken by extrusion and cracks. In view of this situation, the single-pass brick ring should be changed into a double-pass brick ring, and the brick should be built on the retaining ring to avoid processing the special-shaped brick.
2. Thermal damage
Local overheating in the kiln causes the refractory brick to melt to form a pit. In order to avoid this, it is appropriate to adjust the burner correctly and to select a reasonable refractory material at different locations.
2 thermal shock phenomenon
The cracking of the brick surface due to the thermal stress caused by the sudden change of the temperature is mainly due to the frequent start of the extreme cold and extreme heat. The production operation shall be stabilized, and the system of reasonable temperature rise and cold kiln shall be formulated.
3. Chemical erosion damage
1 alkali erosion
The gas phase alkali salt compound penetrates into the brick body to be condensed and solidified, and the horizontal permeable layer of the basic salt is formed in the brick body, so that the content of the alkali salt in the kiln can be reduced in the production.
the phenomenon of water-water hydration
MgO reacts with water to form Mg (OH) 2, which destroys the whole structure of refractory brick by increasing the volume. Due to the hydration reaction of refractory bricks containing MgO and CaO, the storage, transportation and masonry of refractory bricks should be ensured to avoid moisture, waterproofing and rain protection.
From the above damage mechanism of refractory brick, it can be seen that the standardization of refractory construction can effectively prolong the service life of refractory, and professional and dedicated masonry personnel are important factors to ensure the quality of refractory construction.
Quality requirements for refractory masonry
1. Pre-construction control
The refractory materials shall be carefully engaged in handling, and the damage rate of refractory bricks shall be controlled within 3%.
The longitudinal datum line of kiln should be arranged in "ten" shape along the circle, with 4 lines symmetrically, each line parallel to the kiln axis, and the circular datum line should be placed one line every 2m, each line should be parallel and perpendicular to the kiln axis.
Ensure that the kiln body steel plate is clean and the corrosion-free iron sheet is removed, the side loss of the refractory brick is strictly prohibited, and the refractory brick with the angle loss exceeding the control range is put into operation.
2. Construction process control
In the construction process to ensure that refractories are not dampened, the processing brick is processed by brick cutting machine. After cutting, the length of the brick must exceed 50% of the original brick length and the thickness must reach more than 70% of the original thickness.
The ring masonry method is adopted, and the brick is close to the kiln body, so it is necessary to ensure that the four corners of the brick are in contact with the kiln body.
The following common problems should be avoided in masonry: inverted head, drawing lots, mixing slurry, dislocation, tilt, uneven gray joint, climbing, middle, heavy joint, through joint, opening mouth, void, wool joint, serpentine bend, masonry drum bag, missing edge angle.
A wooden hammer or a rubber hammer shall be used when the refractory brick is built. It is strictly forbidden to use the hammer.
The modulated fire-resistant mud shall be clean water, accurately weighed, mixed and used with the adjustment, and the prepared mud shall not be used in any water, and the initially set mud shall not be used again, and the mixed slurry shall be cleaned and cleaned in a timely manner.
3. Lock seam control of brick ring
Can only use the original brick to lock the brick, do not use the processed brick.
If several bricks are used to lock the joints, the locking bricks shall not be used in conjunction with each other, and the standard type shall be used to be used to connect with them;Each ring of refractory bricks shall have not more than two lock joints of each type.
In the locking belt, it is necessary to ensure that the horizontal seam of the brick is parallel to the kiln shaft.
The thickness of the locking metal plate is not more than 2 mm.
Only one locking steel plate can be used in each seam. If several steel plates are needed, it should be distributed in the whole locking brick area, and the number of blocks per ring locking steel plate shall not exceed 4.
Selection principle of refractory material
In the selection of refractory materials, the following requirements shall be guaranteed to be met.
Firstly, the high-temperature resistance is high. And can be operated in a high-temperature environment for a long time.
And the second is high strength and good wear resistance. The refractory material in the rotary kiln must have a certain mechanical strength to bear the stress caused by the expansion stress at high temperature and the deformation of the shell of the rotary kiln. And the refractory material needs to have better wear resistance due to the wear of the material and the smoke to the refractory material.
Third, it has good chemical stability. To resist the erosion of chemicals in the smoke.
And the fourth is good thermal stability. Can bear the alternating stress in the burning state. The temperature in the kiln is relatively large when the boiler is shut down, the starting furnace and the rotating operation condition are not stable, and the condition of cracking or peeling can not be provided.
And fifth, the thermal expansion stability. The refractory material may be larger and easy to fall off than the rotary kiln shell.